1 Scope

NOTE This standard covers the zone airflow, ventilation compliance, energy-limit, control sequence, and field verification requirements of pressure-independent variable air volume terminal units serving individual thermal zones from a central variable-volume air system. (1.1)

NOTE The unit types in scope are the single-duct variable-volume unit with or without a reheat coil, the parallel fan-powered unit, the series fan-powered unit, and the dual-duct variable-volume unit. (1.2)

NOTE This standard is the variable-volume layer over Air Terminal UnitsAir Terminal UnitsResolves to the current edition.sync/air-terminal-units. The family standard establishes what an air terminal is made of and how it is built, listed, installed, identified, warranted, and spared; this standard establishes the setpoints it holds, the compliance basis those setpoints answer to, the sequences it runs, and the evidence that it does. (1.3)

1.4 Terminal units furnished under this standard shall also comply with Air Terminal UnitsAir Terminal UnitsResolves to the current edition.sync/air-terminal-units.

1.5 Where a requirement of this standard and a requirement of Air Terminal UnitsAir Terminal UnitsResolves to the current edition.sync/air-terminal-units address the same subject, the requirement of this standard shall govern.

1.6 Delivery, storage, handling, installation, identification, warranty, and spare parts for units furnished under this standard shall be as required by Air Terminal UnitsAir Terminal UnitsResolves to the current edition.sync/air-terminal-units.

NOTE The following are outside the scope of this standard: (1.7)

Room-boundary outlets, being diffusers, grilles, registers, and linear slot outlets, which are covered by HVAC Air Distribution DevicesHVAC Air Distribution DevicesResolves to the current edition.sync/hvac-air-distribution-devices
The central air handling unit that conditions and distributes the primary air, together with its supply fan, its outdoor air control, and the supervisory reset and ventilation algorithms resident in it, which are covered by Air Handling UnitsAir Handling UnitsResolves to the current edition.sync/air-handling-units and Building Automation SystemBuilding Automation SystemResolves to the current edition.sync/building-automation-system
Ductwork upstream of the primary inlet and downstream of the unit outlet, and duct-mounted accessories, which are covered by HVAC DuctworkHVAC DuctworkResolves to the current edition.sync/hvac-ductwork and Duct AccessoriesHVAC Duct AccessoriesResolves to the current edition.sync/duct-accessories
In-line sound attenuators, which are covered by HVAC Sound AttenuatorsHVAC Sound AttenuatorsResolves to the current edition.sync/hvac-sound-attenuators
Hydronic supply, return, and balancing piping serving a reheat coil, which is covered by Hydronic PipingHydronic PipingResolves to the current edition.sync/hydronic-piping
Condensate drainage from a fan-powered unit cooling coil, which is covered by Condensate Drainage PipingHVAC Condensate Drainage PipingResolves to the current edition.sync/condensate-drainage-piping
Variable frequency drives serving the central supply fan, which are covered by HVAC Variable Frequency DrivesHVAC Variable Frequency DrivesResolves to the current edition.sync/hvac-variable-frequency-drives
Constant-volume terminal units, induction units, and bypass terminal units, which are covered by Air Terminal UnitsAir Terminal UnitsResolves to the current edition.sync/air-terminal-units
Fan coil units and chilled beams, which recirculate room air rather than meter central primary air, and which are covered by Fan Coil UnitsFan-Coil UnitsResolves to the current edition.sync/fan-coil-units and Chilled BeamsActive and Passive Chilled BeamsResolves to the current edition.sync/chilled-beams
Makeup air units and dedicated outdoor air units that deliver outdoor air without zone-level variable-volume metering, which are covered by Makeup Air UnitsMakeup Air UnitsResolves to the current edition.sync/makeup-air-units and Dedicated Outdoor Air SystemsDedicated Outdoor Air SystemsResolves to the current edition.sync/dedicated-outdoor-air-systems
Laboratory venturi airflow control valves used for critical space pressurization and fume hood face velocity control

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 880	Performance Rating of Air Terminals
ANSI/AHRI 885	Procedure for Estimating Occupied Space Sound Levels in the Application of Air Terminals and Air Outlets
ANSI/ASHRAE 62.1	Ventilation and Acceptable Indoor Air Quality
ANSI/ASHRAE 130	Methods of Testing Air Terminal Units
ANSI/ASHRAE 135	BACnet — A Data Communication Protocol for Building Automation and Control Networks
ANSI/ASHRAE 170	Ventilation of Health Care Facilities
ANSI/ASHRAE 202	Commissioning Process for Buildings and Systems
ANSI/ASHRAE/IES 90.1	Energy Standard for Sites and Buildings Except Low-Rise Residential Buildings
ASHRAE Guideline 36	High-Performance Sequences of Operation for HVAC Systems
ANSI/AMCA 210	Laboratory Methods of Testing Fans for Certified Aerodynamic Performance Rating

NOTE ASHRAE Guideline 36 is a guideline rather than a code, so it carries no obligation of its own; where a project selects its terminal unit sequences under Air Terminal UnitsAir Terminal UnitsResolves to the current edition.sync/air-terminal-units, the requirements of this standard describe the same behavior in the terms this standard uses. (2.3)

3 Submittals

3.1 Zone Airflow Compliance Submittals

3.1.1 The Contractor shall submit the following for the Engineer of Record's review and return, and no terminal unit controller shall be programmed until the submittal covering it has been reviewed and returned:

Zone airflow schedule listing, for each unit tag, the design peak supply airflow, the cooling minimum, the heating minimum, the heating maximum, and the zone conditioned floor area used to establish them
The ventilation calculation establishing the zone outdoor airflow at the scheduled minimum, including the zone air distribution effectiveness used at the minimum airflow condition
The simultaneous heating and cooling compliance calculation showing the governing airflow limit for each zone and the basis of any exception claimed
The manufacturer's published airflow control tolerance and minimum controllable airflow for each unit at its selected inlet size
The air density correction applied to each airflow setpoint, stating the site elevation used and the party that applied it
Fan power at the design operating point for each fan-powered unit tag, derived from testing in accordance with ANSI/AMCA 210

Zone Airflow Compliance Submittals Requiredcheckbox

☑ Zone airflow schedule with the floor area used

☑ Zone ventilation calculation

☑ Simultaneous heating and cooling compliance calculation

☑ Published airflow control tolerance and minimum controllable airflow

☐ Air density correction record

☐ Fan power at the design operating point

3.2 Control Sequence and Integration Submittals

3.2.1 The Contractor shall submit the following for the Engineer of Record's review and return before the terminal unit controllers are released for shipment:

Written sequence of operation for each zone type, covering occupied, occupied-standby, unoccupied, morning warm-up, and morning cool-down operation
The zone request logic by which the unit signals duct static pressure, supply air temperature, and hot water temperature reset, stating the condition that raises each request and the condition that clears it
Protocol implementation conformance statement to ANSI/ASHRAE 135 and BACnet Testing Laboratories listing evidence for the controller model furnished
Point list mapping each zone airflow, damper position, temperature, mode, and request value to its network object
The trend log configuration to be delivered, covering zone airflow, damper position, discharge air temperature, reheat output, and each reset request

Control Sequence and Integration Submittals Requiredcheckbox

☑ Written sequence of operation for each zone type

☑ Zone request logic with raise and clear conditions

☑ Protocol conformance statement and BACnet Testing Laboratories listing

☑ Network point list

☑ Trend log configuration

3.3 Closeout Records of Zone Airflow and Sequences

3.3.1 The Contractor shall submit the following before the date of Substantial Completion:

As-left airflow setpoints for every operating mode at every unit tag, with the as-left calibration constant for each unit
The functional test record covering pressure-independence verification, reset request generation, and mode transitions
Trend logs covering not less than fourteen consecutive days of occupied operation at the units functionally tested
The final controller parameter file for each unit type, in a format the Owner can reload without assistance from the manufacturer

Closeout Records Requiredcheckbox

☑ As-left setpoints and calibration constants

☑ Functional test record

☑ Fourteen-day occupied trend logs

☑ Reloadable controller parameter file

4 Pressure-Independent Airflow Control

4.1 Airflow Control Basis

4.1.1 Terminal units furnished under this standard shall be pressure-independent, controlling to a commanded primary airflow setpoint from a measured airflow signal rather than to a damper position.

NOTE A pressure-independent unit closes its control loop on measured airflow, so the airflow the zone receives is the airflow the ventilation and load calculations assumed, no matter how the upstream static pressure moves as other zones open and close. A pressure-dependent unit closes its loop on damper position, so its delivered airflow rises and falls with system pressure and the zone minimum becomes a quantity that exists only on the schedule. (4.1.2)

4.1.3 Each unit shall hold the commanded primary airflow within the control tolerance indicated in the datasheet at every setpoint between the scheduled minimum and the scheduled maximum, over the inlet static pressure range from the unit's minimum operating differential pressure to the available inlet static pressure scheduled for it.

Primary Airflow Control Tolerance About the Commanded Setpointrange

%

235101520

NOTE The control tolerance in this article is the airflow the unit delivers about the commanded setpoint. It is a different and wider quantity than the measurement error of the sensing element specified under Air Terminal UnitsAir Terminal UnitsResolves to the current edition.sync/air-terminal-units, which is the error of the reading the control loop drives to. (4.1.4)

4.1.5 Each unit shall return to within its control tolerance, following a step change in inlet static pressure within its operating range, in not more than the settling time the manufacturer publishes for the unit.

4.1.6 The manufacturer shall state the settling time and the minimum operating differential pressure for each scheduled unit in the action submittal.

4.1.7 Where the parties disagree whether a unit meets its control tolerance, the Engineer of Record shall make the initial determination from measurements taken in accordance with ANSI/ASHRAE 130.

4.2 Airflow Setpoint Density Correction

4.2.1 Primary airflow setpoints and the airflow sensing calibration at each unit shall be corrected for AltitudeAltitudeParameterEach project supplies its own value.altitude.

NOTE A cataloged airflow rating and the relation between velocity pressure and volumetric flow are both established at standard air density. At elevation the same velocity pressure corresponds to a larger volumetric flow and a smaller mass flow, so an uncorrected controller holds the zone at less outdoor air than the ventilation calculation credited it with, and the shortfall grows with elevation. (4.2.2)

4.2.3 The party responsible for applying the density correction shall be as indicated in the datasheet.

Responsibility for Airflow Setpoint Density Correctionselect

Terminal unit manufacturer, applied to the factory calibration before shipment

Controls contractor, applied at the terminal unit controller during startup

Testing and balancing agent, applied against a density-corrected reference instrument during balancing

4.2.4 Where the datasheet does not indicate a responsible party, the controls contractor shall apply the density correction.

4.2.5 The airflow values the controller reports to the building automation system shall be expressed either as standard cubic feet per minute or as actual cubic feet per minute, consistently at every unit on the project, and the convention used shall be stated in the closeout record.

4.2.6 The correction applied at each unit shall be recorded in the closeout record.

5 Zone Ventilation Compliance

5.1 Basis of the Zone Minimum Primary Airflow

5.1.1 The basis on which the zone minimum primary airflow setpoint is established shall be as indicated in the datasheet.

Basis of the Zone Minimum Primary Airflow Setpointselect

Ventilation Rate Procedure of ANSI/ASHRAE 62.1

IAQ Procedure of ANSI/ASHRAE 62.1

Prescriptive outdoor airflow table of the adopted mechanical code

Space-type ventilation rate of ANSI/ASHRAE 170

Space-type ventilation rate of an accreditation or licensing standard governing the occupancy

5.1.2 The zone minimum primary airflow setpoint shall deliver not less than the zone outdoor airflow required by the selected basis at the outdoor air fraction the central system maintains.

5.1.3 The zone air distribution effectiveness used in the ventilation calculation shall be the value corresponding to the supply air temperature and outlet type at the zone's minimum airflow condition rather than at its design cooling condition.

NOTE A ceiling outlet supplying cool air is credited with full air distribution effectiveness, and the same outlet supplying warm air is credited with less, because the warm jet does not reach the breathing zone. A zone that satisfies its ventilation rate in cooling can therefore fall short of it in heating at the same measured airflow. (5.1.4)

5.1.5 The zone primary airflow used in the multiple-zone system ventilation efficiency calculation shall be the minimum setpoint actually programmed into the controller.

5.1.6 Where a zone minimum setpoint is raised or lowered after the system ventilation efficiency calculation is complete, the Contractor shall report the change to the Engineer of Record before it is programmed.

NOTE The outdoor air fraction the central system must maintain is set by the zone with the highest ratio of required outdoor air to primary air, so one box minimum changed in the field to settle a comfort complaint moves the outdoor air requirement of the whole air handler. The change is invisible at the zone and surfaces as an unexplained rise in outdoor air damper position at the central unit. (5.1.7)

5.1.8 The central system outdoor air control and the system ventilation efficiency calculation shall be coordinated with Air Handling UnitsAir Handling UnitsResolves to the current edition.sync/air-handling-units.

5.2 Dynamic Ventilation Reset

5.2.1 The zone dynamic ventilation reset input shall be as indicated in the datasheet.

Zone Dynamic Ventilation Reset Inputselect

No dynamic reset, with the zone holding a fixed minimum outdoor airflow

Zone carbon dioxide sensor

Zone occupancy sensor

Occupant count from an access control or people counting system

Scheduled occupancy profile resident in the building automation system

Derived — the demand-control ventilation thresholds of Adopted Energy CodeAdopted Energy CodeParameterEach project supplies its own value.adopted-energy-code applied to the zone design occupant density and conditioned floor area (by default)

5.2.2 Where a dynamic reset input is indicated, the controller shall reset the zone minimum primary airflow between the airflow required at the reset condition and the airflow required at the zone design population.

5.2.3 The reset shall not reduce the zone minimum below the airflow required by the building component of the zone ventilation rate.

NOTE Resetting a zone minimum on measured occupancy recovers the fan energy and the reheat energy that a fixed design-population minimum spends during the hours the zone is lightly occupied. The saving is proportional to the gap between design population and actual population, which is large in a conference room and small in an open office at full census. (5.2.4)

5.2.5 Sensor selection, placement, and calibration for a dynamic reset input shall be as required by Building Automation SystemBuilding Automation SystemResolves to the current edition.sync/building-automation-system.

6 Energy Standard Airflow and Reheat Limits

6.1 Deadband and Cooling Minimum Airflow Limit

6.1.1 The zone minimum primary airflow setpoint shall not exceed the governing airflow limit indicated in the datasheet, determined under the simultaneous heating and cooling limitation of Adopted Energy CodeAdopted Energy CodeParameterEach project supplies its own value.adopted-energy-code.

Governing Deadband Airflow Limitselect

20 percent of the zone design peak supply airflow

30 percent of the zone design peak supply airflow

0.4 cfm per square foot of zone conditioned floor area

The zone outdoor airflow required by the selected ventilation basis

The airflow required to maintain the zone pressurization relationship

Derived — the simultaneous heating and cooling limitation of Adopted Energy CodeAdopted Energy CodeParameterEach project supplies its own value.adopted-energy-code evaluated against the zone design peak supply airflow, the zone conditioned floor area, and the zone outdoor airflow requirement (by default)

NOTE The listed allowances are alternatives and the limit is the largest of them, so the governing allowance is whichever computes highest for the particular zone. The limit is a ceiling rather than a target: it fixes only how high a minimum a zone is permitted to hold while it remains capable of reheating, and any setpoint at or below it satisfies the limitation. (6.1.2)

6.1.3 A zone shall claim the direct digital control allowance only where its terminal unit controller is under direct digital control and reports to the building automation system.

6.1.4 The governing allowance and the airflow it computes shall be recorded for each unit tag in the zone airflow compliance submittal.

6.1.5 Where the parties disagree which allowance governs a zone, the Engineer of Record shall make the initial determination.

6.2 Heating Airflow Limit

6.2.1 The primary airflow at the zone heating maximum shall not exceed the percentage of the zone design peak supply airflow indicated in the datasheet.

Zone Heating Maximum Primary Airflowrange

%

2030405060708090100

Derived — the direct digital control heating allowance of Adopted Energy CodeAdopted Energy CodeParameterEach project supplies its own value.adopted-energy-code applied to the zone design peak supply airflow (by default)

6.2.2 The first stage of zone heating shall raise the discharge air temperature setpoint while the primary airflow is held at the zone minimum.

6.2.3 The primary airflow shall be increased toward the heating maximum only after the discharge air temperature setpoint has reached its upper limit.

NOTE The heating allowance rests on that sequence. A zone that raises airflow and discharge temperature together spends cooling energy at the central coil and heating energy at the reheat coil on the same air at the same time, which is the condition the limitation exists to bound. (6.2.4)

6.2.5 The zone airflow control logic selected under Air Terminal UnitsAir Terminal UnitsResolves to the current edition.sync/air-terminal-units shall be consistent with the heating allowance claimed under this article.

6.2.6 The discharge air temperature sensor and the controller capability that sequence requires shall be furnished under Air Terminal UnitsAir Terminal UnitsResolves to the current edition.sync/air-terminal-units.

6.3 Reheat Limitation Exceptions

6.3.1 Any exception to the simultaneous heating and cooling limitation claimed for a zone shall be as indicated in the datasheet.

Simultaneous Heating and Cooling Exception Claimedselect

No exception claimed

Zone outdoor airflow requirement exceeds the airflow limit

Zone humidity control requirement fixes the airflow

Zone pressurization relationship fixes the airflow

Zone heating energy is supplied predominantly from site-recovered or site-solar energy

Zone is served by a laboratory exhaust system subject to the laboratory provision of the energy standard

6.3.2 The calculation supporting each claimed exception shall be included in the zone airflow compliance submittal.

NOTE An exception claimed under this article bears only on the airflow limit of the simultaneous heating and cooling limitation. The zone's ventilation basis and its control sequences are established elsewhere in this standard and are unchanged by the exception. (6.3.3)

7 Zone Operating Modes

7.1 Occupied-Standby Operation

7.1.1 The extent of occupied-standby operation shall be as indicated in the datasheet.

Extent of Occupied-Standby Operationradio

○ Provided at every zone served by a terminal unit

○ Provided at zones furnished with an occupancy sensing input

○ Not provided

Derived — the occupied-standby requirements of Adopted Energy CodeAdopted Energy CodeParameterEach project supplies its own value.adopted-energy-code for the space types served (by default)

7.1.2 In occupied-standby the controller shall hold the zone at its standby minimum primary airflow and shall widen the zone temperature setpoints to the standby band stated in the sequence of operation submittal.

7.1.3 The controller shall return the zone to occupied operation within one minute of receiving an occupancy signal.

NOTE Standby operation differs from unoccupied operation in that the zone stays available: the setpoints widen and the ventilation that serves people is withdrawn, while the ventilation that serves the building materials and the temperature control of the space continue. (7.1.4)

7.2 Unoccupied-Period Operation

7.2.1 The primary damper position during unoccupied periods shall be as indicated in the datasheet.

Unoccupied-Period Primary Damper Positionradio

● Closed, until an unoccupied setback call

○ Held at the zone minimum ventilation setpoint

○ Held at a reduced setback airflow below the occupied minimum

7.2.2 During an unoccupied setback call the controller shall open the primary damper to the airflow required to deliver the setback heating or cooling, and shall return it to its unoccupied position when the call is satisfied.

7.2.3 Where a series or parallel fan section is furnished, the controller shall enable the fan section for an unoccupied setback call before it increases primary airflow.

NOTE A zone that holds its occupied minimum through unoccupied hours runs the central fan and carries the outdoor air load all night. Closing the damper concentrates the night's operation into the setback calls that actually occur, at the cost of a longer morning recovery. (7.2.4)

7.3 Morning Warm-Up and Cool-Down

7.3.1 The zone operation during morning warm-up shall be as indicated in the datasheet.

Zone Operation During Morning Warm-Upselect

Primary damper driven to the zone heating maximum airflow

Primary damper driven fully open

Primary damper held at the zone minimum primary airflow

Zone excluded from morning warm-up and started at occupancy

7.3.2 During morning warm-up the zone reheat output shall be disabled while the primary air temperature is above the zone temperature.

7.3.3 During morning cool-down the zone shall operate at its cooling maximum primary airflow and the zone reheat output shall be disabled.

7.3.4 The controller shall report to the building automation system whether the zone has reached its occupied setpoint, so that the central system can end the warm-up or cool-down mode on zone readiness rather than on elapsed time.

NOTE Ending warm-up on a timer leaves the slowest zones cold at occupancy and runs every other zone past the point it needed. Ending it on zone readiness shortens the mode to the length the worst zone actually requires. (7.3.5)

8 System Reset Participation

8.1 Duct Static Pressure Reset Requests

8.1.1 The means by which the terminal unit signals its need for duct static pressure shall be as indicated in the datasheet.

Duct Static Pressure Reset Signal from the Zoneselect

Network request generated by the terminal unit controller from damper position and airflow error

Damper position published to the network for a supervisory reset algorithm

Hardwired analog damper position signal to the supervisory controller

No signal, with the system holding a fixed duct static pressure setpoint

8.1.2 Where a request or a signal is indicated, the terminal unit controller shall raise it whenever the primary damper reaches the position at which the unit can no longer hold its commanded airflow setpoint, and shall clear it when the unit recovers the setpoint.

8.1.3 Each terminal unit's contribution to the reset shall be individually removable from the reset algorithm at the operator workstation without disabling the unit's other points.

NOTE A single zone with an undersized inlet, an obstructed approach, or a stuck damper holds its request permanently and pins the system at maximum static pressure, which raises fan energy and terminal unit sound for every other zone at every hour. Being able to remove one zone from the algorithm is what lets the operator restore the reset while the underlying defect is corrected. (8.1.4)

8.1.5 The reset algorithm, its trim and respond parameters, and the alarm for a zone that drives the reset continuously shall be provided under Building Automation SystemBuilding Automation SystemResolves to the current edition.sync/building-automation-system.

8.1.6 Terminal unit sound shall be projected in accordance with ANSI/AHRI 885 at the highest duct static pressure the reset algorithm is permitted to command, rather than at the reset pressure expected in normal operation.

NOTE Selecting sound at the pressure the reset is expected to settle at, and then commissioning the system with a higher upper limit, is how a project arrives at an acoustically acceptable design and an acoustically unacceptable building. (8.1.7)

8.2 Supply Air Temperature Reset Requests

8.2.1 The zone's participation in supply air temperature reset shall be as indicated in the datasheet.

Zone Participation in Supply Air Temperature Resetradio

○ The zone generates cooling supply air temperature reset requests

○ The zone generates no reset requests

8.2.2 Where the zone generates requests, the controller shall raise a request from the zone cooling loop output and shall clear it when the zone cooling loop is satisfied.

NOTE Raising the supply air temperature lowers the reheat energy and the central cooling energy a zone consumes at part load, and raises the primary airflow the zone needs for the same sensible load, which raises fan energy and reduces the moisture the central coil removes. Where the outdoor dew point is high for a large part of the year, the moisture consequence governs the upper limit of the reset. (8.2.3)

8.2.4 The reset limits and the outdoor air temperature reset schedule shall be established under Air Handling UnitsAir Handling UnitsResolves to the current edition.sync/air-handling-units.

8.3 Hot Water Temperature Reset Requests

8.3.1 Requirements in this article apply where a hydronic reheat coil is furnished at the terminal unit.

8.3.2 The zone's participation in hot water temperature reset shall be as indicated in the datasheet.

Zone Participation in Hot Water Temperature Resetradio

○ The zone generates hot water temperature reset requests

○ The zone generates no reset requests

8.3.3 Where the zone generates requests, the controller shall raise a request from the reheat valve position and shall clear it when the valve position falls below the threshold stated in the sequence of operation submittal.

NOTE A hot water supply temperature reset driven by the most demanding zone lowers distribution losses, and where the heating plant is a condensing boiler or a heat pump it moves the plant into the return-temperature region where its efficiency is highest. (8.3.4)

8.3.5 The reset algorithm and the heating plant interface shall be provided under Building Automation SystemBuilding Automation SystemResolves to the current edition.sync/building-automation-system.

9 Fan-Powered Terminal Unit Energy Requirements

9.1 Fan Power and Speed Modulation

9.1.1 Requirements in this article apply where a parallel or series fan section is furnished at the terminal unit.

9.1.2 Fan-powered terminal units shall be furnished with electronically commutated motors where Adopted Energy CodeAdopted Energy CodeParameterEach project supplies its own value.adopted-energy-code requires them for fan-powered terminal units.

9.1.3 The fan motor type selected under Air Terminal UnitsAir Terminal UnitsResolves to the current edition.sync/air-terminal-units shall be consistent with that requirement.

9.1.4 The fan power at the design operating point shall not exceed the value indicated in the datasheet.

Fan Power at the Design Operating Pointrange

W/cfm

0.10.150.20.250.30.350.40.50.751

Derived — the fan power allowance of Adopted Energy CodeAdopted Energy CodeParameterEach project supplies its own value.adopted-energy-code for the fan section arrangement furnished (by default)

9.1.5 The fan power stated for each unit shall be the total input power to the motor and its integral electronics at the design fan airflow and the design external resistance, derived from testing in accordance with ANSI/AMCA 210.

NOTE Input power stated at the motor shaft, or stated at a resistance lower than the installed unit will see, understates the quantity the limit applies to, and the gap between shaft power and input power is proportionally largest on the small motors these units use. (9.1.6)

9.1.7 The controller shall vary the fan speed as a function of the zone heating and cooling load.

9.1.8 The lowest speed at which the fan is operated shall not exceed the fraction of design fan airflow permitted by Adopted Energy CodeAdopted Energy CodeParameterEach project supplies its own value.adopted-energy-code.

9.1.9 The as-commissioned fan speed setting for each operating mode shall be recorded in the closeout record.

9.2 Parallel Fan Operation

9.2.1 Requirements in this article apply where a parallel fan section is furnished at the terminal unit.

9.2.2 The condition at which the parallel fan is enabled shall be as indicated in the datasheet.

Parallel Fan Enable Conditionselect

On a call for zone heating

When the primary airflow falls to the zone minimum primary airflow

When the primary airflow falls below a scheduled fraction of the zone design peak supply airflow

Continuously through occupied hours

9.2.3 The parallel fan shall be disabled once the enabling condition has been absent for not less than the fan off-delay stated in the sequence of operation submittal.

NOTE Enabling the fan at the zone minimum rather than on a call for heat raises the discharge airflow at the outlet through the whole low-load range, which holds diffuser throw and reduces the cold air that would otherwise drop into the occupied zone. It also runs the fan for many more hours a year. (9.2.4)

9.2.5 The induced-air backdraft damper and the induced-air filter that keep primary air out of the plenum while the fan is off shall be furnished under Air Terminal UnitsAir Terminal UnitsResolves to the current edition.sync/air-terminal-units.

9.3 Series Fan Operation

9.3.1 Requirements in this article apply where a series fan section is furnished at the terminal unit.

9.3.2 The series fan shall run continuously through occupied hours.

9.3.3 The total airflow delivered to the zone shall be held constant as the primary damper modulates.

9.3.4 The series fan operation during unoccupied periods shall be as indicated in the datasheet.

Series Fan Operation During Unoccupied Periodsradio

● Fan cycles on a call for unoccupied heating or cooling

○ Fan runs continuously

○ Fan off until the system returns to occupied operation

NOTE A series fan runs every occupied hour, so its input power is a continuous load rather than an intermittent one, and it appears in the building's cooling load as well as in its electrical load. (9.3.5)

10 Field Verification of Zone Airflow and Sequences

10.1 Pressure-Independence Verification

10.1.1 The extent of pressure-independence verification shall be as indicated in the datasheet.

Extent of Pressure-Independence Verificationradio

○ Not required

○ Required at a representative sample of units of each inlet size

○ Required at a representative sample of units on each supply branch

○ Required at every installed unit

10.1.2 Where verification is required, the airflow delivered at a fixed commanded setpoint shall be measured at the design duct static pressure and again at the lowest duct static pressure the reset algorithm is permitted to command, and both measurements shall fall within the unit's control tolerance.

10.1.3 Verification shall be performed with the ceiling complete, the design filter media installed, and the central system operating under its normal static pressure control.

10.1.4 Where a unit fails verification, the Contractor shall correct the condition and shall bear the cost of retesting that unit.

10.1.5 Where a unit within a sample fails, the sample for the population it represents shall be doubled at the Contractor's expense.

10.2 Zone Minimum Airflow Verification

10.2.1 The testing and balancing agent shall verify the as-left minimum primary airflow at every terminal unit against the zone airflow compliance submittal, in accordance with Testing Adjusting And BalancingTesting, Adjusting, and Balancing for HVACResolves to the current edition.sync/testing-adjusting-and-balancing.

10.2.2 Where the as-left minimum at a unit differs from the submitted value, the testing and balancing agent shall report the difference to the Engineer of Record rather than revising the submitted value.

NOTE The zone minimum is the one setpoint in the installation that carries a code obligation of its own. Once it has been changed to settle a comfort or noise complaint, the ventilation and reheat compliance calculations no longer describe the building, and nothing in the balancing report says so. (10.2.3)

10.3 Sequence and Reset Request Verification

10.3.1 Functional testing of the zone control sequences shall be conducted in accordance with ANSI/ASHRAE 202, and shall exercise occupied, occupied-standby, unoccupied, morning warm-up, and morning cool-down operation at each unit tested.

10.3.2 Testing shall confirm that each reset request the unit is configured to generate is raised at its stated condition, is cleared at its stated condition, and is received at the supervisory controller.

10.3.3 Trend logs covering not less than fourteen consecutive days of occupied operation shall be reviewed for zones held continuously at a damper limit, for reset requests that never clear, and for zones operating in simultaneous heating and cooling.

NOTE A sequence can pass a functional test point by point and still not work in service, because the failures that matter most are visible only over days of normal operation: a zone that never releases its pressure request, a reheat valve that never fully closes, a standby mode that never engages. (10.3.4)

10.3.5 Deficiencies identified in the trend review shall be corrected by the party assigned controller programming responsibility under Air Terminal UnitsAir Terminal UnitsResolves to the current edition.sync/air-terminal-units.