Trane LPC, Install And Operation Instructions

Page: 66 / 110

66 LPC-SVX01C-EN
Operation
sequence of
operation
Point 2 on the curve indicates the active
heat setpoint. The space temperature
must fall below the active heat setpoint
before the controller can change to
heating. Conversely, the space
temperature must rise above the active
cooling setpoint before the controller can
change to cooling.
Point 3 on the curve indicates the point at
which the controller switches to heat
(from cool) after the error integrator
exceeds 900°F • seconds.
The controller must be able to heat
before it will switch to heat. A unit that
cannot heat will not switch to heat. A unit
that cannot cool will not switch to cool.
Heat/cool changeover: error integration
example
If the active space temperature is 66.5°F,
the current mode is cooling, the cooling
capacity is 0°F, and the space cooling
setpoint is 70°F. The error calculation is 70
– 0.5 – 66.5 = 3°F. If the same error exists
for 60 seconds, the error integration term
is (3°F • 60 seconds = 180°F seconds).
Therefore, after five minutes (3°F • 300
seconds = 900°F seconds), the controller
will switch from cooling to heating mode
if the space temperature is below the
occupied heating setpoint.
Cooling operation
The heating and cooling space setpoint
high and low limits are always
applied to the occupied and occupied
standby setpoints. During the cooling
mode, the Tracer AH540/541 controller
attempts to maintain the active space
temperature at the active space cooling
setpoint. Based on the controller
occupancy mode, the active space
cooling setpoint is one of the following:
• Occupied cooling setpoint
• Occupied standby cooling setpoint
• Unoccupied cooling setpoint
Cooling outputs are controlled based on
unit configuration and required machine
cooling capacity. At 0% machine cooling
capacity, the cooling valve closes and the
outdoor air damper is at its minimum
position. As the required machine cooling
capacity increases, the cooling valve and/
or the outdoor air damper opens above
their minimum positions.
The discharge air temperature control
algorithm calculates a desired discharge
air temperature to maintain the space
cooling setpoint. Cool capacity is con-
trolled to achieve the desired discharge
air setpoint. Heat capacity can also be
used to temper cold outdoor air condi-
tions to maintain ventilation and the
discharge air setpoint.
The outdoor air damper provides cooling
whenever economizing is possible and
there is a need for cooling. If economizing
is not possible, it will not be used in
cooling. If economizing is possible, it is
always the first stage of cooling. See
“Outdoor air damper operation” section
for more information.
Heating operation
In the heating mode, the Tracer AH540/
541 controller attempts to maintain the
space temperature at the active heating
setpoint. Based on the controller
occupancy mode, the active space
heating setpoint is one of the following:
• Occupied heating setpoint
• Occupied standby heating setpoint
• Unoccupied heating setpoint
The outputs are controlled based on the
unit configuration and the required
machine heating capacity. At 0% ma-
chine heating capacity, heating capacity is
at its minimum position. As the required
machine heating capacity increases,
heating capacity opens above its mini-
mum position. At 100% machine heating
capacity, heating capacity opens to its
maximum position.
The economizer outdoor air damper is
never used as a source of heating. It is
used only for ventilation when the unit is
heating. For more information, see
“Outdoor air damper operation” section.
Space temperature setpoint arbitration
The space temperature setpoint is
communicated by a building automation
system or peer-to-peer using a binding
(see “Communication with other
controllers”). When the Tracer AH540/541
is in occupied mode, occupied standby
mode, or occupied bypass mode, a
communicated setpoint takes
precedence over a local (hard-wired)
setpoint.
When neither a communicated nor a
local (hard-wired) setpoint is present, the
controller uses the locally stored default
heating and cooling setpoints.
The exception is when the controller is in
unoccupied mode. Then the controller
always uses locally stored default
unoccupied setpoints. These setpoints are
configured at the factory prior to ship-
ment. Use the Rover service tool to
modify these default unoccupied
setpoints.
Zone sensor setpoint thumbwheel
Zone sensors with an internal or external
setpoint thumbwheel (1
Ω
) provide the
Tracer AH540/541 controller with a local
setpoint (50ºF to 85ºF [10ºC to 29.4ºC]).
An internal setpoint thumbwheel is
concealed under the front cover of the
zone sensor. To access it, remove the
zone sensor cover. An external setpoint
thumbwheel (when present) is accessible
from the front cover of the zone sensor.
When the local (hard-wired) setpoint
thumbwheel is used to determine the
setpoints, all unit setpoints are calculated
based on the local setpoint value, the
configured setpoints, and the active
mode of the controller.
For example, assume the controller is
configured with the following default
setpoints:
• Unoccupied cooling setpoint 85°F
(29.4ºC)
• Occupied standby cooling setpoint 76°F
(24.4ºC)
• Occupied cooling setpoint 74°F (23.3ºC)
• Occupied heating setpoint 70°F (21.1ºC)
• Occupied standby heating setpoint 66°F
(18.9ºC)
• Unoccupied heating setpoint 60°F
(15.6ºC)
Absolute Setpoint Offset = Setpoint Input
– Mean Setpoint
From the default setpoints in this ex-
ample, the mean setpoint is the mean of
the occupied cooling and heating
setpoints, which is 72°F [(74+70) / 2]. The
absolute setpoint offset is the difference
between the setpoint input and the mean
setpoint.