Static air horsepower

The effective output of the fan is static air horsepower (SAHP), which is obtained by the following equation ... 

Effects of Variations in Revolutions Per Minute, Volume, Pressure, Horsepower, Efficiency, Etc.— Where a given fan is operating with a given restriction on its inlet or outlet, the volume delivered will vary directly with the revolutions per minute (N), the various pressures as and the air horsepower as iV The mechanical efficiency will remain the same, therefore the brake horsepower will also vary as N. The volume delivered by symmetrical fans will vary as for any given peripheral speed of the wheel and resistance or static pressure. Under these conditions the mechanical efficiency remains constant, since the area of friction surfaces varies directly with the change in volume. The horsepower will therefore vary as It is sometimes erroneously assumed that at very... 

Fan Laws Flow rate, pressure produced, and horsepower vary with fan speed. However, fan speed has a different relationship with each parameter. These relationships are fan laws (refer to Equations (25-10) through (25-12)). Flow rate varies directly with fan speed, whereas total pressure and fan static pressure (ESP) vary with the square of fan speed. Air horsepower (AHP) or brake horsepower (BHP) varies with the cube of fan speed. These relationships make the selection of an efficient system and an economical one a complex process, particularly when the properties of the system vary with time. 

Note that this less dense air requires less horsepower, and also that the fan can produce only 1.66 in. static as compared to 2 in. with standard air. The system resistance must he adjusted to accommodate this lower static pressure otherwise, the fan will follow its characteristic curve hy reducing its flow until it discharges at the static pressure of 1.66 in. 

Axial Flow Propeller fan Tubeaxlal (duct) fan Vane axial fan Moves large quantities of air low static pressure used for relatively clean air and no duct resistance common for general ventilation Fabricated in a round duct used for condensable fumes, pigments and other materials that collect on blades larger diameters at slow speeds are better for abrasives and accumulating material Develops higher pressures than other axial flow fans more economical in horsepower and space... 

At constant cfin, the fan horsepower and static pressure vary directly with the air density. 

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