Ventilation Rate: Method

ASHRAE 62.1 Ventilation Rate Procedure

Standard 62.1 sets the minimum outdoor air a space needs for acceptable indoor air quality as two parts: a people component that dilutes the contaminants occupants produce, R_p per person, and an area component for what the building and its furnishings emit, R_a per unit of floor area. The breathing-zone outdoor airflow is V_bz = R_p P_z + R_a A_z. The rates come from the standard's Table 6-1 by occupancy category; the rows offered here are the common ones, and any category can be entered.

Not all the air delivered to a zone reaches the breathing zone. The zone air-distribution effectiveness E_z of Table 6-2 credits or penalizes the supply arrangement: 1.0 for cool air from the ceiling, 0.8 for warm air from the ceiling that short-circuits to a ceiling return, 1.2 for displacement ventilation from the floor. The zone outdoor airflow the system must deliver is V_oz = V_bz / E_z.

For a single-zone system that is the outdoor-air intake. A multiple-zone recirculating system serves zones with different outdoor-air fractions Z_p = V_oz / V_pz, and the system intake follows from the critical zone by the standard's Appendix A; the tool reports Z_p for the entered supply airflow as the input to that step. Local codes may adopt an earlier edition of the standard or different rates.