AS&HF Article

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BUILDING CONTROLS
Energy-Harvesting Sensors Power Building
Controls to New Levels of Sustainability

For the past few years, self-powered wireless technology has been gaining traction in building automation
applications, especially in Europe and now in North America. Besides simplifying the cabling run of just about
any type of building—from health care facilities to schools and commercial offices to single-family residences self-powered wireless technology allows a quicker response to changing how a facility is internally configured and cutting cost by saving time and expense in needed retrofits.

Also attractive from an operations and maintenance standpoint, self-powered wireless sensors require no regular servicing and as an added benefit, provide office occupants with maximum freedom of movement and convenience in locating the various control devices that impact their “quality of life” in the work environment. If there are no batteries to replace, for example, there is no restriction in where a building control device can be located. Indeed, why install that rocker switch operating the sun blinds on a wall across the room, when it could be placed as easily as a cup of coffee on your desktop, or off to the side on your credenza?

Maintenance-Free Energy at No Cost
Wireless sensor modules that harvest the power they need for operation from their surroundings are able to do so by means of super-efficient energy converters and ultra-low-power electronic circuitry that transmits in the 868 MHz or 315 MHz frequency band, which makes them suitable for worldwide application (Figure 1). The wireless control signals themselves, called “telegrams,” are just one millisecond long, or about thirty times shorter than the signal of a conventional wireless switch.

To prevent transmission errors, these telegrams are randomly repeated twice in the space of about 30 milliseconds. Transmitting data packets in random intervals makes the probability of a data collision extremely rare and allows the reliable parallel operation of hundreds of wireless switches and sensors in close proximity to one another. Statistics show that, even in a situation where you have 200 wireless sensors each sending their signals once a minute; the probability of a data collision is only one in every ten thousand transmissions!

Figure 1: This batteryless wireless rocker switch contains the energy conversion and
ultra-low-power electronic circuitry needed to transmit a low-level signal at 868 or
315 MHz to operate a lighting system, window blinds or other device. Because it is wireless
it may be put anywhere, even loose on a desktop or in one’s pocket. EnOcean Alliance photo

A Technology for Every Need
Self-powered wireless modules are suitable for use in many different surroundings, in applications ranging from room thermostats with preset temperatures to maintenance-free wireless window contacts and handles. The range of typical batteryless wireless sensors is around 1000’ (300m) in the open and up to 100’ (30m) inside buildings. To prevent the possibility of overlap with other wireless switches, modules typically come with a
unique 32-bit identification number that allows them to function reliably without “stepping on the toes” of other nearby wireless devices.

The energy that powers these devices is produced by the pressing of a button, the turning of a handle, or from tiny solar cells. Another form of energy harvesting now under development is the generation of operating power from the difference between two temperatures. As “Buck Rogers” as this may sound, we will soon see sensors that generate the current they need to wirelessly transmit signals by sensing the difference in temperature
between, for example, the radiator heating a room and the surrounding air.

Case Study: Intelligent Heating
Control Cuts Hospital’s Energy Costs
An analysis of 30 clinics of a leading health care provider revealed that heating accounted for some two percent of overall operating expenses. To reduce this without an expensive retrofit construction project, energy harvesting wireless sensor technology was installed in a test scenario at a 200-room university teaching hospital. A wireless receiver was centrally positioned to create the best possible connection to all 16 test rooms. Solar-powered window contacts were stuck to the window frames. The wiring of the new radiator valves to the router went smoothly and, to allow central heating control, the installation was linked to the clinic’s LAN network. The test demonstrated annualized savings of around 800 kWh per room, or more than $22,500 dollars based on the facility’s 200 rooms. Among other demonstrated benefits, system payback is expected to be less than three years.

Case Study: Inexpensive
Climate-Control Retrofit Lowers
School’s Energy Bill 30 Percent
St. Joseph Elementary School’s inefficient “too hot or too cold” dual-zone climate-control system was recently upgraded using self-powered wireless control sensor technology in all 28 rooms. Wireless connection to the school’s BACnet system now allows individual temperature regulation for every room. Installed over the period of one week, the entire system, including central control and monitoring elements, saved 20 percent on installation cost and took less than half the time versus typically disruptive, construction-intensive cabling installations. With an expected return on investment of less than two years, the installation has already produced a remarkable
improvement in the facility’s AS&HF J/A 2010 • FacilityManagement.com 9 eInquiry #107 • ashfmag.com
comfort level, along with a30 percent lower energy bill.

Flexibility Made to Measure
In this brave new world of the ever-greening facility, intelligent building automation will continue to provide
the key to future sustainability advancements, as new strides are made in cutting operating costs and reducing
the energy consumed during normal building operations.

The turning of this window handle produces the energy needed to transmit a low-power wireless signal
to control a radiator valve that will adjust the heating level of the room based on the position of the window.
EnOcean Alliance photo courtesy of Hoppe AG

Thanks to technology developers, self-powered wireless switches and sensors will continue to greatly simplify cabling requirements while, at the same time, increase flexibility. No minor advantage, this technology allows the ability to attach and re-attach sensors, switches and other devices wherever they provide optimum benefit and by so doing, the complexity and cost of internal building retrofitting is greatly reduced.

Another spot of good news, the inherent interoperability of batteryless wireless technology, products and systems ensures easy integration with leading building automation systems, including LONWorks, KNX,
BACnet, TCP/IP and Ethernet. At the bottom line, batteryless wireless sensors may be viewed as an enabling
technology that will help building professionals across the sustainable facility landscape to implement high-performance energy management strategies with less effort and expense.

Graham Martin, chairman and CEO of EnOcean Alliance (www.enocean-alliance. org), is an electronics industry veteran with more than 25 years’ experience in analog and RF solutions.

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American School & Hospital Facility magazine and FacilityManagement.com are educational tools that teach institutional facilities professionals and the building team to operate, maintain and design structures efficiently, economically, safely, securely and green. The editorial mission is to report on the topics, issues, trends and products that impact facilities management.