CNT-SVX07D-EN
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Sequence of operations
Entering water temperature sampling function
The entering water temperature sampling function is used with two-pipe and four-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 Tracer ZN521 supports up to three fan speeds. Every time the fan is enabled, the fan will begin
operation and run 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 any other speed. This is done to provide
adequate torque to start the fan motor from the off position. The fan will always operate
continuously while either heating or cooling during occupied, occupied standby, and occupied
bypass operation. During unoccupied operation, the fan will cycle between off and high regardless
of the fan configuration. The controller can be configured to auto, to a specific fan speed, or to off.
If both a communicated and hard-wired value (fan-speed switch) is present, the communicated
value has priority.
Note:
In occupied mode, The Tracer ZN521 zone controller requires continuous fan operation
because of cascade zone control. In unoccupied mode, the fan cycles.
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 will operate in the auto mode. In the auto
mode, the fan will operate according to the fan default (configurable using the Rover service tool).
The fan speed can be configured to default to auto, a specific speed, or off for both heating and
cooling operation.
Configured as auto and with multiple speeds available, the fan will automatically switch speeds
depending on the difference between the zone temperature and the active zone temperature
setpoint. The fan speed will increase as the difference increases and decrease as the difference
decreases.
When the controller receives a communicated fan-speed signal (high, medium, low) or the
associated fan-speed switch is set to a specific fan speed, the fan will run continuously at the
desired fan speed during occupied, occupied standby, and occupied bypass operation. During
unoccupied operation, the fan will cycle between off and high regardless of the communicated fan-
speed signal or fan-speed switch setting (unless either of these is off, which will control the fan off).
The fan will turn off when the controller receives a communicated off signal, when the fan-speed
switch is set to
OFF
, when specific diagnostics are generated, or when the default fan speed is set
to off and the fan is operating in the auto mode.
The ability to enable or disable the controller’s associated fan speed switch is configurable.
Exhaust control
Exhaust control is accomplished by a single-speed exhaust fan or a two-position exhaust damper.
BOP2 controls this function. To enable exhaust control, configure the controller by selecting
Exhaust Fan/Damper Present and by selecting the number of fan speeds as either
One
or
Two
.
The exhaust function is coordinated with the supply fan and outdoor/return air dampers as follows:
Содержание Tracer ZN521
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