Utility Fans
7
Rota
tio
n
Rota
tio
n
Turning
Vanes
POOR
GOOD
Turning
Vanes
GOOD
Three fan wheel diameters
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.
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
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
Bases (Foundation and Isolation)
Critical to every fan installation is a strong, level
foundation. A reinforced poured concrete pad with
a steel base or inertia base provides an excellent
foundation. Bases must be sturdy enough, with
welded construction, to prevent flexing and vibration.
To eliminate vibration and noise from being
transferred to the building, vibration isolators should
be used. The fan is mounted directly on the isolation
base and must be supported for the entire length of
the fan base angle. Isolators are installed between the
isolation base and the foundation.
After the fan, isolation base,
and isolators are installed,
the entire assembly must be
leveled. Position the level
on the isolation base, not
the fan shaft, for proper
leveling. Additionally,
the motor and fan
shafts must be
level and parallel
relative to each
other for proper
alignment.
Typical Fan on Isolation Base
