MEP Engineering · Engineering Glossary
Variable Air Volume (VAV) is an HVAC distribution system where a central air handling unit supplies conditioned air at a constant temperature, and VAV terminal units at each zone vary the volume of airflow to match the zone's heating or cooling load. VAV systems are common in medium and large commercial office buildings.
Each VAV box contains a motorized damper and a controller that modulates airflow between a minimum (required for ventilation) and a maximum (design cooling or heating capacity) based on a room thermostat signal. Reheat VAV boxes add a small heating coil — usually hot water or electric — to warm the supply air when cooling loads are low. VAV systems are more energy-efficient than constant-volume systems because the supply fan can reduce speed when zone loads decrease. The engineer must design the central AHU, the duct distribution network, and size each VAV box for the zone load and minimum outdoor air requirements per ASHRAE 62.1.
Apex Grid Engineering maintains this glossary as a resource for architects, contractors, developers, and property owners who encounter unfamiliar engineering terminology on their projects.
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