BCXC-SVX01A-EN
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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 controller reduces heating/
cooling demand for the space. Also, units
with Tracer ZN520 and the fresh air
economizer damper use the economizer
standby minimum position to reduce
heating and cooling demand.
When no occupancy request is communi-
cated, 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 ZN510 or
ZN520 Only
The controller can be placed in occupied
bypass mode by either communicating
an occupancy bypass request to the
controller or by using the timed override
“on” button on the zone sensor. When
the controller is in unoccupied mode,
pressing the “on” button will place the
controller into occupied bypass mode for
the duration of the bypass time (typically
120 minutes).
Tracer Summit With Supply Fan Control,
Tracer ZN510 or ZN520 Only
All Tracer ZN lockouts (latching
diagnostics) are manually reset
whenever the fan mode switch is set to
the off position or when power is restored
to the unit. The last diagnostic to occur is
retained until the unit power is
disconnected. Refer to Trane publication,
CNT-SVX04A-EN Installation Operation
and Programming Guide, for specific
Tracer ZN520 operating procedures.
Cooling Operation
During cooling mode,
the Tracer ZN
controller attempts to maintain the space
temperature at the active cooling
setpoint. Based on the controller’s
occupancy mode, the active cooling
setpoint is either the:
• occupied cooling setpoint,
• occupied standby cooling setpoint
(Tracer ZN510 or ZN520 only), or
• unoccupied cooling setpoint.
The controller uses the measured space
temperature, the active cooling setpoint,
and discharge air temperature (Tracer
ZN520 only) along with the control
algorithm to determine the requested
cooling capacity of the unit (0-100%). The
outputs are controlled based on the unit
configuration and the required cooling
capacity. To maintain space temperature
control, the cooling outputs (modulating
or 2-position hydronic valve, or econo-
mizer damper) are controlled based on
the cooling capacity output.
Note: Economizer dampers and modulat-
ing valves are only available on units
with the Tracer ZN520 controller. Two-
position dampers are only available on
units with Tracer ZN010 and ZN510.
Cooling output is controlled based on the
cooling capacity. At 0% capacity, all
cooling capacities are off and the damper
is at minimum position. Between 0 and
100% capacity, the cooling outputs are
controlled according to modulating valve
logic (Tracer ZN520 only) or cycled with
2-position valves. As the load increases,
modulating outputs open further and
binary outputs are energized longer. At
100% capacity, the cooling valve or
damper is fully open (modulating valves)
or on continuously (2-position valves).
Note: Unit diagnostics can affect fan
operation, causing occupied and occu-
pied standby fan operation to be defined
as abnormal. Refer to the Troubleshoot-
ing section for more information about
abnormal fan operation.
Economizer Cooling (Tracer ZN520 Only)
The economizer provides cooling
whenever the outdoor temperature is
below the economizer enable setpoint
and there is a need for cooling. The
economizer operates to meet the space
demand, with other forms of cooling
enabling when the economizer cannot
meet the demand alone. See economizer
air damper operation for additional
information.
DX Cooling (Tracer ZN520 only)
The controller does not use both the DX
compressor and the economizer at the
same time. This prevents problems
where the entering air temperature is too
low for the evaporator coil to operate as
designed, which leads to compressor
short cycling due to low discharge air
temperatures.
Discharge Air Tempering (Tracer ZN520
Only)
Cascade cooling control initiates a
discharge air tempering function if:
• the discharge air temperature falls
below the discharge air temperature
control low limit,
• all cooling capacity is at minimum, and
• the discharge control loop determines a
need to raise the discharge air
temperature.
The controller then provides heating
capacity to raise the discharge air
temperature to its low limit.
The discharge air tempering function
enables when cold, fresh air is brought in
through the fresh air damper and causes
the discharge air to fall below the
discharge air temperature control low
limit. The controller exits the discharge air
tempering function when heat capacity
has been at 0% for five minutes.
Heating Operation
During heating mode, the Tracer ZN
controller attempts to maintain the space
temperature at the active heating
setpoint. Based on the controller’s
occupancy mode, the active heating
setpoint can be:
• occupied heating,
• occupied standby heating (Tracer ZN510
or ZN520 only), or
• unoccupied heating.
Note: Unit diagnostics can affect the
controller operation, causing unit
operation to be defined as abnormal.
Refer to the Troubleshooting section for
more information about abnormal unit
operation.
Heating output is controlled based on the
heating capacity. At 0% capacity, the
heating output is off continuously.
Operation
Sequence of
Operation
