VARIABLE FREQUENCY DRIVE EFFICIENCY V010-1

A VFD is often a sensible method to increase the efficiency of your pump – as an example:

Assume a change in production demand results in a pump speed reduction of 10%. The power required by a 100 hp pump is reduced by the cube of the speed, so at 90% the power required is 0.90 cubed, times 100 horse power, or 0.729 times 100, which equals 72.9 hp.

At 90% of full speed, the efficiency of the VFD may be reduced by about 10% of that at full speed and power.

If we assume the full load efficiency of the driver is 92%, then:

Full load electrical power = pump power/ driver

= 100/ 0.92 = 108.7-hp.

At 90% full speed and 90% reduction in efficiency:

Variable speed electrical power = pump power/ VFD efficiency

= 72.9/ (0.92 x 0.90) =88.0 hp.

This results in a almost a 20% reduction in power.