Lennox LGM Series Manual page 45

H-Economizer (all units)
(Field or Factory Installed)
The optional E1ECON15 economizer can be used with
downflow and horizontal air discharge applications. See
figure 36. 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 21 for modes.
See figure 37 for factory-installed sensors. Temperature
offset is the default free cooling mode.
Free
Free Cooling
Cooling
Setpoint
Mode
TEMP OFFSET
TEMP OAT STPT
Remote Remote
ENTH DIFF OFFSET
ENTH ODE STPT
GLOBAL GLOBAL
*
Enthalpy includes effects of both temperature and humidity.
**Energy management systems may require additional field-provided sensors; refer to manufacturer's instructions.
ECONOMIZER MODES AND SETPOINT
Field-
Dampers will modulate to 55
Provided
discharge air (RT6) when outdoor air is suitable:
Sensors
Outdoor air temperature (RT17) is less than return air temperature (RT16)
None Needed
by at least the OFFSET value (10
Outdoor air temperature (RT17) is less than the OAT STPT value (75
None Needed
default; parameter 160).
Either of the TEMP modes can be used when a network OAS signal is pro­
Energy vided by an energy management or building control system, via BACnet,
Management
LonTalk, or L Connection. The network can command OAS, NOT OAS, or
System** AUTO. AUTO returns to local control of OAS, which is the selected TEMP
mode.
Outdoor air enthalpy* (A7) is less than return air enthalpy (A62) by at least
(Two) C7400
the OFFSET value (1mA = 2
Outdoor air enthalpy (A7) is less than free cooling setpoint (12mA = 75
C7400
default, parameter 162).
Global input is energized by (P297-9). This setting is also used for outdoor
24VAC Input air damper applications. Global input also brings on the blower. (This mode
Signal
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.)
ECONOMIZER
ECONOMIZER
FIGURE 36
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 configu­
ration ID be entered to enable the economizer. Refer to
economizer installation instructions and Unit Controller in­
stallation and application manuals.
TABLE 21
°
F (default, parameter 159)
°
F default; parameter 161).
°
F default; parameter 163).
Page 45
ACCESSORY
PANEL MULLION
DIVIDER PANEL
BOTTOM OF
COMPRESSOR
SECTION
FLANGED
RETURN AIR
OPENING
Input Ranges
°
F
0mA-4mA
°
F
°
0-40 F
°
41-75 F
NA
12-19mA
NA