Sequence Of Operation - Trane VUV Installation, Operation And Maintenance Manual

Start-Up
3. Rotate the setpoint dial on the zone sensor module to 55°F
for cooling or 85°F for heating.
The appropriate control valve will actuate assuming the
following conditions:
• Room temperature should be greater than 55°F and less
than 85°F.
• For a 2-pipe fan-coil unit with an entering water
temperature sensor, the water temperature input is
appropriate for the demand placed on the unit. For
example, cooling operation is requested and cold water
(5° lower than room temperature) flows into the unit.
• Select the correct temperature setpoint.
Select and enable zone sensor temperature settings to
prevent freeze damage to unit.
ZN520 Operation
Off: Fan is off; control valve options and mixing box damper
options close. The low air temperature detection option is still
active.
Auto: Fan speed control in the auto setting allows the
modulating control valve option and single- or three-speed fan
to work cooperatively to meet precise capacity requirements,
while minimizing fan speed (motor/energy/acoustics) and
valve position (pump energy/chilled water reset). As the
capacity requirement increases at low fan speed, the water
valve opens. When the low fan speed capacity switch point is
reached, the fan switches to the next higher speed and the
water valve repositions to maintain an equivalent capacity. The
reverse sequence takes place with a decrease in required
capacity.
Units with three-speed fans on low, medium, or high: The
fan runs continuously at the selected speed and the valve
option cycles to meet setpoint.

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
74
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.
UV-SVX005G-EN