HVAC Economizers (sometimes known as air-side Economizers) are useful for data centers which are located in regions of the world where the outdoor temperature is lower than the desired data center temperature (for at least some of the day or year) and the outdoor humidity is mild. Economizers save energy by cooling buildings with outside air rather than using refrigeration equipment to cool the recirculated air. Economizers can reduce energy use significantly.

An economizer is constructed from electronic controls, actuators, sensors and dampers that together decide how much outside air is to be brought into the building. When the enthalpy of the outside air is less than the enthalpy of the recirculated air, conditioning the outside air is more energy efficient than conditioning recirculated air. When the outside air is sufficiently cool, no additional conditioning of it is needed; this portion of the air-side economizer control scheme is called free cooling.