What is KNX?

Let’s start with an official definition from the KNX site, KNX is the worldwide standard for home and building control. Pretty clear. Let us break down this definition.

Worldwide means that it is used all over the world. If we can trust the data which KNX provides, there are over 370 KNX member companies around the world, more than 7000 certified product groups and several million of KNX installation running.

We can take a formal definition of a standard from ISO site which states: “A standard is a document that provides requirements, specifications, guidelines or characteristics that can be used consistently to ensure that materials, products, processes and services are fit for their purpose.” What this actually means is that there is an agreed and defined way of doing something. KNX is approved as an International Standard (ISO/IEC 14543-3) as well as an European Standard (CENELEC EN 50090 and CEN EN 13321-1) and Chinese Standard (GB/T 20965).

Home and building control is self explanatory. KNX can be used to control homes and residential buildings. It is worth pointing out that KNX is not intended to be an industrial standard and is not used in industrial plants.

What can be controlled with the KNX?

There is broad spectre of possible use cases for the KNX devices. From basic control of lights and power sockets, to a more advanced control of the shades and blinds, to some exotic use cases of security and metering. All KNX devices can be classified in next categories:

• Lighting
• Blinds and Shutters
• Security Systems
• Energy Management
• HVAC Systems
• Monitoring SYstems
• Remote Control
• Metering
• Audio and Video Controls
• White Goods

How does a KNX installation work?

Enough with the definitions, let’s dig a little bit deeper and investigate how does a KNX installation work. Core component of every KNX installation is a KNX Bus. KNX Bus represents infrastructure which connects all the KNX devices in an installation and lets them communicate to each other.

Since the KNX Bus represents physical bus system there are a couple of options (mediums) how it can be implemented:

• TP – twisted pair
• RF – radio frequency
• PL – power line
• IP – internet protocol

All KNX devices can be grouped into two categories: Sensors and Actuators.

Sensors are devices which are responsible to identify that a certain event has happened. After an event is identified sensor will send a message in the KNX network with information about the event. All other devices in a KNX network can receive this message and act upon it.

Actuators are devices which are responsible for executing a certain action. Actuators are always listening on a KNX Bus, waiting for a message that a certain event has occurred. When that message is received actuator will execute an action it is programmed to do.

How does this work in practice. We can take a simple example of a light bulb in a room. In a traditional electric installation user will flip the switch. When the switch is turned on it will close the electrical circuit and the light will go on. When the switch is turned off the switch will open the electric circuit and the light will go off.

In a KNX installation everything works a bit differently. To turn the light on, the user will go to the push button sensor and press the ON button. The sensor will send a message on the bus which indicates that the ON button was pressed. Over the bus this message is delivered to all other devices in the KNX installation. Actuator which is responsible for controlling the light will receive the ON message and switch the light on. The same thing is happening when the user wants to turn the light off, with minimal difference that the OFF message is sent.

In this post I have covered some of the basic topics regarding the KNX:

• What is the KNX?
• What are the areas of the home and building control which are covered by KNX?
• How does the KNX installation work?

Everything that I have covered in this post is very high level and low details. But it has a purpose and that purpose is to give you a general feeling of what the KNX is. In my next post I will cover the main reasons why someone would use KNX installation in his house or building facility.