Wikipedia

Refrigerant

Arefrigerantis aworking fluidused incooling, heating or reverse cooling and heatingofair conditioningsystems andheat pumpswhere they undergo a repeatedphase transitionfrom aliquidto agasand back again. Refrigerants are heavily regulated because of theirtoxicityandflammability[1]and the contribution of CFC and HCFC refrigerants toozone depletion[2]and that of HFC refrigerants toclimate change.[3]

ADuPontR-134arefrigerant

Refrigerants are used in a direct expansion (DX- Direct Expansion) system (circulating system)to transfer energy from one environment to another, typically from inside a building to outside (or vice versa) commonly known as an air conditioner cooling only or cooling & heating reverse DX system or heat pump a heating only DX cycle. Refrigerants can carry 10 times more energy per kg than water, and 50 times more than air.

Refrigerants are controlled substances and classified by International safety regulations ISO 817/5149, AHRAE 34/15 & BS EN 378 due to high pressures (700–1,000 kPa (100–150 psi)), extreme temperatures (−50 °C [−58 °F] to over 100 °C [212 °F]), flammability (A1 class non-flammable, A2/A2L class flammable and A3 class extremely flammable/explosive) and toxicity (B1-low, B2-medium & B3-high). The regulations relate to situations when these refrigerants are released into the atmosphere in the event of an accidental leak not while circulated.

Refrigerants (controlled substances) must only be handled by qualified/certified engineers for the relevant classes (in the UK, C&G 2079 for A1-class and C&G 6187-2 for A2/A2L & A3-class refrigerants).

Refrigerants (A1 class only) Due to their non-flammability, A1 class non-flammability, non-explosivity, and non-toxicity, non-explosivity they have been used in open systems (consumed when used) like fire extinguishers, inhalers, computer rooms fire extinguishing and insulation, etc.) since 1928.

History

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The observed stabilization of HCFC concentrations (left graphs) and the growth of HFCs (right graphs) in earth's atmosphere.

The first air conditioners andrefrigeratorsemployed toxic or flammable gases, such asammonia,sulfur dioxide,methyl chloride,orpropane,that could result in fatal accidents when they leaked.[4]

In 1928Thomas Midgley Jr.created the first non-flammable, non-toxic chlorofluorocarbon gas,Freon(R-12). The name is atrademarkname owned byDuPont(nowChemours) for anychlorofluorocarbon(CFC),hydrochlorofluorocarbon(HCFC), orhydrofluorocarbon(HFC) refrigerant. Following the discovery of better synthesis methods, CFCs such asR-11,[5]R-12,[6]R-123[5]and R-502[7]dominated the market.

Phasing out of CFCs

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See also:Montreal Protocol

In the mid-1970s, scientists discovered that CFCs were causing major damage to theozone layerthat protects the earth from ultraviolet radiation, and to theozone holesover polar regions.[8][9]This led to the signing of theMontreal Protocolin 1987 which aimed to phase out CFCs and HCFC[10]but did not address the contributions that HFCs made to climate change. The adoption of HCFCs such asR-22,[11][12][13]and R-123[5]was accelerated and so were used in most U.S. homes in air conditioners and inchillers[14]from the 1980s as they have a dramatically lower Ozone Depletion Potential (ODP) than CFCs, but their ODP was still not zero which led to their eventual phase-out.

Hydrofluorocarbons(HFCs) such asR-134a,[15][16]R-407A,[17]R-407C,[18]R-404A,[7]R-410A[19](a 50/50 blend ofR-125/R-32) and R-507[20][21]were promoted as replacements for CFCs and HCFCs in the 1990s and 2000s. HFCs were not ozone-depleting but did haveglobal warming potentials(GWPs) thousands of times greater than CO2with atmospheric lifetimes that can extend for decades. This in turn, starting from the 2010s, led to the adoption in new equipment of Hydrocarbon and HFO (hydrofluoroolefin) refrigerants R-32,[22]R-290,[23]R-600a,[23]R-454B,[24]R-1234yf,[25][26]R-514A,[27]R-744 (CO2),[28]R-1234ze(E)[29]and R-1233zd(E),[30]which have both an ODP of zero and a lower GWP. Hydrocarbons and CO2are sometimes called natural refrigerants because they can be found in nature.

The environmental organizationGreenpeaceprovided funding to a former East German refrigerator company to research alternative ozone- and climate-safe refrigerants in 1992. The company developed a hydrocarbon mixture ofpropaneandisobutane,or pure isobutane,[31]called "Greenfreeze", but as a condition of the contract with Greenpeace could not patent the technology, which led to widespread adoption by other firms.[32][33][34]Policy and political influence by corporate executives resisted change however,[35][36]citing the flammability and explosive properties of the refrigerants,[37]and DuPont together with other companies blocked them in the U.S. with the U.S. EPA.[38][39]

Beginning on 14 November 1994, theU.S.Environmental Protection Agencyrestricted the sale, possession and use of refrigerants to only licensed technicians, per rules under sections 608 and 609 of the Clean Air Act.[40]In 1995, Germany made CFC refrigerators illegal.[41]

In 1996Eurammon,a European non-profit initiative fornatural refrigerants,was established and comprises European companies, institutions, and industry experts.[42][43][44]

In 1997, FCs and HFCs were included in theKyoto Protocolto the Framework Convention on Climate Change.

In 2000 in the UK, the Ozone Regulations[45]came into force which banned the use of ozone-depleting HCFC refrigerants such as R22 in new systems. The Regulation banned the use of R22 as a "top-up" fluid for maintenance from 2010 for virgin fluid and from 2015 for recycled fluid.[citation needed]

Addressing greenhouse gases

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With growing interest innatural refrigerantsas alternatives to synthetic refrigerants such as CFCs, HCFCs and HFCs, in 2004, Greenpeace worked with multinational corporations likeCoca-ColaandUnilever,and laterPepsicoand others, to create a corporate coalition called Refrigerants Naturally!.[41][46]Four years later, Ben & Jerry's of Unilever and General Electric began to take steps to support production and use in the U.S.[47]It is estimated that almost 75 percent of the refrigeration and air conditioning sector has the potential to be converted to natural refrigerants.[48]

In 2006, the EU adopted a Regulation onfluorinated greenhouse gases(FCs and HFCs) to encourage to transition to natural refrigerants (such as hydrocarbons). It was reported in 2010 that some refrigerants are being used asrecreational drugs,leading to an extremely dangerous phenomenon known asinhalant abuse.[49]

From 2011 the European Union started to phase out refrigerants with aglobal warming potential(GWP) of more than 150 in automotive air conditioning (GWP = 100-year warming potential of one kilogram of a gas relative to one kilogram of CO2) such as the refrigerantHFC-134a(known as R-134a in North America) which has a GWP of 1526.[50]In the same year the EPA decided in favour of the ozone- and climate-safe refrigerant for U.S. manufacture.[32][51][52]

A 2018 study by the nonprofit organization "Drawdown"put proper refrigerant management and disposal at the very top of the list of climate impact solutions, with an impact equivalent to eliminating over 17 years of US carbon dioxide emissions.[53]

In 2019 it was estimated that CFCs, HCFCs, and HFCs were responsible for about 10% of directradiative forcingfrom all long-lived anthropogenic greenhouse gases.[54]and in the same year theUNEPpublished new voluntary guidelines,[55]however many countries have not yet ratified theKigali Amendment.

From early 2020 HFCs (including R-404A, R-134a and R-410A) are being superseded: Residential air-conditioning systems and heat pumps are increasingly usingR-32.This still has a GWP of more than 600. Progressive devices use refrigerants with almost no climate impact, namely R-290 (propane), R-600a (isobutane) orR-1234yf(less flammable, in cars). In commercial refrigeration also CO2(R-744) can be used.

Requirements and desirable properties

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A refrigerant needs to have: aboiling pointthat is somewhat below the target temperature (although boiling point can be adjusted by adjusting thepressureappropriately), a highheat of vaporization,a moderatedensityin liquid form, a relatively high density in gaseous form (which can also be adjusted by setting pressure appropriately), and a highcritical temperature.Working pressures should ideally be containable bycopper tubing,a commonly available material. Extremely high pressures should be avoided.[citation needed]

The ideal refrigerant would be:non-corrosive,non-toxic,non-flammable,with noozone depletionandglobal warmingpotential. It should preferably be natural with well-studied and low environmental impact. Newer refrigerants address the issue of the damage that CFCs caused to the ozone layer and the contribution that HCFCs make to climate change, but some do raise issues relating to toxicity and/or flammability.[56]

Common refrigerants

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Refrigerants with very low climate impact

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With increasing regulations, refrigerants with a very lowglobal warming potentialare expected to play a dominant role in the 21st century,[57]in particular, R-290 and R-1234yf. Starting from almost no market share in 2018,[58]low GWPO devices are gaining market share in 2022.

Code Chemical Name GWP20yr[59] GWP 100yr[59] Status Commentary
R-290 C3H8 Propane 3.3[60] Increasing use Low cost, widely available and efficient. They also have zeroozone depletion potential.Despite their flammability, they are increasingly used in domestic refrigerators and heat pumps. In 2010, about one-third of all household refrigerators and freezers manufactured globally used isobutane or an isobutane/propane blend, and this was expected to increase to 75% by 2020.[61]
R-600a HC(CH3)3 Isobutane 3.3 Widely used See R-290.
R-717 NH3 Ammonia 0 0[62] Widely used Commonly used before the popularisation of CFCs, it is again being considered but does suffer from the disadvantage of toxicity, and it requires corrosion-resistant components, which restricts its domestic and small-scale use. Anhydrous ammonia is widely used in industrial refrigeration applications and hockey rinks because of its highenergy efficiencyand low cost.
R-1234yfHFO-1234yf C3H2F4 2,3,3,3-Tetrafluoropropene <1 Less performance but also less flammable than R-290.[57]GM announced that it would start using "hydro-fluoro olefin",HFO-1234yf,in all of its brands by 2013.[63]
R-744 CO2 Carbon dioxide 1 1 In use Was used as a refrigerant prior to the discovery of CFCs (this was also the case for propane)[4]and now having a renaissance due to it being non-ozone depleting, non-toxic and non-flammable. It may become the working fluid of choice to replace current HFCs in cars, supermarkets, andheat pumps.Coca-Colahas fielded CO2-based beverage coolers and theU.S. Armyis considering CO2refrigeration.[64][65]Due to the need to operate at pressures of up to 130 bars (1,900 psi; 13,000 kPa), CO2systems require highly resistant components, however these have already been developed for mass production in many sectors.

Most used

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Code Chemical Name Global warming potential20yr[59] GWP 100yr[59] Status Commentary
R-32 HFC-32 CH2F2 Difluoromethane 2430 677 Widely used Promoted as climate-friendly substitute for R-134a and R-410A, but still with high climate impact. Has excellent heat transfer and pressure drop performance, both in condensation and vaporisation.[66]It has anatmospheric lifetimeof nearly 5 years.[67]Currently used in residential and commercialair-conditionersandheat pumps.
R-134aHFC-134a CH2FCF3 1,1,1,2-Tetrafluoroethane 3790 1550 Widely used Most used in 2020 for hydronic heat pumps in Europe and the United States in spite of high GWP.[58]Commonly used in automotive air conditioners prior to phase out which began in 2012.
R-410A 50% R-32 / 50% R-125 (pentafluoroethane) Between 2430 (R-32) and 6350 (R-125) > 677 Widely Used Most used in split heat pumps / AC by 2018. Almost 100% share in the USA.[58]Being phased out in the US starting in 2022.[68][69]

Banned / Phased out

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Code Chemical Name Global warming potential20yr[59] GWP 100yr[59] Status Commentary
R-11 CFC-11 CCl3F Trichlorofluoromethane 6900 4660 Banned Production was banned in developed countries byMontreal Protocolin 1996
R-12 CFC-12 CCl2F2 Dichlorodifluoromethane 10800 10200 Banned Also known as Freon, a widely usedchlorofluorocarbonhalomethane(CFC). Production was banned in developed countries byMontreal Protocolin 1996, and in developing countries (article 5 countries) in 2010.[70]
R-22 HCFC-22 CHClF2 Chlorodifluoromethane 5280 1760 Being phased out A widely usedhydrochlorofluorocarbon(HCFC) and powerfulgreenhouse gaswith a GWP equal to 1810. Worldwide production of R-22 in 2008 was about 800Gg per year, up from about 450Gg per year in 1998. R-438A (MO-99) is a R-22 replacement.[71]
R-123 HCFC-123 CHCl2CF3 2,2-Dichloro-1,1,1-trifluoroethane 292 79 US phase-out Used in large tonnage centrifugal chiller applications. All U.S. production and import of virgin HCFCs will be phased out by 2030, with limited exceptions.[72]R-123 refrigerant was used to retrofit some chiller that used R-11 refrigerantTrichlorofluoromethane.The production of R-11 was banned in developed countries byMontreal Protocolin 1996.[73]

Other

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Code Chemical Name Global warming potential20yr[59] GWP 100yr[59] Commentary
R-152a HFC-152a CH3CHF2 1,1-Difluoroethane 506 138 As a compressed air duster
R-407C Mixture of difluoromethane andpentafluoroethaneand 1,1,1,2-tetrafluoroethane A mixture of R-32, R-125, and R-134a
R-454B Difluoromethane and 2,3,3,3-Tetrafluoropropene HFOs blend of refrigerants Difluoromethane (R-32) and 2,3,3,3-Tetrafluoropropene (R-1234yf).[74][75][76][77]
R-513A An HFO/HFC blend (56% R-1234yf/44%R-134a) May replace R-134a as an interim alternative[78]
R-514A HFO-1336mzz-Z/trans-1,2- dichloroethylene (t-DCE) An hydrofluoroolefin (HFO)-based refrigerant to replace R-123 in low pressure centrifugal chillers for commercial and industrial applications.[79][80]

Refrigerant reclamation and disposal

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Main article:Refrigerant reclamation

Coolant and refrigerants are found throughout the industrialized world, in homes, offices, and factories, in devices such as refrigerators, air conditioners, central air conditioning systems (HVAC), freezers, and dehumidifiers. When these units are serviced, there is a risk that refrigerant gas will be vented into the atmosphere either accidentally or intentionally, hence the creation of technician training and certification programs in order to ensure that the material is conserved and managed safely. Mistreatment of these gases has been shown to deplete the ozone layer and is suspected to contribute toglobal warming.[81]

With the exception of isobutane and propane (R600a, R441A and R290), ammonia and CO2underSection 608of the United States'Clean Air Actit is illegal to knowingly release any refrigerants into the atmosphere.[82][83]

Refrigerant reclamationis the act of processing used refrigerant gas which has previously been used in some type ofrefrigeration loopsuch that it meets specifications for new refrigerant gas. In theUnited States,theClean Air Actof 1990 requires that used refrigerant be processed by a certified reclaimer, which must be licensed by theUnited States Environmental Protection Agency(EPA), and the material must be recovered and delivered to the reclaimer by EPA-certified technicians.[84]

Classification of refrigerants

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R407Cpressure-enthalpydiagram, isotherms between the two saturation lines
Main article:List of refrigerants

Refrigerants may be divided into three classes according to their manner of absorption or extraction of heat from the substances to be refrigerated:[citation needed]

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

R numbering system

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The R- numbering system was developed byDuPont(which owned theFreontrademark), and systematically identifies the molecular structure of refrigerants made with a single halogenated hydrocarbon. ASHRAE has since set guidelines for the numbering system as follows:[85]

R-X1X2X3X4

  • 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

Series

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Ethane Derived Chains

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  • Number OnlyMost symmetricalisomer
  • Lower Case Suffix (a, b, c, etc.)indicates increasingly unsymmetrical isomers

Propane Derived Chains

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  • Number OnlyIf only one isomer exists; otherwise:
  • First lower case suffix (a-f):
    • a SuffixCl2central carbon substitution
    • b SuffixCl, F central carbon substitution
    • c SuffixF2central carbon substitution
    • d SuffixCl, H central carbon substitution
    • e SuffixF, H central carbon substitution
    • f SuffixH2central carbon substitution
  • 2nd Lower Case Suffix (a, b, c, etc.)Indicates increasingly unsymmetrical isomers

Propene derivatives

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  • First lower case suffix (x, y, z):
    • x SuffixCl substitution on central atom
    • y SuffixF substitution on central atom
    • z SuffixH substitution on central atom
  • Second lower case suffix (a-f):
    • a Suffix=CCl2methylenesubstitution
    • b Suffix=CClF methylene substitution
    • c Suffix=CF2methylene substitution
    • d Suffix=CHCl methylene substitution
    • e Suffix=CHF methylene substitution
    • f Suffix=CH2methylene substitution

Blends

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

Miscellaneous

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  • R-CxxxCyclic compound
  • R-ExxxEther groupis present
  • R-CExxxCyclic compound with an ether group
  • R-4xx/5xx + Upper Case Suffix (A, B, C, etc.)Same blend with different composition of refrigerants
  • R-6xx + Lower Case LetterIndicates increasingly unsymmetrical isomers
  • 7xx/7xxx + Upper Case LetterSame molar mass, different compound
  • R-xxxxB#Bromineis present with the number after B indicating how many bromine atoms
  • R-xxxxI#Iodineis present with the number after I indicating how many iodine atoms
  • R-xxx(E)Trans Molecule
  • R-xxx(Z)Cis Molecule

For example,R-134ahas 2 carbon atoms, 2 hydrogen atoms, and 4 fluorine atoms, an empirical formula of tetrafluoroethane. The "a" suffix indicates that the isomer is unbalanced by one atom, giving1,1,1,2-Tetrafluoroethane.R-134 (without the "a" suffix) would have a molecular structure of 1,1,2,2-Tetrafluoroethane.

The same numbers are used with an R- prefix for generic refrigerants, with a "Propellant" prefix (e.g., "Propellant 12" ) for the same chemical used as a propellant for anaerosol spray,and with trade names for the compounds, such as "Freon12 ". Recently, a practice of using abbreviations HFC- forhydrofluorocarbons,CFC- forchlorofluorocarbons,and HCFC- forhydrochlorofluorocarbonshas arisen, because of the regulatory differences among these groups.[citation needed]

Refrigerant safety

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ASHRAE Standard 34,Designation and Safety Classification of Refrigerants,assigns safety classifications to refrigerants based upontoxicityandflammability.

Using safety information provided by producers, ASHRAE assigns a capital letter to indicate toxicity and a number to indicate flammability. The letter "A" is the least toxic and the number 1 is the least flammable.[86]

See also

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References

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