ASHRAE+62.1-2022+(1) - Page 026
Extracted Content
Ev = 0.88 × D + 0.22 for D < 0.60 (6-7)
Ev = 0.75 for D 0.60 (6-8)
6.2.4.3.2 Zone Minimum Primary Airflow. For each zone, the minimum primary airflow ( Vpz-min ) shall be determined in accordance with Equation 6-9.
Vpz-min = Voz × 1.5 (6-9)
6.2.4.4 Outdoor Air Intake. The design outdoor air intake flow ( Vot ) shall be determined in accordance with Equation 6-10.
Vot = Vou / Ev (6-10)
6.2.5 Design for Varying Operating Conditions 6.2.5.1 Variable Load Conditions. Ventilation systems shall be designed to be capable of providing not less than the minimum ventilation rates required in the breathing zone where the zones served by the system are occupied, including all full- and part-load conditions.
Informative Note: The minimum outdoor air intake flow may be less than the design value at part-load conditions.
6.2.5.2 Short-Term Conditions. Where it is known that peak occupancy will be of short duration, ventilation will be varied or interrupted for a short period of time, or both, the design shall be permitted to be based on the average conditions over a time period ( T ) determined by Equation 6-11a (I-P) or 6-11b (SI).
T = 3 v / Vbz (6-11a)
T = 50 v / Vbz (6-11b)
where
T = averaging time period, min
v = the volume of the ventilation zone where averaging is being applied, ft [3] (m [3] )
Vbz = the breathing zone outdoor airflow calculated using Equation 6-1 and the design value of the zone population ( Pz ), cfm (L/s)
Acceptable design adjustments based on this optional provision include the following:
a. Zones with fluctuating occupancy: The zone population ( Pz ) shall be permitted to be averaged over time
( T ). b. Zones with intermittent interruption of supply air: The average outdoor airflow supplied to the breathing
zone over time ( T ) shall be not less than the breathing zone outdoor airflow ( Vbz ) calculated using Equation 6-1. c. Systems with intermittent closure of the outdoor air intake: The average outdoor air intake over time ( T )
shall be not less than the minimum outdoor air intake ( Vot ) calculated using Equation 6-3, 6-4, or 6-5 as appropriate.
6.2.6 Dynamic Reset. The system shall be permitted to be designed to reset the outdoor air intake flow ( Vot ), the space or ventilation zone airflow ( Voz ) as operating conditions change, or both.
6.2.6.1 Demand Controlled Ventilation. DCV shall be permitted as an optional means of dynamic reset. Exception to 6.2.6.1: CO2-based DCV shall not be applied in zones with indoor sources of CO2 other
than occupants, or with CO2 removal mechanisms such as gaseous air cleaners.
6.2.6.1.1 For DCV zones in the occupied mode, breathing zone outdoor airflow ( Vbz ) shall be reset in response to current population. Current population estimates used in DCV control calculations shall not result in ventilation rates that are less than those required by the actual population during any one-hour time period.
6.2.6.1.2 For DCV zones in the occupied mode, breathing zone outdoor airflow ( Vbz ) shall be not less than the building component ( Ra × Az ) for the zone.
6.2.6.1.3 Where CO2 sensors are used for DCV, the CO2 sensors shall be certified by the manufacturer to be accurate within ±75 ppm at concentrations of both 600 and 1000 ppm when measured at sea level at 77°F (25°C). Sensors shall be factory calibrated and certified by the manufacturer to require calibration not more frequently than once every five years. Upon detection of sensor failure, the system shall provide a signal that resets the ventilation system to supply the required minimum quantity of outdoor air ( Vbz ) to the breathing zone for the design zone population ( Pz ).
24 ANSI/ASHRAE Standard 62.1-2022