Variable-Speed Pumps & Fans, Affinity-Law Screening, Annual kWh Savings, Payback, NPV & ROI

Marine VFD Pump / Fan Energy Savings & ROI Tool

Estimate the energy and commercial value of reducing centrifugal pump or fan speed with a variable frequency drive. The model starts from measured or estimated baseline electrical kW, then applies an entered speed-power relationship and VFD efficiency instead of assuming that every marine auxiliary automatically follows the ideal cube law.

Data type
Currency
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Need multiple pump/fan groups, non-cubic loads, NPV and sensitivity? Click Advanced above.Advanced lets each equipment group use its own measured baseline kW, speed ratio, power-law exponent, operating hours and VFD efficiency. It also checks minimum process speed and separates maintenance economics from energy savings.

Fast VFD Savings Screen

Exactly 10 primary inputs. Simple assumes a variable-torque centrifugal load with power approximately proportional to speed cubed. Baseline electrical power should be measured or realistically estimated at the entered baseline speed.

kW measured/estimated input power per operating unit.
% of rated speed.
% of rated speed.
hours/year per operating unit.
%.
Selected currency per kWh.
Selected currency.
Selected currency/year.

Advanced Financial & Carbon Basis

Selected currency per kWh.
Selected currency.
Selected currency/year.
Selected currency/year, separate from energy savings.
years.
%/year.
%/year.
kg CO₂/kWh avoided electricity.

VFD Equipment Register

Equipment names are excluded from Tool Data. Exponent 3 is the ideal variable-torque affinity-law screen for applicable centrifugal loads. Use a lower exponent only when engineering data, measurements or a system model supports it.

Equipment groupTypeQtyBaseline input kW / unitBaseline speed %VFD speed %Power exponentAnnual hoursVFD efficiency %Minimum process speed %

VFD Retrofit Readiness

Energy / investment screen only: this tool does not prove that a pump or fan can safely operate at the proposed speed. It does not calculate a pump system curve, fan curve, NPSH margin, minimum cooling flow, motor thermal derating, bearing currents, harmonics, EMC, torsional behavior, generator interaction or class acceptance. For systems with substantial static head or fixed-pressure requirements, ideal cube-law savings can materially overstate real savings.
Engineering context: U.S. Department of Energy guidance describes centrifugal pumps and fans as typical variable-torque loads and notes that affinity laws can be used where applicable, with power varying approximately with the cube of speed for systems dominated by friction rather than static lift or fixed pressure. DOE also cautions that not every pump/fan application follows ideal affinity-law behavior. DNV identifies VFDs for large marine pumps, fans and motors as an energy-efficiency measure, including sea-water cooling and ballast-pump applications. U.S. DOE Motor-Driven Systems Guidebook · DOE Variable Speed Pumping Guide · DNV Marine Energy-Efficiency Example
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