In a system with poor zone air distribution effectiveness, what happens to required outdoor air flow?

• A. It decreases
• B. It remains the same
• C. It becomes zero
• D. It increases

Answer: (D)

Poor zone air distribution effectiveness means only a fraction of the outdoor air actually reaches the breathing zone. To meet the required ventilation in the occupied space, more outdoor air must be supplied overall because the delivered air to the occupants is less efficient. In design terms, the required outdoor air flow is roughly the zone ventilation requirement divided by the zone air distribution effectiveness; if εz is low, the needed outdoor air flow goes up. So, when distribution is poor, outdoor air flow increases. It wouldn’t stay the same or drop to zero, since that would fail to satisfy the ventilation needs for the occupants.