VFD Pump Savings Calculator

Energy saved by slowing a pump with a VFD instead of throttling, via affinity laws.

Power at full speed (kW)Average required flow (% of full)Running hours/year (h)Tariff (per kWh)

Power at reduced speed (kW)

Annual saving vs throttling

Friction-dominated systems see the full cube-law win; high-static systems (boiler feed) save much less — model your system curve before buying.

Formula

P_vfd = P₁·(Q/Q₁)³/η_vfd; throttled P ≈ P₁·(0.4+0.6·Q/Q₁)

References: US DOE — Adjustable Speed Drive Part-Load Efficiency

Note: Throttled-power approximation is typical for centrifugal pumps near BEP; use the real curve for guarantees.

VFD Pump Savings Calculator is a free vfd savings for pump engineers, plumbers and plant designers — instant, accurate and 100% client-side, with the governing formula and reference shown next to the result so the number can be defended, not just quoted.

About VFD Pump Savings Calculator

Energy saved by slowing a pump with a VFD instead of throttling, via affinity laws. The calculation implements P_vfd = P₁·(Q/Q₁)³/η_vfd; throttled P ≈ P₁·(0.4+0.6·Q/Q₁) (US DOE — Adjustable Speed Drive Part-Load Efficiency). Friction-dominated systems see the full cube-law win; high-static systems (boiler feed) save much less — model your system curve before buying.

How to use VFD Pump Savings Calculator

1Enter Power at full speed in kW.
2Enter Average required flow in % of full.
3Enter Running hours/year in h.
4Enter Tariff in per kWh.
5Read Power at reduced speed, Annual saving vs throttling instantly — no submit button needed.
6Need US units? Flip the SI/Imperial toggle and every field converts.

Why use VFD Pump Savings Calculator?

✓Implements the standard formula — P_vfd = P₁·(Q/Q₁)³/η_vfd; throttled P ≈ P₁·(0.4+0.6·Q/Q₁)
✓Reference cited on-page: US DOE — Adjustable Speed Drive Part-Load Efficiency
✓One-click SI ⇄ Imperial toggle — values convert in place, physics stays in SI
✓Runs entirely in your browser — nothing uploaded, free forever

Frequently asked questions

What formula does the VFD Pump Savings Calculator use?+

It computes P_vfd = P₁·(Q/Q₁)³/η_vfd; throttled P ≈ P₁·(0.4+0.6·Q/Q₁), per US DOE — Adjustable Speed Drive Part-Load Efficiency. The formula is displayed under the result.

What should I keep in mind when using this calculator?+

Friction-dominated systems see the full cube-law win; high-static systems (boiler feed) save much less — model your system curve before buying. Note: Throttled-power approximation is typical for centrifugal pumps near BEP; use the real curve for guarantees.

Can I use this for pump selection?+

Use it to establish the duty (flow, head, NPSH, power) and then pick a pump whose curve passes through that point near best efficiency. The tool gives you the engineering numbers a supplier will ask for.

Is the VFD Pump Savings Calculator free to use?+

Yes — completely free, no sign-up, no limits. It runs client-side in your browser, so inputs stay private and results are instant even on slow connections.

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