Centrifugal, Industrial and Filtered Supply
5
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.
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.
3/4 to
one fan
wheel
diameter
One fan
diameter
3/4 to
one fan
wheel
diameter
Parallel Fan Installation
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 one fan wheel
diameter between parallel fan units and 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.
Rota
tio
n
Rota
tio
n
Turning
Vanes
POOR
GOOD
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
Turning
Vanes
GOOD
Three fan wheel diameters
Move the fan to the desired location. Check and tighten
fasteners throughout the unit and then fasten securely
through mounting holes provided in the base angles.
The unit must be set level (shimming may be necessary).
Flexible duct connections and vibration isolators should
be used where noise is a factor.
The motor voltage and ampere rating must be checked
for compatibility with the electrical supply prior to final
electrical connection. Supply wiring to the fan must
be properly fused, and conform to local and national
electrical codes.
Installations with inlet or discharge configurations that
deviate from this standard 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.
R
o
ta
tion
R
o
ta
tion
POOR
Length of Straight Duct
GOOD
3/4 to one
fan
wheel
diameter
3/4 to one
fan
wheel
diameter
Single Fan Installation
Installation
