How does a VAV terminal unit typically maintain zone temperature?

How does a VAV terminal unit typically maintain zone temperature?

• A. It always delivers maximum cooling regardless of demand.
• B. The thermostat sets a desired zone temperature; the VAV controller modulates the supply air damper (and sometimes fan speed) to meet demand while maintaining a relatively constant supply air temperature.
• C. It uses a fixed damper position.
• D. It maintains temperature by adjusting room lights.

Answer: (B)

VAV terminals control zone temperature by varying the amount of conditioned air delivered to the space while keeping the supply air temperature relatively constant. The thermostat sets the desired zone temperature, and the VAV controller compares the actual temperature to that setpoint. It then adjusts the damper opening to meet the load: more cooling by opening the damper to deliver more air when the space is warmer than desired, or less cooling by closing it when the space is near the setpoint. In some systems, the fan speed of the air handler can also be modulated to aid delivery and accuracy. This approach is energy-efficient because it tones airflow up or down rather than repeatedly changing the temperature of the supplied air. The other options don’t fit: delivering maximum cooling all the time wastes energy; a fixed damper cannot respond to changing loads; and adjusting room lights has no effect on air temperature.

VAV terminals control zone temperature by varying the amount of conditioned air delivered to the space while keeping the supply air temperature relatively constant. The thermostat sets the desired zone temperature, and the VAV controller compares the actual temperature to that setpoint. It then adjusts the damper opening to meet the load: more cooling by opening the damper to deliver more air when the space is warmer than desired, or less cooling by closing it when the space is near the setpoint. In some systems, the fan speed of the air handler can also be modulated to aid delivery and accuracy. This approach is energy-efficient because it tones airflow up or down rather than repeatedly changing the temperature of the supplied air. The other options don’t fit: delivering maximum cooling all the time wastes energy; a fixed damper cannot respond to changing loads; and adjusting room lights has no effect on air temperature.