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Image by Leon Contreras

FAN SELCTION

OPERATING POINT

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Before we go into the selection criteria, it is essential to know about the point of operation. The fan ONLY operates at the point of intersection of the fan performance curve and the system curve. Therefore we have to chose a fan whose operating point lies within the recommended region of the fan selection curve.

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FAN SELECTION

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While selecting a fan it is very important to consider the energy consumption. Usually fan manufacturers provide fan curves along with their efficiencies and it is the duty of the engineers to select the fan that reduces usage and serves the purpose in the most efficient manner.

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Fan curves provided by the producers offer engineers to select the operating point over a recommended region on the performance curve. This recommended portion describes the region over which a fan operates with much ease. If we chose the operating point outside the recommended region, the air flow provided by the fan can cause effects that are undesirable as well as dissipate energy.

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The following performance curve shows a recommended region ………

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The DO NOT SELECT PORTION on the curve indicates the stall and/or surge region. If we chose an operating point in this region the fan might STALL (the airflow over the fan blades begins to break away giving rise to a discontinuous, noisy and unsteady flow) or SURGE (fans that are not provided with sufficient inlet pressure cause the air to move in the reverse direction).

It is not recommended to operate a fan above :

  • MAX FLOW or the design flowrate as it might lead to highly objectionable noises.

  • MAX POWER since this may cause the motor to trip or fail

  • MAX STATIC PRESSURE because to much pressure (or -ve pressure downstream) in the duct can lead to increased air leaks and altered quantities of supply air to the zones.

  • MAX FAN SPEED as this may reduce the fan life and increase mechanical wear and tear.

It is also not wise to operate the fan below the MIN POWER because the motor might not provide sufficient torque to spin the blades of the fan.

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