Trane VUV Installation, Operation And Maintenance Manual page 76

Start-Up
Heating Operation
During heating mode, the 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 standby heating
• Unoccupied heating
During dehumidification in the heating mode, the controller
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 controller operation, causing
unit operation to be defined as abnormal. Refer to
and Troubleshooting," p. 96
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 (3-wire
modulating valves) or cycled on (two-position valves). As the
load increases, modulating outputs open further and binary
outputs are energized longer. At 100 percent capacity, the
heating valve is fully open (3-wire modulating valves) or on
continuously (two-position valves).
The fan output(s) normally run continuously during the
occupied and occupied standby modes, but cycle between
high and off speeds with heating/cooling during the
unoccupied mode. When in the occupied mode or occupied
standby mode and the fan speed is set at the high, medium, or
low position, the fan runs continuously at the selected speed.
Refer to the Troubleshooting section for more information on
abnormal fan operation.
When the unit's supply fan is set to auto, the controller's
configuration determines the fan speed when in the occupied
mode or occupied standby mode. The fan runs continuously at
the configured heating fan speed or cooling fan speed. For all
fan speed selections except off, the fan cycles off during
unoccupied mode.
The economizer outdoor air damper is never used as a source
of heating. Instead, the economizer damper (when present) is
only used for ventilation; therefore, the damper is at the
occupied minimum position in the occupied mode. The damper
control is primarily associated with occupied fan operation.
76
"Diagnostics
for more information about
Fan Mode Operation
For multiple fan speed applications, the controller offers
additional fan configuration flexibility. Separate default fan
speeds for heating and cooling modes can be configured. The
fan runs continuously for requested speeds (off, high, medium,
or low). When the fan mode switch is in the Auto position or a
hard-wired fan mode input does not exist, the fan operates at
the default configured speed. See the table below for default
fan configuration for heat and cool mode. During unoccupied
mode, the fan cycles between high speed and off with heating
and cooling fan modes. If the requested speed is off, the fan
always remains off.
Table 23. Fan configuration for Tracer® ZN520 units
Auto Fan Operation
Heating Continuous
Cooling Continuous
During dehumidification, when the fan is on Auto, the fan
speed can switch depending on the error. Fan speed increases
as the space temperature rises above the active cooling
setpoint.
Additional flexibility built into the controller allows you to enable
or disable the local fan switch input. The fan mode request can
be either hard-wired or communicated to the controller. When
both are present, the communicated request has priority over
the hard-wired input. See the tables below.
Table 24. Local fan switch enabled
Communicated Fan Speed Input Fan Switch (Local) Fan Operation
Off
Low
Medium
High
Auto
Low
Medium
High
Auto
Low
Medium
High
Note: Auto (configured default, determined by heat/cool mode)
Table 25. Fan operation in heating and cooling modes
Heating
Fan Mode Occupied Unoccupied
Off Off
Low Low Off/high
Medium Med Off/high
High High Off/high
Default fan
Auto Off/high
speed
Fan Speed Default
Off
Low
Medium
High
Off
Low
Medium
High
Ignored
Ignored Low
Ignored Medium
Ignored High
Off
Off
Cooling
Occupied Unoccupied
Off Off Off
Low Off/high
Med Off/high
High Off/high
Default fan
Off/high
speed
UV-SVX005G-EN
Off