°C-Lite Thermostat as an OEM Platform

°C-Lite Thermostat as an OEM Product Platform

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Each manufacturer of heating, air-conditioning or ventilation systems (HVAC) focuses its product development on different system types, relies on its own unique selling proposition strategies to differentiate itself from the competition and pursues its own individual product philosophy. As an OEM specialist, SOREL provides the HVAC industry with the new °C-Lite platform, an intentionally modular construction kit that is designed for customer-specific functional adaptations.


At its core, the °C-Lite platform is a compact room unit with integrated multi-sensor and touch-based user interface. This basic idea can be expanded as desired, especially through various connectivity options, equipable signal inputs and switching outputs, as well as application-specific adaptations of the user interface. HVAC manufacturers can thus put together a product that is optimally adapted to their system.

4 in 1 Multisensor

Touch operation

Hidden LEDs

Switch range mounting

In the following, we present the most important assembly options and possible applications. For individual advice with more details, please contact our OEM product management.

1. Power Supply

5VDC, 12VDC, 24VDC, 24VAC, 230VAC

The electronics of the °C-Lite can be designed for different voltage sources depending on the respective application. If the °C-Lites are used in conjunction with other SOREL controllers, these can usually also provide the power supply. For example, the °CALEONbox for surface heating can supply up to 8 °C-Lites with 5V DC.

Heating controllers of the HCC series or the HCC Fresh for heat interface units, on the other hand, can provide 24V DC and thus feed the °C-Lite even if it is to have a WiFi chip (see 3. Connectivity).

If the °C-Lite is to be designed as a stand-alone device without connection to other controllers and/or is to have a WiFi chip, a 230VAC supply is the obvious choice. Since °C-Lite is optimally suited for installation in outlet sockets, suitable supply lines are usually in place already. The °C-Lites must then be equipped with a corresponding power supply unit for conversion to the internal operating voltage.

2. Sensor Options

Temperature, rel. humidity, indoor air quality, CO2 eq, air pressure

The integrated multi-sensor collects measurement data on room temperature, relative humidity, air pressure, indoor air quality and CO2 equivalent. The room temperature is often essential for most HVAC applications anyway. Humidity measurement can be an important component for room cooling, especially dew point monitoring, as well as for humidity regulation by dehumidifiers or fan coils.

The air quality sensor determines the so-called Indoor Air Quality Index and derives the CO2 equivalent from it. At the latest with the Corona pandemic, general awareness of indoor air quality has increased, which opens up new market opportunities for system providers. The technical background to the Indoor Air Quality Index and its possible applications can also be found in the article “The Indoor Air Quality Index in HVAC Applications“.

The extent to which the sensor data should only be displayed, transmitted or integrated into control strategies can be flexibly implemented according to the preferences of the product management.

3. Konnektivität

Modbus, RS485, CAN, WiFi, BLE, PWM, 1-Wire Master/Slave, OpenTherm

In the digital age, connectivity plays an increasingly important role. This can refer both to the composition of several devices into an intelligent network and to Internet connectivity for remote access and monitoring. Some tips on what product managers should consider when designing can be found in the article “Design for connected systems, not connected products“.

Via Modbus RTU, °C-Lite can be connected to the entire building management systems (BMS) or communicate directly with other devices such as heat pumps. Alternatively, other proprietary bus protocols can be implemented via the RS485 interface used by Modbus. It is also possible to implement the OpenTherm protocol, which has historically been supported primarily by gas boilers / condensing boilers, but can also be used in heat pumps.

Two bus systems frequently used by SOREL are the CAN bus and 1-Wire. The CAN bus is supported by most SOREL controllers and thus offers the possibility of a cross-device control system. However, own CAN applications can also be implemented.

On the 1-wire bus, °C-Lite can function as master and/or slave. Thus, floor or ceiling sensors can be connected to the °C-Lite in the same room, or the °C-Lite itself can be part of a larger system such as the °CALEONbox multi-zone control for underfloor heating.

For wireless communication, the °C-Lite platform also offers two options. We have examined the advantages and disadvantages of radio-based systems specifically in heating technology here.

Via Bluetooth Low Energy (BLE), which is built into many common smartphones, a commissioning menu or further parameterisation options could be realised via a mobile app. A direct connection to BLE actuators, such as heating actuators, is also possible.

A WiFi chip can also be used for local communication with other devices. Compared to Bluetooth LE, WiFi scores with the greater range, so that, for example, several °C-Lites can be connected to each other across rooms.

A major advantage of the WiFi module is also the possibility of internet connection to control the entire system via smartphone app, to perform professional monitoring, or to transfer and analyse data on a smart server.

4. Inputs and Outputs

PWM (2x), dry contact |PWM (2x), 0-10V (2x), dry contact

In addition to the 1-wire sensor, PWM input signals can also be used to receive information from the °C-Lites. As mentioned, the 1-wire sensor can record additional temperature values in the room and incorporate them into the control strategies. The PWM input, on the other hand, could be used to count a pulse with a flow meter or energy meter, for example. By means of pulse width modulation (PWM), status or error messages can also be transmitted from high-efficiency pumps or valves.

A status can be transmitted via a potential-free logic contact (0/I), which is evaluated by the °C-Lite. This could be a collective fault message from a larger system, for example.

Switching operations can also be carried out directly via the °C-Lite. A potential-free relay or up to two 0-10V/PWM outputs can be used for this. For the latter, there are various pumps, valves and other actuators available on the market for technical building equipment that can be addressed and modulated via this.

By connecting a Switchbox, a switching command and/or the exchange of sensor values can be transmitted wirelessly between the °C-Lite and another point in the room. This could be a fan coil unit in the ceiling, for example. A WiFi module must be provided for this as described under “3. Connectivity”.

5. User Interface

Up to 3 capacitive touch surfaces and RGB LEDs

The °C-Lite platform offers the user three capacitive touch zones for navigation and command input. The RGB LEDs underneath indicate the position and function of the touch areas – for example, a blue LED can signal the user to lower the temperature by touching there.

The LEDs can also be used for status indication. Depending on the LED colouring, the air quality could be visualised or the operating status could be signalled when two WiFi devices are connected.

n the centre of the unit are 46 additional LEDs that can be used to display larger characters such as individual letters or numbers. These are particularly suitable for displaying the measured sensor values, but can also contain simple navigation elements. In the case of more complex menu structures, however, it is strongly recommended for reasons of usability to do it via a suitable smartphone app.

For further suggestions on the usability of networked devices, see “The User Experience (UX) of Connected Heating and Cooling Systems“.

6. Enclosure options for different mounting situations

Individual design and colours

°C-Lite is optimised for installation in European switch ranges with a standard diameter of 55mm. This means that °C-Lites can be elegantly integrated into existing switch rows and remain unobtrusive in the room ambience. Ideally, suitable supply lines are already available or can be easily placed.


If no flush-mounted outlet socket is available, two different surface-mounted frames are available for extra-low voltage or mains voltage operation. In some countries, such as Italy, Switzerland or the UK, switch ranges sometimes have different standard dimensions. The electronics of the °C-Lite can also be integrated there in a visually flawless manner using corresponding adapter panels.

Depending on the application, it may be desired to make the
°C-Lites portable. For example, if they are primarily intended as air quality sensors, the °C-Lite electronics could be installed in special countertop housings. To simplify installation, an insert for standard power sockets is also conceivable, which completely eliminates any wiring effort.

Application Examples

The following schemes represent exemplary use cases for which the °C-Lite platform could be ideally used. There are no limits to further creativity based on the hardware variants described above. Our OEM team is at your disposal for further questions and suggestions.

Jonas Bicher

About the Author

Jonas Bicher has been managing director at SOREL since 2013.
He likes innovative ideas, usability design and software-based technologies

14. November 2022