Industrial Fans and
Ventilation Blowers FAQ
Q. What specifications do I need to select industrial fans?
A. In the US, industrial fans are spec’d using air flow in cfm, static pressure in inches
of water gage, altitude and approximate air temperature.
Q. What features allow ventilation blowers to be low-noise?
A. Tri-Mer ventilation blowers with direct-drive coupling motor set-up are an excellent
choice for low-noise ventilation blowers. Tri-Mer ventilation blowers are manufactured
from polypro or PVC, which is quieter, compared to metal. If the blower is large and
pressure is high (10” or above), an attenuator on the ventilation blowers outlet will
help. Also, inlet and outlet ductwork can be designed so that noise is minimized.
Also, if the ventilation blower can be moved away from a corner, or if dampening
blankets can be added to the ventilation blowers housing, those things are helpful, too.
Q. What is the preferred material for industrial blowers in a process plant?
A. Polypropylene is recommended for industrial blowers in corrosive environments.
Polypro industrial blowers are preferable to fiberglass industrial blowers because
they provide greater structural integrity and corrosion resistance, and will never
de-laminate. Where temperatures are above 220°, fiberglass will be necessary.
And when pressure is above 10” w.g., industrial blowers should be metal.
Q. What’s the cost difference between industrial blowers that
are metal vs. polypro?
A. Industrial blowers that are metal cost 10-20% less, depending on capacity.
Q. Are there special considerations for choosing industrial blowers
for high volume flow rate?
A. Choosing industrial blowers is always based on air flow and static pressure.
So even high volume flow rates applications, such as a make-up unit that replaces
air 300 cu. ft. on air requires industrial blowers rated at 250 cfm.
Q. How do I select industrial fans to use less energy?
A. Industrial fans with lower horsepower, or that are backwardly-inclined,
use less energy.
An industrial fans applications with 20,000 cfm at 6” of pressure needs 12 industrial
fans ranging 30 to 60hp. This is achievable with a 24” diameter wheel, or up to a
6’ wheel. The optimum is a 36” wheel, with a 30 hp motor.
Industrial fans are sized based on outlet velocity, and that value should not be
above 3000 ft. per minute The 36” industrial fans are 2611 ft. per minute outlet.
If the customer wants the 6’ diameter wheel, he’ll get 653’ per minute. That’s the
worse choice for most – but not all – industrial fans applications. If the application
is air make-up, for example, slow speeds are appropriate.
Q. Is it useful for industrial fans to have adjustable blade pitch?
A. Adjustable pitch is for inline air foil or inline tube axials;
this doesn’t apply to most industrial fans.
Q. What are the differences between centrifugal fans and axial fans?
A. Centrifugal fans have an impeller with blades set in a spiral. Centrifugal fans
move the air at right angles to the fan intake, centrifugally spinning air toward the
outlet. As the impeller turns, air enters the fan close to the shaft and moves
perpendicularly to the opening in the fan casing. The blades of axial fans force
air to move parallel to the shaft.
Q. How is horsepower calculated for centrifugal industrial fans?
A. Use the air flow and static pressure to determine size, add 10% to brake
horsepower to allow for belt loss, and select the next nominal hp above that.
Q. When do we need shaft seals for industrial blowers?
A. On positive air flow industrial blowers, where the air is ‘pushed,” a shaft seal
is needed. If the industrial blowers are negative air flow design, shaft seals
are not required.
“This information is for general information purposes only.
For specific applications, please consult Tri-Mer.
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