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Minimum Damper Position Range
The motorized outdoor air damper operation is optimized
as shown in the shaded area of Chart 2. Unit operation
during minimum damper position above this curve
increases the potential for rain being drawn into the unit.
1- Remove the metal mesh filter from the hood.
Measure the static pressure differential between the
return compartment (through horizontal return air
panel is recommended) and outside the unit.
Operate the unit with the damper open to minimum
position. Record the single blower speed pressure
differential in table 2.
2- Units With More Than One Blower Speed -
Repeat the static pressure measurement at each
blower speed and minimum set point combination.
Record the multiple blower speed pressure
differential in table 2.
3- Read the damper percentage open.
Units Equipped With Unit Controller -
The damper percentage open was entered into the
Unit Controller.
Units Not Equipped With Unit Controller -
Operate the unit with the damper open to minimum
position. Measure the voltage between pins 7 and 9
from the damper motor plug P4. Calculate the
percentage open from the formula:
% Open = [(Measure voltage - 2.5) / 7.0] X 100
4- Plot the damper % open and static pressure drop on
Chart 2. Plot additional blower speeds in the same
manner.
5- Replace the metal mesh filter.
TABLE 2
Single Blower Speed Multiple Blower Speed
Static Pressure Differential - “w.c. Damper % Open Static Pressure Differential - “w.c. Damper % Open
CHART 2
OPTIMAL OUTDOOR AIR OPERATION
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1.10
0 100 200 300 400 500 600 700 800 900
Measured Static Pressure Drop Across Damper (inch w.c.)
Measured Airflow Through Damper (CFM)
20%
25%
33%
40%
46%
53%
67%
80%
100%
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