Startup
UNT-SVX07E-EN
119
Electric Heat Operation
The 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 controller 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 controller will operate electric heat only
when hot water is not available (for example, in a
changeover unit). In addition, the controller 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
The 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.
Peer-to-Peer Communication
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
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
The 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
For more information, refer to:
•
BAS-SVX48C-EN Tracer UC400 Programmable
Controller for Blower Coil, Fan Coil, and Unit Ventilator
Installation, Operation, and Programming Guide
and the preceding section,
“Smart Reset”
.
Condensate Overflow
For more information, refer to:
•
BAS-SVX48C-EN Tracer™ UC400 Programmable
Controller for Blower Coil, Fan Coil, and Unit Ventilator
Installation, Operation, and Programming Guide
Fan Status
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:
•
If the fan is not operating when the controller has the
fan controlled to
ON
, the controller generates a Low
Airflow-Supply Fan Failure diagnostic.
•
If the controller energizes the fan output for 1 minute,
and the fan status switch indicates no fan operation,
the controller performs a unit shutdown and generates
a Low Airflow-Supply Fan Failure diagnostic.
•
If the fan has been operating normally for one minute,
but the fan status switch indicates no fan operation, the
same diagnostic is generated.
This manual diagnostic discontinues unit operation until
the diagnostic has been cleared from the controller. If a
diagnostic reset is sent to the controller, and the fan
condition still exists, the controller attempts to run the fan
for 1 minute before generating another diagnostic and
performing a unit shutdown. A diagnostic reset can be
sent to the controller from the Tracer TU Alarms page or by
