VAV System

In Variable Air Volume (VAV) systems, supply of cool air increases as the cooling load increases, and the air supply decreases as the load decreases. VAV systems are the most modern, energy efficient all air systems available for comfort air conditioning. VAV systems require less fan capacity than a comparable constant volume system because with VAV only the required air is used. Control of air flow in a VAV system is accomplished through an electronic device, which regulate the amount of supply air to the space in response to a proportional room/space temperature controller.

Series Fan Powered VAV System

In a series fan-powered variable air volume (VAV) system, each zone is conditioned by a box with a small fan that draws-in plenum return air and mixes it with

supply air from a primary system. The primary system is similar to variable air volume (VAV), with the primary air supplied at a fixed temperature. Series fan-powered systems provide each zone with variable temperature-constant flow supply air.

The fan operates constantly while the space is occupied. As the primary air is reduced to minimum flow, the fan draws in more plenum air, raising the supply air temperature delivered to the zone. If the primary air is at minimum flow and more heat is required, a reheat coil (either electric or hot water) can be used to further raise the supply air temperature. In many cases baseboard perimeter heating is not required, offering capital savings.

As more boxes reduce the primary air, the duct system static pressure increases. The primary supply fan is then modulated to maintain duct static pressure either by discharge dampers (FC fans only), inlet guide vanes, or variable frequency drives (VFDs).