Refrigeration cycle system

Abstract

To provide a refrigeration cycle system capable of satisfactorily suppressing or alleviating a disproportionation reaction even when a refrigeration cycle working medium containing a fluoroolefin and another refrigerant and a refrigerating machine oil are used in combination.SOLUTION: In the refrigeration cycle system, a mixed refrigerant containing a hydrofluoroolefin and a highly soluble refrigerant having higher solubility in a refrigerating machine oil than the hydrofluoroolefin is used as a refrigeration cycle working medium. During a period from startup of a compressor until a predetermined time t1 passes, a control unit sets an upper limit value of an internal pressure to P0 (P0<P1) and sets an upper limit value of a discharge gas temperature to T0 (T0<T1) to control at least one of the compressor and an expansion valve. After the predetermined time t1 passes, the control unit 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 to control at least one of the compressor and the expansion valve.SELECTED DRAWING: Figure 2

Description

[Technical field]

[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. [Background technology]

[0002] As a working medium (refrigerant or heat transfer medium) for the refrigeration cycle, the use of hydrofluoroolefins (HFOs) with a smaller global warming potential (GWP) has been proposed in recent years. A representative hydrofluoroolefin is 1,1,2-trifluoroethylene (HFO1123). 1,1,2-trifluoroethylene is less stable than conventional HFCs and is 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] The disproportionation reaction is easily induced by heat generated during use of the working fluid for the refrigeration cycle, and is accompanied by a large amount of heat release. It is also known that the disproportionation reaction occurs 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 compressor equipped in the system.

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

[0006] A technique is known for improving the performance of a refrigeration cycle system by adjusting the refrigerant dissolution viscosity of such a working medium-containing composition within a predetermined range under high temperature and high pressure conditions. For example, Patent Document 1 discloses that a working fluid (working medium-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 refrigerant solution viscosity is adjusted to 1 / s. Specific refrigerants include hydrofluoroolefins (HFOs) such as fluoroethylene or fluoropropene, fluorine-containing refrigerants such as 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 sealing performance of the compressor is reduced, etc., resulting in a reduction in the refrigeration capacity or cooling capacity of the refrigerator (refrigeration cycle system). Also, if the refrigerant solution viscosity of the working fluid is too high, the energy consumption increases and the refrigeration capacity or cooling capacity also decreases due to factors such as increased stirring resistance or resistance at the start-up of the refrigerator. Therefore, by adjusting the refrigerant solution viscosity to within the above range, the coefficient of performance (COP) of the refrigeration cycle system is improved. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2017-141974 A Summary of the Invention [Problem to be solved by the invention]

[0009] However, in the refrigeration cycle system disclosed in Patent Document 1, as described above, the refrigerant is not limited to hydrofluoroolefin, and there is no description of the disproportionation reaction of hydrofluoroolefin. In addition, although the use of a mixed refrigerant 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 only the relationship between the refrigerant solution viscosity of the working fluid and the COP of the refrigerator is verified.

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

[0011] The present invention has been made to solve such problems, and has an object 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. [Means for solving the problem]

[0012] In order to solve the above problems, 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. As a working medium for the refrigeration cycle, 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. When the upper limit value of the internal pressure preset in the compressor is P1 and the upper limit value of the discharge gas temperature is T1, the control unit sets the upper limit value of the internal pressure to P0 (P0 < P1) smaller than P1 and the upper limit value of the discharge gas temperature to T0 (T0 < T1) smaller than T1 from the start of the compressor until a predetermined time t1 elapses, and controls at least one of the rotational speed of the compressor and the opening degree of the expansion valve. After the predetermined time t1 elapses, 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, and at least one of the rotational speed of the compressor and the opening degree of the expansion valve is controlled.

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

[0014] Therefore, according to the above configuration, at the initial stage of operation start until a predetermined time t1 elapses from the start of the compressor, the upper limit values of the internal pressure and discharge gas temperature that start the protection control are set to P0 and T0 lower than the default values P1 and T1. The control unit controls the compressor or the expansion valve, or both the compressor and the expansion valve based on this P0 / T0 at the initial stage of operation start. After the initial stage of operation start ends and the operation shifts 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 values P1 / T1, and controls at least one of the compressor and the expansion valve.

[0015] This makes it possible to effectively suppress the occurrence probability of the disproportionation reaction even in the early stage of operation when the concentration of hydrofluoroolefins is relatively high and the disproportionation reaction is likely to occur. In addition, even after the operation is shifted from the early stage of operation to normal operation, the occurrence of the disproportionation reaction can be effectively suppressed or mitigated. As a result, the reliability of the refrigeration cycle system can be further improved. Effect of the Invention

[0016] The present invention has the above-mentioned configuration, and has an 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. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1A is a schematic piping diagram showing a typical configuration of an air conditioner, which is an example of a refrigeration cycle system relating to one embodiment of the present disclosure, and FIG. 1B is a block diagram of essential parts showing a typical control configuration of the air conditioner shown in FIG. [Diagram 2] Graph (A) is a schematic diagram showing the transition of conditions for the disproportionation reaction of hydrofluoroolefins after a predetermined time has elapsed since immediately after the start of the compressor, and graph (B) is a diagram showing an example of pressure / temperature control until a predetermined time has elapsed in a refrigeration cycle system according to the present disclosure. [Diagram 3] 4 is a flowchart showing an example of a representative control of the air conditioner shown in FIG. 1(B). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] [Knowledge that formed the basis of this disclosure] According to intensive studies by the present inventors, it has become clear that when a hydrofluoroolefin in which a disproportionation reaction occurs 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 have to be taken into account in conventional refrigeration cycle systems.

[0019] For example, assume that the refrigerant component of the working fluid for the 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 refrigeration 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 the disproportionation reaction in the hydrofluoroolefin.

[0020] 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.

[0021] When the compressor starts from a stopped state and enters an operating state, the internal pressure and temperature change significantly, and as a result, the other refrigerants dissolved in the refrigeration oil return to a mixed refrigerant. That is, when the compressor is stopped or immediately after starting, the other refrigerants are relatively small and the hydrofluoroolefin is large, and when the compressor transitions to normal operation, the content of the other refrigerants returns to the original amount. In other words, the refrigerant composition when the compressor is stopped or immediately after starting is different from the refrigerant composition during normal operation of the compressor.

[0022] When a compressor starts operating, the inside of the compressor quickly becomes hot and pressure-rich. However, it is difficult for the change in the amount of hydrofluoroolefin and other refrigerants dissolved therein, that is, the change in the refrigerant composition, to quickly follow the changes in the internal temperature and pressure. This is because the solubility of the refrigerant in the refrigeration oil is basically premised on a state in which the refrigerant and the refrigeration oil coexist quasi-statically. Therefore, the refrigerant composition when the compressor is stopped or immediately after it is started is different from the refrigerant composition during normal operation of the compressor (high temperature and high pressure).

[0023] As mentioned 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 in 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 disproportionation reaction may occur even under conditions of relatively low pressure and low temperature compared to normal operation.

[0024] Furthermore, during the period from when the compressor is started and begins operation until a predetermined time has elapsed, i.e., in the initial stage of operation, the refrigerant composition at the time of stopping 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, in the initial stage of operation, it is no longer possible to effectively suppress the disproportionation reaction, and as a result, in the initial stage of operation, the disproportionation reaction of hydrofluoroolefins is more likely to occur.

[0025] As a result of further intensive research by the inventors, it was found that 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 preset values ​​to control the operation of the compressor, thereby effectively suppressing or mitigating the disproportionation reaction, particularly at the beginning of operation, and thus completed the present invention.

[0026] That is, the refrigeration cycle system according to the present disclosure includes a refrigeration cycle including a compressor and an expansion valve that store refrigerating oil therein, and a control unit. As a working medium for the refrigeration cycle, a mixed refrigerant containing at least one hydrofluoroolefin and at least one high-solubility refrigerant having a higher solubility in the refrigerating oil than the hydrofluoroolefin is used. When the upper limit value of the internal pressure preset in the compressor is P1 and the upper limit value of the discharge gas temperature is T1, the control unit sets the upper limit value of the internal pressure to P0 (P0 < P1) smaller than P1 and the upper limit value of the discharge gas temperature to T0 (T0 < T1) smaller than T1 from the start of the compressor startup until a predetermined time t1 elapses, and controls at least one of the rotational speed of the compressor and the opening degree of the expansion valve. After the predetermined time t1 elapses, 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, and at least one of the rotational speed of the compressor and the opening degree of the expansion valve is controlled.

[0027] When the working medium for the refrigeration cycle is a mixed refrigerant containing hydrofluoroolefin and a high-solubility refrigerant as described above, a relatively large amount of the high-solubility refrigerant will dissolve in the refrigerating oil when the compressor stops. Therefore, at the start of the compressor, the hydrofluoroolefin in the mixed refrigerant becomes relatively more, and the conditions of the internal pressure and internal temperature (discharge gas temperature) (disproportionation conditions) under which the disproportionation reaction occurs are lower than those of the normal refrigerant composition.

[0028] 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 the 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 the discharge gas temperature from P0 / T0 to the default value P1 / T1, and controls at least one of the compressor and the expansion valve.

[0029] This makes it possible to effectively suppress the occurrence probability of the disproportionation reaction even in the early stage of operation when the concentration of hydrofluoroolefins is relatively high and the disproportionation reaction is likely to occur. In addition, even after the operation is shifted from the early stage of operation to normal operation, the occurrence of the disproportionation reaction can be effectively suppressed or mitigated. As a result, the reliability of the refrigeration cycle system can be further improved.

[0030] In the refrigeration cycle system of the above configuration, a pressure sensor is provided for measuring the internal pressure of 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 pressure value measured by the pressure sensor.

[0031] In addition, in the refrigeration cycle system of the above configuration, a first temperature sensor is provided 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.

[0032] In addition, in the refrigeration cycle system of the above configuration, a second temperature sensor is provided to measure 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.

[0033] 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).

[0034] In the refrigeration cycle system having the above configuration, the working fluid for the refrigeration cycle may further contain a disproportionation inhibitor.

[0035] Representative embodiments of the present disclosure will be described below with reference to the drawings. In the following, the same or corresponding elements are denoted by the same reference numerals throughout the drawings, and duplicated descriptions thereof will be omitted.

[0036] [Example of refrigeration cycle system configuration] First, an air conditioner 10 shown in Fig. 1(A) and (B) 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 Fig. 1(A), 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, 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 connection parts 13a and 13b.

[0037] The air conditioner 10 circulates refrigerant compressed in the outdoor unit 11 between the outdoor unit 11 and the indoor unit 12 to 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.

[0038] 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, which contains a refrigerant. Refrigeration oil is stored inside the compressor 20. The outdoor heat exchanger 14 exchanges heat of 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.

[0039] 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 in the target space. The indoor fan 19 blows air within the target space (indoors) in the target space.

[0040] 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).

[0041] The specific type of refrigeration oil stored inside compressor 20 is not particularly limited, and an example of the type is a configuration in which a lubricating oil known in the compressor field is used as a base oil and known additives are contained as necessary.

[0042] 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; oxygen-containing oils such as ether oils such as polyalkylene glycols, polyvinyl ethers, polyphenyl ethers, and perfluoroethers; etc. Only one of these base oils may be used, or two or more of them may be used in appropriate combination.

[0043] The additives contained in the refrigeration oil are not particularly limited, and examples thereof include an oiliness agent, a sliding property modifier, an extreme pressure additive, an antioxidant, an acid scavenger, a metal deactivator, an antifoaming agent, a corrosion inhibitor, and a dispersant.

[0044] In this embodiment, the base oil of the refrigerating machine oil is preferably at least one selected from polyol ester, polyalkylene glycol, and polyvinyl ether as a main component, and more preferably polyol ester or polyvinyl ether as a main component. The main component here means that it is 50% by mass or more based on 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 based on the total amount (100% by mass) of the refrigerating machine oil.

[0045] As shown in the block diagram of main parts in Fig. 1(B), 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 and closing of the expansion valve 16, control of flow path switching of the changeover valve 17, and controls the operation and / or stopping of the outdoor fan 15 and the indoor fan 19. Note that, for ease of explanation, Fig. 1(B) shows only the compressor 20 and the expansion valve 16 as objects to be controlled by the control unit 21.

[0046] 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 operation 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 operation frequency of the compressor 20.

[0047] The pressure sensor 22 measures the internal pressure of the compressor 20. Examples of such pressure sensors 22 include those that indirectly measure the internal pressure of the compressor 20, those that approximately measure the internal pressure from the temperature inside the compressor 20 (temperature sensor), and those that directly measure the internal pressure. In general, 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. As a specific pressure sensor 22, a sensor known in the field of refrigeration cycle systems such as the air conditioner 10 can be suitably used, and is not particularly limited.

[0048] 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, but the 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 from each other. Therefore, for convenience, in this specification, the temperature sensor used as the pressure sensor 22 is referred to as the "first temperature sensor" and the temperature sensor that measures the discharge gas temperature is referred to as the "second temperature sensor" to distinguish them. A specific temperature sensor 23 (second temperature sensor) can be suitably used that is known in the field of refrigeration cycle systems such as the air conditioner 10, and is not particularly limited.

[0049] As described later, in the refrigeration cycle system according to the present disclosure, the control unit 21 sets the upper limits of the internal pressure and discharge gas temperature of the compressor 20 lower during the period from the start of the compressor 20 until a predetermined time t1 has elapsed, i.e., at the beginning of the operation, and then controls the rotation speed of the compressor 20 or the opening degree of the expansion valve 16, or both the rotation speed and the opening degree (at least one of the rotation speed and the opening degree), and thereafter changes the upper limits of 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).

[0050] 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 the 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 (switching valve 17, outdoor fan 15, indoor fan 19, etc.).

[0051] In the example shown in Fig. 1(A), the flow direction of the refrigerant in the cooling operation mode is indicated by a block arrow. 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 the opposite side to the block arrow shown in Fig. 1(A). 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.

[0052] The pipe connection parts 13a and 13b of the air conditioner 10 are provided between the outdoor unit 11 and the indoor unit 12 in the inter-unit pipes 13 that are connected in a circular shape. For example, a two-way valve or a three-way valve is used as these pipe connection parts 13a and 13b. This allows the outdoor unit 11 and the indoor unit 12 to be connected to each other, enabling the flow of refrigerant. Furthermore, the opening degree and / or opening and closing of the pipe connection parts 13a and 13b can be controlled manually or by the control of the control unit 21.

[0053] The specific configurations of the air conditioner 10, outdoor unit 11, indoor unit 12, and each of the components constituting 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.

[0054] 1(A) and (B), other components may be included, or some components may not be included. The refrigeration cycle system is not limited to the air conditioner 10, and may be a dehumidifier, a showcase, an ice maker, a heat pump water heater, a heat pump washer / dryer, a vending machine, etc.

[0055] [Refrigerant components] In the refrigeration cycle system according to the present disclosure, a working fluid for a refrigeration cycle is used that contains a hydrofluoroolefin (HFO) in which a disproportionation reaction occurs and one or more other refrigerants. The other refrigerants have a higher (larger) solubility in the refrigeration oil stored inside the compressor 20 than the hydrofluoroolefin.

[0056] 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 types of refrigerants other than hydrofluoroolefins, at least one of the refrigerants may be a high solubility refrigerant.

[0057] Specific examples of hydrofluoroolefins include, but are not limited to, those having a carbon number of 2, 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)). Only one of these hydrofluoroolefins may be used as a refrigerant component, or two or more of them may be used in combination as a refrigerant component.

[0058] These hydrofluoroolefins have a skeleton 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 replaced by a fluorine atom, or at least one of the two hydrogen atoms bonded to both carbon atoms is replaced by a fluorine atom. Note that in the hydrofluoroolefins, some of the hydrogen atoms may be replaced by other atoms or other substituents.

[0059] For example, 1,1,2-trifluoroethylene has a structure in which both of the two hydrogen atoms bonded to one carbon atom of the ethylene structure (the carbon atom at position 1) are replaced by fluorine atoms, and one of the two hydrogen atoms bonded to the other carbon atom (the carbon atom at position 2) is replaced by a fluorine atom.

[0060] 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 facing the carbon atom at position 1 across the double bond, not the hydrogen atom adjacent to the carbon atom at position 2, is substituted with a fluorine atom.

[0061] 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, ozone in the atmosphere generates hydroxyl radicals (OH radicals) through photochemical reactions, and these hydroxyl radicals can cause addition reactions with double bonds, making the hydrofluoroolefins easily decomposed. Therefore, hydrofluoroolefins have little impact on ozone layer destruction and global warming.

[0062] The working fluid for the refrigeration cycle used in the present disclosure may contain, for example, propane (R290) as a refrigerant component in addition to hydrofluoroolefin. 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 dissolved in refrigeration oil than hydrofluoroolefin. Therefore, propane is a high-solubility refrigerant that has a high solubility in refrigeration oil (oil solubility) compared to hydrofluoroolefin.

[0063] In addition, in the working fluid for a refrigeration cycle used in the present disclosure, the "other refrigerants" that may be contained other than the hydrofluoroolefin are not particularly limited, but representative examples include hydrofluorocarbons (HFCs), saturated hydrocarbons, carbon dioxide, etc.

[0064] 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.

[0065] 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), methylcyclobutane, and the like.

[0066] These other refrigerants may be used alone or in combination of two or more. Among these, R32 (difluoromethane) is typically used. As described later, some saturated hydrocarbons can be used as disproportionation inhibitors. Therefore, saturated hydrocarbons can be used in combination with other refrigerants and as disproportionation inhibitors.

[0067] 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 combination of two or more. These other refrigerants also include high solubility refrigerants. For example, saturated hydrocarbons are easily dissolved in refrigerating machine oils, similar to propane, and therefore can be suitably used as high solubility refrigerants.

[0068] The content (content rate) of hydrofluoroolefin and other refrigerants (including high solubility refrigerants) in the working fluid for the refrigeration cycle is 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, may be 60% by mass or more, may be 70% by mass or more, or may be 80% by mass or more. In addition, 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, may be 40% by mass or less, may be 30% by mass or less, or may be 20% by mass or less.

[0069] 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 a large content of other refrigerants, and therefore the advantage of using a hydrofluoroolefin with a small GWP in a working fluid for a refrigeration cycle will not be fully obtained.

[0070] Furthermore, for example, if the other refrigerant is propane or a saturated hydrocarbon as described above, the flammability of propane may have a large effect on the mixed refrigerant, i.e., the working fluid for a refrigeration cycle containing the mixed refrigerant, and in this case, the advantage of realizing good handling while reducing the GWP of the working fluid for a refrigeration cycle cannot be fully obtained.

[0071] [Other ingredients that can be used in combination] As described above, the working fluid for the refrigeration cycle used in the present disclosure can be used in combination with a refrigerating machine oil (lubricating oil) stored inside the compressor 20 of the refrigeration cycle system. As described above, the working fluid for the refrigeration cycle used in the present disclosure may be configured as a mixed refrigerant substantially containing hydrofluoroolefin and at least one type of high solubility refrigerant as "main components". Furthermore, when the working fluid for the refrigeration cycle is used in combination with a refrigerating machine oil, the mixed refrigerant and the refrigerating machine oil, as well as other components, can be considered to constitute a working fluid-containing composition.

[0072] The refrigerating machine oil contained in the working medium-containing composition (used together with the working medium for the refrigeration cycle) can be suitably selected from various refrigerating machine oils (lubricants) known in the refrigeration cycle system. Specific examples of the refrigerating machine oil include, but are not limited to, ester-based lubricants, ether-based lubricants, glycol-based lubricants, alkylbenzene-based lubricants, fluorine-based lubricants, mineral oils, and hydrocarbon-based synthetic oils. Only one type of these refrigerating machine oils may be used, or two or more types may be used in appropriate combination.

[0073] In addition, various known additives may be added to the working medium-containing composition. Specific additives include, but are not limited to, antioxidants, moisture trapping agents, metal deactivators, anti-wear agents, and anti-foaming agents. The antioxidant is used to improve the thermal stability, oxidation resistance, chemical stability, and the like of the mixed refrigerant or refrigerating machine oil. The moisture trapping agent is used to remove moisture when the moisture infiltrates into the refrigeration cycle system, and is particularly used to suppress changes in the properties of the refrigerating machine oil. The metal deactivator is used to suppress or prevent chemical reactions caused by the catalytic action of metal components. The anti-wear agent is used to reduce wear in the sliding parts in the compressor 20, especially wear during high-pressure operation. The anti-foaming agent is used to suppress the generation of bubbles in the refrigerating machine oil.

[0074] The specific types of these additives are not particularly limited, and known compounds can be suitably used depending on various conditions. In addition, as these additives, only one type of compound may be used, or two or more types of compounds may be appropriately combined. Furthermore, the amount of these additives added is not particularly limited, and they can be added within a known range as long as it does not impair the properties of the working fluid for the refrigeration cycle used in the present disclosure or the working fluid-containing composition containing the same.

[0075] Here, as described above, the working fluid for a refrigeration cycle used in the present disclosure may have a disproportionation inhibitor that is gaseous or liquid at normal temperature and normal pressure added to it in advance. Specifically, for example, the disproportionation inhibitor may be at least one of 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) having a boiling point of 0° C. or less. Only one of these disproportionation inhibitors may be used, or two or more of them may be used in appropriate combination.

[0076] Specific examples of disproportionation inhibitors 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), methylcyclobutane, etc. Among these, n-propane is particularly preferred.

[0077] Examples of haloalkanes having one carbon atom, that is, 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), difluoroiodomethane (CHF2I), and the like. Among these, dibromomethane (CH2Br2), bromomethane (CH3Br), dibromodichloromethane (CBr2Cl2), trifluoroiodomethane (CF3I) and the like are preferred, with trifluoroiodomethane (CF3I) being more preferred.

[0078] Examples of haloalkanes having 2 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 in consideration of availability, ODP value, handling, etc.

[0079] Examples of 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), 1, Examples of the 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).

[0080] 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 mass%, the upper limit of the amount (content) of disproportionation inhibitor to be added may be 10 mass% or less of the total amount of refrigerant-related components, preferably 5 mass% or less, and more preferably 3 mass% or less. This is because if the content of disproportionation inhibitor exceeds 10 mass% of the total amount of refrigerant-related components, the content of disproportionation inhibitor becomes too high when viewed as a working fluid for a refrigeration cycle, and there is a possibility that it 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, 10 mass% or more of the total amount of refrigerant-related components may be added.

[0081] 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, the preferred total content 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 in an appropriate mixing ratio within this range.

[0082] In the present disclosure, a plurality of types of compounds may be used in combination as each of saturated hydrocarbons, haloalkanes, and fluoroalkanes. Therefore, the combination of two or more types of saturated hydrocarbons, haloalkanes, and fluoroalkanes means that two or more types of compounds may be used in combination among one 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.

[0083] Here, the saturated hydrocarbon, haloalkane, and fluoroalkane can suppress or slow down the progress of the disproportionation reaction even when added in an amount of 10% by mass or less. Furthermore, as disclosed herein, when two or more of the saturated hydrocarbon, haloalkane, and fluoroalkane are used in combination, it is possible to suppress or slow down the progress of the disproportionation reaction with even smaller amounts than when each is added alone. More specifically, the upper limit of the amount of disproportionation inhibitor added in the total amount (total amount of two or more of the saturated hydrocarbon, haloalkane, and fluoroalkane) may be 10% by mass or less, and may be 5% by mass or less, but when the saturated hydrocarbon and the haloalkane are combined, a more preferable upper limit is 3% by mass or less.

[0084] At this time, the mixing ratio of two or more of the saturated hydrocarbon, haloalkane, and fluoroalkane is not particularly limited. For example, in the case of using a combination of a saturated hydrocarbon and a haloalkane, when the amount added is 3 mass% or less, a representative example of the mixing ratio of the saturated hydrocarbon and the haloalkane 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 the 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.

[0085] The lower limit of the amount of two or more of saturated hydrocarbons, haloalkanes, and fluoroalkanes is not particularly limited, but a representative lower limit is 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 suppressing disproportionation reactions, but if it is 1.2 mass% or more, the effect of suppressing disproportionation reactions can be more suitably realized. Therefore, in the present disclosure, a more preferable range of 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.

[0086] Generally, impurities contained in refrigerants used in refrigeration cycle systems are often 2 to 3 mass% or less. For example, commercially available 1,1,2-trifluoroethylene is known to have a purity of about 97 mass%, and impurities include residues of synthetic raw materials or by-products at less than 3 mass%.

[0087] 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 mass% or less). Therefore, the amount of the saturated hydrocarbon and haloalkane added as the disproportionation inhibitor cannot necessarily be specified, and the above-mentioned upper limit, lower limit, or amount of the disproportionation inhibitor added is merely a representative preferred example.

[0088] [Example of refrigeration cycle system control] Next, a control example of the refrigeration cycle system according to the present disclosure will be specifically described with reference to Figs. 2(A), (B) and 3.

[0089] Fig. 2(A) is a graph showing a typical change 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 the compressor 20 was started. The vertical axis of Fig. 2(A) is the internal pressure of the compressor 20 (unit: Pa), and the horizontal axis is the discharge gas temperature of the compressor 20 (unit: °C).

[0090] In Fig. 2(A), a case is illustrated in which 1,1,2-trifluoroethylene (HFO1123) is used as the hydrofluoroolefin and propane (R290) is used as the other refrigerant (high solubility refrigerant) among the refrigerants contained in the working fluid for the refrigeration cycle. That is, in Fig. 2(A), the mixed refrigerant as the working fluid for the 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".

[0091] 2(A) indicates the disproportionation conditions immediately after the compressor 20 starts from a stopped state. Moreover, the diamond-shaped symbols indicate the disproportionation conditions after a predetermined time t1 has elapsed, that is, after the compressor 20 has transitioned to a normal operating state. In a state in which the compressor 20 is stopped, the mixed refrigerant can be considered to be in contact with the refrigeration oil inside the compressor 20 at normal temperature and pressure. Therefore, propane, which has a relatively high oil solubility, dissolves in the refrigeration oil in a relatively large amount, but 1,1,2-trifluoroethylene, which has a relatively low oil solubility, dissolves in the refrigeration oil in a smaller amount than propane.

[0092] In this state, the control unit 21 starts the compressor 20. At this time, the composition of the mixed refrigerant is different from the refrigerant composition in the stable operation state, and the content of propane is relatively low due to the dissolution of propane, and the content of 1,1,2-trifluoroethylene is relatively high. If this composition is, for example, an "HFO-rich refrigerant composition", in the HFO-rich composition, the disproportionation reaction occurs at a relatively low pressure and low temperature compared to the composition in the stable operation state. This is the disproportionation condition immediately after startup, shown by the circular symbol in FIG. 2(A). Note that the internal pressure of the compressor 20 in 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).

[0093] Thereafter, if the start-up conditions of 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 in the refrigeration cycle and the temperature of the target space (room) in which the indoor unit 12 is installed approaches the set temperature. This causes the internal pressure of the compressor 20 to gradually increase, and the discharge gas temperature to also gradually increase. Then, the operation of the compressor 20 becomes stable and transitions to a normal operating state.

[0094] In this normal operating state, the propane dissolved in the refrigeration 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., an HFO-rich composition. The refrigerant composition in the normal operating state is a composition that is predicted in advance, and the disproportionation reaction that occurs in 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, shown by the diamond symbol in Figure 2(A).

[0095] In addition, if the internal pressure of the compressor 20 under disproportionation conditions in normal operating state is PiiPa and the discharge gas temperature is Tii°C, the internal pressure PiiPa is greater than the internal pressure PiPa immediately after startup (Pii>Pi), and the discharge gas temperature Tii°C is greater than the discharge gas temperature Ti°C immediately after startup (Tii>Ti).

[0096] 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 and low pressure conditions to high temperature and high pressure conditions, as shown by the dotted arrow in the figure.

[0097] When the working fluid for the refrigeration cycle contains a hydrofluoroolefin, if it is assumed that the occurrence of a disproportionation reaction is suppressed, 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 a normal operating state. 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 started. 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.

[0098] In the present embodiment, for example, when the upper limit value of the internal pressure is set as "pressure upper limit value P1" and the upper limit value of the discharge gas temperature corresponding to the upper limit value of the internal pressure is set as "temperature upper limit value T1", as shown by the dashed line in FIG. 2(A). Both the pressure upper limit value P1 and the temperature upper limit value T1 are set values smaller than the internal pressure Pii Pa and the discharge gas temperature Tii °C, which are the disproportionation conditions in the normal operation state.

[0099] On the other hand, when the refrigerant used in the refrigeration cycle contains a high-solubility refrigerant with a higher oil solubility than hydrofluoroolefin, as shown in FIG. 2(A), the disproportionation conditions immediately after startup are relatively lower in pressure and temperature than the disproportionation conditions in the normal operation state. Therefore, the internal pressure Pi Pa and the discharge gas temperature Ti °C under the disproportionation conditions immediately after startup may fall below the pressure upper limit value P1 and the temperature upper limit value T1.

[0100] Therefore, in the refrigeration cycle system according to the present disclosure, as shown in FIG. 2(B), immediately after the compressor 20 starts, that is, when the refrigerant composition is HFO-rich, an "initial pressure upper limit value P0" (P0 < P1) lower than the pressure upper limit value P1 is set, and an "initial temperature upper limit value T0" (T0 < T1) lower than the temperature upper limit value T1 is set. When the operation of the compressor 20 continues and the mixed refrigerant circulates sufficiently in the refrigeration cycle and the refrigerant composition returns to the assumed composition from the HFO-rich composition, the initial pressure upper limit value P0 is returned to the original pressure upper limit value P1, and the initial temperature upper limit value T0 is returned to the original temperature upper limit value T1, and the operation control of the compressor 20 is continued.

[0101] Thereby, the probability of the disproportionation reaction occurring in the hydrofluoroolefin can be favorably suppressed while the HFO-rich refrigerant composition continues immediately after the startup of the compressor 20. As a result, the reliability of the refrigeration cycle system (for example, the air conditioner 10) can be further improved.

[0102] The control of such a refrigeration cycle system will be described in more detail with reference to Fig. 2(B). Fig. 2(B) 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. 2(B) is the ratio between the internal pressure and the discharge gas temperature of the compressor 20, and the horizontal axis is time. Also, the circular symbols and diamond symbols in Fig. 2(B) respectively represent the disproportionation conditions immediately after start-up and the disproportionation conditions in a normal operating state, as in Fig. 2(A).

[0103] 2(B), time=0 corresponds to the start-up of compressor 20. When compressor 20 satisfies the start-up condition, control unit 21 increases the operation frequency of compressor 20 at a preset speed. Thereafter, while compressor 20 continues to operate, control unit 21 operates compressor 20 at the maximum frequency until the mixed refrigerant circulates sufficiently in 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 operation state).

[0104] At this time, the control unit 21 sets the upper limit values ​​of the internal pressure and internal temperature to an initial pressure upper limit value P0 and an initial temperature upper limit value T0. In Fig. 2(B), this is written as P0 / T0. 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 mixed refrigerant has an HFO-rich refrigerant composition.

[0105] Thereafter, as the compressor 20 continues to operate at the maximum frequency, the dissolved high solubility refrigerant separates from the refrigeration oil inside the compressor 20, and the concentration of the high solubility refrigerant in the mixed refrigerant gradually increases, and the concentration of the hydrofluoroolefin decreases relatively. Finally, when the time reaches tf in FIG. 2(B), the concentration of the high solubility refrigerant becomes a specified value, and the refrigerant composition returns to the refrigerant composition expected in advance. At this time, the disproportionation condition becomes the disproportionation condition Pii / Tii in the normal operating state, as indicated by the diamond symbol in the figure.

[0106] The control unit 21 changes the upper limits of the internal pressure and the internal temperature from the initial pressure upper limit value P0 / initial temperature upper limit value T0 to the pressure upper limit value P1 / temperature upper limit value T1 (P1 / T1) when the time tf reaches time = t1 with a margin of error. This makes it possible to effectively suppress the occurrence probability of the disproportionation reaction even if the mixed refrigerant has an HFO-rich refrigerant composition at the start of the compressor 20. Note that the period from immediately after the start of the compressor 20 (time = 0) until time = t1 is the initial period of operation of the compressor 20.

[0107] Regarding such control of the refrigeration cycle system by the control unit 21, a more specific control example will be described with reference to FIG. 3 (and FIG. 1(B)).

[0108] First, when the control unit 21 starts up 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 operation frequency, as described above. At this time, the upper limit values ​​of the internal pressure and internal temperature in the control of the compressor 20 are the initial pressure upper limit value P0 and the initial temperature upper limit value T0, as described above (see FIG. 2(B)). 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).

[0109] Next, the control unit 21 measures the internal pressure of the compressor 20 by the pressure sensor 22 and measures the discharge gas temperature by the temperature sensor 23 (step S02). After that, the control unit 21 judges whether or not the time=t1 (see FIG. 2(B)) has elapsed since the compressor 20 started operating (step S03). If t1 has not elapsed (No in step S03), it judges whether or not 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), it judges whether or not 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 process returns to the normal control of step S01.

[0110] 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, when a certain time has elapsed (step S07), the process returns to step S02 again and measures the internal pressure and discharge gas temperature of the compressor 20.

[0111] In other words, when the compressor 20 is operating, if the measured internal pressure value reaches a preset pressure (initial pressure upper limit value P0) (Yes in step S04), a protective control is activated to lower the operating frequency of the compressor 20, increase the opening of the expansion valve 16, or execute both a lowering of the operating frequency and an increase in 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. After that, the measurement of the internal pressure is repeated again (step S02).

[0112] The expansion valve 16 is controlled in the same manner, and when the measured discharge gas temperature reaches a preset temperature (initial temperature upper limit T0) (Yes in step S05), protective control is activated to increase the opening of the expansion valve 16, decrease the operating frequency of the compressor 20, or execute both the opening control and the operating frequency control of the expansion valve 16 (step S06). 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 opening of the expansion valve 16 is restored to the normal opening. Thereafter, measurement of the discharge gas temperature is repeated again (step S02).

[0113] Here, if the time t1 has elapsed since the compressor 20 started operating (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. 2(B)). 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).

[0114] If the discharge gas temperature does not exceed T1 (No in step S09), the process returns to 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 to measure the internal pressure and discharge gas temperature of the compressor 20.

[0115] The control when the default values ​​of the internal pressure and the internal temperature change from P0 / T0 to P1 / T1 is the same as the control in the case of P0 / T0 described above. That is, when the measured internal pressure value reaches the default pressure (pressure upper limit value P1) (Yes in step S08), the protective control is activated (step S06), and when the internal pressure of the compressor 20 drops (step S07), the compressor 20 returns to normal control, and the measurement of the internal pressure is repeated again (step S02). When the measured discharge gas temperature value reaches the default temperature (temperature upper limit value T1) (Yes in step S09), the protective control is activated (step S06). When the discharge gas temperature of the compressor 20 drops (step S07), the expansion valve 16 returns to normal control, and the measurement of the discharge gas temperature is repeated again (step S02).

[0116] Here, the specific configuration of the control unit 21 that controls the above-mentioned refrigeration cycle system is not particularly limited. For example, the control unit 21 described in the present embodiment may be configured with an arithmetic device of a microcomputer or a microcontroller, a storage device, and the like.

[0117] The storage device constituting the control unit 21 may be configured as an internal memory of a microcomputer or a microcontroller, or may be configured as an independent memory or storage. In addition, 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.).

[0118] 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 according to a program stored in a storage device.

[0119] A processor as an arithmetic device is a circuit (or processing circuit) as hardware since it includes a circuit configured with a large number of transistors, memories, etc. An integrated circuit or ASIC is also a circuit as hardware since it includes a processor such as a CPU or a processing block, etc. An FPGA is a circuit as hardware since it includes a large number of integrated logic circuits (functional blocks). A GPU is a circuit as hardware since 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, the arithmetic device may be configured as a logic circuit, etc., using known switching elements, subtractors, comparators, etc.

[0120] As described above, the refrigeration cycle system according to the present disclosure uses 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 as a working medium for the refrigeration cycle. When the upper limit value of the internal pressure preset in the compressor 20 is defined as the pressure upper limit value P1 and the upper limit value of the discharge gas temperature is defined as the temperature upper limit value T1, the control unit 21 sets the upper limit value of the internal pressure to the initial pressure upper limit value P0 (P0 < P1) and the upper limit value of the discharge gas temperature to the initial temperature upper limit value T0 (T0 < T1) until a predetermined time t1 elapses from the start of the operation of the compressor 20, and controls at least one of the rotational speed of the compressor 20 and the opening degree of the expansion valve 16. After the 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, and at least one of the rotational speed of the compressor 20 and the opening degree of the expansion valve 16 is controlled.

[0121] When the working medium for the refrigeration cycle is a mixed refrigerant containing hydrofluoroolefin and a high-solubility refrigerant as described above, a relatively large amount of the high-solubility refrigerant will dissolve in the refrigeration oil when the compressor 20 stops. Therefore, at the start of the operation of the compressor 20, the hydrofluoroolefin in the mixed refrigerant becomes relatively more, and the conditions of the internal pressure and the internal temperature (discharge gas temperature) (disproportionation conditions) under which the disproportionation reaction occurs are lower than those of the normal refrigerant composition.

[0122] Therefore, in the refrigeration cycle system according to the present disclosure, at the initial stage of the start of operation until a predetermined time t1 elapses from the start of the operation of the compressor 20, the upper limit values of the internal pressure and the discharge gas temperature at which the protection control starts are set to P0 and T0, which are lower than the predetermined values P1 and T1. The control unit 21 controls the compressor 20 and the expansion valve 16 based on this P0 / T0 at the initial stage of the start of operation. After the initial stage of the start of operation ends and the operation shifts to the normal operation, the control unit 21 changes the upper limit values of the internal pressure and the discharge gas temperature from P0 / T0 to the predetermined values P1 / T1 and controls the compressor 20 and the expansion valve 16.

[0123] As a result, the concentration of the hydrofluoroolefin becomes relatively high, and even at the initial stage of operation where the disproportionation reaction is likely to occur, the probability of occurrence of the disproportionation reaction can be favorably suppressed. Further, even after the transition from the initial stage of operation to the normal operation, the occurrence of the disproportionation reaction can be favorably suppressed or mitigated. As a result, the reliability of the refrigeration cycle system can be further improved.

[0124] Note that the present invention is not limited to the description of the above embodiments, and various modifications are possible within the scope shown in the claims. Embodiments obtained by appropriately combining technical means disclosed in different embodiments and a plurality of modification examples are also included in the technical scope of the present invention.

[0125] (Supplementary Note) From the description of each of the above embodiments, the following technology is disclosed in this specification. (Technology 1) A refrigeration cycle system including a compressor that stores refrigerating machine oil therein and an expansion valve, and a control unit. As a working medium for the refrigeration cycle, a mixed refrigerant containing at least one hydrofluoroolefin and at least one high-solubility refrigerant having a higher solubility in the refrigerating machine oil than the hydrofluoroolefin is used. When an upper limit value of the internal pressure preset in the compressor is P1 and an upper limit value of the discharge gas temperature is T1, the control unit sets the upper limit value of the internal pressure to P0 (P0 < P1) smaller than P1 and sets the upper limit value of the discharge gas temperature to T0 (T0 < T1) smaller than T1 from the start of the operation of the compressor until a predetermined time t1 elapses, and controls at least one of the rotational speed of the compressor and the opening degree of the expansion valve. After the predetermined time t1 elapses, 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, and at least one of the rotational speed of the compressor and the opening degree of the expansion valve is controlled.

[0126] (Technology 2) The refrigeration cycle system according to Technology 1, further comprising a pressure sensor that measures an internal pressure of the compressor, and the control unit controls at least one of a rotation speed of the compressor and an opening degree of the expansion valve using a pressure value measured by the pressure sensor.

[0127] (Technology 3) The refrigeration cycle system according to Technology 1, further comprising a first temperature sensor that approximately measures an internal pressure of the compressor from a temperature, and the control unit controls at least one of a rotation speed of the compressor and an opening degree of the expansion valve by using a pressure value indirectly measured by the first temperature sensor.

[0128] (Technology 4) A refrigeration cycle system according to any one of Technology 1 to Technology 3, 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 a rotation speed of the compressor and an opening degree of the expansion valve using the discharge gas temperature measured by the second temperature sensor.

[0129] (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.

[0130] (Technology 6) The refrigeration cycle system according to Technology 5, wherein the saturated hydrocarbon is propane (R290).

[0131] (Technical 7) The working fluid for a refrigeration cycle according to any one of Technical 1 to Technical 6, further comprising a disproportionation inhibitor. [Industrial Applicability]

[0132] The present invention can be widely and suitably used 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 in the field of refrigeration cycle systems, 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. [Explanation of symbols]

[0133] 10: Air conditioner (refrigeration cycle system) 11: Outdoor unit 12: Indoor unit 13: Inter-unit piping 13a: Pipe connection 13b: Pipe connection 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. The refrigeration cycle includes a compressor that stores refrigeration oil therein and an expansion valve, and a control unit. As a working fluid for a refrigeration cycle, a mixed refrigerant is used, which contains at least one hydrofluoroolefin and at least one high-solubility refrigerant having a higher solubility in the refrigerating machine oil than the hydrofluoroolefin, When the upper limit value of the internal pressure and the upper limit value of the discharge gas temperature, both of which are preset in the compressor, are P1 and T1, respectively, the control unit sets the upper limit value of the internal pressure to P0 (P0<P1) which is smaller than P1, and sets the upper limit value of the discharge gas temperature to T0 (T0<T1) which is smaller than T1, during a period from the start-up of the compressor until a predetermined time t1 has elapsed, to control at least one of the rotation speed of the compressor and the opening degree of the expansion valve; 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. Refrigeration cycle system.

2. A pressure sensor is provided to measure an internal pressure of the compressor. The control unit controls at least one of a rotation speed of the compressor and an opening degree of the expansion valve using the pressure value measured by the pressure sensor. The refrigeration cycle system according to claim 1 .

3. a first temperature sensor for approximately measuring an internal pressure of the compressor based on a temperature; The control unit controls at least one of a rotation speed of the compressor and an opening degree of the expansion valve by using the pressure value indirectly measured by the first temperature sensor. The refrigeration cycle system according to claim 1 .

4. a second temperature sensor for measuring a temperature of gas discharged from the compressor; The control unit controls at least one of a rotation speed of the compressor and an opening degree of the expansion valve by using the discharge gas temperature measured by the second temperature sensor. The refrigeration cycle system according to claim 1 .

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

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

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

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