Carrier Performance 50VT-A24 Installation Instructions Manual page 38

CONTROL CONTROL POINT
CURVE APPROX ˚F (˚C)
AT 50% RH
A 73 (23)
70 (21)
B
C 67 (19)
D 63 (17)
60
(16)
55
(13)
B
50
C
(10)
45
D
(7)
40
(4)
35
(2)
35 40 45 50 55 60
(2) (4) (7) (10) (13) (16)
APPROXIMATE DRY BULB TEMPERATURE — ˚F (˚C)
Fig. 42 - - Enthalpy Changeover Setpoints
6000
5000
4000
3000
2000
1000
0
2 3 4 5
Fig. 43 - - CO Sensor Maximum Range Setting
2
OUTDOOR ENTHALPY CHANGEOVER—For enthalpy
control, accessory enthalpy sensor (part number HH57AC078) is
required. Replace the standard outdoor dry bulb temperature sensor
with the accessory enthalpy sensor in the same mounting location.
When the outdoor air enthalpy rises above the outdoor enthalpy
changeover set point, the outdoor- -air damper moves to its
minimum position. The outdoor enthalpy changeover set point is
set with the outdoor enthalpy set point potentiometer on the
Economizer controller. The set points are A, B, C, and D. See Fig.
42. The factory- -installed 620- -ohm jumper must be in place across
terminals SR and SR+ on the Economizer controller. See Fig. 44
and Fig. 45.
85 90 95 100 105 110
(29) (32) (25) (38) (41) (43)
80
(27)
75
(24)
70
(21)
65
(18)
A
A
B
C
D
65 70 75 80 85 90 95 100 105
(18) (21) (24) (27) (29) (32) (36) (38) (41) (43)
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800 ppm
900 ppm
1000 ppm
1100 ppm
6 7 8
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N1
N
2V
EXH
P1
P
T1
T
2V
AQ+
DCV
AQ
SO+
2V
SO
Free
SR+
Cool
SR
Fig. 44 - - Economizer Controller
DIFFERENTIAL ENTHALPY CONTROL — For differential
110
enthalpy control, the Economizer controller uses two enthalpy
sensors (HH57AC078 and CRENTDIF004A00), one in the outside
air and one in the return airstream. The Economizer controller
compares the outdoor air enthalpy to the return air enthalpy to
determine Economizer use. The controller selects the lower enthalpy
air (return or outdoor) for cooling. For example, when the outdoor air
has a lower enthalpy than the return air and is below the set point, the
Economizer opens to bring in outdoor air for free cooling. Replace the
standard outside air dry bulb temperature sensor with the accessory
enthalpy sensor in the same mounting location. Mount the return air
enthalpy sensor in the return air duct. See Fig. 41. When using this
mode of changeover control, turn the enthalpy set point poten-
tiometer fully clockwise to the D setting.
INDOOR AIR QUALITY (IAQ) SENSOR INPUT —The IAQ
input can be used for demand control ventilation control based on the
level of CO measured in the space or return air duct. Mount the
2
accessory IAQ sensor according to manufacturer specifications. The
IAQ sensor should be wired to the AQ and AQ1 terminals of the
controller. Adjust the DCV potentiometers to correspond to the DCV
voltage output of the indoor air quality sensor at the user determined
set point. See Fig. 43. If a separate field- -supplied transformer is used
to power the IAQ sensor, the sensor must not be grounded or the
Economizer control board will be damaged.
EXHAUST SET POINT ADJUSTMENT—The exhaust set point
will determine when the exhaust fan runs based on damper position
(if power exhaust is installed). The set point is modified with the
Exhaust Fan Set Point (EXH SET) potentiometer. See Fig. 45 for
Wiring Diagram. The set point represents the damper position above
which the exhaust fans will be turned on. When there is a call for
exhaust, the Economizer controller provides a 45 ± 15 second delay
before exhaust fan activation to allow the dampers to open. This delay
allows the damper to reach the appropriate position to avoid
unnecessary fan overload.
MINIMUM POSITION CONTROL — There is a minimum
damper position potentiometer on the Economizer controller. See
Fig. 39 and 45. The minimum damper position maintains the
minimum airflow into the building during the occupied period. When
using demand ventilation, the minimum damper position represents
the minimum ventilation position for VOC (volatile organic
compound) ventilation requirements. The DCV Max potentiometer
must be fully closed (CCW) to allow the Minimum Position
potentiometer to function correctly.
38
TR
EXH
Set
10V
24
Vac
HOT
Min
Pos
Open
DCV
1
Max
10V
DCV
3
Set
10V
EF
B C
A D
TR1
24 Vac
COM
2
5
4
EF1
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