BAS-SVX48H-EN
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main hydronic valve and waits 60 minutes to attempt another sampling. If the entering water
temperature value falls within the required range, it resumes normal heating/cooling operation
and disables the sampling function.
Fan Operation
The UC400 Controller supports 1-, 2-, 3-speed fans and variable-speed fans. The fan continuously
operates while either heating or cooling during occupied, occupied standby, and occupied
bypass operation. During unoccupied operation, the fan cycles between OFF and HIGH,
regardless of the fan configuration. When running in AUTO mode, the fan operates differently
based on the mode and the type of fan. For 1-, 2-, and 3-speed fans, each time the fan is enabled,
the fan begins operation and runs on high speed for a period of time (0.5 seconds for fan coils
and 3 seconds for unit ventilators and blower coils) before changing to another speed. Initially
running on high speed provides adequate torque to start the fan motor from the OFF position.
NNoottee:: In occupied mode, the UC400 Controller requires continuous fan operation because of
cascade zone control. In unoccupied mode, the fan cycles.
Manual Fan Speed Control
Regardless of the fan type, the fan continuously runs at the desired fan speed during occupied,
occupied standby, and occupied bypass operation as follows:
• When the UC400 Controller receives a communicated fan speed signal (HIGH, MEDIUM,
LOW).
• The associated fan speed switch is set to a specific fan speed.
• The Supply Fan Speed Request point is overridden.
During unoccupied operation, the fan cycles between OFF and HIGH, regardless of the
communicated fan speed signal or fan speed switch setting (unless either of these is OFF, which
in turn, will control the fan OFF). The fan turns OFF when:
• The UC400 Controller receives a communicated OFF signal.
• The fan speed switch is set to OFF.
• Specific diagnostics are generated.
• The default fan speed is set to OFF and the fan is operating in the AUTO mode.
NNoottee:: The supply fan speed source can be configured for BAS, local, or default value control
using the Tracer TU service tool.
Auto Fan Operation; 1–, 2–, 3–Speed
When the UC400 Controller receives a communicated auto signal (or the associated fan speed
switch is set to AUTO with no communicated value present), the fan operates in the AUTO mode.
In AUTO mode, the fan operates according to the fan default (configured using the Tracer TU
service tool). The fan speed has multiple speed configurations (default is AUTO) or set to OFF for
both heating and cooling operation. When configured as AUTO (and with multiple speeds
available), the fan changes based on the required capacity calculated by the controller algorithm.
Single Zone VAV
The UC400 Controller varies the speed of the fan motor as the zone cooling or heating load
changes as shown below. At high cooling loads, the fan speed modulates to maintain the zone
temperature at cooling setpoint, while the cooling capacity modulates or cycles to maintain the
discharge air temperature (DAT) at minimum limit setpoint. At lower cooling loads, once the fan
has turned down to minimum speed, it remains at minimum speed while cooling capacity
modulates or cycles to maintain the zone temperature at cooling setpoint.
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