Variable-Frequency Drive Operating Cost Calculator
Estimate the annual electricity use and running cost of a motor operating through a VFD. Enter motor-side power, average loading, VFD efficiency and the actual operating schedule to avoid treating drive losses as zero.
Calculate VFD running cost
VFD operating-cost result
| Component | Power / Energy basis | Annual quantity | Annual cost |
|---|
How VFD operating cost is calculated
The calculator first estimates motor electrical input from mechanical output and motor efficiency. The VFD then increases the required electrical supply by accounting for its conversion losses.
Motor input = Mechanical output ÷ Motor efficiency
VFD supply power = Motor input ÷ VFD efficiency
Only the percentage of annual hours identified as VFD-controlled hours uses this VFD operating model. Optional auxiliary energy can be added separately.
Why VFD efficiency matters
The drive is not lossless. A small percentage of power is lost during conversion. The effect becomes more material for continuously operating equipment, which is why VFD efficiency is kept separate from motor efficiency.
Use measured data where possible
For an operating-cost assessment, measured motor or drive input power can be stronger than a nameplate-based estimate. A real load profile is also preferable when speed and load vary throughout the year.
Limitations
- The model uses one average motor loading value.
- Motor and VFD efficiencies are treated as constant.
- Standby, bypass, control and harmonic behavior are not separately modeled.
- Electricity price is user-entered and may not represent demand charges or time-of-use pricing.
FAQs
Does the calculator estimate VFD savings?
No. It calculates the operating cost of the VFD scenario. Savings require a separate baseline comparison.
Why enter both motor and VFD efficiency?
They describe different conversion stages and should not be combined into one invented efficiency number.
Can VFD-controlled hours be less than total hours?
Yes. This is useful when equipment operates in bypass, standby or another mode for part of the year.
Does this include demand charges?
No. The primary cost is based on energy consumption in kWh.