Fan performance follow some simple laws. They are as follows:

VOLUME FLOW is proportional to speed. A change in speed of impeller results in a proportional change in air volume.

V2 = V1 x (N2 / N1 )

For example 800m3/hr @ impeller speed 2000 rpm. At 1000 rpm the same fan would produce:

V2 = 800 x (1000/2000) = 400m³/hr.

PRESSURE development varies with change in impeller speed by a factor of the speed change to the power of 2.

p2 = p1 x (N2 / N1 )²

For example if the fan produced 200 Pa at an impeller speed of 1000 rpm. At 2000rpm the same fan would produce:

p2 = 200 x (2000/1000 )² = 800 Pa.

The POWER required to rotate the impeller varies by a factor of the change in speed to the power of 3.

Pl2 = Pl1 x (N2 / N1 )³

For example if the power input to the impeller is 500 watts at 1000 rpm. At 2000rpm the same fan would require:

Pl2 = 500 x (2000/1000 )³ = 4000 watts.