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HFC-134a as working fluid in refrigeration and air conditioning systems is increasingly regarded to be an intermediate solution. Alternative systems/cycles using “natural refrigerants” are gaining more attention internationally. “Natural refrigerants” are ecologically safe fluids with no ozone depletion potential and none, or very little, global warming potential. Examples are substances like air, water, hydrocarbons, NH3 and CO2. Much effort is now directed towards developing alternative technologies, and some of this in the field of mobile air conditioning systems. This paper is focused on environmentally safe systems for automotive air conditioning. A brief overview on this is presented. The main focus is on CO2 vapour compression technology with respect to safety, environmental effects and design. Results are compared with the current status of automotive A/C and Total Equivalent Warming Impact (TEWI) for various alternatives are discussed.

By introducing HFC-134a as the replacement refrigerant for CFC-12 in motorcar air conditioning, the automobile industry will comply with the present national and international legislation for the phase-out of ozone-depleting substances. A transition to this new fluid will, however, result in emissions of several hundred thousand tonnes of a new and unfamiliar chemical compound to the atmosphere each year, involving both known negative consequences like global warming, and potential risks of serious unknown environmental effects. A new, efficient and environmentally benign automobile air conditioning system “MAC-2000” has been developed at The Norwegian Institute of Technology, in cooperation with Hydro Aluminium. The new system is based on a trans-critical vapour compression cycle with carbon dioxide as the refrigerant. Although working pressures and component design are different, the basic principle of the CO2 system is similar to present CFC/HFC units.