UNT-SVX07B-EN 89
Start-Up
Tracer ZN520 Sequence of Operation
The Tracer ZN520 operates the fan in the following modes:
1. occupied
2. unoccupied
3. occupied standby
4. occupied bypass
5. Tracer Summit with supply fan control
Occupied
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 occupied or in occupied standby is described in the
following sections. Additional information related to the handling of the controller setpoints can
be found in the previous Setpoint operation section.
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 heating mode, when the space temperature is below the heat setpoint, the primary heating
capacity turns on. All capacity is turned off when the space temperature is between the unoccupied
cooling and heating setpoints. Note that primary heating or cooling capacity is defined by unit type
and whether heating or cooling is enabled or disabled. For example, if the economizer is enabled
and possible, it will be the primary cooling capacity. If hydronic heating is possible, it will be the
primary heating capacity.
(a) Whenever two states are listed for the fan:
The first state (off) applies when there is not a call for heating or cooling.
The second state (varies) applies when there is a call for heating or cooling.
The heat default is factory configured for low fan speed, and the cool default is medium.
Table 20. Valid operating range and factory default setpoints
Setpoint/parameter Default Setting Valid Operating Range
Unoccupied cooling setpoint 85°F 40°F to 115°F
Occupied cooling setpoint 74°F 40°F to 115°F
Occupied heating setpoint 71°F 40°F to 115°F
Unoccupied heating setpoint 60°F 40°F to 115°F
Cooling setpoint high limit 110°F 40°F to 115°F
Cooling setpoint low limit 40°F 40°F to 115°F
Heating setpoint high limit 105°F 40°F to 115°F
Heating setpoint low limit 40°F 40°F to 115°F
Power-up control wait 0 sec 0 sec to 240 sec
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