Patent Application
20250002769
The present disclosure relates to a refrigeration cycle device.
The refrigerant used for a refrigeration cycle device is currently restricted by, for example, the Fluorocarbon Emissions Control Act (enacted on April 2015). Specifically, the upper limit is set on the Global Warming Potential (GWP) value of the refrigerant to be used. Thus, use of a refrigerant having a further low GWP is needed.
In recent years, for example, hydrocarbons having 1 to 4 carbon atoms such as R-290 (propane), R-1270 (propylene), R-600a (isobutane) are examined as the refrigerant having a low GWP value. The hydrocarbons having 1 to 4 carbon atoms have a further lower GWP value than saturated fluorinated hydrocarbon compounds (hydrofluorocarbons), which are refrigerants having a relatively low GWP value.
However, the hydrocarbons having 1 to 4 carbon atoms have higher flammability than hydrofluorocarbons. For example, in the international standard ISO-817, which defines safety classification for refrigerants, R-32 (difluoromethane), one of the hydrofluorocarbons, is registered as lower flammability (Class 2L), and on the other hand, R-290, R-1270, and R-600a are registered as higher flammability (Class 3).
For example, when a refrigerant having high flammability, such as a hydrocarbon having 1 to 4 carbon atoms, is used as the refrigerant for a refrigeration cycle device, it is preferable to take a measure of making the refrigerant recognizable by the sense of smell or the sense of vision. In addition, to suppress the dissolution of the refrigerant into a refrigeration oil and to reduce the amount of the refrigerant to be filled, it is preferred to use a refrigeration oil having a low solubility with the refrigerant.
As the measure of making the refrigerant recognizable by the sense of smell, for example, Patent Literature 1 (Japanese Patent Laying-Open No. 2020-112285) discloses a method including mixing a sulfur-based odorant such as mercaptan, sulfide, or thiophene with the refrigerant to detect the leakage of the refrigerant by an unpleasant odor. Patent Literature 1 also discloses that use of polyalkylene glycol as a refrigeration oil enables reduction in the amount of the refrigerant dissolved in the refrigeration oil, and can thus ensure necessary refrigeration cycle performance with a lower amount of the refrigerant to be filled.
Patent Literature 2 (Japanese Patent Laying-Open No. 2002-38135) discloses that tetrahydrothiophene (THT) is preferable as an odorant since it does not react with the material for the refrigerating circuit, has miscibility with the refrigerant, and has miscibility with refrigeration oil.
However, the inventors have found the following: sulfur-based odorants such as THT have polarity due to the bias of charge in the molecule; thus, when a refrigeration oil having high polarity is used, the sulfur-based odorant is dissolved in the refrigeration oil in a compressor so that the amount of the sulfur-based odorant that circulates in the refrigerant circuit with the refrigerant is reduced; and when the refrigerant is released from the refrigeration cycle device, the refrigerant is hardly detectable by the sense of smell. In addition, since polyalkylene glycol contain a large amount of oxygen (O), which is an element having a large electronegativity in the molecular structure, they are refrigeration oils having high polarity and dissolve a large amount of sulfur-based odorants depending on the composition.
The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide a refrigeration cycle device that suppresses the dissolution of a sulfur-based odorant in polyalkylene glycol and makes the leakage of a refrigerant recognizable by the sense of smell.
A refrigeration cycle device according to the present disclosure includes a refrigerant circuit including a compressor, wherein
According to the present disclosure, a refrigeration cycle device that suppresses the dissolution of the sulfur-based odorant in polyalkylene glycol and makes the leakage of the refrigerant recognizable by the sense of smell can be provided.
Hereinafter, the embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the dimensional relationship of the length, width, thickness, depth, and the like is appropriately changed for the purpose of clarity and simplification of the drawing, and does not indicate the actual dimensional relationship.
First, the outline of the refrigeration cycle device of the present embodiment is briefly described.
Compressor 3 of outdoor unit 1 and evaporator 7 of indoor unit 2 are connected via a gas pipe 10. Condenser 4 of outdoor unit 1 and expansion valve 6 of indoor unit 2 are connected via a liquid pipe 9.
A refrigerant circuit 100 is formed by such a refrigeration cycle device configuration, and a refrigerant is circulated in refrigerant circuit 100 via liquid pipe 9 and gas pipe 10.
Compressor 3 compresses the refrigerant that has turned into a gaseous state in gas pipe 10. Condenser 4 cools the gaseous refrigerant that has been compressed by compressor 3 to form a high-pressure liquid refrigerant or a gas-liquid two-phase refrigerant. Expansion valve 6 reduces the pressure of the high-pressure liquid refrigerant or the gas-liquid two-phase refrigerant. Evaporator 7 heats the refrigerant reduced in pressure to form a low-pressure gaseous refrigerant. Compressor 3 sucks and recompresses the refrigerant that has turned into a low-pressure gaseous state by evaporator 7.
Outdoor blower 5 is a constituent that sends air to condenser 4, and is provided to promote the absorption and release of heat by the heat exchange of the refrigerant flowing in condenser 4 with air. Indoor blower 8 is a constituent that sends air to evaporator 7, and is provided to promote the absorption and release of heat by the heat exchange of the refrigerant flowing in evaporator 7 with air.
In the present embodiment, the configuration for carrying out the heat exchange of condenser 4 and evaporator 7 with air is described, but the configuration is not limited to this configuration. For example, condenser 4 and evaporator 7 may be configured so as to exchange heat with not air but a liquid such as water.
In the present embodiment, the configuration in which evaporator 7 is provided in indoor unit 2 is described, but the configuration is not limited to this configuration. For example, condenser 4 may be arranged on the inside, and evaporator 7 may be arranged on the outside.
With respect to outdoor unit 1 as described above, for example, a four-way valve or a combination of a plurality of valves may be arranged, or a switching mechanism that switches an inlet pipe and a discharge pipe of compressor 3 may be provided. By providing a switching mechanism, the heat exchanger in outdoor unit 1 functions as evaporator 7 and the heat exchanger in indoor unit 2 functions as condenser 4, whereby heating of the indoor using the outdoor heat is enabled.
The refrigeration cycle device may be, for example, any of a device capable of carrying out both cooling and heating, a device capable of carrying out only cooling, or a device capable of carrying out only heating.
In the present embodiment, the configuration in which expansion valve 6 is provided in indoor unit 2 is described, but the configuration is not limited to this configuration. For example, expansion valve 6 may be arranged in outdoor unit 1. For example, expansion valve 6 may be provided on both outdoor unit 1 and indoor unit 2. Further, for example, a plurality of indoor units 2 or a plurality of outdoor units 1 may be provided in refrigerant circuit 100.
Next, the refrigerant enclosed in the refrigerant circuit in the present embodiment will be described. The refrigerant contains a main component that functions as the refrigerant, and further contains a sulfur-based odorant for detecting the leakage of the refrigerant.
Herein, the aforementioned “main component” is the component whose proportion in the total amount of the refrigerant (including the sulfur-based odorant and the others) (content in the refrigerant) is more than 50% by mass. The content of the main component in the refrigerant is preferably 90% by mass or more, and more preferably 95% by mass or more.
The main component that functions as the refrigerant is a hydrocarbon having 1 to 4 carbon atoms. Examples of the hydrocarbon having 1 to 4 carbon atoms include R-290 (propane), R-1270 (propylene), and R-600a (isobutane). The hydrocarbon having 1 to 4 carbon atoms is preferably propane, propylene, or a mixture thereof. This is because they have an operating pressure suitable for use for the refrigeration cycle device. In view of oxidation stability, propane is more preferable. Propane has a GWP value significantly as low as 3 and also high cooling performance, and may thus contribute to the reduction in environmental load during the production and operation of the refrigeration cycle device.
The sulfur-based odorant blended in the refrigerant is an odorant containing a sulfur element. Examples of the sulfur-based odorant include mercaptans, sulfides, and thiophenes. Examples of mercaptans include tertiary butyl mercaptan (TBM) and ethyl mercaptan (EM); examples of sulfides include dimethyl sulfide (DMS) and diethyl sulfide (DES); and examples of thiophenes include tetrahydrothiophene (THT). These sulfur-based odorants are compounds that have been used in fuel gas and have an unpleasant odor. One of these sulfur-based odorants may be used singly, or two or more thereof may be used in combination.
The sulfur-based odorant is preferably TBM, EM, DMS, THT, which are also used in fuel gas for households, or a mixture thereof. Mixing a sulfur-based odorant used in fuel gas for households in the refrigerant enables the leakage of the refrigerant to be easily detected by an unpleasant odor inherent in the sulfur-based odorant.
The sulfur-based odorant is more preferably THT. THT is chemically stable as compared with TBM, EM, DMS and the like, so that it hardly causes a decomposition reaction or a corrosion reaction in the refrigerant circuit, and THT also hardly causes solidification in the refrigerant circuit because of its melting point as low as −96° C.
The content of the sulfur-based odorant is preferably 50 ppm by weight or more and less than 1,100 ppm by weight. The reason for this is as follows: when the content of the sulfur-based odorant is within the above range, the leakage of the refrigerant from the refrigerant circuit can be easily detected and a not excessively unpleasant odor is obtained. The content of the sulfur-based odorant is more preferably 90 ppm by weight or more and less than 1026 ppm by weight, and further preferably 176 ppm by weight or more and less than 987 ppm by weight.
In the present embodiment, the refrigeration cycle device includes a compressor. The refrigerant passes through the inside of the compressor. The compressor contains a refrigeration oil that contains polyalkylene glycol as a main component.
The refrigerant that has passed through accumulator 16 flows from inlet pipe 14 into compression mechanism 12 in shell 11. The refrigerant that has flowed into compression mechanism 12 is compressed to have high temperature and high pressure, and is discharged from discharge pipe 15. That is, compression mechanism 12 is configured to compress the refrigerant that has flowed from inlet pipe 14 into shell 11 and discharge the refrigerant from discharge pipe 15.
Compression mechanism 12 is a rotary-type compression mechanism composed of a combination of a rolling piston 17 and a vane (not shown) and the like. The refrigerant is compressed by changing the volume of a space surrounded by the inner peripheral surface of a cylinder chamber 19 of a cylinder 18 and the outer peripheral surface of rolling piston 17 and the vane (not shown) by an eccentric rotary motion of rolling piston 17.
The compressed refrigerant is discharged from a discharge hole 21 of an upper bearing 20 to a muffler space 22, and then discharged from a discharge hole 24 of a discharge muffler 23 into shell 11. The discharged refrigerant passes through a gap in electric motor 13 (such as a gap between an electric motor rotor 25 and an electric motor stator 26 or a groove provided on the outer peripheral surface of the electric motor stator 26), and is then discharged from discharge pipe 15 to the downstream side of the refrigerant circuit 100.
Compressor 3 has a sliding part on the inside of compression mechanism 12. For lubrication of the sliding part, a refrigeration oil is stored in an oil reservoir part 27, which is located below compressor 3. The refrigeration oil stored in oil reservoir part 27 is supplied through an oil supply hole (not shown) provided in the shaft of a driving shaft 28 to the sliding part in the inside of compression mechanism 12 by pumping action. The refrigeration oil is brought into contact with the refrigerant in compressor 3.
Next, the refrigeration oil that fills the inside of the compressor for lubrication in the present embodiment will be described. The main component which functions as the refrigeration oil is polyalkylene glycol (PAG).
Herein, the aforementioned “main component” is the component whose proportion in the total amount of the refrigeration oil is more than 50% by mass. The content of the main component in the refrigeration oil is preferably 80% by mass or more, and more preferably 90% by mass or more.
PAG is a polymer of at least one selected from the group consisting of an ethylene oxide group (EO group) and a propylene oxide group (PO group) and is represented by the following chemical formula.
In the above chemical formula 1, m and n are each an integer of 0 or more and represent the number of EO groups and PO groups, and R1 and R2 are a hydrogen atom (H) or a hydrocarbon chain having one or more carbon atoms (C). The arrangement of EO groups and PO groups may be any of a random copolymer, an alternating copolymer, and a block copolymer.
In the above chemical formula 1, m and n preferably satisfy the relationships of the following formulas (1) and (2). When the relationships of the following formulas (1) and (2) are not satisfied, PAG may be solidified at low temperatures. R1 and R2 are preferably a hydrocarbon chain having one or more carbon atoms (C). When R1 and R2 are a hydrogen atom (H), the hygroscopicity of PAG increases, and the moisture may be mixed.
The ratio of the number of oxygen atoms (O) to the number of carbon atoms (C) in the molecular structure of PAG (O/C ratio) (hereinafter, also simply referred to as the “O/C ratio”) is 0.50 or less. When the O/C ratio is 0.50 or less, the amount of the sulfur-based odorant dissolved in PAG is small, and the refrigerant released from the refrigerant circuit is recognizable by the sense of smell. The O/C ratio is preferably 0.43 or less, and more preferably 0.39 or less. The lower limit of the O/C ratio is not particularly limited, and the O/C ratio may be 0.25 or more, or may be 0.30 or more.
Other refrigeration oils may be mixed in the refrigeration oil, as long as the O/C ratio in the molecular structure of PAG is lower than that of PAG. Examples of other refrigeration oils include polyol ester, polyvinyl ether, alkylbenzene, alkylnaphthalene, mineral oil, poly α-olefin, or a mixture thereof. Since polyol ester and polyvinyl ether have low miscibility with a hydrocarbon having 1 to 4 carbon atoms like PAG, the amount of the refrigerant to be dissolved therein is small so that the amount of the refrigerant to be filled can be reduced. Accordingly, polyol ester and polyvinyl ether are preferable.
The refrigeration oil may contain an antioxidant, an acid scavenger, or an extreme-pressure agent (anti-wear agent) as a lubricant additive.
Examples of the antioxidant include phenol-based antioxidants such as 2,6-di-tert-butyl-4-methyl phenol, 2,6-di-tert-butyl-4-ethylphenol, and 2,2′-methylenebis(4-methyl-6-tert-butylphenol), and amine-based antioxidants such as phenyl-α-naphthylamine and N,N′-di-phenyl-p-phenylenediamine.
Examples of the acid scavenger include epoxy compounds such as phenyl glycidyl ether, alkyl glycidyl ester, alkyl glycidyl ether, alkylene glycol glycidyl ether, cyclohexene oxide, α-olefin oxide, and epoxidized soybean oil. The acid scavenger is preferably alkyl glycidyl ester, alkyl glycidyl ether, or α-olefin oxide.
Examples of the extreme-pressure agent (anti-wear agent) include phosphorus-based extreme-pressure agents such as phosphate esters, thiophosphate esters, acid phosphate esters, phosphite esters, acid phosphite esters and amine salts thereof. The extreme-pressure agent (anti-wear agent) is preferably a phosphate ester, a thiophosphate ester, or a mixture thereof. Specifically, tricresyl phosphate (O═P—(OC7H7)3), triphenyl phosphorothioate (S═P—(OC6H5)3), triphenyl phosphate (O═P—(OC6H8)3), derivatives thereof, or a mixture thereof is preferable.
The refrigeration oil may contain an oxygen scavenger. Examples of the oxygen scavenger include sulfur-containing aromatic compounds such as 4,4′-thiobis(3-methyl-6-tert-butylphenol), diphenyl sulfide, dioctyl diphenyl sulfide, dialkyl diphenylene sulfide, benzothiophene, dibenzothiophene, phenothiazine, benzothiapyran, thiapyran, thianthrene, dibenzothiapyran, and diphenylene disulfide; aliphatic unsaturated compounds such as various olefins, diene, and triene; and cyclic terpenes having an unsaturated bond, such as α-pinene, β-pinene, limonene, and phellandrene. The oxygen scavenger is preferably an aliphatic unsaturated compound or a cyclic terpene having an unsaturated bond.
Also, the refrigeration oil may contain a fluorescent agent, a colorant, or the like so as to visually detect the refrigerant and the refrigeration oil.
However, if moisture is contained in the refrigeration oil, the deterioration of the refrigerant, refrigeration oil, and materials in the compressor may be promoted, and thus, it is necessary to control the amount of the moisture contained in the refrigeration oil to be filled so as to be 100 ppm by weight or less.
The refrigeration cycle device has been described above with reference to a mode in which a rotary compressor is used as compressor 3, but the refrigeration cycle device is not limited thereto. For example, a low-pressure shell or high-pressure shell scroll compressor, a screw compressor, or the others may be used as compressor 3.
The difference between the HSP distance between PAG and the sulfur-based odorant and the HSP distance between PAG and the refrigerant is −2.0 or more. Hereinafter, the HSP distance between PAG and the sulfur-based odorant is sometimes referred to as “the HSP distance to the sulfur-based odorant”, and the HSP distance between PAG and the refrigerant is sometimes referred to as “the HSP distance to the refrigerant”.
Herein, “HSP” means “Hansen Solubility Parameter”, and is a value used to predict the solubility of substances based on the idea that “substances having similar intramolecular interactions are easily dissolved in each other”. Specifically, HSP is represented as a three-dimensional vector by three parameters (dD, dP, and dH), which are a dispersion term, a polar term, and a hydrogen bond term, respectively. As for two substances, the solubility is higher, as their vectors (dD, dP, and dH) are similar.
The HSP of a substance can be cited from the database and calculated from the molecular structure by using computer software, HSPiP (Hansen Solubility Parameter in Practice). When HSPiP is not used, the calculation method for HSP is described in literatures (e.g., Van Krevelen, Properties of Polymers, 4th Edition, 2009).
The “HSP distance” is the distance between HSP values of two substances, and is a value indicating the similarity of vectors ((dD1, dP1, and dH1) and (dD2, dP2, and dH2)) of two substances. Specifically, it is determined by the following formula (3) based on the above three parameters (dD, dP, and dH). With respect to two substances whose HSP distances are to be calculated, dD, dP, and dH of one substance are represented by dD1, dP1, and dH1, and dD, dP, and dH of another substance are represented by dD2, dP2, and dH2, in the following formula (3). As for two substances, the solubility is lower, as the HSP distance is larger.
As the amount of the sulfur-based odorant dissolved in PAG is smaller, the amount of the sulfur-based odorant that circulates in the refrigerant circuit is larger, and the refrigerant released from the refrigerant circuit is recognizable by the sense of smell. In addition, as the amount of the refrigerant excluding the sulfur-based odorant dissolved in PAG is larger, the amount of the sulfur-based odorant dissolved in PAG is smaller due to the influence of the refrigerant excluding the sulfur-based odorant dissolved in PAG for the reason described below, and as a result, the amount of the sulfur-based odorant that circulates in the refrigerant circuit is larger, so that the refrigerant released from the refrigerant circuit is recognizable by the sense of smell. Namely, as the difference between the HSP distance to the sulfur-based odorant and the HSP distance to the refrigerant (the HSP distance to the sulfur-based odorant—the HSP distance to the refrigerant) is larger, the amount of the sulfur-based odorant dissolved in PAG is smaller, a larger amount of the sulfur-based odorant is contained in the refrigerant released from the refrigerant circuit, and the refrigerant released from the refrigerant circuit is recognizable by the sense of smell.
When the difference between the HSP distance to the sulfur-based odorant and the HSP distance to the refrigerant is −2.0 or more, the amount of the sulfur-based odorant dissolved in PAG is sufficiently small, and the refrigerant released from the refrigerant circuit is recognizable by the sense of smell. The difference between the HSP distance to the sulfur-based odorant and the HSP distance to the refrigerant is preferably-0.5 or more, and more preferably 0 or more. The upper limit of the difference between the HSP distance to the sulfur-based odorant and the HSP distance to the refrigerant is not particularly limited, and the difference may be 5.0 or less, or 3.0 or less.
Hereinafter, the present disclosure will be described in detail with reference to Examples, but the present disclosure is not limited to these Examples.
Refrigerant gas in which a refrigerant, a sulfur-based odorant, and PAG were mixed was prepared under the conditions shown in Table 1 to evaluate the amount of the sulfur-based odorant released with the refrigerant when the refrigerant, the sulfur-based odorant, and PAG were mixed. In PAG used, m=7, n=36, and R1 and R2 were CH3. The concentration of the sulfur-based odorant (THT) in the refrigerant gas is shown in Table 2.
The above refrigerant gas was enclosed in a test container, which was shaken at 140° C. to stir the refrigerant gas, and then, the test container was allowed to stand still at 25° C. 24 hours after the start of still standing, a tedlar bag (1-2711-05 manufactured by AS ONE Corporation) was connected to the discharge port of the test container, and the refrigerant gas was collected at 25° C. For the collected refrigerant gas, the concentration of THT was measured by using a gas chromatography mass spectrometer (JMS-K9 manufactured by JEOL Ltd.).
The relationship between the concentration of THT in the enclosed refrigerant gas and the concentration of THT in the collected refrigerant gas is shown in
Even when THT was mixed in R-290 as described above, THT was dissolved in PAG, so that only a part of THT in the enclosed refrigerant gas was released with R-290, and the refrigerant was demonstrated to be hardly detectable by the sense of smell when the refrigerant was released from the refrigeration cycle device.
Each sample gas in which air was mixed with a sulfur-based odorant (THT) was prepared under the conditions shown in Table 3 to quantitatively evaluate the relationship between the concentration of the sulfur-based odorant in air and the intensity of the odor. The concentration of THT in the sample gas is shown in Table 4.
The odor index (equivalent value) of the above sample gas was measured. Herein, the “odor index” is a numerical expression for the degree of odor using the human sense of smell, and is a value obtained by multiplying the common logarithm of the odor concentration of an odor component (the concentration of the odor component when the odor is diluted with air to the extent that the odor can no longer be sensed by the human sense of smell) by 10. The “odor index (equivalent value)” is a numerical value corresponding to the odor index and obtained by the measurement with an odor identification device. In the measurement, nitrogen (N2) was used as the carrier gas, and the dilution factor of the sample with the carrier gas was set to 100.
The relationship between the concentration of THT in the sample gas and the odor index (equivalent value) is shown in
The odor index has a relationship with the odor intensity in the 6-step odor intensity display method as shown in Table 5. The concentrations of THT shown in Table 5 were the results of the determination of the concentration of THT corresponding to an odor intensity of 2.5 to 3.5, based on the relationship between the concentration of THT and the odor index (equivalent value) in
To recognize the refrigerant by the sense of smell, the presence of the sulfur-based odorant contained in the refrigerant is needed to be recognized. Accordingly, the odor intensity of the refrigerant is preferably 2 (a weak odor whose odor source can be seen) or more, and more preferably 3 (an odor is sensed with ease) or more.
The refrigerant released from the refrigerant circuit into the atmosphere is diluted with air, and the concentration of THT is reduced. The international standard ISO-13734 relating to the odorization treatment of natural gas states that the natural gas is needed to have an odor even when being diluted to 20% by volume of the lower flammability limit (LFL). The LFL of R-290 is 21,000 ppm by volume in ISO-817, and 20% of the LFL is thus 4,200 ppm by volume.
As for the odorization treatment of gas, the Japanese ordinance on the odorization treatment of gas (an ordinance that establishes technical standards of gas facilities (Ordinance of the Ministry of International Trade and Industry No. 111 of 2000)) states that it is necessary to enable “the presence or absence of an odor to be sensed when the mixed volume ratio of gas to the air is 1/1,000”. Accordingly, when the concentration of R-290 is diluted to 1,000 ppm by volume in the air, R-290 needs to be recognized by the odor, and thus, a stronger odorization treatment than ISO-13734 is required.
In mixed gas of the air and THT in which 1,000 ppm of R-290 is contained, THT needs to be contained in a concentration of 2.1 ppb by volume or more in order to make the odor intensity of the mixed gas 2 or more. That is, in the mixed gas of R-290 and THT, 2.1 ppm by volume (4.2 ppm by weight) or more of THT is needed to be contained.
To make the odor intensity of the mixed gas to 3 or more, THT needs to be contained in a concentration of 4.1 ppb by volume or more. That is, in the mixed gas of R-290 and THT, 4.1 ppm by volume (8.2 ppm by weight) or more of THT needs to be contained.
As described above, the concentration of THT needed to recognize the refrigerant by the sense of smell was demonstrated by quantitatively clarifying the relationship between the concentration of THT in the sample gas and the intensity of the odor.
In the results of evaluation test 1 shown in
Meanwhile, when the odor intensity of the air containing the refrigerant gas is 5 (intense odor), the released odor of the refrigerant gas is too unpleasant. In the results of evaluation test 1 shown in
To demonstrate the influence on the results of evaluation test 1 by the molecular structure of PAG, each refrigerant gas in which R-290 containing the sulfur-based odorant (THT) serving as the refrigerant was mixed with PAG shown in Table 6 was prepared under the conditions shown in Table 7. The concentration of THT in the refrigerant was 600 ppm by weight so that the odor intensity of the refrigerant described in Table 5 was 3.
The values for the molecular structure of PAG shown in Table 6 were determined based on the number average degree of polymerization of the composition of each PAG. The O/C ratio is a value representing the ratio of the number of oxygen atoms (O) to the number of carbon atoms (C) in the molecular structure by two significant figures.
The above refrigerant gas was enclosed in a test container, which was shaken at 140° C. to stir the refrigerant gas, and then, the test container was allowed to stand still at 25° C. 24 hours after the start of still standing, a tedlar bag (1-2711-05 manufactured by AS ONE Corporation) was connected to the discharge port of the test container, and the refrigerant gas was collected at 25° C. The collected refrigerant gas was diluted to 1/1,000 with high purity air (ZERO-A manufactured by Sumitomo Seika Chemicals Company, Limited.), and then, the evaluation of the odor intensity was carried out by the odor sensory test method with reference to the literature (Journal of Japan Society of Air Pollution, Vol. 27, No. 2, P. A17-A24, 1992). The results of the odor intensity of the collected refrigerant gas represented by the 6-level odor intensity display method are shown in Table 8. The evaluation was such that the odor intensity of 2 or more was rated as “A”, and the odor intensity of 2 or more was rated as “B”.
The evaluation was carried out by 5 examiners.
As a result of the above evaluation, the refrigerant gas in which PAG (Test No. 3 to 13) having an O/C ratio of 0.43 or less was mixed had an odor in the range of the odor intensity of 2 (a weak odor whose odor source can be seen) to the odor intensity of 4 (strong odor), and THT was demonstrated to be contained in the refrigerant gas. The refrigerant gas in which PAG (Test No. 1 and 2) having an O/C ratio of 0.53 or more was mixed had an odor in the range of the odor intensity of 0 (odorless) to the odor intensity of 1 (an odor is sensed with difficulty), and THT was not demonstrated to be contained in the refrigerant gas.
These results mean that the amount of THT that is dissolved in PAG and not released with the refrigerant gas can be explained by the ratio of the polar groups (C—O—C and C—O—H) in the molecular structure of PAG.
THT is a polar molecule having a dipole moment due to bias of charge, in a molecule. According to the literature (J. Am. Chem. Soc., Vol. 61, P. 1769-1780, 1939), the magnitude of the dipole moment of THT is 1.87 D. Since the dipole moments of H2O and CH3OH, which are considered as polar solvents, are 1.9 D and 1.7 D, respectively, it can be seen that THT is a polar molecule having a large dipole moment.
Since THT is a polar molecule, THT is incorporated into the molecular chain of PAG by an electrical interaction with polar groups (C—O—C and C—O—H) of PAG and dissolved therein. Since PAG having a large O/C ratio has a large number of polar groups in the molecular structure, a strong electrical interaction of incorporating THT occurs. Consequently, when PAG having a large O/C ratio is mixed with THT, THT is hardly released.
Since R-290 does not have a polar group in the molecule, it is a nonpolar molecule having a significantly small bias of charge. According to the literature (J. Chem. Phys., Vol. 33, No. 5, P. 1514-1518, 1960), the dipole moment of R-290 is 0.083 D, which is smaller, and it can thus be seen that R-290 is a nonpolar molecule. Thus, the solubility of THT in R-290 is low, and when R-290 is dissolved in PAG, the solubility of THT in PAG is reduced. Since PAG having a large O/C ratio has a larger number of polar groups in the molecular structure, the solubility of R-290, which is a nonpolar molecule, is lower. Since PAG having a low O/C ratio has higher solubility of R-290, a larger amount of R-290 is dissolved in PAG. Accordingly, that the solubility of THT in PAG is lower and THT is more easily released. It is considered that, when the O/C ratio is 0.50 or less, the proportion of the polarized group of atoms in the molecular structure of PAG becomes half or less and that the effect of increasing the amount of THT released is achieved. Thus, the O/C ratio is preferably 0.50 or less.
From the above results, to circulate THT with R-290 in the refrigerant circuit by suppressing the dissolution of THT in PAG, PAG having an O/C ratio of 0.43 or less is preferably used.
From the results shown in evaluation test 1, the relationship of the O/C ratio and the odor intensity is considered to be obtained also when a hydrocarbon having 1 to 4 carbon atoms other than R-290, a sulfur-based odorant other than THT, and a refrigeration oil other than PAG are used. The reason for this is as follows: hydrocarbons having 1 to 4 carbon atoms other than R-290 are nonpolar molecules having a significantly small bias of charge in the molecule like R-290, and sulfur-based odorants other than THT are polar molecules like THT. According to the literature (J. Chem. Phys., Vol. 1, P. 337-340, 1933), it is reported that the dipole moments of mercaptans are about 1.3 D to 1.5 D, and that the dipole moments of sulfides are about 1.4 D to 1.58 D. Thus, they are polar molecules unlike hydrocarbons having 1 to 4 carbon atoms.
The results of evaluation test 3 demonstrated that use of PAG having a low O/C ratio enabled reduction in the solubility of THT in PAG and release of THT with R-290. However, the difference in the odor intensities of the refrigerants of Test No. 3 to 13 in PAG cannot be explained. Thus, the correlation between the molecular structure of PAG and the amount of THT released was examined by using HSP. Each HSP of THT, R-290, and PAG of each Test No. is shown in Table 9. For HSP, HSPiP Ver. 5.3, which is computer software, was used, and PAG of each Test No. was calculated by the Van Krevelen method.
The HSP distance between R-290 and THT is a larger value than the HSP distance between PAG and THT, and the solubility of THT in R-290 is lower than the solubility of THT in PAG. Accordingly, when R-290 is dissolved in PAG, the amount of THT dissolved in PAG is considered to be reduced.
As the HSP distance between PAG and THT is larger, the solubility of THT in PAG is lower. As the HSP distance between PAG and R-290 is smaller, the solubility of R-290 in PAG is larger. Thus, a larger amount of R-290 is dissolved in PAG, and THT is more hardly dissolved in PAG. Accordingly, it is considered that, as the difference between the HSP distance between PAG and THT and the HSP distance between PAG and R-290 is a larger value, the amount of THT dissolved in PAG is smaller, and a large amount of THT is contained in the refrigerant gas released from the refrigerant circuit. The relationship between the difference between the HSP distance between PAG and THT and the HSP distance between PAG and R-290, and the odor intensity in evaluation test 3 is shown in Table 10.
As a result of the above evaluation, the following was demonstrated: when the difference between the HSP distance between PAG and THT and the HSP distance between PAG and R-290 is −1.6 or more, the released refrigerant gas has an odor intensity of 2 or more; and when the difference is −0.4 or more, the released refrigerant gas has an odor intensity of 3 or more.
From the above results, to circulate THT with R-290 in the refrigerant circuit, PAG having a difference in the HSP distance of −1.6 or more is preferably used, and PAG having a difference in the HSP distance of −0.4 or more is more preferably used.
As a result of the present test, the solubility of THT in PAG was successfully demonstrated in detail with the use of HSP. However, HSP is needed to be calculated from the molecular structure of PAG. On the other hand, the O/C ratio can be easily analyzed by using a CHNSO element analyzer even in a state where the molecular structure is unknown.
By using a commercially available air conditioner for households (indoor unit model number: MSZ-GV5620S/outdoor unit model number: MUCZ-G5620S manufactured by Mitsubishi Electric Corporation) having a refrigerant circuit, the refrigerant gas released from the refrigerant circuit was collected. In the refrigerant circuit, 450 g of R-290 was enclosed as the main component of the refrigerant, and 290 mg (643 ppm by weight based on the mass of the refrigerant) of THT was enclosed as the sulfur-based odorant. In the compressor, 400 g of PAG (Test No. 10 of evaluation test 3) used in evaluation test 1 was enclosed as the refrigeration oil.
The air conditioner for households was operated, and then, while stopping the air conditioner for households, the refrigerant gas was released from the point between the expansion valve and the evaporator and collected in a tedlar bag (1-2711-05 manufactured by AS ONE Corporation). The collected refrigerant gas was diluted to 1/1,000 with using high purity air (ZERO-A manufactured by Sumitomo Seika Chemicals Company, Limited.), and then, the sensory evaluation of the odor was carried out. The sensory evaluation was carried out by 5 examiners as in evaluation test 3.
As the result, the odor of the refrigerant gas was an odor intensity of 3 to 4. For ascertainment, the concentration of THT of the collected refrigerant gas was analyzed by using a gas chromatography mass spectrometer (JMS-K9 manufactured by JEOL Ltd.) as in evaluation test 1, and as the result, THT was contained in the refrigerant gas in a concentration of 80 ppm by weight (40 ppm by volume). That is, the THT concentration was 40 ppm by volume when the collected refrigerant gas was diluted to 1/1,000 with high purity air. Accordingly, it corresponds to the odor intensity of 4 in the odor intensity in evaluation test 2, and it was demonstrated to be not inconsistent with the results of the sensory evaluation.
From the above results, the following was demonstrated: when PAG having a low solubility of THT is used, the dissolution of THT in PAG is suppressed, THT is allowed to circulate in the refrigerant circuit with R-290, and the refrigerant gas released from the refrigerant circuit is recognizable by the sense of smell.
The embodiments and examples disclosed herein should be considered to be exemplary in all respects and not restrictive. The scope of the present disclosure is indicated by the scope of claims rather than the above description, and is intended to include the meaning equivalent to the scope of claims and all modifications within the scope.
1 Outdoor unit; 2 Indoor unit; 3 Compressor; 4 Condenser; 5 Outdoor blower; 6 Expansion valve; 7 Evaporator; 8 Indoor blower; 9 Liquid pipe; 10 Gas pipe; 11 Shell; 12 Compression mechanism; 13 Electric motor; 14 Inlet pipe; 15 Discharge pipe; 16 Accumulator; 17 Rolling piston; 18 Cylinder; 19 Cylinder chamber; 20 Upper bearing; 21 Discharge hole of upper bearing; 22 Muffler space; 23 Discharge muffler; 24 Discharge hole of discharge muffler; 25 Electric motor rotor; 26 Electric motor stator; 27 Oil reservoir part; 28 Driving shaft; 100 Refrigerant circuit.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/040982 | 11/8/2021 | WO |
