MIL-HDBK-1027/1B
(1) Maximum suction pressure of the exhaust fan
at no flow conditions.
(2)
Wind loads.
(3) Live load of 100 kg/sq. m on the top of
horizontal exterior duct and inside horizontal duct areas of
access.
(4) Interior horizontal duct loading of 14 g
dust/(System L/s) equally distributed across the duct system
horizontal surfaces.
(5) High temperature ductwork should be designed
and constructed in accordance with Sheet Metal and Air
Conditioning Contractors' National Association, Inc. (SMACNA),
Industrial Duct Construction Standards and ACGIH, Industrial
Ventilation Guide. Ductwork should be welded. Welding
procedures should be carefully specified and should be either
American Society of Mechanical Engineers (ASME) or American
Welding Society, Inc. (AWS) and should incorporate pure argon
shielding gas. Suitable procedures are described in AWS
B2.1.005, Standard Welding Procedure Specification (WPS) for Gas
Metal Arc Welding of Austenitic Stainless Steel (for austenitic
stainless steel) and AWS B2.1.006, Standard Welding Procedure
Specification (WPS) for Gas Metal Arc Welding of Carbon Steel to
Austenitic Stainless Steel (for carbon steel to stainless
steel), except use pure argon shielding gas. Procedure AWS
B2.1.006 is used for welding the duct to any structural support
member. Use a low carbon and low hydrogen welding rod.
b) Several factors should be considered in the
selection of a fan type. The fan horsepower and energy
consumption should be as low as possible. Motors for exhaust
fans should be sized for the lowest outside ambient temperature.
The fan should be able to ride the fan curve to 50 percent of
its design flow rate without adverse effects.
c) Noise is a consideration. A fan should be chosen
for quiet operation and located in a sufficiently remote area so
as to not interfere with training.
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