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Dedicated Outdoor Air Systems

Rev8
IssuedOct 12, 2026
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1 Scope

NOTE A dedicated outdoor air unit conditions the building's ventilation air and nothing else. It draws 100% outdoor air, recovers energy from the exhaust where the code or the project calls for it, cools the air below the dew point the spaces need and holds that dew point, reheats the air to a chosen supply temperature, tempers it in winter, filters it, and delivers it either to the spaces or to the inlets of the parallel equipment that carries the sensible load. What separates it from a mixed-air air handler is that the latent load of the building is assigned to this one unit and the dry-bulb load to other equipment, so the leaving air dew point rather than the supply air temperature is the quantity the unit is selected and controlled on. (1.1)
NOTE The following are covered when they form part of the unit: (1.2)
  • Casing, base, access provisions, and exterior finish
  • Supply fan, exhaust fan, motors, and drives
  • The air-to-air energy recovery section, its purge and frost control provisions, and its bypass
  • Direct-expansion and heat pump refrigerant circuits, compressors, condensers, and expansion devices
  • Chilled water cooling coils
  • Hot gas, wraparound, sensible wheel, hydronic, and electric reheat sections
  • Heat pump, gas-fired, electric resistance, hydronic, and steam heating sections
  • Refrigerant detection and mitigation provisions
  • Filter sections on the outdoor air and exhaust air streams
  • Outdoor air and exhaust air dampers, hoods, and louvers furnished with the unit
  • Drain pans, condensate connections, and traps
  • Humidifier sections furnished within the unit
  • Roof curb, vibration isolation, and seismic and wind restraint at the curb
  • Unit-mounted controls, the dew point and supply air temperature control sequence, safety devices, and the physical interface to the building automation system
  • Rigging, setting, connection, startup, and commissioning of the installed unit
NOTE The following are outside this standard: (1.3)
  • Ductwork, duct accessories, and duct insulation beyond the unit connections, covered by HVAC DuctworkHVAC DuctworkResolves to the current adopted revision.sync/hvac-ductwork, Duct AccessoriesHVAC Duct AccessoriesResolves to the current adopted revision.sync/duct-accessories, and Mechanical InsulationMechanical InsulationResolves to the current adopted revision.sync/mechanical-insulation
  • Central station air handling units, whether mixed-air or field-erected for 100% outdoor air without a packaged dew point sequence, covered by Air Handling UnitsAir Handling UnitsResolves to the current adopted revision.sync/air-handling-units
  • Packaged rooftop units that mix return air, covered by Packaged Rooftop UnitsPackaged Rooftop UnitsResolves to the current adopted revision.sync/packaged-rooftop-units
  • Make-up air units that replace exhausted air to hold building pressure without controlling leaving air dew point, covered by Makeup Air UnitsMakeup Air UnitsResolves to the current adopted revision.sync/makeup-air-units
  • Stand-alone packaged energy recovery ventilators, and the recovery component as a rated product, covered by Energy Recovery VentilatorsEnergy Recovery VentilatorsResolves to the current adopted revision.sync/energy-recovery-ventilators
  • The parallel sensible equipment the unit works alongside, covered by Variable Refrigerant Flow SystemsVariable Refrigerant Flow (VRF) SystemsResolves to the current adopted revision.sync/variable-refrigerant-flow-systems, Fan Coil UnitsFan-Coil UnitsResolves to the current adopted revision.sync/fan-coil-units, Water Source Heat PumpsWater-Source Heat PumpsResolves to the current adopted revision.sync/water-source-heat-pumps, Chilled BeamsActive and Passive Chilled BeamsResolves to the current adopted revision.sync/chilled-beams, and Air Terminal UnitsAir Terminal UnitsResolves to the current adopted revision.sync/air-terminal-units
  • Field refrigerant piping between a split unit and its remote condensing section, covered by Refrigerant PipingRefrigerant PipingResolves to the current adopted revision.sync/refrigerant-piping
  • Field-installed and replacement coils, covered by Heating And Cooling CoilsHeating and Cooling CoilsResolves to the current adopted revision.sync/heating-and-cooling-coils
  • The humidifier equipment itself, covered by HumidifiersHumidifiersResolves to the current adopted revision.sync/humidifiers
  • An indirect or direct evaporative stage built into the unit, covered by Evaporative CoolersEvaporative CoolersResolves to the current adopted revision.sync/evaporative-coolers
  • Hydronic piping, valves, and specialties serving the coils, covered by Hydronic PipingHydronic PipingResolves to the current adopted revision.sync/hydronic-piping
  • Gas piping to the unit connection, covered by Natural Gas PipingNatural Gas PipingResolves to the current adopted revision.sync/natural-gas-piping and Fuel Gas PipingFacility Liquefied-Petroleum and Fuel Gas PipingResolves to the current adopted revision.sync/fuel-gas-piping
  • Condensate drain piping beyond the unit trap, covered by Condensate Drainage PipingHVAC Condensate Drainage PipingResolves to the current adopted revision.sync/condensate-drainage-piping
  • The roofing membrane and the flashing of the curb into it, covered by Membrane RoofingMembrane RoofingResolves to the current adopted revision.sync/membrane-roofing and Sheet Metal Flashing And TrimSheet Metal Flashing and TrimResolves to the current adopted revision.sync/sheet-metal-flashing-and-trim
  • The building automation system, its supervisory sequences, and control devices not mounted on the unit, covered by Building Automation SystemBuilding Automation SystemResolves to the current adopted revision.sync/building-automation-system and HVAC Controls InstrumentationHVAC Instrumentation and Control DevicesResolves to the current adopted revision.sync/hvac-controls-instrumentation
  • The fire alarm system that receives the duct smoke detector signal, covered by Fire Alarm SystemsFire Alarm SystemsResolves to the current adopted revision.sync/fire-alarm-systems
  • Testing, adjusting, and balancing of the completed system, covered by Testing Adjusting And BalancingTesting, Adjusting, and Balancing for HVACResolves to the current adopted revision.sync/testing-adjusting-and-balancing
NOTE Where the unit supplies make-up air to laboratory spaces, the exhaust system, the hood performance, and the room pressure relationship are covered by Laboratory Exhaust And Fume HoodsLaboratory Exhaust and Fume HoodsResolves to the current adopted revision.sync/laboratory-exhaust-and-fume-hoods; this standard covers the outdoor air unit that feeds that make-up. (1.4)
1.5 Each unit shall be furnished as a complete assembly by a single manufacturer, who shall be responsible for the energy recovery, refrigeration, dehumidification, reheat, heating, air-side, and control performance of the unit as a whole.
NOTE The interaction of the recovery device, the cooling coil, and the reheat source is what decides whether the unit holds its leaving air dew point, and that interaction is resolved at the factory on a packaged unit or not at all. A unit assembled in the field from separately procured sections has no party who owns the dew point. (1.6)
1.7 The unit locations and tags shall be as indicated on the mechanical plans.
NOTE Per-tag quantities are scheduled and project-wide policy is selected in the datasheet. Airflows, static pressures, leaving air dew point, capacities, heating inputs, and electrical characteristics vary with every unit on the project and live on the mechanical equipment schedule; the construction, options, control strategy, and warranty decisions that apply to every unit on the project are made once here. (1.8)
1.9 Where a requirement of this standard conflicts with a requirement of a standard that governs a connected system, the Engineer of Record shall make the initial determination of which requirement governs.

2 Referenced Standards

2.1 Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
2.2 Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
Standard Title
ANSI/AHRI 920 (I-P) Performance Rating of Direct Expansion-Dedicated Outdoor Air System Units
ANSI/AHRI 1060 (I-P) Performance Rating of Air-to-Air Exchangers for Energy Recovery Ventilation Equipment
ANSI/AHRI 410 Performance Rating of Forced-Circulation Air-Cooling and Air-Heating Coils
ANSI/AHRI 430 (I-P) Performance Rating of Central Station Air-handling Unit Supply Fans
ANSI/AHRI 270 Sound Performance Rating of Outdoor Unitary Equipment
ANSI/AHRI 370 Sound Performance Rating of Large Air-cooled Outdoor Refrigerating and Air-conditioning Equipment
ANSI/ASHRAE 62.1 Ventilation and Acceptable Indoor Air Quality
ANSI/ASHRAE/IES 90.1 Energy Standard for Sites and Buildings Except Low-Rise Residential Buildings
ANSI/ASHRAE 55 Thermal Environmental Conditions for Human Occupancy
ANSI/ASHRAE 15 Safety Standard for Refrigeration Systems
ANSI/ASHRAE 34 Designation and Safety Classification of Refrigerants
ANSI/ASHRAE 52.2 Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size
ANSI/ASHRAE 84 Method of Testing Air-to-Air Heat/Energy Exchangers
ANSI/ASHRAE 170 Ventilation of Health Care Facilities
ANSI/AMCA 210 / ANSI/ASHRAE 51 Laboratory Methods of Testing Fans for Certified Aerodynamic Performance Rating
ANSI/AMCA 300 Reverberant Room Method for Sound Testing of Fans
ANSI/AMCA 500-D Laboratory Methods of Testing Dampers for Rating
ANSI/AMCA 500-L Laboratory Methods of Testing Louvers for Rating
ANSI/AMCA 610 Laboratory Methods of Testing Airflow Measurement Stations for Performance Rating
UL 60335-2-40 Household and Similar Electrical Appliances - Safety - Particular Requirements for Electrical Heat Pumps, Air-Conditioners and Dehumidifiers
UL 1995 Heating and Cooling Equipment
UL 900 Air Filter Units
UL 508A Industrial Control Panels
ANSI Z21.47 / CSA 2.3 Gas-Fired Central Furnaces
ANSI Z83.8 / CSA 2.6 Gas Unit Heaters, Gas Packaged Heaters, Gas Utility Heaters, and Gas-Fired Duct Furnaces
NFPA 54 / ANSI Z223.1 National Fuel Gas Code
NFPA 70 National Electrical Code
NFPA 72 National Fire Alarm and Signaling Code
NFPA 90A Standard for the Installation of Air-Conditioning and Ventilating Systems
NEMA MG 1 Motors and Generators
ASTM A653 Steel Sheet, Zinc-Coated or Zinc-Iron Alloy-Coated by the Hot-Dip Process
ASTM B117 Operating Salt Spray (Fog) Apparatus
ASCE 7 Minimum Design Loads and Associated Criteria for Buildings and Other Structures
IMC International Mechanical Code
IECC International Energy Conservation Code
SMACNA HVAC Duct Construction Standards HVAC Duct Construction Standards - Metal and Flexible
40 CFR Part 82 Subpart F Recycling and Emissions Reduction
40 CFR Part 84 Phasedown of Hydrofluorocarbons, Technology Transition

3 Submittals

3.1 Action Submittals

3.1.1 The Contractor shall submit the following for each unit tag:
  • Unit configuration drawing showing the section sequence from the outdoor air intake to the supply connection and from the exhaust inlet to the exhaust discharge, overall dimensions, connection sizes and locations, operating and shipping weights, center of gravity, corner weights, and the service clearances on every side
  • A psychrometric analysis plotting the state of the air entering the unit, leaving the energy recovery section, leaving the cooling coil, leaving the reheat section, and leaving the unit, at the dehumidification design condition and at the heating design condition, with the leaving air dew point and supply air temperature stated at each
  • Certified performance under the certification program indicated in the datasheet, giving the moisture removal capacity and the rated efficiency metrics, and for heat pump units the heating capacity and efficiency, at the standard rating conditions and at the project design conditions
  • Dehumidification capacity at the design condition and at the minimum capacity step of the unit, demonstrating the leaving air dew point held at each
  • Energy recovery data giving the device type, the sensible, latent, and total effectiveness at the design airflows, the exhaust air transfer ratio and outdoor air correction factor, the pressure drop added to each airstream, the frost control method and its initiation temperature, and the purge arrangement where furnished
  • Refrigerant designation, safety group, and factory charge by circuit, and where a refrigerant detection system is furnished, the sensor locations, the mitigation action, and the charge limit the listing establishes for the unit
  • Compressor data giving type, quantity, capacity control method, and the minimum capacity step
  • Reheat section data giving the reheat source, the capacity available at the design condition, and the control method
  • Heating section data giving input and output for gas-fired sections with the certification identified, capacity and stage count for electric sections, integrated heating capacity at the outdoor design temperature and at the compressor heating operation limit for heat pumps, and coil selection data for hydronic and steam sections
  • Coil selection data for every coil, giving entering and leaving air conditions, face velocity, rows, fin spacing, fin and tube material and any coating, and air-side and fluid-side pressure drop
  • Supply and exhaust fan selection data showing the certified fan curve with the design operating point plotted against the calculated system resistance, the shaft power at that point, and the fan power compliance calculation
  • Motor data giving nameplate power, speed, voltage, phase, full-load amperes, efficiency, enclosure, and inverter-duty rating where applicable
  • Sound power levels for the outdoor radiated path under the applicable sound rating program, and for the supply discharge, the outdoor air intake, and the exhaust discharge in octave bands
  • Casing construction details giving panel construction, insulation type and thermal resistance, casing air leakage, exterior finish and its salt spray rating, and access panel arrangement
  • Filter data for each filter bank giving efficiency rating, depth, quantity and size, initial resistance, and recommended change-out resistance
  • Drain pan drawing giving material, slope, extent, connection size and location, and the trap arrangement
  • Roof curb drawing giving curb height, plan dimensions, insulation, wood nailer, opening locations, cross supports, gasketing, and the unit-to-curb attachment
  • Vibration isolation data and, where restraint is required, seismic and wind restraint details and calculations bearing the seal of an engineer licensed in the jurisdiction of the project
  • Electrical data giving minimum circuit ampacity, maximum overcurrent protective device, short-circuit current rating of the control panel, disconnect configuration, and the wiring diagram with field termination points
  • Unit controller data giving the control configuration, the written dew point and supply air temperature sequence, the communication interface, and a complete point list with object names, types, units, and read or write access
Action Submittals Requiredcheckbox
☑ Unit configuration drawing with weights and service clearances
☑ Psychrometric analysis at the design conditions
☑ Certified performance and efficiency ratings
☑ Dehumidification capacity at design and at minimum capacity
☑ Energy recovery data
☑ Refrigerant, charge, and detection system data
☑ Compressor and capacity control data
☑ Reheat section data
☑ Heating section data
☑ Coil selection data
☑ Certified fan curves and fan power compliance
☑ Motor data
☑ Sound power levels
☑ Casing construction details
☑ Filter data
☑ Drain pan and trap drawing
☑ Roof curb drawing
☑ Vibration isolation and restraint data
☑ Electrical data and wiring diagram
☑ Unit controller data, sequence, and point list
3.1.2 No unit shall be released for fabrication until the action submittal for that unit has been reviewed and returned.
3.1.3 The psychrometric analysis shall be prepared at the dehumidification design condition indicated in the datasheet and not at the cooling dry-bulb design condition alone.
NOTE The psychrometric analysis is the submittal that proves the unit. A catalog capacity at a standard rating point says nothing about whether the recovery section, the coil, and the reheat together reach the scheduled dew point on the site's wettest design hour, and the state points are what the reviewer checks against the schedule and what the commissioning agent later compares the running unit to. (3.1.4)

3.2 Informational Submittals

3.2.1 The Contractor shall submit the following for information at the times indicated in each item:
  • Rigging and setting plan, submitted before the unit ships, showing the crane location, the pick radius, the lifting points and spreader arrangement, and the temporary loads imposed on the roof structure
  • Refrigerant handling certification under 40 CFR Part 82 Subpart F for every individual who will open, evacuate, charge, or recover a refrigerant circuit on the project
  • Evidence of training in mildly flammable refrigerant handling for every individual who will work on a unit carrying a refrigerant in a flammable safety group
  • Manufacturer's field service report for each site visit made during the warranty period
  • Written record of the pre-existing condition of any roofing or adjacent surface the Contractor is required to restore
Informational Submittals Requiredcheckbox
☑ Rigging and setting plan before shipment
☑ Refrigerant handling certifications
☐ Flammable refrigerant training records
☑ Field service reports during the warranty period
☐ Pre-existing condition record for restored surfaces

3.3 Closeout Submittals

3.3.1 The Contractor shall submit the following at or before substantial completion:
  • Operation and maintenance manuals for each unit, indexed by unit tag, containing installation, operation, maintenance, and troubleshooting instructions, a parts list for every furnished component, and the maintenance schedule for filters, coils, the recovery device and its seals and drive, the condensate system, belts, and refrigerant detection sensors
  • As-built wiring diagrams and the building automation system point list with the terminal designations used on the unit
  • Certified factory run-test report for each unit
  • Startup report for each unit signed by the person who performed the startup, recording refrigerant charge by circuit, operating pressures and temperatures, motor current, the measured leaving air dew point and supply air temperature, and the setpoint of every safety device
  • Refrigerant charge record for each unit giving the refrigerant designation, the factory charge by circuit, and any field adjustment with the weight added or removed
  • Commissioning record demonstrating dew point control, reheat and supply air temperature control, energy recovery operation and frost control, the interlock to the parallel sensible system, safety lockouts, and refrigerant detection and mitigation where furnished
  • Air balance report for the units and their connected systems, recording the outdoor and exhaust airflows through the recovery device
  • Record of the filter media installed at substantial completion, giving efficiency rating, quantity, size, and installation date
  • Warranty documentation correlating each unit serial number to its installation date and to the expiration date of the unit, compressor, recovery component, and heat exchanger warranties
  • Signed receipt from the Owner for the spare parts delivered
Closeout Submittals Requiredcheckbox
☑ Operation and maintenance manuals indexed by unit tag
☑ As-built wiring diagrams and point list
☑ Certified factory run-test report for each unit
☑ Signed startup report for each unit
☑ Refrigerant charge record for each unit
☑ Commissioning record
☑ Air balance report with recovery device airflows
☑ Installed filter media record
☑ Warranty documentation correlated to serial numbers
☑ Spare parts receipt

4 Quality Assurance

4.1 Manufacturer Qualifications

4.1.1 The unit manufacturer shall have produced packaged dedicated outdoor air equipment of the type furnished for not less than the number of years indicated in the datasheet.
Manufacturer Experiencerange
years
025
Default: Not less than 5 years
4.1.2 The manufacturer shall make replacement parts available for the units furnished for not less than ten years after the date of manufacture.
NOTE An experience requirement is a proxy for production maturity, not a measure of it, and it excludes new entrants along with unproven ones. A project prepared to accept a well-capitalized new manufacturer can set the requirement to zero and rely on the certification, testing, and warranty requirements instead. (4.1.3)

4.2 Performance Certification

4.2.1 Published dehumidification capacity and efficiency ratings shall be certified under the program indicated in the datasheet.
Unit Performance Certification Programradio
○ AHRI 920
○ No unit certification program applies
Derived — the cooling source selected in the datasheet, with direct-expansion and heat pump units rated under AHRI 920 and chilled water units outside any unit certification program (by default)
4.2.2 Units rated under AHRI 920 shall bear the certification mark of that program, and the integrated seasonal moisture removal efficiency and, for heat pump units, the integrated seasonal coefficient of performance stated in the submittal shall be the certified values.
4.2.3 Where no unit certification program applies, the manufacturer shall state that fact in the submittal and shall furnish the test data on which the published capacity is based.
4.2.4 The energy recovery component shall be rated under AHRI 1060 and tested in accordance with ANSI/ASHRAE 84, and the published effectiveness, exhaust air transfer ratio, and outdoor air correction factor shall bear the AHRI certification mark.
4.2.5 Coils shall be rated in accordance with AHRI 410.
4.2.6 Fan performance shall be rated from tests in accordance with ANSI/AMCA 210.
4.2.7 Capacities and efficiencies stated in the submittal shall be the certified ratings and not uncertified catalog selections.
NOTE AHRI 920 rates a direct-expansion dedicated outdoor air unit on the moisture it removes per unit of electrical energy across a set of outdoor conditions, which is the quantity the unit exists to deliver, rather than on the cooling capacity a comfort unit is rated on. A chilled water unit has no compressor to meter, so the program does not cover it and its capacity rests on the coil rating and the manufacturer's test. (4.2.8)

4.3 Safety Listing

4.3.1 The complete unit, including every factory-installed electrical and refrigerant-system component, shall be listed and labeled by a Nationally Recognized Testing Laboratory under the standard indicated in the datasheet.
Unit Safety Listing Standardradio
○ UL 60335-2-40
○ UL 1995
4.3.2 A unit charged with a refrigerant in a flammable safety group shall be listed under UL 60335-2-40.
4.3.3 Units listed to UL 1995 are acceptable only where the refrigerant is in a nonflammable safety group and the Authority Having Jurisdiction accepts that listing for the equipment furnished.
4.3.4 Gas-fired heating sections shall additionally be certified to ANSI Z21.47 / CSA 2.3, or to ANSI Z83.8 / CSA 2.6 where the section is a duct furnace.
4.3.5 Factory-wired control panels shall be listed to UL 508A.
4.3.6 Each factory-wired control panel shall bear a label giving the short-circuit current rating of the panel.
NOTE UL 60335-2-40 is the listing standard that contains the charge limits, the refrigerant detection requirements, and the mitigation logic for mildly flammable refrigerants, which is why a flammable-refrigerant unit cannot be listed under the older standard. For a nonflammable refrigerant, both listings cover the same hazards and the choice follows the manufacturer's certification history and what the Authority Having Jurisdiction has seen before. (4.3.7)

4.4 Refrigerant Handling Qualification

4.4.1 Refrigerant circuits shall be opened, evacuated, charged, and recovered only by an individual certified under 40 CFR Part 82 Subpart F.
4.4.2 Where the unit carries a refrigerant in a flammable safety group under ASHRAE 34, the individuals working on the circuit shall have completed training covering the handling, storage, leak response, and tool requirements that apply to that refrigerant.
4.4.3 Recovery machines, vacuum pumps, manifolds, leak detectors, and charging equipment used on a unit carrying a refrigerant in a flammable safety group shall be rated by their makers for that service.

4.5 Preinstallation Conference

4.5.1 A preinstallation conference shall be held before the first unit is set, attended by the Contractor, the mechanical installer, the roofing installer where units are curb-mounted, the electrical installer, the controls installer, the installer of the parallel sensible system, the testing and balancing agent, the commissioning agent where one is engaged, and the Owner's representative.
4.5.2 The conference agenda shall cover the curb setting and flashing sequence, the structural readiness at each unit location, the crane plan, the utility connections and their sequence, the refrigerant safety provisions, the division of control responsibility between the unit controller, the parallel system, and the building automation system, and the startup and commissioning schedule including any seasonal test that cannot be run at substantial completion.

5 Service Conditions and Site Data

5.1 Dehumidification Design Condition

5.1.1 Each unit shall be selected to deliver its scheduled leaving air dew point at the dehumidification design outdoor air condition indicated in the datasheet.
Dehumidification Design Outdoor Air Conditiontext
Enter value...
Per drawings — the mechanical equipment schedule (deferred by default)
5.1.2 The dehumidification design condition shall be the outdoor dew point design condition with its mean coincident dry-bulb for the project location, and not the cooling dry-bulb design condition.
5.1.3 Each unit shall also deliver its scheduled supply air temperature at Site Ambient Temperature MaximumSite Ambient Temperature MaximumParameterEach project supplies its own value.site-ambient-temperature-maximum with the condenser coil clean.
NOTE The hottest hour of the year is rarely the wettest. The peak dry-bulb hour pairs a high temperature with a moderate humidity ratio, while the peak dew point hour pairs a moderate temperature with the highest moisture content the site sees, and it is the second one that loads a coil whose job is to remove moisture. A unit selected at the dry-bulb design can be short on latent capacity on an overcast, humid afternoon by a margin that the dry-bulb selection never reveals. (5.1.4)

5.2 Heating Design Condition

5.2.1 The heating capacity of each unit, net of energy recovery, at Site Ambient Temperature MinimumSite Ambient Temperature MinimumParameterEach project supplies its own value.site-ambient-temperature-minimum shall be not less than the value required to deliver the scheduled heating-season supply air temperature at the design outdoor airflow.
5.2.2 The integrated heating capacity of each heat pump unit at Site Ambient Temperature MinimumSite Ambient Temperature MinimumParameterEach project supplies its own value.site-ambient-temperature-minimum shall be stated in the submittal.
NOTE A unit handling 100% outdoor air sees the full winter design temperature at its entering face with no return air to temper it, so the heating section is sized on the design outdoor airflow and the full temperature rise from outdoor design to supply setpoint, less only what the recovery device returns. The recovery contribution at the design hour is itself reduced by frost control, which is why the capacity is stated net of recovery as the unit actually operates. (5.2.3)

5.3 Altitude

5.3.1 Cooling, heating, fan, and motor ratings shall be corrected for AltitudeAltitudeParameterEach project supplies its own value.altitude in accordance with the manufacturer's published correction factors.
5.3.2 The altitude-corrected ratings shall be the values published in the submittal.
5.3.3 Gas-fired heating sections shall be de-rated for AltitudeAltitudeParameterEach project supplies its own value.altitude in accordance with the listing and NFPA 54.
5.3.4 The altitude de-rated gas input shall be stated in the submittal.

5.4 Corrosive Atmospheres

5.4.1 The corrosion protection of coils in the outdoor airstream shall be as indicated in the datasheet.
Outdoor Airstream Coil Corrosion Protectionselect
Uncoated aluminum fin on copper tube
Aluminum fin on copper tube with an electrodeposited epoxy coating
Aluminum fin on copper tube with an applied phenolic coating
Copper fin on copper tube
5.4.2 The corrosion protection of the air-cooled condenser coil shall be as indicated in the datasheet.
Condenser Coil Corrosion Protectionselect
Uncoated aluminum fin on copper tube
Aluminum fin on copper tube with an electrodeposited epoxy coating
Aluminum fin on copper tube with an applied phenolic coating
Microchannel aluminum coil with an electrodeposited coating
Copper fin on copper tube
5.4.3 Where a coil coating is selected, the coating shall be applied after fin and tube assembly so that the tube-to-fin interface is coated.
5.4.4 Where a coil coating is selected, the manufacturer shall state in the submittal the salt spray exposure the coated coil has been tested to.
NOTE Every coil in a dedicated outdoor air unit sees the outdoor atmosphere all of the time, not through a return air fraction, and the cooling coil sees it wet for most of the cooling season. Chloride from marine air and sulfur compounds from industrial and vehicular exhaust supply the electrolyte that turns the aluminum-to-copper pair active, so the fin corrodes, the bond to the tube opens, and capacity falls. An electrodeposited coating is applied by immersing the finished coil and curing a uniform film onto every surface, so it protects the fin-to-tube joint where a sprayed coating cannot reach, at the cost of a small thermal resistance the submittal capacity accounts for. (5.4.5)

6 Unit Arrangement

6.1 Unit Construction for Location

6.1.1 The casing construction for the installed location shall be as indicated in the datasheet.
Unit Construction for Locationradio
○ Outdoor weatherproof construction
○ Indoor construction
Derived — the unit location indicated on the mechanical plans, with units set outdoors furnished in weatherproof construction and units set in a mechanical room or penthouse in indoor construction (by default)
6.1.2 Outdoor units shall be furnished with a weatherproof casing, a sloped roof panel, a drainable base rail, a rain hood and bird screen at the outdoor air intake, and a weather hood at the exhaust discharge.
6.1.3 Indoor units shall be furnished with the outdoor air intake and exhaust discharge arranged for duct connection to the building louvers.
NOTE An outdoor unit carries its own weather enclosure and sits where the outdoor air is, which keeps the cold, wet intake duct out of the building; an indoor unit puts the intake and exhaust ducts through the envelope and the condensate, service, and noise inside, and is the arrangement where a roof cannot take the weight, the roof is leased or inaccessible, or the unit is replaced in an existing mechanical room. (6.1.4)

6.2 Refrigeration Arrangement

6.2.1 Requirements in this article apply to units with a direct-expansion refrigerant circuit.
6.2.2 The refrigeration arrangement shall be as indicated in the datasheet.
Refrigeration Arrangementradio
● Packaged, with the condensing section integral to the unit
○ Split, with a remote condensing section and field refrigerant piping
6.2.3 Where a split arrangement is selected, the remote condensing section shall be furnished by the unit manufacturer and matched to the unit.
6.2.4 Where a split arrangement is selected, the field refrigerant piping shall conform to Refrigerant PipingRefrigerant PipingResolves to the current adopted revision.sync/refrigerant-piping.
6.2.5 Where a split arrangement is selected, the manufacturer shall state in the submittal the maximum equivalent line length and the maximum vertical separation the match is rated for.
NOTE A packaged unit leaves the factory charged and run-tested with its condenser, so the refrigerant circuit arrives proven. A split arrangement exists for the indoor unit whose condenser has to be outdoors, and it moves the charge, the line sizing, the oil return, and the leak test into the field, which is why the piping standard governs it and the manufacturer's match limits bound it. (6.2.6)

6.3 Supply Air Delivery

6.3.1 The point at which the unit delivers its supply air shall be as indicated in the datasheet.
Supply Air Delivery Pointselect
Directly to the occupied spaces through dedicated outlets
To the return or inlet side of the parallel terminal units
To the supply side of the parallel terminal units, downstream of their coils
6.3.2 Where the unit delivers to the inlet side of the parallel terminal units, the terminal units shall be selected for the combined airflow and the entering condition the unit delivers.
6.3.3 Where the unit delivers to the supply side of the parallel terminal units, the supply air temperature setpoints of the two systems shall be coordinated so that neither system reheats or recools what the other has just conditioned.
6.3.4 Where the unit delivers directly to the spaces, the outlets shall be selected in accordance with HVAC Air Distribution DevicesHVAC Air Distribution DevicesResolves to the current adopted revision.sync/hvac-air-distribution-devices for the supply air temperature indicated in the datasheet at the ventilation airflow.
NOTE Delivering to the terminal inlet mixes the ventilation air with room air before the terminal coil, which hides a cold supply from the occupants and lets the terminal see a steadier entering condition, but ventilation then stops whenever the terminal fan stops and the terminal has to be sized for the extra air. Delivering to the terminal discharge keeps ventilation independent of the terminal fan and avoids the resizing, at the cost of a pressure interaction between two fans in one duct. Dedicated outlets keep the two systems entirely separate and are the arrangement with chilled beams and radiant systems that have no fan at all, and they put a low-airflow outlet in every room that has to throw cold air without a draft. (6.3.5)

7 Airflow and Static Pressure

7.1 Design Airflows

7.1.1 Each unit shall deliver the design outdoor airflow indicated in the datasheet at the design supply external static pressure, at the site elevation, and with the filters at their change-out resistance.
Design Outdoor Airflowrange
cfm
200100000
Per drawings — the mechanical equipment schedule (deferred by default)
Design Supply External Static Pressurerange
in. w.g.
0.15
Per drawings — the mechanical equipment schedule (deferred by default)
7.1.2 Each unit furnished with an exhaust fan shall move the design exhaust airflow indicated in the datasheet through the recovery device at the design exhaust external static pressure.
Design Exhaust Airflow Through the Recovery Devicerange
cfm
0100000
Per drawings — the mechanical equipment schedule (deferred by default)
Design Exhaust External Static Pressurerange
in. w.g.
05
Per drawings — the mechanical equipment schedule (deferred by default)
7.1.3 The design outdoor airflow shall be not less than the ventilation ANSI/ASHRAE 62.1 requires for the spaces served, and for health care spaces not less than ANSI/ASHRAE 170 requires.
NOTE The external static pressure is the resistance of the ductwork, accessories, and outlets beyond the unit connections; the unit's own sections are inside it and are the manufacturer's to account for. (7.1.4)
7.1.5 The manufacturer shall add the internal resistance of every furnished section, including the recovery device, the coils, the reheat section, the heating section, and the filters at change-out resistance, to the external static pressure to establish the total static pressure at which each fan is selected.
NOTE The ratio of exhaust airflow to outdoor airflow through the recovery device decides the effectiveness the device delivers and the direction the carryover leaks, so the two airflows are scheduled together and balanced together. A unit whose exhaust is well below its outdoor airflow recovers less than its rating, and a unit whose exhaust exceeds its outdoor airflow depressurizes the building through the recovery section. (7.1.6)

7.2 Supply Airflow Control

7.2.1 The supply airflow control shall be as indicated in the datasheet.
Supply Airflow Controlselect
Constant volume at the design outdoor airflow
Two airflows, occupied and reduced
Variable volume on a demand-controlled ventilation signal
Variable volume to a duct static pressure setpoint
7.2.2 Where variable volume is selected, the unit shall hold its leaving air dew point and supply air temperature setpoints across the full airflow range, and the minimum airflow at which it does so shall be stated in the submittal.
7.2.3 Where variable volume is selected, the exhaust fan shall track the supply fan so that the airflow ratio through the recovery device stays within the range the device is rated for.
7.2.4 Where variable volume to a duct static pressure setpoint is selected, the terminal devices that modulate the ventilation airflow shall conform to Air Terminal UnitsAir Terminal UnitsResolves to the current adopted revision.sync/air-terminal-units.
NOTE A dedicated outdoor air unit runs at a fixed ventilation rate on most projects because the airflow is the code minimum for the design occupancy and nothing in the space changes it. Demand-controlled ventilation trims that rate when the spaces are below design occupancy, which is where the fan and conditioning energy of a 100% outdoor air unit goes, and it is worth the sensors where occupancy swings widely; a duct static setpoint is the arrangement where zone-level ventilation dampers or terminals meter the air and the unit merely keeps the duct charged. A unit that modulates has to keep its coil wet and its compressor in its operating range at the reduced airflow, which is the submittal item. (7.2.5)

7.3 Airflow Measurement

7.3.1 Airflow measurement stations shall be furnished in the airstreams indicated in the datasheet.
Airflow Measurement Stations Furnishedcheckbox
☑ Outdoor airflow measurement station
☐ Exhaust airflow measurement station
☐ Supply discharge airflow measurement station
7.3.2 Airflow measurement stations shall be rated in accordance with ANSI/AMCA 610.
7.3.3 Airflow measurement stations shall be accurate across the range from the minimum airflow the unit operates at to the design airflow.
7.3.4 Measured airflows shall be exposed to the building automation system as points.
NOTE The outdoor airflow of a 100% outdoor air unit is the building's ventilation rate, and a measured value is the only record that the rate is being met after the balance report is filed. A unit that modulates on a demand signal has no fixed damper position to fall back on, so the measurement is what the control loop closes on. (7.3.5)

8 Dehumidification and Cooling

8.1 Leaving Air Dew Point

8.1.1 Each unit shall cool and dehumidify the outdoor air to the leaving air dew point setpoint indicated in the datasheet at the dehumidification design condition.
Leaving Air Dew Point Setpointrange
°F
3560
Per drawings — the mechanical equipment schedule (deferred by default)
8.1.2 The unit shall hold the leaving air dew point setpoint at every outdoor condition between the dehumidification design condition and the outdoor dew point at which dehumidification is no longer called for.
8.1.3 The dew point control sensing shall be as indicated in the datasheet.
Dew Point Control Sensingselect
Dew point sensor in the leaving air
Temperature and relative humidity sensors in the leaving air with the dew point computed
Cooling coil leaving air temperature as the dew point proxy
8.1.4 The dew point control loop shall modulate the cooling capacity to hold the dew point setpoint independently of the supply air temperature loop.
NOTE The dew point is the quantity that decides whether the spaces stay dry, because the ventilation air is the only air in the building being dehumidified and the moisture it carries in has to be below what the spaces can tolerate after the occupants and infiltration add theirs. A comfort space at a typical setpoint tolerates a supply dew point in the low fifties; spaces with chilled beams, radiant cooling, or a stated humidity limit need lower, and the schedule carries the value because it follows from the space criteria rather than from the unit. (8.1.5)
NOTE A direct dew point sensor reads the controlled variable and nothing else, and its cost is a sensor that needs periodic calibration. Computing the dew point from temperature and relative humidity doubles the sensors and compounds their errors at the low humidities where the computation is least sensitive. Using the coil leaving temperature as a proxy assumes the air leaves the coil saturated, which holds at design and drifts at part load when the coil is not fully wet, and it is the arrangement on units whose controls were built around a temperature sensor. (8.1.6)

8.2 Cooling Source

8.2.1 The cooling source shall be as indicated in the datasheet.
Cooling Sourceselect
Direct expansion
Chilled water coil
No mechanical cooling section
8.2.2 Where no mechanical cooling section is selected, the unit shall temper the outdoor air by energy recovery and heating only, and the dew point requirements of this standard do not apply to that unit.
NOTE Direct expansion is the norm for a packaged unit because it brings its own cooling and, with it, the condenser heat that supplies reheat at no purchased energy. A chilled water coil is the arrangement where a central plant already serves the building and the unit is one more load on it, and it has to find its reheat elsewhere. A unit with no cooling at all serves a dry or cold climate where the ventilation air needs tempering and filtration but never dehumidification. (8.2.3)

8.3 Direct-Expansion Cooling

8.3.1 Requirements in this article apply where the datasheet selects direct-expansion cooling.
8.3.2 The heat rejection of the direct-expansion circuit shall be as indicated in the datasheet.
Direct-Expansion Heat Rejectionradio
● Air-cooled condenser
○ Water-cooled condenser on a condenser water or ground loop
8.3.3 Where a water-cooled condenser is selected, the condenser water piping shall conform to Hydronic PipingHydronic PipingResolves to the current adopted revision.sync/hydronic-piping and the condenser shall be rated for the entering water temperature range of the loop it serves.
8.3.4 The compressor type shall be as indicated in the datasheet.
Compressor Typeselect
Hermetic scroll
Semi-hermetic reciprocating
Semi-hermetic screw
8.3.5 The cooling capacity control shall be as indicated in the datasheet.
Cooling Capacity Controlselect
Single stage
Two stages
Three or more stages
Variable capacity by digital scroll unloading
Variable capacity by inverter-driven compressor
8.3.6 The smallest cooling capacity step shall be not more than the percentage of full capacity indicated in the datasheet.
Largest Permitted Minimum Cooling Capacity Steprange
%
101520253350100
8.3.7 Where the datasheet does not state a minimum capacity step, the manufacturer shall state the minimum step of the furnished unit in the submittal.
8.3.8 The unit shall hold the leaving air dew point setpoint at the minimum capacity step without cycling the compressor more often than the manufacturer's anti-short-cycle timing permits.
NOTE The latent load on a ventilation unit varies far more across a year than the sensible load on a comfort unit. Many of the wettest hours are mild, and a rainy day near saturation carries a large moisture load with almost no temperature difference to work against, so a unit that can only run at full capacity overcools, trips on low coil temperature, cycles off, and delivers wet air on exactly those hours. Staged compressors buy part of that range at low cost; a modulating compressor follows the latent load continuously and is the arrangement where the dew point has to hold through shoulder seasons, at the price of an inverter and an electronic expansion valve. Scroll compressors cover the capacity range packaged units are built in; reciprocating and screw machines appear on large custom units. (8.3.9)
8.3.10 The minimum number of independent refrigerant circuits per unit shall be as indicated in the datasheet.
Number of Independent Refrigerant Circuitsrange
circuits
1234
8.3.11 Each independent circuit shall have its own compressor or compressors, expansion device, evaporator coil section, and condenser coil section, so that a failure in one circuit does not disable the others.
8.3.12 Where the minimum circuit count indicated in the datasheet is not offered by the manufacturer at a tag's capacity, the Contractor shall report the conflict to the Engineer of Record before the unit is released for fabrication.
8.3.13 The expansion device on each circuit shall be as indicated in the datasheet.
Expansion Deviceselect
Thermostatic expansion valve
Electronic expansion valve
Fixed orifice
8.3.14 Where the datasheet selects variable capacity, the expansion device shall be one that maintains superheat control across the full modulation range of the compressor.
8.3.15 Each circuit shall be furnished with a high-pressure cutout, a low-pressure cutout or loss-of-charge protection, and a compressor motor overload, each of which shall stop the compressor independently of the unit controller.
8.3.16 Each circuit shall be furnished with a liquid line filter-drier and with service access ports on the high and low sides.
8.3.17 Each compressor shall be mounted on vibration isolators within the cabinet and furnished with a crankcase heater.
8.3.18 Mechanical cooling shall be available down to the outdoor temperature indicated in the datasheet.
Lowest Outdoor Temperature for Mechanical Cooling Operationrange
°F
-20-1010203040505565
8.3.19 Where the datasheet does not state a minimum outdoor temperature for mechanical cooling, the unit shall be furnished for mechanical cooling down to the manufacturer's published low-ambient limit, and that limit shall be stated in the submittal.
NOTE A thermostatic valve controls superheat mechanically and holds a stable feed across the range of a staged compressor; a modulating compressor runs at mass flows a mechanical valve was not sized for at both ends of its range, which is what an electronic valve exists for. A ventilation unit dehumidifies on cool, damp days that a comfort unit would spend in economizer, so the outdoor temperature at which the compressor still has to run is lower than for a rooftop unit, and the head pressure control that keeps a compressor alive at that temperature follows from the temperature the project needs dehumidification at. (8.3.20)

8.4 Refrigerant and Safety Group

8.4.1 Requirements in this article apply where the datasheet selects direct-expansion cooling or a heat pump heating source.
8.4.2 The refrigerant shall be as indicated in the datasheet.
Refrigerant Designation (ASHRAE 34)select
R-454B
R-32
R-410A
Manufacturer's standard (by default)
8.4.3 Where the datasheet leaves the refrigerant to the manufacturer, the manufacturer shall state in the submittal the refrigerant the unit is charged with and its safety group.
8.4.4 The refrigerant shall be one that 40 CFR Part 84 permits in equipment of the unit's class on the unit's date of manufacture.
8.4.5 Where a unit is furnished as a replacement that retains existing refrigerant piping or components, the refrigerant selected in the datasheet shall be compatible with the retained components.
8.4.6 The refrigerant safety group shall be as indicated in the datasheet.
Refrigerant Safety Group (ASHRAE 34)select
A1
A2L
Derived — the safety classification ASHRAE 34 publishes for the refrigerant the unit is charged with (by default)
NOTE Under the technology transition rule at 40 CFR Part 84, packaged equipment manufactured after the compliance date for its class is limited to refrigerants below a stated global warming potential, and the refrigerants that meet that limit at the pressures this equipment runs at are classified A2L. The refrigerant is therefore a property of the product line rather than a specification choice for new equipment, and the datasheet asserts one only where a project has a reason to, such as matching a retained circuit. (8.4.7)
NOTE The safety group is the switch that turns the detection, mitigation, marking, and training articles of this standard on or off, and it follows from the refrigerant rather than from any project decision. (8.4.8)

8.5 Refrigerant Detection and Mitigation

8.5.1 The refrigerant detection provision shall be as indicated in the datasheet.
Refrigerant Detection Systemradio
○ Factory-installed refrigerant detection system with mitigation
○ No refrigerant detection system
Derived — the refrigerant safety group and the charge per circuit, compared against the releasable charge limit UL 60335-2-40 establishes for the unit and the smallest space it serves (by default)
8.5.2 Where a refrigerant detection system is furnished, the sensors, their locations, and the mitigation sequence shall be as covered by the unit listing.
8.5.3 The Contractor shall not relocate a refrigerant detection sensor or alter the mitigation sequence in the field.
8.5.4 On detection, the mitigation sequence shall start the supply fan to dilute the released refrigerant, shall de-energize the ignition sources the listing identifies, and shall continue until the measured concentration has fallen below the reset threshold.
8.5.5 Where a refrigerant detection system is furnished, its alarm shall be exposed to the building automation system as a discrete point regardless of the control points selected in the datasheet.
8.5.6 Detection sensors shall be installed with the date of installation recorded on the device, and the end of their published service life shall be recorded in the closeout documents.
NOTE A refrigerant in the A2L group burns only within a narrow concentration band and only with a strong ignition source, so the listing manages the hazard by keeping the concentration in any space below a fraction of the lower flammability limit. A ventilation unit has one property that matters here: its supply fan runs whenever the building is occupied and it serves every space on its duct, so a leak diluted through its supply reaches many rooms at once, and the charge limit is set against the smallest of them. Whether a given unit needs detection is a calculation on the charge and the space, which is why it is derived rather than chosen. (8.5.7)

8.6 Chilled Water Cooling Coil

8.6.1 Requirements in this article apply where the datasheet selects a chilled water cooling coil.
8.6.2 The chilled water coil shall be selected at the entering and leaving water temperatures indicated in the datasheet.
Chilled Water Coil Entering Water Temperaturerange
°F
3660
Per drawings — the mechanical equipment schedule (deferred by default)
Chilled Water Coil Leaving Water Temperaturerange
°F
4470
Per drawings — the mechanical equipment schedule (deferred by default)
8.6.3 The chilled water coil shall be selected to reach the leaving air dew point setpoint at the design entering water temperature with the water-side pressure drop stated in the submittal.
8.6.4 The coil control valve shall modulate the water flow to hold the leaving air dew point setpoint.
8.6.5 Coil connections shall pass through the casing in a gasketed, insulated penetration, and piping serving the coil shall be independently supported so that no part of its weight or thermal movement is carried by the coil header.
NOTE A coil can only cool the air to within a few degrees of the water entering it, so the leaving air dew point a chilled water unit can reach is bounded by the plant's supply temperature. A plant that runs warm for efficiency cannot serve a unit that needs a low dew point, and the two schedules have to agree before either is fixed. (8.6.6)

8.7 Cooling Coil Construction

8.7.1 Cooling coils shall be rated in accordance with AHRI 410, with copper tubes, fins of the material and protection selected under Corrosive Atmospheres, and headers and connections of a material compatible with the tubes.
8.7.2 The face velocity across the cooling coil at the design outdoor airflow shall not exceed the value indicated in the datasheet.
Cooling Coil Face Velocityrange
fpm
250300350400450500550600
8.7.3 Where the datasheet does not state a maximum face velocity, the coil shall be selected at or below the face velocity the manufacturer publishes as the carryover limit for that coil wet, and that velocity shall be stated in the submittal.
NOTE A dedicated outdoor air coil runs wet at design and at most of the hours it cools, with the air leaving it near saturation. Moisture carries off a wet coil face above a velocity the fin geometry sets, and the droplets land in the reheat coil and the downstream casing, where they re-evaporate into the air the coil just dried or pool where there is no pan. The limit is lower than for a mixed-air coil that spends much of its life dry, and it is the reason a ventilation unit's coil is larger in face area than its airflow alone suggests. (8.7.4)

9 Reheat

9.1 Reheat Source

9.1.1 The source of the reheat applied after the cooling coil shall be as indicated in the datasheet.
Reheat Sourceselect
No reheat section
Hot gas reheat coil
Wraparound heat pipe
Wraparound pumped coil loop
Sensible wheel around the cooling coil
Hot water reheat coil
Electric reheat coil
9.1.2 Where hot gas reheat is selected, the reheat coil shall be served by the unit's own refrigerant circuit and shall be arranged so that reheat is available whenever the compressor is dehumidifying.
9.1.3 Where a wraparound heat pipe or pumped coil loop is selected, the precool section shall be upstream of the cooling coil and the reheat section downstream of it in the same airstream, and the capacity transferred at the design condition shall be stated in the submittal.
9.1.4 Where a sensible wheel around the cooling coil is selected, the wheel shall transfer heat from the air entering the cooling coil to the air leaving it without transferring moisture, and its exhaust air transfer ratio shall be stated in the submittal.
9.1.5 Where a hot water or electric reheat coil is selected, the arrangement shall be one Adopted Energy CodeAdopted Energy CodeParameterEach project supplies its own value.adopted-energy-code permits for reheat following dehumidification, and the provision relied on shall be identified in the submittal.
9.1.6 Where a hot water reheat coil is selected, the coil shall conform to the Hydronic Heating Section article of this standard.
9.1.7 Where an electric reheat coil is selected, the coil shall conform to the Electric Resistance Heating Section article of this standard.
NOTE Reaching a low dew point means cooling the air to that dew point, which is colder than most spaces want delivered, and reheat is what lifts it back without putting the moisture back. Where the heat comes from is the decision. Hot gas reheat takes the heat the condenser is rejecting anyway, costs nothing to run, and is available only on a direct-expansion unit while its compressor runs. A wraparound heat pipe or pumped loop precools the entering air with heat it then returns downstream, so it both deepens the dehumidification for the same compressor capacity and reheats for free, with no controls at all on the passive heat pipe and a pump on the loop; it is also the reheat a chilled water unit can have without purchased energy. A sensible wheel does the same job with a rotating mass and a drive. A hot water or electric coil spends purchased energy heating air the unit just cooled, which the energy code limits to the exceptions it lists, and it is the arrangement where no recovered source exists or where the leaving temperature has to be held precisely regardless of load. No reheat at all delivers the air at the coil leaving temperature, which is a legitimate arrangement where the parallel system is sized to take cold ventilation air. (9.1.8)

9.2 Reheat Control

9.2.1 The reheat capacity control shall be as indicated in the datasheet.
Reheat Capacity Controlradio
● Modulating
○ Staged or two-position
9.2.2 Reheat shall be controlled to hold the supply air temperature setpoint independently of the dew point control loop.
9.2.3 Where a passive wraparound device is furnished and the datasheet selects modulating reheat control, the device shall be furnished with a bypass damper, a modulating valve, or a variable-speed pump that controls the heat transferred.
9.2.4 Where hot gas reheat is furnished, the reheat shall be controlled so that the compressor continues to run for dehumidification when the supply air temperature setpoint is satisfied.
NOTE Reheat that cannot modulate delivers a supply temperature that swings between the coil leaving temperature and the full reheat rise, which the parallel system then corrects at its own cost. A passive heat pipe transfers what the temperature difference across it drives, so on its own it tracks the load roughly but cannot be set; adding a bypass or a valve turns it into a controlled device. The one failure to design out is a reheat loop that satisfies the supply temperature by shutting the compressor off, because the dew point then floats. (9.2.5)

10 Supply Air Temperature Strategy

10.1 Cooling-Season Supply Temperature

10.1.1 The cooling-season supply air temperature basis shall be as indicated in the datasheet.
Cooling-Season Supply Air Temperature Basisradio
○ Neutral, reheated to near the space temperature
○ Cold, delivered below the space temperature to carry part of the sensible load
10.1.2 The cooling-season supply air temperature setpoint shall be as indicated in the datasheet.
Cooling-Season Supply Air Temperature Setpointrange
°F
4578
Per drawings — the mechanical equipment schedule (deferred by default)
10.1.3 Where a cold supply basis is selected, the parallel sensible system shall be sized on the sensible load remaining after the ventilation air's contribution is deducted, and that deduction shall be stated on the mechanical equipment schedule.
10.1.4 Where a cold supply basis is selected and the unit delivers directly to the spaces, the outlets shall be selected so that the occupied-zone air speed and temperature criteria of ANSI/ASHRAE 55 are met at the supply air temperature indicated in the datasheet.
NOTE Neutral air neither heats nor cools the space, so the parallel system carries the whole sensible load and the two systems never work against each other; it costs the reheat energy, recovered or purchased, that lifts the air from the coil to the room temperature. Cold air uses the dehumidified ventilation air as part of the cooling, which shrinks the parallel equipment and spends less on reheat, and it ties the parallel system's sizing to the ventilation airflow, puts cold air at a low airflow through every outlet, and leaves the spaces overcooled on a mild day unless the supply temperature resets. The choice follows from what the parallel system is: a chilled beam or radiant system wants the ventilation air to do as much as it can, and a variable refrigerant flow or fan coil system usually wants it out of the way. (10.1.5)

10.2 Heating-Season Supply Temperature

10.2.1 The heating-season supply air temperature basis shall be as indicated in the datasheet.
Heating-Season Supply Air Temperature Basisradio
○ Neutral, tempered to near the space temperature
○ Warm, delivered above the space temperature to carry part of the heating load
10.2.2 The heating-season supply air temperature setpoint shall be as indicated in the datasheet.
Heating-Season Supply Air Temperature Setpointrange
°F
55110
Per drawings — the mechanical equipment schedule (deferred by default)
10.2.3 Where a warm supply basis is selected, the unit shall be arranged so that heating is locked out when the parallel system is in cooling in the same zones.
NOTE Neutral tempering keeps the ventilation air from chilling the spaces or the parallel equipment's inlets and leaves the heating to the parallel system; a warm supply offsets part of the envelope load through the ventilation air and lets a parallel system with marginal heating capacity, such as a heat pump at its low-ambient limit, keep up. A warm supply into a zone whose parallel unit is cooling an internal load is the simultaneous heating and cooling the energy code forbids, which is why the lockout exists. (10.2.4)

10.3 Setpoint Reset

10.3.1 The supply air temperature reset shall be as indicated in the datasheet.
Supply Air Temperature Resetselect
None, fixed setpoints by season
Reset on outdoor air temperature
Reset on the heating and cooling demand of the zones served
Reset by the building automation system supervisory logic
10.3.2 The leaving air dew point reset shall be as indicated in the datasheet.
Leaving Air Dew Point Resetradio
○ None, fixed setpoint
○ Reset on the measured space humidity
10.3.3 Where any reset is selected, the reset limits shall be stated in the sequence of operation and shall not drive the dew point setpoint above the value at which the spaces served exceed their design humidity.
10.3.4 Where reset by the building automation system is selected, the reset logic shall reside in the building automation system and shall write the setpoints to the unit controller through the interface, in accordance with Building Automation SystemBuilding Automation SystemResolves to the current adopted revision.sync/building-automation-system.
NOTE A fixed supply temperature is the simplest sequence and the one most units ship with. Resetting it on outdoor temperature warms the supply as the weather cools, which cuts reheat in the shoulder seasons without any zone information; resetting on zone demand uses the parallel system's own calls to decide whether the ventilation air should help or stay neutral, which is the sequence that captures the most energy and needs the most integration. Resetting the dew point upward when the spaces are dry saves compressor energy on the many hours when the design dew point is not needed, and it is only safe where the space humidity is measured and the reset is capped. (10.3.5)

11 Heating

11.1 Heating Source

11.1.1 The heating source integral to the unit shall be as indicated in the datasheet.
Heating Sourceselect
No heating section, tempering by energy recovery only
Reverse-cycle heat pump
Natural gas-fired indirect
Propane-fired indirect
Electric resistance
Hot water coil
Steam coil
11.1.2 Where no heating section is selected, the submittal shall state the supply air temperature the unit delivers at Site Ambient Temperature MinimumSite Ambient Temperature MinimumParameterEach project supplies its own value.site-ambient-temperature-minimum with the recovery device operating and with the recovery device in frost control.
NOTE The heating source is independent of the cooling source, the reheat source, and the recovery device, and no combination of those selections constrains it. (11.1.3)
NOTE No heating source is the norm across projects. A heat pump heats from the same compressor that dehumidifies and is the arrangement where the project is electrifying, with its capacity falling as the weather gets colder; gas heat is common where gas is at the site and the winter temperature rise is large; electric resistance where gas is not available or the rise is small; a hydronic or steam coil where a plant already serves the building; and recovery alone where the climate is mild enough that the recovered heat tempers the air to a usable supply temperature on its own. Each is a live choice and the datasheet takes no side. (11.1.4)

11.2 Heat Pump Heating

11.2.1 Requirements in this article apply where the datasheet selects a reverse-cycle heat pump heating source.
11.2.2 Compressor heating shall continue in operation down to the outdoor temperature indicated in the datasheet.
Lowest Outdoor Temperature for Compressor Heating Operationrange
°F
-25-15-551017253545
11.2.3 The integrated heating capacity at the compressor heating operation limit shall be stated in the submittal.
11.2.4 The supplemental heat source shall be as indicated in the datasheet.
Heat Pump Supplemental Heat Sourceselect
None
Electric resistance
Natural gas-fired
Propane-fired
Hot water coil
11.2.5 Supplemental heat shall be locked out by the unit controls above the outdoor temperature indicated in the datasheet.
Supplemental Heat Lockout Outdoor Temperaturerange
°F
10202530354045505565
11.2.6 Below the lockout temperature, supplemental heat shall be energized only when compressor heating cannot hold the supply air temperature setpoint.
11.2.7 The defrost control method shall be as indicated in the datasheet.
Heat Pump Defrost Controlselect
Demand defrost initiated by coil temperature and pressure
Time-initiated and temperature-terminated defrost
11.2.8 During a defrost cycle the supplemental heat, where furnished, shall be energized as the listing permits so that the supply air is not delivered below the heating-season supply air temperature setpoint by more than the manufacturer's published defrost depression.
11.2.9 The reversing valve shall be energized in the mode the manufacturer designates so that a loss of control signal leaves the unit in that mode, and the mode shall be stated in the submittal.
NOTE A heat pump's heating capacity falls as the outdoor temperature falls while a 100% outdoor air unit's heating load rises in direct proportion to the same temperature, so the two curves cross at a balance point that sits higher than it would for a comfort unit with return air. Below it the compressor cannot carry the rise alone and the supplemental source makes up the difference; the lockout is set at or below the balance point so the supplemental source does not displace compressor heat that is cheaper to deliver. A ventilation unit cannot pause its supply during defrost the way a comfort unit can, which is why the defrost depression is a submittal value and the supplemental heat covers it. Demand defrost runs a cycle when the coil actually frosts; timed defrost runs cycles the coil did not need on dry days. (11.2.10)

11.3 Gas-Fired Heating Section

11.3.1 Requirements in this article apply where the datasheet selects a natural gas-fired or propane-fired heating source, or a gas-fired supplemental heat source.
11.3.2 The gas heating input of each unit shall be as indicated in the datasheet.
Gas Heating Inputrange
MBH
303000
Per drawings — the mechanical equipment schedule (deferred by default)
11.3.3 The gas heat exchanger material shall be as indicated in the datasheet.
Gas Heat Exchanger Materialselect
Aluminized steel
Type 409 stainless steel
Type 304 stainless steel
Type 316 stainless steel
11.3.4 The gas heating capacity control shall be as indicated in the datasheet.
Gas Heating Capacity Controlselect
Single stage
Two stages
Modulating
11.3.5 The low-fire input of a staged or modulating burner shall be not more than the percentage of full input indicated in the datasheet.
Low-Fire Gas Input as a Percentage of Full Inputrange
%
510202533405065100
11.3.6 The thermal efficiency of the gas heating section shall be not less than the value indicated in the datasheet.
Gas Heating Thermal Efficiencyrange
%
78808182909597
Derived — the minimum Adopted Energy CodeAdopted Energy CodeParameterEach project supplies its own value.adopted-energy-code requires for a warm-air furnace of the unit's heating input (by default)
11.3.7 The gas supply pressure available at each unit connection shall be as indicated in the datasheet.
Gas Supply Pressure at the Unit Connectionrange
in. w.c.
3.514
Per drawings — the gas piping drawings (deferred by default)
11.3.8 The unit gas train shall be rated for the gas supply pressure available at the unit connection.
11.3.9 The burner shall be furnished with electronic ignition, flame supervision, a redundant gas valve, a high-limit thermal cutout, and a rollout switch.
11.3.10 The burner and gas train shall be certified as an assembly to ANSI Z21.47 / CSA 2.3, or to ANSI Z83.8 / CSA 2.6 where the section is a duct furnace.
11.3.11 The heat exchanger shall be furnished with an induced-draft combustion blower and a proof-of-draft switch that prevents ignition without combustion airflow.
11.3.12 Where a modulating or condensing heat exchanger is furnished, the flue products shall be handled and the flue condensate drained as the listing requires, and flue condensate shall be neutralized before it enters a drain the adopted plumbing code requires to be protected.
NOTE The heat exchanger on a 100% outdoor air unit sees the winter design temperature at its entering face on every heating hour, which drops the flue gas below its dew point inside the exchanger at a higher outdoor temperature than a return-air unit ever reaches. An aluminized surface corrodes from the inside under that condensation; the stainless grades resist it at a higher cost, with the higher grades for corrosive combustion air or a condensing design. No material is the norm here, because the condensing exposure depends on the climate and the turndown together. (11.3.13)
NOTE Turndown decides how the section behaves across the heating season. A single-stage burner delivers full input in short cycles, which swings the supply temperature the parallel system then has to absorb; a modulating burner holds a steady supply temperature across the whole range of outdoor temperatures the unit tempers from, which on a 100% outdoor air unit is the full span from the design low to the heating balance point, and the deeper the turndown the lower the outdoor temperature at which the burner first has to cycle. (11.3.14)

11.4 Electric Resistance Heating Section

11.4.1 Requirements in this article apply where the datasheet selects an electric resistance heating source, an electric resistance supplemental heat source, or an electric reheat coil.
11.4.2 The electric heating capacity of each unit shall be as indicated in the datasheet.
Electric Heating Capacityrange
kW
2400
Per drawings — the mechanical equipment schedule (deferred by default)
11.4.3 The electric heating capacity control shall be as indicated in the datasheet.
Electric Heating Capacity Controlselect
Single stage
Two stages
Three or more stages
Modulating by silicon-controlled rectifier
11.4.4 Electric heating elements shall be open-coil nickel-chromium or sheathed elements listed as part of the unit, furnished with a primary automatic-reset thermal cutout and a secondary manual-reset thermal cutout.
11.4.5 Electric heating elements shall be interlocked with the supply fan so that the elements cannot be energized without proven airflow.
11.4.6 The electric heater airflow interlock shall be hardwired independently of the unit controller and the building automation system.
11.4.7 Where the electric heater is furnished with its own power connection, the heater and the unit shall each be furnished with their own disconnecting means.
NOTE Staged elements deliver the capacity in steps that the supply temperature swings across; a silicon-controlled rectifier modulates continuously and is the arrangement where the heater holds a supply temperature setpoint directly, as a reheat coil does, rather than tempering toward one. An airflow interlock that depends on the controller fails in the one scenario it exists for, which is the controller being offline while the elements have power, and the hardwired path is what makes the interlock a safety rather than a sequence. (11.4.8)

11.5 Hydronic Heating Section

11.5.1 Requirements in this article apply where the datasheet selects a hot water or steam heating source, a hot water supplemental heat source, or a hot water reheat coil.
11.5.2 The hydronic coil shall be selected at the entering and leaving fluid temperatures indicated in the datasheet.
Hydronic Heating Coil Entering Fluid Temperaturerange
°F
90220
Per drawings — the mechanical equipment schedule (deferred by default)
Hydronic Heating Coil Leaving Fluid Temperaturerange
°F
70210
Per drawings — the mechanical equipment schedule (deferred by default)
11.5.3 The freeze protection method for the hydronic coil shall be as indicated in the datasheet.
Hydronic Heating Coil Freeze Protectionselect
Glycol solution in the heating circuit
Constant coil flow with a modulating three-way valve
Constant coil flow maintained by an injection pump
Face and bypass dampers with a constant-capacity coil
11.5.4 Every hydronic coil shall be furnished with a low-limit temperature device downstream of the coil, arranged to stop the supply fan, close the outdoor air damper, and open the coil control valve when it trips.
11.5.5 Hydronic piping to the coil shall conform to Hydronic PipingHydronic PipingResolves to the current adopted revision.sync/hydronic-piping, and the coil connections shall pass through the casing in a gasketed, insulated penetration with the piping independently supported.
11.5.6 Steam coils shall be of distributing tube non-freeze construction, pitched toward the return connection, and trapped separately from every other coil.
NOTE A hydronic coil in a 100% outdoor air unit sits in undiluted outdoor air on every hour of the year and can see it with the fan off, so it is the coldest service a heating coil has. Every method in the field is a way of keeping fluid moving through every tube or of lowering its freezing point, and a two-way valve throttled to a trickle on the coldest night is the arrangement that splits the coil. Glycol protects the coil regardless of what the controls do and lowers the plant's capacity by its share; the flow and bypass arrangements keep the fluid moving and depend on the pump and the controls doing their job. (11.5.7)

12 Energy Recovery

12.1 Energy Recovery Requirement

12.1.1 Exhaust air energy recovery shall be as indicated in the datasheet.
Exhaust Air Energy Recoveryradio
○ Energy recovery furnished
○ Not furnished
Derived — the energy recovery requirement Adopted Energy CodeAdopted Energy CodeParameterEach project supplies its own value.adopted-energy-code sets for the unit's design outdoor airflow, outdoor air fraction, and operating hours in Climate ZoneClimate ZoneParameterEach project supplies its own value.climate-zone, including the exceptions that code lists (by default)
12.1.2 Where the datasheet selects no energy recovery on a unit for which the adopted energy code would otherwise require it, the exception relied on shall be identified in the submittal.
12.1.3 Where energy recovery is furnished, the enthalpy recovery ratio at design conditions shall be not less than the value indicated in the datasheet.
Enthalpy Recovery Ratiorange
%
090
Derived — the minimum enthalpy recovery ratio Adopted Energy CodeAdopted Energy CodeParameterEach project supplies its own value.adopted-energy-code requires where energy recovery is required (by default)
12.1.4 Where energy recovery is furnished, the pressure drop the device adds to the supply and exhaust airstreams shall be included in the fan selections and stated in the submittal.
12.1.5 Where energy recovery is furnished, the construction, rating, and testing of the recovery component itself shall conform to Energy Recovery VentilatorsEnergy Recovery VentilatorsResolves to the current adopted revision.sync/energy-recovery-ventilators.
NOTE A unit that handles 100% outdoor air at every hour it runs is the equipment the energy recovery rules were written for, and almost every such unit above the smallest airflow falls inside the requirement in every climate zone. The derivation exists so that a project does not have to look the table up, and the exceptions, chiefly for exhaust that cannot be brought to the unit and for systems that run few hours, are what the submittal documents when a project opts out. (12.1.6)

12.2 Recovery Device Type

12.2.1 Requirements in this article and the remaining articles of this section apply where energy recovery is furnished.
12.2.2 The recovery device shall be as indicated in the datasheet.
Energy Recovery Deviceselect
Total energy rotary wheel
Sensible-only rotary wheel
Fixed-plate total energy membrane core
Fixed-plate sensible core
Heat pipe
Runaround coil loop
12.2.3 The sensible, latent, and total effectiveness of the furnished device at the design outdoor and exhaust airflows shall be stated in the submittal.
NOTE A total energy device transfers moisture as well as heat, so in summer it pre-dries the incoming air with the drier exhaust and cuts the latent load the coil has to remove, and in winter it returns moisture the building would otherwise lose. A rotary wheel reaches the highest total effectiveness and carries a drive, seals, and a measurable carryover between the streams; a membrane plate has no moving parts and lower carryover at a larger size and a higher pressure drop. A sensible device transfers heat only, which is the arrangement where moisture transfer is unwanted or where the exhaust is contaminated: a sensible wheel and a sensible plate still share a face between the streams, while a heat pipe and a runaround loop keep the streams physically apart, and the runaround loop is the only device that works when the intake and exhaust cannot be brought to one unit. The choice turns on the exhaust air class, the climate's balance of latent and sensible load, and whether the two airstreams can meet. (12.2.4)

12.3 Exhaust Air Class and Cross-Leakage

12.3.1 The air class under ANSI/ASHRAE 62.1 of the exhaust airstream passing through the recovery device shall be as indicated in the datasheet.
Exhaust Air Class Through the Recovery Device (ASHRAE 62.1)select
Class 1
Class 2
Class 3
Class 4
Per drawings — the mechanical ventilation schedule (deferred by default)
12.3.2 The exhaust air transfer ratio of the recovery device shall not exceed the value indicated in the datasheet.
Exhaust Air Transfer Ratiorange
%
010
Derived — the transfer ANSI/ASHRAE 62.1 permits from the exhaust air class through the recovery device into the outdoor air, with no transfer permitted where that standard prohibits recirculation of the class (by default)
12.3.3 Where the exhaust air class prohibits any transfer into the supply, the recovery device shall be a heat pipe or a runaround coil loop with the airstreams fully separated.
12.3.4 Where the exhaust air class limits the transfer to a stated ratio, the outdoor airflow shall be increased by the transferred quantity in accordance with ANSI/ASHRAE 62.1, and the increase shall be shown in the ventilation calculation.
12.3.5 The purge provision on a rotary device shall be as indicated in the datasheet.
Rotary Device Purge Sectionradio
○ Purge section furnished
○ No purge section
Derived — the exhaust air transfer ratio limit indicated in the datasheet compared against the certified ratio of the wheel without a purge (by default)
12.3.6 Where a purge section is furnished, the supply and exhaust fans shall be arranged so that the pressure difference across the wheel drives the purge flow from the outdoor air side toward the exhaust side.
12.3.7 Where the unit serves laboratory spaces, the exhaust air class of every airstream brought to the recovery device shall be confirmed against Laboratory Exhaust And Fume HoodsLaboratory Exhaust and Fume HoodsResolves to the current adopted revision.sync/laboratory-exhaust-and-fume-hoods before the recovery device is selected.
NOTE Every device that shares a surface between the two airstreams leaks a little exhaust into the supply, and the certified exhaust air transfer ratio is that leak as a fraction of the supply. A rotary wheel carries exhaust air in its flutes as it turns, and a purge section sweeps those flutes with outdoor air before they reach the supply side, which brings the carryover down to a fraction of a percent; it works only when the pressures across the wheel push the right way, which is a fan arrangement question. The ventilation standard sets what fraction of each exhaust class may come back, and any air that does come back is not outdoor air and has to be made up. (12.3.8)

12.4 Frost Control

12.4.1 The frost control method for the recovery device shall be as indicated in the datasheet.
Energy Recovery Frost Control Methodselect
Wheel speed modulation
Timed wheel stop and defrost cycle
Preheat of the entering outdoor air upstream of the device
Exhaust-side face and bypass dampers
Supply-side bypass dampers
Recirculation of exhaust air to the outdoor air side during defrost
Not required at the site design temperature
Derived — the recovery device type and Site Ambient Temperature MinimumSite Ambient Temperature MinimumParameterEach project supplies its own value.site-ambient-temperature-minimum compared against the manufacturer's published frost threshold for the device at the exhaust condition served (by default)
12.4.2 The frost control method, the outdoor temperature at which it initiates, and the reduction in outdoor airflow or recovery effectiveness while it operates shall be stated in the submittal.
12.4.3 Where frost control reduces the outdoor airflow delivered, the unit shall still deliver not less than the ventilation ANSI/ASHRAE 62.1 requires for the spaces served during frost control, or the sequence shall limit frost control to unoccupied periods.
12.4.4 Where preheat is the frost control method, the preheat section shall be sized for the design outdoor airflow and the temperature rise from Site Ambient Temperature MinimumSite Ambient Temperature MinimumParameterEach project supplies its own value.site-ambient-temperature-minimum to the frost threshold of the device.
NOTE Frost forms on the exhaust side of the device when the exhaust air is cooled below its dew point and below freezing before it leaves, and it blocks the exhaust path and ends the recovery. A total energy device also removes moisture from the exhaust as it cools it, so it frosts at a lower outdoor temperature than a sensible device does, and a building with a dry winter interior frosts later than a humid one. Slowing or stopping a wheel reduces the recovery so the exhaust leaves warmer; bypass dampers do the same for a plate; preheat keeps the entering air above the threshold at a purchased-energy cost that the recovery still repays; recirculating warm exhaust onto the outdoor side defrosts the device but dilutes the ventilation while it does. The method follows from the device and the climate, which is why it is derived. (12.4.5)

12.5 Recovery Bypass

12.5.1 The recovery bypass arrangement shall be as indicated in the datasheet.
Energy Recovery Bypass Arrangementselect
Bypass dampers around the recovery device on both airstreams
Bypass damper around the recovery device on the outdoor air side
Wheel stop or speed reduction with no bypass dampers
12.5.2 The recovery device shall be stopped or bypassed when the outdoor air condition is closer to the supply air setpoint than the exhaust condition is, so that the device does not transfer heat or moisture into the supply that the unit would then have to remove.
12.5.3 Bypass dampers, where furnished, shall be rated in accordance with ANSI/AMCA 500-D with a leakage class not worse than the outdoor air damper on the unit.
12.5.4 The bypass shall be controlled by the unit controller on the outdoor and exhaust air conditions, with the control points exposed to the building automation system.
NOTE There are hours in spring and fall when the outdoor air is nearer the supply setpoint than the exhaust air is, and running the recovery device on those hours moves heat the wrong way. Stopping a wheel ends its transfer at no cost in dampers, and the air still passes through the stopped wheel and pays its pressure drop; bypass dampers route the air around the device, which saves the fan energy of the pressure drop on every bypassed hour and is the only way to stop transfer through a plate, which has no drive to stop. Bypassing both airstreams halves the fan penalty again at the cost of a second set of dampers and the casing length to hold them. (12.5.5)

13 Fans and Motors

13.1 Fan Arrangement

13.1.1 The exhaust fan arrangement shall be as indicated in the datasheet.
Exhaust Fan Arrangementselect
Exhaust fan integral to the unit, drawing building exhaust through the recovery device
No exhaust fan in the unit, with recovery exhaust moved by separate building exhaust fans
No exhaust section
13.1.2 Where the exhaust is moved by separate building exhaust fans, those fans shall conform to HVAC FansHVAC FansResolves to the current adopted revision.sync/hvac-fans, and the pressure drop of the recovery device and the unit's exhaust path shall be included in their selection.
13.1.3 The supply fan arrangement shall be as indicated in the datasheet.
Supply Fan Arrangementradio
○ Single fan
○ Fan array of two or more fans in parallel
Manufacturer's standard (by default)
13.1.4 Where the datasheet leaves the fan arrangement to the manufacturer, the manufacturer shall state the arrangement furnished in the submittal.
13.1.5 Where a fan array is furnished, each fan shall be furnished with a backdraft damper or the array shall be controlled so that a stopped fan does not recirculate air backward through the array.
13.1.6 Where a fan array is furnished, the unit shall deliver not less than the airflow indicated in the datasheet for a unit with one fan of the array out of service.
Airflow With One Array Fan Out of Service as a Percentage of Designrange
%
0100
NOTE An integral exhaust fan is what makes the unit's recovery self-contained: the unit controls both airstreams, keeps their ratio where the device was rated, and drives the purge. Leaving the exhaust to building fans is the arrangement where the exhaust is already collected by fans that exist for another reason and the recovery section is placed in their path, and it hands the airflow ratio to a balance between two systems. A unit with no exhaust section at all has no recovery and tempers the outdoor air with heating alone. A fan array spreads the airflow across small direct-drive wheels, which shortens the unit and keeps partial airflow through a fan failure, at the cost of more motors and the backflow provision. (13.1.7)

13.2 Fan Construction and Drive

13.2.1 The supply and exhaust fan wheel type shall be as indicated in the datasheet.
Fan Wheel Typeselect
Forward-curved centrifugal
Backward-curved centrifugal
Airfoil centrifugal
Unhoused plenum fan
Manufacturer's standard (by default)
13.2.2 Where the datasheet leaves the wheel type to the manufacturer, the manufacturer shall state the wheel type furnished in the submittal.
13.2.3 The fan drive arrangement shall be as indicated in the datasheet.
Fan Drive Arrangementradio
● Direct drive
○ Belt drive
13.2.4 Where a belt drive is furnished, the fan shall be provided with an adjustable motor base, a belt guard with a tachometer opening, and a sheave combination that produces the design fan speed within ±5%.
13.2.5 Fan wheels shall be dynamically balanced as an assembly, and fan balance shall be verified by measurement at the bearings during the factory run test.
13.2.6 Fans shall be selected with the capacity to maintain the design airflow with the filters at change-out resistance and the recovery device in frost control.
NOTE The wheel type is a property of the manufacturer's product line at a given capacity more than a project choice: small units are built around forward-curved wheels because they are compact and quiet at low speed, and larger units around backward-curved, airfoil, or plenum wheels because those reach their efficiency at the pressures a long duct run imposes. A project asserts a wheel type only where a sound or efficiency target requires one. Direct drive removes the belt, the sheave, and the belt dust from an airstream that goes to the occupants without any further filtration, which is why it is the norm on this equipment. (13.2.7)

13.3 Fan Speed Control

13.3.1 The fan speed control shall be as indicated in the datasheet.
Fan Speed Controlselect
Variable frequency drive
Electronically commutated motor
Constant speed
13.3.2 The fan speed control shall provide not less than the modulation Adopted Energy CodeAdopted Energy CodeParameterEach project supplies its own value.adopted-energy-code requires for a unit of the design outdoor airflow and the supply airflow control selected in the datasheet.
13.3.3 Where variable speed is furnished, the fan shall operate stably without surge or stall down to the minimum airflow the unit operates at.
13.3.4 Variable frequency drives furnished with the unit shall be factory-mounted outside the airstream in a compartment ventilated for the drive's heat at Site Ambient Temperature MaximumSite Ambient Temperature MaximumParameterEach project supplies its own value.site-ambient-temperature-maximum, accessible without opening a section that is under pressure during operation, and shall conform to HVAC Variable Frequency DrivesHVAC Variable Frequency DrivesResolves to the current adopted revision.sync/hvac-variable-frequency-drives.
NOTE A constant-speed fan holds the design airflow and nothing else, which is enough for a unit that runs at a fixed ventilation rate and has no filter loading compensation. A variable frequency drive on an induction motor and an electronically commutated motor both modulate; the drive is the arrangement at larger motor sizes and where the project standardizes on one drive type, and the commutated motor is built into the fan at the sizes an array or a small unit uses and needs no drive compartment. Either lets the unit trim speed as filters load and follow a demand signal. (13.3.5)

13.4 Fan Motors

13.4.1 Motor voltage and phase shall match the branch circuit serving the unit as indicated in the datasheet.
Unit Supply Voltagerange
V
208230460575
Per drawings — the electrical drawings and panel schedules (deferred by default)
Unit Supply Phaseradio
○ Single phase, 1Φ
○ Three phase, 3Φ
Per drawings — the electrical drawings and panel schedules (deferred by default)
13.4.2 Any discrepancy between the mechanical schedule and the electrical documents on the voltage or phase serving a unit shall be resolved before the unit is released for fabrication.
13.4.3 Motors shall conform to Electric MotorsCommon Motor Requirements for Electrical EquipmentResolves to the current adopted revision.sync/electric-motors and shall meet the NEMA Premium efficiency level of NEMA MG 1 where a motor of that size and enclosure is covered by that level.
13.4.4 Motors shall be selected so that the nameplate power is not exceeded at any operating point the fan can reach with clean filters and every damper full open.
13.4.5 Motors operated from a variable frequency drive shall be rated for inverter duty in accordance with NEMA MG 1 Part 31.

13.5 Fan Power and Sound

13.5.1 The fan power of each unit at the design airflows and external static pressures shall not exceed the limit Adopted Energy CodeAdopted Energy CodeParameterEach project supplies its own value.adopted-energy-code sets for the unit, with every pressure drop credit claimed identified in the submittal.
13.5.2 Fan power shall be computed from the fan shaft power and the motor and drive efficiencies at the design operating point rather than from the motor nameplate.
13.5.3 Outdoor radiated sound power of outdoor units with an integral air-cooled condenser shall be rated under the program indicated in the datasheet.
Outdoor Sound Rating Programradio
○ AHRI 270
○ AHRI 370
Derived — the unit's cooling capacity, with units below 135,000 Btu/h rated under AHRI 270 and 135,000 Btu/h and above under AHRI 370 (by default)
13.5.4 Supply discharge, outdoor air intake, and exhaust discharge sound power shall be reported in each of the eight octave bands from 63 Hz through 8,000 Hz from tests in accordance with ANSI/AMCA 300.
13.5.5 The A-weighted outdoor sound power level of each outdoor unit shall not exceed the value indicated in the datasheet.
A-Weighted Outdoor Sound Power Levelrange
dB
60110
13.5.6 Where the datasheet does not state a maximum outdoor sound power level, the manufacturer shall state the rated value in the submittal and the design team shall confirm it against the property line and adjacent occupancy criteria stated in the Contract Documents.
13.5.7 Where the unit serves a space with a stated noise criterion, the design team shall carry the submitted discharge sound power through the attenuation of the connected duct path to the receiving room and shall confirm the result against the criterion, with attenuation furnished in accordance with HVAC Sound AttenuatorsHVAC Sound AttenuatorsResolves to the current adopted revision.sync/hvac-sound-attenuators where the criterion is not met.
NOTE The fan power limit is a statement about the whole air system rather than the fan, and a dedicated outdoor air unit pushes through a recovery device, a deep cooling coil, a reheat coil, and often two filter banks before the duct begins, which is why the credits for those components exist and have to be documented. The unit radiates to the roof through its condenser fans and sends fan sound down its supply duct and out its intake and exhaust hoods, and the duct path at a low airflow into a quiet room is the one occupants notice. (13.5.8)

14 Filtration

14.1 Outdoor Air Filtration

14.1.1 Filter efficiency shall be rated in accordance with ANSI/ASHRAE 52.2.
14.1.2 The outdoor air pre-filter shall have not less than the efficiency indicated in the datasheet.
Outdoor Air Pre-Filter Efficiencyrange
MERV
8101113
Default: Not less than 8 MERV
14.1.3 The final filter bank shall be as indicated in the datasheet.
Final Filter Bankradio
● Filter bank downstream of the cooling coil and reheat section
○ No final filter bank
14.1.4 Where a final filter bank is furnished, it shall have not less than the efficiency indicated in the datasheet.
Final Filter Efficiencyrange
MERV
11131416
14.1.5 Air delivered to an occupiable space shall pass through filtration of not less than MERV 8 upstream of the cooling coil and every other wetted surface, in accordance with ANSI/ASHRAE 62.1.
14.1.6 Where the outdoor air at the site exceeds the national ambient air quality standard for fine particulate matter, the outdoor air shall additionally be filtered to the efficiency ANSI/ASHRAE 62.1 requires for that condition.
14.1.7 Where the unit serves health care spaces, the filtration shall be not less than ANSI/ASHRAE 170 requires for the space served.
14.1.8 The filter depth shall be as indicated in the datasheet.
Filter Depthrange
in.
12412
14.1.9 The fan selection shall accommodate the resistance of the selected filters at their change-out condition without falling below the design airflow.
14.1.11 Filter media shall be listed to UL 900.
NOTE Every particle the unit admits comes from outdoors, and the outdoor air is dirtier than the return air a mixed-air unit mostly recirculates, so the pre-filter on this equipment loads faster than a comfort unit's and exists to protect the recovery device and the coil as much as the occupants. A final filter after the coils catches what the wet coil and the casing shed and is where a project puts the fine-particulate efficiency, since a high-efficiency filter upstream of the recovery device sees the full outdoor loading and the full pressure penalty. Moving from MERV 8 to MERV 13 adds a few tenths of an inch of water across the bank at change-out, paid by the fan for the life of the unit; a deeper filter of the same rating holds more dust and lengthens the change interval. (14.1.12)

14.2 Exhaust Air Filtration

14.2.1 The exhaust air filter shall be as indicated in the datasheet.
Exhaust Air Filterradio
● Filter bank upstream of the recovery device on the exhaust side
○ No exhaust air filter
14.2.2 Where an exhaust air filter is furnished, it shall have not less than the efficiency indicated in the datasheet.
Exhaust Air Filter Efficiencyrange
MERV
8101113
Default: Not less than 8 MERV
NOTE The exhaust side of the recovery device sees the dust, lint, and aerosol the building generates, and a wheel or a plate that fouls on its exhaust face loses effectiveness and pressure drop margin together, with the exhaust fan paying for both. A filter on the exhaust protects the device and is the norm on a wheel; it is left out where the exhaust is clean and the device can be washed, or where the exhaust pressure budget is already spent. (14.2.3)

14.3 Filter Rack and Access

14.3.1 Each filter rack shall hold the filters against a gasketed seating frame so that no air path exists around the media.
14.3.2 Filters shall be removable without tools.
14.3.3 Each filter section shall be accessible through its own access panel or door without disturbing the coil, the fan, the recovery device, or the electrical compartment.
14.3.4 Filter face velocity at design airflow shall not exceed the velocity at which the selected media is rated.
14.3.5 A differential pressure switch or transmitter shall be furnished across each filter bank and reported to the building automation system.
NOTE Bypass around the media is the dominant filtration defect in installed units, and it is invisible at every point except a measurement of what reaches the space. A rack that lets filters rattle in their track delivers an in-place efficiency far below the media rating, because unfiltered air is a parallel path with almost no resistance while the media path has a great deal. (14.3.6)

15 Casing Construction

15.1 Casing Panels

15.1.1 The casing panel construction shall be as indicated in the datasheet.
Casing Panel Constructionselect
Double-wall insulated panels
Double-wall insulated panels with a thermally broken frame
Single-wall panels with an interior insulation liner
15.1.2 Casing panels in every section that carries conditioned air shall be insulated to a thermal resistance not less than the value indicated in the datasheet.
Casing Panel Thermal Resistancerange
hr·ft²·°F/Btu
220
15.1.3 Where the datasheet does not state a thermal resistance, the manufacturer shall state the thermal resistance of the panel furnished and shall confirm that the exterior surface of the sections downstream of the cooling coil stays above the dew point of the surrounding air at the design cooling condition and that the interior surface of the sections upstream of the heating section stays above the dew point of the surrounding air at Site Ambient Temperature MinimumSite Ambient Temperature MinimumParameterEach project supplies its own value.site-ambient-temperature-minimum.
15.1.4 Insulation in the airstream shall be faced, coated, or encapsulated so that fibers are not eroded into the supply air at the maximum velocity the section sees.
15.1.5 The casing structure shall be galvanized steel conforming to ASTM A653 with a G90 coating designation as a minimum.
15.1.6 The unit base shall be a full-perimeter rail that supports the unit on the curb or pad without point loads on the casing panels.
NOTE A dedicated outdoor air casing has cold air on the inside of the upstream sections in winter and cold, saturated air on the inside of the downstream sections in summer, with the outdoor or mechanical room air on the other face of the same panel in both cases, so it condenses on whichever face is the cold one in each season. A double-wall panel keeps the insulation out of the airstream and cleans without eroding; the thermal break stops the frame from bridging the insulation and sweating along every panel edge, which is where a double-wall casing in a cold climate or a humid one first drips. The single-wall liner does the thermal job at lower cost and leaves the liner facing exposed. (15.1.7)

15.2 Casing Air Leakage

15.2.1 Casing air leakage at the design operating pressure of each section shall not exceed the percentage of the design outdoor airflow indicated in the datasheet.
Casing Air Leakage as a Percentage of Design Airflowrange
%
0.511.5235
15.2.2 Where the datasheet does not state a leakage limit, the manufacturer shall state the casing leakage of the furnished unit at its design pressures in the submittal.
15.2.3 The partition between the outdoor air and exhaust air paths within the unit shall be sealed so that leakage across it is included in the certified exhaust air transfer ratio of the recovery device or is separately stated in the submittal.
NOTE Air that leaks out of the supply section is conditioned ventilation air the building never receives, and air that leaks from the exhaust path into the outdoor air path upstream of the recovery device is exhaust returned to the supply by a route the recovery device's rating never measured. On a 100% outdoor air unit the second path is the one that matters, because it defeats the air class separation the recovery section was selected for. (15.2.4)

15.3 Exterior Finish

15.3.1 Exterior casing panels of outdoor units shall receive a factory-applied finish that withstands salt spray exposure in accordance with ASTM B117 for not less than the duration indicated in the datasheet without red rust or blistering.
Exterior Finish Salt Spray Exposurerange
hours
50075010001500200025003000
15.3.2 Where the datasheet does not state a salt spray exposure, the manufacturer shall state in the submittal the finish system furnished and the exposure it has been tested to.
15.3.3 Exposed fasteners, hinges, latches, and hardware shall be stainless steel or a coated steel with equivalent corrosion resistance.
15.3.4 Cut edges, field-drilled penetrations, and fasteners shall receive a zinc-rich touch-up coating before the unit is placed in service.
NOTE The salt spray rating is a comparative durability number rather than a service life, and the same finish that passes a short exposure on an inland roof fails within a few years on a coastal one. The number is the lever a project has, so it is stated here as a duration and selected by the exposure at the site rather than defaulted. (15.3.5)

15.4 Access Panels

15.4.1 Access shall be provided to each filter section, the recovery device for removal of a wheel or core, the cooling coil and drain pan, the reheat section, each fan and motor, the compressor compartment, the heating section, the dampers and actuators, and the control panel.
15.4.2 Each access shall permit service of the component behind it without removing the unit from its curb or pad.
15.4.3 The access panel construction shall be as indicated in the datasheet.
Access Panel Constructionselect
Hinged doors with quarter-turn latches
Hinged doors with compression latches
Removable gasketed panels with captive fasteners
15.4.4 Access panels and doors shall be gasketed so that they seal against air leakage at the casing pressure in every operating mode.
15.4.5 Doors on sections under positive pressure shall be furnished with a safety latch that holds the door against the pressure as it is opened.
15.4.6 Panels that must be removed to service a component shall be light enough for one person to handle on a roof, or shall be hinged.
15.4.7 Access panels shall be labeled on the exterior with the section behind them.
NOTE A hinged door with compression latches seals a casing that runs at the pressures a recovery device and two coils impose and opens for the weekly filter check without a wrench; quarter-turn latches are quicker and seal less; a removable panel seals as well as its gasket and takes two hands and a place to lean it, which on a roof in weather is the reason the one-person rule exists. (15.4.8)

15.5 Duct Connection Orientation

15.5.1 The supply and exhaust duct connection orientation shall be as indicated in the datasheet.
Duct Connection Orientationradio
● Vertical, through the curb
○ Horizontal, from the unit end or side
15.5.2 Where horizontal connections are selected on an outdoor unit, the supply and exhaust openings shall be furnished with weathertight flanged collars, and the openings in the unit base shall be closed and insulated.
NOTE Vertical connections put the ductwork inside the curb and through the roof beneath the unit, so the roof penetration is the curb itself and the cold supply duct is never outdoors; horizontal connections leave the ductwork exposed on the roof between the unit and its own penetration, which is why they are the arrangement for a unit that sits on a rail, a frame, or a pad rather than a curb, or for a replacement whose existing ductwork already arrives that way. (15.5.3)

15.6 Outdoor Air and Exhaust Dampers

15.6.1 The outdoor air intake and the exhaust discharge shall each be furnished with a motorized damper that drives closed when the unit is off and on loss of power or control signal.
15.6.2 The outdoor air and exhaust damper leakage class shall be as indicated in the datasheet, tested in accordance with ANSI/AMCA 500-D.
Outdoor Air and Exhaust Damper Leakage Classselect
AMCA Class 1A
AMCA Class 1
AMCA Class 2
AMCA Class 3
Derived — the maximum damper leakage Adopted Energy CodeAdopted Energy CodeParameterEach project supplies its own value.adopted-energy-code permits for the damper's service in Climate ZoneClimate ZoneParameterEach project supplies its own value.climate-zone (by default)
15.6.3 Damper blades shall be airfoil or double-skin construction with blade edge seals and jamb seals, and no felt or fibrous seal shall be furnished on any damper in the unit.
15.6.4 Damper actuators shall be direct-coupled to the damper shaft and sized with not less than 25% reserve torque at the unit's design static pressure.
15.6.5 Outdoor air intake hoods and louvers furnished with the unit shall be rated in accordance with ANSI/AMCA 500-L and sized so that water is not carried into the unit at the design wind-driven rain condition.
15.6.6 Exhaust discharge hoods shall direct the exhaust away from the outdoor air intake of the same unit.
NOTE A 100% outdoor air unit that is off admits the full winter outdoor air through any damper that leaks, onto a hydronic coil with no fan to carry the cold past it, which is the mechanism behind most frozen coils on this equipment and the reason the closed-position leakage class is derived from the energy code rather than left to the product. (15.6.7)

16 Drain Pans and Condensate

16.1 Drain Pan Construction

16.1.1 A drain pan shall be furnished beneath the cooling coil, beneath the reheat section where carryover can reach it, beneath the recovery device where it can condense, and beneath every other section in which condensate can form.
16.1.2 The drain pan material shall be as indicated in the datasheet.
Drain Pan Materialselect
Type 304 stainless steel
Type 316 stainless steel
Galvanized steel with a factory-applied corrosion-resistant coating
Molded polymer
16.1.3 The drain pan shall extend the full width of the coil and beneath the coil headers and return bends, and downstream of the leaving-air face of the coil far enough to capture carryover at the design face velocity.
16.1.4 The drain pan shall be sloped in two planes toward the drain connection and shall hold no standing water when the unit is not operating.
16.1.5 Drain pans shall be insulated on the underside or double-walled where the surface beneath the pan can fall below the dew point of the surrounding air.
NOTE A dedicated outdoor air coil condenses for most of the cooling season rather than in cycles, so its pan carries water continuously and ages under a permanent condensate film. Every geometric requirement on the pan exists to make it empty rather than merely drain, because a pan that holds water in a supply airstream is the growth condition the ventilation standard's wetted-surface rules are written around. A coated steel pan is fine until the coating is scratched, a polymer pan cannot corrode but can crack, and the stainless grades do neither, with the higher grade for coastal or chemical exposure. (16.1.6)

16.2 Condensate Trap and Drain

16.2.1 The drain pan shall be furnished with a primary drain connection not smaller than 3/4 in. at the low point.
16.2.2 The condensate trap arrangement shall be as indicated in the datasheet.
Condensate Trapradio
○ Factory-installed trap integral to the unit
● Field-installed trap by the installing contractor
16.2.3 The trap seal depth shall be not less than the maximum negative static pressure at the drain pan, expressed in inches water gauge, plus 1 in., and the trap outlet shall be below the pan outlet by not less than twice that pressure.
16.2.4 The trap shall be furnished with a cleanout or a union that permits disassembly without cutting the drain line, and shall be primed at startup.
16.2.5 The condensate drain line from the trap shall be routed to an approved point of disposal in accordance with Condensate Drainage PipingHVAC Condensate Drainage PipingResolves to the current adopted revision.sync/condensate-drainage-piping, with the slope and freeze protection the climate requires.
16.2.6 Where the unit is outdoors in a climate with freezing temperatures, the trap and the drain line to the roof penetration shall be heat-traced and insulated or arranged to drain dry when the unit is not cooling.
NOTE A drain trap on a draw-through unit holds water against the fan, not against a sewer. If the seal is shallower than the negative pressure at the pan, the fan pulls the seal out, the pan stops draining, and the unit draws unfiltered air backward through the drain line. On a unit that dehumidifies into the shoulder seasons the trap can be full of water on a night that freezes, and a frozen trap backs the pan up on the first warm morning. (16.2.7)

17 Humidifier Section

17.1 Where the datasheet selects a humidifier section, the section shall be furnished within the unit downstream of the heating section with an absorption distance to the next downstream component not less than the humidifier manufacturer's published distance at the design conditions.
Humidifier Sectionradio
○ Humidifier section furnished in the unit
● No humidifier section
17.2 Where a humidifier section is furnished, the humidifier itself shall conform to HumidifiersHumidifiersResolves to the current adopted revision.sync/humidifiers, and the section shall be furnished with a drain pan, a stainless steel or polymer liner over the absorption distance, and a high-limit humidity sensor downstream that stops the humidifier.
17.3 Where a humidifier section is furnished, the winter design supply air humidity ratio shall be stated on the mechanical equipment schedule, and the heating section shall be sized to supply the evaporation energy of an adiabatic humidifier in addition to the tempering rise.
NOTE A total energy recovery device returns much of the building's moisture to the incoming air in winter, which is why most dedicated outdoor air units in humid-interior buildings need no humidifier; the section is furnished where the recovery is sensible-only, where the exhaust is too dry to return anything, or where the space criterion demands a humidity the recovery alone cannot hold. Humidifying the ventilation air at the unit puts the whole building's moisture through one section and one absorption distance, which is simpler than humidifying at zones and demands that the section never wet the downstream filter. (17.4)

18 Roof Curb, Isolation, and Restraint

18.1 Roof Curb

18.1.1 Requirements in this article apply where the unit is set on a roof.
18.1.2 Each unit shall be set on a roof curb of the type indicated in the datasheet.
Roof Curb Typeselect
Manufacturer's matched insulated curb
Manufacturer's matched curb with integral isolation rails
Manufacturer's matched curb of seismic-rated construction
Adapter curb fitted to an existing curb
Curb fabricated by the roofing or sheet metal trade to the manufacturer's curb drawing
18.1.3 Where a curb is fabricated by a trade other than the unit manufacturer, it shall be built to the manufacturer's published curb drawing for the unit furnished, and the fabricating trade shall be responsible for the fit of the unit to the curb and of the curb to the roof structure.
18.1.4 Where an adapter curb is furnished, the adapter shall be engineered by the unit manufacturer for the existing curb dimensions, which the Contractor shall field-verify before the adapter is released for fabrication.
18.1.5 The curb shall be a welded or mechanically fastened galvanized steel assembly with a continuous wood nailer for roof flashing, internal cross supports beneath the duct openings, insulation on the interior faces, and a gasket at the unit-to-curb joint.
18.1.6 The curb height shall be as indicated in the datasheet, measured from the top of the roof deck to the top of the curb.
Roof Curb Heightrange
in.
812141618243036
Per drawings — the roof curb detail on the contract documents (deferred by default)
18.1.7 The curb height shall provide the flashing height above the finished roof surface that Membrane RoofingMembrane RoofingResolves to the current adopted revision.sync/membrane-roofing requires, including the thickness of the roof insulation and any tapered insulation at the curb.
18.1.8 The curb shall be set level on the roof structure, shimmed as required over a sloped deck, and fastened to the structure as Vibration Isolation And Seismic RestraintVibration Isolation and Seismic RestraintResolves to the current adopted revision.sync/vibration-isolation-and-seismic-restraint and the restraint provisions of this standard require.
18.1.9 Where the unit is set on grade, it shall be set on a level concrete housekeeping pad extending not less than 4 in. beyond the unit base on every side, with the pad detail as indicated on the mechanical site plan.
NOTE The curb is the interface between three trades. The unit manufacturer sizes it to the unit, the roofer flashes it into the membrane, and the structural engineer checks the framing beneath it, and the curb height is the dimension all three have to agree on before the first one starts. The matched curb fits by construction; a seismic curb carries the engineered attachment where the restraint derivation calls for it; an isolation curb breaks the vibration path at the cost of flexible connections at every service; an adapter or a trade-built curb is the arrangement for a replacement or for a roof whose structure dictates the curb. (18.1.10)

18.2 Vibration Isolation

18.2.1 The vibration isolation arrangement shall be as indicated in the datasheet.
Vibration Isolation Arrangementselect
Unit-integral fan and compressor isolation on a rigid curb or pad
Spring isolation rails within the curb
Elastomeric isolation rails within the curb
Restrained spring isolators beneath a unit set on a structural frame or pad
18.2.2 Where isolation rails or isolators are furnished, they shall be selected in accordance with Vibration Isolation And Seismic RestraintVibration Isolation and Seismic RestraintResolves to the current adopted revision.sync/vibration-isolation-and-seismic-restraint for a static deflection not less than the value indicated in the datasheet.
Isolator Static Deflectionrange
in.
0.250.350.7511.522.53
18.2.3 Where the datasheet does not state a static deflection, the isolator selection shall be made from the lowest fan operating speed so that the isolation system natural frequency is not more than one third of that speed.
18.2.4 Where isolation rails or isolators are furnished, the duct, piping, gas, electrical, and condensate connections to the isolated unit shall be made through flexible elements, and the calculated isolation efficiency at the lowest fan operating speed shall be stated in the submittal.
NOTE The fans and compressors are isolated inside the casing as built, and for a unit over a heavy deck remote from occupancy that internal isolation is what most projects rely on. A unit over a light long-span roof, or over a noise-sensitive space, transmits what the internal isolators pass into a structure that amplifies it, and an isolation curb breaks that path at the cost of flexible connections at every service and a curb built for the movement. Springs reach the deflections a low-speed fan needs; elastomeric rails take less height and suit the higher fan speeds of a small unit. (18.2.5)

18.3 Seismic and Wind Restraint

18.3.1 Seismic restraint of the unit and its curb or pad shall be as indicated in the datasheet.
Seismic Restraintradio
○ Engineered seismic restraint of the unit to the curb or pad and of the curb to the structure
○ No seismic restraint beyond the manufacturer's attachment hardware
Derived — Seismic Design CategorySeismic Design CategoryParameterEach project supplies its own value.seismic-design-category applied to the unit weight, the component importance factor assigned to the unit, and the attachment height in accordance with ASCE 7 Chapter 13 (by default)
18.3.2 Wind restraint of the unit and curb shall be as indicated in the datasheet.
Wind Restraintradio
○ Engineered wind restraint of the unit to the curb and of the curb to the structure
○ No wind restraint beyond the manufacturer's attachment hardware
Derived — the wind load ASCE 7 Chapter 29 assigns to rooftop equipment at the unit's height and exposure at the site (by default)
18.3.3 Where engineered restraint is furnished, the restraints and their anchorage shall be designed by an engineer licensed in the jurisdiction of the project, and the design shall state the forces delivered to the structure.
18.3.4 Restraints on an isolated unit shall permit the isolators to function through their normal range and shall engage only under seismic or wind displacement.
18.3.5 Restraint details and anchorage shall be as indicated on the structural drawings.
NOTE Seismic and wind restraint are two separate calculations that happen to use the same hardware, and a unit that needs neither in one place can need both in another. A dedicated outdoor air unit is long for its airflow because of the sections it carries in series, which makes it a larger sail than a comfort unit of the same tonnage, and the calculation is what says whether the manufacturer's clips are enough. (18.3.6)

19 Electrical Provisions

19.1 Power Connection

19.1.1 The unit's minimum circuit ampacity and maximum overcurrent protective device shall be as published by the manufacturer for the configuration furnished, and the branch circuit, feeder, and overcurrent protection serving the unit shall be as indicated on the electrical drawings.
19.1.2 The unit power connection arrangement shall be as indicated in the datasheet.
Unit Power Connectionradio
● Single-point power connection for the complete unit including any electric heater
○ Separate power connections for the unit and the electric heater
19.1.3 The unit disconnecting means shall be as indicated in the datasheet.
Unit Disconnecting Meansselect
Factory-installed non-fused disconnect switch
Factory-installed fused disconnect switch
Factory-installed circuit breaker
Field-installed disconnect by the electrical trade
19.1.4 The disconnecting means shall be lockable in the open position and located within sight of the unit in accordance with NFPA 70.
19.1.5 Where the disconnect is field-installed, it shall conform to Enclosed Switches And DisconnectsEnclosed Switches and DisconnectsResolves to the current adopted revision.sync/enclosed-switches-and-disconnects and shall be mounted on a stand or on the unit at a location the manufacturer permits, clear of every access panel swing.
19.1.6 The short-circuit current rating of the unit control panel shall be not less than the available fault current at the unit terminals indicated in the datasheet.
Available Fault Current at the Unit Terminalsrange
kA
5101418222535425065100
Per drawings — the electrical drawings (deferred by default)
19.1.7 Three-phase units shall be furnished with a phase loss and phase reversal monitor that prevents compressor operation on a lost or reversed phase.
NOTE A factory disconnect arrives wired and listed with the unit and saves the electrical trade a stand on the roof; a fused switch or a breaker adds the unit's own overcurrent protection where the feeder protection is remote or oversized for the unit; a field disconnect is the arrangement where the electrical contract standardizes on one device or the Authority Having Jurisdiction wants it separate from the equipment. A scroll compressor run backward on a reversed phase makes no pressure, heats rapidly, and can fail within minutes, and the phase monitor turns that wiring error into a nuisance trip. (19.1.8)

19.2 Service Receptacle

19.2.1 A receptacle for servicing the unit shall be provided as indicated in the datasheet and in accordance with NFPA 70.
Service Receptacleselect
Factory-installed ground-fault protected receptacle fed from a separate field branch circuit
Factory-installed ground-fault protected receptacle fed through a unit transformer ahead of the unit disconnect
Receptacle furnished and installed by the electrical trade within 25 ft of the unit
19.2.2 The receptacle shall remain energized when the unit disconnecting means is open.
NOTE The receptacle exists so that a technician can run a vacuum pump, a recovery machine, or a light with the unit itself de-energized, which is the condition under which most of the work on a refrigerant circuit is done. A receptacle on the load side of the unit disconnect goes dead at the moment it is needed, which is why the code forbids that arrangement. (19.2.3)

20 Controls and Safeties

20.1 Unit Control Configuration

20.1.1 The unit control configuration shall be as indicated in the datasheet.
Unit Control Configurationselect
Factory-installed unit controller integrated with the building automation system
Factory-installed unit controller operating stand-alone
Factory-installed devices and wiring with control by the building automation system contractor
20.1.2 The party responsible for the dew point and supply air temperature sequence shall be identified in the submittal, and the sequence shall be reviewed before any control device is released for fabrication.
20.1.3 The unit controller shall sequence the recovery device and its bypass and frost control, the cooling capacity to the dew point setpoint, the reheat to the supply air temperature setpoint, the heating section, the dampers, and the supply and exhaust fans.
20.1.4 The unit controller shall carry the manufacturer's compressor protection logic, including minimum run and off times and anti-short-cycle timing, regardless of which party controls the setpoints.
20.1.5 The dew point loop and the supply air temperature loop shall be separate loops with separate setpoints, and satisfying one shall not stop the other.
NOTE A factory controller arrives tested with the sequence that makes a dedicated outdoor air unit hold its dew point, which is a sequence a field programmer has usually not written before, and it also arrives with a fixed sequence and a proprietary tool for changing it. Field-engineered controls put the sequence in one place with the rest of the building and put the responsibility for protecting the compressors and for the two-loop logic on the party that did not build the unit. The compressor protection has to work regardless of who wrote the sequence, which is why it is required of the unit in every configuration. (20.1.6)

20.2 Interlock With the Parallel System

20.2.1 The unit shall run in the occupied mode whenever any space it ventilates is scheduled occupied, independent of the heating or cooling demand of the parallel sensible system.
20.2.2 The unit shall be interlocked with the parallel sensible system through the building automation system so that the parallel system's space temperature control cannot drive the space humidity above the design value by cooling the space below the setpoint at which the ventilation air's dew point holds.
20.2.3 Where the unit delivers to the inlet or supply side of parallel terminal units, the unit supply fan and the terminal fans shall be interlocked so that neither runs against a closed path.
20.2.4 Morning warm-up and cool-down modes of the parallel system shall run with the unit off or with the outdoor air damper at its minimum ventilation position as the sequence directs.
20.2.5 The ventilation demand control shall be as indicated in the datasheet.
Ventilation Demand Controlselect
None, scheduled occupancy only
Carbon dioxide sensors in the spaces served
Occupancy sensor inputs from the spaces served
Occupancy signal from the building automation system
20.2.6 Where ventilation demand control is selected, the outdoor airflow shall be reset between the minimum ANSI/ASHRAE 62.1 requires for the area served and the design outdoor airflow, and shall not be reduced below the area-based component of the ventilation rate.
NOTE The two systems share the spaces and nothing else, and the failures are all at the seam. A parallel unit that overcools a space raises its relative humidity without adding any moisture, and the occupants read that as the ventilation unit failing; a ventilation unit that stops when the parallel system is satisfied leaves the room without outdoor air on a mild day. Demand control on a 100% outdoor air unit saves the conditioning energy of air for people who are not there, and a space sensor resets on the fullest room while a schedule signal resets on the plan. (20.2.7)

20.3 Building Automation System Interface

20.3.1 The communication interface to the building automation system shall be as indicated in the datasheet.
Building Automation System Interfaceselect
BACnet MS/TP
BACnet/IP
Modbus RTU
Modbus TCP
LonWorks FT-10
Hardwired point-to-point interface with no network connection
20.3.2 The interface shall conform to Building Automation SystemBuilding Automation SystemResolves to the current adopted revision.sync/building-automation-system.
20.3.3 The manufacturer shall furnish a complete point list for the interface, giving the object name, object type, engineering units, and read or write access for every exposed point.
20.3.4 Field control connections shall terminate on a labeled terminal block in a compartment accessible without opening a section that is pressurized during operation, and the terminal designations shall match the submitted wiring diagram and point list.
20.3.5 The points exposed to the building automation system shall include those indicated in the datasheet.
Control Points Exposed to the Building Automation Systemcheckbox
☑ Outdoor air temperature and humidity
☑ Supply air temperature
☑ Supply air dew point or humidity
☐ Cooling coil leaving air temperature
☐ Exhaust air temperature and humidity entering the recovery device
☐ Outdoor air temperature leaving the recovery device
☐ Measured outdoor and exhaust airflows
☑ Supply and exhaust fan command, speed, and status
☑ Compressor stage or capacity command and status by circuit
☑ Reheat command and status
☑ Heating stage or modulation command and status
☑ Recovery device command, speed, and status
☐ Recovery bypass damper position
☑ Frost control status
☑ Outdoor air and exhaust damper command and end-switch status
☑ Filter differential pressure for each bank
☐ Refrigerant detection alarm
☐ Condensate overflow alarm
☑ Compressor lockout and general alarm status
☑ Occupied and unoccupied mode command
☑ Supply air temperature and dew point setpoints, writable
20.3.6 Control devices furnished with the unit shall conform to HVAC Controls InstrumentationHVAC Instrumentation and Control DevicesResolves to the current adopted revision.sync/hvac-controls-instrumentation and shall be accessible for calibration and replacement from a service position without entering an operating section.
NOTE The networked protocols differ in what they cost to integrate rather than in what they can carry: the BACnet pair is what most building automation systems speak natively, with the serial form run over a twisted pair to a roof and the IP form over the building network; the Modbus pair is common on equipment controllers and needs a mapping at the automation system; the LonWorks interface serves a building that already runs that network. A hardwired interface exposes only what has a wire, which is enough for a stand-alone unit and not for a unit whose setpoints are written from the automation system. (20.3.7)

20.4 Duct Smoke Detection

20.4.1 Duct smoke detection shall be furnished at the locations indicated in the datasheet.
Duct Smoke Detector Locationsselect
Supply air only
Supply air and exhaust air
None required for the unit
Derived — the unit's supply airflow and exhaust arrangement against the detector thresholds NFPA 90A and the adopted mechanical code set (by default)
20.4.2 The responsibility for furnishing and installing duct smoke detectors shall be as indicated in the datasheet.
Duct Smoke Detector Responsibilityselect
Furnished and installed by the fire alarm contractor
Furnished by the fire alarm contractor and installed by the mechanical contractor
Furnished and installed by the mechanical contractor
Factory-installed by the unit manufacturer
20.4.3 Duct smoke detectors shall be installed in accordance with NFPA 90A, NFPA 72, and the adopted mechanical code, with sampling tubes spanning the duct or plenum cross-section.
20.4.4 Smoke detection shall shut down the supply and exhaust fans through a hardwired interlock that does not depend on the unit controller or the building automation system, and shall report to the fire alarm system in accordance with Fire Alarm SystemsFire Alarm SystemsResolves to the current adopted revision.sync/fire-alarm-systems.
NOTE The supply detector threshold in the mechanical code is set on airflow, so for a given unit the locations are a lookup rather than a choice; the responsibility for furnishing them is a genuine project decision that turns on how the fire alarm contract was written. (20.4.5)

20.5 Unit Safety Devices

20.5.1 Each unit shall be furnished with the safety devices the listing requires, including high and low refrigerant pressure cutouts on each circuit, compressor motor overloads, heating section high-limit and rollout devices, and the low-limit temperature device on every hydronic coil required under Hydronic Heating Section.
20.5.2 A low-limit temperature device shall be furnished downstream of the recovery device on every unit with a hydronic coil or a chilled water coil, arranged to stop the fans, close the outdoor air damper, and open the coil valves when it trips.
20.5.3 A condensate overflow switch shall be furnished in the cooling coil drain pan, arranged to stop the compressors or close the chilled water valve and to alarm when it trips.
20.5.4 A high static pressure safety device shall be furnished in the supply air section of every variable-volume unit whose fan can develop a pressure exceeding the pressure class of the connected ductwork, arranged to stop the supply fan through a hardwired interlock with manual reset.
20.5.5 Every safety device that requires manual reset shall be reset only at the unit, and the unit controller shall report the trip of every safety device to the building automation system where an interface is furnished.
20.5.6 The setpoint of every safety device shall be recorded in the startup report.

21 Factory Testing

21.1 Production Run Test

21.1.1 Every unit shall be run-tested at the factory before shipment.
21.1.2 The factory tests performed on each unit shall include those indicated in the datasheet.
Factory Tests Requiredcheckbox
☑ Refrigerant circuit evacuation, charge, and leak test
☑ Compressor and condenser fan operation on each stage or across the modulation range
☑ Refrigerant operating pressures and temperatures recorded on each circuit
☑ Supply and exhaust fan operation with motor current recorded
☑ Recovery device rotation or flow, purge, and bypass operation
☑ Dehumidification and reheat sequence operated with the leaving air dew point and supply temperature recorded
☑ Heating section fired or energized on each stage
☑ Damper stroke and fail-position test
☑ Safety device trip verification
☐ Refrigerant detection system function test
☑ Controls point-to-point verification
☐ Casing leakage test
☐ Casing water intrusion test
21.1.3 A unit that fails any required test shall be corrected and retested, and the cost of correcting a failed factory test and of every retest shall be borne by the manufacturer.
21.1.4 No unit shall be shipped until every required test has been passed and the results recorded on a report that identifies the unit by serial number.
NOTE The factory run test is the only opportunity to find a charge, a wiring, or a sequence defect while the unit is on a floor with the parts and the people to fix it, and it is the only place the dew point sequence can be exercised at a known entering condition before the site's weather decides when it can be exercised again. A unit that ships untested is repaired on a roof, by crane, in whatever weather the schedule lands on. (21.1.5)

21.2 Test Witnessing

21.2.1 Factory test witnessing shall be as indicated in the datasheet.
Factory Test Witnessingradio
● Unwitnessed, with a certified test report submitted
○ Witnessed at the factory by the Owner's representative
○ Witnessed remotely by live video with the instrumentation in view
21.2.2 Where witnessed testing is selected, the manufacturer shall give not less than ten business days notice of test readiness and shall submit the test procedure for review before the test is scheduled.
21.2.3 Where witnessed testing is selected and the unit fails, the cost of the witness attending each retest shall be borne by the manufacturer.
NOTE A certified report is what most projects rely on, because the test is a production step and the report records it. Attending the test buys a look at the unit under a controlled entering condition that the site may not provide for months, which is worth the trip on a large or custom unit; remote witnessing buys most of that for the cost of a camera and is the arrangement where the factory is far away. (21.2.4)

22 Delivery, Storage, and Handling

22.1 Units shall be shipped fully assembled, charged, and with every opening covered and sealed against water and debris, with a rotary recovery device blocked against rotation in transit.
22.2 Units shall be stored on a level surface, off the ground, in their protective packaging, with the openings sealed, until they are set.
22.3 Units stored for more than 30 days before setting shall have the crankcase heaters energized where the manufacturer requires it, the fan shafts and the recovery wheel rotated by hand at intervals not exceeding 30 days, and shall be inspected by the Contractor for water intrusion, corrosion, and pest intrusion before setting.
22.4 Units shall not be stacked or used as a storage surface.
22.5 The crane, pick radius, and temporary roof loads shown on the rigging and setting plan shall be reviewed by the structural engineer before the pick.
22.6 Units damaged in transit, in storage, or in handling shall be repaired or replaced as the Engineer of Record directs in writing.
22.7 A unit whose refrigerant circuit has been opened by damage shall be evacuated and recharged at the factory or by the manufacturer's representative.

23 Installation

23.1 Rigging and Setting

23.1.1 Units shall be rigged using the lifting points, spreader arrangement, and rigging hardware the manufacturer designates, with no sling bearing against casing panels, coils, hoods, or fan guards.
23.1.2 Before the pick, the Contractor shall verify that the curb or pad is set, level, flashed, and dried in, that the curb openings align with the unit, and that the roof structure and curb have been confirmed adequate for the unit operating weight.
23.1.3 The unit shall be set on the curb gasket so that the gasket is continuous and compressed on all four sides, and level within the tolerance the manufacturer publishes so that the drain pans slope to their connections.
23.1.4 Shipping restraints, shipping bolts, transit blocks on the fan and compressor mounts, and the rotation block on the recovery wheel shall be removed after the unit is set and before the unit is energized.
NOTE A shipping restraint left on a compressor mount holds the compressor rigid against the base, so the first start delivers the full vibration into the casing and into refrigerant tubing that was not designed to flex there; a block left on a wheel stalls its drive on the first start. Both are same-week failures rather than slow ones, and the pre-startup inspection exists to catch them. (23.1.5)

23.2 Roofing and Flashing

23.2.1 The curb shall be flashed into the roofing membrane by the roofing installer in accordance with Membrane RoofingMembrane RoofingResolves to the current adopted revision.sync/membrane-roofing and Sheet Metal Flashing And TrimSheet Metal Flashing and TrimResolves to the current adopted revision.sync/sheet-metal-flashing-and-trim, and the flashing shall be complete and watertight before the unit is set.
23.2.2 Every penetration of the roof for ductwork, piping, gas piping, electrical conduit, condensate drainage, and control wiring shall pass through a flashed curb, sleeve, or pitch pocket, and no penetration shall be made through the unit-to-curb gasket line.
23.2.3 Where the Contractor is required to restore roofing disturbed by the work, restoration shall match the pre-existing condition recorded in the informational submittal, and where no record was submitted, the Engineer of Record shall make the initial determination of the pre-existing condition.

23.3 Intake and Exhaust Placement

23.3.1 The outdoor air intake of each unit shall be separated from exhaust fan discharges, the unit's own exhaust discharge, plumbing vents, flue outlets, cooling tower drift, loading docks, and the other contaminant sources ANSI/ASHRAE 62.1 lists by the distances that standard and the adopted mechanical code require.
23.3.2 Units shall be located so that the condenser discharge of one unit is not drawn into the condenser intake or the outdoor air intake of another.
23.3.3 Intake and exhaust locations shall be as indicated on the mechanical roof plan.
NOTE Every cubic foot the unit supplies is drawn at its intake, so a contaminant at the intake is delivered to every space on the duct at full strength with no return air to dilute it. The separation distances are written for that case, and the unit's own exhaust, a few feet from its own intake on the same casing, is the source most often overlooked. (23.3.4)

23.4 Duct Connections at the Unit

23.4.1 Supply and exhaust ductwork shall connect to the unit in accordance with HVAC DuctworkHVAC DuctworkResolves to the current adopted revision.sync/hvac-ductwork and the SMACNA HVAC Duct Construction Standards, independently supported so that no duct weight is carried by the unit or the curb, and through flexible connectors on an isolated unit.
23.4.2 Supply ductwork carrying air below the dew point of the surrounding space shall be insulated and vapor-sealed in accordance with Mechanical InsulationMechanical InsulationResolves to the current adopted revision.sync/mechanical-insulation from the unit connection to the outlets.
23.4.3 Duct transitions at the unit shall not exceed the transition angle at which the fan outlet loss published in the submittal remains valid, and ductwork within the curb shall be sealed to the curb opening.
NOTE A dedicated outdoor air duct carries air at or near its dew point in summer and air that is still cold in winter wherever recovery alone tempers it, so it sweats on the outside wherever the vapor seal is incomplete, in ceilings and over finishes. The vapor seal on this duct is the difference between a dry ceiling and a stained one, and it is continuous or it is not there. (23.4.4)

23.5 Utility Connections

23.5.1 Gas piping to each gas-fired unit shall be installed in accordance with Natural Gas PipingNatural Gas PipingResolves to the current adopted revision.sync/natural-gas-piping or Fuel Gas PipingFacility Liquefied-Petroleum and Fuel Gas PipingResolves to the current adopted revision.sync/fuel-gas-piping as applicable to the fuel, with a shutoff valve, a sediment trap, and a union at the unit connection, leak-tested before the burner is fired, and with a pressure regulator vented to the outdoors clear of the outdoor air intake where the supply pressure exceeds the gas train rating.
23.5.2 Hydronic and condenser water piping to the unit shall be installed in accordance with Hydronic PipingHydronic PipingResolves to the current adopted revision.sync/hydronic-piping, with isolation valves, strainers, and drains at the unit connection, and through flexible connectors on an isolated unit.
23.5.3 Electrical connections shall be made in accordance with NFPA 70, and conduit to an isolated unit shall include not less than 18 in. of flexible conduit at the unit.
23.5.4 The condensate trap and drain line shall be installed, sloped, and primed before the unit is started in cooling.
23.5.5 Control wiring shall be run in the raceway the unit manufacturer designates, segregated from power wiring, and terminated on the labeled terminals shown on the submitted wiring diagram.

23.6 Service Clearances

23.6.1 The service clearances shown on the reviewed configuration drawing shall be maintained clear of ductwork, piping, conduit, and other equipment after installation, including the withdrawal path of the recovery wheel or core, the coil pull, each filter bank, and the compressor compartment.
23.6.2 Where a service clearance conflicts with other work, the conflict shall be resolved before either is installed, and the Engineer of Record shall make the initial determination of which work relocates.

24 Startup, Commissioning, and Balancing

24.1 Pre-Startup Inspection

24.1.1 Before any unit is energized, the Contractor shall complete and record the inspection items indicated in the datasheet.
Pre-Startup Inspection Itemscheckbox
☑ Roof structure and curb or pad load verified
☑ Curb flashing complete and watertight
☑ Unit level and drain pans sloping to their connections
☑ Unit-to-curb gasket continuous and compressed
☑ Shipping restraints and wheel rotation block removed
☑ Fan and compressor mounts free to move
☑ Supply and exhaust duct connections complete and sealed
☑ Condensate trap installed, sized for the pan static pressure, and primed
☑ Electrical connections complete and phase rotation verified
☑ Disconnect and service receptacle operable
☐ Gas piping connected, leak-tested, and supply pressure verified
☐ Hydronic piping connected, flushed, and filled
☑ Filters installed in every bank
☑ Service clearances verified clear
☐ Refrigerant detection sensors in place and dated
24.1.2 The inspection record shall mark as not applicable the items for sections the unit does not carry, rather than omitting them.

24.2 Startup Service

24.2.1 The startup service shall be as indicated in the datasheet.
Startup Serviceselect
Startup performed by a factory-authorized service representative
Startup performed by the installing contractor with factory technical support
Startup performed by the installing contractor
24.2.2 Startup shall verify the refrigerant charge on each circuit against the nameplate and the published subcooling or superheat target, the operation of each compressor and condenser fan across its capacity range, the recovery device drive, purge, bypass, and frost control, the dehumidification and reheat sequence holding the dew point and supply temperature setpoints, the heating section on each stage with the input measured on gas-fired units, the dampers, the trip of every safety device at its setpoint, and the refrigerant detection and mitigation sequence where a detection system is furnished.
24.2.3 Each safety device shall be tested by driving the condition it senses to its setpoint rather than by simulating the device output.
24.2.4 The startup report shall record the measured outdoor and exhaust airflows, external static pressures, fan speeds, motor currents, refrigerant operating pressures and temperatures by circuit, gas input and manifold pressure, the measured leaving air dew point and supply air temperature with the outdoor condition at the time, and the setpoint of every safety device.
NOTE A factory representative arrives knowing the two-loop sequence and the manufacturer's charge and superheat targets for a circuit that runs colder than a comfort unit's, and the manufacturer's warranty commonly starts from that visit. An installing contractor with factory support on the phone covers most of that at lower cost on a unit the contractor has started before; the contractor alone is the arrangement where the maintaining staff will own the unit and wants to learn it from the first start. (24.2.5)

24.3 Commissioning

24.3.1 The commissioning scope shall be as indicated in the datasheet.
Commissioning Scopecheckbox
☑ Manufacturer startup with a signed report
☑ Point-to-point verification of every control device
☑ Functional performance testing of the dew point and supply air temperature sequences
☑ Verified trip of every safety device at its setpoint
☐ Energy recovery effectiveness verified from measured airstream conditions
☐ Frost control sequence verification by induced condition or trend
☐ Recovery bypass changeover verification
☑ Interlock with the parallel sensible system verified in every mode
☐ Ventilation demand control response verification
☐ Refrigerant detection and mitigation verification by introduced signal
☑ Verification of drain pan drainage during dehumidification
☑ Integrated testing with the fire alarm system
☑ Seasonal dehumidification test at an outdoor dew point near design
☐ Trend review over a seasonal period
24.3.2 Commissioning shall be performed in accordance with CommissioningTotal Building CommissioningResolves to the current adopted revision.sync/commissioning.
24.3.3 Where the seasonal dehumidification test is selected and the outdoor dew point at substantial completion is not within 5°F of the design dew point, the test shall be deferred to the first period in which it is, under a written deferred-testing plan that names the party who returns to perform it and the condition that triggers it.
24.3.4 Drain pan drainage shall be verified during dehumidification, with the coil condensing and the fan at design speed, by observing continuous flow at the drain and no accumulation in the pan.
24.3.5 Energy recovery effectiveness shall be verified by measuring the dry-bulb temperature and humidity of all four airstreams at the device and the two airflows, and comparing the computed effectiveness against the submitted value at the measured airflow ratio.
NOTE A dedicated outdoor air unit can only be proven on a humid day, and substantial completion lands on a humid day by chance. The functional test at any other condition shows the sequence works and says nothing about whether the coil reaches the design dew point at the design load, which is the one question the Owner is paying the unit to answer; the deferred test is how that question gets answered rather than assumed. (24.3.6)

24.4 Air Balancing

24.4.1 Testing, adjusting, and balancing shall be performed in accordance with Testing Adjusting And BalancingTesting, Adjusting, and Balancing for HVACResolves to the current adopted revision.sync/testing-adjusting-and-balancing after startup is complete and after the control sequences have been verified.
24.4.2 The balancing agent shall set and record the design outdoor airflow and the design exhaust airflow through the recovery device, and shall confirm that the airflow ratio is within the range the recovery device is rated for.
24.4.3 Measured outdoor airflow after balancing shall be within the tolerance indicated in the datasheet of the design value, and not below the ventilation ANSI/ASHRAE 62.1 requires.
Airflow Balancing Tolerancerange
%
015
Default: Not more than 10 %
24.4.4 Where the design airflow cannot be achieved within the tolerance, the balancing agent shall report the measured fan speed, static pressure, and motor current, and the Engineer of Record shall determine the remedy.
24.4.5 Filters shall be clean at the time of the final balance, and the filter differential pressure across each bank shall be recorded.
24.4.6 The balance report shall record the as-left fan speeds, drive component designations for belt drives, outdoor and exhaust airflows, external static pressures, motor currents, and the airflow measurement station readings against the measured values.

25 Identification and Labeling

25.1 Each unit shall be furnished with a permanent nameplate on the exterior of the casing, mechanically fastened rather than adhered, of the material indicated in the datasheet.
Unit Nameplate Materialselect
Stainless steel
Anodized aluminum
Laminated phenolic
25.2 The nameplate shall state the unit tag, the manufacturer, the model and serial number, the design outdoor and exhaust airflows, the leaving air dew point and supply air temperature at the design condition, the heating input or capacity, the refrigerant designation and factory charge by circuit, the electrical characteristics including minimum circuit ampacity and maximum overcurrent protective device, and the date of manufacture.
25.3 The unit tag on the nameplate shall match the tag used in the Contract Documents, on the building automation system, and in the operation and maintenance manuals.
25.4 Units charged with a refrigerant in a flammable safety group shall bear the flammable refrigerant marking UL 60335-2-40 and ASHRAE 15 require, applied at the location the listing designates.
25.5 Each filter access panel shall be labeled with the filter efficiency and sizes the bank holds, and the recovery device access shall be labeled with the device type and the direction of rotation or flow.
25.6 The electrical compartment shall contain a permanently mounted copy of the unit wiring diagram, and control terminal strips shall be labeled to match the submitted point list.
NOTE A stainless or anodized plate outlasts the unit on a roof; a phenolic plate is cheaper and legible indoors and fades under sun, which is why the material is a choice rather than a default and follows the unit's location. (25.7)

26 Warranty

26.1 Unit Warranty

26.1.1 The manufacturer shall warrant each unit against defects in materials and workmanship for the terms indicated in the datasheet.
Unit Parts Warranty Termrange
years
123510
Default: Not less than 1 years
Unit Labor Warranty Termrange
years
1235
Default: Not less than 1 years
Warranty Start Milestoneradio
● Date of substantial completion
○ Date the Owner takes beneficial use of the system
○ Date of shipment
26.1.2 A component repaired or replaced under warranty shall carry a warranty for a full term from the date of the repair or for the remainder of the original term, whichever ends later.
NOTE Parts and labor are separate commitments commonly sold at different terms, which is why they are stated separately here. A parts-only extension transfers the cost of the component and leaves the Owner paying for the technician, the crane, and the refrigerant, so the two terms have to be read together to know what the coverage is worth on a roof. Starting the term at substantial completion is the usual arrangement; beneficial use protects an Owner whose completion is delayed past the first cooling season, and shipment is the manufacturer's preferred start and shortens the coverage by the construction period. (26.1.3)

26.2 Compressor Warranty

26.2.1 Each compressor shall be warranted against defects in materials and workmanship for the term indicated in the datasheet, in addition to the unit warranty.
Compressor Warranty Termrange
years
123510
Default: Not less than 5 years
26.2.2 The compressor warranty shall not be conditioned on service by the manufacturer's own organization where the service is performed by a technician certified under 40 CFR Part 82 Subpart F and, for a flammable refrigerant, trained for that refrigerant.

26.3 Energy Recovery Component Warranty

26.3.1 The recovery device, including a wheel's drive, bearings, and seals or a plate core, shall be warranted against defects in materials and workmanship and against loss of certified effectiveness from a defect for the term indicated in the datasheet, in addition to the unit warranty.
Energy Recovery Component Warranty Termrange
years
123510
Default: Not less than 5 years

26.4 Gas Heat Exchanger Warranty

26.4.1 Requirements in this article apply where the datasheet selects a gas-fired heating source or a gas-fired supplemental heat source.
26.4.2 The gas heat exchanger shall be warranted against failure by cracking, burn-through, and corrosion for the term indicated in the datasheet, in addition to the unit warranty.
Gas Heat Exchanger Warranty Termrange
years
1510152025
Default: Not less than 10 years
26.4.3 Where a heat exchanger warranty term is conditioned on the heat exchanger material, the term stated in the datasheet shall apply to the material selected in the datasheet.

26.5 Warranty Service

26.5.1 The manufacturer shall maintain factory-trained service capability for the units furnished within the region of the project for the duration of the warranty term, and shall respond to a warranty notification within 2 business days.
26.5.2 The Contractor shall warrant the installation, including the curb setting, flashing, duct and utility connections, isolation, and condensate and control connections, for the term indicated in the datasheet.
Installation Warranty Termrange
years
1235
Default: Not less than 1 years
26.5.3 A defect attributable to the installation shall be corrected at the Contractor's expense, and where a warranty repair requires removal or modification of roofing or other adjacent work, the cost of removing and restoring that work shall be borne by the party responsible for the defect.
26.5.4 The manufacturer's warranty shall not be voided by a field refrigerant charge adjustment, a detection sensor replacement, a wheel seal or belt replacement, or a filter change performed in accordance with the operation and maintenance manual by a qualified technician.

27 Spare Parts

27.1 The Contractor shall furnish the spare parts indicated in the datasheet at substantial completion.
Spare Parts Furnishedcheckbox
☑ One complete set of filters of every size and efficiency installed
☐ Two complete sets of filters of every size and efficiency installed
☑ One complete set of drive belts for every belt-driven fan and recovery wheel
☐ One set of recovery wheel seals for each wheel size installed
☐ One set of access panel and door gaskets for each unit
☑ One set of every fuse type installed
☐ One spare dew point or humidity sensor of each type installed
☐ One spare refrigerant detection sensor for each unit on which a detection system is furnished
☐ One spare ignition control and flame sensor for each gas-fired heating section type installed
27.2 The Contractor shall obtain a signed receipt from the Owner for the spare parts delivered.
27.3 Spare parts shall be delivered in the manufacturer's packaging, labeled with the unit tag they serve and with the manufacturer's part designation, and spare filters shall be stored in sealed packaging in a clean, dry location the Owner designates.
27.4 The Contractor shall furnish a written inventory correlating each spare item to the unit it serves and the location where it was stored.
27.5 The operation and maintenance manual shall include a filter change schedule for each bank derived from the initial and change-out resistances stated in the submittal, the recovery device seal, belt, and cleaning schedule, the condensate trap cleaning procedure, and, where a detection system is furnished, the replacement date of each refrigerant detection sensor.

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"Dedicated Outdoor Air Systems." SynC Standards. Licensed under CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/). Source: https://synergyinconstruction.com/wiki/sync/dedicated-outdoor-air-systems — reference material only; not professional engineering advice and provided without warranty. Verify against governing codes and have a licensed professional review before use.