VAV Air Handlers are ideal for providing zones in a commercial building. Office space typically has several offices and open areas that need to be conditioned for the comfort of the people working in those areas or offices. By installing VAV boxes and zoning the duct work from those VAV boxes these areas and offices can be kept comfortable using a VAV air handler system. Each box can have its own thermostat and that area or office served by that particular VAV box can be maintained and conditioned for the people working in that space. The VAV box will receive its conditioned air from a VAV air handler through a primary duct that feeds air to the VAV box. The VAV box then determines the amount of air to the secondary duct by a damper located in the VAV box. Depending on what the thermostat temperature set point is and the temperature in the space will determine the amount of air flow the space will receive from the VAV box. Additionally, A VAV box with reheat will energize the heat strips or open the actuator for the hot water coil if the set point and room temperatures calls for the reheat to provide heat to the space (If the VAV box is equipped with reheat).
The primary air is typically conditioned at the VAV air handler to provide a constant set point of whatever the engineer determines the set point needs to be maintained at. Control systems with trim and respond capabilities can modulate the primary air set point up and down depending on the demand. If the VAV boxes are all calling for cooling the program responds by lowering the discharge air temperature set point on the VAV air handler to say 50 degrees Fahrenheit. If the VAVs are calling for heat then the control program responds by increasing the discharge air temperature set point to say 65 degrees Fahrenheit. Trim and respond is not an option that comes with all control programs or widely used in HVAC VAV air handler applications however if one was to crunch the numbers one can see where a trim and respond program can save a lot of money by way of energy dollars by automatically changing the discharge air temperature set point on the VAV air handler based on load demand.
The two VAV’s pictured to the left are VAV boxes that will get their primary air from the VAV air handler in the zone which they are installed.
VAV Air Handler and HVAC Zoning