Europilsmes
`Patent: mt
`European
`Patent Office
`
`
`
`“
`
`(11)
`
`EP 1 491 608 B1
`
`(12)
`
`EUROPEAN PATENT SPECIFICATION
`
`(45) Date of publication and mention
`of the grant of the patent:
`14.01.2009 Bulletin 2009/03
`
`(21) Application number: 04014512.0
`
`(22) Date of filing: 21.06.2004
`
`(51) Int CI.:
`C09K 5/04 (”’5'“)
`
`(54) Refrigerant mixture and refrigeration cycle apparatus using the same
`
`Kiihlmittelmischung und Kéltekreislaufgerét, die diese verwendet
`
`Melange refrigerant et appareil a cycle frigorifique l’utilisant
`
`
`(84) Designated Contracting States:
`DK SE
`
`(30) Priority: 26.06.2003 JP 2003182316
`
`(43) Date of publication of application:
`29.12.2004 Bulletin 2004/53
`
`(60) Divisional application:
`050255629 /1 632 543
`
`(73) Proprietor: Panasonic Corporation
`Kadoma-shi
`Osaka 571-8501 (JP)
`
`(72) Inventor: Fujitaka, Akira
`Otsu-shi
`
`Shiga 520—2144 (JP)
`
`(74) Representative: K6rfer, Thomas et al
`Mitscherlich & Partner
`Patent- und Rechtsanwélte
`Postfach 33 06 09
`80066 MLinchen (DE)
`
`(56) References cited:
`EP-A- 0 992 572
`US-A- 5 360 566
`
`EP-A- 1 234 868
`
`0 KIM S G ET AL: "Experiment and simulation on
`the performance of an autocascade refrigeration
`system using carbon dioxide as a refrigerant"
`INTERNATIONAL JOURNAL OF
`
`REFRIGERATION, OXFORD, GB, vol. 25, no. 8,
`December 2002 (2002—12), pages 1093—1101,
`XP004388591 ISSN: 0140-7007
`
`0 MCLINDEN M 0 ET AL: "Thermodynamic
`properties for the alternative refrigerants"
`INTERNATIONAL JOURNAL OF
`REFRIGERATION, OXFORD, GB, vol. 21, no. 4,
`June 1998 (1998-06), pages 322-338,
`XP004287254 ISSN: 0140-7007
`
`- HOSHINA K ET AL: " Lorentz angle measurement
`for COZIisobutane gas mixtures" NUCLEAR
`INSTRUMENTS & METHODS IN PHYSICS
`RESEARCH, SECTION - A: ACCELERATORS,
`SPECTROMETERS, DETECTORS AND
`ASSOCIATED EQUIPMENT, NORTH-HOLLAND
`PUBLISHING COMPANY. AMSTERDAM, NL, vol.
`479, no. 2-3, 1 March 2002 (2002-03-01), pages
`278-293, XP004344547 ISSN: 0168-9002
`
`EP1491608B1
`
`
`
`Note: Within nine months of the publication of the mention of the grant of the European patent in the European Patent
`Bulletin, any person may give notice to the European Patent Office of opposition to that patent, in accordance with the
`Implementing Regulations. Notice of opposition shall not be deemed to have been filed until the opposition fee has been
`paid. (Art. 99(1) European Patent Convention).
`
`Printed by Jouve, 75001 PARIS (FR)
`
`

`

`EP 1 491 608 B1
`
`Description
`
`Technical Field
`
`[0001] The present invention relates to a refrigerant mixture comprising specific hydrocarbon and carbon dioxide, and
`to a refrigeration cycle apparatus using the refrigerant mixture.
`
`Background Technique
`
`In a refrigeration cycle apparatus, in general, a compressor, a condenser, an expansion device such as a
`[0002]
`capillary tube and an expansion valve, an evaporator are connected to one another through pipes to constitute a refrig-
`eration cycle, and refrigerant is allowed to circulate through the pipes, thereby carrying out a cooling or heating operation.
`As a refrigerant used in such a refrigeration cycle apparatus, hydrocarbon halide induced from methane or ethane is
`known. For convenience in writing, the refrigerant is expressed with a letter "R" followed by two- or three-digit numerals
`in accordance with ASH RAE STANDARD 34.
`
`[0003] As a refrigerant for the refrigeration cycle apparatus, there is used a refrigerant mixture (R41OA, hereinafter)
`of difluoromethane (R32, hereinafter) having a molecular formula of CH2F2 and a boiling point of -51.7°C, and pen-
`tafluoroethane (R125, hereinafter) having a molecular formula of C2H F5 and a boiling point of -48.1°C. This R41OA is
`a fluorocarbon—based refrigerant mixture in which chlorine is not included but hydrogen is included in its molecular
`structure (H FC refrigerant, hereinafter). The R410A is used as an alternative refrigerant of afluorocarbon—based refrig—
`erant including chlorine in its molecularstructure (HCFC, hereinafter). The hidroclorofluorocar‘oon, e.g. ,HCFC refrigerant
`such as R22 has a depleting ability of ozone layer in the stratosphere, and its using amount and its production amount
`are restricted by the international regulation (i.e. Montreal Protocol concerning the Ozone Depleting Substances). But
`the HFC refrigerant has a problem that its global warming potential (GWP, hereinafter) is high.
`[0004] As a natural refrigerant having low GWP which shows an adverse influence for global warming which is another
`problem of global environment problem, a carbon dioxide (R744, hereinafter) is used as a refrigerant for a heat pump
`water heater which supplies hot water. The R744 has molecular formula of CO2, a triple point of —56.6°C and a critical
`temperature of 31.1 °C.
`[0005]
`In a refrigeration cycle apparatus using R744, the refrigeration cycle can be a trans-critical cycle in which
`condensation process is not included. A discharging pressure in a compressor of the refrigeration cycle apparatus is
`increased to about three times of 4.2M Pa which is a general set pressure (saturation pressure at 65°C) when R41 0A is
`used in an air conditioner, and the compressor discharging temperature is also prone to rise, and there is a problem
`that a pressure resistance of a refrigeration cycle part must be enhanced as compared with devices using R410A, the
`reliability of an insulative material of a compressor motor and a lubricant for a compressor must be enhanced.
`[0006] The main purpose of the study in KIM S G ET AL: "experiment and simulation on the performance of an
`autocascade refrigeration system using carbon dioxide as a refrigerant" INTERNATIONAL JOURNAL OF REFRIGER-
`ATION, OXFORD, GB, vol. 25, no. 8, December 2002 (2002-12), pages 1093-1101 is to investigate the performance
`of an autocascade refrigeration system using zeotropic refrigerant mixtures of R744/134a and R744/290. One of the
`advantages of this system is the possibility of keeping the highest pressure of the system within a limit by selecting the
`composition of a refrigerant mixture as compared to that in the vapor compression system using pure carbon dioxide.
`Performance test and simulation have been carried out for an autocascade refrigeration system by varying secondary
`fluid temperatures at evaporator and condenser inlets. Variations of mass flow rate of refrigerant, compressor power,
`refrigeration capacity, and coefficient of performance, COP, with respect to the mass fraction of R744 in R744/134a and
`R744/290 mixtures are presented at different operating conditions. Experimental results show similartrends with those
`from the simulation. As the composition of R744 in the refrigerant mixture increases, cooling capacity is enhanced, but
`COP tends to decrease while the system pressure rises.
`[0007]
`In MCLINDEN M 0 ET AL: "Thermodynamic properties forthe alternative refrigerant" INTERNATIONAL JOU R-
`NAL OF REFRIGERATION, OXFORD, GB, vol. 21, no. 4, June 1998 (1 998-06), pages 322-338 models commonly used
`to calculate thermodynamic properties of refrigerants are summarized. For pure refrigerants, the virial, cubic, Martin—
`Hou, Benedict-Webb-Rubin, and Helmholtz energy equations of state and the extended corresponding states model
`are discussed. High-accuracy formulations for 16 refrigerants are recommended. These models may be extended to
`mixtures through the use of mixing rules applied either to the parameters of the equation of state or to some property
`of the mixture components. Mixtures of a specific composition may also be modeled as a pseudo-pure fluid. Five mixture
`models, employing four distinct approaches, have been compared by a group working underthe auspices of the Inter—
`national Energy Agency. These comparisons show all five models to be very capable in representing mixture properties.
`No single model was best in all aspects, but based on its combination of excellent accuracy and great generality, the
`mixture Helmholtz energy model was recommended as the best available.
`MCLINDEN M 0 ET AL also presents a survey of the data available for mixtures of the HFC refrigerants R32, R125,
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`EP 1 491 608 B1
`
`R143a, R134a, and R152a and for mixtures ofthe natural refrigerants propane, butane, isobutane, and carbon dioxide.
`More than 60 data references are identified. Further data needs include caloric data for additional mixtures, compre-
`hensive pressure density-temperature data for additional mixture compositions, and improved accuracy for vapor-liquid
`equilibria data.
`[0008]
`EP—A—0 992 572 discloses a refrigerating machine oil for use with a CO2 refrigerant which comprises an ester
`oil. The refrigerating machine oils have an excellent lubricity, miscibility with a refrigerant, stability and electric insulation.
`[0009] HOSHINA K ET AL: "Lorentz angle measurementfor CO2/isobutane gas mixtures" NUCLEAR INSTRUMENTS
`& METHODS IN PHYSICS RESEARCH, SECTION - A: ACCELERATORS, SPECTROMETERS, DETECTORS AND
`ASSOCIATED EQUIPMENT, NORTH-HOLLAND PUBLISHING COMPANY. AMSTERDAM, NL, vol. 479, no. 2-3, 1
`March 2002 (2002-03-01), pages 278-293 have developed a Lorentz angle measurement system for cool gas mixtures
`for a proposed JLC central drift chamber. The measurement system is characterized by the use of two laser beams to
`produce primary electrons and flash ADCs to read their signals simultaneously. With the system Lorentz angles for
`CO2/isobutane gas mixtures with different proportions 95:5, 90:10, and 85:15, varying drift field from 0.6 to 2.0 kV/cm
`and magnetic field up to 1.5T were measured. The results of the measurement are in good agreement with GARFI ELD/
`MAGBOLTZ simulations.
`
`EP-A-1 234 868 discloses a refrigerating oil composition for a carbon dioxide refrigerant which comprises as
`[0010]
`a main component a mixture comprising a polyvinyl ether having a kinematic viscosity of 3 to 50 mmZ/s at 100°C in an
`amount exceeding 40% by weight and of 99.1% by weight or less and a polyoxyalkylene glycol having a kinematic
`viscosity of3 to 50 mmZ/s at 100°C in an amount of 0.1% byweight or more and less than 40% byweight. The composition
`exhibits an excellent lubricating property and a great viscosity index even when a carbon dioxide refrigerantis used.
`The composition exhibits excellent stability and an excellent lubricating property underthe atmosphere of carbon dioxide
`in the supercritical condition while the above advantageous properties are maintained and can be used for a long period
`of time.
`
`In view of the problem of the HFC refrigerant and R744 refrigerant and previous publications, it is an object of
`[0011]
`the present invention to provide an alternative refrigerant having excellent characteristics which can be used in an
`apparatus having a pressure resistance such as an air conditioner using R41 OA. It is another object of the invention to
`provide a refrigeration cycle apparatus using a refrigerant mixture of HC refrigerant and R744 and capable of lowering
`the compressor discharging temperature.
`
`Disclosure of the Invention
`
`[0012] To achieve the above object, the present invention provides a refrigerant mixture, characterized in that the
`refrigerant mixture comprises isobutane and R744, the concentration of R744 in the entire refrigerant mixture is 60% or
`lower by weight.
`[0013]
`In each of the above refrigerant mixtures, a leakage detecting additive of odorant or coloring agent is added.
`[0014] The invention also provides a refrigeration cycle apparatus using the above refrigerant mixture.
`[0015]
`In the refrigeration cycle apparatus of the invention, a compressor, a condenser, an expansion device and an
`evaporator are connected to one another in an annular form to form a refrigeration cycle, the refrigerant and a fluid, i.e.
`water, are allowed to flow such that they are opposed to each other in the condenser, thereby exchanging heat.
`[0016]
`In the refrigeration cycle apparatus, a gas-liquid separator is provided between an outlet of the expansion
`device and an inlet of the evaporator, the refrigerant mixture is separated by the gas—liquid separator into a gas phase
`refrigerant mixture and a liquid phase refrigerant mixture, a pipe ofthe gas—liquid separatoris connected to the evaporator
`such thatthe liquid phase refrigerant mixture flows into the evaporator, and a pipe ofthe gas-liquid separatoris connected
`to a suction line ofthe compressorsuch thatthe gas phase refrigerant mixtureflows into the suction line ofthe compressor.
`[0017]
`In the refrigeration cycle apparatus, a lubricant which is solved into the refrigerant mixture under an operation
`condition of the compressor and which has viscosity of 2 cm stokes or higher is used as a lubricant to be charged into
`the compressor.
`[0018]
`In the refrigeration cycle apparatus, a low pressure shell type compressor is used as the compressor.
`
`Brief Description of the Drawings
`
`[001 9]
`
`Fig. 1 shows characteristics of an embodiment of refrigerants according to an embodiment of the present invention;
`Fig. 2 is a circuit diagram of an embodiment of a refrigeration cycle apparatus using a refrigerant of the present
`invention;
`Fig. 3 shows characteristics of variation of condensed refrigeranttemperature and watertemperature of a refrigeration
`cycle apparatus using a refrigerant of the present invention; and
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`Fig. 4 is a circuit diagram showing another embodiment of the refrigeration cycle apparatus using the refrigerant of
`the invention.
`
`EP 1 491 608 B1
`
`Detailed Description of Preferred Embodiments
`
`[0020] Concrete embodiments of the present invention will be explained using Figs. 1 to 4.
`
`(Embodiment 1)
`
`1 shows gas-liquid equilibrium characteristics of a refrigerant mixture of R744 andHC refrigerant at 70°C.
`Fig.
`[0021]
`Examples of H0 refrigerants are propane (R290) having a molecularformula of 0H3-0H2-0H3, a boiling point of -42.1 °C
`and a critical temperature of 967°C; cyclopropane (R0270, hereinafter) having a molecularformula of 03H6, a boiling
`point of -32.9°0 and a critical temperature of 125.2°C; isobutane (R600a, hereinafter) having a molecular formula of i-
`04H8, a boiling point of -1 1 .7°C and a critical temperature of 134.7°0; and butane (R600, hereinafter) having a molecular
`formula of n-04H8, a boiling point of -.0.5°C and a critical temperature of 152.0°0.
`[0022]
`It can be found from Fig. 1 that R290, R0270, R600a, R600 and the like which are H0 refrigerants and R744
`constitute a non-azeotropic refrigerant mixture. It can be found from Fig.
`1 that as compared with 4.2MPa which is a
`general design pressure (saturation pressure of 65°C) when R410A is used for an airconditioner, a saturation pressure
`of a refrigerant mixture of R290 and R744 becomes equal to the designed pressure when the concentration of R744 is
`about 30% by weight or lower, a saturation pressure of a refrigerant mixture of R270 and R744 becomes equal to the
`designed pressure when the concentration of R744 is about 40% by weight or lower, a saturation pressure of a refrigerant
`mixture of R600a and R744 becomes equal to the designed pressure when the concentration of R744 is about 60% by
`weight or lower, and a saturation pressure of a refrigerant mixture of R600 and R744 becomes equal to the designed
`pressure when the concentration of R744 is about 70% by weight or lower,
`[0023] That is, when the concentration of R744 is equal to or lower than the above value, the saturation pressure of
`the refrigerant mixture becomes equal to or lower than 4. 2MPa which is a general design pressure (saturation pressure
`of 65°C) when R410A is used for an air conditioner. Therefore, the refrigerant mixture can be used for a refrigeration
`apparatus using R410A and having same pressure resistance as R410A.
`[0024] As can be found from Fig. 1 showing the characteristic curves, it is preferable that in the case of the refrigerant
`mixture comprising R290 and R744, the concentration of R744 is 15% by weight or lower, and in the cases of the
`refrigerant mixtures respectively comprising R0270 and R744; R600a and R744; and R600 and R744, the concentration
`of R744 is 30% by weight or lower.
`[0025]
`A critical temperature of H0 refrigerant such as R290, R0270, R600a and R600 is higher than that of R744.
`Therefore, a critical temperature of a non—azeotropic refrigerant mixture in which H0 refrigerant is mixed is equal to or
`higherthan that of R744. Thus, in a refrigeration cycle using R744, the cycle can become a trans- critical cycle which
`does not include a condensation process, but in a refrigeration cycle using non-azeotropic refrigerant mixture in which
`H0 refrigerant is mixed, subcritical cycle including a condensation process can be established depending upon a tem-
`peratu re condition.
`[0026] The non-azeotropic refrigerant mixture comprising H0 refrigerant and R744 shows excellent characteristics
`when it is used as a refrigerant for a refrigeration cycle apparatus, and this refrigerant mixture can solve the problem of
`the device.
`
`lfthe refrigerantmixture including R744 and H0 refrigerantwhich is natural refrigerant is used forthe refrigeration
`[0027]
`cycle apparatus, it is possible to eliminate the adverse influence acting on the ozone layer in the stratosphere. Further,
`since this refrigerant mixture includes only R744 and H0 refrigerant, and a GWP value of R744 is 1, and a GWP value
`of H0 refrigerant is less than 10, the refrigerant mixture has little effect on global warming. It is preferable that the upper
`limit of the concentration ("/0 by weight) of the natural H0 refrigerant is as specified by claims.
`[0028]
`Even if a very small amount of odorant mainly having methyl mercaptan, tetrahydrothiophene, ammonia or the
`like; coloring agent mainly having azoic pigment, fluorescent dye, fluorescent pigment orthe like, as a leakage detecting
`additive; or dissolve additive of odorant, dissolve additive of coloring agent or the like is added to H0 refrigerant such
`as R290, R0270, R600a or R600, the effect can be exhibited with a very small amount on the order of ppm.
`
`(Embodiment 2)
`
`Fig. 2 shows a schematic block diagram of the refrigeration cycle apparatus according to the embodiment 2 of
`[0029]
`this invention. In Fig. 2, a compressor 1 1 , a condenser 12, an expansion device 13 and an evaporator 14 are connected
`to one another through pipes to form a closed—circuit.
`In the condenser 12, water and a refrigerant mixture flow such
`that they are opposed to each other to exchange heat, thereby constituting a heat pump water heater. A refrigerant
`mixture comprising H0 refrigerant and R744 having non-azeotropic properties is charged as a refrigerant.
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`EP 1 491 608 B1
`
`Fig. 3 shows variations in refrigerant temperature and water temperature of the condenser when it is operated
`[0030]
`under a condition that 85% R290 by weight and 15% R744 by weight are charged into the refrigeration cycle apparatus
`of the present invention. Here, the pressure of the condensed refrigerant is controlled such that the water temperature
`at the outlet of the condenser becomes 90° under a condition that the water supply temperature is 10°C, the pinch
`temperature ofthe condenser between the refrigeranttemperatu re and the watertemperature is 5 degrees, the refrigerant
`temperature at the outlet of the condenser is 19°C, and the average evaporation temperature of the evaporator is 2°C.
`As a result, the water temperature can be heated to 90°C underthe condensed refrigerant pressure of 4.2MPa.
`[0031]
`In Table 1, heating performance is compared among single refrigerants of R290 and R744 using the following
`refrigerant mixtures 1) to 4) in the heat pump water heater: 1) a refrigerant mixture of R290 and R744, and R744 is in
`a range of 0% to 20% by weight is included (when R744 is 0% by weight, this refrigerant is propane single refrigerant);
`2) a refrigerant mixture comprising RC270 and R744; 3) a refrigerant mixture comprising R600a and R744; and 4) a
`refrigerant mixture comprising R600 and R744 wherein the concentration of R744 is 30% by weight.
`
`Refrigerant
`
`R290/R744
`
`Table 1
`
`RC270
`/R744
`
`R600a
`/R744
`
`R600 /R744
`
`
`
`concentrfmon
`%by weight
`co
`
`100/0
`
`95/5
`
`90/10
`
`35/15
`
`80/20
`
`0/100
`
`70/30
`
`70/30
`
`70/30
`
`Td °C
`
`103
`
`104
`
`105
`
`106
`
`107
`
`107
`
`108
`
`109
`
`_
`
`if the concentration of R744 is set in the following ranges, it is possible to supply water
`[0032] As apparent Table 1,
`of 90°C at a discharging pressure of the compressor less than 4.2MPa which is a general set pressure (saturation
`pressure of 65°C) when R410A is used for an air conditioner. That is, the concentration of R744 is: 15% by weight or
`lower in the case of the refrigerant mixture comprising R290 and R744; and 30% byweight or lower in the case of the
`refrigerant mixture comprising RC270 and R744, the refrigerant mixture comprising R600a and R744, and the refrigerant
`mixture comprising R600 and R744.
`[0033]
`In the case of a single refrigerant of R290 and a refrigerant mixture of R290 and R744, although the condensing
`pressure (Pd) is increased as the concentration of R744 is increased, these refrigerants show coefficient of performance
`(COP) which is equal to or higher than those of R290 and R744.
`is a feature of the non-azeotropic refrigerant mixture,
`[0034] The condensation temperature gradient (ATc) in Table 1
`and at this gradient shows a temperature variation when a refrigerant is condensed by the condenser under a constant
`pressure. Since the refrigerant mixture of R290 and R744 has non-azeotropic properties, the condensation temperature
`gradient is as high as 17.6 degrees when the concentration of R744 is 15% by weight.
`In a cycle of a water heater in
`which water and refrigerant flow such that they are opposed to each other in the condenser to exchange heat, the
`average condensation temperature is lowered, the compression ratio is lowered, and performance is enhanced. The
`same effect can be obtained also when other HC refrigerant such as RC270, R600a, R600 is mixed. When HC refrigerant
`and R744 are mixed and they are used in a refrigeration cycle apparatus, performance can be enhanced.
`[0035]
`It can befound from Table 1 that the discharge temperature lowering effect of R290 is higheras the concentration
`of R290 is higher, and that when the concentration of R744 is 15% by weight and the concentration of R290 is 85%
`byweight, the discharge temperature is lowered by about 2 degrees as compared with a single refrigerant of R744. When
`the refrigerant mixture of HC refrigerant and R744 is used as a refrigerant for a refrigeration cycle apparatus, excellent
`characteristics are exhibited.
`
`(Embodiment 3)
`
`[0036]
`
`Fig. 4 is a schematic block diagram of a refrigeration cycle apparatus according to an embodiment 3 of the
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`EP 1 491 608 B1
`
`present invention. In Fig. 4, the compressor 11, the condenser 12, the expansion device 13, a gas-liquid separator 15
`and the evaporator 14 are connected to one another through pipes to form a closed-circuit. In this refrigeration cycle, a
`refrigerant circulates in a direction of the arrow. A refrigerant mixture having HC refrigerant and R744 having non-
`azeotropic properties is charged into the refrigeration cycle as a refrigerant.
`[0037]
`In the gas—liquid separator 15, the pipe thereof is connected to the evaporator 14 such that a gas phase
`refrigerant and a liquid phase refrigerant of the refrigerant mixture are separated from each other and the liquid phase
`refrigerant flows into the evaporator 14, and the pipe of the pipe of the gas-liquid separator 15 is connected to a suction
`line of the compressor 11 such that the gas phase refrigerant flows into the suction line of the compressor 11.
`[0038] Here, since the non-azeotropic properties of the HC refrigerant and R744 are high, the gas phase refrigerant
`separated by the gas-liquid separator 15 becomes a refrigerant having high concentration of R744 having low boiling
`point, and the liquid phase refrigerant becomes a refrigerant having high concentration of HC refrigerant having high
`boiling point. Since a refrigerant mixture having higher concentration than that of the charged HC refrigerant flows into
`the evaporator 14, the non-azeotropic properties become smaller, and the temperature gradient also becomes smaller.
`As a result, a difference between the inlet refrigerant temperature and the outlet refrigeranttem perature of the evaporator
`becomes smaller. When the outside temperature is low, the temperature of the refrigerant mixture of the evaporator
`becomes 0°C or lower, and frost is formed on a fin portion having temperature of 0°C or lower. However, since gas and
`liquid of the refrigerant mixture are separated from each other by the gas-liquid separator and the difference between
`the inlet refrigerant temperature and the outlet refrigerant temperature of the evaporator can be lowered, it is possible
`to prevent frost from being partially formed on the evaporator.
`[0039]
`If HC refrigerant and R744 refrigerant mixture coexist, since HC refrigerant is selectively dissolved into the
`lubricant in an operation state, the lubricant for the compressor 11 may be a lubricant having an insoluble region with
`respect to R744 in an operation condition of the compressor 11, and it becomes easy to select the lubricant and to
`manage the viscosity.
`It is known that solubility between R744 and various lubricants becomes insoluble not only at a
`low temperature but also at a high temperature. If HC refrigerant is allowed to selectively be solved in a lubricant in the
`compressor 11, the lubricant discharged from the compressor 11 can easily return to the compressor 1 1, the amount of
`the lubricantin the compressor1 1 can sufficiently be maintained, andthe reliability ofthe compressor 1 1 can be enhanced.
`[0040] Viscosity indices of lubricants having viscosity grade of 5 cm stokes or higher at 100°C are varied depending
`upon the kinds of lubricants, but such lubricants have viscosity grade of 50 cm stokes at 40°C.
`If a lubricant having
`viscosity grade of 5 cm stokes of higher at 100°C and a refrigerant mixture having HC refrigerant and R744 coexist, HC
`refrigerant is selectively solved in the lubricant in a compressor operation state, and the viscosity of lubricant is lowered.
`[0041] That is, even if the HC refrigerant is selectively solved in the lubricant and the viscosity of the lubricant is
`lowered, if a lubricant having viscosity grade of 2 cm stokes or higher is selected, the reliability is enhanced.
`[0042]
`Further, even with a lubricant in which the refrigerant mixture having HC refrigerant and R744 is not solved at
`all or partially solved, if a lubricant having viscosity grade of 2 cm stokes or higher in the compressor operation state is
`selected, the reliability is enhanced.
`[0043] The upper limit of the viscosity grade is not especially limited, but an appropriate upper limit is 20 cm stokes
`or lower at 100°C because electric consumption caused by sliding friction is prevented from being increased. As a
`lubricant, the following base oil may be used alone or in combination: naphthene-base, paraffin-base mineral oil, alkyl-
`benzene oil, ether oil, ester oil, pollyalkylene glycol oil, carbonate oil and the like.
`[0044] When a low pressure sell type compressor is used as the compressor 11 used in the embodiments of the
`present invention, since the lubricant comes into contact with a low pressure refrigerant of the refrigeration cycle, the
`amount of refrigerant solved into the lubricant can be reduced to an extremely small value and thus, the amount of
`refrigerant including hydrocarbon which is flammable refrigerant can be reduced, and safety of the apparatus can be
`enhanced.
`
`[0045] According to the present invention, the refrigerant mixture comprises R600a and R744. The concentration of
`R744 is 60% or lower by weight and is more preferably 30% or lower by weight. With this refrigerant mixture, adverse
`influences acting on ozone layer in the stratosphere and on global warming can be eliminated almost at all, high pressure
`can be reduced, and a part for an air conditioner using R41OA can be used.
`[0046]
`Further, according to the present invention, the non—azeotropic properties of the refrigerant mixture is enhanced
`by mixing HC refrigerant and R744, and when this is used in a refrigeration cycle apparatus such as a heat pump water
`heater, the coefficient of performance can be made higher than that of a single refrigerant of HC refrigerant.
`[0047]
`Further, according to the present invention, since HC refrigerant and R744 are mixed, when it is used in a
`refrigeration cycle apparatus, the discharging temperature in the compressor can be lowered than R744.
`[0048]
`Further, according to the present invention, since HC refrigerant is solved in the compressor lubricant, it is
`possible to secure an oil return of the compressor lubricant which coexists with R744 into the compressor.
`[0049]
`Further, according to the present invention, since a lubricant having viscosity grade of 2 cm stokes or higher
`in a compressor operation state is selected, the reliability is enhanced.
`[0050]
`Further, accordingto the present invention, since a low pressure shell type compressoris used as acompressor,
`
`10
`
`15
`
`20
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`25
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`30
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`35
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`40
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`45
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`50
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`55
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`

`

`the amount of HC refrigerant solved into a lubricant can be reduced, and a charging amount of refrigerant into a refrig-
`eration cycle can be reduced.
`
`EP 1 491 608 B1
`
`Claims
`
`A refrigerant mixture, characterized in that said refrigerant mixture comprises isobutane and carbon dioxide, the
`concentration of carbon dioxide in the entire refrigerant mixture is 60% or lower by weight, and the concentration of
`isobutane in the entire refrigerant mixture is remaining % by weight obtained by subtracting said the concentration
`of carbon dioxide from said refrigerant mixture.
`
`, characterized in that a leakage detecting additive of odorant or
`The refrigerant mixture according to claim 1
`coloring agent is added to the refrigerant mixture.
`
`A refrigeration cycle apparatus using the refrigerant mixture according to claim 1 or 2.
`
`The refrigeration cycle apparatus according to claim 3. characterized in that a compressor. a condenser. an
`expansion device and an evaporator are connected to one another in an annular form to form a refrigeration cycle,
`a refrigerant mixture flowing through said condenser and a non—heated fluid are allowed to flow such that they are
`opposed to each other, thereby exchanging heat.
`
`The refrigeration cycle apparatus according to claim 4, characterized in that a gas-liquid separator is provided
`between an outlet of said expansion device and an inlet of said evaporator, said refrigerant mixture is separated by
`said gas-liquid separator into a gas phase refrigerant mixture and a liquid phase refrigerant mixture, a pipe of said
`gas-liquid separator is connected to said evaporator such that said liquid phase refrigerant mixture flows into said
`evaporator, and a pipe of said gas-liquid separator is connected to a suction line of said compressor such that said
`gas phase refrigerant mixture flows into said suction line of said compressor.
`
`The refrigeration cycle apparatus according to claims 4 or 5, characterized in that a lubricant which is solved into
`said refrigerant mixture under an operation condition of said compressor and which has viscosity of 2 cm stokes or
`higher is used as a lubricant to be charged into said compressor.
`
`The refrigeration cycle apparatus according to claims 4 or 5, characterized in that a low pressure shell type
`compressor is used as said compressor.
`
`Patentanspriiche
`
`1. KLihlmittelmischung, dadurch gekennzeichnet, dass die Kiihlmittelmischung lsobutan und Kohlendioxid umfasst,
`wobei die Konzentration des Kohlendioxids in der Gesamtkiihlmittelmischung 60 Gewichts-°/o oderweniger betragt
`und die Konzentration des lsobutans in der Gesamtkl'ihlmittelmischung die restlichen Gewichts—% betrégt, die durch
`Subtraktion der Konzentration des Kohlendioxids von der KUhlmittelmischung erhalten wird.
`
`KUhlmittelmischung gemaB Anspruch 1, dadurch gekennzeichnet, dass der Ktihlmittelmischung ein Leckerken-
`nungsadditiv in Form eines Odorier- oder Farbemittels zugegeben wird.
`
`Kaltekreislaufvorrichtung, die die Kilhlmittelmischung gemaB Anspruch 1 oder 2 verwendet.
`
`Kaltekreislaufvorrichtung gemaB Anspruch 3, dadurch gekennzeichnet, dass ein Verdichter, ein Verfliissiger,
`eine Ausdehnungsvorrichtung und ein Verdampfer miteinander in einer Ringform verbunden sind, um einen Kélte-
`kreislauf zu bilden, wobei eine Kijlhlmittelmischung durch den Verfliissiger stromt und ein nicht erwarmtes Fluid
`derart stromen kann, dass sie einander entgegenwirkend sind, wodurch Wérme ausgetauscht wird.
`
`Kaltekreislaufvorrichtung gemaB Anspruch 4, dadurch gekennzeic