Variable frequency drives (VFDs) are versatile, electronic devices used to control motors, fans, and pumps. Variable frequency drives help facilities save energy and control mechanical building systems. They can be used to enhance building automation, and are used frequency for industrial, pumping, irrigation, agricultural, and wastewater applications, amongst others. In the past 10 years, more building designs specify the use of variable frequency drives. Variable frequency drives are affordable and practical, and can be retrofit for use with existing mechanical systems to replace fixed speed and flow-throttling controls.


How do variable frequency drives work?

Variable frequency drives convert AC power that is incoming to DC signals which are then transmitted to a motor at different frequencies and varying voltages. Variable frequency drives are used to operate revolving equipment with speeds between almost 0 revolutions per minute to 150 percent of a motor’s rated speed. To use a variable frequency drive, a Class F insulated high-efficiency motor should also be used, as it will be able to withstand the voltage and current flux variations.

Applications for variable frequency drives

VFDs are ideal for multiple mechanical building system applications, including:

  • Use VFDs to replace outlet dampers and VIVs, variable inlet vanes, in a supply fan system for a variable air volume (VAV) box.
  • Add VFDs along with isolation dampers in buildings with multiple zones, which will work to control air supply across zones with varying occupancy and schedules.
  • Use VFDs to maintain pressure set points when controlling pump speed.

Energy savings from variable frequency drive use

A variable frequency drive saves energy in fan and pump operation. Variable frequency drives reduce the speed of the fan and motor, which improves the performance and efficiency of these components of a mechanical building system. A variable frequency drive provides precise control over equipment speed, optimizing energy use and effectively lowering energy consumption.

Other advantages of using variable frequency drives

Aside from energy savings, variable frequency drives benefit mechanical building systems and reduce costs in other ways. Overall, they reduce wear and tear on HVAC equipment because they reduce torque and speed, they have fewer moving parts, and offer a gentler start due to their gradual acceleration. A variable frequency drive reduces the amount of amps used in starting a motor, which is a significant contributor to energy bills. They are less expensive to maintain than other mechanical control types. Variable frequency drives also reduce the noise of fans and air movement through ducts.