FORUM The next generation of refrigerants — Historical review, considerations, and outlook

James M. Calm, Engineering Consultant

ABSTRACT This article reviews the progression of refrigerants, from early uses to the present, and then addresses future directions and candidates. The article breaks the history into four refrigerant generations based on defining selection criteria. It discusses displacement of earlier working fluids, with successive criteria, and how interest in some early refrigerants re-emerged, for example renewed interest in those now identified as “natural refrigerants.” The paper examines the outlook for current options in the contexts of existing international agreements, including the Montreal and Kyoto Protocols to avert stratospheric ozone depletion and global climate change, respectively. It also examines other environmental concerns and further international and local control measures. The discussion illustrates how isolated attention to individual environmental issues or regulatory requirements, in contrast to coordinated responses to the several issues together, can result in unintended environmental harm that almost certainly will require future reversals. It identifies pending policy and regulatory changes that may impact the next generation of refrigerants significantly.

Keywords — refrigerants, environmental impacts, ozone depletion, climate change, global warming, history, status, outlook

1. Refrigerant Jacob Perkins and Richard Trevithick. industrial solvent that Perkins used in his The latter proposed an air-cycle system business as a printer and therefore had Progression for refrigeration in 1828, but again did available. Refrigeration goes back to ancient not build one. Perkins, however, did times using stored ice, vaporization of so with his invention of the vapor- Figure 1 depicts the progression of water, and other evaporative processes. compression machine in the 1830s, and refrigerants from their advent through Numerous investigators in different thus introduced actual refrigerants as we four generations. countries studied phase-change physics in know them. His 1834 patent describes the 1600s and 1700s; their fundamental a cycle using a “volatile fluid for the 1.1 f irst Generation findings set the foundation for “artificial” purpose of producing the cooling and — Whatever Worked (man-made) refrigeration. Oliver Evans freezing … and yet at the same time first proposed the use of a volatile fluid condensing such volatile fluids, and The most common refrigerants for the in a closed cycle to freeze water into ice bringing them into operation without first hundred years were familiar solvents [1]. He described a system that produced waste” [2]. Many refrigeration experts and other volatile fluids; they constituted refrigeration by evaporating ether under recognize his landmark contribution with the first generation of refrigerants, a vacuum, and then pumped the vapor identification of this mechanical vapor- effectively including whatever worked to a water-cooled heat exchanger to compression approach as the Perkins and was available. Nearly all of these early condense for re-use. While there is no Cycle. Although designed to use sulfuric refrigerants were flammable, toxic, or record that he built a working machine, (ethyl) ether as the refrigerant, the first both, and some were also highly reactive. his ideas probably influenced both tests actually used caoutchoucine, an Accidents were common. For perspective,

This article was originally published as: J. M. Calm, “The Next Generation of Refrigerants – Historical Review, Considerations, and Outlook,” International Journal of Refrigeration, 2008(7):1123-1133, 2008, as a requested expansion and update to “The Next Generation of Refrigerants,” paper ICR07-B2-534, Refrigeration Creates the Future (proceedings of the 22nd International Congress of Refrigeration, Beijing, People’s Republic of China, 21-26 August 2007), Chinese Association of Refrigeration (CAR), Beijing, PRC, and International Institute of Refrigeration (IIR), Paris, France, 2007

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eight elements remained, namely carbon, fourth generation nitrogen, oxygen, sulfur, hydrogen, 2010 fluorine, chlorine, and bromine [6]. global warming Within three days of starting, in 1928, zero/low, ODP, Midgley and his colleagues made critical low GWP, short atm observations regarding flammability high efficiency third generation and toxicity of compounds consisting 1990–2010s of these elements. They also noted that ozone protection every known refrigerant at the time (HCFCs), HFCs, NH3, H 0, HCs, C0 , . . . combined just seven of these elements — second generation 2 2 all but fluorine. Their first publication 1930–1990s on fluorochemical refrigerants shows safety and durability how variation of the chlorination and ethers, CFCs, HCFCs, fluorination of hydrocarbons influences HFCs, NH , H 0, . . . first generation 3 2 the boiling point, flammability, and 1830–1930s toxicity [7]. whatever worked Commercial production of R-12 began ethers, C02, NH3, S02, HC00CH3, HCs, H20, in 1931 followed by R-11 in 1932 [8- CCI4, CHCS, . . . 9]. Chlorofluorocarbons (CFCs) and later — especially starting in the 1950s in residential and small commercial Figure 1: Refrigerant Progression air conditioners and heat pumps — hydrochlorofluorocarbons (HCFCs) dominated the second generation of a number of companies marketed rejected sulfur dioxide (R-764) for safety refrigerants. Ammonia continued as, propane (R-290) as the “odorless safety reasons and carbon tetrachloride (R-10) and remains today, the most popular refrigerant” in promoting it over for incompatibility with metals, especially refrigerant in large, industrial systems ammonia (R-717) [3]. A telling, historic in the presence of water. They finally especially for food and beverage advertisement claimed that propane selected dielene (1,2-dichloroethene, processing and storage. “is a neutral chemical, consequently no R-1130) for the first centrifugal machine, corrosive action occurs” and “is neither though this selection then required an deleterious nor obnoxious and should international search to find a source [5]. 1.3 Third Generation occasion require, the engineer can work — Ozone Protection in its vapor without inconvenience” 1.2 second Generation Linkage of released CFCs — including [3]. Continued preference, even today, — Safety and Durability CFC refrigerants — to depletion of of ammonia over hydrocarbons in protective ozone catalyzed the third The second generation was distinguished industrial applications suggests that high generation with focus on stratospheric by a shift to fluorochemicals for safety flammability was and remains a greater ozone protection. The Vienna and durability. Repeated leaks, of then concern in large systems. Convention and resulting Montreal prevalent methyl formate (R-611) and Protocol forced abandonment of The first documented, systematic search sulfur dioxide (R-764), retarded early ozone-depleting substances (ODSs). for a refrigerant offering a practical efforts to market domestic refrigerators Fluorochemicals retained the primary design with improved performance to replace iceboxes. With direction focus, with emphasis on HCFCs came in the 1920s, with examination that “the refrigeration industry needs for interim (transitional) use and of refrigerants for chillers [4]. Willis a new refrigerant if they expect to get hydrofluorocarbons (HFCs) for the longer H. Carrier, known for his advances in anywhere,” Thomas Midgley, Jr., and his term. The shifts sparked renewed interest psychrometrics and air conditioning, associates Albert L. Henne and Robert R. in “natural refrigerants” — particularly and R. W. Waterfill investigated a range McNary first scoured property tables to ammonia, carbon dioxide, hydrocarbons, of candidate refrigerants for suitability find chemicals with the desired boiling and water — along with expanded use in positive-displacement and centrifugal point. They restricted the search to of absorption and other not-in-kind (radial turbo) compression machines those known to be stable, but neither (those not using vapor-compression with focus on developing the latter. They toxic nor flammable. The published systems with fluorochemical refrigerants) concluded (without analysis of trans- boiling point for carbon tetrafluoride approaches. Public and private research critical cycles) that the performance of (R-14) drew attention to the organic programs systematically examined both carbon dioxide (R-744) would depend fluorides, but they correctly suspected additional non-fluorochemical and on the cycle and amount of liquid the actual boiling temperature to be hydrofluoroether (HFE) candidates, but subcooling, but that it yielded the lowest much lower than published. Turning to yielded few promising options. predicted performance of the fluids the periodic table of elements, Midgley analyzed. They also noted that ammonia quickly eliminated those yielding Manufacturers commercialized the first and water (R-718) would require excessive insufficient volatility. He then eliminated alternative refrigerants in late 1989 and, stages for centrifugal compressors for the those resulting in unstable and toxic within 10 years, introduced replacements conditions sought, and that water “gives compounds as well as the inert gases, for most ozone-depleting refrigerants. a low efficiency of performance.” They based on their low boiling points. Just Non-Article 5 (mostly-developed)

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countries, sometimes referred to as Article 2 countries, phased out CFC refrigerant use in new equipment by 1996, as required by the Montreal Protocol [10]. Article 5 countries will do so by 2010, and some (for example, China) will do so earlier. The “Article 5” distinction relates to the level of prior usage of ozone-depleting substances as defined in the Protocol. Except as restricted by national regulations, continued use and service are allowed for existing equipment employing CFC refrigerants until otherwise retired. The transition from HCFCs also is underway. The Montreal Protocol limits consumption (defined as production plus imports less exports and specified Figure 2: Severity of the Ozone Hole based on NASA data [14]: Ozone levels declined and the “ozone hole” (area with a level less than 220 Dobson units) grew until 1998. destruction) of HCFCs in steps in 1996 Both the minimum ozone level and area reflect stabilization or improvement since 1998, (freeze at calculated cap), 2004 (65% of but with annual variability (most noticeably in 2002 and to a lesser extent in 2006). cap), 2010 (25%), 2015 (10%), and 2020 An orbiting instrument failure precluded meausrements in 1985. (0.5%) with full consumption phaseout by 2030 in non-Article 5 countries [11]. solvents. Second and at least comparable (atm) in selection of alternatives, to Individual countries adopted different in importance to the refrigerant avoid a repetition of atmospheric buildup response approaches. Most Western – replacements, the environmental before discovery of new concerns that and central-European countries concerns prompted major changes in may arise in the future. While short accelerated HCFC phase outs, while the design, manufacturing, installation, lifetime (ideally less than one year) is majority of other developed countries service, and ultimate disposal procedures desired, compounds having too short set limits by phasing out propellant and to reduce avoidable refrigerant emissions (days or weeks depending on the location blowing agent (especially R-141b) uses [12]. Third, the ozone layer is recovering and decomposition products) may early, requiring phaseout of R-22 (the most despite episodic reports of record ozone result in degraded air quality, including widely used refrigerant today) by 2010 holes in the Antarctic [13]. The size of contribution to urban smog. The impacts in new equipment, and then banning all the annual Antarctic hole results from and safety of the decomposition products HCFC use in new equipment by 2020. The variable factors such as southern polar also can be concerns. schedule for Article 5 countries begins with a freeze in 2013 (based on 2009-2010 winds and oscillations, which induce the production and consumption levels) with polar vortex, and winter temperature 1.4 fourth Generation declining limits starting in 2015 (90%), severities that regulate the efficiencies — Global Warming of ozone destruction and natural 2020 (65%), 2025 (32.5%), and 2030 The very successful response to ozone (2.5%) followed by phaseout in 2040 [11]. replenishment. International scientific assessments document that both new depletion stands in sharp contrast to Again, continued future use and service, the deteriorating situation with climate even after 2040, is allowed for existing ODS releases and residual prior emissions are declining [13]. Scientists interpret change, as depicted in Figure 3 based on equipment employing HCFC refrigerants references [15] and [16]. New findings until otherwise retired except as restricted the minimum ozone concentration and minimum ozone area trends depicted and political debate of global warming by national regulations [10,11]. Exports have become daily events, especially in from Article 5 countries into non-Article in Figure 2 as indicating stabilization in recent years and the start of recovery, recent months. The Intergovernmental 5 countries are effectively restricted to Panel on Climate Change (IPCC) Fourth meet the more stringent non-Article 5 since the worst year in 1998 [14]. The progress in ozone recovery is even more Assessment Report (AR4) reflects the schedules. To avoid separate domestic latest scientific consensus, namely evident when measured by global mean and export products and to exploit newer that “warming of the climate system ozone rather than ozone in the isolated technologies derived from joint ventures is unequivocal, as is now evident from Antarctic vortex. and licensing agreements, some products observations of increases in global in Article 5 countries incorporate While increasing ODS emissions could average air and ocean temperatures, replacements earlier than required. exacerbate ozone depletion and prolong widespread melting of snow and ice, Three points warrant notice. First, or preclude recovery, opportunities and rising global average sea level” [17]. refrigerants historically constituted only to accelerate ozone layer recovery The assessment concluded that “most a minor fraction of total ODS emissions, significantly are much more limited, of the observed increase in globally but most of the same CFCs and some of especially considering the huge influence averaged temperatures since the mid-20th the HCFCs in common use as refrigerants of previously released CFCs, halons, and century is very likely due to the observed also were used in much more emissive other ODSs having long atmospheric increase in anthropogenic greenhouse applications, including as aerosol lifetimes. This point suggests focal gas concentrations” and that “discernible propellants, foam blowing agents, and consideration of atmospheric lifetime human influences now extend to

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other aspects of climate, including fourth generation of refrigerants defined measures is a ban on R 134a in its largest ocean warming, continental-average by focus on global warming. and, as a refrigerant, its most emissive temperatures, temperature extremes and application — mobile air conditioners. The European Parliament set the timing wind patterns” [17]. The adopted GWP limit intentionally with a directive that bans fluorochemical allows consideration of low GWP HFCs The Kyoto Protocol, pursuant to the (“F-gas”) refrigerants having GWPs (notably R-152a even though flammable). United Nations Framework Convention exceeding 150 for 100-yr integration The F-gas measures also sanction more- on Climate Change (UNFCCC), sets in air conditioners for new model stringent national regulations, some of binding targets for greenhouse gas automobiles effective 2011 and for all new which prohibit HFCs in large systems, (GHG) emissions based on calculated automobiles starting in 2017 [19]. The explicitly ban HFC use in chillers, or equivalents of carbon dioxide, methane, adopted regulations also require periodic impose GWP-weighted excise taxes on nitrous oxide, HFCs, perfluorocarbons inspection of stationery systems using HFC refrigerants. Unions in Europe are (PFCs), and sulfur hexafluoride [18]. HFCs [20]. The EU Parliament rejected pushing for adoption of more stringent It does not address ODSs covered by recommended measures that would have measures to curb greenhouse gas the Montreal Protocol, although some banned HFCs as aerosol propellants by emissions. A number of states and cities also are very potent GHGs. National 2006, as foam blowing agents by 2009, in the USA have proposed restrictions on laws and regulations to implement and as refrigerants in stationery air GHG emissions, either individually or the Kyoto Protocol differ, but they conditioners and refrigeration by 2010. regionally, though the specific impacts on typically prohibit avoidable releases of The contentious vote on the last item individual HFCs is uncertain. A frequent HFC and PFC refrigerants and in some was 262-368, more than 40% in favor. bellwether state and the one with the countries also control or tax their use. This significant support level invites largest population, California passed More recent measures (either adopted future reconsideration, especially with new legislation in late 2006 imposing or proposed) at regional, national, state, recent scientific findings regarding more a first-in-the-nation emissions cap on and municipal levels are more stringent. rapid and more severe onset of climate utilities, refineries, and manufacturing These restrictions are forcing shifts to a change. The immediate effect of these plants, with a goal of cutting greenhouse

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operating, and servicing technicians. The further rapid and strongly optimistic responses [21-23] to the F-Gas GWP limit for automotive refrigerants — the start of the next generation — send a signal to regulators that refrigerant options exist to meet more sustainable environmental goals than embodied in the current Montreal and Kyoto Protocols. However, four very important points warrant consideration. First, manufacturers previously had examined and even conducted limited tests of key replacement refrigerants. Records specifically document tests of non-ODS refrigerants to replace CFCs, for example developmental use of R-134a in domestic refrigerators, more than ten years before the Montreal Protocol Figure 3: Global Temperature Rise (based on references [15-16])): Analyses of tree rings, coral reefs, ice cores, and other proxy indicators show the 1990s to be the warmest decade [27]. Except as blend components (such in the last millennium and the 20th century to be its warmest century. as R-152a in R-500 and R-23 in R-503), the industry avoided HFC refrigerants gas emissions back to 1990 levels by 2020. These companies have released based on lubricant considerations prior The law requires the state regulatory body preliminary environmental, safety, and to ODS phaseout, though recognized as to determine actual requirements. The performance data, but they are restricting candidates as early as 1928. Second, the California changes are likely to impose full disclosure of the refrigerant replacement refrigerants generally are less requirements for low GWP refrigerants compositions for competitive reasons, efficient than earlier choices. With a few in new vehicle systems and prohibit because final formulations still are exceptions, the efficiency gains achieved in recharging of leaky systems by unlicensed being honed, and because full data do machinery using the alternative refrigerants technicians. Other measures may not exist yet. Some of the underlying derive primarily from improvements in equipment design rather than the properties restrict the HFCs used in commercial patents afford insight into the substances of newer working fluids. Simply put, better refrigeration systems. At least eight other considered, either individually or as blend optimization with the old refrigerants states are prone to follow California’s lead components (for example [25] and [26]). would have yielded even higher efficiency in if it does regulate HFC uses or emissions. Table 1 expands this information with most cases, and the alternative refrigerants A number of Northeastern and Mid- the author’s perceptions on candidate reduce margins for further product Atlantic states joined in a pact in 2007 to components for the next-generation efficiency improvement [28]. Third, none of impose caps on power plant emissions refrigerants. The patents suggest that the current or candidate refrigerants is ideal, and encourage trading of allowances some candidates and uses may require and future discovery of ideal refrigerants is among utilities and the Governors of compatibilizers (such as anti-foam extremely unlikely [28]. The intensifying five states agreed in 2007 to the Western additives or metal-surface deactivators), constraints force new compromises Regional Climate Action Initiative with stabilizers (such as oxidation inhibitors), among different environmental, safety, similar goals. lubricant solubizers, or other additives. performance, cost, and other goals; Some if not all of the manufacturers they do not expand the finite options 2. neXT GENERATION anticipate that the solutions or variants available. And fourth, sequential OF REFRIGERANTS of the solutions identified to satisfy the attention to individual environmental F-Gas requirements will have broader issues risks elimination of important Refrigerant manufacturers quickly application potential. References [21], or even critical options, for balanced responded to the F-Gas directive [25], and [26] specifically identify wider overall solutions, based on minor or even [19] with announcements of new application opportunities, both for negligible impact on single issues [29]. refrigerants. At least three multinational refrigerants in stationary air conditioning manufacturers of refrigerants reported and refrigeration systems and for foam proprietary development of innovative blowing agent and fire suppression 3. Balance refrigerants to meet the GWP limit of applications. The perceived ease in among Different 150 [21-24]. Considering the very large responding to the Montreal Protocol Environmental market value of automotive refrigerant — without apparent compromise in sales, it is safe to assume that most safety, durability, or efficiency — masked Goals refrigerant companies are seeking enormous investments to develop The new refrigerants raise interesting solutions, especially now that some of the third generation refrigerants and questions on the balance between the largest companies are on record as associated lubricants, optimize and build conflicting environmental targets and expecting to meet the F-Gas mandates. manufacturing plants, modify and qualify between environmental goals and Contacts with representative companies component (especially compressor) and safety or compatibility. ODS phase- confirm this expectation. equipment designs, and train installing, outs reduce options to address climate

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both much greater difficulty and more Table 1. Candidates Components urgency for global warming mitigation. These comparisons challenge rote candidates considerations elimination of the few options having “natural refrigerants” efficiency, for NH3 and HCs also insignificant or even indiscernible influence on stratospheric ozone but (NH3, CO2, HCs, H2O, air) flammability significant, or even strong, potential to low GWP HFCs flammability; most suppressants have high mitigate global climate change. Both (R-32, R-152a, R-161, …) GWP environmental issues are important, but the absence of ideal candidates that solve HFEs disappointing thus far, still ? both concerns jointly, without degrading HCs, HEs safety, requires balance among objectives. flammability (R-290, R-600, R-E170, …) Although speculative, the framers of the Montreal Protocol probably would have short atmospheric lifetime and therefore unsaturates (olefins) exercised more care in broad elimination low GWP (R-1234yf, …) of chemicals by class, rather than by flammability? toxicity? compatibility? individual determination, had there been HFICs, FICs expensive, ODP>0 but not in MP current awareness of the severity of global (R-31I1 (CH2FI), R-13I1 (CF3I), …) some are toxic; compatibility? warming and recognition of response limitations at the time. Nevertheless, the fluorinated alcohols (-OH) efficiency? flammability? toxicity? Protocol provided for future adjustments fluorinated ketones (-(C=O)-) compatibility? based on scientific assessments, which offers an option — albeit a difficult one others ??? — no ideal refrigerants politically — for revisions to address the © 2006.10 James M. Calm few but significant cases of this type.

Table 1: Candidates and Blend Components for Low GWP Refrigerants Other issues arise in environmental trade-offs. The primary replacement change either from direct consequences by 2040 in Article 5 countries; these selected by manufacturers for R-22, or from indirect consequences such phaseout mandates address all HCFCs currently the most widely used refrigerant, as energy-related emissions. Two rather than R-123 uniquely. The latest is R-410A (a blend of HFCs R-32 and examples are conflicting goals for R-13I1 [31] and prior international assessments R-125). This substitute offers practically (CF3I, a fluoro-iodocarbon, FIC) as of options notes that R-123 has a very zero ODP. However, it increases the GWP a potential component in low GWP low overall impact on the environment by 16% (from 1810 to 2100 for 100-yr automotive refrigerants [25] and R-123 because of its low ODP, very low GWP, integration) and lowers the attainable (an HCFC) as a chiller refrigerant [30]. very short atmospheric lifetime, very efficiency by 6%, thereby increasing These two refrigerants both offer short low emissions in current chiller designs, energy-related greenhouse gas emissions, atmospheric lifetime, very low GWP, and high efficiency. Another recent for conventional air conditioners with low acute inhalation toxicity, and non- international assessment, also prepared simple cycles based on thermodynamic flammability; both are effective fire to guide revisions of the Montreal cycle analysis [33]. Other factors, such suppressants. However, both have very Protocol, suggests reconsideration of as the blend’s superior heat transfer, and extent of the equipment optimization low, but non-zero ODP — 0.011-0.018 earlier proposals regarding phasing out enable matching or even improvement of (modeled) depending on the latitude all ODSs. It indicates that “production efficiencies at standard rating conditions and altitude of release for R-13I1 and and consumption of specific chemicals for minimum allowable performance 0.02 semi-empirical (0.012 modeled) for proved to be harmless to the ozone layer levels, but not for the best efficiencies that R-123 [13,31]. R-13I1 offers potential as could be permitted after the assessment a blend component in combination with can be reached.. While all refrigerants through an adjustment of the Protocol” theoretically can reach similar efficiencies fluorinated olefins (unsaturated alkenes) [32]. For now, the Montreal Protocol to suppress their flammability while with sufficient cycle modification and allows limited production of R-123 and optimization [34,35], each element minimizing GWP. Despite being an ODS, other HCFCs for service needs until 2030 albeit with very low ODP, R-13I1 is not of added complexity increases costs, in non-Article 5 (developed) countries refrigerant charge (amount), the controlled by the Montreal Protocol since and until 2040 in Article 5 countries. It it was not in commercial use in 1992, potential for leaks, and thermodynamic imposes no limit anywhere for continued irreversibilities and decreases reliability the last time substances were added to use and service of existing equipment the Protocol. R-123 is the most efficient [28]. Hence, refrigerants with high or stockpiled or recovered refrigerant. efficiencies in simple cycles have an refrigerant for water chillers other than These examples illustrate clear conflicts inherent advantage to improve efficiencies R-11 and R-141b [31], both of which have in environmental objectives to address at lower costs and with lower system risk significantly higher ODP and higher ozone depletion and climate change. of environmental harm. GWP [13,31]. Still, R-123 already was phased out in Europe as an HCFC and Comparing Figure 2 and Figure 3, In addition, the efficiency of R-410A is scheduled, barring reconsideration, as well as the options to address and degrades more rapidly than that of R-22 for similar phaseout in new chillers by consequences of stratospheric ozone at increasing ambient temperatures 2020 in non-Article 5 countries and depletion and climate change, suggests approaching the R-125 critical

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temperature, so the peak power demand 4. Recent process control, and possibly also cleanup is higher with R-410A for air-cooled procedures, to prevent inclusion of systems for the same rated capacities and Developments toxic contaminants. As with the R-1225 seasonal efficiencies. The increased peak and the Outlook isomers, further toxicity studies could demand is especially severe in locations for Broader reveal unanticipated, adverse effects, with inadequate electricity generation or Acceptance since unsaturated compounds often transmission reserves, including those in exhibit unacceptable toxicity. The cost developing countries already challenged of “Natural of R-1234yf is likely to be significantly to provide sufficient and affordable Refrigerants” higher than for R-134a, especially power capacity for development. The initially. Still, at least two major chemical Technology, market, and policy changes disadvantage also impairs substitution manufacturers working jointly [24] have influencing future refrigerants are changing redirected their focus to R-1234yf in of sustainable electricity generation, to rapidly. Recent toxicity findings ended reduce combustion of and dependence on direct expansion systems [36] and the further consideration of at least three major automobile manufacturers now are fossil fuels with associated greenhouse gas refrigerant blends (identified as AC-1, evaluating it. emissions, since solar, wind, and similar DP-1, and JDH) to replace R-134a for generation technologies tend to have automotive uses. Likewise, R-13I1 did not Most manufacturers also terminated higher first costs. In contrast to R-410A, meet acceptance criteria, based on stability R-152a pursuit as a global alternative in R-32 and some other R-32 blends avoid and uncertainty regarding the acceptability direct-expansion systems predicated on the sharp performance decline at higher of its ODP, thereby eliminating primary its limited flammability, despite difficulty ambient temperatures and offer both consideration of an R-1234yf/13I1 blend in ignition when released into engine higher seasonal efficiencies and much (Fluid H) [36]. These four blends, often compartments, concluding that it “is not lower GWPs [33]. They are, however, collectively identified as the “Global suitable for use in vehicles not designed for marginally flammable. Alternative Refrigerant” (GAR) candidates flammable refrigerants” [41]. Evaluation progressed from very promising in 2006 continues in indirect systems with Fluoro-olefins, such as those under and early 2007, during vehicle trials, to identified advantages especially in small consideration as low GWP automotive abandoned in late 2007 [36,37]. vehicles and in warm climates [42,43]. refrigerants, generally are more reactive than compounds with only single The automotive industry now is pursuing Many studies are evaluating carbon carbon-carbon bonds. This reactivity three primary candidates to replace R-134a dioxide and other “natural refrigerants” in stationary applications. Carbon leads to shorter atmospheric lifetime, in mobile air conditioners, namely carbon dioxide use in the low stage of cascaded lower ODP (for those containing dioxide and R-1234fy in direct expansion systems for industrial refrigeration is now chlorine, bromine, or iodine), and lower systems and R-152a in indirect (“secondary common, though it primarily displaces GWP, but also to decreased stability and loop”) systems employing an intermediate heat transfer fluid (HTF). Despite carbon ammonia use in this application. higher toxicity. Likewise, chemicals with dioxide’s appeal as a “natural refrigerant” Carbon dioxide use in heat pump the lowest GWPs tend to decompose and favorable findings in some reported water heaters (HPWHs) is increasing, near the surface, often predominantly bench and vehicle tests [38,39], concerns especially in Japan where service-water in proximity to the location of release. exist with the system complexity and heating accounts for approximately Some may be smog progenitors, and weight, especially in small vehicles and 30% of residential energy use. Since others may decompose or contribute hot climates, and resulting impacts on commercialization in 2001, cumulative directly or catalytically to formation overall emissions including penalties from shipments of the EcoCute HPWH topped of other chemicals with higher GWPs increased fuel consumption. Still, several one million units in 2007 [44]. Annual than the original chemical, hence manufacturers plan its introduction to installations now exceed 500,000 units presenting higher indirect than direct meet the EU F-gas schedule and tout its per year [44] and the Japanese industry GWP. The indirect GWPs for most advantages, particularly in a heat pump expects cumulative sales exceed 5.2 small hydrocarbon alkanes and olefins mode now considered an option for vehicle million units by 2010 [45]. Some of the (alkenes) exceed their direct GWPs,but heating for cold climates with anticipated initial EcoCute success depended on the influences of temperature, latitude, improvement in engine efficiency. government and utility subsidies of 47 altitude, and even presence of other billion yen since 2002, or approximately As a single-compound refrigerant, atmospheric pollutants complicate ¥47,000 (€290, $420) per unit [46,47]. R-1234yf offers similar thermophysical determination of net GWPs for them. The costs are still quite high compared properties to R-134a, thus minimizing to those in other countries and broader Resolution of such complications is equipment changes, and has met criteria beyond the focus of this article. The issue application outside Japan is likely to for stability and compatibility [36]. It also require further cost reductions [47]. is raised only to illustrate the complex offers an exceptionally low direct GWP interactions and unavoidable trade-offs of 4 on a 100-yr integration basis [40]. Carbon dioxide use also is increasing, (compromises) among environmental Chronic (long-term, repeat exposure) especially in Europe, for commercial goals even beyond consideration of ozone and reproductive toxicity testing of refrigeration both as a refrigerant and depletion and global warming or between R-1234yf is incomplete, but the results in indirect (“secondary loop”) systems the refrigerant-related (“direct effect”) for acute (short-term, single exposure) as an HTF [31]. The latter application and energy-related (sometimes identified and subchronic (intermediate term, both facilitates significant reduction as “indirect effect,” not the same as repeat exposure) are favorable [36]. in refrigerant charge amount and indirect GWP) emission impacts. Its production will require stringent opens further prospects for use of

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ammonia, ammonia blends (such as one which lead manufacturers to fear having in other locations, particularly in warmer commercialized with R-E170, dimethyl to defend against assertions of cause of or climates commonly using larger chillers ether) hydrocarbons, R-152a, and other contribution to domestic fires given the in proximity to densely occupied spaces. flammable refrigerants for both retail availability of nonflammable alternatives. display cases and preparation and storage The situation is quite different from use Water continues as the primary refrigerant areas in supermarkets [31]. of natural gas and other hydrocarbons in in large absorption chillers and chiller cooking and water-heating appliances, heaters, primarily those using lithium Hydrocarbon refrigerants, notably for which there is general acceptance that bromide as the absorbent. Despite R-600a (isobutane) and isobutane a flammable substance is unavoidable. occasional citation of water use in smaller blends, have displaced R-12 and later Flammability and explosion hazards absorption systems, its primary role R-134a and now dominate in domestic generally impede hydrocarbon use in there is with ammonia as the refrigerant refrigerators in Europe, but not in North large capacities, except in chemical and water as the absorbent. Studies are America and especially not in the United process applications for which the underway to further develop chillers States [31]. Although widely perceived processes themselves present greater using water and especially so to cool deep as a safety concern, that is not the case hazards and already are protected. mines, for which there is heightened for refrigerators that have very small refrigerant charge amounts (typically less One of the oldest refrigerants, ammonia sensitivity pumping burdens and to than 120 g, ¼ lb). The major appliance remains the refrigerant of choice in subsurface refrigerant leaks whether manufacturers operate globally and industrial systems and especially so for flammable or nonflammable. The need could not deem hydrocarbons safe in food and beverage processing, which for operation in deep vacuum and use Europe but unsafe in the USA. Typical often require large internal volumes of multistage compressors — typically refrigerator sizes are larger in the USA and flexibility in system modification, axial designs — in large capacities than in Europe, but are more comparable as well as storage. Ammonia interest employing turbo-compressors, limits to those in Japan and Korea where renewed in Europe and especially so attraction to water for mechanical- isobutane use also is increasing in in northern Europe. Concerns with its vapor-compression chillers, though refrigerators and vending machines. The flammability, and to a lesser extent also research continues with some attention distinction lies in tort laws in the USA, skin corrosivity, limit broader acceptance to innovative compressor designs.

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5. Policies and more than 56% of cumulative R-134a concerns and implicit for fluorochemicals production since 1990 has been released meeting new GWP limits, short (but not Regulations to the atmosphere, based on reported too short) atmospheric lifetime should Changes in the policy and regulatory allocation by application sector between also be a criterion. Most importantly, the environment will significantly impact short-, medium-, and long-banking new generation must offer high efficiency future refrigerant choices, as illustrated times [50]. Of the 174 thousand tonnes of or the change to address low GWP will by the immediate focus on new R-134a produced in 2004, the estimated backfire with increased rather than refrigerants to meet the EU requirements releases exceed 72% [50], equivalent to decreased net GHG emissions. While for a low GWP refrigerant in automobiles, release of more than 180 million tonnes the current regulatory pressures address discussed above. Several proposals could of carbon dioxide and pointing to the mobile air conditioners, future extension have dramatic impacts, among them need for low GWP options along with to other applications is almost certain. reconsideration of the failed EU directives improved system efficiencies. Many refrigerants currently viewed as pertaining to stationary air conditioning new alternatives, including many HFCs, The “America’s Climate Security Act,” a and refrigeration systems, also discussed soon could become old rejects. Given bill pending in the U.S. Senate, proposes above. Likewise, the international the scarcity of viable options, future a cap-and-trade program to reduce community agreed in late 2007 to the refrigerant selections warrant collective greenhouse gas emissions between “Bali Action Plan” (also dubbed the consideration of all environmental issues 2012 and 2050 [51]. ACSA treats HFCs “Bali Roadmap”) to negotiate by 2009 together, with integrated assessments, separately from the other Kyoto Protocol much more aggressive requirements to rather than piecemeal treatments that mitigate climate change after the end gases by imposing a cap on consumption risk elimination of good overall options of the Kyoto Protocol’s current 2008- (production plus imports less export for minor or even indiscernible impacts 2012 commitment period [48]. Even and qualified destruction) at 300 million for individual issues. ❚ though not adopted, the Bali neotitations tonnes on a carbon dioxide equivalent basis in 2010 declining on a scheduled addresed interim commitments of References 25-40% reductions in greenhouse gas basis to 90 million tonnes by 2037. That emissions by 2020 and 50% (with some 70% decrease significantly understates [1] O. 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