Solutions: KNX in a BMS World

Sophie ThomasBy Sophie Thomas, Ivory Egg.

We have been trying to control our built environment since at least 270BCE, when the first automatic control system device, a water clock, was invented. The first HVAC-related system came about in the 1700s through Rene-Antoine Ferchault de Reaumur’s scale thermometer and his ideas on temperature control of incubators based on an invention by Cornelius Drebbel. The 1920s saw the beginnings of building management systems (BMS) as we would recognise them today, with the birth of boiler control systems.

The earliest recorded system control device - where we started in 270BCE.

The earliest recorded system control device – where we started in 270BCE.

Since then, the use of BMS systems has become commonplace, especially in the commercial and public sectors. Buildings are becoming ever more complex, and with economic pressures, more scrutiny of energy consumption and shared and multi-purpose usage of buildings requiring scalability and flexibility, is it any wonder that BMS systems are being relied upon more and more?

Multipurpose office environments, commonplace in today's working world, require very flexible building management systems to keep up with the end users' demands.

Multipurpose office environments, commonplace in today’s working world, require very flexible building management systems to keep up with the end users’ demands.

What does BMS mean in practice?

BMS generally refers to localised or centralised control of HVAC plant, but really it should also include lighting, shading and security control. Plant control requires numerous control points for valves, pumps, variable temperature valves, temperature sensors and fault inputs and a process to handle all of the control algorithms.

What a BMS can control.

What a BMS can control.

In a large building or network of buildings, you can see how the number of control points and devices and the related logic can become extremely complex. Modern buildings often rely on a number of different, sometimes proprietary systems or protocols such as BACnet, LonWorks, C-Bus, Trend or Modbus, to operate the different plant areas, and often use separate software packages, making it difficult to analyse and streamline data and get a harmonised, overview of the building’s performance.

The plant room in a large-scale commercial or public setting.

The plant room in a large-scale commercial or public setting.

Trying to combine data from numerous disparate systems is not only time-consuming but it adds to an already complex set up, and can lead to grey areas, data gaps and overlaps and, at worse, systems can conflict with each other. The outcome is an environment that is less than comfortable for the inhabitants, and harder to control for those responsible for maintenance.

The complexity of using multiple proprietary systems.

The complexity of using multiple proprietary systems.

Where does KNX come in?

KNX is of course a BMS system. It is also a distributed system, and so is ideal for allowing all devices around a building to talk to each other. It could certainly control the entire plant setup, but where a complicated plant room exists, KNX might not be best suited as a standalone solution. The reasons for this are three-fold:

• Plant products such as boilers and burners do not often have native KNX interfaces.
• With the exception of the Siemens Synco range for smaller-scale projects, there are no KNX plant controllers that can take control of complicated plant easily.
• The plant management and building infrastructure are often taken care of by different contracts, and are by nature cross-discipline, meaning it is very unusual for just one person or department to look after the building and plant management.

Not all BMS systems are always able to talk to KNX, and so combining KNX with another BMS could be seen as contentious, but there are products such as the Siemens Synco range that address this issue and allow for the best of both worlds through open data exchange.

Overview of the Siemens Synco KNX BMS system.

Overview of the Siemens Synco KNX BMS system.

KNX is the protocol of choice for building automation and control as it can be used cross-discipline, and it is scalable. In fact all but the most complicated buildings and plant rooms could be entirely run and managed with KNX devices. The number of KNX manufacturers is already large and is growing all the time, so there are KNX devices for all kinds of HVAC applications.

KNX can control all aspects of the building environment using one open protocol.

KNX can control all aspects of the building environment using one open protocol.

Due to the obvious advantages of KNX, it is very common to see a proprietary BMS being used for the plant control with an interface to KNX via a BACnet or Modbus gateway, allowing the extra functionality and the benefit of remote access and alarm notifications using one user interface. KNX integration is made simple when using BMS systems such as Tridium, as they offer direct KNX integration.

How BMS information was communicated in bygone days (image from a report by Bristol University on BMS).

How BMS information was communicated in bygone days (image from a report by Bristol University on BMS).

In cases where BMS systems such as Tridium or Trend are being used for complex plant control, KNX is the ideal choice for the field bus. The field bus is responsible for sensing and collating data from around the building and sending this information to the BMS plant controllers as well as taking data from the plant and relaying this information to users and maintenance staff through visualisation.

Traditional BMS and KNX working together (image courtesy of Entech Ltd).

Traditional BMS and KNX working together (image courtesy of Entech Ltd).

The use of one user interface is beneficial, as data can be analysed, graphed and interpreted so that reports can be made more readily available. With KNX, the option of remote access and the possibility of viewing the data on smart phones, tablets and laptops means that different managers, such as facility managers, electrical managers, IT managers, and security managers, can see the same data and have their input on the building’s operation.

Specifying and Installing a BMS

When choosing a BMS, it is important to consider the different areas that comprise a modern building and how the BMS can offer benefits to these and their inhabitants. Attention should be paid to the design, specification, installation and commissioning process in order to ensure a harmonized and effective BMS and avoid conflicts. With any BMS, maintenance will still be a factor, but with the use of KNX, this can be made simpler and less time-consuming.

According to CIBSE (Chartered Institution of Building Services Engineers) guidelines, any specified BMS must be capable of dealing with a future 20% increase in the number of points without compromising the system’s functionality or speed of operation. The scalability and ease of expansion within a KNX-based system make growth or even major alterations achievable and, very often, much simpler.

Can you use KNX combined with a BMS in residential environments?

Increasingly, we are seeing more complex plant requirements in modern residential projects, especially where technologies such as ground source heat pumps and solar water heating systems are used. As KNX is Europe’s most popular control platform, it makes sense to consider how we can combine the use of BMS systems and KNX in a residential environment. Basically, there are three options:

1. Use KNX for everything outside of the plant itself. All control of remote pumps, valves and all sensing is done within KNX which ensures that the system is cost effective. Room temperature regulation is all within KNX, so it is very easy to keep the cooling and heating systems from fighting each other. In addition, the heating solution is now an integral part of the other systems in the building, reducing complexity. This solution is ideal for applications ranging form the simple to all but the most complex.

The Gira HomeServer user interface allows all rooms to be visualised and controlled.

The Gira HomeServer user interface allows all rooms to be visualised and controlled.

2. Use KNX to provide the room regulation, with the BMS controlling the manifolds, pumps and valves directly. This allows for an integrated KNX keypad, easy integration with other building systems on the KNX bus, but still allows the use of a substantial plant BMS. The benefits however, are limited, as the potential of both the KNX and plant BMS solutions may be not be realised. In addition there could be substantial duplication in infrastructure.

3. KNX provides only the room temperature with all regulation and control performed in the plant BMS. If the systems integrator wants to steer clear of HVAC responsibility, they may prefer this solution. The KNX system however, will be massively under-used and the overall solution is likely to be significantly more expensive.


Proprietary BMS systems certainly have their place, but in order to make a system most efficient ecologically, physically and financially for inhabitants and managers, there is another option to consider.

KNX and BMS should not be seen as mutually exclusive. By understanding the complexities or indeed simplicities of the building, a decision can be reached as to what the best ratio of plant control and the use of KNX is. Both systems are powerful in their own right and their benefits should be harnessed through careful specification, planning and commissioning in order to create a system that will work at its peak now and in years to come.

Sophie Thomas is the Marketing and Events Manager at Ivory Egg (UK) Ltd, a supplier of leading KNX products and provider of KNX training courses.

You are welcome to comment on this article below.

Share via:


Solutions: KNX in a BMS World — 3 Comments

  1. Since when have Lonworks and BACnet, even Modbus to a degree, been proprietary bus systems for building automation (BMS)? without BACnet integration KNX itself would standalone in the grand scheme of ‘inter-operable’ building automation and control systems to a certain point.

  2. Steven,

    Thanks for the comment. The article wasn’t intended to state that any of those protocols are proprietary although some of them certainly were originally. But it raises an interesting point. Is being non-proprietary important to the effectiveness and success of a protocol?
    In the case of KNX, I would suggest its success is at least partly due to having been open and non-proprietary from the outset and the same likely applies to BACnet. On the other hand, both Lonworks and Modbus were developed within a manufacturers internal product range (Echelon and Schneider respectively) but were extremely successful and have since been adopted as industry standards.
    I also take your point about KNX in commercial buildings effectively requiring BACnet as another inter-operable protocol to complete the job. I would also argue the same point the other way around as well, in that BACnet based plant installations could utilise the advantages of a KNX based field bus more often than they currently do.

  3. Dear all:

    I think there is a misunderstanding of what a BMS is.
    KNX, LON, Modbus or BACNet cofigures the field level – and sometimes automation level – of the Automation Pyramid in a building. A BMS (Building Management System) is a diferent layer (the top one) in this pyramid, so with the correct BMS solution we can link every of this systems and even more. The question here is to choose a non propietary or excesive vendor-dependant solution for this layer. In my opinion, for helping KNX to survive with BACnet in future big installations, the best solution is the BMS Server from NETxAutomation. From the past 10 years the NETxAutomation OPC Server have been the recommended OPC solution for KNX International. Now the OPC (only for KNX) have a big brother (the BMS Server) where we can find the complete integration solution for smart buildings in this scalable, independant and interoperable software.
    So, please, do nos assume that systems like KNX are BMS by themselves, althoug they are an important part of the whole solution.
    In my opinion KNX + BACnet (the “hardware”) are the perfect combination of reliability, functionality and performance in a Building Automation Solution. And a good BMS solution (the “software”) is the necessary soul for this body.
    Together they can create a strong front against the rest of propietary solutions.

    Have a nice day!

Leave a reply (comments are moderated)