What is the difference between design occupancy and actual occupancy?

• A. Design occupancy is the assumed peak occupancy for calculations; actual occupancy may vary and impact ventilation.
• B. Actual occupancy is the same as design occupancy in all cases.
• C. Design occupancy has no effect on ventilation calculations.
• D. Actual occupancy is only considered for energy usage, not ventilation.

Answer: (A)

Design occupancy is the assumed peak number of people used when calculating required ventilation. It sets the baseline for how much outdoor air the system must provide to keep IAQ at the needed level. Actual occupancy is the real number of people present in the space at a given time, which can vary. Since ventilation needs scale with how many people are present, the design occupancy determines the worst‑case airflow requirement, while actual occupancy can cause the real ventilation demand to be higher or lower than that baseline. If actual occupancy exceeds the design assumption, ventilation may be insufficient for IAQ; if actual occupancy is lower, the system may over‑ventilate, wasting energy. Modern controls may adjust ventilation based on actual occupancy, but the key difference is that the design figure provides the planning basis, and actual occupancy reflects real conditions.