Supply Fan Speed Control Optimization Using a Fan Airflow Station

This paper provides an overview of the typical variable speed drive (VSD) control for the supply fan in a variable airflow volume (VAV) system. Two new control methods using the fan airflow station (FAS) are presented in this paper. In the first method, the supply fan speed is controlled to maintain a constant system resistance, which is calculated based on the measured fan head, and airflow, which is calculated by the FAS. 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. The innovative methods can be applied to systems with either direct digial control (DDC) or pneumatic control boxes. The case studies show that the new control method can significantly save supply fan power and increase fan efficiency.