Self-Powered Wireless Sensors Eliminate the Need for Batteries

OTHER PARTS OF THIS ARTICLEPt. 1: This PagePt. 2: Installation of Wireless Systems, Integration With Existing Controls Can Be Cost Effective

During the last decade, wireless technologies have created an information revolution. That revolution has changed the landscape for facility professionals as well, who have witnessed seismic shifts in how and where they deploy staff, gather information and automate vital building systems.

"The best concept of wireless is that, in a lot of buildings, it installs like a wired device, but with added flexibility — and you can put the switch anywhere," says Jim O'Callaghan, president of EnOcean North America.

But the flexibility of wireless products has been limited by the need to provide power. Batteries eventually need to be replaced, an ongoing maintenance requirement that adds cost and hassle to wireless deployments.

One wireless, batteryless technology — EnOcean — has been proven in Europe and is now available in North America. The systems offer flexibility, interoperation, and zero wired-power requirements.

Instead of batteries or wired power, EnOcean devices use a variety of methods to generate or store electricity: inductive switches, solar cells and thermo-energy harvesters.

A basic configuration for occupancy sensors using EnOcean devices might look like this: an energy-harvesting wireless switch on the wall for lighting and shading; an additional solar cell wireless occupancy sensor would adjust temperature and turn off lighting when occupants leave. These controllers could communicate with a BAS.

In a more complex installation, sensors could be used for the HVAC, the lighting switch and a window sensor. A separate HVAC actuator would collect information from the window and HVAC sensors. A separate actuator for lighting, similarly, would gather data from the lighting switch. All of these devices would communicate with a room controller, which would pass data through a gateway to the building control system.

In larger buildings, the devices can get tied into the wired infrastructure, O'Callaghan says. "The distance is usually less than 100 feet and there's a BACnet control system."

As a result of their low-power wireless transmissions, the devices consume tiny amounts of power to achieve frequent, repeatable communication between controllers.

"EnOcean wireless devices transmit data at 315 mhz," says O'Callaghan. "It is a very low-powered signal in terms of energy requirements, but goes further than higher-powered radio signals up to 300 meters via line of sight."

Power Without Batteries

The wall-mounted switch uses an inductive switch, according to O'Callaghan. The coil-and-magnet device generates enough electricity, via activation of the switch, that it stores electricity and sends streams of radio signals (repeated several times for reliability).

"The solar cells are about two inches square and, like most EnOcean devices, are 'peel and stick,'" says O'Callaghan.

Solar cells operate off indoor light and are frequently mounted on the ceiling for optimum room coverage. They receive reflected light and store energy to power the on-board transmitter.

In addition, "thermo harvester" controls use temperature differentials within three degrees Celsius change. The change generates a small electrical charge; typically, they are mounted on or above hot-water heaters to govern heating requirements in a space.

To save more energy, O'Callaghan recommends window-contact sensors in buildings with operable windows.

According to Armin Anders, cofounder of EnOcean, a European study carried out by the IFE Krefeld determined that the daily energy requirement for heating can be reduced by 40 percent with window contacts. When a window is opened, a batteryless contact switch transmits a radio signal to set back heating in the room. Europe generally has more operable windows than the United States.

About the Alliance

The EnOcean Alliance is a consortium of manufacturers who produce a relatively new class of self-powered, wireless technology solutions. The EnOcean Alliance was introduced in Europe in 2001 and has recently caught the attention of North American building owners.

EnOcean-equipped devices eliminate batteries and cabling. The company's switches, sensors and actuators communicate via a gateway for integration with open-protocol building automation systems, including BACnet, Lonworks, TCP/IP, DALI, and Modbus. The devices combine miniaturized energy converters, low-power electronic circuitry and reliable low-frequency wireless.

"Energy prices in Europe are about twice what they are in America," says Graham Martin, chairman of the EnOcean Alliance. "But EnOcean is gaining in popularity because it's easy to get the building retrofitted with relatively low investment."

Continue Reading: Wireless Goes Batteryless

Self-Powered Wireless Sensors Eliminate the Need for Batteries

Installation of Wireless Systems, Integration With Existing Controls Can Be Cost Effective

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  posted on 4/28/2010   Article Use Policy

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