Variable frequency drives (VFDs, also referred to as variable speed drives) can reduce output by controlling the motor rather than having the motor work at a constant, almost full load and adjusting the system to obtain a desired result. Variable speed drives are especially effective at reducing power and energy consumption to centrifugal equipment such as pumps and fans. This is because a reduction in flow is directly proportional to a reduction in speed, while the reduction in power is proportional to the cube of the change in speed.
For centrifugal loads, small decreases in equipment rotating speed or fluid flow yield significant reductions in energy use. For example, reducing speed (flow) by 20 percent can reduce power requirements by approximately 50 percent. (See Savings Chart, below)