Motor Efficiency Upgrade Payback Calculator
Compare annual energy costs for existing and replacement motors at equal shaft duty and estimate simple payback from net installed cost.
Enter operating assumptions
Efficiency upgrade comparison
About this calculator
Compare annual energy costs for existing and replacement motors at equal shaft duty and estimate simple payback from net installed cost.
Assumes equal shaft duty and constant efficiencies at that duty. It excludes maintenance differences, demand charges, downtime, financing, taxes, and changes to the driven system.
Method and assumptions
For each motor, input power = equal shaft load ÷ that motor’s efficiency. Annual cost uses the same operating schedule and tariff for both. Annual savings = existing annual cost − replacement annual cost; simple payback = net installed cost ÷ annual savings when savings are positive.
Energy cost uses the entered electricity rate and operating schedule. It does not include demand charges, power-factor penalties, taxes, maintenance, or downtime unless the user includes them separately.
FAQs
Should I use nameplate horsepower as the actual shaft load?
Only if the motor is operating at that shaft load. Use a measured or engineering-estimated operating load when available; nameplate horsepower is a rating, not a continuous-load measurement.
Does the efficiency value remain constant at every load?
No. Motor efficiency changes with load and operating conditions. Enter efficiency data that matches the modeled shaft load and use manufacturer or test data where available.
Sources
Use motor manufacturer efficiency data at the evaluated load and the applicable utility tariff or energy invoice rate.