Startup
UNT-SVX07E-EN
115
occupied standby mode reduces the demand for heating
and cooling the space. The fan will run as configured
(continuously) for occupied mode. The controller always
uses the stored default setpoint values (configurable using
the Tracer TU service tool), regardless of hard wired or
communicated setpoint values. In addition, the outdoor
air damper uses the economizer occupied standby
minimum position setpoint to reduce the ventilation rate.
Occupied Bypass Mode
The controller is placed in occupied bypass mode when
the controller is operating in the unoccupied mode and
when either the timed override
ON
button on the Trane
zone sensor is pressed or the controller receives a
communicated occupied bypass signal from a BAS. In
occupied bypass mode, the controller maintains the space
temperature based on the occupied heating or cooling
setpoints. The fan will run as configured (continuous or
cycling). The outdoor air damper closes when the fan is
OFF
. The controller remains in occupied bypass mode
until either the
CANCEL
button is pressed on the Trane
zone sensor or the occupied bypass time (configurable
using the Tracer TU service tool) expires. The temperature
setpoints can configured as local (hard wired),
communicated, or stored default values using the Tracer
TU service tool.
Timed Override Control
If the controller has a timed override option (ON/CANCEL
buttons), pushing the ON button initiates a timed override
on request. A timed override on request changes the
occupancy mode from unoccupied mode to occupied
bypass mode. In occupied bypass mode, the controller
controls the space temperature based on the occupied
heating or cooling setpoints. The occupied bypass time,
which resides in the controller and defines the duration of
the override, is configurable from 0 to 240 minutes (default
value of 120 minutes). When the occupied bypass time
expires, the unit transitions from occupied bypass mode
to unoccupied mode. Pushing the CANCEL button cancels
the timed override request. In addition, it will end the
timed override before the occupied bypass time has
expired and transition the unit from occupied bypass
mode to unoccupied mode.
If the controller is in any mode other than unoccupied
mode when the
ON
button is pressed, the controller still
starts the occupied bypass timer without changing to
occupied bypass mode. If the controller is placed in
unoccupied mode before the occupied bypass timer
expires, the controller is placed into occupied bypass
mode and remains in this mode until either the
CANCEL
button is pressed on the Trane zone sensor or the occupied
bypass time expires.
Zone Temperature Control
The controller has three methods of zone temperature
control:
•
Cascade zone control
—used in the occupied,
occupied bypass, and occupied standby modes. It
maintains zone temperature by controlling the
discharge air temperature to control the zone
temperature. The controller uses the difference
between the measured zone temperature and the
active zone temperature setpoint to produce a
discharge air temperature setpoint. The controller
compares the discharge air temperature setpoint with
the discharge air temperature and calculates a unit
heating/cooling capacity accordingly (refer to the
illustration below). The end devices (outdoor air
damper, valves, and so on) operate in sequence based
on the unit heating/cooling capacity (0–100 percent).
If the discharge air temperature falls below the
discharge air temperature low limit setpoint,
(configurable using the Tracer TU service tool), and the
cooling capacity is at a minimum, the available heating
capacity is used to raise the discharge air temperature
to the low limit (refer to the following section,
“Discharge Air Tempering.”
).
•
Simplified zone control
— if discharge air
temperature failure occurs, then simplified zone
controls runs. In the unoccupied mode, the controller
maintains the zone temperature by calculating the
required heating or cooling capacity (0–100%)
according to the measured zone temperature and the
active zone temperature setpoint. The active zone
temperature setpoint is determined by the current
operating modes, which include occupancy and heat/
cool modes.
•
Discharge air temperature control
— is the backup
mode that runs only if there is not valid zone
temperature. In this mode, the active space
temperature setpoint is used as the discharge air
temperature setpoint.
Important:
This is not a normal operating mode. The
source of the invalid zone temperature
needs to be corrected to restore normal
operation.
Figure 92.
Cascade zone control
Difference
Active zone
temperature
setpoint
Calculated
discharge air
temperature
setpoint
Calculated unit
heating/cooling
capacity
Measured
zone
temperature
Measured
discharge air
temperature
Difference
