Page 62
FIGURE 44
ACCESSORY
PANEL MULLION
DIVIDER PANEL
BOTTOM OF
COMPRESSOR
SECTION
FLANGED
RETURN AIR
OPENING
ECONOMIZER
ECONOMIZER
H-Economizer (all units)
(Field or Factory Installed)
The optional E1ECON15 economizer can be used with
downflow and horizontal air discharge applications. See
figure 44. The economizer uses outdoor air for free cooling
when outdoor temperature and/or humidity is suitable. The
economizer is controlled by the A55 Unit Controller.
Free Cooling Mode
The Unit Controller will allow free cooling in one of five
modes. Each mode uses different combinations of sensors
to determine outdoor air suitability. See table 24 for modes.
See figure 45 for factory-installed sensors. Temperature
offset is the default free cooling mode.
NOTE - All free cooling modes of operation will modu
late dampers to 55_F (13_C) supply / discharge air.
Unit Controller Settings
On early versions, switches are located on the Unit Con
troller to adjust settings. On newer versions, the display
and keypad on the Unit Controller are used to navigate
through menus to adjust settings. Some versions require
a configuration ID be entered to enable the economizer.
Refer to economizer installation instructions and Unit
Controller installation and application manuals.
TABLE 24
ECONOMIZER MODES AND SETPOINT
Free
Cooling
Mode
Free Cooling
Setpoint
Field-
Provided
Sensors
Dampers will modulate to 55°F (default, parameter 159)
discharge air (RT6) when outdoor air is suitable:
Input Ranges
TEMP OFFSET None Needed
Outdoor air temperature (RT17) is less than return air temperature (RT16)
by at least the OFFSET value (10
°F default; parameter 161).
0-40°F
TEMP OAT STPT None Needed
Outdoor air temperature (RT17) is less than the OAT STPT value (75°F
default; parameter 160).
41-75°F
Remote Remote
Energy
Management
System**
Either of the TEMP modes can be used when a network OAS signal is pro
vided by an energy management or building control system, via BACnet,
LonTalk, or L Connection. The network can command OAS, NOT OAS, or
AUTO. AUTO returns to local control of OAS, which is the selected TEMP
mode.
NA
ENTH DIFF OFFSET (Two) C7400
Outdoor air enthalpy* (A7) is less than return air enthalpy (A62) by at least
the OFFSET value (1mA = 2
°F default; parameter 163).
0mA-4mA
ENTH ODE STPT C7400
Outdoor air enthalpy (A7) is less than free cooling setpoint (12mA = 75°F
default, parameter 162).
12-19mA
GLOBAL GLOBAL
24VAC Input
Signal
Global input is energized by (P297-9). This setting is also used for outdoor
air damper applications. Global input also brings on the blower. (This mode
is NOT used when OAS signal is provided via network connection. GLO is
only used when a 24VAC signal is used to energize the P297-9 GLO input.)
NA
*Enthalpy includes effects of both temperature and humidity.
**Energy management systems may require additional field-provided sensors; refer to manufacturer's instructions.
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