A refrigerant is a working fluid used in the refrigeration cycle of air conditioning systems and heat pumps where in most cases they undergo a repeated phase transition from a liquid to a gas and back again. Refrigerants are heavily regulated due to their toxicity, flammability and the contribution of CFC and HCFC refrigerants to ozone depletion and that of HFC refrigerants to climate change.
Refrigerants are used in a direct expansion (DX) 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" or "heat pump". Refrigerants can carry 10 times more energy per kg than water, and 50 times more than air.
In some countries, refrigerants are controlled substances 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), as classified by ISO 817 & ASHRAE 34.
Refrigerants must only be handled by qualified/certified engineers to the relevant classes of refrigerant (in the UK, C&G 2079 for A1-class, and C&G 6187-2 for A2/A2L & A3 class refrigerants).
The first air conditioners and refrigerators employed toxic or flammable gases, such as ammonia, sulfur dioxide, methyl chloride, or propane, that could result in fatal accidents when they leaked. [1]
In 1928 Thomas Midgley Jr. created the first non-flammable, non-toxic chlorofluorocarbon gas, Freon (R-12). The name is a trademark name owned by DuPont (now Chemours) for any chlorofluorocarbon (CFC), hydrochlorofluorocarbon (HCFC), or hydrofluorocarbon (HFC) refrigerant. Following the discovery of better synthesis methods, CFCs such as R-11, [2] R-12, [3] R-123 [2] and R-502 [4] dominated the market.
In the early 1980s, scientists discovered that CFCs were causing major damage to the ozone layer that protects the earth from ultraviolet radiation, and to the ozone holes over polar regions. This led to the signing of the Montreal Protocol in 1987 which aimed to phase out CFCs and HCFC [5] but did not address the contributions that HFCs made to climate change. The adoption of HCFCs such as R-22, [6] [7] [8] and R-123 [2] was accelerated and so were used in most U.S. homes in air conditioners and in chillers [9] from the 1980s as they have a dramatically lower Ozone Depletion Potential (ODP) than CFCs, but their ODP was still not zero which led to their eventual phase-out.
Hydrofluorocarbons (HFCs) such as R-134a, [10] [11] R-407A, [12] R-407C, [13] R-404A, [4] R-410A [14] (a 50/50 blend of R-125/R-32) and R-507 [15] [16] were promoted as replacements for CFCs and HCFCs in the 1990s and 2000s. HFCs were not ozone-depleting but did have global warming potentials (GWPs) thousands of times greater than CO2 with atmospheric lifetimes that can extend for decades. This in turn, starting from the 2010s, led to the adoption in new equipment of Hydrocarbon and HFO (hydrofluoroolefin) refrigerants R-32, [17] R-290, [18] R-600a, [18] R-454B, [19] R-1234yf, [20] [21] R-514A, [22] R-744 (CO2), [23] R-1234ze(E) [24] and R-1233zd(E), [25] which have both an ODP of zero and a lower GWP. Hydrocarbons and CO2 are sometimes called natural refrigerants because they can be found in nature.
The environmental organization Greenpeace provided funding to a former East German refrigerator company to research alternative ozone- and climate-safe refrigerants in 1992. The company developed hydrocarbon mixes such as isopentane and isobutane,[ citation needed ] propane and isobutane, or pure isobutane, [26] called "Greenfreeze", but as a condition of the contract with Greenpeace could not patent the technology, which led to their widespread adoption by other firms. [27] [28] [29] Policy and political influence by corporate executives resisted change however, [30] [31] citing the flammability and explosive properties of the refrigerants, [32] and DuPont together with other companies blocked them in the U.S. with the U.S. EPA. [33] [34]
Beginning on 14 November 1994, the U.S. Environmental Protection Agency restricted the sale, possession and use of refrigerants to only licensed technicians, per rules under sections 608 and 609 of the Clean Air Act. [35] In 1995, Germany made CFC refrigerators illegal. [36]
In 1996 Eurammon, a European non-profit initiative for natural refrigerants, was established and comprises European companies, institutions, and industry experts. [37] [38] [39]
In 1997, FCs and HFCs were included in the Kyoto Protocol to the Framework Convention on Climate Change.
In 2000 in the UK, the Ozone Regulations [40] 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 ]
With growing interest in natural refrigerants as alternatives to synthetic refrigerants such as CFCs, HCFCs and HFCs, in 2004, Greenpeace worked with multinational corporations like Coca-Cola and Unilever, and later Pepsico and others, to create a corporate coalition called Refrigerants Naturally!. [36] [41] Four years later, Ben & Jerry's of Unilever and General Electric began to take steps to support production and use in the U.S. [42] It is estimated that almost 75 percent of the refrigeration and air conditioning sector has the potential to be converted to natural refrigerants. [43]
In 2006, the EU adopted a Regulation on fluorinated greenhouse gases (FCs and HFCs) to encourage to transition to natural refrigerants (such as hydrocarbons). It was reported in 2010 that some refrigerants are being used as recreational drugs, leading to an extremely dangerous phenomenon known as inhalant abuse. [44]
From 2011 the European Union started to phase out refrigerants with a global warming potential (GWP) of more than 150 in automotive air conditioning (GWP = 100-year warming potential of one kilogram of a gas relative to one kilogram of CO2) such as the refrigerant HFC-134a (known as R-134a in North America) which has a GWP of 1526. [45] In the same year the EPA decided in favour of the ozone- and climate-safe refrigerant for U.S. manufacture. [27] [46] [47]
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. [48]
In 2019 it was estimated that CFCs, HCFCs, and HFCs were responsible for about 10% of direct radiative forcing from all long-lived anthropogenic greenhouse gases. [49] and in the same year the UNEP published new voluntary guidelines, [50] however many countries have not yet ratified the Kigali Amendment.
From early 2020 HFCs (including R-404A, R-134a and R-410A) are being superseded: Residential air-conditioning systems and heat pumps are increasingly using R-32. This still has a GWP of more than 600. Progressive devices use refrigerants with almost no climate impact, namely R-290 (propane), R-600a (isobutane) or R-1234yf (less flammable, in cars). In commercial refrigeration also CO2 (R-744) can be used.
A refrigerant needs to have: a boiling point that is somewhat below the target temperature (although boiling point can be adjusted by adjusting the pressure appropriately), a high heat of vaporization, a moderate density in liquid form, a relatively high density in gaseous form (which can also be adjusted by setting pressure appropriately), and a high critical temperature. Working pressures should ideally be containable by copper tubing, a commonly available material. Extremely high pressures should be avoided.[ citation needed ]
The ideal refrigerant would be: non-corrosive, non-toxic, non-flammable, with no ozone depletion and global warming potential. It should preferably be natural with well-studied and low environmental impact. Newer refrigerants address the issue of the damage that CFCs caused to the ozone layer and the contribution that HCFCs make to climate change, but some do raise issues relating to toxicity and/or flammability. [51]
With increasing regulations, refrigerants with a very low global warming potential are expected to play a dominant role in the 21st century, [52] in particular, R-290 and R-1234yf. Starting from almost no market share in 2018, [53] low GWPO devices are gaining market share in 2022.
Code | Chemical | Name | GWP 20yr [54] | GWP 100yr [54] | Status | Commentary |
---|---|---|---|---|---|---|
R-290 | C3H8 | Propane | 3.3 [55] | Increasing use | Low cost, widely available and efficient. They also have zero ozone depletion potential. Despite their flammability, they are increasingly used in domestic refrigerators and heat pumps. In 2010, about one-third of all household refrigerators and freezers manufactured globally used isobutane or an isobutane/propane blend, and this was expected to increase to 75% by 2020. [56] | |
R-600a | HC(CH3)3 | Isobutane | 3.3 | Widely used | See R-290. | |
R-717 | NH3 | Ammonia | 0 | 0 [57] | Widely used | Commonly used before the popularisation of CFCs, it is again being considered but does suffer from the disadvantage of toxicity, and it requires corrosion-resistant components, which restricts its domestic and small-scale use. Anhydrous ammonia is widely used in industrial refrigeration applications and hockey rinks because of its high energy efficiency and low cost. |
R-1234yf HFO-1234yf | C3H2F4 | 2,3,3,3-Tetrafluoropropene | <1 | Less performance but also less flammable than R-290. [52] GM announced that it would start using "hydro-fluoro olefin", HFO-1234yf, in all of its brands by 2013. [58] | ||
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) [1] and now having a renaissance due to it being non-ozone depleting, non-toxic and non-flammable. It may become the working fluid of choice to replace current HFCs in cars, supermarkets, and heat pumps. Coca-Cola has fielded CO2-based beverage coolers and the U.S. Army is considering CO2 refrigeration. [59] [60] Due to the need to operate at pressures of up to 130 bars (1,900 psi; 13,000 kPa), CO2 systems require highly resistant components, however these have already been developed for mass production in many sectors. |
Code | Chemical | Name | Global warming potential 20yr [54] | GWP 100yr [54] | 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. [61] It has an atmospheric lifetime of nearly 5 years. [62] Currently used in residential and commercial air-conditioners and heat pumps. |
R-134a HFC-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. [53] 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. [53] |
Code | Chemical | Name | Global warming potential 20yr [54] | GWP 100yr [54] | Status | Commentary |
---|---|---|---|---|---|---|
R-11 CFC-11 | CCl3F | Trichlorofluoromethane | 6900 | 4660 | Banned | Production was banned in developed countries by Montreal Protocol in 1996 |
R-12 CFC-12 | CCl2F2 | Dichlorodifluoromethane | 10800 | 10200 | Banned | Also known as Freon, a widely used chlorofluorocarbon halomethane (CFC). Production was banned in developed countries by Montreal Protocol in 1996, and in developing countries (article 5 countries) in 2010. [63] |
R-22 HCFC-22 | CHClF2 | Chlorodifluoromethane | 5280 | 1760 | Being phased out | A widely used hydrochlorofluorocarbon (HCFC) and powerful greenhouse gas with a GWP equal to 1810. Worldwide production of R-22 in 2008 was about 800 Gg per year, up from about 450 Gg per year in 1998. R-438A (MO-99) is a R-22 replacement. [64] |
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. [65] R-123 refrigerant was used to retrofit some chiller that used R-11 refrigerant Trichlorofluoromethane. The production of R-11 was banned in developed countries by Montreal Protocol in 1996. [66] |
Code | Chemical | Name | Global warming potential 20yr [54] | GWP 100yr [54] | Commentary |
---|---|---|---|---|---|
R-152a HFC-152a | CH3CHF2 | 1,1-Difluoroethane | 506 | 138 | As a compressed air duster |
R-407C | Mixture of difluoromethane and pentafluoroethane and 1,1,1,2-tetrafluoroethane | A mixture of R-32, R-125, and R-134a | |||
R-454B | Difluoromethane and 2,3,3,3-Tetrafluoropropene | HFOs blend of refrigerants Difluoromethane (R-32) and 2,3,3,3-Tetrafluoropropene (R-1234yf). [67] [68] [69] [70] | |||
R-513A | An HFO/HFC blend (56% R-1234yf/44%R-134a) | May replace R-134a as an interim alternative [71] | |||
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. [72] [73] |
Coolant and refrigerants are found throughout the industrialized world, in homes, offices, and factories, in devices such as refrigerators, air conditioners, central air conditioning systems (HVAC), freezers, and dehumidifiers. When these units are serviced, there is a risk that refrigerant gas will be vented into the atmosphere either accidentally or intentionally, hence the creation of technician training and certification programs in order to ensure that the material is conserved and managed safely. Mistreatment of these gases has been shown to deplete the ozone layer and is suspected to contribute to global warming. [74]
With the exception of isobutane and propane (R600a, R441A and R290), ammonia and CO2 under Section 608 of the United States' Clean Air Act it is illegal to knowingly release any refrigerants into the atmosphere. [75] [76]
Refrigerant reclamation is the act of processing used refrigerant gas which has previously been used in some type of refrigeration loop such that it meets specifications for new refrigerant gas. In the United States, the Clean Air Act of 1990 requires that used refrigerant be processed by a certified reclaimer, which must be licensed by the United States Environmental Protection Agency (EPA), and the material must be recovered and delivered to the reclaimer by EPA-certified technicians. [77]
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 ]
The R- numbering system was developed by DuPont (which owned the Freon trademark), and systematically identifies the molecular structure of refrigerants made with a single halogenated hydrocarbon. ASHRAE has since set guidelines for the numbering system as follows: [78]
R-X1X2X3X4
For example, R-134a has 2 carbon atoms, 2 hydrogen atoms, and 4 fluorine atoms, an empirical formula of tetrafluoroethane. The "a" suffix indicates that the isomer is unbalanced by one atom, giving 1,1,1,2-Tetrafluoroethane. R-134 (without the "a" suffix) would have a molecular structure of 1,1,2,2-Tetrafluoroethane.
The same numbers are used with an R- prefix for generic refrigerants, with a "Propellant" prefix (e.g., "Propellant 12") for the same chemical used as a propellant for an aerosol spray, and with trade names for the compounds, such as "Freon 12". Recently, a practice of using abbreviations HFC- for hydrofluorocarbons, CFC- for chlorofluorocarbons, and HCFC- for hydrochlorofluorocarbons has arisen, because of the regulatory differences among these groups.[ citation needed ]
ASHRAE Standard 34, Designation and Safety Classification of Refrigerants, assigns safety classifications to refrigerants based upon toxicity and flammability.
Using safety information provided by producers, ASHRAE assigns a capital letter to indicate toxicity and a number to indicate flammability. The letter "A" is the least toxic and the number 1 is the least flammable. [79]
Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are fully or partly halogenated hydrocarbons that contain carbon (C), hydrogen (H), chlorine (Cl), and fluorine (F), produced as volatile derivatives of methane, ethane, and propane.
Isobutane, also known as i-butane, 2-methylpropane or methylpropane, is a chemical compound with molecular formula HC(CH3)3. It is an isomer of butane. Isobutane is a colorless, odorless gas. It is the simplest alkane with a tertiary carbon atom. Isobutane is used as a precursor molecule in the petrochemical industry, for example in the synthesis of isooctane.
Halomethane compounds are derivatives of methane with one or more of the hydrogen atoms replaced with halogen atoms. Halomethanes are both naturally occurring, especially in marine environments, and human-made, most notably as refrigerants, solvents, propellants, and fumigants. Many, including the chlorofluorocarbons, have attracted wide attention because they become active when exposed to ultraviolet light found at high altitudes and destroy the Earth's protective ozone layer.
Difluoromethane, also called difluoromethylene, HFC-32Methylene Fluoride or R-32, is an organic compound of the dihalogenoalkane variety. It has the formula of CH2F2. It is a colorless gas in the ambient atmosphere and is slightly soluble in water, with a high thermal stability. Due to the low melting and boiling point, (-136.0 °C and -51.6 °C respectively) contact with this compound may result in frostbite. In the United States, the Clean Air Act Section 111 on Volatile Organic Compounds (VOC) has listed difluoromethane as an exception (since 1997) from the definition of VOC due to its low production of tropospheric ozone. Difluoromethane is commonly used in endothermic processes such as refrigeration or air conditioning.
1,1,1,2-Tetrafluoroethane (also known as norflurane (INN), R-134a, Klea 134a, Freon 134a, Forane 134a, Genetron 134a, Green Gas, Florasol 134a, Suva 134a, HFA-134a, or HFC-134a) is a hydrofluorocarbon (HFC) and haloalkane refrigerant with thermodynamic properties similar to R-12 (dichlorodifluoromethane) but with insignificant ozone depletion potential and a lower 100-year global warming potential (1,430, compared to R-12's GWP of 10,900). It has the formula CF3CH2F and a boiling point of −26.3 °C (−15.34 °F) at atmospheric pressure. R-134a cylinders are colored light blue. A phaseout and transition to HFO-1234yf and other refrigerants, with GWPs similar to CO2, began in 2012 within the automotive market.
Chlorodifluoromethane or difluoromonochloromethane is a hydrochlorofluorocarbon (HCFC). This colorless gas is better known as HCFC-22, or R-22, or CHClF
2. It was commonly used as a propellant and refrigerant. These applications were phased out under the Montreal Protocol in developed countries in 2020 due to the compound's ozone depletion potential (ODP) and high global warming potential (GWP), and in developing countries this process will be completed by 2030. R-22 is a versatile intermediate in industrial organofluorine chemistry, e.g. as a precursor to tetrafluoroethylene.
Vapour-compression refrigeration or vapor-compression refrigeration system (VCRS), in which the refrigerant undergoes phase changes, is one of the many refrigeration cycles and is the most widely used method for air conditioning of buildings and automobiles. It is also used in domestic and commercial refrigerators, large-scale warehouses for chilled or frozen storage of foods and meats, refrigerated trucks and railroad cars, and a host of other commercial and industrial services. Oil refineries, petrochemical and chemical processing plants, and natural gas processing plants are among the many types of industrial plants that often utilize large vapor-compression refrigeration systems. Cascade refrigeration systems may also be implemented using two compressors.
An air source heat pump (ASHP) is a heat pump that can absorb heat from air outside a building and release it inside; it uses the same vapor-compression refrigeration process and much the same equipment as an air conditioner, but in the opposite direction. ASHPs are the most common type of heat pump and, usually being smaller, tend to be used to heat individual houses or flats rather than blocks, districts or industrial processes.
Natural refrigerants are considered substances that serve as refrigerants in refrigeration systems. They are alternatives to synthetic refrigerants such as chlorofluorocarbon (CFC), hydrochlorofluorocarbon (HCFC), and hydrofluorocarbon (HFC) based refrigerants. Unlike other refrigerants, natural refrigerants can be found in nature and are commercially available thanks to physical industrial processes like fractional distillation, chemical reactions such as Haber process and spin-off gases. The most prominent of these include various natural hydrocarbons, carbon dioxide, ammonia, and water. Natural refrigerants are preferred actually in new equipment to their synthetic counterparts for their presumption of higher degrees of sustainability. With the current technologies available, almost 75 percent of the refrigeration and air conditioning sector has the potential to be converted to natural refrigerants.
2,3,3,3-Tetrafluoropropene, HFO-1234yf, is a hydrofluoroolefin (HFO) with molecular formula CH2=CFCF3. Its primary application is as a refrigerant with low global warming potential (GWP).
1,1-Dichloro-1-fluoroethane is a haloalkane with the formula C
2H
3Cl
2F. It is one of the three isomers of dichlorofluoroethane. It belongs to the hydrochlorofluorocarbon (HCFC) family of man-made compounds that contribute significantly to both ozone depletion and global warming when released into the environment.
1-Chloro-1,1-difluoroethane (HCFC-142b) is a haloalkane with the chemical formula CH3CClF2. It belongs to the hydrochlorofluorocarbon (HCFC) family of man-made compounds that contribute significantly to both ozone depletion and global warming when released into the environment. It is primarily used as a refrigerant where it is also known as R-142b and by trade names including Freon-142b.
Automotive air conditioning systems use air conditioning to cool the air in a vehicle.
Hydrofluoroolefins (HFOs) are unsaturated organic compounds composed of hydrogen, fluorine and carbon. These organofluorine compounds are of interest as refrigerants. Unlike traditional hydrofluorocarbons (HFCs) and chlorofluorocarbons (CFCs), which are saturated, HFOs are olefins, otherwise known as alkenes.
trans-1,3,3,3-Tetrafluoropropene (HFO-1234ze(E), R-1234ze(E)) is a hydrofluoroolefin. It was developed as a "fourth generation" refrigerant to replace fluids such as R-134a, as a blowing agent for foam and aerosol applications, and in air horns and gas dusters. The use of R-134a is being phased out because of its high global warming potential (GWP). HFO-1234ze(E) itself has zero ozone-depletion potential (ODP=0), a very low global warming potential (GWP < 1 ), even lower than CO2, and it is classified by ANSI/ASHRAE as class A2L refrigerant (lower flammability and lower toxicity).
Fluorinated gases (F-gases) are a group of gases containing fluorine. They are divided into several types, the main of those are hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulphur hexafluoride (SF6). They are used in refrigeration, air conditioning, heat pumps, fire suppression, electronics, aerospace, magnesium industry, foam and high voltage switchgear. As they are greenhouse gases with a strong global warming potential, their use is regulated.
Barbara Haviland Minor is an American chemical engineer, known for the development of refrigerants. She was technical leader for chemical company DuPont in the development of R-1234yf, a refrigerant which, as of 2018, was used in 50% of all new vehicles produced by original equipment manufacturers, and which represented an important contribution to countering global warming.
R-454B, also known by the trademarked names Opteon XL41, Solstice 454B, and Puron Advance, is a zeotropic blend of 68.9 percent difluoromethane (R-32), a hydrofluorocarbon, and 31.1 percent 2,3,3,3-tetrafluoropropene (R-1234yf), a hydrofluoroolefin. Because of its reduced global warming potential (GWP), R-454B is intended to be an alternative to refrigerant R-410A in new equipment. R-454B has a GWP of 466, which is 78 percent lower than R-410A's GWP of 2088.
Life Cycle Climate Performance (LCCP) is an evolving method to evaluate the carbon footprint and global warming impact of heating, ventilation, air conditioning (AC), refrigeration systems, and potentially other applications such as thermal insulating foam. It is calculated as the sum of direct, indirect, and embodied greenhouse gas (GHG) emissions generated over the lifetime of the system “from cradle to grave,” i.e. from manufacture to disposal. Direct emissions include all climate forcing effects from the release of refrigerants into the atmosphere, including annual leakage and losses during service and disposal of the unit. Indirect emissions include the climate forcing effects of GHG emissions from the electricity powering the equipment. The embodied emissions include the climate forcing effects of the manufacturing processes, transport, and installation for the refrigerant, materials, and equipment, and for recycle or other disposal of the product at end of its useful life.
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