Sequence of operation
CNT-SVX04A-EN
47
Occupied and unoccupied operation
The valid occupancy modes of the Tracer ZN.520 zone controller are:
■
Occupied—
Normal operating mode for occupied spaces or daytime
operation.
■
Unoccupied—
Normal operating mode for unoccupied spaces or nighttime
operation.
■
Occupied standby—
Mode used to reduce the heating and cooling
operation during the occupied hours when the space is vacant or
unoccupied and adjusts ventilation rate (OA damper). For example, the
controller may use occupied standby mode for a classroom while the
students are out of the room.
■
Occupied bypass—
Mode used for timed override conditions. For example,
if the controller is in unoccupied mode and someone presses the On button
on the zone sensor, the controller is placed in occupied bypass mode for
120 minutes (adjustable) or until someone presses the Cancel button on the
zone sensor.
The occupancy mode can be hardwired to the controller via the occupancy
binary input or communicated to the controller.
Occupied mode
When the controller is in the occupied mode, the unit attempts to maintain the
space temperature at the active occupied heating or cooling setpoint, based on
the measured space temperature, the discharge air temperature, the active
setpoint, and the proportional/integral control algorithm. The modulating
control algorithm used when in occupied or occupied standby is described in
the following sections. Additional information related to the handling of the
controller setpoints can be found in “Setpoint operation” on page 44.
Unoccupied mode
When the controller is in the unoccupied mode, the controller attempts to
maintain the space temperature at the stored unoccupied heating or cooling
setpoint, based on the measured space temperature, the active setpoint and the
control algorithm, regardless of the presence of a hardwired or communicated
setpoint. Similar to other configuration properties of the controller, the locally
stored unoccupied setpoints can be modified using Rover service tool.
In unoccupied mode, a simplified zone control algorithm is run. During the
cooling mode, when the space temperature is above the cool setpoint, the
primary cooling capacity operates at 100%. If more capacity is needed, the
supplementary cooling capacity turns on (or opens to 100%). During the
