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DAMPER SELECTION AND SIZING
Step
1
Calculate the approach velocity:
Approach velocity (m/s) =
2
Using the approach velocity from Step 1, calculate a correction factor:
Correction factor =
3
Calculate the pressure drop at 5.08 m/s:
Pressure drop at 5.08 m/s = Pressure drop at approach velocity x correction factor (Step 2)
4
Calculate free area ratio
For pressure drops (Step 3)
Ratio = [1 + (0.0859 x pressure drop)]
For pressure drops (Step 3) < 57.1 Pa:
Ratio = [1 + (0.3214 x pressure drop)]
5
Calculate damper area (m
For parallel blade dampers:
Damper area (m
For opposed blade dampers:
Damper area (m
a
The free area of a damper is the open portion of the damper through which air flows. The free area ratio is the open area
in a damper divided by the total duct area.
Step
1
Approach velocity (m/s) =
2
3
Pressure drop at 5 m/s = 14.9 Pa x 0.64 = 9.43 Pa
4
5
Damper area (parallel blades) = (1.485 m
Table 4. Damper Sizing Procedure.
Airflow (L/s)
x
Duct Area (m 2 )
25.8
[Approach velocity (m/s)] 2
a
:
57.1 Pa:
–0.2340
2
):
2
2
) = (Duct area (m
) x ratio, x 1.2897)
2
2
) = (Duct area (m
) x ratio, x 1.4062)
Table 5. Damper Sizing Example.
9440 L/s
1.485 m 2
25.8
Correction factor =
= 0.64
16.35
Free area ratio = [1 + (0.3214 x 9.43)]
–0.2340
= 3.03
= 0.772
= 1.3828
= 1.342 m
Procedure
1 m 3
1000L
–0.3903
0.9085
0.9217
Example
1m 3
x
= 6.35 m/s
1000L
–0.2340
2
0.9085
x 0.772 x 1.2897)
0.9085
2
ENGINEERING MANUAL OF AUTOMATIC CONTROL
460
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