Conventional and Alternative Refrigerants - an overview

Transcription

1 Chapter - 2 Conventional and Alternative Refrigerants - an overview There are a variety of factors that affect the choice of refrigerant for new equipment. These include thermodynamic, chemical, safety and environmental properties, as well as practical and market implications such as cost, global availability of the fluids and system components, and technical familiarity of engineers and technicians. In particular equipment producers tend to consider the offset between GWP and flammability/toxicity according to the intended product market. Another important factor for manufacturers adopting new refrigerants are modifications to production processes, system design and component construction, all of which can impose significant costs on new RAC equipment. These factors are more relevant to larger, global manufacturers where they are seen to employ fewer refrigerant types whereas smaller producers exhibit greater diversification in their choice. 2.1 Refrigerant groups Apart from the natural refrigerants, the following are the major category of chemicals which are being used/proposed as refrigerants. CFCs - chlorofluorocarbons HCFCs - hydrochlorofluorocarbons HFCs - hydrofluorocarbons HCs - hydrocarbons FCs - fluorocarbon In organics HFEs - hydrofluoroethers FICs - fluoroiodocarbons HFOs - fluoroalkenes Blends and Mixtures In many countries, the most common refrigerant options for new systems are presently HFCs, HCs, ammonia and carbon dioxide. Table 2.1 lists the specific fluids 15

2 based on an international assessment report produced under the Montreal Protocol (UNEP, 2002), and the previously used CFCs and HCFCs are also included for comparison. It is important to note that older equipment that was produced with HCFCs and particularly CFCs poses problems when subject to repairs. If it is not possible to use the existing ODS refrigerant because of restrictions, several options are considered: replacement of old systems with new ones designed with a non-ods refrigerant. "retrofit" where the old refrigerant is replaced with a non-ods one but accompanies with oil and material change due to compatibility issues. "drop-in" where the old refrigerant is simply swapped with a non-ods refrigerant. The first option is the most costly, but offers other benefits such as more efficient systems and reduced maintenance. The retrofit option may include changing to an HFC, which requires some time and expenditure to remove all the mineral oil and certain materials from the system and replace them with those suitable for use with HFCs. Using a drop-in refrigerant (typically involving mixtures of HFCs with PFCs and HCs) is the cheapest and most accessible option. It is also possible to drop-in using pure HCs, but this involves modifications to equipment so that the safety features required by standards are addressed. A comprehensive list of refrigerants is provided in Table 2.1, including basic information on composition, normal boiling point (NBP), safety and environmental data Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) CFCs and HCFCs were the standard refrigerants for most RAC applications, and R12 and more so R22 are the reference fluids for the development of new refrigerants. The Belgian chemist Frederic Swarts ( ) described the properties of synthetically produced CFCs. Later, Thomas Midgley ( 1929) of General Motors patented the compounds and technical applications begin. CFCs were developed in the 1930s and Rll, R12 entered in the market as safe, non-flammable and non-toxic refrigerants. They were widely used for many purposes like in aerosol insecticides, deodorant sprays, shaving creams, perfumes, paints, cleaning agents in textile and electrical industries, blowing agents etc., until it was confirmed in the 1980s that 16

3 they were the main source of harm to the ozone layer. The most common ozone depleting refrigerants are R12 (CFC) and R22 (HCFC). In 1970 only, the British scientist James E Lovelock detected the presence of R 11 in atmosphere. The California University in 1974 published that CFCs could be destroying ozone layer. A ban was imposed in USA in 1978 for the use of Rl 1 and R12 in aerosols except for pharmaceutical applications. Various companies sell the same CFCs, HCFCs, HFCs and other products under different names. Freon is a trade name for CFC and HCFC refrigerants used by DuPont. Technically speaking, Freon is a trademark used by the DuPont Corporation for their line of refrigerant products. In general, CFCs and HCFCs have broad compatibility with many materials, adequate solubility with most types of refrigeration oils (although most often used with mineral oils) and are relatively tolerant of contaminants in the system. Amongst the various fluids in these groups, a wide range of pressure/temperature characteristics are available and their favourable thermo physical properties result in good cycle/system efficiency Hydrofluorocarbons (HFCs) HFCs such as R134a, R404Al and R407C have dominated the replacement of CFCs and HCFCs, mainly because they broadly possess similar chemical, thermodynamic and flammability/toxicity characteristics as well as having been extensively marketed by manufactures. However HFCs are more difficult to apply because of poor compatibility with construction materials and in particular mineral oils, which has meant that certain synthetic lubricants, typically polyolesters (POEs) and polyalkylglycols (PAGs) have to be used instead. Moreover, they are less tolerant to contaminants within the system. Most HFCs are used in binary or tertiary mixtures, partially to suit certain desired operating characteristics such as replicating R22. HFCs tend to have low toxicity and are largely non-flammable, although a couple of fluids, such as R32 and R152a that are used in several blends are flammable. In terms of environmental impacts, although HFCs have a negligible ODP they do retain the high GWP characteristic of most fluorinated refrigerants, hence the introduction of certain legislation. Of lesser importance are some other environmental impacts associated with HFC production and emissions, including the release of ozone depleting substances during their manufacture and the production of trifluoroacetic acid as a decomposition product which is highly persistent and bio-accumulative may be harmful to aquatic life. 17

4 2.1.3 Hydrocarbons (HCs) HC refrigerants include a broad range of substances (e.g., R600a and R290) that cover the range of pressure-temperature characteristics of the conventional CFC and HCFC fluids and they have been used since the evolution of mechanical refrigeration. This has been recognized as environmentally conscious, whilst energy savings have been outstanding, about 40 %. Also their good material compatibility and solubility with lubricants is comparable to that of the CFCs. Certain thermo physical properties do differ from the fluorinated fluids, particularly in terms of lower density and higher latent heat. The most significant property associated with HCs is that they are all flammable (but low toxicity), which means that certain safety measures not normally applied to refrigeration and air conditioning equipment must be adhered to. Hydrocarbons are highly flammable and when released, contribute to the lower atmospheric ozone pollution (photochemical smog). Apart from this issue, their ease of application, good efficiency and negligible GWP makes them attractive refrigerants. Hydrocarbons such as isobutene, butane and propane are used in some small charge systems such as domestic appliances and small air-conditioners. Chinese refrigerator design and manufacture is being geared to hydrocarbon technology instead of the American HFC chemical refrigerants. The first Australian hydrocarbon refrigerator, using 'Greenfreeze' technology was produced by in Greenfreeze has become the dominant refrigerator technology in Europe. Many models of Greenfreeze refrigerators are now on sale in Germany, Austria, Denmark, France, Italy, Netherlands, Switzerland and Britain. 'MUSICOOL' is an established hydrocarbon refrigerant by PT Pertamina - Indonesia. It is used in motor vehicle airconditioning, split/window systems, water dispensers and cold storage systems, mostly in Australia, Canada, Europe, Japan and US. Hydrocarbon based refrigerators are available in India, also Carbon dioxide (R744) Carbon dioxide (CO 2 ) is another fluid that has been used as a refrigerant in vapour compression systems of many types for over 130 years, but it is only in the last decades that inventive minds and modern techniques have found new ways to exploit the uniquely beneficial properties of this remarkable substance. Carbon dioxide was probably the cheapest available refrigerant. One system patent even describes it as a 18

5 by-product of the production of calcium chloride, used as the brine for the ice-maker [l]. It has good chemical compatibility with common materials and relatively good solubility with a number of oils. Whilst non-flammable, CO 2 is toxic at moderate concentrations, particularly above 5% by volume in air. Also, CO 2 has no ozone depletion potential, negligible GWP and has no other serious environmental problems associated with it. The notable difference between CO 2 and other common refrigerants is its pressure temperature characteristics, and in particular a low critical temperature. This means that it either operates with a limited (low) condensing temperature, or it must be used in a "transcritical" or "supercritical" cycle that differs from conventional compression cycles. In a transcritical cycle the refrigerant in a supercritical state is discharged from the compressor and enters a "gas-cooler" (rather than a condenser) where its temperature is reduced before being expanded into a liquid and vapour state, usually in the evaporator. CO 2 also operates at significantly higher pressures and has a very high latent heat when compared to most conventional refrigerants. The basic transcritical cycle is potentially less efficient than a conventional compression cycle because it suffers from larger thermodynamic losses. Higher heat rejection temperatures result in greater throttling losses and so the theoretical cycle work increases and refrigerating capacity is reduced. Although the excellent thermo physical properties of CO 2 mean that performance within the heat exchangers and compressor are generally better than with conventional refrigerants, it is not always sufficient to overcome the additional losses associated with transcritical operation. This is manifest in the significant research efforts on means to improve cycle efficiency, such as development of expanders (instead of expansion valves), ejectors and interchangers so that losses can be recovered Ammonia (R 717) Ammonia has been used a lot in freezing works and large cold-stores continuously for many years and is well understood. Unlike HCFC, HFC and HC refrigerants, ammonia (in the presence of small amounts of contaminants) is incompatible with a number of materials otherwise commonly used in refrigeration systems, and it is immiscible with most lubricants. The pressure temperature characteristics of ammonia are similar to R22, whilst the latent heat is significantly greater than most fluorinated fluids. Ammonia also possesses favourable thermo physical properties, resulting in 19

6 good efficiency. There are safety implications with ammonia both in terms of toxicity (although perceived to be much more severe due to its pungent smell) and moderate flammability. On the other hand it has negligible environmental impacts, i.e., no ODP and nogwp Mixtures and other fluids There are a number of available mixtures that may contain various components including HFCs, HCFCs, HCs, FICs, HFO, and PFCs. These mixtures are generally produced for the purpose of drop-in or retrofit refrigerants. The inclusion of HCFCs or HCs is to provide some solubility with the mineral oils that are used in existing CFC or HCFC systems. In other cases, such mixtures are developed to match particular characteristics of a specific refrigerant that it is intended to replace, or to achieve an improvement in cycle efficiency. Given the possible number of combinations of the various fluids mentioned above, the extent of different characteristics is vast. Mixtures fall into two categories: azeotropes (refrigerants with R5XX designation) and zeotropes (with R4XX designation). Azeotropes behave more or less identically to pure fluids, whereas zeotropes exhibit certain unique characteristics particularly during change of phase. In flooded systems, zeotropes will demonstrate a composition change due to the different vapour pressures of the refrigerant components and a larger difference in vapour pressures normally causes a greater extent of composition change. As the system operates, the component(s) with a lower boiling point accumulate within the high pressure side, and higher boiling point component(s) shift to the low pressure side of the cycle. Consequently compression ratio increases, refrigerating capacity reduces leading to a degradation in system efficiency. In flooded systems, the degree of composition change causes sufficient disruption to the performance of the cycle that they are not recommended for use. In direct expansion (DX) systems composition change occurs to a much smaller extent and instead the range of component vapour pressures is exhibited as a variation in saturation temperature across the phase change, which is known as "glide". Temperature glide for common refrigerants ranges from 0.5 K to about 10 K, and for a given mixture it gets smaller as the saturation pressure I temperature approaches the critical point. In DX systems, glide can be suitably accommodated provided that heat 20

7 exchanger design is addressed. Another impact of the use of a mixture is degradation of two-phase heat transfer in the evaporator and condenser, occurring because of the differential rate of phase change between the refrigerant components. R- Composition NBP ( Safety PL LFL C) ODP GWP number group {kg/m 3 ) (kg/m 3 ) R-11 R-11 (CFC) 24 A R-12 R-12 {CFC) -30 A "100 R-1281 R-12B1 (BCFC) h R-13 R-13 (CFC) -8 1 A R R-1361 (BFC) -58 A R-14 R-14 (PFC) -128 A1 nfa R-22 R-22 (HCFC) -41 A R-23 R-23 (HFC) -82 A R-30 R-30 (HCC) R-32 R-32 (HFC) -52 A R-50 R-50 (methane) -161 A R-113 R-113 (CFC) 48 A R-114 R-114 (CFC) 4 A h R-115 R-115 (CFC) -39 A h R-116 R-116 (PFC) -78 A R-123 R-123 (HCFC)

8 R- Composition NBP ( Safety C) PL LFL number group (kg/m 3 ) (kg/m 3 ) ODP GWP R-124 R-124 (HCFC) - 12 A R-125 R-125 (HFC) -49 A R-'134a R-134a (PFC) -26 A '1300 R-141b R-141b (HCFC) 32 B2 0.0' R-142b R-142b (HCFC) -10 A '1800 R-143a R-143a (HFC) -47 A R-152a R-152a (HFC) -25 A '140 R-170 R-170 (ethane) -89 A R-1150 R (ethene) -104 A R-EHO R-E170 (dimethyl ether) -25 A R-218 R-218 (PFC) -37 A R-227ea R-227ea {HFC) -16 A R-236fa R-236fa (HFC) -1 A R-245fa R-245fa (HFC) 15 B R-290 R-290 (propane) -42 A R-1270 R-1270 (propene) -48 A R-365rnfc R-365rnfc (HFC) 40.'I R-43-10rnee R-43-10mee (FC) A1 0 '1500 R-C3'18 R-C318 (PFC) -6 A R-600 R-600 (butane) 0 A R-600a R-600a (isobutane) - 12 A R-601 R-601 (pentane) 36 A R-601a R-60'1a (isopentane) 28 A R-717 R-717 (ammonia) -33 B R-744 R-744 (carbon dioxide) -78 A R-401A R-22/152a/ /-28.8 A R-40'18 R-22/152a/ /-30.8 A '1060 R-401C R-22/152a/ /-23.8 A R-402A R-125/290/ /-47.0 A R-4026 R-125/290/ /-44.9 A '1960 R-403A R-290/22/ /-42.3 A R-403B R-290/22/ /-42.3 A R-404A R-125/143a/134a -46.6/-45.8 A R-405A R-22/152a/142b/C3' /-24.5 A R-406A R-22/600a/142b -32.7/-23.5 A '1560 R-407A R-32/125/134a -45.2/ A R-4076 R-32/125/'134a -46.8/-42.4 A R-407C R-32/125/134a -43.8/ A

9 R- Composition NBP ( C) number group (kg/m 3 ) (kg/m 3 ) Safety PL LFL ODP GWP R-4070 R-32/125/134a -39.4/-32.7 A R-407E R-32/125/134a -42.8/-35.6 A R-408A R-125/143a/ /-45.0 A R-409A R-22/124/142b -35.4/-27.5 A R-409B R-22/124/142b -36.5/-29.7 A1 0." R-410A R-32/ /-51.5 A R-410B R-32/ /-51.4 A R-41 "IA R-1270/22/152a -39.7/-37.2 A "1330 R-41 "1B R-1270/22/152a -41.6/-41.3 A '1410 R-4 12A R-22/218/142b -36.4/-28.8 A "1850 R-4'13A R-2 18/134a/600a -29.3/-27.6 A "1770 R-414A R-22/124/600a/142b -34.0i-25.8 A R-4146 R-22/124/600a/'142b -34.4/ A R-415A R-22/152a -37.5/-34.7 A R-416A R-134a/124/ /-21.8 A R-417A R-125/134a/ /-32.9 A1 0.'15-0 '1950 R-500 R-12/152a A R-501 R-22/ A R-502 R-22/ A R-503 R-23/ A '13'!00 R-504 R-32/ A R-505 R-12/ A n/k R-506 R-31/ A n/k R-507A R-125/143a A R-508A R-23/ A R-508B R-23/ A '11850 Table 2.1: Refrigerants with R number designation and selected characteristics [52] The environmental protection agency EPA through the Clean Air Act is regulating the production and use of refrigerants. Practically there is no such thing as a perfect refrigerant. All candidates, although technically efficient with regards to energy efficiency for example have undesirable intrinsic properties with regards to health, safety and the environment. In response to the Montreal Protocol, alternative refrigerants were sought, and this search gained importance for a number of existing and new potential substances for applications (where only CFCs and HCFCs were previously used) like hydrofluorocarbons (HFCs), hydrocarbons (HCs), ammonia and carbon dioxide. Simultaneously, attention focussed on the issue of climate change. Subsequently, the 23

10 Kyoto Protocol was developed under the UN in 1997, which prescribes the limitation and reduction of emissions of a group of anthropogenic "greenhouse gases" (GHGs): CO 2, nitrous oxide (N20), methane (CH4), HFCs, perfluorocarbons (PFCs) and sulphur hexafluoride (SF6). Many countries have since published legislation to help meet the Kyoto targets for emissions reduction. In order to quantify the contribution of these gases to climate change, the discussions on climate change in 1990 adopted the use of Global Warming Potential (GWP) of the gas (IPCC, 1990). GWP is a measure of the insulating properties that a gas has on the heat radiating away from the surface of the earth, and is relative to the effect of one kilogram of CO2 I Rl 1 Ozone depletion potential (ODP) = amount of 0 3 depleted by the material I amount depleted by Rl 1 or R12 Global warming potential (GWP) = warming due to unit mass of material emitted I warming due to unit mass of CO 2 or R 11 Ultimately, the political actions have resulted in a drive by the refrigeration and airconditioning (RAC) industry to reduce the environmental impact of systems, manifest as development of new refrigerants and cooling technologies. The related issues like refrigerant options, characteristics of alternative refrigerants, environmental impact, efficiency and applications of alternative refrigerants, refrigerant leakage, recent developments and technical barriers are also to be addressed along with it. The number of available refrigerants is vast. Out of about 110 designated refrigerants (excluding CFCs) only a few are being used extensively in industry. In addition there are several hundred commercially available fluids that have not been allocated an R-number to date. 2.2 Refrigeration & Air Conditioning - End use categories The refrigeration and air-conditioning sector includes eight major end-uses: Domestic refrigeration, commercial refrigeration motor vehicle air-conditioning (MV AC), chillers, 24

11 retail food refrigeration, cold storage warehouses, refrigerated transport, industrial process refrigeration, and residential and small commercial air-conditioning I heat pumps. Each end-use is composed of a variety of equipment types that have historically used ODSs such as chlorofluorocarbons (CFCs) or hydrochlorofluorocarbons (HCFCs). As the ODS phase-out is taking effect under the Montreal Protocol, equipment is being retrofitted or replaced to use RFC-based substitutes or intermediate substitutes (e.g., HCFCs) that will eventually need to be replaced by non-ozone-depleting alternatives. HCFCs are beginning to be replaced with HFCs or other alternative refrigerants. The eight major end-uses are explained in more detail below Domestic Refrigeration This end-use consists of household refrigerators and freezers. Following the phase-out of R12, R134a was adopted within the domestic refrigeration sector in the US and most developing countries but since then R600a has become the established choice throughout Europe and much of Asia including Japan. This is primarily because it enables lower noise levels to be achieved, which is an important factor for residential environments. In addition, R600a offers a slight efficiency improvement over the competing fluids suitable for this application and despite the minute likelihood of leakage its negligible GWP is considered an advantage. Also hydrocarbon (HC) refrigerant, especially isobutane (R600a) is dominating much of the European market and continuing to grow in market share. HC systems are about 40 percent smaller than R 134a (HFC) systems. The equipment has an expected lifetime of 20 years. This end-use is one of the largest in terms of the number of units in use; however, because the charge sizes are small and the units are hermetically sealed (and, therefore, rarely require recharging), emissions are relatively low. Thus, the potential for reducing emissions through leak repair is small. In most Annex I countries [47], where regulations are in place that require the recovery of refrigerant from appliances prior to disposal, the retirement of old refrigerators is not expected to result in significant refrigerant emissions. Refrigerant emissions at 25

12 disposal from developing countries, where refrigerant recovery 1s not generally required, are expected to be greater Commercial refrigeration Commercial refrigeration means the retail food refrigeration systems which include stand-alone units such as vending machines, ice cream freezers, bottle coolers, refrigerated equipment found in supermarkets, convenience stores, restaurants, and other food service retail outlets. Charge sizes range from 6 to 1,800 kilograms, with a lifetime of about 15 years. Convenience stores and restaurants typically use standalone refrigerators, freezers, and walk-in coolers. In contrast, supermarkets usually employ large parallel systems that connect many display cases to a central compressor rack and condensing unit by means of extensive piping. Because the connection piping can be miles long, these systems contain very large refrigerant charges and often experience high leakage rates. During the earlier phases of the CFC phase-out in developed countries, the use of HCFC-22 in retail food refrigeration was expanded considerably. Retail food equipment is being retrofitted with HCFC based blends, although HFC blends are also used as a retrofit refrigerant. Integral units generally use R134a (mainly for medium temperature applications) and R404A (mainly for low temperatures). The HFC blend R-404A is the preferred refrigerant in new retail food equipment in developed countries, while R-507 A is also used extensively in the market. In developed countries, both distributed and centralized systems that use HFCs, HCs, ammonia, and carbon dioxide are being developed (both with and without secondary loops). More recently, the use of R290 and CO 2 and to a smaller extent R600a have been adopted. Remote systems that employ condensing units or a central multi-compressor pack have become limited to R404A because of established industry practice. However, a number of alternative concepts such as indirect and cascade systems are being installed with increasing frequency, and these allow for the use of HCs, CO 2 and ammonia since the various safety implications can be handled in a relatively straight-forward manner. Stationary air conditioning systems includes small window and split units, multi-split systems and central chillers that provide cooling water to air handlers. Most integral and split systems previously used R22 until R407C was introduced, but the larger manufacturers are now adopting R410A due to smaller components and marginal gains in efficiency. R290 is also being used because of its 26

13 favourable environmental characteristics and good efficiency, and for similar reasons systems using CO 2 are being investigated. Although the efficiency of CO 2 in a split type air conditioner has been demonstrated to match that of an R410A system under most conditions, the technology required to achieve comparable efficiencies at higher ambient temperatures (i.e., in the transcritical cycle) are likely to be costly. Multisplit systems are following the trend of shifting from R407C to R410A for much the same reasons, but HCs are not viable because the significantly higher refrigerant charges invoke impractical safety measures prescribed by standards. Most chillers for air conditioning within Europe are positive displacement machines, using reciprocating, scroll or screw compressors. R22 had been the primary choice for these chillers, but the most common refrigerants are now R134a and R407C. Some manufacturers offer chillers using R290, R1270 and ammonia since their installation outside buildings means that conformity to safety requirements is easier. Heat pumps are used for heating occupancies and also to produce domestic hot water, and are in common use in central and northern Europe. These systems had almost exclusively used R22, but recently most manufacturers have offered units with a selection of refrigerants including R290, R407C and lately R410A Motor Vehicle Air Conditioning (MV AC) The global warming issue has led the auto industry to take steps to reduce the emission of green house gases into the atmosphere. But aside from a vehicles IC engine, it also poses a threat to the environment due to the refrigerants they use on automobile cooling units. Currently, automobile air conditioning systems uses HFC 134a. The said refrigerant poses a serious threat to the environment because of its comparable GWP. The quantity of refrigerant contained in a typical large capacity car air conditioner is approximately!kilogram-generally from 1 to 1.2 kilograms for vehicles containing CFC-12 systems, and an average of approximately 0.8 kilograms for vehicles containing HFC-134a systems - although this varies by car and region. Because of concerns over the environmental impact of refrigerants, the average charge size of MV ACs-as well as associated leak rates-have been reduced over time; this trend is expected to continue. The expected lifetime of MVACs is approximately 12 years. Refrigerant use in this sector is significant because more than 700 million motor vehicles are registered globally. In developed countries, CFC-12 was used in MVACs 27

14 until being phased out of new cars in 1992 through Since then, all air conditioners installed in new automobiles use HFC-134a refrigerant. HFC-134a is also used as a retrofit chemical for existing CFC-12 systems. CFC-12 availability in developing countries and in some developed countries (e.g., the United States) has resulted in its use for servicing older MV ACs that were originally manufactured as CFC-12 systems. A variety of refrigerant blends are approved for use in the United States by the USEPA as replacements for CFC-12 in MV ACs. However, these blends have not been endorsed by vehicle or system manufacturers. Globally, these blends have captured only a small and declining share of the retrofit market. There are number of alternative refrigerants from which to choose. One is R-134a, which is the only alternative refrigerant currently approved by all vehicle manufacturers for retrofitting older R-12 NC systems. The vehicle manufacturers say R-134a will cool reasonably well in most R-12 NC systems provided the proper retrofit procedures are followed. They also recommend R-134a because it is a single component refrigerant, unlike most of the alternatives which are actually blends of two to more ingredients. Blends can sometimes undergo "fractionation." This is when the individual ingredients in a blend separate for various reasons. Fractionation can be caused by chemical differences between the refrigerants (lighter and heavier elements do not want to stay mixed), different rates of leakage through seals and hoses (smaller molecules leak at a higher rate than larger ones), and different rates of absorption by the compressor oil and desiccant. Fractionation is a concern because it can change the overall composition of the blend once it is in use, which can affect the performance characteristics of the refrigerant. Fractionation also makes it difficult to recycle a blended refrigerant because what comes out of the system may not be the same mix that went into the system Chillers Chillers are used to regulate the temperature and reduce humidity in offices, hotels, shopping centers, and other large buildings, as well as in specialty applications on ships, submarines, nuclear power plants, and other industrial applications. The four primary types of chillers are centrifugal, reciprocating, scroll, and screw, each of 28

15 which is named for the type of compressor employed. The majority of operating chillers will remain in service for more than 20 years, and some will last 30 years or more. A wide variety of chillers is available, with cooling capacities from 7 kilowatts to over 30,000 kilowatts. The charge size of a chiller depends mostly on cooling capacity and ranges from less than 25 kilograms (reciprocating) to over 2,000 kilograms (centrifugal). HCFC-123 has been the refrigerant of choice as a retrofit option for newer CFC-11 units, and HFC-134a has been the refrigerant of choice as a retrofit option for newer CFC-12 units. The replacement market for CFC-12 highpressure chillers and CFC-11 low-pressure chillers is dominated by both HCFC-123 chillers and HFC-134a chillers in developed and developing countries. Following phase-out of the production of HCFCs (in 2030 for developed countries and 2040 for developing countries), recycled, recovered, and reclaimed HCFCs will continue to be used in most countries. This trend is not the case, however in the European Union, where there are restrictions on the use of HCFCs in new equipment, the production of HCFCs is not permitted beyond 2010, and recycled HCFCs may not be reused beyond In the European Union, HFC-134a will be an important option for chillers, but because of its global warming impact, ammonia chillers are being used as an alternative in some countries. Additionally, HFC-245fa is a potential refrigerant for new low pressure chillers. High pressure chillers that currently use HCFC-22 will ultimately be replaced by several HFC refrigerant blends and HFC-134a chillers. Likewise, existing CFC-11 chillers have been converted to HFC-236fa or replaced with HFC-134a chillers, for use primarily in special applications (e.g., on ships and submarines, and in nuclear power plants). Recently, the commercial feasibility of the use of water vapour as refrigerant for vapour compression chillers with a capacity of 1000 TR has been studied in detail by Brandon et al. [6] Cold Storage Warehouses Cold storage warehouses are used to store meat produce, dairy products, and other perishable goods. The expected lifetime of a cold storage warehouse is 20 to 25 years, and although charge sizes vary widely with system size and design, a rough average is about 4,000 kilograms. Warehouses in developed countries have historically used CFC-12 and R-502 refrigerants and currently use HCFC-22, R-404A, and R-507 A. The latter two refrigerants are expected to replace HCFC-22 in new warehouses. 29

16 Retrofits are also possible; for example, existing CFC-12 cold storage warehouses can be retrofitted with R-401A, and existing R-502 warehouses can be retrofitted with R-402A. Not all cold storage warehouses use halocarbon refrigerants. Many facilities, for example, use ammonia in secondary loop brine systems Refrigerated Transport The refrigerated transport end-use includes refrigerated ship holds, truck trailers, railway freight cars, refrigerated rigid vans/trucks and other shipping containers. Although charge sizes vary greatly, the average charge sizes are relatively small (7 to 8 kilograms). The expected lifetime of a refrigerated transport system is 12 years. Trailers, railway cars, and shipping containers using CFC-substitute refrigerants are commonly charged with HFC-134a, R-404A, and HCFC-22. Ship holds, on the other hand, rely on HCFC-22 and ammonia. In addition to HFC-134a, R-404A can be used in new equipment. Existing equipment can be retrofitted with R-401A, R-402A, R-404A, R-507 A, and other refrigerants. In addition, refrigerated transport equipment includes systems that operate based on the evaporation and expansion of liquid CO 2 or nitrogen Industrial Process Refrigeration Industrial process refrigeration includes complex, often custom-designed refrigeration systems used in the chemical, petrochemical, food processing, pharmaceutical, oil and gas, metallurgical industries; in sports and leisure facilities; and in many other applications. Charge sizes typically range from 650 to 9000 kilograms, and the average lifetime is approximately 25 years. Ammonia, HCs, HCFC-123, and HFC-134a are expected to be the most widely used substitute refrigerants for new equipment in the near future. Upon completion of the HCFC phase-out, HFC-134a, R-404A, and R-507 A are expected to be the primary refrigerants used in this end-use Residential and Small Commercial Air-Conditioning and Heat Pumps Residential and small commercial air-conditioning (e.g., window units, unitary air conditioners, and packaged terminal air conditioners) and heat pumps are another source of HFC emissions. Most of these units are window and through-the-wall units, ducted central air conditioners, and non-ducted split systems. The charge sizes of the 30

17 equipment in this sector range from 0.5 to 10 kilograms for residential systems, and about 10 to 180 kilograms for commercial systems based on cooling capacity requirements. The average lifetime of this type of equipment is 15 years. Residential and commercial air-conditioning has been relying almost exclusively on HCFC-22 refrigerant. R-410A, R-407C and HFC-134a are currently used to replace HCFC-22 in some new equipment for most end-uses, and this trend is expected to continue as HCFC-22 is phased out. In particular, R-410A is expected to dominate the U.S. residential market in the future, whereas R-407C is expected to replace HCFC-22 in retrofit applications and some new residential and commercial equipment. Other countries may experience different patterns of R-410A and R-407C use. 2.3 New refrigerant products The announcement of the European Commission that refrigerants with a GWP > 150 are to be prohibited from MAC systems has generated the development of a number of substances not previously considered, in those countries. The current standard refrigerant for automotive air conditioning is R134a and its high GWP means that it is subject to this restriction. Automotive applications account for approximately half of the global HFC sales (UNEP, 2002) and therefore a significant proportion of the HFC refrigerant business is threatened. Consequently, a number of new synthetic refrigerants are under development as replacements for R134a, and possible fluids include hydrofluoroethers (HFEs, low GWP and low pressure), fluoroiodocarbons (FICs, low GWP and generally toxic) and a group of unsaturated HFCs or fluoroalkenes (HFOs, low GWP), although little else is known about their other properties. There are specific fluids and mixtures (including with HFCs) that are currently under consideration and these include: R152a (HFC) and R1311 (FIC) R32 (HFC) and R1311 (FIC) R1234yf (HFO) and R1311 (FIC) R1234ze (HFO) and R1311 (FIC) R1234yf (HFO) and R1225yez (HFO) R1243zf (HFO) and R1311 (FIC) Manufacturer's claims vary and to date detailed technical information is scarce, but in general they are indicated to have GWP < 150 but potential volatile organic compounds (VOCs), non-flammable, pressure-temperature characteristics and performance close to existing refrigerants, and can use with conventional lubricants. 31

18 2.4 Legislative requirements The possible choice of refrigerant for new systems varies globally as a result of national and regional legislation, but is largely dictated by the requirements of the Montreal Protocol and subsequent amendments. In general, CFCs have already been prohibited in developed countries and phase-out of HCFCs is occurring at present. However, a large number of countries have made national legislation that accelerates these phase-out schedules. Similarly, national and regional legislation for climate change mitigation originating from the Kyoto Protocol will also impact on refrigerant choice. For example, in Denmark, Norway, Austria and Switzerland the use of high-gwp refrigerants is being prohibited in a number of different applications and/or a GWP tax is applied to the purchase of such refrigerants. The UK Government has not produced any specific legislation, although in their Climate Change Programme they provide a general policy on HFCs. This states that "HFCs should only be used where other safe, technically feasible, cost effective and more environmentally acceptable alternatives do not exist", and that "HFCs are not sustainable in the long term [47]. New European legislation (which was agreed in January 2006) has imposed some controls on the use of HFCs (the "F-gas" regulation and directive). The main provisions in the regulation cover: containment through responsible handling during use recycling and end-of-life recovery training and certification for personnel involved in the containment and recovery of f-gases reporting on quantities produced, supplied, used and emitted labelling of products and equipment certain application specific controls on use certain placing on the market prohibitions The directive (Directive 2006/40/EC relating to emissions from air-conditioning systems in motor vehicles) will place restrictions on the types of Mobile Air Conditioning (MAC) systems fitted to vehicles before vehicles are approved for sale, and specifically: 32

19 a two-step phase out of MACs that use f-gases with a GWP greater than 150: 1 January 2011 for new types of vehicle, and 1 January 2007 the sunset date for all new vehicles maximum annual leakage limits within the interim period before the phase out controls on refilling and retrofitting for these systems Both the Regulation and Directive will enter into force in 2006 with the main body of the provisions in the set to apply from one or two years after that date. 2.5 Illegal refrigerants Another class of alternative refrigerants has also appeared on the global market scene: illegal refrigerants. Some products that have been introduced (OZ-12, HC-12a, R-176 and R-405a) do not meet the EPA criteria for environmental acceptability or safety. Flammable refrigerants such as OZ-12 and HC-12a that contain large quantities of hydrocarbons (propane, butane, isobutane, etc.) have been declared illegal for use in MV AC applications, but are still turning up in vehicle systems anyway because of their cheap price. Flammable refrigerants pose a significant danger to the occupants inside a vehicle, should a leak occur. A spark from a cigarette or a switch can ignite the leaking refrigerant causing an explosion and turning the car into a bomb. It takes only a small quantity of a flammable hydrocarbon refrigerant such as propane or butane to create an explosive mixture inside a typical automobile passenger compartment. Frontal collisions can also release the refrigerant if the condenser is damaged, which could result in a severe under hood fire causing extensive damage to the vehicle. There is also a risk to service technicians who might encounter leaks while servicing a vehicle or operating recovery/recycling equipment. Merely topping off an NC system with a flammable hydrocarbon can make the entire charge of refrigerant flammable if the amount added exceeds a certain percentage: 10% in the case of an R-12 system and only 5% with R-134a. That is only a small fraction of hydrocarbon depending on the overall capacity of the system. Flammable refrigerants are used in some stationary applications as well as truck trailer refrigeration units because there is less risk of leakage or fire. Also, the amount of refrigerant is typically much less. 33

20 2.6 Contaminated refrigerants The high price of a refrigerant has also lead to an increase in incidences of virgin refrigerant being adulterated with other less expensive refrigerants. Some suppliers say they now test every single tank of refrigerant to make sure it contains the proper refrigerant and that the quality of the refrigerant meets specifications. The primary threat of contamination is that of accidentally cross-contaminating refrigerants when vehicles are serviced. Because the law requires all refrigerants to be recovered, there is a potential risk of contaminating when recovery and recycling equipment is connected to a vehicle. The problem is compounded by the proliferation of alternative and illegal refrigerants. The dangers of cross-contamination are the effects it can have on cooling performance and component reliability. R-12 and R-134a are not compatible refrigerants because R-134a will not mix with and circulate mineral-based compressor oil (which may lead to compressor failure). Nor is R-134a compatible with the moisture-absorbing desiccant called XH-5, which is used in many R-12 systems. Intermixing refrigerants can also raise compressor head pressures dangerously. Adding R-22 (which is used in many stationary A/C systems but is not designed for use in mobile A/C applications) to an R-12 or R-134a system may raise head pressures to the point where it causes the compressor to fail. Straight R-22 can cause extremely high discharge pressure readings (up to 400 or 500 psi) when under hood temperatures are high. R-22 is also not compatible with XH-5 and XH-7 desiccants used in most mobile A/C systems. R-134a also requires its own special type of oil: either a polyalkylene (P AG) oil or a polyol ester (POE) oil. Some compressors require heavier or lighter viscosity oil for proper lubrication. The aftermarket generally favors POE oil because POE is compatible with both R-12 and R-134a and unlike PAG oil it will mix with mineral oil. Mineral oil, as a rule, should still be used in older R-12 systems. To protect recycling equipment against cross-contamination or bad refrigerant, service facilities should use a refrigerant identifier to check every system before it is serviced. Intermixing different refrigerants can cause cooling problems as well as shorten the life of the A/C compressor. 34

21 2.7 Alternative refrigerants - Indian scenario The following gives the sector wise application of alternative refrigerants used in India. Sub-sector Application Alternative Technology Domestic Household HFC-134a, HFC-152a, Blends and mixtures, Refrigeration Refrigerators and Freezers Hydrocarbons (for refrigerants) and HCFC-22, HCFC b, HCFC-141 b, Hydrocarbons for foaming) Commercial Refrigeration Refrigerated Cabinets HCFC-134a, HFC-152a, Blends and mixtures, Hydrocarbons (for refrigerants) and HCFC-22, HCFC b, Hydrocarbons (for foaming) Water Coolers HCFC-22, HFC-134a Ice-candy machines Walk-in coolers HCFC-22, HFC-134a (refrigerants) and HCFC-14b (foaming) Industrial Cold Storages HCFC-22, HFC-134a, Ammonia Refrigeration Process Chillers HCFC-22, HFC-134a, Ammonia Transport Perishable Transport HCFC-22, HFC-134a, Blends and mixtures Refrigeration Air Conditioning Chillers, Automotive HCFC-123, HFC-134a,HCFC-22 air-conditioning HFC-134a, Blends and mixtures Table 2.2: Application of alternative refrigerants used in India [53] 2.8 Environmental legislations in India - Global Warming, Ozone Depletion The following are the major milestones in the past decades, regarding the global warming and ozone depletion environmental legislations in India. 1. The Air Act 1981, The Air rules The air rules

22 4. The environment (protection) Act, EPA The environment protection rules Environmental Impact Assessment The noise pollution (regulation and control) rules The ozone depleting substances (regulation) rules 2000, subsequent amendments. 2.9 Remarks The current trend all over the world particularly in industry is "sustainability". Sustainable development or sustainability is development that meets the needs of the present without compromising the ability of future generations to meet their own needs. Refrigeration & Air-Conditioning is no exception to it and it is in the mode of sustainability in tune with time. The Montreal Protocol which phases out CFCs and HCFCs initiated the significant research efforts into refrigerants and refrigeration technology, and subsequent environmental legislation arising from the Kyoto Protocol to reduce emissions of GHGs has continued to drive that research. There is an adequate choice of both synthetic and natural refrigerants available for all types of systems and applications. HFCs are the most common fluids used in new systems, typically R134a, R404A, R407C and more recently R410A, and their uptake is largely due to convenience despite having a high GWP. Non-synthetic refrigerants - primarily ammonia (R717), carbon dioxide (R744) and HCs (R600a, R290, R1270) - are increasing in use because of their favourable environmental and performance characteristics. Compared to CFCs and HCFCs, use of these alternative refrigerants poses greater technical challenges, mainly including compatibility, efficiency and safety issues. The tendency until recently had been to adopt new refrigerants that possess similar pressuretemperature and operating characteristics as the ODSs they replace because of convenience in using existing system and component designs. However, the introduction of R600a, R410A and most significantly, CO 2, new systems are being designed in a fashion that departs from the conventional R12, R502 and R22 baselines. Many obstacles exist that have resulted in a slow uptake of certain alternatives. These include actual technical barriers such as overcoming safety issues of flammable and/or toxic refrigerants, design of components for high pressure refrigerants and achieving certain efficiency baselines for refrigerants with poor thermo physical properties. Another form of barrier arises from the perception of the 36

23 field-level industry where the consequence of certain characteristics (such as temperature glide or high operating pressure) is interpreted out of context. Similarly, market competition means that organisations with interests in a particular technology use a number of tactics to promote their own alternatives. Finally, the mindset of the industry as a whole is one that expects a return to a standardised set of a small number of refrigerants for the majority of applications. However, it appears that the norm is actually a disparate group of various refrigerants that will continue to evolve over the next few decades at least. Trad~ (II IIrm liarne Marllfat:1Ufef ijjel); li'omments Table 2.3: Air-conditioning, Commercial and Residential sector [49] 37