Which formula correctly computes breathing zone outdoor airflow Vbz?

• A. Vbz = RpPz + RaAz
• B. Vbz = Rp + Ra + Pz + Az
• C. Vbz = (RpPz) - (RaAz)
• D. Vbz = RpPz / RaAz

Answer: (A)

Breathing-zone outdoor airflow is determined by combining two separate requirements: the amount of outdoor air needed to dilute contaminants generated by people, and the amount needed to address contaminants associated with the space itself. The correct formula expresses this as a sum of two products: Rp times Pz plus Ra times Az.

Rp is the outdoor-air rate per person (how much outdoor air is needed for each occupant), and Pz is the number of people in the zone. Multiplying them gives the total outdoor air required to serve all occupants in that zone.

Ra is the outdoor-air rate per unit area (how much outdoor air is needed per square meter of floor space), and Az is the floor area of the zone. Multiplying them accounts for contaminants tied to the space size.

Adding these two contributions yields Vbz, the total outdoor airflow required into the breathing zone to meet the ventilation criteria. This ensures both occupant-related and area-related sources are adequately diluted.

The other forms are not correct because they mix terms without proper multiplication, or use addition, subtraction, or division in a way that doesn’t reflect the two distinct, additive requirements (per-person and per-area) for outdoor air.