Trane LPC Install And Operation Instructions page 74

Timed override control
This sequence applies to both space
temperature control and discharge air
temperature control, with differences as
noted.
If the zone sensor has a timed override
option (ON/CANCEL buttons), pushing the
ON button initiates a timed override
request. A timed override request
changes the occupancy mode from
unoccupied mode to occupied bypass
mode. In occupied bypass mode, the
controller controls the zone temperature
based on the occupied heating or cooling
setpoints. The occupied bypass time,
which resides in the Tracer AH540/541
and defines the duration of the override,
is configurable from 0 to 240 minutes. The
default value is 120 minutes for space
temperature control; the default value is 0
minutes (disabled) for discharge air
temperature control. When the occupied
bypass time expires, the unit transitions
from occupied bypass mode to unoccu-
pied mode. Pushing the CANCEL button
cancels the timed override request. A
timed override cancel request will end the
timed override before the occupied
bypass time has expired and will transi-
tion the unit from occupied bypass mode
to unoccupied mode.
If the controller is in any mode other than
unoccupied when the ON button is
pressed, the controller still starts the
occupied bypass timer without changing
the mode to occupied bypass. If the
controller is placed in unoccupied mode
before the occupied bypass timer
expires, the controller will be placed in
occupied bypass mode and remain in that
mode until either the CANCEL button is
pressed on the Trane zone sensor or the
occupied bypass time expires.
Morning warmup
The morning warm-up function initiates a
special heating sequence to raise space
temperature to occupied conditions. This
sequence is especially useful for a
building occupancy transition from
unoccupied to occupied.
The Tracer AH540/541 controller oper-
ates this sequence according to the
configured control mode.
74
Operation
Space temperature control: Morning
warmup
The controller keeps the outdoor air
damper closed (when a mixing box is
present) anytime during a occupied,
occupied bypass, or occupied standby
mode when the space temperature is 3ºF
or more below the heating setpoint.
The damper remains closed indefinitely
(no time limit). As the space temperature
increases above this threshold, the
outdoor damper progressively opens
toward the minimum position setpoint.
When the space temperature is within 2ºF
of the effective heating setpoint, the
outdoor air damper will be at the
minimum position setpoint.
The outdoor air damper normally is open
to a minimum position during the occu-
pied mode when the controller turns On
the supply fan. The damper normally is
closed during:
• Warmup/cool-down mode
• Unoccupied mode
• Certain diagnostic conditions
• Low ambient damper lockout
• Anytime the supply fan is Off
Morning warmup can also be a communi-
cated request from a Trane Tracer
Summit building automation system.
When the Tracer AH540/541 controller
receives a communicated morning
warm-up request, heating mode is
enabled and the outdoor air damper
closes. The controller remains in morning
warmup until a different request is
communicated.
Discharge air temperature control:
Morning warmup
If the controller is configured for
discharge air temperature control, the
controller requires a space temperature
input (hard-wired or communicated) and
setpoint input (local, communicated, or
default value) to initiate the morning
warmup sequence of operation. The
space temperature and setpoint inputs
are used by the controller to determine if
heating or cooling air should be supplied
to the space.
On a transition from unoccupied to
occupied, occupied bypass, or occupied
standby, the controller compares the
space temperature to the heating
setpoint. If the space temperature is 1.5°F
below the heating setpoint, morning
sequence of
operation
warmup is initiated. The outdoor air
damper closes (or remains closed) and
heat/cool mode is heating. The morning
warmup control sequence has no time
limit upon a transition from unoccupied to
occupied, when the controller is config-
ured for discharge air temperature
control.
Morning warmup can also be a commu-
nicated request from a building automa-
tion system. When the Tracer AH540/541
controller receives a communicated
morning warmup request, heating mode
is enabled and the outdoor air damper
closes. The controller remains in morning
warmup until a different request is
communicated.
Daytime warmup
This sequence applies to controllers
configured for discharge air temperature
control. The air-handling units must have
heating capacity (hydronic or steam) and
a communicated or wired space
temperature must exist.
Daytime warmup allows the controller to
automatically change to heating if the
space temperature is below the effective
heating setpoint by a temperature that is
more than the configured daytime warm-
up enable differential. Daytime warmup
coordinates the controller heat/cool to
heating, as well as communicates the
controller mode of operation to the duct
system for changeover.
The daytime warmup start setpoint is a
configurable temperature below the
effective space heating setpoint. When
the space temperature drops to below
the start setpoint, the daytime warmup
function is initiated by the controller.
The daytime warmup terminate setpoint
is a configurable temperature above the
start setpoint. When the space tempera-
ture rises above the stop setpoint, the
warmup function is terminated by the
controller.
Unlike morning warmup, the outdoor air
damper is at the configured minimum
position or at the communicated mini-
mum damper position according to the
effective occupancy.
LPC-SVX01C-EN