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66 UNT-SVX041D-EN
desired heating or cooling operation is verified. This is
done using the entering water temperature sampling
function, for which a valid entering water temperature is
required. When neither a hard wired nor a communicated
entering water temperature value is present on
changeover units, the controller operates in only heating
mode and assumes the coil water is hot. The sampling
function is not used.
The entering water temperature sampling function is used
only for changeover applications and for information and
troubleshooting. It does not affect the operation of the
controller. (For more information, refer to the Water
Temperature Sampling Function section.)
Water Temperature Sampling Function
The entering water temperature sampling function is used
with 2-pipe and 4-pipe changeover units and requires a
valid entering water temperature value. If the entering
water temperature value is less than 5°F (2.8°C) above a
valid zone temperature value for hydronic heating, and
greater than 5°F (2.8°C) below a valid zone temperature
value for hydronic cooling, the sampling function is
enabled. When the sampling function is enabled, the
controller opens the main hydronic valve to allow the
water temperature to stabilize. After 3 minutes, the
controller again compares the entering water temperature
value to the zone temperature value to determine if the
desired heating or cooling function can be accomplished.
If the entering water temperature value remains out of
range to accomplish the desired heating/cooling function,
the controller closes the 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 controller supports 1-, 2-, 3-speed fans and variable-
speed fans. The fan operates in fan cycling or continuous
fan 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.
Manual Fan Speed Control
Regardless of the fan type, the fan runs continuously at the
desired fan speed during occupied, occupied standby, and
occupied bypass operation as follows:
• When the 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 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
Note: 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 Fans
When the 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 (configurable 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 control
algorithm.
AUTO Fan Operation; ECM Energy Efficient
Mode
When the controller is configured for Energy Efficient
Mode, by means of the Fan Operating Mode Request MV
point, the controller will minimize energy use by running
the fan at the lowest possible speed while maintaining
space temperature. The controller will fully utilize valves,
economizer, or electric heat which increases fan speed to
meet space temperature (unless the fan has been
manually controlled. Refer to the preceding section,
“Manual Fan Speed Control”).
AUTO Fan Operation; ECM Acoustical Mode
When the controller is configured for Acoustical Mode, by
means of the Fan Operating Mode Request MV point, the
controller will minimize acoustical nuisance by balancing
changes in fan speed and total fan noise. The controller
will fully OPEN cooling and heating valves before
increasing fan speed to meet space temperature (unless
the fan has been manually controlled. Refer to the
preceding section, “Manual Fan Speed Control”). If
multiple stages of electric heat exist the controller will use
a single minimum air flow for each stage.
Exhaust Control
Exhaust control is achieved by a single-speed exhaust fan
and controlled by binary output 2 (BO2). Exhaust control,
if not present, can be enabled by selecting Yes under the
Exhaust Fan Selection on the Tracer® TU Configuration
page under the Equipment Options group.
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