Which of the following will not change building pressure?

• A. Supply fan speed change
• B. Exhaust fan speed change
• C. Ventilation damper position
• D. Door opening

Answer: (A)

Building pressure comes from the balance of air flows into and out of the space and any leakage paths in the building envelope. When you change exhaust flow or the position of a ventilation damper, you directly alter the net air leaving the space, and the pressure will shift unless the control system compensates. Opening a door provides a large, direct air path to the outdoors, so the pressure moves toward outside very quickly. In a typical pressure-controlled BAS setup, the supply fan speed can vary without changing the measured building pressure because the control loop adjusts other paths (exhaust, dampers, relief) to maintain the setpoint. That’s why changing supply fan speed is the action that will not change building pressure.