56
Outdoor Enthalpy Changeover
For enthalpy control, accessory enthalpy sensor (p/n:
HH57AC078) is required. Replace the standard outdoor
dry bulb temperature sensor with the accessory enthalpy
sensor in the same mounting location. See Fig. 73. When
the out door air enthalpy rises above the outdoor enthalpy
change over setpoint, t he outdoor-air damper moves to its
minimum position. The outdoor enthalpy changeover
setpoint is set with the outdoor enthalpy setpoint
potentiometer on the EconoMi$er IV controller. The
setpoints are A, B, C, and D. See Fig. 74. The
factory-installed 620-ohm jumper must be in place across
terminals S
R
and SR+ on the EconoMi$er IV controlle r.
TR1
24 Vac
COM
TR
24
Va c
HOT
12
3
4
5
EF
EF1
+
_
P1
T1
P
T
N
EXH
2V 10V
EXH
Set
Set
2V 10V
2V 10V
DCV
DCV
Free
Cool
B
C
A
D
SO+
SR+
SR
SO
AQ1
AQ
DCV
Min
Pos
Open
Max
N1
C06038
Fig. 72 -- EconoMi$er IV Control
Differential Enthalpy Control
For differential e nthalpy control, the EconoMi$er IV
controller uses two enthalpy sensors (HH57AC078 and
CRENTDIF004A00), one in the outside air and one in the
return air duct. The EconoMi$er IV controller compares
the outdoor air enthalpy to the return air enthalpy to
determine EconoMi$er IV use. The controller selects the
lower enthalpy air (return or outdoor) for cooling. For
exam ple, when the outdoor air has a lower enthalpy than
the return air, t he EconoMi$er IV opens to bring in
outdoor air for free cooling.
Replace the sta ndard outside air dry bulb temperature
sensor with the accessory enthalpy sensor in the same
mounting location. See Fig. 63. Mount the return air
enthalpy sensor in the return air duct. See Fig. 71. Wiring
is provided in the EconoMi$er IV wiring harness. See Fig.
64. The outdoor enthal py changeover setpoint is set with
the outdoor enthalpy setpoint potentiometer on the
EconoMi$e r IV controller. When using this mode of
change over control, turn the enthalpy setpoint
potentiometer fully clockwise to the D setting.
CONTROL
CURVE
A
B
C
D
CONTROL POINT
APPROX.
deg. F (deg. C)
AT 50% RH
73 (23)
70 (21)
67 (19)
63 (17)
1
2
1
4
1
6
1
8
2
0
2
2
2
4
26
28
30
32
3
4
3
6
3
8
40
42
4
4
46
9
0
1
0
0
80
70
6
0
50
4
0
30
20
1
0
ENTHALPY BTU PER POUND DRY AIR
85
(29)
90
(32)
95
(35)
100
(38)
105
(41)
110
(43)
35
(2)
35
(2)
40
(4)
40
(4)
105
(41)
110
(43)
45
(7)
45
(7)
50
(10)
50
(10)
55
(13)
55
(13)
60
(16)
60
(16)
65
(18)
65
(18)
70
(21)
70
(21)
75
(24)
75
(24)
80
(27)
80
(27)
85
(29)
90
(32)
95
(35)
100
(38)
A
A
B
B
C
C
D
D
RELATIVE HUMIDITY (%)
HIGH LIMIT
CURVE
APPROXIMATE DRY BULB TEMPERATURE--degrees F (degrees C)
C06037
Fig. 73 -- Enthalpy Changeover Setpoints
48HC
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