An absorption refrigerator is a refrigerator that uses a heat source (e.g., solar energy, a fossil-fueled flame, waste heat from factories, or district heating systems) to provide the energy needed to drive the cooling process. The system uses two coolants, the first of which performs evaporative cooling and is then absorbed into the second coolant; heat is needed to reset the two coolants to their initial states. The principle can also be used to air-condition buildings using the waste heat from a gas turbine or water heater. Using waste heat from a gas turbine makes the turbine very efficient because it first produces electricity, then hot water, and finally, air-conditioning—trigeneration. Absorption refrigerators are commonly used in recreational vehicles (RVs), campers, and caravans because the heat required to power them can be provided by a propane fuel burner, by a low-voltage DC electric heater (from a battery or vehicle electrical system) or by a mains-powered electric heater. Unlike more common vapor-compression refrigeration systems, an absorption refrigerator has no moving parts. History In the early years of the 20th century, the vapor absorption cycle using water-ammonia systems was popular and widely used, but after the development of the vapor compression cycle it lost much of its importance because of its low coefficient of performance (about one fifth of that of the vapor compression cycle). Absorption refrigerators are a popular alternative to regular compressor refrigerators where electricity is unreliable, costly, or unavailable, or where noise from the compressor is problematic; or where surplus heat is available (e.g., from turbine exhausts or industrial processes, or from solar plants). In 1748 in Glasgow, William Cullen invented the basis for modern refrigeration, although is not credited with a usable application. More on history of refrigeration can be found in the paragraph Refrigeration Research on page Refrigeration. Absorption refrigeration uses the same principle as adsorption refrigeration, which was invented by Michael Faraday in 1821, but instead of using a solid adsorber, in an absorption system an absorber absorbs the refrigerant vapour into a liquid. Absorption cooling was invented by the French scientist Ferdinand Carré in 1858. The original design used water and sulphuric acid. In 1922, two students at the Royal Institute of Technology in Stockholm, Sweden, Baltzar von Platen and Carl Munters enhanced the principle with a three-fluid configuration. This "Platen-Munters" design can operate without a pump. Commercial production began in 1923 by the newly-formed company