Economizer control

Abstract

The present disclosure provides a method for operating an HVAC system for conditioning air of an inside space. The HVAC system has an economizer configured to control the intake of outside air into an HVAC air stream of the HVAC system. The method includes determining at least two parameters of the air of the inside space, where the at least two parameters are selected from a set of parameters from which an inside air dry bulb temperature, an inside air dew point, an inside air relative humidity, and an inside air enthalpy can be determined, either directly or indirectly. The method also includes determining at least two parameters of the outside air, where the at least two parameters being selected from a set of parameters from which an outside air dry bulb temperature, an outside air dew point, and an outside air enthalpy can be determined, either directly or indirectly. Based on one or more of the inside air dry bulb temperature, the inside air dew point, the inside air relative humidity, and the inside air enthalpy, a determination is made of whether dehumidification of the inside space is needed, and if dehumidification is not needed, the economizer is commanded to increase the intake of outside air into the HVAC air stream if the outside air dry bulb temperature is less than a dry bulb temperature reference, and if the outside air enthalpy is less than an enthalpy reference. If, alternatively, dehumidification is needed, the economizer is commanded to increase the intake of outside air into the HVAC air stream if the outside air enthalpy is less than the enthalpy reference, and if the outside air dew point is less than a dew point reference.