What is the effect of occupancy duration on required outdoor air flow?

• A. Longer occupancy durations may require higher outdoor air flow to maintain air quality.
• B. Longer occupancy durations reduce outdoor air flow requirements.
• C. Occupancy duration has no effect on outdoor air flow.
• D. Short occupancy duration increases filtration need.

Answer: (A)

As people stay in a space longer, they generate contaminants (CO2, odors, VOCs, moisture) over a longer time, and those contaminants have more opportunity to accumulate. Outdoor air is used to dilute and carry away these contaminants, so extending occupancy duration increases the amount that must be diluted to keep IAQ within acceptable limits. That’s why longer occupancy durations may require higher outdoor air flow to maintain air quality.

The other ideas don’t fit because simply reducing occupancy time doesn’t bring down the need for dilution if people are present; reducing outdoor air is not a goal for maintaining IAQ, and increasing filtration isn’t the primary mechanism addressed by outdoor air requirements.