If occupancy Pz increases while zone area Az and per-area flow Ra remain constant, what happens to Vbz?

• A. Decrease
• B. Stay the same
• C. Become negative
• D. Increase

Answer: (D)

In ASHRAE 62.1, the zone outdoor air flow required, Vbz, is made up of two parts: a per-person component and a per-area component. Specifically, Vbz = Rp × Pz + Ra × Az, where Rp is the ventilation rate per person, Pz is the number of occupants, Ra is the ventilation rate per unit area, and Az is the zone area. If the zone area and the per-area flow rate stay the same, the only part that can change when occupancy rises is the Rp × Pz term. Since Pz increases and Rp is constant, Rp × Pz increases, so the total Vbz increases. For example, with Rp = 5 cfm/person and Ra × Az fixed, increasing occupancy from 20 to 25 people raises Vbz by 5 × 5 = 25 cfm.