"We expect to have about 600 people from 30 countries," said Eckhard Groll, an associate professor of mechanical engineering. Groll worked with mechanical engineering professors Werner Soedel and James Braun to organize the 10th International Refrigeration and Air Conditioning Conference and the 17th International Compressor Engineering Conference.

The conferences, organized through Purdue's Ray W. Herrick Laboratories, take place every two years at the university. Researchers have submitted 113 technical papers for this year's refrigeration and air conditioning conference and 104 papers for the compressor conference, Groll said.

Sessions will include an update on ozone depletion and climate change, a panel discussion on the use of carbon dioxide as an environmentally friendly alternative to more conventional refrigerants and a presentation on homeland security issues for building systems.

Groll said Purdue is a major player in air conditioning and refrigeration research, and last year the university organized the International Congress of Refrigeration in Washington, D.C.

Because compressors, air conditioners and refrigerators are responsible for a huge portion of the world's total energy consumption, many talks will deal with energy efficiency and innovative technologies, he said.

Compressors range from one-horsepower units in household appliances to powerful monsters that have hundreds or even thousands of horsepower and are used for such applications as pumping natural gas and creating seismic waves for ocean exploration.

Engineers are constantly trying to improve compressor designs to make them faster, quieter, more reliable and more energy efficient.

"In the U.S., power consumption of commercial buildings is about one-third of the total power consumption in the nation," Groll said. "Air conditioning represents a significant portion of that one-third."

Braun recently completed a three-year project funded by the state of California and industry to create a computerized system that uses software and sensors to automatically detect and diagnose problems in commercial air conditioning units and then recommend specific repairs.

The system promises to save time and money by automatically sending diagnostic information to a central location through the Internet or other means, quickly alerting technicians to problems and reducing the need for field tests.

"The system can reduce service costs, improve overall comfort conditions in buildings and improve energy efficiency," Braun said.

A special session will be held on this subject, called automated diagnostics for cooling equipment.

"There is really a lot of activity on this general topic, and we've made some significant contributions," said Braun, who has written three technical papers on the subject with doctoral student Haorong Li.

Researchers also are working on a wide range of innovative refrigeration concepts that are less harmful to the environment than conventional technologies.

"I think environmental issues are in the forefront," Groll said. "There is a lot of research going on to develop alternative refrigerants that don't harm the ozone layer or cause global warming."

For example, the meeting will include a session devoted to research regarding refrigeration and air conditioning systems that use carbon dioxide as a refrigerant

Carbon dioxide was the refrigerant of choice during the early 20th century but was later replaced with man-made chemicals. Now carbon dioxide may be on the verge of a comeback, thanks to technological advances that include the manufacture of extremely thin aluminum tubing called "microchannels."

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 offers few advantages for large air conditioners, which do not have space restrictions and can use wide-diameter tubes capable of carrying enough of the conventional refrigerants to provide proper cooling capacity.

Carbon dioxide, however, is promising for systems that must be small and lightweight, such as automotive or portable air conditioners. Various factors, including the high operating pressure required for carbon dioxide systems, enable the refrigerant to flow through small-diameter tubing, which allows engineers to design more compact air conditioners.

During the 1930s carbon dioxide was replaced by synthetic chlorofluorocarbon refrigerants, known as 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. Groll said that recent advances in manufacturing and other technologies are increasing the practicality of using natural refrigerants such as carbon dioxide and ammonia.

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