36
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. 51 shows the new single enthalpy bound-
aries in the W7220. There are 5 boundaries (setpoints ES1
through ES5), which are defined by dry bulb temperature, en-
thalpy 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 sensor. When the OA temperature, OA humidity and
OA dew point are all below the selected boundary, the econo-
mizer 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 51 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
cooling energized and HL (high limit) when a compressor
stage is energized.
Fig. 51 — Single Enthalpy Curve Boundaries
Table 12 — Single Enthalpy and Dual Enthalpy High Limit Curves
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
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
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