Multi-Zone VAV Sequence of Operation
Supply Air Temperature Controls
Cooling/Economizer
During occupied cooling mode of operation, the economizer (if available) and primary cooling are used to control the supply air temperature. The supply air temperature setpoint is user-defined at the unit mounted VAV Setpoint Potentiometer or at the remote panel. If the enthalpy of the outside air is appropriate to use “free cooling”, the economizer will be used first to attempt to satisfy the supply setpoint. On units with economizer, a call for cooling will modulate the fresh air dampers open.
The rate of economizer modulation is based on deviation of the discharge temperature from setpoint, i.e., the further away from setpoint, the faster the fresh air damper will open. Note that the economizer is only allowed to function freely if ambient conditions are below the enthalpy control setting or below the return air enthalpy if unit has comparative enthalpy installed. If outside air is not suitable for “economizing”, the fresh air dampers drive to the minimum open position. A field adjustable
potentiometer on the Economizer Actuator, or a remote potentiometer can provide the input to establish the minimum damper position. At outdoor air conditions above the enthalpy control setting, primary cooling only is used and the fresh air dampers remain at minimum position. If the unit does not include an economizer, primary cooling only is used to satisfy cooling requirements.
WARNING:
Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.