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13
Basics of Fan Selection
Direct Drive Model Number Code
The model number system is designed to completely identify the fan. The correct code letters must be
specified to designate direct drive with exhaust or supply air configuration. The remainder of the model
number is determined by the size and performance selected from pages 15 through 21.
S E 2 - 24 - 6 20 - B 7
Motor HP
4 =
1
⁄4 10 = 1 30 = 3
3 =
1
⁄3 15 = 1
1
⁄2 50 = 5
5 =
1
⁄2 20 = 2 75 = 7
1
⁄2
7 =
3
⁄4
Motor RPM (50Hz)
A = 1750 F = 690
B = 1160 G = 1300
C = 860 J = 1440
D = 1550 L = 1290
E = 1050 P = 1650
Blade Pitch
Sidewall Roof Propeller
S - Fabricated Prop
SC - Cast Prop
(Level 3 only)
E - Exhaust
S - Supply
R - Reversible
Level of
Construction
1, 2, 3
Fan Size
No of Blades
How Accessories Affect Static Pressure
All accessory losses must be accounted for when
calculating a fan’s 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
3
⁄
8
in. wg).
However, in cases where airflow velocities exceed
1500 fpm 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 9 and 10.
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 a 1.0
bhp service factor. The second speed selection is
at 1.2 bhp service factor. Direct drive performance
tables show BHP levels with service factors ranging
up to 1.2 bhp. When a selection at 1.2 bhp service
factor is not desirable for the application, specify
the next higher motor horsepower.
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.
The first consideration in any fan selection is the amount of air to be moved and the resistance to this air
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
movement. With specific performance and application criteria in mind, propeller fan selections typically
require decisions based on the following criteria.
require decisions based on the following criteria.