Energy Saver: Wireless Window Contacts

Tuesday, October 11, 2011 @ 02:10 PM gHale


Here is one potential energy saving enhancement in development: Wireless contacts that can let the user know which of a house’s windows are open or closed. But this new technology could go further than that.

An easy to use fail-safe system needs no wiring or batteries where the sensors harvest the energy they need to run from ambient radio signals, researchers said.

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Window contacts fit onto window handles, and they can tell from the position of the handle whether the window is wide open, tilted open or closed. They transmit the information to a base station, and the house’s occupants can then see at a glance which window is open.

A version of this sensor arrangement is reliable and easy to use and needs no wiring or batteries, said Research scientists at the Fraunhofer Institute for Microelectronic Circuits and Systems IMS in Duisburg, Germany.

“Our wireless window contacts draw all their energy from ambient radio signals,” said Dr. Gerd vom Bögel, a scientist at the IMS. Until now, wireless models have been reliant on batteries or solar cells, but both have drawbacks.

Batteries need a regular change to keep window contacts operational. Solar-powered systems avoid this problem, but they too are liable to fail: All it takes is for blocked sunlight and there is a power problem.

Solar systems are also aesthetically less pleasing because the user cannot tuck them away in a dark corner of the window. That leaves the classic setup: Window contacts with cable connections. These systems have been on the market for years and the main argument against them is the effort it takes to install them – quite apart from the fact it is often impossible to retrofit them to existing buildings.

The new system, however, can fit in with little effort – and you can position them very discreetly. Aside from window contacts, each room comes equipped with a room controller. This transmitter module not only receives the data from individual window contacts, it also actively provides the sensors with energy via its radio signal. The room controller also has the function of passing the sensor data on to a central base station in the building, from which users can query the status of all windows. Alternatively, the system can permit remote querying, for instance from a user’s smartphone. The only prerequisite for this is a DSL connection for the base station.

Energy management was the issue that caused the most headaches during development.

“Room controllers, too, have to comply with certain limits on the strength of their radio output. This makes it particularly tricky to get enough energy to all the window contacts in bigger rooms,” vom Bögel said. “But we have made sure all the sensor modules, antennas and components are so finely tuned to each other that the system works reliably even over considerable distances.”

The IMS research scientists have already constructed an initial prototype, and they know which way they want to head next. They want to integrate other types of sensors into the system along the same lines – to regulate room temperature, for example.

At the moment, thermostats generally fit somewhere just inside the room. If a door is open, the temperature by the door will be lower than in the middle of the room. As a result, the thermostat will then unnecessarily regulate the temperature upwards. The new system would allow a temperature sensor to be placed unobtrusively precisely where a particular temperature is desired – for instance on the display cabinet by the dining room table.



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