The KNX standard

The KNX standard

A communication protocol that renders buildings intelligent and interoperable
Thanks to KNX technology, Building Automation solutions are becoming increasingly indispensable components, able to integrate all functions pertaining to energy and comfort within buildings. The decentralised management of each individual component, hailing from the distributed intelligence, guarantees the safety of the system in terms of service and helps reduce the Operating Expense (OpEx) for management.

A single standard recognised worldwide
KNX is a unique standard for intelligent building management that has received worldwide recognition from over 400 producers.

A certified system
Regardless of the manufacturer, all KNX products are certified by the Association, guaranteeing their compatibility and interoperability. KNX is the first globally-standardised system for automation control and management in residential and commercial buildings, in conformity with EN50090 and ISO/IEC 14543.

The scalable system ensures rapid implementation
The KNX system renders it possible to adapt the building to the changing needs of users. No masonry work or invasive operations are needed – in a few steps, it is possible to change the intended use or simply increase internal performance.

An advantageous choice
The economic parameters that characterise the management of a building are generally connected to the Capital Expense (CapEx) and Operating Expense (OpEx). The latter are substantially those that most affect the average life of a building, calculated over a period of 25 years. The choice of adopting a KNX-standard Building Automation solution means significant savings compared to a traditional system together with greater possibilities for growth in terms of integration.

On average, operating costs during the life-cycle of the building account for more than 70%. Often even simple functions – such as scenarios or commands that change position within the areas –
are extremely advantageous if made with intelligent KNX solutions. With a traditional installation, it proves complicated and burdensome to follow the various evolutions of a building. Yet with KNX solutions, adapting to organisational changes is simple and economical. From lighting control to temperature regulation, controlling curtains and blinds through to the management of alarms and automatisms, everything is aimed at achieving an optimal running of energy efficiency.

The three phases that define a KNX solution
Almost all Building Automation systems work well in the laboratory but it is only on real units that these systems demonstrate their validity and effectiveness. In fact, many factors can compromise the final result, from installation and sizing to the choice of the most suitable device, not to mention the actual commissioning and proper configuration. To ensure that everything works according to expectations, it is important to define the three main phases: design, configuration and commissioning.

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The KNX standard

The right choice of what to install is the basic aspect behind any design. Interoperability is assured with the KNX protocol, allowing the most suitable device to be chosen from the thousands of certified products. On the basis of the functional specifications, it is then possible to identify the list of necessary components, in developing a suitable type of system.

The correct flow of data is guaranteed via a suitable architecture behind the lines and areas that comprise the system. A protocol based on the transmission to an event prevents the proliferation of data and the saturation of the bus.
The individual products are configured through the ETS software, which is certified and distributed by the international KNX association. Each device is distinguished by a physical address (comparable to the name) and by a group address (attributable to the function). Through ETS, it is possible to parameterise each individual component by choosing from amongst dozens of features made available for each product. When done well, programming guarantees the operation and efficiency of the system. It is throughout this phase that the scenarios and automatisms that characterise each system are also created.
Commissioning follows the configuration phase. At this point, together with the end customer, the aspects related to performance and personalisation are undertaken. During commissioning, each individual object is fully tested both electrically and functionally.

System architecture

The basic component of each KNX system is the line. Each line requires at least one power supply, sized according to the number of connected devices. Up to 64 devices can be connected to each line. Indeed, it is possible – through the use of special Line Couplers (LCs) to connect up to a maximum of 15 lines (AREA).

A system can consist in up to a maximum of 15 Areas linked together by area or field couplers (AAs). The power supply necessary for operating the devices and data signal (telegrams) is conveyed by the same bus cable, also certified (twisted pair). All devices are characterised by specific addresses on the bus.

To avoid collisions between the telegrams and any loss of data, the CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) protocol is utilised.


The characteristics of the KNX communication protocol offer the utmost freedom of connection between the devices connected to the line. Indeed, there is no limit or topological constraint. What’s more, it is possible to connect the components in series, in a star, tree or in mixed configuration. There are also few installation rules which, if respected, ensure the utmost reliability of the system in any application.

Within the bus line, the following precautions must be observed:

  • Maximum cable length between the power supply and the bus device: 350 m.
  • Maximum line length between two bus devices: 700 m.
  • Total length of all cables within a line: 1,000 m.
  • Maximum number of power supplies on the same line: 2 (at least 200 m apart).

The sizing of the power supply to be utilised on each line is also simple. It is possible to associate a maximum consumption of 10mA for each KNX bus device, an assumption which renders the choice of power supply type swift and intuitive, being now available in three different sizes:

  • 160mA for up to 16 devices
  • 320mA for up to 32 devices
  • 640mA for up to 64 devices

Principle of operation

If more than one line is present, the sizing must take into account an additional power supply capable of powering the backbone and the same number of line couplers as there are lines present.

The principle of operation is simple: every device is assigned a physical address that is unique and even traceable within the architecture to the single component. Via the bus, each component communicates with one or more devices by means of a data telegram. Within the telegram there is generally a range of useful information for operation, in addition to the address of the sender and the recipient. To allow communication between the devices, the group address is utilised. This can have either a 2-level (main group/sub-group) or 3-level (main group/intermediate group/sub-group) structure.

Each device also has its own intelligence, which makes it completely independent from the other devices. This characteristic of distributed intelligence ensures the general continuity of service to the system and allows to immediately recognise any system failure.

The physical address identifies the name of the device and its location within the system, being generally defined in the configuration phase by pressing a button. The group address, rather, defines the logical connection and determines the mutual assignment of the devices connected to the bus.

Different solutions for different areas of application

The office is where the main automation of the building must converge. An intelligent environment will react and adapt to the various conditions of the day, ensuring everyday comfort only when it serves to benefit greater energy efficiency. The constant luminosity varies and adjusts according to sunlight, with fan coils that are activated only in case of presence detection, air quality is constantly monitored, along with the activation of preferential sockets whilst security is guaranteed by elegant numeric code keypads.

Thanks to Blumotix’s KNX systems, it becomes easy to setup a room for a presentation or meeting. The room thus adapts to the needs at hand, hence it proves no longer necessary to make adjustments to suit the various nature of each event. In a “smart” meeting room, there is no need to turn the lights on or off individually – simply press a single button or – even more simply – control the desired scenario from a smartphone to simultaneously activate a series of functions: the presentation screen automatically lowers, the blinds come down, the projector and microphone switch on and the lighting dims.

Blumotix srl
Via Bedazzo, 2
48022 Lugo (RA) – Italy
tel. +39 0545 1895254

P.I. 02136200397
Cap. soc. € 70.000 i.v.

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