Air Terminal Units
Neutrality remake campaign: from-scratch field derivation per authoring cheatsheet; project parameters and derived dispositions
Showing changes from Rev 7
to Rev 8
in Air Terminal Units.
−---
−title: Air Terminal Units
−category: Mechanical / Air Distribution
−toc_depth: 3
−description: >
− When to use: Factory-fabricated air terminal units (ATUs) used to regulate primary airflow and provide zone-level heating in commercial, institutional, and industrial buildings served by central air handling units. Covers single-duct variable air volume (VAV) units with electric or hydronic reheat, parallel and series fan-powered boxes (PFPB and SFPB), dual-duct mixing boxes, constant-volume reheat units, pressure-independent and pressure-dependent damper controls, primary inlet airflow sensors, attenuator-lined casings, hydronic and electric reheat coils with their valves and actuators, and integrated DDC controllers communicating with the building automation system.
−
− Not intended for: Diffusers, grilles, and registers at the room boundary (see [[sync/hvac-air-distribution-devices]]); central air handlers and rooftop units (see [[sync/air-handling-units]]); fan coil units (room-level four-pipe or two-pipe units that recirculate room air rather than condition primary air from a central system); chilled beams; induction units; underfloor air distribution plenum boxes; laboratory venturi-style airflow control valves used in critical pressurization service; transfer fans serving relief or makeup air paths.
−---
−
−# Scope {toc}
−
−## This standard covers the materials, construction, performance, testing, installation, and commissioning of factory-fabricated air terminal units that meter primary supply air to occupied zones and, where indicated, provide local reheat or fan-powered induction of plenum return air. {note}
−## Equipment covered includes single-duct VAV units, parallel fan-powered boxes (PFPB), series fan-powered boxes (SFPB), dual-duct units, and constant-volume reheat units, together with their primary airflow sensors, dampers, reheat coils, fan assemblies, casing and attenuator construction, valves and actuators, and integral DDC controllers. {note}
−
−## Air terminal units are the points at which a central air system meets each thermal zone; their selection determines minimum ventilation airflow at part-load conditions, zone-level acoustical performance, and the energy used by reheat and fan-powered induction. {note}
−
−## Undersized inlets create excessive pressure drop and starve the zone of design airflow; oversized inlets put the airflow sensor below its low-flow accuracy threshold and result in poor minimum-ventilation control. {note}
−
−## All air terminal units shall be rated and certified under the AHRI Certification Program for Air Terminals per ANSI/AHRI 880, with sound performance rated per ANSI/AHRI 885 and performance testing per ANSI/ASHRAE 130.
−
−## This standard establishes the performance, construction, and control requirements needed to deliver design airflow within accuracy limits, to comply with ASHRAE 62.1 minimum ventilation rates, and to meet the reheat and fan-power limits of ASHRAE 90.1. {note}
−
−## Coordinate primary inlet sizing with the upstream duct system specified in [[sync/hvac-ductwork]].
−
−## Coordinate outlet connections and downstream distribution with [[sync/hvac-ductwork]] and [[sync/hvac-air-distribution-devices]].
−
−## Coordinate hot water reheat piping with [[sync/hydronic-piping]].
−
−## Coordinate central system pressure profile and fan control with [[sync/air-handling-units]].
−
−## Coordinate DDC controllers and zone control sequences with [[sync/building-automation-system]].
−
−## Coordinate post-installation airflow verification with [[sync/testing-adjusting-and-balancing]].
−
−# Referenced Standards {toc}
−
−## Equipment, materials, and installation shall comply with the latest adopted edition of each standard below unless a specific edition is referenced by contract documents or by the local building code.
−
−## Where conflicts exist between referenced standards, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
−
−## Referenced standards list {toc}
−
−| Standard | Title |
−|----------|-------|
−| ANSI/AHRI 880 | Performance Rating of Air Terminals |
−| ANSI/AHRI 885 | Procedure for Estimating Occupied Space Sound Levels in the Application of Air Terminals and Air Outlets |
−| ANSI/ASHRAE 130 | Methods of Testing Air Terminal Units |
−| ANSI/ASHRAE/IES 90.1 | Energy Standard for Buildings Except Low-Rise Residential Buildings |
−| ANSI/ASHRAE 62.1 | Ventilation and Acceptable Indoor Air Quality |
−| NFPA 90A | Standard for the Installation of Air-Conditioning and Ventilating Systems |
−| NFPA 70 (NEC) | National Electrical Code, Article 424 (Fixed Electric Space-Heating Equipment) |
−| UL 1995 | Heating and Cooling Equipment (where accepted by AHJ for legacy listings) |
−| UL 60335-2-40 | Safety of Household and Similar Electrical Appliances — Particular Requirements for Electrically Operated Heat Pumps, Air-Conditioners, and Dehumidifiers |
−| UL 181 | Standard for Factory-Made Air Ducts and Air Connectors (terminal unit casing liner) |
−| ASTM E84 | Standard Test Method for Surface Burning Characteristics of Building Materials |
−| ASTM C1071 | Standard Specification for Fibrous Glass Duct Lining Insulation (Thermal and Sound Absorbing Material) |
−| SMACNA HVAC Duct Construction Standards | HVAC Duct Construction Standards — Metal and Flexible |
−| ASHRAE Handbooks | HVAC Systems and Equipment; Applications |
−
−# Submittals {toc}
−
−## Action Submittals {toc}
−
−### The Contractor shall submit the following for the Engineer's review and return prior to fabrication or procurement of the air terminal units.
−
−### No fabrication or shipment shall proceed until the associated submittal has been reviewed and returned with no outstanding engineering questions.
−
−### Submit the following action submittals: {toc}
−
−- Product data and configuration schedule for each unit tag, including inlet size, primary maximum and minimum airflow, casing dimensions, weight, reheat coil capacity and rows, fan motor type and rating, controller make and protocol, and outlet configuration
−- AHRI 880 certified performance data for each unit configuration, including primary airflow accuracy, casing leakage, casing pressure drop, induction ratio for fan-powered units, and reheat coil performance
−- AHRI 885 sound power data at the selected primary airflow and inlet static pressure, in octave bands 2 through 7 (125 Hz through 4,000 Hz), separated into radiated and discharge paths; include the NC calculation for each scheduled zone using the project room absorption and distance
−- Damper assembly product data including blade material, shaft and bearing type, blade and frame seal materials, close-off leakage at design close-off pressure, and minimum and maximum operating differential pressure
−- Primary inlet airflow sensor product data including the sensor type (multi-point center-averaging or equivalent), the published accuracy (percent of reading) across the operating range, and the manufacturer's required upstream and downstream straight-duct lengths for rated accuracy
−- Reheat coil product data including row count, fin spacing, tube material, fin material, working pressure, design hot water entering and leaving temperatures, design air entering and leaving temperatures, and waterside pressure drop at design flow
−- Electric reheat coil product data including stage count or SCR control range, kW rating per stage, sheath material, NEC Article 424 compliance documentation, primary and backup over-temperature protection, and airflow proving switch information
−- Control valve and actuator product data including Cv, close-off rating, fail-safe position, modulating signal type, and stroke time
−- Fan motor data for fan-powered boxes including motor type (ECM or PSC), nameplate power, efficiency, speed range, and ECM controller communication
−- DDC controller product data including communication protocol, hardwired input and output count, supported control sequences, and BAS network topology
−- Acoustical attenuator and casing liner construction data including liner thickness, ASTM C1071 compliance, ASTM E84 flame-spread and smoke-developed indices, and UL 181 listing
−- Shop drawings showing each unit in plan and section with all field connection points dimensioned (primary inlet, induced air opening for fan-powered units, outlet duct collars, hot water supply and return, electric service, control wiring, condensate where applicable), required service clearances, and access panel locations
−
−```datasheet
−label: Action Submittals Required
−type: checkbox
−options:
− - "Product data and configuration schedule per tag"
− - "AHRI 880 certified performance data"
− - "AHRI 885 sound data (radiated and discharge, octave bands)"
− - "Damper assembly product data and close-off leakage"
− - "Primary inlet airflow sensor data with accuracy and straight-duct requirements"
− - "Hydronic reheat coil data (rows, fin spacing, pressure drop)"
− - "Electric reheat coil data (stages, sheath, NEC 424 compliance)"
− - "Control valve and actuator data"
− - "Fan motor data (ECM or PSC) for fan-powered units"
− - "DDC controller data and BAS protocol"
− - "Casing liner / attenuator construction (UL 181, ASTM E84)"
− - "Shop drawings with clearances and field connections"
−default: "Product data and configuration schedule per tag"
−```
−
−## Closeout Submittals {toc}
−
−### At substantial completion the Contractor shall provide the following closeout submittals:
−
−- Operation and maintenance manuals including manufacturer's installation, operation, and maintenance instructions; controller programming reference; troubleshooting guide; and recommended preventive maintenance schedule
−- As-built configuration drawings reflecting any field modifications to the submitted configuration
−- Factory test reports for each unit, including the primary airflow sensor calibration curve where the sensor is factory-calibrated to the specific unit
−- Field commissioning records, including the airflow verification at minimum and maximum airflow setpoints, the reheat valve or stage stroke verification, and the BAS point verification for each unit
−- Controller parameter file in the manufacturer's native format for each unit, listing the as-commissioned setpoints, calibration constants, and control loop tuning parameters
−- Warranty documentation from the air terminal unit manufacturer and from any separately warranted sub-supplier components (ECM motor, DDC controller, electric heater)
−
−```datasheet
−label: Required Closeout Submittals
−type: checkbox
−options:
− - Operation and maintenance manuals
− - As-built configuration drawings
− - Factory test reports for each unit
− - Field commissioning records
− - Controller parameter file (native format)
− - Warranty documentation
−default: [Operation and maintenance manuals, As-built configuration drawings, Factory test reports for each unit, Field commissioning records, Controller parameter file (native format), Warranty documentation]
−```
−
−# Quality Assurance {toc}
−
−## Manufacturer Qualifications {toc}
−
−### Air terminal units shall be the product of a single manufacturer with a minimum of ten years of continuous experience designing and producing factory-fabricated air terminal units for commercial HVAC service.
−
−### The manufacturer shall maintain an ISO 9001 certified quality management system.
−
−### The manufacturer shall be capable of providing replacement parts and service support for a minimum of fifteen years after the date of manufacture.
−
−## Single-Source Responsibility {toc}
−
−### All air terminal units on the project shall be furnished by a single manufacturer to maintain consistent control interfaces, consistent service-access patterns, and a single source for spare parts.
−
−### Where DDC controllers are factory-installed and factory-tested with the terminal unit, the controller shall be installed and warranted by the air terminal unit manufacturer.
−
−### Field-mounted controllers from a separate controls contractor are acceptable only where the contract documents specifically permit, and shall be furnished, mounted, and wired before the unit is started.
−
−### Controller furnish and install responsibility datasheet {toc}
−
−```datasheet
−label: Controller Furnish and Install Responsibility
−type: radio
−options:
− - "Factory-installed and factory-tested by ATU manufacturer (standard)"
− - "Factory-installed by ATU manufacturer; programmed by controls contractor at startup"
− - "Field-mounted by controls contractor (shipped loose by ATU manufacturer)"
−default: "Factory-installed and factory-tested by ATU manufacturer (standard)"
−```
−
−## AHRI 880 Certification {toc}
−
−### Each air terminal unit configuration furnished on the project shall be rated under the AHRI Certification Program for Air Terminals (CP-ATU) per ANSI/AHRI 880.
−
−### Published primary airflow ratings, casing leakage ratings, sound ratings (when combined with AHRI 885), reheat coil capacities, and pressure drop data shall reflect AHRI-certified values.
−
−### The certification mark shall appear on the product data submitted with the unit schedule.
−
−### Equipment not certified under AHRI 880 is not acceptable.
−
−### AHRI certification datasheet {toc}
−
−```datasheet
−label: AHRI Certification
−type: radio
−options:
− - "AHRI 880 certified — all unit configurations on project"
− - "AHRI 880 certified — manufacturer participates and configuration is within certified range"
−default: "AHRI 880 certified — all unit configurations on project"
−```
−
−## NRTL Listing {toc}
−
−### Air terminal units containing electric reheat coils, fan motors, or electrically powered controls shall be listed and labeled by a Nationally Recognized Testing Laboratory (NRTL) to UL 60335-2-40, or to UL 1995 where the AHJ continues to accept legacy listings for equipment manufactured prior to the transition date.
−
−### Electric reheat coils shall additionally comply with NFPA 70 Article 424 for fixed electric space-heating equipment.
−
−### Listed assemblies shall bear the NRTL label affixed to the casing in a visible location.
−
−## Pre-Installation Conference {toc}
−
−### Before installation of air terminal units begins, the Contractor shall hold a pre-installation conference attended by the mechanical sub-contractor, the controls sub-contractor, the electrical sub-contractor where electric reheat is provided, the testing and balancing agent, and the Owner's commissioning representative where one is engaged.
−
−### The pre-installation conference agenda shall include unit access and service-clearance requirements, sequencing of duct connections relative to controller calibration, hot water piping and electric reheat connection sequencing, and the schedule for primary airflow verification and BAS point checkout.
−
−# Environmental and Service Conditions {toc}
−
−## Air terminal units shall be selected and rated for the conditions of their installed location and for the central system pressure profile they will operate against.
−
−## The unit shall function within its certified accuracy and acoustical performance over the entire airflow range scheduled for the zone it serves.
−
−## Ambient and Installation Location {toc}
−
−### Air terminal units shall be suitable for continuous operation in indoor conditioned or semiconditioned plenum spaces at ambient temperatures from 50°F to 104°F and relative humidity from 10% to 90% non-condensing.
−
−### Units installed in unconditioned spaces, in interstitial floors with no temperature control, or in spaces with elevated humidity shall be reviewed with the manufacturer for any required casing, controller enclosure, or condensate provisions before ordering.
−
−### Air terminal units are not weatherproof and shall not be installed outdoors or in any location subject to driving rain, condensation, or freezing temperatures.
−
−### Installation location datasheet {toc}
−
−```datasheet
−label: Installation Location
−type: select
−options:
− - "Concealed above accessible ceiling — conditioned plenum"
− - "Concealed above accessible ceiling — non-conditioned return plenum"
− - "Mechanical room or service corridor"
− - "Interstitial floor (full-height service space)"
−default: "Concealed above accessible ceiling — conditioned plenum"
−```
−
−## Inlet Static Pressure {toc}
−
−### Air terminal units shall be selected so that the available inlet static pressure at the unit is sufficient to deliver design airflow through the unit casing, damper, downstream coil (if any), and downstream low-pressure duct distribution to the air outlets, with adequate margin for control authority at minimum airflow.
−
−### The minimum inlet static pressure for pressure-independent VAV units to maintain primary airflow control at all flow setpoints shall be 0.3 in. w.g. unless the manufacturer's published data certifies stable control at a lower value.
−
−### The maximum inlet static pressure shall not exceed 3.0 in. w.g. unless the unit is specifically rated for high-pressure inlet service.
−
−### Excessive inlet pressure increases damper noise and may exceed the certified sound rating. {note}
−
−### Inlet static pressure datasheet {toc}
−
−```datasheet
−label: Inlet Static Pressure at Design (At Unit Inlet)
−type: range
−unit: in. w.g.
−drawing_ref: true
−options:
− min: 0.3
− max: 3.0
− setpoints: [0.3, 0.5, 0.75, 1.0, 1.5, 2.0, 2.5, 3.0]
−default: 0.75
−```
−
−### Sizing units to AHU discharge static pressure rather than the static pressure available at the terminal unit inlet after upstream duct losses is a common selection error. {note}
−
−### The Engineer shall calculate inlet static pressure for the most remote and most disadvantaged unit on each branch and shall size both the central fan and the units accordingly.
−
−### Static pressure reset based on the most-open damper position is the preferred control strategy for energy performance and shall be coordinated with [[sync/building-automation-system]].
−
−# Unit Type and Configuration {toc}
−
−## Air terminal unit selection is determined by the zone's heating requirement, the use of plenum return air for induction, the central system control strategy, and the acoustical sensitivity of the zone served. {note}
−## This section establishes the type of unit for each tag. {note}
−
−## Box Type {toc}
−
−### Single-duct units regulate a single primary airstream from the central air handler and are the standard selection for interior zones served by a constant-discharge-temperature central system. {note}
−
−### Parallel fan-powered boxes include an intermittent fan that draws plenum return air through the casing in parallel with primary air, and are used where perimeter zones require warm air during unoccupied or low-cooling-demand periods without continuous fan power. {note}
−
−### Series fan-powered boxes include a continuous fan that mixes primary and induced plenum air at all times, are used where constant zone airflow is required regardless of primary airflow, and provide better cold-air-dump prevention at the cost of continuous fan energy. {note}
−
−### Dual-duct units accept separate primary cold and warm airstreams and proportion the mixture to the zone, and are used in dual-duct distribution systems. {note}
−
−### Constant-volume reheat units regulate to a fixed airflow setpoint and provide reheat for temperature control, and are used in spaces with fixed ventilation requirements such as some laboratory and healthcare applications. {note}
−
−### Box type datasheet {toc}
−
−```datasheet
−label: Box Type
−type: select
−drawing_ref: true
−options:
− - "Single-duct VAV"
− - "Parallel fan-powered box (PFPB) — intermittent fan"
− - "Series fan-powered box (SFPB) — continuous fan"
− - "Dual-duct mixing box"
− - "Constant-volume reheat (CV)"
−default: "Single-duct VAV"
−```
−
−## Pressure-Independence {toc}
−
−### Pressure-independent units include a primary inlet airflow sensor and a closed-loop control strategy that maintains the commanded airflow setpoint regardless of variations in inlet static pressure within the operating range. {note}
−
−### Pressure-dependent units modulate the damper based on a zone temperature signal directly, with no airflow feedback; their actual delivered airflow varies with system pressure and cannot reliably hold a minimum ventilation rate. {note}
−
−### Pressure-independent control is required to maintain ASHRAE 62.1 minimum ventilation rates at all part-load conditions and is the standard selection for new construction.
−
−### Control mode datasheet {toc}
−
−```datasheet
−label: Control Mode
−type: radio
−options:
− - "Pressure-independent — airflow sensor closed-loop control (standard)"
− - "Pressure-dependent — temperature signal direct to damper (not recommended)"
−default: "Pressure-independent — airflow sensor closed-loop control (standard)"
−```
−
−## Inlet Size {toc}
−
−### The primary inlet is identified by its nominal round duct diameter. {note}
−
−### Inlet size shall be selected so that the unit's primary maximum airflow lies within the certified flow range of the inlet sensor, with margin above the minimum-flow accuracy threshold at the unit's primary minimum airflow setpoint.
−
−### Oversizing the inlet relative to the actual airflow range degrades minimum-airflow control because the sensor velocity falls below the calibrated accuracy floor; undersizing increases pressure drop and noise. {note}
−
−### Coordinate the inlet size with the AHRI 880 certified flow range published by the manufacturer.
−
−### Inlet nominal diameter datasheet {toc}
−
−```datasheet
−label: Inlet Nominal Diameter
−type: select
−unit: in
−drawing_ref: true
−options:
− - "4 in."
− - "5 in."
− - "6 in."
− - "7 in."
− - "8 in."
− - "9 in."
− - "10 in."
− - "12 in."
− - "14 in."
− - "16 in."
−default: "8 in."
−```
−
−## Primary Airflow Setpoints {toc}
−
−### Primary maximum airflow defines the unit's cooling-design airflow. {note}
−
−### Primary minimum airflow defines the lowest commanded airflow under the central control sequence, which is typically the larger of the ASHRAE 62.1 zone outdoor air requirement (adjusted for system ventilation effectiveness), the heating airflow setpoint, and any acoustical or stratification floor established by the design team. {note}
−
−### ASHRAE 90.1 limits the reheat-airflow minimum to no more than the larger of 30% of design or the ventilation rate, except for specific exceptions for laboratories, occupancy-sensed zones, and DDC-with-airflow-reset systems; the Engineer shall determine the controlling minimum for each zone and shall set the controller minimum airflow accordingly.
−
−### Primary airflow setpoint datasheets {toc}
−
−```datasheet
−label: Primary Maximum Airflow
−type: range
−unit: CFM
−drawing_ref: true
−options:
− min: 50
− max: 6000
− step: 50
−default: 800
−```
−
−```datasheet
−label: Primary Minimum Airflow (Cooling)
−type: range
−unit: CFM
−drawing_ref: true
−options:
− min: 0
− max: 3000
− step: 25
−default: 250
−```
−
−```datasheet
−label: Primary Minimum Airflow (Heating)
−type: range
−unit: CFM
−drawing_ref: true
−options:
− min: 0
− max: 3000
− step: 25
−default: 400
−```
−
−### A frequent source of comfort complaints is a heating airflow setpoint identical to the cooling minimum, which produces a cold-air dump at the diffusers when the unit transitions to heating. {note}
−
−### ASHRAE 90.1 recognizes this and permits a higher heating-airflow setpoint (typically 30% to 50% of design) so that the supply air temperature delta at the diffuser is sufficient to overcome cold-air dump. {note}
−
−### For fan-powered boxes, induction adds plenum air to primary air at the diffuser and the cold-air dump risk is reduced; the heating setpoint for fan-powered units may be set to the same value as the cooling minimum where the fan provides adequate discharge airflow. {note}
−
−# Casing Construction {toc}
−
−## Casing Material and Gauge {toc}
−
−### Air terminal unit casings shall be fabricated from galvanized steel sheet conforming to ASTM A653 with G60 or G90 coating, of gauge not less than 22 gauge for the casing wrapper and 20 gauge for the inlet collar and outlet flanges.
−
−### Casing shall be of welded, mechanically fastened, or interlocked-seam construction with all joints sealed to the leakage class certified under AHRI 880.
−
−### Loose-fitting casing seams sealed only with tape are not acceptable.
−
−### Casing material datasheet {toc}
−
−```datasheet
−label: Casing Material
−type: radio
−options:
− - "Galvanized steel, ASTM A653, G60 coating (standard)"
− - "Galvanized steel, ASTM A653, G90 coating (high-humidity plenum)"
− - "Aluminized steel"
− - "Stainless steel (special service)"
−default: "Galvanized steel, ASTM A653, G60 coating (standard)"
−```
−
−## Casing Air Leakage {toc}
−
−### Casing leakage shall not exceed the values certified under AHRI 880 for the unit configuration, and in no case shall exceed 1% of nominal cataloged primary airflow at 1.0 in. w.g. internal static pressure.
−
−### Casing leakage on a closed damper shall not exceed 2% of nominal cataloged primary airflow at 3.0 in. w.g. inlet static pressure, measured at the unit inlet with the damper closed and the outlet open.
−
−### Excessive casing leakage and damper-closed leakage both degrade minimum-airflow control and add to the central system's outdoor-air dilution calculation. {note}
−
−### Casing air leakage datasheet {toc}
−
−```datasheet
−label: Casing Air Leakage at 1 in. w.g.
−type: select
−options:
− - "≤ 1% of nominal primary airflow (standard)"
− - "≤ 2% of nominal primary airflow (legacy applications only)"
−default: "≤ 1% of nominal primary airflow (standard)"
−```
−
−## Casing Liner / Attenuator {toc}
−
−### Casings shall be lined with thermal-acoustical insulation to attenuate primary damper noise and to reduce thermal transmission between the conditioned primary air and the plenum.
−
−### Liner shall conform to ASTM C1071 with a flame-spread index not greater than 25 and a smoke-developed index not greater than 50 when tested per ASTM E84, and shall be UL 181 listed.
−
−### Liner shall be coated, encapsulated, or covered with a perforated metal facing on the airstream side to prevent fiber erosion at the certified maximum face velocity.
−
−### Casing liner / attenuator datasheet {toc}
−
−```datasheet
−label: Casing Liner / Attenuator Construction
−type: select
−options:
− - "1/2 in. dual-density fiberglass with foil-faced or coated airstream surface"
− - "1 in. dual-density fiberglass with foil-faced or coated airstream surface"
− - "1 in. fiberglass with perforated metal liner (closed-cell airstream protection)"
− - "Closed-cell foam liner (fiber-free)"
− - "Double-wall casing — fiber encapsulated between solid metal skins (fiber-free airstream)"
−default: "1 in. fiberglass with perforated metal liner (closed-cell airstream protection)"
−```
−
−### Fiber-free liner constructions (closed-cell foam liners and double-wall casings with encapsulated fiber) are required for healthcare critical spaces, laboratory exhaust serving classified airstreams, and projects whose program documents specify fiber-free distribution.
−
−### For general office and institutional service, a perforated-metal-faced fiberglass liner is the standard selection because it provides superior acoustical attenuation per unit thickness with no fiber exposure to the airstream. {note}
−
−## Hanger and Mounting Provisions {toc}
−
−### Casings shall include integral mounting brackets, hanger lugs, or threaded inserts for suspension from structure.
−
−### The Contractor shall not penetrate the casing for hanger attachment after manufacture because field penetrations breach the casing liner and create thermal bridges and leak paths.
−
−### Each unit shall be supplied with the manufacturer's recommended hanger pattern indicated on the shop drawings.
−
−# Damper Assembly {toc}
−
−## Damper Construction {toc}
−
−### The primary damper shall be a single-blade or multi-blade assembly of galvanized or aluminum construction with a continuous shaft running through self-lubricated bushings or bearings rated for the operating temperature and the design number of operating cycles.
−
−### Damper blades shall be of stiffened construction sized to resist deflection at maximum inlet differential pressure without binding.
−
−### Damper shaft seals shall prevent leakage past the casing penetration at the maximum operating differential pressure.
−
−### Damper blade configuration datasheet {toc}
−
−```datasheet
−label: Damper Blade Configuration
−type: radio
−options:
− - "Single-blade — round, internally mounted (standard for single-duct VAV)"
− - "Multi-blade opposed — for rectangular inlets and dual-duct mixing"
− - "Multi-blade parallel — for fan-powered induction air openings"
−default: "Single-blade — round, internally mounted (standard for single-duct VAV)"
−```
−
−## Damper Close-Off Leakage {toc}
−
−### Damper close-off leakage at 3.0 in. w.g. inlet static pressure shall not exceed 2% of nominal cataloged primary airflow, with the damper commanded to its fully closed position and the outlet open.
−
−### Higher leakage rates degrade the unit's ability to deliver an actual zero-flow condition during unoccupied-mode operation and undermine the dilution accounting that supports ASHRAE 62.1 ventilation compliance at the system level. {note}
−
−### Damper close-off leakage datasheet {toc}
−
−```datasheet
−label: Damper Close-Off Leakage at 3 in. w.g.
−type: select
−options:
− - "≤ 2% of nominal primary airflow (standard)"
− - "≤ 1% of nominal primary airflow (tight close-off for occupied/unoccupied control)"
−default: "≤ 2% of nominal primary airflow (standard)"
−```
−
−## Damper Actuator {toc}
−
−### Damper actuators shall be electronic, direct-coupled to the damper shaft, with stroke time matched to the controller's airflow control loop.
−
−### Spring-return actuators are used where a defined fail-safe position is required by the central system control sequence; non-spring-return actuators are acceptable where the controller maintains last-known-position on signal loss and the unit serves a non-critical zone.
−
−### Pneumatic actuators are acceptable only on retrofit projects extending existing pneumatic control systems.
−
−### Damper actuator datasheets {toc}
−
−```datasheet
−label: Damper Actuator Type
−type: select
−options:
− - "Electronic non-spring-return, modulating 0–10 V or 4–20 mA (standard)"
− - "Electronic spring-return, fail-closed (life-safety or fume-isolation zones)"
− - "Electronic spring-return, fail-open"
− - "Pneumatic, modulating (retrofit only)"
−default: "Electronic non-spring-return, modulating 0–10 V or 4–20 mA (standard)"
−```
−
−```datasheet
−label: Damper Actuator Stroke Time
−type: range
−unit: seconds
−options:
− min: 30
− max: 180
− setpoints: [30, 60, 90, 120, 180]
−default: 90
−```
−
−# Primary Airflow Sensor {toc}
−
−## Sensor Type and Accuracy {toc}
−
−### The primary inlet airflow sensor shall be a multi-point center-averaging differential-pressure sensor (multiple sensing ports averaged across the inlet cross-section) integral to the inlet collar, factory-installed and factory-calibrated to the specific unit.
−
−### The sensor shall be certified under AHRI 880 to maintain accuracy within ±5% of reading from 100% of nominal airflow down to the certified low-flow threshold for the inlet size.
−
−### Sensors providing a single-point or pitot-style differential pressure are acceptable only on inlet sizes 6 in. and below where multi-point averaging is not commercially available, and only with documented manufacturer accuracy data.
−
−### Primary inlet airflow sensor type datasheet {toc}
−
−```datasheet
−label: Primary Inlet Airflow Sensor Type
−type: radio
−options:
− - "Multi-point center-averaging differential pressure (standard)"
− - "Single-point pitot or velocity element (inlet ≤ 6 in. only)"
− - "Thermal anemometer / hot-wire array (manufacturer-specific)"
−default: "Multi-point center-averaging differential pressure (standard)"
−```
−
−## Straight-Duct Inlet Requirement {toc}
−
−### The sensor's published accuracy is valid only when the certified minimum length of straight duct is provided upstream of the unit inlet.
−
−### The manufacturer's required upstream and downstream straight-duct lengths shall be honored on shop drawings and during field installation.
−
−### A common installation defect is an elbow, transition, or branch tee located within one diameter of the unit inlet, which distorts the velocity profile and renders the multi-point average inaccurate; this is one of the leading causes of airflow imbalance during commissioning and is correctable only by adding duct length or accepting field recalibration of the unit's K-factor against a calibrated flow station. {note}
−
−### Minimum straight duct upstream of inlet datasheet {toc}
−
−```datasheet
−label: Minimum Straight Duct Upstream of Inlet
−type: range
−unit: inlet diameters
−options:
− min: 1
− max: 5
− setpoints: [1, 1.5, 2, 3, 5]
−default: 3
−```
−
−# Reheat {toc}
−
−## Reheat Type {toc}
−
−### The reheat strategy at each terminal unit shall be coordinated with the central plant capability and the zone's heating load.
−
−### Hot water reheat is the standard selection where a central hot water plant is provided; it offers high turndown, low operating cost, and quiet operation. {note}
−
−### Electric reheat is used where no central hot water plant is provided or where the heating load is small enough that the cost of running hot water piping to the zone exceeds the lifecycle cost of electric resistance. {note}
−
−### ASHRAE 90.1 limits the use of new electric resistance heating in many building types and climate zones; verify code compliance before specifying electric reheat as the default for the building.
−
−### Reheat type datasheet {toc}
−
−```datasheet
−label: Reheat Type
−type: select
−options:
− - "None (cooling-only)"
− - "Hydronic — hot water coil"
− - "Electric — staged resistance"
− - "Electric — SCR-modulated resistance"
−default: "Hydronic — hot water coil"
−```
−
−## Hydronic Reheat Coil {toc}
−
−### Hot water reheat coils shall be 1-row, 2-row, or 3-row construction as selected to deliver the scheduled coil capacity at the design hot water entering temperature, the design air entering temperature (typically the supply air temperature from the central AHU), and the design primary minimum heating airflow.
−
−### Tubes shall be seamless copper not less than 0.020 in. wall thickness, mechanically expanded into aluminum or copper plate fins.
−
−### Coils shall be factory-pressure-tested to not less than 300 psig before shipment.
−
−### Hydronic reheat coil datasheets {toc}
−
−```datasheet
−label: Hot Water Coil Rows
−type: radio
−options:
− - "1 row (interior zones, low capacity)"
− - "2 rows (standard perimeter)"
− - "3 rows (high-load perimeter or low hot water temperature)"
−default: "2 rows (standard perimeter)"
−```
−
−```datasheet
−label: Reheat Coil Capacity
−type: range
−unit: MBH
−drawing_ref: true
−options:
− min: 1
− max: 60
− step: 1
−default: 12
−```
−
−```datasheet
−label: Hot Water Design Entering / Leaving Temperatures
−type: text
−drawing_ref: true
−default: "140 °F EWT / 120 °F LWT (typical for low-temperature hot water; see mechanical schedules)"
−```
−
−### Modern building hot water plants increasingly operate at 140 °F or lower entering water temperature to allow condensing boiler operation and to integrate with heat pump heat recovery. {note}
−
−### A 1-row coil sized for 180 °F EWT will not deliver design capacity on a 140 °F plant. {note}
−
−### Coil row counts shall be selected for the actual entering water temperature of the project plant.
−
−### Verify the coil selection against the actual scheduled hot water temperature for the project and not against a generic catalog rating.
−
−## Hydronic Control Valve {toc}
−
−### Each hydronic reheat coil shall be served by a modulating control valve.
−
−### Pressure-independent control valves (PICVs) are the preferred selection on projects with variable-flow hydronic distribution because they maintain the commanded flow regardless of differential pressure variations across the building; conventional two-way globe valves are acceptable on smaller systems where differential pressure stability is achieved at the plant. {note}
−
−### Two-position (on-off) valves are acceptable only on cooling-only systems with no need for heating modulation or in unconditioned spaces with low control authority. {note}
−
−### Hydronic reheat control valve datasheets {toc}
−
−```datasheet
−label: Hydronic Reheat Control Valve
−type: select
−options:
− - "Pressure-independent modulating valve (PICV) with electric actuator"
− - "Two-way modulating globe valve with electric actuator"
− - "Three-way modulating valve with electric actuator (constant-flow systems only)"
− - "Two-position valve (on-off heating only)"
−default: "Pressure-independent modulating valve (PICV) with electric actuator"
−```
−
−```datasheet
−label: Hydronic Valve Actuator Fail Position
−type: radio
−options:
− - "Fail open to heating (freeze protection)"
− - "Fail closed"
− - "Fail in last position"
−default: "Fail open to heating (freeze protection)"
−```
−
−### Hydronic reheat valves shall fail open to heating where the unit serves a perimeter zone in a climate subject to freezing exterior temperatures, so that loss of control power does not allow a glass-line zone to freeze on a winter night.
−
−### Interior zones with no freeze exposure may fail closed to prevent overheating on signal loss.
−
−## Electric Reheat {toc}
−
−### Electric reheat coils shall be open-coil resistance or finned-tubular elements installed in a NEC-compliant heater section integral to or downstream of the unit casing.
−
−### Electric reheat coils shall comply with NFPA 70 Article 424 and shall be UL listed for use in HVAC distribution.
−
−### Every electric reheat coil shall include primary automatic-reset over-temperature protection, secondary manual-reset over-temperature protection, and a differential-pressure airflow proving switch that disables the heater when primary airflow falls below the manufacturer's minimum heating airflow.
−
−### Operating a resistance heater without airflow proof is a recurring root cause of duct fires and is not acceptable under any circumstances.
−
−### Electric reheat datasheets {toc}
−
−```datasheet
−label: Electric Reheat Capacity
−type: range
−unit: kW
−drawing_ref: true
−options:
− min: 0.5
− max: 30
− step: 0.5
−default: 4
−```
−
−```datasheet
−label: Electric Reheat Control Method
−type: radio
−options:
− - "Staged contactors (1, 2, or 3 stages)"
− - "Solid-state relay / SCR modulation (linear control, recommended for low ΔT applications)"
−default: "Staged contactors (1, 2, or 3 stages)"
−```
−
−```datasheet
−label: Electric Reheat Stage Count (Staged Control)
−type: radio
−options:
− - "1 stage"
− - "2 stages"
− - "3 stages"
−default: "2 stages"
−```
−
−```datasheet
−label: Electric Reheat Element Sheath
−type: radio
−options:
− - "Open-coil nichrome resistance (lowest cost)"
− - "Finned-tubular element (longer life, lower watt density)"
−default: "Open-coil nichrome resistance (lowest cost)"
−```
−
−```datasheet
−label: Electric Reheat Safety Devices
−type: checkbox
−options:
− - "Primary automatic-reset over-temperature cutout"
− - "Secondary manual-reset over-temperature cutout"
− - "Differential-pressure airflow proving switch"
− - "Branch-circuit fusing or breaker integral to heater"
− - "Magnetic disconnect / safety switch within sight of unit"
−default: "Primary automatic-reset over-temperature cutout"
−```
−
−```datasheet
−label: Electric Heater Voltage
−type: select
−options:
− - "120V / 1-phase (small zones only)"
− - "208V / 1-phase"
− - "208V / 3-phase"
− - "240V / 1-phase"
− - "277V / 1-phase"
− - "480V / 3-phase"
−default: "208V / 3-phase"
−```
−
−### SCR-modulated electric reheat provides linear control of leaving air temperature and avoids the staircase of supply temperature steps inherent in staged control. {note}
−
−### Where the zone has a tight setpoint or low primary minimum airflow that would amplify the staged-control discharge temperature swing, SCR control is the preferred selection. {note}
−
−### Staged control is the simpler and lower-cost solution for routine office zones with two-stage zone calls. {note}
−
−# Fan-Powered Units {toc}
−
−## Fan Section Construction {toc}
−
−### Parallel and series fan-powered boxes shall include an integral fan section with a forward-curved or backward-curved centrifugal fan, fan housing, motor, and induced-air opening with a backdraft damper (parallel boxes only).
−
−### The fan section shall be acoustically lined and shall include a removable access panel sized to allow fan and motor service without removing the unit from the ceiling.
−
−## Fan Motor Type {toc}
−
−### Electronically commutated motors (ECM) shall be the standard fan motor selection for new construction.
−
−### ECM motors provide variable-speed control through a 0–10 V or PWM signal, achieve substantially higher efficiency than PSC motors across the operating range, and allow the controller to adjust fan output during commissioning without changing pulleys or motor taps. {note}
−
−### PSC (permanent split capacitor) motors are acceptable only where the contract documents specifically permit, and only with stepped fan speed control via tap selection at startup.
−
−### Fan motor datasheets {toc}
−
−```datasheet
−label: Fan Motor Type
−type: radio
−options:
− - "ECM — electronically commutated (variable speed, high efficiency) — standard"
− - "PSC — permanent split capacitor (multi-speed, lower efficiency)"
−default: "ECM — electronically commutated (variable speed, high efficiency) — standard"
−```
−
−```datasheet
−label: Fan Motor Nameplate Power
−type: range
−unit: HP
−drawing_ref: true
−options:
− min: 0.05
− max: 1.5
− setpoints: [0.05, 0.083, 0.125, 0.167, 0.25, 0.333, 0.5, 0.75, 1.0, 1.5]
−default: 0.333
−```
−
−## Parallel Fan-Powered Box (PFPB) Operation {toc}
−
−### In a parallel fan-powered box, the fan is offset from the primary airstream; the fan operates only during heating or unoccupied modes, and during normal cooling the fan is off and primary air passes through the unit and out to the zone. {note}
−
−### A backdraft damper at the induced-air opening prevents primary air from backflowing into the plenum when the fan is off, and parallel boxes save fan energy compared to series boxes during the dominant cooling-mode operating hours. {note}
−
−## Series Fan-Powered Box (SFPB) Operation {toc}
−
−### In a series fan-powered box, the fan is in series with the primary airstream; the fan operates continuously during occupied hours and delivers a constant total airflow to the zone, mixing primary air with induced plenum air in a ratio that varies with the primary damper position. {note}
−
−### Series boxes provide constant zone airflow and constant outlet velocity regardless of cooling demand, which is preferred where diffuser performance is sensitive to airflow turndown. {note}
−
−### Series boxes consume continuous fan energy and shall be selected only where the constant airflow benefit justifies the parasitic energy.
−
−## Induced-Air Backdraft Damper (PFPB Only) {toc}
−
−### Parallel fan-powered boxes shall include a low-leakage backdraft damper at the induced-air opening to prevent reverse flow of cooled primary air into the return plenum during cooling-mode operation when the fan is off.
−
−### Backdraft damper leakage shall not exceed 10 CFM at 0.5 in. w.g. differential pressure for the smallest opening size and shall be proportionally limited for larger sizes.
−
−### Induced-air backdraft damper datasheet {toc}
−
−```datasheet
−label: Induced-Air Opening Backdraft Damper (PFPB)
−type: radio
−options:
− - "Gravity backdraft damper — low leakage, no power required"
− - "Motorized damper interlocked with fan operation"
− - "Not applicable — series fan-powered or single-duct unit"
−default: "Gravity backdraft damper — low leakage, no power required"
−```
−
−# Sound Performance {toc}
−
−## Rating Method {toc}
−
−### Sound performance shall be rated per ANSI/AHRI 885 using sound power data developed per ANSI/ASHRAE 130.
−
−### The manufacturer shall publish radiated and discharge sound power levels in octave bands 2 through 7 (125 Hz through 4,000 Hz) at the unit's selected primary airflow and at the specified inlet static pressure.
−
−### The published data shall include the standard AHRI 885 calculation of room NC for a reference room configuration so that the designer can compare units on a consistent basis.
−
−## Project NC Targets {toc}
−
−### Room NC criteria shall be established by the design team for each scheduled zone and shall be indicated on the mechanical drawings or in the room finish schedule.
−
−### Air terminal unit selections shall demonstrate compliance with the room NC target using the AHRI 885 procedure applied to the actual room volume, room absorption, and acoustical path from the unit to the listener.
−
−### Project NC target datasheets {toc}
−
−```datasheet
−label: Radiated Sound Rating (NC at Receiver)
−type: select
−drawing_ref: true
−options:
− - "NC 25 (recording studios, concert halls)"
− - "NC 30 (private offices, classrooms, conference rooms)"
− - "NC 35 (open offices, retail)"
− - "NC 40 (large open spaces, transient occupancy)"
− - "NC 45 (back-of-house, mechanical, light industrial)"
−default: "NC 30 (private offices, classrooms, conference rooms)"
−```
−
−```datasheet
−label: Discharge Sound Rating (NC at Receiver)
−type: select
−drawing_ref: true
−options:
− - "NC 25"
− - "NC 30"
− - "NC 35"
− - "NC 40"
− - "NC 45"
−default: "NC 30"
−```
−
−### Discharge sound is attenuated by the downstream duct, internal liner, and the diffusers, while radiated sound passes directly through the ceiling tile to the room below. {note}
−
−### Radiated sound is typically the controlling acoustical path for ceiling-installed units serving open-plan offices, and units shall be selected for radiated NC compliance even where discharge NC is acceptable.
−
−### Increasing primary inlet static pressure significantly increases both radiated and discharge sound; the central system static-pressure-reset strategy reduces both inlet static and unit sound at most operating hours. {note}
−
−# Controls and BAS Integration {toc}
−
−## DDC Controller {toc}
−
−### Each air terminal unit shall be furnished with a factory-installed or factory-supplied direct digital control (DDC) controller capable of executing the project's zone control sequence.
−
−### The controller shall include sufficient hardwired inputs and outputs for the unit's damper actuator, primary airflow sensor, reheat valve or stage outputs, fan-motor control output (where applicable), zone temperature sensor, and any optional inputs (CO₂, occupancy, window contact) indicated in the BAS sequence.
−
−### DDC controller datasheets {toc}
−
−```datasheet
−label: Controller Communication Protocol
−type: select
−options:
− - "BACnet MS/TP (RS-485) — most common for terminal-unit networks"
− - "BACnet IP (Ethernet) — IP-native controllers"
− - "Modbus RTU (RS-485)"
− - "LonWorks (FT-10)"
− - "Manufacturer-proprietary protocol with gateway to BACnet"
−default: "BACnet MS/TP (RS-485) — most common for terminal-unit networks"
−```
−
−```datasheet
−label: Required Controller I/O
−type: checkbox
−options:
− - "Damper actuator output (modulating)"
− - "Primary airflow sensor input (differential pressure)"
− - "Zone temperature sensor input"
− - "Hot water valve output (modulating)"
− - "Electric reheat stage outputs (binary)"
− - "Electric reheat modulating output (SCR control)"
− - "Fan motor speed output (0–10 V ECM)"
− - "Fan run/stop output"
− - "Zone CO2 sensor input"
− - "Occupancy / motion sensor input"
− - "Window contact input"
− - "Discharge air temperature sensor input"
−default: "Damper actuator output (modulating)"
−```
−
−## Coordination with Building Automation System {toc}
−
−### The terminal unit controller shall be commissioned by the controls contractor on the project's BAS network per [[sync/building-automation-system]].
−
−### Controller addressing, network segmentation across MS/TP trunks, and supervisory controller assignments shall be coordinated before unit shipment so that the factory-applied address and unit tag are consistent with the BAS database.
−
−### Re-addressing controllers in the field after installation is permissible but introduces a recurring source of error during commissioning; factory addressing per the project tag schedule is preferred. {note}
−
−## Zone Sensor {toc}
−
−### Each zone served shall be provided with a wall-mounted zone temperature sensor.
−
−### Zone sensors shall be furnished by the controls contractor unless the air terminal unit supplier includes them as a packaged option.
−
−### Where the project zoning includes occupant-adjustable setpoints, the wall sensor shall include a setpoint adjustment within a defined deadband relative to the system setpoint.
−
−### Zone sensor datasheet {toc}
−
−```datasheet
−label: Zone Sensor Type
−type: select
−options:
− - "Temperature only — no occupant adjustment"
− - "Temperature with limited setpoint adjustment (±2 °F)"
− - "Temperature with setpoint adjustment and override pushbutton"
− - "Temperature with humidity and CO2 (multi-function room sensor)"
−default: "Temperature with setpoint adjustment and override pushbutton"
−```
−
−# Factory Testing {toc}
−
−## Each air terminal unit shall undergo the following factory tests before shipment.
−
−## Failure of any factory test shall require correction and retest; no unit shall be shipped until all tests pass.
−
−## Each air terminal unit shall undergo the following factory tests before shipment: {toc}
−
−- Performance test of the primary damper through its full stroke, verifying close-off and full-open positions at design inlet pressure
−- Calibration of the primary inlet airflow sensor against a calibrated reference flow station, recording the K-factor or calibration curve in the unit's factory test record
−- Hydrostatic pressure test of the hot water coil at 300 psig minimum for the manufacturer's standard duration (1 row, 2 row, and 3 row coils all shall be pressure tested)
−- Electrical functional test of the heater section, including verification of the airflow proving switch, primary cutout, and secondary cutout operation
−- Functional test of the DDC controller communication and I/O, with the controller addressed per the project tag schedule
−- Casing leakage test on a sample basis per the manufacturer's quality control program
−
−```datasheet
−label: Factory Acceptance Test (FAT)
−type: radio
−options:
− - "Standard production tests (manufacturer-certified, no witness)"
− - "Witnessed factory test on sample units — provide 10 days notice"
− - "100% witnessed factory test (critical or healthcare projects)"
−default: "Standard production tests (manufacturer-certified, no witness)"
−```
−
−# Installation {toc}
−
−## Coordination and Service Clearances {toc}
−
−### Before fabricating ceiling layouts and ductwork, the Contractor shall verify that each air terminal unit can be installed with the manufacturer's required service clearances and access panels accessible through the ceiling.
−
−### Service clearance shall include access to the primary damper actuator, the reheat coil connections, the controller enclosure, and the fan and motor for fan-powered units.
−
−### Where ceiling-tile access is not sufficient, an access door shall be coordinated with the architectural finish schedule.
−
−### Service access provision datasheet {toc}
−
−```datasheet
−label: Service Access Provision
−type: radio
−options:
− - "Accessible ceiling (lay-in tile)"
− - "Hard ceiling with access panel below unit"
− - "Hard ceiling — entire ceiling segment removable"
− - "Mechanical room or exposed structure (full access)"
−default: "Accessible ceiling (lay-in tile)"
−```
−
−## Hanger and Support {toc}
−
−### Air terminal units shall be suspended from structure using all-thread rod, hanger straps, or trapeze hangers attached to the integral mounting provisions on the casing.
−
−### Units shall not be supported by the ceiling suspension system, by the connected ductwork, or by piping.
−
−### Each unit shall be supported by a minimum of four hanger points, one at each corner of the casing, sized for the operating weight of the unit (including the weight of water-filled coils for hydronic units) with a safety factor consistent with SMACNA HVAC Duct Construction Standards.
−
−### Hanger location and weights are [[drawing: as indicated on the mechanical drawings and unit schedule]].
−
−## Inlet Duct Connection {toc}
−
−### Primary inlet duct shall connect to the unit collar with a minimum straight-duct length upstream of the inlet as required by the airflow sensor manufacturer (typically 3 inlet diameters; verify per sensor product data).
−
−### Flexible duct at the inlet shall be fully extended and shall not be used to make the final connection within the required straight-duct length.
−
−### Elbows, branch tees, and transitions within the required straight-duct length shall be relocated during shop drawing coordination.
−
−### Connection of the inlet duct to the unit collar shall be sealed to the duct seal class specified in [[sync/hvac-ductwork]].
−
−## Outlet Duct Connection {toc}
−
−### Downstream low-pressure duct shall connect to the unit outlet with a transition appropriate to the outlet shape and dimensions.
−
−### For units serving multiple diffusers from a single downstream plenum, the outlet plenum shall be sized to limit velocity to a value that controls discharge sound.
−
−### Where the manufacturer publishes a recommended downstream straight-duct length to achieve the certified discharge sound rating, the Contractor shall provide that length before the first branch or fitting.
−
−## Hydronic Piping Connections {toc}
−
−### Hot water supply and return piping to reheat coils shall comply with [[sync/hydronic-piping]].
−
−### Each coil shall be served by a piping arrangement including an upstream isolation valve, a balancing or pressure-independent control valve, a strainer, an air vent at the high point, and a drain at the low point.
−
−### Piping shall be supported independently of the air terminal unit and shall be arranged to permit coil removal without dismantling the piping.
−
−### Hot water piping shall be insulated within the conditioned plenum to limit unwanted heat loss; insulation shall be continuous and shall not be omitted at the unit connection.
−
−## Electric Power Connections {toc}
−
−### Electric reheat power circuits shall comply with NFPA 70 Article 424.
−
−### Each electric reheat coil shall be served by a dedicated branch circuit sized for the heater nameplate load plus 25%, with branch overcurrent protection coordinated with the heater manufacturer's recommendations.
−
−### A disconnecting means shall be provided within sight of each unit served by a 120 V or higher heater circuit, or a means of lockout shall be provided at the branch panelboard.
−
−### Low-voltage control wiring shall be routed separately from line-voltage power wiring as required by the NEC.
−
−### Electric reheat disconnect provision datasheet {toc}
−
−```datasheet
−label: Electric Reheat Disconnect Provision
−type: radio
−options:
− - "Factory-installed integral disconnect within unit enclosure"
− - "Field-installed disconnect within sight of unit"
− - "Lockable means at branch panelboard (where permitted by NEC)"
−default: "Field-installed disconnect within sight of unit"
−```
−
−## Control Wiring {toc}
−
−### Low-voltage control wiring between the air terminal unit controller, the zone temperature sensor, the BAS network trunk, and any optional inputs shall be Class 2 cable, routed and supported per the NEC and the BAS contractor's wiring standards.
−
−### Plenum-rated cable shall be used in air-handling plenums.
−
−### Communication trunk wiring shall be the manufacturer's specified twisted shielded pair for MS/TP networks, with continuous shield drain conductor and terminations at the BAS terminations only.
−
−## Pre-Startup Inspection {toc}
−
−### Before energizing the air terminal unit and starting the central air system, the Contractor shall confirm the following:
−
−- All shipping restraints and protective films are removed
−- Primary damper strokes freely from fully closed to fully open by manual rotation of the actuator shaft
−- Primary airflow sensor tubing is connected without kinks or leaks at the sensor and at the controller
−- Hot water coil piping is filled, vented, and pressure-tested per [[sync/hydronic-piping]]
−- Electric reheat circuit is energized at the panelboard, control voltage is present at the heater contactor, and the airflow proving switch is in the open (no-flow) state
−- BAS network communication is established with the controller at its assigned address
−- Zone sensor is wired and reading a plausible room temperature
−
−```datasheet
−label: Pre-Startup Inspection Checklist
−type: checkbox
−options:
− - "Shipping restraints removed"
− - "Damper strokes freely full range"
− - "Airflow sensor tubing intact and connected"
− - "Hot water coil filled, vented, pressure-tested"
− - "Electric branch circuit energized and verified"
− - "Airflow proving switch tested and clears at no-flow"
− - "BAS communication established at correct address"
− - "Zone sensor wired and reading plausible temperature"
− - "Access panels closed and ceiling tiles in place"
−default: "Shipping restraints removed"
−```
−
−# Field Testing and Commissioning {toc}
−
−## Airflow Verification {toc}
−
−### The testing, adjusting, and balancing agent shall verify the primary airflow at each unit at the cooling maximum, cooling minimum, and heating airflow setpoints per [[sync/testing-adjusting-and-balancing]].
−
−### Measured airflow at each setpoint shall be within ±10% of the commanded value.
−
−### Where measured airflow falls outside this band, the controller K-factor or airflow calibration constants shall be adjusted against the calibrated TAB instrument.
−
−### After adjustment, the K-factor and as-commissioned setpoints shall be recorded in the closeout submittal.
−
−### Field airflow verification tolerance datasheet {toc}
−
−```datasheet
−label: Field Airflow Verification Tolerance
−type: radio
−options:
− - "±10% of commanded value at each setpoint (standard)"
− - "±5% of commanded value at each setpoint (critical zones, healthcare)"
−default: "±10% of commanded value at each setpoint (standard)"
−```
−
−## Functional Performance Testing {toc}
−
−### For projects with formal commissioning, each air terminal unit shall be subjected to functional performance testing by the commissioning authority.
−
−### Functional performance testing shall verify the full zone control sequence at occupied, unoccupied, and override modes; verify the heating valve or stage operation through the heating range; verify the fan-powered box fan operation and induction at the appropriate primary airflow; verify the airflow proving interlock for electric reheat; and verify the BAS reporting of all hardwired points and calculated values.
−
−## Acoustical Spot Check {toc}
−
−### A representative subset of installed units, including the most acoustically sensitive zones, shall be measured in place by the TAB agent or by an acoustical consultant where required.
−
−### Measured room NC at the receiver location shall be compared to the design NC target.
−
−### Where measured NC exceeds the target, the contributing path (radiated through ceiling, discharge through diffusers, inlet duct noise) shall be identified and corrective action coordinated with the design team.
−
−### Common corrective actions for excess NC include lowering the central system static pressure setpoint at part-load via reset, adding a lined discharge plenum, or substituting a unit with a larger casing and lower face velocity. {note}
−
−# Delivery, Storage, and Handling {toc}
−
−## Air terminal units shall be delivered to the project site in original factory packaging with inlet and outlet openings sealed against construction dust.
−
−## Units shall be stored indoors in a clean, dry, conditioned space.
−
−## Units shall not be stored on bare concrete, in standing water, or in any space subject to freezing or to roof leaks.
−
−## Stacking of units shall conform to the manufacturer's instructions and shall not exceed the rated stack height; stacked units shall be supported only at the corner brackets, never on the casing wrap.
−
−## Hot water coils on stored units shall be protected from freezing during storage; where storage temperature can fall below 35 °F at any time, coils shall be drained, blown out with compressed air, and tagged as drained, with a corresponding note on the unit tag schedule so that the coils are refilled and vented before startup.
−
−# Identification {toc}
−
−## Each air terminal unit shall include a permanent identification label on the exterior of the casing, in a location visible from below an accessible ceiling.
−
−## The identification label shall include the unit tag number matching the unit schedule, the manufacturer's model and serial number, the primary maximum and minimum airflow setpoints, the reheat capacity, the electrical service requirements where applicable, the controller communication address, and the date of manufacture.
−
−## Labels shall be applied to the casing exterior and shall not be placed on removable access panels.
−
−## Identification nameplate material datasheet {toc}
−
−```datasheet
−label: Identification Nameplate Material
−type: radio
−options:
− - "Adhesive laminated label (standard interior plenum)"
− - "Engraved phenolic plate, mechanically fastened (premium / long service)"
− - "Stainless steel etched plate (corrosive plenums)"
−default: "Adhesive laminated label (standard interior plenum)"
−```
−
−# Warranty {toc}
−
−## Equipment Warranty {toc}
−
−### The air terminal unit manufacturer shall warrant the equipment against defects in materials and workmanship for the period specified below, beginning from the date of substantial completion.
−
−### The equipment warranty shall cover the casing, damper, airflow sensor, controller, reheat coil (hydronic or electric), valve and actuator, fan and motor (for fan-powered units), and all factory-installed components.
−
−### The manufacturer shall maintain service capability within the project region with factory-trained service personnel.
−
−### Equipment warranty period datasheet {toc}
−
−```datasheet
−label: Equipment Warranty Period
−type: select
−options:
− - "1 year parts and labor from substantial completion (minimum)"
− - "2 years parts and labor from substantial completion"
− - "5 years parts, 1 year labor"
−default: "1 year parts and labor from substantial completion (minimum)"
−```
−
−## ECM Motor and Coil Extended Warranty {toc}
−
−### ECM fan motors and hydronic reheat coils shall carry an extended warranty consistent with industry practice for these components.
−
−### ECM motor and coil extended warranty datasheets {toc}
−
−```datasheet
−label: ECM Motor Extended Warranty
−type: radio
−options:
− - "Standard — 1 year, same as equipment warranty"
− - "Extended — 5 years on ECM motor and controller"
−default: "Extended — 5 years on ECM motor and controller"
−```
−
−```datasheet
−label: Hot Water Coil Warranty
−type: select
−options:
− - "1 year (minimum)"
− - "5 years against leakage in tube and fin assembly"
−default: "5 years against leakage in tube and fin assembly"
−```
−
−## Installation Warranty {toc}
−
−### The Contractor shall warrant the installation workmanship — including hangers, duct and piping connections, electrical connections, control wiring, sealing, and labeling — for one year from the date of substantial completion.
−
−### The Contractor shall maintain access to all installed units during the warranty period by keeping access doors, ceiling tiles, and adjacent finishes clear of permanent obstructions.
−
−# Spare Parts {toc}
−
−## The following spare parts datasheet establishes the spares to be delivered at substantial completion. {note}
−
−## Spare parts shall be delivered to the Owner in manufacturer's original packaging with each part tagged with the unit model number, part number, and date of delivery.
−
−```datasheet
−label: Spare Parts at Substantial Completion
−type: checkbox
−options:
− - "Spare damper actuator — one per unit type and size"
− - "Spare control valve actuator (hydronic reheat) — one per valve size"
− - "Spare ECM motor — one per motor size (fan-powered units)"
− - "Spare DDC controller — one per controller model"
− - "Spare zone temperature sensor — quantity 5% of installed sensors"
− - "Spare over-temperature cutout (electric reheat) — one per heater model"
−default: "Spare damper actuator — one per unit type and size"
−```
−
−## Spare parts shall be stored in a designated maintenance storage location identified by the Owner.
−
−## The O&M manual shall include a spare-parts inventory list with manufacturer part numbers and reorder information so that additional spares can be procured during the building's service life.
+---
+title: Air Terminal Units
+category: Mechanical / Air Distribution
+description: >
+ When to use: Factory-fabricated air terminal units that meter primary air from a central air system into an individual thermal zone in commercial, institutional, healthcare, and industrial buildings. Covers single-duct, dual-duct, and bypass metering arrangements; variable-volume and constant-volume airflow control; pressure-independent and pressure-dependent control basis; parallel and series fan sections; hot water, steam, and electric reheat with their valves, actuators, and safety devices; casing construction and acoustic treatment; primary damper and actuator; primary airflow sensing; radiated and discharge sound; the zone controller, zone sensor, and building automation interface; factory testing; installation; and field airflow, functional, and acoustic verification.
+ Not intended for: Diffusers, grilles, registers, and transfer openings at the room boundary; central station air handling units and rooftop units; duct construction and leakage testing; the hot water plant and its distribution piping; supervisory controllers and system-level control sequences; fan coil units, blower coil units, chilled beams, and induction units that condition recirculated room air rather than metering primary air; venturi-style airflow control valves used for critical pressurization in laboratory and containment service; underfloor air distribution plenum boxes fed from a pressurized supply plenum.
+---
+
+# Scope {toc}
+
+## This standard covers the performance, construction, control, installation, and field verification of factory-fabricated air terminal units - the equipment at which a central air system is divided among individual thermal zones, and at which the air delivered to each zone is metered and, where the zone requires it, reheated or supplemented with induced plenum air. {note}
+
+## Equipment covered includes the unit casing and its acoustic treatment, the primary damper and its actuator, the primary airflow sensing element, hot water, steam, and electric reheat sections with their valves and safety devices, the fan section of a fan-powered unit, and the zone controller and zone sensor furnished with the unit. {note}
+
+## The terminal unit is the point at which system-level design intent becomes zone-level reality: its minimum airflow setting determines whether the zone receives the ventilation rate the system calculation assumed, its sound performance determines whether the space is usable for its program, and its reheat energy is consumed at every hour the zone is not at its cooling design load. {note}
+
+## The following are outside the scope of this standard: {note}
+
+- Diffusers, grilles, registers, and transfer openings at the room boundary, covered by [[sync/hvac-air-distribution-devices]]
+- Central station air handling units, rooftop units, and their fans, coils, and filter sections, covered by [[sync/air-handling-units]]
+- Duct construction, sealing, hangers, and leakage testing upstream and downstream of the unit, covered by [[sync/hvac-ductwork]]
+- Hot water and steam distribution piping, specialties, and the heating plant serving reheat coils, covered by [[sync/hydronic-piping]]
+- Supervisory controllers, network infrastructure, graphics, trending, and system-level control sequences, covered by [[sync/building-automation-system]]
+- System-wide balancing procedure, instrumentation, and report format, covered by [[sync/testing-adjusting-and-balancing]]
+- Fan coil units, blower coil units, chilled beams, and induction units, whose primary function is conditioning recirculated room air rather than metering primary air
+- Venturi-style airflow control valves used for critical pressurization in laboratory, vivarium, and containment service
+- Underfloor air distribution plenum boxes and floor-mounted terminal units fed from a pressurized supply plenum
+- Standalone fire dampers, smoke dampers, and combination fire and smoke dampers furnished separately from the terminal unit
+
+## Airflow, capacity, pressure drop, and leakage performance cited for any unit under this standard shall be derived from testing in accordance with ANSI/ASHRAE 130 and rated in accordance with ANSI/AHRI 880.
+
+## Sound power cited for any unit under this standard shall be derived from testing in accordance with ANSI/ASHRAE 130 in a room qualified to ANSI/AHRI 220, and occupied-space sound levels shall be estimated in accordance with ANSI/AHRI 885.
+
+## Where a requirement of this standard conflicts with the equipment listing under which a unit is certified by a Nationally Recognized Testing Laboratory, the listing shall govern and the Contractor shall report the conflict to the Engineer of Record before fabrication.
+
+# 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 880 | Performance Rating of Air Terminals |
+| ANSI/AHRI 885 | Procedure for Estimating Occupied Space Sound Levels in the Application of Air Terminals and Air Outlets |
+| ANSI/AHRI 220 | Reverberation Room Qualification for Determining Sound Power of HVAC Equipment |
+| ANSI/ASHRAE 130 | Methods of Testing Air Terminal Units |
+| 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 111 | Measurement, Testing, Adjusting, and Balancing of Building HVAC Systems |
+| ANSI/ASHRAE 135 | BACnet - A Data Communication Protocol for Building Automation and Control Networks |
+| ANSI/ASHRAE 52.2 | Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size |
+| ANSI/ASHRAE 202 | Commissioning Process for Buildings and Systems |
+| ASHRAE Guideline 36 | High-Performance Sequences of Operation for HVAC Systems |
+| ANSI/ASA S12.2 | Criteria for Evaluating Room Noise |
+| NFPA 90A | Standard for the Installation of Air-Conditioning and Ventilating Systems |
+| NFPA 70 | National Electrical Code, Article 424, Fixed Electric Space-Heating Equipment |
+| UL 60335-2-40 | Household and Similar Electrical Appliances - Particular Requirements for Electrical Heat Pumps, Air-Conditioners and Dehumidifiers |
+| UL 1995 | Heating and Cooling Equipment |
+| UL 1996 | Electric Duct Heaters |
+| UL 2043 | Fire Test for Heat and Visible Smoke Release for Discrete Products and Their Accessories Installed in Air-Handling Spaces |
+| UL 181 | Factory-Made Air Ducts and Air Connectors |
+| ASTM E84 | Standard Test Method for Surface Burning Characteristics of Building Materials |
+| ASTM C1071 | Standard Specification for Fibrous Glass Duct Lining Insulation, Thermal and Sound Absorbing Material |
+| ASTM C1338 | Standard Test Method for Determining Fungi Resistance of Insulation Materials and Facings |
+| ASTM A653 | Standard Specification for Steel Sheet, Zinc-Coated or Zinc-Iron Alloy-Coated by the Hot-Dip Process |
+| ASTM A240 | Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip |
+| ASTM B75 | Standard Specification for Seamless Copper Tube |
+| ANSI/AMCA 210 / ANSI/ASHRAE 51 | Laboratory Methods of Testing Fans for Certified Aerodynamic Performance Rating |
+| NEMA MG 1 | Motors and Generators |
+| SMACNA HVAC Duct Construction Standards | HVAC Duct Construction Standards - Metal and Flexible |
+
+# Submittals {toc}
+
+## Action Submittals {toc}
+
+### The Contractor shall submit the following for the Engineer of Record's review and return, and shall not release any terminal unit for fabrication until the submittal covering it has been reviewed and returned:
+
+- Unit schedule keyed to the mechanical drawings, listing for each tag the metering arrangement, fan section, inlet size, primary maximum and minimum airflow, available inlet static pressure, reheat capacity, electrical characteristics, controller address, and outlet configuration
+- Certified rating data for each unit configuration, identifying the rating standard and the certification program under which the data is published
+- Casing pressure drop and casing air leakage at the scheduled airflow and at the scheduled inlet static pressure
+- Radiated and discharge sound power in octave bands 2 through 7 at the scheduled primary airflow and inlet static pressure, with the occupied-space sound level for each scheduled zone and the room correction values used to produce it
+- Primary airflow sensor data giving the sensing element type, the measurement error as a percentage of reading across the scheduled airflow range, the low-flow threshold below which the published accuracy no longer applies, and the straight duct length required upstream and downstream of the inlet for rated accuracy
+- Primary damper data giving blade arrangement, blade and frame material, shaft and bearing type, seal material, close-off leakage at the rated differential pressure, and the maximum differential pressure against which the actuator will stroke the damper
+- Actuator data giving control signal type, fail-safe behavior, stroke time, and torque
+- Hot water or steam coil data giving row count, fin spacing, tube and fin material, working pressure rating, entering and leaving air and fluid conditions, capacity, and air-side and fluid-side pressure drop
+- Control valve and valve actuator data giving flow coefficient, close-off pressure rating, fail position, control signal type, and stroke time
+- Electric heater data giving element construction, capacity control method, stage count, capacity per stage, watt density, electrical characteristics, minimum airflow for heater operation, and the safety devices furnished
+- Fan section data giving wheel type, motor type, nameplate power, electrical characteristics, speed control means, airflow and static pressure at the design operating point, and the induced-air opening arrangement
+- Controller data giving the network protocol, the hardwired point count by type, the control sequences the controller executes, and the fire performance listing for products installed in air-handling spaces
+- Casing liner and attenuator data giving liner type, thickness, airstream facing, surface burning characteristics, fungal resistance, and the maximum airstream velocity at which the facing is rated against erosion
+- Shop drawings showing each unit in plan and section with every field connection point dimensioned, the required service clearance, the access panel locations, and the operating weight
+- Evidence of the Nationally Recognized Testing Laboratory listing for each unit configuration containing an electric heater, a fan motor, or an electrically powered control
+
+```datasheet
+label: Action Submittals Required
+type: checkbox
+options:
+ - "Unit schedule keyed to the mechanical drawings"
+ - "Certified rating data for each unit configuration"
+ - "Casing pressure drop and casing air leakage data"
+ - "Radiated and discharge sound data with occupied-space levels"
+ - "Primary airflow sensor accuracy and straight duct requirements"
+ - "Primary damper data with close-off leakage"
+ - "Actuator data with signal type, fail behavior, and stroke time"
+ - "Hot water or steam coil selection data"
+ - "Control valve and valve actuator data"
+ - "Electric heater data with safety devices"
+ - "Fan section data for fan-powered units"
+ - "Controller data with protocol and point count"
+ - "Casing liner and attenuator construction data"
+ - "Shop drawings with clearances and field connections"
+ - "Nationally Recognized Testing Laboratory listing evidence"
+default:
+ - "Unit schedule keyed to the mechanical drawings"
+ - "Certified rating data for each unit configuration"
+ - "Casing pressure drop and casing air leakage data"
+ - "Radiated and discharge sound data with occupied-space levels"
+ - "Primary airflow sensor accuracy and straight duct requirements"
+ - "Primary damper data with close-off leakage"
+ - "Actuator data with signal type, fail behavior, and stroke time"
+ - "Controller data with protocol and point count"
+ - "Casing liner and attenuator construction data"
+ - "Shop drawings with clearances and field connections"
+ - "Nationally Recognized Testing Laboratory listing evidence"
+```
+
+### Where the Contractor proposes a unit from a manufacturer other than the one on which the design was based, the submittal shall include a side-by-side comparison of radiated sound, discharge sound, casing pressure drop, and airflow sensor low-flow threshold at the scheduled airflow for the proposed and the scheduled unit.
+
+### Where the Contractor proposes a substitution that changes the inlet size, the casing dimensions, or the required service clearance of any unit, the submittal shall identify every duct, pipe, and ceiling coordination item affected.
+
+## Closeout Submittals {toc}
+
+### Before final acceptance of the air distribution system, the Contractor shall submit the following:
+
+- Operation and maintenance manuals covering installation, operation, maintenance, and troubleshooting, with the recommended preventive maintenance interval for each serviceable component
+- As-built unit schedule recording every field substitution and every field modification to the submitted configuration, together with the review documentation for each
+- Factory test record for each unit, including the airflow sensor calibration constant established at the factory
+- Field commissioning record for each unit, giving the measured airflow at every commanded setpoint, the reheat stroke or stage verification, and the point-by-point verification of the controller interface
+- Controller parameter file for each unit in the manufacturer's native format, listing the as-commissioned setpoints, calibration constants, and control loop tuning values
+- Warranty documentation from the terminal unit manufacturer and from each separately warranted component supplier
+
+```datasheet
+label: Closeout Submittals Required
+type: checkbox
+options:
+ - "Operation and maintenance manuals"
+ - "As-built unit schedule with field modifications"
+ - "Factory test record for each unit"
+ - "Field commissioning record for each unit"
+ - "Controller parameter file in native format"
+ - "Warranty documentation"
+default:
+ - "Operation and maintenance manuals"
+ - "As-built unit schedule with field modifications"
+ - "Factory test record for each unit"
+ - "Field commissioning record for each unit"
+ - "Controller parameter file in native format"
+ - "Warranty documentation"
+```
+
+### The controller parameter file is the only complete record of what the units were actually commissioned to do, and it is the difference between a rebalancing effort that starts from the as-left condition and one that starts from scratch. {note}
+
+# Quality Assurance {toc}
+
+## Manufacturer Qualifications {toc}
+
+### Terminal units shall be produced by a manufacturer that has continuously produced factory-fabricated air terminal units for commercial service for not less than five years.
+
+### The manufacturer shall publish a catalog covering the full range of units supplied to the project, including rated performance at each cataloged inlet size.
+
+### The manufacturer shall maintain replacement dampers, actuators, airflow sensors, coils, motors, and controllers for the units supplied for not less than ten years after the date of Substantial Completion.
+
+### All terminal units on the project shall be furnished by a single manufacturer so that the control interface, the service access pattern, and the spare parts inventory are common across the installation.
+
+### Where the Contract Documents divide the project into separately bid phases or buildings, the single-manufacturer requirement applies within each phase or building rather than across the project.
+
+## Basis of Published Performance Data {toc}
+
+### The basis on which the performance of each unit configuration is established shall be as indicated in the datasheet.
+
+```datasheet
+label: Basis of Certified Performance Ratings
+type: radio
+options:
+ - "AHRI 880 certified ratings for every unit configuration furnished"
+ - "AHRI 880 certified ratings, with independent laboratory test data to ANSI/ASHRAE 130 accepted for a configuration outside the certified range"
+ - "Independent laboratory test data to ANSI/ASHRAE 130 for every unit configuration furnished"
+default: "AHRI 880 certified ratings for every unit configuration furnished"
+```
+
+### The certification mark or the independent laboratory test report reference, as applicable to the basis selected, shall appear on the product data submitted for each unit configuration.
+
+### A certification program covers a defined range of sizes and configurations, and a manufacturer that participates in the program may still catalog a unit outside that range. The distinction matters because ratings inside the range are verified by a third party on a sampling basis, while ratings outside it rest on the manufacturer's own test data. {note}
+
+### Where the parties disagree whether a proposed unit configuration falls within the certified range, the Engineer of Record shall make the initial determination.
+
+## Product Listing and Labeling {toc}
+
+### Terminal units containing an electric heater, a fan motor, or an electrically powered control shall be listed and labeled by a Nationally Recognized Testing Laboratory to UL 60335-2-40, to UL 1995 where the Authority Having Jurisdiction accepts that listing, or to UL 1996 where the heater section is listed as a duct heater.
+
+### Electric heater sections shall comply with NFPA 70 Article 424.
+
+### Products installed in a ceiling plenum or other air-handling space used to convey environmental air shall comply with the heat and smoke release limits of UL 2043 or shall be enclosed in a manner that NFPA 90A accepts for that space.
+
+### The listing label shall be affixed to the casing exterior in a location that remains visible after installation.
+
+## Pre-Installation Conference {toc}
+
+### Before installation of terminal units begins, the Contractor shall convene a pre-installation conference attended by the mechanical, controls, and electrical subcontractors, the testing and balancing agent, and the commissioning authority where one is engaged.
+
+### The pre-installation conference agenda shall include service clearance and access panel coordination, the straight duct length required at each unit inlet, the sequence in which duct, pipe, power, and control connections are made, controller addressing against the unit tag schedule, and the schedule for airflow verification and point checkout.
+
+### The straight duct length at the inlet is the item most often lost between shop drawing coordination and installation, because it competes for the same overhead space as every other trade and it is the only one of them whose loss is invisible until the unit will not hold its airflow setpoint. {note}
+
+# Service Environment {toc}
+
+## Terminal unit locations, tags, and orientations are [[drawing: as indicated on the mechanical plans]].
+
+## The ceiling or enclosure construction below each terminal unit is [[drawing: as indicated on the reflected ceiling plan]].
+
+## Terminal units shall be suitable for continuous operation at an ambient dry-bulb temperature from 50 °F to 104 °F and at a relative humidity from 10% to 90% without condensation on any surface of the casing or the controller enclosure.
+
+## Terminal units are not weather-resistant as manufactured, and shall not be installed outdoors or in any location exposed to precipitation, wind-driven moisture, or freezing temperatures unless the manufacturer certifies the unit for that exposure in writing.
+
+## Where a unit is installed in a space whose ambient conditions fall outside the range stated above, the Contractor shall obtain the manufacturer's written confirmation of suitability, together with any required change to the casing, the controller enclosure, or the condensate provisions, before the unit is released for fabrication.
+
+## The controller and actuator enclosure rating shall be as indicated in the datasheet.
+
+```datasheet
+label: Controller and Actuator Enclosure Rating
+type: select
+options:
+ - "NEMA 1, general purpose"
+ - "NEMA 1 with a gasketed cover"
+ - "NEMA 3R, rain resistant"
+ - "NEMA 4, watertight"
+ - "NEMA 4X, watertight and corrosion resistant"
+default: "NEMA 1, general purpose"
+```
+
+## The exterior casing insulation provided for condensation control shall be as indicated in the datasheet.
+
+```datasheet
+label: Exterior Casing Insulation for Condensation Control
+type: radio
+options:
+ - "No exterior insulation"
+ - "Factory-applied exterior insulation with a vapor retarder"
+ - "Field-applied exterior insulation with a vapor retarder"
+default: "No exterior insulation"
+```
+
+## A unit metering cold primary air through a plenum whose dew point exceeds the primary air temperature will condense on the casing, and the water reaches the ceiling tile below before anything is visible from the space. The exposure is set by the plenum, not by the unit, so it has to be evaluated for the actual return path rather than assumed from the building type. {note}
+
+## Where the ceiling plenum is unconditioned, is open to outdoor air, or has a design dew point above the design primary air temperature, terminal unit casings shall be insulated on the exterior and the insulation shall be continuous and sealed at every penetration and connection.
+
+# Terminal Unit Configuration {toc}
+
+## Named terminal unit products in the market are combinations of a small number of independent decisions: how many primary airstreams the unit meters, whether it carries a fan, whether it modulates airflow or holds it constant, and whether it closes the airflow loop on a measured signal. A parallel fan-powered box, for example, is a single-duct variable-volume pressure-independent unit with an intermittent fan section. Selecting each decision separately keeps every legal combination available and keeps each one queryable on its own. {note}
+
+## Primary Air Metering Arrangement {toc}
+
+### The primary air metering arrangement shall be as indicated in the datasheet.
+
+```datasheet
+label: Primary Air Metering Arrangement
+type: select
+options:
+ - "Single-duct"
+ - "Dual-duct mixing"
+ - "Bypass, diverting excess primary air to the return path"
+default: "Single-duct"
+```
+
+### A single-duct unit meters one primary airstream from a central system that delivers air at a single temperature, and it is the arrangement most central variable-volume systems are built around. {note}
+
+### A dual-duct unit accepts separate cold and warm primary airstreams and proportions the mixture delivered to the zone, which lets a zone be heated without a local heat source at the cost of running two duct systems to every unit. {note}
+
+### A bypass unit passes a fixed total airflow and diverts the portion the zone does not need into the return path, which lets a constant-volume central unit serve multiple zones without a variable-speed fan. The diverted air is conditioned but does no work, so the central fan energy does not fall as the zones unload. {note}
+
+### The bypass path of a bypass unit shall discharge into a return plenum or a ducted return that returns to the same central unit, and shall not discharge into an occupied space.
+
+## Fan Section Arrangement {toc}
+
+### The fan section arrangement shall be as indicated in the datasheet.
+
+```datasheet
+label: Fan Section Arrangement
+type: radio
+options:
+ - "No fan section"
+ - "Parallel arrangement, fan intermittent and offset from the primary airstream"
+ - "Series arrangement, fan continuous and in line with the primary airstream"
+default: "No fan section"
+```
+
+### In a parallel arrangement the fan sits beside the primary airstream and runs only when the zone calls for heating or when the unit is in an unoccupied mode, so the fan consumes no energy through the cooling hours that dominate most operating schedules. {note}
+
+### In a series arrangement the fan sits in the primary airstream and runs whenever the zone is occupied, so the zone receives a constant total airflow and a constant outlet velocity regardless of how far the primary damper has closed. {note}
+
+### Where diffuser performance at low airflow governs comfort, or where the zone requires a constant discharge velocity, the constant total airflow of a series arrangement holds outlet conditions steady at part load that a single-duct unit cannot. Where fan energy over the full operating schedule governs, the intermittent fan of a parallel arrangement runs for a small fraction of the hours a series fan runs. {note}
+
+### Where a fan section is selected, the induced-air opening shall draw from the ceiling return plenum or from a ducted return, and shall not draw from an unconditioned space, a shaft, or a space subject to contaminant migration.
+
+## Primary Airflow Control Mode {toc}
+
+### The primary airflow control mode shall be as indicated in the datasheet.
+
+```datasheet
+label: Primary Airflow Control Mode
+type: radio
+options:
+ - "Variable air volume"
+ - "Constant volume"
+default: "Variable air volume"
+```
+
+### A constant-volume unit holds a fixed airflow setpoint and controls zone temperature entirely by reheat, which suits spaces whose ventilation or pressurization requirement is fixed by function rather than by load. Every Btu of cooling delivered above the zone's need is then paid for twice, once at the central coil and once at the reheat coil. {note}
+
+## Primary Airflow Control Basis {toc}
+
+### The primary airflow control basis shall be as indicated in the datasheet.
+
+```datasheet
+label: Primary Airflow Control Basis
+type: radio
+options:
+ - "Pressure independent, closed-loop control on a measured primary airflow signal"
+ - "Pressure dependent, damper position commanded directly from the zone temperature loop"
+default: "Pressure independent, closed-loop control on a measured primary airflow signal"
+```
+
+### A pressure-independent unit measures its own primary airflow and drives the damper to hold the commanded setpoint, so the airflow it delivers is the airflow the ventilation calculation assumed no matter what the upstream static pressure is doing. {note}
+
+### A pressure-dependent unit has no airflow feedback, so its delivered airflow rises and falls with system static pressure and cannot be relied upon to hold a minimum ventilation rate as other zones open and close. Where a project's ventilation compliance path depends on a known minimum airflow at every zone, a pressure-dependent unit cannot supply the evidence. {note}
+
+### Where pressure-dependent control is selected, the Engineer of Record shall document how the zone's minimum outdoor air rate under ANSI/ASHRAE 62.1 is maintained across the range of system static pressures the unit will see.
+
+## Dual-Duct Mixing Section {toc}
+
+### Requirements in this article apply where a dual-duct metering arrangement is selected in the datasheet.
+
+### The dual-duct mixing section shall be as indicated in the datasheet.
+
+```datasheet
+label: Dual-Duct Mixing Section
+type: radio
+options:
+ - "Common outlet with no internal mixing section"
+ - "Internal mixing attenuator ahead of the outlet"
+```
+
+### Where a dual-duct metering arrangement is selected, each inlet shall be furnished with its own damper, its own actuator, and its own airflow sensing element.
+
+### Cold and warm air entering a common outlet without a mixing section leave the unit in stratified layers that persist for several duct diameters, so a discharge temperature sensor placed close to the outlet reads the layer it happens to sit in rather than the mixed temperature the zone receives. {note}
+
+### Where a discharge air temperature sensor is provided on a dual-duct unit with no internal mixing section, it shall be located downstream of the mixing distance the manufacturer publishes for the unit.
+
+# Primary Airflow and Inlet Sizing {toc}
+
+## Inlet Size {toc}
+
+### The primary inlet nominal size shall be as indicated in the datasheet.
+
+```datasheet
+label: Primary Inlet Nominal Diameter
+type: range
+unit: in.
+drawing_ref: "inlet size as indicated on the terminal unit schedule"
+min: 4
+max: 24
+setpoints: [4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 20, 24]
+default: deferred
+```
+
+### Where a unit is cataloged with a rectangular primary inlet rather than a round inlet, the inlet shall be sized for an equivalent free area not less than that of the scheduled nominal diameter, and the shop drawing shall dimension the rectangular inlet.
+
+### The inlet size shall be selected so that the scheduled primary maximum airflow falls within the certified flow range of the unit and the scheduled primary minimum airflow falls above the low-flow threshold published for the airflow sensing element at that inlet size.
+
+### Inlet size is the single selection that most often decides whether a terminal unit performs. Sized too small, the unit consumes inlet static pressure the system does not have and generates sound at the damper that no downstream treatment removes. Sized too large, the velocity at the sensing element at minimum airflow falls below the threshold at which the published accuracy applies, and the zone's minimum ventilation rate becomes a number on a graphic rather than a measured quantity. {note}
+
+### The manufacturer shall state, for each scheduled unit, the low-flow threshold of the airflow sensing element at the selected inlet size in the same units as the scheduled minimum airflow.
+
+## Scheduled Airflow Setpoints {toc}
+
+### The primary maximum airflow shall be as indicated in the datasheet.
+
+```datasheet
+label: Primary Maximum Airflow
+type: range
+unit: cfm
+drawing_ref: "airflow as indicated on the terminal unit schedule"
+min: 25
+max: 8000
+step: 5
+default: deferred
+```
+
+### The primary minimum airflow in cooling shall be as indicated in the datasheet.
+
+```datasheet
+label: Primary Minimum Airflow in Cooling
+type: range
+unit: cfm
+drawing_ref: "airflow as indicated on the terminal unit schedule"
+min: 0
+max: 8000
+step: 5
+default: deferred
+```
+
+### The primary minimum airflow in heating shall be as indicated in the datasheet.
+
+```datasheet
+label: Primary Minimum Airflow in Heating
+type: range
+unit: cfm
+drawing_ref: "airflow as indicated on the terminal unit schedule"
+min: 0
+max: 8000
+step: 5
+default: deferred
+```
+
+### The Engineer of Record shall determine the controlling minimum airflow for each zone as the largest of the zone outdoor air rate required by ANSI/ASHRAE 62.1 adjusted for system ventilation efficiency, the airflow required to deliver the design heating capacity, the reheat airflow limit of ANSI/ASHRAE/IES 90.1 applicable to the zone, and any stratification or acoustic floor the design establishes.
+
+### Setting the heating minimum equal to the cooling minimum is the most common origin of the complaint that a zone is cold while its box is calling for full heat. At the cooling minimum the reheat coil cannot raise the discharge temperature far enough above room temperature to overcome the buoyancy of the jet, so the warm air stays at the ceiling and the occupied zone is served by whatever room air the jet entrains. {note}
+
+### Where a fan section is provided, the fan adds induced plenum air to the primary air at the diffuser, so the discharge airflow in heating is set by the fan rather than by the primary minimum, and the primary minimum in heating can be set independently of the cold-air-dump consideration. {note}
+
+## Zone Airflow Control Logic {toc}
+
+### The zone airflow control logic shall be as indicated in the datasheet.
+
+```datasheet
+label: Zone Airflow Control Logic
+type: radio
+options:
+ - "Single maximum, one primary airflow maximum governing in both heating and cooling"
+ - "Dual maximum, a separate cooling maximum and heating maximum with a discharge temperature reset band between them"
+```
+
+### Under single-maximum logic the unit holds one minimum through the deadband and the heating range, so the reheat coil works against the full minimum airflow whenever the zone calls for heat. {note}
+
+### Under dual-maximum logic the unit drops to a low minimum through the deadband, raises the discharge temperature before it raises airflow, and only then increases airflow toward a separate heating maximum, which reduces both the simultaneous heating and cooling energy and the airflow the central fan must deliver at part load. {note}
+
+### Where dual-maximum logic is selected, the terminal unit shall be furnished with a discharge air temperature sensor and the controller shall be capable of resetting discharge temperature independently of primary airflow.
+
+## Inlet Static Pressure and Casing Pressure Drop {toc}
+
+### The available inlet static pressure at the primary maximum airflow shall be as indicated in the datasheet.
+
+```datasheet
+label: Available Inlet Static Pressure at Primary Maximum Airflow
+type: range
+unit: in. w.g.
+drawing_ref: "inlet static pressure as indicated on the terminal unit schedule"
+min: 0.05
+max: 6
+step: 0.05
+default: deferred
+```
+
+### The maximum casing pressure drop at the primary maximum airflow shall be as indicated in the datasheet.
+
+```datasheet
+label: Maximum Casing Pressure Drop at Primary Maximum Airflow
+type: range
+unit: in. w.g.
+min: 0.05
+max: 1
+setpoints: [0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.4, 0.5, 0.75, 1]
+```
+
+### Each unit shall maintain the commanded primary airflow within the specified measurement accuracy from the available inlet static pressure indicated in the datasheet down to the minimum operating differential pressure the manufacturer publishes for the unit.
+
+### The manufacturer shall state the minimum operating differential pressure for each scheduled unit in the action submittal.
+
+### The Engineer of Record shall calculate the available inlet static pressure for the most hydraulically remote unit on each branch and shall size the central fan and the terminal units against that value.
+
+### Selecting terminal units against the central fan discharge static pressure rather than against the static pressure remaining at the unit inlet after the upstream duct losses produces units that appear adequate on paper and starve at the end of the run. {note}
+
+### Inlet static pressure above the value at which a unit is rated raises both radiated and discharge sound, so the central system static pressure control strategy and the terminal unit sound selection are the same decision viewed from two ends of the duct. Static pressure reset driven by damper position holds the inlet static near the minimum the most-open zone needs, which lowers sound at every hour the system is not at design. {note}
+
+### The central system static pressure control strategy shall be coordinated with [[sync/building-automation-system]].
+
+# Casing Construction {toc}
+
+## Casing Material and Thickness {toc}
+
+### The casing material shall be as indicated in the datasheet.
+
+```datasheet
+label: Casing Material
+type: select
+options:
+ - "Galvanized steel sheet to ASTM A653 with G60 coating"
+ - "Galvanized steel sheet to ASTM A653 with G90 coating"
+ - "Aluminized steel sheet"
+ - "Type 304 stainless steel sheet to ASTM A240"
+ - "Type 316 stainless steel sheet to ASTM A240"
+default: "Galvanized steel sheet to ASTM A653 with G60 coating"
+```
+
+### The casing wrapper thickness shall be as indicated in the datasheet.
+
+```datasheet
+label: Casing Wrapper Thickness
+type: select
+unit: gauge
+options:
+ - "22 gauge"
+ - "20 gauge"
+ - "18 gauge"
+default: "22 gauge"
+```
+
+### Inlet collars, outlet flanges, and any surface that receives a hanger or a duct connection shall be not lighter than 20 gauge.
+
+### Casings shall be of welded, riveted, or interlocked-seam construction, and every joint shall be sealed so that the assembled casing meets the specified leakage limit.
+
+### Seams closed only with adhesive tape shall not be used, because the tape adhesive fails at the elevated plenum temperatures and sustained pressure differentials the casing sees over its service life.
+
+## Casing Air Leakage {toc}
+
+### The maximum casing air leakage shall be as indicated in the datasheet, expressed as a percentage of the nominal cataloged primary airflow for the unit and measured at 1 in. w.g. internal static pressure.
+
+```datasheet
+label: Maximum Casing Air Leakage at 1 in. w.g.
+type: range
+unit: '%'
+min: 0.5
+max: 5
+setpoints: [0.5, 1, 2, 3, 5]
+default: 2
+```
+
+### Air that leaks out of the casing has been conditioned by the central system and metered by the unit, but it never reaches the zone. It is therefore subtracted twice: once from the airflow the zone actually receives and once from the ventilation the system-level calculation credited to that zone. {note}
+
+## Casing Liner and Attenuation {toc}
+
+### The casing liner type shall be as indicated in the datasheet.
+
+```datasheet
+label: Casing Liner Type
+type: select
+options:
+ - "Fibrous glass liner to ASTM C1071 with a coated or foil-faced airstream surface"
+ - "Fibrous glass liner to ASTM C1071 with a perforated metal facing on the airstream side"
+ - "Closed-cell elastomeric foam liner with no exposed fiber"
+ - "Double-wall construction with fibrous glass encapsulated between solid metal skins"
+ - "Double-wall construction with fibrous glass encapsulated behind a perforated inner skin"
+ - "Unlined single-wall casing"
+default: "Fibrous glass liner to ASTM C1071 with a coated or foil-faced airstream surface"
+```
+
+### The casing liner thickness shall be as indicated in the datasheet.
+
+```datasheet
+label: Casing Liner Thickness
+type: range
+unit: in.
+min: 0.5
+max: 2
+setpoints: [0.5, 1, 1.5, 2]
+default: 0.5
+```
+
+### The liner is the unit's only broadband attenuator, and it works on the damper noise generated a few inches upstream of it. Attenuation rises with thickness, most strongly in the mid and upper octave bands that govern the perceived level, while the added thickness reduces the free area of the casing and raises the velocity through it. {note}
+
+### Where a fiber-free airstream is required by the project program, by an infection control risk assessment, or by the process the space serves, a closed-cell liner or a double-wall construction with the fiber fully encapsulated provides the acoustic treatment without an exposed fibrous surface. {note}
+
+### Unless the datasheet selects an unlined casing, every unit shall be furnished with acoustic treatment complying with this article.
+
+### Liner materials and adhesives shall have a flame spread index not greater than 25 and a smoke developed index not greater than 50 when tested to ASTM E84.
+
+### Fibrous glass liner shall comply with ASTM C1071 and shall show no fungal growth when tested to ASTM C1338.
+
+### Liner airstream surfaces shall be coated, encapsulated, or faced so that no fiber erodes into the airstream at the maximum face velocity for which the unit is cataloged, and the manufacturer shall state that velocity in the action submittal.
+
+### Liner shall be secured mechanically as well as adhesively at every edge exposed to the airstream, and every cut edge shall be sealed.
+
+### Liner constructions carrying a UL 181 listing may be identified as such in the submittal, and the listing shall not be used in place of the surface burning and erosion requirements of this article.
+
+## Hanger, Mounting, and Access Provisions {toc}
+
+### Casings shall be furnished with integral mounting brackets, hanger lugs, or threaded inserts sized for the operating weight of the unit.
+
+### The Contractor shall not penetrate the casing to attach a hanger, because a field penetration breaches the liner, creates a leak path, and voids the leakage rating the unit was certified to.
+
+### Each unit shall be furnished with a removable access panel giving service access to the damper actuator, the airflow sensing element, the controller, the reheat section, and the fan and motor where present.
+
+### The access panel arrangement shall be as indicated in the datasheet.
+
+```datasheet
+label: Access Panel Arrangement
+type: radio
+options:
+ - "Bottom access"
+ - "Side access"
+ - "Bottom and side access"
+default: "Bottom access"
+```
+
+### Access panels shall be removable and replaceable without disturbing the duct connections, the piping connections, or the electrical connections at the unit.
+
+### Access panel fasteners shall be captive or shall be furnished in a quantity that permits replacement, and loose fasteners shall not be relied upon to maintain the casing leakage rating.
+
+# Primary Damper Assembly {toc}
+
+## Damper Construction {toc}
+
+### The primary damper blade arrangement shall be as indicated in the datasheet.
+
+```datasheet
+label: Primary Damper Blade Arrangement
+type: select
+options:
+ - "Single blade in a round inlet"
+ - "Opposed multiple blades in a rectangular inlet"
+ - "Parallel multiple blades in a rectangular inlet"
+default: "Single blade in a round inlet"
+```
+
+### The damper blade and frame material shall be as indicated in the datasheet.
+
+```datasheet
+label: Damper Blade and Frame Material
+type: radio
+options:
+ - "Galvanized steel"
+ - "Aluminum"
+ - "Type 304 stainless steel"
+ - "Type 316 stainless steel"
+default: "Galvanized steel"
+```
+
+### The damper shaft bearing type shall be as indicated in the datasheet.
+
+```datasheet
+label: Damper Shaft Bearing Type
+type: radio
+options:
+ - "Self-lubricating synthetic bushings"
+ - "Oil-impregnated sintered bronze bearings"
+ - "Sealed ball bearings"
+default: manufacturer
+```
+
+### Bearings on a terminal damper carry almost no load and turn slowly, so the property that decides service life is resistance to seizing after long periods at a fixed position rather than load rating. Manufacturers meet that requirement with different bearing constructions across their product lines. {note}
+
+### The manufacturer shall state the bearing construction supplied for each scheduled unit in the action submittal.
+
+### The damper shaft shall be continuous through the casing and shall be indexed or marked so that the blade position is visible from outside the casing without removing an access panel.
+
+### Damper blades shall be stiffened as required to stroke without binding and without permanent deflection at the maximum differential pressure for which the unit is rated.
+
+### Damper shaft penetrations through the casing shall be sealed so that leakage past the penetration is included within the casing leakage limit at the rated differential pressure.
+
+## Damper Close-Off Leakage {toc}
+
+### The maximum damper close-off leakage shall be as indicated in the datasheet, expressed as a percentage of the nominal cataloged primary airflow for the unit and measured at 3 in. w.g. inlet static pressure with the damper commanded closed and the outlet open.
+
+```datasheet
+label: Maximum Damper Close-Off Leakage at 3 in. w.g.
+type: range
+unit: '%'
+min: 0.5
+max: 5
+setpoints: [0.5, 1, 2, 3, 5]
+default: 2
+```
+
+### Close-off leakage is what the zone receives when the control system believes it is delivering nothing. Where a sequence relies on a true zero-flow condition - unoccupied setback, a zone isolated for pressurization, a space shut down for a process - the leakage rate is the floor beneath which the sequence cannot go, and the tighter close-off is bought with a heavier blade, a positive seal, and more actuator torque. {note}
+
+### Where a zone control sequence commands a zero-airflow condition, the unit serving that zone shall be furnished with a damper seal rated for the close-off leakage indicated in the datasheet at the maximum inlet static pressure the branch can develop.
+
+## Damper Actuator {toc}
+
+### The damper actuator control signal shall be as indicated in the datasheet.
+
+```datasheet
+label: Damper Actuator Control Signal
+type: select
+options:
+ - "Analog modulating, 0–10 VDC"
+ - "Analog modulating, 4–20 mA"
+ - "Floating point, three-wire tri-state"
+ - "Pulse-width modulated"
+ - "Pneumatic modulating, 3–15 psig"
+ - "Two-position, line or low voltage"
+default: "Analog modulating, 0–10 VDC"
+```
+
+### The damper actuator fail-safe behavior shall be as indicated in the datasheet.
+
+```datasheet
+label: Damper Actuator Fail-Safe Behavior
+type: radio
+options:
+ - "Non-spring-return, holding last position on loss of control signal or power"
+ - "Spring-return to the closed position"
+ - "Spring-return to the open position"
+default: "Non-spring-return, holding last position on loss of control signal or power"
+```
+
+### The damper actuator stroke time shall be as indicated in the datasheet.
+
+```datasheet
+label: Damper Actuator Stroke Time
+type: range
+unit: seconds
+min: 15
+max: 300
+setpoints: [15, 30, 45, 60, 90, 120, 180, 300]
+default: 90
+```
+
+### Actuators shall be direct-coupled to the damper shaft without a linkage, and shall be secured so that the coupling cannot slip on the shaft over the rated cycle life.
+
+### Where a spring-return fail-safe behavior is selected, the actuator shall drive the damper to the selected position on loss of control signal and on loss of power, and the position shall be reached within the stroke time indicated in the datasheet.
+
+### A stroke time far shorter than the airflow control loop's response time causes the loop to overshoot and hunt, because the damper reaches its commanded position before the sensor has registered the effect of the previous move. A stroke time far longer than the loop's response time leaves the zone unable to follow a load change. The two have to be matched, and the match is a property of the controller and the sensor as much as of the actuator. {note}
+
+### The Contractor shall verify that the actuator torque rating exceeds the damper torque required at the maximum inlet static pressure the branch can develop, including the torque required to compress a damper seal where one is provided.
+
+# Primary Airflow Sensing {toc}
+
+## Sensing Element {toc}
+
+### The primary airflow sensing element type shall be as indicated in the datasheet.
+
+```datasheet
+label: Primary Airflow Sensing Element Type
+type: select
+options:
+ - "Multi-point center-averaging differential pressure element"
+ - "Single-point differential pressure element"
+ - "Thermal dispersion sensing element"
+default: "Multi-point center-averaging differential pressure element"
+```
+
+### The sensing element shall be integral to the inlet collar, factory-installed, and factory-calibrated against a reference flow station for the specific unit it serves.
+
+### A multi-point element averages the pressure signal across the inlet cross-section, so a velocity profile that is not uniform still produces a representative average. A single-point element reads the profile at one location and therefore depends more heavily on the approach condition, while a thermal dispersion element reads velocity directly and holds usable resolution to a lower velocity than a differential pressure element of the same inlet size. {note}
+
+### The maximum primary airflow measurement error shall be as indicated in the datasheet, expressed as a percentage of reading over the scheduled airflow range.
+
+```datasheet
+label: Maximum Primary Airflow Measurement Error
+type: range
+unit: '%'
+min: 1
+max: 15
+setpoints: [1, 2, 3, 5, 10, 15]
+default: 5
+```
+
+### The manufacturer shall state the low-flow threshold below which the specified measurement error no longer applies, for each scheduled unit at its selected inlet size.
+
+### An accuracy stated as a percentage of reading holds proportionally across the range, while an accuracy stated as a percentage of full scale becomes a larger and larger fraction of the reading as airflow falls. At a minimum airflow that is a fifth of the maximum, the two conventions differ by a factor of five in the quantity that governs minimum ventilation. {note}
+
+## Approach Duct Condition {toc}
+
+### The minimum straight duct length upstream of the unit inlet shall be as indicated in the datasheet, expressed in inlet diameters.
+
+```datasheet
+label: Minimum Straight Duct Upstream of the Inlet
+type: range
+unit: inlet diameters
+min: 0
+max: 5
+setpoints: [0, 1, 1.5, 2, 3, 5]
+```
+
+### Where the datasheet does not indicate a straight duct length, the length published by the sensing element manufacturer for rated accuracy at the selected inlet size shall govern, and the manufacturer shall state that length in the action submittal.
+
+### An elbow, tee, transition, or partly closed damper within the approach length skews the velocity profile at the inlet, and the sensing element reports the skewed average as though it were the true airflow. The unit then controls precisely to a wrong number, which is why the symptom appears at commissioning as a zone that balances only after its calibration constant is overridden. {note}
+
+### Where the required straight duct length cannot be provided at a unit, the Contractor shall report the condition to the Engineer of Record during shop drawing coordination rather than after installation.
+
+### Where the Engineer of Record accepts an installation with less than the required straight duct length, the calibration constant for that unit shall be established in the field against a calibrated reference instrument and shall be recorded in the closeout record.
+
+# Reheat {toc}
+
+## Reheat Medium {toc}
+
+### The reheat medium shall be as indicated in the datasheet.
+
+```datasheet
+label: Reheat Medium
+type: select
+options:
+ - "None"
+ - "Hot water coil"
+ - "Steam coil"
+ - "Electric resistance"
+```
+
+### The reheat medium available to a project is set by the plant the project builds or already has, and by what the local energy code permits for new electric resistance heating in the building type and climate zone. Hot water offers high turndown and quiet operation at the cost of piping every zone; electric resistance eliminates the piping and the freeze exposure at the cost of a demand-coincident electrical load; steam suits an existing central steam plant and brings condensate return and trap maintenance to every zone. {note}
+
+### The Engineer of Record shall confirm that the selected reheat medium complies with the limits ANSI/ASHRAE/IES 90.1 and the adopted energy code place on new electric resistance heating for the building type and climate zone before the medium is released for fabrication.
+
+### Where no reheat is selected for a unit, the zone shall be served by a heat source outside this standard or shall be documented as requiring no heating.
+
+## Hot Water Reheat Coil {toc}
+
+### Requirements in this article apply where a hot water reheat coil is selected in the datasheet.
+
+### The reheat coil capacity shall be as indicated in the datasheet.
+
+```datasheet
+label: Reheat Coil Capacity
+type: range
+unit: MBH
+drawing_ref: "coil capacity as indicated on the terminal unit schedule"
+min: 1
+max: 150
+step: 0.5
+default: deferred
+```
+
+### The reheat coil row count shall be as indicated in the datasheet.
+
+```datasheet
+label: Reheat Coil Row Count
+type: range
+unit: rows
+drawing_ref: "coil rows as indicated on the terminal unit schedule"
+min: 1
+max: 4
+setpoints: [1, 2, 3, 4]
+default: deferred
+```
+
+### The design hot water entering temperature shall be as indicated in the datasheet.
+
+```datasheet
+label: Hot Water Entering Temperature
+type: range
+unit: °F
+drawing_ref: "design fluid temperatures as indicated on the mechanical schedules"
+min: 100
+max: 200
+step: 1
+default: deferred
+```
+
+### The design hot water leaving temperature shall be as indicated in the datasheet.
+
+```datasheet
+label: Hot Water Leaving Temperature
+type: range
+unit: °F
+drawing_ref: "design fluid temperatures as indicated on the mechanical schedules"
+min: 80
+max: 190
+step: 1
+default: deferred
+```
+
+### Coil capacity falls steeply with entering water temperature, so a row count that satisfies a scheduled capacity on a 180 °F plant can fall short of the same capacity on a 140 °F plant by a margin no field adjustment recovers. Plants designed for condensing boilers or for heat pump heat recovery operate at the lower end of the range, which is why the row count has to be selected against the project's own scheduled water temperature rather than against a catalog reference condition. {note}
+
+### The coil tube material shall be as indicated in the datasheet.
+
+```datasheet
+label: Reheat Coil Tube Material
+type: radio
+options:
+ - "Seamless copper tube to ASTM B75"
+ - "Type 304 stainless steel tube"
+ - "Type 316 stainless steel tube"
+default: "Seamless copper tube to ASTM B75"
+```
+
+### The coil fin material shall be as indicated in the datasheet.
+
+```datasheet
+label: Reheat Coil Fin Material
+type: radio
+options:
+ - "Aluminum plate fin"
+ - "Copper plate fin"
+default: "Aluminum plate fin"
+```
+
+### The coil working pressure rating shall be as indicated in the datasheet.
+
+```datasheet
+label: Reheat Coil Working Pressure Rating
+type: range
+unit: psig
+min: 100
+max: 400
+setpoints: [100, 150, 200, 250, 300, 400]
+default: 300
+```
+
+### Fins shall be mechanically expanded onto the tubes to form a continuous metal-to-metal bond over the full finned length.
+
+### Coils shall be leak tested at the factory at not less than 1.5 times the specified working pressure rating and shall be shipped with the connections capped.
+
+### Coil connections shall extend beyond the casing far enough for the piping specialties required at the unit to be installed without cutting or modifying the casing.
+
+## Hot Water Reheat Control Valve {toc}
+
+### Requirements in this article apply to the control valve serving a hot water reheat coil selected in the datasheet.
+
+### The reheat control valve shall be as indicated in the datasheet.
+
+```datasheet
+label: Hot Water Reheat Control Valve
+type: select
+options:
+ - "Pressure-independent control valve with a modulating actuator"
+ - "Two-way modulating globe valve"
+ - "Two-way modulating characterized ball valve"
+ - "Three-way modulating valve"
+ - "Two-position two-way valve"
+```
+
+### A pressure-independent valve holds the commanded flow regardless of the differential pressure across it, so a zone's flow does not shift as other zones on the same distribution modulate. A conventional two-way valve delivers the flow its authority and the local differential pressure produce, which is stable where the plant controls differential pressure closely and drifts where it does not. {note}
+
+### A three-way valve maintains flow through the distribution when the coil is not calling, which suits a constant-flow arrangement and defeats the flow reduction a variable-flow distribution is built to achieve. {note}
+
+### A two-position valve delivers full coil capacity or none, so the zone temperature cycles about the setpoint at an amplitude set by the coil capacity and the zone's thermal mass. {note}
+
+### The reheat control valve actuator fail position shall be as indicated in the datasheet.
+
+```datasheet
+label: Reheat Control Valve Actuator Fail Position
+type: radio
+options:
+ - "Fail to the open position"
+ - "Fail to the closed position"
+ - "Fail in the last position"
+```
+
+### Where a unit serves a zone with an exterior exposure in a climate that reaches freezing temperatures, the reheat control valve shall fail to the open position so that a loss of control power does not leave a glazed zone without heat.
+
+### Where a unit serves a zone with no freeze exposure, the reheat control valve may fail to the closed position so that a loss of control power does not overheat the zone.
+
+### Control valves shall be rated to close off against the maximum differential pressure the hot water distribution can develop at the unit with the pump at shutoff head.
+
+### Each control valve actuator shall drive the valve through its full stroke within the time the control sequence allows for the heating loop to respond, and the manufacturer shall state the stroke time in the action submittal.
+
+## Steam Reheat Coil {toc}
+
+### Requirements in this article apply where a steam reheat coil is selected in the datasheet.
+
+### The design steam supply pressure at the coil shall be as indicated in the datasheet.
+
+```datasheet
+label: Design Steam Supply Pressure at the Coil
+type: range
+unit: psig
+drawing_ref: "steam pressure as indicated on the mechanical schedules"
+min: 2
+max: 100
+step: 1
+default: deferred
+```
+
+### Steam reheat coils shall be of distributing-tube construction so that steam is delivered along the full tube length and condensate drains freely to the return connection.
+
+### Steam coils shall be installed so that the condensate connection is at the low point and the coil drains by gravity to the trap without a lift in the condensate line.
+
+### Each steam coil shall be served by a trap, a strainer, and a vacuum breaker sized by the Contractor for the scheduled coil load at the design supply pressure.
+
+### A steam coil that cannot drain fills with condensate, and the condensate is then accelerated by incoming steam into the closed end of the tube. The resulting impact damages the coil, and it is loud enough in an occupied ceiling to be reported as a building defect. {note}
+
+### Steam and condensate piping at the coil shall comply with [[sync/hydronic-piping]].
+
+## Electric Reheat {toc}
+
+### Requirements in this article apply where electric resistance reheat is selected in the datasheet.
+
+### The electric reheat capacity shall be as indicated in the datasheet.
+
+```datasheet
+label: Electric Reheat Capacity
+type: range
+unit: kW
+drawing_ref: "heater capacity as indicated on the terminal unit schedule"
+min: 0.5
+max: 50
+step: 0.1
+default: deferred
+```
+
+### The electric heater element construction shall be as indicated in the datasheet.
+
+```datasheet
+label: Electric Heater Element Construction
+type: radio
+options:
+ - "Open-coil nickel-chromium resistance wire on ceramic insulators"
+ - "Sheathed tubular element without fins"
+ - "Finned tubular sheathed element"
+default: "Open-coil nickel-chromium resistance wire on ceramic insulators"
+```
+
+### An open-coil element transfers heat directly from the resistance wire to the airstream, which gives it a fast response and the lowest first cost and leaves the energized wire exposed to whatever the airstream carries. A sheathed element places a metal barrier between the wire and the air, which tolerates contaminated or intermittent airflow at a higher first cost and a slower thermal response. {note}
+
+### The electric heater capacity control method shall be as indicated in the datasheet.
+
+```datasheet
+label: Electric Heater Capacity Control Method
+type: radio
+options:
+ - "Staged contactors"
+ - "Solid-state relay with time-proportioned staging"
+ - "Silicon-controlled rectifier providing a modulating output"
+default: "Staged contactors"
+```
+
+### The electric heater stage count shall be as indicated in the datasheet.
+
+```datasheet
+label: Electric Heater Stage Count
+type: range
+unit: stages
+drawing_ref: "heater staging as indicated on the terminal unit schedule"
+min: 1
+max: 4
+setpoints: [1, 2, 3, 4]
+default: deferred
+```
+
+### Staged control moves the discharge temperature in steps whose height is the capacity of one stage divided by the airflow, so the step is largest where the heater is large relative to the minimum airflow. Where the zone has a narrow setpoint band or a low heating airflow, that step appears at the diffuser as a cycle the occupants feel. Modulating control removes the step at the cost of a device that generates electrical harmonics and requires its own thermal management. {note}
+
+### The electric reheat supply voltage shall be as indicated in the datasheet.
+
+```datasheet
+label: Electric Reheat Supply Voltage
+type: range
+unit: V
+drawing_ref: "electrical drawings and panel schedules"
+min: 120
+max: 600
+setpoints: [120, 208, 240, 277, 480, 600]
+default: deferred
+```
+
+### The electric reheat supply phase shall be as indicated in the datasheet.
+
+```datasheet
+label: Electric Reheat Supply Phase
+type: radio
+drawing_ref: "electrical drawings and panel schedules"
+options:
+ - "Single phase, 1Φ"
+ - "Three phase, 3Φ"
+default: deferred
+```
+
+### The heater electrical characteristics shown on the mechanical schedule and those shown on the electrical documents shall be reconciled before the heater is released for fabrication, and any discrepancy shall be resolved by the Engineer of Record.
+
+### Every electric heater shall be furnished with a primary automatic-reset thermal cutout.
+
+### Every electric heater shall be furnished with a secondary manual-reset thermal cutout independent of the primary cutout.
+
+### Every electric heater shall be furnished with an airflow proving device that de-energizes the heater whenever primary airflow falls below the minimum airflow the manufacturer requires for heater operation.
+
+### An electric heater energized without airflow raises the element to a temperature limited only by radiation and by the cutouts, and the cutout is a backstop rather than a control. Airflow proof is therefore a hard interlock, not a software permissive, and it is the requirement in this standard that admits no project-specific exception. {note}
+
+### The airflow proving interlock shall be wired in series with the heater control circuit so that a controller failure, a network failure, or a software error cannot energize the heater without airflow.
+
+### The manufacturer shall state the minimum airflow required for heater operation for each scheduled unit, and the controller minimum airflow in heating shall not be set below that value.
+
+### The electric heater accessories furnished shall be as indicated in the datasheet.
+
+```datasheet
+label: Electric Heater Accessories Furnished
+type: checkbox
+options:
+ - "Door interlock disconnect switch"
+ - "Branch-circuit fusing within the heater enclosure"
+ - "Control power transformer within the heater enclosure"
+ - "Magnetic contactor for each stage"
+ - "Current-limiting fuse for the modulating power device"
+ - "Heater section removable without disturbing the duct connection"
+default:
+ - "Door interlock disconnect switch"
+ - "Magnetic contactor for each stage"
+```
+
+### The electric reheat disconnecting means shall be as indicated in the datasheet.
+
+```datasheet
+label: Electric Reheat Disconnecting Means
+type: radio
+options:
+ - "Disconnecting means factory-installed within the heater enclosure"
+ - "Disconnecting means field-installed within sight of the unit"
+ - "Lockable disconnecting means at the branch panelboard"
+default: "Disconnecting means factory-installed within the heater enclosure"
+```
+
+# Fan Section {toc}
+
+## Fan and Motor {toc}
+
+### Requirements in this article apply where a parallel or series fan section arrangement is selected in the datasheet.
+
+### The fan wheel type shall be as indicated in the datasheet.
+
+```datasheet
+label: Fan Wheel Type
+type: radio
+options:
+ - "Forward-curved centrifugal"
+ - "Backward-inclined centrifugal"
+ - "Mixed-flow"
+default: "Forward-curved centrifugal"
+```
+
+### The fan motor type shall be as indicated in the datasheet.
+
+```datasheet
+label: Fan Motor Type
+type: radio
+options:
+ - "Electronically commutated motor"
+ - "Permanent split capacitor motor"
+default: "Electronically commutated motor"
+```
+
+### An electronically commutated motor holds high efficiency across its speed range and accepts a speed command directly, so output is set during commissioning by changing a signal rather than by changing a tap or a pulley. A permanent split capacitor motor is efficient near its design point and falls away sharply below it, and its output is set in discrete steps at the winding taps. {note}
+
+### The fan motor nameplate power shall be as indicated in the datasheet.
+
+```datasheet
+label: Fan Motor Nameplate Power
+type: range
+unit: hp
+drawing_ref: "motor power as indicated on the terminal unit schedule"
+min: 0.03
+max: 2
+setpoints: [0.03, 0.05, 0.083, 0.125, 0.167, 0.25, 0.333, 0.5, 0.75, 1, 1.5, 2]
+default: deferred
+```
+
+### The fan motor supply voltage shall be as indicated in the datasheet.
+
+```datasheet
+label: Fan Motor Supply Voltage
+type: range
+unit: V
+drawing_ref: "electrical drawings and panel schedules"
+min: 115
+max: 480
+setpoints: [115, 208, 230, 277, 460, 480]
+default: deferred
+```
+
+### The fan motor supply phase shall be as indicated in the datasheet.
+
+```datasheet
+label: Fan Motor Supply Phase
+type: radio
+drawing_ref: "electrical drawings and panel schedules"
+options:
+ - "Single phase, 1Φ"
+ - "Three phase, 3Φ"
+default: deferred
+```
+
+### The fan airflow at the design operating point shall be as indicated in the datasheet.
+
+```datasheet
+label: Fan Airflow at the Design Operating Point
+type: range
+unit: cfm
+drawing_ref: "fan airflow as indicated on the terminal unit schedule"
+min: 50
+max: 5000
+step: 5
+default: deferred
+```
+
+### Fan motors shall comply with the applicable construction and performance provisions of NEMA MG 1.
+
+### The manufacturer shall state the fan airflow and the fan power at the design operating point, derived from testing in accordance with ANSI/AMCA 210, in the action submittal.
+
+### The fan and motor assembly shall be removable through the access panel without disconnecting the primary inlet duct, the outlet duct, or the reheat piping.
+
+### The fan and motor assembly shall be mounted on vibration isolators selected so that no fan-generated vibration is transmitted through the casing to the hangers.
+
+## Fan Speed Control {toc}
+
+### The fan speed control means shall be as indicated in the datasheet.
+
+```datasheet
+label: Fan Speed Control Means
+type: select
+options:
+ - "Fixed speed set at the motor taps during startup"
+ - "Adjustable speed set at a potentiometer on the unit"
+ - "Modulating speed commanded by the zone controller over an analog output"
+ - "Modulating speed commanded by the zone controller over the network"
+default: "Modulating speed commanded by the zone controller over an analog output"
+```
+
+### The speed control means available to a unit is constrained by the motor selected: a permanent split capacitor motor accepts only the discrete speeds its winding taps provide, while an electronically commutated motor accepts a continuous speed command. The two selections shall be made together.
+
+### The as-commissioned fan speed setting shall be recorded for each unit in the field commissioning record.
+
+## Induced-Air Opening {toc}
+
+### The induced-air opening backdraft damper shall be as indicated in the datasheet.
+
+```datasheet
+label: Induced-Air Opening Backdraft Damper
+type: radio
+options:
+ - "Gravity-operated backdraft damper"
+ - "Motorized damper interlocked with fan operation"
+ - "No backdraft damper"
+default: "Gravity-operated backdraft damper"
+```
+
+### The induced-air opening filter shall be as indicated in the datasheet.
+
+```datasheet
+label: Induced-Air Opening Filter
+type: select
+options:
+ - "No filter at the induced-air opening"
+ - "Cleanable aluminum mesh filter"
+ - "Disposable pleated filter rated MERV 8 to ANSI/ASHRAE 52.2"
+ - "Disposable pleated filter rated MERV 11 to ANSI/ASHRAE 52.2"
+ - "Disposable pleated filter rated MERV 13 to ANSI/ASHRAE 52.2"
+default: "Cleanable aluminum mesh filter"
+```
+
+### Where a parallel fan section is selected, primary air at the outlet is at a higher pressure than the plenum whenever the fan is off, so without a backdraft damper the unit discharges conditioned primary air into the return plenum through the induced-air opening at every cooling hour. {note}
+
+### The filter at the induced-air opening shall be accessible for replacement or cleaning through the unit access panel without removing the unit from its hangers.
+
+### The pressure drop of the selected filter at the design fan airflow shall be included in the fan selection, and the manufacturer shall state the fan operating point at the filter's recommended final resistance in the action submittal.
+
+# Sound Performance {toc}
+
+## Rating Basis {toc}
+
+### Radiated and discharge sound power shall be reported separately for each scheduled unit in octave bands 2 through 7, at the scheduled primary airflow and at the scheduled inlet static pressure.
+
+### Occupied-space sound levels shall be estimated from the reported sound power in accordance with ANSI/AHRI 885, and the submittal shall state the room absorption, the unit-to-listener distance, and the ceiling and plenum attenuation values used.
+
+### Radiated sound leaves the casing and passes through the ceiling construction directly into the space below the unit, while discharge sound travels down the outlet duct and is attenuated by the duct, its lining, any plenum, and the outlet itself before it reaches the room. For a unit in an acoustically absorbent lay-in ceiling over an open plan, the radiated path usually reaches the listener with the least attenuation of the two. {note}
+
+### Sound criteria expressed as noise criteria values shall be evaluated by the tangent method of ANSI/ASA S12.2 where field measurement is performed.
+
+## Occupied-Space Sound Limits {toc}
+
+### The maximum radiated sound level in the occupied space attributable to the terminal unit shall be as indicated in the datasheet.
+
+```datasheet
+label: Maximum Radiated Sound Level in the Occupied Space
+type: range
+unit: NC
+min: 15
+max: 55
+setpoints: [15, 20, 25, 30, 35, 40, 45, 50, 55]
+```
+
+### The maximum discharge sound level in the occupied space attributable to the terminal unit shall be as indicated in the datasheet.
+
+```datasheet
+label: Maximum Discharge Sound Level in the Occupied Space
+type: range
+unit: NC
+min: 15
+max: 55
+setpoints: [15, 20, 25, 30, 35, 40, 45, 50, 55]
+```
+
+### Sound criteria vary by how the space is used, and the ranges commonly applied are: {note}
+
+- NC 20 to NC 25 for performance spaces, recording and broadcast rooms, and sound-critical research areas
+- NC 25 to NC 30 for executive offices, board rooms, courtrooms, and worship spaces
+- NC 30 to NC 35 for private offices, classrooms, conference rooms, patient rooms, and operating rooms
+- NC 35 to NC 40 for open offices, libraries, laboratories, retail sales areas, and restaurants
+- NC 40 to NC 45 for corridors, lobbies, public circulation, and light industrial spaces
+- NC 45 to NC 50 for kitchens, gymnasiums, and mechanical and service areas
+
+### Where the Contract Documents indicate a lower sound limit for a specific space, that limit shall govern in that space.
+
+### The unit selection submitted for each scheduled zone shall demonstrate compliance with the applicable limit using the actual room volume, room absorption, ceiling construction, and unit-to-listener distance for that zone.
+
+## Discharge Attenuation {toc}
+
+### The discharge attenuation provided beyond the unit casing shall be as indicated in the datasheet.
+
+```datasheet
+label: Discharge Attenuation Beyond the Unit Casing
+type: select
+options:
+ - "No attenuation beyond the unit casing"
+ - "Lined discharge plenum furnished with the unit"
+ - "Lined discharge plenum furnished under the ductwork scope"
+ - "Sound attenuator in the discharge duct"
+default: "No attenuation beyond the unit casing"
+```
+
+### Where a lined discharge plenum is provided, its pressure drop at the primary maximum airflow shall be included in the branch pressure calculation.
+
+### Discharge attenuation added to a unit does nothing for the radiated path, so a unit selected on discharge sound alone and then found noisy in the room is rarely improved by treating the duct. {note}
+
+### Downstream duct and outlet selections that affect the discharge path shall be coordinated with [[sync/hvac-ductwork]] and [[sync/hvac-air-distribution-devices]].
+
+# Zone Control and Building Automation Interface {toc}
+
+## Controller and Responsibility {toc}
+
+### The zone control type shall be as indicated in the datasheet.
+
+```datasheet
+label: Zone Control Type
+type: select
+options:
+ - "Networked direct digital controller"
+ - "Standalone direct digital controller with no network connection"
+ - "Analog electronic control"
+ - "Pneumatic control"
+default: "Networked direct digital controller"
+```
+
+### The controller furnishing and mounting responsibility shall be as indicated in the datasheet.
+
+```datasheet
+label: Controller Furnishing and Mounting Responsibility
+type: select
+options:
+ - "Furnished and factory-mounted by the terminal unit manufacturer"
+ - "Furnished by the terminal unit manufacturer and shipped loose for field mounting"
+ - "Furnished by the controls contractor and shipped to the terminal unit manufacturer for factory mounting"
+ - "Furnished by the controls contractor and field-mounted"
+default: "Furnished and factory-mounted by the terminal unit manufacturer"
+```
+
+### The controller programming and startup responsibility shall be as indicated in the datasheet.
+
+```datasheet
+label: Controller Programming and Startup Responsibility
+type: radio
+options:
+ - "Programmed and tested at the factory by the terminal unit manufacturer"
+ - "Programmed at startup by the controls contractor"
+ - "Programmed at startup by the terminal unit manufacturer's authorized representative"
+default: "Programmed at startup by the controls contractor"
+```
+
+### Who furnishes a controller, who mounts it, and who programs it are three separate commercial decisions, and a project can combine them in any order. Factory mounting removes a field labor operation and lets the unit ship tested; controls contractor programming keeps the sequence, the graphics, and the trending in one party's hands. The failure mode a project should avoid is leaving any one of the three unassigned, because the gap surfaces at startup when the schedule has no room for it. {note}
+
+### The party responsible for programming shall also be responsible for the cost of any reprogramming required to correct a sequence that does not match the Contract Documents.
+
+## Network Protocol and Points {toc}
+
+### The controller network protocol shall be as indicated in the datasheet.
+
+```datasheet
+label: Controller Network Protocol
+type: select
+options:
+ - "BACnet MS/TP to ANSI/ASHRAE 135"
+ - "BACnet/IP to ANSI/ASHRAE 135"
+ - "BACnet Secure Connect to ANSI/ASHRAE 135"
+ - "Modbus RTU"
+ - "LonWorks FT-10"
+ - "Wireless mesh with a gateway to a wired network"
+ - "Manufacturer-proprietary protocol with a gateway to a wired network"
+default: "BACnet MS/TP to ANSI/ASHRAE 135"
+```
+
+### The controller points required at each terminal unit shall be as indicated in the datasheet.
+
+```datasheet
+label: Required Controller Points
+type: checkbox
+options:
+ - "Primary damper actuator output, modulating"
+ - "Primary airflow sensor input, differential pressure"
+ - "Zone temperature sensor input"
+ - "Discharge air temperature sensor input"
+ - "Hot water reheat valve output, modulating"
+ - "Steam reheat valve output, modulating"
+ - "Electric reheat stage outputs, binary"
+ - "Electric reheat modulating output"
+ - "Fan start and stop output, binary"
+ - "Fan speed output, modulating"
+ - "Fan status input, binary"
+ - "Zone carbon dioxide sensor input"
+ - "Occupancy sensor input"
+ - "Window or door contact input"
+ - "Condensate overflow switch input"
+default:
+ - "Primary damper actuator output, modulating"
+ - "Primary airflow sensor input, differential pressure"
+ - "Zone temperature sensor input"
+ - "Discharge air temperature sensor input"
+```
+
+### The controller shall be furnished with sufficient spare hardwired points of each type used to accommodate the points indicated in the datasheet without an expansion module.
+
+### The zone control sequence basis shall be as indicated in the datasheet.
+
+```datasheet
+label: Zone Control Sequence Basis
+type: radio
+options:
+ - "Terminal unit sequences of ASHRAE Guideline 36"
+ - "Project-specific sequence included in the Contract Documents"
+ - "Terminal unit manufacturer's published application sequence"
+default: "Project-specific sequence included in the Contract Documents"
+```
+
+### Controller addressing, network segmentation, and supervisory controller assignment shall be established against the unit tag schedule before the units are released for shipment.
+
+### Where a controller is addressed at the factory, the address shall match the unit tag schedule, and the unit shall be labeled with both the tag and the address.
+
+### Re-addressing a controller in the field is a normal operation, and each occurrence introduces an opportunity for a duplicate address on a trunk that presents at commissioning as an intermittent communication fault on units unrelated to the one being changed. {note}
+
+### The controller and the network shall be commissioned on the project network in accordance with [[sync/building-automation-system]].
+
+## Zone Sensor {toc}
+
+### The zone sensor measured parameters shall be as indicated in the datasheet.
+
+```datasheet
+label: Zone Sensor Measured Parameters
+type: checkbox
+options:
+ - "Dry-bulb temperature"
+ - "Relative humidity"
+ - "Carbon dioxide concentration"
+ - "Occupancy"
+ - "Total volatile organic compounds"
+default:
+ - "Dry-bulb temperature"
+```
+
+### The zone sensor occupant interface shall be as indicated in the datasheet.
+
+```datasheet
+label: Zone Sensor Occupant Interface
+type: select
+options:
+ - "No occupant adjustment"
+ - "Setpoint adjustment within a limited band"
+ - "Setpoint adjustment within a limited band and a timed override button"
+ - "Digital display with setpoint adjustment, timed override, and fan mode selection"
+default: "Setpoint adjustment within a limited band"
+```
+
+### The zone sensor setpoint adjustment range shall be as indicated in the datasheet, expressed as the permitted deviation above and below the system setpoint.
+
+```datasheet
+label: Zone Sensor Setpoint Adjustment Range
+type: range
+unit: °F
+min: 0
+max: 10
+setpoints: [0, 1, 2, 3, 4, 5, 10]
+default: 2
+```
+
+### The zone sensor connection shall be as indicated in the datasheet.
+
+```datasheet
+label: Zone Sensor Connection
+type: radio
+options:
+ - "Hardwired to the terminal unit controller"
+ - "Wireless to a receiver at the terminal unit controller"
+default: "Hardwired to the terminal unit controller"
+```
+
+### A wide adjustment band gives occupants control of their own comfort and gives the building an energy result that follows occupant preference rather than the design intent; a narrow band or none holds the setpoint the design assumed and moves every comfort complaint to the facility staff. {note}
+
+### Zone sensors shall be located out of direct sunlight, away from a supply air path, and away from a heat-generating device, and the Contractor shall report any scheduled location that cannot meet these conditions to the Engineer of Record before rough-in.
+
+### Wireless zone sensors shall be furnished with a means of verifying signal quality at the sensor location during installation, and the as-installed signal quality shall be recorded in the field commissioning record.
+
+# Factory Testing {toc}
+
+## Each terminal unit shall be subjected to the manufacturer's production test program before shipment, and the following shall be included in that program:
+
+- Full-stroke operation of the primary damper, verifying the closed and full-open positions against the actuator command
+- Calibration of the primary airflow sensing element against a reference flow station, with the calibration constant recorded in the unit test record
+- Leak test of the hot water or steam coil at the specified test pressure for the manufacturer's standard duration
+- Electrical functional test of the heater section, verifying the airflow proving interlock, the primary cutout, and the secondary cutout
+- Functional test of the fan and motor assembly at the design operating point where a fan section is furnished
+- Communication and point-by-point test of the controller where the controller is factory-mounted
+
+## No unit shall ship until every test in the production test program has passed, and a unit that fails a test shall be corrected and retested at the manufacturer's expense.
+
+## The factory test witnessing requirement shall be as indicated in the datasheet.
+
+```datasheet
+label: Factory Test Witnessing
+type: radio
+options:
+ - "Production test program with certified reports and no witness"
+ - "Witnessed test on a sample of units of each configuration"
+ - "Witnessed test on every unit furnished"
+default: "Production test program with certified reports and no witness"
+```
+
+## Where a witnessed test is required, the Contractor shall give the Engineer of Record not less than ten working days notice of the test date.
+
+## Where a witnessed test is required and the units are not ready on the scheduled date, the Contractor shall bear the cost of the Engineer of Record's return visit.
+
+# Installation {toc}
+
+## Coordination and Service Access {toc}
+
+### Before ceiling suspension is installed and before ductwork is fabricated, the Contractor shall verify that each terminal unit can be installed with the service clearance the manufacturer publishes and that its access panel is reachable from below the finished ceiling.
+
+### Service access shall be provided to the damper actuator, the airflow sensing element, the controller, the reheat section and its valve, and the fan and motor where present.
+
+### Where the ceiling construction below a unit does not permit access through the ceiling itself, an access panel shall be coordinated with the finish schedule and installed below the unit access panel.
+
+### Where a conflict cannot be resolved without relocating a unit from its scheduled position, the Contractor shall obtain the Engineer of Record's acceptance of the revised position, including the effect on the inlet approach duct length, before installing it.
+
+## Suspension and Support {toc}
+
+### Terminal units shall be suspended from the building structure by threaded rod, hanger strap, or trapeze hanger attached to the mounting provisions furnished on the casing.
+
+### Terminal units shall not be supported by the ceiling suspension system, by connected ductwork, or by connected piping.
+
+### Each unit shall be supported at not fewer than four points sized for the operating weight of the unit, including the weight of a water-filled coil where one is furnished.
+
+### Hanger points and operating weights are [[drawing: as indicated on the terminal unit schedule]].
+
+### Hanger attachment to structure shall comply with the support provisions of the SMACNA HVAC Duct Construction Standards.
+
+### Units shall be installed level within the tolerance the manufacturer publishes, so that a coil drains as designed and a gravity backdraft damper seats.
+
+## Primary Inlet Duct Connection {toc}
+
+### The primary inlet duct shall connect to the unit inlet collar with the straight duct length required by this standard, measured from the face of the collar to the nearest fitting, transition, or damper.
+
+### Flexible duct shall not be used within the required straight duct length at the unit inlet.
+
+### Where flexible duct is used beyond the required straight duct length, it shall be fully extended and shall comply with the support, bend radius, and length provisions of [[sync/hvac-ductwork]].
+
+### The joint between the inlet duct and the unit collar shall be mechanically fastened and sealed to the duct seal class established in [[sync/hvac-ductwork]].
+
+### A balancing damper shall not be installed within the required straight duct length upstream of the unit inlet.
+
+## Outlet Duct Connection {toc}
+
+### The outlet duct shall connect to the unit outlet with a transition appropriate to the outlet shape and dimensions, and shall be sealed to the duct seal class established in [[sync/hvac-ductwork]].
+
+### Where a single unit serves multiple outlets through a common downstream plenum, the plenum shall be sized so that the velocity through it does not exceed the value used in the discharge sound estimate for that unit.
+
+### Where the manufacturer publishes a downstream straight duct length required to achieve the rated discharge sound, that length shall be provided before the first branch, fitting, or outlet.
+
+## Hydronic and Steam Piping Connections {toc}
+
+### Hot water, steam, and condensate piping serving reheat coils shall comply with [[sync/hydronic-piping]].
+
+### Each hot water coil shall be served by an isolation valve on the supply, an isolation valve on the return, a strainer ahead of the control valve, a means of balancing or a pressure-independent control valve, a high-point air vent, and a low-point drain.
+
+### Piping at the unit shall be supported independently of the terminal unit so that no piping load is carried by the casing or the coil connections.
+
+### Piping shall be arranged so that the coil can be removed without dismantling the piping beyond the isolation valves.
+
+### Hot water and steam piping within a conditioned or unconditioned plenum shall be insulated continuously, and the insulation shall not be interrupted at the unit connection.
+
+### An uninsulated run of reheat piping in a return plenum heats the return air, which the central system reads as a rise in return temperature and answers by cooling harder. The load is real, it is present at every hour the heating plant is up, and it does not appear in any zone-level measurement. {note}
+
+## Electric Power Connections {toc}
+
+### Electric heater branch circuits shall comply with NFPA 70 Article 424.
+
+### Each electric heater shall be served by a branch circuit sized for the heater nameplate load as a continuous load, with overcurrent protection coordinated with the heater manufacturer's published requirement.
+
+### A disconnecting means shall be provided in accordance with the disconnecting means selection indicated in the datasheet, and where a lockable means at the branch panelboard is selected, the panelboard shall be permanently labeled with the unit tags it serves.
+
+### Fan motor branch circuits shall be sized and protected for the motor nameplate data furnished with the approved submittal.
+
+## Control Wiring {toc}
+
+### Control wiring between the terminal unit controller, the zone sensor, the network trunk, and any auxiliary input shall be Class 2 cable installed in accordance with NFPA 70.
+
+### Cable installed in a ceiling plenum or other air-handling space shall be listed for that use.
+
+### Network trunk wiring shall be the twisted shielded pair the controller manufacturer specifies, with the shield continuous through every device and grounded at one point only.
+
+### Control wiring shall be routed and supported separately from line-voltage power wiring, and shall not be laid on ceiling tile, on pipe insulation, or on the terminal unit casing.
+
+### A shield grounded at more than one point creates a current path through the shield that couples noise into the signal it was installed to protect, and the symptom is an intermittent communication fault that moves around the trunk as devices are added. {note}
+
+## Pre-Startup Inspection {toc}
+
+### Before the terminal units are energized and the central air system is started, the Contractor shall confirm the following at each unit:
+
+- Shipping restraints, blocking, and protective films have been removed
+- The primary damper strokes freely from closed to full open
+- Airflow sensor tubing is connected at the sensing element and at the controller, and is free of kinks, crimps, and disconnected fittings
+- The hot water or steam coil is filled, vented, and pressure tested in accordance with [[sync/hydronic-piping]]
+- The electric heater branch circuit is energized, control power is present at the heater, and the airflow proving device reads a no-flow condition
+- The fan and motor assembly rotates freely and in the correct direction
+- Network communication is established with the controller at its assigned address
+- The zone sensor is connected and reporting a plausible space temperature
+- Access panels are closed and the ceiling is complete
+
+```datasheet
+label: Pre-Startup Inspection Checklist
+type: checkbox
+options:
+ - "Shipping restraints and protective films removed"
+ - "Primary damper strokes freely through its full range"
+ - "Airflow sensor tubing connected and intact"
+ - "Reheat coil filled, vented, and pressure tested"
+ - "Electric heater circuit energized and airflow proving device verified"
+ - "Fan and motor rotate freely in the correct direction"
+ - "Network communication established at the assigned address"
+ - "Zone sensor connected and reporting a plausible temperature"
+ - "Access panels closed and ceiling complete"
+default:
+ - "Shipping restraints and protective films removed"
+ - "Primary damper strokes freely through its full range"
+ - "Airflow sensor tubing connected and intact"
+ - "Network communication established at the assigned address"
+ - "Zone sensor connected and reporting a plausible temperature"
+ - "Access panels closed and ceiling complete"
+```
+
+### Terminal units shall not be operated to provide temporary heating, cooling, or ventilation during construction unless the Engineer of Record accepts the temporary use in writing and the Contractor replaces every filter and cleans every unit so operated before Substantial Completion.
+
+# Field Testing and Commissioning {toc}
+
+## Airflow Verification {toc}
+
+### The testing and balancing agent shall verify the primary airflow at each unit at the cooling maximum, the cooling minimum, and the heating airflow setpoint, in accordance with [[sync/testing-adjusting-and-balancing]].
+
+### The airflow verification tolerance shall be as indicated in the datasheet, applied as a plus-or-minus band about the commanded value at each setpoint.
+
+```datasheet
+label: Airflow Verification Tolerance at Each Setpoint
+type: range
+unit: '%'
+min: 2
+max: 20
+setpoints: [2, 5, 10, 15, 20]
+default: 10
+```
+
+### Airflow verification shall be performed with the system clean, the design filter media installed, the ceiling complete, and the central system operating at its design static pressure control setpoint.
+
+### Where measured airflow at a setpoint falls outside the tolerance, the calibration constant for that unit shall be adjusted against a calibrated reference instrument and the setpoint reverified.
+
+### The as-left calibration constant and every as-commissioned setpoint shall be recorded for each unit in the field commissioning record.
+
+### Where a unit cannot be brought within tolerance by adjustment of its calibration constant and its branch damper, the testing and balancing agent shall report the condition to the Engineer of Record rather than adjusting the setpoint to match the measurement.
+
+### Adjusting the commanded setpoint until it matches what the unit actually delivers makes the balancing report agree with itself and leaves the zone with an airflow the ventilation calculation never contemplated. The report then certifies the wrong number for the life of the building. {note}
+
+## Functional Performance Testing {toc}
+
+### The extent of functional performance testing shall be as indicated in the datasheet.
+
+```datasheet
+label: Extent of Functional Performance Testing
+type: radio
+options:
+ - "Not required"
+ - "Representative sample of units of each configuration"
+ - "Every installed unit"
+```
+
+### Where functional performance testing is required, it shall be conducted in accordance with ANSI/ASHRAE 202 and shall verify the zone control sequence in occupied, unoccupied, and override modes.
+
+### Functional performance testing shall verify the reheat output through its full range, the fan operation and induced airflow where a fan section is furnished, the airflow proving interlock where an electric heater is furnished, and the reporting of every hardwired and calculated point at the operator workstation.
+
+### Where a functional performance test fails, the Contractor shall correct the deficiency and shall bear the cost of retesting that unit.
+
+### Where a sample-based extent is selected and a unit in the sample fails, the sample for that configuration shall be doubled at the Contractor's expense.
+
+## Acoustic Verification {toc}
+
+### The extent of field acoustic verification shall be as indicated in the datasheet.
+
+```datasheet
+label: Extent of Field Acoustic Verification
+type: radio
+options:
+ - "Not required"
+ - "Required in spaces with a sound limit of NC 30 or lower"
+ - "Required in a representative space of each space type"
+ - "Required in every space served by a terminal unit"
+default: "Not required"
+```
+
+### Where acoustic verification is required, sound pressure shall be measured in octave bands at the listener position with the system operating at design airflow, with the space otherwise quiet, and the result evaluated to ANSI/ASA S12.2.
+
+### Where a measured level exceeds the specified limit and the excess is attributable to the terminal unit or its installation, the Contractor shall correct the condition and shall bear the cost of re-measurement.
+
+### Where a measured level exceeds the specified limit and the excess is attributable to a source outside the scope of this standard, the Engineer of Record shall determine the responsible scope.
+
+### Corrective actions available for an excess attributable to the terminal unit include lowering the central system static pressure setpoint through reset, adding a lined discharge plenum, upgrading the ceiling construction below the unit, and substituting a unit with a larger casing and a lower face velocity. {note}
+
+# Delivery, Storage, and Handling {toc}
+
+## Terminal units shall be delivered in the manufacturer's packaging with each unit marked with its project tag and with the inlet and outlet openings sealed against construction dust.
+
+## Terminal units shall be stored indoors in a clean, dry, weather-protected space until installation.
+
+## Terminal units shall not be stored on bare ground or bare slab, in standing water, or in a space subject to freezing or to water intrusion.
+
+## Stacked units shall be supported only at the corner brackets, shall not exceed the stack height the manufacturer publishes, and shall not bear on the casing wrapper.
+
+## Where a hot water or steam coil may be exposed to a storage temperature below 35 °F, the coil shall be drained, blown clear with compressed air, and tagged as drained, and a corresponding entry shall be made on the unit tag schedule so that the coil is refilled and vented before startup.
+
+## Where the ceiling is not ready to receive terminal units, the Contractor shall hold the units in protected storage rather than installing them and covering the openings.
+
+# Identification {toc}
+
+## Each terminal unit shall be furnished with a permanent identification label applied to the casing exterior in a location visible from below the finished ceiling.
+
+## The identification label shall state the unit tag matching the unit schedule, the manufacturer's model and serial number, the primary maximum and minimum airflow setpoints, the reheat capacity where reheat is furnished, the electrical characteristics where an electrical connection is made, the controller address where a controller is furnished, and the date of manufacture.
+
+## Identification labels shall not be applied to a removable access panel.
+
+## The identification nameplate material shall be as indicated in the datasheet.
+
+```datasheet
+label: Identification Nameplate Material
+type: radio
+options:
+ - "Adhesive laminated label"
+ - "Engraved phenolic plate, mechanically fastened"
+ - "Etched stainless steel plate, mechanically fastened"
+default: "Adhesive laminated label"
+```
+
+## Where a unit is replaced or its configuration is changed after the label is applied, the label shall be replaced to reflect the as-installed configuration.
+
+# Warranty {toc}
+
+## The manufacturer shall warrant each terminal unit against defects in material and workmanship for the period indicated in the datasheet, beginning at the date of Substantial Completion.
+
+```datasheet
+label: Equipment Warranty Period
+type: range
+unit: years
+min: 1
+max: 5
+setpoints: [1, 2, 3, 5]
+default: 1
+```
+
+## The equipment warranty shall cover the casing, the liner, the damper and its actuator, the airflow sensing element, the reheat coil or heater, the control valve and its actuator, the fan and motor, and the controller where the controller is furnished by the terminal unit manufacturer.
+
+## The manufacturer shall warrant the fan motor and its integral electronics for the period indicated in the datasheet, beginning at the date of Substantial Completion.
+
+```datasheet
+label: Fan Motor Warranty Period
+type: range
+unit: years
+min: 1
+max: 10
+setpoints: [1, 2, 3, 5, 7, 10]
+default: 5
+```
+
+## The manufacturer shall warrant the reheat coil against leakage in the tube and fin assembly for the period indicated in the datasheet, beginning at the date of Substantial Completion.
+
+```datasheet
+label: Reheat Coil Warranty Period
+type: range
+unit: years
+min: 1
+max: 10
+setpoints: [1, 2, 3, 5, 10]
+default: 1
+```
+
+## The Contractor shall warrant the installation, including hangers, duct and piping connections, electrical connections, control wiring, sealing, and identification, for one year from the date of Substantial Completion.
+
+## Warranty coverage shall include the cost of removing and reinstalling the ceiling, ductwork, and piping disturbed to reach a unit being repaired or replaced, and the cost of repairing collateral damage caused by that work.
+
+## Where a unit or a component is repaired or replaced under warranty, the repaired or replacement item shall carry a fresh warranty of the full original period from the date of the repair, or the remainder of the original period, whichever ends later.
+
+## The Contractor shall keep every installed unit accessible during the warranty period by keeping access panels, ceiling tiles, and adjacent construction clear of permanent obstruction.
+
+## The manufacturer shall maintain factory-trained service capability within the region of the project for the duration of the equipment warranty period.
+
+# Spare Parts {toc}
+
+## The Contractor shall deliver the following to the Owner at Substantial Completion:
+
+- One damper actuator for each actuator model installed
+- One control valve actuator for each valve size and model installed
+- One fan motor for each motor size installed on fan-powered units
+- One terminal unit controller for each controller model installed
+- Zone temperature sensors equal to five percent of the installed quantity, and not fewer than two
+- One primary thermal cutout and one secondary thermal cutout for each electric heater model installed
+- One set of induced-air filters for each filter size installed on fan-powered units
+
+```datasheet
+label: Spare Parts at Substantial Completion
+type: checkbox
+options:
+ - "One damper actuator for each actuator model"
+ - "One control valve actuator for each valve size and model"
+ - "One fan motor for each motor size on fan-powered units"
+ - "One terminal unit controller for each controller model"
+ - "Zone temperature sensors equal to five percent of the installed quantity"
+ - "One primary and one secondary thermal cutout for each heater model"
+ - "One set of induced-air filters for each filter size"
+default:
+ - "One damper actuator for each actuator model"
+ - "One control valve actuator for each valve size and model"
+ - "One terminal unit controller for each controller model"
+ - "Zone temperature sensors equal to five percent of the installed quantity"
+```
+
+## Spare parts shall be delivered in the manufacturer's original packaging, each tagged with the model number, the unit tags it serves, and the date of delivery.
+
+## Spare parts shall be turned over at a storage location the Owner designates, and the transfer shall be documented in the closeout submittal.
+
+## The operation and maintenance manual shall include a spare parts inventory listing the manufacturer part number and reorder information for every component of the units furnished, so that additional spares can be procured over the service life of the installation.