Trane LPC Install And Operation Instructions page 67

Assume a thumbwheel setpoint input of
73°F , resulting in an absolute setpoint
offset of 1°F (73–72=1). The controller
adds the absolute setpoint offset (1°F) to
occupied and occupied standby default
setpoints to derive the effective setpoints,
as follows.
• Unoccupied cooling setpoint 85°F (same
as default)
• Occupied standby cooling setpoint 77°F
(default+1=77)
• Occupied cooling setpoint 75°F
(default+1=75)
• Occupied heating setpoint 71°F
(default+1=71)
• Occupied standby heating setpoint 67°F
(default+1=67)
• Unoccupied heating setpoint 60°F (same
as default)
When a building automation system or
other controller communicates a setpoint
to the controller, the controller ignores the
hard-wired setpoint input and uses the
communicated value. The exception is
the unoccupied mode, when the control-
ler always uses the stored default
unoccupied setpoints.
After the controller completes all setpoint
calculations based on the requested
setpoint, the occupancy mode, the
heating and cooling mode, and other
factors, the calculated setpoint is vali-
dated against the following setpoint limits:
• Heating setpoint high limit
• Heating setpoint low limit
• Cooling setpoint high limit
• Cooling setpoint low limit
LPC-SVX01C-EN
Operation
These setpoint limits only apply to the
occupied and occupied standby heating
and cooling setpoints. These setpoint
limits do not apply to the unoccupied
heating and cooling setpoints stored in
the controller configuration.
Unit configuration also exists to enable or
disable the local (hard-wired) setpoint at
the zone sensor module. This parameter
provides additional flexibility to allow you
to apply communicated, hard-wired, or
default setpoints without having to make
physical wiring changes to the controller.
Discharge air temperature control
The controller requires a discharge air
temperature sensor (10Ω thermistor
only) to operate in the discharge air
temperature control mode.
Discharge air temperature control
modulates the heating or cooling outputs
to maintain discharge air temperature at
the discharge air temperature
setpoint regardless of the entering air
conditions of the air-handling
unit.
Figure O-SO-4 shows the steps the Tracer
AH540/541 controller takes to control
discharge air. First the controller deter-
Table O-SO-4. Example of configuration parameters
Dishcharge-air cooling setpoint
Maximum discharge-air cooling setpoint
Minimum discharge-air cooling setpoint
Discharge-air heating setpoint
Maximum discharge-air heating setpoint
Minimum discharge-air heating setpoint
Note1. When the controller is applied to an air-handling unit with a draw-through supply fan,
the maximum discharge-air heating setpoint should be set to 104ºF (default setpoint). This
prevents the discharge air temperature from exceeding the high temperature limit of the
supply fan motor. Exceeding the motor temperature limit can cause premature failures.
Table O-SO-5. Example of communicated values
Discharge-air cooling setpoint input
Discharge-air heating setpoint input
Effective heat cool mode
sequence of
operation
mines if a communicated discharge-air
heating setpoint and discharge-air cooling
setpoint are present. The communicated
setpoint has precedence over the
configured (default) setpoint. If no
communicated value is present, the
controller uses the configured discharge
air temperature setpoint.
Discharge air temperature setpoint
minimum and maximum limits are
placed on the discharge air setpoint
depending on the effective heat or cool
mode. If the effective heat/cool mode is
cool, the maximum discharge air cooling
setpoint limit and minimum discharge-air
cooling setpoint limit the discharge-air
cooling setpoint.
The effective discharge air temperature
setpoint is determined from:
• Communicated or configured discharge
air temperature setpoint value
• Minimum and maximum heat/cool
setpoint limits
• Effective heat/cool mode
See Table O-SO-4 and Table O-SO-5 for
an example of how the controller
determines the effective discharge air
temperature setpoint.
55°F (18.2°C)
68ºF (20.0ºC)
50ºF (10.0ºC)
100ºF (37 .8ºC)
104ºF (40.0ºC)
1
86ºF (30.0ºC)
50°F (10.0ºC)
None
Cool
67