The e-magazine for KNX home & building control

The Bigger Picture: how to avoid protocol soup through building-wide networks

By Simon Buddle, Future Ready Homes

Three days ago, it was a balmy 24°C, but now I am looking at the beginning of the ‘long grey’. The holiday season is over too – at least what there was of it. In Europe, we the British are blessed that almost everyone can speak our language in part or fully. Restaurant staff are happy to converse with tourists in a multitude of languages, albeit with limited vocabulary, and by and large, it works perfectly as a system. Plus, we get to enjoy more than steak and kidney pie for dinner. But can you imagine what might happen if we had to pass our menu order through multiple languages before it finally arrived with the chef? It seems too preposterous to contemplate.

Interesting, but didn’t I order knödel?

And yet that is exactly the scenario I have come across recently on several ‘recovery’ projects over the last few months. For example, a KNX thermostat in the wall that connects to a block-wide Tridium BMS via BACnet IP. Now on the surface, that would seem to be fine, except that the Tridium then communicates with the apartment’s fan coils over BACnet/MSTP and controls the underfloor heating with a local relay device. The primary user interface is a Crestron touchscreen. This number of different communication protocols does not seem logical.

Levels of control

When I looked into the reasons behind this setup, it became apparent that one simple factor was driving the need to effectively use the Tridium as a master gatekeeper for all signals, and that was a centralised control point for the building. What had, in effect, happened, was that the building BMS had created a data network between all apartments, back-of-house facilities manager and the concierge desk. Why? Because no one had designed a building-wide data network. To be fair, even a simple KNX bus network would have worked, but at some point, it would have needed to break out onto a data network for the central controls.

At one point during the fault-finding that we carried out with this system, we had three engineers holding laptops connected to various parts of the communications path and someone else making changes at the touchscreen. By any measure, that cannot be considered reasonable.

A soup of communication protocols can result in fault-finding nightmares.

A building-wide data network as part of the design process

Insular (by that I mean single apartment) thinking means that even today, most multi-dwelling units (MDUs) do not have a building-wide data network designed and installed. Surely this is a CPD course in the making! Designing the network is simple – it is the same as an apartment network, just on a larger scale. However, the item that has to be addressed here is that we, as the KNX professional community, must make every effort to embed ourselves and our skills in the design process at the earliest stage. In the UK, this means being included in the RIBA (Royal Institute of British Architects) Plan of Work at Stage 2, the Concept Design Stage. The building data infrastructure should be designed and costed before budgets are prepared and quotes tendered, otherwise there is too little wiggle room in an MDU financial package once it has all been agreed. Indeed, the most likely cost change is to value-engineer it down further.

The RIBA Plan of Work organises the process of briefing, designing, constructing and operating building projects into eight stages and explains the stage outcomes, core tasks and information exchanges required at each stage.

KNX as the central control platform

Clearly, we can deal with all of the elements within the apartment using KNX as the central control platform. We can connect to the fan coil by placing a local device by the side of the unit. All manifold controls and floor temperature alarms can likewise be dealt with. From there, it is a simple switching or 0-10V actuator to deal with MVHRs (Mechanical Ventilation with Heat Recovery), HIUs (Heating Interface Units) and CIUs (Cooling Interface Units). Lighting falls into line easily. The bigger question is, ‘How do I give users in the apartment control from their smart phone as well as enabling the concierge desk to control the apartment when needed?’

Taking advantage of the fourth utility

A landlord’s data network that uses VLANs to secure each apartment provides the communications infrastructure. Is it feasible to route all data to the Internet via a single landlord’s router and simply have the Internet service provided at a building level, literally as a utility from the landlord? Why not? We call it the 4th utility anyway, so why not make that real? It makes much more sense than thirty or forty independent routers all over the building. Wifinity, for example, has been rolling out such networks across the UK for several years.

Wifinity is an example of a network provider that offers Internet service for a whole building via a single landlord router.


Whether we create KNX bus lines all the way down to the central plant or use a common data network as the backbone of the communications, they are both KNX-secure, but moreover they provide a great opportunity to create robust and simple communications pathways. It gives a one-stop solution for apartment controls and the flexibility for multiple users and user interfaces to be able access controls in a safe and secure way across multiple secure networks. What is not to like about that? Anyone fancy doing a CPD?

Simon Buddle CEng MIET, is a consultant for Future Ready Homes, a specialist in BMS and ELV services system design.

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