An economizer is not always a single component but rather a control method that relies on several components in a system. Primarily, an economizer is used to reduce energy consumption.
In HVAC Applications
An air-side economizer includes programming the system to bring in more outside air when its temperature is lower than the inside air. The system opens up an outside air damper to bring in more outside air. To balance the airflow volume in the system a return air damper in the return air duct closes by the same amount.
Since the outside air is already chilled, there isn’t a need to push chilled water all the way from a chiller in a central plant to the air handling unit’s chilled water coil to absorb heat from the air to cool it down.
This reduced need for mechanical cooling allows the system to save on that energy consumption.