Engineering Tool — Estimate
VFD Energy Savings Calculator
Estimate annual fan or pump energy savings when replacing damper, throttling valve or constant-speed control with variable-speed operation, based on affinity law principles.
Existing annual energy
239,805kWh
Existing annual cost
28,777EUR
VFD annual energy
121,960kWh
Annual energy savings
117,845kWh
Annual cost savings
14,141EUR
Relative savings
49.1%
Input power vs speed
Estimates are based on simplified affinity-law part-load curves with an allowance for drive and motor losses, assuming operation at a single average speed. Actual savings depend on the load profile, static head, system curve and control strategy. Results are indicative and should not replace a detailed system energy analysis.
How the estimate works
Centrifugal fans and pumps follow the affinity laws: flow scales with speed, pressure with the square of speed and shaft power with the cube of speed. Mechanical throttling — dampers on fans, valves on pumps — reduces flow but leaves the motor running near rated speed, so much of the input power is wasted across the throttling element.
The calculator compares a simplified part-load power curve for the existing control method against cube-law variable-speed operation with an allowance for drive and motor losses. It assumes the system operates at a single average speed for all operating hours; real load profiles vary, and systems with significant static head deviate from the ideal cube law.