ToolnozaENGINEERING TOOL
VFD Energy Savings Calculator
Estimate centrifugal fan or pump electricity savings using speed ratio, drive efficiency, operating hours and tariff.
VFD Energy Savings Calculator
FREE ONLINE TOOLSTEP BY STEP
How to use vfd energy savings calculator
- Check the input units and assumptions.
- Review the result and example.
IN PRACTICE
Example
Pbase = 30 kW; speed = 80%; ηVFD = 96%; 4000 h/year; tariff = 0.15/kWh → Pnew = 16 kW; ΔE = 56000 kWh/year; savings = 8400/year.
GOOD TO KNOW
Does this work for a conveyor?
No. A conveyor often behaves as a constant-torque load and does not follow the cubic fan/pump model used here.
Formula and worked example
r = speed%/100; Pnew = Pbase × r³/(ηVFD/100); ΔE = (Pbase − Pnew) × hours; cost savings = ΔE × tariff.
Pbase = 30 kW; speed = 80%; ηVFD = 96%; 4000 h/year; tariff = 0.15/kWh → Pnew = 16 kW; ΔE = 56000 kWh/year; savings = 8400/year.
How to interpret the result
The result is a modeled comparison, not a guaranteed reduction in electricity bills. Drive losses are included through efficiency; motor and hydraulic efficiency changes are not. At full speed, adding a drive can increase input energy in this model.
For a varying duty profile, calculate each speed band with its own hours and sum savings. Use logged power and flow measurements to validate the estimate; preserve the minimum flow and pressure required by the process.
Frequently asked questions
Does this work for a conveyor?
No. A conveyor often behaves as a constant-torque load and does not follow the cubic fan/pump model used here.
What assumptions limit this calculation?
Planning scenario for variable-torque loads, not conveyors or constant-torque loads. Static head and actual system curves can invalidate cube-law savings. Baseline must represent the comparator at the same service requirement; this does not model throttling automatically.
How to Calculate VFD Energy Savings: Formula & Example