The Fan Laws are the basic proportional relationships between fan speed, flow, pressure, and power. They are most useful for determining the impact of extrapolating from a known fan performance to a desired performance.

The most common change made to a fan is that of altering its rotational speed. For a given speed change percentage:

Flow change is directly proportional.

Pressure changes by the square of the proportion.

Power changes by the cube of the proportion.

The Fan Laws are frequently used to estimate air moving device requirements in both of the above situations. Additionally the Fan Laws can be used to calculate the performances of air movers of different sizes and speeds, assuming proportionality regarding linear and angular dimensions, fluid velocities, and internal fluid forces.

Fan_Laws.pdf

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