Intelligent Machines

Environmentally Friendly Fridges

A new magnetic-cooling system could lead to more-energy-efficient refrigerators.

Modern coolers and fridges may not cause holes in the ozone layer like their pre-1994 counterparts, but they still use greenhouse gases that are warming the planet. Their compressors also consume a lot of energy: air conditioners and refrigerators used about 340 billion kilowatt hours in 2005–nearly 30 percent of the total energy used in U.S. homes.

Cool tool: This preliminary version of an energy-efficient magnetic fridge shows a ring-shaped 1.2-tesla magnet. The magnet can encompass a movable cylinder containing materials that heat up in the presence of a magnetic field and cool down when the field is removed. As it cools, the material absorbs heat from its surroundings.

Researchers at the Risoe National Laboratory, in Roskilde, Denmark, are now one step closer to building a magnetic-cooling system that promises energy-efficient, environmentally friendly, and completely silent fridges. Temperatures in conventional fridges swing between −20 and 20 ºC. Achieving this 40 ºC temperature span is one of the most significant challenges with magnetic refrigeration. The Danish researchers have built a refrigerator that can vary temperature by almost 9 ºC.

This is an important step toward practical temperature spans of 40 ºC, says Nini Pryds, a senior scientist at Risoe who is leading the work. The research team is now working with Danfoss, one of the largest compressor manufacturers in the world, to build a commercial prototype; the company says that it should be ready by 2010.

Magnetic-cooling technology exploits materials that heat up when exposed to a magnetic field and cool down when the magnetic field is removed. As the material cools down, it pulls heat out of its surroundings. The larger the difference between the hottest and coldest temperatures achieved under the influence of a magnetic field, the better the material is at cooling.

Magnetic coolers have been used for years in laboratories for cryogenic temperatures tens of degrees below zero. In 1995, Ames Laboratory, in Iowa, demonstrated the first magnetic refrigerator that cooled contents in a room-temperature environment. The company used the metal gadolinium.

Since then, researchers have found many other materials that work at room temperature. The problem is that the temperature swings in all these substances is only a few degrees. “Achieving a large change of temperature is easy if you use a superconducting magnet,” Pryds says. But superconducting magnets are large and require cooling themselves, making them impractical for everyday appliances such as household fridges and air conditioners. For these applications, he says, “the only way to go is a permanent magnet.” Ideally, it should be a small, cheap magnet with a field of less than one tesla.

Getting large temperature spans with a permanent magnet calls for some clever engineering. Typically, it means using cooling liquids such as water. The material, with water circulating around it, is alternately placed in and out of a magnetic field. When it’s in the field, it heats up. The circulating water draws heat from the material and transfers it to a heat sink. Then the magnetic field is removed, and the material, which was already being cooled by the water, cools down even more. As it cools, it absorbs heat from the water, making it cold enough to be used as the refrigerator. This hot-cold cycle is repeated over and over.

Putting the different pieces–material, magnets, liquid cooling–together in a practical magnetic refrigerator is tough. Researchers need to design a system that gets at least a 40 ºC temperature change and enough cooling power–fridges currently have powers of as much as 150 watts–using a permanent magnet with a magnetic field less than one tesla. That requires a delicate balance between the system’s parameters. For instance, as researchers expand the temperature span, the cooling power might go down, or the system may need more energy. “It’s an engineering nightmare,” says Ames Laboratory researcher Karl Gschneidner, a pioneer in magnetic cooling.

But the rewards will be plenty. Magnetic refrigerators will be much more energy efficient than conventional fridges because they only need energy to circulate the water. “The energy consumption of magnetic refrigerators [should] be as much as 60 percent lower than traditional refrigeration,” Pryds says. Also, unlike conventional fridges, magnetic systems do not need refrigerants such as hydrofluorocarbons, which are potent greenhouse gases.

Pryds is confident that his group’s work will lead to commercial magnetic fridges. Like other research teams, the Risoe group is using the water-cooling design. But while most research teams are using gadolinium powder, the Danish researchers use plates made from a ceramic material containing lanthanum, strontium, calcium, and manganese. Pryds says that “ceramics are chemically stable; they don’t corrode in corroding fluids such as water.” The ceramic plates should also be easier to manufacture on a large scale. The combination of ceramic material and the researchers’ final refrigerator design–which is not yet public–could lead to practical success, he says.

The researchers face some tough competitors, though. Ames Laboratory researchers, working with Milwaukee-based Aeronautics Corporation of America, have made systems with temperature spans of 25 ºC and 95 watts of cooling power using 1.5-tesla magnets. Andrew Rowe and his colleagues at the University of Victoria, in Canada, have made 15-watt cooling systems with temperature spans of 30 ºC. Meanwhile, researchers at Chubu Electric Power and Toshiba, in Japan, have gone down to about 0.8 teslas to get a 10 ºC span.

Things are looking up, Gschneidner says, and in another 5 to 10 years, magnetic fridges should be on the market. Many research groups are now working on magnetic refrigerators, making better materials and coming up with better system designs. Also, adds Rowe, permanent magnets are getting smaller and cheaper. “The basic principles have been shown and demonstrated,” he says. “Magnetic refrigeration works. Now we need some hard thinking [and] good designs, and hopefully these things will come together.”

Tech Obsessive?
Become an Insider to get the story behind the story — and before anyone else.

Subscribe today

Uh oh–you've read all of your free articles for this month.

Insider Premium
$179.95/yr US PRICE

More from Intelligent Machines

Artificial intelligence and robots are transforming how we work and live.

Want more award-winning journalism? Subscribe and become an Insider.
  • Insider Premium {! insider.prices.premium !}*

    {! insider.display.menuOptionsLabel !}

    Our award winning magazine, unlimited access to our story archive, special discounts to MIT Technology Review Events, and exclusive content.

    See details+

    What's Included

    Bimonthly home delivery and unlimited 24/7 access to MIT Technology Review’s website.

    The Download. Our daily newsletter of what's important in technology and innovation.

    Access to the Magazine archive. Over 24,000 articles going back to 1899 at your fingertips.

    Special Discounts to select partner offerings

    Discount to MIT Technology Review events

    Ad-free web experience

    First Look. Exclusive early access to stories.

    Insider Conversations. Listen in as our editors talk to innovators from around the world.

  • Insider Plus {! insider.prices.plus !}* Best Value

    {! insider.display.menuOptionsLabel !}

    Everything included in Insider Basic, plus ad-free web experience, select discounts to partner offerings and MIT Technology Review events

    See details+

    What's Included

    Bimonthly home delivery and unlimited 24/7 access to MIT Technology Review’s website.

    The Download. Our daily newsletter of what's important in technology and innovation.

    Access to the Magazine archive. Over 24,000 articles going back to 1899 at your fingertips.

    Special Discounts to select partner offerings

    Discount to MIT Technology Review events

    Ad-free web experience

  • Insider Basic {! insider.prices.basic !}*

    {! insider.display.menuOptionsLabel !}

    Six issues of our award winning magazine and daily delivery of The Download, our newsletter of what’s important in technology and innovation.

    See details+

    What's Included

    Bimonthly home delivery and unlimited 24/7 access to MIT Technology Review’s website.

    The Download. Our daily newsletter of what's important in technology and innovation.

/
You've read all of your free articles this month. This is your last free article this month. You've read of free articles this month. or  for unlimited online access.