Device to Measure Energy Use

MacArthur Fellow recognized for his work.

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By Marlene Cimons, National Science Foundation

Most Americans don’t have a clue how much electricity or water each of their household appliances or fixtures uses on any given day. If they did, they might be surprised. Moreover, they also might change their habits.

To be sure, electric and water bills arrive regularly, providing a good idea of a family’s total consumption. But computer scientist Shwetak Patel doesn’t think that’s good enough, particularly when the nation has become increasingly aware of the need to develop new renewable energy sources, and conserve what it has available now.

Patel, assistant professor of computer sciences at the University of Washington and a recent winner of a prestigious $500,000 “no strings attached” MacArthur Fellowship, or “genius” grant, has invented a simple, low-cost device that measures household energy and water consumption for each fixture and appliance.

Furthermore it does this without the need for an elaborate network of expensive instruments. The system uses gas lines, electrical wiring, plumbing, and ventilation ducts, and requires only a minimal number of small, wirelessly connected sensors attached to the central hookup of each of these utility sources. It screws into a water spigot or hose bib, for example, and plugs into an existing electrical outlet.

When coupled with a machine learning algorithm that analyzes patterns of activity and the signature noise produced by each appliance, the sensors tell consumers how much energy each appliance is using, and can help detect whether a fixture or appliance is performing inefficiently.

“It monitors the minute water pressure fluctuation in your home from that one location and then toilet, dishwasher, shower use can be broken down,” says Patel, whose other research projects have received National Science Foundation funding. “It gives you information in real time, so you can make decisions about what is happening. The same for electrical appliances. The device plugs into an electrical outlet, and looks at electrical noise over the power line to see when certain devices are running, and breaks it down in terms of appliance usage.”

While not yet available commercially, the sensor has the potential to transform the ways in which consumers use precious resources, and holds the promise for additional far reaching applications, such as in home security systems, for example, or in elder care for monitoring medical conditions, daily activities and movement throughout a building’s rooms.

Ultimately, the goal of using these devices is a 10-15 percent reduction in energy consumption globally, he says. “On a massive scale, that is huge,” he says. But he predicts the greatest impact will occur in personal energy practices.

“People don’t know their energy consumption,” he says. “It’s a challenge, since the information they receive now is in aggregate. This will empower them to know more and give them better knowledge about where their energy is going. It will help in buying decisions, and it could start some very interesting discussions within the home.”

Patel, who has been using these experimental devices in his own home, found an “eye-opening” revelation in his personal energy consumption, he says.

“I discovered that my DVR and cable boxes consume the same amount of energy throughout the year as my clothes dryer, even when the television set isn’t on,” he says. “I have three cable boxes plugged into the wall, and they are always running because it’s too much trouble to unplug, then re-plug and reboot them. We don’t use our clothes dryer all that often, but over the year it used the same amount of energy as our DVRs. It was mind-boggling.”

He also learned that lighting ate up the largest share of his electricity. “It was the biggest consumer in our house,” he says. “And we thought we turned off the lights more. So we switched one light switch away from a dimmer, put a CFL there and turned it into a normal switch.”

Patel, who “thought I knew everything about energy,” predicts the information will be similarly revealing for others, depending, of course, on where they live.

“The average consumer doesn’t have this knowledge, and much of what they assume is inconsistent with what is really happening, as I found out,” he says. “We live in Seattle, where we don’t much use air conditioning. So that’s not a big factor for us. In other parts of the country, it might be. Some people think the dishwasher uses the most water, but actually it doesn’t. Dishwashers are usually pretty efficient. Number one is the toilet, followed by showers and washing machines.

“For different people, it’s different things,” he adds. “That’s why this technology is useful. People live their lives in different ways, and energy and water use are very specific to the home itself, and to the family itself.”

Patel created his own company aimed at commercializing the devices; in 2010, Belkin, a major manufacturer of computers and consumer electronics, acquired Patel’s startup. He still consults with the company, helping with technology transfer.

“A division within Belkin called Conserve is in charge of this technology and is working with Commonwealth Edison to use these devices, and putting them in peoples’ homes, “ Patel says. “They also are working with Best Buy on the retailing. Depending on the pilot, the hope is to make the devices commercially available in 2012.”

He expects eventually most consumers will be able to afford them. “It’s not going to be like buying a computer,” he says. “It will be more like buying a couple of video games.”

Furthermore, he predicts that the data generated by his invention will encourage consumers to buy more energy efficient products, and manufacturers to make them.

He still checks his own household monitors frequently. And he is considering turning in one of his cable boxes. “Also, you can be sure that the next time around I’ll make a different decision about what device I use to run my TV,” he says.


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