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ECONOMIZING
AVAILABLE
NOT AVAILABLE
TEMPERATURE
Table 17 — 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, en-
thalpy and dew point are below the respective setpoints, the
Outdoor Air can be used for economizing. Fig. 41 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 17 for ENTH CURVE setpoint values.
The W7220 calculates the enthalpy and dew point using the
OA temperature and humidity input from the OA enthalpy sen-
sor. 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. 41 shows the 5 current boundaries. There is also a high
limit boundary for differential enthalpy. The high limit bound-
ary is ES1 when there are no stages of mechanical cooling en-
ergized and HL (high limit) when a compressor stage is ener-
gized.
Table 17 provides the values for each boundary limit.
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, see
Table 18.
Table 18 — Fan Speed
STATE
OCC
Y1
Y2
W
Fig. 41 — 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 damper
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 diagrams.
For checkout, review the Status of each configured parame-
ter and perform the Checkout tests.
NOTE: For information about menu navigation and use of the
keypad see Interface Overview on page 22.
32
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
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