Carrier 50FC 08-16 Series Service And Maintenance Instructions page 55

Enthalpy Settings
When the OA temperature, enthalpy and dew point are below the
respective setpoints, the Outdoor Air can be used for economiz-
ing. Figure 77 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 14 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 bound-
ary, the conditions are not good to economize and the mode is
set to NO.
Figure 77 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.
2 Speed Fan Operation
The W7220 controller has the capability to work with a system us-
ing a 2 speed supply fan. The W7220 does not control the supply
directly but uses the following input status to determine the speed
of the supply fan and controls the OA damper to the required posi-
tion, see Table 13.
Economizing
Available
Not Available
Temperature
ENTHALPY TEMP. DRY
CURVE BULB (°F)
ES1 80
ES2 75
ES3 70
ES4 65
ES5 60
HL 86
Fig. 77 — Single Enthalpy Curve Boundaries
Table 14 — Single Enthalpy and Dual Enthalpy High Limit Curves
TEMP. ENTHALPY
DEWPOINT (°F) (BTU/LB/DA)
60 28.0
57 26.0
54 24.0
51 22.0
48 20.0
66 32.4
Table 13 — Fan Speed
STATE
OCC
Y1
Y2
W
The W (heating mode) is not controlled by the W7220 but it re-
quires the status to know where to position the OA damper for
minimum position for the fan speed.
The 2 speed fan delay is available when the system is programmed
for 2 speed fan (in the System Setup menu item). The 2 speed fan
delay is defaulted to 5 minutes and can be changed in the Ad-
vanced Setup menu item. When the unit has a call for Y1 In and in
the free cooling mode and there is a call for Y2 In, the 2-speed fan
delay starts and the OA damper will modulate 100% open, the
supply fan should be set to high speed by the unit controller.
After the delay one of two actions will happen:
• The Y2 In call will be satisfied with the damper 100%
open and fan on high speed and the call will turn off
OR
• If the call for additional cooling in the space has not been
satisfied then the first stage of mechanical cooling will be
enabled through Y1 Out or Y2 Out.
Refer to Table 15 for economizer operation.
POINT P1
HUMIDITY
TEMP. (°F)
(%RH)
80 36.8
75 39.6
70 42.3
65 44.8
60 46.9
86 38.9
55
FAN SPEED
Low
Low
High
High
Dual Enthalpy
High Limit
Single Enthalpy
P2 (T,RH)
P1
(T,RH)
ES4 ES3 ES2 ES1
ES5
POINT P2
HUMIDITY
TEMP. (°F)
66.3
63.3
59.7
55.7
51.3
72.4
HL
(%RH)
80.1
80.0
81.4
84.2
88.5
80.3