What is the significance of the three ventilation time constants in occupancy design?

• A. They determine the maximum outdoor air rate.
• B. They set the filtration minimum efficiency.
• C. They provide an appropriate averaging time for occupancy to ensure adequate ventilation.
• D. They define ventilation rates for peak occupancy.

Answer: (C)

Ventilation time constants tell you how quickly a space responds to changes in outdoor air and pollutant generation. Using three time constants lets you pick an averaging window that matches how occupants come and go and how long they stay, so the ventilation design reflects typical exposure rather than instantaneous spikes. This ensures the air changes and outdoor air delivery are adequate over the actual occupancy period, keeping pollutant levels within acceptable ranges. The other options aren’t about this time-based averaging: outdoor air rate is set by load and space conditions, filtration efficiency by equipment specs, and peak-occupancy ventilation is addressed separately from the averaging approach.