Unit Operation
Power-Up
When 24 VAC is initially applied to the controller, the following se- quence of events occurs:
qGreen status LED turns ON .
qAll outputs are controlled OFF.
qThe controller reads input values to determine initial values.
q
qWhen
is enabled, the controller waits
qAll modulating valves and dampers calibrate closed.
qNORMAL operation begins.
Occupancy
The valid occupancy modes for the Tracer ZN.520 controller are:
qOCCUPIED - Normal operating mode for occupied spaces or daytime operation.
qUNOCCUPIED - Normal
operating mode for unoccupied spaces or nighttime operation.
qOCCUPIED STANDBY - Mode
used to reduce the heating and cooling demands, while providing ventilation, during the occupied hours when the space is vacant or unoccupied.
qOCCUPIED BYPASS
temporarily place the unit into the occupied operation.
The occupancy mode can be hard- wired to the controller via the oc- cupancy binary input or communicated to the controller.
OCCUPIED mode
When the controller is in the OCCU- PIED mode, the unit attempts to maintain the space temperature at the active occupied heating or cooling setpoint.
OCCUPIED mode is the default mode of the Tracer ZN.520 control- ler.
UNOCCUPIED mode
When the controller is in the UN- OCCUPIED mode, the unit attempts to maintain space temperature at the stored unoccupied heating or cooling setpoint (i.e., config- urable through Tracer Summit or the Rover service tool) regardless of the presence of a hardwired or communicated setpoint. When the space temperature exceeds the stored unoccupied setpoint, the controller brings on 100% of the primary heating or cooling ca- pacity.
The UNOCCUPIED mode can be ini- tiated through a hardwired signal to the occupancy binary input or by a communicated request.
OCCUPIED STANDBY mode
The OCCUPIED STANDBY mode al-
lows the unit to operate at a heat- ing or cooling setpoint between the occupied and unoccupied set- points to help maintain the envi- ronment while decreasing energy consumption.
This mode decreases the ventila- tion for heating or cooling during brief periods of vacancy in the space. Unit operation in this mode is similar to the occupied mode ex- cept for the different heating and cooling setpoints and a different outside air damper position.
The OCCUPIED STANDBY mode is
initiated only when occupancy is communicated to the Tracer ZN.520 controller and the hard- wired signal to the occupancy in- put is calling for unoccupied operation.
OCCUPIED BYPASS mode
The OCCUPIED BYPASS mode is
used to transition the unit from the
UNOCCUPIED mode to the OCCU-
PIED mode for a period of time from 0 to 4 hours (configurable through Rover. Default=RUN). The controller can be placed in OCCU- PIED BYPASS mode by either com- municating an occupancy request of BYPASS or by using the TIMED OVERRIDE (i.e., ON) button on the Trane zone sensor.
ON and CANCEL Buttons
Some Trane zone sensors have ON and CANCEL buttons for timed over- ride operation. Pressing the ON button on the zone sensor when the unit is in the UNOCCUPIED mode initiates the OCCUPIED BY- PASS mode and initializes the by- pass timer. The CANCEL button is used to send the unit back into UN- OCCUPIED mode before the bypass timer has expired.
The ON button may also be used for the unit identification or the
“WINK” feature. (See “Winking” on page38.for more information.) When the Tracer ZN.520 controller is connected to a Tracer Summit system or the Rover service tool, the ON button may be used in place of the service pin for easy unit identification.
Heating And Cooling Changeover Logic
The Tracer™ ZN.520 Unit Control- ler can receive communicated re- quests for heating or cooling operation. The communicated variable nviApplicMode is used to communicate the requests for the controller's operating mode based on the following values:
0 = Auto (mode determined by controller)
1 = Heat (uses heating setpoints)
2= Morning
3= Cool (uses cooling setpoints)
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