Refrigerant
Refrigerants are working fluids that carry heat from a cold environment to a warm environment while circulating between them. For example, the refrigerant in an 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">Template:Cite book</ref><ref name = "moran">Template:Cite book</ref>
Refrigerants are also used in 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 or isobutane, and synthetic fluids, such as chlorofluorocarbons. Many older synthetic refrigerants are banned to protect the Earth's ozone layer or to limit climate change. Newer synthetic refrigerants do not contribute to those problems. 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 propelling aerosols, polymer foam production, chemical feedstocks, fire suppression, and solvents.<ref>Template:Cite report</ref>
Chillers are refrigeration systems that have a secondary loop which circulates a refrigerating liquid (as opposed to a refrigerant), with vapor compression refrigeration used to chill the secondary liquid.<ref>Template:Cite book </ref> 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">Template:Cite book</ref><ref name="domanski-2022">Template:Cite report</ref>
Thermophysical property requirements
In 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 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. 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">Template:Cite book</ref> The evaporator pressure should be above atmospheric pressure to prevent air from leaking into it.<ref name="legg">Template:Cite book</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 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. 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">Template:Cite journal</ref>
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 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 refrigeration cycles, the condenser must be replaced by a gas cooler operating over a wider temperature range.<ref name="hundy"/><ref name="lorentzen">Template:Cite journal</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 temperature glide. It results from the difference between vapor and liquid phase composition that is present in most mixtures.<ref name="hundy"/><ref>Template:Cite book</ref>
Other requirements
The refrigerant 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 shaft seals compatible with the refrigerant must be available. For hermetically sealed systems, the refrigerant vapor may have contact with the motor windings, and so it should have a high dielectric strength.<ref name="hundy"/><ref name="legg"/><ref name="mclinden-didion"/>
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>Template:Cite journal</ref>
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">Template:Cite book</ref>
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">Template:Cite report</ref><ref>Template:Cite book</ref> In the 1850s, 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>Template:Australian Dictionary of Biography</ref>
Template:See also Many more inventions followed during the second half of the 19th century. In the 1860s, Thaddeus Lowe developed a carbon dioxide system.<ref name="r7">Template:Cite conference </ref> The 1870s saw the introduction of systems based on ammonia, sulfur dioxide, dimethyl ether, and methyl chloride.<ref name="asme-HHC" /><ref>Template:Cite web</ref> Several 19th century refrigerants continue in use to this day, but others have been discarded for safety or performance reasons.<ref name="mclinden">Template:Cite journal</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, methyl chloride, 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 HCHCs)
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 chlorofluorocarbons, or CFCs, and R-22 is a hydrochlorofluorocarbons, or HCFC.<ref name="mclinden"/> The trade name Freon was used for R-12, which at that time was also called F-12.<ref>Template:Cite journal</ref>
Template:See The R- numbering system for refrigerants was developed by DuPont in the years that followed.<ref>Template:Cite web</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)
In the mid-1970s, scientists discovered that CFCs were causing substantial damage to the ozone layer that protects the earth from ultraviolet radiation.<ref>Template:Cite journal</ref><ref>Template:Cite book</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 depletionTemplate:Emdashan ozone holeTemplate:Emdashabove Antarctica.<ref>Template:Cite journal</ref>
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 have lower ozone depletion potentials (ODP) than CFCs, and so HCFCs were scheduled to phase out over a longer period. During this transition time, the adoption of HCFCs, such as R-22, was accelerated.<ref name="AnnexA">Template:Cite web</ref><ref name="AnnexC">Template:Cite web</ref><ref name="UNEP-hcfc">Template:Cite web</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 R-123 as a replacement for R-11 in large chillers.<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>Template:Cite journal</ref> and CFCs were prohibited in new equipment starting in 1995.<ref>Template:Cite web</ref>
US home air conditioners and industrial chillers moved toward HCFCs starting in the 1980s. Beginning on 14 November 1994, the US Environmental Protection Agency (EPA) restricted the sale, possession and use of refrigerants to only licensed technicians, per rules under the Clean Air Act.<ref>Template:Cite web</ref> The US banned the production and import of CFCs on January 1, 1996.<ref>Template:Cite web</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>Template:Cite web</ref> In 2010, US EPA banned the use of R-22 (HCFC-22) in new equipment,<ref name="Phaseout">Template:Cite web</ref> much of which shifted to the HFC mixture, R-410A.<ref name="mclinden" /><ref name="calm-2008">Template:Cite journal</ref> All production and import of R-22 was banned on January 1, 2020.<ref>Template:Cite web</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 potentials than the refrigerants that replaced them. As a result, the Montreal Protocol very significantly reduced global warming.<ref>Template:Cite journal</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 refrigerants.
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. By 1996, Greenfreeze accounted for 35% of Western European production; and, by 2001, hydrocarbon refrigeration covered 100% of German production.<ref name="mate">Template:Cite journal</ref> Greenfreeze systems use varying mixtures of isobutane (R-600a), propane (R-290), and other hydrocarbons.<ref name="mate-unep">Template:Cite report</ref><ref>Template:Cite report</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>Template:Cite web</ref>
Corporations that manufactured synthetic refrigerants resisted the move toward hydrocarbons, however, citing the flammability and explosive properties of hydrocarbons.<ref name="mate" /><ref>Template:Cite book</ref> This resistance extended to attempts to block the approval of hydrocarbon refrigerants by the US EPA.<ref>Template:Cite web</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>Template:Cite journal</ref> By 2010, Japan had converted almost all refrigeration from R-134a to isobutane.<ref>Template:Cite report</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">Template:Cite web</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 Template:CO2 as its refrigerant of choice.<ref>Template:Cite web</ref>
Phase-down of HFCs (climate-change mitigation)
Hydrofluorocarbons (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 potentials (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>Template:Cite journal</ref>
Different HFCs were adopted for different purposes. In domestic refrigerators and automobiles, R-134a replaced the CFC, R-12. In low-pressure chillers, R-123 replaced R-11. In small air conditioners, the blended refrigerant R-410A ultimately replaced 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" />
During this era, the atmospheric concentrations of HCFC's began to stabilize, while the concentrations of HFCs rose sharply (see figure).
The situation began to change in 1997, when HFCs and fluorocarbons (FCs) were included in the Kyoto Protocol to the Framework Convention on Climate Change.<ref>Template:Cite treaty</ref><ref>Template:Cite web</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 greenhouse gases (FCs and HFCs) to encourage to transition to natural refrigerants.<ref>Template:Cite journal</ref>
During the 2010s, new equipment increasingly used lower-GWP HFCs, hydrocarbons, and hydrofluoroolefins (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">Template:Cite web</ref><ref>Template:Cite web</ref> R-514A, R-1233zd(E), and R-1234ze(E) for chillers;<ref name="trane">Template:Cite web</ref><ref name="carrier">Template:Cite web</ref><ref>Template:Cite web</ref> and R-32, R-290 (propane), R-407A, and R-744 (CO2) for commercial refrigeration.<ref name="auto">Template:Cite web</ref><ref>Template:Cite web</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">Template:Cite journal</ref>
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>Template:Cite web</ref> These regulatory decisions aligned with the opinion of the auto industry, which in 2010 had recommended R-1234yf for automotive air conditioning.<ref>Template:Cite web</ref>
The lower GWP of R-1234yf relative to R-134a is primarily due to its very short atmospheric lifetimeTemplate:Em-dash12 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>Template:Cite journal</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>Template:Cite treaty</ref><ref>Template:Cite web</ref> In 2019, the UNEP published new voluntary guidelines for air conditions and refrigerators.<ref>Template:Cite web</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>Template:Cite web</ref>
The United States ratified the Kigali Amendment on October 31, 2022.<ref>Template:Cite web</ref> The US Environmental Protection Agency has published phase-out schedules for HFCs,<ref name="epa-final-rule-HFC">Template:Cite web</ref> with restrictions on GWP by sector of use.<ref name="epa-hfc-transitions-sector">Template:Cite web</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>Template:Cite web</ref><ref>Template:Cite web</ref><ref name="honeywell-1234yf">Template:Cite web</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>Template:Cite web</ref><ref>Template:Cite web</ref> Each country may proceed differently, however. For example, China had widely adopted isobutane refrigerators long before the Kigali amendment,<ref>Template:Cite web</ref> and it has banned HFCs from new refrigerators starting in 2026.<ref>Template:Cite web</ref>
Refrigerant safety, environmental management, and 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 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> Template:Cite book</ref><ref>Template:Cite web</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.
| 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 extinguishers and fire suppressants using HCFCs or HFCs,<ref>Template:Cite web</ref><ref>Template:Cite web</ref> gas dusters with HFC-152a or hydrocarbon propellants, metered-dose inhalers using HFC propellants,<ref>Template:Cite report</ref> and disposable lighters containing the A3 refrigerant isobutane (R-600a).<ref>Template:Cite web</ref>
To mitigate the environmental hazards, strict regulations apply to refrigerant handling. In the United States, Section 608 of the 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>Template:Cite web</ref><ref>Template:Cite web</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>Template:Cite web</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>Template:Cite web</ref>
To minimize emissions, used refrigerants must be recovered during service or decommissioning. Refrigerant reclamationTemplate:Emdashprocessing used refrigerant so that it meets purity specifications of new gasTemplate:Emdashmust be carried out in the US by EPA-licensed reclaimers, with recovery handled by certified technicians.<ref>Template:Cite web</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 °C and a condenser temperature of 30.0 °C. These temperatures might approximate a domestic refrigerator.
| Values per kilowatt of refrigeration.<ref name="ashrae-fund-29"/> Evaporator Template:Convert /condenser Template:Convert | ||||||
|---|---|---|---|---|---|---|
| Refrigerant code | Name | Evaporator pressure (kPa) | Condenser pressure (kPa) | Refrigerant circulation Template:Nowrap | Compressor displacement Template:Nowrap | Power consumption (kW) |
| R-32 | Difluoromethane | 653 | 1928 | 3.87 | 0.218 | 0.169 |
| R-134a | 1,1,1,2-Tetrafluoroethane | 228 | 770 | 6.45 | 0.575 | 0.165 |
| R-290 | Propane | 385 | 1079 | 3.47 | 0.409 | 0.167 |
| R-600a | Isobutane | 123 | 405 | 3.60 | 1.072 | 0.162 |
| R-410A | Mixture: R-32 (50%) / R-125 (50%) | 643 | 1886 | 5.85 | 0.238 | 0.173 |
| R-717 | Ammonia | 332 | 1167 | 0.90 | 0.331 | 0.160 |
| R-744 | Carbon dioxide | 2909 | 7213 | 7.72 | 0.098 | 0.285 |
| R-1234yf | 2,3,3,3-Tetrafluoropropene | 250 | 783 | 8.30 | 0.595 | 0.172 |
In this table, 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)Template:Emdashthe refrigeration effect per unit power inputTemplate:Emdashis equal to 1Template:NbspkW/(power consumption), since the power is given per 1Template:NbspkW of refrigeration. The volumetric capacity, Qvol (MJ/m3)Template:Emdashthe cooling effect per unit volume entering the compressorTemplate:Emdashis similarly equal to 1Template:NbspkW/(compressor displacement). Higher COP means greater energy efficiency and higher Qvol means a smaller system size.<ref name="mclinden-2016"/>
ASHRAE also provides additional data, other operating conditions, and additional refrigerants. 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
Template:See also All refrigerants in these tables are safety class A1 (non-toxic, non-flammable), unless otherwise indicated. GWP = Global warming potential.
Refrigerants with very low climate impact
| Code | Chemical | Name | GWP 20yr | GWP 100yr | Status | Notes |
|---|---|---|---|---|---|---|
| R-290 | C3H8 | Propane | 0.072<ref name="ar6">Template:Cite book</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>Template:Cite web</ref><ref>Template:Cite web</ref> |
| R-600a | HC(CH3)3 | Isobutane | <<1<ref name="wmo">Template:Cite book</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 | <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 | Template:CO2 | 1<ref name="ar6" /> | 1<ref name="ar6"/> | In use | Transcritical refrigeration cycle leads to pressures of up to Template:Convert 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">Template:Cite journal</ref> Used in most new US and EU vehicles by 2021, replacing R-134a.<ref name="honeywell-1234yf"/> |
| 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
| Code | Chemical | Name | GWP 20yr | GWP 100yr | Status | Notes |
|---|---|---|---|---|---|---|
| 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. Atmospheric lifetime of 5.27 years.<ref name = "wmo" /> Used in residential and commercial air-conditioners and heat pumps.<ref name="daikan"/><ref>Template:Cite web</ref> |
| R-454B | Mixture: 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>Template:Cite web</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>Template:Cite journal</ref> |
Banned or phasing-out CFCs, HCFCs, and HFCs
| Code | Chemical | Name | GWP 20yr | GWP 100yr | Status | Notes |
|---|---|---|---|---|---|---|
| R-11 CFC-11 | CCl3F | Trichlorofluoromethane | 8320<ref name="ar6"/> | 6230<ref name="ar6"/> | Banned | Widely used in water chillers with centrifugal compressors during 20th C.<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"/> |
| 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 20th C.<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"/> |
| 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 20th C.<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" /> |
| 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>Template:Cite report</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>Template:Cite web</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: 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">Template:Cite web</ref><ref name="epa-hfc-aim">Template:Cite web</ref> | |
| R-410A | Mixture: R-32 (50%), R-125 (50%) | 4705<ref name="unep23">Template:Cite web</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>Template:Cite web</ref> Most used in split heat pumps / AC in 2018, with almost 100% share in the US,<ref name="bsria">Template:Cite web</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 20th C.<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
| Code | Chemical | Name | GWP 20yr | 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>Template:Cite web</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>Template:Cite web</ref><ref>Template:Cite web</ref> Being displaced by non-toxic HFO-1233zd(E).<ref>Template:Cite web</ref> |
Numbered classification of refrigerants
The R- numbering system, maintained by ASHRAE and ISO, uniquely identifies refrigerants according to their composition.<ref>Template:Cite web</ref><ref name="iso817">Template:Cite book</ref> The system originated for numbering halogenated hydrocarbons, but it encompasses blended refrigerants and inorganic refrigerants as well.
Main numbering system
According to ISO:<ref name="iso817"/> Template:Quote
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, 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).
The prefix, when present, is an upper-case letter "C" for cyclic compounds, "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.
| Rules for lower-case suffixes<ref name="iso817"/> | |
|---|---|
| Ethane derived chains • Number only: most symmetrical isomer Propane derived chains
• Second lower case suffix (a, b, c, etc.): increasingly unsymmetrical isomers |
Propene derived chains
• First lower case suffix (x, y, z):
• Second lower case suffix (a–f):
|
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 blend. The number xx is assigned. An upper-case suffix (A, B, etc.) distinguishes different compositions of the same blend.
- R-5xx: 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
The standard allows the prefix R- to be replaced by a prefix describing the molecular components of the refrigerant. Examples include: CFC- for chlorofluorocarbons; HCFC- for hydrochlorofluorocarbons; HFC- for hydrofluorocarbons; and HFO- for hydrofluoroolefins.<ref name="iso817"/><ref>Template:Cite web</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
Wikipedia pages also exist for many individual refrigerants.
References
Template:Reflist Template:Reflist
External links
- ASHRAE Template:SndAmerican Society of Heating, Refrigerating and Air-Conditioning Engineers
- Green Cooling Initiative
- What Are Refrigerants? Types, Uses & Their Environmental Impact
- International Institute of Refrigeration
- Template:Cite book
- Template:Cite book