Purdue News

March 10, 2006

Carbon dioxide promises green alternative for air conditioners, refrigerators

WEST LAFAYETTE, Ind. — Engineers developing technologies that use environmentally friendly carbon dioxide as a refrigerant instead of conventional, synthetic global-warming and ozone-depleting chemicals will meet at Purdue University in mid-March to discuss the latest research.

Eckhard Groll demonstrating a carbon dioxide air conditioner
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The conference will include talks about applications ranging from soft drink vending machines to portable air conditioners used by the U.S. Army for a variety of roles, such as cooling troops and electronic equipment. Talks also will cover the use of carbon dioxide to run "heat pumps," which operate like air conditioners in reverse, to warm swimming pools and homes, said Eckhard Groll, a Purdue professor of mechanical engineering who is organizing the conference.

Although carbon dioxide is a global-warming gas, conventional refrigerants, called hydrofluorocarbons, cause about 1,400 times more global warming than the same quantity of carbon dioxide. The tiny quantities of carbon dioxide that would be released from air conditioners would be insignificant compared to the huge amounts produced from burning fossil fuels for energy and transportation, Groll said.

"Carbon dioxide has unique characteristics that make it an ideal green-technology alternative for certain applications in refrigeration and heating," said Groll, who is developing carbon dioxide-based air conditioning systems as part of his research at Purdue's Ray W. Herrick Laboratories.

Engineers from industry and academia will discuss their work during the annual meeting of the Carbon Dioxide Interest Group, an international organization promoting carbon dioxide as a refrigerant. The conference will take place March 16-17 at the Burton D. Morgan Center for Entrepreneurship at Purdue's Discovery Park, the university's hub for interdisciplinary research.

Registration will be at 8 a.m. on the opening day of the two-day conference. The fee is $50 for members of the organization and $250 for non-members. All talks will take place in Burton D. Morgan Center, Room 121.

The conference will include presentations at:

• 9 a.m. Thursday (March 16) by a researcher from the United Technology Research Center, which is part of Carrier Corp., regarding the use of carbon dioxide to heat swimming pools, buildings and other spaces. Carbon dioxide is used instead of conventional refrigerants to run a heat pump, which uses the same refrigerants as air conditioners to provide heating instead of cooling. Air conditioners draw heat from inside homes and release it to the outside, while heat pumps do just the opposite. Because refrigerants are colder than outdoor temperatures even during winter months, they can absorb heat from outdoors that can be used to warm other spaces. Carbon dioxide offers cost advantages over natural gas and environmental advantages over conventional refrigerants, Groll said.

• 9:30 a.m. Thursday by a researcher from Modine Manufacturing Co. in Racine, Wis., regarding the use of carbon dioxide in portable air conditioners for the U.S. Army. Thousands of these environmental control units, which now use conventional refrigerants, are currently in operation for mobile weapons systems and other applications. Federal environmental regulations will phase out those refrigerants in 2010, and the Army is considering replacing the refrigerants with carbon dioxide.

• 10 a.m. Thursday by a Purdue postdoctoral researcher working with Groll in research related to the Army's environmental control units. Findings from the Purdue research will demonstrate how to build a carbon dioxide system that outperforms systems using a conventional refrigerant called R22. The Purdue engineers have designed and built a prototype at the Herrick Laboratories.

• 11 a.m. Thursday by a researcher from Tecumseh Products Co. in Tecumseh, Mich., regarding compressors specifically designed for systems that use carbon dioxide. The higher pressures required for carbon dioxide pose design challenges for compressors, which are critical components of air conditioning and refrigeration systems.

• 11:30 a.m. Thursday by a Purdue graduate student regarding the special challenges regarding lubrication in carbon dioxide-based systems.

• 1:30 p.m. Thursday by a researcher from Technical University of Dresden in Germany regarding a design that harnesses pressure changes in carbon dioxide systems to drive an "expansion work recovery machine" to increase efficiency. The machine could use a turbine or pistons to supplement the main drive system.

• 10 a.m. on Friday (March 17) by an engineer from Carrier Corp. regarding the use of technology called centrifugal compressors for large air conditioning systems.

• 11 a.m. Friday by a graduate student from the University of Illinois regarding computational models for "ejector systems" that promise to increase the efficiency of carbon dioxide units.

Carbon dioxide was the refrigerant of choice during the early 20th century but was later replaced with manmade chemicals. A major drawback to carbon dioxide systems is that they must be operated at pressures up to five times higher than current systems. The need to operate at high pressure posed certain engineering challenges and required the use of heavy steel tubing.

During the 1930s, carbon dioxide was replaced by synthetic refrigerants, called chlorofluorocarbons, or CFCs, which worked well in low-pressure systems. But scientists later discovered that those refrigerants were damaging the Earth's stratospheric ozone layer, which filters dangerous ultraviolet radiation. CFCs have since been replaced by hydrofluorocarbons, which are not hazardous to the ozone layer but still cause global warming.

Now carbon dioxide may be on the verge of a comeback because of technological advances that include the manufacture of extremely thin yet strong aluminum tubing, replacing the heavy steel tubing, said Groll, who is affiliated with the Energy Center at Discovery Park.

Writer: Emil Venere, (765) 494-4709, venere@purdue.edu

Source: Eckhard Groll, (765) 496-2201, groll@ecn.purdue.edu

Purdue News Service: (765) 494-2096; purduenews@purdue.edu


Eckhard Groll, a professor of mechanical engineering at Purdue University, demonstrates a prototype portable air conditioning unit that uses carbon dioxide as a refrigerant instead of conventional chemicals. The prototype has been developed as part of research funded by the U.S. Army. Carbon dioxide is a green alternative to conventional refrigerants, which cause about 1,400 times more global warming than the same quantity of carbon dioxide. Engineers working at Purdue's Ray W. Herrick Laboratories will discuss the prototype during a conference March 16-17 focusing on using carbon dioxide as a refrigerant. (Purdue News Service photo/David Umberger)

A publication-quality photo is available at http://news.uns.purdue.edu/images/+2006/groll-Co2cool.jpg


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