Understand the widely used Variable Air Volume (VAV) Systems

Variable air volume (VAV) is a technique for controlling the capacity of a heating, ventilating, and/or air-conditioning (HVAC) system. The simplest VAV system incorporates one supply duct that, when in cooling mode, distributes approximately 55 degree F supply air. Because the supply air temperature, in this simplest of VAV systems, is constant, the air flow rate must vary to meet the rising and falling heat gains or losses within the thermal zone served. The air flow rate control is provided via two techniques; for single zone systems the blower's flow rate is varied. For a single VAV air handler that serves multiple thermal zones, the flow rate to each zone must be varied as well.