Fan Affinity Laws

Overview

Engineering reference data for Fan Affinity Laws in miscellaneous.

Key Formulas

Unit Conversion

$y = x \cdot k$

Multiply by conversion factor.

Linear Interpolation

$y = y_1 + \frac{(x - x_1)(y_2 - y_1)}{x_2 - x_1}$

Estimate between two known points.

Percentage

$p = \frac{\text{part}}{\text{whole}} \times 100\%$

Part as fraction of whole.

Variables

Practical Implications

Note: When the speed of a fan is increased by 10%:

• Volume flow increases by 10%
• Head increases by 21%
• Power increases by 33%

If the volume flow capacity of an existing system is increased by 10%, the power supply increases by 33%, and the electrical motor and power supply may need an upgrade.

Equivalent Static Pressure

Equivalent Static Pressure (ESP) is defined as the pressure that would be developed by a fan operating at standard air density instead of the actual air density. It is useful when selecting fans from published data based on standard conditions.

$ESP = dp_{act} \frac{\rho_{std}}{\rho_{act}}$

Where:

• $ESP$ = Equivalent Static Pressure (Pa)
• $dp_{act}$ = actual pressure (Pa)
• $\rho_{std}$ = standard density of air (kg/m³)
• $\rho_{act}$ = actual density of air (kg/m³)

References

• Original Source