Enthalpy Settings; Two- -Speed Fan Operation - Carrier 50TCQD14 Installation Instructions Manual

ECONOMIXING
AVAILABLE
NOT AVAILABLE
TEMPERATURE
Table 21 – Single Enthalpy and Dual Enthalpy High Limit Curves (EN Units)
Enthalpy Temp.
Curve Dry---Bulb (_F)
ES1 80.0
ES2 75.0
ES3 70.0
ES4 65.0
ES5 60.0
HL 86.0

Enthalpy Settings

When the OA temperature, enthalpy and dew point are
below the respective setpoints, the outdoor air can be used
for economizing. Fig. 47 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 21 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 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.
Fig. 47 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 21 provides the values for each boundary limit.
Fig. 47 - - Single Enthalpy Curve and Boundaries
Temp. Enthalpy
Dewpoint (_F) (btu/lb/da)
60.0 28.0
57.0 26.0
54.0 24.0
51.0 22.0
48.0 20.0
66.0 32.4
SINGLE ENTHALPY
ES5
Point P1
Temp. (_F) Humidity %RH
80.0 36.8
75.0 39.6
70.0 42.3
65.0 44.8
60.0 46.9
86.0 38.9

Two- -Speed Fan Operation

The W7220 controller has the capability to work with a
system using 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 position.
State
OCC
Y1
Y2
W
The W (heating mode) is not controlled by the W7220 but
it requires 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 Advanced 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:
40
DUAL ENTHALPY
HIGH LIMIT
P2 (T,RH)
P1
(T,RH)
ES4 ES3 ES2 ES1
Point P2
Temp. (_F) Humidity %RH
66.3 80.1
63.3 80.0
59.7 81.4
55.7 84.2
51.3 88.5
72.4 80.3
Fan Speed
Low
Low
High
High
HL
C12015