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Common Refrigerants

Today, there are three specific types of refrigerants used in refrigeration and air-conditioning systems:

Chlorofluorocarbons or CFCs, such as R-11, R-12, and R-114
Hydrochlorofluorocarbons or HCFCs, such as R-22 or R-123
Hydrofluorocarbons or HFCs, such as R-134a.

All these refrigerants are "halogenated," which means they contain chlorine, fluorine, bromine, astatine, or iodine. In practice, halogenated refrigerants only contain chlorine or fluorine atoms, since bromine and astatine-containing substances are highly toxic.

Refrigerants are classified into groups. The National Refrigeration Safety Code catalogs all refrigerants into three groups:

Group I – safest of the refrigerants, such as R-12, R-22, and R-502
Group II – toxic and somewhat flammable, such as R-40 (Methyl chloride) and R-764 (Sulfur dioxide)
Group III – flammable refrigerants, such as R-170 (Ethane) and R-290 (Propane).

Refrigerants are also divided into two classes according to toxicity:

Class A: refrigerants for which toxicity has not been identified at concentrations less than or equal to 400 ppm
Class B: refrigerants for which there is evidence of toxicity at concentrations below 400 ppm


Traditional Refrigerants

R-12
Dichlorodifluoromethane, commonly referred to as R-12, is colorless and odorless in concentrations of less than 20 percent by volume in air. In higher concentrations, its odor resembles that of carbon tetrachloride (aka R-10). It is nontoxic, noncorrosive, nonflammable, and has a boiling point of -21.7°F (-29°C) at atmospheric pressure. One hazard of R-12 as a refrigerant is the health risk. Should leaking vapor come into contact with an open flame of high temperature (about 1022°F), it can decompose into phosgene gas, which is highly toxic.

R-12 has a relatively low latent heat value, and, in smaller refrigerating machines, this is an advantage. Due to its properties, the automotive industry fell in love with it. As a result, it was used almost exclusively for air conditioning systems in vehicles until just recently. R-12 is a CFC and has been banned because of its high ozone depletion potential.

R-20
Trichloromethane, commonly referred to as chloroform, is no longer used as a refrigerant, thank God! However, it shares the same properties as many of the lower-numbered refrigerants.

R-22
Monochlorodifluoromethane, normally called R-22, is a synthetic refrigerant developed for refrigeration systems that need a low evaporating temperature, which explains its extensive use in household refrigerators and window air conditioners. It is nontoxic, noncorrosive, nonflammable, and has a boiling point of -41°F at atmospheric pressure. Being an HCFC, it is an ozone depleter, and has been phased out by attrition. What this means is that no new units can be built that use it as the primary refrigerant. However, there are still millions of working R-22 systems in operation today.

R-32
Difluoromethane is commonly referred to as HFC-32. It has a boiling point of -62 degF at atmoshperic pressure. It has zero ozone depletion potential and relatively low global warming potential. Due to its high heat of compression, it has not been aggressively exploited as a mainstream refrigerant. Instead, it is blended with other refrigerants to avoid high compressor discharge temperatures.

R-125
Pentafluoroethane is commonly referred to as HFC-125. It has a boiling point of -55.3 degF at atmoshperic pressure. It is considered to be the polar opposite of R-32 in the HFC family of refrigerants. Besides being blended with other compounds, it is also used as a fire extinguishing agent, and has replaced Halon in this realm.

R-134a
Tetrafluoroethane is very similar to R-12 in operation. The major difference is that it has zero ozone depletion potential. Noncorrosive, nonflammable, and nontoxic, it has a boiling point of -15°F at atmospheric pressure. Used for medium-temperature applications, such as air conditioning and commercial refrigeration, this refrigerant is now widely used in automobile air conditioners.


All of the above refrigerants are single compounds. When pressure is released or applied, they don't separate into fractions or decompose. Most of all, they do their job very well over a wide range of conditions. Until recently, they represented over 95% of all refrigerant used in consumer products of any type (refrigeration, heating/cooling, automotive, etc). However, they all have targets on their backs, marked by the EPA as bad for the Earth. They either eat the ozone layer, or are potent greenhouse gases, or both.

Modern / Retrofit Refrigerants

R-410A
R-410A is a non-ozone-depleting blend of two HFC refrigerants, R-32 and R-125. It has a boiling point of -55.3°F at atmospheric pressure. Due to this low boiling point, systems run at much higher pressures and refrigeration capacity than R22, and these in turn deliver performance benefits. It offers a better Energy Efficiency Ratio (EER) than R22. It is a suitable replacement for systems previously operating with R22. Many refrigeration and air-conditioning manufacturers have equipment specifically developed for R-410A. Chances are, if your existing R-22 system quits today, it will be replaced by a new system running on R-410A.

R-422A/B/C/D
The R-422 series of refrigerant blends are only approved for certain systems, and R-422A does not appear on EPA's list of approved HFCs. They are a retrofitting blend, designed to replace R-22 in refrigeration and air-conditioning applications. There is a sizable drop in efficiency from R-22. R-422B, C and D are all on EPA's approved list for use in new and retrofitted systems.

There are many more modern refrigerants being used today. These fall into the R-4xx or R-5xx numbering standard, and are all blends of previously developed refrigerants. They all have been invented to replace a particular traditional refrigerant that has been phased out of existence. Lucky for us, not much of this stuff is used in the residential sector. The only exception is R-410a.

Natural Refrigerants

Natural refrigerants are naturally occurring substances, such as hydrocarbons (propane, propylene, iso-butane), CO2, ammonia, water and (believe it or not) air. In general, they have zero ozone depletion potential, very low global warming potential, and operate well in a wide variety of systems. However, most natural refrigerants are not considered for retrofits in existing systems. Hydrocarbon refrigerants are extremely flammable or explosive, so extra safety measures must be integrated into products to prevent catastrophic failures in case a leak occurs. CO2 systems operate at extremely high pressures, so the refrigeration circuit must be made heavy enough to contain this high pressure. Despite the risks, many have been in use since the 1850's when refrigeration was invented.

R744 (Carbon Dioxide)
R744 can be applied in most heating and cooling systems such as mobile air-conditioning in vehicles and buses, vending machines, coolers, commercial cabinets for supermarkets, containers and climate control systems for residences. CO2 technology has also shown to be extremely efficient in heating water. This explains the success of the Japanese "Eco Cute" heat pump water heaters, which can also be combined efficiently with floor heating. In Japan, more than 300,000 CO2 based Eco Cute water heaters were sold in 2006.

R717 (Ammonia)

Ammonia refrigeration is the backbone of the food industry for freezing and storage of both frozen and unfrozen foods in many parts of the world (including fruits, vegetables, meat, poultry, fish, dairy, ice cream, beverages). In the range of 50 kW to 200 kW ammonia may be used, and for larger freezers ammonia is almost always preferred due to improved energy efficiency and reduced leakage.

Hydrocarbons (Propane, Propylene, Butane, Ethane, Ethylene)
R600 - Butane
R290 - Propane
R1270 - Propylene
R170 - Ethane
R1150 - Ethylene

By far the largest application for hydrocarbon refrigerants to date has been in domestic refrigerators and freezers. For example, R-600a (isobutane) is used in more than 400 million so-called Greenfreeze fridges and freezers worldwide. R-290 (propane) is used in commercial freezers & refrigerators.

Although largely ignored by policy makers to date, hydrocarbons have a long track record of safe, efficient and high performance use in mobile air conditioning systems in North America, Australia, many parts of South East Asia and other countries around the world. This strong empirical evidence of the suitability of hydrocarbons for use in servicing existing systems cannot continue to be overlooked in the urgent search for emissions abatement opportunities.

EDIT: In 2015, the EPA added Ethane (R–170), HFC–32 (R–32),
isobutane (R–600a), propane (R–290), and the hydrocarbon blend R–441A to its list of approved refrigerants. There are limits to this approval in residential refrigeration, air conditioning, and heat pump systems, but the approval itself is a testament to the future direction of the industry.

Many multinational corporations have adopted natural refrigerants as part of their business development plans. Coca Cola, Pepsi, McDonalds, Wal-Mart, and many others have begun changing their "old" equipment out with modern systems that use natural refrigerants. Literally millions of vending machines, display cases, and unit coolers have been installed worldwide. Due to this massive demand, natural refrigerants are gaining traction in an industry who has shunned them for decades.

The bottom line is this: if you have an existing heat pump or air conditioner, it probably runs off R-22 and it's living on borrowed time. If you purchase a new one, it will most likely be filled with R-410a. If you look hard enough, new units are available that use natural refrigerants.