8
TEMPERATURE
ENTHALPY
RA
TEMP
ABSOLUTE HUMIDITY
ECONOMIXING
AVAILABLE
NOT AVAILABLE
ES5
ES4
ES3
ES2
ES1
HL
DUAL ENTHALPY
HIGH LIMIT
SINGLE ENTHALPY
P2 (T,RH)
P1
(T,RH)
RA
H
UM
(%
RH
)
C12015
Fig. 4 -- Single Enthalpy Curve and Boundaries
Table 5 – Single Enthalpy and Dual Enthalpy High Limit Curves
Enthalpy
Curve
Temp.
Dry---Bulb (
_
F)
Temp.
Dewpoint (
_
F)
Enthalpy
(btu/lb/da)
Point P1
Point P2
Temp. (
_
F)
Humidity %RH
Temp. (
_
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
Enthalpy Settings
When the OA temperature, enthalpy and dew point are
below the respective setpoints, the Outdoor Air can be
used for economizing. Fig. 4 shows the new single
enthalpy boundaries in the W7220. There are 5 boundaries
(setpoints ES1 through ES5), which are defined by dry
bulb temperature, enthalpy and dew point.
Refer to Table 5 for ENTH CURVE setpoint values.
To use enthalpy the W7220 must have a HH57A081
enthalpy control sensor for OA. The W7220 calculates the
enthalpy and dew point 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.
Fig. 4 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 5 provided the values for each boundary limit.
Enthalpy Control Sensor Configuration
The Enthalpy Control sensor (Part Number: HH57AC081)
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 all OAT (Outdoor Air Temperature), RAT (Return
Air Temperature) and DAT (Discharge Air Temperature),
depending on how its three position DIP switch is set.
Use Fig. 5 and Table 6 to locate the wiring terminals for
each Enthalpy Control sensor.
Use Fig. 5 and Table 7 to set the DIP switches for the
desired use of the sensor.
LLECO
N
--
01
S
I
