16
Table 7 - Single Enthalpy and Dual Enthalpy High Limit Curves
Enthalpy Settings (Enthalpy Optional)
If installing the optional enthalpy sensor. The ECD-SRT**TA-D2
(CORRECT?) dry bulb outside air sensor must rst be removed.
Wire enthalpy to S-BUS connections on W7220 controller thru (2)
gray wires.
When the OA temperature, enthalpy and dew point are below the
respective setpoints, the Outdoor Air can be used for economizing.
Fig. 15 shows the new single enthalpy boundaries in the W7220.
There are 5 boundaries (setpoints ES1 thru ES5), which are dened
by dry bulb temperature, enthalpy and dew point.
Refer to Table 11 for ENTH CURVE setpoint values.
To use enthalpy the W7220 must have a enthalpy control sensor
for OA. The W7220 calculates the enthalpy and dewpoint using the
OA temperature and humidity input from the OA sensor. When the
OA temperature, OA humidity and OA dew point are all below the
selected boundary, the economizer sets the economizing mode to
YES, economizing is available.
When all of the OA conditions are above the selected boundary, the
conditions are not good to economize and the mode is set to NO.
If using OA enthalpy sensor option, remove and discard the dry
bulb sensor shipped with the economizer. System default is ES3
enthalpy curve.
Fig. 15 shows the 5 current boundaries. There is also a high limit
boundary for differential enthalpy. The high limit boundary is ES1
when there are no stages of mechanical cooling energized and HL
(high limit) when a compressor stage is energized.
Table 10 provided the values for each boundary limit.
Enthalpy control Sensor Conguration
The optional Enthalpy Control sensor (Part Number:
communicates with the W7220 Economizer controller on the two-
wire communications bus and can either be wired using a two
pin header or using a side connector. This sensor is used for OA
enthalpy, and return (differential dry bulb or enthalpy), depending
on how its three position DIP switch is set.
Use Fig. 17 to locate the wiring terminals for each Enthalpy Control
sensor.
Use Fig. 17 and Table 9 to set the DIP switches for the desired use
of the sensor.
If using differential (return) enthalpy or temperature option, see
Table 4 for California Title 24 setting requirements by region.
Enthalpy
Curve
Temp.
Dry Bulb (
o
F)
Temp.
Dewpoint (
o
F)
Enthalpy
(btu/lb/da)
Point P1 Point P2
Temp (
o
F) Humidity %RH Temp (
o
F)
Humidity
%RH
ES1 80.0 60.0 28.0 80.0 36.8 66.3 80.1
ES2 75.0 57.0 26.0 75.0 39.6 63.3 80.0
ES3 70.0 54.0 24.0 70.0 42.3 59.7 81.4
ES4 65.0 51.0 22.0 65.0 44.8 55.7 84.2
ES5 60.0 48.0 20.0 60.0 46.9 51.3 88.5
HL 86.0 66.0 32.4 86.0 38.9 72.4 80.3
Fig. 17 - C7400S Sensor (Used as OA Enthalpy
and Return (Differential) Dry Bulb or Enthalpy)
Table 8 - Sensor Wiring Terminations
a
Table 9 - Enthalpy Control Sensor DIP Switch
Terminal
Type Description
Nbr Label
1 S─BUS S─BUS
S─Bus Communications
(Enthalpy Control Sensor Bus)
2 S─BUS S─BUS
S─Bus Communications
(Enthalpy Control Sensor Bus)
Use
DIP Switch Positions for Switches 1,2, & 3
1 2 3
DA
a
OFF ON OFF
RA
b
ON OFF OFF
OA
c
OFF OFF OFF
a DA = Discharge Air or Supply Sensor
b RA = Return Air
c OA = Outside Air
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