Fans - Air and Brake Horsepower

AHP - Air Horse Power, and BHP - Brake Horse Power

Air Horse Power - AHP

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

PAHP = q dpinWG SG / 6356     (1)


PAHP =  Air Horse Power (hp)

q = air flow (cfm)

SG = Specific Gravity Air (= 1.0)

dpinWG = total pressure (in. W.G)

Brake Horse Power - BHP

Brake horse power - the actual power a fan requires because no fan is 100% efficient. BHP can be expressed as

PBHP = q dpinWG / μ 6356     (2)


PBHP =  Brake Horse Power (hp)

μ = fan efficiency 

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