Room units with CO2 sensor

The room unit with CO2 sensor contains temperature sensor, NDIR CO2 sensor for carbon dioxide concentration measurement, optional humidity sensor, and control knob for setpoint control and other settings. The binary output is controlled either on a remote basis, or as thermostat, hygrostat or CO2 controller. The units communicate over Modbus RTU / RS485 and they can be used as open system components with majority of building control system and controllers.


Air handling units and air condition in rooms with variable load – schools, cinemas, lecture halls etc., monitoring and recording of temperature, humidity and CO2 concentration in interiors. The triac output and potential-free input are controllable over the bus and may be used for connecting of room peripherials, such as thermic valve, and presence / window contact.

Easy configuration

There are several predefined menus which can be enabled or disabled. The menus fit most of the HVAC applications, and there may be more menus activated in a single room unit. It is not necessary to control all parameters over Modbus registers – the configuration follows during the commissioning time and it is stored permanently in the EEPROM.

The menus, or functional profiles, are:

  • temperature, actual temperature correction,
  • humidity (actual value only at room units containing the humidity sensor),
  • time (only at room units with RTC),
  • CO2 contents in the air, in % of polluted air (limits are definable over Modbus registers),
  • basic temperature setpoint - day,
  • basic temperature setpoint - night,
  • outside temperature for start of heating mode,
  • DHW temperature – heating curve type (1...4),
  • operation mode (Residential for family houses with Day, Night, Time schedule, Party, Off, or Presence for hotels / offices with Comfort, Standby, Party, Off),
  • fan stage (Auto, Off, St.1, St. 2, St. 3),
  • A/C mode (Auto, Heating, Cooling, Off, Fan only),
  • weekly scheduler: 7 days, up to 6 events per day.

Another 5 variables (air quality, fan speed etc.) may be set and indicated with free definable profiles – each of them has a profile where max. and min. values, step, number of decimals, and corresponding symbol set are defined. It is also possible to set / reset any of the LCD symbols on the display over the Modbus registers. 

User interface

The turn / push knob has three basic functions:

  • instant edit (turning the knob) – settings of one predefined analogue value, mostly room temperature correction,
  • quick edit (short push) – change of predefined state in the default menu, e.g. menu Presence (switching between Comfort / Standby / Party / Off), Operation mode (Day, Night, Auto, Party, Off), Air condition (Auto / Heating / Cooling / Fan only / Off), Fan Coil control (Stage 1 / Stage 2 / Stage 3 / Auto / Off), etc. The resulting state is available as an integer value in the corresponding Modbus register,
  • long push – jump to the Settings menu where items are listed by turning the knob, short push selects the value to be edited, and the value is changed by turning the knob followed by short push for confirmation. After definable inactivity time, the display goes back to its basic state with rolling display of selected values (e.g. actual temperature and CO2).

Room unit as a simple controller

The binary output (SSR) may be controlled either from a PLC over the bus, or configured as one of controllers:

  • thermostat,
  • hygrostat (only at devices with rH sensor),
  • controller switching at a predefined CO2 level. Setpoint and hysteresis are set over the bus. This function is not suitable for standard integrated room control, it is to be used as supplementary only. The setpoints are not influenced by operation modes (Day, Night, Off).


The Modbus address and functionality is defined over the RS485 interface with a free service software ModComTool. After configuration and writing to the EEPROM, the unit can communicate with a PLC and provide room data and user-entered values.

Domat room units and controllers