Differential Enthalpy Control - Carrier 50HJQ014 Installation, Start-Up And Service Instructions Manual

Outdoor Enthalpy Changeover — For enthalpy control, ac-
cessory enthalpy sensor (part number HH57AC078) is
required. Replace the standard outdoor dry bulb temperature
sensor with the accessory enthalpy sensor in the same mount-
ing location. See Fig. 28. 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 EconoMi$erIV controller. The
set points are A, B, C, and D. See Fig. 36. The factory-installed
620-ohm jumper must be in place across terminals SR and SR+
on the EconoMi$erIV controller. See Fig. 31 and 37.
Differential Enthalpy Control — For differential enthalpy
control, the EconoMi$erIV controller uses two enthalpy sen-
sors (HH57AC078 and CRENTDIF004A00), one in the out-
side air and one in the return airstream on the EconoMi$erIV
frame. The EconoMi$erIV controller compares the outdoor air
enthalpy to the return air enthalpy to determine EconoMi$erIV
use. The controller selects the lower enthalpy air (return or out-
door) for cooling. For example, when the outdoor air has a low-
er enthalpy than the return air and is below the set point, the
EconoMi$erIV opens to bring in outdoor air for free cooling.
Replace the standard outside air dry bulb temperature sen-
sor with the accessory enthalpy sensor in the same mounting
location. See Fig. 28. Mount the return air enthalpy sensor in
the return airstream. See Fig. 35. The outdoor enthalpy
changeover set point is set with the outdoor enthalpy set point
potentiometer on the EconoMi$erIV controller. When using
CONTROL
CURVE
A
B
C
D
CONTROL POINT
APPROX. °F (°C)
AT 50% RH
73 (23)
70 (21)
67 (19)
63 (17)
(18)
60
(16)
A
55
(13)
B
50
C
(10)
D
45
(7)
40
(4)
35
(2)
35 40 45 50 55 60
(2) (4) (7) (10) (13) (16)
APPROXIMATE DRY BULB TEMPERATURE— °F (°C)
Fig. 36 — Enthalpy Changeover Set Points
this mode of changeover control, turn the enthalpy set point
potentiometer fully clockwise to the D setting.
NOTE: Remove 620-ohm resistor if differential enthalpy sen-
sor is installed.
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.
2
Mount the 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 potentiome-
ters to correspond to the DCV voltage output of the indoor air
quality sensor at the user-determined set point. See Fig. 38.
If a separate field-supplied transformer is used to power the
IAQ sensor, the sensor must not be grounded or the
EconoMi$erIV control board will be damaged.
Exhaust Set Point Adjustment — The exhaust set point will
determine when the exhaust fan runs based on damper position
(if accessory power exhaust is installed). The set point is modi-
fied with the Exhaust Fan Set Point (EXH SET) potentiometer.
See Fig. 33. The set point represents the damper position above
which the exhaust fan will be turned on. When there is a call
for exhaust, the EconoMi$erIV 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.
85 90 95
(29) (32) (35)
80
(27)
75
(24)
70
(21)
65
A
B
C
D
65 70 75 80 85 90 95
(18) (21) (24) (27) (29) (32) (35)
21
100 105 110
(38) (41) (43)
HIGH LIMIT
CURVE
100 105 110
(38) (41) (43)