ToolnozaInputs and measurement basis
Enter measured baseline electrical kW without the new drive, speed reduction percentage, VFD efficiency, annual hours at that reduced speed and electricity tariff. The model assumes the load follows the cube law and unchanged motor efficiency.
Baseline electrical power (kW); Remaining speed (% of baseline); VFD efficiency (%); Annual hours at reduced speed; Electricity price per kWh (your currency).
Formula and calculation
r = speed%/100; Pnew = Pbase × r³/(ηVFD/100); ΔE = (Pbase − Pnew) × hours; cost savings = ΔE × tariff.
Estimate centrifugal fan or pump electricity savings using speed ratio, drive efficiency, operating hours and tariff.
Worked 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.
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.
Assumptions and limits
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.
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.