25 October 2004
a. Specify duct gage, reinforcement schedule and hanger design and
spacing, in accordance with SMACNA RIDCS, Round Industrial Duct
Construction Standards for round duct and SMACNA RTIDCS,
Rectangular Duct Construction Standards for rectangular duct.
b. Install clean-out doors in ductwork that conveys particulate material
such as wood dust or blasting grit. Mount clean-out doors on top half of
horizontal runs near elbows, junctions, and vertical runs.
Selection. Except where specified below, fan selection criteria for
replacement air fans and exhaust air fans are identical.
a. Select exhaust system industrial fans that meet design pressure and
volume flow rate requirements and have the AMCA-certified performance
seal. The design pressure requirement must account for any system
effects caused by non-uniform airflow into or out of the fan. See AMCA
201, Fans and Systems for more information on system effects. Specify a
fan class that is appropriate for the design operating point. Do not select
fans with forward curved blades.
b. When selecting fan capacity, consider if the process room pressure
will be positive, negative or neutral with respect to the external areas.
Select a fan that will provide the necessary volumetric flow rate to
maintain the desired process room pressure. Ensure that all sources of
exhaust air are considered when selecting fan capacity. See paragraph 2-
4.5 for more details.
c. Specify fan shafts that have a uniform diameter along the entire
length. Use bearings that are rated with an average life of 200,000 hours.
d. Select only energy efficient motors. Select the motor to handle cold
startup amperage for nonstandard air processes.
e. Specify vibration-isolating couplings at the fan inlet and outlet. Mount
all fans on vibration isolating bases.
f. If the planner's forecasts change in the processes to occur within the
next couple of years, which would require an increase in the amount of
replacement or exhaust air, then consider purchasing a larger capacity fan
and oversized wiring.
to protect fan blades from contaminated air-stream. Provide access for maintenance to
all fans, including ladders and guardrails where necessary. Refer to NFPA 70, National