The Engineering ToolBox Web Google

Fan Affinity Laws

Affinity laws can be used to calculate volume capacity, head or power consumption - when speed or rpm, and wheel diameters are changed

Sponsored Links

The Affinity Laws of centrifugal pumps or fans can be used to express the influence on volume capacity, head (pressure) or power consumption of a pump or fan due to

  1. change in speed of wheel - revolutions per minute (rpm)
  2. geometrically similarity - change in impeller diameter

Note that the affinity laws for pumps are not identical with fans.

Fan Affinity Laws

Volume Capacity

The volume capacity of a centrifugal fan can be expressed like

q1 / q2 = (n1 / n2)(d1 / d2)3         (1)

where

q = volume flow capacity (m3/s, gpm, cfm, ..)

n = wheel velocity - revolution per minute - (rpm)

d = wheel diameter

Head or Pressure

The head or pressure of a centrifugal fan can be expressed like

dp1 / dp2 = (n1 / n2)2 (d1 / d2)2         (2)

where

dp = head or pressure  (m, ft, Pa, psi, ..)

Power

The power consumption of a centrifugal fan can be expressed as

P1 / P2 = (n1 / n2)3 (d1 / d2)5         (3)

where

P = power (W, bhp, ..)

Changing the Wheel Velocity

If the wheel diameter is constant - change in fan wheel velocity can simplify the affinity laws to

Volume Capacity

q1 / q2 = (n1 / n2)         (1a)

Head or Pressure

dp1 / dp2 = (n1 / n2)2          (2a)

Power

P1 / P2 = (n1 / n2)3          (3a)

fan affinity laws velocity diagram

Note! If the speed of a fan is increased with 10%

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

Fan Affinity Laws Calculator - Changing Wheel Velocity

Replace the default values with the actual values. The calculator is generic and can be used with all common units as long as the use is consistent. 

q1 - volume capacity - (m3/s, gpm, cfm, ..)

dp1 - head or pressure (m, ft, Pa, psi, ..)

P1 - power (W, bhp)

n1 - initial wheel velocity (rpm)

n2 - final wheel velocity (rpm)

Changing the Impeller Diameter

If wheel velocity is constant a change in impeller diameter can simplify the affinity laws to

Volume Capacity

q1 / q2 = (d1 / d2)3         (1b)

Head or Pressure

dp1 / dp2 = (d1 / d2)2         (2b)

Power

P1 / P2 = (d1 / d2)5         (3b)

fan affinity laws diameter diagram

Fan Affinity Laws Calculator - Changing Wheel Diameter

Replace the default values with the actual values. The calculator is generic and can be used with all common units as long as the use is consistent. 

q1 - volume capacity - (m3/s, gpm, cfm, ..)

dp1 - head or pressure (m, ft, Pa, psi, ..)

P1 - power (W, bhp)

d1 - initial wheel diameter (m, in, ft  ...)

d2 - final wheel diameter (m, in, ft ..)

Sponsored Links

Related Topics

  • Ventilation Systems for ventilation and air handling - air change rates, ducts and pressure drops, charts and diagrams and more

Related Documents

Sponsored Links



Engineering ToolBox - SketchUp Edition - Online 3D modeling!

Engineering ToolBox - SketchUp Edition - enabled for use with the amazing, fun and free Google SketchUp.


Search the ToolBox

Google
Web The Engineering ToolBox

© The Engineering ToolBox 2005

9 6 19

handheld Engineering ToolBox - optimized for mobile devices! 3D Engineering ToolBox - draw and model technical applications!


.
Resources, Tools and Basic Information  for Engineering and Design of Technical Applications!

Resources, Tools and Basic Information for Engineering and Design of Technical Applications!