Variable-Frequency Drive Applications in Nonmakeup-Air Exhaust Systems

Abstract

The constant-speed fan wastes fan energy and causes excessive noises in nonmakeup-air exhaust systems, where stack-exit velocity decreases proportionally to the laboratory exhaust airflow. A variable-frequency drive (VFD) can maintain the required static pressure at the fume hoods by modulating the fan speed. The VFD reduces the fan power and eliminates the noise problems. A theoretical study has been conducted to investigate the system performance of the constant fan nonmakeup-air exhaust system, the impacts of the VFD, and the optimal VFD control for multiple-stack systems. The results show that the VFD can potentially reduce annual fan energy of the constant-speed fan nonmakeup-air exhaust systems by as much as 51%.