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A
APPROXIMATE DRY BULB TEMPERATURE — ˚F (˚C)
ENTHALPY – BTU PER POUND DRY AIR
12
14
16
18
20
22
24
26
28
30
100
90
80
70
60
50
40
32
34
36
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40
42
44
46
CONTROL
CURVE
CONTROL POINT
APPROX ˚F (˚C)
AT 50% RH
A 73 (23)
67 (19)
63 (17)
70 (21)
B
C
D
30
20
10
RELATIVE HUMIDITY (%)
A09711
Fig. 41 -- Enthalpy Changeover Setpoints
6000
5000
4000
3000
2000
1000
0
2345678
800 ppm
900 ppm
1000 ppm
1100 ppm
A09713
Fig. 42 -- CO
2
Sensor Maximum Range Setting
OUTDOOR ENTHALPY CHANGEOVER—For enthalpy
control, accessory enthalpy sensor (part number H H57AC078) 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.
41. The factory--installed 620 --ohm jumper must be in place across
terminals SR and SR+ on the Economizer controller. See Fig. 43
and Fig. 44.
TR TR1
24
Vac
HOT
24 Vac
COM
12
5
43
EF1EF
C
10V
DCV
DCV
Max
DCV
DA
B
Set
2V
10V
10V
Min
Pos
2V
2V
Free
Cool
SR
SO
SO+
AQ+
T1
T
P
P1
N1
N
AQ
SR+
Open
EXH
Set
EXH
A09712
Fig. 43 -- Economizer Controller
DIFFERENTIAL ENTHALPY CONTROL — For differential
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
determineEconomizeruse. Thecontrollerselectsthelowerenthalpy
air(returnoroutdoor)forcooling.Forexample,whentheoutdoorair
hasalowerenthalpythan thereturnairand isbelowtheset point,the
Economizeropenstobringinoutdoorairforfreecooling.Replacethe
standard outside air dry bulb temperature sensor with the accessory
enthalpy sensor in thesame mounting location. Mountthe return air
enthalpy sensor in the return air duct. See Fig. 40. 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
inputcan beused fordemandcontrolventilation controlbased onthe
level of CO
2
measured in the space or return air duct. Mount the
accessory IAQ sensor according to manufacturer specifications. The
IAQ sensor should be wired to the AQ and AQ1 terminals of the
controller. AdjusttheDCVpotentiometersto correspondto theDCV
voltageoutputof the indoor airquality sensor atthe userdetermined
setpoint.SeeFig.42.Ifaseparatefield-- suppliedtransformerisused
to power the IAQ sensor, the sensor must not be grounded or the
Economizer control board will bedamaged.
EXHAUST SETPOINT ADJUSTMENT—Theexhaustsetpoint
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. 44 for
Wiring Diagram. Theset point represents the damper position above
which the exhaust fans will be turned on. When there is a call for
exhaust,theEconomizercontrollerprovidesa45 ±15seconddelay
beforeexhaustfanactivationtoallowthedamperstoopen.Thisdelay
allows the damper to reach the appropriate position to avoid
unnecessary fan overload.
MINIMUM POSITION C ONTROL — There is a minimum
damper position potentiometer on the Economizer controller. See
Fig. 38 and 44. The minimum damper position maintains the
minimumairflowintothebuildingduringtheoccupiedperiod.When
using demand ventilation, the minimum damper position represents
the minimum ventilation position for VOC (volatile or ganic
compound) ventilation requirements. The DCV Max potentiometer
must be fully closed (CCW) to allow the Minimum Position
potentiometer to function correctly.
604D-- --A