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INTERNATIONAL JOURNAL OF ENERGY RESEARCH Int. J. Energy Res. (2010) Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/er.1736

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REVIEW

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A review on recent developments in new refrigerant mixtures for vapour compression-based refrigeration, air-conditioning and heat pump units

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M. Mohanraj,y, C. Muraleedharan and S. Jayaraj

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Department of Mechanical Engineering, National Institute of Technology Calicut, Calicut 673601, India

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SUMMARY

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In the present paper, an attempt has been made to review the performance of new refrigerant mixtures employed in vapour compression-based refrigeration, air-conditioning and heat pump units. The studies reported with refrigerant mixtures are categorized into six groups as follows: (i) hydrocarbon (HC), (ii) hydroflurocarbons (HFC), (iii) HFC/HC, (iv) hydrochloroflurocarbons (HCFC), (v) carbon dioxide (R744) and (vi) ammonia (R717). This paper explores the studies reported with new refrigerant mixtures in domestic refrigerators, commercial refrigeration systems, air conditioners, heat pumps, chillers and in automobile air conditioners. In addition, the technical difficulties faced with new refrigerant mixtures, further research needs in this field and future refrigerant options for new upcoming systems have been discussed in detail. This paper concludes that HC refrigerant mixtures are identified as a long-term alternative to phase out the existing halogenated refrigerants in the vapour compression-based systems. Copyright r 2010 John Wiley & Sons, Ltd.

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KEY WORDS

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vapour compression systems; new refrigerant mixtures; recent developments; refrigerators; commercial refrigeration systems; air conditioners; heat pumps

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Correspondence *M. Mohanraj, Department of Mechanical Engineering, National Institute of Technology Calicut, Calicut 673601, India. y E-mail: [email protected]

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Received 20 December 2009; Revised 28 April 2010; Accepted 28 April 2010

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1. INTRODUCTION 39

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Vapour compression-based systems are generally employed in refrigeration, air-conditioning and heat pump units. During the last century, the halogenated refrigerants have dominated the vapour compressionbased systems due to its good thermodynamic and thermo-physical properties. But, the halogenated refrigerants are having poor environmental properties with respect to ozone depletion potential (ODP) and global warming potential (GWP). The international protocols (Montreal and Kyoto) restrict the use of the halogenated refrigerants in the vapour compressionbased refrigeration systems. As per Montreal protocol 1987, the use of chloroflurocarbon (CFCs) was completely stopped in most of the nations. However, hydrochloroflurocarbons (HCFC) refrigerants can be used until 2040 in developing nations and developed nations should phase out by 2030 [1]. Most of the developed nations reduced the consumption of HCFC

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Copyright r 2010 John Wiley & Sons, Ltd.

refrigerants. The Kyoto Protocol of United Nations Framework Convention on Climate Change (UNFCCC) calls for reduction in emission of six categories of green house gas, which includes hydroflurocarbons (HFCs) used as refrigerants [2]. To meet the global demand in refrigeration and air-conditioning sector, it is necessary to look for long-term alternatives to satisfy the objectives of international protocols. HC and HFC refrigerant mixtures with low environment impacts are considered as potential alternatives to phase out the existing halogenated refrigerants. Only a few pure fluids are having properties closer to the existing halogenated refrigerants. The refrigerant mixtures provide much flexibility in searching new environment-friendly alternatives to match the desirable properties with the existing halogenated refrigerants. The two alternative options are HC and HFC mixtures with lower GWP. HC-based mixtures are environment-friendly, which can be used as 1

M. Mohanraj, C. Muraleedharan and S. Jayaraj

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2.1. Azeotropic mixture

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Azeotropic mixture of the substances is the one which cannot be separated into its components by simple distillation. The Azeotropic mixtures evaporate and condense as a single substance with their properties being different from those of either constituent. The azeotropic mixtures are having boiling points that are lower than either of their constituents. Most of the azeotropic mixtures are binary, which will meet all the system requirements. An azeotropic mixture maintains a constant boiling point and acts as a single substance in both liquid and vapour state. Azeotropic refrigerant mixtures are used in low-temperature refrigeration applications. Ternary azeotrope offers more flexibility in property selection, but exists rarely. The Azeotropic mixtures are most widely used in refrigeration applications. American Society for Heating Refrigeration Air Conditioning Engineers (ASHRAE) designates the azeotropic mixtures with 500 series.

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The use of refrigerant mixtures is becoming of great interest due to the phase-out of pure halogenated refrigerants. Very limited pure fluids are having suitable properties to provide alternatives to the existing halogenated refrigerants. The mixing of two or more refrigerants provides an opportunity to adjust the properties, which are most desirable. The three categories of mixtures used in refrigeration and airconditioning applications are azeotropes, near azeotropes and zeotropes [12].

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2. THEORY OF REFRIGERANT MIXTURES

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alternatives without modifications in the existing systems. But HC refrigerant mixtures are highly flammable, which limits the usage in large capacity systems [3]. The HC refrigerant mixtures are preferred only for small capacity refrigeration units such as, domestic refrigerators, bottle coolers, visi coolers, deep freezers, etc., which require less refrigerant quantity compared with the halogenated refrigerants. HFC mixtures are ozone-friendly, but it has significant GWP. HFC mixtures are not miscible with mineral oil, which require synthetic lubricants (such as polyolester). The synthetic lubricants used with HFC refrigerants are highly hygroscopic in nature, expensive, cause irritation when it comes in contact with skin, which leads to several service issues while retrofitting [4]. To overcome the problems with HC and HFC refrigerant mixtures, hydrocarbons are mixed with HFC refrigerants, which improves the miscibility (with mineral oil) and also reduces the flammability (of HC mixtures) [5]. Earlier investigations reported that HFC/HC mixtures are miscible with mineral oil. The GWP of HFC/HC mixture was also reported to be less than one-third of HFC, when it is used alone. It is possible to mix HC refrigerants with HFC to replace the existing halogenated refrigerants [6]. Earlier reviews in this area include that of Wang and Li [7], who summarized the perspectives of natural working fluids in China for refrigeration and airconditioning applications, which includes both compression and absorption-based refrigeration systems. Gryand [8] presented an overview of various pure HC refrigerants used for refrigeration and air-conditioning applications. Corberań et al. [9] reviewed the standards followed for vapour compression refrigeration system working with HC refrigerants and reported the specific requirements for air-conditioning and refrigerating equipment selected for operating with hydrocarbons. Calm [10] compiled the historical development of pure refrigerants from early use to the present and also addressed future options. Mohanraj et al. [11] collected the performance of the vapour compression-based refrigeration systems working with environment-friendly alternatives and suggested that the refrigerant mixtures are good substitutes for phasing out existing halogenated refrigerants. Following the previous reviews cited above, it is understood that there is no specific reviews reported on refrigerant mixtures. Hence, the present review sets out more broadly about up-to-date study covering the performance of new refrigerant mixtures with special emphasis on studies reported during the last decade. In addition, environmental impact assessment, cost analysis associated with retrofitting, methods for prediction of refrigerant properties, current scenario of refrigerant in refrigeration and airconditioning sectors, technical difficulties and future research needs with refrigerant mixtures are discussed in detail.

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Developments in new refrigerant mixtures

Int. J. Energy Res. (2010) r 2010 John Wiley & Sons, Ltd. DOI: 10.1002/er

2.2. Near azeotropic mixture The objective with near azeotropic mixtures is to extend the range of refrigerant alternatives beyond single compounds. Near azeotropes have most of the same attributes as azeotropes and provide a much wider selection possibilities. A near azeotrope is similar to an azeotrope considering hardware systems design. Near azeotropic mixtures are having very low temperature glide in the range between 0.2 and 0.61C. However, near azeotopic mixtures may alter their composition and properties under leakage conditions. ASHRAE designations for near azeotropic mixtures are in R400 series.

2.3. Zeotropic mixture)

mixture

(non-azeotropic

Zeotropic refrigerant mixtures are blends of two or more refrigerants that deviate from perfect mixtures (like azeotropes). A zeotropic mixture does not behave like a single substance when it changes state. Instead, it evaporates and condenses between two temperatures (temperature glide). The temperature glide range for 2


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3. PROPERTIES OF MIXTURES

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A mixture used as a refrigerant should have certain properties closer to the existing halogenated refrigerants to meet the requirements of system performance, material compatibility and environment considerations. The properties (such as thermodynamic, thermo physical, chemical and environmental) of mixtures used as refrigerants to replace the halogenated refrigerants are discussed in this section [13].

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The thermodynamic requirements of the alternatives pertain to vapour pressure of mixtures, critical pressure, critical temperature, freezing point, normal boiling point, volume of suction vapour per ton, coefficient of performance (COP), power consumption per ton, specific heat ratio, etc. A positive pressure inside the system is required to eliminate the possibility of ambient moisture infiltration into the system. The critical temperature should be very high, so that the condenser temperature line on the pressure enthalpy diagram is far from the critical point, which ensures reasonable refrigeration effect. The critical pressure of the new mixtures should be low. Boiling point of the refrigerants should be low, which will produce low temperature. Freezing point of the alternatives should be lower than system temperatures. The specific heat ratio of the alternative mixtures should be low. Hence, lower discharge temperature can be expected, which will improve the compressor life. Molecular weight of the refrigerant affects the compressor size because the specific volume of the vapour is directly related to it. A low molecular weight refrigerant is preferred for the reciprocating refrigerant compressor. The volume of suction vapour required per ton of refrigeration is an

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3.1. Thermodynamic and thermo-physical properties

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3.2. Chemical properties Under retrofit conditions, compatibility of the refrigerant with materials and chemical interaction between refrigerant and lubricant inside the system is the most important. The refrigerant–lubricant combinations will affect electric insulation properties of the motor winding varnishes and ground insulation sheets. The chlorine-based refrigerant mixtures are miscible with mineral oil, which is user-friendly. However, HFC refrigerant mixtures are not miscible with mineral oil, which requires a synthetic lubricant. This synthetic lubricant is highly hygroscopic in nature and has many service issues. Hence, user-friendly lubricants are preferred for the use of HFC-based refrigerant mixtures. HC refrigerant mixtures are miscible with both mineral oil and synthetic lubricants. Hence, HC refrigerants are preferred as additives with HFC mixtures to overcome the miscibility issue with mineral oil. The safety classification of the refrigerants consists of two alphanumeric characters: alphabet indicates the toxicity and numeric digit indicates flammability of refrigerant as listed in Table I [14].

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indication of the size of the compressor. Reciprocating compressors are preferred with refrigerants having high pressure and small volume of vapour. Rotary compressors are used with refrigerants having low pressure and large volume of suction vapour. Thermodynamic properties of pure refrigerants are listed in Table I [14]. Thermo physical properties such as thermal conductivity and viscosity are required for choosing an alternative. A high thermal conductivity in both liquid and vapour phases is desirable to achieve high heat transfer coefficient in both condenser and evaporator. Similarly, low viscosity in both liquid and vapour phases is desirable to achieve high heat transfer coefficient with reduced power consumption. All the pure and mixed HC refrigerants have lower viscosity and higher thermal conductivity, which results in better condenser and evaporator performance. The liquid density is another factor considered for choosing an alternative. Lower liquid density is preferable to reduce the refrigerant charge requirement. Most of the pure and mixed HC refrigerants are having lower liquid density, which results in less refrigerant charge requirement.

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zeotropic refrigerant mixtures is between 4 and 71C, which depends on the pressure drop in the heat exchangers. The phase change characteristics of the zeotropic refrigerant mixture (boiling and condensation) are non-isothermal. Zeotropic mixtures show different vapour and liquid compositions in equilibrium condition. Zeotropic substances have greater potential for improvements in energy efficiency and capacity modulation. ASHRAE has classified all zeotropic mixtures into a 400 series of refrigerant number. The zeotropic refrigerant mixture offers certain advantages, such as the entropy generation during phase change can be reduced by matching the temperature glides of the refrigerant mixture and secondary heat transfer fluid. However, the major drawback of the zeotropic refrigerant mixture is the preferential leakage of more volatile components leading to change in mixture composition.

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3.3. Environmental properties The halogenated refrigerants are the family of chemical compounds derived from the hydrocarbons (methane and ethane) by substitution of chlorine and fluorine atoms for hydrogen. The presence of halogenated atoms is responsible for ODP and GWP. The first major environmental impact that struck the refrigeration industries is ODP due to man-made chemicals into Int. J. Energy Res. (2010) r 2010 John Wiley & Sons, Ltd. DOI: 10.1002/er


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Table I. Properties of pure refrigerants, Calm and Hourahan [14]. Critical properties

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Boiling point (1C)

ASHRAE code

ODP R11 5 1

GWP 100 year

137.37 120.9 86.47 70.01 52.02 34.03 152.93 136.48 120.02 102.03 100.49 84.04 66.05 48.06 30.07 46.07 188.02 170.03 134.05 44.1 58.12 58.12 17.03 44.01 42.08

198.0 112.0 96.2 25.9 78.2 44.1 82.0 122.3 66.2 101.1 137.2 72.9 113.3 102.2 90 128.8 71.9 102.8 154.1 96.7 152.0 134.7 132.3 31.1 92.4

4.41 4.14 4.99 4.84 5.8 5.90 3.66 3.62 3.63 4.06 4.12 3.78 4.52 4.70 4.87 5.32 2.68 2.98 4.43 4.25 3.80 3.64 11.34 7.38 4.67

23.7 29.8 41.4 82.1 51.7 78.1 27.8 12 54.6 26.1 9 47.2 24 34.8 88.9 24.8 36.6 15.6 15.1 42.2 0.5 11.7 33.3 78.4 47.7

A1 A1 A1 A1 A1 A1 B1 A1 A1 A1 A1 A2 A2 A1 A3 A3 A1 A1 B1 A3 A3 A3 B2 A1 A3

1 0.82 0.034 0 0 0 0.012 0.026 0 0 0.043 0 0 0 0 0 0 0 0 0 0 0 0 0 0

4600 10 600 1700 12 000 550 97 120 620 3400 1300 2400 4300 120 12 20 0.015 8600 3500 950 20 20 20 o1 1 20

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the atmosphere. The chlorine-based refrigerants are stable enough to reach the stratosphere, where the chlorine atoms act as a catalyst to destroy the stratospheric ozone layer which protects the earth’s surface from direct UV rays. The second major environmental impact is GWP, which is due to the absorption of infrared emissions from the earth, causing an increase in global earth’s surface temperature. The infrared radiation cannot pass through the atmosphere because of absorption by green house gases including the halogenated refrigerants. HFC refrigerants have significant values of atmospheric lifetime and GWP compared with chlorine-based refrigerants. The environmental properties of pure fluids are listed in Table I [14].

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Pressure (MPa)

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Temperature (1C)

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R11 R12 R22 R23 R32 R41 R123 R124 R125 R134a R142b R143a R152a R161 R170 RE170 R218 R227ea R245fa R290 R600 R600a R717 R744 R1270

Molecular weight

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4. EXPERIMENTAL AND THEORETICAL STUDIES WITH REFRIGERANT MIXTURES During the last decade, many experimental and theoretical investigations have been reported with new refrigerant mixtures. In this section, the performance of the new refrigerant mixtures used in different Int. J. Energy Res. (2010) r 2010 John Wiley & Sons, Ltd. DOI: 10.1002/er

applications, such as, domestic refrigeration, commercial refrigeration, air-conditioning, heat pump, chiller, automobile air-conditioning and other special purpose applications, is discussed. The refrigerant mixtures are grouped as HC mixtures [15–35], HFC mixtures [36–66], HFC/HC mixtures [67–83], HCFC mixtures [84–87], R744 mixtures [88–91] and R717 mixtures [92,93]. In addition, environmental impact assessment, cost analysis associated with retrofitting, prediction of properties of refrigerant mixtures, lubricants recommended for new refrigerant mixtures are discussed. The refrigerant mixtures that are not designated by ASHRAE are referred as NRM in the tables.

4.1. Hydrocarbon mixtures (HC) Many HC refrigerant mixtures were developed to replace the halogenated refrigerants. HC mixtures are miscible with both mineral oil and synthetic lubricants. Hence, HC mixtures can be used as substitutes without changing the lubricant in the existing systems using HCFC and HFC refrigerants. The properties of HC mixtures discussed in this section used are listed in Table II. 4.1.1. Domestic refrigeration. Jung et al. [15] examined with HC mixture (R290/R600a) as substitute in two 4


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Table II. Properties of HC mixtures as alternatives.

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Refrigerant designation

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R432A R433A NRM NRM NRM NRM

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Composition

By mass

Replaces

Molecular weight

Critical temperature (1C)

Critical pressure MPa

Boiling point (1C)

ODP

GWP

R1270/RE170 R290/R1270 R290/R170 R290/R600a R290/R600 R290/R600/R600a

80:20 30:70 94:06 45.2:54.8 60:40 60:20:20

R22 R22 R22 R134a R134a R134a

42.87 42.68 43.25 51.78 49.7 49.7

99.68 93.69 96.29 117.52 118.7 115.36

4.8 4.54 4.28 3.91 4.07 4.038

43.12 46.05 45 25.48 25.2 27.76

0 0 0 0 0 0

20 20 20 20 20 20

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R600a (with propane mass fractions from 0.5 to 0.7) is closer to R134a with equal volumetric cooling capacity. Fatouh and Kafafy [19] have also experimentally evaluated the performance of a 280-l (inner volume) R134a domestic refrigerator (at 431C ambient temperature) working with LPG (composed of R290/ R600/R600a in the ratio of 60:20:20, by mass) as an alternative. Their results reported that 60 g of LPG mixture (with 5 m capillary tube length) has 4.3% lower power consumption with 7.6% higher COP compared with R134a. The pull-down time and ON time ratio of the refrigerator working with LPG were reported to be lower than that of R134a by about 7.6 and 14.3%, respectively. Lee et al. [20] studied the performance of a small capacity directly cooled refrigerator using HC mixture (R290/R600a, in the ratio of 55:45, by mass) as an alternative to R134a. Their results concluded that the power consumption of HC mixture was lower than that of R134a by about 12.3% with improved cooling rate by 28.8% compared with R134a. The refrigerant charge requirement is approximately 50% lower than that of R134a. The length of the capillary tube was 500 mm higher for HC-based refrigeration system. Mohanraj et al. [21] tested with zeotropic HC mixture composed of R290 and 600a (in ratio of 45.2:54.8, by mass) as substitute to R134a in a domestic refrigerator having an inner volume of 200 l. Continuous running tests were carried out with a wide range of ambient temperature range between 24 and 431C, whereas cycling running tests were carried out at 321C. Their results showed that the HC mixture has lower values of energy consumption; pull down time and ON time ratio by about 11.1, 11.6 and 13.2%, respectively, with 3.25–3.6% higher COP. The discharge temperature of HC mixture was found to be 8.5–13.4 K lower than that of R134a. They also indicated that charge requirement of HC mixture was about 45% lower than that of R134a due to its lower liquid density. The environmental impacts of HC mixture were reported to be lower than that of R134a due to its lower energy consumption. Jwo et al. [22] compared the performance of a 400-l refrigerator working with R134a and HC refrigerant mixture composed of R290 and R600a (in the ratio of 50:50, by mass). They reported that the HC mixture has a higher refrigeration effect with 4.4%

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R12 domestic refrigerators of inner volume 299 and 465 l. It was reported that, R290/R600a (with R290 mass fraction in the range from 0.2 to 0.6) yields an increase in COP up to 2.3% as compared with R12. Power consumption and pull-down tests indicates that the energy efficiency was improved by 3–4% with slightly higher capacity than that of R12. The HC mixture showed lower compressor running time and lower compressor discharge temperature compared with R12. Hence, the life of the refrigeration compressor can be improved with HC mixture. Akash and Said [16] studied the performance of a 240-l (inner volume) R12 domestic refrigerator retrofitted system with liquefied petroleum gas (LPG) composed of R290, R600 and R600a (in the ratio of 30:55:15, by mass) as an alternative. They studied the performance of refrigerator with 160 g of R12 for base line tests and 50, 80 and 100 g of LPG for retrofitted tests (at a condensing temperature of 471C with evaporator temperatures between 0 and 281C). Their results showed that 80 g of LPG gave higher COP and cooling capacities compared with that of R12. Wongwises and Chimres [17] have investigated the performance with two binary HC mixtures (R290:R600a, in the ratio of 60:40 and R290:R600, in the ratio of 60:40, by mass) and two ternary HC mixtures (composed of R290:R600:R600a and in the ratio of 70:25:5 and 50:40:10, by mass) in a 240-l (inner volume) domestic refrigerator to replace R134a. During their investigations, ambient temperature was maintained at 251C. Their results reported that R290/ R600 mixture in the ratio of 60:40 (by mass) is the most appropriate alternative to replace R134a due to its good thermodynamic and environmental properties. The refrigerator working with above HC mixture requires less energy consumption per day with lower compressor ON time compared with R134a due to its high latent heat. Fatouh and Kafafy [18] theoretically assessed the performance of an R134a domestic refrigerator working with R290/commercial butane mixtures with different mass fractions of R290 (propane). Their results indicated that pure HC refrigerants are not possible to use as alternatives to R134a due to its mismatch in operating pressure and volumetric cooling capacity. They also reported that COP of the ternary HC mixture composed of R290, R600 and

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4.1.3. Air-conditioning, heat pumps and chiller applications. Purkayastha and Bansal [26] experimented with LPG mixture composed of R290, R170, R600a (in the ratio of 98.95: 1.007: 0.0397, by mass) as substitute for R22 in a 15-kW heat pump. It has been reported that COP of LPG mixture was higher than that of R22 by 12%. The volumetric refrigeration capacity of LPG was reported to be 14% higher than that of R22 with 10% lower condenser capacity. Chang et al. [27] studied the performance and heat transfer characteristics of HC mixtures composed of R290, R600a and R600 as alternatives to R22 in a heat pump. Their results concluded that cooling and heating capacities of HC refrigerant mixtures increase with increase in R290 mass fraction, which are lower than that of R22. The COP of binary HC mixtures composed of R290/R600a (in the ratio of 50:50, by mass) and R290/R600 (in the ratio of 75:25, by mass) was reported to be higher than R22 by 7 and 11%, respectively. Park and Jung [28] have investigated the thermodynamic performance of a heat pump working with R22 and its alternative refrigerant mixtures composed of R170 and R290, with five different mass percentage of R170 (2, 4, 6, 8 and 10%). It has been reported that COP of the new refrigerant mixture gets decreased with increase in R170 mass percentage. The COP of the mixture was reported to be higher than that of R22 in the composition range up to 6% of R170. The refrigeration and heating capacities of R170/R290 mixture increased with increase in R170 mass percentage. The capacities were similar in the composition range between 4 and 6% of R170. The compressor discharge temperature of the R170/R290 was reported to be lower in the range of 16.6–28.21C. Hence, higher compressor life can be expected with this mixture. The refrigerant charge requirement was observed to be lower by about 58% due to its lower liquid density. The refrigerant mixture R170/R290 with 4–6% of R170 was identified as long-term energy efficient and environment-friendly drop in substitute for phasing out R22 in heat pump applications. Park et al. [29] experimentally studied the thermodynamic performance of seven mixtures composed of R1270, R290, RE170 and R152a as alternatives for R22 in residential air conditioner. The results reported

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and can be used as long-term substitutes for R502 due to their lower environmental properties.

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4.1.2. Commercial refrigeration. Cleland et al. [23] compared the performance of milk cooling equipment working with R22 and CARE-40 (propane) and CARE50 (composed of propane and ethane) with a temperature glide of 4 K. Their results showed that the energy consumption of CARE50 was reduced by about 6–8% with a similar cooling capacity relative to R22. The performance of the system was improved by about 7–9% compared with that of R22. Hence, the total equivalent warming impact (TEWI) of CARE50 was reported to be lower than that of R22 due to its lower energy consumption. Mani and Selladurai [24] conducted experimental studies in a vapour compression refrigeration system working with R290/R600a (in the ratio of 68:32, by mass) as an alternative to R134a and R12. It was reported that R290/R600a mixture has 19.9–50 and 21.2–28.5% higher refrigerating capacity than that of R12 at lower and higher evaporating temperatures, respectively. The refrigeration capacity of R290/R600a was reported to be higher than that of R134a by about 28.6–87.2 and 30.7–41.4% in the lower and higher evaporating temperatures, respectively. The energy consumption of the new refrigeration mixture was reported to be 6.8–17.4 and 8.9–20% higher than R12 and R134a, respectively. The compressor discharge temperature was reported to be equal to R12 and R134a and the COP of the mixture was higher than that of R12 and R134a. Park and Jung [25] experimented with three binary mixtures composed of R1270, R290 and R152a as alternatives to R502 in low-temperature refrigeration applications. They tested the performance of the system at 28 and 451C in the evaporator and condenser temperatures, respectively. The results obtained in their study are compared in Table III. Their results concluded that refrigerant mixtures have higher refrigeration capacity and COP compared with that of R502 with lower compressor discharge temperature compared with that of R502. The charge requirement with refrigerant mixtures was reduced up to 60% as compared with R502. Miscibility of the refrigerant mixtures with mineral oil was reported to be good. The above discussed alternatives offer better system performance and system reliability compared with R502

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lower energy consumption. The charge requirement of the HC mixture was also reduced by 40% compared with R134a due to its lower liquid density.

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Table III. Performance comparison of refrigerant mixtures with R502, Park and Jung [25].

Refrigerant mixture composition

By mass (%)

COP

Evaporator capacity (W)

Compressor discharge temperature (1C)

Refrigerant quantity (g)

R502/(R22/R115) R1270/R290 R1270/R290 R290/R152a

48.8:52.2 10:90 20:80 90:10

0.633 0.806 0.793 0.785

2823 3122 3117 3094

176.2 151.4 152.5 148.3

1450 550 560 530


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Table IV. Performance comparison of refrigerant mixtures with R22, Park et al. [29].

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Refrigerant mixture composition

By mass (%)

COP

Evaporator capacity (W)

Compressor discharge temperature (1C)

Refrigerant quantity (g)

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R22 R1270/R290 R1270/R290 R1270/R290 R290/R152a R290/R152a R290/R152a R1270/R290/RE170

20:80 50:50 80:20 60:40 71:29 75:25 45:40:15

3.78 3.9 3.91 3.92 3.84 3.91 3.91 3.99

3600 3362 3589 3729 3572 3533 3527 3551

80.2 63.8 65.5 67.4 64.9 64.4 64.6 67.5

1170 525 550 530 630 600 600 540

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higher COP. The compressor discharge temperature and capacity of the mixture are similar to R12. The binary HC mixture composed of R290/R600a with 60% of R290 showed good performance in existing automobile air conditioners. Joudi et al. [33] investigated the performance of an automobile air-conditioning system working with R12 and HC mixture (composed of R290 and R600a, in the ratio of 62:38, by mole percentage). They performed the experiments at three different ambient temperatures (35, 40 and 501C) with six speeds 700, 1000, 1500, 2000, 2500 and 3000 rpm. During their experiments the evaporator chamber was maintained at 45, 50, 55, 60 and 651C. It has been reported that COP of the air-conditioner working with HC mixture was lower than that of R12 between 0.86 and 2.27%. The compressor discharge temperature was reported to be lower than that of R12 by about 2–61C. The volumetric displacement of R12 is similar to that of HC mixture. Temperature of air leaving the evaporator coil (using HC mixture) was reported to be lower than that of R12 by 1–31C. However, the power consumption of the mixture was slightly higher than R12 system. Maclaine-cross [34] has studied the usage and risk of HC mixture (R290/ R600a, in the ratio of 60:40, by mass) in automobile air conditioners for Australia and United States during 1993–2003. It has been reported that the accident frequency of using HC mixture in automobile air conditioners was found to be very low during the above period. Wongwises et al. [35] have experimentally investigated ternary HC mixture composed of R290/ R600/R600a with different mass percentages (20:60:20, 50:40:10 and 70:25:5, by mass) to replace R134a in an automobile air-conditioning system. Their results reported that HC mixture composed of R290, R600 and R600a (in the ratio of 50:40:10, by mass) is a good alternative to replace R134a. This mixture has higher COP and refrigeration capacity by 17 and 41%, respectively. The power consumption of mixture was observed as 21% higher than that of R134a. This HC refrigerant mixture has lower compressor discharge temperature. Hence, higher compressor life can be expected with this HC refrigerant mixture.

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in their study are compared in Table IV. The compressor discharge temperature of the refrigerant mixtures is found to be lower than that of R22. Hence, increased compressor life can be expected with refrigerant mixtures. The refrigerant charge requirement is also found to be lower than that of R22 due to its lower liquid density. Park et al. [30] have conducted an experimental investigation in an R22-based residential air conditioner working with R432A (near azeotrope mixture composed of R1270 and RE170, in the ratio of 80:20, by mass) as an alternative. It has been reported that R432A has 8.5–8.7% higher COP than that of R22 with 1.9–6.4% higher refrigeration capacity. The compressor discharge temperature of R432A was reported to be lower in the range between 14 and 171C. Hence, the life of the system can be improved. The charge requirement of new R432A was found to be 50% lower than that of R22. R432A has zero ODP and very low GWP of less than 5. Hence, R432A was reported as a good environment-friendly and energyefficient alternative to replace R22 in air-conditioner and heat pump applications. Park et al. [31] investigated the performance of a R22-based residential air-conditioner and heat pumps working with R433A (near azeotrope mixture composed of R1270 and R290, in the ratio of 70:30, by mass) as an alternative. It has zero ODP and very low GWP with a low temperature glide of 0.41C. The results reported that COP of R433A is 4.9–7.6% higher than that of R22 with 1–5.5% higher capacity. The compressor discharge temperature was reported to be lower in the range between 22.6 and 27.91C. The charge requirement of R433A is about 57% lower than that of R22 due to its lower liquid density. R433A was reported as a good energy efficient and environment-friendly alternative option to replace R22 in air-conditioning and heat pump applications.

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4.1.4. Automobile air conditioning. Jung et al. [32] evaluated the performance of alternative refrigerant mixtures for R12-based automobile air-conditioners. Their experimental and thermodynamic results reported that the R134a/RE170 mixture with zero ODP is the best long-term alternative to R12, which has 4% 7



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4.2.1. Domestic refrigeration. Gang et al. [37] have studied the performance (both theoretically and experimentally) of a R12-based domestic refrigerator working with a new HFC mixture composed of R152a and R125 at different mass percentages (80:20, 85:15, 90:10, by mass). It was reported that the discharge temperature of the mixtures was higher than that of R12. Hence, life of the compressor may be slightly affected. The energy consumption of the refrigerant mixture (R152a/R125, in the ratio of 85:15, by mass) with mass charge of 97 g has energy consumption of 1.156 kW h per day. The COP of the mixture is

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The HFC-based mixtures such as R404A, R407C and R410A are reported as potential alternatives to R22 in refrigeration, air-conditioning and heat pump applications [36]. However, HFC mixtures are not miscible with mineral oil, which is used as a lubricant in CFC and HCFC systems. HFC mixtures require synthetic lubricant like polyolester. Hence, a major modification is required for HFC mixtures to retrofit in HCFC systems. The properties of commonly used HFC mixtures are compared in Table V [14]. The properties of new refrigerant mixtures are calculated based on their mass fraction and properties of individual pure refrigerants.

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4.2. HFC mixtures

45 47 49

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R404A R407C R410A R507 NRM NRM NRM NRM

53 55 57

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4.2.2. Commercial refrigeration. Doring et al. [38] investigated R507 (binary mixture composed of R125/R143a, in the ratio of 50/50, by mass) as an alternative for R502 in a low-temperature freezer. Their results revealed that the compressor discharge temperature of R507 was approximately 8 K lower than that of R502 with 4–5% higher COP. The refrigeration capacities of R507 are 5–6% higher than the capacities of R502. Venkatarathnam and Murthy [39] studied the performance of four zeotropic mixtures composed of R32, R134a, R125, R143a and R32. The four mixtures investigated are M1 (R23/R143a/R134a in the ratio of 10:70:20, by mass), M2 (R23/R143a/ R134a, in the ratio of 10:80:10, by mass), M3 (R23/ R125/R134a/R32 in the ratio of 10:45:40:5, by mass) and R407C (in the ratio of 23:25:52, by mass fraction) as alternatives to R22 and R502. They compared the mixtures in terms of thermodynamic performance and pinch point formation in condensers and evaporators. Their results reported that COP of M1, M2 and M3 are closer to R502 and found to be lower than that of R22 and R407C. The compressor discharge temperature of M1, M2 and M3 is reported to be lower than that of R22 and R407C, but compressor discharge temperature is higher than that of R502. They also reported that pinch points can occur in condensers and evaporators when M1 and M2 are used. In the case of mixture M3, maximum temperature difference between the streams can occur in the condenser, particularly at low temperature, whereas pinching was insignificant in the evaporator. Pinch points were not formed in the condenser and evaporator, when R407C was used. Pinch analysis confirmed that R407C has superior performance compared with other mixtures. Aprea and Renno [40] investigated the performance of variable speed vapour compression refrigeration system

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2.8–3.2% higher compared with that of R12. This new HFC refrigerant mixture seems to be a good longterm substitute to phase out R12, due to its good environment-friendly acceptable properties and its favourable energy performances. However, this refrigerant mixture requires change of lubricant. Hence, major modification is required for retrofitting.

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The short atmospheric lifetime of HC refrigerant mixtures makes their GWP close to zero and their favourable thermodynamic and thermo-physical properties assure that the efficiencies are comparable to the halogenated refrigerants. The charge requirement of HC refrigerants is also reported to be half of the halogenated refrigerants due to its lower liquid density. The above investigations confirmed that HC refrigerant mixtures (composed of R290/R600 and R290/R600a) are considered as long-term alternatives to replace the existing halogenated refrigerants in domestic refrigerators, small capacity refrigeration units and in automobile air-conditioning systems. HC mixtures such as R432A and R433A are accepted as environment-friendly option for replacing R22 in airconditioning and heat pump applications.

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Composition

Table V. Properties of HFC mixtures as alternatives.

By mass Replaces

R125/R143a/R134a 44:52:4 R32/R125/R134a 23:25:52 R32/R125 50:50 R125/R143a 50:50 R152a/R125 85:15 R161/R125/R143a 10:45:45 R32/R134a 25:75 R32/R125/R134a 20:40:40

R22 R22 R22 R502 R12 R502 R22 R502


Boiling point 46.6 43.8 51.6 50.98 28.59 49.29 32.5 42.62

Molecular Critical Critical ASHRAE weight temperature pressure safety code ODP 97.60 86.2 72.8 98.86 74.14 96.63 89.52 99.22

72.1 87.3 72.5 70.9 106.2 72.81 95.37 82.56

3.74 4.63 4.95 3.79 4.38 3.80 4.49 4.23

A1 A1 A1 A1 A1 A1 A1 A1

0 0 0 0 0 0 0 0

GWP 3800 1700 2000 3900 612 3466 1112.5 1990

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system working with four HFC mixtures (such as R404A, R407C, R410A and R507) under various liquid injection ratios. Their results indicated that liquid injection has a positive effect in reducing the compressor discharge temperature and pressure, which improves the compressor life. Their study showed that the effect of liquid injection on the mixture behaviour varied depending upon the mixture composition. Sami and Desjardins [46] analysed the performance of R22 and its alternatives such as R404A, R407C, R408A, R410A and R507 in an air source heat pump with enhanced surface tubing. During their experiments the evaporator was maintained in the temperature range between 16 and 201C, with a condenser air inlet temperature of 211C. It was reported that R404A has a better performance among the proposed blends for low temperature heat pump applications. They also pointed out that R22 has the highest COP followed by R408A, R410A, 404A, R507 and R407C, respectively. However, R410A and R408A are having high compressor discharge temperature, which will reduce the compressor life. Gong et al. [47] studied the performance of three azeotropic refrigerant mixtures composed of R170, R23 and R116 (R170/R23, R170/R116, R170/R23/ R116) and compared with R508B in the two-stage cascade refrigeration system. It has been reported that binary mixtures composed of R170 and R116 (in the ratio of 0.703:0.297, by mass) has 10% higher COP compared with that of R508B, whereas R170/R23 (in the ratio of 0.58:0.42, by mass) has lower COP by 8%. The COP of the ternary mixture composed of (R170/ R23/R116, in the ratio of 0.512:0.346:0.142, by mass) is closer to R508B. The binary mixture (R170/R23) has the highest discharge temperature, which is about 20 K higher than that of R508B, while the R170/R116 mixture has the lowest discharge temperature, which is about 10 K lower than that of R508B. R170-based mixtures have higher cooling capacities compared with R508B due to its higher evaporating pressure. R170based mixtures have lower environmental impact due to its lower GWP.

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working with R407C used for cold storage applications. Their results concluded that exergy loss in the components of the system increases with increase in compressor speed. The COP of the system was reported to be higher at lower compressor speed and gets decreased with increase in compressor speed. Mark et al. [41] evaluated three options (R404A, R410A, R290) based on life cycle climatic performance analysis for replacing R22 in medium temperature refrigeration system (walk in cooler). Their results showed that R410A is an energy efficient and environmentally acceptable option to replace R22. TEWI of R410A was reported to be lower than that of R22, R290 and R404A. Xuan et al. [42] experimented with near-azeotropic ternary mixture composed of R161/R125/R143a (in the ratio of 10:45:45, by mass percentage). During their experimentation, the operating temperatures were maintained at 43 and 351C (condenser temperature) and 23 and 351C (evaporator temperature). It has been reported that physical properties of R161 mixture are similar to R502 and environmental properties of R161 mixture are lower than that of R502 and R404A. The COP of R161 mixture and R404A were equal at low evaporator temperature and its discharge temperature was slightly higher than R404A. The COP of the mixture was greater than that of R404A at higher evaporator temperatures and its compressor discharge temperature was found to be lower. Arora and Kaushik [43] theoretically analysed the performance (in terms of energy and exergy aspects) of a vapour compression refrigeration system working with R502 and its alternatives such as R404A and R507A. It was reported that COP and exergy efficiency for R404A and 507A are lower than that of R502 by about 4–17%. They also identified the condenser as the most inefficient component in the system followed by compressor, expansion valve and evaporator, respectively, based on exergy analysis. The liquid line-suction heat exchanger was identified as the most efficient component in the system. They also suggested that the COP and exergy efficiency of the system can be improved by sub-cooling the condensed liquid refrigerant. Kizilkan et al. [44] studied the exergitic performance of a variable-speed R404A refrigeration system. It has been reported that the major irreversibility occurs in the compressor (62%) followed by condenser by (17%), evaporator (13%) and expansion valve (6%) for different compressor frequencies. They also pointed out that exergy loss (irreversibility) gets increased with increase in compressor speed. The main reasons for these are higher electrical, mechanical and isentropic efficiency loses, friction loses at compressor, higher temperature differences at heat exchangers and pressure loses at higher frequencies. The major source of irreversibility is reported in high-pressure side, which is mainly due to its lower critical temperature. Sami and Aucoin [45] analysed the performance characteristics of a vapour compression refrigeration

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4.2.3 Air-conditioning, heat pump and chiller applications. Sami et al. [48] investigated the performance of five HFC mixtures such as R32/R125 (in the ratio of 60:40, by mass), R410A, R32/R125/R23 (in the ratio of 25:70:5, by mass), R407C and R32/R125/R143a/ R134a (in the ratio of 50.5:5:5:39.5, by mass) as alternatives to R22 in a heat pump. Their results showed that ternary mixture composed of R32/R125/ R23 (in the ratio of 25:70:5, by mass) is a good substitute to replace R22 in low-temperature heat pumps, which has higher heating COP compared with other investigated refrigerants. The quaternary blend composed of R32/R125/R143a/R134a has higher cooling COP compared with other investigated refrigerants. Payne and Domanski [49] tested with R410A in Int. J. Energy Res. (2010) r 2010 John Wiley & Sons, Ltd. DOI: 10.1002/er

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with increase in condensing and evaporator temperature. Hence, they suggested R407C as a good substitute for R22 in air-conditioning and heat pump applications. Rakesh et al. [55] experimentally investigated the performance (in terms of exergy point of view) of R407C and R407A as alternatives to R22 in a heat pump. Their results showed that R22 gives the highest overall COP at all condensing and evaporator temperatures. The overall COP of R407C is slightly higher than that of R407A. At low evaporator temperature, the performance of R407C and R407A is comparable. The isentropic efficiency is the highest for R22 and the lowest for R407A. The volumetric efficiency of the compressor is the highest for R22 and lowest for R407C. The heating capacity is highest with R22 followed by R407C and R407A. The variation of cooling capacity is the highest with R22 and the lowest with R407A at all temperatures. Devotta et al. [56] experimentally studied the performance of a 1.5-ton capacity window air conditioner working with R22 and R407C by changing the mineral oil with synthetic lubricant (POE). Their results revealed that the cooling capacity of R407C was found to be lower in the range of 2.1–7.9% with 6–7% higher power consumption than that of R22. The COP of the air conditioner was reported to be lower than that of R22, which is in between 7.9 and 13.1%. The discharge pressure of R407C is also reported to be high compared with that of R22. Their results indicated that the pressure drop of R407C in condensers and evaporators is lower than that of R22. Liu et al. [57] studied the dynamic performance of air source heat pump working with R22 and R407C under frosting and defrosting conditions. It has been reported that the performance of the R407C system attains its steady state faster than the R22 system after defrosting. They also reported that R407C can be used in existing systems or in new systems that were originally designed for R22. The above studies confirmed that R407C is an ozone-friendly alternative to R22 in air-conditioning and heat pump applications. Retrofitting of existing R22 systems with R407C is an option to extend its life. Jung et al. [58] simulated the performance of multistage heat pumps using refrigerant mixtures such as R32/R134a and R125/R134a as alternatives to R22. They revealed that the zeotropic refrigerant mixture composed of R32 and R134a (in the ratio of 25:75, by mass) yields an increase in COP of 15.7% with similar capacity as compared with R22. A temperature glide of 7.21C was reported in the evaporator. The performance of R32/R134a was reported to be better compared with R22 and another mixture of R125/R134a. Gabrielii and Vamling [59] developed drop-in substitutes for replacing R22 in vapour compression refrigeration system applications. An initial screening was made with 2000 mixtures containing R134a, R125, R32 and R143a based on condenser pressure, Mach

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an R22-based vapour compression-based systems working at outdoor temperature ranging from 27 to 551C. R410A is a near azeotropic refrigerant mixture composed of R32 and R125 (in the ratio of 50:50, by mass). Their results reported that capacity and efficiency of both systems decreased linearly with increasing outdoor temperature. The capacities of both systems were approximately equal at 351C, whereas at 551C outdoor temperature, the capacity with R410A was reduced by about 9% compared with that of R22. Owing to its lower critical temperature, the performance of R410A was degraded more than R22 when ambient temperature gets increased. Henderson et al. [50] compared the performance of a domestic and commercial heat pumps working with R22 and its alternatives (R410A and R290). They suggested that R410A is a good substitute compared with R290 to replace R22 in domestic and commercial heat pumps. Chen [51] made a comparative study on the performance and environmental characteristics of R410A and R22 in residential air conditioners. He reported that the use of R410A systems will reduce the size of the heat exchangers and also improved the power saving. He also reported that the overall environmental impact of R410A is 4–11% lower than that of R22 in residential air conditioners. Hepbasli [52] studied the exergy performance of a solar-assisted ground source heat pump system for residences using R410A as refrigerant. It has been reported that the maximum exergy destruction occurs at the high-pressure side (in the compressor and condenser) due to its lower critical pressure. The exergy destruction in the low-pressure side (expansion valve and evaporator) is found to be lower. Hence, R410A is not suitable for the high-temperature heat pump applications. R410A has about 50% higher saturation pressure compared with R22, which affects the characteristics of the system components. Hence, R410A requires change in system modifications. Many researchers reported the performance of a heat pump and air-conditioning units using R407C as an alternative to replace R22. R407C is a ternary zeotropic HFC mixture composed of R32, R125 and R134a (in the ratio of 23:25:52, by mass) with a temperature glide of 5–61C. Mongey et al. [53] compared the performance of R407C and R22 in a compressionbased refrigeration system. It was reported that the performance of R407C approached that of R22 at higher evaporator temperatures. They also indicated that the temperature glide of R407C in the evaporator will lead to change the composition resulting in reduction of evaporator capacity and COP. Greco et al. [54] experimentally compared the performance of R22 and R407C in a vapour compression refrigeration plant. Their results showed that COP of R407C was found to be lower than that of R22 by about 5–17% with high electric power consumption. They also reported that R407C has shown increasing performance

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than R407C. The above mixture has high refrigeration capacity and COP compared with R407C. The discharge temperature was also found to be slightly higher than R407C, which might affect the life of the compressor. Gorozabel et al. [65] theoretically predicted the performance of a direct expansion solar-assisted heat pump using different refrigerants such as R12, R22, R134A, R404A, R407C and R410A. It has been reported that the refrigerant mixtures (R404A, R407C and R410A) gave 15–20% lower COP compared with R12 and R22 due to its lower critical temperature. Sami and Aucoin [66] studied the performance of HFC refrigerant mixtures (R404A, R407C, R410A, R507) under the influence of magnetic field in an ambient source heat pump. Their results reported that COP of the system can be improved under the influence of magnetic field. They also pointed out that the effect of magnetic field on the mixture behaviour depends on its composition and its boiling point. Most of the studies reported in the literature are using HFC mixtures such as R404A, R407C and R410A as alternatives to R22. R404A can be used as an alternative to R22 in low-temperature refrigeration applications. R407C and R410A can be used as an alternative to R22 in air-conditioning applications and heat pump applications. However, R410A cannot be used for high-temperature heat pump applications due to its lower critical temperature. The HFC refrigerant mixtures have zero ODP with significant GWP. Owing to the GWP, HFC refrigerant mixtures are considered as interim alternatives to phase out the CFC and HCFC-based refrigerants. However, the HFC refrigerant mixtures will continue to dominate the refrigeration and air-conditioning industries for next decade because of their safety and the current strong position in the market.

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number and temperature glide. It has been reported that the mixture containing 30% of R143a, 25% of R125 and 45% of R134a has higher capacity, where as the mixture composed of 75% of R134a and 25% of R32 has higher COP. Kim et al. [60] studied the performance of a heat pump with HFC mixtures composed of R32 and R134a at different compositions. It was reported that the enhancement of COP was obtained at 50/50 (by mass) in cooling mode operation. Cooling capacity was increased from 2.64 to 3.38 kW in the cooling test, whereas COP was reduced from its peak value of 3.26 to 2.85. In the heating condition, heating capacity was increased from 1.82 to 2.38 kW but COP degraded slightly from 2.19 to 2.05. It is recommended that the composition of R32 in the circulating mixture is enriched for heating mode operation in order to improve heating capacity. For cooling mode operation, it is desirable to adjust the refrigerant composition to obtain the highest COP to reduce the energy consumption. Arcaklioglu et al. [61] found better environmentfriendly alternatives in terms of second law of thermodynamics based on rational efficiency. Their results showed that binary mixture composed of R32 and R134a (in the ratio 25/75 and 30/70, by mass) and ternary mixture composed of R32, R125 and R134a (in the ratio of 30:10:60, by mass) has rational efficiency close to that of R22. The ternary mixture composed of R32, R125 and R134a (in the ratio of 20:40:40, by mass) has a rational efficiency value close to that of R502. Wu et al. [62] experimentally studied the performance and flammability of a new refrigerant mixture (composed of R152a/R125/R32, in the ratio of 48:18:34, by mass, respectively) in an R22-based domestic air conditioner. Their results concluded that COP of the mixture was slightly lower than that of R22. The variation of COP and gliding temperature under the leakage conditions (leaking ratio between 0 and 20%) was reported to be very low. The flammability test of refrigerant mixture reported that it could be safely used in the domestic air conditioners. Chen and Yu [63] theoretically compared the performance of a new modified refrigeration cycle with the conventional refrigeration cycle using non-azeotropic mixture R32/R134a in residential air conditioner. The new refrigeration cycle was composed of a compressor, a phase separator, a sub cooler, two condenser, two evaporators, two recuperators and two expansion valves. It has been reported that the refrigerant mixture composed of R32/R134a in the ratio of 0.3:0.7 (by mass fraction) has 9.5% higher volumetric refrigerating capacity with 8–9% higher COP compared with the conventional refrigeration cycle. In the conventional refrigeration cycle, the performance of the mixture was closer to R22. Han et al. [64] investigated with ternary HFC mixture composed of R32/R125/R161 as an alternative to R407C. It was reported that the pressure ratio and power consumption are found to be lower

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4.3. HFC/HC mixtures To overcome the problems faced with HFC and HC refrigerants (oil miscibility and flammability), many investigators tried with HFC/HC mixtures as alternatives to HCFC and CFC refrigerants by retaining the mineral oil as lubricant. The flammable nature of HC refrigerants can be reduced by mixing it with HFC refrigerants. On the other hand, the miscibility of HFC refrigerant with mineral oil can be tackled. The properties of the new HFC/HC mixtures discussed in this section are listed in Table IV. The properties of new refrigerant mixtures are calculated based on their mass fraction and properties of individual pure refrigerants. 4.3.1. Domestic refrigeration. Tashtoush et al. [67] tested with ternary mixture (composed of R600/R290/ R134a) at various quantities in a 320-l (inner volume) R12 domestic refrigerator. It has been reported that it is possible to use HFC/HC mixture as an alternative to Int. J. Energy Res. (2010) r 2010 John Wiley & Sons, Ltd. DOI: 10.1002/er


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4.3.2. Commercial refrigeration. Sekhar and Lal [69] conducted experiments using HFC/HC mixture in R12-based commercial refrigeration units (such as 400-l deep freezer, 165-l visi cooler operating and in a 3.5-kW walk in cooler) with mineral oil as the lubricant. The zeotropic refrigerant mixture composed of R134a and 9% of HC blend (consists of 45% of R290 and 55% of R600a) had better performance resulting in 10–30 and 5–15% less energy consumption in medium- and low-temperature applications, respectively. The energy consumption per day of the retrofitted system was reported to be 28% lower than that of R12 with 6–10% higher COP at standard operating conditions. The compressor discharge temperature of the mixture was found to be lower than that of R12, which ensures better compressor life. The oil miscibility of new mixture with mineral oil was found to be good. Aprea and Renno [70] compared the performance of R22 and R417A (zeotropic mixture composed of R125/R134a/R600, in the ratio of 46.6:50:3.4, by mass) in a vapour compression refrigeration system used for cold storage applications. It was reported that COP of the mixture working with R417A was lower than that of R22 by about 15%. The compressor discharge temperature of R417A is lower than that of R22. Hence, the life of the compressor could be improved by using R417A. The exergy destruction of

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4.3.3. Air-conditioning, heat pump and chiller applications. Kim et al. [72] experimented with two mixtures of R134a/R290 (45/55, by mass percentage) and R134a/R600a (80/20, by mass) as alternatives to R22 and R12, respectively, by retaining the same lubricant. The performance characteristics of the refrigerant mixtures are compared with R12, R290, R134a and R22. The cooling and heating capacity of R290/R134a was reported to be higher than that of R22 and COP was reported to be lower than that of R22 and R290. They also reported that COP of the R134a/600a mixture was higher than that of R12 and R134a. The discharge temperature of the refrigerant mixtures studied was found to be lower than R22 and R12. Hence, higher compressor life can be expected with new refrigerant mixture. Jung et al. [73] studied the performance of 14 refrigerant mixtures composed of R32, R125, R134a, R152a, R290 and R1270 as alternatives to R22 for heat pump applications. It has been reported that COP of ternary mixtures composed of R32, R125 and R134a are 4–5% higher than that of R22. The COP values of binary mixture composed of R32 and R134a are 7% higher, capacities are similar to that with R22 and COP of binary azeotrope of R290, and R134a are 3–5% higher than that of R22. Compressor dome temperature and discharge temperature were found to be lower than that of R22 and hence the system reliability and fluid stability with these mixtures would be better than that of R22. Jabaraj et al. [74,75] experimented with new refrigerant mixture composed of R407C with 10, 15, 20 and 25% of HC blend (composed of R290 and R600a, in the ratio of 45.2:54.8, by mass) as alternatives to R22 in a window air conditioner. It has been reported that R407C with 20% of HC blend demands an increase in condenser tube length of 19% compared with R22. The energy consumption of 10 and 20% of HC blend were 1.31–2.5 and 4.83–9.46% less than R22.

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R417A was about 14% higher than that of R22. Maximum exergy destruction was found to occur in the compressor followed by condenser, evaporator and expansion valve, respectively. R417A can be used in the existing systems without changing the lubricant (mineral oil). Park and Jung [71] investigated the performance of a domestic water purifiers using R430A (a near azeotropic mixture composed of R152a and R600a in the ratio of 76:24, by mass) as an alternative to R134a. They reported that R430A had higher COP by 19.1% with 13.4% lower energy consumption. The compressor discharge temperature of R430A was reported to be slightly higher than that of R134a. The charge requirement of R430A was reported to be 50% lower than that of R134a. R430A has zero ODP with very low GWP of 107. The presence of R600a confirms that R430A is miscible with mineral oil.

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R12 in a domestic refrigerator without changing mineral oil (lubricant). The mixture composed of R290, R600 and R134a (in the mass of 25/25/30, 80 g) had performance characteristics very close to R12. The discharge temperature of the mixture was found to be lower than that of R12 for the wide range of evaporator capacity. Hence, improved compressor life can be expected with the refrigerant mixture. The volumetric efficiency of the compressor was slightly higher and mass flow rate of the mixture was found to be 40% lower, which are the advantages of the mixture for R12 retrofitting. Sekar et al. [68] experimented with ozone-friendly refrigerant mixture (R134a/HC mixture composed of R290 and R600a in the ratio of 45.2:54.8, by mass) as an alternative to R12 in a 165-l (inner volume) domestic refrigerator by retaining the same lubricant. They studied the performance of the refrigerator with three different compositions (7, 9 and 11%) of HC mixture with R134a. It has been reported that R134a/HC mixture (in the ratio of 91:9, by mass) has lower energy consumption of 4.8–6.4% with 3–12% improved COP. The TEWI of this refrigerant mixture is expected to be lower than that of R12 due to its higher energy efficiency. The temperature variation in the evaporator was reported to be within 31C, which will not affect the evaporator performance. The compressor dome temperature of this mixture was reported to be lower than that of R12. Hence, higher compressor life can be expected with this new refrigerant mixture.

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charge requirement of NRM is 50% lower than that of R134a due to its lower liquid density. Arora and Sachdev [80] made thermodynamic analysis of a vapour compression refrigeration system working with R22 and its alternatives (R422A, R422B, R422C and R422D). It has been reported that R422A and R422C have lower compressor ratios compared with R22, whereas R422B and R422D have higher pressure ratio compared with R22. The compressor discharge temperatures of the R422 series of refrigerants are lower than that of R22 compressor. Hence, R422 mixtures will offer better system reliability and longer compressor life. The volumetric cooling capacities of R422 mixtures are greater than that of R22, which requires change in compressor design. The COP and exergy efficiency of R422 series of refrigerants are lower than that of R22. However, R422B has better COP and exergy efficiency compared with other R422 series refrigerants. R422 series refrigerants have more exergy destruction in compressor and expansion valve. Hence, the operating parameters of the compressor and expansion valve are to be optimized to improve the performance of the system. R422 series of refrigerants are the HFC/HC mixtures, which can be used in the existing R22 compressors without changing the lubricant. Nanxi et al. [81] studied the performance, thermodynamic properties, miscibility with mineral oil and flammability of a near azeotropic refrigerant mixture composed of R124/R142b/R600a in the ratio of 0.9:0.08:0.02, by mass fraction. It has been reported that COP of the new refrigerant mixture was in the range of 3. Maximum condenser outlet temperature of about 901C was reached. The oil miscibility test showed that mineral oil is miscible with the new refrigerant mixture above 101C. The flammability test results reported that the refrigerant mixture is nonflammable. Zhang et al. [82] studied the performance of non-azeotropic refrigerant mixtures composed of R152a/R245fa at three different compositions (20:80, 37:63, 50:50, by mass) in an R134a-based water to water heat pump. It has been reported that R152a/ R245fa in the ratio of 37:63 (by mass) has better COP and thermodynamic perfection at higher condensing temperatures, which can be used as an alternative to R134a due to its lower environmental impact.

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The COP of the above mixtures was 8.19–11.15 and 1.68–3.23% higher than, and the discharge temperatures were 7.95–9.81 and 10.79–12.37% lower than R22. Pull-down time was reduced by 32.51 and 13.88%. The refrigeration capacity was 9.54–12.76 and 4.02–5.85% higher than R22. The compressor discharge temperature of the system working with new refrigerant mixture was found to be lower compared with R22. Hence, higher compressor life can be expected with new refrigerant. They also reported that oil miscibility of R407C/HC mixture working with mineral oil was good. The charge requirement of this refrigerant mixture was lower than that of R22 by 300 g due to its lower liquid density. Mohanraj et al. [76] investigated the performance of a direct expansion solar assisted heat pump (DXSAHP) working with R22 and mixture of R407C/LPG as an alternative. It was reported that R407C/LPG (in the ratio of 70:30, by mass) has 1.2% higher instantaneous compressor power consumption with 1–4.5% lower heating capacity compared with R22. The energy performance ratio of the mixture was reported to be lower in the range of 2–5% compared with that of R22. The solar energy input ratio of the new mixture was reported to be higher than that of R22 in the range of 7–14%. TEWI of R407C/LPG was reported to be lower compared with R22. The charge requirement of R407C/LPG is about 25% lower than that of R22 due to its lower liquid density. Mohanraj et al. [77] also reported the exergy performance of a DXSAHP working with R22 and R407C/LPG mixture. Their results indicated that R407C/LPG mixture has higher exergy destruction in the compressor and expansion valve due to its higher operating pressure, where as R407C/LPG mixture has lower exergy destruction in the heat exchangers (condensers and evaporators) due to its non-linear behaviour during phase change. Aprea et al. [78] performed an experimental study of vapour compression plant working as a heat pump and chiller using R22 and its substitute R417A (composed of R125, R134a and R600, in the ratio of 46.6:50:3.4, by mass). Their results reported that R417A does not require a change of lubricant and it is quite compatible with mineral oil. The COP of the R22 is higher than that of R417A of about 18% in the case of water chiller and 15% in the case of heat pump applications. The compressor discharge temperature of R417A was reported to be lower than that of R22, which ensures better compressor life. Park et al. [79] studied the performance of a vapour compression system working as an air-conditioner and heat pump using R431A (composed of R290 and R152a, in the ratio of 71:29, by mass) as an R22 alternative. It has been reported that R431A has zero ODP and lower GWP of 43. The COP of the mixture was 3.5–3.8% higher than that of R22 with similar refrigerating capacity under both conditions. The compressor discharge temperature was observed to be lower in the range of 21–271C. The

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4.3.4. Automobile air conditioners. Ravikumar and Lal [83] investigated the on-road performance analysis of ozone-friendly zeotropic refrigerant mixture composed of R134a and HC blend (R290/R600a, in the ratio of 45.2:54.8, by mass) in the ratio of 91:9, by mass as an alternative to R12 in an automobile air-conditioning system. It has been reported that COP of the air conditioner was found to be lower in the range of 6–12% with 28–30% higher work of compression. However, the refrigerating effect of the mixture is 22–27% lower compared with R12. The compressor Int. J. Energy Res. (2010) r 2010 John Wiley & Sons, Ltd. DOI: 10.1002/er


7 9 11 13 15 17 19

4.4. HCFC-based mixtures

31 33 35 37 39 41

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Carbon dioxide (R744) is a natural refrigerant. R744 has several attractive properties and was used before the introduction of CFC and HCFCs. The two major drawbacks of R744 are its high critical pressure with lower critical temperature and lower cycle efficiency. Owing to its lower critical temperature, R744 can be operated with trans-critical cycle. To overcome the drawbacks, R744 can be blended with other refrigerants to improve the performances. The properties of the R744-based refrigerant mixtures are listed in Table VI. Maczek et al. [88] investigated with ternary zeotropic mixture composed of R744/R32/R134a in R22 heat pump. It has been reported that R744/R32/ R134a mixture with mass fraction (7/31/62) showed an

Table VI. Properties of HFC/HC mixtures as alternatives.

45 47

4.5. Carbon dioxide-based mixtures

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HCFC mixtures are considered as interim alternatives due to its ODP. R123 is an HCFC refrigerant having very low value of ODP with lower GWP of 120. Owing to its lower GWP, R123-based mixtures can be used as temporary replacements in the existing systems. The properties of HCFC-based refrigerant mixtures are listed in Table V. Sami and Desjardins [84] studied the behaviour of R415A (composed of R23/R22/R152a, in the ratio of 5:5:90, by mass) and R415B (composed of R23/R22/ R152a, in the ratio of 5:15:80, by mass) as alternative to R502 in an air source heat pump. Their results concluded that R415A and R415B have better COP compared with R502 with the use of suction accumulators at lower ambient temperatures below 51C. They also reported that heated suction accumulator contributes in evaporating the more volatile component of refrigerant mixture, which results in increasing the mixture thermal capacity. Kumar and Rajagopal [85] investigated the performance of R12 and the mixture composed of R123 and R290 with different

Refrigerant R417A R422A R430A R431A NRM NRM NRM NRM NRM NRM

Composition

By mass

Replaces

Boiling point

Molecular weight

Critical temperature

Critical pressure

ODP

GWP

R125:R134a:R600 R125/R134a/R600a R152a/R600a R290/R152a R407C/HC blend R407C/LPG R124/R142b/R600a R134a/HC blend R134a/R290 R134a/R600a

46.6:50:3.4 85.1:11.5:3.4 76:24 71:29 80:20 70:30 90:08:02 91:09 45:55 80:20

R22 R22 R134a R22 R22 R22 R22 R12 R22 R12

38 49.86 21.04 43.1 40.13 35 13 26.18 34.95 23.22

106.75 115.84 64.14 50.46 79.31 69.7 129.3 97.50 70.16 93.24

89.9 72.54 118.43 101.51 93.34 95.7 124.5 102.57 98.68 107.82

4.10 3.67 4.30 4.32 4.486 4.27 3.75 4.04 4.16 3.97

0 0 0 0 0 0 0.026 0 0 0

2200 3043 104 43 1364 1133 750.4 1184 596 1044

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mass percentages. It has been reported that the COP of mixture (R123/R290, in the ratio of 70:30, by mass) had better COP than that of R12. The discharge temperature of the mixture was also found to be lower than that of R12 by about 5–221C. The environmental impact of this NRM was reported to be lower. Zhao et al. [86] investigated the performance of a geothermal heat pump working with two non-azeotropic refrigerant mixtures composed of R123/R290 (in the ratio of 50:50, by mass) and R290/R600a/R123 (in the ratio of 50:10:40, by mass). It has been reported that COP of the R123/R290 mixture is above 3. The volumetric heating capacity of this refrigerant mixture was calculated to be about 3200 kJ m3. The COP of the ternary refrigerant mixture (R290/R600a/R123) was reported to be 3.5. However, HCFC-based mixtures could be used as an interim alternative to extend the life of HCFC-based systems. Nuntaphan et al. [87] studied the performance of a zeotropic HCFC-based refrigerant mixture composed of R22/R124/R152a (in the ratio of 20:57:23, by mass) in a solar-assisted heat pump water heater. Their results showed that R22/ R124/R152a mixture has highest COP in the range between 2.5 and 5.0. They also reported that mixture has lower environmental impact compared with R22.

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discharge pressure is 10–15% higher with 2–5% lower discharge temperature. The average cabin temperature for the refrigerant mixture was reported to be 2–31C higher than that of R12. However, this new refrigerant mixture eliminates the use of synthetic lubricant (POE), which is highly hygroscopic in nature. The HFC/HC refrigerant mixtures can be used to replace CFC and HCFC refrigerants to extend the life of the existing systems. Low volatile HC refrigerants are preferred to be uses as an additive with HFC refrigerants to tackle the oil miscibility issue. The HFC/ HC refrigerant mixture eliminates the possibility of using synthetic oils, which are highly hygroscopic in nature and also have servicing problems. The literatures discussed in this section confirmed that HC refrigerant mixtures are used as additives with HFC refrigerants to tackle the oil miscibility issue and also eliminate the flammability of HC mixture.

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15 17 19 21 23 25 27 29 31 33 35 37

43

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45 47 Refrigerant

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NRM NRM NRM NRM NRM NRM NRM NRM NRM

15

Composition

By mass

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R123/R290 R290/R600a/R123

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4.7. Environmental impact assessment The environmental impacts of refrigeration and airconditioning systems are due to the release of refrigerants and the emission of greenhouse gases for associated energy use. The TEWI is used as an indicator for environmental impact of the system for its entire lifetime [94]. TEWI can be calculated by the following relation: TEWI ¼ ðGWP L NÞ1ðn E bÞ

ð1Þ

Table VII. Properties of HCFC-based refrigerants.

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Krauss and Schenk [92] studied the performance of R723 (an azeotropic mixture composed of ammonia and dimethylether in the ratio of 60:40, by mass) as an alternative to R717. It has been reported that the discharge temperature of the mixture can be reduced by approximately 20–251C. Hence, higher compressor life can be expected. This refrigerant mixture is miscible with mineral oil, which is user-friendly. Hence, the possibility of using synthetic oil can be eliminated. Cox et al. [93] developed a new ammoniabased azeotropic mixture (composed of R717 and R170, in the ratio of 35:65, by mass). It has been reported that R717/R170 mixture has lower compressor discharge temperature, which favours system reliability and improves the cycle efficiency. The mixture has good miscibility with mineral oil, thereby reducing the usage of highly hygroscopic synthetic oils. This refrigerant mixture has been used for industrial applications, food and blast freezing applications and in carbon dioxide/ammonia cascade systems.

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refrigerating effect of R290. The COP of R744/R290 mixture was higher than that of R744/R134a mixture.

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increase in capacity and COP by 18.6 and 2.5% respectively. This mixture was found to be a promising alternative only for low-temperature heat pump applications because of its excessive condensing temperature. Nicola et al. [89] studied the performance of cascade refrigerating system working with blends of carbon dioxide and HFC mixtures such as R744/R41 (0.5:0.5, by mass fraction), R744/R32 (0.5:0.5, by mass fraction), R744/R23 (0.4:0.6, by mass fraction) and R744/R125 (0.27:0.73, by mass fraction) as working fluids in low-temperature circuit. It has been reported that the COP of the R744/HFC blends are (less than 5%) lower than that of HFC fluids used in the low temperature medium (Tables VII and VIII). Sarkar and Bhattacharyya [90] assessed the performance of heat pumps for medium and high-temperature applications working with two binary zeotropic mixtures such as R744/R600 (in the ratio of 50:50 by mass) and R744/R600a (in the ratio of 50:50, by mass) as alternatives to R114. It has been reported that the mixture (R744/R600a) yields higher performance compared withR744/R600 and R114 for high-temperature heat pump applications. The exergy efficiency of the R744/R600a mixture was reported to be higher than that of R744/R600 mixture. Kim and Kim [91] studied the performance of an auto cascade refrigeration system using zeotropic refrigerant mixtures of R744/R134a (in the ratio of 30:70, by mass) and R744/ R290 (in the ratio of 30:70, by mass). It has been reported that COP of both the refrigerant mixtures got decreased with increase in R744 percentage, which was due to the increase in compressor power consumption. The cooling capacity of both the mixtures gets increased with increase in R744 mass fraction. The cooling capacity of R744/R290 mixture is about twice greater than that of R744/R134a, because of higher

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Boiling point

Molecular weight


Critical pressure

ODP

GWP

R12 R22

6.8 11.15

120.28 89.03

86.41 94.62

3.83 3.95

0.0084 0.0048

90 60

Table VIII. Properties of carbon dioxide-based refrigerants.

Composition

By mass

Molecular weight

Boiling point


Critical pressure

R744/R23 R744/R125 R744/R32/R134a R744/R600 R744/R600a R744/R134a R744/R290 R744/32 R744/R41

40:60 27:73 07:31:62 50:50 50:50 30:70 30:70 50:50 50:50

59.61 99.49 82.46 51.06 51.06 84.62 44.07 48.01 39.02

80.62 61.02 36.69 39.45 45.05 41.79 53.06 65.05 78.25

27.98 56.72 89.1 91.5 82.9 80.1 77.02 54.65 37.6

5.85 4.64 4.83 5.59 5.51 5.056 5.189 6.59 6.64



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4.8. Cost analysis associated with refrigerant replacement Many investigators reported the cost analysis of the compression-based refrigeration system working with refrigerant mixtures as alternatives. Ozkaymak et al. [95] made a thermo economic optimization of a vapour compression refrigeration system integrated with sub cooling and super-heating based on energy and exergy analysis. This method involves complexity due to more theoretical calculations and assumptions. Douglas et al. [96] presented a cost-based optimization technique for the performance of R22 alternatives in a compressionbased window air conditioners. This method of optimization involves determining design variables for the system. Said et al. [97] presented a simple approach for calculating the replacement cost of refrigerant. Hence, the equations presented in their work are discussed in this section. The annual cost savings of the retrofitted system can be calculated by using the following equation: AS ¼ EC RT EFL CE C

37 39 41 43 45 47 49 51 53 55 57

ð5Þ

Here m is the mass fraction of the individual components.

4.10. Lubricants for new refrigerant mixtures The lubricants recommended for new refrigerant mixtures are presented in Table IX.

4.11. Current scenario The current scenario of refrigerants used in different refrigeration and air-conditioning sectors is listed in Table X.

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Here AS is annual cost saving (in INR), EC is the energy consumption (in kW h), RT is the running time (in h), EFL is the equivalent full load capacity (in tons), CE is the cost of electricity (in INR) and C is the capacity of the system (kW). The equation for calculating the cost for refrigerant replacement (CR) can be given by the following equation: CR ¼ Cref 1Clab 1Cacce 1Ccom 1Cov

ð3Þ

Here Cref, Clab, Cace, Ccom, Cov are the cost of refrigerant (in INR), cost of labour (in INR), cost of accessories (in INR) and over head charges (in INR), respectively. The payback period of the retrofitted system can be calculated by the following equation: CR N¼ ð4Þ AS Here N is the pay back period (in years), CR is the cost of replacement (in INR), and AS is the annual savings (in INR).

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(R407C) have been developed using artificial neural networks [98–100]. However, REFPROP is the widely accepted user-friendly software database used for predicting the thermodynamic and thermo physical properties of the new refrigerant mixtures based on mass fraction and mole fractions. The GWP of refrigerant is not available in the REFPROP database. The GWP of the new refrigerant mixtures can be predicted by using following equation based on the mass fraction of the individual components:

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Table IX. Recommended lubricants for different mixtures.

Refrigerant HC mixtures HFC mixtures HFC/HC mixtures HCFC mixtures R744/HC mixtures Ammonia-based refrigerant mixtures

Lubricants Mineral oil, synthetic lubricants Synthetic lubricants Mineral oil and synthetic lubricants Mineral oil Mineral oil Mineral oil

Table X. Current scenario of refrigerant. Equipment

Existing refrigerants

Domestic refrigerators/freezers Small capacity refrigeration units Low temperature freezers Walk in coolers Air conditioning and heat pump units Automobile air conditioning Chillers Cold storages

R134a R134a, R404A, R22 R502 R134a, R22, R404A R22, R407C, R410A R134a R22, R123, R407C R717

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(xvii)

Based on the extensive literature reviewed on refrigerant mixtures, it was observed that refrigerant mixtures are going to replace the halogenated refrigerants in future. The suitability of new refrigerant mixtures in the existing refrigeration system requires further research in the following areas:

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(i) Zeotropic refrigerant mixtures are having high temperature glide due to the difference in boiling point of their components [101]. (ii) Under leakage conditions, the zeotropic mixtures could cause problems in the refrigeration controls (pressure controls) due to their composition shift. (iii) Owing to the effect of temperature glide in evaporator, it is difficult to locate the thermostat in the evaporator to control the refrigeration system. (iv) Use of zeotropic refrigerant mixtures in lowtemperature refrigeration systems will form uneven frost formation in evaporator coils, which results in the loss of evaporator performance [102]. (v) Usually the refrigerant mixtures exhibit lower heat transfer coefficient in both condensers and evaporators due to its non-linear behaviour [103]. (vi) Non-linear behaviour of zeotropic refrigerant mixtures creates an ambiguity in design and selection components of the system [104]. (vii) Low volatile component that is miscible with lubricant (like R600a or R600) is required to carry the lubricant oil to the compressor. Use of such low volatile component in refrigerant mixture leads to more composition shift. (viii) Zeotropic refrigerant mixtures require an increased heat exchange area to achieve the desired capacity. (ix) Conventional method of heat exchange design (LMTD and NTU) is not valid for refrigerant mixtures, which requires correction factor [104]. (x) The zeotropic mixtures may get change in their composition under leakage conditions, which affects the performance of the system [105]. (xi) Non-isothermal behaviour of refrigerant mixtures in condensers and evaporators during phase change leads to the formation of pinch points, which affects the effectiveness of condensers and evaporators [106]. (xii) Mixed refrigerants requires liquid line receiver (in liquid line) and suction line accumulator (in the vapour line) to accommodate the non-linear behaviour of refrigerant mixtures [107]. (xiii) It is difficult to control the capacity of the system, due to the non-linear behaviour of zeotropic refrigerant mixtures. (xiv) Owing to change in running composition of zeotropic mixtures, the pressure, capacity and

(xvi)

(i) Reliability of refrigerant compressors working with environment-friendly alternatives. (ii) Wear studies on refrigerant compressors working with new refrigerant mixtures. (iii) Refrigerant–lubricant interaction of new refrigerant mixtures. (iv) Exergy optimization of refrigeration system working with new refrigerant mixtures. (v) Development of a new user-friendly lubricant is necessary to replace the existing synthetic lubricant. (vi) Development of a new method for heat exchanger design is required to accommodate the nonlinear variation of new refrigerant mixtures during phase change. (vii) Development of new refrigeration system with low refrigerant inventory is required. (viii) The environmental properties, flammability and safety issues of new refrigerant mixtures. (ix) Start up and shunt down (dynamic) characteristics of new refrigerant mixtures. (x) Phase change characteristics of new refrigerant mixtures. (xi) Development of simplified correlations for predicting the properties of refrigerant mixtures. (xii) Thermo economic optimization of vapour compression refrigeration system working with new refrigerant mixture. (xiii) Clean development mechanism in refrigeration and air-conditioning sector working with new refrigerant mixtures.

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Very few pure refrigerants have properties closer to the existing halogenated refrigerants. Refrigerant mixtures are the only choice to replace the halogenated refrigerants. However, the refrigerant mixtures are having following technical difficulties to replace the existing pure halogenated refrigerants.

temperature get changed inside the system, which affects the overall system performance [108,109]. HC refrigerants mixtures are identified as the good substitutes to replace the halogenated refrigerants. But HC refrigerant mixtures are highly flammable in nature. The zeotropic mixtures should be transferred in liquid condition to retain the composition. Zeotropic refrigerant mixtures are not suitable for automobile air conditioners due to its frequent leakage. Zeotropic mixtures have strong deviation from ideal evaporation processes of a pure fluid, which makes errors in thermal design of evaporators [110].

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Table XI. New refrigerant mixtures needs further investigation.

3

ASHRAE designation

5

R419A R421A R423A R425A R426A

11

R427A R428A

13 15 17

R429A R435A R437A R510A

Replaces

R125/R134a/RE170 (77:19:4) R125/R134a (58:42) R134a/R227ea (52.5:47.5) R32/R134a/R227ea (18.5:69.5:12) R125/R134a/R600/R601a (5.1:93:1.3:0.6) R32/R125/R143a/R134a (15:25:10:50) R125/R143a/R290/R600a (77.5:20:0.6:0:1.9) RE170/R152a/R600a (60:10:30) RE170/R152a (80:20) R125/R134a/R600/R600a (19.5:78.5:1.4:0.6) RE170/R600a (88:12)

R22 R22 R22 R22 R12 R22 R22

Domestic refrigeration Freezers Low temperature freezers Walk in coolers Air conditioning Heat pump units

R22 R22 R22

Air conditioning Chillers Cold storages

R502

19

25 27 29

7. FUTURE MIXTURE OPTIONS

33

The fourth-generation refrigerants (refrigerants with zero or low ODP, low GWP (less than 150), short atmospheric lifetime with high efficiency) will turn up by 2010 onwards [10]. The refrigerant mixtures having lower environmental impacts with higher energy efficiency are considered to be fourth generation refrigerants. Some HFC refrigerant mixtures are having high GWP, which are identified as interim alternatives. The refrigerant mixtures identified for manufacturing new upcoming refrigeration, air-conditioning and heat pump units are listed in Table XII.

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HC mixtures, R430A

Commercial Transport commercial Commercial Domestic, commercial Domestic, commercial Automobile Commercial

HC mixtures, R430A R507, R510A, R1270/R152a mixtures R404A, R134a/HC mixture R407C, R410A, R431A, R432A, R433A R407C, R410A, R431A, R432A, R433A R430A, R152a R407C, R410A, R431A, R432A R723

Industrial and commercial

R152a are good substitutes to replace R134a and R12 in automobile air-conditioning units. HC mixtures (such as R432A and R433A) are identified as long-term replacement for phasing out R22 in air-conditioning and heat pump applications. HFC mixtures (such as R404A, R407C and R410A) are identified as interim replacements for R22. R404A is a good substitute to replace R22 in medium temperature refrigeration units such as walk in coolers. R407C and R410A are identified as good replacement in air-conditioning and heat pump units to replace R22. R507 is found to be provisional substitutes to phase out R502 in low- and medium-temperature refrigeration applications. HC and HFC/HC mixtures like R290/R1270 and R152a/R290 are found to be good long-term replacement to phase out R502. The use of HFC/HC mixtures will eliminate the use of synthetic lubricant, which is hygroscopic in nature. HFC/HC mixtures are having lower environmental impacts compared with HFC mixtures. It is observed that the use of environment-friendly refrigerant mixtures plays a crucial role for reducing the environmental impacts of the halogenated refrigerants to protect the environment. The information provided in this paper may be helpful to the researchers working with refrigerant mixtures.

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(xiv) The performance of the new refrigerant mixtures in different heat exchanger geometries. (xv) The performance of new refrigerant mixtures designated by ASHRARE [111] listed in Table XI needs further study on the performance. (xvi) The performance of the systems working with a new nano lubricant reported by Bi et al. [112].

Future options

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Equipment Composition (by mass)

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Table XII. Future options for newly manufactured units.

49 51 53 55 57

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This paper consolidates the experimental and theoretical investigations with new refrigerant mixtures carried out around the world. Thermodynamic performance of about 50 new refrigerant mixtures was discussed in this paper. Based on the literature reviewed with reference to the system performance of new refrigerant mixtures, it can be understood that HC mixtures (such as R290/R600a, R290/R600 and R290/ R600a/R600) and HFC/HC mixtures (like R430A) are found to be the good substitutes for replacing R12 and R134a in small capacity refrigeration units. R430A and Int. J. Energy Res. (2010) r 2010 John Wiley & Sons, Ltd. DOI: 10.1002/er

REFERENCES 1. Richard LP. CFC phase out; have we met the challenge. Journal of Fluorine Chemistry 2002; 114:237–250. 2. Johnson E. Global warming from HFC. Environmental Impact Assessment Review 1998; 18: 485–492. 3. Palm B. Hydrocarbons as refrigerants in small heat pump and refrigeration systems—a review. 18


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