System
Considerations
Air Plenum Design Guidelines
To assure optimum performance and be able to use the system effect coefficients below, the following guidelines should be adhered to in the plenum design:
1.Flexible connections at the inlet are recommended to isolate vibration. The inlet connection can be square (connected to the inlet panel) or round (connected to an optional inlet collar).
2.Plenum walls should be at least
3.Dampers or coils should be at least
4.For fans operating in parallel:
Have one wheel diameter clearance between adjacent fans.
#BDLTUPQDMVUDIFTPSCBDLGMPXDPOUSPMEBNQFST should be used to prevent windmilling of wheels if fans are started or stopped at different times.
Do not select fans near the top of the fan curve to prevent unstable operation.
8IFFMTTIPVMECFTFMFDUFEBTDPOUSBSPUBUJOH $8$$8$8FUD UPJNQSPWFBJSGMPXQBUUFSOT between the fans.
See AMCA Publication 201 for additional information on this subject.
Duct System Effect
Reduction in cataloged air performance due to a plenum around the fan is called a system effect. System effect is a pressure loss, which must be added to the total external static pressure of the duct system in order to make the proper fan selection from catalog data. The pressure loss calculation is based on the velocity of the air in the discharge ductwork. As shown below, it is derived by multiplying the appropriate coefficient by the velocity pressure.
Discharge Configuration Coefficients
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| Unducted | 2.0 | 2.3 |
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| Ducted | 1.8 | |
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| Ducted | 1.1 | 1.4 |
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Effects of Air Density
Ratings in the fan performance tables and curves of this catalog are based on standard air: clean and dry XJUIBEFOTJUZPGMCTGU3 at 70°F at a pressure of
29.92in. of mercury. A change in elevation, temperature or the type of gas handled will affect density. A fan running at a constant speed and installed in a fixed system will experience changes in pressure output and horsepower consumption if the density of the airstream varies. The air volume delivered by the fan will remain constant regardless of air density.
24 in. x 27 in.
(Radial)
24 in. x 27 in.
(Axial)
Example of Performance Correction
Select a fan to meet the following requirements:
7PMVNF | DGN | |
4UBUJD1SFTTVSF | JOXH | |
| Airstream Temperature: | 70°F |
| Installation Elevation: | 13,000 ft. |
Plenum Discharges (ducted): 24 in. x 27 in. Radial 24 in. x 27 in. Axial
1.The selection is at
DPOEJUJPOT UP VTF DBUBMPHFE EBUB 7PMVNF SFNBJOT at 20,000 cfm, since the volume delivered is not affected by air density.
2.An air density correction factor must be applied to the static pressure. For an elevation of 13,000 ft. and a temperature of 70°F, 1.6 is the required correction
GBDUPS 5BCMF" 6TFUIFDPSSFDUJPOGBDUPSUPBEKVTU the static pressure by multiplying the required static pressure by the correction factor.
JOXHY JOXH
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