What is the role of an economizer in an AHU and how is it controlled by BAS?

• A. It uses outdoor air to meet cooling loads when suitable, controlled by outdoor-air damper position and economizer logic.
• B. It increases heating using indoor air
• C. It filters outdoor air
• D. It restricts outdoor air to minimize energy

Answer: (B)

The economizer’s job is to use suitable outdoor air to meet part of the cooling load, providing energy savings by free cooling when outdoor conditions are favorable. The building automation system controls this by adjusting the outdoor-air damper and applying economizer logic that compares current outdoor conditions (often temperature or enthalpy) to the indoor cooling needs. If outdoor air is cooler (and appropriate in humidity), the BAS opens the outdoor-air damper to bring in outside air to help meet cooling, reducing coil energy use. If outdoor conditions aren’t favorable, the damper stays closed or partially closed and the AHU relies on return air and mechanical cooling as needed. This control also considers ventilation requirements and safety, ensuring minimum outdoor-air rates are met. The option stating heating with indoor air isn’t the economizer role, and filtration or simply restricting outdoor air aren’t the primary functions of an economizer.