Basics Of Fan Selection - Greenheck SE-1 Manual

Selection Basics
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The first consideration in any fan selection is the
amount of air to be moved and the resistance to this air
movement. With specific performance and application
criteria in mind, propeller fan selections typically require
decisions based on the following criteria.
Belt Drive vs. Direct Drive
Belt drive fans offer the ability to adjust fan speed for
system balancing if necessary. They also offer more
flexibility in speeds and motor selections. In a cost
comparison, belt drive fans are typically less costly
than comparable size direct drive fans with low
speed motors.
Direct drive fans are often preferred for jobs where
maintenance access is difficult. Maintenance costs are
generally lower with direct drive fans, since there are no
belts or bearings to replace and no pulleys to adjust.
Larger Fans vs. Smaller Fans
In most applications, several fans may meet the
specified airflow and pressure requirements. Just as
larger fans tend to turn slower and generate less sound,
they also tend to have higher initial costs but lower
operating costs. Smaller fans, with their higher speeds,
have more stable performance curves, lower initial
costs, higher sound levels, and higher
operating costs.
Low Sound vs. High Static Pressure
Fans selected for high static pressures run at higher
speeds and produce higher tip speeds, resulting
in higher sound levels. Conversely, in low pressure
applications, fans generally run at lower speed
producing lower sound levels and are recommended
for sound sensitive applications.
How Accessories Affect Static Pressure
All accessory losses must be accounted for when
calculating static pressure load. In most cases
dampers, guards and weatherhoods actually add
very little to the total system pressure. This means
that propeller fans used in conjunction with common
accessories can typically be specified with low pressure
capabilities below .375 in. wg (93 Pa). However, in
cases where airflow velocities exceed 1,500 ft/min
(7.6 m/s) through the damper or where filters are
used, static pressure loss may be significant. For
more specific information on pressure losses due to
accessories, refer to pages 10 and 11.
Motor Service Factor
Motors for sidewall propeller fans are cooled by the
airstream. With an uninterrupted flow of cooling air,
motors may be operated in their service factor range
(up to 20% above the motor's nameplate horsepower)
without damage due to overheating. Lesser overloads
are recommended for applications using totally
enclosed or explosion resistant motors.
Belt drive performance tables in this catalog
show two speed selections for each propeller
type (L or H) at a given motor hp. The first selection is
at 1.0 service factor. The second speed selection is at
1.2 service factor. Direct drive performance tables show
Bhp levels with service factors ranging up to 1.2. When
a selection at 1.2 service factor is not desirable for the
application, specify the next higher motor horsepower.
Propeller Fan Rotation Guide
Propeller blade should cup and throw the air when
rotating in the correct direction as shown below.
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