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Exhaust control
CNT-SVX07C-EN 41
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.
When the controller receives a communicated auto signal (or the associ-
ated 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 auto-
matically 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 occu-
pied, occupied standby, and occupied bypass operation. During unoccu-
pied 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 sig-
nal, 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 oper-
ating 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:
• The exhaust output is energized only when the supply fan is operat-
ing and the outdoor air damper position (%) is greater than or equal
to the Exhaust Fan/Damper Enable Setpoint (configurable using the
Rover service tool).
Note:
In occupied mode, The Tracer ZN521 zone controller requires
continuous fan operation because of cascade zone control. In
unoccupied mode, the fan cycles.