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Alternate Mode
Fan Control
8
Technical Bulletin—TC-9102
When pressed for about one second, the occupancy button on the Room
Command Module changes the mode of operation of the controller to the
"Alternate Mode" or back to the normal "Control Mode" as shown in
Table 2. The "COMFORT (T)" alternate mode is active only for a period
of one hour, after which the controller reverts to the normal control
mode.
The controllers with on/off fan control switch the fan on when the room
temperature is below the working set point for heating and above the
working set point for cooling, and switch the fan off when the room
temperature has entered the zero energy band by the value set for the fan
differential. The fan can optionally be set to continue running in the zero
energy band in the COMFORT (occupied) mode, using the software
commissioning tool.
In controllers with 3-speed fan control outputs, the fan stages are
switched in sequence as the room temperature decreases or increases, and
Speed 1 remains on in the zero energy band.
In controllers with a 0 to 10 VDC output for a fan speed controller, the
output increases as the room temperature falls below the working set
point for heating or rises above the working set point for cooling, and
maintains a minimum output (set by default at 50%) when the room
temperature has entered the zero energy band.
For all controllers, in OFF mode the fan is switched off and the heating
and cooling outputs are set to the fully closed or off level. Fan control
sequences are shown in figures 10, 11 and 12.
3-Speed Fan Override
The speed of a 3-speed fan may be set manually from the Room
Command Module when the controller is in COMFORT (occupied)
mode. In the "AUTO" position the speed is set by the controller
according to the room temperature. In the manual "OFF-1-2-3" positions
the fan runs at the selected speed. The fan override is not active in
STANDBY, NIGHT or OFF modes.
In controller models with 2-stage on/off heating and cooling outputs, all
outputs are switched off when the fan speed is set to "OFF" to protect
electrical heating and cooling devices that require a minimum air flow for
normal operation. This feature can be enabled for other types of outputs,
if required, using the software commissioning tool. Refer to
Commissioning later in this document.
Low Limit Mode
The low limit mode is active when the room temperature falls below the
low limit set point. The fan is switched on at full speed and the heating
output is set to the maximum level until the room temperature rises by the
low limit differential value.
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