June 25, 2002
Purdue conferences in July highlight cooling technologies
WEST LAFAYETTE, Ind. Engineers are close to perfecting automotive air conditioning systems that use carbon dioxide instead of synthetic refrigerants thought to damage the atmospheric ozone layer and contribute to global warming.
Carbon dioxide also is playing a critical role in another technology under development that will heat up a car's passenger compartment as soon as the vehicle is started, even though the engine is still cold.
These are just two of the numerous research topics to be discussed July 16-19 during the 16th International Compressor Engineering Conference and the Ninth International Refrigeration and Air Conditioning Conference at Purdue University.
Engineers will present more than 250 technical papers during the conferences, which will attract about 600 researchers from Europe, Asia and North and South America.
Edward Pollock, director of the Office of Building Research and Standards for the U.S. Department of Energy, will deliver a keynote address to kick off the conferences.
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, said Werner Soedel, Purdue's Ray W. Herrick Professor of Mechanical Engineering.
"In every refrigerator is a compressor, every air conditioner, every freezer they are everywhere," said Soedel, who founded the compressor conference in 1972 with Raymond Cohen, professor emeritus of mechanical engineering. "I would estimate that there must be close to 300 million compressors in the United States alone. They are one of the major energy users in the world."
Compressors range from one-horsepower units seen 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, making them faster, quieter, more reliable and more energy efficient.
Researchers also are working on a wide range of innovative refrigeration technologies. These include air conditioners that use environmentally friendly refrigerants, "thermoacoustic" refrigerators that use sound waves to induce cooling and solid-state devices that cool through electronic principles with no moving parts, said James E. Braun, a professor of mechanical engineering at Purdue who heads the organizing committee for both conferences.
Braun and his students have developed new computer models that will help engineers create more efficient designs and better electronic controls for large, commercial air conditioning and refrigeration systems.
Meanwhile, automotive air conditioning systems that use carbon dioxide as a refrigerant are getting closer to reality, said Eckhard Groll, an associate professor of mechanical engineering at Purdue.
"It's still in the research phase, but almost all major car manufacturers have prototype systems, which means systems in running cars," Groll said. "I have driven a BMW with a carbon dioxide air conditioning system, and it was very comfortable."
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 ducts 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.
"I think manufacturers are getting close to the point where they could deliver a product and put it in a car," he said. "The main concern is not so much the technology as the service that is associated with it."
Mechanics would have to be educated about the new systems, and carbon dioxide distribution networks would have to be developed.
"You need to think about the service and distribution end," Groll said. "It probably will happen in Europe first."
A related technology, new "heat pumps" that provide instant warmth to a car's occupants instead of waiting for the vehicle to warm up, also are on the drawing boards of auto manufacturers, he said.
These systems will use carbon dioxide as a working fluid, but they will reverse the heat-exchange cycle seen in air conditioning, collecting heat from the outside and transferring it to the car's interior.
"I am convinced that in northern climates we will see this technology, not so much in the U.S. market, but in places like Scandinavia, Canada countries that have long, tough winters," Groll said.
However, designing such heat pumps presents several major obstacles. The system would ideally maintain a temperature of about 75 degrees Fahrenheit in the car's passenger compartment, while the outside temperature might be below zero, representing a difference of 75 degrees. The large difference in temperatures is about twice as great as that handled by air conditioning systems, in which a car's interior temperature of about 75 degrees is only roughly 40 degrees lower than outdoors.
The larger temperature difference places a much greater strain on the system's compressor. At the same time, lubricating fluids inside of compressors do not work well in the frigid temperatures of winter, contributing to wear and causing breakdowns.
"What we are looking at is compressor performance and compressor reliability," Groll said. "We've already broken two compressors because of lubrication problems. So it's going to be a challenge. We've seen the performance after several hours of testing really drop off drastically, and when we take the compressor apart we see piston wear. In one case a bearing failed, so that means you have to go back and redesign the compressor."
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. Rather, carbon dioxide 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.
One drawback to carbon dioxide systems is that they must be operated at high pressures up to five times as high as commonly seen in current technology which posed certain engineering challenges and required the use of heavy steel tubing during the early 20th century.
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. However, recent advances in manufacturing and other technologies are making carbon dioxide practical again. Extremely thin yet strong aluminum tubing can now be manufactured, replacing the heavy steel tubing.
Most of the conference sessions will be in Purdue's Stewart Center. Registration will be in the east foyer from 7-10 a.m. Tuesday (7/16).
Conference highlights will include:
8-9:15 a.m. Tuesday. Loeb Theatre, Stewart Center. Opening remarks by Purdue University President Martin C. Jischke, followed by a keynote address by Edward Pollock, director of the Office of Building Research and Standards for the U.S. Department of Energy.
6-7:30 p.m. Tuesday. Reception, South Ballroom, Purdue Memorial Union.
1-3 p.m. Wednesday. Stewart Center. Purdue researchers will present findings about two new mathematical models. One model accurately predicts the performance of commercial air conditioners depending on how much refrigerant is put into the units. The other model simulates the performance of large commercial air conditioners, called "chillers," depending on various changing conditions. This model will help engineers design better electronic controls for more efficient operation of the units.
9:15-11:45 a.m. Thursday. Stewart Center. Purdue researchers present findings in three technical papers about ongoing research to develop air conditioning equipment that uses carbon dioxide as a refrigerant.
Writer: Emil Venere, (765) 494-4709, email@example.com
Eckhard Groll, (765) 496-2201, firstname.lastname@example.org
Werner Soedel, (765) 494-8613, email@example.com
Purdue News Service: (765) 494-2096; firstname.lastname@example.org
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NOTE TO JOURNALISTS: Several research papers referred to in this news release are available electronically from Emil Venere, (765) 494-4709, email@example.com.
A publication-quality photograph is available at ftp://ftp.purdue.edu/pub/uns/braun.airconditioning.jpeg.