Which of the following is NOT a recognized control strategy for outside air economizers?

• A. Dry-bulb control
• B. Enthalpy control
• C. Optimized control considering temperature and humidity
• D. Constant humidity control

Answer: (D)

Outside air economizers are designed to reduce cooling energy by using outdoor air when conditions are favorable, and the control methods you’ll see are built around evaluating outdoor air quality and energy impact. Dry-bulb control uses simple outdoor temperature comparisons to decide when to open the economizer damper. Enthalpy control looks at the total heat content of the outdoor air, which includes both temperature and humidity, to determine if bringing in outside air saves energy. Optimized control takes this further with a more advanced algorithm that weighs temperature and humidity together to achieve the best balance between energy savings and indoor conditions.

Constant humidity control, however, isn’t a strategy for deciding when to bring in outdoor air. Maintaining indoor humidity at a fixed level doesn’t evaluate the energy trade-offs of outdoor air use and can lead to unnecessary latent loads or comfort issues, so it isn’t considered a recognized economizer control method.