Variable frequency drives

A variable frequency drive (VFD) is a piece of equipment that, when added to an induction motor, lets you adjust motor speeds in step with motor output. As a result, a motor can continue to operate smoothly and efficiently at any speed.

In addition to promoting energy savings, VFDs also:

  • allow for the control of process temperature, pressure and flow without the use of separate controllers
  • help reduce maintenance costs by enabling motors to be run at lower operating speeds
  • eliminate the need for throttle valves, dampers and soft starters
  • eliminate water hammers in liquid systems that require controlled ramp-up speeds
  • protect equipment that cannot tolerate excessive torque.

For a comprehensive guide, download NRCan’s Variable Frequency Drives: Energy Efficiency Reference Guide [PDF - 23.5 MB].

Buying tips

There are several steps to consider before purchasing a VFD.

Study your system.
The equipment you use and how you use it will greatly affect your choice of VFD.

Obtain specifications.
Engineering specifications for each machine can help you understand performance curves. Review specifications for all system components.

Build a profile.
Create a load/time profile for the whole system to identify potential energy savings.

Calculate operating points.
Understand the input power required by each VFD-driven motor.

Do the sums.
To obtain your projected energy savings for each operating point, calculate the difference in power consumed that results from the addition of a VFD and multiply by the number of hours of annual operation.

Hire a pro.
Qualified professionals can help perform these assessments if you need help.