A Variable Frequency Drive (VFD) controls the rotational speed of an electric motor by controlling the frequency of the electrical power supplied to the motor. They are proven to substantially reduce energy use. Non-VFD motor-driven systems are often designed to handle peak loads and the VFD can slow down the motor to better match the part load requirements.
Controlling motors with a variable frequency drive offers energy savings when motor-driven processes and power demand vary over time. Energy savings from variable-frequency drives can be significant, although the amount of energy reduction will vary depending on the motor's operation and energy usage. The base case for this opportunity is a turbine-style pump that is used for irrigation purposes that operates at a fixed speed but has a variation of flow or head requirements. On a turbine pump, even a small reduction in motor speed can reduce a pump's energy use by as much as 30 percent. Payback can range from few months to less than 10 years. Variable frequency drives also allow more control of processes such as water distribution, aeration and chemical feed. The variable frequency lessens mechanical and electrical stress on motors and can reduce maintenance and repair costs as well as extending motor life.