Related Resources: motors

### Fan Laws and Performance Formulae

Fan Laws and Performance Formulae

The following Formulae can be applied to any fan provided the diameter does not change. If the diameter does not change the fans must be geometrically similar. The units of density, fan rotational speed and diameter are not important as long as both are the same.

Fan Volume Flow Equation Fan Pressure Equation Fan Absorbed Power Equation Fan Sound Power Level Equation The following formulae the units shown in the nomenclature must be used to satisfy the formulae.

Density Fan Total Efficiency % Equation Fan Total Pressure Equation Fan Static Pressure Equation Fan Velocity Pressure Equation Where:

qv = volume flow of air, m3/sec
n = rotational speed of fan
d = diameter of fan
p = pressure developed by the fan
ρ = density of air, kg/m3
PR = power absorbed by the fan, kW
B = barometric pressure (millibars)
T = absolute temperature, K (K = °C + 273)
ptF = fan total pressure, Pa
psF = fan static pressure, Pa
pdF = fan dynamic/velocity pressure, Pa
pd = system dynamic/velocity pressure, Pa
V = velocity of air, m/sec
PWL = sound power level  