[ Focus: KNX technology ]


without rewiring by a KNX integrator, simply by connecting a laptop anywhere on the bus to re-confi gure the system. A completely scalable system, KNX is installed in a basic


‘line’ layout which can accommodate up to 64 devices per line and, for larger installations, lines can be joined together via line couplers up to a maximum of 15 per area and areas can then be linked together with ‘area’ couplers. Fry continues: ‘This modular approach to installation not


only makes installation faster and simpler, it also increases fault tolerance on the system, as each line requires an independent power supply, so a failure on one line does not affect any of the others. What’s more, local data traffi c on one line does not affect data throughput on the others.’ Each installation comprises inputs (such as light switches,


presence detectors and daylight sensors), outputs (such as relay actuators, dimming actuators, blind actuators and heating actuators) and controllers (such as timers, event- driven sequencing, mood scene setting, data logging and programming devices). These three elements are combined to provide the foundation for the installation’s functionality and can be pre-programmed to provide ‘scenes’ or linked ‘events’. Manual control is also built into the system, and this can be done via conventional controls such as light switches and thermostats or, as in the case of the Jung Facility Pilot system distributed in the UK by Wandsworth, by control and visualisation software that allows the end user to control, monitor and visualise all functions on a single, touchpad, wall-mounted screen. ‘Ease of control and visualisation for the end user is one of


the key advantages of the KNX system,’ Fry adds, ‘and this can be done from both within the building and remotely via a secure internet connection or smartphone app. For residential properties, this can allow the occupier to activate “welcome” mode to switch on heating and lighting when they’re returning from holiday, for example, and for commercial properties it


might allow the facilities management team to monitor energy wastage and adjust settings accordingly.’


This modular approach to installation not only makes installation faster and simpler, it also increases fault tolerance on the system


How it works The success of the KNX system is founded on the reliability of communication between the various devices. Commands and messages are exchanged between devices by telegrams that are transmitted symmetrically on the line, ensuring a high level of noise immunity to the signal and preventing any interference that affects both lines from infl uencing transmission of the information. At 9600 bits/second, the transmission speed is low, but it is perfectly acceptable for the type of data traffi c required, and means that no terminating resistor is required and that any wiring topology can be used. Fry explains: ‘The telegrams are made up of packets


of information – the source address, the device’s physical address and the target address – along with the data fi eld which provides the instruction of what to do – turn on/off, dim up/down, set value, etc. – and fi nally a checksum fi eld to ensure correct transmission.’ For the devices to communicate effectively, information


must be transmitted on the bus line without colliding with other information. The bus protocol is such that the telegrams are transmitted when the bus is clear and retransmitted if they are not acknowledged as received. However, this is made simpler by the fact that all telegrams are event-driven, ensuring that information is only transmitted when required, thereby reducing the amount of data traffi c on the bus.


A smarter approach Intelligent homes will always carry the ‘bespoke’ label, as systems like KNX allow the installation to be tailored to the needs of the property and its residents. However, with the challenges of climate change facing specifi ers, there is a need to think smarter, and intelligent homes could just provide one of the key responses to creating lower carbon homes. ‘KNX, as an established technology, brings an exciting


opportunity to the electrical industry,’ Fry enthuses, ‘and its ability to reduce a building’s energy consumption by as much as 50 per cent means that it looks set to play a key role in the zero carbon buildings agenda.’ What’s more, this technology is continuing to grow and


About the author


Giuliano Digilio Giuliano Digilio is the head of ECA Technical Services. He has extensive experience in the electrical and electronic engineering building services industry, and sits on numerous technical committees for the ECA in the UK and Europe.


develop. Wireless radio transmission of KNX systems is now possible, making KNX suitable for renovation projects where rewiring is not an option. And the support of the KNX Association continues to make the fi eld more accessible, with initiatives such as the introduction of the ETS4 software package, developed by the association to help the designer and installer put together a system that addresses the specifi c requirements of an individual building and its occupier(s). In the 21st century the built environment not only needs


to address the way we live and work now, it also needs to be fl exible enough to continue adapting to the way we live and work as trends and technology change. KNX provides that fl exibility while enhancing comfort and energy effi ciency, and it is time the UK’s electrical sector began to reap the benefi ts of this integrated building automation technology by learning more about it and building on our skills base.


■ This article was put together with information from Gordon Fry of The Wandsworth Group, an ECA member.


November 2011 ECA Today 51


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