A packaged rooftop unit’s air-side economizer is a mechanical device intended to reduce energy consumption and perform other functions such as regulating the amount of ventilation airflow being introduced to the building and controlling the building static pressure. Air-side economizers can save energy in buildings by using cool outside air as a means of cooling the indoor space instead of consuming energy by running compressors. When the outside air is sufficiently cool, no additional mechanical air-conditioning is needed. This portion of the air-side economizer control design is frequently called "free cooling." At other times it is possible to conserve energy by using a minimal amount of compressor capacity to further cool the outside air, when it would take a greater amount of compressor capacity to condition the air being re-circulated from the space. This control process is referred to as “Integrated Economizer” operation. When the outside air conditions are not suitable for free cooling or integrated economizer operation, the economizer dampers are positioned to provide only the required amount of ventilation airflow.
The economizer controls must be able to decide when it is appropriate to provide free cooling or integrated economizer operation versus minimum ventilation airflow. This “economizer changeover” control can be based on a number of different inputs: