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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.
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.
ECONOMIXING
AVAILABLE
NOT AVAILABLE
TEMPERATURE
Table 11 – Single Enthalpy and Dual Enthalpy High Limit Curves (EN Units)
Enthalpy
Temp.
Curve
Dry---Bulb (_F)
ES1
80.0
ES2
75.0
ES3
70.0
ES4
65.0
ES5
60.0
HL
86.0
Fig. 52 - - Single Enthalpy Curve and Boundaries
Temp.
Enthalpy
Dewpoint (_F)
(btu/lb/da)
60.0
28.0
57.0
26.0
54.0
24.0
51.0
22.0
48.0
20.0
66.0
32.4
Fig. 52 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 11 provides the values for each boundary limit.
SINGLE ENTHALPY
ES5
Point P1
Temp. (_F)
Humidity %RH
80.0
36.8
75.0
39.6
70.0
42.3
65.0
44.8
60.0
46.9
86.0
38.9
41
DUAL ENTHALPY
HIGH LIMIT
P2 (T,RH)
P1
(T,RH)
ES4
ES3
ES2
ES1
Point P2
Temp. (_F)
Humidity %RH
66.3
80.1
63.3
80.0
59.7
81.4
55.7
84.2
51.3
88.5
72.4
80.3
HL
C12015
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