Carrier 48FC M20 Series Service And Maintenance Instructions page 65

ENTHALPY SETTINGS
When the OA temperature, enthalpy and dew point are below
the respective set points, the Outdoor Air can be used for econ-
omizing. Figure 79 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 21 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.
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.
Economizing
Available
Not Available
Temperature
ENTHALPY TEMP. DRY
CURVE BULB (
°
ES1 80
ES2 75
ES3 70
ES4 65
ES5 60
HL 86
Fig. 79 — Single Enthalpy Curve Boundaries
Table 21 — Single Enthalpy and Dual Enthalpy High Limit Curves
TEMP. ENTHALPY
F) DEWPOINT ( F) (BTU/LB/DA)
°
60
57
54
51
48
66
When all of the OA conditions are above the selected bound-
ary, the conditions are not good to economize and the mode is
set to NO.
Figure 79 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.
Table 21 provides the values for each boundary limit.
POINT P1
TEMP. ( F)
°
28.0 80
26.0 75
24.0 70
22.0 65
20.0 60
32.4 86
65
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