From Cold Air Distribution: System Design Guide

4.4 Fan Heat Gain and Temperature Rise

4.4.1 Fan Heat

Fan heat is a significant cooling load that must be included in the cooling load calculation. Supply fans produce the largest heat gains, but heat from return fans and mixing-box fans must also be considered if these are present in the system.

If the supply fan is downstream of the cooling coil in a draw-through configuration, the fan heat increases the supply air temperature, increasing the supply air volume required to meet a given space load. If the fan is upstream of the coil in a blow-through configuration, the fan heat is absorbed directly by the coil. In either case, the fan heat adds to the cooling coil load.

Fan heat gain can be calculated from the following equations:

If the fan motor is in the airstream.

(4-6)

or

(4-7)

If the fan motor is outside the airstream:

(4-8)

or

(4-9)

where

q fan =

fan heat gain, Btu/h (W)

Q =

fan airflow volume, cfm (L/s)

ptot =

fan total pressure, in. w.g. (Pa)

? fan =

fan efficiency

? mot =

motor and drive efficiency

bhp =

fan brake horsepower (kW)

C 4 =

0.40 Btu min/in. w.g. ft 3 (9.99 10 -4 W s/L Pa)

C 5 =

2,545 Btu/hp h (1 kW/kW)

If the specific horsepower rating for the fan to be used is not known, Equation 4-6 or 4-8 can be used with an estimate of the fan efficiency. Fan...

Copyright American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. 1996 under license agreement with Books24x7

Products & Services
Cooling Towers
Cooling towers are defined as any open water recirculation device that uses fans or natural draft to draw or force air to contact and cool water by evaporation.
Fan Blades and Propellers
Fan blades and propellers are used to convey power from a source (such as a jet engine) for propulsion or the movement of air. Propellers are an array of fan blades that transmit power by converting rotational motion into thrust. They are sometimes referred to as props.
Variable Air Volume (VAV) Units
Variable air volume (VAV) units are manufactured assemblies of air valves and dampers contained in a single enclosure. As HVAC system components, they regulate airflow to a room or zone in response to a thermostat or other signaling device.
Air Handlers
Air handlers are a system-like device used in ventilating systems. They typically consist of a blower, heat exchange medium for heat or air conditioning, and housing.
Ceiling Fans
Ceiling fans are suspended from the ceiling of a room to provide a cooling or de-stratification effect. To circulate the air, they employ hub-mounted, rotating paddles that are made of metal or plastic.

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