Mercedes Air-Conditioning Technology Goes Green

STUTTGART – Mercedes-Benz will use liquid carbon dioxide as the refrigerant in the air-conditioning systems of gasoline- and diesel-powered E- and S-class models beginning in 2016, and will make it standard in other models, including A-, B- and C-Class models in coming years.

The move brings the German automaker into line with European Union regulations calling for car companies to employ air-conditioning refrigerants with a global warming potential (GWP) score under 150.

With a GWP score of 1, liquid carbon dioxide is 99.3% below the EU’s prescribed refrigerant limit. Its inherent properties also make it non-flammable and provide greater cooling efficiency than any current alternatives, Mercedes says.

The announcement, made official Oct. 20, follows a tense standoff between the automaker and EU regulators over a ban on the widely used synthetic Tetrafluoroethane R123a refrigerant in all cars and light-commercial vehicles cars sold in Europe after Jan. 1, 2013.

Tetrafluoroethane R123a had been widely used by Mercedes and other automakers as an air-conditioning refrigerant for more than 25 years. Increasingly tighter environmental laws and moves by the EU to adopt a refrigerant with a low GWP led to its ban.

An EU proposal to replace R123a, which possesses a GPW score of 1300, with the newer and more environmentally friendly synthetic Tetrafluorpropen R-1234yf refrigerant was heavily criticized by Mercedes following internal testing that raised concerns about flammability under certain conditions during heavy frontal impacts.

Mercedes Turns Up Heat on EU

In findings provided to the media in late 2012, the automaker said R-1234yf could prove to be flammable in a hot engine compartment despite being difficult to ignite under laboratory conditions.

In a controversial move at the time, Mercedes said it would oppose the EU directive and continue to use the less environmentally friendly but proven Tetrafluoroethane R134a refrigerant.

Subsequent tests carried out by the German Transport Authority also questioned the safety of R-1234yf with relation to its volatility when placed in contact with high-temperature engine components such as turbochargers. The test results prompted BMW and Volkswagen to join Mercedes in calls for reconsideration of its use by the EU directive.

The EU last year threatened to take legal action against Mercedes over its continued use of R123a, which could have resulted in massive continuing fines and a ban on vehicle sales outside Germany.

Despite adopting plans to begin using liquid carbon dioxide R744 in E- and S-class models, Mercedes says it will adhere to the EU order by using R-1234yf – albeit with changes to the air-conditioning systems in all models to alleviate concerns about its flammability – from 2017.

With a GWP score of 4, R-1234yf and liquid carbon dioxide are the only EU-compliant refrigerants produced on an industrial scale.

Mercedes has modified the air-conditioning system in gasoline-engine models that use R-1234yf to include a gas generator. It releases inert argon gas specifically at relevant hot spots, keeping the refrigerant from igniting when it comes into contact with hot engine components, the automaker claims.

Owing to lower operating temperatures, the argon-gas generator is not deemed necessary to prevent R-1234yf from igniting in diesel-powered models involved in heavy frontal-impact collisions.

Hybrid models, including those included in the ’16 model-year E- and S-Class lineups, for the foreseeable future will receive air-conditioning systems that use R-1234yf refrigerant during Mercedes’ ongoing development of an electrically operated compressor, the automaker says.