If HFC refrigerants were ever to come under fire in the United States, the mobile and stationary HVACR sectors appear more and more ready to offer CO2. as an alternative. Four representatives of industry manufacturers and an enduser from the U.S. Army talked about work they are doing with CO2to an audience of engineers at the combinedCompressor Engineering Conference and Refrigeration & Air Conditioning Conference at Purdue University.

Their efforts are being driven by pending legislation in Europe that may end up banning the use of HFCs in automotive air conditioning; by environmentally and politically driven efforts among such high-profile end-users as Coca-Cola and McDonalds to end the use of HFCs in stationary equipment; and by research that is showing cost and energy efficiencies of CO2 systems starting to fall in line with similar equipment running on HFCs.

Steve Memory of Modine Manufacturing reported on proposals and pending legislation within the European Union that could start a phaseout of the use of HFC-134a in mobile air conditioning by 2010. While such legal action is yet to be finalized, Memory said, "It is going to happen. They are just wrangling over a few points." He noted that since many European car manufacturers are in a five-year cycle to introduce new cars to the market, work with alternatives to 134a means research "has to start now." He also said that the EU nations manufacture 17 million vehicles a year, making that the largest car market in the world.

He noted such research currently involves CO2 air conditioning systems with variable displacement compressors, gas coolers, an accumulator tank, and a hot gas circuit to provide heating as well as air conditioning.

"CO2 is good for that because its high volumetric efficiencies can make packaging smaller and the efficiencies are very good in these systems."

He noted that even in the early stages of CO2 research, "the cost versus 134a has little cost penalties, and they will come down." He added that CO2 is also not regulated regarding recovery and recycling, and it can be legally vented. He also noted there are charging stations and leak detection devices available for use with CO2 refrigerant.

John Manzione, an engineer with the U.S. Army, said the military currently uses 134a in mobile air conditioning applications and has no plans to change from that. But he said other options are being looked at and currently experiments are being conducted with CO2. The process began with computer modeling, then moved to lab experiments, and has now reached the prototype stage. The next step would be full-scale system development and demonstration.

He said CO2 systems would have to be "embedded into the industry" and available "off the shelf" before the Army would consider switching. But he did note the zero ozone depletion, a "zero net global warming potential," non-flammability, and non-toxicity as factors to consider. And because the Army often has to do equipment servicing "in the field and on the fly," the legal venting aspects of CO2 as well as no need to recover and recycle are also considerations.

Travis Horton of Tecumseh Products said his company is "committed to understanding and developing technology that will enable the use of CO2 in HVACR. CO2 will find a future."

He said Tecumseh is currently focusing on the issue of what lubricants work best with CO2 in various applications. This includes use with and without additives and various viscosities. The company is looking at CO2 in rotary and recip compressors and in single-stage and two-stage models. Other considerations involve seals and valve stress. He added that decisions would be based on both technical feasibility and good business sense.

Jurgen Suss of Danfoss said CO2 is currently being reviewed on the heating side in heat pumps and in cooling applications for reach-in refrigerators. He noted Danfoss began the studies in 2001 by looking at redesigned HFC compressors. Then the following year efforts were directed to a simplified drive system, followed by performance and safety aspects. Currently attention is being given to cost and reliability.

"There is an energy savings for CO2 in certain configurations. Tests have been done in the lab and in the field, often with a CO2 unit next to an HFC unit." He cautioned, "We still have a long way to go," especially to reach the stage where reliable units can be mass-produced at a cost that is competitive with HFC units.

Gaku Shimada of Sanyo said his company is looking at CO2 in two-stage rotary compressors. He said the company is coping with the high working pressures of CO2 by use of what he called an "internal intermediate pressure structure."

He said, "The advantage of two-stage is the inter-cooler which can reduce the temperature of final discharge." He added that the Japanese market has embraced CO2 heat pump/water coolers since 2002 when the government provided a subsidy to endusers. The August Summer Olympics in Athens will have soft drink vending machines running on CO2.

He said in addition to heat pump/water coolers and vending machines, Sanyo is looking at CO2 in glass door merchandisers, ice cream cases, and other refrigeration applications.