What is the purpose of a demand-controlled ventilation system?

• A. To heat the outside air independent of occupancy.
• B. To treat outdoor air chemically.
• C. To reduce air filtration requirements.
• D. To adjust outside air intake based on occupancy or CO2 levels.

Answer: (D)

Demand-controlled ventilation is about matching outdoor air delivery to actual need by using occupancy or CO₂ levels as the gauge. When more people are in the space, the system increases outside air to meet the required ventilation rate; when fewer people are present, it lowers outside air to save energy while still maintaining adequate air quality. This approach keeps IAQ within the target range without the energy waste of ventilating at a constant, fixed rate. The other options don’t describe adjusting outside air based on how many people are present or how CO₂ indicates occupancy.