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Cool and Green: Vehicle Thermal Management

Air conditioning is a ‘must-have’ for most new cars. But the fluorocarbon refrigerant HFC-134a – the global standard – is one of the ozone-depleting greenhouse gases causing global warming. With these concerns, the European Union has passed regulations phasing out the compound beginning in 2011 and mandating the use of alternatives with less environmental impact.

By 2018, HFC-134a is to be totally banned in new cars sold in the EU. Japan is expected to soon follow suit.

At the top of the alternative list is the refrigerant CO2, also known as R-744. This gas is significantly more eco-friendly than fluorocarbons and provides 25% faster cool-down. Moreover, CO2 systems can be reversed and thereby serve as a passenger cabin heater in cold weather – a definite plus in electric cars that otherwise drain power from batteries as well as internal-combustion engines (particularly diesels) that need high operating temperatures to run efficiently.

Small eco-footprints. Major challenges.

Moving to CO2 won’t be easy, however. Gas pressures can be ten times greater than fluorocarbon-based systems, requiring compressors, seals and other major components to be specially designed. For the most efficient performance, the CO2 refrigerant must be kept above its “supercritical” temperature of 31°C, so a gas cooler must replace a classic R134a loop condenser. CO2 systems also require a special heat exchanger separating the high and low pressure sides. According to some industry observers, these design complexities – plus a longer development cycle and additional physical prototype- testing to refine the designs – could mean that some of the first CO2-based systems could cost 30 percent more than conventional units.