There never has been and never will be just one
In the mid 1750s, Ben Franklin experimented with using vacuum to evaporate liquid ether, and he recorded a significant temperature drop in the remaining liquid. About 100 years later, Australian James Harrison patented a machine that compressed a gas to a liquid and evaporated it again in a continuous cycle, carrying away enough heat to make ice on a commercial scale. Within a year, Australians were refrigerating meat and drinking cold beer. By 1895, compression/evaporation-cycle refrigeration was being used in most of the industrialized world.
In these early commercial machines, just about any gas or mixture of gasses that could be compressed into a liquid was tried as a refrigerant, even air, each with some degree of success. Which one works best? Actually, it’s a balance of several factors. In broad terms, a refrigerant with higher mass will carry more heat, while one with lower mass will be easier to compress and therefore require less energy to run the compressor. Ultimately the best refrigerant for the job depends on the job and the design of the machine, so the refrigerant is just one component of an entire system. In those days, efficiency was the only real design objective, and the most commonly used refrigerants just happened to be either flammable or toxic.
By the 1920s, hazardous refrigerants had become a major issue, so the biggest companies in the industry pooled their resources to find something safer. The result was a new class of chemicals called chlorofluorocarbons (CFC), a compound made of fluorine, chlorine and carbon atoms. Basic CFC is a non-toxic non-flammable gas with relatively high mass. It’s a great refrigerant because it compresses easily to a liquid and carries away lots of heat when it evaporates. In fact, it’s well suited to a variety of applications because it doesn’t react with anything; it works well as a solvent, a blowing agent, a fire extinguishing agent and an aerosol propellant. Because it’s a single molecule, not a mixture, it doesn’t separate out at different pressures or temperatures. In fact, it’s so stable that the only thing in nature that breaks it down is ultraviolet light. And that, as it turns out, is part of the reason it’s no longer made.
In the 1970s, after decades of dumping about a million tons of the stuff into the air each year, scientists learned that CFC isn’t harmless after all. Weather slowly carries it up into the stratosphere, where it’s eventually destroyed by the sun’s ultraviolet rays. When the chemical bonds are broken, the chlorine atoms drift free, and they become a catalyst that breaks unstable ozone molecules (O3) into oxygen molecules (O2). The chlorine isn’t consumed in the reaction, so it continues ruining ozone for years. This is a big deal, because stratospheric ozone is the shield that protects all living things on the planet from the Sun’s ultraviolet radiation. Once this was clearly understood, governments all over the world signed a treaty to ban the production of CFC. The mobile A/C industry switched to a new refrigerant in 1995, and the stationary refrigeration industry began using non-ozone depleting refrigerants soon after. Although CFC is still used in some applications, it’s no longer manufactured, and recent studies indicate it’s presence in the atmosphere is finally beginning to decrease.
Some stationary and industrial systems are now using the old flammable refrigerants because better technology has made the safety hazards manageable. However, most systems today use new types of refrigerants based on hydrochlorofluorocarbon (HCFC) and hydrofluorocarbon (HFC). These offer most of the same advantages as CFC without damaging the Earth’s ozone shield, but they were developed before the environmental impact of fluorine was fully understood. Today that impact is regulated as Global Warming Potential (GWP). One of the primary design criteria of every air conditioner and refrigeration system, from cradle to grave, is its potential contribution to global warming. Therefore, HCFC and HFC gasses are on a schedule to be phased out by 2030. Right now the most likely replacement is another new class of fluorocarbon refrigerants called hydrofluoro-olefin (HFO). Its primary advantage, other than its low GWP, is that it can be used with existing refrigeration system designs. This is good for the industry and their customers, but it’s still a fluorinated gas, among the most potent and long-lived greenhouse gases made by humans. There’s growing political pressure to regulate it out of production and force the industry to develop an even lower-impact refrigeration technology. So the search continues.
As noted earlier, refrigerant is only one component of a whole system, and almost any compressible gas will work if the system is designed to use it. With on-going advances in technology and even more promising advances in material science, it’s unlikely there will ever be one universal refrigerant. But there will always be cold beer.
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When having your mobile A/C system professionally serviced, insist on proper repair procedures and quality replacement parts. Insist on recovery and recycling so that refrigerant can be reused and not released into the atmosphere.
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The 34th annual Mobile Air Conditioning Society (MACS) Worldwide Training Conference and Trade Show, Power Up will take place January 16-18 2014 at the Sheraton New Orleans.