Beyond occupant comfort, there are three main criteria for properly controlling a variable-airvolume (VAV) system.

The first criterion is ventilation, which is needed to adequately ventilate all spaces of a building at all operating and load conditions. Drivers for this include perceived occupant comfort, indoor air quality as mandated by ASHRAE’s requirements for ventilation air, and potential legal liability.

The second is energy costs. It is necessary to control and operate the system at the lowest cost. Outdoor air that requires conditioning can result in higher energy costs. It is important to bring in and condition only as much air as required. Bringing in more air than required consumes more energy.

The third criterion includes such pragmatic considerations as having the required hardware, software and proper system design to perform as specified. The control system must function consistently over a long time. It also must be usable by the building operating staff.