UpCodes logo
Jump To Full Code Chapter
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 to 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.
HVAC zones that are expected to experience relatively constant loads typically include electronic equipment rooms and interior zones.
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 recovered energy or site-solar energy.
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.
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.

Related Code Sections

6.5 Heating, Ventilating, and Air Conditioning, Prescriptive Compliance Path
temperature. The controls shall reset the supply air temperature at least 25% of the difference between the design supply air temperature and the design ...
6.5.3.2 Heating, Ventilating, and Air Conditioning, Fan Control
with the following requirements: DX and chilled-water cooling units that control the capacity of the mechanical cooling directly based on space temperature shall ...