What is KNX and why is it considered the smart home standard?

KNX comes up often when a smart home, a hotel or an office is being designed. In this guide you will see what KNX is in simple terms, how devices connect to the bus cable, what the ETS software does and what you can control with such a system.

What is KNX, in simple terms

KNX is an open international standard for home and building automation. It defines a common “language”, so that devices from different manufacturers can communicate reliably with each other within the same installation.

In practice, lighting, heating, blinds, security and energy management work as one system rather than as separate devices. The standard has been around for more than 30 years, and today it is supported by more than 500 manufacturers.

KNX is used in detached houses and flats, as well as in hotels, hospitals and offices. Its core functions run locally, within the installation, without needing a constant internet connection.

How the bus wiring works

In wired KNX, all devices are connected to a shared bus cable, which carries their commands. In KNX TP, the most widespread form, the bus is a special twisted-pair cable designed for building automation.

Two groups of devices are connected to the bus. The first gives commands or takes measurements, such as push buttons, presence sensors and thermostats. The second carries out the commands, such as switch actuators, which switch 230 VAC loads on and off, and dimmers, which adjust the light level.

The KNX power supplies, the USB interface and the line coupler from Comelit are mounted on a DIN rail in the distribution board. During installation, the bus runs in a conduit separate from the 230 V lines, and mains voltage is never connected to it at any point.

Apart from cable, KNX also uses other transmission media:

What is ETS and who does the programming

ETS is the software used to design and configure every KNX project. It is a single tool for all brands, because it includes all certified KNX devices, regardless of their manufacturer.

Programming is done from a computer, which connects to the bus via an IP router or through a KNX Secure USB interface. The basic steps are:

1. Project design. The details of the devices in the project are entered into ETS, whatever their manufacturer.
2. Physical address. Each device is given its own address on the bus.
3. Parameters. The functions of each device are set, for example the activation time of a presence sensor.
4. Linking the functions. You define which push button or sensor controls which output by linking the communication objects into groups.
5. Download. The parameters and links are downloaded from the computer to the devices.

ETS is used by installers. KNX certification is not mandatory to use it, but it is strongly recommended, and those who obtain it become KNX Partners. ETS licences differ mainly in project size: the basic editions suit training and small jobs, while the professional editions have no size limit.

What you control: lighting, heating, blinds, scenes

With KNX you control lighting, heating and air conditioning, blinds, security and energy from one system. In the Comelit wired KNX system, these functions are covered as follows:

A scene, such as “Leaving home” or “Good night”, brings many commands together in a single press. You operate the system from push buttons, the 4.3-inch SMARTTOUCH2 touch screen or your mobile phone.

The ETHBUS4 web server provides remote access through free apps for iOS and Android or from a browser, and works with Google Home and Alexa. SMARTTOUCH2 also has voice control and a built-in thermostat.

Why an open standard protects your investment

An open standard does not tie you to one manufacturer. The installation can be maintained and extended later, because KNX devices are interoperable and backward compatible.

KNX complies with the European standard EN 50090 and the international standard ISO/IEC 14543 for home and building automation. KNX devices go through official certification, which ensures compliance and interoperability and gives the right to use the KNX trademark.

This has practical value over the years. If you later want a function that the original manufacturer does not offer, you add a certified device from another brand to the same ETS project. The same applies when the project grows: KNX covers everything from the renovation of a single room to complexes with many buildings.

KNX in Comelit systems

Comelit has a wired KNX automation system with equipment for homes, buildings and hotels. It is one of its three wired automation systems, together with SIMPLEHOME and BUSING, while WINGS covers wireless automation.

The system includes switch actuators with 2 to 22 16A outputs and a 30A version, dimmers, sensors, power supplies and KNX gateways for air conditioners. For the bus infrastructure there is an IP router, a USB interface and a line coupler, all with KNX Secure support.

For hotels there are Mini PCs with management software for up to 50 rooms and a USB device for Mifare RFID cards. Comelit's BUSING system also has gateways for connection to KNX.

If you want to combine automation with video door entry, an alarm system and CCTV in one app, see Comelit Smart Home. On the page with the Comelit partners you will see which of them also cover automation in your area.

Frequently asked questions