Installation and Maintenance Manual

Startup
72 UV-SVN02C-EN
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 (Tracer ZN520)
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 (Tracer ZN520)
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
bu
tton
• 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
the controller is determined by using time-of-day
scheduling of the building automation system. The result
of the time-of-day schedule can then be communicated to
the unit controller.
Tracer Summit with Supply Fan Control
(Tracer ZN520)
If the unit is communicating with Tracer Summit and the
supply fan control programming point is configured for
Tracer (the factory configures as local), Tracer Summit will
control the fan regardless of the fan mode switch position.
When the fan mode switch is set to Off or when power is
restored to the unit, all Tracer ZN520 lockouts (latching
diagnostics) are manually reset. The last diagnostic to
occur is retained until the unit power is disconnected.
Refer to Trane publication, CNT-SVX04A-EN (Tracer ZN520
Unit Controller: Installation, Operation and Programming
Guide) for specific instructions regarding the procedure
for running the Tracer ZN520.
Cooling Operation (Tracer ZN520)
The heating and cooling setpoint high and low limits are
always applied to the occupied and occupied standby
setpoints. During the cooling mode, the Tracer ZN520
controller attempts to maintain the space temperature at
the active cooling setpoint. Based on the controller’s
occupancy mode, the active cooling setpoint is one of the
following:
• Occupied cooli
ng setpoint
• Occupied standby cooling set
point
• Unoccupied cool
ing setpoint
The controller uses the measured space te
mperature, the
active cooling setpoint, and discharge air temperature
along with the control algorithm to determine the
requested cooling capacity of the unit (0 percent–
100 percent). The outputs are controlled based on the unit
configuration and the required cooling capacity. To
maintain space temperature control, the Tracer ZN520
cooling outputs (modulating hydronic valve, two-position
hydronic valve, or outdoor air economizer damper) are
controlled based on the cooling capacity output.
The cooling output is controlled based on the cooling
capacity. At 0 percent capacity, all cooling capacities are
off and the damper is at minimum position. Between
0 percent and 100 percent capacity, the cooling outputs
are controlled according to modulating valve logic
(modulating valves) or cycled on (2-position valves). As
the load increases, modulating outputs open further and
binary outputs are energized longer. At 100 percent
capacity, the cooling valve or damper is fully open
(modulating valves) or on continuously (and 2-position
valves).
Unit diagnostics can affect fan operation, causing
occupied and occupied standby fan operation to be
defined as abnormal. Refer to “Troubleshooting (Wireless
Controls),” p. 94 for more information about abnormal fan
operation.
The Tracer ZN520 controller operates the supply fan
continuously when the controller is in the occupied and
occupied standby modes, for either heating or cooling.
UV-SVN02_-EN.book Page 72 Thursday, January 24, 2013 4:48 PM