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BYPASS DAMPERS – ELECTRONIC
ELECTRONIC BYPASS DAMPERS
Bypass dampers are used to provide constant air delivery through the air handling unit. This
is done by bypassing excess air from the supply duct back to the return duct. As a zone
is satisfied its zone damper closes. When this happens, the bypass damper opens just enough
to bypass the excess air. This will control static pressure and noise at the diffusers.
The Electronic Bypass Damper can be used on any size system over. The damper can be
round or rectangular and multiple dampers can be slaved together. The Electronic Bypass
Damper consists of a medium pressure round or a heavy duty rectangular damper and
a static pressure sensor.
SIZING ELECTRONIC BYPASS DAMPERS
When only the smallest zone is calling, the maximum amount of excess supply air will flow
through the bypass damper.
CFM CALCULATION
To determine the proper size bypass damper:
A) Calculate total air volume at 400 CFM per Ton.
B) Calculate air volume of smallest zone in CFM .
C) Calculate bypass CFM by subtracting the smallest zone air volume from the total.
(A - B = C).
ROUND BYPASS DAMPER SELECTION
When you know the bypass CFM requirement as
determined in the “CFM calculation” section, use the
ROUND BYPASS SELECTION TABLE. From the table,
select the bypass damper with the CFM rating equal to
or greater than the value calculated in step C of CFM
Calculation.
Example:
We know the smallest zone air volume is
400 CFM and we have a four ton system. Thus the
air volume we need to bypass is (400 * 4) – 400
which equals 1200 CFM. Using the ROUND BYPASS SELECTION TABLE, we would select a 12 inch
bypass since it can handle up to 1250 CFM of air.
Never exceed 16 inches for the round bypass damper. If you need to bypass more than 2200 CFM,
either use a rectangular bypass or slave multiple round bypass dampers.
L
D
W
SIZE
6
8
10
12
14
16
6"
8"
10"
12"
14"
16"
D
10"
10"
14"
18"
L
9"
11"
13"
15"
17"
19"
W
ROUND DIMENSIONAL DATA
16"
STMPD06
PART #
STMPD08
STMPD10
STMPD12
STMPD14
STMPD16
12"
RECTANGULAR & ROUND BYPASS DAMPER
WITH THE STATIC PRESSURE CONTROL
RECTANGULAR BYPASS DAMPERS
SELECT FROM 8 X 8 THRU 48 X 48
DEPTH
H
16"
W
WIDTH HEIGHT
D
H
Rectangular bypass dampers should operate at 1500 FPM
*
E.G. A 24" x 12" damper = 2 square feet.
2 square feet X 1500FPM = 3000 CFM.
*
FPM = Feet Per Minute
48" MAXIMUM WIDTH
4"
W
Part Number STCD W X H
RECTANGULAR BYPASS DAMPER SELECTION
When you know the bypass CFM requirement as determined in the
“CFM calculation” section, use the RECTANGULAR BYPASS SELEC-
TION TABLE. From the table, select the bypass damper with the CFM
rating equal to or greater than the value calculated in step C of CFM
Calculation.
Example:
We know the smallest zone air volume is 250 CFM and we
have a 7-1/2 ton system. Thus the air volume we need to bypass is
(400 X 7.5) -250) which equals 2750 CFM. Using the RECTANGULAR
BYPASS SELECTION TABLE, we see the smallest damper we can use
is a 12” x 22” or a 22” x 12”.
Diameter
CFM
6”
320
8”
560
10”
900
12”
1250
14”
1700
16”
2200
ROUND BYPASS SELECTION TABLE
