What is the function of VAV boxes in a variable air volume system?

• A. To filter outdoor air.
• B. To control primary air flow in a Variable Air Volume system.
• C. To measure humidity in the zone.
• D. To heat spaces.

Answer: (B)

VAV boxes regulate how much conditioned air is delivered to each zone. They achieve this by modulating the damper inside the box so the volume of supply air can increase or decrease to meet the zone’s cooling or heating load. The central system may provide a relatively constant or predetermined airflow, but the box adjusts the actual amount reaching the space to maintain the setpoint. Some boxes include a reheat coil to raise air temperature if needed, but the primary function is adjusting airflow, not filtration or sensing humidity. Filtration is typically handled upstream in the air handling unit, and humidity measurements are made by zone sensors rather than the VAV box itself. Heating of the space is accomplished mainly via the reheat coil (if present) or the central system, with the box serving to control airflow rather than act as the heater.