KNX Basics - KNX - KNX

KNX Basics

The KNX standard – the basicsIntroducing bus systemsIntelligent bus systems makebuildings more cost-effective to operate, safer, moreflexible, more energy-efficient and – above all – morecomfortable and convenient. The KNX standard occupies a large share of themarket for building automation systems.Past, presentand futurePeople live differently fromhow they did just a decade ortwo ago. We get money fromcash dispensers, buy and sellgoods and services over the internet, phone friends all overthe world from our mobilephones, and start to moan ifan MMS or e-mail takes morethan 5 minutes to reach a destination in the USA. In our carswe are guided around by satnavs, and we lock and unlockthe doors remotely withouta key. The interior light goeson the moment we step inside,then after a while slowly dimsdown again. In short, for quitesome time we have been enjoying cutting-edge developments in the areas of communication, entertainmentand automotive technology.If we look at how technology in buildings has developedover the same period, it’s avery different story. We stillopen our flat doors with conventional keys; and if we can’tfind our keys fast enough, thestaircase light timer switches the lights off and plungesus into darkness. True, whilewe’re out working all day, theheating automatically keepsour homes at a pleasant temperature – but it doesn’t notice whether we left the livingroom window open when wewent out. Only the electricity meter, ticking away quietly in a switch cabinet, notices2Figure 1. “Smart” houses that adapt to users’ needs? It sounds like somethingfrom a sci-fi novel, but it is already a reality. Intelligent buildings incorporatingnetworks of sophisticated devices that control the building as needed alreadyexist, and are making life easier for their occupants on a day-to-day basis.that. Before going away forthe weekend, it is wise to turndown the temperature in ourhot water tanks and to turn offall those electrical applianceson standby. But no one actually does – at least, not reliably. It takes too long.Time to dosome catching upSo electrical installations inbuildings have some substantial catching up to do. Networked sensors and actuatorshave long since been a standardfeature of motor cars; buildings, on the other hand, arelagging some way behind. Achange of mindset is needed,not least because of the longservice life of an electrical installation. Today’s new buildings will have to adapt to numerous changes over the nextfew decades. Now, more thanever, buildings need to be flexible and capable of accommodating networked building services. In technical terms, all ofthis is already entirely feasible (Fig. 1).More networkingThe key to making a building“intelligent” is to equip it withnetworked sensors and actuators. There are several different ways of doing this:Conventional methodsThe immediately obvious solution is to employ a star topology, i.e. an arrangementwhere every socket outletcircuit, ceiling or wall outlet, and light switch is linkedby its own (ideally five-core)NYM cable to a central distribution board in which thelogical relationships are created by contactors, switch relays, and a programmable logiccontroller (PLC). This workswell in reasonably small dwellings. However, the size of thehouse only needs to increaseby a fairly small amount beforethe extent of the wiring workand size of the power distribution boards required becomesexcessive. In a star topology,adding to or extending the system is also very time-consuming in terms of installation andprogramming.Bus technologyA far better solution is to linkall sensors and actuators in thebuilding with a “data cable”,and enable them to share information with each other (Fig. 2).Each device can then communicate with every other device,for example: a light switch can“talk” to a dimmer and tell ithow bright to set the ceilinglight; a motion sensor can tellthe actuator for the corridorlighting that someone has entered the corridor, or tell theroom thermostat that there isno one in the room any more,so it can turn down the temperature. The following areexamples of sensors that cansend information to the bus: Light switches Dimmer switches Motion sensors Presence detectors (whichcan detect whether thereis a person in a room evenif they are not moving) Window and door contacts(for security and heatingcontrol) Doorbell buttons for frontdoors Water, gas, electricity andheat meters Overvoltage sensors Temperature sensors for indoor and outdoor air Temperature sensors in heating and hot water circuits Modules for preselectingroom temperature setpoints Brightness sensors for indoors and outdoors, e.g. forconstant lighting control Wind sensors for controlling blinds Fault and system status messages for white goods (washing machine, clothes dryer,dishwasher, cooker, etc.) Leak sensors, e.g. in laundryroom Level measurements e.g. forrain water tank, oil tank,wood pellet store

The KNX standard – the basicsFigure 2. A bus system is a system of sensors and actuators joined togetherby a “bus cable”. KNX is standardised in Europe, the USA, China andinternationally, through e.g.CENELEC EN 50090 (Europe), CEN 13321-1/2 (Europe), ISO/IEC 14543-3(International), GB/T 20965(China), and ANSI/ASHRAE135 (USA). More than 350KNX members in 37 countries manufacture productsaccording to the KNX standard. Because the technologyis standardised, KNX products are all mutually compatible and KNX installations can be easily modifiedor extended at a later stage.Do bus installationsmake sense financially?This is one of the first questions that building owners andtradespeople ask when considering bus technology. Asso often – it depends. At firstglance, bus systems appearmore expensive than conventional installations. But appearances can be very deceptive!What need to be consideredare the benefits offered by asystem over its entire servicelife. Depending on the building type, the following maybe compelling arguments forchoosing a bus system:Reduced energy consumption in %808070605040605040304520Automationof Ventilation10Automationof LightingThere are several bus technologies on the market. Allof them are beneficial andappropriate for certain areas of application. But no other bus system is supported byas many different manufacturers as KNX. This is because: All strong brands in the building installation sector arepushing KNX technology KNX was developed specifically to meet the needsof electrical installations inbuildings KNX devices are installed,programmed and parameterised by fully qualified system integrators KNX is well-established andcan accommodate a hugerange of functions There are several thousand KNX-certified product groups available, covering every conceivable fieldof application KNX products are tested forconformity by an independent third party test laboratories KNX products are compatible with products from allmanufacturers (interworking) End customers benefit froman extensive network of specialist tradesmen with solid KNX skills accredited byKNX-certified training centres The PC software ETS canbe used to plan, design andcommission installationsof KNX-certified productsfrom any manufacturer KNX supports all communication media: TP (based ona standalone 2-wire bus cable), PL (Powerline), RF (Radio Frequency), and IP/Ethernet/WLANAutomationof Sun shadingExamples of functional modules (may be self-contained orintegrated in devices): Room temperature controllers Timer functions Freely-programmable logicmodules PLCs with KNX interface Constant lighting controlmodules Alarming and alerting Telephone switchboardsconnected to the bus Media control Heating control Pump controlWhy KNX?Automationof HeatingThe following are examplesof actuators that can be controlled via the bus: Relays for switching roomlights on and off Dimmers and DALI-gateways Electric thermostatic radiator valves Temperature displays Drive mechanisms for awnings, blinds, curtains and garage doors Drive mechanisms for windows Circulator pumps for heating systems Valve control systems, e.g.for solar thermal installations Alarms (lights and buzzers) Information displays and indicator LEDs Relays for making and breaking socket outlet circuits(standby cut-off) Well pumps Air conditioning systems Ventilation systems (toilet/bathroom extractor fans,controlled ventilation forliving areas) Control of washing machine,dryer, dishwasher Consumer electronics Trigger signals for alarm systems Telephone systems Electric door openers anddoor locking systems Presence simulation Displays and user interfaces Modules for connecting buswith telephone Modules for automaticallysending warning messagesby text Modules for accessing building data from outside via theinternet or a phoneIndividualRoom control Radio receivers for doorlocks Receivers for infrared remote controls Fingerprint modules and cardreaders for access controlFigure 3. A study conducted by the Institute for Building and Energy Systemsat Biberach University of Applied Sciences, entitled “The potential offered bymodern electrical installations for saving energy”, has revealed that the use ofa KNX-based, networked home and building control system can reduce energyconsumption by as much as 50 %.3