Motor Speed Reduction Energy Savings Calculator
Compare energy use before and after a motor speed reduction when a variable-load relationship is appropriate. The power-speed exponent is configurable so the calculation does not assume the same relationship for every application.
Calculate speed-reduction savings
Speed reduction result
Power-speed relationship
The calculator uses a generalized relationship:
Reduced power = Baseline power × (Speed ratio)n
where n is the user-entered power-speed exponent. The model is useful only when the driven equipment follows a suitable variable-load relationship over the speed range being evaluated.
Why the exponent is configurable
Different driven loads behave differently. Treating every motor as though power always falls with the same speed relationship can produce unrealistic savings. Enter an exponent supported by the relevant equipment model or engineering analysis.
Example use
A baseline application consuming 30 kW at full speed with an 80% speed case and an exponent of 3 would be modeled at 15.36 kW before other losses are considered. The calculator then applies the percentage of annual hours during which that lower-speed case actually occurs.
Important limits
- The calculation is not valid simply because a motor is capable of running slower.
- Process requirements must still be met at the reduced speed.
- Drive and motor efficiency changes are not separately modeled.
- A constant baseline power is assumed before the speed relationship is applied.
- Actual measured power is preferable for project-grade analysis.
FAQs
What should the exponent be?
Use the relationship supported by the specific driven equipment. Do not choose a value simply because it produces a larger saving.
Can speed be zero?
The interface allows zero for mathematical scenarios, but a zero-speed point normally represents no motion and may not be a useful operating condition.
Does this include VFD losses?
No. This page isolates the speed-related load model. VFD losses can be included separately in a VFD-specific analysis.
Is the result guaranteed?
No. It is an estimate based on the inputs and assumed power-speed relationship.