Bryant Preferred 549K 04-06 Service And Maintenance Instructions page 47

Enthalpy Settings
When the OA temperature, enthalpy and dew point are below
the respective setpoints, the Outdoor Air can be used for econ-
omizing. Figure 70 shows the new single 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 18 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
ECONOMIZING
AVAILABLE
NOT AVAILABLE
TEMPERATURE
ENTHALPY TEMP. DRY
CURVE BULB (F)
ES1 80
ES2 75
ES3 70
ES4 65
ES5 60
HL 86
Fig. 70 — Single Enthalpy Curve Boundaries
Table 18 — Single Enthalpy and Dual Enthalpy High Limit Curves
TEMP. ENTHALPY
DEWPOINT (F) (btu/lb/da)
60 28.0
57 26.0
54 24.0
51 22.0
48 20.0
66 32.4
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 bound-
ary, the conditions are not good to economize and the mode is
set to NO.
Figure 70 shows the 5 current boundaries. There is also a high
limit boundary for differential enthalpy. The high limit bound-
ary is ES1 when there are no stages of mechanical cooling en-
ergized and HL (high limit) when a compressor stage is
energized.
POINT P1
HUMIDITY
TEMP. (F)
(%RH)
80 36.8
75 39.6
70 42.3
65 44.8
60 46.9
86 38.9
47
DUAL ENTHALPY
HIGH LIMIT
SINGLE ENTHALPY
P2 (T,RH)
P1
(T,RH)
ES4 ES2 ES1
ES5 ES3
POINT P2
HUMIDITY
TEMP. (F)
(%RH)
66.3
63.3
59.7
55.7
51.3
72.4
HL
80.1
80.0
81.4
84.2
88.5
80.3