Work out vfd energy savings instantly with clear inputs, formula shown and shareable results.
For centrifugal fans and pumps the affinity laws make power proportional to the cube of speed, so running at 80% speed needs only about 51% of the power. That cubic relationship is why VFD retrofits on throttled fans and pumps pay back so quickly.
Affinity law
P2 = P1 x (N2/N1)^3, then divided by drive efficiency
Only to variable-torque loads: centrifugal fans, pumps and blowers. Conveyors and positive displacement pumps are constant torque, so power falls only linearly with speed.
The VFD itself consumes 2-4% of throughput power, so the saving is slightly less than the affinity law alone suggests.