Trane Tracer ZN.520 Manual page 76

Sequence of operation
Night setback operation
The controller always operates in one of these occupancy modes:
I Occupied
I Occupied standby
I Occupied bypass
I Unoccupied
Occupied operation normally is used during the daytime hours when people
occupy the space. In occupied mode, the controller uses occupied heating and
cooling setpoints.
Occupied standby operation is desired during daytime hours when people are
not present in the space. An occupancy sensor or some other device is used to
determine if the space is unoccupied. In occupied standby mode, the controller
uses occupied standby heating and cooling setpoints as well as the occupied
standby damper position. The occupied standby setpoints are usually wider
than the occupied setpoints.
Example: The occupied standby cooling setpoint is normally higher than the
occupied cooling setpoint and the occupied standby heating setpoint is
normally lower than the occupied heating setpoint.
Occupied bypass operation is associated with timed override (from unoccupied
mode). In occupied bypass mode, the controller uses all the occupied setpoints,
but reports occupied bypass as the active mode to represent the override
mode.
Unoccupied operation is normally associated with evening hours when the
space is vacant. In the unoccupied mode, the controller always uses the default
unoccupied heating and cooling setpoints, which are stored in the controller.
When the controller sets the space to unoccupied, the occupant may have the
ability to request timed override. Based on the controller or system setup, the
controller interprets the request and initiates the occupied setpoint operation.
During a timed override, the controller applies all occupied setpoints, but
reports the effective occupancy mode as occupied bypass.
Morning warm-up
The controller keeps the economizer and the modulating outdoor air damper
closed (when configured for modulating outdoor air damper control and an
outdoor air damper is present) anytime during the occupied mode when the
space temperature is three degrees or more below the heating setpoint.
The damper remains closed indefinitely (no time limit) during morning warmup
until the space temperature is greater than 3ºF below the effective heating
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