Greenheck USF and CSW (479870) - Manual (Page 6)

Utility and Centrifugal Fans 6
®
Ducted Outlet Installations
Discharge Duct Turns - Duct turns located near the
fan discharge should always be in the direction of the
fan rotation.
Fan performance is reduced when duct turns
are made immediately off the fan
discharge. To achieve cataloged fan
performance there should be at least
three equivalent
duct diameters of
straight ductwork
between the fan
discharge and
any duct turns.
Non-Ducted Installations
Inlet Clearance - Installation of a fan with an open
inlet too close to a wall or bulkhead will cause
reduced fan performance. It is desirable to have
a minimum of three-fourths of a wheel diameter
between the fan inlet and the wall.
Free Discharge - Free or abrupt discharge into a
plenum results in a reduction in fan performance. The
effect of discharge static regain is not realized.
R
o
ta
tion
R
o
ta
tion
POOR
Length of Straight Duct
GOOD
3/4 to one
fan
wheel
diameter
Single Fan Installation
Inlet Spin - Inlet spin is a frequent cause of reduced
fan performance. The change in fan performance is a
function of the intensity of spin and not easily defined.
The best solution is proper duct design and airflow
patterns. Turning vanes reduce the effects of inlet
spin.
Rota
tio
n
Rota
tio
n
Turning
Vanes
POOR GOOD
Turning
Vanes
GOOD
Three fan wheel diameters
Installations with inlet or discharge configurations
that deviate from this manual may result in reduced
fan performance. Restricted or unstable flow at the
fan inlet can cause pre-rotation of incoming air or
uneven loading of the fan wheel yielding large system
losses and increased sound levels. Free discharge
or turbulent flow in the discharge ductwork will also
result in system effect losses. Refer to the following
diagrams for the most efficient installation conditions.
Ducted Inlet Installations
Inlet Duct Turns - Installation of a duct turn or elbow
too close to the fan inlet
reduces fan performance
because air is loaded
unevenly into the fan
wheel. To achieve full
fan performance, there
should be at least three
fan wheel diameters
between the turn or
elbow and the fan inlet.
POOR