Trane LPC Install And Operation Instructions page 75

Cool-down
In cool-down operation the controller
closes the outdoor air damper eliminating
any additional cooling load due to warm
outdoor temperatures. Normally the
outdoor air damper is closed in this mode
of operation and hydronic or mechanical
cooling is provided to cool-down the
space. However if the outdoor air
temperature is suitable economizer
cooling is allowed.
The Tracer AH540/541 controller oper-
ates this sequence according to the
configured control mode.
Space temperature control: Cool-down
If configured for space temperature
control, the controller provides an
automatic cool-down function on a
transition from unoccupied to occupied or
occupied standby mode of operation.
Cool-down is initiated and the outdoor air
damper remains closed if space
temperature is greater than 3ºF above
the active cooling setpoint. As the space
temperature decreases below this
threshold, the outdoor damper
progressively opens toward the
minimum position setpoint. When the
space temperature is within 2ºF of the
effective cooling setpoint, the outdoor
damper will be at the occupied or
occupied-standby minimum position
setpoint.
Cool-down can also be initiated by a
building automation system with a mode
command of pre-cool (optimal-start). The
controller will stay in the pre-cool until the
mode is removed by the system. A
heating-only air-handling-unit configura-
tion, with no cooling capacity, disables the
automatic cool-down function. The
outdoor air damper (if present) will open
to minimum position and provide
economizing, if enabled.
Discharge air temperature control: Cool-
down
If configured for discharge air
temperature control, the controller enters
a cool-down mode only when
coordinated by a building automation
system (optimal-start). In cool-down, the
controller's heat-cool mode is reported
LPC-SVX01C-EN
Operation
as pre-cool. The controller will stay in the
pre-cool until the mode is removed by the
automation system.
Supply fan operation
The controller determines fan operation
based on the selected control mode. If the
controller is configured for space
temperature control, the supply fan
operates in constant-volume. If
configured for discharge air temperature
control, the supply fan can be configured
to operate either with constant-volume or
variable-air-volume.
With both constant-volume and variable-
air volume supply fan operation, the
controller turns the supply fan binary
output (BO1) On continuously during
occupied, occupied standby, and occupied
bypass modes.
During the unoccupied heating and
cooling modes of operation, the supply
fan will cycle Off when the space tem-
perature is between the heating and
cooling setpoints. If electric heat is
energized during unoccupied heating
periods of operation, the supply fan will
run for an additional 120 seconds after
electric heat capacity is de-energized. The
supply fan is normally Off during air-
handler operation with the following
exceptions:
• During unoccupied mode when there is
no requirement for heating and cooling
• When entering water temperature
sampling is initiated
• As a result of certain diagnostic
conditions
• During manual or system overrides
If a supply fan status binary input sensor
is wired to the controller (at IN10) it is
used to verify fan operation before
heating and cooling start.
Upon energizing the supply fan output
BO1, the Tracer AH540/541 controller
waits a configurable time period (fan
status delay) to allow the fan time to
reach a desired air flow. Then the
controller verifies fan operation (fan
status).
sequence of
operation
A Low Supply Fan Air Flow diagnostic is
generated if the controller powers the fan
On and the fan status switch is not in the
fan running position, or if the fan status
switch is not set to make the fan run
within the configured time limit after the
controller commands the fan On. This
latching diagnostic discontinues unit
operation until the diagnostic is cleared
from the controller. Fan operation can
also be affected by other diagnostic
conditions that cause the controller to
shut down the unit.
Constant-volume supply fan operation
For constant-volume supply fan
operation, the controller must be
configured either for space temperature
control or for discharge air temperature
control with constant-volume.
In constant-volume operation, the fan
runs continuously during occupied,
occupied standby, and occupied bypass
modes of operation, except when the
controller is in occupied mode and turns
the fan Off during entering water sam-
pling periods. During unoccupied periods,
the supply fan binary output BO1 controls
the supply fan Off and On depending on
heating or cooling requirements. The
supply fan is normally Off during unoccu-
pied modes of operation when space
temperature is between the unoccupied
heating and cooling setpoints.
If the controller is wired to a Trane zone
sensor, the user can change the supply
fan operation through the fan mode
switch (when present). When the fan
mode switch is in the Off position, the
controller shuts down the unit. If the fan
mode switch is moved to the Auto
position, the controller operates the fan
On and Off according to heat and cool
demands and the active occupancy
mode.
Variable-air-volume supply fan operation:
Duct static pressure
For variable-air-volume supply fan
operation, the controller must be
configured for both discharge air
temperature control and for variable-air-
volume fan operation. When configured
for variable-air-volume operation, the
controller uses a duct static pressure
control routine.
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