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Free Cooling Setpoint
Outdoor air is considered suitable when temperature and
humidity are less than the free cooling setpoints shown in
table 8. Setting A is recommended. See figure 20. At setting
A, free cooling will be energized when outdoor air is approx
imately 73°F (23°C) and 50% relative humidity. If indoor air
is too warm or humid, lower the setpoint to B. At setting B,
free cooling will be energized at 70°F (21°C) and 50% rela
tive humidity.
When an optional A62 differential sensor is installed, turn
A6 enthalpy control free cooling setpoint potentiometer
completely clockwise to position “D”.
TABLE 8
ENTHALPY CONTROL SETPOINTS
Control Setting
Free Cooling Setpoint At 50% RH
A
73
°
F (23
°
C)
B
70
°
F (21
°
C)
C
67
°
F (19
°
C)
D
63
°
F (17
°
C)
Damper Minimum Position
NOTE - A jumper is factory-installed between TB1 R and
OC terminals to maintain occupied status (allowing mini
mum fresh air). When using an electronic thermostat or
energy management system with an occupied/unoccu
pied feature, remove jumper.
1- Set thermostat to occupied mode if the feature is avail
able. Make sure jumper is in place between TB1 termi
nals R and OC if using a thermostat which does not
have the feature.
2- Rotate MIN POS SET potentiometer to approximate
desired fresh air percentage.
Note - Damper minimum position can be set lower than
traditional minimum air requirements when an IAQ sensor
is specified. Dampers will open to DCV MAX setting (if CO2
is above setpoint) to meet traditional ventilation require
ments.
3- Measure outdoor air temperature. Mark the point on
the bottom line of chart 1 and label the point “A” (40
_
F,
4
_
C shown).
4- Measure return air temperature. Mark that point on the
top line of chart 1 and label the point “B” (74
_
F, 23
_
C
shown).
5- Measure mixed air (outdoor and return air) tempera
ture. Mark that point on the top line of chart 1 and label
point “C” (70
_
F, 21
_
C shown).
6- Draw a straight line between points A and B.
7- Draw a vertical line through point C.
8- Draw a horizontal line where the two lines meet. Read
the percent of fresh air intake on the side.
9- If fresh air percentage is less than desired, adjust MIN
POS SET potentiometer higher. If fresh air percentage
is more than desired, adjust MIN POS SET potentiom
eter lower. Repeat steps 3 through 8 until calculation
reads desired fresh air percentage.
-20
-29
-10
-23
0
-18
10
-12
20
-7
30
-1
40
4
50
10
60
16
70
21
80
27
90
32
100
38
0
10
30
40
50
60
70
80
90
100
20
OUTDOOR AIR TEMPERATURE
0
10
30
40
50
60
70
80
90
100
20
MIXED AND RETURN AIR TEMPERATURE
CHART 1
CALCULATE MINIMUM FRESH AIR PERCENTAGE
A
B
C
_
F
_
C
_
F
_
C
-20
-29
-10
-23
0
-18
10
-12
20
-7
30
-1
40
4
50
10
60
16
70
21
80
27
90
32
100
38
_
F
_
C
_
F
_
C
