Estimate the annual energy and dollar savings from adding a variable frequency drive to a centrifugal pump or fan.
On a centrifugal pump or fan, power follows the affinity laws: flow is proportional to speed, but power is proportional to the cube of speed. Slow the motor to 70% with a variable frequency drive and it draws roughly 37% of full power — versus about 88% if you throttle a valve while the motor runs flat out. That gap is the saving.
The cube law only applies to variable-torque loads. Conveyors, mixers, and positive-displacement pumps are constant-torque, so a VFD saves far less energy there (though it still helps with soft starting and process control). For constant-speed motors that only need a gentle start, compare a soft starter instead — see VFD vs soft starter.
Free PLC simulator
Sizing the savings is step one. Learn to program, parameterize, and control a VFD from a PLC, then practice the motor-control logic free in your browser.