VFD Energy Savings Calculator

Work out vfd energy savings instantly with clear inputs, formula shown and shareable results.

About VFD Energy Savings Calculator

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.

Formula

Affinity law

P2 = P1 x (N2/N1)^3, then divided by drive efficiency

Worked example

With the default values below, VFD Energy Savings Calculator returns Annual saving of $14,784.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Motor rating: 22 kW
Operating speed: 80 %
Operating hours per year: 6,000 h
Electricity tariff: 0.24

Results

Annual saving: $14,784.00
Power at reduced speed: 11.73 kW
Energy saved: 61,600 kWh/year
Power reduction: 46.7% %

Step by step

1Values used
2Affinity law
3Annual saving= 14,784.00
4Power at reduced speed= 11.73 kW
5Energy saved= 61,600 kWh/year
6Power reduction= 46.7 %

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or fees or charges into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Does this apply to all motors?

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.

Why divide by drive efficiency?

The VFD itself consumes 2-4% of throughput power, so the saving is slightly less than the affinity law alone suggests.