What is the formula for calculating the required outdoor air intake (Vot) in a multiple zone system with 100% outdoor air?

• A. Vot = average of Voz across all zones.
• B. Vot = product of Voz values across all zones.
• C. Vot = Σ Voz for all zones (system with 100% outdoor air).
• D. Vot = maximum Voz among zones.

Answer: (C)

In a 100% outdoor-air multi-zone system, you must provide the outdoor air required by each zone, with no recirculated air to meet that need. Each zone has its own Voz (outdoor air requirement) to maintain air quality and occupant comfort. Because the air going to one zone cannot be reused for another in a 100% outdoor-air setup, the system’s total outdoor-air intake (Vot) must add up all the zones’ Voz values. This additive approach ensures every zone receives its required amount of fresh air.

If you averaged the Voz values, you would under-ventilate zones with higher needs. If you took the maximum, zones with lower requirements would be over-constrained or you’d still fail to meet the needs of other zones. The product has no meaningful interpretation in this context. Therefore, Vot equals the sum of Voz for all zones.