Neutrality remake campaign: from-scratch field derivation per authoring cheatsheet; project parameters and derived dispositions
---
title: Variable Air Volume Terminal Units
category: Mechanical / Air Distribution
−toc_depth: 3
description: >
− When to use: zone-level pressure-independent VAV terminal units (VAV boxes) metering primary air from a central variable-air-volume air handler in commercial, institutional, and healthcare HVAC systems — single-duct cooling-only and reheat units, series and parallel fan-powered terminal units, and dual-duct VAV mixing boxes, including casing, modulating damper and actuator, averaging airflow sensor, reheat coil, ECM fan, and integral DDC/BACnet controller. Emphasizes ASHRAE 90.1 reheat and minimum-airflow compliance, static pressure reset participation, ASHRAE Guideline 36 control sequences, and ECM motor requirements.
− Not intended for: room-boundary diffusers, grilles, and slot outlets (see [[sync/hvac-air-distribution-devices]]); central air handling units that generate the primary air (see [[sync/air-handling-units]]); upstream and downstream ductwork and fittings (see [[sync/duct-accessories]]); the broad air-terminal family including constant-volume reheat, induction, and the general construction/QA baseline (see [[sync/air-terminal-units]]); in-line sound attenuators (see [[sync/hvac-sound-attenuators]]); 100%-outdoor-air makeup units (see [[sync/makeup-air-units]]); fan coils and chilled beams; laboratory venturi airflow control valves for critical pressurization; reheat coil hydronic supply and return piping (see [[sync/hydronic-piping]]); fan-powered cooling-coil condensate drainage (see [[sync/condensate-drainage-piping]]); and AHU fan VFDs (see [[sync/hvac-variable-frequency-drives]]).
+ When to use: zone-level pressure-independent variable air volume terminal units metering primary air from a central variable-volume air system, covering single-duct cooling-only and reheat units, parallel and series fan-powered units, and dual-duct variable-volume units. This standard establishes the zone airflow setpoint basis, the ventilation compliance basis, the energy-standard reheat and fan-power limits, the zone operating modes, the system reset requests the unit generates, and the field verification that confirms all of it.
+ Not intended for: the air terminal family baseline of casing, damper, actuator, airflow sensing element, reheat section, fan section, listing, installation, identification, warranty, and spare parts requirements, which is carried by [[sync/air-terminal-units]] and applies to units furnished under this standard; room-boundary diffusers, grilles, registers, and linear slot outlets ([[sync/hvac-air-distribution-devices]]); the central air handling unit and the system-level algorithms resident in it ([[sync/air-handling-units]]); duct and duct accessories upstream or downstream of the unit ([[sync/hvac-ductwork]], [[sync/duct-accessories]]); constant-volume, induction, and bypass terminal units ([[sync/air-terminal-units]]); fan coil units and chilled beams ([[sync/fan-coil-units]], [[sync/chilled-beams]]); makeup air and dedicated outdoor air units ([[sync/makeup-air-units]], [[sync/dedicated-outdoor-air-systems]]); and laboratory venturi airflow control valves for critical space pressurization.
---
# Scope {toc}
−## This standard covers factory-fabricated variable air volume (VAV) terminal units serving as the primary zone-level airflow control device in central VAV air systems.
+## 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. {note}
−### This standard governs single-duct pressure-independent VAV units (cooling-only and with reheat), parallel fan-powered terminal units, series fan-powered terminal units, and dual-duct VAV units. {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. {note}
−### The unit assembly covered here comprises the galvanized-steel casing, the modulating primary-air damper and actuator, the multi-point averaging airflow sensor, the acoustic liner, the hydronic or electric reheat coil, the fan and motor assembly on fan-powered types, the integral or remote DDC controller, and the BACnet network interface. {note}
+## This standard is the variable-volume layer over [[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. {note}
−### This standard is deliberately VAV-specific and complementary to [[sync/air-terminal-units]], which is the broad air-terminal family standard. {note}
+## Terminal units furnished under this standard shall also comply with [[sync/air-terminal-units]].
−### The broad family standard carries the general casing construction, materials, and baseline quality-assurance requirements common to all air terminals; this standard goes deeper on the VAV-specific topics: pressure independence, ASHRAE 90.1 Section 6.5.2 reheat and minimum-airflow compliance, static pressure reset participation, ASHRAE Guideline 36 control sequences, and ECM fan motor requirements. {note}
+## Where a requirement of this standard and a requirement of [[sync/air-terminal-units]] address the same subject, the requirement of this standard shall govern.
−### Where this standard and [[sync/air-terminal-units]] both address a topic, the more stringent or more specific requirement shall govern.
+## Delivery, storage, handling, installation, identification, warranty, and spare parts for units furnished under this standard shall be as required by [[sync/air-terminal-units]].
−### VAV terminal units shall be selected, furnished, and installed in accordance with this standard, the contract drawings, and the equipment schedule.
+## The following are outside the scope of this standard: {note}
−```datasheet
−label: VAV terminal unit type
−type: radio
−options:
− - Single-duct cooling-only (no reheat)
− - Single-duct with hydronic reheat
− - Single-duct with electric reheat
− - Parallel fan-powered (PFPTU)
− - Series fan-powered (SFPTU)
− - Dual-duct VAV (mixing box)
−default: Single-duct with hydronic reheat
−```
+- Room-boundary outlets, being diffusers, grilles, registers, and linear slot outlets, which are covered by [[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 [[sync/air-handling-units]] and [[sync/building-automation-system]]
+- Ductwork upstream of the primary inlet and downstream of the unit outlet, and duct-mounted accessories, which are covered by [[sync/hvac-ductwork]] and [[sync/duct-accessories]]
+- In-line sound attenuators, which are covered by [[sync/hvac-sound-attenuators]]
+- Hydronic supply, return, and balancing piping serving a reheat coil, which is covered by [[sync/hydronic-piping]]
+- Condensate drainage from a fan-powered unit cooling coil, which is covered by [[sync/condensate-drainage-piping]]
+- Variable frequency drives serving the central supply fan, which are covered by [[sync/hvac-variable-frequency-drives]]
+- Constant-volume terminal units, induction units, and bypass terminal units, which are covered by [[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 [[sync/fan-coil-units]] and [[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 [[sync/makeup-air-units]] and [[sync/dedicated-outdoor-air-systems]]
+- Laboratory venturi airflow control valves used for critical space pressurization and fume hood face velocity control
−## Applications
−
−### This standard applies to new construction and replacement-in-kind in office buildings, schools, hospitals, laboratories, and similar occupancies where a central air handler delivers conditioned primary air above 0.5 in. w.g. static pressure to a distributed duct system with individual zone temperature control. {note}
−
−### The energy-code context is ASHRAE 90.1 Section 6 (VAV reheat limits, minimum airflow setpoints, fan power, and static pressure reset) and ASHRAE 62.1 (minimum part-load ventilation by demand-controlled ventilation or fixed minimums). {note}
−
−## Exclusions
−
−### Room-boundary outlets — diffusers, grilles, registers, and linear slot outlets — are excluded and are covered by [[sync/hvac-air-distribution-devices]]. {note}
−
−### The central air handling unit that generates and distributes the primary air stream is excluded and is covered by [[sync/air-handling-units]]. {note}
−
−### Ductwork and fittings upstream of the inlet collar and downstream of the outlet collar are excluded and are covered by [[sync/duct-accessories]] and the broader ductwork standard. {note}
−
−### Constant-volume reheat units, dual-duct mixing boxes in non-VAV service, and induction units are excluded and are covered by [[sync/air-terminal-units]]. {note}
−
−### Fan coil units and chilled beams that recirculate room air rather than meter central primary air are excluded. {note}
−
−### Laboratory venturi-style airflow control valves used for critical pressurization, such as fume hood face-velocity control, are excluded. {note}
−
−### Makeup air units that supply 100% outdoor air without zone-level damper metering are excluded and are covered by [[sync/makeup-air-units]]. {note}
−
−### In-line sound attenuators installed in ductwork upstream of the terminal unit are excluded and are covered by [[sync/hvac-sound-attenuators]]. {note}
−
−### Hydronic piping serving the reheat coil and condensate drainage from fan-powered cooling coils are excluded and are covered by [[sync/hydronic-piping]] and [[sync/condensate-drainage-piping]] respectively. {note}
−
−### Variable frequency drives on the central air-handler fan are excluded and are covered by [[sync/hvac-variable-frequency-drives]]. {note}
−
# Referenced Standards {toc}
…4 unchanged lines
| Standard | Title |
|----------|-------|
−| ANSI/AHRI 880-2017 (R2023) | Performance Rating of Air Terminals |
−| ANSI/AHRI 885-2008 (R2021) | Procedure for Estimating Occupied Space Sound Levels in the Application of Air Terminals and Air Outlets |
−| ANSI/ASHRAE 130-2016 | Methods of Testing Air Terminal Units |
−| ANSI/ASHRAE/IES 90.1-2022 | Energy Standard for Buildings Except Low-Rise Residential Buildings |
−| ANSI/ASHRAE 62.1-2022 | Ventilation and Acceptable Indoor Air Quality |
−| ASHRAE Guideline 36-2021 | High-Performance Sequences of Operation for HVAC Systems |
−| NFPA 90A-2024 | Standard for the Installation of Air-Conditioning and Ventilating Systems |
−| NFPA 70 (NEC) | National Electrical Code (Article 424, Fixed Electric Space-Heating Equipment) |
−| UL 60335-2-40 | Safety — Electrically Operated Heat Pumps, Air-Conditioners, and Dehumidifiers |
−| UL 181-2019 | Factory-Made Air Ducts and Air Connectors |
−| ASTM C1071-16 | Fibrous Glass Duct Lining Insulation (Thermal and Sound Absorbing Material) |
−| ASTM E84-24 | Surface Burning Characteristics of Building Materials |
−| SMACNA HVAC Duct Construction Standards (4th ed., 2021) | HVAC Duct Construction Standards — Metal and Flexible |
−| ANSI/NEMA MG 1-2021 | Motors and Generators |
−| ANSI/ASHRAE/ACCA 180-2012 | Standard Practice for Inspection and Maintenance of Commercial Building HVAC Systems |
+| 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 |
−## ASHRAE Guideline 36 is a consensus best-practice document, not a mandatory code, but it is the preferred basis for VAV terminal unit control sequences under this standard. {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 [[sync/air-terminal-units]], the requirements of this standard describe the same behavior in the terms this standard uses. {note}
# Submittals {toc}
−## Action Submittals
+## Zone Airflow Compliance Submittals {toc}
−### The Contractor shall submit the following action submittals for review before fabrication:
+### 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:
−- Product data for each VAV terminal unit type, including AHRI 880 certified ratings for primary airflow, casing leakage, pressure drop, and sound power
−- Shop drawings showing casing dimensions, inlet and outlet sizes, service clearances, access locations, and mounting details
−- Equipment schedule confirming maximum and minimum primary airflow setpoints, inlet size, inlet velocity, and reheat capacity for each tagged unit
−- Reheat coil performance data: hydronic capacity at scheduled entering water temperature and flow, or electric kW, stages, and sheath material
−- Fan and ECM motor data for fan-powered units, including watts per CFM at design airflow
−- DDC controller data sheets, BACnet protocol and profile, point list, and object mapping
−- Acoustic performance: AHRI 885 occupied-space NC calculation for each representative zone at design conditions
+- 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
```datasheet
−label: Action submittals required
+label: Zone Airflow Compliance Submittals Required
type: checkbox
options:
− - AHRI 880 certified product data
− - Shop drawings with service clearances
− - Airflow setpoint schedule (max/min/velocity)
− - Reheat coil performance data
− - ECM fan/motor watts-per-CFM data
− - DDC controller data and BACnet point list
− - AHRI 885 NC acoustic calculation
+ - 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
default:
− - AHRI 880 certified product data
− - Shop drawings with service clearances
− - Airflow setpoint schedule (max/min/velocity)
− - DDC controller data and BACnet point list
+ - 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
```
−## Informational Submittals
+## Control Sequence and Integration Submittals {toc}
−### The Contractor shall submit the following informational submittals before delivery to the site:
+### The Contractor shall submit the following for the Engineer of Record's review and return before the terminal unit controllers are released for shipment:
−- NRTL listing evidence (UL 60335-2-40) for units containing electric heat, motors, or electronic controls
−- Liner material certification showing ASTM C1071 compliance and ASTM E84 flame-spread/smoke-developed indices
−- Factory flow-calibration certificate for each unit
−- Manufacturer's installation, start-up, and balancing instructions
+- 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
```datasheet
−label: Informational submittals required
+label: Control Sequence and Integration Submittals Required
type: checkbox
options:
− - NRTL listing (UL 60335-2-40)
− - Liner ASTM C1071 / E84 certification
− - Factory flow-calibration certificate
− - Installation and start-up instructions
+ - 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
default:
− - NRTL listing (UL 60335-2-40)
− - Liner ASTM C1071 / E84 certification
− - Factory flow-calibration certificate
+ - 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
```
−## Closeout Submittals
+## Closeout Records of Zone Airflow and Sequences {toc}
−### The Contractor shall submit the following closeout submittals before substantial completion:
+### The Contractor shall submit the following before the date of Substantial Completion:
−- Operation and maintenance manuals covering damper, actuator, reheat coil, fan, and controller service
−- As-built BACnet point list and final control sequence documentation
−- Field commissioning and air-balance reports showing achieved maximum and minimum airflow at each unit
−- Warranty documentation
+- 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
```datasheet
−label: Closeout submittals required
+label: Closeout Records Required
type: checkbox
options:
− - O&M manuals
− - As-built BACnet point list and sequences
− - Commissioning and air-balance reports
− - Warranty documentation
+ - As-left setpoints and calibration constants
+ - Functional test record
+ - Fourteen-day occupied trend logs
+ - Reloadable controller parameter file
default:
− - O&M manuals
− - As-built BACnet point list and sequences
− - Commissioning and air-balance reports
− - Warranty documentation
+ - As-left setpoints and calibration constants
+ - Functional test record
+ - Fourteen-day occupied trend logs
+ - Reloadable controller parameter file
```
−# Quality Assurance {toc}
+# Pressure-Independent Airflow Control {toc}
−## Certification
+## Airflow Control Basis {toc}
−### Every VAV terminal unit furnished under this standard shall be certified to ANSI/AHRI 880 and shall bear the AHRI certification mark.
+### 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.
−### AHRI 880 certified values for primary airflow, casing leakage, pressure drop, and sound power shall be the basis of selection; manufacturer's uncertified ratings shall not be substituted. {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. {note}
−### Sound performance shall be projected to the occupied space using ANSI/AHRI 885 before the unit selection is finalized.
+### 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.
−### Units containing electric heating elements, motors, or electronically controlled components shall be listed and labeled by a Nationally Recognized Testing Laboratory to UL 60335-2-40.
+```datasheet
+label: Primary Airflow Control Tolerance About the Commanded Setpoint
+type: range
+unit: '%'
+min: 2
+max: 20
+setpoints: [2, 3, 5, 10, 15, 20]
+default: 10
+```
−## Manufacturer Qualifications
+### 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 [[sync/air-terminal-units]], which is the error of the reading the control loop drives to. {note}
−### The manufacturer shall have produced AHRI 880 certified VAV terminal units of the specified types for not less than five years.
+### 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.
−### All VAV terminal units on the project shall be the product of a single manufacturer.
+### The manufacturer shall state the settling time and the minimum operating differential pressure for each scheduled unit in the action submittal.
−### Mixing controller makes or models across a single project, without a confirmed BACnet object map for each, drives integration RFIs and programming change orders during controls startup; standardizing on one make avoids this and ensures consistent controller make, BACnet object mapping, and service parts. {note}
+### 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.
−## Source Quality Control
+## Airflow Setpoint Density Correction {toc}
−### Each unit shall be flow-calibrated at the factory across its specified airflow range per ANSI/ASHRAE 130.
+### Primary airflow setpoints and the airflow sensing calibration at each unit shall be corrected for [[parameter: altitude]].
−### Casing leakage shall be verified at the rated close-off pressure as part of the AHRI 880 certification program.
+### 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. {note}
−# Environmental and Service Conditions {toc}
+### The party responsible for applying the density correction shall be as indicated in the datasheet.
−## Operating Conditions
−
−### VAV terminal units shall be suitable for indoor installation in a conditioned ceiling plenum or above an accessible ceiling, not exposed to weather.
−
−### Units shall operate with primary air supplied by the central air handler at static pressure above 0.5 in. w.g. and across the inlet static pressure range scheduled for the project.
−
−### The casing and components shall be rated for continuous operation at the supply-air temperature range delivered by the central system, including morning warm-up.
−
```datasheet
−label: Inlet static pressure operating range
−type: range
−unit: in. w.g.
−min: 0.5
−max: 3.0
−step: 0.1
−```
−
−```datasheet
−label: Damper close-off pressure rating
+label: Responsibility for Airflow Setpoint Density Correction
type: select
−unit: in. w.g.
options:
− - "4"
− - "5"
− - "6"
−default: "4"
+ - 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
```
−## Pressure Independence
+### Where the datasheet does not indicate a responsible party, the controls contractor shall apply the density correction.
−### VAV terminal units shall be pressure-independent, with an integral averaging airflow sensor and DDC controller that maintain the commanded airflow setpoint regardless of variations in inlet static pressure.
+### 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.
−```datasheet
−label: Airflow control mode
−type: radio
−options:
− - Pressure-independent (integral airflow sensor)
− - Pressure-dependent (legacy low-pressure only)
−default: Pressure-independent (integral airflow sensor)
−```
+### The correction applied at each unit shall be recorded in the closeout record.
−### Pressure-dependent units shall not be used in a central VAV system.
+# Zone Ventilation Compliance {toc}
−### A pressure-dependent unit reads damper position rather than airflow, so it delivers an incorrect, drifting flow whenever system static pressure changes — which in a VAV system is continuous; only pressure-independent control holds the ventilation and load setpoints the design relies on. {note}
+## Basis of the Zone Minimum Primary Airflow {toc}
−# Unit Sizing and Airflow {toc}
+### The basis on which the zone minimum primary airflow setpoint is established shall be as indicated in the datasheet.
−## Inlet Sizing
−
−### The unit frame size shall be selected from the maximum primary airflow and inlet velocity, not from the connecting duct size.
−
−### Sizing the inlet to match the duct rather than the airflow oversizes the inlet, which drives the airflow sensor below its accurate range at minimum setpoint and produces poor ventilation control and unstable DDC hunting; size to velocity first. {note}
−
−### The design inlet velocity shall not exceed 1,200 FPM, and shall not exceed 900 FPM for units whose minimum airflow setpoint is 50% or more of maximum, per ASHRAE 90.1.
−
```datasheet
−label: Primary inlet diameter (round)
+label: Basis of the Zone Minimum Primary Airflow Setpoint
type: select
−unit: in.
options:
− - "4"
− - "5"
− - "6"
− - "7"
− - "8"
− - "9"
− - "10"
− - "12"
− - "14"
− - "16"
− - "18"
− - "20"
−default: "8"
+ - 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
+default: Ventilation Rate Procedure of ANSI/ASHRAE 62.1
```
−```datasheet
−label: Maximum primary airflow (design cooling)
−type: range
−unit: CFM
−min: 40
−max: 7000
−step: 10
−```
+### 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.
−```datasheet
−label: Design inlet velocity (maximum)
−type: range
−unit: FPM
−min: 600
−max: 1200
−step: 25
−```
+### 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.
−## Minimum Airflow Setpoint
+### 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. {note}
−### The minimum primary airflow setpoint shall be the greatest of the ASHRAE 62.1 part-load ventilation requirement, the applicable ASHRAE 90.1 Section 6.5.2.1 reheat minimum, and the manufacturer's published low-flow accuracy limit.
+### The zone primary airflow used in the multiple-zone system ventilation efficiency calculation shall be the minimum setpoint actually programmed into the controller.
−### The minimum setpoint shall not be set below approximately 10% to 15% of maximum without verifying the manufacturer's published low-flow accuracy data at that flow; setting a minimum below the sensor's reliable range produces unstable readings and ventilation faults that surface only at commissioning.
+### 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.
−```datasheet
−label: Minimum primary airflow setpoint (% of maximum)
−type: range
−unit: "%"
−min: 10
−max: 50
−step: 5
−```
+### 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. {note}
−```datasheet
−label: AHRI 880 primary airflow accuracy
−type: radio
−options:
− - "±10% of setpoint (standard)"
− - "±5% of setpoint (labs / critical spaces)"
−default: "±10% of setpoint (standard)"
−```
+### The central system outdoor air control and the system ventilation efficiency calculation shall be coordinated with [[sync/air-handling-units]].
−## ASHRAE 90.1 Reheat Compliance
+## Dynamic Ventilation Reset {toc}
−### Where reheat is provided, the minimum primary airflow setpoint at which reheat is permitted shall comply with ASHRAE 90.1-2022 Section 6.5.2.1.
+### The zone dynamic ventilation reset input shall be as indicated in the datasheet.
−### The permitted minimum for reheat shall be the greater of 20% of the design zone supply airflow, 0.4 CFM/ft² of conditioned floor area, or the minimum required by ASHRAE 62.1.
−
−### The design documents shall confirm and record the governing reheat minimum for each zone before the setpoints are programmed.
−
```datasheet
−label: ASHRAE 90.1 reheat minimum basis
−type: radio
+label: Zone Dynamic Ventilation Reset Input
+type: select
+derived: "the demand-control ventilation thresholds of [[parameter: adopted-energy-code]] applied to the zone design occupant density and conditioned floor area"
options:
− - 20% of design zone supply airflow
− - 0.4 CFM/ft² of conditioned floor area
− - ASHRAE 62.1 minimum ventilation
−default: 20% of design zone supply airflow
+ - 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
+default: derived
```
−### Specifying a minimum setpoint lower than ASHRAE 90.1 permits is a code violation that is frequently not caught until commissioning or energy inspection; confirming compliance at design avoids rework. {note}
+### 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.
−# Casing and Acoustic Construction {toc}
+### The reset shall not reduce the zone minimum below the airflow required by the building component of the zone ventilation rate.
−## Casing
+### 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. {note}
−### The casing shall be galvanized steel of not less than 20 gauge for the body and damper, with reinforced corners and a static pressure class consistent with the supply-air pressure class of the system per the SMACNA HVAC Duct Construction Standards.
+### Sensor selection, placement, and calibration for a dynamic reset input shall be as required by [[sync/building-automation-system]].
−### Inlet and outlet collars shall be round or rectangular as scheduled and shall be sized to suit the connecting ductwork.
+# Energy Standard Airflow and Reheat Limits {toc}
−### Casing air leakage at the rated close-off pressure shall not exceed the AHRI 880 leakage class specified below.
+## Deadband and Cooling Minimum Airflow Limit {toc}
−### The casing static pressure class shall be not less than 2 in. w.g.
+### 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 [[parameter: adopted-energy-code]].
```datasheet
−label: Casing gauge (galvanized steel)
−type: radio
+label: Governing Deadband Airflow Limit
+type: select
+derived: "the simultaneous heating and cooling limitation of [[parameter: adopted-energy-code]] evaluated against the zone design peak supply airflow, the zone conditioned floor area, and the zone outdoor airflow requirement"
options:
− - 20 gauge (standard)
− - 22 gauge
−default: 20 gauge (standard)
+ - 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
+default: derived
```
−```datasheet
−label: AHRI 880 casing leakage class
−type: radio
−options:
− - "Class A (≤ 2% of max airflow)"
− - "Class B (≤ 5% of max airflow)"
−default: "Class A (≤ 2% of max airflow)"
−```
+### 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. {note}
−```datasheet
−label: Casing cross-section
−type: radio
−options:
− - Rectangular (standard)
− - Round
− - Low-profile flat-oval (shallow plenum)
−default: Rectangular (standard)
−```
+### 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.
−## Acoustic Liner
+### The governing allowance and the airflow it computes shall be recorded for each unit tag in the zone airflow compliance submittal.
−### The acoustic liner shall be UL 181 listed so that it will not delaminate and enter the airstream, and shall comply with ASTM C1071. {note}
+### Where the parties disagree which allowance governs a zone, the Engineer of Record shall make the initial determination.
−### The liner shall be UL 181 listed and shall comply with ASTM C1071.
+## Heating Airflow Limit {toc}
−### The liner material shall achieve a flame-spread index not greater than 25 and a smoke-developed index not greater than 50 per ASTM E84, as required by NFPA 90A.
+### The primary airflow at the zone heating maximum shall not exceed the percentage of the zone design peak supply airflow indicated in the datasheet.
−### Where the project is a healthcare, cleanroom, or food-service application, the liner shall be a double-wall perforated metal inner liner rather than exposed fibrous glass.
−
−### Healthcare and similar applications shall use a double-wall perforated-metal liner to prevent fiber shedding into the airstream.
−
```datasheet
−label: Acoustic liner construction
−type: radio
−options:
− - 1 in. fibrous glass at 1.5 lb/ft³ (standard)
− - 1.5 in. fibrous glass (higher attenuation)
− - Double-wall perforated steel (healthcare/cleanroom)
−default: 1 in. fibrous glass at 1.5 lb/ft³ (standard)
+label: Zone Heating Maximum Primary Airflow
+type: range
+unit: '%'
+derived: "the direct digital control heating allowance of [[parameter: adopted-energy-code]] applied to the zone design peak supply airflow"
+min: 20
+max: 100
+setpoints: [20, 30, 40, 50, 60, 70, 80, 90, 100]
+default: derived
```
−## Acoustic Performance
+### The first stage of zone heating shall raise the discharge air temperature setpoint while the primary airflow is held at the zone minimum.
−### The occupied-space sound level shall be projected per ANSI/AHRI 885 from the AHRI 880 sound power data at design conditions, accounting for both the radiated and the discharge sound paths.
+### The primary airflow shall be increased toward the heating maximum only after the discharge air temperature setpoint has reached its upper limit.
−### The unit and liner selection shall meet the NC target scheduled for the zone.
+### 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. {note}
−```datasheet
−label: Occupied-space NC target
−type: select
−options:
− - "NC 20-30 (conference rooms)"
− - "NC 25-35 (open office)"
− - "NC 30-40 (corridors)"
−default: "NC 25-35 (open office)"
−```
+### The zone airflow control logic selected under [[sync/air-terminal-units]] shall be consistent with the heating allowance claimed under this article.
−### The controlling sound path — radiated through the casing or discharged through the outlet — shall be identified for each critical zone, and the liner thickness and density selected accordingly.
+### The discharge air temperature sensor and the controller capability that sequence requires shall be furnished under [[sync/air-terminal-units]].
−### Skipping the AHRI 885 calculation and selecting liner by habit is the most common cause of post-occupancy noise complaints; run the calculation per zone before finalizing. {note}
+## Reheat Limitation Exceptions {toc}
−# Reheat Coils {toc}
+### Any exception to the simultaneous heating and cooling limitation claimed for a zone shall be as indicated in the datasheet.
−## Where the zone requires heating, the reheat coil type shall be selected from hydronic or electric based on the availability and cost-effectiveness of hot water distribution at the unit.
−
```datasheet
−label: Reheat coil type
−type: radio
+label: Simultaneous Heating and Cooling Exception Claimed
+type: select
options:
− - None (cooling-only)
− - Hydronic (hot water)
− - Electric (staged or SCR)
−default: Hydronic (hot water)
+ - 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
+default: No exception claimed
```
−## Interior and perimeter zones with hot water available are most economically served by a one- or two-row hydronic coil; small isolated zones without practical hot water distribution are served by staged or SCR electric reheat. {note}
+### The calculation supporting each claimed exception shall be included in the zone airflow compliance submittal.
−## Hydronic Reheat Coils
+### 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. {note}
−### The hydronic reheat coil entering water temperature scheduled for the unit shall match the hot water distribution system design temperature.
+# Zone Operating Modes {toc}
−### A reheat coil selected for an entering water temperature that does not match the building hydronic system delivers inadequate capacity that cannot be corrected without replacing the coil; coordinate the temperature with the hydronic design before selection. {note}
+## Occupied-Standby Operation {toc}
−### The coil shall be selected to deliver the scheduled heating capacity at the scheduled entering water temperature and flow rate.
+### The extent of occupied-standby operation shall be as indicated in the datasheet.
−### Coil tubes and fins shall be copper tubes with aluminum or copper fins, mechanically bonded.
−
−### The coil waterside pressure drop shall not exceed the value scheduled for the unit.
−
−### The reheat control valve shall be selected for the scheduled Cv and shall be rated for close-off against the system pump head.
−
−### Hydronic supply, return, and balancing for the reheat coil are provided under [[sync/hydronic-piping]] and are not part of this standard.
−
```datasheet
−label: Hydronic coil rows
+label: Extent of Occupied-Standby Operation
type: radio
+derived: "the occupied-standby requirements of [[parameter: adopted-energy-code]] for the space types served"
options:
− - 1 row (perimeter heating, typical)
− - 2 rows (higher capacity)
−default: 1 row (perimeter heating, typical)
+ - Provided at every zone served by a terminal unit
+ - Provided at zones furnished with an occupancy sensing input
+ - Not provided
+default: derived
```
−```datasheet
−label: Entering water temperature (EWT)
−type: range
−unit: °F
−min: 120
−max: 180
−step: 5
−```
+### 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.
−```datasheet
−label: Leaving water temperature (LWT)
−type: range
−unit: °F
−min: 100
−max: 130
−step: 5
−```
+### The controller shall return the zone to occupied operation within one minute of receiving an occupancy signal.
−```datasheet
−label: Coil waterside pressure drop (maximum)
−type: range
−unit: ft H₂O
−min: 1
−max: 4
−step: 0.5
−```
+### 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. {note}
−## Electric Reheat Coils
+## Unoccupied-Period Operation {toc}
−### Electric reheat coils shall comply with NFPA 70 (NEC) Article 424 for fixed electric space-heating equipment.
+### The primary damper position during unoccupied periods shall be as indicated in the datasheet.
−### An airflow-proving interlock shall prevent energizing the heating elements until proven airflow is established across the coil, per NEC Article 424.20.
−
−### Omitting the airflow-proving switch is both a code violation under NEC Article 424 and a fire risk, and is frequently missed when the electric heater is furnished as a field accessory. {note}
−
−### The coil shall include integral over-temperature protection with automatic and manual reset thermal cutouts.
−
−### The heating element sheath shall be of the material scheduled for the application.
−
−### Branch-circuit conductors and overcurrent protection shall be sized per NEC Article 424 for the scheduled total kW.
−
```datasheet
−label: Electric reheat total capacity
−type: range
−unit: kW
−min: 0.5
−max: 10
−step: 0.5
−```
−
−```datasheet
−label: Electric reheat control
+label: Unoccupied-Period Primary Damper Position
type: radio
options:
− - 2 stages
− - 3 stages
− - SCR modulating
−default: 2 stages
+ - Closed, until an unoccupied setback call
+ - Held at the zone minimum ventilation setpoint
+ - Held at a reduced setback airflow below the occupied minimum
+default: Closed, until an unoccupied setback call
```
−# Fan-Powered Terminal Units {toc}
+### 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.
−## Fan-Powered Type Selection
+### 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.
−### The fan-powered terminal unit type — series or parallel — shall be selected to match the zone application, not treated as interchangeable.
+### 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. {note}
+## Morning Warm-Up and Cool-Down {toc}
+
+### The zone operation during morning warm-up shall be as indicated in the datasheet.
+
```datasheet
−label: Fan-powered configuration
−type: radio
+label: Zone Operation During Morning Warm-Up
+type: select
options:
− - Series (SFPTU, constant volume to space)
− - Parallel (PFPTU, fan on heating only)
−default: Parallel (PFPTU, fan on heating only)
+ - 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
```
−### A series unit runs its fan continuously and delivers a constant total airflow to the space regardless of primary airflow, which suits high-ceiling, high-air-change, or mixed-occupancy zones; a parallel unit runs its fan only on a call for heat and saves fan energy, which suits standard office perimeter zones. Selecting the wrong type for the application creates comfort complaints. {note}
+### During morning warm-up the zone reheat output shall be disabled while the primary air temperature is above the zone temperature.
−## Fan Motors
+### During morning cool-down the zone shall operate at its cooling maximum primary airflow and the zone reheat output shall be disabled.
−### Fan-powered VAV terminal units shall use electronically commutated motors (ECM); permanent split capacitor (PSC) motors shall not be used.
+### 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.
−### ASHRAE 90.1 mandates ECM motors for fan-powered VAV units; a PSC unit specified in error will fail plan check or commissioning. {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. {note}
−### The fan motor power shall not exceed 0.5 W/CFM at design airflow, per ASHRAE 90.1 Section 6.5.3.1.1.
+# System Reset Participation {toc}
−### The fan and motor shall comply with the applicable provisions of ANSI/NEMA MG 1.
+## Duct Static Pressure Reset Requests {toc}
−### The fan airflow shall be set to deliver the scheduled total airflow and induction ratio for the unit.
+### The means by which the terminal unit signals its need for duct static pressure shall be as indicated in the datasheet.
```datasheet
−label: Fan motor type
−type: radio
+label: Duct Static Pressure Reset Signal from the Zone
+type: select
options:
− - Electronically commutated (ECM) — required by 90.1
−default: Electronically commutated (ECM) — required by 90.1
+ - 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
```
−```datasheet
−label: Fan motor power limit
−type: range
−unit: W/CFM
−min: 0.3
−max: 0.5
−step: 0.05
−```
+### 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.
−### Where a fan-powered unit includes a cooling coil, a condensate drain pan shall be provided; the condensate drain piping is provided under [[sync/condensate-drainage-piping]].
+### 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.
−# Dual-Duct VAV Units {toc}
+### 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. {note}
−## Dual-Duct Mixing
+### The reset algorithm, its trim and respond parameters, and the alarm for a zone that drives the reset continuously shall be provided under [[sync/building-automation-system]].
−### Dual-duct VAV units shall accept independent hot-deck and cold-deck primary air streams and blend them with separate pressure-independent damper control to maintain the zone setpoint.
+### 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.
−### Each deck shall have its own averaging airflow sensor and damper actuator so that each inlet is independently metered and pressure-independent.
+### 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. {note}
−### The minimum setpoint strategy for a dual-duct unit shall account for the simultaneous hot-deck and cold-deck contributions to avoid excess reheat under ASHRAE 90.1. {note}
+## Supply Air Temperature Reset Requests {toc}
−### Applying a single-duct minimum-setpoint strategy to a dual-duct unit understates the combined airflow and produces simultaneous heating and cooling that violates the ASHRAE 90.1 reheat intent; set the deck minimums for the blended condition. {note}
+### The zone's participation in supply air temperature reset shall be as indicated in the datasheet.
−# Controls and BACnet Integration {toc}
+```datasheet
+label: Zone Participation in Supply Air Temperature Reset
+type: radio
+options:
+ - The zone generates cooling supply air temperature reset requests
+ - The zone generates no reset requests
+```
−## DDC Controller
+### 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.
−### Each VAV terminal unit shall be furnished with a DDC controller, either factory-integral or field-mounted as scheduled, capable of standalone occupied and unoccupied scheduling.
+### 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. {note}
−### The controller shall communicate on BACnet, either BACnet MS/TP or BACnet/IP as scheduled for the project network.
+### The reset limits and the outdoor air temperature reset schedule shall be established under [[sync/air-handling-units]].
−### The controller object list shall include, at minimum, analog outputs for damper position, analog inputs for airflow and room temperature, and binary points for occupancy and fan status.
+## Hot Water Temperature Reset Requests {toc}
−### The controller shall expose, at minimum, AO for damper position, AI for measured airflow and room temperature, and BI/BO for occupancy and fan status.
+### Requirements in this article apply where a hydronic reheat coil is furnished at the terminal unit.
−### The BACnet protocol version and device profile shall be confirmed with the BAS integrator before the controllers are ordered.
+### The zone's participation in hot water temperature reset shall be as indicated in the datasheet.
−### Confirming the BACnet profile with the integrator before ordering prevents costly firmware updates or gateway additions when an ATU controller profile does not match the BAS front-end. {note}
−
−### Where a CO2 or occupancy sensor input is scheduled for demand-controlled ventilation, the controller shall accept and act on that input.
−
```datasheet
−label: DDC controller mounting
+label: Zone Participation in Hot Water Temperature Reset
type: radio
options:
− - Factory-integral
− - Field-mounted
−default: Factory-integral
+ - The zone generates hot water temperature reset requests
+ - The zone generates no reset requests
```
−```datasheet
−label: BACnet communication
−type: radio
−options:
− - BACnet MS/TP
− - BACnet/IP
−default: BACnet MS/TP
−```
+### 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.
−```datasheet
−label: BACnet MS/TP baud rate
−type: select
−unit: bps
−options:
− - "9600"
− - "19200"
− - "38400"
− - "76800"
−default: "38400"
−```
+### 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. {note}
−```datasheet
−label: Demand-controlled ventilation input
−type: radio
−options:
− - None
− - CO2 sensor input
− - Occupancy sensor input
−default: None
−```
+### The reset algorithm and the heating plant interface shall be provided under [[sync/building-automation-system]].
−## Control Sequences
+# Fan-Powered Terminal Unit Energy Requirements {toc}
−### The VAV terminal unit control sequence shall be based on ASHRAE Guideline 36-2021 unless the contract documents specify an alternative sequence.
+## Fan Power and Speed Modulation {toc}
−```datasheet
−label: Control sequence basis
−type: radio
−options:
− - ASHRAE Guideline 36-2021 (preferred)
− - Manufacturer-standard sequence
−default: ASHRAE Guideline 36-2021 (preferred)
−```
+### Requirements in this article apply where a parallel or series fan section is furnished at the terminal unit.
−### ASHRAE Guideline 36 is the industry-consensus best-practice sequence for VAV terminal units, covering zone setpoints, morning warm-up, demand-controlled ventilation, static pressure reset, and trim-and-respond logic; it is the preferred basis here even though it is a guideline rather than a mandatory code. {note}
+### Fan-powered terminal units shall be furnished with electronically commutated motors where [[parameter: adopted-energy-code]] requires them for fan-powered terminal units.
−### Each VAV terminal unit shall participate in the system static pressure reset, reporting its damper demand so the central fan static pressure can be trimmed and responded down to the lowest setpoint that satisfies all zones.
+### The fan motor type selected under [[sync/air-terminal-units]] shall be consistent with that requirement.
+### The fan power at the design operating point shall not exceed the value indicated in the datasheet.
+
```datasheet
−label: Static pressure reset participation
−type: radio
−options:
− - Trim-and-respond (damper demand reported)
− - Fixed duct static pressure (legacy)
−default: Trim-and-respond (damper demand reported)
+label: Fan Power at the Design Operating Point
+type: range
+unit: W/cfm
+derived: "the fan power allowance of [[parameter: adopted-energy-code]] for the fan section arrangement furnished"
+min: 0.1
+max: 1
+setpoints: [0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.5, 0.75, 1]
+default: derived
```
−### ASHRAE 90.1-2022 Section 6.5.3.3 requires VAV systems with DDC controls to reset duct static pressure based on zone demand; the terminal unit must contribute its damper demand for that reset to function. {note}
+### 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.
−# Testing {toc}
+### 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. {note}
−## Field Testing and Balancing
+### The controller shall vary the fan speed as a function of the zone heating and cooling load.
−### Each VAV terminal unit shall be field-commissioned and air-balanced by the testing, adjusting, and balancing agency under [[sync/testing-adjusting-and-balancing]].
+### The lowest speed at which the fan is operated shall not exceed the fraction of design fan airflow permitted by [[parameter: adopted-energy-code]].
−### The measured maximum and minimum primary airflow at each unit shall be within ±10% of the scheduled setpoints, or within ±5% for laboratory or critical applications.
+### The as-commissioned fan speed setting for each operating mode shall be recorded in the closeout record.
−### The airflow-proving interlock on electric reheat coils shall be functionally verified before the coil is energized.
+## Parallel Fan Operation {toc}
−### The control sequence and BACnet points shall be verified against the as-built point list during functional testing.
+### Requirements in this article apply where a parallel fan section is furnished at the terminal unit.
+### The condition at which the parallel fan is enabled shall be as indicated in the datasheet.
+
```datasheet
−label: Field airflow commissioning tolerance
−type: radio
+label: Parallel Fan Enable Condition
+type: select
options:
− - "±10% of design setpoint (standard)"
− - "±5% of design setpoint (labs / critical)"
−default: "±10% of design setpoint (standard)"
+ - 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
+default: On a call for zone heating
```
−# Installation {toc}
+### 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.
−## Mounting and Clearance
+### 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. {note}
−### VAV terminal units shall be installed level and supported independently of the connecting ductwork, with hangers sized for the unit operating weight.
+### 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 [[sync/air-terminal-units]].
−### Adequate service clearance shall be provided for access to the damper actuator, reheat coil, controller, and fan, with a ceiling access panel where the unit is above a hard ceiling.
+## Series Fan Operation {toc}
−### Locating a unit in a tight plenum without access creates long-term maintenance problems and warranty claims; clearance and access shall be coordinated before installation.
+### Requirements in this article apply where a series fan section is furnished at the terminal unit.
−### Unit locations shall be coordinated with the ceiling grid, light fixtures, sprinkler heads, and structure before installation.
+### The series fan shall run continuously through occupied hours.
−### Field relocation of units after installation generates coordination RFIs and potential duct rerouting; resolve conflicts during coordination, not in the field. {note}
+### The total airflow delivered to the zone shall be held constant as the primary damper modulates.
−## Connections
+### The series fan operation during unoccupied periods shall be as indicated in the datasheet.
−### The primary inlet shall be connected to the upstream duct with a straight run of the length recommended by the manufacturer to maintain airflow sensor accuracy.
+```datasheet
+label: Series Fan Operation During Unoccupied Periods
+type: radio
+options:
+ - Fan cycles on a call for unoccupied heating or cooling
+ - Fan runs continuously
+ - Fan off until the system returns to occupied operation
+default: Fan cycles on a call for unoccupied heating or cooling
+```
−### Outlet connections shall be made to the discharge collars or plenum as scheduled, single-outlet or multiple-outlet per the unit configuration.
+### 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. {note}
−### Electrical connections to electric reheat coils and fan motors shall be made per NEC and the manufacturer's wiring diagrams.
+# Field Verification of Zone Airflow and Sequences {toc}
−### Control and BACnet network wiring shall be installed under [[sync/building-automation-system]].
+## Pressure-Independence Verification {toc}
+### The extent of pressure-independence verification shall be as indicated in the datasheet.
+
```datasheet
−label: Outlet configuration
+label: Extent of Pressure-Independence Verification
type: radio
options:
− - Single-outlet
− - Multiple-outlet
− - Discharge plenum box
−default: Single-outlet
+ - 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
```
−# Delivery, Storage, and Handling {toc}
+### 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.
−## Protection
+### Verification shall be performed with the ceiling complete, the design filter media installed, and the central system operating under its normal static pressure control.
−### Units shall be delivered in the manufacturer's packaging with inlet and outlet collars capped to keep the interior clean and dry.
+### Where a unit fails verification, the Contractor shall correct the condition and shall bear the cost of retesting that unit.
−### Units shall be stored indoors, protected from weather, dust, and construction debris until installation.
+### Where a unit within a sample fails, the sample for the population it represents shall be doubled at the Contractor's expense.
−### Damaged casings, liners, coils, or controllers shall be repaired or replaced before installation; field-patched liner shall not be accepted.
+## Zone Minimum Airflow Verification {toc}
−# Warranty {toc}
+### 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 [[sync/testing-adjusting-and-balancing]].
−## Warranty Coverage
+### 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.
−### The manufacturer shall warrant each VAV terminal unit against defects in materials and workmanship for not less than the period scheduled below from the date of substantial completion.
+### 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. {note}
−### The warranty shall cover the casing, damper and actuator, airflow sensor, reheat coil, fan and ECM motor, and integral controller.
+## Sequence and Reset Request Verification {toc}
−```datasheet
−label: Warranty period
−type: radio
−options:
− - 1 year
− - 2 years
− - 5 years
−default: 1 year
−```
+### 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.
−# Spare Parts {toc}
+### 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.
−## Recommended Spares
+### 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.
−### The Contractor shall furnish the spare parts scheduled below to support the maintenance intervals of ANSI/ASHRAE/ACCA 180.
+### 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. {note}
−- Spare damper actuator for each unit frame size on the project
−- Spare ECM motor for each fan-powered unit frame size
−- Spare DDC controller of each type furnished
−- Manufacturer's recommended consumables for the first year of operation
−
−```datasheet
−label: Spare parts to be furnished
−type: checkbox
−options:
− - Damper actuator (one per frame size)
− - ECM motor (one per fan-powered frame size)
− - DDC controller (one per type)
− - First-year consumables
−default:
− - Damper actuator (one per frame size)
− - DDC controller (one per type)
−```
+### Deficiencies identified in the trend review shall be corrected by the party assigned controller programming responsibility under [[sync/air-terminal-units]].