AIRFOIL FANS - Aerovent

Accessories
Nested Inlet Vanes
External Inlet Vanes
Volume Control Devices
Outlet dampers, variable inlet vanes, and variable frequency
drives are three popular devices used to control
volume for fan systems.
Variable Inlet Vanes
Variable inlet vanes cause the entering air to spin in
the direction of wheel rotation, resulting in reduction in
volume, static pressure and brake horsepower and thus
providing an infinite number of fan curves approximately
parallel to the original fan curve. Variable inlet vanes
cost about 50% to 80% more than outlet dampers but
offer significant savings in energy. Because of their simplicity,
inlet vanes can be more reliable when compared
to variable frequency drives.
STATIC PRESSURE
10
8
6
4
2
0
0
Performance Curves
at Different Vane Settings
25
50
25
100
75
50
75
100
200
160
120
80
40
BRAKE HORSEPOWER
There are two types of variable inlet vanes: nested
(internal type) and bolted on (external type).
Nested inlet vanes are built into the fan inlet cone and
offer the advantage of saving space and lower cost as
opposed to the external type. They are available on all
fan sizes 165 and larger. Aerovent offers cantilevered
vanes to size 890 Class II fans to minimize insertion
losses and noise associated with center hub design.
External inlet vanes are bolted to the inlet of the fan
and are available from size 122 to size 890. Use of
external vanes should be considered for hostile environments
since operating linkages are shielded from the
airstream. Both types of inlet vanes are available to
600°F construction.
0 2 4 6 8 10
CFM IN 10000's
SYSTEM CURVE
SP @ VANE SETTING
BHP @ VANE SETTING
Outlet Dampers
The closing of the damper adds to the resistance that
the fan is working against. This moves the operating
point to the left of the initial rating point. The savings in
horsepower depends on the relative position on the fan
curve and is usually much less than offered by other
methods. Outlet dampers are typically the least expensive
option and should be considered when infrequent
operation at lesser capacity is desired or when handling
hot, humid or particulate laden air.
Parallel Blade
Outlet Damper
Opposed Blade
Outlet Damper
There are two types of outlet dampers: parallel blade
and opposed blade.
Parallel blade dampers are recommended for systems
where air volume is modulated between full-open to
about 75% of open.
Opposed blade dampers cost about 10% more and
are recommended for systems where volume is modulated
over the entire range. Opposed blades reduce
air volume in a closer relationship to the control arm
movement.
8 Aerovent Catalog 725