CFCs

Chlorofluorocarbons are man-made substances containing carbon, chlorine, and fluorine, produced as a volatile derivative of methane and ethane. CFCs are largely to blame for the hole in the ozone layer. The Montreal Protocol was drawn up in 1987 in response to depletion of the ozone layer over Antarctica, and called for a phase-out and ultimate ban of CFCs manufacture. In Germany, CFCs have been banned as refrigerants since the mid-1990s. Global Warming Potential (GWP) is a figure that refers to the amount of global warming caused by a substance: it is the ratio of the warming caused by a substance to the warming caused by a similar mass of carbon dioxide. The GWP of CFCS is very high.

HCFCs

Hydrochlorofluorocarbons are man-made compounds containing hydrogen, chlorine, fluorine and carbon. HCFC production began to take off after countries agreed to phase out the use of CFCs in the 1980s, because they are less harmful to the atmosphere. HCFCs are less stable in the lower atmosphere, enabling them to break down before reaching the ozone layer. However, HCFCs are also very potent greenhouse gases, and have an extremely high GWP.

HFCs

Hydrofluorocarbons are compounds consisting of hydrogen, fluorine, and carbon. HFCs are a class of replacements for CFCs. Because they do not contain chlorine or bromine, they do not deplete the ozone layer. HFCs are not ozone-toxic and have an ozone depletion potential (ODP) of 0. However, HFCs contribute to the greenhouse effect and have high GWPs.

HCs

From a chemical point of view, a hydrocarbon is the simplest organic compound, consisting entirely of hydrogen and carbon. Hydrocarbons include methane, ethane, propane, cyclopropane, butane, and cyclopentane. The properties of HCs make them ideal refrigerants. Since hydrocarbons are flammable, some basic safety rules need to be respected by manufacturers, installers and users, which may differ slightly depending on the application. HCs may offer advantages as substitutes to ozone depleting substances because they are inexpensive to produce and they have an ODP of zero, low GWP, and low toxicity. The most commonly used HC refrigerants are propane (mainly in commercial and industrial freezers, air conditioning and heat pumps), and isobutane (in domestic refrigerators and freezers).

CO2

Carbon Dioxide is a greenhouse gas but an excellent refrigerant due to its high cooling capacity. It is also non-combustible, and available worldwide at low cost in the required qualities. Conventional refrigerants such as HFCs cause about 1,400 times more global warming than the same quantity of carbon dioxide. CO2 has an ODP of zero and a negligible GWP. Because of its thermodynamic properties, CO2 differs from the other refrigerants and can operate even in extremely low outside temperatures. CO2 is increasingly used in car air-conditioning systems; supermarket refrigeration units and air conditioning systems. Carbon dioxide has a number of advantages as a refrigerant. Systems using CO2 operate at very high pressure.

Water and Air

Water and air are natural refrigerants that are non-toxic and widely available. Technologies allowing their wider use as alternative refrigerants are still in development. Although various research projects are underway worldwide, the demanding technology involved remains a challenge in terms of cost and design.

Martin Schrader (jp)
Editor: Sonia Phalnikar