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. (1.1.1)

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. (1.1.2)

NOTE This standard is deliberately VAV-specific and complementary to Air Terminal Units, which is the broad air-terminal family standard. (1.1.3)

NOTE 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. (1.1.4)

NOTE 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. (1.2.1)

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). (1.2.2)

NOTE Room-boundary outlets — diffusers, grilles, registers, and linear slot outlets — are excluded and are covered by Hvac Air Distribution Devices. (1.3.1)

NOTE The central air handling unit that generates and distributes the primary air stream is excluded and is covered by Air Handling Units. (1.3.2)

NOTE Ductwork and fittings upstream of the inlet collar and downstream of the outlet collar are excluded and are covered by Duct Accessories and the broader ductwork standard. (1.3.3)

NOTE Constant-volume reheat units, dual-duct mixing boxes in non-VAV service, and induction units are excluded and are covered by Air Terminal Units. (1.3.4)

NOTE Fan coil units and chilled beams that recirculate room air rather than meter central primary air are excluded. (1.3.5)

NOTE Laboratory venturi-style airflow control valves used for critical pressurization, such as fume hood face-velocity control, are excluded. (1.3.6)

NOTE Makeup air units that supply 100% outdoor air without zone-level damper metering are excluded and are covered by Makeup Air Units. (1.3.7)

NOTE In-line sound attenuators installed in ductwork upstream of the terminal unit are excluded and are covered by Hvac Sound Attenuators. (1.3.8)

NOTE Hydronic piping serving the reheat coil and condensate drainage from fan-powered cooling coils are excluded and are covered by Hydronic Piping and Condensate Drainage Piping respectively. (1.3.9)

NOTE Variable frequency drives on the central air-handler fan are excluded and are covered by Hvac Variable Frequency Drives. (1.3.10)

NOTE 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. (2.3)

NOTE 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. (4.1.2)

NOTE 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. (4.2.3)

NOTE VAV terminal units shall be suitable for indoor installation in a conditioned ceiling plenum or above an accessible ceiling, not exposed to weather. (5.1.1)

NOTE 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. (5.1.2)

NOTE 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. (5.2.3)

NOTE The unit frame size shall be selected from the maximum primary airflow and inlet velocity, not from the connecting duct size. (6.1.1)

NOTE 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. (6.1.2)

NOTE 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. (6.2.2)

NOTE The design documents shall confirm and record the governing reheat minimum for each zone before the setpoints are programmed. (6.3.3)

NOTE 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. (6.3.4)

NOTE The acoustic liner shall be UL 181 listed so that it will not delaminate and enter the airstream, and shall comply with ASTM C1071. (7.2.1)

NOTE 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. (7.2.4)

NOTE 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. (7.3.3)

NOTE 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. (7.3.4)

NOTE 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. (8.1.1)

NOTE 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. (8.1.2)

NOTE The hydronic reheat coil entering water temperature scheduled for the unit shall match the hot water distribution system design temperature. (8.2.1)

NOTE 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. (8.2.2)

NOTE 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. (8.3.3)

NOTE The fan-powered terminal unit type — series or parallel — shall be selected to match the zone application, not treated as interchangeable. (9.1.1)

NOTE 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. (9.1.2)

NOTE ASHRAE 90.1 mandates ECM motors for fan-powered VAV units; a PSC unit specified in error will fail plan check or commissioning. (9.2.2)

NOTE Where a fan-powered unit includes a cooling coil, a condensate drain pan shall be provided; the condensate drain piping is provided under Condensate Drainage Piping. (9.2.6)

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. (10.1.3)

NOTE 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. (10.1.4)

NOTE 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. (11.1.3)

NOTE 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. (11.1.6)

NOTE Where a CO2 or occupancy sensor input is scheduled for demand-controlled ventilation, the controller shall accept and act on that input. (11.1.7)

NOTE 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. (11.2.2)

NOTE 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. (11.2.4)

NOTE 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. (13.1.3)

NOTE Unit locations shall be coordinated with the ceiling grid, light fixtures, sprinkler heads, and structure before installation. (13.1.4)

NOTE Field relocation of units after installation generates coordination RFIs and potential duct rerouting; resolve conflicts during coordination, not in the field. (13.1.5)