History
Early mechanical refrigeration systems employed sulfur dioxide, methyl chloride and ammonia. Being toxic, sulfur dioxide and methyl chloride rapidly disappeared from the market with the introduction of CFCs.
Occasionally, one may encounter older machines methyl formate, chloromethane, or dichloromethane (called carrene in the trade).
Until concerns about depletion of the ozone layer arose in the 1980s, the most widely used refrigerants were the halomethane chlorofluorocarbons.
Following legislative regulations on ozone depleting chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), substances used as substitute refrigerants such as perfluorocarbons (FCs) and hydrofluorocarbons (HFCs) have also come under criticism. They are currently subject to prohibition discussions on account of their harmful effect on the climate. In 1997, FCs and HFCs were included in the Kyoto Protocol to the Framework Convention on Climate Change. In 2006, the EU adopted a Regulation on fluorinated greenhouse gases, which makes stipulations regarding the use of FCs and HFCs with the intention of reducing their emissions. The provisions do not affect climate-neutral refrigerants.
Ammonia (R717) has been used in industrial refrigeration plants for more than 130 years and is thought to be environment-friendly, economical, and energy-efficient. Carbon dioxide (R744) has a similarly long tradition in refrigeration technology.
Read more about this topic: Refrigerant
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