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Air Handling Units

Rev8
IssuedAug 29, 2026
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1 Scope

NOTE A central station air handling unit is an assembly of a casing, one or more fans, and the coil, filter, damper, and accessory sections needed to condition air, all of which depend on field-installed ductwork to carry that air to the spaces served. That dependence is what separates the equipment covered here from unitary and terminal equipment, which conditions air for the space it sits in or immediately adjacent to. (1.1)
NOTE The following sections and provisions are covered when they form part of the unit: (1.2)
  • Casing, structural base, and access provisions
  • Supply, return, relief, and exhaust fan sections
  • Chilled water, direct-expansion, hot water, steam, and electric heating coils
  • Air filtration sections
  • Mixing sections, outdoor air, return air, and relief air dampers, and the air-side economizer
  • Energy recovery sections
  • Humidifier sections
  • Drain pans, condensate connections, and traps
  • Vibration isolation, seismic restraint, and flexible connections
  • Unit-mounted controls, safety devices, and the physical interface to the building automation system
NOTE The following are outside this standard: (1.3)
  • Ductwork, duct accessories, and duct insulation beyond the unit connection, covered by HVAC DuctworkHVAC DuctworkResolves to the current adopted revision.sync/hvac-ductwork
  • Fan coil units, blower coil units, and air terminal units, covered by Fan Coil UnitsFan-Coil UnitsResolves to the current adopted revision.sync/fan-coil-units
  • Unitary packaged equipment with an integral refrigeration circuit, covered by Packaged Rooftop UnitsPackaged Rooftop UnitsResolves to the current adopted revision.sync/packaged-rooftop-units
  • Variable frequency drives, covered by HVAC Variable Frequency DrivesHVAC Variable Frequency DrivesResolves to the current adopted revision.sync/hvac-variable-frequency-drives
  • Hydronic piping, valves, and specialties serving the coils, covered by Hydronic PipingHydronic PipingResolves to the current adopted revision.sync/hydronic-piping
  • Chilled water and heating water plant equipment, covered by HVAC PumpsHVAC PumpsResolves to the current adopted revision.sync/hvac-pumps
  • The building automation system, its sequences of operation, and control devices not mounted on the unit, covered by Building Automation SystemBuilding Automation SystemResolves to the current adopted revision.sync/building-automation-system
  • Testing, adjusting, and balancing of the completed air distribution system, covered by Testing Adjusting And BalancingTesting, Adjusting, and Balancing for HVACResolves to the current adopted revision.sync/testing-adjusting-and-balancing
1.4 Each air handling unit shall be furnished as a coordinated assembly by a single manufacturer, who shall be responsible for the aerodynamic, structural, thermal, acoustic, and hydraulic interaction of the sections furnished.
1.5 Where the Contract Documents direct that a unit be field-erected from separately procured sections, the Contractor shall identify in the submittal the party responsible for the coordinated performance of the assembly.
1.6 Where a requirement of this standard conflicts with a requirement of a standard that governs a component covered elsewhere, 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 430 (I-P) Performance Rating of Central Station Air-handling Unit Supply Fans
ANSI/AHRI 410 Performance Rating of Forced-Circulation Air-Cooling and Air-Heating Coils
ANSI/AHRI 1350 (I-P) Mechanical Performance Rating of Central Station Air-handling Unit Casings
ANSI/AHRI 1060 Performance Rating of Air-to-Air Exchangers for Energy Recovery Ventilation Equipment
ANSI/AMCA 210 / ANSI/ASHRAE 51 Laboratory Methods of Testing Fans for Certified Aerodynamic Performance Rating
ANSI/AMCA 208 Calculation of the Fan Energy Index
ANSI/AMCA 214 Test Procedure for Calculating Fan Energy Index for Commercial and Industrial Fans and Blowers
ANSI/AMCA 300 Reverberant Room Method for Sound Testing of Fans
ANSI/AMCA 301 Methods for Calculating Fan Sound Ratings from Laboratory Test Data
ANSI/AMCA 500-D Laboratory Methods of Testing Dampers for Rating
AMCA 511 Certified Ratings Program - Product Rating Manual for Air Control Devices
ANSI/AMCA 610 Laboratory Methods of Testing Airflow Measurement Stations for Performance Rating
ANSI/ASHRAE 52.2 Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size
ANSI/ASHRAE 62.1 Ventilation and Acceptable Indoor Air Quality
ANSI/ASHRAE 84 Method of Testing Air-to-Air Heat/Energy Exchangers
ANSI/ASHRAE 111 Measurement, Testing, Adjusting, and Balancing of Building HVAC Systems
ANSI/ASHRAE/IES 90.1 Energy Standard for Sites and Buildings Except Low-Rise Residential Buildings
ANSI/ASHRAE 188 Legionellosis: Risk Management for Building Water Systems
NFPA 90A Standard for the Installation of Air-Conditioning and Ventilating Systems
NFPA 70 National Electrical Code
NFPA 72 National Fire Alarm and Signaling Code
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
UL 214 Tests for Flame Propagation of Fabrics and Films
NEMA MG 1 Motors and Generators
ASTM A653 Steel Sheet, Zinc-Coated or Zinc-Iron Alloy-Coated by the Hot-Dip Process
ASCE 7 Minimum Design Loads and Associated Criteria for Buildings and Other Structures
SMACNA HVAC Duct Construction Standards HVAC Duct Construction Standards - Metal and Flexible
ASHRAE Handbook HVAC Systems and Equipment

3 Submittals

3.1 Action Submittals

3.1.1 The Contractor shall submit the following for each air handling unit tag and shall not release any unit for fabrication until the submittal has been reviewed and returned:
  • Unit configuration drawing showing section order, overall dimensions, shipping splits, connection sizes and locations, operating and shipping weights, center of gravity, and required service clearances
  • Fan selection data showing the certified fan curve with the design operating point plotted against the calculated system resistance, and the shaft power, speed, and static efficiency at that point
  • Fan energy index at the highest design airflow rate, with the calculation basis identified
  • For variable-air-volume units, the fan operating point at minimum design airflow and the surge or stall boundary of the selected wheel
  • Fan sound power levels in each of the eight octave bands from 63 Hz through 8,000 Hz, reported separately for inlet, outlet, and casing radiated paths
  • Motor data including nameplate power, speed, voltage, phase, full-load amperes, efficiency at 100%, 75%, and 50% load, service factor, insulation system, enclosure, and inverter-duty rating
  • Coil selection data for each coil giving entering and leaving air and fluid conditions, face area, face velocity, rows, fin spacing, circuiting, capacity, and air-side and fluid-side pressure drop
  • Filter data for each stage giving efficiency rating, media construction, face area, face velocity, initial resistance, recommended final resistance, and dust-holding capacity
  • Casing construction details showing panel section, insulation type and thickness, thermal break arrangement, door and panel gasketing, and the fastening of interior liners
  • Casing performance ratings for air leakage, deflection, and thermal performance, with the rating basis identified
  • Damper schedule giving blade arrangement, frame and blade material, seal material, free area, leakage class, pressure rating, and actuator torque and fail position
  • Drain pan drawings showing material, gauge, extent relative to the coil face, slope directions, and the location and size of primary and secondary drain connections
  • Vibration isolation data giving isolator type, rated and operating load, static deflection at operating load, and the calculated isolation efficiency at the lowest operating fan speed
  • Seismic restraint details and calculations bearing the seal of an engineer licensed in the jurisdiction of the project, where seismic restraint is required
  • Electrical schematic and point-to-point wiring diagram showing factory wiring, field terminations, and the terminal designations used on the unit
  • Schedule of control devices furnished with the unit, identifying signal type, range, and terminal designation for each point
Action Submittals Requiredcheckbox
☑ Unit configuration drawing with weights and service clearances
☑ Certified fan curve with the design point plotted
☑ Fan energy index with calculation basis
☐ Variable-air-volume minimum-flow operating point
☑ Octave band fan sound power levels
☑ Motor data with efficiency and inverter-duty rating
☑ Coil selection data for each coil
☑ Filter data for each stage
☑ Casing construction details
☐ Casing leakage, deflection, and thermal ratings
☑ Damper schedule with leakage class and actuator data
☑ Drain pan drawings
☑ Vibration isolation data with static deflection
☐ Seismic restraint details and calculations
☑ Electrical schematic and wiring diagram
☑ Control device schedule with terminal designations
3.1.2 The configuration drawing shall show the coil pull clearance, the filter withdrawal clearance, and the fan wheel and motor removal path for each section, dimensioned from the unit face.
NOTE A submittal that omits the service clearances is the single most expensive omission in this equipment class, because a unit that fits the mechanical room but cannot have its coils pulled is discovered only when the first coil fails, by which time the surrounding piping, ductwork, and often a wall are already in place. (3.1.3)

3.2 Closeout Submittals

3.2.1 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 and a parts list for every furnished component
  • As-built configuration drawings recording every field modification to the reviewed configuration
  • Certified factory test report for each unit
  • Startup report for each unit signed by the person who performed the startup
  • Record of the as-installed drive components for belt-driven fans, giving sheave designations, bore, bushing, belt designation, and center distance
  • Record of the filter media installed at substantial completion, giving efficiency rating, media designation, quantity, size, and installation date
  • Air balance report for the units and their connected systems
  • Warranty documentation correlating each unit serial number to its installation date and warranty expiration date
Closeout Submittals Requiredcheckbox
☑ Operation and maintenance manuals indexed by unit tag
☑ As-built configuration drawings
☑ Certified factory test report for each unit
☑ Signed startup report for each unit
☐ As-installed drive component record
☑ Installed filter media record with installation dates
☑ Air balance report
☑ Warranty documentation correlated to serial numbers

3.3 Informational Submittals

3.3.1 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 delivery route, lifting points, spreader arrangement, and the temporary loads imposed on the structure
  • Manufacturer's field service report for each site visit made during the warranty period
  • Certification that the coils have been hydrostatically tested after field piping connections, with the test pressure and duration recorded
  • Written record of the pre-existing condition of any surface or assembly the Contractor is required to restore
Informational Submittals Requiredcheckbox
☑ Rigging and setting plan before shipment
☑ Field service reports during the warranty period
☑ Field hydrostatic test certification for coils
☐ Pre-existing condition record for restored surfaces

4 Quality Assurance

4.1 Manufacturer Qualifications

4.1.1 The unit manufacturer shall have produced central station air handling units of the type furnished for not less than the number of years indicated in the datasheet.
Minimum Manufacturer Experiencerange
years
025
Default: 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 that would 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 Certification of Rated Performance

4.2.1 Published performance ratings shall be certified under the programs indicated in the datasheet.
Certification Programs Requiredcheckbox
☑ Supply fan performance certified under AHRI 430
☑ Coil performance certified under AHRI 410
☐ Casing mechanical performance certified under AHRI 1350
☐ Energy recovery performance certified under AHRI 1060
☑ Fan aerodynamic performance licensed to bear the AMCA seal
☐ Fan sound performance licensed to bear the AMCA seal
☐ Damper leakage licensed to bear the AMCA seal
4.2.2 Ratings claimed as certified shall bear the certification mark of the applicable program on the published data submitted.
4.2.3 Where a selected component is outside the scope of the certification program named for it, the manufacturer shall state that fact in the submittal and shall furnish the test data on which the rating is based.
NOTE A certification program is a statement about how a rating was produced, not about how good the rating is. AHRI 430 certifies that the supply fan performance published for a central station unit was verified by an independent laboratory under a program AHRI administers, so two certified selections can be compared directly. Participation in the casing program under AHRI 1350 is narrower than participation in the fan program, so requiring it can restrict the bidder list. (4.2.4)

4.3 Electrical Safety Listing

4.3.1 The complete unit assembly, including all factory-installed electrical components, shall be listed and labeled by a Nationally Recognized Testing Laboratory.
4.3.2 Units listed to UL 1995 are acceptable where the Authority Having Jurisdiction accepts that listing for the equipment furnished.
4.3.3 Factory-wired control and power panels shall be listed to UL 508A and shall bear a label giving the short-circuit current rating of the panel.
4.3.4 Field-installed electrical components not covered by the unit listing shall be individually listed for the application.

4.4 Preinstallation Conference

4.4.1 A preinstallation conference shall be held before the first unit is delivered to the site, attended by the Contractor, the mechanical installer, the controls installer, the testing and balancing agent, the commissioning agent where one is engaged, and the Owner's representative.
4.4.2 The conference agenda shall cover the delivery and rigging sequence, the structural readiness of each equipment location, the utility connections and their sequence, the vibration isolation procedure, the controls interface and point responsibility, and the startup and commissioning schedule.

5 Service Conditions and Site Data

5.1 Installation Environment

5.1.1 The casing weather protection furnished shall be as indicated in the datasheet.
Casing Weather Protectionselect
Indoor casing with no weather protection
Outdoor casing with sloped roof, weather hoods, and drainable base
Outdoor casing with a walk-in weather enclosure over the service side
Indoor casing within a field-erected weather enclosure by others
5.1.2 The unit locations and orientations are as indicated on the mechanical plans.
NOTE Weather protection is a construction decision rather than a location, which is why it is a selection here even though the location that drives it is shown on the drawings. A unit set in a rooftop penthouse is indoors for the purpose of casing construction and outdoors for the purpose of the ambient temperature its motors and controls see. (5.1.3)
5.1.4 Outdoor units shall be furnished with bird screens on all outdoor air intakes and relief openings.
5.1.5 Exposed fasteners, hinges, latches, and hardware on outdoor units shall be stainless steel or a coated steel with equivalent corrosion resistance.

5.2 Site Elevation

5.2.1 Fan, coil, filter, and motor ratings shall be corrected for the air density at the site elevation indicated in the datasheet, and the corrected values shall be the values published in the submittal.
Site Elevationrange
ft
012000
Per drawings — site elevation as indicated on the contract documents (deferred by default)
NOTE Air density falls roughly 3% per 1,000 ft of elevation. A fan selected from a sea-level catalog and installed in Denver moves the same volume of air but develops about 17% less static pressure and draws proportionally less power, so the unit makes its airflow only if the selection was corrected. The same thinning air also reduces the convective cooling of an open motor, which is why motor ratings carry their own altitude correction. (5.2.2)

5.3 Outdoor Design Conditions

5.3.1 Coil capacities and economizer operation shall be evaluated at the outdoor design conditions indicated in the datasheet.
Summer Outdoor Design Dry-Bulb Temperaturerange
°F
70125
Per drawings — design conditions as indicated on the mechanical schedules (deferred by default)
Summer Outdoor Design Wet-Bulb Temperaturerange
°F
5090
Per drawings — design conditions as indicated on the mechanical schedules (deferred by default)
Winter Outdoor Design Dry-Bulb Temperaturerange
°F
-4060
Per drawings — design conditions as indicated on the mechanical schedules (deferred by default)
5.3.2 Where the design conditions in the datasheet differ from the conditions used in the manufacturer's selection, the manufacturer shall reselect at the datasheet conditions before the unit is released for fabrication.

6 Airflow and Static Pressure

6.1 Design Airflow

6.1.1 Each fan shall deliver the airflow indicated in the datasheet at the design external static pressure, at the site elevation, and at the design entering air conditions.
Supply Airflowrange
cfm
500150000
Per drawings — airflow as indicated on the mechanical schedules (deferred by default)
Return or Relief Airflowrange
cfm
0150000
Per drawings — airflow as indicated on the mechanical schedules (deferred by default)
Minimum Outdoor Airflowrange
cfm
0150000
Per drawings — ventilation airflow as indicated on the mechanical schedules (deferred by default)
6.1.2 For variable-air-volume units, the fan shall operate stably and without surge, stall, or audible instability from design airflow down to the minimum airflow indicated in the datasheet.
Minimum Controlled Airflow as a Percentage of Designrange
%
5100
Per drawings — turndown as indicated on the mechanical schedules and control sequences (deferred by default)
NOTE Turndown is a property of the whole system rather than the fan alone. The fan sets a floor below which the wheel becomes unstable, the terminal units set a floor below which zones lose control authority, and the ventilation calculation sets a floor below which the outdoor air fraction can no longer be maintained. The binding one is usually not the fan. (6.1.3)

6.2 Static Pressure

6.2.1 The design external static pressure for each fan shall be as indicated in the datasheet.
Design External Static Pressurerange
in. w.g.
0.112
Per drawings — external static pressure as indicated on the mechanical schedules (deferred by default)
6.2.2 The manufacturer shall state the internal static pressure loss of each furnished section at design airflow, with clean filters and dry coils, and shall add it to the external static pressure to establish the total static pressure at which the fan is selected.
6.2.3 The fan shall be selected at the total static pressure increased by the selection margin indicated in the datasheet.
Fan Selection Static Pressure Marginrange
%
025
NOTE A selection margin buys insurance against an underestimated system resistance and pays for it in installed fan power, casing pressure class, and sound. A margin large enough to matter also moves the operating point far enough left on the curve that a constant-volume unit runs permanently throttled, so on variable-speed units the margin costs little and on constant-volume units it costs continuously. (6.2.4)
6.2.5 Where the datasheet margin is zero, the fan shall be selected at the calculated total static pressure without addition.
6.2.6 Internal static pressure losses shall be stated with dirty-filter resistance excluded from the fan selection point and reported separately, so that the fan curve reserve available at the filter change-out condition is visible in the submittal.

7 Fan Selection

7.1 Fan Arrangement

7.1.1 The supply fan arrangement shall be as indicated in the datasheet.
Supply Fan Arrangementselect
Single housed centrifugal fan
Multiple housed centrifugal fans in parallel
Single unhoused plenum fan
Array of unhoused plenum fans
Mixed-flow fan in a cylindrical housing
Vaneaxial fan
NOTE A housed centrifugal fan discharges into a scroll and then into a duct connection, which concentrates the discharge into one opening and makes the unit longer where the discharge has to turn. An unhoused plenum fan discharges into the casing itself and lets the downstream section draw from a pressurized plenum, which shortens the unit and frees the discharge location. (7.1.2)
NOTE A fan array replaces one large wheel with several small ones sharing the same plenum. Sound power drops because the tip speed needed for a given pressure falls with wheel diameter, the array continues to operate at reduced capacity when one fan is out of service, and the individual assemblies are small enough to be carried through a door. The array adds motor count, drive count, and backdraft dampers to maintain. (7.1.3)
7.1.4 Each fan in an array shall be furnished with a backdraft damper or an equivalent means of preventing reverse flow through an idle fan.
7.1.5 The manufacturer shall state the fan energy index of an array in accordance with ANSI/AMCA 208 for the array as a whole rather than for an individual fan.

7.2 Fan Wheel Type

7.2.1 The supply fan wheel type shall be as indicated in the datasheet.
Supply Fan Wheel Typeselect
Airfoil centrifugal
Backward-inclined flat blade centrifugal
Backward-curved single-thickness centrifugal
Forward-curved centrifugal
Mixed flow
Axial with adjustable-pitch blades
NOTE Airfoil and backward-inclined wheels reach their peak efficiency at higher specific speeds and have a power curve that peaks and then falls, so the motor is not overloaded if the system resistance turns out lower than calculated. Forward-curved wheels are quieter at low speed and physically smaller for a given airflow, and their power rises continuously with airflow, so a forward-curved selection carries a real risk of motor overload when the actual system resistance is below the design value. (7.2.2)
7.2.3 Where a forward-curved wheel is selected, the motor shall be sized for the power the fan draws at the point where the fan curve crosses a system curve representing the ductwork with clean filters and the dampers in their full-open position.
7.2.4 Fan wheels and shafts shall be dynamically balanced as an assembly before installation in the unit.
7.2.5 Balance quality shall be verified by measurement at the fan bearing housings during the factory run test, and the measured values shall be recorded in the factory test report.

7.3 Drive Arrangement

7.3.1 The fan drive arrangement shall be as indicated in the datasheet.
Fan Drive Arrangementradio
● Direct drive
○ Belt drive
7.3.2 Requirements in this article that address sheaves, belts, and drive alignment apply where a belt drive is selected in the datasheet.
7.3.3 Belt-driven fans shall be furnished with an adjustable motor base that permits belt tensioning and sheave alignment without removing the motor.
7.3.4 The furnished sheave combination shall produce the specified fan speed within ±5% and shall permit a speed change of at least ±10% by sheave replacement without changing the belt centerline distance beyond the adjustment range of the motor base.
7.3.5 Belt-driven fans operating at variable speed shall be selected so that the drive ratio and the frequency range together keep the fan below the maximum speed published by the fan manufacturer at every point in the operating range.
7.3.6 Belt guards shall be furnished on every belt drive accessible through a service door, and shall include an opening that permits a tachometer reading on the fan shaft without removing the guard.
NOTE A belt drive is a speed-matching device and a maintenance item at the same time. It lets one motor frame serve a range of fan speeds, which is why it survived so long, and it wears, sheds dust into the airstream, and loses a few percent of the shaft power to slip. Direct drive removes all of that and fixes the fan speed at the motor speed, so the speed matching has to come from somewhere else, which in practice means a variable frequency drive or an electronically commutated motor. (7.3.7)

7.4 Fan Capacity Control

7.4.1 The means of fan capacity control shall be as indicated in the datasheet.
Fan Capacity Controlselect
Variable speed by variable frequency drive
Variable speed by electronically commutated motor
Constant speed
Inlet guide vanes with a constant-speed motor
Discharge dampers with a constant-speed motor
Fan staging within an array with constant-speed motors
7.4.2 Variable frequency drives furnished for fan motors shall conform to HVAC Variable Frequency DrivesHVAC Variable Frequency DrivesResolves to the current adopted revision.sync/hvac-variable-frequency-drives.
7.4.3 Where a drive is factory-mounted on the unit, it shall be mounted outside the airstream, shall be accessible without opening a section that is under pressure during operation, and shall be provided with the cooling airflow its manufacturer requires at the maximum ambient temperature at the unit location.
NOTE Reducing airflow by speed follows the fan laws, so power falls with roughly the cube of the speed. Reducing airflow by throttling moves the operating point up the fan curve instead, so power falls only a little and the difference is dissipated across the throttling device as heat and noise. Inlet guide vanes sit between the two because they pre-swirl the air and reshape the curve rather than simply adding resistance. (7.4.4)

7.5 Fan Efficiency

7.5.1 Each fan and fan array shall have a fan energy index at its highest design airflow rate not less than the value indicated in the datasheet, determined in accordance with ANSI/AMCA 208.
Minimum Fan Energy Index at Design Airflowrange
0.81.5
Default: 1
7.5.2 Fan system power at design conditions shall not exceed the limit set by the energy code adopted for the project.
7.5.3 The submittal shall document the fan power compliance calculation, including every pressure credit claimed and the section that generates it.
NOTE The fan energy index compares the electrical power of the selected fan at its duty point against a reference fan at the same duty point, so a value of 1.00 means the selection is exactly as efficient as the reference and a value above 1.00 means it beats it. Because it is a ratio at a single duty point, it rewards selecting close to the peak of the fan curve and it does not reward oversizing. (7.5.4)
NOTE The fan energy index and the energy code fan power limit answer different questions. The index asks whether this fan is a good way to produce this duty point; the power limit asks whether the whole air system was allowed to be this resistive in the first place. A selection can pass one and fail the other. (7.5.5)

7.6 Fan Redundancy

7.6.1 The fan redundancy provided shall be as indicated in the datasheet.
Supply Fan Redundancyselect
None
Fan array sized to deliver design airflow with one fan out of service
Dual fans operating in parallel, each sized for design airflow
Dual fans with one fan on standby
7.6.2 Where redundancy is provided, the unit controls shall be capable of transferring operation to the redundant capacity without manual intervention at the unit.
7.6.3 Where redundancy is provided, the casing shall permit isolation of an out-of-service fan from the airstream so that maintenance can be performed while the remaining capacity operates.

7.7 Return and Relief Fans

7.7.1 Where the datasheet indicates a return or relief fan, that fan shall be furnished as part of the unit and shall be selected at the airflow and static pressure indicated in the datasheet.
Return or Relief Fanselect
None
Return fan
Relief fan
Exhaust fan serving the energy recovery section
NOTE A return fan sits in the return path upstream of the mixing section and moves the full return airflow, so it can overcome return duct resistance and its speed can be tracked against the supply fan to hold a building pressure setpoint. A relief fan sits downstream of the mixing section and runs only when the economizer opens far enough that the building cannot relieve the excess air passively, so it moves less air, for fewer hours, at lower pressure. (7.7.2)
7.7.3 Where a return fan is furnished, the control sequence shall establish the airflow or pressure relationship the fan is to maintain relative to the supply fan, coordinated with Building Automation SystemBuilding Automation SystemResolves to the current adopted revision.sync/building-automation-system.
7.7.4 Where the building can relieve economizer air through gravity relief dampers and transfer paths without exceeding the design building pressure, neither a return nor a relief fan is required.

8 Fan Motors

8.1 Motor Electrical Characteristics

8.1.1 Motor voltage and phase shall match the branch circuit serving the unit as shown on the electrical documents, and any discrepancy between the mechanical schedule and the electrical documents shall be resolved before the motor is released for fabrication.
Motor Supply Voltagerange
V
115208230460480575600
Per drawings — electrical drawings and panel schedules (deferred by default)
Motor Supply Phaseradio
○ Single phase, 1Φ
○ Three phase, 3Φ
Per drawings — electrical drawings and panel schedules (deferred by default)
Supply Fan Motor Nameplate Powerrange
hp
0.250.50.7511.52357.5101520253040506075100125150200250
Per drawings — motor power as indicated on the mechanical schedules (deferred by default)
NOTE Motor voltage is a fact about the building's electrical distribution rather than a property of the air handling unit, which is why it defers to the electrical documents. The recurring coordination failure is a mechanical schedule naming a nominal utilization voltage while the panel schedule serving the unit carries another, discovered when the motor arrives. (8.1.2)
8.1.3 Motors shall be selected so that the nameplate power is not exceeded at any operating point the fan can reach with clean filters, dry coils, and the system dampers in their full-open position.
8.1.4 Motor service factor shall be not less than 1.15 for belt-driven fans.
8.1.5 The service factor shall not be used as selection capacity, and the motor shall be capable of continuous operation at or below its nameplate power at every design operating point.

8.2 Motor Enclosure and Efficiency

8.2.1 The motor enclosure shall be as indicated in the datasheet.
Motor Enclosureselect
Totally enclosed fan cooled, TEFC
Totally enclosed air over, TEAO
Totally enclosed nonventilated, TENV
Totally enclosed blower cooled, TEBC
Open drip proof, ODP
Explosionproof
8.2.2 The motor efficiency level shall be as indicated in the datasheet.
Motor Efficiency Levelradio
● NEMA Premium efficiency per NEMA MG 1
○ NEMA energy efficient per NEMA MG 1
○ Efficiency not specified
NOTE A motor mounted in the airstream is cooled by the air the fan is moving, which is why an air-over enclosure exists and why an open enclosure in that position sheds its winding heat directly into the supply air. On a variable-speed fan the airstream cooling falls with the airflow while the motor losses do not fall as fast, so the enclosure selection and the turndown range are linked. (8.2.3)
8.2.4 Motors mounted within the airstream shall be rated for continuous operation at the minimum airflow in the operating range without exceeding the temperature rise of the insulation system.

8.3 Inverter Duty Construction

8.3.1 Requirements in this article apply where the datasheet selects variable speed control by variable frequency drive.
8.3.2 Motors operated from a variable frequency drive shall be rated for inverter duty in accordance with NEMA MG 1 Part 31.
8.3.3 Motors 100 hp and larger operated from a variable frequency drive, and motors of any size where the drive is more than 100 ft from the motor, shall be furnished with a shaft grounding ring or an insulated bearing at the non-drive end.
NOTE The inverter output is a switched waveform rather than a sine wave. Its fast voltage transitions reflect off the impedance mismatch at the motor terminals and can arrive as a voltage roughly double the bus voltage, which is what the Part 31 insulation system is built to survive. The same switching puts a common-mode voltage on the rotor that discharges through the bearing lubricant film, and that discharge current is what shaft grounding and insulated bearings interrupt. (8.3.4)

8.4 Fan and Motor Bearings

8.4.1 Fan shaft bearings shall be selected for a rated life not less than the value indicated in the datasheet at the design operating speed and load.
Minimum Fan Bearing Rated Liferange
hours
400005000080000100000150000200000
8.4.2 The bearing lubrication arrangement shall be as indicated in the datasheet.
Fan Bearing Lubricationselect
Regreasable with fittings extended to the exterior of the fan section
Regreasable with fittings inside the fan section
Sealed and lubricated for the rated life
8.4.3 Where sealed bearings are selected, the bearing rated life requirement applies to the sealed bearing itself, and no bearing whose rated life is shorter than the requirement shall be furnished on the basis that it is not serviceable.
NOTE Extending grease fittings to the outside of the fan section converts a bearing service that requires opening a pressurized casing, entering the airstream, and reaching past a rotating wheel into one that takes a minute at a labeled fitting. On a unit that runs continuously, that difference is usually what decides whether the bearings actually get greased. (8.4.4)
8.4.5 Where grease fittings are extended, each line shall be labeled at the exterior with the bearing it serves and the grease type the manufacturer requires.

9 Fan Sound

9.1 Sound Data Basis

9.1.1 Fan sound power levels shall be determined from laboratory data taken in accordance with ANSI/AMCA 300 and calculated in accordance with ANSI/AMCA 301.
9.1.2 Sound power levels shall be reported in each of the eight octave bands from 63 Hz through 8,000 Hz.
9.1.3 Inlet, outlet, and casing radiated sound power shall be reported separately.
NOTE A single A-weighted number is not sufficient to evaluate an air handling unit. The blade passage frequency of a large slow wheel falls in the 63 Hz and 125 Hz bands, where A-weighting discounts it heavily and where duct linings, plenums, and building constructions all attenuate poorly. A unit that compares well on an A-weighted basis can still be the one occupants complain about. (9.1.4)
9.1.5 Where the unit serves or adjoins a space with a stated noise criterion, the design team shall perform an octave band analysis carrying the submitted sound power levels through the attenuation of the connected path to the receiving room, and shall confirm the result against the criterion stated in the Contract Documents.
9.1.6 Where the analysis shows the criterion is not met with the submitted selection, the Engineer of Record shall determine whether the remedy is a different fan selection, added attenuation, or a revised criterion.

9.2 In-Unit Sound Attenuation

9.2.1 Sound attenuation furnished within the unit shall be as indicated in the datasheet.
In-Unit Sound Attenuationselect
None
Acoustically lined discharge plenum section
Packaged sound attenuator section within the unit
Acoustically lined discharge plenum and inlet plenum sections
9.2.2 Acoustic media exposed to the airstream shall be faced or encapsulated so that fibers are not eroded into the airstream at the maximum velocity the section sees.
9.2.3 Acoustic media shall not be installed downstream of a humidifier or in any section where condensation can occur.

10 Casing Construction

10.1 Panel Construction

10.1.1 The casing panel construction shall be as indicated in the datasheet.
Casing Panel Constructionselect
Double-wall insulated panel
Double-wall insulated panel with a thermally broken frame
Double-wall insulated panel with a perforated inner liner
Single-wall panel with an applied interior liner
Single-wall uninsulated panel
Casing Panel Insulationselect
Injected polyurethane foam
Rigid fiberglass board
Mineral wool board
Closed-cell elastomeric board
NOTE A double-wall panel puts a sheet metal skin on both faces of the insulation, so the insulation is never in the airstream, cleaning does not erode it, and the panel behaves as a structural sandwich. A single-wall panel with an applied liner leaves the liner facing exposed to the air, and the panel gets its stiffness from the frame instead of the sandwich. (10.1.2)
10.1.3 Any casing section in which the interior surface can fall below the dew point of the air on either side of the panel shall be insulated and shall be constructed so that no continuous metal path connects the interior skin to the exterior skin.
NOTE A thermal bridge is a continuous metal path from the inside skin to the outside skin, usually through a panel frame or a fastener. It carries heat around the insulation and drops the exterior surface temperature at that line, so the visible symptom is a grid of condensation tracing the panel joints on an otherwise dry casing. Thermal break framing interrupts that path with a low-conductivity section. (10.1.4)
10.1.5 Fasteners securing interior liners shall not penetrate to the exterior skin.

10.2 Panel Thermal Performance

10.2.1 The casing panel thermal resistance shall be not less than the value indicated in the datasheet.
Minimum Casing Panel Thermal Resistancerange
hr·ft²·°F/Btu
020
10.2.2 Where the datasheet does not state a thermal resistance, the manufacturer shall state the thermal resistance of the panel furnished and the calculated exterior surface temperature at the design conditions, and shall confirm that the surface stays above the dew point of the air surrounding the unit.
NOTE Panel thermal resistance is selected against two separate criteria that usually give different answers. The energy criterion asks how much heat is lost or gained through the casing over a season, and it favors more insulation on outdoor units and on units carrying air far from the surrounding temperature. The condensation criterion asks whether the exterior surface stays above the dew point of the air around the unit, and it can require more insulation on a small indoor unit in a humid mechanical room than on a large rooftop unit in a dry climate. (10.2.3)

10.3 Casing Air Leakage

10.3.1 The casing air leakage class shall be as indicated in the datasheet.
Casing Air Leakage Classselect
AHRI 1350 Class L1
AHRI 1350 Class L2
AHRI 1350 Class L3
Leakage rate tested and reported without a certified class
10.3.2 The casing shall be leak tested at 1.5 times the design static pressure of the section under test, and the measured leakage shall be recorded in the factory test report.
NOTE Among the AHRI 1350 leakage classes, L1 is the tightest and L3 the loosest. (10.3.3)
NOTE Casing leakage costs differently on each side of the fan. Downstream of the fan the casing is above the surrounding pressure, so conditioned air leaks out of the unit and is paid for twice, once to condition it and once to move it. Upstream of the fan the casing is below the surrounding pressure, so mechanical room air is drawn in downstream of the filters, past the point where it would have been cleaned, and in a cooling unit it arrives after the coil has already dehumidified the air it mixes with. (10.3.4)
10.3.5 Penetrations through the casing for piping, conduit, drains, and control tubing shall be sealed with a gasketed or grommeted fitting that maintains the leakage class of the section.

10.4 Casing Deflection and Pressure Class

10.4.1 The casing deflection class shall be as indicated in the datasheet.
Casing Deflection Classselect
AHRI 1350 Class D1
AHRI 1350 Class D2
AHRI 1350 Class D3
Deflection tested and reported without a certified class
10.4.2 The casing pressure class shall be as indicated in the datasheet, and shall be not less than the maximum static pressure the fan can develop at shutoff with the unit dampers closed.
Casing Pressure Classrange
in. w.g.
216
NOTE Among the AHRI 1350 deflection classes, D1 permits the least panel movement and D3 the most. (10.4.3)
NOTE Panel deflection matters because the panel is also half of every gasketed joint around it. A panel that bows under pressure opens the door gasket line and the panel-to-panel joint at the same time, so the leakage class measured on a stiff casing at low pressure is not the leakage the unit delivers once it is running at its real operating pressure. (10.4.4)
NOTE Sizing the casing for the fan's shutoff pressure rather than its operating pressure is what keeps a unit intact when a downstream damper fails closed or a smoke damper drops while the fan is running. (10.4.5)

10.5 Casing Sheet Materials

10.5.1 The interior liner material shall be as indicated in the datasheet.
Casing Interior Liner Materialselect
G90 galvanized steel
G90 galvanized steel with a factory-applied coating
Type 304 stainless steel
Type 316 stainless steel
Aluminum
10.5.2 The exterior panel material shall be as indicated in the datasheet.
Casing Exterior Panel Materialselect
G90 galvanized steel, painted
G90 galvanized steel, unpainted
Type 304 stainless steel
Aluminum
10.5.3 Galvanized steel sheet shall conform to ASTM A653 with a G90 coating designation as a minimum.
10.5.4 Interior surfaces that are wetted by condensate in normal operation shall be stainless steel, aluminum, or galvanized steel carrying a factory-applied coating rated for continuous exposure to condensate.
NOTE Uncoated galvanized steel is durable in a dry airstream and much less so under a continuous condensate film. The zinc layer is consumed rather than merely scratched, so the failure shows up as white corrosion product and then base metal perforation in the wettest part of the section, which is where the drain pan meets the coil. (10.5.5)
10.5.6 Exposed fasteners on interior surfaces in contact with the airstream shall be stainless steel.

10.6 Exterior Finish

10.6.1 The exterior finish system shall be as indicated in the datasheet.
Exterior Finish Systemselect
Factory-applied powder coat over a treated substrate
Factory-applied baked enamel over a treated substrate
Corrosion-inhibiting epoxy primer with a polyester powder coat topcoat
Unpainted galvanized or aluminum with no applied finish
Manufacturer's standard (by default)
10.6.2 Where the datasheet leaves the finish system to the manufacturer, the manufacturer shall state in the submittal the system furnished and its dry film thickness.
10.6.3 Where the Contract Documents require a color selection, the color shall be selected by the Owner from the range the manufacturer offers for the finish system furnished, and the selection shall be made before the unit is released for fabrication.
10.6.4 Outdoor unit finishes shall have a total dry film thickness of not less than 3 mils.
10.6.5 Cut edges, field-drilled penetrations, and fasteners on outdoor units shall receive a zinc-rich touch-up coating before the unit is placed in service.

10.7 Access Doors

10.7.1 An access door shall be furnished at every section containing a component that requires periodic inspection, cleaning, adjustment, or replacement, including at minimum every fan section, filter section, coil section, mixing section, drain pan, humidifier section, and energy recovery section.
10.7.2 The access door construction shall be as indicated in the datasheet.
Access Door Constructionselect
Hinged insulated door with compression latches operable from both sides
Hinged insulated door with compression latches operable from outside only
Hinged insulated door with a sliding hardware set where the swing is obstructed
Removable gasketed access panel
Access Door Viewportradio
○ Sealed double-glazed viewport in each fan and coil section door
○ Sealed double-glazed viewport in each fan section door
● No viewport
Interior Service Lightingradio
○ Factory-installed luminaires with an exterior switch and a marked disconnect in each accessible section
○ Factory-installed luminaires with an exterior switch in each fan section
● No interior lighting
10.7.3 Access doors on sections a person can enter shall be openable from the inside without a tool whenever the latching hardware can be secured from the outside.
NOTE A door latch that can be secured from outside on a section large enough to enter is the mechanism behind entrapment in operating equipment. The inside release is what makes the section safe to work in, and it is the reason a double-sided latch set is not merely a convenience. (10.7.4)
10.7.5 Clear door opening dimensions shall be not less than 18 in. wide by 45 in. high for sections a person is expected to enter, and not less than 12 in. by 12 in. for sections served by reaching in.
10.7.6 Where a component is removed through a door, the clear door opening shall be large enough to pass that component.
10.7.7 Door gaskets shall be mechanically retained or bonded to the door and shall be replaceable without replacing the door.

10.8 Weather Protection for Outdoor Units

10.8.1 Requirements in this article apply where the datasheet selects an outdoor casing.
10.8.2 The unit roof shall be sloped to drain and shall extend beyond the casing wall at every edge.
10.8.3 Roof seams shall be located away from the low point of the slope and shall be sealed with a sealant rated for continuous exterior exposure and the design surface temperature range.
10.8.4 Outdoor air intakes and relief openings shall be furnished with weather hoods and moisture eliminators sized so that water is not carried into the unit at the design wind-driven rain condition.
10.8.5 Base rails shall be drainable and shall not create a standing water condition on the roof surface beneath the unit.
10.8.6 Doors on outdoor units shall be furnished with a rain lip or drip edge above the opening.
10.8.7 Electrical enclosures on outdoor units shall be rated for the exposure and shall be furnished with condensation heaters where the unit can be energized before the space it serves is conditioned.

11 Coils

11.1 Coil Rating and Certification

11.1.1 Coil performance shall be rated in accordance with ANSI/AHRI 410.
11.1.2 Published coil capacities shall be stated at the actual selected face velocity, entering conditions, fluid flow rate, and circuiting rather than at generic catalog conditions.
11.1.3 Coil selections shall be resubmitted where any of the entering conditions, the fluid temperatures, or the airflow change after the original selection.
NOTE An AHRI 410 rating certifies the heat transfer relationships of the coil, not the accuracy of the conditions someone typed into the selection program. The recurring failure is a certified selection made at an entering air temperature that the mixing section never produces, which is a coordination error the certification cannot catch. (11.1.4)

11.2 Coil Materials

11.2.1 Coil tube material shall be as indicated in the datasheet.
Coil Tube Materialselect
Copper
Type 304 stainless steel
Type 316 stainless steel
Copper-nickel alloy
11.2.2 Coil fin material and coating shall be as indicated in the datasheet.
Coil Fin Material and Coatingselect
Aluminum
Aluminum with an applied epoxy coating
Aluminum with an applied phenolic coating
Aluminum with an electrodeposited coating
Copper
Copper with an applied epoxy coating
11.2.3 Cooling coil casings and tube sheets shall be as indicated in the datasheet.
Cooling Coil Casing Materialselect
Type 304 stainless steel
Type 316 stainless steel
G90 galvanized steel
Aluminum
Heating Coil Casing Materialselect
G90 galvanized steel
Type 304 stainless steel
Type 316 stainless steel
Aluminum
NOTE Aluminum fin stock in contact with copper tube forms a galvanic pair that stays benign while the fin surface is dry and becomes active once a persistent electrolyte film exists between them. Chloride from marine air and sulfur compounds from industrial and vehicular exhaust both supply that electrolyte, so the fin corrodes preferentially, the bond to the tube opens, and capacity falls while air-side pressure drop rises. Applied fin coatings and cupronickel construction both address the same mechanism at different cost. (11.2.4)
11.2.5 Where the datasheet selects a fin coating, the coating shall be applied after fin and tube assembly so that the tube-to-fin interface is coated.

11.3 Coil Pressure and Construction

11.3.1 Coils shall be rated for a working pressure not less than the value indicated in the datasheet and for a working temperature not less than the maximum fluid temperature the connected system can deliver.
Coil Working Pressure Ratingrange
psig
150200250300400600
11.3.2 The maximum cooling coil fin spacing shall be as indicated in the datasheet.
Maximum Cooling Coil Fin Spacingrange
fins per inch
416
Default: 12 fins per inch
11.3.3 Coil headers shall be furnished with a manual air vent at the high point and a drain at the low point of each circuit.
11.3.4 Every coil shall be factory pressure tested and the test pressure shall be recorded on the coil.
NOTE Fin spacing trades heat transfer surface against cleanability and fouling tolerance. A tight fin pattern gets the same capacity from a smaller coil, and it also holds the condensate film longer, resists cleaning, and loses face area faster as it loads. On a coil that runs wet, the fin spacing effectively sets how often the coil has to be cleaned to keep its rated capacity. (11.3.5)

11.4 Cooling Coils

11.4.1 The cooling coil medium shall be as indicated in the datasheet.
Cooling Coil Mediumradio
● Chilled water
○ Direct expansion refrigerant
○ None
Cooling Coil Entering Fluid Temperaturerange
°F
3060
Per drawings — design fluid temperatures as indicated on the mechanical schedules (deferred by default)
Cooling Coil Leaving Fluid Temperaturerange
°F
3880
Per drawings — design fluid temperatures as indicated on the mechanical schedules (deferred by default)
Maximum Cooling Coil Fluid-Side Pressure Droprange
ft w.g.
245
11.4.2 Hydronic cooling coils shall be circuited for counterflow, with the fluid entering at the leaving-air face of the coil.
11.4.3 Where the datasheet does not state a maximum fluid-side pressure drop, the manufacturer shall state the pressure drop of the selected coil, and the Engineer of Record shall confirm it against the pump head available.
11.4.4 Requirements in this article that address refrigerant circuiting apply where the datasheet selects a direct expansion coil.
11.4.5 Direct expansion coils shall be circuited with an interlaced or face-split arrangement matched to the capacity steps of the connected condensing unit, and the arrangement shall be shown in the submittal.
11.4.6 Direct expansion coils shall be furnished with a distributor sized for the design refrigerant flow, and the distributor and expansion device shall be selected together by the party responsible for the refrigeration circuit.
NOTE A direct expansion coil is part of a refrigeration circuit, so the coil, the distributor, the expansion device, and the compressor staging behave as one machine. A row-split arrangement lets an unloaded circuit sit in the airstream doing nothing but adding pressure drop; an interlaced arrangement keeps every part of the face active at every capacity step but needs matched distributors to avoid starving circuits at low load. (11.4.7)

11.5 Cooling Coil Face Velocity

11.5.1 The cooling coil face velocity at design airflow shall not exceed the value indicated in the datasheet.
Maximum Cooling Coil Face Velocityrange
fpm
200700
Default: 500 fpm
11.5.2 Where the selected face velocity exceeds 550 fpm, moisture eliminators shall be furnished downstream of the coil and the drain pan shall extend to the eliminator face.
NOTE Condensate on a cooling coil leaves the fin edge as droplets that the airstream then has to be slow enough not to carry away. The threshold is not sharp and it moves with fin spacing, fin surface treatment, and how wet the coil runs, but somewhere above roughly 500 to 550 fpm carryover starts and no amount of drain pan depth downstream will recover water that is already airborne and heading into the duct. (11.5.3)
11.5.4 Face velocity shall be calculated on the finned face area of the coil rather than on the casing cross-section.

11.6 Heating Coils

11.6.1 The heating coil medium shall be as indicated in the datasheet.
Heating Coil Mediumselect
Hot water
Steam
Electric resistance
None
Heating Coil Entering Fluid Temperaturerange
°F
90220
Per drawings — design fluid temperatures as indicated on the mechanical schedules (deferred by default)
Heating Coil Leaving Fluid Temperaturerange
°F
70210
Per drawings — design fluid temperatures as indicated on the mechanical schedules (deferred by default)
11.6.2 Requirements in this article that address resistance elements apply where the datasheet selects an electric heating coil.
11.6.3 Electric heating coils shall be furnished with a primary automatic-reset thermal cutout and a secondary manual-reset thermal cutout, both listed for the application.
11.6.4 Electric heating coils shall be interlocked with the supply fan so that the elements cannot be energized without proven airflow, and the interlock shall be hardwired independently of the building automation system.
NOTE An airflow interlock that depends on the building automation system fails in the one scenario it exists for, which is the system being offline while the heater has power. The hardwired path is what makes the interlock a safety rather than a sequence. (11.6.5)

11.7 Steam Heating Coils

11.7.1 Requirements in this article apply where the datasheet selects a steam heating coil.
11.7.2 The steam coil type shall be as indicated in the datasheet.
Steam Coil Typeradio
○ Distributing tube, non-freeze construction
○ Standard single-tube construction
11.7.3 Where entering air below 40°F can reach the steam coil face, the coil shall be of distributing tube non-freeze construction.
11.7.4 Steam coils shall be pitched toward the return connection and shall be furnished with a condensate return connection at the low point of each coil.
11.7.5 Each steam coil shall be trapped separately, and coils shall not be manifolded into a shared trap.
11.7.6 Steam coils shall be controlled by modulating the steam supply pressure rather than by throttling the condensate return.
NOTE A steam coil freezes from the condensate side. When a control valve throttles the supply, the pressure inside the tube can fall below the pressure needed to push condensate through the trap, condensate stacks in the bottom tubes, and the first tube full of stationary water at sub-freezing entering air splits. A distributing tube carries steam the full length of the coil inside an inner tube and feeds it outward along the whole run, so every part of the outer tube stays hot at part load rather than only the end nearest the supply. (11.7.7)

11.8 Preheat Freeze Protection

11.8.1 The preheat freeze protection method shall be as indicated in the datasheet.
Preheat Coil Freeze Protectionselect
Constant coil flow with a modulating three-way valve
Constant coil flow maintained by an injection pump
Glycol solution in the preheat circuit
Face and bypass dampers with a constant-capacity coil
None
11.8.2 Where a hydronic preheat coil can see entering air below 35°F, the coil circuit shall maintain flow through every tube whenever the outdoor air damper is open.
NOTE A hydronic preheat coil with a two-way modulating valve is a freeze risk by construction, because the condition that calls for the least heat is the condition with the coldest air on the coil, and at low valve position the water in the tubes is nearly stationary. Every method in the field is a way of keeping water moving through the coil while still varying the heat it delivers, whether by recirculating around a three-way valve, injecting to hold flow, lowering the freezing point of the fluid, or moving the air around the coil instead of modulating the water. (11.8.3)
11.8.4 Glycol concentration and the resulting capacity correction shall be stated in the submittal where a glycol solution is selected.

11.9 Coil Access and Connections

11.9.1 Coils shall be removable from the unit without cutting tubes, disassembling adjacent sections, or removing the fan.
11.9.2 Coil connections shall pass through the casing in a gasketed, insulated penetration that maintains the leakage class of the section.
11.9.3 Coil connections shall be arranged so that the piping can be disconnected and the coil withdrawn from the service side of the unit.
11.9.4 Piping serving the coils shall conform to Hydronic PipingHydronic PipingResolves to the current adopted revision.sync/hydronic-piping.
11.9.5 Piping shall be independently supported within 12 in. of the coil connection, and no part of the connected piping weight or thermal movement shall be carried by the coil header.

12 Filtration

12.1 Filtration Stages

12.1.1 The number of filtration stages shall be as indicated in the datasheet.
Filtration Stagesradio
○ Single stage
● Two stages, prefilter and final filter
○ Three stages, prefilter, intermediate filter, and final filter
12.1.2 Air delivered to an occupiable space shall pass through filtration of not less than MERV 8 upstream of every cooling coil and every other component with a wetted surface.
12.1.3 Where a final filter of MERV 13 or higher is furnished, a prefilter stage shall be furnished upstream of it.
NOTE A prefilter is an economic device rather than an air quality device. It removes the coarse fraction that would otherwise load the final filter, and because the coarse fraction is most of the mass and almost none of the health-relevant particle count, it extends the final filter's life at a fraction of the media cost. The stage count therefore follows from the final filter efficiency and the change-out economics, not from the cleanliness target. (12.1.4)
12.1.5 Filter media shall be listed to UL 900.

12.2 Filter Efficiency

12.2.1 Filter efficiency shall be rated in accordance with ANSI/ASHRAE 52.2 and shall be as indicated in the datasheet.
Prefilter Efficiencyselect
MERV 4
MERV 6
MERV 7
MERV 8
MERV 11
No prefilter stage
Final Filter Efficiencyselect
MERV 8
MERV 11
MERV 13
MERV 14
MERV 15
MERV 16
HEPA rated at 99.97% on 0.3 µm particles
HEPA rated at 99.995% on the most penetrating particle size
12.2.2 The fan selection shall accommodate the airside resistance of the selected filters at their change-out condition without falling below the design airflow.
NOTE Filter efficiency and fan power are directly coupled. Moving from MERV 8 to MERV 13 typically adds a few tenths of an inch of water gauge across the filter bank at the change-out condition, and that increment is paid continuously by the fan for the life of the system. It is a real cost and a small one relative to the fan's total, but it has to be in the selection rather than discovered during balancing. (12.2.4)
12.2.5 Filter face velocity at design airflow shall not exceed the velocity at which the selected media is rated.

12.3 Filter Media and Frames

12.3.1 The final filter media configuration shall be as indicated in the datasheet.
Final Filter Media Configurationselect
Pleated panel
Rigid box with mini-pleat media
Rigid box with deep-pleat media
Extended surface pocket
Cartridge
12.3.2 The filter holding frame seal shall be as indicated in the datasheet.
Filter Holding Frame Sealselect
Positive seating against a gasketed frame with spring clips
Knife-edge frame against a gasketed filter
Fluid-seal gel channel
Clamped sealed housing with bag-in bag-out change provisions
12.3.3 Holding frames shall be continuous and rigid, and shall seal to the casing on all four sides so that no air path exists around the media.
12.3.4 Frame-to-filter sealing shall be achieved by mechanical contact pressure rather than by friction fit.
NOTE Bypass around the media is the dominant filtration defect in installed systems, and it is invisible at every point in the process except a measurement of what actually reaches the space. A bank of MERV 14 filters with a 1% leakage path around the frames delivers an in-place efficiency far below its media rating, because unfiltered air is a parallel path with almost no resistance while the media path has a great deal. (12.3.5)

12.4 Filter Access

12.4.1 The filter access arrangement shall be as indicated in the datasheet.
Filter Access Arrangementradio
● Side access through the casing
○ Front access through the filter section face
○ Side access from either side of the unit
○ Walk-in access upstream of the filter bank
12.4.2 Filters shall be removable and replaceable without tools.
12.4.3 The clear withdrawal space required to change filters shall be shown on the configuration drawing and shall be maintained clear of piping, conduit, and ductwork after installation.
12.4.4 Where the filter section is accessed by entering the unit, the walking surface shall be rated for the load of a person and shall not be the drain pan.

12.5 Filter Pressure Monitoring

12.5.1 Filter differential pressure monitoring shall be as indicated in the datasheet.
Filter Differential Pressure Monitoringselect
Local differential pressure gauge at each stage
Differential pressure transmitter at each stage reporting to the building automation system
Local gauge and differential pressure transmitter at each stage
Differential pressure switch with an adjustable setpoint at each stage
12.5.2 Pressure taps shall be installed upstream and downstream of each filter stage, in the plane of the media and clear of the frame.
12.5.3 Local indicating devices shall be readable from outside the unit without opening any door.
12.5.4 Each indicating device shall be labeled with the filter stage it serves and with the change-out resistance from the submittal.

12.6 High-Efficiency Particulate Air Filter Sections

12.6.1 Requirements in this article apply where the datasheet selects a HEPA final filter.
12.6.2 HEPA filters shall be installed in a sealed housing with a gasketed or fluid-seal frame, and shall not be installed in a slide-in track frame.
12.6.3 The housing shall include upstream and downstream test ports and an aerosol injection port permitting in-place leak testing of the installed filter and its seal.
12.6.4 Each installed HEPA filter and its housing seal shall be leak tested in place after installation, and the test report shall be a closeout submittal.
12.6.5 Where the airstream carries a hazard to maintenance personnel, the housing shall include bag-in bag-out change-out provisions.
NOTE A HEPA filter's rating is a property of the media measured at the factory, and the number that matters in a building is the in-place leak test of the installed assembly. That test is the only step that catches a pinhole in the media, a rolled gasket, or a frame that is not flat. (12.6.6)

13 Mixing Section and Dampers

13.1 Mixing Section Arrangement

13.1.1 The mixing section arrangement shall be as indicated in the datasheet.
Mixing Section Arrangementselect
Outdoor air, return air, and relief or exhaust air dampers
Outdoor air and return air dampers
Outdoor air damper only with no return air connection
No outdoor air connection
13.1.2 Damper positions and the mixing section geometry shall be arranged so that the two airstreams are mixed before they reach the face of the first coil or the low-limit sensing element.
13.1.3 Where the mixing section geometry cannot achieve mixing before the coil face, an air blender shall be furnished.
NOTE Stratification in a mixing box is the source of several failures that look unrelated. The low-limit thermostat reads a warm layer while the coil face sees a cold one, so freeze protection does not trip until the coil has already split. The mixed air temperature sensor reads a single point in a plane that varies by tens of degrees, so the economizer control loop hunts. And the cold layer against a coil face produces localized condensation and frost on a coil that the average temperature says is safe. (13.1.4)

13.2 Damper Construction

13.2.1 The damper blade arrangement shall be as indicated in the datasheet.
Damper Blade Arrangementradio
○ Opposed blade
○ Parallel blade
13.2.2 Damper frames shall be galvanized steel, extruded aluminum, or stainless steel, and shall be rigid enough that the blades close against the seals without binding across the full frame width.
13.2.3 Damper blades shall be airfoil or double-skin construction, and single-skin flat blades shall not be furnished on dampers that modulate.
13.2.4 Blade edge seals shall be extruded synthetic elastomer, and jamb seals shall be flexible metal or elastomer.
13.2.5 Felt and fibrous seals shall not be furnished on any damper in the unit.
NOTE Opposed blades close toward each other, so the air leaving a partly open opposed-blade damper continues roughly straight and the flow-versus-position relationship stays closer to linear across the stroke. Parallel blades all rotate the same way, so a partly open parallel-blade damper throws the airstream to one side, which is unhelpful for control authority and useful for driving mixing in a mixing box. Where the damper is both the control device and the mixing device, those two effects point in opposite directions. (13.2.6)

13.3 Damper Leakage

13.3.1 Damper leakage shall be tested in accordance with ANSI/AMCA 500-D, and the leakage class shall be as indicated in the datasheet.
Outdoor and Relief Air Damper Leakage Classselect
AMCA Class 1A
AMCA Class 1
AMCA Class 2
AMCA Class 3
Return Air Damper Leakage Classselect
AMCA Class 1A
AMCA Class 1
AMCA Class 2
AMCA Class 3
NOTE The AMCA leakage classes set the following maximum leakage at 1 in. w.g. differential pressure across the closed damper: (13.3.2)
Leakage class Maximum leakage
Class 1A 3 cfm/ft²
Class 1 4 cfm/ft²
Class 2 10 cfm/ft²
Class 3 40 cfm/ft²
13.3.3 Damper leakage class shall be selected to meet or exceed the maximum leakage the energy code adopted for the project permits for the damper's service and the project climate zone.
NOTE Damper leakage is measured per square foot of damper face, so its consequence scales with the damper, and a large outdoor air damper on a unit that shuts down overnight in a cold climate is the case that matters. The leaked air arrives unconditioned, upstream of the coil, into a unit with no airflow, which is the exact condition a coil freezes in. (13.3.4)
13.3.5 Dampers shall be rated for a differential pressure not less than the casing pressure class and for a velocity not less than the design face velocity through the damper.

13.4 Damper Actuators

13.4.1 The damper actuator type shall be as indicated in the datasheet.
Damper Actuator Typeselect
Electronic modulating, spring return
Electronic modulating, non-spring return
Electronic two-position, spring return
Electronic two-position, non-spring return
Pneumatic modulating
13.4.2 Actuators shall be direct-coupled to the damper shaft.
13.4.3 Actuators shall be sized for the torque required to seat the blades against the seals at the casing pressure class, with not less than 25% reserve torque.
13.4.4 Outdoor air and relief air dampers shall drive to the closed position on loss of control signal or loss of power.
13.4.5 Return air dampers shall drive to the open position on loss of control signal or loss of power.
NOTE The fail positions are chosen so that a unit that loses control still has a path for the fan to move air through and no path for outdoor air to reach an unheated coil. A unit that fails with the outdoor damper open and the return damper closed in January is the classic way to split a preheat coil during a power interruption. (13.4.6)
13.4.7 Actuators shall be mounted outside the airstream, or shall be rated for continuous operation in the airstream temperature and humidity range where mounting outside is not practical.

13.5 Minimum Outdoor Air Control

13.5.1 The minimum outdoor air control method shall be as indicated in the datasheet.
Minimum Outdoor Air Control Methodselect
Fixed minimum position stop on the outdoor air damper
Separate minimum outdoor air damper sized for the minimum airflow
Outdoor airflow measuring station with closed-loop damper control
Demand-controlled ventilation using space carbon dioxide sensors
Constant outdoor airflow maintained by a dedicated outdoor air unit upstream
13.5.2 Where an outdoor airflow measuring station is furnished, it shall be rated in accordance with ANSI/AMCA 610 and shall be accurate across the full range from the minimum to the maximum outdoor airflow indicated in the datasheet.
NOTE A large damper controlling a small flow is operating in the part of its stroke where a small position change produces a large flow change and where the flow also depends on the pressure across the damper. That is why a fixed minimum position holds the ventilation rate only under the conditions it was set at, and why a separate small damper or a measured closed loop are the two ways of getting a minimum outdoor airflow that survives a change in system pressure. (13.5.3)
13.5.4 Where the ventilation rate is set by a fixed minimum position, the position shall be established during balancing at the design supply airflow and recorded in the balance report.

14 Air-Side Economizer

14.1 Economizer Provision

14.1.1 The economizer provision shall be as indicated in the datasheet.
Air-Side Economizerradio
● Air-side economizer with modulating outdoor, return, and relief dampers
○ No air-side economizer
14.1.2 Where an economizer is furnished, the outdoor air damper, the return air damper, and the relief path shall be sized for 100% of the design supply airflow.
14.1.3 Where an economizer is furnished, the unit shall be capable of modulating from the minimum outdoor airflow to 100% outdoor air without exceeding the design fan power or the design building pressure.
NOTE An economizer is a sizing decision as much as a control decision. Dampers, relief path, and casing all have to pass the full supply airflow through the outdoor side, which is a different unit from one that only ever admits a ventilation fraction. Adding economizer capability to a unit after it is selected is usually not possible. (14.1.4)

14.2 High-Limit Shutoff Control

14.2.1 The economizer high-limit shutoff control type shall be as indicated in the datasheet.
Economizer High-Limit Shutoff Controlselect
Fixed dry-bulb
Differential dry-bulb
Fixed enthalpy with a fixed dry-bulb limit
Differential enthalpy with a fixed dry-bulb limit
Electronic enthalpy curve
14.2.2 The high-limit control type and its setpoints shall be permitted by the energy code adopted for the project for the project climate zone.
Fixed Dry-Bulb High-Limit Setpointrange
°F
5580
14.2.3 Where the datasheet does not state a fixed dry-bulb setpoint, the setpoint shall be the value the adopted energy code prescribes for the project climate zone.
NOTE The high limit exists to stop the economizer before free cooling becomes an added cooling load. A dry-bulb limit compares only temperature, so in a humid climate it can admit outdoor air that is cooler than the return air and carries far more moisture, which the coil then has to remove. An enthalpy limit compares total heat and closes that gap, at the cost of a humidity sensor whose drift is harder to notice than a temperature sensor's. Which one is permitted, and at what setpoint, is set by the energy code for the climate zone rather than by preference. (14.2.4)
14.2.5 Economizer sensors shall be located where they read the condition being controlled, with the outdoor sensor shielded from solar gain and away from exhaust discharges.

15 Energy Recovery

15.1 Energy Recovery Device

15.1.1 The energy recovery device shall be as indicated in the datasheet.
Energy Recovery Deviceselect
None
Rotary wheel, sensible only
Rotary wheel, total energy
Fixed-plate sensible heat exchanger
Fixed-plate membrane enthalpy exchanger
Heat pipe
Runaround coil loop with a pumped glycol circuit
15.1.2 Requirements in this article apply where the datasheet selects an energy recovery device.
15.1.3 Energy recovery performance shall be rated in accordance with ANSI/AHRI 1060 and tested in accordance with ANSI/ASHRAE 84.
15.1.4 The recovery effectiveness at design conditions shall be not less than the value indicated in the datasheet.
Minimum Energy Recovery Effectivenessrange
%
085
Default: 50 %
15.1.5 The pressure drop the recovery device adds to both the supply and the exhaust airstreams shall be included in the fan selections and stated in the submittal.
NOTE A recovery device is a heat exchanger placed in series with two fans, so it collects its energy by spending fan power continuously. The recovery is worth more where the outdoor and exhaust conditions are far apart and the outdoor air fraction is high, and the fan penalty is the same either way, which is why the same device is a clear gain on a dedicated outdoor air unit and a marginal one on a mixed-air unit with a low ventilation fraction. (15.1.6)
15.1.7 A means of reducing or stopping recovery shall be furnished so that the device does not transfer heat into the supply airstream when the economizer is calling for free cooling.

15.2 Cross-Contamination Control

15.2.1 The exhaust air transfer ratio of the selected device shall be stated in the submittal.
15.2.2 Rotary wheels shall be furnished with a purge sector where the datasheet indicates one.
Rotary Wheel Purge Sectorradio
● Purge sector furnished
○ No purge sector
15.2.3 Where the exhaust airstream carries a contaminant that is not acceptable in the supply airstream, the recovery device shall be of a type that provides no leakage path between the airstreams.
NOTE A rotary wheel carries a small volume of exhaust air trapped in its matrix across into the supply side on every revolution. A purge sector reduces that carryover by sweeping the matrix with outdoor air before it reaches the supply stream, but it does not eliminate it, which is why laboratory and isolation exhaust are usually recovered with a runaround loop or a plate exchanger instead of a wheel. (15.2.4)
15.2.5 The supply fan and the exhaust fan shall be arranged so that the supply side of the recovery device is at a higher static pressure than the exhaust side wherever leakage direction matters.

15.3 Frost Control

15.3.1 The frost control method shall be as indicated in the datasheet.
Energy Recovery Frost Controlselect
Wheel speed modulation
Preheat coil upstream of the recovery device
Outdoor air bypass around the recovery device
Exhaust air bypass around the recovery device
Timed defrost cycle
None
15.3.2 The outdoor temperature at which frost control is initiated shall be established from the exhaust air condition and the effectiveness of the selected device, and shall be stated in the submittal.
NOTE Frost forms on the exhaust side of a recovery device when the exhaust air is cooled below its dew point and then below freezing on its way through the exchanger. The consequence is a rising exhaust pressure drop and eventually a blocked passage, and every control method works by raising the coldest surface temperature in the device, either by admitting less cold air, moving the matrix faster, or preheating. (15.3.3)

16 Humidifier Sections

16.1 Humidifier Provision

16.1.1 The humidifier section shall be as indicated in the datasheet.
Humidifier Sectionselect
None
Steam dispersion panel
Steam dispersion tube manifold
Evaporative media
High-pressure water atomizing
Ultrasonic
16.1.2 Requirements in this article apply where the datasheet selects a humidifier section.
16.1.3 The humidifier section shall be furnished with a stainless steel liner and a stainless steel drain pan beneath the dispersion device.
16.1.4 The humidifier shall be interlocked with the supply fan so that it cannot operate without proven airflow.
16.1.5 A high-limit humidity sensor shall be installed in the supply duct downstream of the humidifier and shall stop humidification before the supply air reaches saturation.

16.2 Absorption and Drainage

16.2.1 The manufacturer shall state the absorption distance for the selected dispersion device at the design airflow and the design supply air condition.
16.2.2 No component, duct fitting, turning vane, sensor, or filter shall be located within the stated absorption distance downstream of the dispersion device.
NOTE The absorption distance is where the water is still liquid. Anything inside it gets wet, and in a duct that means a wetted surface downstream of the last filter, which is precisely the condition the filtration requirements exist to prevent. Steam dispersion panels exist because they shorten that distance to a fraction of a manifold's, which is what makes humidification possible in a short duct run. (16.2.3)
16.2.4 The section downstream of the humidifier shall drain to the humidifier drain pan, and that pan shall be piped and trapped independently of the cooling coil drain pan.

17 Drain Pans and Condensate

17.1 Drain Pan Construction

17.1.1 A drain pan shall be furnished beneath every cooling coil, every humidifier dispersion device, every energy recovery device that can condense, and every other section in which condensate can form.
17.1.2 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
Aluminum
17.1.3 Drain pans shall be of welded or mechanically seamed construction with no fastener penetrating the wetted surface.
17.1.4 Drain pans shall be insulated on the underside where the surface beneath the pan can fall below the dew point of the surrounding air.
NOTE A drain pan that holds water between operating cycles is a warm, dark, nutrient-bearing reservoir in the supply airstream, which is the growth condition ANSI/ASHRAE 188 is written around. Every geometric requirement on the pan, the slope, the extent, and the connection height exists to make the pan empty rather than merely drain. (17.1.5)

17.2 Drain Pan Extent and Slope

17.2.1 The drain pan shall extend the full width of the coil section and shall extend beneath the coil headers, return bends, and any piping within the section.
17.2.2 The drain pan shall extend downstream of the leaving-air face of the coil by not less than one half of the coil height and not less than 6 in.
17.2.3 The drain pan shall be sloped in two planes toward the drain connection at not less than the slope indicated in the datasheet.
Minimum Drain Pan Sloperange
in. per ft
0.1250.250.3750.5
17.2.4 Where the section geometry produces more than one low point, a drain connection shall be furnished at each low point.
17.2.5 The pan shall be constructed so that no part of the wetted surface holds standing water when the unit is not operating.
NOTE The downstream extension catches condensate that leaves the fin edge into a moving airstream and lands some distance beyond the coil face. How far it travels depends on the face velocity, so a pan sized only to the coil footprint is adequate at a low face velocity and lets water past the pan lip at a high one, where it reaches the fan section, the duct, and the lining. (17.2.6)
NOTE The pan slope determines how fast the pan empties after the coil stops condensing, not whether it drains at all. A slope that clears the pan in minutes rather than hours is what closes the standing water window that biological growth needs, and steeper slopes cost only casing height. (17.2.7)

17.3 Drain Connections and Traps

17.3.1 The drain pan shall be furnished with a primary drain connection at the low point and a secondary overflow connection with its invert not less than 1 in. above the primary connection.
17.3.2 Drain connections shall be not smaller than 1 in. and shall be sized for the design condensate rate.
17.3.3 The condensate trap arrangement shall be as indicated in the datasheet.
Condensate Trapradio
○ Factory-installed trap with a cleanout, integral to the unit base
● Field-installed trap by the installing contractor
17.3.4 The trap seal depth on a drain pan in a section below the surrounding pressure shall be not less than the maximum negative static pressure in that section, expressed in inches water gauge, plus 1 in.
17.3.5 The vertical distance between the pan outlet and the trap outlet on a drain pan in a section below the surrounding pressure shall be not less than twice the maximum negative static pressure in that section, expressed in inches water gauge.
NOTE A drain trap on a draw-through unit is holding water against the fan, not against a sewer. If the seal is shallower than the negative pressure in the section, the fan simply pulls the seal out, the pan stops draining, and the unit starts drawing unfiltered air backward through the drain line. The trap therefore has to be sized from the section's static pressure rather than from plumbing practice, and it is one of the few dimensions on the unit that changes if the fan selection changes. (17.3.6)
17.3.7 Traps shall be furnished with a cleanout or a union that permits disassembly for cleaning without cutting the drain line.
17.3.8 Traps shall be primed at startup and shall be provided with a means of priming that does not require entering the unit.
17.3.9 The condensate drain line shall be sloped not less than 1/8 in. per ft toward the point of disposal.

18 Vibration Isolation and Seismic Restraint

18.1 Isolation Arrangement

18.1.1 The vibration isolation arrangement shall be as indicated in the datasheet.
Vibration Isolation Arrangementselect
Internal spring isolation of the fan assembly within the casing
External spring floor isolators beneath the unit base
External restrained spring floor isolators beneath the unit base
External spring hanger isolators
External elastomeric mounts
Housekeeping pad with no isolators
18.1.2 Where the fan assembly is internally isolated, the casing shall not be a load path between the isolated assembly and the unit base.
NOTE Isolating the fan inside the casing keeps the isolated mass small and the casing rigid, so the isolators are sized for the fan and motor rather than for the entire unit including its coils and water. Isolating the whole unit externally puts a much larger mass on the springs, which lowers the natural frequency for the same deflection but also means every duct, pipe, and conduit connection has to accommodate the movement of the entire unit. (18.1.3)

18.2 Isolator Selection

18.2.1 Isolators shall be selected for a static deflection at operating load not less than the value indicated in the datasheet.
Minimum Isolator Static Deflectionrange
in.
0.250.350.7511.522.534
18.2.2 Isolators shall be selected so that the isolation system natural frequency is not more than one third of the lowest fan operating frequency in the control range.
18.2.3 Where the datasheet does not state a static deflection, the isolator selection shall be made from the natural frequency requirement, and the calculated natural frequency and isolation efficiency at the lowest operating speed shall be stated in the submittal.
NOTE Isolation depends on the ratio between the disturbing frequency and the natural frequency of the isolated system, and the natural frequency is set by the static deflection. A variable-speed fan changes the disturbing frequency continuously, so an isolator chosen for the design speed can be near resonance at the bottom of the turndown range. Selecting from the lowest operating speed rather than the design speed is what keeps the ratio above one across the whole range. (18.2.4)
18.2.5 Isolators shall operate within the load range for which they are rated at the installed load, and the installed operating height shall be verified after the unit is set and filled.
18.2.6 A structural engineer shall review the isolator selection where the unit is supported on a floor structure rather than on grade.

18.3 Flexible Connections

18.3.1 Every connection between an isolated assembly and the building structure, including ductwork, piping, conduit, and drain lines, shall be made through a flexible element.
18.3.2 The flexible duct connection material shall be as indicated in the datasheet.
Flexible Duct Connection Materialselect
Neoprene-coated woven glass fabric
Silicone-coated woven glass fabric
Vinyl-coated polyester fabric
Elastomeric composite
18.3.3 Flexible duct connection fabric shall be tested to UL 214 and shall be rated for the temperature and pressure of the airstream it serves.
18.3.4 Flexible duct connections shall have not less than 3 in. of clear fabric between the metal edges and shall be installed with the fabric slack in every operating condition.
18.3.5 Piping connections shall include not less than two flexible elements arranged in different planes.
18.3.6 Electrical conduit shall include not less than 18 in. of flexible conduit at the unit.
NOTE A single rigid connection to an isolated unit short-circuits the entire isolation system, and it does not matter which connection it is. A conduit run tight to the casing carries structure-borne vibration into the building exactly as effectively as a bolted duct flange, which is why the requirement covers every connection rather than only the ducts. (18.3.7)
18.3.8 Flexible connections shall not be used to correct misalignment between the unit and the connected service.

18.4 Seismic Restraint

18.4.1 Seismic restraint of the unit shall be designed for the project Seismic Design CategorySeismic Design CategoryParameterEach project supplies its own value.seismic-design-category.
18.4.2 Where the applicable building code requires seismic restraint for the unit, restraints shall be designed in accordance with ASCE 7 for the component importance factor assigned to the unit.
18.4.3 Seismic restraints on isolated units shall permit the isolators to function through their normal operating range and shall engage only under seismic displacement.
18.4.4 Anchorage to the supporting structure shall be designed by an engineer licensed in the jurisdiction of the project, and the design shall state the forces delivered to the structure.
NOTE A snubber that touches the isolated unit in normal operation is a rigid connection, so a restraint installed without its design clearance quietly cancels the isolation it was installed alongside. The clearance is a set dimension rather than a tolerance, and it is worth verifying after the unit is filled and running. (18.4.5)

19 Controls Interface and Safeties

19.1 Control Configuration

19.1.1 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
Field-installed devices and control by the building automation system contractor
19.1.2 The party responsible for the sequence of operation shall be identified in the submittal, and the sequence shall be reviewed before any control device is released for fabrication.
NOTE A factory controller arrives tested with the equipment it controls and carries the manufacturer's own protective logic, 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 equipment on the party that did not build it. The division matters most for the safeties, which have to work regardless of who wrote the sequence. (19.1.3)

19.2 Building Automation System Interface

19.2.1 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
19.2.2 The interface shall conform to Building Automation SystemBuilding Automation SystemResolves to the current adopted revision.sync/building-automation-system.
19.2.3 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.
19.2.4 Field control connections shall terminate on a labeled terminal block in an enclosure accessible without opening a section that is pressurized during operation.
19.2.5 Terminal designations on the unit shall match the designations in the submitted wiring diagram and in the point list.

19.3 Control Points

19.3.1 The control devices furnished with the unit shall be as indicated in the datasheet.
Control Devices Furnished with the Unitcheckbox
☑ Supply air temperature sensor
☑ Return air temperature sensor
☑ Mixed air temperature sensor
☐ Outdoor air temperature sensor
☐ Supply air humidity sensor
☐ Return air humidity sensor
☐ Outdoor air humidity sensor
☐ Supply duct static pressure sensor
☐ Coil leaving air temperature sensor at each coil
☐ Outdoor airflow measuring station
☐ Supply fan airflow measuring station
☑ Filter differential pressure device at each stage
☑ Fan status by differential pressure switch
☐ Fan status by drive feedback
☐ Drain pan high water level switch
☑ Low-limit temperature device
☑ Duct high static pressure switch
19.3.2 Every furnished device shall be accessible for calibration and replacement from a service position, and no device shall require entering an operating section to reach.
19.3.3 Sensors installed in an airstream that varies across the duct section shall be averaging elements rather than single-point elements.

19.4 Duct Smoke Detection

19.4.1 Duct smoke detection shall be furnished at the locations indicated in the datasheet and shall be installed in accordance with NFPA 90A and NFPA 72.
Duct Smoke Detector Locationscheckbox
☑ Supply air, downstream of the filters and the supply fan
☐ Return air, upstream of any outdoor air connection
☐ Return air at each story connection to a common return
☐ No duct smoke detection furnished with the unit
19.4.2 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
19.4.3 Detector sampling tubes shall span the duct or plenum cross-section and shall be oriented and sized in accordance with the detector manufacturer's instructions for that cross-section.
NOTE A sampling tube that is short for the duct it is in produces a reading from one part of the section, and a tube installed with its inlet holes facing the wrong way produces almost no sample at all. Either way the detector tests as functional on a puff of aerosol at the tube and does not detect a fire, which is why the tube dimension is an installation requirement rather than a detail. (19.4.4)
19.4.5 Smoke detection shall shut down the supply fan through a hardwired interlock that does not depend on the building automation system.

19.5 Freeze Protection

19.5.1 A low-limit temperature device shall be furnished downstream of the mixing section and upstream of the first heating or cooling coil on every unit that admits outdoor air.
19.5.2 The low-limit device type shall be as indicated in the datasheet.
Low-Limit Temperature Deviceselect
Averaging element thermostat, manual reset
Averaging element thermostat, automatic reset
Temperature sensor array reporting to the building automation system
None
19.5.3 Where an averaging element device is furnished, the element shall be arranged so that not less than 1 lin ft of element covers each 1 ft² of coil face area, distributed across the full face.
19.5.4 The low-limit device shall respond to the coldest portion of its sensing element rather than to the average of the element.
19.5.5 The low-limit device shall stop the supply fan, drive the outdoor air damper closed, and drive the heating coil control valve open when it trips.
19.5.6 The trip setpoint and any alarm setpoint shall be recorded in the startup report.
NOTE A single-point temperature device in a mixing section reports the temperature at one point in a plane that can vary by tens of degrees across its area, so its reading depends on where the installer happened to put it. An averaging element spread across the coil face does not average away a cold streak if the device responds to the coldest part of the element, and that response characteristic is what makes the device useful for freeze protection rather than for temperature control. (19.5.7)

19.6 Static Pressure Safety

19.6.1 A high static pressure safety device shall be furnished in the supply air section of every unit whose fan can develop a pressure exceeding the pressure class of the connected ductwork.
19.6.2 The high static pressure device shall stop the supply fan through a hardwired interlock and shall require manual reset.
19.6.3 A low static pressure safety device shall be furnished in the return or suction section of every unit whose fan can collapse the connected ductwork or the casing when a return path closes.
19.6.4 The setpoints of the static pressure safety devices shall be established from the pressure class of the connected ductwork and the casing pressure class, and shall be recorded in the startup report.

20 Factory Testing

20.1 Production Tests

20.1.1 Each unit shall receive the factory tests indicated in the datasheet before shipment.
Factory Tests Requiredcheckbox
☑ Fan airflow and static pressure at the design operating point
☑ Motor current at the design operating point
☑ Vibration measurement at the fan and motor bearings
☐ Casing leakage test at 1.5 times design static pressure
☐ Casing deflection measurement at design static pressure
☑ Drain pan water hold test
☑ Damper stroke and fail-position test
☐ Door and panel gasket seal verification under pressure
☑ Coil pressure test
☑ Electrical continuity and insulation resistance test
☐ Controls point-to-point verification
20.1.2 Measured airflow and static pressure shall be within ±5% of the values published in the reviewed submittal.
20.1.3 The drain pan water hold test shall fill the pan to the overflow connection and shall show no leakage at any seam, connection, or penetration after 15 minutes.
20.1.4 A unit that fails any required test shall be corrected and retested, and the cost of the correction and of every retest shall be borne by the manufacturer.
20.1.5 No unit shall be shipped until every required test has been passed and the results recorded.

20.2 Run Test

20.2.1 Each unit shall be operated at design conditions for not less than the duration indicated in the datasheet.
Factory Run Test Durationrange
hours
0.250.51248
20.2.2 Where the datasheet does not state a duration, the run test shall continue until bearing temperatures and motor current have been stable for 30 minutes.
20.2.3 Bearing housing temperature rise above ambient and vibration at each bearing shall be recorded at the start and at the end of the run test.
20.2.4 A bearing housing temperature rise exceeding 40°F above ambient, or a vibration reading that increases during the run, shall be corrected before shipment.
NOTE The run test is the only opportunity to find a balance or alignment defect while the unit is still on the factory floor with a crane over it. A bearing that heats or a vibration reading that climbs during the run is the signature of a defect that will not improve in service, and it is much cheaper to find there than after the unit is set, piped, and ducted. (20.2.5)

20.3 Test Witnessing

20.3.1 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
20.3.2 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.
20.3.3 Where witnessed testing is selected and the unit fails, the cost of the witness attending each retest shall be borne by the manufacturer.

21 Delivery, Storage, and Handling

21.1 Shipping Configuration

21.1.1 The shipping configuration shall be as indicated in the datasheet.
Shipping Configurationselect
Single assembled piece
Shipping sections with factory-applied joint gaskets and field-bolted flanges
Shipping sections with field-applied joint sealant
Knocked down for field assembly
21.1.2 The Contractor shall verify the rigging path from the point of delivery to the final location, including every door, corridor, stair, elevator, and structural opening, before the unit is released for fabrication.
21.1.3 Where the verified rigging path cannot pass the configuration selected in the datasheet, the Contractor shall notify the Engineer of Record before fabrication and shall propose a shipping split that the path can pass.
21.1.4 Field joints between shipping sections shall be made with the gasket and hardware the manufacturer furnishes for that joint, and shall be sealed to the leakage class specified for the section.
NOTE The shipping split is the one dimension on the unit that is set by the building rather than by the equipment, and it is the constraint most often confirmed after the order is placed. A unit that cannot reach its room is a total loss on the schedule, not a rework item. (21.1.5)

21.2 Protection in Transit and Storage

21.2.1 The protective packaging furnished for shipment shall be as indicated in the datasheet.
Shipping Protectionselect
Weather-resistant wrap on every section
Palletized with corner protection and stretch wrap
Crated
Interior sections wrapped and openings sealed
Manufacturer's standard (by default)
21.2.2 Openings in shipped sections shall be covered and sealed against water and debris until the connecting work is made.
21.2.3 Units shall be stored in a clean, dry, and heated space until they are set.
21.2.4 Where indoor storage is not available, units shall remain in their protective packaging, shall be supported clear of standing water, and shall have condensation heaters in electrical compartments energized.
21.2.5 Units stored outdoors for more than 30 days shall be inspected by the Contractor before installation for water intrusion, corrosion, and pest intrusion, and the inspection findings shall be reported in writing to the Owner.
21.2.6 Fan assemblies stored more than 30 days shall have the shaft rotated by hand through several revolutions at intervals not exceeding 30 days.
NOTE A bearing under a stationary load for months develops a wear mark at the loaded contact point because the lubricant film is squeezed out and does not re-form without motion. Rotating the shaft periodically moves the contact and is the difference between a fan that is quiet at startup and one that has to be rebuilt before it is ever commissioned. (21.2.7)

22 Installation

22.1 Rigging and Setting

22.1.1 Units shall be rigged using the lifting points, spreader arrangement, and rigging hardware the manufacturer designates.
22.1.2 Slings or chains shall not bear against casing panels, coil connections, or drain connections.
22.1.3 Units shall be set level within 1/8 in. over the unit length and within 1/8 in. across the unit width, and the drain pans shall be verified to slope to their connections after setting.
22.1.4 Shipping braces, shipping bolts, and transit restraints shall be removed after the unit is set and before the fan is operated.
22.1.5 The Contractor shall confirm in the startup report that every shipping restraint has been removed.
NOTE A shipping brace left in a fan assembly holds the isolated mass rigid against the casing, so the first start delivers the full unbalance force into the structure and into bearings that are not free to move. This is a same-day failure rather than a slow one. (22.1.6)

22.2 Service Clearances

22.2.1 The service clearances shown on the reviewed configuration drawing shall be maintained clear of piping, conduit, ductwork, and stored material after installation.
22.2.2 The coil pull clearance, the filter withdrawal clearance, and the fan and motor removal path shall remain unobstructed for the life of the installation.
22.2.3 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.

22.3 Duct Connections

22.3.1 The unit-to-duct connection type shall be as indicated in the datasheet.
Unit-to-Duct Connectionselect
Factory flanged connection with a flexible connector
Factory sheet metal collar with a flexible connector
Field-fabricated transition with a flexible connector
22.3.2 Connecting ductwork shall be independently supported so that no duct weight is carried by the unit casing.
22.3.3 Connecting ductwork shall be installed after the unit is set on its final supports or isolators.
22.3.4 Duct transitions at the unit shall conform to the SMACNA HVAC Duct Construction Standards and shall not exceed the transition angle at which the fan outlet loss published in the submittal remains valid.
NOTE A duct that leaves the fan discharge into an abrupt transition or an immediate elbow does not develop the velocity profile the fan was rated with, and the resulting system effect can consume a meaningful fraction of the fan's rated pressure. It shows up during balancing as a unit that will not make its airflow at a fan speed the curve says should be ample. (22.3.5)

22.4 Piping and Electrical Connections

22.4.1 Hydronic connections shall include a shutoff valve on the supply and the return at each coil so that the coil can be isolated without draining the system.
22.4.2 Coils shall be hydrostatically tested at 1.5 times the design working pressure, and not less than 150 psig, for not less than 2 hours after field piping connections are complete and before the unit is placed in service.
22.4.3 The condensate drain connection shall include a union or a cleanout that permits the trap to be disassembled without cutting the line.
22.4.4 Electrical connections shall be made in accordance with NFPA 70, and the unit disconnecting means shall be located within sight of the unit it serves.
22.4.5 Penetrations made in the field through the casing shall be sealed and touched up so that the leakage class and the corrosion protection of the section are maintained.

23 Startup, Commissioning, and Balancing

23.1 Startup Service

23.1.1 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
23.1.2 Before the fan is energized, the Contractor shall verify that shipping restraints are removed, that the fan wheel turns freely without contact, that belt tension and sheave alignment are correct on belt drives, that motor rotation matches the direction marked on the fan, that access doors are closed and latched, that the drain trap is installed and primed, that flexible connections are installed, and that casing penetrations are sealed.
23.1.3 The fan shall be started at its lowest speed and shall be run for not less than 15 minutes while bearing temperature, motor current, and sound are observed before the speed is increased.
23.1.4 The startup report shall record the measured airflow, external static pressure, fan speed, motor current at each measured condition, bearing temperatures, and the setpoints of every safety device.

23.2 Functional Testing

23.2.1 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 control sequences
☑ Verified trip of every safety device at its setpoint
☐ Economizer changeover verification across the high-limit setpoint
☑ Verification of drain pan drainage during operation
☑ Integrated testing with the fire alarm system
☐ Trend review over a seasonal period
23.2.2 Each safety device shall be tested by driving the condition it senses to its setpoint rather than by simulating the device output.
NOTE Testing a freeze protection device by shorting its contacts proves the wiring and nothing else. The failure modes that matter are an element installed in the wrong plane, a setpoint that drifted, and a device that responds to its average rather than its coldest point, none of which a contact closure test can find. (23.2.3)
23.2.4 Drain pan drainage shall be verified during operation, with the coil condensing and the fan at design speed, by observing continuous flow at the drain and no accumulation in the pan.

23.3 Air Balancing

23.3.1 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.
23.3.2 Measured airflow after balancing shall be within the tolerance indicated in the datasheet of the design value.
Airflow Balancing Tolerancerange
%
015
Default: 10 %
23.3.3 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.
23.3.4 Filters shall be clean and the filter differential pressure shall be recorded at the time of the final balance.
23.3.5 The balance report shall record the as-left fan speed, drive component designations for belt drives, airflow, static pressure at the unit inlet and discharge, motor current, and the outdoor air damper minimum position.

24 Identification and Labeling

24.1 Unit Nameplate

24.1.1 Each unit shall be furnished with a permanent nameplate on the exterior of the casing, mechanically fastened rather than adhered.
Unit Nameplate Materialselect
Laminated phenolic
Stainless steel
Anodized aluminum
24.1.2 The nameplate shall state the unit tag, the manufacturer, the model and serial number, the design supply airflow, the design external static pressure, the supply fan motor nameplate power, the electrical characteristics, and the date of manufacture.
24.1.3 The unit tag on the nameplate shall match the tag used in the Contract Documents and in the operation and maintenance manuals.

24.2 Section and Component Labeling

24.2.1 Each access door shall be labeled on its exterior with the section it opens.
24.2.2 Labels shall be legible from 5 ft.
24.2.3 Filter section doors shall be labeled with the filter efficiency and filter sizes the section holds, and shall be furnished with a holder for recording the date of each filter change.
24.2.4 Fan section doors shall be labeled with a warning that the section contains a rotating assembly.
24.2.5 Electrical enclosure doors shall contain a permanently mounted copy of the unit wiring diagram.
24.2.6 Control terminal strips shall be labeled to match the designations in the submitted point list and wiring diagram.

25 Warranty

25.1 Warranty Term

25.1.1 The manufacturer shall warrant each unit against defects in materials and workmanship for the terms indicated in the datasheet.
Equipment Parts Warranty Termrange
years
123510
Equipment Labor Warranty Termrange
years
1235
Warranty Start Milestoneradio
● Date of substantial completion
○ Date the Owner takes beneficial use of the system
○ Date of shipment
NOTE Parts and labor are separate commitments and they are 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 downtime, so the two terms have to be read together to know what the coverage is actually worth. (25.1.2)
25.1.3 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.

25.2 Component Warranties

25.2.1 Coils shall be warranted against leakage and against defects in materials and workmanship for the term indicated in the datasheet.
Coil Warranty Termrange
years
123510
Fan and Motor Warranty Termrange
years
123510
25.2.2 The coil warranty shall not cover damage caused by water chemistry outside the range the manufacturer publishes, by freezing that results from system operation outside the design conditions, or by physical damage from tools or from filter service.
25.2.3 Where the coil manufacturer conditions its warranty on water chemistry, the party responsible for water treatment shall furnish the water quality records the warranty requires, and the responsible party shall be identified in the submittal.
25.2.4 Motor and drive manufacturers' warranties shall pass through to the Owner in addition to the unit warranty.
NOTE A coil warranty conditioned on water chemistry is only as good as the party that keeps the records. When nobody is named, the records do not exist, and the first coil failure turns into an argument the Owner loses on evidence rather than on merit. (25.2.5)

25.3 Warranty Service

25.3.1 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.
25.3.2 The manufacturer shall respond to a warranty notification within 2 business days.
25.3.3 Where a warranty repair requires removal or modification of adjacent work, the cost of removing and restoring that work shall be borne by the party responsible for the defect.
25.3.4 Restoration of adjacent work disturbed by a warranty repair 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.

26 Spare Parts

26.1 Spare Parts Furnished

26.1.1 The Contractor shall furnish the spare parts indicated in the datasheet at substantial completion.
Spare Parts Furnishedcheckbox
☑ One complete set of filters of every type and size installed
☐ Two complete sets of filters of every type and size installed
☑ One complete set of drive belts for every belt-driven fan
☐ One spare sheave set for every belt-driven fan
☐ One set of door and panel gaskets for each unit
☐ One set of damper blade and jamb seals for each unit
☐ One spare fan bearing of each type installed
☐ One tube of the specified bearing grease with a grease gun
☑ One set of every fuse type installed
☐ One spare control sensor of each type installed
26.1.2 Spare parts shall be delivered in the manufacturer's packaging, labeled with the unit tag they serve and with the manufacturer's part designation.

26.2 Spare Parts Storage

26.2.1 Spare filters shall be stored in sealed packaging in a clean, dry location the Owner designates.
26.2.2 The Contractor shall furnish a written inventory of the spare parts delivered, correlating each item to the unit it serves and the location where it was stored.
26.2.3 The operation and maintenance manual shall include a filter change schedule derived from the initial and change-out resistances stated in the submittal.

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