54
ECONOMIZER CONTROL CONFIGURATIONS
Enthalpy Changeover Control
Economizer changeover based on outdoor air enthalpy requires an
outdoor air enthalpy sensor to replace the OAT sensor. The enthal-
py sensor is available as a factory-installed option or as a field-in-
stalled accessory (P/N HH57AC081). See Fig. 1 for model num-
ber nomenclature; check Position #15 for codes R or S indicating
a factory-installed enthalpy sensor. Use Fig. 72 and Table 10 to
select the enthalpy changeover setting to enter in menu item
SETPOINTS –> ENTH CURVE.
Enthalpy Settings
When the OA temperature, enthalpy and dew point are below the
respective setpoints, the Outdoor Air can be used for economiz-
ing. Fig. 72 shows the 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 10 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 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 72 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 10 provides the values for each boundary limit.
Fig. 72 — Single Enthalpy Curve Boundaries
Table 10 — 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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