As for a variable air volume (VAV) system, the supply fan speed typically modulate to maintain a duct static pressure setpoint. Traditionally, this setpoint is a constant based on system characteristics at design condition and the pressure sensor location. The static pressure is the summation of the duct pressure loss downstream of the sensor and box inlet static pressure. Under partial load conditions, the pressure loss in the duct is much less than the design value due to reduced airflow. Thus, the static pressure set point can be reset lower. This can reduce fan power, avoid noise at terminal box dampers and prevent box damper malfunction due to excessive pressure. This paper develops theoretical models to demonstrate the impacts of static pressure reset on air leakage, fan power and thermal energy for both pressure independent and pressure dependent terminal boxes.

Units: Dual