10
Fig. 13 - Single Enthalpy Curve boundaries
Table 8 - Single Enthalpy and Dual Enthalpy High Limit Curves
Enthalpy Settings
When the OA temperature, enthalpy and dew point are below the
respective setpoints, the Outdoor Air can be used for economizing. Fig.
13 shows the new single enthalpy boundaries in the W7220. There are
5 boundaries (setpoints ES1 thru ES5), which are defined by dry bulb
temperature, enthalpy and dew point.
Refer to Table 8 for ENTH CURVE setpoint values.
To use enthalpy the W7220 must have a HH57AC081 enthalpy control
sensor for OA. The W7220 calculates the enthalpy and dewpoint 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 all of the OA conditions are above the selected boundary, the
conditions are not good to economize and the mode is set to NO.
Enthalpy
Curve
Temp.
Dry Bulb (
o
F)
Temp.
Dewpoint (
o
F)
Enthalpy
(btu/lb/da)
Point P1
Point P2
Temp (
o
F)
Humidity %RH
Temp (
o
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
Fig. 13 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.
Table 8 provided the values for each boundary limit.
Enthalpy control Sensor Configuration
The Enthalpy Control sensor (Part Number: HH57AC081)
communicates with the W7220 Economizer controller on the two-wire
communications bus and can either be wired using a two pin header or
using a side connector. This sensor is used for all OAT (Outdoor Air
Temperature), RAT (Return Air Temperature), and DAT (discharge Air
Temperature), depending on how its three position DIP switch is set.
Use Fig. 13 and Table 9 to locate the wiring terminals for each Enthalpy
Control sensor.
Use Fig. 13 and Table 10 to set the DIP switches for the desired use of
the sensor.
