Section 6.2.1/Zone Outdoor Air Rate
ASHRAE 62.1 Section 6.2.1 defines the breathing zone outdoor air rate equation with people and area components.
The breathing zone outdoor air rate (Vbz) for each zone is the sum of two components: the people outdoor air rate (Rp times the zone population Pz) plus the area outdoor air rate (Ra times the zone floor area Az). Rp and Ra values are provided in Table 6.2.2.1 for each occupancy category. The zone outdoor air rate (Voz) is then calculated by dividing Vbz by the zone air distribution effectiveness (Ez) from Table 6.2.2.2.
Why this section exists
The two-component ventilation rate procedure accounts for both occupant-generated contaminants (CO2, bioeffluents, addressed by the people rate Rp) and building-generated contaminants (off-gassing from materials, addressed by the area rate Ra). A conference room needs more outdoor air per person than an office because the occupant density is higher. A storage area needs less people-based ventilation but still needs area-based ventilation for building materials off-gassing.
What plan reviewers look for
Plan reviewers check the outdoor air calculation schedule for each zone. They verify that the correct Rp and Ra values from Table 6.2.2.1 are used for each space type, that the zone population matches the architectural occupant load, and that the zone air distribution effectiveness (Ez) is correctly applied (typically 1.0 for ceiling supply, 0.8 for floor supply heating mode).
Common violations
Related ASHRAE 62.1 requirements
Section 6.2.2 covers the zone-level calculations in detail. Section 6.2.4 covers exhaust ventilation. Section 6.3.1 covers the system- level ventilation efficiency calculation for multi-zone systems. The IMC Table 403.3 provides equivalent prescriptive ventilation rates.