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position and 100 percent) to control the amount of outdoor
air cooling capacity. When the outdoor air temperature
rises 5°F (2.8°C) above the economizer enable point, the
controller disables economizing and moves the outdoor
air damper back to its predetermined minimum position,
based on the current occupancy mode or communicated
minimum outdoor air damper position. If an outdoor air
temperature value is not present, economizing is disabled.
Two-position Control Of A Modulating
Outdoor Air Damper (UC400)
The UC400 controller supports two-position outdoor air
damper actuators. However, a modulating outdoor/return
air damper actuator can be used for two-position control.
Two-position control can be achieved by not providing an
outdoor air temperature (neither hard wired nor
communicated) to the controller, and by setting the
damper minimum position (using the Tracer TU service
tool) to the desired value, typically 100 percent.
Electric Heat Operation (UC400)
The UC400 controller supports both SCR (modulating) and
staged electric heat (1- or 2-stages). SCR heat is only a
field-installed option. In a unit configured with staged
electric heat, the electric heating circuit(s) are cycled ON
and OFF appropriately to maintain the desired space
temperature at the active heating setpoint. In a unit
configured with SCR (modulating) electric heat, the UC400
will send a 0 to 10 Volt DC signal to adjust SCR capacity in
order to maintain the desired space temperature.
In both staged and modulating electric heat applications,
the simultaneous use of electric and hydronic heat is not
supported and the UC400 will operate electric heat only
when hot water is not available (for example, in a
changeover unit). In addition, the UC400 will run the
supply fan for 30 seconds after electric heat is turned OFF
in order to dissipate heat from the unit
Note: This delay does not apply to steam or hydronic
heating.
Factory-configured electric heat units have built-in
mechanical protections to prevent dangerously high
discharge air temperatures.
Dehumidification Operation (UC400)
The UC400 controller supports space dehumidification
when:
•
Mechanical (DX or hydronic) cooling is available
•
The heating capacity is located in the reheat position
•
The space relative humidity is valid
The space relative humidity can be a BAS-communicated
value or come directly from a wired relative humidity
sensor. The controller begins to dehumidify the space
when the space humidity exceeds the humidity setpoint.
The controller continues to dehumidify until the sensed
humidity falls below the setpoint minus the relative
humidity offset.
UV-SVN02C-EN
Peer-to-peer Communication (UC400)
Peer-to-peer communication is accomplished by means of
custom TGP2 programming in the Tracer SC system
controller or via hard wiring only between controllers.
Unit Protection Strategies (UC400)
The following unit protection strategies are initiated when
specific conditions exist in order to protect the unit or
building from damage:
•
Smart reset
•
Low coil temperature protection
•
Condensate overflow
•
Fan status
•
Fan off delay
•
Filter maintenance timer
•
Freeze avoidance
•
Freeze protection (discharge air temperature low limit)
Smart Reset (UC400)
The UC400 controller will automatically restart a unit that
is locked out as a result of a Low Coil Temp Detection
(BI3) diagnostic. Referred to as smart reset, this automatic
restart will occur 30 minutes after the diagnostic occurs. If
the unit is successfully restarted, the diagnostic is cleared.
If the unit undergoes another Low Coil Temp Detection
diagnostic within a 24-hour period, the unit will be locked
out until it is manually reset.
Note: Freeze protection will also perform a smart reset.
Low Coil Temperature Protection (UC400)
For more information refer to BAS-SVX48B-EN
(Installation, Operation, and Programming: Tracer UC400
Programmable Controller), or the most recent revision,
and the preceding section,
Condensate Overflow (UC400)
For more information refer to BAS-SVX48B-EN
(Installation, Operation, and Programming: Tracer UC400
Programmable Controller), or the most recent revision.
Fan Status (UC400)
In 1-, 2- and 3-speed fans, the status is based on the
statuses of the supply fan output multistate and analog
points dedicated to fan control. The fan status is reported
as HIGH, MEDIUM, LOW, and as a percentage, whenever
the fan is running. The fan status is reported as OFF
whenever the fan is not running. In addition, a fan status
switch can be connected to binary input 5 (BI5) to monitor
the status of the fan for belt-driven or direct-driven units
(except Trane Macon factory ECM fan motor units). The fan
status switch provides feedback to the controller as
follows:
Startup
"Smart Reset
(UC400)".
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