Dampers for Centrifugal Fans - Greenheck

Damper Selection
INLET VANE DAMPER
functioning of the damper and fan combination. Damper rotations are viewed from the air inlet side of the fan, and
air inlet side, and will be the opposite of the damper. If the wrong rotation is selected, there will be a moderate
pressure increase, Bhp will increase significantly, and pulsations may occur.
The graphs below show the effects that blade actuation has on static pressure, Bhp, and cfm with inlet vane
Static Pressure vs. Wide Open Volume
Brake Horsepower vs. Wide Open Volume
100
100
Without Vanes
90
90
80
80
75% Open
100% Open
% Peak Static Pressure
70
60
50
40
30
50% Open
75% Open
Without Vanes
100% Open
% Peak Brake Horsepower
70
60
50
40
30
25% Open
50% Open
25% Open
0% Open
20
10
0
0 10 20 30 40 50 60 70 80 90 100
% Wide Open Volume
20
10
0
0 10 20 30 40 50 60 70 80 90 100
% Wide Open Volume
CLASS
MINIMUM RECOMMENDED ACTUATOR TORQUE FOR INLET VANES (in.-lbs.)
for SINGLE WIDTH FANS (Model BISW and AFSW)*
*Consult factory for Class IV applications
DAMPER SELECTION GUIDE
FAN SIZE
12 13 15 16 18 20 22 24 27 30 33 36 40 44 49 54 60 66 73
I 26 30 33 38 47 57 68 110 130 140 160 180 270 320 370 430 500 600 700
II 38 43 49 58 73 88 110 160 180 200 230 260 420 490 580 680 800 960 1100
III 54 63 72 86 110 130 160 220 260 280 330 380 620 740 880 1000 1200 1500 1700
The following table is useful in determining the type of damper that is appropriate for a given application.
Additional considerations are to used only outlet dampers
when Variable Air Volumes (VAV) are required, either outlet volume control dampers or inlet dampers are the correct
choice.
SELECTION
FACTORS
Control
Airflow
downstream
from fan
Cost
Horsepower
Backdraft
Damper
Prevents
backflow
Minor
downward
direction
Low start-up and
maintenance costs
OUTLET DAMPERS
Parallel Blade
Outlet Volume
Control Damper
Good control from
75% to 100% wide
open volume
*Prevents backflow
Directs air
to one side
Opposed Blade
Outlet Volume
Control Damper
Best when used to
control the entire
operation range
Distributes
air evenly
Higher initial cost than
Backdraft dampers
Unchanged from the original undampered
Bhp curve as blades modulate
Vane Damper
Increased costs
over nested
inlet damper
INLET DAMPERS
Vane Damper
Used in variable air volume
systems, provides control
the entire operating range
Pre-spins air before entering
fan, no affect on airflow
downstream of the fan
Least expensive
inlet dampers
Inlet Box
Damper
Highest
initial cost
Decreased Bhp requirements with airflow
(cfm) reduction provides energy savings
6