Startup
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UNT-SVX07E-EN
switches to medium speed and the water valve repositions
to maintain an equivalent capacity. The reverse sequence
takes place with a decrease in required capacity.
Low/Med/High (Continuous Fan)
- Fan operates
continuously while control valve option cycles to maintain
setpoint temperature.
Sequence of Operation
Occupancy Modes
The controller operates the fan in the following modes:
•
Occupied
•
Unoccupied
•
Occupied standby
•
Occupied bypass
•
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
hard-wired 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 percent. If more capacity
is needed, the supplementary cooling capacity turns on (or
opens to 100 percent). 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.
Occupied Standby Mode
The controller can be placed into the occupied standby
mode when a communicated occupancy request is
combined with the local (hard-wired) occupancy binary
input signal. When the communicated occupancy request
is unoccupied, the occupancy binary input (if present)
does not affect the controller’s occupancy. When the
communicated occupancy request is occupied, the
controller uses the local occupancy binary input to switch
between the occupied and occupied standby modes.
During occupied standby mode, the controller’s
economizer damper position goes to the economizer
standby minimum position. The economizer standby
minimum position can be changed using Rover service
tool.
In the occupied standby mode, the controller uses the
occupied standby cooling and heating setpoints. Because
the occupied standby setpoints typically cover a wider
range than the occupied setpoints, the Tracer ZN520
controller reduces the demand for heating and cooling the
space. Also, the outdoor air economizer damper uses the
economizer standby minimum position to reduce the
heating and cooling demands.
When no occupancy request is communicated, the
occupancy binary input switches the controller’s operating
mode between occupied and unoccupied. When no
communicated occupancy request exists, the unit cannot
switch to occupied standby mode.
Occupied Bypass Mode
The controller can be placed in occupied bypass mode by
either communicating an occupancy request of Bypass to
the controller or by using the timed override On button on
the Trane zone sensor.
When the controller is in unoccupied mode, you can press
the On button on the zone sensor to place the controller
into occupied bypass mode for the duration of the bypass
time (typically 120 minutes).
Occupancy Sources.
There are four ways to control the
controller’s occupancy:
•
Communicated request (usually provided by the
building automation system or peer device)
•
By pressing the zone sensor’s timed override On
button
•
Occupancy binary input
•
Default operation of the controller (occupied mode)
A communicated request from a building automation
system or another peer controller can change the
controller’s occupancy. However, if communication is lost,
the controller reverts to the default operating mode
(occupied) after 15 minutes (configurable, specified by the
“receive heartbeat time”), if no local hard-wired
occupancy signal exists.
A communicated request can be provided to control the
occupancy of the controller. Typically, the occupancy of
