# Refrigerant

A refrigerant is a working fluid used in the cooling, heating, or reverse cooling/heating cycles of air conditioning systems and heat pumps, where they undergo a repeated phase transition from a liquid to a gas and back again. Refrigerants are heavily regulated because of their toxicity and flammability, as well as the contribution of CFC and HCFC refrigerants to ozone depletion and the contribution of HFC refrigerants to climate change.
Refrigerants are used in a direct expansion (DX) circulating system to transfer energy from one environment to another, typically from inside a building to outside or vice versa. These can be air conditioner cooling only systems, cooling & heating reverse DX systems, or heat pump and heating only DX cycles. Refrigerants can carry 10 times more energy per kg than water, and 50 times more than air.
Refrigerants are controlled substances that are classified by international safety regulations ISO 817/5149, AHRAE 34/15 & BS EN 378 due to high pressures (700–1,000 kPa (100–150 psi)), extreme temperatures (−50 °C [−58 °F] to over 100 °C [212 °F]), flammability (A1 class non-flammable, A2/A2L class flammable and A3 class extremely flammable/explosive) and toxicity (B1-low, B2-medium & B3-high). The regulations relate to situations where these refrigerants are released into the atmosphere in the event of an accidental leak, not while circulated. Due to these regulations, most refrigerants may only be handled by qualified/certified engineers for the relevant classes (in the UK, C&G 2079 for A1-class and C&G 6187-2 for A2/A2L & A3-class refrigerants). Due to their non-flammability, non-explosivity, and non-toxicity, A1 class refrigerants have been used in open systems (where they are consumed when used rather than circulated) like fire extinguishers, inhalers, computer rooms, and insulation since 1928.

## History

The first air conditioners and refrigerators employed toxic or flammable gases, such as ammonia, sulfur dioxide, methyl chloride, or propane, that could result in fatal accidents when they leaked.
In 1928 Thomas Midgley Jr. created the first non-flammable, non-toxic chlorofluorocarbon gas, Freon (R-12). The name is a trademark name owned by DuPont (now Chemours) for any chlorofluorocarbon (CFC), hydrochlorofluorocarbon (HCFC), or hydrofluorocarbon (HFC) refrigerant. Following the discovery of better synthesis methods, CFCs such as R-11, R-12, R-123 and R-502 dominated the market.

### Phasing out of CFCs

In the mid-1970s, scientists discovered that CFCs were causing major damage to the ozone layer that protects the earth from ultraviolet radiation, and to the ozone holes over polar regions. This led to the signing of the Montreal Protocol in 1987 which aimed to phase out CFCs and HCFC but did not address the contributions that HFCs made to climate change. The adoption of HCFCs such as R-22, and R-123 was accelerated and so were used in most U.S. homes in air conditioners and in chillers from the 1980s as they have a dramatically lower Ozone Depletion Potential (ODP) than CFCs, but their ODP was still not zero which led to their eventual phase-out.
Hydrofluorocarbons (HFCs) such as R-134a, R-407A, R-407C, R-404A, R-410A (a 50/50 blend of R-125/R-32) and R-507 were promoted as replacements for CFCs and HCFCs in the 1990s and 2000s. HFCs were not ozone-depleting but did have global warming potentials (GWPs) thousands of times greater than CO$_2$ with atmospheric lifetimes that can extend for decades. This in turn, starting from the 2010s, led to the adoption in new equipment of Hydrocarbon and HFO (hydrofluoroolefin) refrigerants R-32, R-290, R-600a, R-454B, R-1234yf, R-514A, R-744 (CO$_2$), R-1234ze(E) and R-1233zd(E), which have both an ODP of zero and a lower GWP. Hydrocarbons and CO$_2$ are sometimes called natural refrigerants because they can be found in nature.
The environmental organization Greenpeace provided funding to a former East German refrigerator company to research alternative ozone- and climate-safe refrigerants in 1992. The company developed a hydrocarbon mixture of propane and isobutane, or pure isobutane, called "Greenfreeze", but as a condition of the contract with Greenpeace could not patent the technology, which led to widespread adoption by other firms. Policy and political influence by corporate executives resisted change however, citing the flammability and explosive properties of the refrigerants, and DuPont together with other companies blocked them in the U.S. with the U.S. EPA.
Beginning on 14 November 1994, the U.S. Environmental Protection Agency restricted the sale, possession and use of refrigerants to only licensed technicians, per rules under sections 608 and 609 of the Clean Air Act. In 1995, Germany made CFC refrigerators illegal.
In 1996 Eurammon, a European non-profit initiative for natural refrigerants, was established and comprises European companies, institutions, and industry experts.
In 1997, FCs and HFCs were included in the Kyoto Protocol to the Framework Convention on Climate Change.
In 2000 in the UK, the Ozone Regulations came into force which banned the use of ozone-depleting HCFC refrigerants such as R22 in new systems. The Regulation banned the use of R22 as a "top-up" fluid for maintenance from 2010 for virgin fluid and from 2015 for recycled fluid.

### Addressing greenhouse gases

With growing interest in natural refrigerants as alternatives to synthetic refrigerants such as CFCs, HCFCs and HFCs, in 2004, Greenpeace worked with multinational corporations like Coca-Cola and Unilever, and later Pepsico and others, to create a corporate coalition called Refrigerants Naturally!. Four years later, Ben & Jerry's of Unilever and General Electric began to take steps to support production and use in the U.S. It is estimated that almost 75 percent of the refrigeration and air conditioning sector has the potential to be converted to natural refrigerants.
In 2006, the EU adopted a Regulation on fluorinated greenhouse gases (FCs and HFCs) to encourage to transition to natural refrigerants (such as hydrocarbons). It was reported in 2010 that some refrigerants are being used as recreational drugs, leading to an extremely dangerous phenomenon known as inhalant abuse.
From 2011 the European Union started to phase out refrigerants with a global warming potential (GWP) of more than 150 in automotive air conditioning (GWP = 100-year warming potential of one kilogram of a gas relative to one kilogram of CO$_2$) such as the refrigerant HFC-134a (known as R-134a in North America) which has a GWP of 1526. In the same year the EPA decided in favour of the ozone- and climate-safe refrigerant for U.S. manufacture.
A 2018 study by the nonprofit organization "Drawdown" put proper refrigerant management and disposal at the very top of the list of climate impact solutions, with an impact equivalent to eliminating over 17 years of US carbon dioxide emissions.
In 2019 it was estimated that CFCs, HCFCs, and HFCs were responsible for about 10% of direct radiative forcing from all long-lived anthropogenic greenhouse gases. and in the same year the UNEP published new voluntary guidelines, however many countries have not yet ratified the Kigali Amendment.
From early 2020 HFCs (including R-404A, R-134a, and R-410A) are being superseded: Residential air-conditioning systems and heat pumps are increasingly using R-32. This still has a GWP of more than 600. Progressive devices use refrigerants with almost no climate impact, namely R-290 (propane), R-600a (isobutane), or R-1234yf (less flammable, in cars). In commercial refrigeration also CO$_2$ (R-744) can be used.

## Requirements and desirable properties

A refrigerant needs to have: a boiling point that is somewhat below the target temperature (although boiling point can be adjusted by adjusting the pressure appropriately), a high heat of vaporization, a moderate density in liquid form, a relatively high density in gaseous form (which can also be adjusted by setting pressure appropriately), and a high critical temperature. Working pressures should ideally be containable by copper tubing, a commonly available material. Extremely high pressures should be avoided.
The ideal refrigerant would be: non-corrosive, non-toxic, non-flammable, with no ozone depletion and global warming potential. It should preferably be natural with well-studied and low environmental impact. Newer refrigerants address the issue of the damage that CFCs caused to the ozone layer and the contribution that HCFCs make to climate change, but some do raise issues relating to toxicity and/or flammability.

## Common refrigerants
### Refrigerants with very low climate impact

With increasing regulations, refrigerants with a very low global warming potential are expected to play a dominant role in the 21st century, in particular, R-290 and R-1234yf. Starting from almost no market share in 2018, low GWPO devices are gaining market share in 2022.
| Code | Chemical | Name | GWP 20yr | GWP 100yr | Status | Commentary |
| R-290 | C$_3$H$_8$ | Propane | | 3.3 | Increasing use | Low cost, widely available, and efficient. They also have zero ozone depletion potential. Despite their flammability, they are increasingly used in domestic refrigerators and heat pumps. In 2010, about one-third of all household refrigerators and freezers manufactured globally used isobutane or an isobutane/propane blend, and this was expected to increase to 75% by 2020. |
| R-600a | HC(CH$_3$)$_3$ | Isobutane | | 3.3 | Widely used | See R-290. |
| R-717 | NH$_3$ | Ammonia | 0 | 0 | Widely used | Commonly used before the popularisation of CFCs, it is again being considered but does suffer from the disadvantage of toxicity, and it requires corrosion-resistant components, which restricts its domestic and small-scale use. Anhydrous ammonia is widely used in industrial refrigeration applications and hockey rinks because of its high energy efficiency and low cost. |
| R-1234yf HFO-1234yf | C$_3$H$_2$F$_4$ | 2,3,3,3-Tetrafluoropropene | | <1 | | Less performance but also less flammable than R-290. GM announced that it would start using "hydro-fluoro olefin", HFO-1234yf, in all of its brands by 2013. |
| R-744 | CO$_2$ | Carbon dioxide | 1 | 1 | In use | Was used as a refrigerant prior to the discovery of CFCs (this was also the case for propane) and now having a renaissance due to it being non-ozone depleting, non-toxic and non-flammable. It may become the working fluid of choice to replace current HFCs in cars, supermarkets, and heat pumps. Coca-Cola has fielded CO$_2$-based beverage coolers and the U.S. Army is considering CO$_2$ refrigeration. Due to the need to operate at pressures of up to 130 bars (1,900 psi; 13,000 kPa), CO$_2$ systems require highly resistant components, however these have already been developed for mass production in many sectors. |

### Most used

| Code | Chemical | Name | Global warming potential 20yr | GWP 100yr | Status | Commentary |
| R-32 HFC-32 | CH$_2$F$_2$ | Difluoromethane | 2430 | 677 | Widely used | Promoted as climate-friendly substitute for R-134a and R-410A, but still with high climate impact. Has excellent heat transfer and pressure drop performance, both in condensation and vaporisation. It has an atmospheric lifetime of nearly 5 years. Currently used in residential and commercial air-conditioners and heat pumps. |
| R-134a HFC-134a | CH$_2$FCF$_3$ | 1,1,1,2-Tetrafluoroethane | 3790 | 1550 | Widely used | Most used in 2020 for hydronic heat pumps in Europe and the United States in spite of high GWP. Commonly used in automotive air conditioners prior to phase out which began in 2012. |
| R-410A | | 50% R-32 / 50% R-125 (pentafluoroethane) | Between 2430 (R-32) and 6350 (R-125) | > 677 | Widely Used | Most used in split heat pumps / AC by 2018. Almost 100% share in the USA. Being phased out in the US starting in 2022. |

### Banned / Phased out

| Code | Chemical | Name | Global warming potential 20yr | GWP 100yr | Status | Commentary |
| R-11 CFC-11 | CCl$_3$F | Trichlorofluoromethane | 6900 | 4660 | Banned | Production was banned in developed countries by Montreal Protocol in 1996 |
| R-12 CFC-12 | CCl$_2$F$_2$ | Dichlorodifluoromethane | 10800 | 10200 | Banned | Also known as Freon, a widely used chlorofluorocarbon halomethane (CFC). Production was banned in developed countries by Montreal Protocol in 1996, and in developing countries (Article 5 countries) in 2010. |
| R-22 HCFC-22 | CHClF$_2$ | Chlorodifluoromethane | 5280 | 1760 | Being phased out | A widely used hydrochlorofluorocarbon (HCFC) and powerful greenhouse gas with a GWP equal to 1810. Worldwide production of R-22 in 2008 was about 800 Gg per year, up from about 450 Gg per year in 1998. R-438A (MO-99) is a R-22 replacement. |
| R-123 HCFC-123 | CHCl$_2$CF$_3$ | 2,2-Dichloro-1,1,1-trifluoroethane | 292 | 79 | US phase-out | Used in large tonnage centrifugal chiller applications. All U.S. production and import of virgin HCFCs will be phased out by 2030, with limited exceptions. R-123 refrigerant was used to retrofit some chiller that used R-11 refrigerant Trichlorofluoromethane. The production of R-11 was banned in developed countries by Montreal Protocol in 1996. |

### Other

| Code | Chemical | Name | Global warming potential 20yr | GWP 100yr | Commentary |
| R-152a HFC-152a | CH$_3$CHF$_2$ | 1,1-Difluoroethane | 506 | 138 | As a compressed air duster |
| R-407C | | Mixture of difluoromethane and pentafluoroethane and 1,1,1,2-tetrafluoroethane | | | A mixture of R-32, R-125, and R-134a |
| R-454B | | Difluoromethane and 2,3,3,3-Tetrafluoropropene | | | HFOs blend of refrigerants Difluoromethane (R-32) and 2,3,3,3-Tetrafluoropropene (R-1234yf). |
| R-513A | | An HFO/HFC blend (56% R-1234yf/44%R-134a) | | | May replace R-134a as an interim alternative |
| R-514A | | HFO-1336mzz-Z/trans-1,2- dichloroethylene (t-DCE) | | | An hydrofluoroolefin (HFO)-based refrigerant to replace R-123 in low-pressure centrifugal chillers for commercial and industrial applications. |

## Refrigerant reclamation and disposal

Coolant and refrigerants are found throughout the industrialized world, in homes, offices, and factories, in devices such as refrigerators, air conditioners, central air conditioning systems (HVAC), freezers, and dehumidifiers. When these units are serviced, there is a risk that refrigerant gas will be vented into the atmosphere either accidentally or intentionally, hence the creation of technician training and certification programs in order to ensure that the material is conserved and managed safely. Mistreatment of these gases has been shown to deplete the ozone layer and is suspected to contribute to global warming.
With the exception of isobutane and propane (R600a, R441A, and R290), ammonia and CO$_2$ under Section 608 of the United States' Clean Air Act it is illegal to knowingly release any refrigerants into the atmosphere.
Refrigerant reclamation is the act of processing used refrigerant gas that has previously been used in some type of refrigeration loop such that it meets specifications for new refrigerant gas. In the United States, the Clean Air Act of 1990 requires that used refrigerant be processed by a certified reclaimer, which must be licensed by the United States Environmental Protection Agency (EPA), and the material must be recovered and delivered to the reclaimer by EPA-certified technicians.

## Classification of refrigerants

Refrigerants may be divided into three classes according to their manner of absorption or extraction of heat from the substances to be refrigerated:
* Class 1: This class includes refrigerants that cool by phase change (typically boiling), using the refrigerant's latent heat.
* Class 2: These refrigerants cool by temperature change or 'sensible heat', the quantity of heat being the specific heat capacity x the temperature change. They are air, calcium chloride brine, sodium chloride brine, alcohol, and similar nonfreezing solutions. The purpose of Class 2 refrigerants is to receive a reduction of temperature from Class 1 refrigerants and convey this lower temperature to the area to be cooled.
* Class 3: This group consists of solutions that contain absorbed vapors of liquefiable agents or refrigerating media. These solutions function by the nature of their ability to carry liquefiable vapors, which produce a cooling effect by the absorption of their heat of solution. They can also be classified into many categories.

### R numbering system

The R- numbering system was developed by DuPont (which owned the Freon trademark), and systematically identifies the molecular structure of refrigerants made with a single halogenated hydrocarbon. ASHRAE has since set guidelines for the numbering system as follows:
R-X$_1$X$_2$X$_3$X$_4$
* X$_1$ = Number of unsaturated carbon-carbon bonds (omit if zero)
* X$_2$ = Number of carbon atoms minus 1 (omit if zero)
* X$_3$ = Number of hydrogen atoms plus 1
* X$_4$ = Number of fluorine atoms

#### Series

* R-xx Methane Series
* R-1xx Ethane Series
* R-2xx Propane Series
* R-4xx Zeotropic blend
* R-5xx Azeotropic blend
* R-6xx Saturated hydrocarbons (except for propane which is R-290)
* R-7xx Inorganic Compounds with a molar mass < 100
* R-7xxx Inorganic Compounds with a molar mass ≥ 100

#### Ethane Derived Chains

* Number Only Most symmetrical isomer
* Lower Case Suffix (a, b, c, etc.) indicates increasingly unsymmetrical isomers

#### Propane Derived Chains

* Number Only If only one isomer exists; otherwise:
* First lower case suffix (a-f):
** a Suffix Cl$_2$ central carbon substitution
** b Suffix Cl, F central carbon substitution
** c Suffix F$_2$ central carbon substitution
** d Suffix Cl, H central carbon substitution
** e Suffix F, H central carbon substitution
** f Suffix H$_2$ central carbon substitution
* 2nd Lower Case Suffix (a, b, c, etc.) Indicates increasingly unsymmetrical isomers

#### Propene derivatives

* First lower case suffix (x, y, z):
** x Suffix Cl substitution on central atom
** y Suffix F substitution on central atom
** z Suffix H substitution on central atom
* Second lower case suffix (a-f):
** a Suffix =CCl$_2$ methylene substitution
** b Suffix =CClF methylene substitution
** c Suffix =CF$_2$ methylene substitution
** d Suffix =CHCl methylene substitution
** e Suffix =CHF methylene substitution
** f Suffix =CH$_2$ methylene substitution

#### Blends

* Upper Case Suffix (A, B, C, etc.) Same blend with different compositions of refrigerants

#### Miscellaneous

* R-Cxxx Cyclic compound
* R-Exxx Ether group is present
* R-CExxx Cyclic compound with an ether group
* R-4xx/5xx + Upper Case Suffix (A, B, C, etc.) Same blend with different composition of refrigerants
* R-6xx + Lower Case Letter Indicates increasingly unsymmetrical isomers
* 7xx/7xxx + Upper Case Letter Same molar mass, different compound
* R-xxxxB# Bromine is present with the number after B indicating how many bromine atoms
* R-xxxxI# Iodine is present with the number after I indicating how many iodine atoms
* R-xxx(E) Trans Molecule
* R-xxx(Z) Cis Molecule
For example, R-134a has 2 carbon atoms, 2 hydrogen atoms, and 4 fluorine atoms, an empirical formula of tetrafluoroethane. The "a" suffix indicates that the isomer is unbalanced by one atom, giving 1,1,1,2-Tetrafluoroethane. R-134 (without the "a" suffix) would have a molecular structure of 1,1,2,2-Tetrafluoroethane.
The same numbers are used with an R- prefix for generic refrigerants, with a "Propellant" prefix (e.g., "Propellant 12") for the same chemical used as a propellant for an aerosol spray, and with trade names for the compounds, such as "Freon 12". Recently, a practice of using abbreviations HFC- for hydrofluorocarbons, CFC- for chlorofluorocarbons, and HCFC- for hydrochlorofluorocarbons has arisen, because of the regulatory differences among these groups.

## Refrigerant safety

ASHRAE Standard 34, Designation and Safety Classification of Refrigerants, assigns safety classifications to refrigerants based upon toxicity and flammability.
Using safety information provided by producers, ASHRAE assigns a capital letter to indicate toxicity and a number to indicate flammability. The letter "A" is the least toxic and the number 1 is the least flammable.