Going Green: Self-Powered Switches for Intelligent Buildings
Intelligent control of services such as heating and lighting has long been proposed as a means of saving much of the energy wasted every day and every night, in all types of buildings. Controlling room temperatures individually, for example by maintaining 20-22°C in offices or living rooms, but a lower acceptable temperature in corridors or side-rooms, could achieve up to 30% energy savings according to figures from the Bremer Energieinstitut. The IFE (Ingenieurbüro für Energieberatung) of Krefeld, Germany, says that even more energy, around 40%, can be saved if window contacts are used to automatically reduce heating settings when a window is opened. Lighting, too, can be made far more energy efficient; not only by using room-occupancy sensors but also by using ambient-light sensors to adjust dimming levels continuously throughout the course of the day.
Although the idea of such an autonomous building is not new, today's economic and environmental climates demand more urgent action. However, the cost and complexity of installing large numbers of sensors and interactive controllers has always been a major barrier to adoption. Wireless communication offers a solution to the cabling challenges, allowing the required infrastructure to be installed easily and quickly without the cost of cabling components or the disruption of a protracted wiring project.
The drawback is that wireless devices require a power supply in order to transmit and receive data, but installing a power cable to each node would negate the advantage of using wireless technology. Battery-powered nodes are an alternative, but have implications in terms of cost and maintenance overheads.
Ideally, the sensors and switches should be self-powered, requiring no power cables, no batteries, and no regular maintenance. Until recently, this idea would have been dismissed as fanciful. But self-powered switches and sensors are available today, and are operating successfully in over 10,000 buildings across the world.
Self-powered switches
Self-powered wireless switches offer a practical solution to the problems of rising heating and lighting costs, and can be installed conveniently and cost-effectively in almost any type of residential or commercial property.
Self-powered devices are based on two principles. The first is to fulfil all the required functional objectives using an extremely small amount of energy. In fact the energy requirements of low-data-rate wireless devices have been successfully reduced to the point where a small sensor can complete a wireless transmission of less than one millisecond over a 30m range using only 50 microjoules of energy - less than that required to push a button such as a light switch.
The second requirement is to harvest the necessary energy from ambient sources, rather than relying on a battery. The quantities of energy required are within reach of the latest motion converters, which use electromagnetic induction to convert small quantities of mechanical energy - when a switch is operated for example - into electrical energy. Other energy harvesting opportunities include thermal converters, which use the Peltier effect to convert the energy from a hot surface into electrical energy. Small solar cells, of course, are well developed, and can be used where sufficient ambient light is available.
By combining low-power wireless technology with a suitable energy-harvesting element to collect, convert and store ambient energy, it is possible to build sensors to detect room temperature, window opening, the presence of occupants, or ambient light levels, and communicate this information back to a central switch or controller.
An example of a commercially-available self-powered device is the EnOcean PTM 200 pushbutton transmitter module. This can be used as a wall-mounted rocker switch, and collects sufficient energy from each actuation of the switch to transmit a complete RF telegram, including its 32-bit module ID, to a central controller. The module operates in the unlicensed 868MHz band and communicates using a proprietary protocol, which is becoming a de facto standard as new member companies join the international EnOcean Alliance. It is compatible with other established standards such as the DALI lighting-control standard. Other available switches and sensors combine the low-energy wireless technology of the PTM 200 with solar- or thermal-energy conversion units, providing several choices for system designers to select the most suitable energy source for a given location within the building.
The self-powered present and future
Recent successful projects using self-powered technology for autonomous building management include the new SAP headquarters at Walldorf in Germany. Here, 2000 battery-free switches control lighting and HVAC systems, including external window blinds.
Self-powered modules also partner well with domestic housing where sustainable living is a priority. An example of this was published recently as a case study by HiddenWires. The ultra-modern home near Stuttgart in Germany, successfully uses self-powered modules to overcome the complex wiring challenges involved in managing the numerous energy conservation systems installed in the house.
Also in Germany, the ecological construction company WeberHaus is offering four home automation options to self-build customers, using battery-free modules to control single-room and central management of lighting, under-floor heating, blinds and window monitoring, door-entry security, and central monitoring.
With each successful project, the benefits of self-powered networks become more widely understood and the supporting protocols more widely used. This, in turn, should lead to a larger installed base, increased knowledge within the installer community, and a broader choice of modules offering a variety of visual styles as well as new sensing and control functions. There is almost no limit to the variety of sensors and switches that can be combined with energy harvesting and low-energy wireless technologies. In the future, for example, heating, lighting, ventilation and other systems may be made to respond automatically to humidity changes, detection of water or condensation, or the presence of certain types of chemicals or odours.
Conclusion
Apart from the obvious energy-saving advantages for owners and users of all types of buildings, contractors, too, can benefit from being among the first to offer this technology to their customers. By eliminating the need for wiring, self-powered wireless switches allow the delivered price to be highly competitive compared to conventional lighting and heating systems, and require only a small amount of additional expertise in order to deliver a large number of benefits to building owners, users and the environment.Andreas Schneider is the Executive Vice President and Co-founder of EnOcean GmbH. EnOcean manufactures and markets patented battery-free wireless sensor technology.
(Source www.ecommercetimes.com, Feb 1)