403.6 Design for Varying Operating 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. The minimum outdoor air intake flow shall be permitted to be less than the design value at part-load conditions. [ASHRAE 62.1:6.2.6.1] 403.6.1 Short-Term Conditions. Where it is known that peak occupancy will be of short duration, or the ventilation will be varied or interrupted for a short period of time, the design shall be permitted to be based on the average conditions over a time period ( T ) determined in accordance with Equation 403.6.1.

T = 3 v/Vbz (Equation 403.6.1)

Where: T = averaging time period, minutes. v = the volume of the ventilation zone for which

averaging is being applied, cubic foot (m ³ ).

v = the volume of the ventilation zone for which

averaging is being applied, cubic foot (m ³ ). Vbz = the breathing zone outdoor airflow determined

in accordance with Equation 403.2.1 and design

Vbz = the breathing zone outdoor airflow determined

in accordance with Equation 403.2.1 and design value of the zone population ( Pz ), cubic foot per minute (cfm) (m ³ /min). Acceptable design adjustments based on this optional provision shall be in accordance with the following: (1) Zones with fluctuating occupancy: The zone popu lation ( Pz ) shall be permitted to be averaged over

[Equation 403.5.3(1)] Vou = D ∑ all zones ( Rp•Pz ) + ∑ all zones ( Ra•Az )

The occupant diversity ratio ( D) shall be determined in accordance with Equation 403.5.3(2) to account for variations in population within the ventilation zones served by the system.

(1) Zones with fluctuating occupancy: The zone popu lation ( Pz ) shall be permitted to be averaged over time ( T ). (2) Zones with intermittent interruption of supply air:

The average outdoor airflow supplied to the breath

(2) 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 403.2.1. (3) Systems with intermittent closure of the outdoor air

intake: The average outdoor air intake over time ( T )

D = Ps/∑ all zones Pz [Equation 403.5.3(2)]

Where the system population ( Ps ) is the total population in the area served by the system. Exception: Alternative methods to account for occupant diversity shall be permitted, provided that the resulting ( Vou ) value is not less than that determined in accordance with Equation 403.5.3(1). [ASHRAE 62.1:6.2.5.3.1]

(3) 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 403.3, Equation 403.4, or Equation 403.5.4. [ASHRAE 62.1:6.2.6.2]