scope:

Two supply fan speed control methods for a variable airflow volume (VAV) system using the fan airflow station (FAS) are introduced in this paper. In the first method, the supply fan speed is controlled to maintain an optimized system resistance (S), which is calculated based on the measured fan head, and airflow. In the second method, the supply fan speed is controlled to maintain the duct static pressure set point, which is reset based on the airflow ratio measured by the FAS. Both methods can make the terminal box open more compared with the conventional supply fan speed control using a fixed duct static pressure set point. These innovative methods can be applied to systems with either direct digital control (DDC) or pneumatic control terminal boxes. The case studies show that the new control methods can significantly save supply fan power and improve fan efficiency.