Control functions
2 Control functions
2.1 Control modes
The thermostat can be used both for 4-pipe systems and 2-pipe systems. The control mode function enables
the thermostat to support control of various room HVAC systems, that is, different combinations of heating
and cooling devices that are part of a room. The thermostat can be set to one of the following two control
modes:
✓ Four pipe system: Heating and Cooling
✓ Two pipe system: Heating or Cooling (change-over)
2.1.1 Four pipe system
In the four pipe system, the thermostat automatically switches between being a heat thermostat and a cool
thermostat. This control mode is suitable for room HVAC systems that use a fan coil as heating or cooling
device.
The thermostat works as a heat thermostat when the room temperature is lower than a specified
temperature, and as a cool thermostat when the room temperature is higher than a specified temperature.
2.1.2 Two pipe system
This control mode is suitable for room HVAC systems that use a 2-pipe fan coil as heating and cooling
device (see Figure 2-1). A change-over function makes it possible to use the thermostat in a 2-pipe change-
over system, where warm or cold media flow in the same pipes and one valve is used to regulate both heating
and cooling distribution. The thermostat is either in heating or cooling mode, and switches between the
modes according to the change-over function settings. The change-over function is further described in
chapter 2.3.
Figure 2-1 A two pipe system
2.1.3 Control mode settings
Parameter Description
8 Control mode
0 = 2-pipe system
1= 4-pipe system
Modbus register Modbus addess Description
Holding register 5
Control mode
0 = 2-pipe system
1= 4-pipe system
6 RCFD-230C manual, Rev. A
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