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 ductwork from those VAV boxes these areas and offices can be kept comfortable using a VAV air handler system. More on how VAV boxes work.
VAV Air Handler | HVAC Zoning
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 an 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 airflow the room will receive from the VAV box. Additionally, A box with reheat will energize the heat strips or open the actuator for the hot water coil if the setpoint and room temperatures call for the reheat to provide heat to the room (If the VAV box is equipped with reheat).
HVAC Zoning - Primary Air
The primary air is typically conditioned at the VAV air handler to provide a constant setpoint 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 setpoint 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 setpoint on the 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 setpoint to say 65 degrees Fahrenheit. Trim and respond is not an option that comes with all control programs or widely used in AHU applications however if one was to crunch the numbers one can see where the trim and respond program can save a lot of money by way of energy dollars by automatically changing the discharge air temperature setpoint 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 in which they are installed. They are in the construction phase being stored in an empty room.
VAV Air Handler and HVAC Zoning