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i n t e r n a t i o n a l j o u r n a l o f g r e e n h o u s e g a s c o n t r o l 3 ( 2 0 0 9 ) 1 0 8 – 1 1 9
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Review
Environment friendly alternatives to halogenatedrefrigerants—A review
l
l
M. Mohanraj a,*, S. Jayaraj b, C. Muraleedharan b
aDepartment of Mechanical Engineering, Dr. Mahalingam College of Engineering and Technology, Pollachi 642003, IndiabDepartment of Mechanical Engineering, National Institute of Technology Calicut, Calicut 673601, India
a r t i c l e i n f o
Article history:
Received 10 August 2007
Received in revised form
10 March 2008
Accepted 15 July 2008
Published on line 28 August 2008
Keywords:
Environment friendly
Refrigerant mixtures
Alternative refrigerants
a b s t r a c t
In developing country like India, most of the vapor compression based refrigeration, air
conditioning and heat pump systems continue to run on halogenated refrigerants due to its
excellent thermodynamic and thermo-physical properties apart from the low cost. How-
ever, the halogenated refrigerants have adverse environmental impacts such as ozone
depletion potential (ODP) and global warming potential (GWP). Hence, it is necessary to look
for alternative refrigerants to full fill the objectives of the international protocols (Montrea
and Kyoto) and to satisfy the growing worldwide demand. This paper reviews the various
experimental and theoretical studies carried out around the globe with environment
friendly alternatives such as hydrocarbons (HC), hydroflurocarbons (HFC) and their mix-
tures, which are going to be the promising long-term alternatives. In addition, the technica
difficulties of mixed refrigerants and future challenges of the alternatives are discussed. The
problems pertaining to the usage of environment friendly refrigerants are also analyzed.
# 2008 Elsevier Ltd. All rights reserved.
Contents
1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
2. Environmental impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
2.1. Ozone layer depletion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
2.2. Global warming potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
3. Refrigerant properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
3.1. Thermodynamic properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
3.2. Thermo-physical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
3.3. Mixture behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
3.4. Chemical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
4. Experimental and theoretical studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
4.1. Domestic refrigeration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
4.1.1. Hydrocarbon refrigerants as alternatives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
4.1.2. HFC mixtures as alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
4.1.3. HC/HFC mixtures as alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
* Corresponding author. Tel.: +91 9486411896; fax: +91 4259236070.E-mail address: [email protected] (M. Mohanraj).
1750-5836/$ – see front matter # 2008 Elsevier Ltd. All rights reserved.doi:10.1016/j.ijggc.2008.07.003
i n t e r n a t i o n a l j o u r n a l o f g r e e n h o u s e g a s c o n t r o l 3 ( 2 0 0 9 ) 1 0 8 – 1 1 9 109
4.2. Commercial and industrial refrigeration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
4.2.1. Commercial refrigeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
4.2.2. Industrial refrigeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
4.3. Air conditioners, heat pumps and chillers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
4.3.1. Hydrocarbons refrigerants as alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
4.3.2. Carbon dioxide as an alternative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
4.3.3. HFC mixtures as alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
4.3.4. HFC/HC mixtures as alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
4.4. Automobile air conditioners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
5. Indian scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
5.1. Domestic refrigeration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
5.2. Commercial and Industrial refrigeration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
5.3. Air conditioners, heat pumps and chillers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
5.4. Automobile air conditioners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
6. Recovery and recycling of refrigerants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
7. Technical difficulties of mixed alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
8. Future research needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
9. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
1. Introduction
Green house gas (GHG) emissions from fossil fuel combustion
for power generation and emission of halogenated refriger-
ants from vapor compression based refrigeration, air con-
ditioning and heat pump systems contribute significantly to
the global warming. A reduction in GHG emissions can only be
achieved by using environment friendly and energy efficient
refrigerants. The high environmental impacts due to haloge-
nated refrigerant emissions lead to identifying a long-term
alternative to meet all the system requirements including
system performance, refrigerant–lubrication interaction,
energy efficiency, safety and service. Halogenated refrigerants
have dominating the refrigeration and air conditioning
industries over many decades due to its excellent thermo-
dynamic and thermo-physical properties. As per the Montreal
protocol 1987, developing countries like India, with a per
capita consumption of less than 0.3 kg of ozone depletion
substance have been categorized as Article–5 countries. These
countries are required to phase out all chlorofluorocarbons
(CFCs) by 2010 and all hydrochloroflurocarbons (HCFCs) by
2040 (Powell, 2002). Johnson (1998) has reported that HFC
refrigerants are considered as one among the six targeted
green house gas under Kyoto protocol of United Nations
Framework Convention on Climate Change (UNFCCC) in 1997.
Most of the developed countries reduced the production and
consumption of halogenated refrigerants, which demands for
suitable alternatives. HC and HFC based refrigerants with zero
ODP and low GWP are considered to be long-term alternatives.
On the other hand, HC refrigerants have flammability issues,
which restrict the usage in existing systems. However, the
reduction in flammability can be achieved by blending HC
refrigerants with HFC refrigerants (Yang et al., 2004). For-
meglia et al. (1998) reported that, it is possible to mix HC
refrigerants with other alternatives such as HFC refrigerants.
The miscibility of HC/HFC mixtures with mineral oil has been
reported to be good (Avinash et al., 2005). The GWP of HC/HFC
mixtures is less than one third of HFC, when it is used alone
(Tashtoush et al., 2002). This paper gives a comprehensive
review of the various experimental and theoretical studies
carried out with environment friendly alternatives in refrig-
eration, air conditioning and heat pump applications. In
addition, the technical difficulties, future options and research
needs of the alternatives are also discussed.
2. Environmental impacts
The halogenated refrigerants have a long history of emission
from refrigeration, air conditioning and other uses. The
halogenated refrigerants are a family of chemical compounds
derived from the hydrocarbons (methane and ethane) by
substitution of chlorine and fluorine atoms for hydrogen. The
emission of chlorine and fluorine atoms present in haloge-
nated refrigerants is responsible for the major environmental
impacts with serious implications for the future development
of the refrigeration based industries. It is evident from the
Fig. 1 that the sale of CFC refrigerants reported to Alternative
Fluorocarbons Environmental Acceptability Study (AFEAS)
1975–2004 is significantly reduced during the past two decades
(AFEAS, 2005). The sale of R134a is increasing significantly
during the past decade. The increase in emission of refrigerant
to the atmosphere is steadily increasing the concentration of
green house gases resulting in the reported adverse climatic
changes being noticed recently.
2.1. Ozone layer depletion
The first major environmental impact that struck the
refrigeration based industries is ODP due to man made
chemicals into the atmosphere. Molina and Rowland (1974)
give in detail that 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 surface from direct UV rays). About
90% of the ozone exists in the stratosphere between 10 and
Fig. 1 – Production of halocarbon refrigerants.Fig. 3 – Global warming of pure CFC and HCFC refrigerants.
Fig. 4 – Global warming of pure HFC refrigerants.
i n t e r n a t i o n a l j o u r n a l o f g r e e n h o u s e g a s c o n t r o l 3 ( 2 0 0 9 ) 1 0 8 – 1 1 9110
50 km above the earth surface. The first phase out schedule for
the harmful refrigerants formulated by the Montreal protocol
(1987) and was made stringent during the follow-up interna-
tional meetings. The ODP values of pure CFC and HCFC
refrigerants are shown pictorially in Fig. 2 (Calm and
Hourahan, 2001).
2.2. Global warming potential
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 surface temperature. While solar
radiation at 5800 K and 1360 W/m2 arrives the earth, more
than 30% is reflected back into space and most of the
remaining radiation passes through the atmosphere and
reaches the ground. This solar radiation heats up the earth,
which approximately as a black body, radiating energy with a
spectral peak in the infrared wavelength range. This infrared
radiation cannot pass through the atmosphere because of
absorption by GHG including the halogenated refrigerants. As
a result, the temperature of atmosphere increases, which is
called as the global warming (McCulloch and Lindley, 2003).
During the formulation of Kyoto protocol, countries around
the world have voluntarily committed to reduce the GHG
emissions. HFC refrigerants have relatively large values of
Fig. 2 – Ozone depletion potential of pure CFC and HCFC
refrigerants.
Fig. 5 – Global warming of HFC mixtures.
atmospheric lifetime and GWP compared to chlorine based
refrigerants. The GWP values of pure and mixed refrigerants
are illustrated in Figs. 3–5 (Calm and Hourahan, 2001).
3. Refrigerant properties
3.1. Thermodynamic properties
The thermodynamic requirements of the alternative refriger-
ants pertain to many parameter values including operating
Table 1 – Properties of refrigerants (Calm and Hourahan, 2001)
Refrigerant Composition Replaces Molecular(wt)
Criticaltemperature (8C)
Boilingpoint (8C)
ASHARAEsafety code
R404A R125/R143a/R134a (44:52:4) R502, R22 97.6 72.1 �46.5 A1
R407C R32/R125/R134a (23:25:52) R22 86.2 87.3 �43.56 A1
R410A R32/R125 (50:50) R22 72.58 72.5 �51.53 A1
R417A R125/R134a/R600 (46.6:50:3.4) R22 106.75 89.9 �38.0 A1
R161 Pure fluid R502 89.41 102.2 �46.08 A1
R134a Pure fluid R12 102.03 101.1 �26.5 A1
R152a Pure fluid R12, R134a 66.05 113.3 �24 A2
R600a Pure fluid R12, R134a 58.12 134.7 �11.6 A3
R600 Pure fluid R12, R22 58.12 152 �0.5 A3
R290 Pure fluid R12, R22 44.1 96.7 �42.1 A3
RC270 Pure fluid R12, R134a 42.08 125.2 �33.5 A3
R1270 Pure fluid R22 42.08 92.4 �47.7 A3
R717 Pure fluid 17.03 132.3 �33.3 B1
R744 Pure fluid R22, R12 44.01 31.1 �78.4 A1
R507 R125/R143a (50:50) R502 98.9 70.9 �47.1 A1
R123 Pure fluid R22, R11, R12 152.93 183.8 27.8 A1
R12 Pure fluid – 120.93 112 �29.79 A1
R22 Pure fluid – 86.47 96.2 �40.8 A1
R502 R22/R115 (48.8/51.2) – 111.64 80.7 �45.4 A1
i n t e r n a t i o n a l j o u r n a l o f g r e e n h o u s e g a s c o n t r o l 3 ( 2 0 0 9 ) 1 0 8 – 1 1 9 111
pressures, critical pressure, critical temperature, freezing
point, normal boiling point, specific volume, coefficient of
performance (COP), specific power consumption, specific
heat ratio, etc. A positive system pressure is required
everywhere in order to eliminate the possibility of air and
moisture entering into the system. The critical temperature
of the refrigerant should be very high, so that the condenser
temperature line on the pressure enthalpy diagram is far
away from the critical point (which ensures reasonable
refrigeration effect). Boiling point of the refrigerants should
be low enough in order to produce low temperature in the
evaporator. Freezing point of the alternative refrigerants
should be lower than the system temperatures. The specific
heat ratio of the alternatives also should be low. Hence, lower
discharge temperature can be expected, which will improve
the compressor life. The volume of suction vapor required per
ton of refrigeration is an indication of the size of the
compressor. Reciprocating compressors are preferred with
refrigerants having high pressure and corresponding small
volume of the vapor. Rotary compressors are used with
refrigerants having low pressure and large volume of the
suction vapor (Arora, 2000). Thermodynamic properties of
pure and mixed refrigerants are listed in the Table 1 (Calm and
Hourahan, 2001).
3.2. Thermo-physical properties
Thermo-physical properties such as, thermal conductivity,
viscosity, specific heat are required for choosing an alter-
native. A high thermal conductivity in both liquid and vapor
phases is desirable to archive high heat transfer coefficient in
both condensers and evaporators. Low viscosity in both liquid
and vapor phases is desirable to archive a high heat transfer
coefficient with reduced power consumption. All the pure and
mixed hydrocarbon refrigerants have lower viscosity and
higher thermal conductivity, which results in better con-
denser and evaporator performance.
3.3. Mixture behavior
Very limited number of pure fluids has suitable properties
to provide alternatives to the halogenated refrigerants.
The mixtures of refrigerants provide a solution to this
problem. Didion and Bivens (1990) have reported three
different types of refrigerant mixtures as alternative work-
ing fluids (azeotropes, near azeotropes and zeotropes).
Azeotropic mixture of the substances is one, which cannot
be separated into its components by simple distillation. An
azeotrope evaporates and condenses as single substance
with properties that are different from those of either
constituent. Near azeotropes may alter their composition
and properties under leakage conditions. Zeotropic mixture
does not behave like a single substance when it changes the
state. Instead, it evaporates and condenses between two
temperatures (temperature glide). Hydrocarbon blends
are the zeotropic substances which have greater potential
for improvements in energy efficiency and capacity
modulation.
3.4. Chemical properties
The chemical properties pertain to flammability, toxicity,
reaction with other substance (lubricant and construction
materials). The HFC, HFC/HC and HC mixtures are found to be
chemically stable for a wide range of operating temperatures.
The compatibility of these mixed refrigerants with compres-
sor materials and chemical interaction between refrigerant–
lubricant inside the system are found to be good. The HC
refrigerants are flammable, but it is non-toxic. The lower
flammable limits of the HC refrigerants are listed in the
Table 1. The flammability of HC refrigerants can be reduced by
blending them with HFC refrigerants (Yang et al., 2004). The
main advantage of HC refrigerants is their solubility with
mineral oil, which is traditionally used as a lubricant for
chlorine based refrigeration systems.
i n t e r n a t i o n a l j o u r n a l o f g r e e n h o u s e g a s c o n t r o l 3 ( 2 0 0 9 ) 1 0 8 – 1 1 9112
4. Experimental and theoretical studies
A large number of experimental and theoretical studies are
found in literature pertaining to HC, HFC and their mixtures as
alternatives to halogenated refrigerant by researchers from
various parts of the world. A brief summary of these results is
given in the following sections.
4.1. Domestic refrigeration
4.1.1. Hydrocarbon refrigerants as alternativesWongwises and Chimres (2005) investigated with HC mixtures
composed of R290 and R600 at different mass ratio in a 240 l
capacity domestic refrigerator by replacing the R134a. They
have reported that R290/R600 mixture (in the ratio of 60:40, by
mass fraction) is the most appropriate alternative to R134a due
to its excellent thermodynamic and environmental properties.
The refrigerator working with above HC mixture requires less
energy consumption per day compared to R134a due to its high
latent heat. Fatouh and El Kafafy (2006) studied the perfor-
mance of 280 l R134a based domestic refrigerator with
liquefied petroleum gas (LPG) composed of R290, R600a and
R600 (60:20:20 by mass fraction) as an alternative. The results
reported that the pull-down time, pressure ratio and power
consumption of LPG mixture with a combination of 5 m
capillary tube length and charge of 60 g was reduced by 7.6%,
5.5% and 4.3% respectively with a 7.6% higher COP. Lower on-
time ratio and energy consumption of LPG refrigerator by
nearly 14.3% and 10.8% respectively, compared to that of
R134a.
Hammed and Alsaad (1999) studied the performance of
320 l R12 based domestic refrigerator using R290:R600:R600a
(50:38.3:11.7 by weight) as an alternative. It has been reported
that the COP of refrigerator using this mixture is 3.7 with an
evaporator temperature of �16 8C and condensing tempera-
ture of 27 8C (compared to R12, which has a COP of 3.6). Jung
Table 2 – Experimental investigations carried out in India wit
Authors Refrigerant Alternative
Devotta and Kulkarni (1996) R12 R290/R600a
Sekhar et al. (2004) R12 R134a/(R290/R600a)
(R134a/9% HC mixtur
Mohanraj et al. (2007) R134a R290/R600a (45/55)
et al. (2000b) examined R290/R600a as an alternative in 299 and
465 l R12 domestic refrigerators. A thermodynamic analysis
indicated that the R290/R600a in composition range 0.2–0.6
mass fraction of HC290 yields an increase in COP up to 2.3% as
compared to R12. Power consumption and pull-down test
indicate that the energy efficiency was improved by 3–4% with
slightly higher capacity than that of R12. Akash and Said (2003)
studied the performance of the R12 retrofitted system with
LPG (30% R290, 55% R600 and 15% R600a by weight) as an
alternative at various charge amounts (50 g, 80 g and 100 g) for
R12 in 240 l domestic refrigerator. The results reported that
80 g of LPG mixture showed best performance and higher
cooling capacities compared to that of R12.
4.1.2. HFC mixtures as alternatives
He et al. (2005) studied theoretically and experimentally with
HFC mixture composed of R152a and R125 at different weight
percentage (80:20, 85:15 and 90:10) as R12 alternative in a
domestic refrigerator. It has been reported that the discharge
temperature of the mixture was found to be slightly higher
than that of R12. The energy consumption of the domestic
refrigerator with optimum proportion 85:15 by weight per-
centage at 97 g is 1.156 kW h per day with 2.8–3.2% higher COP
than that of R12. The mixed refrigerant R152a/R125 seems to
be the long-term alternative to replace R12 as a new
generation refrigerant of domestic refrigerators, due to its
better environmentally acceptable properties and its favorable
refrigeration performance.
4.1.3. HC/HFC mixtures as alternativesTashtoush et al. (2002) tested with (R600/R290/R134a) at
various quantities in R12 domestic refrigerator. It has been
reported that it is possible to use HC/HFC mixture as an
alternative to R12 in a domestic refrigerator with out changing
the mineral oil (lubricant). The hydrocarbon mixture (R290/
R600/R134a) in the mass ratio of 25:25:30 and the charge
h domestic refrigerators
Conclusion
Energy consumption for CFC-12 and the hydrocarbon
mixture are comparable
The pull-down test results revealed that the final
freezer and food compartment temperatures are
very much higher when the refrigerator is retrofitted
either with a hydrocarbon blend
The performance was improved by optimum capillary
length and refrigerant charge
The ice making time for both the refrigerants are
more or less the same
e)
The energy consumption was reduced by 4–11% with
3–8% higher COP
The discharge temperature was found to be lower than R12
Temperature glide in the evaporator is with in 3 8C
It has been reported that above mixture is an energy
efficient and environment friendly alternative due to
its reduced energy consumption about by about 4% with
12 K lower than that of R134a
The environmental impacts of hydrocarbon refrigerant
mixture are negligible compared to R134a
i n t e r n a t i o n a l j o u r n a l o f g r e e n h o u s e g a s c o n t r o l 3 ( 2 0 0 9 ) 1 0 8 – 1 1 9 113
amount of 80 g had performance characteristics very close to
that of R12. The discharge temperature of the mixture was
found to be lower than that of R12 for a wide range of
evaporator capacity. The volumetric efficiency of the com-
pressor is slightly higher and mass flow rate of the mixture
was found to be 40% lower. These are the major advantages for
R12 retrofitting with above mixture. Table 2 summarizes some
of the experimental investigations carried out in India with
domestic refrigerators.
4.2. Commercial and industrial refrigeration
4.2.1. Commercial refrigerationPeixoto et al. (2000) studied the performance of a commercial
bottle cooler working with R600a as an alternative to R134a. It
has been reported that about 13% reduction in energy
consumption was observed with a corresponding improve-
ment in COP. Charge requirement for R600a was about 50% of
R134a. Elefsen et al. (2003) conducted field tests in 25 R404a and
50 R290 ice cream freezers in Australia. Based on the field tests,
it has been reported that freezers using R290 as refrigerant can
operate more satisfactorily and consume 9% less energy than
that of R404A freezers. Spatz and Yana Motta (2004) evaluated
three options based on life cycle climatic performance
analysis (R404A, R410A, R290) for replacing R22 in medium
temperature refrigeration system (walk in cooler). The results
reported that R410A is shown to be an efficient and
environmentally acceptable option to replace R22 based on
life cycle climate performance analysis.
Sekhar and Lal (2005) conducted experiments using HFC/
HC mixture in two low temperature (165 l domestic refrig-
erators and 400 l deep freezers) and in two medium tempera-
ture applications (3.5 kW walk in cooler and 165 l visi cooler)
operating with R12 with mineral oil as the lubricant. The oil
miscibility of new mixture with mineral oil was found to be
good. The zeotropic refrigerant mixture composed of R134a
and 9% of hydrocarbon blend consists of 45% of R290 and 55%
Table 3 – Air conditioners, heat pumps and chiller units
Authors Refrigerant Alternative Equipmen
Devotta et al. (2005a) R22 R290 Window a
conditione
Devotta et al. (2005b) R22 R407C Window a
conditione
Jabaraj et al. (2006) R22 R407C/20% HC Window a
conditione
Kumar and
Rajagopal (2007)
R12 (70/30) R123/R290 Chiller
of R600a had better performance resulting in 10–30% and 5–
15% less energy consumption in medium and low temperature
applications, respectively. The discharge temperature of this
mixture was found to be lower than R12. The COP is also found
to be higher than that of R12 at standard operating conditions.
4.2.2. Industrial refrigerationDoring et al. (1997) experimented with R507 (binary mixture of
composed of R125/R143a in equal proportion by weight) as an
alternative for R502 in a low temperature freezer. The
discharge temperature was found to be approximately 8 K
below and COP was 4–5% higher than that of R507. The
refrigeration capacities of R507 are 5–6% higher than the
capacities of R502. Goktun (1998) compared the performance
of R502 and five HFC mixtures (R404a, R407A, R407B, R507 and
quaternary HFC mixture composed of R32, R125, R143a and
R134a) as alternatives in low temperature applications. The
results reported that R404A is the best alternative on the basis
of environmental properties and safety with similar volu-
metric capacity and lower discharge temperature. Xuan and
Chen (2005) experimented with ternary mixture R161/R125/
R143a (10:45:45 percentage by weight). It has been reported
that physical properties of R161 mixture are similar to R502
and environmental properties of R161 mixture are lesser than
R502 and R404A. The COP of R161 mixture and R404A are equal
at low evaporator temperatures and its discharge temperature
is slightly higher than R404A. The COP of the mixture was
greater than R404A at higher evaporator temperatures and its
discharge temperature was found to be lower. Baolian and
Zhang (2006) experimented with binary mixture composed of
R744 and R290 at 71:29 mole fraction as alternative to R13 in
cascade refrigeration system. It has been reported that COP
and capacity of the mixture are greater than R13. The
discharge temperature of the mixture is found to be greater
than that of R13.
Park and Jung (2007) experimented with two pure HC
refrigerants (R1270 and R290) and three binary mixtures
t Conclusion
ir
rs
Cooling capacity of R290 was lower by 6.6–9.7%
Energy consumption was lower by 12.4–13.5%
COP was higher by 2.8%–7.9%
R290 has low condenser capacity than R22 in
the range between 12.3–18.7%
Pressure drop in both evaporator and condenser
were found to be lower than R22
ir
rs
Cooling capacity was lower in the range of 2.1–7.9%
Power consumption was higher in the range of 6–7%
COP was lowered by 8.2%–13.6%
Discharge pressure of R407C was higher in the range 11–13%
Evaporator capacity was lower by 3.3–6%
ir
rs
5–10.5% lower energy consumption with 8–11% higher COP
9.5–12.5% higher refrigeration capacity
Pull-down time was lower than that of R22 by about 32.51%
3.7–11.46% higher discharge pressure
Discharge temperature is less than R12 by about 5–22 8CThe actual COP of the mixture was found to be higher
The operating pressure is slightly higher than that of R12
i n t e r n a t i o n a l j o u r n a l o f g r e e n h o u s e g a s c o n t r o l 3 ( 2 0 0 9 ) 1 0 8 – 1 1 9114
composed of R1270, R290 and R152a as alternatives to R502 in
low temperature refrigeration applications. It has been
reported that all refrigerants tested had 9.6–18.7% higher
capacity with 17.1–27.3% higher COP than that of R502. The
compressor discharge temperature of R1270 was similar to
that of R502, while those of all the other refrigerants were 23.7–
27.9 8C lower than that of R502. The charge requirement was
reduced up to 60% as compared to R502. Miscibility of all these
refrigerants with mineral oil was reported to be good. The
above alternatives offer better system performance and
reliability than R502 and can be used as long-term substitutes
for R502 due to their excellent environmental properties.
4.3. Air conditioners, heat pumps and chillers
A wide variety of alternative refrigerants and mixtures re
found to be experimented in this category. The various
experiments carried out in India with air conditioners, heat
pump and chiller applications are listed in Table 3.
4.3.1. Hydrocarbons refrigerants as alternativesChoi et al. (1996) evaluated the performance of flammable
refrigerants as R22 alternative for water-to-water residential
heat pump applications at different compressor speeds. The
results showed that based on the capacity R32/R152a was
found to be the best performer due to good glide matching in
the heat exchangers and have good thermodynamic and
transport properties. The HC mixture (R290/R600a) is found to
have the highest COP with a loss in the system capacity.
Purkayastha and Bansal (1998) experimented with R290 and
LPG (R290 – 98.95%, R170 – 1.007%, R600a – 0.0397%) as
substitute for R22 in a 15 kW heat pump. It has been reported
than COP of HC refrigerants (R290 and LPG mixture) were
respectively 18% and 12% higher compared to that of R22.
However volumetric refrigeration capacity and condenser are
highly lower by 16% and 14% and 13% and 10%. Chang et al.
(2000) investigated with R290, R1270, R600, and R600a and
binary mixtures of R290/R600a and R290/R600 as R22 alter-
natives in a heat pump. It has been reported that cooling and
heating capacity of R290 were smaller and COP was slightly
higher than that of R22. The capacity and COP of the R1270
were slightly greater than R22. The COP of the zeotropic
mixture R290/R600a with 50% mass percentage of R290 was
enhanced by 7% and R290/R600 at composition of 75:25 (by
mass percentage) showed 11% improved performance. It has
been found that system is degraded for zeotropic HC mixtures
due to composition variation in phase change.
Granryd (2001) reviewed the HC refrigerants for different
applications. He compared R290 with R22 and reported that
R290 gave lower capacity by 3–15% than that of R22. The heat
transfer coefficient of R290 in condenser was also found to be
lower than that of R22. Urchueguıa et al. (2004) reported the
experimental characterization of two commercial scroll and
reciprocating compressors working with R22 and R290 with
same mineral oil as lubricant. His experiments reported that
the refrigerating capacity in both types of units was reduced
13–20% due to the use of propane but at the same time COP
was increased by 1–3%. Chaichana et al. (2003) studied the
options of using natural working fluids (R717, R744, R290, R600,
R600a and R1270) as substitutes for R22 in solar boosted heat
pumps based on thermo-physical properties and the thermal
performance. Their results indicate that R744 is not suitable
for solar boosted heat pumps because of its low critical
temperature and high operating pressure values. R717 seems
to be more appropriate in terms of operating parameters and
performance which requires major changes in the system.
Condensing pressure values of R600 and R600a are 50–70% less
than R22. Hence R600 and R600a cannot be used as drop in
substitute for R22. R290 and R1270 have close saturation
pressure values compared to that of R22. The performance of
R22, R290 and R1270 was comparable. Hence, R290 and R1270
were identified as direct drop in substitutes for R22. Park and
Jung (2006) studied the thermodynamic performance of two
hydrocarbon refrigerants and seven mixtures composed of
R1270, R290, RE170 and R152a as alternatives for R22 in
residential air conditioning applications. It has been reported
that all the pure and mixed fluids tested have low GWP of 3–58
as compared to that of R22. Also their test results showed that
expect R1270, all the other refrigerants have higher COP with
lower discharge temperature and similar refrigeration capa-
city.
4.3.2. Carbon dioxide as an alternativeBrown et al. (2002a) compared the performance of CO2 and R22
in a residential air conditioning system using semi-theoretical
vapor compression and transcritical cycle models. The
simulated R22 system has conventional component config-
uration, while CO2 system includes liquid-line/suction-line
heat exchanger. It has been reported that COP of the CO2
system is 10% less and power consumption is 38% higher than
that of R22. The cooling capacities of both the systems were
identical at 35 8C ambient temperatures and will decrease
linearly with increase in the ambient temperature.
4.3.3. HFC mixtures as alternativesJung et al. (2000a) studied the performance of HFC and
hydrocarbon mixtures as alternatives to R22. It has been
reported that COP of ternary mixtures composed of R32, R125,
R134a is 4–5% higher than that of R22. The COP of binary
mixture composed of R32 and R134a is 7% higher and
capacities are similar to R22 and COP of binary azeotrope of
R290 and R134a is 3–5% higher than 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. Yana Motta and Domanski (2000) reported the simulation
results of R22 and its alternatives R410A and R407C at high
outdoor temperatures. Their results indicate that R410A has
more pronounced performance degradation than R22 and
R407C because of low critical temperature. R410A has the
highest COP degradation. The change of COP for R22 and R407C
is similar because their critical temperatures are within 10 K of
each other. The presence of liquid-line/suction-line heat
exchanger will improve the capacity and COP of all refriger-
ants studied. Payne and Domanski (2002) tested with R410A in
a R22 based split air-conditioning systems with outdoor
temperature ranging from 27 to 55 8C. The capacity and
efficiency of both systems decreased linearly with increasing
outdoor temperature. The capacities of both systems were
approximately equal at 35 8C whereas at 55 8C outdoor
i n t e r n a t i o n a l j o u r n a l o f g r e e n h o u s e g a s c o n t r o l 3 ( 2 0 0 9 ) 1 0 8 – 1 1 9 115
temperature, the R410A capacity was reduced by 9% compared
to that of R22. The performance of R410A was degraded more
than R22 when ambient temperature gets increased more than
68 8C due to its lower critical temperature.
Rakhesh et al. (2003) experimentally studied the perfor-
mance of R407C and R407A as alternatives for R22 in a heat
pump. The results reported that R22 gives highest overall COP
at all condensing and evaporator temperatures. The overall
COP of R407C is slightly higher than R407A. At low evaporator
temperature, the performance of R407C and R407A are
comparable. The isentropic efficiency is highest for R22 and
lowest for R407A. The volumetric efficiency of the compressor
is 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 highest with R22 and lowest with R407A
at all temperatures. Calm and Domanski (2004) reported that
R410A and R407C are the leading replacements for R22 in
unitary air conditioners and heat pump applications.
Kim et al. (2004) studied the performance of a heat pump
with HFC mixtures (R32/R134a) at different compositions. It
has been reported that the enhancement of COP was obtained
at equal proportions of mass fraction in cooling mode
operation. Cooling capacity was increased from 2.64 to
3.38 kW in the cooling test, whereas COP changed from its
peak value of 3.26 and 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 in order to obtain the highest
COP and to reduce the energy consumption. Devotta et al.
(2005b) reported that retrofitting R22 systems with R407C is a
better option to extend the life of R22 systems even though the
performance is slightly lower. Han et al. (2007) investigated
with ternary mixture composed of R32/R125/R161 as an
alternative to R407C. It has been reported that, pressure ratio,
power consumption are found to be lower than R407C. The
above mixture has high refrigeration capacity and coefficient
of performance compared to R407C. The discharge tempera-
ture also was found to be slightly higher than R407C.
4.3.4. HFC/HC mixtures as alternativesKim et al. (1994) experimented with two azeotropic mixtures of
R134a/R290 (45/55 by mass percentage) and R134a/R600a (80:20
mass percentage). The performance characteristics of the
azeotropes are compared with that of R12, R290, R134a and
R22. The cooling and heating capacity of R290/R134a was
greater than that of R22 and COP was found to be lower than
that of R22 and R290. The COP of the R134a/600a mixture is
higher than R12 and R134a. The cooling capacity is also found
to be higher than R134a and R600a. The discharge temperature
of the azeotropic mixtures studied are found be lower than
that of R22 and R12. Maczek et al. (1997) investigated with
ternary zeotropic mixture composed of R744/R32/R134a as an
alternative for R22 in a heat pump. It has been reported that
above mixture with mass fraction (7:31:62) showed an increase
in capacity and COP by 18.6% and 2.5% respectively. This
mixture was found to be promising alternative only for low
temperature heat pump applications because of its excessive
condensing temperature. Payne et al. (1998) compared the
performance of R22, R290 and the flammable zeotropic
mixtures R32/R290 and R32/R152a in a residential water-to-
water heat pump. In cooling mode at constant capacity R32/
R290 (50:50) mixture produced 8% higher COP than R22. In
heating mode, the COP of R32/R290 was 13% lower and the COP
of R290 was 1% higher than that of R22 in the water to air
system. R290 shows the best performance compared to the
other fluids due to its zero environmental impacts, thermo-
physical properties and oil solubility. Yang et al. (1999)
investigated with HFC/HC ternary mixtures (R32/R125/R152a
and R32/R125/R290) and binary mixtures (R125/R290 and R32/
R290) as alternatives to R22. Their experimental investigations
reported that performance of R32/R125/R152a mixture was
found to be close to R22 over wide range of operating
conditions and also have better efficiency.
Aprea et al. (2004) made performance study of vapor
compression plant working as water chiller and heat pump
using R22 and its substitute R417A. It has been reported that
R417A does not require a change of lubricant and it is quite
compatible with mineral oil, alkyl-benzene and ester oils. The
compression ratio of R417A is higher than R22 in both the
cases. 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 discharge temperature of R417A was
also found to be lower than R22 in both chiller and heat pump
applications. It is observed that the exergy destroyed in the
components of the plant working with R417A as working fluid
are greater than the exergy destroyed while using R22 on an
average of about 14%. Experimental investigation with R407C
with 10% and 20% HC blend composed of 45% of R290 and 55%
of R600a (by weight) as an alternative in window air
conditioners without changing the mineral oil (Jabaraj et al.,
2006). It has been reported that 19% increase in condenser tube
length is required to suit the mixtures as compared to R22. The
experimental results reported that R407C with 20% HC blend
was found to be the promising alternative to R22 in window air
conditioners without changing the mineral oil. Calm (2006)
has investigated 28 different pure refrigerants for chiller
applications. The results reported that R123 remains the best
current option to reduce the substantial global warming
contributions from chiller and air conditioning applications.
R123 has low ODP and very low GWP, very short atmospheric
lifetime and the highest energy efficiency of all the current
options.
4.4. Automobile air conditioners
Mahmoud (1999) theoretically investigated with R152a and
hydrocarbon refrigerants such as (R290, R600a and R270) as
alternatives to R134a in an automobile air conditioning
system. It has been reported that all four refrigerants
investigated that are having less GWP and better transport
properties compared to R134a. R152a and R270 showed better
performance whereas R290 and R600a are not suitable due to
its mismatch in operating pressure and volumetric cooling
capacity. R152a and R270 have higher COP than that of R134a.
At the actual road load conditions, R152a and R270 systems
performed better than R134a by about 11% and 9%, respec-
tively where as at idling conditions COP of R270 and R152a are
i n t e r n a t i o n a l j o u r n a l o f g r e e n h o u s e g a s c o n t r o l 3 ( 2 0 0 9 ) 1 0 8 – 1 1 9116
15% and 7% higher than R134a system, respectively. Brown
et al. (2002b) compared the performance of CO2 and R134a in
an automobile air conditioning system using a semi-theore-
tical cycle model. It has been reported that COP of CO2 was
lower by about 21% and 34% at 32.2 and 34 8C respectively.
Maclaine-cross (2004) studied usage and risk of HC refrigerant
mixture (R290/R600a) for motor cars in Australia and United
States. His studies reported that R290/R600a has low environ-
mental impact but mixed with air will form flammable
mixture and cabin over pressure were predicted. No such
accidents are known from 1993 to mid-2003 in above two
countries. Jung et al. (1999) evaluated the retrofit refrigerant
mixtures for R12 based automobile air conditioners. Their
experimental and thermodynamic results reported that
R134a/RE170 mixture with zero ODP is the best long-term
alternative to R12, which has 4% higher COP. The discharge
temperature and capacity of the mixture are similar to R12.
The binary hydrocarbon mixture composed of R290/R600a
with 60% R290 showed good performance in existing
automobile air conditioners. Wongwises et al. (2006) experi-
mentally investigated with ternary hydrocarbon mixture
composed of R290/R600/R600a to replace R134a in automobile
air conditioning system. They have reported that propane/
butane/isobutene at 50:40:10 (by weight) is a best alternative to
replace R134a with higher COP and lower discharge tempera-
ture and similar refrigeration capacity.
Table 4 – Future options
Equipment Application Future options
Refrigerator Household
(domestic)
HC mixtures, R152a
Walk in coolers Commercial HC mixtures, R134a/HC
mixtures, R152a
Chest freezer Commercial HC mixtures, R152a
Air conditioners Residential and
commercial
R290, R407C, R410A,
R407C/HC mixtures
Automobile R152a, HC mixtures
Chillers Industrial R123
Cold storages Industrial Ammonia
5. Indian scenario
The refrigeration and air conditioning sector in India has a
long history from the early years of last century. India is
presently producing R134a, R22, R717 and hydrocarbon based
refrigeration and air conditioning units in large quantities. The
use of CFC refrigerants in new systems was stopped since the
year 2002. The factors that dictate the adoption of a particular
refrigerant apart from its suitability for the specific application
are its availability and cost. The halogenated refrigerants such
as R12, R22 R134a and natural refrigerant like R717 are readily
available at low prices. The HC and HFC mixtures (such as
R404a, R407C, and R410A) are not currently manufactured
indigenously and hence have to be imported at a higher cost.
This is likely to affect the growth in refrigeration and air
conditioning sector in India and also the total conversion to
environmental friendly alternatives in the near future.
5.1. Domestic refrigeration
The Indian household refrigerator industry is more than 50
years old. Eight major domestic refrigerator manufacturers
were catering this market, of which, four are manufacturing
hermetic compressors. Domestic refrigerators manufactured
in India range in capacities from 65 to 580 l. Most of the
currently produced Indian refrigerators use R134a as the
refrigerant. The choice of alternative to R134a is narrowed
down to R152a and hydrocarbon refrigerants. Refrigerators
manufactured before 2000 were still running on R12. To full fill
the objectives of the Montreal protocol, R12 has to be replaced
by either hydrocarbon mixtures or R134a/hydrocarbon mix-
tures without modification in the exiting system.
5.2. Commercial and Industrial refrigeration
Most of commercial freezers like chest freezers, bottle coolers,
visi coolers, display cabinets, water coolers and walk in coolers
are use R134a and R12 as the refrigerant. Annual production of
commercial refrigerated cabins (such as chest freezers, dis-
play cabinets, bottle coolers and visi coolers), water coolers
and walk in coolers in India were estimated to be about 40,000,
27,000 and 500 units, respectively. About 80% of theses units
are manufactured by small and medium enterprises (Ministry
of environment and forest, 2005). The choice of suitable
alternative to R134a in commercial applications is R152a and
hydrocarbon mixtures. The estimated population of milk
chilling and cold storages in India was about 14,000. Most of
the cold storages and milk chilling plants are working on
ammonia and some on R502. Ammonia will dominate the
industrial refrigeration sector due to its favorable environ-
ment properties (zero ODP and GWP). The alternative choice
for R502 is R507 and hydrocarbon mixtures for low tempera-
ture industrial applications.
5.3. Air conditioners, heat pumps and chillers
In India it is estimated that 1 million room air conditioners is
being manufactured with R22 as refrigerant every year, which
comprises of window, split and packaged air conditioning
units (Devotta et al., 2005b). The capacity of the window air
conditioners ranges from 0.5 TR to 2 TR. The choice of
alternative to R22 in air conditioning applications is R407C and
R410 which are available in the Indian market. Annually about
4000 central air conditioning chillers were installed, most of
these chillers was based on R22 and R11. Very limited chillers
were presently installed with R123 due to the lack of
availability of this refrigerant. The long-term alternative to
R11 and R22 for the chiller applications is R123.
5.4. Automobile air conditioners
Three manufacturers in India are producing about 50,000 units
of automobile air conditioners annually. Most of these units
are R134a based system. The choice of alternative to R134a is
R152a and hydrocarbon mixtures. The car air conditioning
units installed before 2000 were still running on R12 only. The
choice of alternative to R12 and R134a is the mixture
composed of R134a with hydrocarbon mixture or hydrocarbon
mixtures and R152a.
i n t e r n a t i o n a l j o u r n a l o f g r e e n h o u s e g a s c o n t r o l 3 ( 2 0 0 9 ) 1 0 8 – 1 1 9 117
The halogenated refrigerants like R22, R134a, R123, R404A,
R407C, R410A and R507 will continue to be dominating during
the next decade due to its high efficiency, safety and their
current strong position in the Indian market. The technologies
identified for manufacturing new products in this sector are
listed in Table 4
6. Recovery and recycling of refrigerants
Refrigerant recovery, recycling and reclamation is one way of
reducing emissions and encouraging timely phase out of
halogenated refrigerants (Devotta et al., 2004). The study of
Indian refrigeration and air conditioning sector revealed that
recovery and recycling is not yet practiced in domestic and
commercial refrigeration sector. The refrigerant charge
requirement in domestic refrigerator application is very small.
Hence recovery and recycling may not be a cost effective
option in the domestic refrigeration sector. Large commercial
and industrial refrigeration units (such as walk in coolers,
refrigerated cabins, heat pumps) have some potential for
recovery and recycling. The charge requirement of refrigerant
in these units is quite high compared to domestic refrigera-
tors. Automobile air conditioning sector accounts a major
share of refrigerant emissions due to frequent charging of
refrigerants during its less life time due to substandard road
conditions. The high growth in automobile sector in India and
the increased use of automobile air conditioners is likely keep
this sector with a high potential for recovery and recycling of
refrigerants.
7. Technical difficulties of mixed alternatives
The technical difficulties of the alternative refrigerant mix-
tures are listed below:
(a) T
he major problem of the refrigerant mixtures is theoccurrence of pinch points in the condensers and
evaporators during phase change due to non-linear
variation in refrigerant properties, which reduces con-
denser and evaporator effectiveness (Venkatarathnam
and Sirinivasamoorthy, 1999).
(b) N
on-isothermal behavior of the refrigerant mixturescreates ambiguity in selecting the components of the
refrigeration system from the manufacturer’s catalogue.
(c) P
erfect glide matching can be achieved only in certain heatexchanger geometries such as shell and tube, concentric
tubes, counter flow and flat plate heat exchangers.
(d) C
onventional method of heat exchanger design is notfully valid for the case of mixed refrigerants (Rajapaksha,
2007).
(e) N
on-linearity of the mixtures influences to decreasing thetemperature difference at inlet and outlet may lead to
increase in heat exchanger area to achieve the desired
capacity.
(f) C
omposition shift due to leakage of refrigerant of themixed refrigerants leads to change in pressure, tempera-
ture, capacity and efficiency (Johansson and Lundqrist,
2001).
(g) M
ixed refrigerants require liquid receiver and suction lineaccumulator due to composition variation in phase change
(Rajapaksha and Suen, 2004).
8. Future research needs
The following are the important future research needs with
respect to environment friendly alternative refrigerants:
(a) H
ydrocarbon refrigerants will be considered as a long-termalternative for halogenated refrigerants, which are flam-
mable. Hence, the development of new refrigeration
system with low refrigerant inventory is essential.
(b) V
ery limited pure alternatives are available. Therefore, thenew refrigeration system designs should accommodate
the non-linear property variation of environment friendly
mixed refrigerants.
(c) C
ompatibility of the alternative refrigerant mixtures withlubricants and the construction materials is required to be
studied further.
(d) In
ert nature of hydrocarbons with hydroflurocarbonrefrigerants needs further investigation.
(e) A
n environmental property of new refrigerant mixturesalso needs further investigation.
9. Conclusion
Researchers from various parts of the world reported the
experimental and theoretical results with environment
friendly alternatives. Based on the results regarding the
performance, it can be understood that HC mixtures and
R152a are found to be better substitutes for R12 and R134a in
domestic refrigeration sector. R290, R1270, R290/R152a, R744
and HC/HFC mixtures are found to be the best long-term
alternatives for R22 in air conditioning and heat pump
applications. R123 was found to be an attractive alternative
to R11, R12 and R22 in chiller applications. R152a and HC
mixtures are found to be a best option for automobile air
conditioners. The use of low environmental impact refriger-
ants like the natural refrigerants (R290, R1270 and R744) and
HC/HFC refrigerants in air conditioning and heat pump
applications play a vital role in the developing countries India
for reducing the environmental impact of halogenated
refrigerants.
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