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Motor & VFD Energy Savings

Assess actual motor energy, speed-control relevance, practical savings and investment return without assuming that every motor needs a VFD.

No plant data is prefilled. Results appear only from the project information you enter.

01

Motor and duty

Rated power is mechanical nameplate output; it is never treated as continuous input power.

02

Operating point and VFD opportunity

Affinity-law calculation is available for this variable-torque application.

AUTIXON calculated assessment

Motor energy dashboard

Low benefitLow confidence

Calculated recommendation

Application
Pump
Current control
Throttle valve
Recommendation
Low benefit
Estimated saving
— kWh/year (—%)
Payback
— years

The available duty data does not support a strong VFD energy case. Verify process requirements before investment.

Preliminary VFD class

— kW

Required output-current duty : — A

Screening power classes: 0.75, 1.1, 1.5, 2.2, 3, 4, 5.5, 7.5, 11, 15, 18.5, 22, 30, 37, 45, 55, 75, 90, 110, 132, 160, 200, 250, 315, 400, 500, 630 kW. Final selection must use manufacturer current, overload profile, environment, EMC, harmonics, cable length and application requirements.

Ideal affinity-law reference

100% speed100%
90% speed72.9%
80% speed51.2%
70% speed34.3%
60% speed21.6%

Flow ∝ speed; head/pressure ∝ speed²; ideal shaft power ∝ speed³. Actual savings depend on system curve, static head, efficiency, operating point and drive losses.

Engineering warnings and evidence

WARNINGMotor efficiency is missing; rated-load energy cannot be estimated.
INFOMeasured active power would improve the confidence of this assessment.
Engineering reference

Motor & VFD Energy Savings Calculator

Assess motor input energy, throttled pump or fan control, VFD scenarios, motor efficiency improvement and project payback from explicit operating data.

Calculation method

The tool establishes the current motor duty from electrical or load data, applies the selected pump/fan affinity-law model only where relevant, and compares operating hours, efficiencies and investments across traceable scenarios.

Formulas used

  • Electrical energy = input power × operating hours
  • Ideal variable-torque power ratio = (speed ratio)³
  • Simple payback = investment / annual cost saving

Worked example

For an eligible centrifugal load, reducing speed to 80% gives an ideal affinity-law power ratio of 0.8³ = 51.2%; practical factors and drive losses must then be applied explicitly.

How to interpret the result

A large theoretical affinity-law saving is not proof of a viable retrofit. Verify the system curve, static head, minimum speed, duty profile, harmonics, motor insulation and process constraints.

Common mistakes

  • Applying the cube law to constant-torque loads.
  • Using average flow as a complete load profile.
  • Ignoring drive efficiency, minimum speed and static head.

Scope and limitations

  • The result is a screening study, not a harmonic, thermal, torsional or detailed hydraulic analysis.

Frequently asked questions

When is a VFD most relevant?

Usually when a compatible pump or fan spends significant hours below full demand while flow is throttled or bypassed.

Can the cube law be used for conveyors?

No. Conveyors are generally constant-torque applications and require a different model.

Does a premium-efficiency motor always pay back?

No. Annual hours, load, current efficiency, replacement timing and investment determine the economics.

What data improves the estimate?

Measured kW, speed or flow profile, operating hours by duty point, system curve and quoted installed cost.