ASHRAE-90.1-2022- - Page 096

Extracted Content

6.5.3.4 Parallel-Flow Fan-Powered VAV Air Terminal Control. Parallel-flow fan-powered VAV air terminals shall have automatic controls configured to

a. turn off the terminal fan except when space heating is required or if required for ventilation ; b. turn on the terminal fan as the first stage of heating before the heating coil is activated; and c. during heating for warm-up or setback temperature control, either

1. operate the terminal fan and heating coil without primary air or
2. reverse the terminal damper logic and provide heating from the central air handler through primary air. Informative Note: ASHRAE Guideline 36 includes detailed sequences of control for both constantspeed and variable-speed parallel fan-powered VAV air terminal units.

6.5.3.5 Supply Air Temperature Reset Controls. Multiple zone HVAC systems shall include controls that are capable of and configured to automatically reset the supply air temperature in response to representative building loads or outdoor air temperature. The controls shall reset the supply air temperature at least 25% of the difference between the design supply air temperature and the design room air temperature. Controls that adjust the reset based on zone humidity are allowed in Climate Zones 0B, 1B, 2B, 3B, 3C, and 4 through 8. HVAC zones that are expected to experience relatively constant loads shall have maximum airflow designed to accommodate the fully reset supply air temperature.

Exceptions to 6.5.3.5:

1. Systems in Climate Zones 0A, 1A, and 3A with less than 3000 cfm of design outdoor air .
2. Systems in Climate Zone 2A with less than 10,000 cfm of design outdoor air .
3. Systems in Climate Zones 0A, 1A, 2A, and 3A with at least 80% outdoor air and employing exhaust air energy recovery complying with Section 6.5.6.1.
4. Systems that prevent reheating, recooling, or mixing of heated and cooled supply air.
5. Systems in which at least 75% of the energy for reheating (on an annual basis) is from site recov- ered energy or on-site renewable energy .

Informative Notes:

1. HVAC zones that are expected to experience relatively constant loads typically include electronic equipment rooms and interior zones.
2. ASHRAE Guideline 36 includes detailed sequences of control for resetting supply air temperature set point on multiple zone air handling units based on both zone air terminal unit demand and outdoor air temperature.

6.5.3.5.1 Dehumidification Control Interaction. In Climate Zones 0A, 1A, 2A, and 3A, the system design shall allow supply air temperature reset while dehumidification is provided. When dehumidification control is active, air economizers shall be locked out.

Informative Note: Examples of HVAC systems that can allow supply air temperature reset while dehumidifying include cooling of outdoor air with a separate cooling coil, bypassing return air around the cooling coil, a dedicated outdoor air system, and series energy recovery.

6.5.3.6 Fractional Horsepower Fan Motors. Motors for fans that are 1/12 hp or greater and less than 1 hp shall be electronically commutated motors or shall have a minimum motor efficiency of 70% when rated in accordance with DOE 10 CFR 431. These motors shall also have the means to adjust motor speed for either balancing or remote control. Belt-driven fans may use sheave adjustments for airflow balancing in lieu of a varying motor speed.

Exceptions to 6.5.3.6:

1. Motors in the airstream within fan-coils and terminal units that operate only when providing heating to the space served.
2. Motors installed in space conditioning equipment certified under Section 6.4.1.
3. Motors covered by Table 10.8-3 or 10.8-4.

6.5.3.7 Low Power Fans. Fans that are not covered by Section 6.5.3.6 and having a fan nameplate elec- trical input power of less than 180 W, or having a motor nameplate horsepower less than 1/12 hp, shall meet the fan efficacy requirements of Table 6.5.3.7 at one or more rating points.

Exceptions to 6.5.3.7:

1. Fans in space -conditioning equipment .
2. Intermittently operating dryer exhaust duct power ventilators, domestic range hoods, and domestic range booster fans.
3. Fans in radon mitigation systems .
4. Fans not covered within the scope of the test methods referenced in Table 6.5.3.7.
5. Ceiling fans regulated under 10 CFR 430 Appendix U.

94 ANSI/ASHRAE/IES Standard 90.1-2022 (I-P)