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Unit Options
Enthalpy Control
Outside air enthalpy control (OAE)
Units with MicroTech control and an economizer come
standard with an electromechanical enthalpy control device
(OAE) which senses both the humidity and temperature of
the outside air entering the unit. This device has an enthalpy
scale marked A through D. Table 12 shows the control points
at 50% RH for settings A through D. Figure 29 shows this
scale on a psychrometric chart. When the outside air condi-
tions exceed the setting of the device, the outside air damp-
ers are positioned to the minimum outside air intake position
by the MicroTech controller.
Table 12. Enthalpy control settings
CONTROL POINT
CONTROL CURVE
TEMP. AT 50% RH
A
73
°
F (23
°
C)
B
70
°
F (21
°
C)
C
67
°
F (19
°
C)
D
63
°
F (17
°
C)
Differential enthalpy control (OAE/RAE)
An optional electric differential enthalpy control arrangement
(OAE/RAE) is available on units with MicroTech control. In this
configuration a solid-state humidity and temperature sens-
ing device is located in both the return (RAE) and outside
intake (OAE) airstreams. This OAE device has the same A
through D scale as the device described above. However,
with the OAE/RAE arrangement the switch on OAE must be
set all the way past the “D” setting. With this done, the
Figure 29. Enthalpy control settings
The phase voltage monitor protects against phase loss
(single phasing) when any one of three line voltages drops to
74% or less of setting. This device also protects against
phase reversal when improper phase sequence is applied to
equipment, and low voltage (brownout) when all three line
voltages drop to 90% or less of setting. An indicator run light
is “on” when all phase voltages are within specified limits.
The phase voltage monitor is located on the load side of the
power block with a set of contacts wired to the 115 volt
control circuit to shut the unit down whenever the phase
voltages are outside the specified limits.
The optional Remote Monitor Panel provides indicator lights
and fan on-off and system heat-auto-cool switches remote
from the MicroTech unit controller. Refer to Figure 30.
Wiring should be sized in accordnace with Table 13 and
connected to the panel terminals in accordance with the unit
wiring diagram. The panel can be mounted on a standard 4x4
junction box
If the Remote Monitor Panel is not used, terminals 101 and
105 must be jumpered to enable cooling, and terminals 101
and 106 must be jumpered to enable heating. The fan is
enabled when either cooling or heating is enabled.
Table 13. Low voltage field wiring
MAXIMUM WIRE LENGTH*
WIRE SIZE
IN FEET (M)
22
757 (231)
20
1204 (367)
18
1915 (584)
16
3045 (928)
*Maximum wire length is based on a voltage drop of 2 volts.
Figure 30. Optional Remote Monitor Panel
®
HEAT
AUTO
COOL
ON
OFF
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
ENTHALPY — BTU PER POUND DR
Y AIR
35
(1.5)
40
(4.5)
50
(10)
55
(13)
60
(15.5)
65
(18.5)
70
(21)
75
(24)
80
(26.5)
85
(29.5)
90
(32)
95
(35)
100
(38)
105
(40.5)
DRY BULB TEMPERATURE (APPROXIMATE) — FAHRENHEIT (CELSIUS)
35
(1.5)
45
(7)
40
(4.5)
45
(7)
50
(10)
60
(15.5)
55
(13)
80
(26.5)
85
(29.5)
90
(32)
95
(35)
100
(38)
105
(40.5)
65
(18.5)
70
(21)
75
(24)
0.90
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
RELA
TIVE
HUMIDITY
A
D
C
B
D
C
A
B
MicroTech controller will adjust the return and outside air
dampers to use the airstream with the lowest enthalpy.
Phase Voltage Monitor
Remote Monitor Panel
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