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Enthalpy Settings
When the OA temperature, enthalpy and dew point are be-
low the respective setpoints, the Outdoor Air can be used for
economizing. Fig. 49 shows the new single enthalpy boundar-
ies 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 12 for ENTH CURVE setpoint values.
The W7220 calculates the enthalpy and dew point using the
OA temperature and humidity input from the OA enthalpy sen-
sor. When the OA temperature, OA humidity and OA dew
ECONOMIZING
AVAILABLE
NOT AVAILABLE
TEMPERATURE
ENTHALPY
TEMP. DRY
CURVE
BULB (F)
ES1
80
ES2
75
ES3
70
ES4
65
ES5
60
HL
86
Fig. 49 — Single Enthalpy Curve Boundaries
Table 12 — Single Enthalpy and Dual Enthalpy High Limit Curves
TEMP.
ENTHALPY
DEWPOINT (F)
(btu/lb/da)
60
57
54
51
48
66
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.
Figure 49 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 cool-
ing energized and HL (high limit) when a compressor stage is
energized.
POINT P1
TEMP. (F)
28.0
80
26.0
75
24.0
70
22.0
65
20.0
60
32.4
86
36
DUAL ENTHALPY
HIGH LIMIT
SINGLE ENTHALPY
P2 (T,RH)
P1
(T,RH)
ES4
ES2
ES5
ES3
POINT P2
HUMIDITY
TEMP. (F)
(%RH)
36.8
66.3
39.6
63.3
42.3
59.7
44.8
55.7
46.9
51.3
38.9
72.4
ES1
HL
HUMIDITY
(%RH)
80.1
80.0
81.4
84.2
88.5
80.3
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