Hydrofluorocarbons are the current refrigerant of choice in commercial refrigerators, they replaced chlorofluorocarbons when the world in general and the refrigeration industry in particular realised that chemicals containing chlorine and bromine attacked the ozone layer, causing global warming. However there is increasing concern that Hydrofluorocarbons still contribute to greenhouse gas global warming - most hydrofluorcarbons used in commercial refrigeration applications have relatively high global warming potential (GWP), and in any case HCFC-22, the commonest Hydrofluorocarbon in use in the commercial refrigeration industry, is in short supply with many companies specialising in reclaiming HCFC-22 from old refrigerators to be able to reuse it. In steps the fourth generation of commercial refrigerant, HFOs. HFOs, hydroflouroolefins, are chemical compounds derived from hydrogen, flourine and carbon, just as hydrofluorocarbons are, but are derived from alkenes rather than alkanes, so 2,3,3,3-tetrafluoropropene rather than 1,1,1-tetrahydropropane. This apparently small difference results in much lower global-warming potential than HFCs. Additional options come in the shape of natural refrigerants such as hydrocarbons (HCs) and especially carbon dioxide (CO2). Danfoss in particular have been experimenting with CO2 systems. Danfoss say their systems that utilize CO2 technology offer several distinct advantages over traditional refrigeration systems. Their CO2 systems deliver superior refrigeration performance as well as enhanced sustainability and reduced refrigerant requirements they claim. In addition they say that these CO2 systems are the most energy-efficient and environmentally friendly refrigeration systems available in the industry today. Foster already offer a hydrocarbon option all all refrigeration cabinets and aims to offer a CO2 option soon.