Lennox ALLIED Commercial TCA180S2B Standard Manual page 39

1− Set thermostat to occupied mode if the feature is avail-
able. Make sure jumper is in place between A45 con-
trol board TB1 terminals A1 and A2 if using a thermo-
stat which does not have the feature.
2− Rotate MIN POS SET potentiometer to approximate
desired fresh air percentage.
Note − Damper minimum position can be set lower than
traditional minimum air requirements when an IAQ sensor
is specified. Dampers will open to DCV MAX setting (if CO2
is above setpoint) to meet traditional ventilation require-
ments.
3− Measure outdoor air temperature. Mark the point on
the bottom line of chart 1 and label the point A" (40_F,
4_C shown).
4− Measure return air temperature. Mark that point on the
top line of chart 1 and label the point B" (74_F, 23_C
shown).
5− Measure mixed air (outdoor and return air) tempera-
ture. Mark that point on the top line of chart 1 and label
point C" (70_F, 21_C shown).
6− Draw a straight line between points A and B.
7− Draw a vertical line through point C.
8− Draw a horizontal line where the two lines meet. Read
the percent of fresh air intake on the side.
9− If fresh air percentage is less than desired, adjust MIN
POS SET potentiometer higher. If fresh air percentage
is more than desired, adjust MIN POS SET potentiom-
eter lower. Repeat steps 3 through 8 until calculation
reads desired fresh air percentage.
DCV Set and Max Settings
Adjust settings when an optional IAQ sensor is installed.
The DCV SET potentiometer is factory−set at approxi-
mately 50% of the potentiometer range. Using a standard
1−2000ppm CO sensor, dampers will start to open when
2
the IAQ sensor reads approximately 1000ppm. Adjust
the DCV SET potentiometer to the approximate setting
specified by the controls contractor. Refer to figure 24.
The DCV MAX potentiometer is factory−set at approxi-
mately 50% of the potentiometer range or 6VDC. Damp-
ers will open approximately half way when CO
above setpoint. Adjust the DCV MAX potentiometer to
the approximate setting specified by the controls con-
tractor. Refer to figure 24.
Note − DCV Max must be set higher than economizer mini-
mum position setting for proper demand control ventilation.
The occupied time period is determined by the thermostat
or energy management system.
During the unoccupied time period dampers are closed.
During the occupied time period a cooling demand will
open dampers to minimum position and mechanical cool-
ing functions normally. See table 18.
During the occupied time period dampers will open to DCV
MAX when IAQ reading is above setpoint (regardless of
thermostat demand or outdoor air suitability).
See table 19 for economizer operation with a standard
three−stage thermostat.
During the occupied period, dampers will open to DCV
MAX when IAQ reading is above setpoint (regardless of
thermostat demand or outdoor air suitability). DCV MAX
will NOT override damper full−open position. When an R1
mixed air sensor for modulating dampers is installed, DCV
MAX may override damper free cooling position when oc-
cupancy is high and outdoor air temperatures are low. If R1
senses discharge air temperature below 45_F (7_C),
dampers will move to minimum position until discharge air
temperature rises to 48_F (9_C).
B−Outdoor Air Dampers
T1DAMP20 used on TCA units consists of a set of dampers
which may be manually or motor (M) operated to allow out-
side air into the system (see figure 27). Either air damper
can be installed in TCA units.The motorized damper as-
sembly opens to minimum position during the occupied
time period and remains closed during the unoccupied
rises
period. Manual damper assembly is set at installation
2
and remains in that position. See figure 25. Washable fil-
ter supplied with the outdoor air dampers can be cleaned
with water and a mild detergent. It should be sprayed with
Filter Handicoater when dry prior to reinstallation. Filter
Handicoater is R.P. Products coating no. 418.
Page 39
Economizer Operation
Outdoor Air Not Suitable:
Outdoor Air Suitable: