Carrier 50KC04-06 Service And Maintenance Instructions page 48

ENTHALPY SETTINGS
When the OA temperature, enthalpy and dew point are below the
respective set points, the Outdoor Air can be used for economiz-
ing. Figure 62 shows the new single enthalpy boundaries in the
W7220. There are 5 boundaries (set points ES1 through ES5),
which are defined by dry bulb temperature, enthalpy and dew
point.
Refer to Table 18 for ENTH CURVE set point values.
The W7220 calculates the enthalpy and dew point using the OA
temperature and humidity input from the OA enthalpy sensor.
ECONOMIZING
AVAILABLE
NOT AVAILABLE
TEMPERATURE
ENTHALPY TEMP. DRY
CURVE BULB (F)
ES1
80
ES2
75
ES3
70
ES4
65
ES5
60
HL
86
Fig. 62 — Single Enthalpy Curve Boundaries
Table 18 — Single Enthalpy and Dual Enthalpy High Limit Curves
TEMP. ENTHALPY
DEWPOINT (F) (btu/lb/da)
60
57
54
51
48
66
When the OA temperature, OA humidity and OA dew point are
all below the selected boundary, the economizer sets the econo-
mizing 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 62 shows the 5 current boundaries. There is also a high lim-
it 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.
POINT P1
TEMP. (F)
28.0 80
26.0 75
24.0 70
22.0 65
20.0 60
32.4 86
48
DUAL ENTHALPY
HIGH LIMIT
SINGLE ENTHALPY
P2 (T,RH)
P1
(T,RH)
ES4 ES3 ES2
ES5
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