What is the role of outdoor air (OA) sensors in BAS decisions?

• A. They monitor indoor CO2 only.
• B. They provide ambient conditions for economizer decisions and ventilation calculations.
• C. They control lighting.
• D. They are used for security.

Answer: (B)

Outdoor air sensors provide the ambient conditions the BAS uses to make energy-saving and ventilation decisions. By measuring outside temperature (and often humidity or enthalpy), these sensors feed the economizer logic so the system can decide when it’s advantageous to bring in outdoor air for cooling instead of using mechanical cooling. If outdoor conditions are favorable (cooler and drier than indoors), the economizer can open dampers to introduce more outdoor air and reduce energy use; if conditions are unfavorable, outdoor air is limited to protect comfort and humidity control.

Those same ambient readings are also used to determine how much outdoor air is needed to meet ventilation requirements, ensuring the building receives the required amount of fresh air per codes or design standards. This integration of outdoor conditions into both economizer and ventilation calculations is why this role is best described as providing ambient conditions for economizer decisions and ventilation calculations.

The other options aren’t the primary function: outdoor air sensors don’t monitor indoor CO2 or control lighting, and they aren’t used for security.