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UNT-SVX07J-EN 109
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.
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.
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.
Continuous Fan Operation
During occupied and occupied standby modes, the fan
normally is on. For multiple speed fan applications, the fan
normally operates at the selected or default speed (off,
high, medium, or low). When fan mode is auto, the fan
operates at the default fan speed.
During unoccupied mode, the controller controls the fan
off. While unoccupied, the controller heats and cools to
maintain the unoccupied heating and cooling setpoints. In
unoccupied mode, the fan is controlled on high speed only
with heating or cooling.
The unit fan is always off during occupied, occupied
standby, and unoccupied modes when the unit is off due
to a diagnostic or when the unit is in the off mode due to
the local zone sensor module, a communicated request, or
the default fan speed (off).
If both a zone sensor module and communicated request
exist, the communicated request has priority.
Fan Cycling Operation
Tracer
®
ZN520 does not support fan cycling in
occupied mode. The fan cycles between high speed and
off in the unoccupied mode only. The controller’s cascade
control algorithm requires continuous fan operation in the
occupied mode.
Fan Off Delay
When a heating output is controlled off, the controller
automatically holds the fan on for an additional 30
seconds. This 30-second delay gives the fan time to blow
off any residual heat from the heating source, such as a
steam coil. When the unit is heating, the fan off delay is
normally applied to control the fan; otherwise, the fan off
delay does not apply.
Table 49. Fan configuration for Tracer® ZN520 units
Auto Fan Operation Fan Speed Default
Heating Continuous
Off
Low
Medium
High
Cooling Continuous
Off
Low
Medium
High
Table 50. Local fan switch enabled
Communicated Fan Speed
Input
Fan Switch
(Local)
Fan
Operation
Off Ignored Off
Low Ignored Low
Medium Ignored Medium
High Ignored High
Auto Off
Low
Medium
High
Auto Off
Low
Medium
High
Note: Auto (configured default, determined by heat/cool mode)
Table 51. Fan operation in heating and cooling modes
Fan
Mode
Heating Cooling
Occupied Unoccupied Occupied Unoccupied
Off Off Off Off Off
Low Low Off/high Low Off/high
Medium Med Off/high Med Off/high
High High Off/high High Off/high
Auto
Default fan
speed
Off/high
Default fan
speed
Off/high
Table 52. Local fan switch disabled or not present
Communicated Fan
Speed Input Fan Operation
Off Off
Low Low
Medium Medium
High High
Auto (or not present)
Auto (fan runs at the default
speed)
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