General motor power savings calculator

Subtract electrical inputs while preserving required mechanical service.

Units

\Delta \mathrm{kW} = 0.746 \times \left(\frac{\mathrm{HP}_{\text{old}} \times \mathrm{LF}_{\text{old}}}{\eta_{\text{old}}} - \frac{\mathrm{HP}_{\text{new}} \times \mathrm{LF}_{\text{new}}}{\eta_{\text{new}}}\right)

Calculator

Enter the values you know and leave one box empty. Calculate finds the empty one, the result or any input.

Worked example

Given

$\mathrm{HP}_{\text{old}}$ = 100 HP
$\mathrm{LF}_{\text{old}}$ = 0.6 —
$\mathrm{HP}_{\text{new}}$ = 75 HP
$\mathrm{LF}_{\text{new}}$ = 0.75 —
$\eta_{\text{old}}$ = 0.88 —
$\eta_{\text{new}}$ = 0.945 —

\Delta \mathrm{kW} = 0.746 \times \left(\frac{100 \times 0.6}{0.88} - \frac{75 \times 0.75}{0.945}\right) \approx 6.459

Symbols and units

Symbol	Meaning	Unit
$\Delta \mathrm{kW}$	electrical input reduction	kW
$\mathrm{HP}_{\text{old}}$	old rated shaft horsepower	HP
$\mathrm{LF}_{\text{old}}$	old load fraction	—
$\mathrm{HP}_{\text{new}}$	new rated shaft horsepower	HP
$\mathrm{LF}_{\text{new}}$	new load fraction	—
$\eta_{\text{old}}$	old efficiency	—
$\eta_{\text{new}}$	new efficiency	—

Symbol	Meaning	Unit
$\Delta \mathrm{kW}$	electrical input reduction	kW
$P_{\text{rated,old}}$	old rated shaft power	kW
$\mathrm{LF}_{\text{old}}$	old load fraction	—
$P_{\text{rated,new}}$	new rated shaft power	kW
$\mathrm{LF}_{\text{new}}$	new load fraction	—
$\eta_{\text{old}}$	old efficiency	—
$\eta_{\text{new}}$	new efficiency	—

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Results are estimates for study and screening. Check the inputs, units and assumptions before you use them for design, billing or contract decisions.