A variable air volume (VAV) box controller is ...

• A. A controller that modulates the damper inside a variable air volume terminal box to maintain a specific building space temperature.
• B. A controller that sets thermostat schedules.
• C. A controller that measures outside air temperature.
• D. A controller that logs energy usage.

Answer: (A)

The main idea is that a VAV box controller regulates space temperature by adjusting the damper inside the terminal box to control how much conditioned air enters the zone. It uses feedback from a room temperature sensor or thermostat and modulates the damper position to reach the desired setpoint. This approach lets the system vary airflow rather than constantly delivering a fixed amount of air, which is efficient for cooling or heating a zone. In some setups, a reheat coil may be used if heating is needed, but the core action remains damper modulation to maintain the room temperature.

Other functions described, like setting thermostat schedules, measuring outside air temperature, or logging energy usage, are handled by separate components of the building automation system or by sensors and meters, not the VAV box controller itself.