﻿ Variable Frequency Drives | Sustainability | Facilities Planning and Management | UW-La Crosse

Variable Frequency DrivesVariable Frequency Drives

Variable frequency drives (VFD’s) reduce electrical energy consumption by adjusting a motor’s speed to match the required load.  Many electric motors simply do not need to run at 100-percent capacity all of the time.  VFD’s typically control motors that power fans and pumps used in heating, ventilation, air conditioning and other systems were motor speeds can vary.    Prior to VFD’s motor speed had only two options: on or off. Variable frequency drives allow us to adjust motor speed to save considerable amounts of energy.

The amount of energy saved with VFD’s depends upon the application of the motor.  Consider a 25 horsepower fan motor operating for 23 hours a day.  It’s unlikely the fan needs to run at full capacity for the full 23 hours.  If the unit runs at full capacity for two hours, 75-percent capacity for eight hours, 67 percent for eight hours and 50 percent for five hours, a VFD would reduce energy use by 32 percent.