How much energy can a VFD (Frequency Inverter) save?

Pump/fan power according to the law of affinity with the cube of speed değişir (P ∝ n³). Hız %70’e düşünce güç ≈ 0,70³ = %34’e iner; kısma (vana/damper) yönteminde güç yaklaşık sabit kaldığından aradaki fark tasarruftur. Örneğin 30 kW motorda ≈ 19,7 kW tasarruf mümkündür (üst sınır).

P_VFD ≈ P × (speed ratio)³ · Savings ≈ P − P_VFD
Example calculation: 30 kW motor, hız %70 → VFD gücü ≈ 30×0,70³ ≈ 10,3 kW; kısmaya göre ≈ 19,7 kW tasarruf. 12 sa/gün, 3,5 TL/kWh → ≈ 86.330 kWh, ≈ 302.000 TL/yıl (üst sınır).

VFD (Frequency Inverter) Energy Saving

Calculate the approximate energy savings achievable with velocity control (VFD) in a pump/fan application using the law of affinity.

Power via VFD
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Saving power
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Annual energy savings
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Notes: Law of affinity: pump/fan power varies with the cube of speed (P ∝ n³). When the speed drops to %r, the power becomes P·r³; in the throttling (valve/damper) method, the power remains approximately constant, the difference being a saving. Since static height and system curve are neglected, the result is an upper limit; Actual savings are verified through field measurements.
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How is it calculated?

  1. Enter the engine power (kW).
  2. Enter the average velocity/flow rate (%).
  3. Click Calculate to see daily opening hours and rates.

Frequently Asked Questions

How do VFDs save energy?
Reducing the pump/fan speed according to the load provides significant savings compared to throttling, since, according to the law of affinity, power decreases cubed by speed.
What is the law of affinity?
In centrifugal pumps/fans, flow rate is proportional to speed, pressure is proportional to the square of speed, and power is proportional to the cube of speed.
Are the calculated savings realistic?
This is an upper limit since static height and system curve are neglected; actual savings will be verified by field measurement.

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