Specifications

Engineering Data
Zephyr Fans
PENNBARRY
21
Outlet System Effect Factors
Outlet Duct Elbows
Centrifugal Fans Outlet Duct Elbows. The outlet velocity of
centrifugal fans is generally higher toward one or adjacent
sides of the rectangular duct (See Figure 6). If an elbow must
be located near the fan outlet it should have a minimum
radius to duct diameter ratio of 1.5, and should be arranged
to give the most uniform airflow possible. Refer to Figure 7.
PennBarry Zephyr flexibility eliminates the need for many
outlet elbows. See “Typical Applications”.
Turning Vanes. Turning vanes will usually reduce the pres-
sure loss through an elbow. However, where a non-uniform
approach velocity profile exists, such as at a fan outlet, the
vanes may actually serve to continue the non-uniform profile
beyond the elbow. This may result in increased losses in
other system components downstream of the elbow.
Inlet Duct Elbows
Non-uniform flow into a fan inlet is the most common cause
of deficient fan performance. An elbow located at, or in close
proximity to the fan inlet will not allow the air to enter the
impeller uniformly. The result is less than cataloged air per-
formance.
Reprinted from AMCA Publication 201, Fans and Systems, with the express written permission from the Air Movement and Control Association, Inc.
To calculate 100% effective length, assume a minimum of 2 1/2 duct
diameters for 2500 FPM or less. Add 1 duct diameter for each additional 100
FPM.
Example: 500 FPM = 5 equivalent duct diameters. If the duct is rectangular
with side dimensions a and b, the equivalent duct diameter is equal to
(4ab/š)0.5.
Controlled diffusion and establishment of a uniform velocity profile in a
straight length of outlet duct.
Figure 6
Figure 7
Fan Outlet Velocity Profile