Application mode
The behavior of the thermostat can be influenced by a building automation and control system (BACS) via bus with the command "Application mode".
With this signal, cooling and/or heating activity can be enabled or disabled. Application mode is supported in LTE Mode and S-Mode.
The RDF KNX thermostats support the following commands:
# | Application mode | Description | Control sequence enabled |
---|---|---|---|
0 | Auto | Thermostat automatically changes between heating and cooling | Heating and/or cooling |
1 | Heat | Thermostat is only allowed to heat | Heating only |
2 | Morning warm-up | If "Morning warm-up" is received, the room should be heated up as fast as possible (if necessary). The thermostat will only allow heating | Heating only |
3 | Cool | Thermostat is only allowed to provide cooling | Cooling only |
4 | Night purge | Not supported by fan coil applications | N/A (= Auto) |
5 | Pre-cool | If "Pre-cool" is received, the room should be cooled down as fast as possible (if necessary). The thermostat will only allow cooling | Cooling only |
6 | OFF | Thermostat is not controlling the outputs, which means all outputs go to off or 0% | Neither heating nor cooling |
8 | Emergency heat | The thermostat should heat as much as possible. The thermostat will only allow heating | Heating only |
9 | Fan only | All control outputs are set to 0% and only the fan is set to high speed. Function will be terminated by any operation on the thermostat |
Run fan in high speed |
With all other commands, the thermostat behaves like in Auto mode, i.e. heating or cooling according to demand.
ACS
The state (heating or cooling) of the thermostat can be monitored with the ACS tool (diagnostic value "Control sequence"). The last active mode is displayed when the thermostat is in the dead zone or temperature control is disabled.
Heating OR cooling
With a 2 pipe application, the control sequence state is determined by the application mode (see section 3.6.3) and by the state of the heating / cooling changeover signal (via local sensor or bus), or fixed according to the selected control sequence (P01 = heating (0) / cooling (1)).
Application mode (via bus) | State changeover / continuous heating or cooling | Control sequence state |
---|---|---|
Auto (0) | Heating | Heating |
Cooling | Cooling | |
Heat (1), (2), (8) | Heating | Heating |
Cooling | Heating | |
Cool (3), (5) | Heating | Cooling |
Cooling | Cooling | |
Night purge (4), Fan only (9) |
Heating | Heating |
Cooling | Cooling |
Heating AND cooling
With a 4-pipe, 2-pipe with electric heater, and 2-pipe with radiator application, the control sequence state depends on the application mode and on the heating / cooling demand.
Application Mode (via bus) | Heating / cooling demand | Control sequence state |
---|---|---|
Auto (0) | Heating | Heating |
No demand | Heating / cooling depending on last active sequence | |
Cooling | Cooling | |
Heat (1), (2), (8) | Heating | Heating |
No demand | Heating | |
Cooling | Heating | |
Cool (3), (5) | Heating | Cooling |
No demand | Cooling | |
Cooling | Cooling | |
Night purge (4), Fan only (9) |
No temperature control active | Heating / cooling depending on last active sequence |
The value of the output as a function of the room temperature is shown in the following diagram in case of a heating and cooling system:
Wheat = current heating setpoint Wcool = current cooling setpoint |