Carrier WeatherMaster 50HC14 Installation Instructions Manual page 37

ECONOMIZING
AVAILABLE
NOT AVAILABLE
TEMPERATURE
Table 18 — Single Enthalpy and Dual Enthalpy High Limit Curves
ENTHALPY TEMP. DRY
CURVE BULB (F)
ES1 80
ES2 75
ES3 70
ES4 65
ES5 60
HL 86
ENTHALPY SETTINGS
When the OA temperature, enthalpy and dew point are below
the respective setpoints, the Outdoor Air can be used for econo-
mizing. Figure 53 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 18 for ENTH CURVE setpoint values.
The W7220 calculates the enthalpy and dew point using
the OA temperature and humidity input from the OA enthal-
py sensor. When the OA temperature, OA humidity and OA
dew point are all below the selected boundary, the economiz-
er sets the economizing mode to YES and 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 53 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 18 provides the values for each boundary limit.
TWO-SPEED FAN OPERATION
The W7220 controller has the capability to work with a sys-
tem using a 2-speed supply fan. The W7220 does not control
the supply directly but uses the following input status to deter-
mine the speed of the supply fan and controls the OA damper
to the required position, see Table 19.
Table 19 — Fan Speed
STATE
OCC
Y1
Y2
W
Fig. 53 — Single Enthalpy Curve Boundaries
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
FAN SPEED
Low
Low
High
High
POINT P1
HUMIDITY
TEMP. (F)
(%RH)
80 36.8
75 39.6
70 42.3
65 44.8
60 46.9
86 38.9
The W (heating mode) is not controlled by the W7220 but
it requires the status to know where to position the OA damp-
er for minimum position for the fan speed.
The 2-speed fan delay is available when the system is pro-
grammed 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:
• 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.
CHECKOUT
Inspect all wiring connections at the economizer module's
terminals, and verify compliance with the installation wiring dia-
grams.
For checkout, review the Status of each configured param-
eter and perform the Checkout tests.
NOTE: For information about menu navigation and use of the
keypad, see Interface Overview on page 27.
37
DUAL ENTHALPY
HIGH LIMIT
SINGLE ENTHALPY
P2 (T,RH)
P1
(T,RH)
ES4 ES3 ES2 ES1
ES5
POINT P2
HUMIDITY
TEMP. (F)
(%RH)
66.3
63.3
59.7
55.7
51.3
72.4
HL
80.1
80.0
81.4
84.2
88.5
80.3