5725848-XIM-A-0319
24 Johnson Controls Ducted Systems
Enthalpy settings
When the OA temperature, enthalpy and dew point are below
the respective setpoints, the Outdoor Air can be used for
economizing. Fig. 9 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 5 for the ENTH CURVE setpoint values.
To use enthalpy the W7220 must have a C7400S Sylkbus
sensor for OA. The W7220 calculates the enthalpy and dew
point using the OA temperature and humidity input from the OA
sensor. When the OA temperature, OA humidity and OA dew
point are all below the selected boundary, the economizer sets
the economizing mode to YES, economizing is available.
When conditions are above the selected boundary, the
conditions are not good to economize and the mode is set to
NO.
Fig. 9 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 when a compressor stage is energized.
Table 5 provides the values for each boundary limit.
Table 6: 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 80.0 60.0 28.0 80.0 36.8 66.3 80.1
ES2 75.0 57.0 26.0 75.0 39.6 63.3 80.0
ES3 70.0 54.0 24.0 70.0 42.3 59.7 81.4
ES4 65.0 51.0 22.0 65.0 44.8 55.7 84.2
ES5 60.0 48.0 20.0 60.0 46.9 51.3 88.5
HL 86.0 66.0 32.4 86.0 38.9 72.4 80.3
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