Dedicated Outdoor Air Systems
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in Dedicated Outdoor Air Systems.
−---
−title: Dedicated Outdoor Air Systems
−category: Mechanical / Air Distribution
−toc_depth: 3
−description: >
− When to use: Packaged dedicated outdoor air systems (DOAS) that condition 100% outdoor air to satisfy the building's ventilation requirement independently of the spaces' sensible cooling and heating. Covers indoor and outdoor/rooftop units, the air-to-air energy recovery section (enthalpy wheel, fixed-plate, heat-pipe, or runaround loop), the deep-cooling and dehumidification section (integrated DX, air-source or water-source heat pump, or chilled water), the reheat method that controls leaving dewpoint and supply air temperature (hot-gas reheat, modulating reheat, wraparound heat pipe, or dehumidification wheel), the heating source, filtration, fans, casing, and the controls integration that coordinates the DOAS with the parallel sensible system it serves. Applicable to DOAS paired with variable refrigerant flow, fan coils, chilled beams, water-source heat pumps, or sensible-only rooftop units, in commercial, institutional, multifamily, and light-industrial buildings.
− Not intended for: General mixed-air central station air handlers that recirculate return air (see [[sync/air-handling-units]]); unitary packaged rooftop units with return-air mixing and integral economizer (see [[sync/packaged-rooftop-units]]); the parallel sensible terminal equipment itself, such as variable refrigerant flow systems (see [[sync/variable-refrigerant-flow-systems]]) and air terminal units (see [[sync/air-terminal-units]]); the field refrigerant piping interconnecting split DX components (see [[sync/refrigerant-piping]]); supply and exhaust ductwork beyond the unit connections (see [[sync/hvac-ductwork]]); supply diffusers and grilles (see [[sync/hvac-air-distribution-devices]]); testing, adjusting, and balancing after installation (see [[sync/testing-adjusting-and-balancing]]); and building automation controls programming and integration (see [[sync/building-automation-system]]).
−---
−
−# Scope {toc}
−
−## This specification covers factory-assembled dedicated outdoor air systems (DOAS) that draw 100% outdoor air, recover energy from the building exhaust, deep-cool and dehumidify the ventilation air to a controlled leaving dewpoint, reheat and temper the supply air as required, and deliver it to occupied spaces or to the inlets of a parallel sensible-conditioning system. {note}
−## Equipment covered includes the unit casing, the outdoor air and exhaust air fans, the air-to-air energy recovery section, the cooling and dehumidification section and its cooling source, the reheat section, the heating section, filtration, dampers, drain pans, and the factory controls that sequence dehumidification and reheat. {note}
−## Both indoor and outdoor (rooftop or grade-mounted) arrangements are addressed. {note}
−
−## A DOAS exists to decouple the building's latent (moisture) load, handled by the ventilation air at a controlled low dewpoint, from the sensible (temperature) load handled by the parallel zone system, because the two loads do not track each other and a single mixed-air coil cannot serve both without overcooling and wasteful reheat. {note}
−
−## The DOAS takes responsibility for the entire latent load of the building by delivering air at a low, controlled dewpoint, and the parallel sensible system handles only the dry sensible load of each space without ever having to dehumidify, which is why the dewpoint of the supply air, not its dry-bulb temperature alone, is the controlling design parameter. {note}
−
−## Air-to-air energy recovery is mandatory in most climates and at most ventilation rates under ASHRAE 90.1, and the recovery device's effectiveness, frost behavior, and cross-leakage are central engineering decisions, not accessories. {note}
−
−## Achieving a low leaving dewpoint requires cooling the air well below the desired supply temperature and then reheating it, and how that reheat is supplied (recovered "free" reheat or purchased energy) is the second central design decision. {note}
−
−## Equipment shall comply with AHRI 920 for performance rating of DX and heat-pump DOAS units, AHRI 1060 for air-to-air energy recovery ventilation equipment, AHRI 430 and AHRI 410 where central-station fans and coils are used, ASHRAE 62.1 for ventilation rates and air-stream classification, ASHRAE 90.1 for energy recovery and fan power, ASHRAE 55 for occupant comfort, the applicable AMCA fan and damper/louver standards, NFPA 90A for fire and smoke safety, and the applicable UL listing for electrical and refrigerant safety.
−
−## The boundary of work under this standard is the DOAS unit and its factory components, from the outdoor air intake and exhaust air connections to the supply air discharge connection. {note}
−
−## Supply and exhaust ductwork is covered by [[sync/hvac-ductwork]]; the diffusers, grilles, and registers that distribute DOAS air are covered by [[sync/hvac-air-distribution-devices]]; the parallel sensible terminal equipment is covered by its own standards; field refrigerant piping for split DX arrangements is covered by [[sync/refrigerant-piping]]; chilled water and hot water piping to coils is covered by the hydronic piping standard; and controls programming, graphics, and trending are covered by [[sync/building-automation-system]]. {note}
−
−# Referenced Standards {toc}
−
−## Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
−
−## Where conflicts exist between referenced standards, the adopted energy and mechanical codes, the equipment manufacturer's instructions, or the contract documents, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
−
−## Referenced standards list {toc}
−
−| Standard | Title |
−|----------|-------|
−| ANSI/AHRI 920 (I-P) | Performance Rating of DX-Dedicated Outdoor Air System Units |
−| ANSI/AHRI 1060 (I-P) | Performance Rating of Air-to-Air Exchangers for Energy Recovery Ventilation Equipment |
−| ANSI/AHRI 430 (I-P) | Performance Rating of Central Station Air-handling Unit Supply Fans |
−| ANSI/AHRI 410 | Performance Rating of Forced-Circulation Air-Cooling and Air-Heating Coils |
−| ANSI/ASHRAE 51 / ANSI/AMCA 210 | Laboratory Methods of Testing Fans for Certified Aerodynamic Performance Rating |
−| ANSI/AMCA 300 | Reverberation Room Methods of Sound Testing of Fans |
−| ANSI/AMCA 500-L | Laboratory Methods of Testing Louvers for Rating |
−| ANSI/AMCA 500-D | Laboratory Methods of Testing Dampers for Rating |
−| ANSI/ASHRAE 52.2 | Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size |
−| ANSI/ASHRAE 62.1 | Ventilation and Acceptable Indoor Air Quality |
−| ANSI/ASHRAE 55 | Thermal Environmental Conditions for Human Occupancy |
−| ANSI/ASHRAE/IES 90.1 | Energy Standard for Buildings Except Low-Rise Residential Buildings |
−| ANSI/ASHRAE 170 | Ventilation of Health Care Facilities (where DOAS serves health-care spaces) |
−| ASHRAE Guideline 36 | High-Performance Sequences of Operation for HVAC Systems |
−| NFPA 90A | Standard for the Installation of Air-Conditioning and Ventilating Systems |
−| UL 1995 | Heating and Cooling Equipment (where accepted by AHJ) |
−| UL 60335-2-40 | Safety of Household and Similar Electrical Appliances — Particular Requirements for Heat Pumps, Air-Conditioners, and Dehumidifiers |
−| SMACNA HVAC Duct Construction Standards | SMACNA HVAC Duct Construction Standards — Metal and Flexible |
−| ASHRAE Handbooks | HVAC Systems and Equipment, Fundamentals, Applications |
−
−# Submittals {toc}
−
−## Action Submittals {toc}
−
−### The Contractor shall submit the following for the Engineer's review and acceptance before equipment is ordered.
−
−### Fabrication and procurement shall not proceed until action submittals have been reviewed and returned.
−
−### Submittals shall be internally coordinated with the parallel sensible system and with the building automation system before any item is submitted.
−
−### Submit the following action submittals: {toc}
−
−- Manufacturer's product data for each DOAS unit, including model designation, an airflow schematic showing the sequence of energy recovery, cooling, reheat, heating, and filter sections, and the component schedule
−- AHRI 920 certified performance ratings for DX and heat-pump units, including the integrated seasonal moisture removal efficiency (ISMRE2, or ISMRE270 where the unit reheats to a neutral leaving temperature with supplemental heat) and, for heat-pump units, the integrated seasonal coefficient of performance (ISCOP2)
−- AHRI 1060 certified performance ratings for the energy recovery component, including sensible and latent effectiveness at 100% and 75% of rated airflow for both summer and winter conditions, the exhaust air transfer ratio (EATR), and the outdoor air correction factor (OACF)
−- A psychrometric analysis for each unit plotting the air state points (entering outdoor air, after energy recovery, after the cooling/dehumidification coil, and supply air) at the cooling/dehumidification design condition, and the corresponding heating-season state points, with the leaving dewpoint and supply air temperature at each
−- Capacity data at the cooling design condition and at the specified part-load (turndown) condition, demonstrating that the unit holds the leaving dewpoint setpoint at reduced ventilation flow and reduced load, where part-load dehumidification is required
−- Fan performance curves at the design operating point per AHRI 430 / AMCA 210, with power and efficiency, and octave-band sound power levels per AMCA 300 for both supply discharge and casing radiation
−- Coil selection data per AHRI 410 for cooling, reheat, and heating coils, with entering and leaving conditions, face velocity, rows, fin spacing, and air- and water-side pressure drop
−- Filter section data with MERV rating certified per ASHRAE 52.2, initial and final resistance, and frame and seal construction
−- Casing construction details, panel R-value, interior liner material, and, for outdoor units, the weatherproofing and finish system
−- Energy recovery frost-control description (the method, the outdoor temperature at which it activates, and its effect on ventilation delivery during frost control)
−- A controls points list and a written sequence of operation describing dehumidification control, reheat control, supply air temperature/dewpoint reset, energy recovery bypass and frost control, and the interface to the parallel sensible system and the [[sync/building-automation-system]]
−- Electrical data: voltage, phase, minimum circuit ampacity, maximum overcurrent protection, and the refrigerant type and charge for DX and heat-pump units
−
−```datasheet
−label: Action Submittals Required
−type: checkbox
−options:
− - "Product data and unit airflow schematic"
− - "AHRI 920 performance ratings (ISMRE2 / ISMRE270 / ISCOP2)"
− - "AHRI 1060 energy recovery ratings (effectiveness, EATR, OACF)"
− - "Psychrometric state-point analysis (design and heating)"
− - "Capacity at design and part-load dehumidification"
− - "Fan curves and AMCA 300 sound power levels"
− - "Coil selection data (AHRI 410)"
− - "Filter MERV certification (ASHRAE 52.2)"
− - "Casing construction and weatherproofing details"
− - "Energy recovery frost-control description"
− - "Controls points list and sequence of operation"
− - "Electrical data and refrigerant charge"
−default: "Product data and unit airflow schematic"
−```
−
−## Closeout Submittals {toc}
−
−### The Contractor shall provide the following at or before substantial completion:
−
−- Operation and maintenance manuals for each unit and all major components, organized with a table of contents
−- As-built unit configuration and as-built controls points list reflecting any field modifications
−- Factory test reports for each unit
−- Startup and commissioning records, including the functional test of dehumidification, reheat, energy recovery frost control, and the interlock to the parallel sensible system
−- Refrigerant charging records (DX and heat-pump units), documenting refrigerant type and total charge
−- Energy recovery component maintenance data, including wheel drive belt and seal replacement intervals for rotary devices, and core cleaning procedure for fixed-plate devices
−- Filter media installed at substantial completion with MERV certification and installation date tags
−- Warranty documentation from the manufacturer and from any compressor and energy recovery sub-suppliers
−
−```datasheet
−label: Required Closeout Submittals
−type: checkbox
−options:
− - "Operation and maintenance manuals"
− - "As-built unit configuration and controls points list"
− - "Factory test reports for each unit"
− - "Startup and commissioning records"
− - "Refrigerant charging records (DX and heat-pump units)"
− - "Energy recovery component maintenance data"
− - "Filter media with MERV certification and date tags"
− - "Warranty documentation (manufacturer and sub-suppliers)"
−default: "Operation and maintenance manuals"
−```
−
−# Quality Assurance {toc}
−
−## Manufacturer Qualifications {toc}
−
−### DOAS units shall be manufactured by a company with a minimum of ten years of continuous experience designing and fabricating packaged ventilation and air-conditioning equipment.
−
−### The manufacturer shall maintain a quality management system.
−
−### The manufacturer shall be able to provide replacement parts and factory service support for a minimum of fifteen years after the date of manufacture.
−
−## Single-Source Responsibility {toc}
−
−### For each DOAS unit, the casing, fans, energy recovery section, cooling and dehumidification section, reheat and heating sections, filters, and dampers shall be provided as a coordinated factory assembly by or through the DOAS manufacturer.
−
−### The interaction between the energy recovery device, the dehumidification coil, and the reheat source is what determines whether the unit holds its leaving dewpoint, and resolving that interaction at the factory rather than assembling independent components in the field is the reason for the single-source requirement. {note}
−
−## AHRI Certification {toc}
−
−```datasheet
−label: AHRI Certification Required
−type: checkbox
−options:
− - "DOAS unit performance per AHRI 920 (ISMRE2 / ISCOP2)"
− - "Energy recovery component per AHRI 1060"
− - "Supply fan performance per AHRI 430"
− - "Coils per AHRI 410"
−default: "DOAS unit performance per AHRI 920 (ISMRE2 / ISCOP2)"
−```
−
−### DX and heat-pump DOAS units shall be rated under the AHRI Certification Program for DX-Dedicated Outdoor Air System Units per AHRI 920, and published ISMRE2, ISMRE270 (where applicable), and ISCOP2 ratings shall bear the AHRI certification mark.
−
−### Air-to-air energy recovery components shall be rated under the AHRI Certification Program for energy recovery ventilation equipment per AHRI 1060, and the published effectiveness, EATR, and OACF shall bear the AHRI certification mark.
−
−### Where central-station fans and coils are used, ratings shall conform to AHRI 430 and AHRI 410.
−
−### AHRI-certified ratings, not generic catalog values, shall be the basis of selection.
−
−## Factory Run Test {toc}
−
−### Each unit shall receive a factory functional run test before shipment, operating the refrigeration or heat-pump circuit (where integral), the fans, the energy recovery drive, and the dehumidification and reheat sequence, and confirming that the unit produces the specified leaving dewpoint at the test condition.
−
−## NRTL Listing {toc}
−
−### The complete DOAS assembly, including all electrical and (where integral) refrigerant components, shall be listed and labeled by a Nationally Recognized Testing Laboratory to UL 60335-2-40, or to UL 1995 where the Authority Having Jurisdiction continues to accept that listing for equipment manufactured before the transition date.
−
−# Environmental and Service Conditions {toc}
−
−## The unit shall be selected and rated for the design conditions at the installation site.
−## The design outdoor air condition, the supply air leaving condition, and the exhaust air entering condition are [[drawing: as indicated on the mechanical schedules and the psychrometric process diagrams]]. {note}
−
−## Design Outdoor Air Condition {toc}
−
−```datasheet
−label: Cooling/Dehumidification Design Outdoor Air Condition
−type: text
−drawing_ref: true
−default: deferred
−```
−
−```datasheet
−label: Heating Design Outdoor Air Temperature
−type: range
−unit: °F
−drawing_ref: true
−options:
− min: -30
− max: 40
− setpoints: [-30, -20, -10, 0, 10, 20, 30, 40]
−default: 0
−```
−
−### Because the DOAS conditions 100% outdoor air, it shall be selected at the project's dehumidification design condition — the design dewpoint or design wet-bulb condition from ASHRAE Fundamentals for the project location — and not merely at the cooling dry-bulb design.
−
−### The dehumidification design condition, which typically pairs a moderate dry-bulb with a high coincident moisture content, is the condition that sizes the cooling coil and the reheat, and it is frequently more demanding for a DOAS than the peak dry-bulb hour. {note}
−
−## Supply Air Leaving Targets {toc}
−
−### The controlling leaving condition is the supply air dewpoint, because the DOAS is selected to absorb the building latent load. {note}
−
−### The supply air dry-bulb strategy shall be specified, coordinated with the leaving dewpoint setpoint and the parallel sensible system serving the space.
−
−```datasheet
−label: Supply Air Dry-Bulb Strategy
−type: radio
−options:
− - "Neutral supply — reheat ventilation air to near space-neutral temperature (68-72°F); space load carried entirely by parallel sensible system (standard)"
− - "Cold (DOAS-to-space) supply — deliver cool, dry air directly to the space to offset part of the sensible load; reheat only to the dewpoint-control minimum"
− - "Reset supply temperature — neutral in cooling season, warm (tempered) in heating season"
−default: "Neutral supply — reheat ventilation air to near space-neutral temperature (68-72°F); space load carried entirely by parallel sensible system (standard)"
−```
−
−### The leaving dewpoint setpoint shall be low enough that the DOAS supply air, after mixing with space air and absorbing the space moisture gains, holds the space relative humidity within the design range under ASHRAE 55.
−
−```datasheet
−label: Supply Air Leaving Dewpoint Setpoint
−type: range
−unit: °F
−drawing_ref: true
−options:
− min: 40
− max: 58
− setpoints: [40, 45, 48, 50, 52, 55, 58]
−default: 52
−```
−
−### A leaving dewpoint of about 50°F to 55°F is typical for comfort applications; lower dewpoints are specified for spaces with strict humidity limits. {note}
−
−### A neutral-supply DOAS delivers ventilation air at a temperature close to the space setpoint so it neither heats nor cools the space, and it is the most common and most forgiving arrangement because the parallel system and the DOAS never fight each other. {note}
−
−### A cold-supply (DOAS-to-space) arrangement intentionally delivers cool dry air to offset part of the space sensible load, which reduces the parallel system's capacity but requires careful diffuser selection to avoid drafts and requires that the parallel system not overcool and drive the space humidity back up; this strategy decouples humidity control from the parallel system only if the DOAS dewpoint is held independent of its dry-bulb, which is exactly what the reheat section provides. {note}
−
−## Unit Installation Location {toc}
−
−```datasheet
−label: Unit Installation Location
−type: select
−options:
− - "Outdoor — rooftop on roof curb"
− - "Outdoor — grade-mounted on housekeeping pad"
− - "Indoor — mechanical room or penthouse"
−default: "Outdoor — rooftop on roof curb"
−```
−
−# Unit Configuration and Arrangement {toc}
−
−## The energy recovery type, the cooling source, the dehumidification and reheat method, and the supply strategy are interdependent and shall be selected together and reviewed against the psychrometric analysis as a set.
−
−## Airflow Capacity {toc}
−
−```datasheet
−label: Design Outdoor Air (Ventilation) Airflow
−type: range
−unit: cfm
−drawing_ref: true
−options:
− min: 500
− max: 60000
− step: 250
−default: 4000
−```
−
−```datasheet
−label: Exhaust Air Airflow Through Energy Recovery
−type: range
−unit: cfm
−drawing_ref: true
−options:
− min: 0
− max: 60000
− step: 250
−default: 3500
−```
−
−### Design outdoor (ventilation) airflow and exhaust airflow shall be [[drawing: as indicated on the mechanical schedules]].
−
−### The ventilation rate shall be established by the ASHRAE 62.1 ventilation rate procedure for the served spaces.
−
−## External Static Pressure {toc}
−
−```datasheet
−label: Supply External Static Pressure
−type: range
−unit: in. wg
−drawing_ref: true
−options:
− min: 0.5
− max: 4.0
− setpoints: [0.5, 0.75, 1.0, 1.25, 1.5, 2.0, 2.5, 3.0, 4.0]
−default: 1.5
−```
−
−## Configuration Summary {toc}
−
−```datasheet
−label: Energy Recovery Type
−type: select
−options:
− - "Enthalpy (total energy) rotary wheel"
− - "Sensible-only rotary wheel with purge sector"
− - "Fixed-plate enthalpy (membrane) core"
− - "Fixed-plate sensible (aluminum) core"
− - "Heat-pipe (sensible)"
− - "Runaround coil loop (sensible, separated air streams)"
− - "None (energy recovery not required by code for this unit)"
−default: "Enthalpy (total energy) rotary wheel"
−```
−
−```datasheet
−label: Cooling Source
−type: select
−options:
− - "Integrated DX (packaged compressorized cooling)"
− - "Air-source heat pump (DX cooling and heating)"
− - "Water-source heat pump (DX, condenser water loop)"
− - "Chilled water coil (central plant)"
−default: "Integrated DX (packaged compressorized cooling)"
−```
−
−```datasheet
−label: Dehumidification Reheat Method
−type: select
−options:
− - "Hot-gas (refrigerant) reheat — recovered condenser heat (DX/heat-pump units)"
− - "Modulating hot-gas reheat — variable leaving-temperature control"
− - "Wraparound heat pipe — passive precool/reheat around the cooling coil"
− - "Wraparound runaround coil — pumped passive reheat"
− - "Dehumidification (passive desiccant) wheel — sensible reheat from process air"
− - "Hot water or electric reheat coil — purchased reheat energy"
− - "None — supply delivered cold (cold-supply strategy)"
−default: "Hot-gas (refrigerant) reheat — recovered condenser heat (DX/heat-pump units)"
−```
−
−```datasheet
−label: Heating Source
−type: select
−options:
− - "Heat pump (integral, air-source or water-source)"
− - "Indirect gas-fired furnace"
− - "Electric resistance heating coil"
− - "Hot water heating coil (central plant)"
− - "None — supplemental heating provided downstream"
−default: "Heat pump (integral, air-source or water-source)"
−```
−
−```datasheet
−label: Supply Air Strategy
−type: radio
−options:
− - "Neutral supply (standard)"
− - "Cold supply (DOAS-to-space)"
− - "Reset (neutral cooling, tempered heating)"
−default: "Neutral supply (standard)"
−```
−
−```datasheet
−label: Filtration (Final Filter MERV)
−type: select
−options:
− - "MERV 8 — minimum for ventilation air"
− - "MERV 11 — enhanced commercial"
− - "MERV 13 — fine particulate (PM2.5), standard for occupied ventilation"
− - "MERV 14 — superior filtration"
−default: "MERV 13 — fine particulate (PM2.5), standard for occupied ventilation"
−```
−
−```datasheet
−label: Fan Type
−type: radio
−options:
− - "Direct-drive plenum (plug) fan with ECM or VFD-driven motor (standard)"
− - "Direct-drive backward-curved plenum fan, VFD-driven"
− - "Belt-driven centrifugal fan (legacy / large units)"
−default: "Direct-drive plenum (plug) fan with ECM or VFD-driven motor (standard)"
−```
−
−# Energy Recovery {toc}
−
−## Air-to-air energy recovery is the feature that makes a DOAS practical. {note}
−## Recovering most of the conditioning load from the building exhaust, which is already near the space condition, cuts the cooling and heating capacity the unit must purchase by half or more.
−
−## ASHRAE 90.1 requires exhaust air energy recovery for most ventilation systems based on the percentage of outdoor air and the design supply airflow, with a minimum enthalpy recovery ratio of at least 50% at the design condition for the climate zone.
−
−## Recovery shall be provided wherever required by the adopted energy code; the only DOAS units that omit it are those that fall below the code threshold or that qualify for a specific exception.
−
−## Recovery Device Type — Sensible vs. Total {toc}
−
−```datasheet
−label: Recovery — Sensible or Total Energy
−type: radio
−options:
− - "Total energy (sensible + latent) — recover moisture; reduces coil latent load (standard for comfort DOAS)"
− - "Sensible only — temperature recovery, no moisture transfer (contaminated exhaust or no-cross-transfer applications)"
−default: "Total energy (sensible + latent) — recover moisture; reduces coil latent load (standard for comfort DOAS)"
−```
−
−### Total-energy (enthalpy) devices — rotary enthalpy wheels and fixed-plate membrane cores — transfer both heat and moisture between the air streams; in summer they pre-dry the incoming air using the drier exhaust, and in winter they return moisture to the incoming air, reducing dry indoor conditions and the need for humidification. {note}
−
−### Sensible-only devices — heat pipes, sensible plates, sensible wheels, and runaround loops — transfer heat only, and a sensible device shall be selected where moisture transfer is undesirable or prohibited, where the exhaust is contaminated and any cross-transfer to the supply is unacceptable, or where the design intent is to maximize the moisture removed by the cooling coil rather than recover it.
−
−## Cross-Contamination and EATR {toc}
−
−### AHRI 1060 quantifies cross-transfer from the exhaust stream into the supply stream as the exhaust air transfer ratio (EATR) and the outdoor air correction factor (OACF). {note}
−
−### The exhaust air stream classification shall be specified, establishing the permissible EATR limit and energy-recovery device type for the exhaust's contamination class.
−
−```datasheet
−label: Exhaust Air Stream Classification (ASHRAE 62.1)
−type: select
−options:
− - "Class 1 — general comfort exhaust (any recovery type acceptable)"
− - "Class 2 — moderate-contaminant exhaust (EATR ≤ 10%; purge required on wheels)"
− - "Class 3/4 — high-contaminant exhaust (separated-stream sensible recovery only)"
−default: "Class 1 — general comfort exhaust (any recovery type acceptable)"
−```
−
−```datasheet
−label: Rotary Wheel Purge Sector
−type: radio
−options:
− - "Purge sector required (Class 2 exhaust or low-EATR requirement)"
− - "Purge sector not required (Class 1 exhaust)"
− - "Not applicable (non-rotary recovery device)"
−default: "Purge sector not required (Class 1 exhaust)"
−```
−
−### Where the exhaust is ASHRAE 62.1 Class 1 air (general comfort exhaust), a small EATR is acceptable.
−
−### Where the exhaust contains Class 2 air, ASHRAE 62.1 limits the EATR to no more than 10% and requires that any transferred air be accounted for in the ventilation calculation.
−
−### Where the exhaust is Class 3 or Class 4, energy recovery that allows cross-transfer is prohibited and a sensible device with fully separated streams (heat pipe or runaround loop) shall be used.
−
−### Rotary wheels intended for Class 1/Class 2 service shall include a purge sector, which uses a small pressure-driven flow to sweep carryover air back to the exhaust before the wheel rotates into the supply stream, reducing EATR.
−
−## Frost Control {toc}
−
−### In cold climates the warm, moist exhaust gives up its moisture as it is cooled by the incoming air, and that moisture can freeze on the recovery surface, blocking the exhaust path and destroying recovery. {note}
−
−### Every recovery device in a freezing climate shall have a defined frost-control strategy.
−
−```datasheet
−label: Energy Recovery Frost Control Method
−type: select
−options:
− - "Modulating wheel speed (rotary wheels)"
− - "Timed defrost cycle (rotary wheels)"
− - "Preheat of entering outdoor air upstream of recovery (plates, heat pipes)"
− - "Exhaust-side or supply-side bypass damper"
− - "Not required (climate does not produce recovery frost)"
−default: "Not required (climate does not produce recovery frost)"
−```
−
−### Wheels shall be frost-controlled by modulating wheel speed or by a timed defrost; fixed plates and heat pipes shall be frost-controlled by preheating the incoming air, by an exhaust-side bypass, or by recirculation.
−
−### The frost-control method, its activation temperature, and its effect on ventilation flow during frost control shall be submitted.
−
−## Recovery Bypass {toc}
−
−```datasheet
−label: Energy Recovery Bypass
−type: radio
−options:
− - "Provide recovery bypass damper (economizer-capable or code-required)"
− - "No bypass (recovery active whenever the unit runs)"
−default: "Provide recovery bypass damper (economizer-capable or code-required)"
−```
−
−### A bypass damper around the recovery device shall be provided where the recovery would otherwise be active during economizer hours, or where frost control or the energy code economizer provisions require the recovery to be bypassed.
−
−### Bypass shall be controlled by the [[sync/building-automation-system]].
−
−# Cooling and Dehumidification {toc}
−
−## The cooling section of a DOAS is selected to drive the air to a low leaving dewpoint, which usually means cooling the air below the temperature the space actually wants, then reheating it to the desired supply temperature while the moisture stays removed. {note}
−
−## To reach a 50°F to 55°F leaving dewpoint at a humid design condition, the coil leaving dry-bulb must be at or below that dewpoint (the air leaves the coil at or near saturation), which is colder than a comfortable supply temperature.
−
−## AHRI 920 rates this behavior directly through its integrated seasonal moisture removal efficiency (ISMRE2, in pounds of moisture removed per kilowatt-hour), and AHRI 920 testing is run to a 55°F leaving dewpoint reference. {note}
−
−## Cooling Source {toc}
−
−```datasheet
−label: Cooling Source (detail)
−type: radio
−options:
− - "Integrated DX — single or multiple compressor stages"
− - "Integrated DX with variable-capacity (variable-speed or digital) compressor"
− - "Heat pump — reversible refrigerant circuit (cooling and heating)"
− - "Chilled water coil — central plant"
−default: "Integrated DX with variable-capacity (variable-speed or digital) compressor"
−```
−
−```datasheet
−label: Cooling Coil Leaving Air Dewpoint (Design)
−type: range
−unit: °F
−options:
− min: 40
− max: 55
− setpoints: [40, 45, 48, 50, 52, 55]
−default: 52
−```
−
−### The cooling source shall be selected to match the project's energy infrastructure and the unit type.
−
−### A chilled water DOAS shall obtain its reheat from a separate source, since there is no condenser heat to recover.
−
−### Integrated DX is the most common cooling source for standalone packaged DOAS because it makes recovered reheat available from the condenser, a heat pump adds heating from the same circuit, and a chilled water coil is used where a central chilled water plant exists and the DOAS is one of many loads on it. {note}
−
−### Variable-capacity compressors are strongly preferred for DOAS because the latent load varies enormously across the year, and a variable-capacity circuit can hold the leaving dewpoint at part-load ventilation rates and at the many mild, humid hours when a fixed-stage unit would short-cycle and deliver wet air. {note}
−
−## Part-Load Dehumidification {toc}
−
−```datasheet
−label: Minimum Dehumidification Turndown
−type: select
−options:
− - "Single stage — full capacity only (small units, mild climates)"
− - "Two-stage — approximately 50% capacity at low stage"
− - "Variable capacity — continuous modulation to approximately 25% capacity"
−default: "Variable capacity — continuous modulation to approximately 25% capacity"
−```
−
−### The DOAS shall hold the leaving dewpoint setpoint across the range of operating conditions, not only at the design hour.
−
−### The unit shall provide dehumidification down to the specified minimum turndown, by compressor staging or variable capacity, and the part-load performance shall be documented in the submittal.
−
−### Many of the wettest hours of the year are mild — a rainy 70°F day at near-saturation carries a large latent load with almost no sensible load — and a unit that can only dehumidify at peak sensible conditions will deliver humid air during exactly those hours. {note}
−
−## Reheat (Dehumidification Reheat) {toc}
−
−### Reheat is the mechanism that makes low-dewpoint dehumidification possible without delivering uncomfortably cold air, and on a neutral-supply unit it is a continuous part of normal operation. {note}
−### The decision is where the reheat energy comes from. {note}
−
−### Recovered reheat shall be used wherever the unit type allows it.
−
−```datasheet
−label: Reheat Method (detail)
−type: radio
−options:
− - "Hot-gas reheat — single-circuit condenser heat to a reheat coil (standard DX)"
− - "Modulating hot-gas reheat — staged or valved for variable leaving-temperature control"
− - "Wraparound heat pipe — passive, sealed refrigerant loop around the cooling coil"
− - "Wraparound runaround coil — pumped glycol loop around the cooling coil"
− - "Dehumidification (desiccant) wheel — passive sensible reheat from the process air"
− - "Hot water reheat coil — purchased energy (where recovered reheat unavailable)"
− - "Electric reheat coil — purchased energy (where recovered reheat unavailable)"
−default: "Modulating hot-gas reheat — staged or valved for variable leaving-temperature control"
−```
−
−### Purchased reheat (a hot water or electric coil) shall be limited to applications where no recovered source is available or where the energy code permits it.
−
−### Recovered reheat — hot-gas (refrigerant) reheat that takes heat rejected by the unit's own condenser, a wraparound heat pipe or runaround coil that precools the entering air and reuses that captured heat to rewarm the leaving air, or a passive dehumidification wheel — spends no purchased energy on reheat, whereas purchased reheat spends energy heating air that was just cooled, which the energy code restricts. {note}
−
−### A wraparound device (heat pipe or runaround coil) improves dehumidification while it reheats: by precooling the entering air before the cooling coil it lets the coil reach a lower dewpoint for the same compressor capacity, and it then uses that captured heat to reheat the leaving air — typically lifting the supply from roughly 48°F to roughly 55°F — with no purchased energy and no controls. {note}
−
−### A passive wraparound is largely self-regulating and cannot independently set the supply temperature; where precise leaving-temperature control is needed, modulating hot-gas reheat or a controlled wraparound is required.
−
−```datasheet
−label: Reheat Leaving Air Temperature Setpoint
−type: range
−unit: °F
−options:
− min: 55
− max: 75
− setpoints: [55, 60, 65, 68, 70, 72, 75]
−default: 70
−```
−
−# Heating {toc}
−
−## In the heating season the DOAS shall temper the cold ventilation air so that it does not chill the spaces or the inlets of the parallel sensible system.
−## With energy recovery active, much of the heating is recovered from the exhaust and the heating source supplies the remainder; for a neutral-supply unit the heating section warms the air to near the space-neutral temperature, and for a tempered-reset unit it may warm it further to offset part of the space heating load.
−
−```datasheet
−label: Heating Source (detail)
−type: select
−options:
− - "Heat pump — integral reversible circuit"
− - "Heat pump with auxiliary electric or gas backup for low ambient"
− - "Indirect gas-fired furnace (stainless heat exchanger)"
− - "Electric resistance coil"
− - "Hot water coil — central plant"
− - "None — tempering by energy recovery only"
−default: "Heat pump with auxiliary electric or gas backup for low ambient"
−```
−
−```datasheet
−label: Heating Supply Air Temperature Setpoint
−type: range
−unit: °F
−drawing_ref: true
−options:
− min: 60
− max: 95
− setpoints: [60, 65, 68, 70, 75, 85, 95]
−default: 70
−```
−
−## Air-source heat-pump DOAS units in cold climates shall include auxiliary heat sized to carry the unit through the heating design condition and any heat-pump defrost cycles.
−
−## Where a hot water coil is the heating source in a freezing climate, freeze protection shall be provided as specified under Casing, Fans, Coils, Filters.
−
−# Casing, Fans, Coils, Filters {toc}
−
−## Casing {toc}
−
−```datasheet
−label: Casing Panel Construction
−type: radio
−options:
− - "Double-wall, injected foam insulation (standard)"
− - "Double-wall, injected foam with thermal break at panel edges (cold climate / high-humidity)"
−default: "Double-wall, injected foam insulation (standard)"
−```
−
−```datasheet
−label: Casing Panel Thermal Value (R-value)
−type: select
−unit: hr·ft²·°F/Btu
−options:
− - "R-6 to R-8 (standard commercial)"
− - "R-10 to R-13 (cold climate / outdoor DOAS)"
−default: "R-6 to R-8 (standard commercial)"
−```
−
−```datasheet
−label: Outdoor Unit Weatherproofing
−type: checkbox
−options:
− - "Sloped/pitched weather top panels"
− - "Drainable intake/exhaust louvers (AMCA 500-L) with bird screen"
− - "Drainable base rail and roof curb seal"
− - "Gasketed access doors with hold-open and lockable latches"
− - "Two-coat corrosion-inhibiting, UV-resistant exterior finish"
−default: "Sloped/pitched weather top panels"
−```
−
−### The casing shall be double-wall construction throughout.
−
−### Panel insulation R-value shall be appropriate for the climate, with cold-climate and outdoor units warranting higher-R panels to prevent exterior condensation and limit conduction loss.
−
−### Double-wall construction is required because a DOAS handles cold, dehumidified air on the supply side and cold outdoor air on the entering side, and condensation will form on any cold single-wall panel. {note}
−
−### Outdoor and rooftop units shall be provided with a factory weatherproof casing including pitched or sloped top panels, weather hoods and drainable louvers (rated per AMCA 500-L) over the outdoor air intake and exhaust, bird screens, a drainable base rail, gasketed access doors with hold-open hardware, and corrosion-resistant exterior hardware.
−
−### The exterior finish on outdoor and rooftop units shall be a two-coat corrosion-inhibiting and UV-resistant system.
−
−## Fans {toc}
−
−```datasheet
−label: Fan Motor and Speed Control
−type: radio
−options:
− - "ECM (electronically commutated) motor — integral variable speed (standard for smaller units)"
− - "Premium-efficiency motor with variable frequency drive (larger units)"
−default: "ECM (electronically commutated) motor — integral variable speed (standard for smaller units)"
−```
−
−### Supply and exhaust fans shall be direct-drive plenum (plug) fans driven by electronically commutated (ECM) motors or by variable-frequency-driven premium-efficiency motors, so that airflow can be held constant as filters and the recovery device load and so that fan power complies with ASHRAE 90.1.
−
−### Fan and airflow performance shall be rated per AHRI 430 / AMCA 210.
−
−### Fans shall be selected at the design airflow and external static pressure with capacity to maintain design airflow at the loaded-filter and frosted-recovery condition.
−
−## Coils {toc}
−
−```datasheet
−label: Cooling Coil Fin Treatment
−type: radio
−options:
− - "Aluminum fins (standard inland environment)"
− - "Coated aluminum fins (coastal/corrosive — within ~3 mi of saltwater or industrial air)"
−default: "Aluminum fins (standard inland environment)"
−```
−
−```datasheet
−label: Cooling Coil Face Velocity (Maximum)
−type: range
−unit: fpm
−options:
− min: 350
− max: 550
− setpoints: [350, 400, 450, 500, 550]
−default: 450
−```
−
−### Cooling, reheat, and heating coils shall be rated and certified per AHRI 410, with tube and fin materials suited to the airstream.
−
−### Coastal and corrosive-environment units shall use corrosion-resistant fin treatment, because the cooling coil runs wet continuously and the entire airstream is outdoor air.
−
−### Cooling coil face velocity shall be selected to limit moisture carryover off a continuously wet coil, with a face velocity at or below 500 ft³/min per ft² (cfm/ft²) of coil face recommended for DOAS, lower than a comparable mixed-air unit because the DOAS coil is always operating wet at design.
−
−## Drain Pan and Condensate {toc}
−
−```datasheet
−label: Drain Pan Material
−type: radio
−options:
− - "Type 304 stainless steel (standard)"
− - "Type 316 stainless steel (coastal/chemical environment)"
−default: "Type 304 stainless steel (standard)"
−```
−
−### A sloped, fully draining stainless steel drain pan shall be provided under the cooling coil and under any other condensing section.
−
−### The drain pan shall fully drain and shall be Type 304 stainless steel minimum (Type 316 in coastal or chemical environments).
−
−### A condensate trap with seal depth matched to the section's static pressure shall be provided so the trap is neither blown nor sucked dry.
−
−### Because a DOAS coil runs wet continuously, standing water is both a Legionella risk and a corrosion risk. {note}
−
−## Hot Water Coil Freeze Protection {toc}
−
−```datasheet
−label: Hot Water Coil Freeze Protection
−type: select
−options:
− - "Serpentine-element low-limit thermostat (full-face coverage)"
− - "Glycol solution in the coil loop"
− - "Not applicable (no hydronic coil, or non-freezing climate)"
−default: "Not applicable (no hydronic coil, or non-freezing climate)"
−```
−
−### Where a hot water heating or reheat coil is used in a freezing climate, freeze protection shall be provided, and protection shall be a serpentine-element low-limit (freeze-stat) covering the coil face, glycol in the coil loop, or a face-and-bypass arrangement, as appropriate.
−
−### Freeze protection is required because the coil sees full design outdoor air with no warm return air to buffer it. {note}
−
−## Filtration {toc}
−
−```datasheet
−label: Pre-Filter MERV Rating
−type: select
−options:
− - "MERV 7 — synthetic media panel pre-filter (standard)"
− - "MERV 8 — pleated pre-filter"
− - "None (single-stage filtration)"
−default: "MERV 7 — synthetic media panel pre-filter (standard)"
−```
−
−### Final filtration shall be MERV 13 for occupied-space ventilation air unless the application requires higher efficiency, with a pre-filter to extend final-filter life.
−
−### Filter frames shall seal positively to prevent bypass, which would void the rated efficiency.
−
−# Controls and BAS Integration {toc}
−
−## The DOAS is a sequence machine: it must coordinate energy recovery, deep cooling, dehumidification, and reheat to hold a leaving dewpoint, and it must coordinate with the parallel sensible system so the two never undo each other's work.
−
−```datasheet
−label: BAS Communication Protocol
−type: select
−options:
− - "BACnet MS/TP (RS-485)"
− - "BACnet IP (Ethernet)"
− - "Modbus RTU (RS-485)"
− - "Modbus TCP/IP (Ethernet)"
− - "Hardwired I/O only (no network)"
−default: "BACnet IP (Ethernet)"
−```
−
−## The unit shall be furnished with factory controls and a labeled terminal interface, and shall integrate with the [[sync/building-automation-system]].
−
−## Sequences should follow the intent of ASHRAE Guideline 36 where applicable.
−
−## Control of Dehumidification and Reheat {toc}
−
−```datasheet
−label: Dehumidification Control Variable
−type: radio
−options:
− - "Leaving air dewpoint sensor (direct dewpoint control)"
− - "Leaving air relative humidity and temperature (computed humidity ratio)"
−default: "Leaving air dewpoint sensor (direct dewpoint control)"
−```
−
−### The primary control loop shall sequence the cooling coil to maintain the leaving dewpoint (or leaving humidity ratio) setpoint.
−
−### The reheat shall be sequenced independently to maintain the supply dry-bulb setpoint.
−
−### Holding these two loops independent is what lets the DOAS control humidity without coupling it to space temperature — the defining behavior of a decoupled-latent system. {note}
−
−## Supply Reset {toc}
−
−```datasheet
−label: Supply Air Reset
−type: select
−options:
− - "Fixed leaving dewpoint and supply temperature setpoints"
− - "Dewpoint reset on space humidity; fixed supply temperature"
− - "Full reset of dewpoint and supply temperature by BAS"
−default: "Dewpoint reset on space humidity; fixed supply temperature"
−```
−
−### Supply air temperature and dewpoint may be reset by the BAS based on outdoor conditions, space humidity, or the load on the parallel sensible system, to save reheat energy when the full dehumidification capacity is not needed.
−
−### Reset logic shall be coordinated with the [[sync/building-automation-system]].
−
−## Interlock with Parallel Sensible System {toc}
−
−### The DOAS and the parallel sensible system shall be interlocked through the BAS so that the parallel system does not satisfy space temperature in a way that drives space humidity up, and so that the DOAS ventilation runs whenever the spaces are occupied.
−
−### Occupancy scheduling, demand-controlled ventilation reset (where CO2 sensing is used), and the night/unoccupied mode shall be coordinated across both systems.
−
−## Minimum Control Points {toc}
−
−```datasheet
−label: Controls Points Package
−type: checkbox
−options:
− - "Outdoor air temperature and humidity sensors"
− - "Supply air temperature sensor"
− - "Supply air dewpoint or humidity sensor"
− - "Cooling coil leaving air temperature sensor"
− - "Compressor / cooling capacity control output"
− - "Reheat control output (hot-gas valve or coil)"
− - "Heating control output"
− - "Energy recovery drive / speed and bypass control"
− - "Energy recovery frost-control status"
− - "Supply and exhaust fan speed control and status"
− - "Filter differential pressure switch or transmitter"
− - "Outdoor and exhaust air damper actuators and end switches"
− - "Smoke detector(s) per NFPA 90A"
− - "Condensate overflow / drain-pan high-level switch"
− - "Unit alarm summary to BAS"
−default: "Supply air dewpoint or humidity sensor"
−```
−
−# Testing {toc}
−
−## Factory Testing {toc}
−
−```datasheet
−label: Factory Test
−type: radio
−options:
− - "Standard production test plus functional run test (certified report submitted)"
− - "Witnessed factory test — provide 10 business days notice"
−default: "Standard production test plus functional run test (certified report submitted)"
−```
−
−### Each unit shall receive the manufacturer's standard production tests plus a functional run test confirming that the refrigeration or heat-pump circuit, fans, energy recovery drive, and the dehumidification-and-reheat sequence operate and that the unit produces the rated leaving dewpoint at the factory test condition.
−
−### A drain-pan tightness test and an electrical continuity and insulation test shall be included.
−
−### A factory test report shall be submitted at closeout.
−
−## Field Testing and TAB {toc}
−
−```datasheet
−label: Field Functional Performance Test
−type: checkbox
−options:
− - "Ventilation and exhaust airflow set and documented (TAB)"
− - "Leaving dewpoint setpoint held at test condition"
− - "Reheat maintains supply temperature setpoint"
− - "Energy recovery effectiveness / airflow ratio verified"
− - "Frost-control sequence verified"
− - "Parallel-system interlock and occupancy modes verified"
−default: "Ventilation and exhaust airflow set and documented (TAB)"
−```
−
−### After installation, the system shall be tested, adjusted, and balanced by an independent certified agency per [[sync/testing-adjusting-and-balancing]].
−
−### The TAB agent shall set and document the design outdoor (ventilation) airflow and the exhaust airflow through the recovery device, and shall confirm that the supply-to-exhaust airflow ratio is within the range the energy recovery device was rated for, since EATR and effectiveness are airflow-ratio dependent.
−
−### Functional testing shall verify that the unit holds the leaving dewpoint setpoint, that reheat maintains the supply temperature setpoint, that energy recovery frost control operates, and that the interlock to the parallel sensible system behaves as designed.
−
−# Installation {toc}
−
−## Rigging and Mounting {toc}
−
−### The unit shall be rigged and set per the manufacturer's instructions using furnished rigging points; cables shall not bear on casing panels.
−
−### Rooftop units shall be set on a level, gasketed roof curb that matches the unit supply, exhaust, and intake openings; grade-mounted units shall be set on a level housekeeping pad.
−
−### After setting, the unit shall be verified level so the drain pan slopes to drain.
−
−### Vibration isolation shall be provided as required by the unit type and location.
−
−## Clearances {toc}
−
−### Service clearances shall be maintained per the manufacturer's instructions for energy recovery wheel or core removal, coil pull, filter access, and compressor and control service, and for the airflow clearance at outdoor intakes and exhausts.
−
−### Clearances shall be coordinated with [[drawing: the roof plan / mechanical equipment layout]].
−
−## Outdoor Air Intake Location {toc}
−
−### The outdoor air intake shall be located to draw clean air and shall comply with the ASHRAE 62.1 separation distances from exhaust outlets, plumbing vents, cooling towers, loading docks, and other contaminant sources.
−
−### The intake and the unit's own exhaust discharge shall be separated so the exhaust is not short-circuited back into the intake.
−
−### The DOAS conditions 100% outdoor air, so a poorly located intake contaminates the entire ventilation supply. {note}
−
−### Intake and exhaust locations are [[drawing: as indicated on the roof plan and the mechanical site plan]].
−
−## Condensate {toc}
−
−### The condensate drain shall be trapped with a seal depth matched to the unit static pressure, run to an approved point of disposal with continuous slope, and provided with a union for trap cleaning.
−
−### Where the unit is in a freezing location, the condensate drain shall be protected from freezing.
−
−## Duct, Intake, and Exhaust Connections {toc}
−
−### Supply and exhaust ductwork shall connect through flexible connectors and shall be independently supported so duct weight is not carried by the casing.
−
−### Ductwork construction shall conform to [[sync/hvac-ductwork]], and supply ductwork carrying cold, dehumidified DOAS air shall be insulated and vapor-sealed per [[sync/mechanical-insulation]] to prevent external condensation.
−
−# Startup and Commissioning {toc}
−
−```datasheet
−label: Startup and Commissioning Level
−type: select
−options:
− - "Manufacturer startup with TAB verification"
− - "Manufacturer startup, TAB, and functional performance testing by commissioning agent (standard)"
− - "Manufacturer startup, TAB, FPT, and deferred seasonal (wet-condition) dehumidification test"
−default: "Manufacturer startup, TAB, and functional performance testing by commissioning agent (standard)"
−```
−
−## Startup shall be performed by a factory-trained representative of the manufacturer.
−
−## The startup sequence shall verify refrigerant charge (DX and heat-pump units), fan rotation and airflow, energy recovery drive operation and purge (where provided), the dehumidification-and-reheat sequence holding the leaving dewpoint, the heating sequence, the frost-control sequence, and the reporting of all BAS points.
−
−## TAB per [[sync/testing-adjusting-and-balancing]] and functional performance testing by the commissioning agent shall follow startup.
−
−## Commissioning shall include a wet-condition test of dehumidification where the season permits, or a documented plan for deferred seasonal testing where it does not.
−
−# Warranty {toc}
−
−## Equipment Warranty {toc}
−
−```datasheet
−label: Equipment Warranty Period
−type: select
−options:
− - "1 year parts and labor"
− - "2 years parts and labor"
− - "5 years parts, 1 year labor"
−default: "1 year parts and labor"
−```
−
−### The manufacturer shall warrant the complete unit against defects in materials and workmanship from the date of substantial completion.
−
−## Compressor Warranty {toc}
−
−```datasheet
−label: Compressor Warranty
−type: radio
−options:
− - "Standard — 1 year same as equipment"
− - "Extended — 5 years on compressor"
−default: "Extended — 5 years on compressor"
−```
−
−### The compressor(s) in DX and heat-pump units shall carry an extended warranty.
−
−### An extended compressor warranty is required because compressor replacement is the most consequential failure on a packaged DOAS. {note}
−
−## Energy Recovery Component Warranty {toc}
−
−```datasheet
−label: Energy Recovery Component Warranty
−type: radio
−options:
− - "1 year (minimum)"
− - "5 years on energy recovery wheel/core and drive"
−default: "5 years on energy recovery wheel/core and drive"
−```
−
−### The energy recovery device — the wheel and its drive and seals, or the fixed-plate core, or the heat-pipe/runaround assembly — shall carry a warranty against defects and against loss of rated effectiveness from a defect.
−
−## Installation Warranty {toc}
−
−### The Contractor shall warrant the installation workmanship, including the curb and intake/exhaust connections, condensate, flexible connections, and controls terminations, for one year from substantial completion.
−
−# Spare Parts {toc}
−
−```datasheet
−label: Spare Parts at Substantial Completion
−type: checkbox
−options:
− - "One complete set of spare filters (each type and MERV)"
− - "One energy recovery wheel drive belt (rotary units)"
− - "One set of energy recovery wheel seals (rotary units)"
− - "One set of access door gaskets"
− - "Set of spare fuses for all fuse types installed"
−default: "One complete set of spare filters (each type and MERV)"
−```
−
−## Spare filters shall be stored in sealed manufacturer's packaging labeled with the unit designation, MERV rating, and the installation date of the set in service.
−
−## The O&M manual shall include the filter change schedule, the energy recovery maintenance schedule (wheel seal and belt inspection, or fixed-plate core cleaning), and the condensate trap cleaning procedure.
+---
+title: Dedicated Outdoor Air Systems
+category: Mechanical / Air Distribution
+description: >
+ When to use: Factory-assembled dedicated outdoor air units that condition 100% outdoor air to a controlled leaving air dew point and supply air temperature, independent of the sensible heating and cooling of the spaces they ventilate. Covers packaged outdoor and indoor units with direct-expansion, heat pump, or chilled water cooling; hot gas, wraparound, hydronic, and electric reheat; heat pump, gas-fired, electric, hydronic, and recovery-only heating; the air-to-air energy recovery section and its exhaust side; supply and exhaust fans; filtration; casing, drain pans, and curbs; the refrigerant, its safety group, and the detection provisions that go with mildly flammable refrigerants; the supply air temperature and dew point control strategy and the unit's interface to the building automation system and to the parallel sensible system; and the setting, connection, startup, and commissioning of the installed unit. Applies to units serving variable refrigerant flow, fan coil, water-source heat pump, chilled beam, and radiant systems, to units supplying laboratory make-up air, and to units delivering ventilation air directly to occupied spaces.
+
+ Not intended for: Central station air handling units that mix return air, and field-erected 100% outdoor air central station units without a packaged dew point control sequence ([[sync/air-handling-units]]); packaged rooftop units with return air mixing and an integral economizer ([[sync/packaged-rooftop-units]]); make-up air units that replace exhaust air without controlling leaving air dew point ([[sync/makeup-air-units]]); stand-alone packaged energy recovery ventilators, and the recovery component as a rated product ([[sync/energy-recovery-ventilators]]); the parallel sensible terminal equipment ([[sync/variable-refrigerant-flow-systems]], [[sync/fan-coil-units]], [[sync/chilled-beams]], [[sync/air-terminal-units]]); field refrigerant piping between split components ([[sync/refrigerant-piping]]); ductwork beyond the unit connections ([[sync/hvac-ductwork]]); diffusers, grilles, and registers ([[sync/hvac-air-distribution-devices]]); hydronic piping to the coils ([[sync/hydronic-piping]]); the building automation system and its supervisory sequences ([[sync/building-automation-system]]); and testing, adjusting, and balancing of the completed system ([[sync/testing-adjusting-and-balancing]]).
+---
+
+# Scope {toc}
+
+## A dedicated outdoor air unit conditions the building's ventilation air and nothing else. It draws 100% outdoor air, recovers energy from the exhaust where the code or the project calls for it, cools the air below the dew point the spaces need and holds that dew point, reheats the air to a chosen supply temperature, tempers it in winter, filters it, and delivers it either to the spaces or to the inlets of the parallel equipment that carries the sensible load. What separates it from a mixed-air air handler is that the latent load of the building is assigned to this one unit and the dry-bulb load to other equipment, so the leaving air dew point rather than the supply air temperature is the quantity the unit is selected and controlled on. {note}
+
+## The following are covered when they form part of the unit: {note}
+
+- Casing, base, access provisions, and exterior finish
+- Supply fan, exhaust fan, motors, and drives
+- The air-to-air energy recovery section, its purge and frost control provisions, and its bypass
+- Direct-expansion and heat pump refrigerant circuits, compressors, condensers, and expansion devices
+- Chilled water cooling coils
+- Hot gas, wraparound, sensible wheel, hydronic, and electric reheat sections
+- Heat pump, gas-fired, electric resistance, hydronic, and steam heating sections
+- Refrigerant detection and mitigation provisions
+- Filter sections on the outdoor air and exhaust air streams
+- Outdoor air and exhaust air dampers, hoods, and louvers furnished with the unit
+- Drain pans, condensate connections, and traps
+- Humidifier sections furnished within the unit
+- Roof curb, vibration isolation, and seismic and wind restraint at the curb
+- Unit-mounted controls, the dew point and supply air temperature control sequence, safety devices, and the physical interface to the building automation system
+- Rigging, setting, connection, startup, and commissioning of the installed unit
+
+## The following are outside this standard: {note}
+
+- Ductwork, duct accessories, and duct insulation beyond the unit connections, covered by [[sync/hvac-ductwork]], [[sync/duct-accessories]], and [[sync/mechanical-insulation]]
+- Central station air handling units, whether mixed-air or field-erected for 100% outdoor air without a packaged dew point sequence, covered by [[sync/air-handling-units]]
+- Packaged rooftop units that mix return air, covered by [[sync/packaged-rooftop-units]]
+- Make-up air units that replace exhausted air to hold building pressure without controlling leaving air dew point, covered by [[sync/makeup-air-units]]
+- Stand-alone packaged energy recovery ventilators, and the recovery component as a rated product, covered by [[sync/energy-recovery-ventilators]]
+- The parallel sensible equipment the unit works alongside, covered by [[sync/variable-refrigerant-flow-systems]], [[sync/fan-coil-units]], [[sync/water-source-heat-pumps]], [[sync/chilled-beams]], and [[sync/air-terminal-units]]
+- Field refrigerant piping between a split unit and its remote condensing section, covered by [[sync/refrigerant-piping]]
+- Field-installed and replacement coils, covered by [[sync/heating-and-cooling-coils]]
+- The humidifier equipment itself, covered by [[sync/humidifiers]]
+- An indirect or direct evaporative stage built into the unit, covered by [[sync/evaporative-coolers]]
+- Hydronic piping, valves, and specialties serving the coils, covered by [[sync/hydronic-piping]]
+- Gas piping to the unit connection, covered by [[sync/natural-gas-piping]] and [[sync/fuel-gas-piping]]
+- Condensate drain piping beyond the unit trap, covered by [[sync/condensate-drainage-piping]]
+- The roofing membrane and the flashing of the curb into it, covered by [[sync/membrane-roofing]] and [[sync/sheet-metal-flashing-and-trim]]
+- The building automation system, its supervisory sequences, and control devices not mounted on the unit, covered by [[sync/building-automation-system]] and [[sync/hvac-controls-instrumentation]]
+- The fire alarm system that receives the duct smoke detector signal, covered by [[sync/fire-alarm-systems]]
+- Testing, adjusting, and balancing of the completed system, covered by [[sync/testing-adjusting-and-balancing]]
+
+## Where the unit supplies make-up air to laboratory spaces, the exhaust system, the hood performance, and the room pressure relationship are covered by [[sync/laboratory-exhaust-and-fume-hoods]]; this standard covers the outdoor air unit that feeds that make-up. {note}
+
+## Each unit shall be furnished as a complete assembly by a single manufacturer, who shall be responsible for the energy recovery, refrigeration, dehumidification, reheat, heating, air-side, and control performance of the unit as a whole.
+
+## The interaction of the recovery device, the cooling coil, and the reheat source is what decides whether the unit holds its leaving air dew point, and that interaction is resolved at the factory on a packaged unit or not at all. A unit assembled in the field from separately procured sections has no party who owns the dew point. {note}
+
+## The unit locations and tags shall be as indicated on [[drawing: the mechanical plans]].
+
+## Per-tag quantities are scheduled and project-wide policy is selected in the datasheet. Airflows, static pressures, leaving air dew point, capacities, heating inputs, and electrical characteristics vary with every unit on the project and live on the mechanical equipment schedule; the construction, options, control strategy, and warranty decisions that apply to every unit on the project are made once here. {note}
+
+## Where a requirement of this standard conflicts with a requirement of a standard that governs a connected system, the Engineer of Record shall make the initial determination of which requirement governs.
+
+# Referenced Standards {toc}
+
+## Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
+
+## Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
+
+| Standard | Title |
+|----------|-------|
+| ANSI/AHRI 920 (I-P) | Performance Rating of Direct Expansion-Dedicated Outdoor Air System Units |
+| ANSI/AHRI 1060 (I-P) | Performance Rating of Air-to-Air Exchangers for Energy Recovery Ventilation Equipment |
+| ANSI/AHRI 410 | Performance Rating of Forced-Circulation Air-Cooling and Air-Heating Coils |
+| ANSI/AHRI 430 (I-P) | Performance Rating of Central Station Air-handling Unit Supply Fans |
+| ANSI/AHRI 270 | Sound Performance Rating of Outdoor Unitary Equipment |
+| ANSI/AHRI 370 | Sound Performance Rating of Large Air-cooled Outdoor Refrigerating and Air-conditioning Equipment |
+| ANSI/ASHRAE 62.1 | Ventilation and Acceptable Indoor Air Quality |
+| ANSI/ASHRAE/IES 90.1 | Energy Standard for Sites and Buildings Except Low-Rise Residential Buildings |
+| ANSI/ASHRAE 55 | Thermal Environmental Conditions for Human Occupancy |
+| ANSI/ASHRAE 15 | Safety Standard for Refrigeration Systems |
+| ANSI/ASHRAE 34 | Designation and Safety Classification of Refrigerants |
+| ANSI/ASHRAE 52.2 | Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size |
+| ANSI/ASHRAE 84 | Method of Testing Air-to-Air Heat/Energy Exchangers |
+| ANSI/ASHRAE 170 | Ventilation of Health Care Facilities |
+| ANSI/AMCA 210 / ANSI/ASHRAE 51 | Laboratory Methods of Testing Fans for Certified Aerodynamic Performance Rating |
+| ANSI/AMCA 300 | Reverberant Room Method for Sound Testing of Fans |
+| ANSI/AMCA 500-D | Laboratory Methods of Testing Dampers for Rating |
+| ANSI/AMCA 500-L | Laboratory Methods of Testing Louvers for Rating |
+| ANSI/AMCA 610 | Laboratory Methods of Testing Airflow Measurement Stations for Performance Rating |
+| UL 60335-2-40 | Household and Similar Electrical Appliances - Safety - Particular Requirements for Electrical Heat Pumps, Air-Conditioners and Dehumidifiers |
+| UL 1995 | Heating and Cooling Equipment |
+| UL 900 | Air Filter Units |
+| UL 508A | Industrial Control Panels |
+| ANSI Z21.47 / CSA 2.3 | Gas-Fired Central Furnaces |
+| ANSI Z83.8 / CSA 2.6 | Gas Unit Heaters, Gas Packaged Heaters, Gas Utility Heaters, and Gas-Fired Duct Furnaces |
+| NFPA 54 / ANSI Z223.1 | National Fuel Gas Code |
+| NFPA 70 | National Electrical Code |
+| NFPA 72 | National Fire Alarm and Signaling Code |
+| NFPA 90A | Standard for the Installation of Air-Conditioning and Ventilating Systems |
+| NEMA MG 1 | Motors and Generators |
+| ASTM A653 | Steel Sheet, Zinc-Coated or Zinc-Iron Alloy-Coated by the Hot-Dip Process |
+| ASTM B117 | Operating Salt Spray (Fog) Apparatus |
+| ASCE 7 | Minimum Design Loads and Associated Criteria for Buildings and Other Structures |
+| IMC | International Mechanical Code |
+| IECC | International Energy Conservation Code |
+| SMACNA HVAC Duct Construction Standards | HVAC Duct Construction Standards - Metal and Flexible |
+| 40 CFR Part 82 Subpart F | Recycling and Emissions Reduction |
+| 40 CFR Part 84 | Phasedown of Hydrofluorocarbons, Technology Transition |
+
+# Submittals {toc}
+
+## Action Submittals {toc}
+
+### The Contractor shall submit the following for each unit tag:
+
+- Unit configuration drawing showing the section sequence from the outdoor air intake to the supply connection and from the exhaust inlet to the exhaust discharge, overall dimensions, connection sizes and locations, operating and shipping weights, center of gravity, corner weights, and the service clearances on every side
+- A psychrometric analysis plotting the state of the air entering the unit, leaving the energy recovery section, leaving the cooling coil, leaving the reheat section, and leaving the unit, at the dehumidification design condition and at the heating design condition, with the leaving air dew point and supply air temperature stated at each
+- Certified performance under the certification program indicated in the datasheet, giving the moisture removal capacity and the rated efficiency metrics, and for heat pump units the heating capacity and efficiency, at the standard rating conditions and at the project design conditions
+- Dehumidification capacity at the design condition and at the minimum capacity step of the unit, demonstrating the leaving air dew point held at each
+- Energy recovery data giving the device type, the sensible, latent, and total effectiveness at the design airflows, the exhaust air transfer ratio and outdoor air correction factor, the pressure drop added to each airstream, the frost control method and its initiation temperature, and the purge arrangement where furnished
+- Refrigerant designation, safety group, and factory charge by circuit, and where a refrigerant detection system is furnished, the sensor locations, the mitigation action, and the charge limit the listing establishes for the unit
+- Compressor data giving type, quantity, capacity control method, and the minimum capacity step
+- Reheat section data giving the reheat source, the capacity available at the design condition, and the control method
+- Heating section data giving input and output for gas-fired sections with the certification identified, capacity and stage count for electric sections, integrated heating capacity at the outdoor design temperature and at the compressor heating operation limit for heat pumps, and coil selection data for hydronic and steam sections
+- Coil selection data for every coil, giving entering and leaving air conditions, face velocity, rows, fin spacing, fin and tube material and any coating, and air-side and fluid-side pressure drop
+- Supply and exhaust fan selection data showing the certified fan curve with the design operating point plotted against the calculated system resistance, the shaft power at that point, and the fan power compliance calculation
+- Motor data giving nameplate power, speed, voltage, phase, full-load amperes, efficiency, enclosure, and inverter-duty rating where applicable
+- Sound power levels for the outdoor radiated path under the applicable sound rating program, and for the supply discharge, the outdoor air intake, and the exhaust discharge in octave bands
+- Casing construction details giving panel construction, insulation type and thermal resistance, casing air leakage, exterior finish and its salt spray rating, and access panel arrangement
+- Filter data for each filter bank giving efficiency rating, depth, quantity and size, initial resistance, and recommended change-out resistance
+- Drain pan drawing giving material, slope, extent, connection size and location, and the trap arrangement
+- Roof curb drawing giving curb height, plan dimensions, insulation, wood nailer, opening locations, cross supports, gasketing, and the unit-to-curb attachment
+- Vibration isolation data and, where restraint is required, seismic and wind restraint details and calculations bearing the seal of an engineer licensed in the jurisdiction of the project
+- Electrical data giving minimum circuit ampacity, maximum overcurrent protective device, short-circuit current rating of the control panel, disconnect configuration, and the wiring diagram with field termination points
+- Unit controller data giving the control configuration, the written dew point and supply air temperature sequence, the communication interface, and a complete point list with object names, types, units, and read or write access
+
+```datasheet
+label: Action Submittals Required
+type: checkbox
+options:
+ - "Unit configuration drawing with weights and service clearances"
+ - "Psychrometric analysis at the design conditions"
+ - "Certified performance and efficiency ratings"
+ - "Dehumidification capacity at design and at minimum capacity"
+ - "Energy recovery data"
+ - "Refrigerant, charge, and detection system data"
+ - "Compressor and capacity control data"
+ - "Reheat section data"
+ - "Heating section data"
+ - "Coil selection data"
+ - "Certified fan curves and fan power compliance"
+ - "Motor data"
+ - "Sound power levels"
+ - "Casing construction details"
+ - "Filter data"
+ - "Drain pan and trap drawing"
+ - "Roof curb drawing"
+ - "Vibration isolation and restraint data"
+ - "Electrical data and wiring diagram"
+ - "Unit controller data, sequence, and point list"
+default:
+ - "Unit configuration drawing with weights and service clearances"
+ - "Psychrometric analysis at the design conditions"
+ - "Certified performance and efficiency ratings"
+ - "Dehumidification capacity at design and at minimum capacity"
+ - "Energy recovery data"
+ - "Refrigerant, charge, and detection system data"
+ - "Compressor and capacity control data"
+ - "Reheat section data"
+ - "Heating section data"
+ - "Coil selection data"
+ - "Certified fan curves and fan power compliance"
+ - "Motor data"
+ - "Sound power levels"
+ - "Casing construction details"
+ - "Filter data"
+ - "Drain pan and trap drawing"
+ - "Roof curb drawing"
+ - "Vibration isolation and restraint data"
+ - "Electrical data and wiring diagram"
+ - "Unit controller data, sequence, and point list"
+```
+
+### No unit shall be released for fabrication until the action submittal for that unit has been reviewed and returned.
+
+### The psychrometric analysis shall be prepared at the dehumidification design condition indicated in the datasheet and not at the cooling dry-bulb design condition alone.
+
+### The psychrometric analysis is the submittal that proves the unit. A catalog capacity at a standard rating point says nothing about whether the recovery section, the coil, and the reheat together reach the scheduled dew point on the site's wettest design hour, and the state points are what the reviewer checks against the schedule and what the commissioning agent later compares the running unit to. {note}
+
+## Informational Submittals {toc}
+
+### The Contractor shall submit the following for information at the times indicated in each item:
+
+- Rigging and setting plan, submitted before the unit ships, showing the crane location, the pick radius, the lifting points and spreader arrangement, and the temporary loads imposed on the roof structure
+- Refrigerant handling certification under 40 CFR Part 82 Subpart F for every individual who will open, evacuate, charge, or recover a refrigerant circuit on the project
+- Evidence of training in mildly flammable refrigerant handling for every individual who will work on a unit carrying a refrigerant in a flammable safety group
+- Manufacturer's field service report for each site visit made during the warranty period
+- Written record of the pre-existing condition of any roofing or adjacent surface the Contractor is required to restore
+
+```datasheet
+label: Informational Submittals Required
+type: checkbox
+options:
+ - "Rigging and setting plan before shipment"
+ - "Refrigerant handling certifications"
+ - "Flammable refrigerant training records"
+ - "Field service reports during the warranty period"
+ - "Pre-existing condition record for restored surfaces"
+default:
+ - "Rigging and setting plan before shipment"
+ - "Refrigerant handling certifications"
+ - "Field service reports during the warranty period"
+```
+
+## Closeout Submittals {toc}
+
+### The Contractor shall submit the following at or before substantial completion:
+
+- Operation and maintenance manuals for each unit, indexed by unit tag, containing installation, operation, maintenance, and troubleshooting instructions, a parts list for every furnished component, and the maintenance schedule for filters, coils, the recovery device and its seals and drive, the condensate system, belts, and refrigerant detection sensors
+- As-built wiring diagrams and the building automation system point list with the terminal designations used on the unit
+- Certified factory run-test report for each unit
+- Startup report for each unit signed by the person who performed the startup, recording refrigerant charge by circuit, operating pressures and temperatures, motor current, the measured leaving air dew point and supply air temperature, and the setpoint of every safety device
+- Refrigerant charge record for each unit giving the refrigerant designation, the factory charge by circuit, and any field adjustment with the weight added or removed
+- Commissioning record demonstrating dew point control, reheat and supply air temperature control, energy recovery operation and frost control, the interlock to the parallel sensible system, safety lockouts, and refrigerant detection and mitigation where furnished
+- Air balance report for the units and their connected systems, recording the outdoor and exhaust airflows through the recovery device
+- Record of the filter media installed at substantial completion, giving efficiency rating, quantity, size, and installation date
+- Warranty documentation correlating each unit serial number to its installation date and to the expiration date of the unit, compressor, recovery component, and heat exchanger warranties
+- Signed receipt from the Owner for the spare parts delivered
+
+```datasheet
+label: Closeout Submittals Required
+type: checkbox
+options:
+ - "Operation and maintenance manuals indexed by unit tag"
+ - "As-built wiring diagrams and point list"
+ - "Certified factory run-test report for each unit"
+ - "Signed startup report for each unit"
+ - "Refrigerant charge record for each unit"
+ - "Commissioning record"
+ - "Air balance report with recovery device airflows"
+ - "Installed filter media record"
+ - "Warranty documentation correlated to serial numbers"
+ - "Spare parts receipt"
+default:
+ - "Operation and maintenance manuals indexed by unit tag"
+ - "As-built wiring diagrams and point list"
+ - "Certified factory run-test report for each unit"
+ - "Signed startup report for each unit"
+ - "Refrigerant charge record for each unit"
+ - "Commissioning record"
+ - "Air balance report with recovery device airflows"
+ - "Installed filter media record"
+ - "Warranty documentation correlated to serial numbers"
+ - "Spare parts receipt"
+```
+
+# Quality Assurance {toc}
+
+## Manufacturer Qualifications {toc}
+
+### The unit manufacturer shall have produced packaged dedicated outdoor air equipment of the type furnished for not less than the number of years indicated in the datasheet.
+
+```datasheet
+label: Minimum Manufacturer Experience
+type: range
+unit: years
+options:
+ min: 0
+ max: 25
+ step: 1
+default: 5
+```
+
+### The manufacturer shall make replacement parts available for the units furnished for not less than ten years after the date of manufacture.
+
+### An experience requirement is a proxy for production maturity, not a measure of it, and it excludes new entrants along with unproven ones. A project prepared to accept a well-capitalized new manufacturer can set the requirement to zero and rely on the certification, testing, and warranty requirements instead. {note}
+
+## Performance Certification {toc}
+
+### Published dehumidification capacity and efficiency ratings shall be certified under the program indicated in the datasheet.
+
+```datasheet
+label: Unit Performance Certification Program
+type: radio
+derived: "the cooling source selected in the datasheet, with direct-expansion and heat pump units rated under AHRI 920 and chilled water units outside any unit certification program"
+options:
+ - "AHRI 920"
+ - "No unit certification program applies"
+default: derived
+```
+
+### Units rated under AHRI 920 shall bear the certification mark of that program, and the integrated seasonal moisture removal efficiency and, for heat pump units, the integrated seasonal coefficient of performance stated in the submittal shall be the certified values.
+
+### Where no unit certification program applies, the manufacturer shall state that fact in the submittal and shall furnish the test data on which the published capacity is based.
+
+### The energy recovery component shall be rated under AHRI 1060 and tested in accordance with ANSI/ASHRAE 84, and the published effectiveness, exhaust air transfer ratio, and outdoor air correction factor shall bear the AHRI certification mark.
+
+### Coils shall be rated in accordance with AHRI 410.
+
+### Fan performance shall be rated from tests in accordance with ANSI/AMCA 210.
+
+### Capacities and efficiencies stated in the submittal shall be the certified ratings and not uncertified catalog selections.
+
+### AHRI 920 rates a direct-expansion dedicated outdoor air unit on the moisture it removes per unit of electrical energy across a set of outdoor conditions, which is the quantity the unit exists to deliver, rather than on the cooling capacity a comfort unit is rated on. A chilled water unit has no compressor to meter, so the program does not cover it and its capacity rests on the coil rating and the manufacturer's test. {note}
+
+## Safety Listing {toc}
+
+### The complete unit, including every factory-installed electrical and refrigerant-system component, shall be listed and labeled by a Nationally Recognized Testing Laboratory under the standard indicated in the datasheet.
+
+```datasheet
+label: Unit Safety Listing Standard
+type: radio
+options:
+ - "UL 60335-2-40"
+ - "UL 1995"
+```
+
+### A unit charged with a refrigerant in a flammable safety group shall be listed under UL 60335-2-40.
+
+### Units listed to UL 1995 are acceptable only where the refrigerant is in a nonflammable safety group and the Authority Having Jurisdiction accepts that listing for the equipment furnished.
+
+### Gas-fired heating sections shall additionally be certified to ANSI Z21.47 / CSA 2.3, or to ANSI Z83.8 / CSA 2.6 where the section is a duct furnace.
+
+### Factory-wired control panels shall be listed to UL 508A.
+
+### Each factory-wired control panel shall bear a label giving the short-circuit current rating of the panel.
+
+### UL 60335-2-40 is the listing standard that contains the charge limits, the refrigerant detection requirements, and the mitigation logic for mildly flammable refrigerants, which is why a flammable-refrigerant unit cannot be listed under the older standard. For a nonflammable refrigerant, both listings cover the same hazards and the choice follows the manufacturer's certification history and what the Authority Having Jurisdiction has seen before. {note}
+
+## Refrigerant Handling Qualification {toc}
+
+### Refrigerant circuits shall be opened, evacuated, charged, and recovered only by an individual certified under 40 CFR Part 82 Subpart F.
+
+### Where the unit carries a refrigerant in a flammable safety group under ASHRAE 34, the individuals working on the circuit shall have completed training covering the handling, storage, leak response, and tool requirements that apply to that refrigerant.
+
+### Recovery machines, vacuum pumps, manifolds, leak detectors, and charging equipment used on a unit carrying a refrigerant in a flammable safety group shall be rated by their makers for that service.
+
+## Preinstallation Conference {toc}
+
+### A preinstallation conference shall be held before the first unit is set, attended by the Contractor, the mechanical installer, the roofing installer where units are curb-mounted, the electrical installer, the controls installer, the installer of the parallel sensible system, the testing and balancing agent, the commissioning agent where one is engaged, and the Owner's representative.
+
+### The conference agenda shall cover the curb setting and flashing sequence, the structural readiness at each unit location, the crane plan, the utility connections and their sequence, the refrigerant safety provisions, the division of control responsibility between the unit controller, the parallel system, and the building automation system, and the startup and commissioning schedule including any seasonal test that cannot be run at substantial completion.
+
+# Service Conditions and Site Data {toc}
+
+## Dehumidification Design Condition {toc}
+
+### Each unit shall be selected to deliver its scheduled leaving air dew point at the dehumidification design outdoor air condition indicated in the datasheet.
+
+```datasheet
+label: Dehumidification Design Outdoor Air Condition
+type: text
+drawing_ref: "the mechanical equipment schedule"
+default: deferred
+```
+
+### The dehumidification design condition shall be the outdoor dew point design condition with its mean coincident dry-bulb for the project location, and not the cooling dry-bulb design condition.
+
+### Each unit shall also deliver its scheduled supply air temperature at [[parameter: site-ambient-temperature-maximum]] with the condenser coil clean.
+
+### The hottest hour of the year is rarely the wettest. The peak dry-bulb hour pairs a high temperature with a moderate humidity ratio, while the peak dew point hour pairs a moderate temperature with the highest moisture content the site sees, and it is the second one that loads a coil whose job is to remove moisture. A unit selected at the dry-bulb design can be short on latent capacity on an overcast, humid afternoon by a margin that the dry-bulb selection never reveals. {note}
+
+## Heating Design Condition {toc}
+
+### The heating capacity of each unit, net of energy recovery, at [[parameter: site-ambient-temperature-minimum]] shall be not less than the value required to deliver the scheduled heating-season supply air temperature at the design outdoor airflow.
+
+### The integrated heating capacity of each heat pump unit at [[parameter: site-ambient-temperature-minimum]] shall be stated in the submittal.
+
+### A unit handling 100% outdoor air sees the full winter design temperature at its entering face with no return air to temper it, so the heating section is sized on the design outdoor airflow and the full temperature rise from outdoor design to supply setpoint, less only what the recovery device returns. The recovery contribution at the design hour is itself reduced by frost control, which is why the capacity is stated net of recovery as the unit actually operates. {note}
+
+## Altitude {toc}
+
+### Cooling, heating, fan, and motor ratings shall be corrected for [[parameter: altitude]] in accordance with the manufacturer's published correction factors.
+
+### The altitude-corrected ratings shall be the values published in the submittal.
+
+### Gas-fired heating sections shall be de-rated for [[parameter: altitude]] in accordance with the listing and NFPA 54.
+
+### The altitude de-rated gas input shall be stated in the submittal.
+
+## Corrosive Atmospheres {toc}
+
+### The corrosion protection of coils in the outdoor airstream shall be as indicated in the datasheet.
+
+```datasheet
+label: Outdoor Airstream Coil Corrosion Protection
+type: select
+options:
+ - "Uncoated aluminum fin on copper tube"
+ - "Aluminum fin on copper tube with an electrodeposited epoxy coating"
+ - "Aluminum fin on copper tube with an applied phenolic coating"
+ - "Copper fin on copper tube"
+default: "Uncoated aluminum fin on copper tube"
+```
+
+### The corrosion protection of the air-cooled condenser coil shall be as indicated in the datasheet.
+
+```datasheet
+label: Condenser Coil Corrosion Protection
+type: select
+options:
+ - "Uncoated aluminum fin on copper tube"
+ - "Aluminum fin on copper tube with an electrodeposited epoxy coating"
+ - "Aluminum fin on copper tube with an applied phenolic coating"
+ - "Microchannel aluminum coil with an electrodeposited coating"
+ - "Copper fin on copper tube"
+default: "Uncoated aluminum fin on copper tube"
+```
+
+### Where a coil coating is selected, the coating shall be applied after fin and tube assembly so that the tube-to-fin interface is coated.
+
+### Where a coil coating is selected, the manufacturer shall state in the submittal the salt spray exposure the coated coil has been tested to.
+
+### Every coil in a dedicated outdoor air unit sees the outdoor atmosphere all of the time, not through a return air fraction, and the cooling coil sees it wet for most of the cooling season. Chloride from marine air and sulfur compounds from industrial and vehicular exhaust supply the electrolyte that turns the aluminum-to-copper pair active, so the fin corrodes, the bond to the tube opens, and capacity falls. An electrodeposited coating is applied by immersing the finished coil and curing a uniform film onto every surface, so it protects the fin-to-tube joint where a sprayed coating cannot reach, at the cost of a small thermal resistance the submittal capacity accounts for. {note}
+
+# Unit Arrangement {toc}
+
+## Unit Construction for Location {toc}
+
+### The casing construction for the installed location shall be as indicated in the datasheet.
+
+```datasheet
+label: Unit Construction for Location
+type: radio
+derived: "the unit location indicated on the mechanical plans, with units set outdoors furnished in weatherproof construction and units set in a mechanical room or penthouse in indoor construction"
+options:
+ - "Outdoor weatherproof construction"
+ - "Indoor construction"
+default: derived
+```
+
+### Outdoor units shall be furnished with a weatherproof casing, a sloped roof panel, a drainable base rail, a rain hood and bird screen at the outdoor air intake, and a weather hood at the exhaust discharge.
+
+### Indoor units shall be furnished with the outdoor air intake and exhaust discharge arranged for duct connection to the building louvers.
+
+### An outdoor unit carries its own weather enclosure and sits where the outdoor air is, which keeps the cold, wet intake duct out of the building; an indoor unit puts the intake and exhaust ducts through the envelope and the condensate, service, and noise inside, and is the arrangement where a roof cannot take the weight, the roof is leased or inaccessible, or the unit is replaced in an existing mechanical room. {note}
+
+## Refrigeration Arrangement {toc}
+
+### Requirements in this article apply to units with a direct-expansion refrigerant circuit.
+
+### The refrigeration arrangement shall be as indicated in the datasheet.
+
+```datasheet
+label: Refrigeration Arrangement
+type: radio
+options:
+ - "Packaged, with the condensing section integral to the unit"
+ - "Split, with a remote condensing section and field refrigerant piping"
+default: "Packaged, with the condensing section integral to the unit"
+```
+
+### Where a split arrangement is selected, the remote condensing section shall be furnished by the unit manufacturer and matched to the unit.
+
+### Where a split arrangement is selected, the field refrigerant piping shall conform to [[sync/refrigerant-piping]].
+
+### Where a split arrangement is selected, the manufacturer shall state in the submittal the maximum equivalent line length and the maximum vertical separation the match is rated for.
+
+### A packaged unit leaves the factory charged and run-tested with its condenser, so the refrigerant circuit arrives proven. A split arrangement exists for the indoor unit whose condenser has to be outdoors, and it moves the charge, the line sizing, the oil return, and the leak test into the field, which is why the piping standard governs it and the manufacturer's match limits bound it. {note}
+
+## Supply Air Delivery {toc}
+
+### The point at which the unit delivers its supply air shall be as indicated in the datasheet.
+
+```datasheet
+label: Supply Air Delivery Point
+type: select
+options:
+ - "Directly to the occupied spaces through dedicated outlets"
+ - "To the return or inlet side of the parallel terminal units"
+ - "To the supply side of the parallel terminal units, downstream of their coils"
+```
+
+### Where the unit delivers to the inlet side of the parallel terminal units, the terminal units shall be selected for the combined airflow and the entering condition the unit delivers.
+
+### Where the unit delivers to the supply side of the parallel terminal units, the supply air temperature setpoints of the two systems shall be coordinated so that neither system reheats or recools what the other has just conditioned.
+
+### Where the unit delivers directly to the spaces, the outlets shall be selected in accordance with [[sync/hvac-air-distribution-devices]] for the supply air temperature indicated in the datasheet at the ventilation airflow.
+
+### Delivering to the terminal inlet mixes the ventilation air with room air before the terminal coil, which hides a cold supply from the occupants and lets the terminal see a steadier entering condition, but ventilation then stops whenever the terminal fan stops and the terminal has to be sized for the extra air. Delivering to the terminal discharge keeps ventilation independent of the terminal fan and avoids the resizing, at the cost of a pressure interaction between two fans in one duct. Dedicated outlets keep the two systems entirely separate and are the arrangement with chilled beams and radiant systems that have no fan at all, and they put a low-airflow outlet in every room that has to throw cold air without a draft. {note}
+
+# Airflow and Static Pressure {toc}
+
+## Design Airflows {toc}
+
+### Each unit shall deliver the design outdoor airflow indicated in the datasheet at the design supply external static pressure, at the site elevation, and with the filters at their change-out resistance.
+
+```datasheet
+label: Design Outdoor Airflow
+type: range
+unit: cfm
+drawing_ref: "the mechanical equipment schedule"
+options:
+ min: 200
+ max: 100000
+ step: 50
+default: deferred
+```
+
+```datasheet
+label: Design Supply External Static Pressure
+type: range
+unit: in. w.g.
+drawing_ref: "the mechanical equipment schedule"
+options:
+ min: 0.1
+ max: 5
+ step: 0.05
+default: deferred
+```
+
+### Each unit furnished with an exhaust fan shall move the design exhaust airflow indicated in the datasheet through the recovery device at the design exhaust external static pressure.
+
+```datasheet
+label: Design Exhaust Airflow Through the Recovery Device
+type: range
+unit: cfm
+drawing_ref: "the mechanical equipment schedule"
+options:
+ min: 0
+ max: 100000
+ step: 50
+default: deferred
+```
+
+```datasheet
+label: Design Exhaust External Static Pressure
+type: range
+unit: in. w.g.
+drawing_ref: "the mechanical equipment schedule"
+options:
+ min: 0
+ max: 5
+ step: 0.05
+default: deferred
+```
+
+### The design outdoor airflow shall be not less than the ventilation ANSI/ASHRAE 62.1 requires for the spaces served, and for health care spaces not less than ANSI/ASHRAE 170 requires.
+
+### The external static pressure is the resistance of the ductwork, accessories, and outlets beyond the unit connections; the unit's own sections are inside it and are the manufacturer's to account for. {note}
+
+### The manufacturer shall add the internal resistance of every furnished section, including the recovery device, the coils, the reheat section, the heating section, and the filters at change-out resistance, to the external static pressure to establish the total static pressure at which each fan is selected.
+
+### The ratio of exhaust airflow to outdoor airflow through the recovery device decides the effectiveness the device delivers and the direction the carryover leaks, so the two airflows are scheduled together and balanced together. A unit whose exhaust is well below its outdoor airflow recovers less than its rating, and a unit whose exhaust exceeds its outdoor airflow depressurizes the building through the recovery section. {note}
+
+## Supply Airflow Control {toc}
+
+### The supply airflow control shall be as indicated in the datasheet.
+
+```datasheet
+label: Supply Airflow Control
+type: select
+options:
+ - "Constant volume at the design outdoor airflow"
+ - "Two airflows, occupied and reduced"
+ - "Variable volume on a demand-controlled ventilation signal"
+ - "Variable volume to a duct static pressure setpoint"
+```
+
+### Where variable volume is selected, the unit shall hold its leaving air dew point and supply air temperature setpoints across the full airflow range, and the minimum airflow at which it does so shall be stated in the submittal.
+
+### Where variable volume is selected, the exhaust fan shall track the supply fan so that the airflow ratio through the recovery device stays within the range the device is rated for.
+
+### Where variable volume to a duct static pressure setpoint is selected, the terminal devices that modulate the ventilation airflow shall conform to [[sync/air-terminal-units]].
+
+### A dedicated outdoor air unit runs at a fixed ventilation rate on most projects because the airflow is the code minimum for the design occupancy and nothing in the space changes it. Demand-controlled ventilation trims that rate when the spaces are below design occupancy, which is where the fan and conditioning energy of a 100% outdoor air unit goes, and it is worth the sensors where occupancy swings widely; a duct static setpoint is the arrangement where zone-level ventilation dampers or terminals meter the air and the unit merely keeps the duct charged. A unit that modulates has to keep its coil wet and its compressor in its operating range at the reduced airflow, which is the submittal item. {note}
+
+## Airflow Measurement {toc}
+
+### Airflow measurement stations shall be furnished in the airstreams indicated in the datasheet.
+
+```datasheet
+label: Airflow Measurement Stations Furnished
+type: checkbox
+options:
+ - "Outdoor airflow measurement station"
+ - "Exhaust airflow measurement station"
+ - "Supply discharge airflow measurement station"
+default:
+ - "Outdoor airflow measurement station"
+```
+
+### Airflow measurement stations shall be rated in accordance with ANSI/AMCA 610.
+
+### Airflow measurement stations shall be accurate across the range from the minimum airflow the unit operates at to the design airflow.
+
+### Measured airflows shall be exposed to the building automation system as points.
+
+### The outdoor airflow of a 100% outdoor air unit is the building's ventilation rate, and a measured value is the only record that the rate is being met after the balance report is filed. A unit that modulates on a demand signal has no fixed damper position to fall back on, so the measurement is what the control loop closes on. {note}
+
+# Dehumidification and Cooling {toc}
+
+## Leaving Air Dew Point {toc}
+
+### Each unit shall cool and dehumidify the outdoor air to the leaving air dew point setpoint indicated in the datasheet at the dehumidification design condition.
+
+```datasheet
+label: Leaving Air Dew Point Setpoint
+type: range
+unit: °F
+drawing_ref: "the mechanical equipment schedule"
+options:
+ min: 35
+ max: 60
+ step: 1
+default: deferred
+```
+
+### The unit shall hold the leaving air dew point setpoint at every outdoor condition between the dehumidification design condition and the outdoor dew point at which dehumidification is no longer called for.
+
+### The dew point control sensing shall be as indicated in the datasheet.
+
+```datasheet
+label: Dew Point Control Sensing
+type: select
+options:
+ - "Dew point sensor in the leaving air"
+ - "Temperature and relative humidity sensors in the leaving air with the dew point computed"
+ - "Cooling coil leaving air temperature as the dew point proxy"
+```
+
+### The dew point control loop shall modulate the cooling capacity to hold the dew point setpoint independently of the supply air temperature loop.
+
+### The dew point is the quantity that decides whether the spaces stay dry, because the ventilation air is the only air in the building being dehumidified and the moisture it carries in has to be below what the spaces can tolerate after the occupants and infiltration add theirs. A comfort space at a typical setpoint tolerates a supply dew point in the low fifties; spaces with chilled beams, radiant cooling, or a stated humidity limit need lower, and the schedule carries the value because it follows from the space criteria rather than from the unit. {note}
+
+### A direct dew point sensor reads the controlled variable and nothing else, and its cost is a sensor that needs periodic calibration. Computing the dew point from temperature and relative humidity doubles the sensors and compounds their errors at the low humidities where the computation is least sensitive. Using the coil leaving temperature as a proxy assumes the air leaves the coil saturated, which holds at design and drifts at part load when the coil is not fully wet, and it is the arrangement on units whose controls were built around a temperature sensor. {note}
+
+## Cooling Source {toc}
+
+### The cooling source shall be as indicated in the datasheet.
+
+```datasheet
+label: Cooling Source
+type: select
+options:
+ - "Direct expansion"
+ - "Chilled water coil"
+ - "No mechanical cooling section"
+default: "Direct expansion"
+```
+
+### Where no mechanical cooling section is selected, the unit shall temper the outdoor air by energy recovery and heating only, and the dew point requirements of this standard do not apply to that unit.
+
+### Direct expansion is the norm for a packaged unit because it brings its own cooling and, with it, the condenser heat that supplies reheat at no purchased energy. A chilled water coil is the arrangement where a central plant already serves the building and the unit is one more load on it, and it has to find its reheat elsewhere. A unit with no cooling at all serves a dry or cold climate where the ventilation air needs tempering and filtration but never dehumidification. {note}
+
+## Direct-Expansion Cooling {toc}
+
+### Requirements in this article apply where the datasheet selects direct-expansion cooling.
+
+### The heat rejection of the direct-expansion circuit shall be as indicated in the datasheet.
+
+```datasheet
+label: Direct-Expansion Heat Rejection
+type: radio
+options:
+ - "Air-cooled condenser"
+ - "Water-cooled condenser on a condenser water or ground loop"
+default: "Air-cooled condenser"
+```
+
+### Where a water-cooled condenser is selected, the condenser water piping shall conform to [[sync/hydronic-piping]] and the condenser shall be rated for the entering water temperature range of the loop it serves.
+
+### The compressor type shall be as indicated in the datasheet.
+
+```datasheet
+label: Compressor Type
+type: select
+options:
+ - "Hermetic scroll"
+ - "Semi-hermetic reciprocating"
+ - "Semi-hermetic screw"
+default: "Hermetic scroll"
+```
+
+### The cooling capacity control shall be as indicated in the datasheet.
+
+```datasheet
+label: Cooling Capacity Control
+type: select
+options:
+ - "Single stage"
+ - "Two stages"
+ - "Three or more stages"
+ - "Variable capacity by digital scroll unloading"
+ - "Variable capacity by inverter-driven compressor"
+```
+
+### The smallest cooling capacity step shall be not more than the percentage of full capacity indicated in the datasheet.
+
+```datasheet
+label: Largest Permitted Minimum Cooling Capacity Step
+type: range
+unit: '%'
+options:
+ min: 10
+ max: 100
+ setpoints: [10, 15, 20, 25, 33, 50, 100]
+```
+
+### Where the datasheet does not state a minimum capacity step, the manufacturer shall state the minimum step of the furnished unit in the submittal.
+
+### The unit shall hold the leaving air dew point setpoint at the minimum capacity step without cycling the compressor more often than the manufacturer's anti-short-cycle timing permits.
+
+### The latent load on a ventilation unit varies far more across a year than the sensible load on a comfort unit. Many of the wettest hours are mild, and a rainy day near saturation carries a large moisture load with almost no temperature difference to work against, so a unit that can only run at full capacity overcools, trips on low coil temperature, cycles off, and delivers wet air on exactly those hours. Staged compressors buy part of that range at low cost; a modulating compressor follows the latent load continuously and is the arrangement where the dew point has to hold through shoulder seasons, at the price of an inverter and an electronic expansion valve. Scroll compressors cover the capacity range packaged units are built in; reciprocating and screw machines appear on large custom units. {note}
+
+### The minimum number of independent refrigerant circuits per unit shall be as indicated in the datasheet.
+
+```datasheet
+label: Minimum Number of Independent Refrigerant Circuits
+type: range
+unit: circuits
+options:
+ min: 1
+ max: 4
+ setpoints: [1, 2, 3, 4]
+```
+
+### Each independent circuit shall have its own compressor or compressors, expansion device, evaporator coil section, and condenser coil section, so that a failure in one circuit does not disable the others.
+
+### Where the minimum circuit count indicated in the datasheet is not offered by the manufacturer at a tag's capacity, the Contractor shall report the conflict to the Engineer of Record before the unit is released for fabrication.
+
+### The expansion device on each circuit shall be as indicated in the datasheet.
+
+```datasheet
+label: Expansion Device
+type: select
+options:
+ - "Thermostatic expansion valve"
+ - "Electronic expansion valve"
+ - "Fixed orifice"
+```
+
+### Where the datasheet selects variable capacity, the expansion device shall be one that maintains superheat control across the full modulation range of the compressor.
+
+### Each circuit shall be furnished with a high-pressure cutout, a low-pressure cutout or loss-of-charge protection, and a compressor motor overload, each of which shall stop the compressor independently of the unit controller.
+
+### Each circuit shall be furnished with a liquid line filter-drier and with service access ports on the high and low sides.
+
+### Each compressor shall be mounted on vibration isolators within the cabinet and furnished with a crankcase heater.
+
+### Mechanical cooling shall be available down to the outdoor temperature indicated in the datasheet.
+
+```datasheet
+label: Minimum Outdoor Temperature for Mechanical Cooling Operation
+type: range
+unit: °F
+options:
+ min: -20
+ max: 65
+ setpoints: [-20, -10, 0, 10, 20, 30, 40, 50, 55, 65]
+```
+
+### Where the datasheet does not state a minimum outdoor temperature for mechanical cooling, the unit shall be furnished for mechanical cooling down to the manufacturer's published low-ambient limit, and that limit shall be stated in the submittal.
+
+### A thermostatic valve controls superheat mechanically and holds a stable feed across the range of a staged compressor; a modulating compressor runs at mass flows a mechanical valve was not sized for at both ends of its range, which is what an electronic valve exists for. A ventilation unit dehumidifies on cool, damp days that a comfort unit would spend in economizer, so the outdoor temperature at which the compressor still has to run is lower than for a rooftop unit, and the head pressure control that keeps a compressor alive at that temperature follows from the temperature the project needs dehumidification at. {note}
+
+## Refrigerant and Safety Group {toc}
+
+### Requirements in this article apply where the datasheet selects direct-expansion cooling or a heat pump heating source.
+
+### The refrigerant shall be as indicated in the datasheet.
+
+```datasheet
+label: Refrigerant Designation (ASHRAE 34)
+type: select
+options:
+ - "R-454B"
+ - "R-32"
+ - "R-410A"
+default: manufacturer
+```
+
+### Where the datasheet leaves the refrigerant to the manufacturer, the manufacturer shall state in the submittal the refrigerant the unit is charged with and its safety group.
+
+### The refrigerant shall be one that 40 CFR Part 84 permits in equipment of the unit's class on the unit's date of manufacture.
+
+### Where a unit is furnished as a replacement that retains existing refrigerant piping or components, the refrigerant selected in the datasheet shall be compatible with the retained components.
+
+### The refrigerant safety group shall be as indicated in the datasheet.
+
+```datasheet
+label: Refrigerant Safety Group (ASHRAE 34)
+type: select
+derived: "the safety classification ASHRAE 34 publishes for the refrigerant the unit is charged with"
+options:
+ - "A1"
+ - "A2L"
+default: derived
+```
+
+### Under the technology transition rule at 40 CFR Part 84, packaged equipment manufactured after the compliance date for its class is limited to refrigerants below a stated global warming potential, and the refrigerants that meet that limit at the pressures this equipment runs at are classified A2L. The refrigerant is therefore a property of the product line rather than a specification choice for new equipment, and the datasheet asserts one only where a project has a reason to, such as matching a retained circuit. {note}
+
+### The safety group is the switch that turns the detection, mitigation, marking, and training articles of this standard on or off, and it follows from the refrigerant rather than from any project decision. {note}
+
+## Refrigerant Detection and Mitigation {toc}
+
+### The refrigerant detection provision shall be as indicated in the datasheet.
+
+```datasheet
+label: Refrigerant Detection System
+type: radio
+derived: "the refrigerant safety group and the charge per circuit, compared against the releasable charge limit UL 60335-2-40 establishes for the unit and the smallest space it serves"
+options:
+ - "Factory-installed refrigerant detection system with mitigation"
+ - "No refrigerant detection system"
+default: derived
+```
+
+### Where a refrigerant detection system is furnished, the sensors, their locations, and the mitigation sequence shall be as covered by the unit listing.
+
+### The Contractor shall not relocate a refrigerant detection sensor or alter the mitigation sequence in the field.
+
+### On detection, the mitigation sequence shall start the supply fan to dilute the released refrigerant, shall de-energize the ignition sources the listing identifies, and shall continue until the measured concentration has fallen below the reset threshold.
+
+### Where a refrigerant detection system is furnished, its alarm shall be exposed to the building automation system as a discrete point regardless of the control points selected in the datasheet.
+
+### Detection sensors shall be installed with the date of installation recorded on the device, and the end of their published service life shall be recorded in the closeout documents.
+
+### A refrigerant in the A2L group burns only within a narrow concentration band and only with a strong ignition source, so the listing manages the hazard by keeping the concentration in any space below a fraction of the lower flammability limit. A ventilation unit has one property that matters here: its supply fan runs whenever the building is occupied and it serves every space on its duct, so a leak diluted through its supply reaches many rooms at once, and the charge limit is set against the smallest of them. Whether a given unit needs detection is a calculation on the charge and the space, which is why it is derived rather than chosen. {note}
+
+## Chilled Water Cooling Coil {toc}
+
+### Requirements in this article apply where the datasheet selects a chilled water cooling coil.
+
+### The chilled water coil shall be selected at the entering and leaving water temperatures indicated in the datasheet.
+
+```datasheet
+label: Chilled Water Coil Entering Water Temperature
+type: range
+unit: °F
+drawing_ref: "the mechanical equipment schedule"
+options:
+ min: 36
+ max: 60
+ step: 0.5
+default: deferred
+```
+
+```datasheet
+label: Chilled Water Coil Leaving Water Temperature
+type: range
+unit: °F
+drawing_ref: "the mechanical equipment schedule"
+options:
+ min: 44
+ max: 70
+ step: 0.5
+default: deferred
+```
+
+### The chilled water coil shall be selected to reach the leaving air dew point setpoint at the design entering water temperature with the water-side pressure drop stated in the submittal.
+
+### The coil control valve shall modulate the water flow to hold the leaving air dew point setpoint.
+
+### Coil connections shall pass through the casing in a gasketed, insulated penetration, and piping serving the coil shall be independently supported so that no part of its weight or thermal movement is carried by the coil header.
+
+### A coil can only cool the air to within a few degrees of the water entering it, so the leaving air dew point a chilled water unit can reach is bounded by the plant's supply temperature. A plant that runs warm for efficiency cannot serve a unit that needs a low dew point, and the two schedules have to agree before either is fixed. {note}
+
+## Cooling Coil Construction {toc}
+
+### Cooling coils shall be rated in accordance with AHRI 410, with copper tubes, fins of the material and protection selected under Corrosive Atmospheres, and headers and connections of a material compatible with the tubes.
+
+### The face velocity across the cooling coil at the design outdoor airflow shall not exceed the value indicated in the datasheet.
+
+```datasheet
+label: Maximum Cooling Coil Face Velocity
+type: range
+unit: fpm
+options:
+ min: 250
+ max: 600
+ setpoints: [250, 300, 350, 400, 450, 500, 550, 600]
+```
+
+### Where the datasheet does not state a maximum face velocity, the coil shall be selected at or below the face velocity the manufacturer publishes as the carryover limit for that coil wet, and that velocity shall be stated in the submittal.
+
+### A dedicated outdoor air coil runs wet at design and at most of the hours it cools, with the air leaving it near saturation. Moisture carries off a wet coil face above a velocity the fin geometry sets, and the droplets land in the reheat coil and the downstream casing, where they re-evaporate into the air the coil just dried or pool where there is no pan. The limit is lower than for a mixed-air coil that spends much of its life dry, and it is the reason a ventilation unit's coil is larger in face area than its airflow alone suggests. {note}
+
+# Reheat {toc}
+
+## Reheat Source {toc}
+
+### The source of the reheat applied after the cooling coil shall be as indicated in the datasheet.
+
+```datasheet
+label: Reheat Source
+type: select
+options:
+ - "No reheat section"
+ - "Hot gas reheat coil"
+ - "Wraparound heat pipe"
+ - "Wraparound pumped coil loop"
+ - "Sensible wheel around the cooling coil"
+ - "Hot water reheat coil"
+ - "Electric reheat coil"
+default: "Hot gas reheat coil"
+```
+
+### Where hot gas reheat is selected, the reheat coil shall be served by the unit's own refrigerant circuit and shall be arranged so that reheat is available whenever the compressor is dehumidifying.
+
+### Where a wraparound heat pipe or pumped coil loop is selected, the precool section shall be upstream of the cooling coil and the reheat section downstream of it in the same airstream, and the capacity transferred at the design condition shall be stated in the submittal.
+
+### Where a sensible wheel around the cooling coil is selected, the wheel shall transfer heat from the air entering the cooling coil to the air leaving it without transferring moisture, and its exhaust air transfer ratio shall be stated in the submittal.
+
+### Where a hot water or electric reheat coil is selected, the arrangement shall be one [[parameter: adopted-energy-code]] permits for reheat following dehumidification, and the provision relied on shall be identified in the submittal.
+
+### Where a hot water reheat coil is selected, the coil shall conform to the Hydronic Heating Section article of this standard.
+
+### Where an electric reheat coil is selected, the coil shall conform to the Electric Resistance Heating Section article of this standard.
+
+### Reaching a low dew point means cooling the air to that dew point, which is colder than most spaces want delivered, and reheat is what lifts it back without putting the moisture back. Where the heat comes from is the decision. Hot gas reheat takes the heat the condenser is rejecting anyway, costs nothing to run, and is available only on a direct-expansion unit while its compressor runs. A wraparound heat pipe or pumped loop precools the entering air with heat it then returns downstream, so it both deepens the dehumidification for the same compressor capacity and reheats for free, with no controls at all on the passive heat pipe and a pump on the loop; it is also the reheat a chilled water unit can have without purchased energy. A sensible wheel does the same job with a rotating mass and a drive. A hot water or electric coil spends purchased energy heating air the unit just cooled, which the energy code limits to the exceptions it lists, and it is the arrangement where no recovered source exists or where the leaving temperature has to be held precisely regardless of load. No reheat at all delivers the air at the coil leaving temperature, which is a legitimate arrangement where the parallel system is sized to take cold ventilation air. {note}
+
+## Reheat Control {toc}
+
+### The reheat capacity control shall be as indicated in the datasheet.
+
+```datasheet
+label: Reheat Capacity Control
+type: radio
+options:
+ - "Modulating"
+ - "Staged or two-position"
+default: "Modulating"
+```
+
+### Reheat shall be controlled to hold the supply air temperature setpoint independently of the dew point control loop.
+
+### Where a passive wraparound device is furnished and the datasheet selects modulating reheat control, the device shall be furnished with a bypass damper, a modulating valve, or a variable-speed pump that controls the heat transferred.
+
+### Where hot gas reheat is furnished, the reheat shall be controlled so that the compressor continues to run for dehumidification when the supply air temperature setpoint is satisfied.
+
+### Reheat that cannot modulate delivers a supply temperature that swings between the coil leaving temperature and the full reheat rise, which the parallel system then corrects at its own cost. A passive heat pipe transfers what the temperature difference across it drives, so on its own it tracks the load roughly but cannot be set; adding a bypass or a valve turns it into a controlled device. The one failure to design out is a reheat loop that satisfies the supply temperature by shutting the compressor off, because the dew point then floats. {note}
+
+# Supply Air Temperature Strategy {toc}
+
+## Cooling-Season Supply Temperature {toc}
+
+### The cooling-season supply air temperature basis shall be as indicated in the datasheet.
+
+```datasheet
+label: Cooling-Season Supply Air Temperature Basis
+type: radio
+options:
+ - "Neutral, reheated to near the space temperature"
+ - "Cold, delivered below the space temperature to carry part of the sensible load"
+```
+
+### The cooling-season supply air temperature setpoint shall be as indicated in the datasheet.
+
+```datasheet
+label: Cooling-Season Supply Air Temperature Setpoint
+type: range
+unit: °F
+drawing_ref: "the mechanical equipment schedule"
+options:
+ min: 45
+ max: 78
+ step: 1
+default: deferred
+```
+
+### Where a cold supply basis is selected, the parallel sensible system shall be sized on the sensible load remaining after the ventilation air's contribution is deducted, and that deduction shall be stated on the mechanical equipment schedule.
+
+### Where a cold supply basis is selected and the unit delivers directly to the spaces, the outlets shall be selected so that the occupied-zone air speed and temperature criteria of ANSI/ASHRAE 55 are met at the supply air temperature indicated in the datasheet.
+
+### Neutral air neither heats nor cools the space, so the parallel system carries the whole sensible load and the two systems never work against each other; it costs the reheat energy, recovered or purchased, that lifts the air from the coil to the room temperature. Cold air uses the dehumidified ventilation air as part of the cooling, which shrinks the parallel equipment and spends less on reheat, and it ties the parallel system's sizing to the ventilation airflow, puts cold air at a low airflow through every outlet, and leaves the spaces overcooled on a mild day unless the supply temperature resets. The choice follows from what the parallel system is: a chilled beam or radiant system wants the ventilation air to do as much as it can, and a variable refrigerant flow or fan coil system usually wants it out of the way. {note}
+
+## Heating-Season Supply Temperature {toc}
+
+### The heating-season supply air temperature basis shall be as indicated in the datasheet.
+
+```datasheet
+label: Heating-Season Supply Air Temperature Basis
+type: radio
+options:
+ - "Neutral, tempered to near the space temperature"
+ - "Warm, delivered above the space temperature to carry part of the heating load"
+```
+
+### The heating-season supply air temperature setpoint shall be as indicated in the datasheet.
+
+```datasheet
+label: Heating-Season Supply Air Temperature Setpoint
+type: range
+unit: °F
+drawing_ref: "the mechanical equipment schedule"
+options:
+ min: 55
+ max: 110
+ step: 1
+default: deferred
+```
+
+### Where a warm supply basis is selected, the unit shall be arranged so that heating is locked out when the parallel system is in cooling in the same zones.
+
+### Neutral tempering keeps the ventilation air from chilling the spaces or the parallel equipment's inlets and leaves the heating to the parallel system; a warm supply offsets part of the envelope load through the ventilation air and lets a parallel system with marginal heating capacity, such as a heat pump at its low-ambient limit, keep up. A warm supply into a zone whose parallel unit is cooling an internal load is the simultaneous heating and cooling the energy code forbids, which is why the lockout exists. {note}
+
+## Setpoint Reset {toc}
+
+### The supply air temperature reset shall be as indicated in the datasheet.
+
+```datasheet
+label: Supply Air Temperature Reset
+type: select
+options:
+ - "None, fixed setpoints by season"
+ - "Reset on outdoor air temperature"
+ - "Reset on the heating and cooling demand of the zones served"
+ - "Reset by the building automation system supervisory logic"
+```
+
+### The leaving air dew point reset shall be as indicated in the datasheet.
+
+```datasheet
+label: Leaving Air Dew Point Reset
+type: radio
+options:
+ - "None, fixed setpoint"
+ - "Reset on the measured space humidity"
+```
+
+### Where any reset is selected, the reset limits shall be stated in the sequence of operation and shall not drive the dew point setpoint above the value at which the spaces served exceed their design humidity.
+
+### Where reset by the building automation system is selected, the reset logic shall reside in the building automation system and shall write the setpoints to the unit controller through the interface, in accordance with [[sync/building-automation-system]].
+
+### A fixed supply temperature is the simplest sequence and the one most units ship with. Resetting it on outdoor temperature warms the supply as the weather cools, which cuts reheat in the shoulder seasons without any zone information; resetting on zone demand uses the parallel system's own calls to decide whether the ventilation air should help or stay neutral, which is the sequence that captures the most energy and needs the most integration. Resetting the dew point upward when the spaces are dry saves compressor energy on the many hours when the design dew point is not needed, and it is only safe where the space humidity is measured and the reset is capped. {note}
+
+# Heating {toc}
+
+## Heating Source {toc}
+
+### The heating source integral to the unit shall be as indicated in the datasheet.
+
+```datasheet
+label: Heating Source
+type: select
+options:
+ - "No heating section, tempering by energy recovery only"
+ - "Reverse-cycle heat pump"
+ - "Natural gas-fired indirect"
+ - "Propane-fired indirect"
+ - "Electric resistance"
+ - "Hot water coil"
+ - "Steam coil"
+```
+
+### Where no heating section is selected, the submittal shall state the supply air temperature the unit delivers at [[parameter: site-ambient-temperature-minimum]] with the recovery device operating and with the recovery device in frost control.
+
+### The heating source is independent of the cooling source, the reheat source, and the recovery device, and no combination of those selections constrains it. {note}
+
+### No heating source is the norm across projects. A heat pump heats from the same compressor that dehumidifies and is the arrangement where the project is electrifying, with its capacity falling as the weather gets colder; gas heat is common where gas is at the site and the winter temperature rise is large; electric resistance where gas is not available or the rise is small; a hydronic or steam coil where a plant already serves the building; and recovery alone where the climate is mild enough that the recovered heat tempers the air to a usable supply temperature on its own. Each is a live choice and the datasheet takes no side. {note}
+
+## Heat Pump Heating {toc}
+
+### Requirements in this article apply where the datasheet selects a reverse-cycle heat pump heating source.
+
+### Compressor heating shall continue in operation down to the outdoor temperature indicated in the datasheet.
+
+```datasheet
+label: Minimum Outdoor Temperature for Compressor Heating Operation
+type: range
+unit: °F
+options:
+ min: -25
+ max: 45
+ setpoints: [-25, -15, -5, 0, 5, 10, 17, 25, 35, 45]
+```
+
+### The integrated heating capacity at the compressor heating operation limit shall be stated in the submittal.
+
+### The supplemental heat source shall be as indicated in the datasheet.
+
+```datasheet
+label: Heat Pump Supplemental Heat Source
+type: select
+options:
+ - "None"
+ - "Electric resistance"
+ - "Natural gas-fired"
+ - "Propane-fired"
+ - "Hot water coil"
+```
+
+### Supplemental heat shall be locked out by the unit controls above the outdoor temperature indicated in the datasheet.
+
+```datasheet
+label: Supplemental Heat Lockout Outdoor Temperature
+type: range
+unit: °F
+options:
+ min: 10
+ max: 65
+ setpoints: [10, 20, 25, 30, 35, 40, 45, 50, 55, 65]
+```
+
+### Below the lockout temperature, supplemental heat shall be energized only when compressor heating cannot hold the supply air temperature setpoint.
+
+### The defrost control method shall be as indicated in the datasheet.
+
+```datasheet
+label: Heat Pump Defrost Control
+type: select
+options:
+ - "Demand defrost initiated by coil temperature and pressure"
+ - "Time-initiated and temperature-terminated defrost"
+```
+
+### During a defrost cycle the supplemental heat, where furnished, shall be energized as the listing permits so that the supply air is not delivered below the heating-season supply air temperature setpoint by more than the manufacturer's published defrost depression.
+
+### The reversing valve shall be energized in the mode the manufacturer designates so that a loss of control signal leaves the unit in that mode, and the mode shall be stated in the submittal.
+
+### A heat pump's heating capacity falls as the outdoor temperature falls while a 100% outdoor air unit's heating load rises in direct proportion to the same temperature, so the two curves cross at a balance point that sits higher than it would for a comfort unit with return air. Below it the compressor cannot carry the rise alone and the supplemental source makes up the difference; the lockout is set at or below the balance point so the supplemental source does not displace compressor heat that is cheaper to deliver. A ventilation unit cannot pause its supply during defrost the way a comfort unit can, which is why the defrost depression is a submittal value and the supplemental heat covers it. Demand defrost runs a cycle when the coil actually frosts; timed defrost runs cycles the coil did not need on dry days. {note}
+
+## Gas-Fired Heating Section {toc}
+
+### Requirements in this article apply where the datasheet selects a natural gas-fired or propane-fired heating source, or a gas-fired supplemental heat source.
+
+### The gas heating input of each unit shall be as indicated in the datasheet.
+
+```datasheet
+label: Gas Heating Input
+type: range
+unit: MBH
+drawing_ref: "the mechanical equipment schedule"
+options:
+ min: 30
+ max: 3000
+ step: 5
+default: deferred
+```
+
+### The gas heat exchanger material shall be as indicated in the datasheet.
+
+```datasheet
+label: Gas Heat Exchanger Material
+type: select
+options:
+ - "Aluminized steel"
+ - "Type 409 stainless steel"
+ - "Type 304 stainless steel"
+ - "Type 316 stainless steel"
+```
+
+### The gas heating capacity control shall be as indicated in the datasheet.
+
+```datasheet
+label: Gas Heating Capacity Control
+type: select
+options:
+ - "Single stage"
+ - "Two stages"
+ - "Modulating"
+```
+
+### The low-fire input of a staged or modulating burner shall be not more than the percentage of full input indicated in the datasheet.
+
+```datasheet
+label: Maximum Low-Fire Gas Input as a Percentage of Full Input
+type: range
+unit: '%'
+options:
+ min: 5
+ max: 100
+ setpoints: [5, 10, 20, 25, 33, 40, 50, 65, 100]
+```
+
+### The thermal efficiency of the gas heating section shall be not less than the value indicated in the datasheet.
+
+```datasheet
+label: Minimum Gas Heating Thermal Efficiency
+type: range
+unit: '%'
+derived: "the minimum [[parameter: adopted-energy-code]] requires for a warm-air furnace of the unit's heating input"
+options:
+ min: 78
+ max: 97
+ setpoints: [78, 80, 81, 82, 90, 95, 97]
+default: derived
+```
+
+### The gas supply pressure available at each unit connection shall be as indicated in the datasheet.
+
+```datasheet
+label: Gas Supply Pressure at the Unit Connection
+type: range
+unit: in. w.c.
+drawing_ref: "the gas piping drawings"
+options:
+ min: 3.5
+ max: 14
+ step: 0.5
+default: deferred
+```
+
+### The unit gas train shall be rated for the gas supply pressure available at the unit connection.
+
+### The burner shall be furnished with electronic ignition, flame supervision, a redundant gas valve, a high-limit thermal cutout, and a rollout switch.
+
+### The burner and gas train shall be certified as an assembly to ANSI Z21.47 / CSA 2.3, or to ANSI Z83.8 / CSA 2.6 where the section is a duct furnace.
+
+### The heat exchanger shall be furnished with an induced-draft combustion blower and a proof-of-draft switch that prevents ignition without combustion airflow.
+
+### Where a modulating or condensing heat exchanger is furnished, the flue products shall be handled and the flue condensate drained as the listing requires, and flue condensate shall be neutralized before it enters a drain the adopted plumbing code requires to be protected.
+
+### The heat exchanger on a 100% outdoor air unit sees the winter design temperature at its entering face on every heating hour, which drops the flue gas below its dew point inside the exchanger at a higher outdoor temperature than a return-air unit ever reaches. An aluminized surface corrodes from the inside under that condensation; the stainless grades resist it at a higher cost, with the higher grades for corrosive combustion air or a condensing design. No material is the norm here, because the condensing exposure depends on the climate and the turndown together. {note}
+
+### Turndown decides how the section behaves across the heating season. A single-stage burner delivers full input in short cycles, which swings the supply temperature the parallel system then has to absorb; a modulating burner holds a steady supply temperature across the whole range of outdoor temperatures the unit tempers from, which on a 100% outdoor air unit is the full span from the design low to the heating balance point, and the deeper the turndown the lower the outdoor temperature at which the burner first has to cycle. {note}
+
+## Electric Resistance Heating Section {toc}
+
+### Requirements in this article apply where the datasheet selects an electric resistance heating source, an electric resistance supplemental heat source, or an electric reheat coil.
+
+### The electric heating capacity of each unit shall be as indicated in the datasheet.
+
+```datasheet
+label: Electric Heating Capacity
+type: range
+unit: kW
+drawing_ref: "the mechanical equipment schedule"
+options:
+ min: 2
+ max: 400
+ step: 0.5
+default: deferred
+```
+
+### The electric heating capacity control shall be as indicated in the datasheet.
+
+```datasheet
+label: Electric Heating Capacity Control
+type: select
+options:
+ - "Single stage"
+ - "Two stages"
+ - "Three or more stages"
+ - "Modulating by silicon-controlled rectifier"
+```
+
+### Electric heating elements shall be open-coil nickel-chromium or sheathed elements listed as part of the unit, furnished with a primary automatic-reset thermal cutout and a secondary manual-reset thermal cutout.
+
+### Electric heating elements shall be interlocked with the supply fan so that the elements cannot be energized without proven airflow.
+
+### The electric heater airflow interlock shall be hardwired independently of the unit controller and the building automation system.
+
+### Where the electric heater is furnished with its own power connection, the heater and the unit shall each be furnished with their own disconnecting means.
+
+### Staged elements deliver the capacity in steps that the supply temperature swings across; a silicon-controlled rectifier modulates continuously and is the arrangement where the heater holds a supply temperature setpoint directly, as a reheat coil does, rather than tempering toward one. An airflow interlock that depends on the controller fails in the one scenario it exists for, which is the controller being offline while the elements have power, and the hardwired path is what makes the interlock a safety rather than a sequence. {note}
+
+## Hydronic Heating Section {toc}
+
+### Requirements in this article apply where the datasheet selects a hot water or steam heating source, a hot water supplemental heat source, or a hot water reheat coil.
+
+### The hydronic coil shall be selected at the entering and leaving fluid temperatures indicated in the datasheet.
+
+```datasheet
+label: Hydronic Heating Coil Entering Fluid Temperature
+type: range
+unit: °F
+drawing_ref: "the mechanical equipment schedule"
+options:
+ min: 90
+ max: 220
+ step: 5
+default: deferred
+```
+
+```datasheet
+label: Hydronic Heating Coil Leaving Fluid Temperature
+type: range
+unit: °F
+drawing_ref: "the mechanical equipment schedule"
+options:
+ min: 70
+ max: 210
+ step: 5
+default: deferred
+```
+
+### The freeze protection method for the hydronic coil shall be as indicated in the datasheet.
+
+```datasheet
+label: Hydronic Heating Coil Freeze Protection
+type: select
+options:
+ - "Glycol solution in the heating circuit"
+ - "Constant coil flow with a modulating three-way valve"
+ - "Constant coil flow maintained by an injection pump"
+ - "Face and bypass dampers with a constant-capacity coil"
+```
+
+### Every hydronic coil shall be furnished with a low-limit temperature device downstream of the coil, arranged to stop the supply fan, close the outdoor air damper, and open the coil control valve when it trips.
+
+### Hydronic piping to the coil shall conform to [[sync/hydronic-piping]], and the coil connections shall pass through the casing in a gasketed, insulated penetration with the piping independently supported.
+
+### Steam coils shall be of distributing tube non-freeze construction, pitched toward the return connection, and trapped separately from every other coil.
+
+### A hydronic coil in a 100% outdoor air unit sits in undiluted outdoor air on every hour of the year and can see it with the fan off, so it is the coldest service a heating coil has. Every method in the field is a way of keeping fluid moving through every tube or of lowering its freezing point, and a two-way valve throttled to a trickle on the coldest night is the arrangement that splits the coil. Glycol protects the coil regardless of what the controls do and lowers the plant's capacity by its share; the flow and bypass arrangements keep the fluid moving and depend on the pump and the controls doing their job. {note}
+
+# Energy Recovery {toc}
+
+## Energy Recovery Requirement {toc}
+
+### Exhaust air energy recovery shall be as indicated in the datasheet.
+
+```datasheet
+label: Exhaust Air Energy Recovery
+type: radio
+derived: "the energy recovery requirement [[parameter: adopted-energy-code]] sets for the unit's design outdoor airflow, outdoor air fraction, and operating hours in [[parameter: climate-zone]], including the exceptions that code lists"
+options:
+ - "Energy recovery furnished"
+ - "Not furnished"
+default: derived
+```
+
+### Where the datasheet selects no energy recovery on a unit for which the adopted energy code would otherwise require it, the exception relied on shall be identified in the submittal.
+
+### Where energy recovery is furnished, the enthalpy recovery ratio at design conditions shall be not less than the value indicated in the datasheet.
+
+```datasheet
+label: Minimum Enthalpy Recovery Ratio
+type: range
+unit: '%'
+derived: "the minimum enthalpy recovery ratio [[parameter: adopted-energy-code]] requires where energy recovery is required"
+options:
+ min: 0
+ max: 90
+ step: 5
+default: derived
+```
+
+### Where energy recovery is furnished, the pressure drop the device adds to the supply and exhaust airstreams shall be included in the fan selections and stated in the submittal.
+
+### Where energy recovery is furnished, the construction, rating, and testing of the recovery component itself shall conform to [[sync/energy-recovery-ventilators]].
+
+### A unit that handles 100% outdoor air at every hour it runs is the equipment the energy recovery rules were written for, and almost every such unit above the smallest airflow falls inside the requirement in every climate zone. The derivation exists so that a project does not have to look the table up, and the exceptions, chiefly for exhaust that cannot be brought to the unit and for systems that run few hours, are what the submittal documents when a project opts out. {note}
+
+## Recovery Device Type {toc}
+
+### Requirements in this article and the remaining articles of this section apply where energy recovery is furnished.
+
+### The recovery device shall be as indicated in the datasheet.
+
+```datasheet
+label: Energy Recovery Device
+type: select
+options:
+ - "Total energy rotary wheel"
+ - "Sensible-only rotary wheel"
+ - "Fixed-plate total energy membrane core"
+ - "Fixed-plate sensible core"
+ - "Heat pipe"
+ - "Runaround coil loop"
+```
+
+### The sensible, latent, and total effectiveness of the furnished device at the design outdoor and exhaust airflows shall be stated in the submittal.
+
+### A total energy device transfers moisture as well as heat, so in summer it pre-dries the incoming air with the drier exhaust and cuts the latent load the coil has to remove, and in winter it returns moisture the building would otherwise lose. A rotary wheel reaches the highest total effectiveness and carries a drive, seals, and a measurable carryover between the streams; a membrane plate has no moving parts and lower carryover at a larger size and a higher pressure drop. A sensible device transfers heat only, which is the arrangement where moisture transfer is unwanted or where the exhaust is contaminated: a sensible wheel and a sensible plate still share a face between the streams, while a heat pipe and a runaround loop keep the streams physically apart, and the runaround loop is the only device that works when the intake and exhaust cannot be brought to one unit. The choice turns on the exhaust air class, the climate's balance of latent and sensible load, and whether the two airstreams can meet. {note}
+
+## Exhaust Air Class and Cross-Leakage {toc}
+
+### The air class under ANSI/ASHRAE 62.1 of the exhaust airstream passing through the recovery device shall be as indicated in the datasheet.
+
+```datasheet
+label: Exhaust Air Class Through the Recovery Device (ASHRAE 62.1)
+type: select
+drawing_ref: "the mechanical ventilation schedule"
+options:
+ - "Class 1"
+ - "Class 2"
+ - "Class 3"
+ - "Class 4"
+default: deferred
+```
+
+### The exhaust air transfer ratio of the recovery device shall not exceed the value indicated in the datasheet.
+
+```datasheet
+label: Maximum Exhaust Air Transfer Ratio
+type: range
+unit: '%'
+derived: "the transfer ANSI/ASHRAE 62.1 permits from the exhaust air class through the recovery device into the outdoor air, with no transfer permitted where that standard prohibits recirculation of the class"
+options:
+ min: 0
+ max: 10
+ step: 0.5
+default: derived
+```
+
+### Where the exhaust air class prohibits any transfer into the supply, the recovery device shall be a heat pipe or a runaround coil loop with the airstreams fully separated.
+
+### Where the exhaust air class limits the transfer to a stated ratio, the outdoor airflow shall be increased by the transferred quantity in accordance with ANSI/ASHRAE 62.1, and the increase shall be shown in the ventilation calculation.
+
+### The purge provision on a rotary device shall be as indicated in the datasheet.
+
+```datasheet
+label: Rotary Device Purge Section
+type: radio
+derived: "the exhaust air transfer ratio limit indicated in the datasheet compared against the certified ratio of the wheel without a purge"
+options:
+ - "Purge section furnished"
+ - "No purge section"
+default: derived
+```
+
+### Where a purge section is furnished, the supply and exhaust fans shall be arranged so that the pressure difference across the wheel drives the purge flow from the outdoor air side toward the exhaust side.
+
+### Where the unit serves laboratory spaces, the exhaust air class of every airstream brought to the recovery device shall be confirmed against [[sync/laboratory-exhaust-and-fume-hoods]] before the recovery device is selected.
+
+### Every device that shares a surface between the two airstreams leaks a little exhaust into the supply, and the certified exhaust air transfer ratio is that leak as a fraction of the supply. A rotary wheel carries exhaust air in its flutes as it turns, and a purge section sweeps those flutes with outdoor air before they reach the supply side, which brings the carryover down to a fraction of a percent; it works only when the pressures across the wheel push the right way, which is a fan arrangement question. The ventilation standard sets what fraction of each exhaust class may come back, and any air that does come back is not outdoor air and has to be made up. {note}
+
+## Frost Control {toc}
+
+### The frost control method for the recovery device shall be as indicated in the datasheet.
+
+```datasheet
+label: Energy Recovery Frost Control Method
+type: select
+derived: "the recovery device type and [[parameter: site-ambient-temperature-minimum]] compared against the manufacturer's published frost threshold for the device at the exhaust condition served"
+options:
+ - "Wheel speed modulation"
+ - "Timed wheel stop and defrost cycle"
+ - "Preheat of the entering outdoor air upstream of the device"
+ - "Exhaust-side face and bypass dampers"
+ - "Supply-side bypass dampers"
+ - "Recirculation of exhaust air to the outdoor air side during defrost"
+ - "Not required at the site design temperature"
+default: derived
+```
+
+### The frost control method, the outdoor temperature at which it initiates, and the reduction in outdoor airflow or recovery effectiveness while it operates shall be stated in the submittal.
+
+### Where frost control reduces the outdoor airflow delivered, the unit shall still deliver not less than the ventilation ANSI/ASHRAE 62.1 requires for the spaces served during frost control, or the sequence shall limit frost control to unoccupied periods.
+
+### Where preheat is the frost control method, the preheat section shall be sized for the design outdoor airflow and the temperature rise from [[parameter: site-ambient-temperature-minimum]] to the frost threshold of the device.
+
+### Frost forms on the exhaust side of the device when the exhaust air is cooled below its dew point and below freezing before it leaves, and it blocks the exhaust path and ends the recovery. A total energy device also removes moisture from the exhaust as it cools it, so it frosts at a lower outdoor temperature than a sensible device does, and a building with a dry winter interior frosts later than a humid one. Slowing or stopping a wheel reduces the recovery so the exhaust leaves warmer; bypass dampers do the same for a plate; preheat keeps the entering air above the threshold at a purchased-energy cost that the recovery still repays; recirculating warm exhaust onto the outdoor side defrosts the device but dilutes the ventilation while it does. The method follows from the device and the climate, which is why it is derived. {note}
+
+## Recovery Bypass {toc}
+
+### The recovery bypass arrangement shall be as indicated in the datasheet.
+
+```datasheet
+label: Energy Recovery Bypass Arrangement
+type: select
+options:
+ - "Bypass dampers around the recovery device on both airstreams"
+ - "Bypass damper around the recovery device on the outdoor air side"
+ - "Wheel stop or speed reduction with no bypass dampers"
+```
+
+### The recovery device shall be stopped or bypassed when the outdoor air condition is closer to the supply air setpoint than the exhaust condition is, so that the device does not transfer heat or moisture into the supply that the unit would then have to remove.
+
+### Bypass dampers, where furnished, shall be rated in accordance with ANSI/AMCA 500-D with a leakage class not worse than the outdoor air damper on the unit.
+
+### The bypass shall be controlled by the unit controller on the outdoor and exhaust air conditions, with the control points exposed to the building automation system.
+
+### There are hours in spring and fall when the outdoor air is nearer the supply setpoint than the exhaust air is, and running the recovery device on those hours moves heat the wrong way. Stopping a wheel ends its transfer at no cost in dampers, and the air still passes through the stopped wheel and pays its pressure drop; bypass dampers route the air around the device, which saves the fan energy of the pressure drop on every bypassed hour and is the only way to stop transfer through a plate, which has no drive to stop. Bypassing both airstreams halves the fan penalty again at the cost of a second set of dampers and the casing length to hold them. {note}
+
+# Fans and Motors {toc}
+
+## Fan Arrangement {toc}
+
+### The exhaust fan arrangement shall be as indicated in the datasheet.
+
+```datasheet
+label: Exhaust Fan Arrangement
+type: select
+options:
+ - "Exhaust fan integral to the unit, drawing building exhaust through the recovery device"
+ - "No exhaust fan in the unit, with recovery exhaust moved by separate building exhaust fans"
+ - "No exhaust section"
+```
+
+### Where the exhaust is moved by separate building exhaust fans, those fans shall conform to [[sync/hvac-fans]], and the pressure drop of the recovery device and the unit's exhaust path shall be included in their selection.
+
+### The supply fan arrangement shall be as indicated in the datasheet.
+
+```datasheet
+label: Supply Fan Arrangement
+type: radio
+options:
+ - "Single fan"
+ - "Fan array of two or more fans in parallel"
+default: manufacturer
+```
+
+### Where the datasheet leaves the fan arrangement to the manufacturer, the manufacturer shall state the arrangement furnished in the submittal.
+
+### Where a fan array is furnished, each fan shall be furnished with a backdraft damper or the array shall be controlled so that a stopped fan does not recirculate air backward through the array.
+
+### Where a fan array is furnished, the unit shall deliver not less than the airflow indicated in the datasheet for a unit with one fan of the array out of service.
+
+```datasheet
+label: Minimum Airflow With One Array Fan Out of Service as a Percentage of Design
+type: range
+unit: '%'
+options:
+ min: 0
+ max: 100
+ step: 5
+```
+
+### An integral exhaust fan is what makes the unit's recovery self-contained: the unit controls both airstreams, keeps their ratio where the device was rated, and drives the purge. Leaving the exhaust to building fans is the arrangement where the exhaust is already collected by fans that exist for another reason and the recovery section is placed in their path, and it hands the airflow ratio to a balance between two systems. A unit with no exhaust section at all has no recovery and tempers the outdoor air with heating alone. A fan array spreads the airflow across small direct-drive wheels, which shortens the unit and keeps partial airflow through a fan failure, at the cost of more motors and the backflow provision. {note}
+
+## Fan Construction and Drive {toc}
+
+### The supply and exhaust fan wheel type shall be as indicated in the datasheet.
+
+```datasheet
+label: Fan Wheel Type
+type: select
+options:
+ - "Forward-curved centrifugal"
+ - "Backward-curved centrifugal"
+ - "Airfoil centrifugal"
+ - "Unhoused plenum fan"
+default: manufacturer
+```
+
+### Where the datasheet leaves the wheel type to the manufacturer, the manufacturer shall state the wheel type furnished in the submittal.
+
+### The fan drive arrangement shall be as indicated in the datasheet.
+
+```datasheet
+label: Fan Drive Arrangement
+type: radio
+options:
+ - "Direct drive"
+ - "Belt drive"
+default: "Direct drive"
+```
+
+### Where a belt drive is furnished, the fan shall be provided with an adjustable motor base, a belt guard with a tachometer opening, and a sheave combination that produces the design fan speed within ±5%.
+
+### Fan wheels shall be dynamically balanced as an assembly, and fan balance shall be verified by measurement at the bearings during the factory run test.
+
+### Fans shall be selected with the capacity to maintain the design airflow with the filters at change-out resistance and the recovery device in frost control.
+
+### The wheel type is a property of the manufacturer's product line at a given capacity more than a project choice: small units are built around forward-curved wheels because they are compact and quiet at low speed, and larger units around backward-curved, airfoil, or plenum wheels because those reach their efficiency at the pressures a long duct run imposes. A project asserts a wheel type only where a sound or efficiency target requires one. Direct drive removes the belt, the sheave, and the belt dust from an airstream that goes to the occupants without any further filtration, which is why it is the norm on this equipment. {note}
+
+## Fan Speed Control {toc}
+
+### The fan speed control shall be as indicated in the datasheet.
+
+```datasheet
+label: Fan Speed Control
+type: select
+options:
+ - "Variable frequency drive"
+ - "Electronically commutated motor"
+ - "Constant speed"
+```
+
+### The fan speed control shall provide not less than the modulation [[parameter: adopted-energy-code]] requires for a unit of the design outdoor airflow and the supply airflow control selected in the datasheet.
+
+### Where variable speed is furnished, the fan shall operate stably without surge or stall down to the minimum airflow the unit operates at.
+
+### Variable frequency drives furnished with the unit shall be factory-mounted outside the airstream in a compartment ventilated for the drive's heat at [[parameter: site-ambient-temperature-maximum]], accessible without opening a section that is under pressure during operation, and shall conform to [[sync/hvac-variable-frequency-drives]].
+
+### A constant-speed fan holds the design airflow and nothing else, which is enough for a unit that runs at a fixed ventilation rate and has no filter loading compensation. A variable frequency drive on an induction motor and an electronically commutated motor both modulate; the drive is the arrangement at larger motor sizes and where the project standardizes on one drive type, and the commutated motor is built into the fan at the sizes an array or a small unit uses and needs no drive compartment. Either lets the unit trim speed as filters load and follow a demand signal. {note}
+
+## Fan Motors {toc}
+
+### Motor voltage and phase shall match the branch circuit serving the unit as indicated in the datasheet.
+
+```datasheet
+label: Unit Supply Voltage
+type: range
+unit: V
+drawing_ref: "the electrical drawings and panel schedules"
+options:
+ min: 208
+ max: 575
+ setpoints: [208, 230, 460, 575]
+default: deferred
+```
+
+```datasheet
+label: Unit Supply Phase
+type: radio
+drawing_ref: "the electrical drawings and panel schedules"
+options:
+ - "Single phase, 1Φ"
+ - "Three phase, 3Φ"
+default: deferred
+```
+
+### Any discrepancy between the mechanical schedule and the electrical documents on the voltage or phase serving a unit shall be resolved before the unit is released for fabrication.
+
+### Motors shall conform to [[sync/electric-motors]] and shall meet the NEMA Premium efficiency level of NEMA MG 1 where a motor of that size and enclosure is covered by that level.
+
+### Motors shall be selected so that the nameplate power is not exceeded at any operating point the fan can reach with clean filters and every damper full open.
+
+### Motors operated from a variable frequency drive shall be rated for inverter duty in accordance with NEMA MG 1 Part 31.
+
+## Fan Power and Sound {toc}
+
+### The fan power of each unit at the design airflows and external static pressures shall not exceed the limit [[parameter: adopted-energy-code]] sets for the unit, with every pressure drop credit claimed identified in the submittal.
+
+### Fan power shall be computed from the fan shaft power and the motor and drive efficiencies at the design operating point rather than from the motor nameplate.
+
+### Outdoor radiated sound power of outdoor units with an integral air-cooled condenser shall be rated under the program indicated in the datasheet.
+
+```datasheet
+label: Outdoor Sound Rating Program
+type: radio
+derived: "the unit's cooling capacity, with units below 135,000 Btu/h rated under AHRI 270 and 135,000 Btu/h and above under AHRI 370"
+options:
+ - "AHRI 270"
+ - "AHRI 370"
+default: derived
+```
+
+### Supply discharge, outdoor air intake, and exhaust discharge sound power shall be reported in each of the eight octave bands from 63 Hz through 8,000 Hz from tests in accordance with ANSI/AMCA 300.
+
+### The A-weighted outdoor sound power level of each outdoor unit shall not exceed the value indicated in the datasheet.
+
+```datasheet
+label: Maximum A-Weighted Outdoor Sound Power Level
+type: range
+unit: dB
+options:
+ min: 60
+ max: 110
+ step: 1
+```
+
+### Where the datasheet does not state a maximum outdoor sound power level, the manufacturer shall state the rated value in the submittal and the design team shall confirm it against the property line and adjacent occupancy criteria stated in the Contract Documents.
+
+### Where the unit serves a space with a stated noise criterion, the design team shall carry the submitted discharge sound power through the attenuation of the connected duct path to the receiving room and shall confirm the result against the criterion, with attenuation furnished in accordance with [[sync/hvac-sound-attenuators]] where the criterion is not met.
+
+### The fan power limit is a statement about the whole air system rather than the fan, and a dedicated outdoor air unit pushes through a recovery device, a deep cooling coil, a reheat coil, and often two filter banks before the duct begins, which is why the credits for those components exist and have to be documented. The unit radiates to the roof through its condenser fans and sends fan sound down its supply duct and out its intake and exhaust hoods, and the duct path at a low airflow into a quiet room is the one occupants notice. {note}
+
+# Filtration {toc}
+
+## Outdoor Air Filtration {toc}
+
+### Filter efficiency shall be rated in accordance with ANSI/ASHRAE 52.2.
+
+### The outdoor air pre-filter shall have not less than the efficiency indicated in the datasheet.
+
+```datasheet
+label: Outdoor Air Pre-Filter Efficiency
+type: select
+options:
+ - "MERV 8"
+ - "MERV 10"
+ - "MERV 11"
+ - "MERV 13"
+default: "MERV 8"
+```
+
+### The final filter downstream of the cooling coil and reheat section shall have not less than the efficiency indicated in the datasheet.
+
+```datasheet
+label: Final Filter Efficiency
+type: select
+options:
+ - "No final filter bank"
+ - "MERV 11"
+ - "MERV 13"
+ - "MERV 14"
+ - "MERV 16"
+```
+
+### Air delivered to an occupiable space shall pass through filtration of not less than MERV 8 upstream of the cooling coil and every other wetted surface, in accordance with ANSI/ASHRAE 62.1.
+
+### Where the outdoor air at the site exceeds the national ambient air quality standard for fine particulate matter, the outdoor air shall additionally be filtered to the efficiency ANSI/ASHRAE 62.1 requires for that condition.
+
+### Where the unit serves health care spaces, the filtration shall be not less than ANSI/ASHRAE 170 requires for the space served.
+
+### The filter depth shall be as indicated in the datasheet.
+
+```datasheet
+label: Filter Depth
+type: range
+unit: in.
+options:
+ min: 1
+ max: 12
+ setpoints: [1, 2, 4, 12]
+```
+
+### The fan selection shall accommodate the resistance of the selected filters at their change-out condition without falling below the design airflow.
+
+### The submittal shall state the initial resistance and the recommended change-out resistance of each selected filter at the design face velocity.
+
+### Filter media shall be listed to UL 900.
+
+### Every particle the unit admits comes from outdoors, and the outdoor air is dirtier than the return air a mixed-air unit mostly recirculates, so the pre-filter on this equipment loads faster than a comfort unit's and exists to protect the recovery device and the coil as much as the occupants. A final filter after the coils catches what the wet coil and the casing shed and is where a project puts the fine-particulate efficiency, since a high-efficiency filter upstream of the recovery device sees the full outdoor loading and the full pressure penalty. Moving from MERV 8 to MERV 13 adds a few tenths of an inch of water across the bank at change-out, paid by the fan for the life of the unit; a deeper filter of the same rating holds more dust and lengthens the change interval. {note}
+
+## Exhaust Air Filtration {toc}
+
+### The exhaust air filter shall be as indicated in the datasheet.
+
+```datasheet
+label: Exhaust Air Filter
+type: radio
+options:
+ - "Filter bank upstream of the recovery device on the exhaust side"
+ - "No exhaust air filter"
+default: "Filter bank upstream of the recovery device on the exhaust side"
+```
+
+### Where an exhaust air filter is furnished, it shall have not less than the efficiency indicated in the datasheet.
+
+```datasheet
+label: Exhaust Air Filter Efficiency
+type: select
+options:
+ - "MERV 8"
+ - "MERV 10"
+ - "MERV 11"
+ - "MERV 13"
+default: "MERV 8"
+```
+
+### The exhaust side of the recovery device sees the dust, lint, and aerosol the building generates, and a wheel or a plate that fouls on its exhaust face loses effectiveness and pressure drop margin together, with the exhaust fan paying for both. A filter on the exhaust protects the device and is the norm on a wheel; it is left out where the exhaust is clean and the device can be washed, or where the exhaust pressure budget is already spent. {note}
+
+## Filter Rack and Access {toc}
+
+### Each filter rack shall hold the filters against a gasketed seating frame so that no air path exists around the media.
+
+### Filters shall be removable without tools.
+
+### Each filter section shall be accessible through its own access panel or door without disturbing the coil, the fan, the recovery device, or the electrical compartment.
+
+### Filter face velocity at design airflow shall not exceed the velocity at which the selected media is rated.
+
+### A differential pressure switch or transmitter shall be furnished across each filter bank and reported to the building automation system.
+
+### Bypass around the media is the dominant filtration defect in installed units, and it is invisible at every point except a measurement of what reaches the space. A rack that lets filters rattle in their track delivers an in-place efficiency far below the media rating, because unfiltered air is a parallel path with almost no resistance while the media path has a great deal. {note}
+
+# Casing Construction {toc}
+
+## Casing Panels {toc}
+
+### The casing panel construction shall be as indicated in the datasheet.
+
+```datasheet
+label: Casing Panel Construction
+type: select
+options:
+ - "Double-wall insulated panels"
+ - "Double-wall insulated panels with a thermally broken frame"
+ - "Single-wall panels with an interior insulation liner"
+default: "Double-wall insulated panels"
+```
+
+### Casing panels in every section that carries conditioned air shall be insulated to a thermal resistance not less than the value indicated in the datasheet.
+
+```datasheet
+label: Minimum Casing Panel Thermal Resistance
+type: range
+unit: hr·ft²·°F/Btu
+options:
+ min: 2
+ max: 20
+ step: 0.5
+```
+
+### Where the datasheet does not state a thermal resistance, the manufacturer shall state the thermal resistance of the panel furnished and shall confirm that the exterior surface of the sections downstream of the cooling coil stays above the dew point of the surrounding air at the design cooling condition and that the interior surface of the sections upstream of the heating section stays above the dew point of the surrounding air at [[parameter: site-ambient-temperature-minimum]].
+
+### Insulation in the airstream shall be faced, coated, or encapsulated so that fibers are not eroded into the supply air at the maximum velocity the section sees.
+
+### The casing structure shall be galvanized steel conforming to ASTM A653 with a G90 coating designation as a minimum.
+
+### The unit base shall be a full-perimeter rail that supports the unit on the curb or pad without point loads on the casing panels.
+
+### A dedicated outdoor air casing has cold air on the inside of the upstream sections in winter and cold, saturated air on the inside of the downstream sections in summer, with the outdoor or mechanical room air on the other face of the same panel in both cases, so it condenses on whichever face is the cold one in each season. A double-wall panel keeps the insulation out of the airstream and cleans without eroding; the thermal break stops the frame from bridging the insulation and sweating along every panel edge, which is where a double-wall casing in a cold climate or a humid one first drips. The single-wall liner does the thermal job at lower cost and leaves the liner facing exposed. {note}
+
+## Casing Air Leakage {toc}
+
+### Casing air leakage at the design operating pressure of each section shall not exceed the percentage of the design outdoor airflow indicated in the datasheet.
+
+```datasheet
+label: Maximum Casing Air Leakage as a Percentage of Design Airflow
+type: range
+unit: '%'
+options:
+ min: 0.5
+ max: 5
+ setpoints: [0.5, 1, 1.5, 2, 3, 5]
+```
+
+### Where the datasheet does not state a leakage limit, the manufacturer shall state the casing leakage of the furnished unit at its design pressures in the submittal.
+
+### The partition between the outdoor air and exhaust air paths within the unit shall be sealed so that leakage across it is included in the certified exhaust air transfer ratio of the recovery device or is separately stated in the submittal.
+
+### Air that leaks out of the supply section is conditioned ventilation air the building never receives, and air that leaks from the exhaust path into the outdoor air path upstream of the recovery device is exhaust returned to the supply by a route the recovery device's rating never measured. On a 100% outdoor air unit the second path is the one that matters, because it defeats the air class separation the recovery section was selected for. {note}
+
+## Exterior Finish {toc}
+
+### Exterior casing panels of outdoor units shall receive a factory-applied finish that withstands salt spray exposure in accordance with ASTM B117 for not less than the duration indicated in the datasheet without red rust or blistering.
+
+```datasheet
+label: Minimum Exterior Finish Salt Spray Exposure
+type: range
+unit: hours
+options:
+ min: 500
+ max: 3000
+ setpoints: [500, 750, 1000, 1500, 2000, 2500, 3000]
+```
+
+### Where the datasheet does not state a salt spray exposure, the manufacturer shall state in the submittal the finish system furnished and the exposure it has been tested to.
+
+### Exposed fasteners, hinges, latches, and hardware shall be stainless steel or a coated steel with equivalent corrosion resistance.
+
+### Cut edges, field-drilled penetrations, and fasteners shall receive a zinc-rich touch-up coating before the unit is placed in service.
+
+### The salt spray rating is a comparative durability number rather than a service life, and the same finish that passes a short exposure on an inland roof fails within a few years on a coastal one. The number is the lever a project has, so it is stated here as a duration and selected by the exposure at the site rather than defaulted. {note}
+
+## Access Panels {toc}
+
+### Access shall be provided to each filter section, the recovery device for removal of a wheel or core, the cooling coil and drain pan, the reheat section, each fan and motor, the compressor compartment, the heating section, the dampers and actuators, and the control panel.
+
+### Each access shall permit service of the component behind it without removing the unit from its curb or pad.
+
+### The access panel construction shall be as indicated in the datasheet.
+
+```datasheet
+label: Access Panel Construction
+type: select
+options:
+ - "Hinged doors with quarter-turn latches"
+ - "Hinged doors with compression latches"
+ - "Removable gasketed panels with captive fasteners"
+```
+
+### Access panels and doors shall be gasketed so that they seal against air leakage at the casing pressure in every operating mode.
+
+### Doors on sections under positive pressure shall be furnished with a safety latch that holds the door against the pressure as it is opened.
+
+### Panels that must be removed to service a component shall be light enough for one person to handle on a roof, or shall be hinged.
+
+### Access panels shall be labeled on the exterior with the section behind them.
+
+### A hinged door with compression latches seals a casing that runs at the pressures a recovery device and two coils impose and opens for the weekly filter check without a wrench; quarter-turn latches are quicker and seal less; a removable panel seals as well as its gasket and takes two hands and a place to lean it, which on a roof in weather is the reason the one-person rule exists. {note}
+
+## Duct Connection Orientation {toc}
+
+### The supply and exhaust duct connection orientation shall be as indicated in the datasheet.
+
+```datasheet
+label: Duct Connection Orientation
+type: radio
+options:
+ - "Vertical, through the curb"
+ - "Horizontal, from the unit end or side"
+default: "Vertical, through the curb"
+```
+
+### Where horizontal connections are selected on an outdoor unit, the supply and exhaust openings shall be furnished with weathertight flanged collars, and the openings in the unit base shall be closed and insulated.
+
+### Vertical connections put the ductwork inside the curb and through the roof beneath the unit, so the roof penetration is the curb itself and the cold supply duct is never outdoors; horizontal connections leave the ductwork exposed on the roof between the unit and its own penetration, which is why they are the arrangement for a unit that sits on a rail, a frame, or a pad rather than a curb, or for a replacement whose existing ductwork already arrives that way. {note}
+
+## Outdoor Air and Exhaust Dampers {toc}
+
+### The outdoor air intake and the exhaust discharge shall each be furnished with a motorized damper that drives closed when the unit is off and on loss of power or control signal.
+
+### The outdoor air and exhaust damper leakage class shall be as indicated in the datasheet, tested in accordance with ANSI/AMCA 500-D.
+
+```datasheet
+label: Outdoor Air and Exhaust Damper Leakage Class
+type: select
+derived: "the maximum damper leakage [[parameter: adopted-energy-code]] permits for the damper's service in [[parameter: climate-zone]]"
+options:
+ - "AMCA Class 1A"
+ - "AMCA Class 1"
+ - "AMCA Class 2"
+ - "AMCA Class 3"
+default: derived
+```
+
+### Damper blades shall be airfoil or double-skin construction with blade edge seals and jamb seals, and no felt or fibrous seal shall be furnished on any damper in the unit.
+
+### Damper actuators shall be direct-coupled to the damper shaft and sized with not less than 25% reserve torque at the unit's design static pressure.
+
+### Outdoor air intake hoods and louvers furnished with the unit shall be rated in accordance with ANSI/AMCA 500-L and sized so that water is not carried into the unit at the design wind-driven rain condition.
+
+### Exhaust discharge hoods shall direct the exhaust away from the outdoor air intake of the same unit.
+
+### A 100% outdoor air unit that is off admits the full winter outdoor air through any damper that leaks, onto a hydronic coil with no fan to carry the cold past it, which is the mechanism behind most frozen coils on this equipment and the reason the closed-position leakage class is derived from the energy code rather than left to the product. {note}
+
+# Drain Pans and Condensate {toc}
+
+## Drain Pan Construction {toc}
+
+### A drain pan shall be furnished beneath the cooling coil, beneath the reheat section where carryover can reach it, beneath the recovery device where it can condense, and beneath every other section in which condensate can form.
+
+### The drain pan material shall be as indicated in the datasheet.
+
+```datasheet
+label: Drain Pan Material
+type: select
+options:
+ - "Type 304 stainless steel"
+ - "Type 316 stainless steel"
+ - "Galvanized steel with a factory-applied corrosion-resistant coating"
+ - "Molded polymer"
+default: "Type 304 stainless steel"
+```
+
+### The drain pan shall extend the full width of the coil and beneath the coil headers and return bends, and downstream of the leaving-air face of the coil far enough to capture carryover at the design face velocity.
+
+### The drain pan shall be sloped in two planes toward the drain connection and shall hold no standing water when the unit is not operating.
+
+### Drain pans shall be insulated on the underside or double-walled where the surface beneath the pan can fall below the dew point of the surrounding air.
+
+### A dedicated outdoor air coil condenses for most of the cooling season rather than in cycles, so its pan carries water continuously and ages under a permanent condensate film. Every geometric requirement on the pan exists to make it empty rather than merely drain, because a pan that holds water in a supply airstream is the growth condition the ventilation standard's wetted-surface rules are written around. A coated steel pan is fine until the coating is scratched, a polymer pan cannot corrode but can crack, and the stainless grades do neither, with the higher grade for coastal or chemical exposure. {note}
+
+## Condensate Trap and Drain {toc}
+
+### The drain pan shall be furnished with a primary drain connection not smaller than 3/4 in. at the low point.
+
+### The condensate trap arrangement shall be as indicated in the datasheet.
+
+```datasheet
+label: Condensate Trap
+type: radio
+options:
+ - "Factory-installed trap integral to the unit"
+ - "Field-installed trap by the installing contractor"
+default: "Field-installed trap by the installing contractor"
+```
+
+### The trap seal depth shall be not less than the maximum negative static pressure at the drain pan, expressed in inches water gauge, plus 1 in., and the trap outlet shall be below the pan outlet by not less than twice that pressure.
+
+### The trap shall be furnished with a cleanout or a union that permits disassembly without cutting the drain line, and shall be primed at startup.
+
+### The condensate drain line from the trap shall be routed to an approved point of disposal in accordance with [[sync/condensate-drainage-piping]], with the slope and freeze protection the climate requires.
+
+### Where the unit is outdoors in a climate with freezing temperatures, the trap and the drain line to the roof penetration shall be heat-traced and insulated or arranged to drain dry when the unit is not cooling.
+
+### A drain trap on a draw-through unit holds water against the fan, not against a sewer. If the seal is shallower than the negative pressure at the pan, the fan pulls the seal out, the pan stops draining, and the unit draws unfiltered air backward through the drain line. On a unit that dehumidifies into the shoulder seasons the trap can be full of water on a night that freezes, and a frozen trap backs the pan up on the first warm morning. {note}
+
+# Humidifier Section {toc}
+
+## Where the datasheet selects a humidifier section, the section shall be furnished within the unit downstream of the heating section with an absorption distance to the next downstream component not less than the humidifier manufacturer's published distance at the design conditions.
+
+```datasheet
+label: Humidifier Section
+type: radio
+options:
+ - "Humidifier section furnished in the unit"
+ - "No humidifier section"
+default: "No humidifier section"
+```
+
+## Where a humidifier section is furnished, the humidifier itself shall conform to [[sync/humidifiers]], and the section shall be furnished with a drain pan, a stainless steel or polymer liner over the absorption distance, and a high-limit humidity sensor downstream that stops the humidifier.
+
+## Where a humidifier section is furnished, the winter design supply air humidity ratio shall be stated on the mechanical equipment schedule, and the heating section shall be sized to supply the evaporation energy of an adiabatic humidifier in addition to the tempering rise.
+
+## A total energy recovery device returns much of the building's moisture to the incoming air in winter, which is why most dedicated outdoor air units in humid-interior buildings need no humidifier; the section is furnished where the recovery is sensible-only, where the exhaust is too dry to return anything, or where the space criterion demands a humidity the recovery alone cannot hold. Humidifying the ventilation air at the unit puts the whole building's moisture through one section and one absorption distance, which is simpler than humidifying at zones and demands that the section never wet the downstream filter. {note}
+
+# Roof Curb, Isolation, and Restraint {toc}
+
+## Roof Curb {toc}
+
+### Requirements in this article apply where the unit is set on a roof.
+
+### Each unit shall be set on a roof curb of the type indicated in the datasheet.
+
+```datasheet
+label: Roof Curb Type
+type: select
+options:
+ - "Manufacturer's matched insulated curb"
+ - "Manufacturer's matched curb with integral isolation rails"
+ - "Manufacturer's matched curb of seismic-rated construction"
+ - "Adapter curb fitted to an existing curb"
+ - "Curb fabricated by the roofing or sheet metal trade to the manufacturer's curb drawing"
+```
+
+### Where a curb is fabricated by a trade other than the unit manufacturer, it shall be built to the manufacturer's published curb drawing for the unit furnished, and the fabricating trade shall be responsible for the fit of the unit to the curb and of the curb to the roof structure.
+
+### Where an adapter curb is furnished, the adapter shall be engineered by the unit manufacturer for the existing curb dimensions, which the Contractor shall field-verify before the adapter is released for fabrication.
+
+### The curb shall be a welded or mechanically fastened galvanized steel assembly with a continuous wood nailer for roof flashing, internal cross supports beneath the duct openings, insulation on the interior faces, and a gasket at the unit-to-curb joint.
+
+### The curb height shall be as indicated in the datasheet, measured from the top of the roof deck to the top of the curb.
+
+```datasheet
+label: Roof Curb Height
+type: range
+unit: in.
+drawing_ref: "the roof curb detail on the contract documents"
+options:
+ min: 8
+ max: 36
+ setpoints: [8, 12, 14, 16, 18, 24, 30, 36]
+default: deferred
+```
+
+### The curb height shall provide the flashing height above the finished roof surface that [[sync/membrane-roofing]] requires, including the thickness of the roof insulation and any tapered insulation at the curb.
+
+### The curb shall be set level on the roof structure, shimmed as required over a sloped deck, and fastened to the structure as [[sync/vibration-isolation-and-seismic-restraint]] and the restraint provisions of this standard require.
+
+### Where the unit is set on grade, it shall be set on a level concrete housekeeping pad extending not less than 4 in. beyond the unit base on every side, with the pad detail as indicated on [[drawing: the mechanical site plan]].
+
+### The curb is the interface between three trades. The unit manufacturer sizes it to the unit, the roofer flashes it into the membrane, and the structural engineer checks the framing beneath it, and the curb height is the dimension all three have to agree on before the first one starts. The matched curb fits by construction; a seismic curb carries the engineered attachment where the restraint derivation calls for it; an isolation curb breaks the vibration path at the cost of flexible connections at every service; an adapter or a trade-built curb is the arrangement for a replacement or for a roof whose structure dictates the curb. {note}
+
+## Vibration Isolation {toc}
+
+### The vibration isolation arrangement shall be as indicated in the datasheet.
+
+```datasheet
+label: Vibration Isolation Arrangement
+type: select
+options:
+ - "Unit-integral fan and compressor isolation on a rigid curb or pad"
+ - "Spring isolation rails within the curb"
+ - "Elastomeric isolation rails within the curb"
+ - "Restrained spring isolators beneath a unit set on a structural frame or pad"
+default: "Unit-integral fan and compressor isolation on a rigid curb or pad"
+```
+
+### Where isolation rails or isolators are furnished, they shall be selected in accordance with [[sync/vibration-isolation-and-seismic-restraint]] for a static deflection not less than the value indicated in the datasheet.
+
+```datasheet
+label: Minimum Isolator Static Deflection
+type: range
+unit: in.
+options:
+ min: 0.25
+ max: 3
+ setpoints: [0.25, 0.35, 0.75, 1, 1.5, 2, 2.5, 3]
+```
+
+### Where the datasheet does not state a static deflection, the isolator selection shall be made from the lowest fan operating speed so that the isolation system natural frequency is not more than one third of that speed.
+
+### Where isolation rails or isolators are furnished, the duct, piping, gas, electrical, and condensate connections to the isolated unit shall be made through flexible elements, and the calculated isolation efficiency at the lowest fan operating speed shall be stated in the submittal.
+
+### The fans and compressors are isolated inside the casing as built, and for a unit over a heavy deck remote from occupancy that internal isolation is what most projects rely on. A unit over a light long-span roof, or over a noise-sensitive space, transmits what the internal isolators pass into a structure that amplifies it, and an isolation curb breaks that path at the cost of flexible connections at every service and a curb built for the movement. Springs reach the deflections a low-speed fan needs; elastomeric rails take less height and suit the higher fan speeds of a small unit. {note}
+
+## Seismic and Wind Restraint {toc}
+
+### Seismic restraint of the unit and its curb or pad shall be as indicated in the datasheet.
+
+```datasheet
+label: Seismic Restraint
+type: radio
+derived: "[[parameter: seismic-design-category]] applied to the unit weight, the component importance factor assigned to the unit, and the attachment height in accordance with ASCE 7 Chapter 13"
+options:
+ - "Engineered seismic restraint of the unit to the curb or pad and of the curb to the structure"
+ - "No seismic restraint beyond the manufacturer's attachment hardware"
+default: derived
+```
+
+### Wind restraint of the unit and curb shall be as indicated in the datasheet.
+
+```datasheet
+label: Wind Restraint
+type: radio
+derived: "the wind load ASCE 7 Chapter 29 assigns to rooftop equipment at the unit's height and exposure at the site"
+options:
+ - "Engineered wind restraint of the unit to the curb and of the curb to the structure"
+ - "No wind restraint beyond the manufacturer's attachment hardware"
+default: derived
+```
+
+### Where engineered restraint is furnished, the restraints and their anchorage shall be designed by an engineer licensed in the jurisdiction of the project, and the design shall state the forces delivered to the structure.
+
+### Restraints on an isolated unit shall permit the isolators to function through their normal range and shall engage only under seismic or wind displacement.
+
+### Restraint details and anchorage shall be as indicated on [[drawing: the structural drawings]].
+
+### Seismic and wind restraint are two separate calculations that happen to use the same hardware, and a unit that needs neither in one place can need both in another. A dedicated outdoor air unit is long for its airflow because of the sections it carries in series, which makes it a larger sail than a comfort unit of the same tonnage, and the calculation is what says whether the manufacturer's clips are enough. {note}
+
+# Electrical Provisions {toc}
+
+## Power Connection {toc}
+
+### The unit's minimum circuit ampacity and maximum overcurrent protective device shall be as published by the manufacturer for the configuration furnished, and the branch circuit, feeder, and overcurrent protection serving the unit shall be as indicated on [[drawing: the electrical drawings]].
+
+### The unit power connection arrangement shall be as indicated in the datasheet.
+
+```datasheet
+label: Unit Power Connection
+type: radio
+options:
+ - "Single-point power connection for the complete unit including any electric heater"
+ - "Separate power connections for the unit and the electric heater"
+default: "Single-point power connection for the complete unit including any electric heater"
+```
+
+### The unit disconnecting means shall be as indicated in the datasheet.
+
+```datasheet
+label: Unit Disconnecting Means
+type: select
+options:
+ - "Factory-installed non-fused disconnect switch"
+ - "Factory-installed fused disconnect switch"
+ - "Factory-installed circuit breaker"
+ - "Field-installed disconnect by the electrical trade"
+```
+
+### The disconnecting means shall be lockable in the open position and located within sight of the unit in accordance with NFPA 70.
+
+### Where the disconnect is field-installed, it shall conform to [[sync/enclosed-switches-and-disconnects]] and shall be mounted on a stand or on the unit at a location the manufacturer permits, clear of every access panel swing.
+
+### The short-circuit current rating of the unit control panel shall be not less than the available fault current at the unit terminals indicated in the datasheet.
+
+```datasheet
+label: Available Fault Current at the Unit Terminals
+type: range
+unit: kA
+drawing_ref: "the electrical drawings"
+options:
+ min: 5
+ max: 100
+ setpoints: [5, 10, 14, 18, 22, 25, 35, 42, 50, 65, 100]
+default: deferred
+```
+
+### Three-phase units shall be furnished with a phase loss and phase reversal monitor that prevents compressor operation on a lost or reversed phase.
+
+### A factory disconnect arrives wired and listed with the unit and saves the electrical trade a stand on the roof; a fused switch or a breaker adds the unit's own overcurrent protection where the feeder protection is remote or oversized for the unit; a field disconnect is the arrangement where the electrical contract standardizes on one device or the Authority Having Jurisdiction wants it separate from the equipment. A scroll compressor run backward on a reversed phase makes no pressure, heats rapidly, and can fail within minutes, and the phase monitor turns that wiring error into a nuisance trip. {note}
+
+## Service Receptacle {toc}
+
+### A receptacle for servicing the unit shall be provided as indicated in the datasheet and in accordance with NFPA 70.
+
+```datasheet
+label: Service Receptacle
+type: select
+options:
+ - "Factory-installed ground-fault protected receptacle fed from a separate field branch circuit"
+ - "Factory-installed ground-fault protected receptacle fed through a unit transformer ahead of the unit disconnect"
+ - "Receptacle furnished and installed by the electrical trade within 25 ft of the unit"
+```
+
+### The receptacle shall remain energized when the unit disconnecting means is open.
+
+### The receptacle exists so that a technician can run a vacuum pump, a recovery machine, or a light with the unit itself de-energized, which is the condition under which most of the work on a refrigerant circuit is done. A receptacle on the load side of the unit disconnect goes dead at the moment it is needed, which is why the code forbids that arrangement. {note}
+
+# Controls and Safeties {toc}
+
+## Unit Control Configuration {toc}
+
+### The unit control configuration shall be as indicated in the datasheet.
+
+```datasheet
+label: Unit Control Configuration
+type: select
+options:
+ - "Factory-installed unit controller integrated with the building automation system"
+ - "Factory-installed unit controller operating stand-alone"
+ - "Factory-installed devices and wiring with control by the building automation system contractor"
+```
+
+### The party responsible for the dew point and supply air temperature sequence shall be identified in the submittal, and the sequence shall be reviewed before any control device is released for fabrication.
+
+### The unit controller shall sequence the recovery device and its bypass and frost control, the cooling capacity to the dew point setpoint, the reheat to the supply air temperature setpoint, the heating section, the dampers, and the supply and exhaust fans.
+
+### The unit controller shall carry the manufacturer's compressor protection logic, including minimum run and off times and anti-short-cycle timing, regardless of which party controls the setpoints.
+
+### The dew point loop and the supply air temperature loop shall be separate loops with separate setpoints, and satisfying one shall not stop the other.
+
+### A factory controller arrives tested with the sequence that makes a dedicated outdoor air unit hold its dew point, which is a sequence a field programmer has usually not written before, and it also arrives with a fixed sequence and a proprietary tool for changing it. Field-engineered controls put the sequence in one place with the rest of the building and put the responsibility for protecting the compressors and for the two-loop logic on the party that did not build the unit. The compressor protection has to work regardless of who wrote the sequence, which is why it is required of the unit in every configuration. {note}
+
+## Interlock With the Parallel System {toc}
+
+### The unit shall run in the occupied mode whenever any space it ventilates is scheduled occupied, independent of the heating or cooling demand of the parallel sensible system.
+
+### The unit shall be interlocked with the parallel sensible system through the building automation system so that the parallel system's space temperature control cannot drive the space humidity above the design value by cooling the space below the setpoint at which the ventilation air's dew point holds.
+
+### Where the unit delivers to the inlet or supply side of parallel terminal units, the unit supply fan and the terminal fans shall be interlocked so that neither runs against a closed path.
+
+### Morning warm-up and cool-down modes of the parallel system shall run with the unit off or with the outdoor air damper at its minimum ventilation position as the sequence directs.
+
+### The ventilation demand control shall be as indicated in the datasheet.
+
+```datasheet
+label: Ventilation Demand Control
+type: select
+options:
+ - "None, scheduled occupancy only"
+ - "Carbon dioxide sensors in the spaces served"
+ - "Occupancy sensor inputs from the spaces served"
+ - "Occupancy signal from the building automation system"
+```
+
+### Where ventilation demand control is selected, the outdoor airflow shall be reset between the minimum ANSI/ASHRAE 62.1 requires for the area served and the design outdoor airflow, and shall not be reduced below the area-based component of the ventilation rate.
+
+### The two systems share the spaces and nothing else, and the failures are all at the seam. A parallel unit that overcools a space raises its relative humidity without adding any moisture, and the occupants read that as the ventilation unit failing; a ventilation unit that stops when the parallel system is satisfied leaves the room without outdoor air on a mild day. Demand control on a 100% outdoor air unit saves the conditioning energy of air for people who are not there, and a space sensor resets on the fullest room while a schedule signal resets on the plan. {note}
+
+## Building Automation System Interface {toc}
+
+### The communication interface to the building automation system shall be as indicated in the datasheet.
+
+```datasheet
+label: Building Automation System Interface
+type: select
+options:
+ - "BACnet MS/TP"
+ - "BACnet/IP"
+ - "Modbus RTU"
+ - "Modbus TCP"
+ - "LonWorks FT-10"
+ - "Hardwired point-to-point interface with no network connection"
+```
+
+### The interface shall conform to [[sync/building-automation-system]].
+
+### The manufacturer shall furnish a complete point list for the interface, giving the object name, object type, engineering units, and read or write access for every exposed point.
+
+### Field control connections shall terminate on a labeled terminal block in a compartment accessible without opening a section that is pressurized during operation, and the terminal designations shall match the submitted wiring diagram and point list.
+
+### The points exposed to the building automation system shall include those indicated in the datasheet.
+
+```datasheet
+label: Control Points Exposed to the Building Automation System
+type: checkbox
+options:
+ - "Outdoor air temperature and humidity"
+ - "Supply air temperature"
+ - "Supply air dew point or humidity"
+ - "Cooling coil leaving air temperature"
+ - "Exhaust air temperature and humidity entering the recovery device"
+ - "Outdoor air temperature leaving the recovery device"
+ - "Measured outdoor and exhaust airflows"
+ - "Supply and exhaust fan command, speed, and status"
+ - "Compressor stage or capacity command and status by circuit"
+ - "Reheat command and status"
+ - "Heating stage or modulation command and status"
+ - "Recovery device command, speed, and status"
+ - "Recovery bypass damper position"
+ - "Frost control status"
+ - "Outdoor air and exhaust damper command and end-switch status"
+ - "Filter differential pressure for each bank"
+ - "Refrigerant detection alarm"
+ - "Condensate overflow alarm"
+ - "Compressor lockout and general alarm status"
+ - "Occupied and unoccupied mode command"
+ - "Supply air temperature and dew point setpoints, writable"
+default:
+ - "Outdoor air temperature and humidity"
+ - "Supply air temperature"
+ - "Supply air dew point or humidity"
+ - "Supply and exhaust fan command, speed, and status"
+ - "Compressor stage or capacity command and status by circuit"
+ - "Reheat command and status"
+ - "Heating stage or modulation command and status"
+ - "Recovery device command, speed, and status"
+ - "Frost control status"
+ - "Outdoor air and exhaust damper command and end-switch status"
+ - "Filter differential pressure for each bank"
+ - "Compressor lockout and general alarm status"
+ - "Occupied and unoccupied mode command"
+ - "Supply air temperature and dew point setpoints, writable"
+```
+
+### Control devices furnished with the unit shall conform to [[sync/hvac-controls-instrumentation]] and shall be accessible for calibration and replacement from a service position without entering an operating section.
+
+### The networked protocols differ in what they cost to integrate rather than in what they can carry: the BACnet pair is what most building automation systems speak natively, with the serial form run over a twisted pair to a roof and the IP form over the building network; the Modbus pair is common on equipment controllers and needs a mapping at the automation system; the LonWorks interface serves a building that already runs that network. A hardwired interface exposes only what has a wire, which is enough for a stand-alone unit and not for a unit whose setpoints are written from the automation system. {note}
+
+## Duct Smoke Detection {toc}
+
+### Duct smoke detection shall be furnished at the locations indicated in the datasheet.
+
+```datasheet
+label: Duct Smoke Detector Locations
+type: select
+derived: "the unit's supply airflow and exhaust arrangement against the detector thresholds NFPA 90A and the adopted mechanical code set"
+options:
+ - "Supply air only"
+ - "Supply air and exhaust air"
+ - "None required for the unit"
+default: derived
+```
+
+### The responsibility for furnishing and installing duct smoke detectors shall be as indicated in the datasheet.
+
+```datasheet
+label: Duct Smoke Detector Responsibility
+type: select
+options:
+ - "Furnished and installed by the fire alarm contractor"
+ - "Furnished by the fire alarm contractor and installed by the mechanical contractor"
+ - "Furnished and installed by the mechanical contractor"
+ - "Factory-installed by the unit manufacturer"
+```
+
+### Duct smoke detectors shall be installed in accordance with NFPA 90A, NFPA 72, and the adopted mechanical code, with sampling tubes spanning the duct or plenum cross-section.
+
+### Smoke detection shall shut down the supply and exhaust fans through a hardwired interlock that does not depend on the unit controller or the building automation system, and shall report to the fire alarm system in accordance with [[sync/fire-alarm-systems]].
+
+### The supply detector threshold in the mechanical code is set on airflow, so for a given unit the locations are a lookup rather than a choice; the responsibility for furnishing them is a genuine project decision that turns on how the fire alarm contract was written. {note}
+
+## Unit Safety Devices {toc}
+
+### Each unit shall be furnished with the safety devices the listing requires, including high and low refrigerant pressure cutouts on each circuit, compressor motor overloads, heating section high-limit and rollout devices, and the low-limit temperature device on every hydronic coil required under Hydronic Heating Section.
+
+### A low-limit temperature device shall be furnished downstream of the recovery device on every unit with a hydronic coil or a chilled water coil, arranged to stop the fans, close the outdoor air damper, and open the coil valves when it trips.
+
+### A condensate overflow switch shall be furnished in the cooling coil drain pan, arranged to stop the compressors or close the chilled water valve and to alarm when it trips.
+
+### A high static pressure safety device shall be furnished in the supply air section of every variable-volume unit whose fan can develop a pressure exceeding the pressure class of the connected ductwork, arranged to stop the supply fan through a hardwired interlock with manual reset.
+
+### Every safety device that requires manual reset shall be reset only at the unit, and the unit controller shall report the trip of every safety device to the building automation system where an interface is furnished.
+
+### The setpoint of every safety device shall be recorded in the startup report.
+
+# Factory Testing {toc}
+
+## Production Run Test {toc}
+
+### Every unit shall be run-tested at the factory before shipment.
+
+### The factory tests performed on each unit shall include those indicated in the datasheet.
+
+```datasheet
+label: Factory Tests Required
+type: checkbox
+options:
+ - "Refrigerant circuit evacuation, charge, and leak test"
+ - "Compressor and condenser fan operation on each stage or across the modulation range"
+ - "Refrigerant operating pressures and temperatures recorded on each circuit"
+ - "Supply and exhaust fan operation with motor current recorded"
+ - "Recovery device rotation or flow, purge, and bypass operation"
+ - "Dehumidification and reheat sequence operated with the leaving air dew point and supply temperature recorded"
+ - "Heating section fired or energized on each stage"
+ - "Damper stroke and fail-position test"
+ - "Safety device trip verification"
+ - "Refrigerant detection system function test"
+ - "Controls point-to-point verification"
+ - "Casing leakage test"
+ - "Casing water intrusion test"
+default:
+ - "Refrigerant circuit evacuation, charge, and leak test"
+ - "Compressor and condenser fan operation on each stage or across the modulation range"
+ - "Refrigerant operating pressures and temperatures recorded on each circuit"
+ - "Supply and exhaust fan operation with motor current recorded"
+ - "Recovery device rotation or flow, purge, and bypass operation"
+ - "Dehumidification and reheat sequence operated with the leaving air dew point and supply temperature recorded"
+ - "Heating section fired or energized on each stage"
+ - "Damper stroke and fail-position test"
+ - "Safety device trip verification"
+ - "Controls point-to-point verification"
+```
+
+### A unit that fails any required test shall be corrected and retested, and the cost of correcting a failed factory test and of every retest shall be borne by the manufacturer.
+
+### No unit shall be shipped until every required test has been passed and the results recorded on a report that identifies the unit by serial number.
+
+### The factory run test is the only opportunity to find a charge, a wiring, or a sequence defect while the unit is on a floor with the parts and the people to fix it, and it is the only place the dew point sequence can be exercised at a known entering condition before the site's weather decides when it can be exercised again. A unit that ships untested is repaired on a roof, by crane, in whatever weather the schedule lands on. {note}
+
+## Test Witnessing {toc}
+
+### Factory test witnessing shall be as indicated in the datasheet.
+
+```datasheet
+label: Factory Test Witnessing
+type: radio
+options:
+ - "Unwitnessed, with a certified test report submitted"
+ - "Witnessed at the factory by the Owner's representative"
+ - "Witnessed remotely by live video with the instrumentation in view"
+default: "Unwitnessed, with a certified test report submitted"
+```
+
+### Where witnessed testing is selected, the manufacturer shall give not less than ten business days notice of test readiness and shall submit the test procedure for review before the test is scheduled.
+
+### Where witnessed testing is selected and the unit fails, the cost of the witness attending each retest shall be borne by the manufacturer.
+
+### A certified report is what most projects rely on, because the test is a production step and the report records it. Attending the test buys a look at the unit under a controlled entering condition that the site may not provide for months, which is worth the trip on a large or custom unit; remote witnessing buys most of that for the cost of a camera and is the arrangement where the factory is far away. {note}
+
+# Delivery, Storage, and Handling {toc}
+
+## Units shall be shipped fully assembled, charged, and with every opening covered and sealed against water and debris, with a rotary recovery device blocked against rotation in transit.
+
+## Units shall be stored on a level surface, off the ground, in their protective packaging, with the openings sealed, until they are set.
+
+## Units stored for more than 30 days before setting shall have the crankcase heaters energized where the manufacturer requires it, the fan shafts and the recovery wheel rotated by hand at intervals not exceeding 30 days, and shall be inspected by the Contractor for water intrusion, corrosion, and pest intrusion before setting.
+
+## Units shall not be stacked or used as a storage surface.
+
+## The crane, pick radius, and temporary roof loads shown on the rigging and setting plan shall be reviewed by the structural engineer before the pick.
+
+## Units damaged in transit, in storage, or in handling shall be repaired or replaced as the Engineer of Record directs in writing.
+
+## A unit whose refrigerant circuit has been opened by damage shall be evacuated and recharged at the factory or by the manufacturer's representative.
+
+# Installation {toc}
+
+## Rigging and Setting {toc}
+
+### Units shall be rigged using the lifting points, spreader arrangement, and rigging hardware the manufacturer designates, with no sling bearing against casing panels, coils, hoods, or fan guards.
+
+### Before the pick, the Contractor shall verify that the curb or pad is set, level, flashed, and dried in, that the curb openings align with the unit, and that the roof structure and curb have been confirmed adequate for the unit operating weight.
+
+### The unit shall be set on the curb gasket so that the gasket is continuous and compressed on all four sides, and level within the tolerance the manufacturer publishes so that the drain pans slope to their connections.
+
+### Shipping restraints, shipping bolts, transit blocks on the fan and compressor mounts, and the rotation block on the recovery wheel shall be removed after the unit is set and before the unit is energized.
+
+### A shipping restraint left on a compressor mount holds the compressor rigid against the base, so the first start delivers the full vibration into the casing and into refrigerant tubing that was not designed to flex there; a block left on a wheel stalls its drive on the first start. Both are same-week failures rather than slow ones, and the pre-startup inspection exists to catch them. {note}
+
+## Roofing and Flashing {toc}
+
+### The curb shall be flashed into the roofing membrane by the roofing installer in accordance with [[sync/membrane-roofing]] and [[sync/sheet-metal-flashing-and-trim]], and the flashing shall be complete and watertight before the unit is set.
+
+### Every penetration of the roof for ductwork, piping, gas piping, electrical conduit, condensate drainage, and control wiring shall pass through a flashed curb, sleeve, or pitch pocket, and no penetration shall be made through the unit-to-curb gasket line.
+
+### Where the Contractor is required to restore roofing disturbed by the work, restoration shall match the pre-existing condition recorded in the informational submittal, and where no record was submitted, the Engineer of Record shall make the initial determination of the pre-existing condition.
+
+## Intake and Exhaust Placement {toc}
+
+### The outdoor air intake of each unit shall be separated from exhaust fan discharges, the unit's own exhaust discharge, plumbing vents, flue outlets, cooling tower drift, loading docks, and the other contaminant sources ANSI/ASHRAE 62.1 lists by the distances that standard and the adopted mechanical code require.
+
+### Units shall be located so that the condenser discharge of one unit is not drawn into the condenser intake or the outdoor air intake of another.
+
+### Intake and exhaust locations shall be as indicated on [[drawing: the mechanical roof plan]].
+
+### Every cubic foot the unit supplies is drawn at its intake, so a contaminant at the intake is delivered to every space on the duct at full strength with no return air to dilute it. The separation distances are written for that case, and the unit's own exhaust, a few feet from its own intake on the same casing, is the source most often overlooked. {note}
+
+## Duct Connections at the Unit {toc}
+
+### Supply and exhaust ductwork shall connect to the unit in accordance with [[sync/hvac-ductwork]] and the SMACNA HVAC Duct Construction Standards, independently supported so that no duct weight is carried by the unit or the curb, and through flexible connectors on an isolated unit.
+
+### Supply ductwork carrying air below the dew point of the surrounding space shall be insulated and vapor-sealed in accordance with [[sync/mechanical-insulation]] from the unit connection to the outlets.
+
+### Duct transitions at the unit shall not exceed the transition angle at which the fan outlet loss published in the submittal remains valid, and ductwork within the curb shall be sealed to the curb opening.
+
+### A dedicated outdoor air duct carries air at or near its dew point in summer and air that is still cold in winter wherever recovery alone tempers it, so it sweats on the outside wherever the vapor seal is incomplete, in ceilings and over finishes. The vapor seal on this duct is the difference between a dry ceiling and a stained one, and it is continuous or it is not there. {note}
+
+## Utility Connections {toc}
+
+### Gas piping to each gas-fired unit shall be installed in accordance with [[sync/natural-gas-piping]] or [[sync/fuel-gas-piping]] as applicable to the fuel, with a shutoff valve, a sediment trap, and a union at the unit connection, leak-tested before the burner is fired, and with a pressure regulator vented to the outdoors clear of the outdoor air intake where the supply pressure exceeds the gas train rating.
+
+### Hydronic and condenser water piping to the unit shall be installed in accordance with [[sync/hydronic-piping]], with isolation valves, strainers, and drains at the unit connection, and through flexible connectors on an isolated unit.
+
+### Electrical connections shall be made in accordance with NFPA 70, and conduit to an isolated unit shall include not less than 18 in. of flexible conduit at the unit.
+
+### The condensate trap and drain line shall be installed, sloped, and primed before the unit is started in cooling.
+
+### Control wiring shall be run in the raceway the unit manufacturer designates, segregated from power wiring, and terminated on the labeled terminals shown on the submitted wiring diagram.
+
+## Service Clearances {toc}
+
+### The service clearances shown on the reviewed configuration drawing shall be maintained clear of ductwork, piping, conduit, and other equipment after installation, including the withdrawal path of the recovery wheel or core, the coil pull, each filter bank, and the compressor compartment.
+
+### Where a service clearance conflicts with other work, the conflict shall be resolved before either is installed, and the Engineer of Record shall make the initial determination of which work relocates.
+
+# Startup, Commissioning, and Balancing {toc}
+
+## Pre-Startup Inspection {toc}
+
+### Before any unit is energized, the Contractor shall complete and record the inspection items indicated in the datasheet.
+
+```datasheet
+label: Pre-Startup Inspection Items
+type: checkbox
+options:
+ - "Roof structure and curb or pad load verified"
+ - "Curb flashing complete and watertight"
+ - "Unit level and drain pans sloping to their connections"
+ - "Unit-to-curb gasket continuous and compressed"
+ - "Shipping restraints and wheel rotation block removed"
+ - "Fan and compressor mounts free to move"
+ - "Supply and exhaust duct connections complete and sealed"
+ - "Condensate trap installed, sized for the pan static pressure, and primed"
+ - "Electrical connections complete and phase rotation verified"
+ - "Disconnect and service receptacle operable"
+ - "Gas piping connected, leak-tested, and supply pressure verified"
+ - "Hydronic piping connected, flushed, and filled"
+ - "Filters installed in every bank"
+ - "Service clearances verified clear"
+ - "Refrigerant detection sensors in place and dated"
+default:
+ - "Roof structure and curb or pad load verified"
+ - "Curb flashing complete and watertight"
+ - "Unit level and drain pans sloping to their connections"
+ - "Unit-to-curb gasket continuous and compressed"
+ - "Shipping restraints and wheel rotation block removed"
+ - "Fan and compressor mounts free to move"
+ - "Supply and exhaust duct connections complete and sealed"
+ - "Condensate trap installed, sized for the pan static pressure, and primed"
+ - "Electrical connections complete and phase rotation verified"
+ - "Disconnect and service receptacle operable"
+ - "Filters installed in every bank"
+ - "Service clearances verified clear"
+```
+
+### The inspection record shall mark as not applicable the items for sections the unit does not carry, rather than omitting them.
+
+## Startup Service {toc}
+
+### The startup service shall be as indicated in the datasheet.
+
+```datasheet
+label: Startup Service
+type: select
+options:
+ - "Startup performed by a factory-authorized service representative"
+ - "Startup performed by the installing contractor with factory technical support"
+ - "Startup performed by the installing contractor"
+default: "Startup performed by a factory-authorized service representative"
+```
+
+### Startup shall verify the refrigerant charge on each circuit against the nameplate and the published subcooling or superheat target, the operation of each compressor and condenser fan across its capacity range, the recovery device drive, purge, bypass, and frost control, the dehumidification and reheat sequence holding the dew point and supply temperature setpoints, the heating section on each stage with the input measured on gas-fired units, the dampers, the trip of every safety device at its setpoint, and the refrigerant detection and mitigation sequence where a detection system is furnished.
+
+### Each safety device shall be tested by driving the condition it senses to its setpoint rather than by simulating the device output.
+
+### The startup report shall record the measured outdoor and exhaust airflows, external static pressures, fan speeds, motor currents, refrigerant operating pressures and temperatures by circuit, gas input and manifold pressure, the measured leaving air dew point and supply air temperature with the outdoor condition at the time, and the setpoint of every safety device.
+
+### A factory representative arrives knowing the two-loop sequence and the manufacturer's charge and superheat targets for a circuit that runs colder than a comfort unit's, and the manufacturer's warranty commonly starts from that visit. An installing contractor with factory support on the phone covers most of that at lower cost on a unit the contractor has started before; the contractor alone is the arrangement where the maintaining staff will own the unit and wants to learn it from the first start. {note}
+
+## Commissioning {toc}
+
+### The commissioning scope shall be as indicated in the datasheet.
+
+```datasheet
+label: Commissioning Scope
+type: checkbox
+options:
+ - "Manufacturer startup with a signed report"
+ - "Point-to-point verification of every control device"
+ - "Functional performance testing of the dew point and supply air temperature sequences"
+ - "Verified trip of every safety device at its setpoint"
+ - "Energy recovery effectiveness verified from measured airstream conditions"
+ - "Frost control sequence verification by induced condition or trend"
+ - "Recovery bypass changeover verification"
+ - "Interlock with the parallel sensible system verified in every mode"
+ - "Ventilation demand control response verification"
+ - "Refrigerant detection and mitigation verification by introduced signal"
+ - "Verification of drain pan drainage during dehumidification"
+ - "Integrated testing with the fire alarm system"
+ - "Seasonal dehumidification test at an outdoor dew point near design"
+ - "Trend review over a seasonal period"
+default:
+ - "Manufacturer startup with a signed report"
+ - "Point-to-point verification of every control device"
+ - "Functional performance testing of the dew point and supply air temperature sequences"
+ - "Verified trip of every safety device at its setpoint"
+ - "Interlock with the parallel sensible system verified in every mode"
+ - "Verification of drain pan drainage during dehumidification"
+ - "Integrated testing with the fire alarm system"
+ - "Seasonal dehumidification test at an outdoor dew point near design"
+```
+
+### Commissioning shall be performed in accordance with [[sync/commissioning]].
+
+### Where the seasonal dehumidification test is selected and the outdoor dew point at substantial completion is not within 5°F of the design dew point, the test shall be deferred to the first period in which it is, under a written deferred-testing plan that names the party who returns to perform it and the condition that triggers it.
+
+### Drain pan drainage shall be verified during dehumidification, with the coil condensing and the fan at design speed, by observing continuous flow at the drain and no accumulation in the pan.
+
+### Energy recovery effectiveness shall be verified by measuring the dry-bulb temperature and humidity of all four airstreams at the device and the two airflows, and comparing the computed effectiveness against the submitted value at the measured airflow ratio.
+
+### A dedicated outdoor air unit can only be proven on a humid day, and substantial completion lands on a humid day by chance. The functional test at any other condition shows the sequence works and says nothing about whether the coil reaches the design dew point at the design load, which is the one question the Owner is paying the unit to answer; the deferred test is how that question gets answered rather than assumed. {note}
+
+## Air Balancing {toc}
+
+### Testing, adjusting, and balancing shall be performed in accordance with [[sync/testing-adjusting-and-balancing]] after startup is complete and after the control sequences have been verified.
+
+### The balancing agent shall set and record the design outdoor airflow and the design exhaust airflow through the recovery device, and shall confirm that the airflow ratio is within the range the recovery device is rated for.
+
+### Measured outdoor airflow after balancing shall be within the tolerance indicated in the datasheet of the design value, and not below the ventilation ANSI/ASHRAE 62.1 requires.
+
+```datasheet
+label: Airflow Balancing Tolerance
+type: range
+unit: '%'
+options:
+ min: 0
+ max: 15
+ step: 1
+default: 10
+```
+
+### Where the design airflow cannot be achieved within the tolerance, the balancing agent shall report the measured fan speed, static pressure, and motor current, and the Engineer of Record shall determine the remedy.
+
+### Filters shall be clean at the time of the final balance, and the filter differential pressure across each bank shall be recorded.
+
+### The balance report shall record the as-left fan speeds, drive component designations for belt drives, outdoor and exhaust airflows, external static pressures, motor currents, and the airflow measurement station readings against the measured values.
+
+# Identification and Labeling {toc}
+
+## Each unit shall be furnished with a permanent nameplate on the exterior of the casing, mechanically fastened rather than adhered, of the material indicated in the datasheet.
+
+```datasheet
+label: Unit Nameplate Material
+type: select
+options:
+ - "Stainless steel"
+ - "Anodized aluminum"
+ - "Laminated phenolic"
+```
+
+## The nameplate shall state the unit tag, the manufacturer, the model and serial number, the design outdoor and exhaust airflows, the leaving air dew point and supply air temperature at the design condition, the heating input or capacity, the refrigerant designation and factory charge by circuit, the electrical characteristics including minimum circuit ampacity and maximum overcurrent protective device, and the date of manufacture.
+
+## The unit tag on the nameplate shall match the tag used in the Contract Documents, on the building automation system, and in the operation and maintenance manuals.
+
+## Units charged with a refrigerant in a flammable safety group shall bear the flammable refrigerant marking UL 60335-2-40 and ASHRAE 15 require, applied at the location the listing designates.
+
+## Each filter access panel shall be labeled with the filter efficiency and sizes the bank holds, and the recovery device access shall be labeled with the device type and the direction of rotation or flow.
+
+## The electrical compartment shall contain a permanently mounted copy of the unit wiring diagram, and control terminal strips shall be labeled to match the submitted point list.
+
+## A stainless or anodized plate outlasts the unit on a roof; a phenolic plate is cheaper and legible indoors and fades under sun, which is why the material is a choice rather than a default and follows the unit's location. {note}
+
+# Warranty {toc}
+
+## Unit Warranty {toc}
+
+### The manufacturer shall warrant each unit against defects in materials and workmanship for the terms indicated in the datasheet.
+
+```datasheet
+label: Unit Parts Warranty Term
+type: range
+unit: years
+options:
+ min: 1
+ max: 10
+ setpoints: [1, 2, 3, 5, 10]
+default: 1
+```
+
+```datasheet
+label: Unit Labor Warranty Term
+type: range
+unit: years
+options:
+ min: 0
+ max: 5
+ setpoints: [0, 1, 2, 3, 5]
+default: 1
+```
+
+```datasheet
+label: Warranty Start Milestone
+type: radio
+options:
+ - "Date of substantial completion"
+ - "Date the Owner takes beneficial use of the system"
+ - "Date of shipment"
+default: "Date of substantial completion"
+```
+
+### A component repaired or replaced under warranty shall carry a warranty for a full term from the date of the repair or for the remainder of the original term, whichever ends later.
+
+### Parts and labor are separate commitments commonly sold at different terms, which is why they are stated separately here. A parts-only extension transfers the cost of the component and leaves the Owner paying for the technician, the crane, and the refrigerant, so the two terms have to be read together to know what the coverage is worth on a roof. Starting the term at substantial completion is the usual arrangement; beneficial use protects an Owner whose completion is delayed past the first cooling season, and shipment is the manufacturer's preferred start and shortens the coverage by the construction period. {note}
+
+## Compressor Warranty {toc}
+
+### Each compressor shall be warranted against defects in materials and workmanship for the term indicated in the datasheet, in addition to the unit warranty.
+
+```datasheet
+label: Compressor Warranty Term
+type: range
+unit: years
+options:
+ min: 1
+ max: 10
+ setpoints: [1, 2, 3, 5, 10]
+default: 5
+```
+
+### The compressor warranty shall not be conditioned on service by the manufacturer's own organization where the service is performed by a technician certified under 40 CFR Part 82 Subpart F and, for a flammable refrigerant, trained for that refrigerant.
+
+## Energy Recovery Component Warranty {toc}
+
+### The recovery device, including a wheel's drive, bearings, and seals or a plate core, shall be warranted against defects in materials and workmanship and against loss of certified effectiveness from a defect for the term indicated in the datasheet, in addition to the unit warranty.
+
+```datasheet
+label: Energy Recovery Component Warranty Term
+type: range
+unit: years
+options:
+ min: 1
+ max: 10
+ setpoints: [1, 2, 3, 5, 10]
+default: 5
+```
+
+## Gas Heat Exchanger Warranty {toc}
+
+### Requirements in this article apply where the datasheet selects a gas-fired heating source or a gas-fired supplemental heat source.
+
+### The gas heat exchanger shall be warranted against failure by cracking, burn-through, and corrosion for the term indicated in the datasheet, in addition to the unit warranty.
+
+```datasheet
+label: Gas Heat Exchanger Warranty Term
+type: range
+unit: years
+options:
+ min: 1
+ max: 25
+ setpoints: [1, 5, 10, 15, 20, 25]
+default: 10
+```
+
+### Where a heat exchanger warranty term is conditioned on the heat exchanger material, the term stated in the datasheet shall apply to the material selected in the datasheet.
+
+## Warranty Service {toc}
+
+### The manufacturer shall maintain factory-trained service capability for the units furnished within the region of the project for the duration of the warranty term, and shall respond to a warranty notification within 2 business days.
+
+### The Contractor shall warrant the installation, including the curb setting, flashing, duct and utility connections, isolation, and condensate and control connections, for the term indicated in the datasheet.
+
+```datasheet
+label: Installation Warranty Term
+type: range
+unit: years
+options:
+ min: 1
+ max: 5
+ setpoints: [1, 2, 3, 5]
+default: 1
+```
+
+### A defect attributable to the installation shall be corrected at the Contractor's expense, and where a warranty repair requires removal or modification of roofing or other adjacent work, the cost of removing and restoring that work shall be borne by the party responsible for the defect.
+
+### The manufacturer's warranty shall not be voided by a field refrigerant charge adjustment, a detection sensor replacement, a wheel seal or belt replacement, or a filter change performed in accordance with the operation and maintenance manual by a qualified technician.
+
+# Spare Parts {toc}
+
+## The Contractor shall furnish the spare parts indicated in the datasheet at substantial completion.
+
+```datasheet
+label: Spare Parts Furnished
+type: checkbox
+options:
+ - "One complete set of filters of every size and efficiency installed"
+ - "Two complete sets of filters of every size and efficiency installed"
+ - "One complete set of drive belts for every belt-driven fan and recovery wheel"
+ - "One set of recovery wheel seals for each wheel size installed"
+ - "One set of access panel and door gaskets for each unit"
+ - "One set of every fuse type installed"
+ - "One spare dew point or humidity sensor of each type installed"
+ - "One spare refrigerant detection sensor for each unit on which a detection system is furnished"
+ - "One spare ignition control and flame sensor for each gas-fired heating section type installed"
+default:
+ - "One complete set of filters of every size and efficiency installed"
+ - "One complete set of drive belts for every belt-driven fan and recovery wheel"
+ - "One set of every fuse type installed"
+```
+
+## The Contractor shall obtain a signed receipt from the Owner for the spare parts delivered.
+
+## Spare parts shall be delivered in the manufacturer's packaging, labeled with the unit tag they serve and with the manufacturer's part designation, and spare filters shall be stored in sealed packaging in a clean, dry location the Owner designates.
+
+## The Contractor shall furnish a written inventory correlating each spare item to the unit it serves and the location where it was stored.
+
+## The operation and maintenance manual shall include a filter change schedule for each bank derived from the initial and change-out resistances stated in the submittal, the recovery device seal, belt, and cleaning schedule, the condensate trap cleaning procedure, and, where a detection system is furnished, the replacement date of each refrigerant detection sensor.