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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.
The W7220 calculates the enthalpy and dew point using
the OA temperature and humidity input from the OA
enthalpy 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.
ECONOMIXING
AVAILABLE
NOT AVAILABLE
TEMPERATURE
Enthalpy
Curve
ES1
ES2
ES3
ES4
ES5
HL
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Fig. 6 - - Single Enthalpy Curve and Boundaries
Table 5 – Single Enthalpy and Dual Enthalpy High Limit Curves (EN Units)
Temp.
Temp.
Dry---Bulb (_F)
Dewpoint (_F)
80.0
60.0
75.0
57.0
70.0
54.0
65.0
51.0
60.0
48.0
86.0
66.0
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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. 6 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 provides the values for each boundary limit.
Point P1
Enthalpy
(btu/lb/da)
Temp. (_F)
Humidity %RH
28.0
80.0
26.0
75.0
24.0
70.0
22.0
65.0
20.0
60.0
32.4
86.0
11
DUAL ENTHALPY
HIGH LIMIT
SINGLE ENTHALPY
P2 (T,RH)
P1
(T,RH)
ES5
ES4
ES3
ES2
Point P2
Temp. (_F)
Humidity %RH
36.8
66.3
80.1
39.6
63.3
80.0
42.3
59.7
81.4
44.8
55.7
84.2
46.9
51.3
88.5
38.9
72.4
80.3
ES1
HL
C12015
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