### Fans

Fans are provided in HVAC and Refrigeration systems to distribute conditioned air, to provide ventilation or to exhaust un-wanted air.

Mechanical Horsepower (MHP): Mechanical horsepower is the measure of the power produced by the fan, a function of the air flow rate measured in cubic feet per minute (CFM) and the total static pressure (TSP) measured in “in. wg.”.

MHP=(CFM*TSP[in.wg])/6,356

Brake Horsepower (BHP): Brake horsepower is the measure of the power drawn by the motor to turn the fan, a function of the fan efficiency and the mechanical horsepower.

BHP=MHP*(1/(fan efficiency))

Horsepower (HP): Horsepower is the motor size. It is a function of the BHP and the motor efficiency.

HP=BHP*(1/(motor efficiency))
*upsize HP to nearest motor size

Velocity Pressure (VP): Velocity pressure is defined as the pressure caused solely by moving air.

VP=FPM/4005 [in.wg]

Static Pressure (SP): Static pressure is the pressure caused solely by compression, the outward force on a duct.

Total Pressure (TSP): Total static pressure is the sum of the velocity pressure and the static pressure at any point.