Speed under a fan power ceiling calculator

Invert the cubic affinity law for an unchanged friction-dominated system with constant efficiency; substantial static pressure or changing efficiency invalidates the simple estimate.

n_{2} = n_{1} \times \left(\frac{P_{\text{limit}}}{P_{1}}\right)^{1/3}

Calculator

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

Worked example

Given

$n_{1}$ = 1,750 rpm
$P_{\text{limit}}$ = 22 kW
$P_{1}$ = 44 kW

n_{2} = 1750 \times \left(\frac{22}{44}\right)^{1/3} \approx 1{,}389

Symbols and units

Symbol	Meaning	Unit
$n_{2}$	maximum speed for the power limit	rpm
$n_{1}$	initial speed	rpm
$P_{\text{limit}}$	electrical power ceiling	kW
$P_{1}$	initial electrical power	kW

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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.