KNX in a listed building - Our own office!

As a specialist in control and automation, KNX is what we do, so visitors would expect to see it in our ‘home’. Having moved our headquarters to Staunton near Gloucester, UK, we decided to take the opportunity to install KNX in the building. This case study covers the practicalities of controlling the building’s lighting and heating, and monitoring our energy consumption, all using KNX.


Formerly a dovecote, our new office is a 17th-century and Grade II listed building of special interest, warranting every effort to preserve it. It is half-timbered with important external and internal features, including brick nogging and a tiled roof. Internally, the walls feature around 600 roosts built into the brickwork.

The building had been standing idle for many years and was in need of considerable repair. The owners (now our landlords) started the process of conversion to a working office building in 2002, initially spending much time working with the planning authorities to ensure the most appropriate and sensitive conversion. The reconstruction process was extensive, including replacement and repair of structural timberwork, whilst retaining as much of the original as possible, where it was sound.
Particular consideration was given to preserving the features of historic interest. For example, although for practical purposes, the internal walls have been largely clad in studwork and skimmed plasterboard, the roosts in the brickwork have been featured in a number of locations around the internal walls with ‘display windows.’ These show off the underlying structure of the building, adding considerable character and interest to the building and helping to retain its historic charm.

During the process of conversion into useful working office space, the owners incorporated a conventional electrical installation that provides lighting and points for electric heating in a number of locations.
We decided to do the KNX conversion in three phases. Phase one would involve automated control of our lighting, and this has now been achieved. We also want to save on energy bills. The electric heating is costly to run and I feel that it will be possible to achieve significant cost savings through correct control and scheduling of the heating system’s operation. This will be undertaken in phase two of the KNX conversion. We also want to be able to monitor energy usage – in phase three – with a view to assessing and managing costs.
All of the building’s light switches were located together adjacent to the main door into the space. The downstairs lighting was all operated from a four-way switchplate which had fortunately been wired with the lighting ring supply fed to the switchplate and switch loops for each circuit taken from there to the appropriate light fittings.

We decided to make the cut out for the KNX flush-mounted DIN-rail enclosure where an existing four-way switchplate was positioned.

 

The basic lighting control using KNX has been the easiest to implement from a practical viewpoint since the conventional installation was ideally configured to be converted. The fact that the internal walls were clad in studwork meant that we could thread the cables through the void behind, which was relatively easy to do.

 

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                Threading cables through the void behind the studwork was easy to do

 

We even found that what we thought was a single group of downlights in the office area was actually wired as two separate groups connected to the same switch. This made it a straightforward conversion from conventional to KNX actuators. In principle, each of the four switches could be replaced by a KNX actuator channel, which meant that the four-way switchplate could be replaced by a flush-mounted DIN-rail enclosure for the KNX actuators and the KNX power supply. The mains supply for that power supply was taken from the lighting ring.
The low power consumption of the KNX supply – in this case, less than 10W – posed a marginal additional load in that ring circuit, that would not impinge on circuit ratings. It was decided to fit dimmer actuators for each of the three halogen downlight circuits and another for a wall light on the stairs. There is a bulkhead light outside of the front door, and it was decided that this did not need to be dimmed, so a switched-only circuit was chosen.
Dimmer modules optimised to handle the difficulties of operating with LED lighting were selected on the basis that it is fully intended over the next weeks to replace all of the halogen GU10 lamps with LED replacement lamps. The expectation is a reduction in power consumption of those circuits to less than 20% of the existing consumption.

 

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                  The completed enclosure for the KNX lighting actuators


Similarly, when we came to consider the upstairs office area lighting, which is fluorescent strip lighting, switched control was the way to go. With regard to the upstairs lighting, the wiring was such that two-way switching had originally been installed at the top and bottom of the stairs. The KNX implementation of this was to route a switch loop behind the studwork across from the four-channel switching actuator module at the new panel location.
We also routed a KNX cable across from the new panel location to the switchplate position at the bottom of the stairs. Our ultimate objective was to replace that switchplate with a KNX pushbutton sensor plate from which we would be able to control all of the lighting.
So, having made these changes, for now, a simple ETS programme has been implemented that allows the operation of each lighting circuit from the pushbuttons of the KNX sensor plate.

 

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           Programming the KNX system's functionality

 

Now that we have the lighting phase of the installation installed, the next step is to add the heating control actuators and contrive a method of making the KNX connection to a much less accessible location.

After many attempts and much careful consideration, we had to reach the conclusion that it was not going to be possible to thread a cable around behind the studwork. The thickness of insulation within the studwork that the developers had included when renovating the building was of a level that made it difficult to thread reliably over any distance. This, coupled with the fact that the intricate wall construction (containing as it does the former pigeons roosts), made the task impossible without stripping back the wall linings to get behind. This would have been exceedingly disruptive and very costly.

 

However, the flexibility of KNX communications media came to the rescue.

 

Here’s what we did. The owners had incorporated a conventional electrical heating installation which comprised four convector radiator termination points, each individually wired back to a distribution board location “under the stairs”. This gave us the benefit of having access to a power cable to each radiator point.


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      Multi-channel KNX Switching Actuator with per-channel current monitoring

 

Taking advantage of this, we fitted a multi-channel KNX Switching actuator to which we connected each radiator point to a separate channel. In due course, this will allow us to have individual control over each radiator point. This is a major step forward from the system as originally installed, which was based on simple panel heaters fitted with a basic timeclock and power level adjustment.

 

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    Conventional panel heater and wireless room temperature sensor (top right of picture)

 

We decided to use the same panel heaters, but set their local controls to be always on and at full power and use the KNX system to regulate the operation of the panel heaters to give optimum room temperature control. Ultimately, we were able to establish a control algorithm that optimises energy usage.

 

Another benefit was that the KNX actuator type that we selected incorporates current monitoring on a per-channel basis. This means that we will eventually be able to use these to gather data on the energy consumption of the heating.

 

The challenge was to incorporate this new KNX switching actuator for the heater panels into the existing lighting control KNX system. Since we were not able to thread a KNX cable, we would have to find another means of realising that integration. After careful consideration, we decided to make use of the KNX/IP protocol.

 

The new actuator was installed and set up with its own KNX power supply and line segment, in effect creating a separate KNX installation for just this actuator. The building now had two KNX lines in separate locations, one for the lighting control panel with its push-button sensor plate and a second for heating control via this new actuator. We equipped each of these lines with KNX/IP routers that would, in principle, allow us to create a single KNX system using Ethernet as the backbone, connecting both parts to each other.

 

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     KNX/IP device shown during testing and after installation

 

However, we still could not establish a wired Ethernet infrastructure because of the difficulties of cabling from one side of the building to the other, but this was easily overcome by using plug-top adaptors implementing Ethernet over Powerline, making use of the mains wiring in the building to carry the Ethernet communications between the two KNX lines. With this in place, it was a simple matter of setting up the appropriate addressing for each of the KNX/IP routers, both on the Ethernet side and on the KNX side using ETS. We now had a single KNX system in the building.

 

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                                                KNX segment for heating control system

 

Despite this, the challenges were not over. We still had to establish a method of measuring room temperature so that the heating system could be properly controlled. Once again, we were in the position of being unable to thread a cable. Unfortunately, in this matter KNX/IP could not offer a resolution. The solution we devised was in the form of a wireless temperature sensor that we linked into the KNX system via a KNX/Wireless gateway.

 

With this in place and set up quickly using ETS, we were able to not only monitor temperature, but place the temperature sensor at the most suitable position in the building, being unencumbered by the constraints of cabling.

 

The result is that we now have a fully integrated control scheme for both the lighting and the heating in the building.