Refrigerant

{{short description|Substance in a refrigeration cycle}}

'''Refrigerants''' are [[working fluid | working fluids]] that carry heat from a cold environment to a warm environment while circulating between them. For example, the refrigerant in an [[air conditioning | air conditioner]] carries heat from a cool indoor environment to a hotter outdoor environment. Similarly, the refrigerant in a kitchen [[refrigerator]] carries heat from the inside the refrigerator out to the surrounding room. A wide range of fluids are used as refrigerants, with the specific choice depending on the temperature range needed and constraints related to the system involved.

Refrigerants are the basis of [[vapor compression refrigeration]] systems. The refrigerant is circulated in a loop between the cold and warm environments (see figure). In the low-temperature environment, the refrigerant absorbs heat at low pressure, causing it to evaporate. The gaseous refrigerant then enters a compressor, which raises its pressure and temperature. The pressurized refrigerant circulates through the warm environment, where it releases heat and condenses to liquid form. The high-pressure liquid is then depressurized and returned to the cold environment as a liquid-vapor mixture.<ref name = "cengel">{{cite book |last1=Çengel |first1=Yunus A. |last2=Boles |first2=Michael A. |last3=Konğlu |first3=Mehmet |title=Thermodynamics: an engineering approach |date=2019 |publisher=McGraw-Hill |isbn=978-1-259-82267-4 |edition=9th |chapter=Chapter 11}}</ref><ref name = "moran">{{cite book |last1=Moran |first1=Michael J. |last2=Shapiro |first2=Howard N. |title=Fundamentals of Engineering Thermodynamics |date=2006 |publisher=John Wiley & Sons |isbn=978-0-470-03037-0 |edition=5th |chapter=Chapter 10}}</ref>

[[File:Air conditioning unit-en.svg|thumb|upright=2| A window air conditioner. The refrigerant circulates through the evaporator/cooling coil (blue), where it absorbs heat from the indoor air, making that air cooler. The refrigerant vapor then flows to the compressor, where an electric motor drives the vapor to higher pressure and temperature. The vapor releases heat and liquefies in the condenser (red). The condensed liquid then flows through an expansion valve, depressurizing and cooling. After expansion, it returns to the evaporator as a cold liquid-vapor mixture.]]

Refrigerants are also used in [[heat pump | heat pumps]], which work like refrigeration systems. In the winter, a heat pump absorbs heat from the cold outdoor environment and releases it into the warm indoor environment. In summer, the direction of heat transfer is reversed.<ref name="cengel" /><ref name = "moran"/>

Refrigerants include naturally occurring fluids, such as [[ammonia]], [[carbon dioxide]], [[propane]], or [[isobutane]], and synthetic fluids, such as [[chlorofluorocarbons]], [[hydrochlorofluorocarbons]], or [[hydrofluorocarbons]]. Many older synthetic refrigerants have been banned to protect the Earth's [[ozone layer]] or to limit [[climate change]].<ref name="domanski-2022"/> Some refrigerants are flammable or toxic, making careful handling and disposal essential.<ref name="cengel" />

Refrigerants, while strongly associated with vapor compression systems, are used for many other purposes. These applications include [[aerosol propellants|propelling aerosols]], polymer foam production, chemical feedstocks, fire suppression, and solvents.<ref>{{cite report | last1 = Booten | first1 = Chuck | last2 = Nicholson | first2 = Scott | last3 = Mann | first3 = Margaret | last4 = Abdelaziz | first4 = Omar | title = Refrigerants: Market trends and supply chain assessment | publisher = National Renewable Energy Laboratory; Oak Ridge National Laboratory, U.S. Department of Energy | date = February 2020 | type = Technical Report | number = NREL/TP–5500–70207 | url = https://docs.nrel.gov/docs/fy20osti/70207.pdf | access-date = 2025-09-01 }}</ref>

[[Chillers]] are refrigeration systems that have a secondary loop which circulates a [[Brine#Refrigerating_fluid | refrigerating liquid]] (as opposed to a refrigerant), with vapor compression refrigeration used to chill the secondary liquid.<ref>{{Cite book | title = 2020 ASHRAE Handbook—HVAC Systems and Equipment (SI edition) | chapter = Chapter 43: Liquid Chilling Systems | publisher = American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) | location = Atlanta, GA | year = 2020 | isbn = 1-5231-3508-5 | language = en }} </ref> [[Absorption refrigerator | Absorption refrigeration]] systems operate by absorbing a gas, such as ammonia, into a liquid, such as water.<ref name="cengel" /><ref name = "moran"/>

==Requirements and desirable properties==

The selection of a refrigerant for a given purpose depends on a combination of factors. Different refrigerants, having different properties, are better suited to some applications than others.<ref name="hundy">{{Cite book | last1 = Hundy | first1 = G. F. | last2 = Trott | first2 = A. R. | last3 = Welch | first3 = T. C. | title = Refrigeration, Air Conditioning and Heat Pumps | edition = 5th | year = 2016 | publisher = Butterworth-Heinemann (Elsevier) | isbn = 978-0-08-100647-4 | chapter = Refrigerants | pages = 41-58 | chapter-url = https://www.sciencedirect.com/book/9780081006474/refrigeration-air-conditioning-and-heat-pumps | url = https://www.sciencedirect.com/book/9780081006474/refrigeration-air-conditioning-and-heat-pumps | access-date = 2025-09-02 }}</ref><ref name="domanski-2022">{{cite report | last1 = Domanski | first1 = Piotr A. | last2 = Motta | first2 = Sergio Y. | title = Low-GWP Refrigerants: Status and Outlook | publisher = International Institute of Refrigeration | date = 1 June 2022 | url = https://iifiir.org/en/fridoc/low-gwp-refrigerants-status-and-outlook-48-lt-sup-gt-th-lt-sup-gt-informatory-145388 | type = 48th Informatory Note on Refrigeration Technologies | access-date = 10 September 2025 }}</ref>

===Thermophysical property requirements=== In [[thermodynamics | thermodynamic]] terms, refrigerants transport thermal energy, which is called [[enthalpy]]. Enthalpy greatly increases or decreases during evaporation or condensation. The difference between the enthalpy of the vapor and liquid phase is called the [[heat of vaporization | latent heat of vaporization]]. The latent heat of vaporization allows substantial energy to be absorbed or released, with minimal temperature change, in the [[evaporator]] or [[Condenser_(heat_transfer) | condenser]]. [[mechanical engineering | Engineers]] control the temperatures in the evaporator and condenser by changing the fluid's pressure.<ref name="cengel" /><ref name = "moran"/>

A refrigerant must achieve a [[boiling point]] below the desired temperature of the cold environment. Heat will then flow from the cold environment into the refrigerant, causing it to evaporate. The boiling point is lower if the refrigerant pressure is lower. For this reason, the refrigerant in the evaporator (on the cold side) will have a reduced pressure.<ref name="hundy"/><ref name="welch-2008">{{cite book | last = Welch | first = Terry | year = 2008 | title = Refrigeration – CIBSE Knowledge Series: KS13 | chapter = 5. How the Vapour Compression Cycle Works | publisher = The Chartered Institution of Building Services Engineers (CIBSE) | isbn = 978-1-903287-91-0 }}</ref> The evaporator pressure should be above atmospheric pressure to prevent air from leaking into it.<ref name="legg">{{Cite book | last = Legg | first = Roger | title = Air Conditioning System Design | year = 2017 | publisher = Butterworth-Heinemann | location = Cambridge, MA | isbn = 978-0-08-101123-2 | pages = 187–188 | url = https://www.sciencedirect.com/book/9780081011232/air-conditioning-system-design | access-date= 2025-09-02 }}</ref>

Similarly, the refrigerant must achieve a boiling point above the temperature of the warm environment, so that heat will flow out of the refrigerant as it condenses. Since boiling point rises with increasing pressure, the refrigerant in the condenser (on the warm side) will have an elevated pressure.<ref name="hundy"/><ref name="welch-2008"/>

For most refrigeration systems, a [[critical point (thermodynamics) | critical point temperature]] well above the condenser temperature is desirable. When the critical point temperature is above the condenser temperature, the refrigerant can condense from the vapor to the liquid phase at nearly constant temperature; but if the critical point were below the condenser temperature, no phase change could occur. For fixed evaporator and condenser temperatures, increasing the critical point temperature farther above the condenser temperature raises the energy efficiency of a refrigeration cycle.<ref name="mclinden-didion">{{cite journal |last1=McLinden |first1=Mark O. |last2=Didion |first2=David A. |title=Quest for alternatives |journal=ASHRAE Journal |year=1987 |volume=29 |issue=12 |pages=32–42 }}</ref>

However, as the critical point temperature rises, the vapor density at the compressor inlet decreases. A lower density raises the [[volumetric flow rate]] of vapor needed for a given amount of cooling (in other words, the compressor must be larger to do the job). Thus, a trade-off between energy efficiency and volumetric efficiency underlies the selection of a refrigerant.<ref name="mclinden-didion" />

The refrigerant vapor's [[specific heat capacity]] also strongly affects performance. A lower specific heat capacity avoids liquid formation in the compressor, but too low a heat capacity can result in undesirably hot vapor at the compressor outlet. Optimization tends to favor refrigerant molecules with fewer atoms.<ref name="mclinden-didion" /> A high latent heat of vaporization and a [[triple point | triple point temperature]] well below the evaporator temperature are also desirable.<ref name="hundy"/><ref name="legg"/>

A few refrigerants, like carbon dioxide, may operate in warm environments that are above the critical point temperature. In these [[Transcritical_cycle#Applications_in_refrigeration_cycles | transcritical refrigeration cycles]], the condenser must be replaced by a gas cooler operating over a wider temperature range.<ref name="hundy"/><ref name="lorentzen">{{cite journal | last = Lorentzen | first = Gustav | author-link = Gustav Lorentzen (scientist) | title = Revival of carbon dioxide as a refrigerant | journal = International Journal of Refrigeration | year = 1994 | volume = 17 | issue = 5 | pages = 292–301 | doi = 10.1016/0140-7007(94)90059-0 }}</ref>

Refrigerants are sometimes blended to achieve a balance of desired properties. Pure refrigerants vaporize at a constant temperature when pressure is held constant (as it is in an evaporator or condenser). In contrast, blended refrigerants vaporize across a small ''range'' of temperature. This phenomenon is called [[Zeotropic_mixture#Dew_and_bubble_points | temperature glide]].<ref name="hundy"/><ref>{{cite book | title = Fundamentals of Refrigeration | publisher = Copeland Corporation | year = 2009 | url = https://media.copeland.com/6c9290aa-5a33-4c40-9e64-b16d00375bf1/AE101-Fundamentals%20of%20Refrigeration.pdf | access-date = 2025-09-09 }}</ref>

For safety, an ideal refrigerant should be non-toxic and non-flammable. For environmental protection, the refrigerant should have no [[ozone depletion potential]], and a very low [[global warming potential]]. Refrigerants that are not naturally present in the atmosphere should have a short [[atmospheric lifetime]] and should decay into environmentally benign by-products.<ref name="domanski-2022"/><ref>{{Cite journal | last1 = Abas | first1 = Naeem | last2 = Kalair | first2 = Ali Raza | last3 = Khan | first3 = Nasrullah | last4 = Haider | first4 = Aun | last5 = Saleem | first5 = Zahid | last6 = Saleem | first6 = Muhammad Shoaib | title = Natural and synthetic refrigerants, global warming: A review | journal = Renewable and Sustainable Energy Reviews | volume = 90 | pages = 557–569 | date = July 2018 | doi = 10.1016/j.rser.2018.03.099 | url = https://www.sciencedirect.com/science/article/pii/S1364032118301977 | access-date = 2025-09-02 | url-access= subscription }}</ref>

===Other requirements=== The refrigerant must be chemically stable during use.<ref name="mclinden-didion"/>

Refrigerants should be non-corrosive to the components in the system. To protect the compressor, the refrigerant should be miscible in the [[lubricant]], and [[radial shaft seal | shaft seals]] compatible with the refrigerant must be available. For [[Compressor#Hermetically_sealed,_open,_or_semi-hermetic | hermetically sealed]] systems, the refrigerant vapor may have contact with the [[Electric motor | motor windings]], and so it should have a high [[dielectric strength]].<ref name="hundy"/><ref name="legg"/><ref name="mclinden-didion"/>

The refrigerant should have a low cost. Legal regulations can also be a strong factor in the selection of refrigerants.<ref name="hundy"/>

The selection of a refrigerant for a specific purpose involves trade-offs among the all factors mentioned. Often, no refrigerant is entirely ideal, and several different refrigerants will appear as reasonable options.<ref name="ashrae-fund-29">{{Cite book | author = American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) | title = ASHRAE Handbook—Fundamentals (SI edition) | year = 2021 | publisher = American Society of Heating, Refrigerating and Air-Conditioning Engineers | location = Atlanta, GA | isbn = 978-1-947192-90-4 | chapter = Chapter 29: Refrigerants }}</ref>

== History == [[Image:Diethyl ether.svg|class=skin-invert-image|thumb|right|upright=.75| [[ Diethyl ether ]] molecule ]]{{See also|Refrigeration#History}} Vapor compression refrigeration was first described theoretically by [[Oliver Evans]] in 1805, using [[ diethyl ether]] as the refrigerant. In 1834, [[Jacob Perkins]] patented a vapor compression system, also describing diethyl ether as the refrigerant. The first working prototype of that system was built by John Hague the same year, but used a rubber distillate, caoutchoucine, as the refrigerant.<ref name="asme-HHC">{{cite report | title = Perkins Vapor-Compression Cycle for Refrigeration | publisher = American Society of Mechanical Engineers, History and Heritage Committee | date = November 2020 | url = https://www.asme.org/getmedia/cb9bea09-6d23-425e-bfe5-5f6d786919fb/274-perkins-vapor-comp-refrig.pdf | type = Historic Mechanical Engineering Landmark booklet (PDF) | series = ASME Historic Mechanical Engineering Landmarks | number = 274 | access-date = 2025-09-01 }}</ref><ref>{{Cite book | last = Radebaugh | first = Ray | year = 2007 | title = Cryogenic Engineering: Fifty Years of Progress | editor-last= Timmerhaus | editor-first= K. D. | editor2-last= Reed | editor2-first= R. P. | publisher = Springer | location = New York, NY | series = International Cryogenics Monograph Series | isbn = 978-0-387-46896-9 | chapter = Historical Summary of Cryogenic Activity Prior to 1950 | pages = 3–27 | chapter-url= https://trc.nist.gov/cryogenics/Papers/Review/2007-Historical_Summary_of_Cryogenics.pdf | doi = 10.1007/0-387-46896-X_1 | access-date= 2025-09-01 }}</ref> In the 1850s, [[James_Harrison_(engineer)#Ice-making_operation_and_later_life |James Harrison]], working in Australia, developed a Perkins-type system also using diethyl ether. Ice making and meat packing were early applications of his technology.<ref name="adb">{{Australian Dictionary of Biography |first=L. G. |last=Bruce-Wallace |title=Harrison, James (1816–1893) |id2=harrison-james-2165 |accessdate=September 9, 2025 }}</ref>

Many more inventions followed during the second half of the 19th century. In the 1860s, [[Thaddeus Lowe]] developed a [[carbon dioxide#Refrigerant | carbon dioxide]] system.<ref name="r7">{{cite conference | last = Pearson | first = S. Forbes | title = Refrigerants past, present and future | book-title = Bulletin IIF-IIR, vol. 84, no. 3 | year = 2004 | pages = 4–28 | url = https://iifiir.org/en/fridoc/refrigerants-past-present-and-future-122964 | access-date = September 7, 2025 }} </ref> The 1870s saw the introduction of systems based on [[Ammonia#Refrigeration-R717 | ammonia]], [[Sulfur_dioxide#As_a_refrigerant | sulfur dioxide]], [[dimethyl ether]], and [[Chloromethane#Obsolete_applications|methyl chloride]].<ref name="asme-HHC" /><ref>{{cite web |last=Nagengast |first=Bernard |author2=Gerald Groff |author3=Wolf Eberhard Kraus |author4=International Institute of Refrigeration |date=May 4, 2006 |title=Air-Conditioning and Refrigeration Chronology: Significant Dates Pertaining to Air Conditioning and Refrigeration |url=https://www.ashrae.org/File%20Library/About/Mission%20and%20Vision/ASHRAE%20and%20Industry%20History/Air-Conditioning-and-Refrigeration-Chronology.pdf |website=American Society of Heating, Refrigerating and Air-Conditioning Engineers |access-date=September 1, 2025 }}</ref> Several 19th-century refrigerants continue in use to this day, but others have been discarded for safety or performance reasons.<ref name="mclinden">{{cite journal |last1=McLinden |first1=Mark O. |last2=Huber |first2=Marcia L.

|title=(R)Evolution of Refrigerants |journal=Journal of Chemical & Engineering Data |year=2020 |volume=65 |issue=9 |pages=4176–4193 |doi=10.1021/acs.jced.0c00338 |pmc=8739722 }}</ref> By start of the 20th century, ammonia was predominant in industrial systems.<ref name="r7"/>

Household use of vapor compression refrigerators and air conditioners emerged in the early 20th century, as small electric motors became available to drive the vapor compressor. These early systems used ammonia, [[isobutane#Refrigerant |isobutane]], methyl chloride, [[propane#Refrigerant | propane]], and sulfur dioxide. Each of these had drawbacks for household use, such as odor, toxicity, or flammability. (Despite their flammability, propane and isobutane had good safety records.)<ref name="r7" />

=== The development of halogenated refrigerants (CFCs and HCFCs) ===

{{See|Refrigerant#Numbered classification of refrigerants}}[[Image:Natta projection of dichlorodifluoromethane.svg|class=skin-invert-image|thumb|right|upright=.6| [[Difluorodichloromethane]] molecule (CFC-12 or R-12) ]] In the 1920s, [[Thomas Midgley Jr.]], working with [[Albert Henne]] and Robert MacNeary, made a systematic study of synthetic refrigerants, seeking a fluid that was non-toxic, non-flammable, and stable. Midgley's team focused in on chlorinated and fluorinated hydrocarbons (chlorine and fluorine are [[halogens]], so these compounds are termed "halogenated"). By 1931, [[dichlorodifluoromethane]] (R-12) came to market. R-12 was soon followed by [[trichlorofluoromethane]] (R-11) in 1932, and [[chlorodifluoromethane]] (R-22) in 1936. R-11 and R-12 are [[chlorofluorocarbon]]s, or CFCs, and R-22 is a [[hydrochlorofluorocarbon]], or HCFC.<ref name="mclinden"/> The trade name [[Freon]] was used for R-12, which at that time was also called F-12.<ref>{{cite journal |last=Thompson |first=R. J. |title=Freon, a Refrigerant |journal=Industrial & Engineering Chemistry |year=1932 |volume=24 |issue=6 |pages=620–623 |doi=10.1021/ie50270a008 }}</ref>

The R- numbering system for refrigerants was developed by DuPont in the years that followed.<ref>{{cite web |last=Marchese |first=Joe |title=Ice Breaker: Refrigerant Numbering System Explained |website=ACHR News |date=14 July 2008 |url=https://www.achrnews.com/articles/108910-ice-breaker-refrigerant-numbering-system-explained |access-date=6 September 2025}}</ref> The letter R is followed by a number that uniquely identifies the chemical structure of the refrigerant. The system has since become an international standard. Often, a more specific group of letters is used in place of R to denote the chemical family of the refrigerant. For example, R-12 may be called CFC-12 to indicate that it is a chlorofluorocarbon.

CFC and HCFC refrigerants were immensely successful, and they dominated the market for half a century.<ref name="r7" /> By 1987, R-12 was used in essentially all refrigerators and R-22 in nearly all air conditioners.<ref name="mclinden"/> Automotive systems relied on R-12, water [[chillers]] using centrifugal compressors favored R-11, and low-temperature commercial refrigeration used a blended refrigerant, R-502.<ref name="domanski-2022"/>

=== Phase-out of CFCs and HCFCs (ozone-layer protection)=== {{See also|Montreal Protocol}} In the mid-1970s, scientists discovered that CFCs were causing substantial damage to the [[ozone layer]] that protects the earth from ultraviolet radiation.<ref>{{cite journal |last1=Molina |first1=Mario J. |last2=Rowland |first2=F. S |title=Stratospheric sink for chlorofluoromethanes: chlorine catalysed destruction of ozone |journal=Nature |date=28 June 1974 |volume=249 |pages=810–812 |doi=10.1038/249810a0 |url=https://courses.seas.harvard.edu/climate/eli/Courses/EPS281r/Sources/Ozone-hole/2-Molina-Rowland-1974.pdf |access-date=October 6, 2024}}</ref><ref>{{cite book |last1=National Research Council |title=Halocarbons: Effects on Stratospheric Ozone |date=1976 |publisher=The National Academies Press |location=Washington, DC |doi=10.17226/19978 |isbn=978-0-309-02532-4 |url=https://nap.nationalacademies.org/catalog/19978/halocarbons-effects-on-stratospheric-ozone |access-date=October 6, 2024}}</ref> The process occurs when CFCs reach the [[stratosphere]] and absorb [[solar radiation]]. The absorbed radiation causes chlorine atoms to separate from CFCs, then catalyzing the breakdown of ozone (O₃) into oxygen gas (O₂). A decade later, researchers showed that CFCs had created a region of ozone depletion{{emdash}}an [[ozone hole]]{{emdash}}above Antarctica.<ref>{{cite journal |last1=Solomon |first1=Susan |last2=Garcia |first2=Rolando R. |last3=Rowland |first3=F. Sherwood |last4=Wuebbles |first4=Donald J. |title=On the depletion of Antarctic ozone |journal=Nature |year=1986 |volume=321 |pages=755–758 |doi=10.1038/321755a0 |hdl=2060/19910073958 |hdl-access=free }}</ref> [[File:CFCs & Ozone.jpg|thumb|upright=2.2|Ozone (O₃) in the stratosphere naturally cycles to oxgen gas (O₂), and back, when it absorbs solar energy. If CFCs are present, solar energy can separate a chlorine atom, which breaks the cycle, forming O₂ and ClO. The net result is [[ozone depletion#Ozone_cycle_overview | more oxygen and less ozone]].]]

These discoveries led to the signing of the [[Montreal Protocol]] in 1987. This international agreement aimed to phase out CFCs and HCFCs to protect the ozone layer.

Under the Montreal Protocol, production of CFCs was scheduled to be banned in most countries by 1996. HCFCs were scheduled to phase out over a longer period because they have lower [[Ozone depletion potential|ozone depletion potentials]] (ODP) than CFCs. During this transition time, the adoption of HCFCs, such as [[Chlorodifluoromethane|R-22]], was accelerated.<ref name="AnnexA">{{cite web |title=Annex A: Controlled Substances under the Montreal Protocol |url=https://ozone.unep.org/treaties/montreal-protocol/articles/annex-controlled-substances |website=Ozone Secretariat |publisher=United Nations Environment Programme |access-date=2025-09-08}}</ref><ref name="AnnexC">{{cite web |title=Annex C, Group I: Hydrochlorofluorocarbons (Consumption) |url=https://ozone.unep.org/treaties/montreal-protocol/annex-c-group-i-hcfcs-consumption |website=Ozone Secretariat |publisher=United Nations Environment Programme |access-date=2025-09-08}}</ref><ref name="UNEP-hcfc">{{cite web |title=Report of the Technology and Economic Assessment Panel: HCFC Task Force (2003, rev. 2005) |url=https://ozone.unep.org/sites/default/files/2019-05/HCFC03R1.pdf |website=Ozone Secretariat |publisher=United Nations Environment Programme |access-date=2025-09-08 }}</ref>

The search for alternatives to CFC and HCFC refrigerants, such as R-12 and R-22, began in the 1970s. By the time Montreal Protocol was signed, [[R-134a]] had been identified as a replacement for R-12 in automotive use and [[2,2-Dichloro-1,1,1-trifluoroethane | R-123]] as a replacement for R-11 in large [[chiller]]s.<ref name="mclinden"/> R-134a is a [[hydrofluorocarbon]] or HFC, but R-123 was a [[hydrochlorofluorocarbon]] (HCFC) that would also eventually be phased out.

Governments made regulations to support the Montreal Protocol. In 1991, Germany enacted legislation to eliminate CFCs in cooling appliances,<ref>{{cite journal |title=Verordnung zum Verbot von bestimmten die Ozonschicht abbauenden Halogenverbindungen (FCKW-Halon-Verbots-Verordnung) |journal=Bundesgesetzblatt I |date=7 May 1991 |issue=24 |pages=1090–1095 |language=de |url=https://www.bgbl.de/xaver/bgbl/start.xav?startbk=Bundesanzeiger_BGBl&jumpTo=bgbl191s1090.pdf |access-date=2025-09-08}}</ref> and CFCs were prohibited in new equipment starting in 1995.<ref>{{cite web |title=Antwort der Bundesregierung auf die Kleine Anfrage – Drucksache 19/23930 |url=https://dserver.bundestag.de/btd/19/239/1923930.pdf |publisher=Deutscher Bundestag |date=March 11, 2020 |language=de |page=1 |quote=...seit 1995 hergestellten Kühlgeräte sind zwar FCKW-frei, da diese Stoffe in den neuen Produkten verboten wurden,... |trans-quote=...cooling appliances manufactured since 1995 are CFC-free, since these substances were banned in new products,... |access-date=2025-09-08}}</ref>

US home air conditioners and industrial [[chillers]] moved toward HCFCs starting in the 1980s. Beginning on 14 November 1994, the [[Federal government of the United States|US]] [[United States Environmental Protection Agency|Environmental Protection Agency]] (EPA) restricted the sale, possession and use of refrigerants to only licensed technicians, per rules under the Clean Air Act.<ref>{{cite web|url= https://www.epa.gov/section608 |title=Complying With The Section 608 Refrigerant Recycling Rule &#124; Ozone Layer Protection - Regulatory Programs |website=Epa.gov |date=21 April 2015|access-date=10 June 2015}}</ref> The US banned the production and import of CFCs on January 1, 1996.<ref>{{cite web | title = EPA Announces Full Phaseout of CFCs and Other Ozone Depleters | work = Environmental Protection Agency | date = April 23, 1993 | url = https://www.epa.gov/archive/epa/aboutepa/epa-announces-full-phaseout-cfcs-and-other-ozone-depleters.html | access-date = 31 August 2025 }}</ref> Stockpiled and reclaimed CFCs continued to be used while supplies were available.

Much later, governments began restricting HCFCs. For example, in 2000 the UK's Ozone Regulations came into force, banning ozone-depleting HCFC refrigerants such as R-22 in new systems. The regulations also banned the use of virgin R-22 as a "top-up" fluid for maintenance from 2010 and of recycled R-22 from 2015.<ref>{{cite web|url=https://www.gov.uk/government/policies/protecting-and-enhancing-our-urban-and-natural-environment-to-improve-public-health-and-wellbeing/supporting-pages/controlling-ozone-depleting-substances-and-fluorinated-greenhouse-gases |title=2010 to 2015 government policy: environmental quality |website=GOV.UK |date=8 May 2015|access-date=10 June 2015}}</ref> In 2010, US EPA banned the use of R-22 (HCFC-22) in new equipment,<ref name="Phaseout">{{cite web |title=Phaseout of Class II Ozone-Depleting Substances |url=https://www.epa.gov/ods-phaseout/phaseout-class-ii-ozone-depleting-substances |publisher=United States Environmental Protection Agency |access-date=2025-09-08 }}</ref> much of which shifted to the HFC mixture, [[R-410A]].<ref name="mclinden" /><ref name="calm-2008">{{cite journal |last=Calm |first=James M. |title=The Next Generation of Refrigerants – Historical Review, Considerations and Outlook |journal=International Journal of Refrigeration |year=2008 |volume=31 |issue=7 |pages=1123–1133 |doi=10.1016/j.ijrefrig.2008.01.013 |url=https://www.sciencedirect.com/science/article/pii/S0140700708000261 |access-date=2025-09-08 |url-access=subscription }}</ref> All production and import of R-22 was banned on January 1, 2020.<ref>{{cite web | title = Technicians and Contractors: Frequent Questions | website = U.S. Environmental Protection Agency | publisher = Environmental Protection Agency | date = 5 November 2024 | url = https://www.epa.gov/ods-phaseout/technicians-and-contractors-frequent-questions | access-date = 31 August 2025 }}</ref>

The Montreal Protocol, which dealt with ozone depletion, did not aim to regulate the global warming impact of refrigerants. Even so, CFCs have much higher [[global warming potential]]s than the refrigerants that replaced them. As a result, the Montreal Protocol very significantly reduced global warming.<ref>{{cite journal |last1=Velders |first1=Guus J. M. |last2=Andersen |first2=S. O. |last3=Daniel |first3=Joel S. |last4=Fahey |first4=David W. |last5=McFarland |first5=Michael |title=The importance of the Montreal Protocol in protecting climate |journal=Proceedings of the National Academy of Sciences of the United States of America |year=2007 |volume=104 |pages=4814–4819 |doi=10.1073/pnas.0610328104 |url=https://www.pnas.org/doi/10.1073/pnas.0610328104 |access-date=2025-09-08 |pmc=1817831 }}</ref>

=== Renewed interest in natural refrigerants ===

Naturally-occurring refrigerants had been used prior to the introduction of CFCs in 1931. These included ammonia, carbon dioxide, isobutane, propane, among others. These refrigerants do not damage the ozone layer, and also have a very low global warming potential.<ref name="wmo"/> These substances gained renewed attention during the 1990s as the damaging effects of many synthetic refrigerants became known.<ref name="mclinden"/> Collectively, they are called [[natural refrigerant]]s.

[[Image:Isobutane 1.svg|class=skin-invert-image|thumb|right|upright=.95| [[Isobutane]] (R-600a) molecule]] European environmentalists were at the forefront of this effort. The environmental organization [[Greenpeace]] established a collaboration with Germany's Dortmund Institute and the German refrigerator manufacturer DKK Scharfenstein to develop a commercially viable domestic refrigerator based on hydrocarbons, rather than fluorocarbons. By 1993, the hydrocarbon-based "Greenfreeze" refrigerator was commercialized in Germany under the brand name [[Foron]], and the technology subsequently spread to other countries.<ref name="mate">{{cite journal |doi=10.1111/1467-9388.00275 |title=Making a Difference: A Case Study of the Greenpeace Ozone Campaign |year=2001 |last1=Maté |first1=John |journal=Review of European Community & International Environmental Law |volume=10 |issue=2 |pages=190–198 | issn = 0962 8797}}</ref>

By 1996, Greenfreeze accounted for 35% of Western European production; and, by 2001, hydrocarbon refrigeration covered 100% of German production.<ref name="mate"/> Greenfreeze systems use varying mixtures of isobutane ([[R-600a]]), propane ([[Propane#Refrigerant |R-290]]), and other hydrocarbons.<ref name="mate-unep">{{cite report | title = Cool Technologies: Working Without HFCs{{endash}}Interim Report | publisher = United Nations Environment Programme (UNEP) | author1 = Máté, Janos | author2 = Papathanasopoulos, Claudette | author3 = Latif, Sultan | date = July 2012 | url = https://ozone.unep.org/system/files/documents/Greenpeace%20INTERIM%20Cool%20Technologies%20Report%20July%202012.pdf | format = PDF | access-date = 9 September 2025 }}</ref><ref>{{cite report | title = 25 years Greenfreeze: A fridge that changed the world | author1 = Gschrey, Barbara | author2 = Müller, Nicole | author3 = Hartwig, Franziska | editor = Öko-Recherche (Büro für Umweltforschung und -beratung GmbH) | date = July 2018 | publisher = Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH | location = Bonn and Eschborn, Germany | url = https://ozone.unep.org/system/files/documents/GIZ_Side%20Event_Greenfreeze_Brochure.pdf | format = PDF | series = Side-Event Brochure, 40th Meeting of the Open-ended Working Group to the Montreal Protocol | access-date = 9 September 2025 }}</ref>

In 2004, Greenpeace worked with a group of multinational corporations, including [[Coca-Cola]], [[Unilever]], and later [[PepsiCo]], to create a coalition called "Refrigerants Naturally!".<ref name="mate-unep" /> This organization promoted the use of natural refrigerants as alternatives to synthetic refrigerants. Four years later, [[Ben & Jerry's]] of Unilever and [[General Electric]] began to take steps to support production and use in the US.<ref>{{cite web|title=Climate-Friendly Greenfreezers Come to the United States|date=2 October 2008 |url=http://www.nbcnewyork.com/news/green/Climate-Friendly_Greenfreezers_Come_to_the_United_States.html|access-date=8 June 2015|publisher=WNBC}}</ref>

Corporations that manufactured synthetic refrigerants resisted the move toward hydrocarbons, however, citing the flammability and explosive properties of hydrocarbons.<ref name="mate" /><ref>{{cite book | last = Benedick | first = Richard Elliot | title = Ozone Diplomacy: New Directions in Safeguarding the Planet | publisher = Harvard University Press | year = 1998 | edition = Enlarged | isbn = 978-0-674-65003-9 | url = https://www.hup.harvard.edu/books/9780674650039 }}</ref> This resistance extended to attempts to block the approval of hydrocarbon refrigerants by the US EPA.<ref>{{cite web | title = Comment on EPA Proposed Rule (SNAP) – Listing of Substitutes for Ozone-Depleting Substances: Hydrocarbon Refrigerants | author = Honeywell International Inc. | date = 2010-07-09 | website = Regulations.gov | publisher = United States Environmental Protection Agency (EPA) | url = https://downloads.regulations.gov/EPA-HQ-OAR-2009-0286-0170/attachment_1.pdf | format = PDF | type = Public comment on rule-making docket EPA-HQ-OAR-2009-0286 | access-date = 9 September 2025 }}</ref> Companies using refrigeration systems, particularly Unilever and its Ben & Jerry's ice-cream subsidiary, helped to overcome the regulatory barriers to hydrocarbon refrigerants.<ref name="mate-unep" />

By 2010, about 1/3 of domestic refrigerators made globally used isobutane or an isobutane/propane blend.<ref>{{cite journal | title = Protection of Stratospheric Ozone: Listing of Substitutes for Ozone-Depleting Substances—Hydrocarbon Refrigerants | journal = Federal Register | volume = 76 | issue = 244 | pages = 78832 (et seq.) | date = December 20, 2011 | url = https://www.govinfo.gov/content/pkg/FR-2011-12-20/pdf/2011-32175.pdf | author = Environmental Protection Agency | doi = <!-- if available --> | publisher = Office of the Federal Register }}</ref> By 2010, Japan had converted almost all refrigeration from R-134a to isobutane.<ref>{{cite report | title = TEAP 2010 Progress Report, Volume 1: Assessment of HCFCs and Environmentally Sound Alternatives; Scoping Study on Alternatives to HCFC Refrigerants under High Ambient Temperature Conditions | author = Technology and Economic Assessment Panel (TEAP) | date = May 2010 | publisher = United Nations Environment Programme (UNEP), Ozone Secretariat | url = https://ozone.unep.org/sites/default/files/2019-05/teap-2010-progress-report-volume1-May2010.pdf | format = PDF | language = English | page = 37 | access-date = 9 September 2025 }}</ref> By 2022, isobutane was used in more than 70% of new EU domestic refrigerators and, by 2025, in more than 60% of new US domestic refrigerators.<ref name="pwc-isobutane">{{cite web | title = Refrigerant Grade IsoButane Market – PW Consulting Chemical & Energy Research Center | website = PW Consulting Chemical & Energy | publisher = PW Consulting Chemical & Energy Research Center | date = February 9, 2025 | url = https://pmarketresearch.com/chemi/refrigerant-grade-isobutane-market/ | access-date = 31 August 2025 }}</ref>

Carbon dioxide also gained new attention during this time. Despite its high operating pressure, CO₂ was seen as a viable refrigerant in automobiles, as well as stationary systems.<ref name="lorentzen"/> By 2014, Coca-Cola, a member of Refrigerants Naturally!, had installed 1 million HFC-free refrigeration units, with {{CO2}} as its refrigerant of choice.<ref>{{cite web | title = Coca-Cola Installs 1 Millionth HFC-Free Cooler Globally, Preventing 5.25 MM Metric Tons of CO₂ | website = The Coca-Cola Company – Investors News & Events | publisher = The Coca-Cola Company | date = January 22, 2014 | url = https://investors.coca-colacompany.com/news-events/press-releases/detail/635/coca-cola-installs-1-millionth-hfc-free-cooler-globally-preventing-5-25mm-metrics-tons-of-co2 | access-date = August 31, 2025 }}</ref>

===Phase-down of HFCs (climate-change mitigation)===

[[Image:1,1,1,2-Tetrafluoroethane.svg|class=skin-invert-image|thumb|right|upright=.6| A [[1,1,1,2-Tetrafluoroethane]] molecule (HFC-134a or R-134a) has an atmospheric lifetime of 13.5 years<ref name="wmo" />]] [[Hydrofluorocarbon]]s (HFCs) were widely adopted as replacements for CFCs and HCFCs in the 1990s and 2000s.<ref name="mclinden" /><ref name="calm-2008"/> HFCs are not ozone-depleting, but they have [[global warming potential]]s (GWPs) hundreds to thousands of times greater than CO₂ and atmospheric lifetimes that can extend for decades.<ref name="wmo"/> The primary reason for HFCs' high global warming potential is the absorption of [[infrared radiation]] (i.e., radiated heat, or [[thermal radiation]]) by the molecular bonds between carbon and fluorine atoms.<ref>{{cite journal | title = Identifying the Molecular Origin of Global Warming | author = Partha P. Bera; Joseph S. Francisco; Timothy J. Lee | journal = The Journal of Physical Chemistry A | year = 2009 | volume = 113 | issue = 45 | pages = 12694–12699 | doi = 10.1021/jp905097g | pmid = 19694447 | bibcode = 2009JPCA..11312694B }}</ref>

Different HFCs were adopted for different purposes. In domestic refrigerators and automobiles, [[R-134a]] replaced the CFC, [[Dichlorodifluoromethane |R-12]]. In low-pressure [[chillers]], [[2,2-Dichloro-1,1,1-trifluoroethane | R-123]] replaced [[Trichlorofluoromethane|R-11]]. In small air conditioners, the blended refrigerant [[R-410A]] ultimately replaced [[Chlorodifluoromethane|R-22]], following initial consideration of [[R-407C]]. And in low-temperature commercial refrigeration, the blend R-404A replaced R-502.<ref name="domanski-2022" />

[[Image:HCFC and HFC atmospheric trends.png|thumb|right|upright=1.7|The observed stabilization of HCFC concentrations (left graphs) and the growth of HFCs (right graphs) in earth's atmosphere.]]During this era, the atmospheric concentrations of HCFCs began to stabilize, while the concentrations of HFCs rose sharply (see figure).

The situation began to change in 1997, when HFCs and [[fluorocarbon]]s (FCs) were included in the [[Kyoto Protocol]] to the Framework Convention on Climate Change.<ref>{{Cite treaty | title = Kigali Amendment to the Montreal Protocol on Substances that Deplete the Ozone Layer | date = 15 October 2016 | location = Kigali, Rwanda | publisher = United Nations Treaty Collection | url = https://treaties.un.org/doc/Publication/CN/2016/CN.872.2016-Eng.pdf }}</ref><ref>{{Cite web | title = The Kigali Amendment to the Montreal Protocol: Another global commitment to stop climate change | website = United Nations Environment Programme (UNEP) | publisher = UNEP | url = https://www.unep.org/ozonaction/who-we-are/about-montreal-protocol/kigali-amendment | access-date = 9 September 2025 }}</ref> The Kyoto Protocol was an agreement to cap emissions of certain [[greenhouse gases]] at a level 5% below 1990 emissions. These gases included HFCs.

In response, governments introduced new regulations. For example, in 2006, the EU adopted a regulation on [[Fluorinated_gases#EU-level_regulation|fluorinated greenhouse gases]] (FCs and HFCs) to encourage to transition to natural refrigerants.<ref>{{cite journal |title=Regulation (EC) No 842/2006 of the European Parliament and of the Council of 17 May 2006 on certain fluorinated greenhouse gases |journal=Official Journal of the European Union |date=14 June 2006 |series=L |volume=161 |pages=1–11 |url=https://eur-lex.europa.eu/eli/reg/2006/842/oj/eng |access-date=6 September 2025}}</ref>

During the 2010s, new equipment increasingly used lower-GWP HFCs, hydrocarbons, and [[hydrofluoroolefin]]s (HFO) as refrigerants. These refrigerants varied by sector of use, as described in contemporaneous press reports: R-600a (isobutane) for domestic refrigeration;<ref name="auto"/> R-32 and R-454B for stationary air conditioning;<ref name="daikan">{{Cite web|url=https://www.coolingpost.com/world-news/daikin-reveals-details-of-r32-vrv-air-conditioner/|title=Daikin reveals details of R32 VRV air conditioner|date=6 February 2020|website=Cooling Post}}</ref><ref>{{Cite web|url=https://www.achrnews.com/articles/144613-an-hvac-technicians-guide-to-r-454b?v=preview|title=An HVAC Technician's Guide to R-454B|website=achrnews.com}}</ref> R-514A, R-1233zd(E), and R-1234ze(E) for [[chillers]];<ref name="trane">{{Cite web|url=https://www.coolingpost.com/world-news/trane-adopts-new-low-gwp-refrigerant-r514a/|title=Trane adopts new low GWP refrigerant R514A|date=15 June 2016|website=Cooling Post}}</ref><ref name="carrier">{{Cite web|url=https://www.coolingpost.com/world-news/carrier-confirms-an-hfo-refrigerant-future/|title=Carrier confirms an HFO refrigerant future|date=5 June 2019|website=Cooling Post}}</ref><ref>{{Cite web|url=https://www.coolingpost.com/products/carrier-expands-r1234ze-chiller-range/|title=Carrier expands R1234ze chiller range|date=20 May 2020|website=Cooling Post}}</ref> and [[Difluoromethane | R-32]],[[Propane#Refrigerant | R-290]] (propane), R-407A, and R-744 (CO₂) for commercial refrigeration.<ref name="auto">{{Cite web|url=https://www.coolingpost.com/world-news/refrigerant-blends-to-challenge-hydrocarbon-efficiencies/|title=Refrigerant blends to challenge hydrocarbon efficiencies|date=22 December 2019|website=Cooling Post}}</ref><ref>{{Cite web|url=https://www.coolingpost.com/features/r404a-the-alternatives/|title=R404A – the alternatives|date=26 February 2014|website=Cooling Post}}</ref> These choices reflected a range of trade-offs between established approaches, flammability, and reduced GWP. Some of these selections had a lower, but still high, GWP and were seen as transitional.<ref name="domanski-2022"/><ref name="mclinden-2016">{{cite journal | last1 = McLinden | first1 = Mark O. | last2 = Brown | first2 = J. Steven | last3 = Brignoli | first3 = Riccardo | last4 = Kazakov | first4 = Andrei F. | last5 = Domanski | first5 = Piotr A. | title = Limited options for low-global-warming-potential refrigerants | journal = Nature Communications | volume = 8 | article-number = 14476 | year = 2017 | doi = 10.1038/ncomms14476 | url = https://www.nature.com/articles/ncomms14476 | access-date = 10 September 2025 | pmc= 5321723 }}</ref>

[[Image:2,3,3,3-Tetrafluorpropen Structural Formula V3.svg|class=skin-invert-image|thumb|right|upright=.65| The [[2,3,3,3-Tetrafluoropropene]] (HFO-1234yf) molecule has an atmospheric lifetime of 12 days<ref name="wmo" />]] From 2011, the European Union started to phase out refrigerants with a 100-year GWP above 150 in automotive air conditioning. The phase out included the refrigerant [[HFC-134a]] (R-134a), which has a 100-year GWP of 1530.<ref name="ar6"/> In the same year, the US EPA decided in favor of the ozone- and climate-safe refrigerant [[HFO-1234yf]] (R-1234yf) for US-manufactured vehicles.<ref>{{cite web | title = Protection of Stratospheric Ozone: New Substitute in the Motor Vehicle Air Conditioning Sector Under the Significant New Alternatives Policy (SNAP) Program | work = Federal Register | publisher = Environmental Protection Agency | date = March 29, 2011 | page = 17488 | volume = 76 | url = https://www.govinfo.gov/content/pkg/FR-2011-03-29/pdf/2011-6268.pdf | access-date = August 31, 2025 }}</ref> These regulatory decisions aligned with the opinion of the auto industry, which in 2010 had recommended R-1234yf for automotive air conditioning.<ref>{{cite web | last = Reisch | first = Marc S. | title = Automakers Go HFO | website = Chemical & Engineering News | publisher = American Chemical Society | date = 26 July 2010 | url = https://cen.acs.org/articles/88/i30/Automakers-HFO.html | access-date = 31 August 2025 }}</ref>

The lower GWP of R-1234yf relative to R-134a is primarily due to its very short atmospheric lifetime{{em-dash}}12 days vs. 13.5 years.<ref name="wmo" /> Both molecules contain carbon-fluorine bonds that absorb thermal radiation, but the carbon double bond in R-1234yf enables its rapid decomposition to [[trifluoroacetic acid]].<ref>{{Cite journal | last1 = Luecken| first1 = D. J.| last2 = Waterland | first2 = R. L. | last3 = Papasavva| first3 = S. | last4 = Taddonio| first4 = K. N.| last5 = Hutzell | first5 = W. T. | last6 = Rugh | first6 = J. P. | last7 = Andersen| first7 = S. O. | title = Ozone and TFA impacts in North America from degradation of 2,3,3,3-tetrafluoropropene (HFO-1234yf), a potential greenhouse gas replacement | journal = Environmental Science & Technology | volume = 44 | issue = 1 | pages = 343–348 | year = 2010 | publisher = American Chemical Society | doi = 10.1021/es902481f | pmid = 19994849 }}</ref>

The [[Kigali Amendment]] to the Montreal Protocol was adopted in 2016. This international agreement implemented a gradual reduction in the consumption and production of [[HFCs]].<ref>{{Cite treaty | title = Kyoto Protocol to the United Nations Framework Convention on Climate Change | date = 11 December 1997 | location = Kyoto, Japan | publisher = United Nations Treaty Collection | url = https://treaties.un.org/doc/Treaties/1998/03/19980316%2000-38%20AM/Ch_XXVII_07_ap.pdf }}</ref><ref>{{Cite web | title = Kyoto Protocol | website = United Nations Framework Convention on Climate Change (UNFCCC) | publisher = UNFCCC | url = https://unfccc.int/kyoto_protocol | access-date = 9 September 2025 }}</ref> In 2019, the [[UNEP]] published new voluntary guidelines for air conditions and refrigerators.<ref>{{cite web|url=http://www.unenvironment.org/news-and-stories/story/new-guidelines-air-conditioners-and-refrigerators-set-tackle-climate-change|title=New guidelines for air conditioners and refrigerators set to tackle climate change|last=Environment|first=U. N.|date=31 October 2019|website=UN Environment|language=en|access-date=30 March 2020}}</ref> At that time, researchers estimated that CFCs, HCFCs, and HFCs were responsible for about 10% of direct [[radiative forcing]] from all long-lived [[anthropogenic greenhouse gases]].<ref>{{Cite web |url=https://www.esrl.noaa.gov/gmd/aggi/aggi.html |title=The NOAA Annual Greenhouse Gas Index (AGGI) |publisher=[[NOAA]] Global Monitoring Laboratory/Earth System Research Laboratories |author=Butler J. and Montzka S. |year=2020 }}</ref>

The United States ratified the Kigali Amendment on October 31, 2022.<ref>{{cite web |title=Frequent Questions on the Phasedown of Hydrofluorocarbons |url=https://www.epa.gov/climate-hfcs-reduction/frequent-questions-phasedown-hydrofluorocarbons |website=U.S. Environmental Protection Agency |publisher=Environmental Protection Agency |access-date=31 August 2025 |date=21 August 2025 }}</ref> The US Environmental Protection Agency has published phase-out schedules for HFCs,<ref name="epa-final-rule-HFC">{{cite web | title = Final Rule – Phasedown of Hydrofluorocarbons: Establishing the Allowance Allocation and Trading Program under the American Innovation and Manufacturing (AIM) Act | work = U.S. Environmental Protection Agency | publisher = EPA Office of Air and Radiation | date = January 2024 | url = https://www.epa.gov/system/files/documents/2024-01/hfc-allocation-rule-fact-sheet_1.19.2024_508.pdf | access-date = 1 September 2025 }}</ref> with restrictions on GWP by sector of use.<ref name="epa-hfc-transitions-sector">{{cite web | title = Technology Transitions—HFC Restrictions by Sector | work = U.S.Environmental Protection Agency | publisher = EPA | date = December 13, 2024 | url = https://www.epa.gov/climate-hfcs-reduction/technology-transitions-hfc-restrictions-sector | access-date = 1 September 2025 }}</ref>

By the mid-2020s, EU and US regulations on HFCs had resulted in broad adoption of some low GWP refrigerants, including R-600a (isobutane) in domestic refrigeration and [[R-1234yf]] in automotive applications.<ref name="pwc-isobutane"/><ref>{{cite web | title = A3 Natural Hydrocarbon Refrigerant Market – PW Consulting Chemical & Energy Research Center | website = PW Consulting Chemical & Energy | publisher = PW Consulting Chemical & Energy Research Center | date = June 23, 2025 | url = https://pmarketresearch.com/chemi/a3-natural-hydrocarbon-refrigerant-market/ | access-date = 31 August 2025 }}</ref><ref>{{cite web | title = Global Number of Vehicles Using HFO-1234yf Refrigerant | website = Institute for Governance & Sustainable Development | publisher = IGSD | date = February 28, 2023 | url = https://igsd.org/wp-content/uploads/2021/12/Global-Number-of-Vehicles-Using-HFO-1234yf.pdf | access-date = 31 August 2025 }}</ref><ref name="honeywell-1234yf">{{cite web | title = Solstice yf 10-Year Milestone | website = Honeywell Advanced Materials | publisher = Honeywell International | date = c. 2022 | url = https://advancedmaterials.honeywell.com/content/dam/advancedmaterials/en/documents/document-lists/refrigerants/Honeywell-Refrigerants-Solstice-yf-10-year-milestone-brochure.pdf | access-date = 31 August 2025 }}</ref> By 2022, more than 70% of new EU household refrigerators used isobutane (R-600a), and by 2025 more than 60% of new US domestic refrigerators also used isobutane.<ref name="pwc-isobutane" /> In 2022, more than 98% of new US vehicles and 99% of new European vehicles used R-1234yf.<ref name="honeywell-1234yf" /> In other sectors of use, the optimal choice of refrigerant was still evolving in the early 2020s.<ref name="domanski-2022"/>

Developing countries generally follow later phase-down timelines than developed countries under the Kigali Amendment. Among the most populous developing countries, China, Indonesia, Nigeria, and Brazil committed to reduce HFC consumption by 10% in 2029 and by 80% in 2045, while India aims for a 10% cut by 2032 and an 80–85% cut by 2047.<ref>{{cite web |title=Fact Sheet 5: HFC Baselines and Phase-down Timetable |url=https://wedocs.unep.org/bitstream/handle/20.500.11822/26842/7880FS05Blines_EN.pdf?sequence=1 |website=UNEP OzonAction |publisher=United Nations Environment Programme |date=2018 |access-date=7 September 2025 }}</ref><ref>{{cite web |title=The Kigali Amendment to the Montreal Protocol: HFC Phase-down |url=https://www.nepa.gov.jm/ozone/sites/default/files/2022-09/UNEP_Fact_Sheet_Kigali_Amendment_to_MP.pdf |website=NEPA Jamaica – UNEP OzonAction |publisher=United Nations Environment Programme |date=September 2022 |access-date=7 September 2025 }}</ref> Each country may proceed differently, however. For example, China had widely adopted isobutane refrigerators long before the Kigali amendment,<ref>{{cite web |title=Transitioning to Low-GWP Alternatives in Domestic Refrigeration |url=https://www.epa.gov/sites/default/files/2015-07/documents/transitioning_to_low-gwp_alternatives_in_domestic_refrigeration.pdf |website=U.S. Environmental Protection Agency |publisher=EPA |date=July 2015 |access-date=7 September 2025 }}</ref> and it has banned HFCs from new refrigerators starting in 2026.<ref>{{cite web |last=Institute for Governance & Sustainable Development |title=China Issues National Plan to Strengthen the Management of Ozone-Depleting Substances and Climate-Polluting Hydrofluorocarbons |url=https://www.igsd.org/china-issues-national-plan-to-strengthen-the-management-of-ozone-depleting-substances-and-climate-polluting-hydrofluorocarbons/ |website=IGSD |date=9 April 2025 |access-date=7 September 2025 }}</ref>

==Refrigerant safety, environmental management, and reclamation== {{See also|List of refrigerants#Type and flammability|Refrigerant reclamation}}

Refrigerants can pose both direct and indirect risks. Depending on their chemistry, they may be flammable, toxic, or environmentally damaging through ozone depletion or [[greenhouse gas | greenhouse effects]]. To standardize the safety hazards of refrigerants, [[ASHRAE]] Standard 34 assigns each one a letter–number code: letters "A" (lower toxicity) or "B" (higher toxicity), and numbers 1 through 3 to indicate flammability.<ref name="ashrae-34"> {{cite book |title=Designation and Safety Classification of Refrigerants. Addendum f to ANSI/ASHRAE Standard 34-2019 |date=2019 |publisher=ASHRAE |url=https://www.ashrae.org/technical-resources/standards-and-guidelines/ashrae-refrigerant-designations |access-date=29 August 2025}}</ref><ref>{{cite web |last1=United Nations Environment Programme (UNEP) |title=Update on New Refrigerants Designations and Safety Classifications |url=https://www.ashrae.org/file%20library/technical%20resources/bookstore/factsheet_ashrae_english_november2022.pdf |access-date=6 October 2024 |publisher=ASHRAE}}</ref> A1 refrigerants are non-toxic and non-flammable, while A2L/A2 are non-toxic but flammable, and A3 refrigerants are non-toxic and highly flammable. B-class refrigerants have higher toxicity.

{| class="wikitable" style="float:right; width:50%; text-align:center; margin:1em" |+ ASHRAE Safety Group Classifications<ref name="ashrae-34" /> ! ! Lower toxicity ! Higher toxicity |- | Highly flammable | '''A3''' | '''B3''' |- | Flammable | '''A2''' | '''B2''' |- | Lower flammability | '''A2L''' | '''B2L''' |- | No flame propagation | '''A1''' | '''B1''' |}

Non-toxic refrigerants (A class) are often used in open systems, where the refrigerant is expended rather than recovered. Such devices include [[Fire_extinguisher#Wet_chemical_types|fire extinguishers and fire suppressants using HCFCs or HFCs]],<ref>{{cite web | title = Handheld Fire Extinguishers | work = FAA Fire Safety | publisher = Federal Aviation Administration | url = https://www.fire.tc.faa.gov/Systems/handheld.asp | access-date = 11 September 2025 }}</ref><ref>{{cite web | title = Substitutes in Total Flooding Agents | work = Significant New Alternatives Policy (SNAP) | publisher = United States Environmental Protection Agency | url = https://www.epa.gov/snap/substitutes-total-flooding-agents | access-date = 11 September 2025 }}</ref> [[gas duster | gas dusters]] with HFC-152a or hydrocarbon propellants, metered-dose [[Inhaler|inhalers]] using HFC propellants,<ref>{{cite report | author = United States Environmental Protection Agency | title = Market Characterization of the U.S. Metered Dose Inhaler Industry (Attachment 1 to EPA-HQ-OAR-2021-0044-0002) | publisher = United States Environmental Protection Agency | date = March 2021 | number = EPA-HQ-OAR-2021-0044-0002 Attachment 1 | url = https://www.epa.gov/sites/default/files/2021-03/documents/epa-hq-oar-2021-0044-0002_attachment_1-mdis.pdf | type = Technical Report | access-date = 11 September 2025 }}</ref> and [[ lighters | disposable lighters]] containing the A3 refrigerant isobutane (R-600a).<ref>{{cite web | title = 16 CFR Part 1210 — Safety Standard for Cigarette Lighters | work = Electronic Code of Federal Regulations (eCFR) | publisher = U.S. Government Publishing Office / Office of the Federal Register | agency = Consumer Product Safety Commission | url = https://www.ecfr.gov/current/title-16/chapter-II/subchapter-B/part-1210 | access-date = 11 September 2025 }}</ref>

To mitigate the environmental hazards, strict regulations apply to refrigerant handling. In the United States, [[Section 608]] of the [[Clean Air Act (United States)|Clean Air Act]] requires certification for anyone servicing or disposing of stationary equipment, while Section 609 applies to technicians working on motor vehicle air conditioning.<ref>{{cite web |title=Section 608 Technician Certification |url=https://www.epa.gov/section608/section-608-technician-certification-0 |website=www.epa.gov |date=11 March 2025 |publisher=US Environmental Protection Agency |access-date=30 August 2025}}</ref><ref>{{cite web |title=Section 609 Technician Training and Certification Programs |url=https://www.epa.gov/mvac/section-609-technician-training-and-certification-programs |website=www.epa.gov |date=16 June 2025 |publisher=US Environmental Protection Agency |access-date=30 August 2025}}</ref> Similarly, the UK requires qualification C&G 2079 for fluorinated and ozone-depleting gases and recognizes C&G 6187-2 for handling hydrocarbons and flammable refrigerants.<ref>{{cite web |title=F GAS and ODS Regulations (2079) |url=https://www.cityandguilds.com/qualifications-and-apprenticeships/building-services-industry/refrigeration-and-airconditioning/2079-f-gas-and-ods-regulations#tab=information |website=City & Guilds |access-date=29 August 2025}}</ref> US law also prohibits knowingly venting most synthetic refrigerants, although it permits discharge of certain natural refrigerants, including ammonia (R-717), carbon dioxide (R-744), isobutane (R-600a), propane (R-290), and the hydrocarbon blend HCR-188C (R-441A).<ref>{{cite web | title = 40 CFR Part 82, Subpart F – Recycling and Emissions Reduction | website = Electronic Code of Federal Regulations (e-CFR) | publisher = Office of the Federal Register, via U.S. Government Publishing Office | url = https://www.ecfr.gov/current/title-40/chapter-I/subchapter-C/part-82/subpart-F | access-date = 31 August 2025 }}</ref>

To minimize emissions, used refrigerants must be recovered during service or decommissioning. Refrigerant reclamation{{emdash}}processing used refrigerant so that it meets purity specifications of new gas{{emdash}}must be carried out in the US by EPA-licensed reclaimers, with recovery handled by certified technicians.<ref>{{cite web | title = 42 U.S.C. § 7671g – National recycling and emission reduction program | website = Legal Information Institute (LII), Cornell Law School | url = https://www.law.cornell.edu/uscode/text/42/7671g | access-date = 31 August 2025 }}</ref>

==Comparative performance of refrigerants== [[ASHRAE]]<ref name="ashrae-fund-29"/> provides the following model data for the comparative performance of refrigerants. These values are computed per kilowatt of refrigeration with an evaporator temperature of −6.7&nbsp;°C and a condenser temperature of 30.0&nbsp;°C. These temperatures might approximate a domestic refrigerator.

{| class="wikitable sortable" ! colspan="7" | Values per kilowatt of refrigeration.<ref name="ashrae-fund-29"/> Evaporator {{convert|-6.7|C}} /condenser {{convert|30.0|C}} |- ! Refrigerant code ! Name ! Evaporator pressure (kPa) ! Condenser pressure (kPa) ! Refrigerant circulation {{Nowrap|(g/s)}} ! Compressor displacement {{Nowrap|(L/s)}} ! Power consumption (kW) |- | [[Difluoromethane |R-32]] || [[Difluoromethane]] || 653 || 1928 || 3.87 || 0.218 || 0.169 |- | [[1,1,1,2-Tetrafluoroethane|R-134a]] || [[1,1,1,2-Tetrafluoroethane]] || 228 || 770 || 6.45 || 0.575 || 0.165 |- | [[Propane#Refrigerant | R-290]] || [[Propane#Refrigerant | Propane]] || 385 || 1079 || 3.47 || 0.409 || 0.167 |- | [[Isobutane#Refrigerant | R-600a]] || [[Isobutane#Refrigerant | Isobutane]] || 123 || 405 || 3.60 || 1.072 || 0.162 |- | [[R-410A]] || Mixture: [[Difluoromethane|R-32]] (50%) / [[R-125]] (50%) || 643 ||1886 || 5.85 || 0.238 || 0.173 |- | [[Ammonia#Refrigeration–R717 | R-717]] || [[Ammonia#Refrigeration–R717 |Ammonia]] || 332 || 1167 || 0.90 || 0.331 || 0.160 |- | [[Carbon_dioxide#Refrigerant | R-744]] || [[Carbon_dioxide#Refrigerant | Carbon dioxide]] || 2909 || 7213 || 7.72 || 0.098 || 0.285 |- | [[2,3,3,3-Tetrafluoropropene | R-1234yf]] || [[2,3,3,3-Tetrafluoropropene]] || 250 || 783 || 8.30 || 0.595 || 0.172 |} For the specific situation modeled in this table, some trade-offs in refrigerant selection are evident. CO₂ (Class A1) has the highest operating pressure by far, and also a much higher power consumption. Ammonia has the least power consumption; but in view of its toxicity and incompatibility with hermetically sealed compressors, ammonia is unsuited to household use.<ref name="r7"/>

Isobutane (Class A3) has the lowest pressure and also the second-lowest power consumption. R-32 (Class A1, but also an HFC) has the second-highest pressure, and a power consumption similar to isobutane. The refrigerants with lowest pressure generally have larger compressor displacements (i.e., they require a larger cylinder size in a [[reciprocating compressor]]).

Two common performance metrics for refrigeration systems can be computed from these data if desired. The [[coefficient of performance]] (COP){{emdash}}the refrigeration effect per unit power input{{emdash}}is equal to 1{{nbsp}}kW/(power consumption), since the power is given per 1{{nbsp}}kW of refrigeration. The volumetric capacity, Q_vol (MJ/m³){{emdash}}the cooling effect per unit volume entering the compressor{{emdash}}is similarly equal to 1{{nbsp}}kW/(compressor displacement). Higher COP means greater energy efficiency and higher Q_vol means a smaller system size.<ref name="mclinden-2016"/>

ASHRAE also provides additional data for this case, and data for other operating conditions and additional refrigerants.<ref name="ashrae-fund-29"/> The values and comparisons here are specific to this temperature range; the performance of a refrigerant may improve or degrade in other temperature ranges.<ref name="calm-2008"/>

==Characteristics of some common refrigerants== {{See also|List of refrigerants}} All refrigerants in these tables are [[#Refrigerant_safety|safety class]] A1 (non-toxic, non-flammable), unless otherwise indicated. GWP = [[Global warming potential]].

===Refrigerants with very low climate impact=== {| class="wikitable sortable" |- ! Code !! Chemical !! Name !! [[Global warming potential | GWP]] 20yr !! [[Global warming potential | GWP]] 100yr !! Status !! Notes |- |[[R-290 (refrigerant)|R-290]] |C₃H₈ | [[Propane#Refrigerant | Propane]] | 0.072<ref name="ar6">{{cite book | last1 = Smith | first1 = C. | last2 = Nicholls | first2 = Z.R.J. | last3 = Armour | first3 = K. | last4 = Collins | first4 = W. | last5 = Forster | first5 = P. | last6 = Meinshausen | first6 = M. | last7 = Palmer | first7 = M.D. | last8 = Watanabe | first8 = M. | chapter = The Earth's Energy Budget, Climate Feedbacks, and Climate Sensitivity Supplementary Material | editor1-last= Masson-Delmotte | editor1-first= V. | editor2-last= Zhai | editor2-first= P. | editor3-last= Pirani | editor3-first= A. | editor4-last= Connors | editor4-first= S.L. | editor5-last= Péan | editor5-first= C. | editor6-last= Berger | editor6-first= S. | editor7-last= Caud | editor7-first= N. | editor8-last= Chen | editor8-first= Y. | editor9-last= Goldfarb | editor9-first= L. | editor10-last= Gomis | editor10-first= M.I. | editor11-last= Huang | editor11-first= M. | editor12-last= Leitzell | editor12-first= K. | editor13-last= Lonnoy | editor13-first= E. | editor14-last= Matthews | editor14-first= J.B.R. | editor15-last= Maycock | editor15-first= T.K. | editor16-last= Waterfield | editor16-first= T. | editor17-last= Yelekçi | editor17-first= O. | editor18-last= Yu | editor18-first= R. | editor19-last= Zhou | editor19-first= B. | title = Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change | year = 2021 | publisher = Cambridge University Press | url = https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter07_SM.pdf | access-date = 30 August 2025 }}</ref> | 0.02<ref name="ar6" /> |Increasing use |Class A3 (highly flammable). Low cost, high efficiency. Generally limited to refrigerant charges of 300 to 500 g. Used in commercial refrigeration.<ref name="domanski-2022"/><ref>{{cite web | title = Long-awaited R-290 charge increase opens new refrigeration opportunities | author = Denise Hoying | date = September 12, 2022 | website = E360 Resources Hub (Copeland) | url = https://e360hub.copeland.com/r-290/long-awaited-r-290-charge-increase-opens-new-refrigeration-opportunities | access-date = September 14, 2025 }}</ref><ref>{{cite web | title = R-290 Second Nature Refrigeration Systems | website = Hillphoenix | publisher = Dover Food Retail | url = https://www.hillphoenix.com/second-nature-r290/ | access-date = September 14, 2025 }}</ref> |- |[[R-600a]] ||HC(CH₃)₃ || [[Isobutane#Refrigerant |Isobutane]] || <<1<ref name="wmo">{{cite book |last1=Burkholder |first1=James B. |last2=Hodnebrog |first2=Oivind |editor1-last=World Meteorological Organization |title=Scientific Assessment of Ozone Depletion: 2022 |date=2023 |publisher=WMO |location=Geneva |isbn=978-9914-733-97-6 |url=https://library.wmo.int/idurl/4/58360 |access-date=30 August 2025 |chapter=Annex: Summary of abundances, Lifetimes, ODPs, REs, GWPs, and GTPs | pages=435–487}}</ref> || <<1<ref name="wmo" /> ||Widely used || Class A3 (highly flammable). Low cost, high efficiency. Isobutane is used in >70% of new EU domestic refrigerators (by 2022) and >60% of new US domestic refrigerators (by 2025).<ref name="pwc-isobutane" /> Mainly used for small refrigerant charges (<150 g)<ref name="domanski-2022"/> |- |[[R-717]] ||NH₃ || [[Ammonia#Refrigeration–R717 |Ammonia]] || <1<ref name="wmo"/> ||<<1<ref name="wmo"/> ||Widely used || Class B2L (toxic, mildly flammable). Anhydrous ammonia is widely used in industrial refrigeration, large buildings, and hockey rinks. High energy efficiency and low cost. Less used domestically or at small-scale due to safety requirements.<ref name="domanski-2022" /> |- |[[R-744]]||{{CO2}}|| [[Carbon_dioxide#Refrigerant | Carbon dioxide]] ||1<ref name="ar6" /> ||1<ref name="ar6"/> ||In use || [[transcritical cycle | Transcritical refrigeration cycle]] leads to pressures of up to {{convert|130|bar|psi}} that require high strength components. Extensive use in commercial refrigeration. Potential use in electric vehicle AC.<ref name="domanski-2022"/> |- |[[R-1234yf]] HFO-1234yf ||C₃H₂F₄ ||[[2,3,3,3-Tetrafluoropropene]]|| 1.81<ref name="ar6"/> || 0.501<ref name="ar6"/> || Widely used ||Class A2L (nontoxic, mildly flammable). Lower performance but lower flammability than R-290.<ref name="Yadav">{{cite journal |last1=Yadav |first1=Saurabh |last2=Liu |first2=Jie |last3=Kim |first3=Sung Chul |title=A comprehensive study on 21st-century refrigerants - R290 and R1234yf: A review |journal=International Journal of Heat and Mass Transfer |date=January 2022 |volume=182 |article-number=121947 |doi=10.1016/j.ijheatmasstransfer.2021.121947 |bibcode=2022IJHMT.18221947Y }}</ref> Used in most new US and EU vehicles by 2021, replacing R-134a.<ref name="honeywell-1234yf"/> |- | [[ 1-Chloro-3,3,3-trifluoropropene | R-1233zd(E)]] HFO-1233zd(E) | HClC=C(H)CF₃ | [[1-Chloro-3,3,3-trifluoropropene]] | 14<ref name="ar6"/> | 3.88<ref name="ar6"/> | In use | Replacement for R-123, R-134a, and R-514A in chillers.<ref name="domanski-2022"/><ref name="trane"/><ref name="carrier"/> |}

===Widely used, HFC refrigerants=== {| class="wikitable sortable" |- ! Code !! Chemical !! Name !! [[Global warming potential | GWP]] 20yr !! [[Global warming potential |GWP]] 100yr !! Status !! Notes |- | [[Difluoromethane |R-32]] HFC-32 ||CH₂F₂ ||[[Difluoromethane]] ||2690<ref name="ar6" /> ||771<ref name="ar6" /> ||Growing use, will eventually phase-down under US AIM Act<ref name="epa-final-rule-HFC" /> ||A2L (nontoxic, mildly flammable). GWP-100 is 50% of R-134a and 37% of R-410A. [[Greenhouse gas#Atmospheric lifetime|Atmospheric lifetime]] of 5.27 years.<ref name = "wmo" /> Used in residential and commercial air-conditioners and heat pumps.<ref name="daikan"/><ref>{{Cite web |title=Johnson Controls-Hitachi Launches New R-32 Ductless Residential Heat Pumps in North America |url=https://hvacpproducts.com/2025/06/johnson-controls-hitachi-launches-new-r-32-ductless-residential-heat-pumps-in-north-america/ |website=HVAC Products |publisher=Johnson Controls-Hitachi |date=June 2025 |access-date=2025-09-12 }}</ref> |- |[[R-454B]] | |Mixture: [[Difluoromethane | R-32]] (68.9%), [[R-1234yf]] (31.3%) |1806<ref name="unep23" /> |516<ref name="unep23" /> | Growing use, but also affected by US AIM Act<ref name="epa-final-rule-HFC" /> |A2L (nontoxic, mildly flammable). [[R-454B]] is intended to replace R-410A in new equipment<ref>{{cite web |title=US manufacturers line up behind R454B |url=https://www.coolingpost.com/world-news/us-manufacturers-line-up-behind-r454b/ |website=Cooling Post |date=10 May 2024 |access-date=7 September 2025 }}</ref> |- |R-513A || ||Mixture: [[R-1234yf]] (56%), [[R-134a]] (44%) |1788<ref name="unep23" /> |647<ref name="unep23" /> | Affected by restrictions of US AIM Act<ref name="epa-final-rule-HFC" /> ||Intended as drop-in replacement for pure R-134a in existing equipment.<ref>{{cite journal | last1 = Allgood| first1 = Chris | last2 = Johnston| first2 = Paul | last3 = Kim| first3 = Samuel | last4 = Kujak| first4 = Stephen | last5 = Motta| first5 = Sergio Y. | title = A Conversation on Refrigerants | journal = ASHRAE Journal | volume = 63 | issue = 3 | year = 2021 | pages = 30–37 }}</ref> |}

=== Banned or phasing-out CFCs, HCFCs, and HFCs === {| class="wikitable sortable" |- ! Code !! Chemical !! Name !! [[Global warming potential | GWP]] 20yr!! [[Global warming potential | GWP]] 100yr !! Status !! Notes |- |[[Trichlorofluoromethane |R-11]] CFC-11 ||CCl₃F ||[[Trichlorofluoromethane]] ||8320<ref name="ar6"/>||6230<ref name="ar6"/> ||Banned ||Widely used in water chillers with centrifugal compressors during the 20th century.<ref name="domanski-2022"/> Production was banned in developed countries by Montreal Protocol in 1996 and in developing (Article 5) countries in 2010.<ref name="AnnexA"/> |- | [[Dichlorodifluoromethane |R-12]] CFC-12 ||CCl₂F₂ ||[[Dichlorodifluoromethane]] ||12700<ref name="ar6"/> ||12500<ref name="ar6"/> ||Banned ||Widely used in domestic refrigerators and automobile air conditioners during the 20th century.<ref name="domanski-2022"/> Production was banned in developed countries by Montreal Protocol in 1996 and in developing (Article 5) countries in 2010.<ref name="AnnexA"/> |- |[[Chlorodifluoromethane|R-22]] HCFC-22 ||CHClF₂ ||[[Chlorodifluoromethane]] ||5690<ref name="ar6"/> ||1960<ref name="ar6"/> ||Banned in US, unless reclaimed || Widely used in small air conditioners and commercial refrigeration during the 20th century.<ref name="domanski-2022"/> US production and import was banned in 2010, and only reclaimed R-22 has been permitted since 2020.<ref name="Phaseout" /> |- |[[2,2-Dichloro-1,1,1-trifluoroethane|R-123]] HCFC-123 |CHCl₂CF₃ |[[2,2-Dichloro-1,1,1-trifluoroethane]] |325<ref name="ar6"/> |90.4<ref name="ar6"/> |US phase-out |Safety class B1 (toxic, nonflammable). Used in large tonnage centrifugal chillers, as transitional successor to R-11.<ref <ref name="domanski-2022"/> Only permitted in systems manufactured before 2020. US production and import will be phased out by 2030.<ref>{{cite report | title = Management of HCFC-123 through the Phaseout and Beyond | publisher = United States Environmental Protection Agency | date = August 2020 | url = https://www.epa.gov/sites/default/files/2020-08/documents/us_management_of_hcfc-123.pdf | number = EPA 430-R-20-006 | access-date = 18 December 2021 }}</ref> |- |[[R-134a]] HFC-134a |CH₂FCF₃ |[[1,1,1,2-Tetrafluoroethane]] |4140<ref name="ar6" /> |1530<ref name="ar6" /> |Wide legacy use, but being phased out | Replaced R-12 in refrigerators and automobiles, and replace R-11 in water chillers.<ref name="domanski-2022"/> Most common refrigerant in US autos from 1990s until phase-out began in 2010s. Largely banned in new stationary equipment in US as of 2025. Banned in new light vehicles as of 2025 and in all new vehicles after 2028.<ref name="epa-hfc-transitions-sector" /><ref>{{cite web | title = Acceptable Refrigerants and their Impacts | website = U.S. Environmental Protection Agency | date = 16 June 2025 | url = https://www.epa.gov/mvac/acceptable-refrigerants-and-their-impacts | access-date = 31 August 2025 }}</ref> |- | R-404A || || Mixture: R-125 (44%) / R-143a (52%) / R-134a (4%) || 7258<ref name="unep23" /> || 4808<ref name="unep23" /> || Being phased out || High GWP successor to R-502 in low-temperature commercial refrigeration.<ref name="domanski-2022" /> Restrictions are increasing over time<ref name="epa-hfc-transitions-sector" /><ref name="usepa-hfc-reduction"/> |- |[[R-407C]] | |Mixture: [[Difluoromethane | R-32]] (23%), [[R-125]] (25%), [[R-134a]] (52%) | 4411<ref name="unep23" /> | 1892<ref name="unep23" /> | Being phased down under US AIM Act |Replacement for R-22. Being phased out in the US starting in 2022.<ref name="usepa-hfc-reduction">{{cite web |title=Protecting Our Climate by Reducing Use of HFCs |url=https://www.epa.gov/climate-hfcs-reduction |website=US Environmental Protection Agency |date=8 February 2021 |access-date=25 August 2022}}</ref><ref name="epa-hfc-aim">{{cite web |title=Background on HFCs and the AIM Act |url=https://www.epa.gov/climate-hfcs-reduction/background-hfcs-and-aim-act |website=www.usepa.gov |date=March 2021 |publisher=US EPA |access-date=27 June 2024}}</ref> |- |[[R-410A]]|| || Mixture: [[Difluoromethane | R-32]] (50%), [[R-125]] (50%) || 4705<ref name="unep23">{{cite web | title = Montreal Protocol on substances that deplete the ozone layer. 2022 Report of the Refrigeration, Air Conditioning and Heat Pumps Technical Options Committee (RTOC). 2022 Assessment | publisher = United Nations Environment Programme (UNEP) | year = 2023 | url = https://iifiir.org/en/fridoc/montreal-protocol-on-substances-that-deplete-the-ozone-layer-2022-146932 | access-date = 2025-08-31 }}</ref> ||2285<ref name="unep23" /> ||Still widely used, but being phased out ||R-410A replaced R-22 and R-407C in most domestic AC systems.<ref name="domanski-2022"/><ref>{{cite web | title = Purchasing and Repairing Home Air-Conditioners or Heat Pumps | website = United States Environmental Protection Agency | date = June 25, 2025 | url = https://www.epa.gov/ods-phaseout/purchasing-and-repairing-home-air-conditioners-or-heat-pumps | access-date = August 31, 2025 }}</ref> Most used in split heat pumps / AC in 2018, with almost 100% share in the US,<ref name="bsria">{{cite web | title = BSRIA's view on refrigerant trends in AC and Heat Pump segments | website = BSRIA | date = 2020 | url = https://www.bsria.com/us/news/article/bsrias_view_on_refrigerant_trends_in_ac_and_heat_pump_segments/ | access-date = 2022-02-14 }}</ref> but banned in new equipment starting January 1, 2025.<ref name="epa-hfc-transitions-sector" /> |- | R-502 || || Mixture: R-22 (48.8%) / R-115 (51.2%) || 6542<ref name="unep23"/> || 5863<ref name="unep23"/> || Banned || CFC/HCFC blend. Widely used in low-temperature commercial refrigeration during the 20th century.<ref name="domanski-2022"/> Production was banned in developed countries by Montreal Protocol in 1996 and in developing (Article 5) countries in 2010.<ref name="AnnexA"/> |}

===Other refrigerants=== {| class="wikitable sortable" |- ! Code !! Chemical !! Name !! [[Global warming potential | GWP]] 20yr !! [[Global warming potential | GWP]] 100yr !! Notes |- |R-152a HFC-152a |CH₃CHF₂ |[[1,1-Difluoroethane]] |591<ref name="ar6"/> |164<ref name="ar6"/> |Class A2 (flammable). Used as [[gas duster]]; concerns about inhalant abuse.<ref>{{cite web |title=Banned Hazardous Substances: Aerosol Duster Products Containing More Than 18 mg in Any Combination of HFC-152a and/or HFC-134a |url=https://www.federalregister.gov/documents/2024/07/31/2024-16716/banned-hazardous-substances-aerosol-duster-products-containing-more-than-18-mg-in-any-combination-of |website=Federal Register |publisher=U.S. Government Publishing Office |agency=Consumer Product Safety Commission |date=2024-07-31 |access-date=2025-09-01 |format=HTML }}</ref> |- |R-514A | |Mixture: HFO-1336mzz(Z) (74.7%), HCO-1330E (25.3%) |7<ref name="unep23" /> |7<ref name="unep23" /> |Safety class B1 (toxic, nonflammable), low GWP. Replacement for R-123 in low-pressure centrifugal chillers for commercial and industrial applications.<ref>{{cite web | title = Opteon™ XP30 (R-514A) Refrigerant | publisher = Chemours | url = https://www.opteon.com/en/products/refrigerants/xp30 | access-date = 11 September 2025 }}</ref><ref>{{cite web | last = Everitt | first = Neil | title = Trane adopts new low GWP refrigerant R514A | work = Cooling Post | date = 15 June 2016 | url = https://www.coolingpost.com/world-news/trane-adopts-new-low-gwp-refrigerant-r514a/ | access-date = 11 September 2025 }}</ref> Being displaced by non-toxic [[1-Chloro-3,3,3-trifluoropropene |HFO-1233zd(E)]].<ref>{{cite web |title=HVAC Industry Refrigerant Update |url=https://www.trane.com/content/dam/Trane/Commercial/global/about-us/decarbonization/REFR-PRB001-EN.pdf |website=Trane |publisher=Trane Technologies |date=2024-03-12 |access-date=2025-09-01 }}</ref> |}

== Numbered classification of refrigerants == {{see also|List of refrigerants}}

The R- numbering system, maintained by [[ASHRAE]] and [[ISO]], uniquely identifies refrigerants according to their composition.<ref>{{cite web |author1=ASHRAE |author2=UNEP |title=Designation and Safety Classification of Refrigerants |url=https://www.ashrae.org/file%20library/technical%20resources/standards%20and%20guidelines/standards%20addenda/34_2004_add-g.pdf |website=ASHRAE |access-date=1 July 2023 |date=Nov 2022}}</ref><ref name="iso817">{{cite book | title = ISO 817:2024 Refrigerants — Designation and safety classification | edition = 4th | publisher = International Organization for Standardization | location = Geneva | date = November 2024 | type = ISO standard | url = https://www.iso.org/standard/83452.html }}</ref> The system originated for numbering halogenated hydrocarbons, but it encompasses blended refrigerants and inorganic refrigerants as well. [[File:Refrigerants-CoolCraft.jpg|thumb|upright=2|Disposable refrigerant gas cylinders, using different colors for different refrigerants. (Current guidelines discourage color-coded cylinders.<ref>{{cite web | title = AHRI Guideline N-2017: Assignment of Refrigerant Container Colors | author = Air-Conditioning, Heating, and Refrigeration Institute | year = 2017 | url = https://www.ahrinet.org/system/files/2023-06/AHRI_Guideline_N_2017.pdf | publisher = AHRI | format = PDF | access-date = September 7, 2025 }}</ref>)]]

===Main numbering system===

According to ISO:<ref name="iso817"/> {{quote | The identifying numbers assigned to the hydrocarbons, halocarbons and ethers of the methane, ethane, ethene, propane, propene, butane, butene, cyclobutene and cyclobutane series are such that the chemical composition of the compounds can be explicitly determined from the refrigerant numbers...}}

For these refrigerants, the R- number has the following form: '''R-[prefix]X₁X₂X₃X₄[suffix]''', where *'''X₁''' = number of unsaturated carbon-carbon bonds (omit if zero), *'''X₂''' = number of carbon atoms minus 1 (omit if zero), *'''X₃''' = number of hydrogen atoms plus 1, *'''X₄''' = number of fluorine atoms, * and any additional atoms attached to the carbon atoms are presumed to be chlorine.

These rules generate the following series of refrigerants (with xx as shorthand for X₃X₄): '''R-xx,''' the [[methane]] series; '''R-1xx,''' the [[ethane]] series; '''R-2xx,''' the [[propane]] series; '''R-11xx,''' the [[ethene]] series; and '''R-12xx,''' the [[propene]] series.

For example, [[difluoromethane | R-32]], a two digit number, has X₁ = X₂ = 0, implying a single carbon atom (the methane series) with two hydrogen atoms (X₃-1) and two fluorine atoms (X₄ = 2), thus CH₂F₂ ([[difluoromethane]]). Similarly, R-290 has X₁ = 0 (no unsaturated carbon-carbon bonds), three carbon atoms (X₂+1), eight hydrogen atoms (X₃-1), and no fluorine atoms (X₄ = 0), so C₃H₈ ([[propane#refrigerant|propane]]).

The prefix, when present, is an upper-case letter "C" for [[cyclic compound]]s, "E" for compounds containing an [[ether]] group, or "CE" for cyclic compounds with ether groups.

The suffix follows more complicated rules. Upper-letters suffixes are added for the following characteristics: "B" and "I", together with a number, indicate how many chlorine atoms have been replaced with bromine or iodine; "(E)" denotes a ''trans'' molecule; and "(Z)" denotes a ''cis'' molecule. The rules for lower-case suffixes depend upon the series of the molecule.

{| class="wikitable" style="width:100%" ! colspan="3" | Rules for lower-case suffixes<ref name="iso817" /> |- | '''Ethane derived chains''' <br/> • Number only: most symmetrical isomer <br/> • Lower-case suffix (a, b, c, etc.): increasingly unsymmetrical isomers | '''Propane derived chains''' <br/> • Number only: only one isomer exists <br/> • First lower case suffix (a–f): <br/> : a – Cl₂ substitution on central carbon : b – Cl,F substitution on central carbon : c – F₂ substitution on central carbon : d – Cl,H substitution on central carbon : e – F,H substitution on central carbon : f – H₂ substitution on central carbon • Second lower case suffix (a, b, c, etc.): increasingly unsymmetrical isomers |'''Propene derived chains''' • First lower case suffix (x, y, z): : x – Cl substitution on central atom : y – F substitution on central atom : z – H substitution on central atom • Second lower case suffix (a–f): : a – CCl₂ methylene substitution : b – CClF methylene substitution : c – CF₂ methylene substitution : d – CHCl methylene substitution : e – CHF methylene substitution : f – CH₂ methylene substitution |}

As an example of the propene series, [[R-1234yf]] has one carbon-carbon double bond (X₁ = 1) with three carbon atoms (X₂+1=3, thus a [[propene]] structure), two hydrogen atoms (X₃-1=2), and four fluorine atoms (X₄ = 4), with fluorine on central bond (y) and a [[methylene group]] (f), which consists of a carbon atom double-bonded to another carbon and two of the hydrogen atoms. These details define [[2,3,3,3-tetrafluoropropene]], with the comma-separated numbers indicating which carbon atom attaches each fluorine atom.

===Series outside the main system=== The R- number is assigned under different rules for blended refrigerants, some hydrocarbons, and inorganic refrigerants.<ref name="iso817"/>

* '''R-4xx:''' [[Zeotropic mixture|zeotropic blend]]. The number xx is assigned. An upper-case suffix (A, B, etc.) distinguishes different compositions of the same blend. * '''R-5xx:''' [[Azeotrope|azeotropic blend]]. The number xx is assigned. An upper-case suffix (A, B, etc.) distinguishes different compositions of the same blend. * '''R-6xx:''' miscellaneous hydrocarbons. For saturated hydrocarbons with 4 to 8 carbon atoms, xx is the number of carbon atoms minus 4 (so that [[butane]] is R-600). For others, xx is assigned. A trailing letter indicates increasingly unsymmetrical isomers. * '''R-7xx/R-7xxx:''' inorganic compounds. For a [[molar mass]] < 100, xx is the molar mass rounded to the nearest integer. For a molar mass ≥ 100, xxx is the molar mass rounded to the nearest integer. A trailing letter distinguishes compounds of equal molar mass.

===Composition-designating prefixes===

{{See also|List of refrigerants#Type and flammability}}

The standard allows the prefix R- to be replaced by a prefix describing the molecular components of the refrigerant. Examples include: CFC- for [[chlorofluorocarbon]]s; HCFC- for [[hydrochlorofluorocarbon]]s; HFC- for [[hydrofluorocarbon]]s; and HFO- for [[hydrofluoroolefins]].<ref name="iso817"/><ref>{{cite web |title=ASHRAE Terminology |url=https://terminology.ashrae.org/ |publisher=ASHRAE |access-date=30 August 2025}}</ref> For example, the [[hydrofluoroolefin]] (HFO) R-1234yf is also called HFO-1234yf.

==See also== * [[Heating, ventilation, and air conditioning]] * [[International Institute of Refrigeration]] * [[Low-temperature technology timeline]] * [[Working fluid selection]] ==References== {{Reflist|30em}} {{reflist|group=EPA}}

==External links== * [https://www.ashrae.org/ ASHRAE ]{{snd}}American Society of Heating, Refrigerating and Air-Conditioning Engineers * [http://www.green-cooling-initiative.org/ Green Cooling Initiative] * [https://www.linkedin.com/pulse/what-refrigerants-types-uses-environmental-impact-vrf-system-6ze4f/ What Are Refrigerants? Types, Uses & Their Environmental Impact] * [https://iifiir.org/en International Institute of Refrigeration] * {{cite book | editor1-last= Masson-Delmotte | editor1-first= V. | editor2-last= Zhai | editor2-first= P. | editor3-last= Pirani | editor3-first= A. | editor4-last= Connors | editor4-first= S.L. | editor5-last= Péan | editor5-first= C. | editor6-last= Berger | editor6-first= S. | editor7-last= Caud | editor7-first= N. | editor8-last= Chen | editor8-first= Y. | editor9-last= Goldfarb | editor9-first= L. | editor10-last= Gomis | editor10-first= M.I. | editor11-last= Huang | editor11-first= M. | editor12-last= Leitzell | editor12-first= K. | editor13-last= Lonnoy | editor13-first= E. | editor14-last= Matthews | editor14-first= J.B.R. | editor15-last= Maycock | editor15-first= T.K. | editor16-last= Waterfield | editor16-first= T. | editor17-last= Yelekçi | editor17-first= O. | editor18-last= Yu | editor18-first= R. | editor19-last= Zhou | editor19-first= B. | title = Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change | year = 2021 | url = https://www.ipcc.ch/report/ }} * {{cite book |editor1-last=World Meteorological Organization |title=Scientific Assessment of Ozone Depletion: 2022 |date=2023 |publisher=WMO |location=Geneva |url=https://library.wmo.int/idurl/4/58360}}

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[[Category:Heating, ventilation, and air conditioning]] [[Category:Refrigerants| ]] [[Category:Industrial gases]] [[Category:Mechanical engineering]] [[Category:Climate change]] [[Category:Atmospheric chemistry]]