The earliest chemical coolants, used for refrigerators before the 1930s, were hydrocarbons -- propane, isobutane and cyclopentane. In the 1930s, chlorofluorocarbons, or CFCs, appeared on the scene.
The brand name for most CFCs was freon, or R22. Hydrofluorocarbon gas, or HFC, replaced CFC when the latter was discovered to add to ozone layer depletion when accidentally leaked into the atmosphere.
Additional names for HFC include tetrafluorethane and HFC-134a. Unfortunately, HFC is also a known contributor to global warming.
Greenpeace, an environmental protection organization, is now campaigning against both CFC and HFC and championing a return to hydrocarbon gases. The hydrocarbons are now the coolants of choice in domestic refrigerators produced in Europe, China, Australia, Japan and Latin America.
Hydrocarbon fridges are labeled "CFC and HFC free" or R600a refrigerant/coolant. Greenpeace calls its hydrocarbon initiative, "Greenfreeze".
Some older, smaller refrigerators commonly used another chlorinated refrigerant called R-12. This refrigerant was phased out in the 1990s and was replaced by tetrafluoroethane, or R134A.
The replacements are referred to by their brand names -- Suva 134aA, HFC-134A and Genetron 134A. Industrial scale refrigeration plants use ammonia, or R-717, which is an efficient, environmentally-friendly coolant.
Propane is another coolant that is gaining popularity as a replacement in older systems that originally ran on R44 or freon.
The ideal gas refrigerant has yet to be developed. Ammonia can be harmful if inhaled and propane has explosive properties.
Hydrocarbons depend on the world's ever-decreasing supply of oil, leaked CFC can deplete the earth's ozone layer, and HFC is a contributor to global warming. Currently, environmentalists can only choose the refrigerant that has the lowest negative impact.
Until a worry-free coolant is developed, the coolants of choice are hydrocarbons.