Installation and Maintenance Manual

Startup
UNT-SVX07D-EN 93
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
ZN.520 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 cooling setpoint
• Occupied standby cooling setpoint
• Unoccupied cooling setpoint
The controller uses the measured spa
ce temperature, 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. 117 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.
The controller only cycles the fan off with heating and
cooling capacity in the unoccupied mode.
The economizer is used for cooling purposes whenever
the outdoor temperature is below the economizer enable
setpoint and there is a need for cooling. The economizer is
used first to meet the space demand, and other forms of
cooling are used if the economizer cannot meet the
demand alone. See modulating outdoor air damper
operation for additional information.
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.
Discharge Air Tempering (Tracer ZN520)
The discharge air tempering function enables when cold
outdoor air is brought in through the outdoor air damper,
causing 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 percent for five minutes.
Heating Operation (Tracer ZN520)
During heating mode, the Tracer ZN520 controller
attempts to maintain the space temperature at the active
heating setpoint. Based on the occupancy mode of the
controller, the active heating setpoint is one of the
following:
• Occupied heating
• Occupied standb
y heating
• Unoccupied heating
During dehumidification in the heating mode, the
con
troller adjusts the heating setpoint up to the cooling
setpoint. This reduces the relative humidity in the space
with a minimum of energy usage.
The controller uses the measured space temperature, the
active heating setpoint, and discharge air temperature,
along with the control algorithm, to determine the
requested heating capacity of the unit (0 percent–
100 percent). The outputs are controlled based on the unit
configuration and the required heating capacity.
Unit diagnostics can affect the Tracer ZN520 controller
operation, causing unit operation to be defined as
abnormal. Refer to the Troubleshooting section for more
information about abnormal unit operation.
The heating output is controlled based on the heating
capacity. At 0 percent capacity, the heating output is off
continuously. Between 0 percent and 100 percent
capacity, the heating output is controlled according to
modulating valve logic (modulating valves) or cycled on
(two-position valves). As the load increases, modulating
outputs open further and binary outputs are energized
UNT-SVX07_-EN.book Page 93 Friday, April 27, 2012 9:40 AM