62
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 74 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 14 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.
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 74 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 14 provides the values for each boundary limit.
Fig. 74 — Single Enthalpy Curve Boundaries
Table 14 — Single Enthalpy and Dual Enthalpy High Limit Curves
Economizing
Available
Not Available
Enthalpy
RA Hum (%RH)
RA Temp
Temperature
Absolute Humidity
ES5
ES4
ES3
ES2 ES1
HL
P1
(T,RH)
P2 (T,RH)
Single Enthalpy
Dual Enthalpy
High Limit
ENTHALPY
CURVE
TEMP. DRY
BULB (°F)
TEMP.
DEWPOINT (°F)
ENTHALPY
(BTU/LB/DA)
POINT P1 POINT P2
TEMP. (
°F)
HUMIDITY
(%RH)
TEMP. (°F)
HUMIDITY
(%RH)
ES1 80 60 28.0 80 36.8 66.3 80.1
ES2 75 57 26.0 75 39.6 63.3 80.0
ES3 70 54 24.0 70 42.3 59.7 81.4
ES4 65 51 22.0 65 44.8 55.7 84.2
ES5 60 48 20.0 60 46.9 51.3 88.5
HL 86 66 32.4 86 38.9 72.4 80.3
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