What does the relief damper D-1 control?

• A. It controls building temperature setpoint.
• B. It controls building pressure to the allowable maximum during 100% outside air economizer operation.
• C. It controls exhaust air humidity.
• D. It controls the fan speed.

Answer: (B)

The main idea here is how relief dampers manage air balance when the system uses 100% outdoor air. When an economizer brings in all outside air, the space can become over-pressurized if exhaust isn’t enough. The relief damper provides a controlled exhaust path to outdoors, opening as needed to keep the building pressure from rising above the allowable maximum. In other words, it prevents over-pressurization during 100% outdoor-air economizer operation.

This function is not about adjusting temperature setpoints, humidity, or the main fan speed; those controls serve different purposes.