Refrigeration cycle system

Abstract

In this refrigeration cycle system, a mixed refrigerant containing a hydrofluoroolefin and a high-solubility refrigerant having a higher solubility in refrigerating machine oil than the hydrofluoroolefin is used as a refrigeration cycle working medium. A control unit controls at least one of a compressor and an expansion valve by setting an upper limit value of an internal pressure to P0 (P0 < P1) and setting an upper limit value of a discharge gas temperature to T0 (T0 < T1) during a period from startup of the compressor until a prescribed time t1 has elapsed. After the prescribed time t1 has elapsed, at least one of the compressor and the expansion valve is controlled by changing the upper limit value of the internal pressure from P0 to P1 and changing the upper limit value of the discharge gas temperature from T0 to T1. This makes it possible to satisfactorily suppress or alleviate a disproportionation reaction even when a refrigeration cycle working medium containing a fluoroolefin and another refrigerant is used in combination with a refrigerating machine oil.

Description

Refrigeration Cycle System

[0001] The present invention relates to a refrigeration cycle system that uses a working fluid for a refrigeration cycle that contains a hydrofluoroolefin, and more particularly to a refrigeration cycle system that can effectively suppress the disproportionation reaction of a hydrofluoroolefin.

[0002] Recently, the use of hydrofluoroolefins (HFOs), which have a lower global warming potential (GWP), has been proposed as working fluids (refrigerants or heat transfer media) for refrigeration cycles. A typical example of a hydrofluoroolefin is 1,1,2-trifluoroethylene (HFO1123). 1,1,2-trifluoroethylene is less stable than conventional HFCs and therefore less likely to remain in the atmosphere, and therefore has a smaller ODP and GWP.

[0003] Such hydrofluoroolefins are known to be prone to a self-decomposition reaction called a disproportionation reaction and a polymerization reaction following this self-decomposition reaction (hereinafter referred to as a disproportionation reaction) due to their low stability.

[0004] Disproportionation reactions are likely to occur due to heat generated during use of the working fluid for a refrigeration cycle, and are accompanied by a large amount of heat release. Therefore, it is known that disproportionation reactions can occur in a chain reaction. As a result, a large amount of soot is generated, which may reduce the reliability of the refrigeration cycle system or the compressors and other components of the system.

[0005] The compressor of a refrigeration cycle system usually stores refrigerating machine oil (lubricating oil) therein for lubrication. Therefore, it can be said that a working fluid for the refrigeration cycle and a refrigerating machine oil are used in combination in the refrigeration cycle system. In this way, when a working fluid for the refrigeration cycle is used in combination with a refrigerating machine oil, it can be considered that a working fluid-containing composition (or working fluid) is composed of at least a refrigerant component (working fluid for the refrigeration cycle) and a refrigerating machine oil component.

[0006] A technique for improving the performance of a refrigeration cycle system by adjusting the refrigerant dissolution viscosity of such a working fluid-containing composition within a predetermined range under high-temperature and high-pressure conditions is known. For example, Patent Document 1 discloses that a working fluid (working fluid-containing composition) consisting of a refrigerant and a refrigerating machine oil has a viscosity of 2 to 4 mm under conditions of a temperature of 80°C and an absolute pressure of 3.4 MPa. 2 The viscosity of the refrigerant solution is adjusted to have a refrigerant solution viscosity of 1 / s. Specific examples of the refrigerant include fluorine-containing refrigerants such as hydrofluoroolefins (HFOs) such as fluoroethylene or fluoropropene, hydrofluorocarbons (HFCs), and natural refrigerants such as hydrocarbon refrigerants, ammonia (R717), and carbon dioxide (R744).

[0007] According to Patent Document 1, if the refrigerant solution viscosity of the working fluid is too low, the refrigeration capacity or cooling capacity of the refrigerator (refrigeration cycle system) will decrease due to factors such as reduced sealing performance of the compressor. Also, if the refrigerant solution viscosity of the working fluid is too high, energy consumption will increase due to factors such as increased stirring resistance or resistance at the start of the refrigerator, and the refrigeration capacity or cooling capacity will also decrease. Therefore, by adjusting the refrigerant solution viscosity within the above range, the coefficient of performance (COP) of the refrigeration cycle system will be improved.

[0008] JP 2017-141974 A

[0009] However, in the refrigeration cycle system disclosed in Patent Document 1, as mentioned above, the refrigerant is not limited to hydrofluoroolefins, and there is no mention of the disproportionation reaction of hydrofluoroolefins. Furthermore, although the use of a mixed refrigerant made by combining multiple types of refrigerants is described, a specific example is the R410A refrigerant, which is a 50 / 50 mixture of difluoromethane (R32) and pentafluoroethane (R125), and the relationship between the refrigerant solution viscosity of the working fluid and the COP of the refrigerator is only verified.

[0010] Therefore, the refrigeration cycle system disclosed in Patent Document 1 does not assume at all that the working fluid for the refrigeration cycle is a mixed refrigerant containing a hydrofluoroolefin, and therefore, it is difficult to effectively suppress the disproportionation reaction of hydrofluoroolefins with the technology described in Patent Document 1.

[0011] The present invention has been made to solve the above problems, and an object of the present invention is to provide a refrigeration cycle system that can effectively suppress or mitigate disproportionation reactions even when a working fluid for a refrigeration cycle containing a hydrofluoroolefin and another refrigerant is used in combination with a refrigerating machine oil.

[0012] In order to solve the above-mentioned problems, the refrigeration cycle system according to the present disclosure includes a refrigeration cycle including a compressor that stores refrigerating machine oil therein and an expansion valve, and a control unit, wherein a mixed refrigerant containing at least one hydrofluoroolefin and at least one high-solubility refrigerant that has a higher solubility in the refrigerating machine oil than the hydrofluoroolefin is used as a working fluid for the refrigeration cycle, and when an upper limit value of an internal pressure and an upper limit value of a discharge gas temperature that are preset in the compressor are set to P1 and T1, respectively, the control unit controls the pressure and the discharge gas temperature to be equal to or higher than the upper limit value of the internal pressure and the upper limit value of the discharge gas temperature that are preset in the compressor. During the period from the start of the compressor until a predetermined time t1 has elapsed, the upper limit value of the internal pressure is set to P0 (P0<P1) which is smaller than P1, and the upper limit value of the discharge gas temperature is set to T0 (T0<T1) which is smaller than T1, thereby controlling at least one of the rotation speed of the compressor and the opening degree of the expansion valve, and after the predetermined time t1 has elapsed, the upper limit value of the internal pressure is changed from P0 to P1, and the upper limit value of the discharge gas temperature is changed from T0 to T1, thereby controlling at least one of the rotation speed of the compressor and the opening degree of the expansion valve.

[0013] When the working fluid for a refrigeration cycle is a mixed refrigerant containing a hydrofluoroolefin and a high-solubility refrigerant as described above, a relatively large amount of the high-solubility refrigerant dissolves in the refrigeration oil when the compressor is stopped. Therefore, when the compressor is started, the mixed refrigerant contains a relatively large amount of hydrofluoroolefin, and the conditions (disproportionation conditions) for the internal pressure and internal temperature (discharge gas temperature) at which the disproportionation reaction occurs are lower than those of a normal refrigerant composition.

[0014] Therefore, according to the above configuration, in the initial stage of operation from the start of the compressor until a predetermined time t1 has elapsed, the upper limit values ​​of the internal pressure and discharge gas temperature at which protective control is initiated are set to P0 and T0, which are lower than the default values ​​P1 and T1. In the initial stage of operation, the control unit controls the compressor or the expansion valve, or both the compressor and the expansion valve, based on this P0 / T0. After the initial stage of operation ends and the system transitions to normal operation, the control unit changes the upper limit values ​​of the internal pressure and discharge gas temperature from P0 / T0 to the default value P1 / T1, and controls at least one of the compressor and the expansion valve.

[0015] This makes it possible to effectively suppress the probability of disproportionation reactions occurring even in the early stages of operation when the concentration of hydrofluoroolefins is relatively high and disproportionation reactions are likely to occur. Furthermore, even after the system transitions from the early stages of operation to normal operation, the occurrence of disproportionation reactions can be effectively suppressed or mitigated. As a result, the reliability of the refrigeration cycle system can be further improved.

[0016] The above and other objects, features, and advantages of the present invention will become apparent from the following detailed description of preferred embodiments, which proceeds with reference to the accompanying drawings.

[0017] The present invention has the above-described configuration, which has the effect of providing a refrigeration cycle system that can effectively suppress or mitigate disproportionation reactions even when a working fluid for a refrigeration cycle containing a hydrofluoroolefin and another refrigerant is used in combination with a refrigerating machine oil.

[0018] Fig. 1A is a schematic piping diagram showing a typical configuration of an air conditioner which is an example of a refrigeration cycle system according to an embodiment of the present disclosure, and Fig. 2B is a block diagram of a main part showing a typical control configuration of the air conditioner shown in Fig. 1A. Fig. 2A is a graph showing a schematic diagram of a state in which conditions for the disproportionation reaction of hydrofluoroolefins change when a predetermined time has elapsed since immediately after the start of the compressor, and Fig. 2B is a graph showing an example of pressure / temperature control until the predetermined time has elapsed in the refrigeration cycle system according to the present disclosure. Fig. 1B is a flowchart showing an example of typical control of the air conditioner shown in Fig. 1B.

[0019] [Knowledge, etc. that forms the basis of the present disclosure] Through intensive studies by the present inventors, it has become clear that when a hydrofluoroolefin that undergoes a disproportionation reaction is used as a refrigerant component of a working fluid for a refrigeration cycle in combination with another refrigerant, it is necessary to take into account the difference in the solubility of the refrigerant in refrigerating machine oil (hereinafter referred to as "oil solubility"), which did not need to be taken into account in conventional refrigeration cycle systems.

[0020] For example, assume that the refrigerant component of a working fluid for a refrigeration cycle is only one type of hydrofluoroolefin (single refrigerant). In this case, when the compressor is stopped, one type of hydrofluoroolefin is dissolved in the refrigerating machine oil according to its oil solubility. Therefore, when the compressor is started, the pressure and temperature of the compressor can be controlled taking into account the conditions for the occurrence of a disproportionation reaction in the hydrofluoroolefin.

[0021] However, in the case of a mixed refrigerant, when the oil solubility of the other refrigerant is greater than the oil solubility of the hydrofluoroolefin, the amount of the other refrigerant that dissolves in the refrigerating machine oil is greater than the amount of the hydrofluoroolefin that dissolves in the refrigerating machine oil.

[0022] When a compressor starts up from a stopped state and enters an operating state, the internal pressure and temperature change significantly, causing other refrigerants dissolved in the refrigerating machine oil to return to a mixed refrigerant. In other words, when the compressor is stopped or immediately after start-up, the content of other refrigerants is relatively low and the content of hydrofluoroolefins is high, and when the compressor transitions to normal operation, the content of other refrigerants returns to its original state. In other words, the refrigerant composition when the compressor is stopped or immediately after start-up is different from the refrigerant composition during normal operation of the compressor.

[0023] When a compressor starts operating, the inside of the compressor rapidly becomes hot and pressure-rich. However, changes in the amount of dissolved hydrofluoroolefins and other refrigerants, i.e., changes in the refrigerant composition, do not readily follow changes in the internal temperature and pressure. This is because the solubility of a refrigerant in a refrigerating machine oil is basically based on the premise that the refrigerant and the refrigerating machine oil coexist quasi-statically. Therefore, the refrigerant composition when the compressor is stopped or immediately after startup differs from the refrigerant composition during normal operation (high temperature and pressure).

[0024] As described above, the disproportionation reaction of hydrofluoroolefins is particularly likely to occur under high-temperature and high-pressure conditions. Therefore, for example, it is assumed that the pressure and temperature inside the compressor are controlled based on the refrigerant composition during normal operation in order to suppress the disproportionation reaction. However, immediately after the compressor is started, the refrigerant composition is relatively high in hydrofluoroolefins, so that the disproportionation reaction may occur even under conditions of relatively low pressure and temperature compared to those during normal operation.

[0025] Furthermore, during the period from when the compressor starts up and begins operation until a predetermined time has elapsed, i.e., in the initial stage of operation, the refrigerant composition at the time of shutdown changes slowly without being able to keep up with the rapid changes in the internal pressure and internal temperature of the compressor. Therefore, even if the compressor is controlled to suppress the disproportionation reaction based on the refrigerant composition during normal operation, the refrigerant composition cannot be effectively adapted to suppress the disproportionation reaction in the initial stage of operation, and as a result, the disproportionation reaction of hydrofluoroolefins is more likely to occur in the initial stage of operation.

[0026] Therefore, as a result of further intensive research by the inventors, in a typical refrigeration cycle system, the upper limit values ​​of the internal pressure and discharge gas temperature, which are preset for compressor protection control, are set to lower values ​​of pressure and temperature at the beginning of operation to control the operation of the compressor, and after a predetermined time has elapsed, the upper limit values ​​of the internal pressure and discharge gas temperature are raised to the preset values ​​to control the operation of the compressor, and thereby it has been found that the disproportionation reaction can be effectively suppressed or mitigated, particularly at the beginning of operation, and this has led to the completion of the present invention.

[0027] In other words, the refrigeration cycle system according to the present disclosure includes a refrigeration cycle including a compressor that stores refrigeration oil therein and an expansion valve, and a control unit; a mixed refrigerant containing at least one hydrofluoroolefin and at least one high-solubility refrigerant that has a higher solubility in the refrigeration oil than the hydrofluoroolefin is used as a working fluid for the refrigeration cycle; and when an upper limit value of an internal pressure and an upper limit value of a discharge gas temperature that are preset in the compressor are defined as P1 and T1, the control unit, during a period from start-up of the compressor until a predetermined time t1 has elapsed, sets the upper limit value of the internal pressure to P0 (P0<P1) that is smaller than P1, and sets the upper limit value of the discharge gas temperature to T0 (T0<T1) that is smaller than T1, thereby controlling at least one of the rotation speed of the compressor and the aperture of the expansion valve; and after the predetermined time t1 has elapsed, changes the upper limit value of the internal pressure from P0 to P1, and changes the upper limit value of the discharge gas temperature from T0 to T1, thereby controlling at least one of the rotation speed of the compressor and the aperture of the expansion valve.

[0028] When the working fluid for a refrigeration cycle is a mixed refrigerant containing a hydrofluoroolefin and a high-solubility refrigerant as described above, a relatively large amount of the high-solubility refrigerant dissolves in the refrigeration oil when the compressor is stopped. Therefore, when the compressor is started, the mixed refrigerant contains a relatively large amount of hydrofluoroolefin, and the conditions (disproportionation conditions) for the internal pressure and internal temperature (discharge gas temperature) at which the disproportionation reaction occurs are lower than those of a normal refrigerant composition.

[0029] Therefore, according to the above configuration, in the initial stage of operation from the start of the compressor until a predetermined time t1 has elapsed, the upper limit values ​​of the internal pressure and discharge gas temperature at which protective control is initiated are set to P0 and T0, which are lower than the default values ​​P1 and T1. In the initial stage of operation, the control unit controls the compressor or the expansion valve, or both the compressor and the expansion valve, based on this P0 / T0. After the initial stage of operation ends and the system transitions to normal operation, the control unit changes the upper limit values ​​of the internal pressure and discharge gas temperature from P0 / T0 to the default value P1 / T1, and controls at least one of the compressor and the expansion valve.

[0030] This makes it possible to effectively suppress the probability of disproportionation reactions occurring even in the early stages of operation when the concentration of hydrofluoroolefins is relatively high and disproportionation reactions are likely to occur. Furthermore, even after the system transitions from the early stages of operation to normal operation, the occurrence of disproportionation reactions can be effectively suppressed or mitigated. As a result, the reliability of the refrigeration cycle system can be further improved.

[0031] In the refrigeration cycle system of the above configuration, a pressure sensor that measures the internal pressure of the compressor may be provided, and the control unit may be configured to control at least one of the rotation speed of the compressor and the opening degree of the expansion valve using the pressure value measured by the pressure sensor.

[0032] Furthermore, the refrigeration cycle system of the above configuration may be configured to include a first temperature sensor that approximately measures the internal pressure of the compressor from the temperature, and the control unit may be configured to control at least one of the rotation speed of the compressor and the opening degree of the expansion valve using the pressure value indirectly measured by the first temperature sensor.

[0033] In addition, the refrigeration cycle system of the above configuration may be configured to include a second temperature sensor that measures the temperature of the discharge gas from the compressor, and the control unit may be configured to control at least one of the rotation speed of the compressor and the opening degree of the expansion valve using the discharge gas temperature measured by the second temperature sensor.

[0034] In the refrigeration cycle system having the above configuration, the high-solubility refrigerant may be a saturated hydrocarbon, and the saturated hydrocarbon may be propane (R290).

[0035] In the refrigeration cycle system having the above configuration, the working fluid for the refrigeration cycle may further contain a disproportionation inhibitor.

[0036] Representative embodiments of the present disclosure will be described below with reference to the drawings. Note that the same or corresponding elements will be designated by the same reference numerals throughout the drawings, and redundant description thereof will be omitted.

[0037] [Configuration example of a refrigeration cycle system] First, an air conditioner 10 shown schematically in Figures 1A and 1B will be described as a representative example of a refrigeration cycle system according to the present disclosure. As shown in the schematic piping diagram of Figure 1A, the air conditioner 10, which is a refrigeration cycle system according to the present disclosure, includes an outdoor unit 11 and an indoor unit 12, and these units 11 and 12 are connected by inter-unit piping 13. The indoor unit 12 is installed in a space to be air-conditioned (referred to as a target space), and the outdoor unit 11 is installed outdoors, outside the target space. The inter-unit piping 13 is provided with piping connections 13a and 13b.

[0038] The air conditioner 10 circulates refrigerant compressed in the outdoor unit 11 between the outdoor unit 11 and the indoor unit 12 to air-condition the target space in which the indoor unit 12 is installed. The air conditioner 10 can switch between a cooling operation mode for cooling the target space and a heating operation mode for heating the target space.

[0039] The outdoor unit 11 includes a compressor 20, an outdoor heat exchanger 14, an outdoor fan 15, an expansion valve 16, and a switching valve 17. The compressor 20 compresses a working medium for a refrigeration cycle, including a refrigerant. Refrigeration oil is stored inside the compressor 20. The outdoor heat exchanger 14 exchanges heat with the refrigerant outside the target space (outdoors). The outdoor fan 15 blows outdoor air to the outdoor heat exchanger 14. The expansion valve 16 reduces the pressure of the refrigerant to expand it. The switching valve 17 switches between a cooling operation mode and a heating operation mode.

[0040] The indoor unit 12 includes an indoor heat exchanger 18 and an indoor fan 19. The indoor heat exchanger 18 performs heat exchange of the refrigerant supplied from the outdoor unit 11 through the inter-unit piping 13 within the target space. The indoor fan 19 blows air within the target space (indoors).

[0041] The outdoor heat exchanger 14 functions as a condenser in the cooling operation mode and as an evaporator in the heating operation mode. The indoor heat exchanger 18 functions as an evaporator in the cooling operation mode and as a condenser in the heating operation mode. The compressor 20, the outdoor heat exchanger 14 (condenser or evaporator), the indoor heat exchanger 18 (evaporator or condenser), and the expansion valve 16 are connected in a ring shape by the inter-unit piping 13 to form a refrigeration cycle (refrigerant circuit).

[0042] The specific type of refrigeration oil stored inside the compressor 20 is not particularly limited, and an example of a configuration is one in which a lubricating oil known in the compressor field is used as a base oil and known additives are contained as necessary.

[0043] Examples of lubricating oils used as base oils for refrigeration oils include, but are not limited to, hydrocarbon oils such as mineral oils, olefin polymers, naphthalene compounds, and alkylbenzenes; ester oils such as monoesters, diesters, polyol esters, and complex esters; and oxygen-containing oils such as ether oils such as polyalkylene glycols, polyvinyl ethers, polyphenyl ethers, and perfluoroethers. These base oils may be used alone or in appropriate combination of two or more.

[0044] The additives contained in the refrigerating machine oil are not particularly limited, and examples thereof include an oiliness agent, a sliding property improver, an extreme pressure additive, an antioxidant, an acid scavenger, a metal deactivator, an antifoaming agent, a corrosion inhibitor, and a dispersant.

[0045] In this embodiment, the base oil of the refrigerating machine oil preferably contains at least one selected from polyol esters, polyalkylene glycols, and polyvinyl ethers as the main component, and more preferably polyol esters or polyvinyl ethers as the main component. The term "main component" here refers to a content of 50% by mass or more of the total amount (100% by mass) of the base oil in the refrigerating machine oil. The content of the lubricating base oil in the refrigerating machine oil is not particularly limited, but may be 80% by mass or more, 90% by mass or more, or 95% by mass or more of the total amount (100% by mass) of the refrigerating machine oil.

[0046] As shown in the block diagram of essential parts in Fig. 1B, the air conditioner 10 further includes a control unit 21, a pressure sensor 22, a temperature sensor 23, etc. The control unit 21 controls the operation of the compressor 20, the opening degree and / or opening / closing of the expansion valve 16, the flow path switching of the changeover valve 17, and the operation and / or stopping of the outdoor fan 15 and the indoor fan 19. For ease of explanation, Fig. 1B illustrates only the compressor 20 and the expansion valve 16 as objects controlled by the control unit 21.

[0047] The control unit 21 also operates the expansion valve 16 and the switching valve 17 to switch the air conditioner 10 between a cooling operation mode and a heating operation mode. Furthermore, the control unit 21 controls the operating frequency (rotation speed), operation and / or stop of the compressor 20, and controls the outdoor fan 15 and the indoor fan 19, based on operations or settings made by an operation unit provided in the air conditioner 10, and conditions the target space according to the target temperature. The rotation speed of the compressor 20 is controlled by changing the operating frequency of the compressor 20.

[0048] The pressure sensor 22 measures the internal pressure of the compressor 20. Examples of such a pressure sensor 22 include a sensor that indirectly measures the internal pressure of the compressor 20, a sensor that approximately measures the internal pressure from the temperature inside the compressor 20 (a temperature sensor), and a sensor that directly measures the internal pressure. Generally, a sensor that indirectly measures the internal pressure of the compressor 20 by measuring the pressure on the high-pressure side of the refrigeration system, for example, the pressure of a discharge pipe provided in the compressor 20 or the pressure at the outlet of a condenser that constitutes the refrigeration system, can be used. Specific pressure sensors 22 that are well known in the field of refrigeration cycle systems such as the air conditioner 10 can be suitably used, and are not particularly limited.

[0049] The temperature sensor 23 measures the temperature (discharge gas temperature) of high-temperature, high-pressure gas discharged from a discharge pipe provided in the compressor 20. The internal temperature of the compressor 20 can be estimated from the measured discharge gas temperature. As described above, a temperature sensor that measures the internal pressure by measuring the temperature inside the compressor 20 can be used as the pressure sensor 22. However, this temperature sensor for measuring the internal pressure and the temperature sensor that measures the discharge gas temperature (internal temperature of the compressor 20) are different. Therefore, for convenience, the temperature sensor used as the pressure sensor 22 will be referred to as the "first temperature sensor" and the temperature sensor that measures the discharge gas temperature will be referred to as the "second temperature sensor" in this specification. The specific temperature sensor 23 (second temperature sensor) is not particularly limited and may be any sensor known in the field of refrigeration cycle systems such as the air conditioner 10.

[0050] As will be described later, in the refrigeration cycle system according to the present disclosure, from the time when the compressor 20 is started until a predetermined time t1 has elapsed, i.e., at the beginning of operation, the control unit 21 sets lower upper limits for the internal pressure and discharge gas temperature of the compressor 20, and then controls the rotation speed of the compressor 20 or the aperture of the expansion valve 16, or both the rotation speed and the aperture (at least one of the rotation speed and the aperture), and thereafter changes the upper limits for the internal pressure and the discharge gas temperature to preset values. In this control, the control unit 21 uses at least the output of the pressure sensor 22 (measured value of the internal pressure) and the output of the temperature sensor 23 (measured value of the discharge gas temperature).

[0051] Of course, the refrigeration cycle system (air conditioner 10, etc.) according to the present disclosure may include sensors or measuring devices other than the pressure sensor 22 and the temperature sensor 23. Furthermore, the control unit 21 can use the measured values ​​or detected values ​​measured by sensors or measuring devices other than these pressure sensor 22 and temperature sensor 23 to control the compressor 20 and the expansion valve 16. Furthermore, the control unit 21 can also use the measured values ​​or detected values ​​measured by these sensors or measuring devices to control other components (such as the switching valve 17, the outdoor fan 15, and the indoor fan 19).

[0052] In the example shown in Fig. 1A, the flow direction of the refrigerant in the cooling operation mode is indicated by block arrows. In the cooling operation mode of the air conditioner 10, the refrigerant (working medium for the refrigeration cycle) flows through the compressor 20, the outdoor heat exchanger 14, the expansion valve 16, the indoor heat exchanger 18, and the switching valve 17, in that order, before returning from the switching valve 17 to the compressor 20. Note that the flow direction of the refrigerant in the heating operation mode is opposite to the block arrows shown in Fig. 1A. In the heating operation mode of the air conditioner 10, the refrigerant flows through the compressor 20, the indoor heat exchanger 18, the expansion valve 16, the outdoor heat exchanger 14, and the switching valve 17, in that order, before returning from the switching valve 17 to the compressor 20.

[0053] The pipe connections 13a and 13b of the air conditioner 10 are provided between the outdoor unit 11 and the indoor unit 12 in the inter-unit pipe 13, which is connected in a circular pattern. These pipe connections 13a and 13b may be, for example, two-way or three-way valves. This allows the outdoor unit 11 and the indoor unit 12 to be connected to each other, enabling refrigerant to flow through them. The opening and / or opening / closing of the pipe connections 13a and 13b can be controlled manually or by the control of the control unit 21.

[0054] The specific configurations of the air conditioner 10, outdoor unit 11, indoor unit 12, and each component of the refrigeration cycle (refrigerant circuit) (compressor 20, outdoor heat exchanger 14, outdoor fan 15, expansion valve 16, switching valve 17, indoor heat exchanger 18, indoor fan 19, inter-unit piping 13, piping connections 13a, 13b, etc.) are not particularly limited, and various known configurations can be suitably adopted. In this embodiment, since the refrigeration cycle system is the air conditioner 10, a rotary type compressor 20 is suitably used, but of course other types of compressors may also be used.

[0055] 1A and 1B, other components may be included, or some components may not be included. The refrigeration cycle system is not limited to the air conditioner 10, but may also be a dehumidifier, a showcase, an ice maker, a heat pump water heater, a heat pump washer / dryer, a vending machine, etc.

[0056] [Refrigerant Components] The refrigeration cycle system according to the present disclosure uses a working fluid for a refrigeration cycle containing, as a refrigerant, a hydrofluoroolefin (HFO) that undergoes a disproportionation reaction and one or more other refrigerants. The other refrigerants have a higher (greater) solubility in the refrigeration oil stored inside the compressor 20 than the hydrofluoroolefin.

[0057] For ease of explanation, a refrigerant having a higher oil solubility than hydrofluoroolefins is referred to as a “high-solubility refrigerant.” When a working fluid for a refrigeration cycle contains two or more refrigerants other than hydrofluoroolefins, at least one of the refrigerants should be a high-solubility refrigerant.

[0058] Specific examples of hydrofluoroolefins include, but are not limited to, those having two carbon atoms, such as 1,1,2-trifluoroethylene (CF2=CHF, HFO1123), trans-1,2-difluoroethylene (CHF=CHF(E), HFO1132(E)), and cis-1,2-difluoroethylene (CHF=CHF(Z), HFO1132(Z)). These hydrofluoroolefins may be used alone or in combination as a refrigerant component.

[0059] These hydrofluoroolefins have a backbone ethylene structure, i.e., a double bond between carbon atoms, and have a chemical structure in which at least one of the two hydrogen atoms bonded to one carbon atom is substituted with a fluorine atom, or at least one of the two hydrogen atoms bonded to both carbon atoms is substituted with a fluorine atom. Note that in hydrofluoroolefins, some of the hydrogen atoms may be substituted with other atoms or other substituents.

[0060] For example, 1,1,2-trifluoroethylene has a structure in which both of the two hydrogen atoms bonded to one carbon atom (the carbon atom at position 1) of the ethylene structure are substituted with fluorine atoms, and one of the two hydrogen atoms bonded to the other carbon atom (the carbon atom at position 2) is substituted with a fluorine atom.

[0061] Alternatively, trans-1,2-difluoroethylene has a structure in which one of the two hydrogen atoms bonded to the carbon atom at position 1 of the ethylene structure is substituted with a fluorine atom, and of the two hydrogen atoms bonded to the carbon atom at position 2, only the hydrogen atom at the position opposite to the carbon atom at position 1 across the double bond, rather than the hydrogen atom adjacent to the carbon atom at position 1, is substituted with a fluorine atom.

[0062] As described above, such hydrofluoroolefins contain an ethylene skeleton, i.e., a carbon-carbon double bond, and this double bond is easily decomposed. That is, atmospheric ozone generates hydroxyl radicals (OH radicals) through photochemical reactions, and these hydroxyl radicals can undergo addition reactions with double bonds, making the hydrofluoroolefins easily decomposed. For this reason, hydrofluoroolefins have little impact on ozone layer depletion and global warming.

[0063] The working fluid for a refrigeration cycle used in the present disclosure may contain, for example, propane (R290) as a refrigerant component in addition to hydrofluoroolefins. As described above, the refrigeration oil exemplified in this embodiment uses a base oil having a molecular structure with a hydrocarbon skeleton. Therefore, propane is more easily soluble in refrigeration oil than hydrofluoroolefins. Therefore, propane is a high-solubility refrigerant that has a high solubility in refrigeration oil (oil solubility) compared to hydrofluoroolefins.

[0064] Furthermore, in the working fluid for a refrigeration cycle used in the present disclosure, the "other refrigerants" that may be contained in addition to the hydrofluoroolefin are not particularly limited, but representative examples include hydrofluorocarbons (HFCs), saturated hydrocarbons, carbon dioxide, etc.

[0065] Specific examples of HFCs include fluoromethanes such as difluoromethane (R32) and trifluoromethane (R23); fluoroethanes such as fluoroethane (R161), 1,1-difluoroethane (R152a), 1,1,1-trifluoroethane (R143a), 1,1,2,2-tetrafluoroethane (R134), 1,1,1,2-tetrafluoroethane (R134a), pentafluoroethane (R125), difluoroethane, and trifluoroethane; and 1,1,1,3,3-pentafluoropropane (R245fa). Fluoropropanes such as 1,1,1,2,3,3-hexafluoropropane (R236ea), 1,1,1,3,3,3-hexafluoropropane (R236fa), and 1,1,1,2,3,3,3-heptafluoropropane (R227ea); fluorobutanes such as 1,1,1,3,3-pentafluorobutane (R365mfc); fluoropentanes such as 1,1,1,2,3,4,4,5,5,5-decafluoropentane (R4310mee) and heptafluorocyclopentane (Rc447ef); and the like.

[0066] Specific examples of saturated hydrocarbons include ethane, n-propane, cyclopropane, n-butane, cyclobutane, isobutane (2-methylpropane), methylcyclopropane, n-pentane, isopentane (2-methylbutane), neopentane (2,2-dimethylpropane), and methylcyclobutane.

[0067] These other refrigerants may be used alone or in combination of two or more. Among these, R32 (difluoromethane) is typically used. As will be described later, saturated hydrocarbons include those that can be used as disproportionation inhibitors. Therefore, saturated hydrocarbons can be used in combination as both other refrigerants and disproportionation inhibitors.

[0068] These other refrigerants are known to have little impact on ozone depletion and global warming, and therefore can be used together with hydrofluoroolefins or hydrofluoroolefins and difluoromethane as refrigerant components. The above-mentioned other refrigerant components may be used alone or in appropriate combinations of two or more. These other refrigerants also include highly soluble refrigerants. For example, saturated hydrocarbons, like propane, are easily soluble in refrigerating machine oil and can therefore be suitably used as highly soluble refrigerants.

[0069] The contents (content ratios) of the hydrofluoroolefin and other refrigerants (including high-solubility refrigerants) in the working fluid for a refrigeration cycle are not particularly limited. For example, when the hydrofluoroolefin and other refrigerants are collectively referred to as a "mixed refrigerant" and the total amount of the mixed refrigerant is taken as 100% by mass, the content of the hydrofluoroolefin may be 50% by mass or more, 60% by mass or more, 70% by mass or more, or even 80% by mass or more. Furthermore, when the total amount of the mixed refrigerant is taken as 100% by mass, the content of the other refrigerants may be less than 50% by mass, and may be 40% by mass or less, 30% by mass or less, or 20% by mass or less.

[0070] If the content of the hydrofluoroolefin is less than 50% by mass of the total amount of the mixed refrigerant, the content of the hydrofluoroolefin in the mixed refrigerant will be too low, resulting in the mixed refrigerant containing a large amount of other refrigerants, and therefore the advantages of using a hydrofluoroolefin with a small GWP in a working fluid for a refrigeration cycle will not be fully obtained.

[0071] Furthermore, if the other refrigerant is, for example, propane or a saturated hydrocarbon, the flammability of propane may have a significant effect on the mixed refrigerant, i.e., the working fluid for a refrigeration cycle containing the mixed refrigerant, making it impossible to fully obtain the advantages of realizing good handling properties while reducing GWP in the working fluid for a refrigeration cycle.

[0072] [Other Components That Can Be Used in Combination] As described above, the working fluid for a refrigeration cycle used in the present disclosure can be used in combination with a refrigerating machine oil (lubricating oil) stored inside the compressor 20 provided in the refrigeration cycle system. As described above, the working fluid for a refrigeration cycle used in the present disclosure may be configured as a mixed refrigerant containing a hydrofluoroolefin and at least one high-solubility refrigerant as substantially the "main components." Furthermore, when the working fluid for a refrigeration cycle is used in combination with a refrigerating machine oil, the mixed refrigerant, the refrigerating machine oil, and other components can be considered to constitute a working fluid-containing composition.

[0073] The refrigerating machine oil contained in the working fluid-containing composition (used in combination with the refrigeration cycle working fluid) can be any of various refrigerating machine oils (lubricants) known in refrigeration cycle systems. Specific examples of refrigerating machine oils include, but are not limited to, ester-based lubricating oils, ether-based lubricating oils, glycol-based lubricating oils, alkylbenzene-based lubricating oils, fluorine-based lubricating oils, mineral oils, and hydrocarbon-based synthetic oils. These refrigerating machine oils may be used alone or in combination of two or more.

[0074] Various known additives may also be added to the working fluid-containing composition. Specific additives include, but are not limited to, antioxidants, moisture scavengers, metal deactivators, anti-wear agents, and anti-foaming agents. Antioxidants are used to improve the thermal stability, oxidation resistance, chemical stability, etc. of mixed refrigerants or refrigerating machine oils. Moisture scavengers are used to remove moisture when moisture infiltrates into the refrigeration cycle system, and are particularly used to suppress changes in the properties of refrigerating machine oils. Metal deactivators are used to suppress or prevent chemical reactions caused by the catalytic action of metal components. Anti-wear agents are used to reduce wear on sliding parts in the compressor 20, particularly during high-pressure operation. Anti-foaming agents are used, particularly, to suppress the generation of bubbles in refrigerating machine oils.

[0075] The specific types of these additives are not particularly limited, and known compounds can be suitably used depending on various conditions. Furthermore, as these additives, only one type of compound or an appropriate combination of two or more types of compounds can be used. Furthermore, the amount of these additives added is not particularly limited, and they can be added within known ranges as long as the properties of the working fluid for a refrigeration cycle used in the present disclosure or the working fluid-containing composition containing the same are not impaired.

[0076] As described above, a disproportionation inhibitor that is gaseous or liquid at room temperature and normal pressure may be added in advance to the working fluid for a refrigeration cycle used in the present disclosure. Specific examples of the disproportionation inhibitor include saturated hydrocarbons having 2 to 5 carbon atoms, haloalkanes having 1 or 2 carbon atoms except for those in which all halogen atoms are fluorine, and fluoroalkanes having 1 to 3 carbon atoms (excluding difluoromethane) with a boiling point of 0°C or lower. These disproportionation inhibitors may be used alone or in appropriate combination of two or more.

[0077] Specific examples of the disproportionation inhibitor include, but are not limited to, saturated hydrocarbons such as ethane, n-propane, cyclopropane, n-butane, cyclobutane, isobutane (2-methylpropane), methylcyclopropane, n-pentane, isopentane (2-methylbutane), neopentane (2,2-dimethylpropane), and methylcyclobutane. Of these, n-propane is particularly preferred.

[0078] Examples of haloalkanes having one carbon atom, i.e., halomethanes, include, but are not limited to, (mono)iodomethane (CH3I), diiodomethane (CH2I2), dibromomethane (CH2Br2), bromomethane (CH3Br), dichloromethane (CH2Cl2), chloroiodomethane (CH2ClI), dibromochloromethane (CHBr2Cl), tetraiodomethane (CI4), carbon tetrabromide (CBr4), bromotrichloromethane (CBrCl3), dibromodichloromethane (CBr2Cl2), tribromofluoromethane (CBr3F), fluorodiiodomethane (CHFI2), difluorodiiodomethane (CF2I2), dibromodifluoromethane (CBr2F2), trifluoroiodomethane (CF3I), and difluoroiodomethane (CHF2I). Among these, dibromomethane (CH2Br2), bromomethane (CH3Br), dibromodichloromethane (CBr2Cl2), trifluoroiodomethane (CF3I), etc. are preferred, and trifluoroiodomethane (CF3I) is more preferred.

[0079] Furthermore, examples of haloalkanes having two carbon atoms, i.e., haloethanes, include 1,1,1-trifluoro-2-iodoethane (CF3CH2I), monoiodoethane (CH3CH2I), monobromoethane (CH3CH2Br), 1,1,1-triiodoethane (CH3CI3), etc. Among these, 1,1,1-trifluoro-2-iodoethane (CF3CH2I) is particularly preferably used, taking into consideration availability, ODP value, handleability, etc.

[0080] Examples of the fluoroalkanes having 1 to 3 carbon atoms include fluoromethane (boiling point -78.2°C), difluoromethane (boiling point -51.6°C), trifluoromethane (boiling point -84.4°C), and tetrafluoromethane (boiling point -127.8°C); fluoroethane (boiling point -37.1°C), 1,1-difluoroethane (boiling point -24.7°C), 1,1,1-trifluoroethane (boiling point -47.2°C), 1,1,1,2-tetrafluoroethane (boiling point -26.3°C), and 1, Examples of suitable fluoroethanes include 1,1,2,2-pentafluoroethane (boiling point: -48.5°C); and fluoropropanes such as 1-fluoropropane (boiling point: -2.5°C), 2-fluoropropane (boiling point: -10.0°C), 2,2-difluoropropane (boiling point: -1.0°C), 1,1,1-trifluoropropane (boiling point: -12.0°C), 1,1,2,2-tetrafluoropropane (boiling point: -0.8°C), and 1,1,1,3,3,3-hexafluoropropane (boiling point: -1.4°C).

[0081] The amount of disproportionation inhibitor to be added is not particularly limited, but when the total amount of refrigerant-related components (total amount of mixed refrigerant and disproportionation inhibitor) is taken as 100% by mass, the upper limit of the amount (content) of disproportionation inhibitor to be added may be 10% by mass or less of the total amount of refrigerant-related components, preferably 5% by mass or less, and more preferably 3% by mass or less. This is because if the content of disproportionation inhibitor exceeds 10% by mass of the total amount of refrigerant-related components, the content of disproportionation inhibitor will be too high when viewed as a working fluid for a refrigeration cycle, and there is a possibility that the working fluid will not be able to exhibit good physical properties as a "refrigerant." Of course, depending on the composition of the working fluid for a refrigeration cycle, the disproportionation inhibitor may be added in an amount of 10% by mass or more of the total amount of refrigerant-related components.

[0082] As the disproportionation inhibitor, as described above, two or more of saturated hydrocarbons, haloalkanes, and fluoroalkanes can be used in combination. In this case, the mixing ratio of saturated hydrocarbons, haloalkanes, and fluoroalkanes is not particularly limited. As described above, a preferred content of the total amount of disproportionation inhibitors is 10 mass% or less, so it is sufficient that two or more of saturated hydrocarbons, haloalkanes, and fluoroalkanes are used in combination at an appropriate mixing ratio within this range.

[0083] In the present disclosure, a plurality of types of saturated hydrocarbons, haloalkanes, and fluoroalkanes may be used in combination. Therefore, the combination of two or more types of saturated hydrocarbons, haloalkanes, and fluoroalkanes as used herein means that two or more types of compounds classified as saturated hydrocarbons, one or more types of compounds classified as haloalkanes, and one or more types of compounds classified as fluoroalkanes may be used in combination.

[0084] Here, saturated hydrocarbons, haloalkanes, and fluoroalkanes can suppress or moderate the progress of disproportionation reactions even when added in amounts of 10% by mass or less, respectively. Furthermore, as disclosed herein, when two or more saturated hydrocarbons, haloalkanes, and fluoroalkanes are used in combination, it is possible to suppress or moderate the progress of disproportionation reactions with even smaller amounts than when each is added alone. More specifically, the upper limit of the amount of disproportionation inhibitor added based on the total amount (total amount of two or more of saturated hydrocarbons, haloalkanes, and fluoroalkanes) may be 10% by mass or less, and may even be 5% by mass or less. However, when saturated hydrocarbons and haloalkanes are combined, a more preferred upper limit is 3% by mass or less.

[0085] At this time, the mixing ratio of two or more of saturated hydrocarbons, haloalkanes, and fluoroalkanes is not particularly limited. For example, when saturated hydrocarbons and haloalkanes are used in combination, when the added amount is 3 mass% or less, a typical example of the mixing ratio of saturated hydrocarbons to haloalkanes can be in the range of 1:0.5 to 1:2 by mass. Here, there are three combinations of saturated hydrocarbons and haloalkanes, and representative mixing ratios for each combination are as follows: [1] A combination of three types of saturated hydrocarbons, haloethane, and halomethane can be in the range of 1:0.25:0.25 to 1:1:1 by mass; [2] A combination of two types of saturated hydrocarbons and haloethane can be in the range of 1:0.25 to 1:1; and [3] A combination of two types of saturated hydrocarbons and halomethane can be in the range of 1:0.25 to 1:1.

[0086] Furthermore, the lower limit of the amount of two or more of saturated hydrocarbons, haloalkanes, and fluoroalkanes added is not particularly limited, but a typical lower limit can be 1.2 mass% or more of the total amount of refrigerant-related components. Even if the total amount of two or more of saturated hydrocarbons, haloalkanes, and fluoroalkanes is less than 1.2 mass%, it is possible to obtain the effect of inhibiting disproportionation reactions, but if it is 1.2 mass% or more, the effect of inhibiting disproportionation reactions can be more suitably achieved. Therefore, in the present disclosure, a more preferred range for the content of two or more of saturated hydrocarbons, haloalkanes, and fluoroalkanes is 1.2 mass% or more and 3 mass% or less of the total amount of refrigerant-related components.

[0087] Generally, the impurities contained in refrigerants used in refrigeration cycle systems are often 2 to 3% by mass or less. For example, commercially available 1,1,2-trifluoroethylene is known to have a purity of about 97% by mass, and contains impurities such as residues or by-products of the synthetic raw materials in an amount of less than 3% by mass.

[0088] The disproportionation inhibitor can effectively inhibit or slow the progress of the disproportionation reaction even when added to the hydrofluoroolefin at an impurity level (3% by mass or less). Therefore, the amounts of saturated hydrocarbon and haloalkane added as disproportionation inhibitors cannot necessarily be specified, and the above-mentioned upper and lower limits, or the amount of disproportionation inhibitor added, are merely representative preferred examples.

[0089] [Control Example of Refrigeration Cycle System] Next, a control example of the refrigeration cycle system according to the present disclosure will be specifically described with reference to FIGS. 2A, 2B, and 3. FIG.

[0090] 2A is a graph showing a transition in the conditions for the disproportionation reaction of hydrofluoroolefins when the compressor 20 transitions from a stopped state to a normal operating state after a certain time has elapsed since startup. The vertical axis of FIG. 2A represents the internal pressure of the compressor 20 (unit: Pa), and the horizontal axis represents the discharge gas temperature of the compressor 20 (unit: °C).

[0091] 2A illustrates a case where, among the refrigerants contained in the working fluid for a refrigeration cycle, 1,1,2-trifluoroethylene (HFO1123) is used as the hydrofluoroolefin and propane (R290) is used as the other refrigerant (high solubility refrigerant). That is, in FIG. 2A, the mixed refrigerant as the working fluid for a refrigeration cycle is composed of 1,1,2-trifluoroethylene and propane. For convenience of explanation, the conditions for the disproportionation reaction of 1,1,2-trifluoroethylene are referred to as "disproportionation conditions."

[0092] 2A, the circular symbols represent the disproportionation conditions immediately after the compressor 20 starts from a stopped state. The diamond symbols represent the disproportionation conditions after a predetermined time t1 has elapsed, that is, after the compressor 20 has transitioned to a normal operating state. When the compressor 20 is stopped, the mixed refrigerant can be considered to be in contact with the refrigerating machine oil inside the compressor 20 at room temperature and normal pressure. Therefore, propane, which has a relatively high oil solubility, dissolves in the refrigerating machine oil in a relatively large amount, but 1,1,2-trifluoroethylene, which has a relatively low oil solubility, dissolves in the refrigerating machine oil in a smaller amount than propane.

[0093] In this state, the control unit 21 starts the compressor 20. At this time, the composition of the mixed refrigerant differs from the refrigerant composition in the stable operation state, and the propane content is relatively low due to the dissolution of propane, resulting in a refrigerant composition with a relatively high content of 1,1,2-trifluoroethylene. If this composition is, for example, an "HFO-rich refrigerant composition," then with an HFO-rich composition, the disproportionation reaction occurs at a relatively lower pressure and temperature than with a composition in the stable operation state. This is the disproportionation condition immediately after startup, indicated by the circular symbol in FIG. 2A. Note that the internal pressure of the compressor 20 under the disproportionation condition immediately after startup is Pi Pa, and the discharge gas temperature is Ti °C. The refrigerant composition in the stable operation state is the refrigerant composition assumed for suppressing the disproportionation reaction in the control of the refrigeration cycle system (air conditioner 10).

[0094] Thereafter, if the start-up conditions for the compressor 20 are satisfied, the control unit 21 increases the operating frequency of the compressor 20 at a preset speed. The control unit 21 operates the compressor 20 at the maximum frequency until the mixed refrigerant circulates sufficiently within the refrigeration cycle and the temperature of the target space (room) where the indoor unit 12 is installed approaches the set temperature. This gradually increases the internal pressure of the compressor 20, and also gradually increases the discharge gas temperature. The operation of the compressor 20 then stabilizes and transitions to a normal operating state.

[0095] In this normal operating state, propane dissolved in the refrigerating machine oil is separated and returned to the mixed refrigerant. Therefore, the refrigerant composition in the normal operating state is relatively rich in 1,1,2-trifluoroethylene compared to the composition immediately after startup, i.e., the HFO-rich composition. The refrigerant composition in the normal operating state is a composition predicted in advance, and the disproportionation reaction occurring at this composition is relatively higher in temperature and pressure than the disproportionation conditions immediately after startup. This is the disproportionation condition in the normal operating state, indicated by the diamond symbol in Figure 2A.

[0096] In addition, if the internal pressure of the compressor 20 under disproportionation conditions in normal operation is PiiPa and the discharge gas temperature is Tii°C, the internal pressure PiiPa is higher than the internal pressure PiPa immediately after startup (Pii>Pi), and the discharge gas temperature Tii°C is higher than the discharge gas temperature Ti°C immediately after startup (Tii>Ti).

[0097] Therefore, when the compressor 20 is started under the control of the control unit 21 and then transitions to a normal operating state, the disproportionation conditions of the mixed refrigerant (working medium for the refrigeration cycle) transition from relatively low-temperature, low-pressure conditions to relatively high-temperature, high-pressure conditions, as indicated by the dotted arrow in the figure.

[0098] When the working fluid for the refrigeration cycle contains a hydrofluoroolefin, if it is intended to suppress the occurrence of a disproportionation reaction, the upper limit values ​​of the internal pressure and internal temperature of the compressor 20 are set to pressure and temperature below the disproportionation conditions in normal operating conditions. The upper limit values ​​of the internal pressure and internal temperature are default values ​​that are set as the pressure and temperature when protective control for the compressor 20 is initiated. The upper limit value of the internal pressure is usually the design pressure of the compressor 20, and the upper limit value of the internal temperature is usually the specification temperature of the compressor 20.

[0099] In this embodiment, for example, if the upper limit of the internal pressure is set to "upper pressure limit P1" and the upper limit of the discharge gas temperature corresponding to the upper limit of the internal pressure is set to "upper temperature limit T1," as shown by the dashed lines in Fig. 2A, both the upper limit of the pressure P1 and the upper limit of the temperature T1 are set to values ​​smaller than the internal pressure PiiPa and the discharge gas temperature Tii°C, which are the disproportionation conditions in the normal operating state.

[0100] In contrast, when the working fluid for a refrigeration cycle contains a high-solubility refrigerant having a higher oil solubility than hydrofluoroolefins, the disproportionation conditions immediately after startup are relatively lower in pressure and temperature than those under normal operating conditions, as shown in Figure 2A. Therefore, the internal pressure Pi Pa and discharge gas temperature Ti °C under the disproportionation conditions immediately after startup may fall below the pressure upper limit P1 and the temperature upper limit T1.

[0101] 2B , immediately after start-up of compressor 20, i.e., when the refrigerant composition is HFO-rich, an "initial pressure upper limit P0" (P0<P1) lower than pressure upper limit P1 is set, and an "initial temperature upper limit T0" (T0<T1) lower than temperature upper limit T1 is set. As compressor 20 continues to operate, the mixed refrigerant circulates sufficiently within the refrigeration cycle, and the refrigerant composition returns from an HFO-rich composition to an expected composition, the initial pressure upper limit P0 is returned to the original pressure upper limit P1, and the initial temperature upper limit T0 is returned to the original temperature upper limit T1, and operation control of compressor 20 is continued.

[0102] This effectively reduces the probability of a disproportionation reaction occurring in hydrofluoroolefins while the HFO-rich refrigerant composition continues from immediately after startup of compressor 20. As a result, the reliability of the refrigeration cycle system (e.g., air conditioner 10) can be further improved.

[0103] The control of such a refrigeration cycle system will be described in more detail with reference to Fig. 2B. Fig. 2B is a graph showing an example of control of the upper limit values ​​of the internal pressure and internal temperature in the compressor 20 by the control unit 21. The vertical axis of Fig. 2B represents the ratio of the internal pressure to the discharge gas temperature of the compressor 20, and the horizontal axis represents time. The circular symbols and diamond symbols in Fig. 2B represent the disproportionation conditions immediately after startup and the disproportionation conditions in normal operation, respectively, as in Fig. 2A.

[0104] 2B, time = 0 corresponds to the start-up of compressor 20. When compressor 20 satisfies the start-up conditions, control unit 21 increases the operating frequency of compressor 20 at a preset speed. Thereafter, as compressor 20 continues to operate, control unit 21 operates compressor 20 at the maximum frequency until the mixed refrigerant circulates sufficiently within the refrigeration cycle and the refrigerant composition returns from the HFO-rich refrigerant composition to the original refrigerant composition (i.e., the refrigerant composition in a normal operating state).

[0105] At this time, the control unit 21 sets the upper limits of the internal pressure and internal temperature to an initial pressure upper limit value P0 and an initial temperature upper limit value T0. These values ​​are expressed as P0 / T0 in FIG. 2B . This upper limit value of P0 / T0 is lower than the disproportionation condition Pi / Ti immediately after startup, which is indicated by a circular symbol in the figure. Under the disproportionation condition Pi / Ti immediately after startup, the refrigerant mixture has an HFO-rich refrigerant composition.

[0106] Thereafter, as compressor 20 continues to operate at the maximum frequency, the dissolved high-solubility refrigerant separates from the refrigeration oil inside compressor 20, gradually increasing the concentration of the high-solubility refrigerant in the mixed refrigerant and relatively decreasing the concentration of hydrofluoroolefins. Eventually, at time = tf in Figure 2B, the concentration of the high-solubility refrigerant reaches a specified value, and the refrigerant composition returns to the previously estimated refrigerant composition. At this time, the disproportionation condition becomes the disproportionation condition Pii / Tii for normal operation, as indicated by the diamond symbol in the figure.

[0107] When time tf reaches time t1 with a margin of error, the control unit 21 changes the upper limits of the internal pressure and internal temperature from an initial pressure upper limit value P0 / initial temperature upper limit value T0 to a pressure upper limit value P1 / temperature upper limit value T1 (P1 / T1). This makes it possible to effectively suppress the probability of a disproportionation reaction occurring even when the mixed refrigerant has an HFO-rich refrigerant composition at the start of the compressor 20. The period from immediately after the start of the compressor 20 (time = 0) until time = t1 corresponds to the initial period of operation of the compressor 20.

[0108] A more specific example of control of the refrigeration cycle system by the control unit 21 will be described with reference to FIG. 3 (and FIG. 1B).

[0109] First, when the control unit 21 starts the compressor 20 to start operation, normal control is performed on the compressor 20 and the expansion valve 16 (step S01). The operation of the compressor 20 is controlled by the operating frequency, as described above. At this time, the upper limit values ​​of the internal pressure and internal temperature of the compressor 20 for control purposes are the initial pressure upper limit value P0 and the initial temperature upper limit value T0, as described above (see FIG. 2B). The opening degree of the expansion valve 16 is controlled based on the discharge gas temperature (or the degree of superheat on the suction side of the compressor 20).

[0110] Next, the control unit 21 measures the internal pressure of the compressor 20 using the pressure sensor 22 and measures the discharge gas temperature using the temperature sensor 23 (step S02). Thereafter, the control unit 21 determines whether time t1 (see FIG. 2B) has elapsed since the compressor 20 started operating (step S03). If t1 has not elapsed (No in step S03), the control unit 21 determines whether the measured pressure value exceeds the initial pressure upper limit value P0 (step S04). If the pressure value does not exceed P0 (No in step S04), the control unit 21 determines whether the measured discharge gas temperature exceeds the initial temperature upper limit value T0 (step S05). If the discharge gas temperature does not exceed T0 (No in step S05), the control unit 21 returns to the normal control of step S01.

[0111] On the other hand, when the measured pressure value exceeds P0 (Yes in step S04) or the measured discharge gas temperature exceeds T0 (Yes in step S05), the control unit 21 decreases the operating frequency of the compressor 20 and increases the opening of the expansion valve 16 (step S06). After that, after a certain time has elapsed (step S07), the process returns to step S02 again, and the internal pressure and discharge gas temperature of the compressor 20 are measured.

[0112] That is, when the compressor 20 is operating, if the measured internal pressure value reaches a predetermined pressure (initial pressure upper limit value P0) (Yes in step S04), protective control is activated to reduce the operating frequency of the compressor 20, increase the opening of the expansion valve 16, or both reduce the operating frequency and increase the opening of the expansion valve 16 (step S06). If this protective control continues for a certain period of time and the internal pressure of the compressor 20 decreases (step S07), the compressor 20 returns to normal control and the operating frequency is restored to the normal frequency. Thereafter, measurement of the internal pressure is repeated again (step S02).

[0113] The expansion valve 16 is controlled in a similar manner. When the measured discharge gas temperature reaches a predetermined temperature (initial upper temperature limit T0) (Yes in step S05), protective control is activated (step S06), which increases the aperture of the expansion valve 16, decreases the operating frequency of the compressor 20, or controls both the aperture of the expansion valve 16 and the operating frequency. If this protective control continues for a certain period of time and the discharge gas temperature of the compressor 20 decreases (step S07), the expansion valve 16 returns to normal control, and the aperture of the expansion valve 16 is restored to the normal aperture. Thereafter, measurement of the discharge gas temperature is repeated again (step S02).

[0114] If the time t1 has elapsed since the start of operation of the compressor 20 (Yes in step S03), the control unit 21 changes the default value of the internal pressure from the initial pressure upper limit value P0 to the pressure upper limit value P1, and changes the default value of the discharge gas temperature from the initial temperature upper limit value T0 to the temperature upper limit value T1 (see FIG. 2B). Therefore, the control unit 21 determines whether the measured pressure value exceeds the pressure upper limit value P1 (step S08), and if the pressure value does not exceed P1 (No in step S08), determines whether the measured discharge gas temperature exceeds the temperature upper limit value T1 (step S09).

[0115] If the discharge gas temperature does not exceed T1 (No in step S09), the process returns to the normal control in step S01, but if the measured pressure value exceeds P1 (Yes in step S08) or the measured discharge gas temperature exceeds T1 (Yes in step S09), the control unit 21 decreases the operating frequency of the compressor 20 and increases the opening of the expansion valve 16 (step S06).The process returns to step S02 again, and the internal pressure and discharge gas temperature of the compressor 20 are measured.

[0116] The control when the preset values ​​of the internal pressure and internal temperature change from P0 / T0 to P1 / T1 is similar to the control for P0 / T0 described above. That is, if the measured internal pressure reaches the preset pressure (pressure upper limit P1) (Yes in step S08), protective control is activated (step S06). If the internal pressure of the compressor 20 drops (step S07), the compressor 20 returns to normal control, and internal pressure measurement is repeated again (step S02). Also, if the measured discharge gas temperature reaches the preset temperature (temperature upper limit T1) (Yes in step S09), protective control is activated (step S06). If the discharge gas temperature of the compressor 20 drops (step S07), the expansion valve 16 returns to normal control, and discharge gas temperature measurement is repeated again (step S02).

[0117] Here, the specific configuration of the control unit 21 that controls the refrigeration cycle system described above is not particularly limited. For example, the control unit 21 described in this embodiment may be configured by an arithmetic unit such as a microcomputer or a microcontroller, a storage device, etc.

[0118] The storage device constituting the control unit 21 may be configured as an internal memory of a microcomputer or microcontroller, or may be configured as an independent memory or storage. Furthermore, the storage device does not need to be a single device, and may be configured as multiple storage devices (for example, an internal memory and an external hard disk drive or SSD, etc.).

[0119] The arithmetic device constituting the control unit 21 may be a general-purpose processor, a dedicated processor, an integrated circuit, an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuits), a GPU, etc., either alone or in combination of two or more types, and may be configured to operate to realize the functions of the control unit in accordance with a program stored in a storage device.

[0120] A processor as an arithmetic device is a circuit (or processing circuit) as hardware because it includes a circuit configured with a large number of transistors, memory, etc. An integrated circuit or ASIC is also a circuit as hardware because it includes a processor or processing block such as a CPU. An FPGA is a circuit as hardware because it includes a large number of integrated logic circuits (functional blocks). A GPU is a circuit as hardware because it includes a large number of arithmetic circuits (cores) mounted in parallel. Software such as programs stored in a storage device is used to configure a circuit (processor, integrated circuit, FPGA, ASIC, GPU, etc.) as hardware. Alternatively, an arithmetic device may be configured as a logic circuit using known switching elements, subtractors, comparators, etc.

[0121] In this manner, the refrigeration cycle system according to the present disclosure uses, as a working fluid for the refrigeration cycle, a mixed refrigerant containing at least one hydrofluoroolefin and at least one high-solubility refrigerant that has a higher solubility in the refrigerating machine oil than the hydrofluoroolefin. When the upper limit of the internal pressure and the upper limit of the discharge gas temperature are preset to a pressure upper limit value P1 and a temperature upper limit value T1, respectively, the control unit 21 controls at least one of the rotation speed of the compressor 20 and the aperture of the expansion valve 16 by setting the upper limit of the internal pressure to an initial pressure upper limit value P0 (P0<P1) and the upper limit of the discharge gas temperature to an initial temperature upper limit value T0 (T0<T1) during a period from the start of the compressor 20 until a predetermined time t1 has elapsed. Furthermore, after a predetermined time t1 has elapsed, the upper limit value of the internal pressure is changed from the initial pressure upper limit value P0 to the pressure upper limit value P1, and the upper limit value of the discharge gas temperature is changed from the initial temperature upper limit value T0 to the temperature upper limit value T1, thereby controlling at least one of the rotation speed of the compressor 20 and the opening degree of the expansion valve 16.

[0122] As described above, when the working fluid for the refrigeration cycle is a mixed refrigerant containing a hydrofluoroolefin and a high-solubility refrigerant, a relatively large amount of the high-solubility refrigerant dissolves in the refrigerating machine oil when the compressor 20 is stopped. Therefore, when the compressor 20 is started, the mixed refrigerant contains a relatively large amount of hydrofluoroolefin, and the conditions (disproportionation conditions) for the internal pressure and internal temperature (discharge gas temperature) at which the disproportionation reaction occurs are lower than those for a normal refrigerant composition.

[0123] Therefore, in the refrigeration cycle system according to the present disclosure, in the initial stage of operation from the start of compressor 20 until a predetermined time t1 has elapsed, the upper limit values ​​of the internal pressure and discharge gas temperature at which protective control is initiated are set to P0 and T0, which are lower than the default values ​​P1 and T1. In the initial stage of operation, control unit 21 controls compressor 20 and expansion valve 16 based on this P0 / T0. After the initial stage of operation ends and the system transitions to normal operation, control unit 21 changes the upper limit values ​​of the internal pressure and discharge gas temperature from P0 / T0 to the default value P1 / T1, and controls compressor 20 and expansion valve 16.

[0124] This makes it possible to effectively suppress the probability of disproportionation reactions occurring even in the early stages of operation when the concentration of hydrofluoroolefins is relatively high and disproportionation reactions are likely to occur. Furthermore, even after the system transitions from the early stages of operation to normal operation, the occurrence of disproportionation reactions can be effectively suppressed or mitigated. As a result, the reliability of the refrigeration cycle system can be further improved.

[0125] The present invention is not limited to the description of the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments or multiple modified examples are also included in the technical scope of the present invention.

[0126] Furthermore, many modifications and other embodiments of the present invention will be apparent to those skilled in the art from the above description. Therefore, the above description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode for carrying out the present invention. Details of the structure and / or function thereof may be substantially changed without departing from the spirit of the present invention.

[0127] (Additional Note) Based on the description of the above embodiments, the following techniques are disclosed in this specification. (Technology 1) A refrigeration cycle system including a compressor that stores refrigeration oil therein and an expansion valve, and a control unit, wherein a mixed refrigerant containing at least one hydrofluoroolefin and at least one high-solubility refrigerant that has a higher solubility in the refrigeration oil than the hydrofluoroolefin is used as a working fluid for the refrigeration cycle, and wherein an upper limit value of an internal pressure and an upper limit value of a discharge gas temperature that are preset in the compressor are set to P1 and T1, respectively, and the control unit, during a period from start-up of the compressor until a predetermined time t1 has elapsed, sets the upper limit value of the internal pressure to P0 (P0<P1) that is smaller than P1, and sets the upper limit value of the discharge gas temperature to T0 (T0<T1) that is smaller than T1, thereby controlling at least one of the rotation speed of the compressor and the aperture of the expansion valve, and after the predetermined time t1 has elapsed, changes the upper limit value of the internal pressure from P0 to P1, and changes the upper limit value of the discharge gas temperature from T0 to T1, thereby controlling at least one of the rotation speed of the compressor and the aperture of the expansion valve.

[0128] (Technology 2) A refrigeration cycle system according to Technology 1, further comprising a pressure sensor that measures the internal pressure of the compressor, and the control unit controls at least one of the rotation speed of the compressor and the opening degree of the expansion valve using the pressure value measured by the pressure sensor.

[0129] (Technology 3) A refrigeration cycle system according to Technology 1, further comprising a first temperature sensor that approximately measures the internal pressure of the compressor from the temperature, and the control unit controls at least one of the rotation speed of the compressor and the opening of the expansion valve using the pressure value indirectly measured by the first temperature sensor.

[0130] (Technology 4) A refrigeration cycle system according to any one of Technology 1 to Technology 3, further comprising a second temperature sensor that measures the temperature of the discharge gas from the compressor, and the control unit controls at least one of the rotation speed of the compressor and the opening degree of the expansion valve using the discharge gas temperature measured by the second temperature sensor.

[0131] (Technology 5) The refrigeration cycle system according to any one of Technology 1 to Technology 4, wherein the high-solubility refrigerant is a saturated hydrocarbon.

[0132] (Technology 6) The refrigeration cycle system according to Technology 5, wherein the saturated hydrocarbon is propane (R290).

[0133] (Technology 7) The working fluid for a refrigeration cycle according to any one of Technology 1 to Technology 6, further containing a disproportionation inhibitor.

[0134] The present invention can be suitably used widely in the field of refrigeration cycle systems that use a working fluid for a refrigeration cycle that uses a hydrofluoroolefin (HFO) in combination with another refrigerant as a refrigerant component, such as air conditioners, refrigerators (for home and commercial use), dehumidifiers, showcases, ice makers, heat pump water heaters, heat pump washer-dryers, and vending machines.

[0135] 10: Air conditioner (refrigeration cycle system) 11: Outdoor unit 12: Indoor unit 13: Inter-unit piping 13a: Pipe connection part 13b: Pipe connection part 14: Outdoor heat exchanger 15: Outdoor fan 16: Expansion valve 17: Switching valve 18: Indoor heat exchanger 19: Indoor fan 20: Compressor 21: Control unit 22: Pressure sensor 23: Temperature sensor

Claims

1. A refrigeration cycle system comprising a compressor that stores refrigeration oil therein and an expansion valve, and a control unit, wherein a mixed refrigerant containing at least one hydrofluoroolefin and at least one high-solubility refrigerant having a higher solubility in the refrigeration oil than the hydrofluoroolefin is used as a working medium for the refrigeration cycle, and wherein, when an upper limit value of an internal pressure and an upper limit value of a discharge gas temperature that are preset in the compressor are P1 and T1, respectively, the control unit, during a period from the start-up of the compressor until a predetermined time t1 has elapsed, sets the upper limit value of the internal pressure to P0 (P0<P1) that is smaller than P1, and sets the upper limit value of the discharge gas temperature to T0 (T0<T1) that is smaller than T1, thereby controlling at least one of the rotation speed of the compressor and the opening of the expansion valve, and after the predetermined time t1 has elapsed, changes the upper limit value of the internal pressure from P0 to P1, and changes the upper limit value of the discharge gas temperature from T0 to T1, thereby controlling at least one of the rotation speed of the compressor and the opening of the expansion valve.

2. A refrigeration cycle system as described in claim 1, further comprising a pressure sensor that measures the internal pressure of the compressor, and the control unit uses the pressure value measured by the pressure sensor to control at least one of the rotation speed of the compressor and the opening degree of the expansion valve.

3. A refrigeration cycle system as described in claim 1, further comprising a first temperature sensor that approximately measures the internal pressure of the compressor from temperature, and wherein the control unit controls at least one of the rotation speed of the compressor and the opening degree of the expansion valve using the pressure value indirectly measured by the first temperature sensor.

4. A refrigeration cycle system as described in claim 1, further comprising a second temperature sensor that measures a temperature of discharge gas from the compressor, and the control unit controls at least one of the rotation speed of the compressor and the opening degree of the expansion valve using the discharge gas temperature measured by the second temperature sensor.

5. The refrigeration cycle system according to any one of claims 1 to 4, wherein the high solubility refrigerant is a saturated hydrocarbon.

6. The refrigeration cycle system according to claim 5, wherein the saturated hydrocarbon is propane (R290).

7. The refrigeration cycle system according to any one of claims 1 to 4, wherein the working fluid for the refrigeration cycle further contains a disproportionation inhibitor.

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