Economizer (Damper) - Lennox LGH 036 Installation Instructions Manual

Economizer (Damper)

General
The economizer, when configured, controls
S
damper position, which determines how much outdoor
air is used to meet free cooling or indoor air quality (IAQ)
requirements, and
S
the optional power exhaust fans.
On a cooling demand, outdoor air is used for free cooling
instead of first-stage compressor(s) when outdoor air is
suitable (OAS).
Outdoor Air Suitable (OAS) LED (Early M2 hardware)
A yellow LED which is labeled OAS provides economizer
status. A steady yellow LED indicates that outdoor air is
suitable for free cooling. A flashing yellow OAS light indicates
the IAQ sensor requires outdoor air. (A flashing yellow LED
can also mean that the economizer dampers are open to
bring in fresh air while a compressor is on.) If the economizer
is already operating, a flashing yellow OAS light indicates the
IAQ sensor requires more outdoor air than is suitable for free
cooling.
DIP Switch Settings (Early M2 hardware)
The DIP switch setting determines the mode used to enable
free cooling. The DIP switch also has a mode to set the
damper minimum position and test damper operation. DIP
switch is factory-set
factory-configured.
Free Cooling Discharge Air Setpoint
When outdoor air conditions are suitable and economizer is
set to provide free cooling, dampers will modulate to achieve
a discharge air temperature of 55°F (13°C) default. This
setpoint is adjustable between 45° and 65°F.
The setpoint can also be automatically increased when
outdoor or return air temperatures drop. See Outdoor Air
Reset and Return Air Reset in the Discharge Air Control
section in the Prodigy Application Guide (Advanced
Features) manual. These settings must be enabled and
adjusted using the Prodigy CONTROL/ECTO menu to make
changes to ECTO values. Refer to the Prodigy Application
Guide. The unit does not have to be operating in discharge air
cooling mode to adjust the free cooling discharge air setpoint,
or to use setpoint reset.
The recommended enthalpy
setpoint is "A". If the econom­
izer is allowing air which is too
warm or too humid to enter the
system, the enthalpy control
may be changed to a lower set­
ting (B, C, or D).
when the economizer
Table 5. Enthalpy Control Setpoints
Control Enthalpy Control Setpoint At 50% Relative Humidity Ap­
Setting
A
B
C
D
During free cooling operation, the damper modulates to
maintain a discharge air temperature equal to the free
cooling discharge air setpoint. If the damper has been
continuously at its maximum open position for at least three
minutes, then a second stage cooling demand will be allowed
to turn on the first stage of mechanical cooling. While the
mechanical cooling is on, the damper is held to its maximum
position, and does not modulate until the second stage
demand is satisfied. On a third stage cooling demand, the
second stage of mechanical cooling will be turned on.
Outdoor Air Suitability
There are five modes which can be used to determine if the
outdoor conditions will enable free cooling.
S
Old hardware: DIP switch is set to
ODE (Outdoor Enthalpy), and the
Enthalpy Setpoint potentiometer
is set A-through-D.
S
New hardware: Configuration is
set to Single
Economizer Control and ECTO 6.26 setpoint value is
set to between 12 and 19mA, 150 to 240 counts.
Enthalpy Setpoint
This setting pertains to the ODE free cooling mode only. The
M2 will enable free cooling when outdoor air enthalpy (A7) is
less than the enthalpy setpoint. Table 5 shows the
is
approximate enthalpy setpoints for each potentiometer
setting at 50% relative humidity. The ECTO 6.26 column is
the correlating values used in the new hardware.
Example:—At setting "A", the enthalpy control will modulate
dampers open when outdoor air is at 73°F and 50% relative
humidity. If space temperatures are too warm, rotate the
potentiometer to "B" (old hardware) or enter a count of 173
(ECTO 6.26 if new hardware). The enthalpy control will now
modulate dampers open when outdoor air is 70°F and 50%
relative humidity.
NOTE - When in outdoor enthalpy mode, a value between
130-240 counts is entered. When in differential enthalpy
mode a 2mA (or 26 count) difference between outdoor and
indoor enthalpy corresponds to about a 3.5°F difference in
temperature at constant relative humidity (or about a 12%RH
difference at constant temperature). When in differential
enthalpy mode, a value between 0-75 counts is entered.
proximate Degrees F (C)
73 (23)
70 (21)
67 (19)
63 (17)
Page 23
Enthalpy
ECTO 6.26
cnt (mA)
150 (11.8)
173 (13.6)
199 (15.5)
224 (17.6)