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Fans - Calculate Air and Brake Horsepower

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Air Horse Power - AHP

Assuming 100% efficiency AHP is the power required to move a given air volume against a given pressure. AHP can be expressed as

P AHP = q dp inWG SG / 6356                                 (1)


P AHP =  Air Horse Power (hp)

q = air flow (cfm)

SG = Specific Gravity Air (= 1.0)

dp inWG = total pressure (in. W.G)

Brake Horse Power - BHP

  • Brake horsepower is the actual power delivered to or by a shaft.

The actual power - brake horse power - a fan requires, because no fan is 100% efficient, can be expressed as

P BHP = q dp inWG / μ 6356                                   (2)


P BHP =  Brake Horse Power (hp)

μ = fan efficiency

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