Refrigerant circuit system

Abstract

To propose a refrigerant circuit system that can switch between refrigeration cycles according to required heating capacity.SOLUTION: A refrigerant circuit system comprises: a high order side circuit (40) comprising a high order side compressor (69), a high order side utilization heat exchanger (70), and a high order side expansion mechanism (71), and using a first refrigerant; a low order side circuit (30) comprising a low order side compressor (51), a low order side utilization heat exchanger (68), low order side expansion mechanisms (54 and 55), and a low order side heat source heat exchanger (52), and using a second refrigerant; and a cascade heat exchanger (67) for exchanging heat between the low order side circuit (30) and the high order side circuit (40). The first refrigerant is propane. The second refrigerant is carbon dioxide. The high order side circuit (40) is arranged indoors.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a refrigerant circuit system. [Background technology]

[0002] Patent Document 1 discloses a refrigeration cycle device that includes a high-side refrigerant circuit using propane, a low-side refrigerant circuit using carbon dioxide, and a heat medium circuit, and that is capable of achieving high capacity for both heating and cooling. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7146117 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, in order to further improve the cooling or heating capacity of the refrigeration cycle device of Patent Document 1, it is necessary to increase the amount of refrigerant charged. However, for example, a flammable natural refrigerant such as propane is limited in use due to its flammability. Therefore, in a refrigeration cycle using a flammable natural refrigerant, for example, the refrigerant cannot be charged to more than a certain amount, and the capacity is limited. The present disclosure proposes a refrigerant circuit system capable of switching between refrigeration cycles depending on the required heating capacity. [Means for solving the problem]

[0005] The refrigerant circuit system of the present disclosure is a two-stage refrigerant circuit system in which a high-stage side circuit (40) using a first refrigerant and a low-stage side circuit (30) using a second refrigerant are connected via a cascade heat exchanger (67). The high-stage side circuit (40) is provided with a high-stage side compressor (69), a high-stage side utilization heat exchanger (70), and a high-stage side expansion mechanism (71). The low-stage side circuit (30) is provided with a low-stage side compressor (50), The refrigeration cycle includes a first cycle in which a refrigerant flows from the low stage side compressor (51) to the cascade heat exchanger (67), and a second cycle in which the refrigerant, which has flowed from the low stage side compressor (51) to the low stage side utilization heat exchanger (68), flows to the cascade heat exchanger (67). In this case, the refrigeration cycle can be switched depending on the required heating capacity. Here, in the refrigerant circuit system of the present disclosure, the high-temperature side utilization heat exchanger (70) and the low-temperature side utilization heat exchanger (68) are water heat exchangers, and the refrigerant circuit system further includes a heat medium circuit (50) including heat medium piping (85, 86, 87, 89), a pump (84), and a tank (82). Here, in the refrigerant circuit system of the present disclosure, the low-temperature side circuit (30) further includes a bypass flow path (811), a first cock (65), and a second cock (66). Here, when it is determined that the required heating capacity is not reached during heating operation using the first cycle, the refrigeration circuit system of the present disclosure switches to the second cycle. In this case, the refrigeration cycle can be switched by comparing the current heating capacity with the required heating capacity. In the refrigerant circuit system of the present disclosure, the required heating capacity is determined based on three factors: a target hot water outlet temperature set by the user, the current inlet water temperature, and the water flow rate. Here, the refrigerant circuit system of the present disclosure can switch to the second cycle when the rotation speed of the high-temperature side compressor (69) is equal to or higher than an upper limit value or a certain threshold value, and a pump command value for controlling the heat medium flow rate is also equal to or lower than a certain threshold value, but the first heat medium temperature from the heat medium pipe (87) has not reached a target value. In addition, the refrigerant circuit system of the present disclosure switches to the second cycle when it is determined that the rotation speed of the high-temperature side compressor (69) is equal to or higher than an upper limit or a certain threshold, the heating capacity estimated from the inlet water temperature, the outlet hot water temperature, and the pump command value has not reached a target capacity, and the heating capacity has not increased for a certain period of time. In this case, it is possible to prevent switching to the refrigeration cycle before the heating capacity has reached its maximum. In addition, in the refrigerant circuit system of the present disclosure, the pump command value used to determine whether to switch from the first cycle to the second cycle is changed depending on the heat medium pipe length setting. In this case, even if the heat medium pipe length is different, water can be made to flow at the same flow rate. Furthermore, when an abnormality occurs in the high-temperature side circuit (40), the refrigerant circuit system of the present disclosure performs heating operation only using the low-temperature side circuit (30). In this case, even if the high-temperature side circuit is unavailable, a certain degree of heating capacity can be ensured only by the low-temperature side circuit. In addition, the refrigerant circuit system of the present disclosure issues an anomaly alert when an anomaly occurs in the high-temperature side circuit (40). In this case, the occurrence of the anomaly can be confirmed even when not in situ, and the user can also decide to perform heating operation using only the low-temperature side circuit. In the refrigerant circuit system of the present disclosure, the high temperature side circuit (40) is provided indoors. In this case, even if a flammable refrigerant is used in the high temperature side circuit, the regulation on the amount of flammable refrigerant to be charged can be satisfied, and the refrigerant circuit system can be installed indoors where only a certain level of ventilation is available. Furthermore, in the refrigerant circuit system of the present disclosure, natural refrigerants are used as the two types of refrigerants. Moreover, the refrigerant circuit system of the present disclosure uses propane in the high-temperature side circuit (40) and carbon dioxide in the low-temperature side circuit (30). In the refrigerant circuit system of the present disclosure, in the heat medium circuit (50), the heat medium supplied from the pump (84) flows through the low-temperature side heat exchanger (68) and then through the high-temperature side heat exchanger (70). In this case, the refrigeration cycle can be switched in accordance with the required heating capacity by switching the switching circuit (80) without switching the flow path on the heat medium circuit (50) side. The refrigerant circuit system of the present disclosure further includes a four-way selector valve (53), and switches between a heating operation and a cooling operation by switching the four-way selector valve (53). [Brief description of the drawings]

[0006] [Figure 1] 1 is a refrigerant circuit diagram showing a configuration example of a refrigerant circuit system according to an embodiment of the present invention. [Diagram 2] 1 is a heat medium circuit diagram showing a configuration example of a heat medium circuit according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a refrigerant circuit diagram showing the flow of refrigerant during heating operation in the first cycle according to the present embodiment. [Figure 4] 4A and 4B are pressure-specific enthalpy diagrams during heating operation in the first cycle, where (a) is the pressure-specific enthalpy diagram in the high-side circuit and (b) is the pressure-specific enthalpy diagram in the low-side circuit. [Diagram 5] FIG. 4 is a refrigerant circuit diagram showing the flow of refrigerant during heating operation in the second cycle according to the present embodiment. [Figure 6] 4A and 4B are pressure-specific enthalpy diagrams during heating operation in the second cycle, where (a) is a pressure-specific enthalpy diagram in the high-side circuit and (b) is a pressure-specific enthalpy diagram in the low-side circuit. [Figure 7A] FIG. 2 is a block diagram showing a configuration example of main devices according to the present embodiment. [Figure 7B] 10A and 10B are flowcharts for switching from the first cycle to the second cycle during heating operation, in which (a) shows an example in which an upper limit value for the rotation speed of the high-side compressor is used, and (b) shows an example in which a threshold value for the rotation speed of the high-side compressor is used. [Figure 7C] 5 is a flowchart showing switching from the second cycle to the first cycle during heating operation, in which (a) shows an example when a required heating capacity is used, and (b) shows an example when a target hot water outlet temperature is used. [Figure 7D] 4 is a flowchart at the time of starting up the refrigerant circuit system according to the present embodiment. [Figure 8A]FIG. 4 is a schematic refrigerant circuit diagram of a switching circuit in a refrigerant circuit system according to a first modified example. [Figure 8B] FIG. 11 is a schematic refrigerant circuit diagram of a switching circuit in a refrigerant circuit system according to a second modification. [Figure 8C] FIG. 11 is a schematic refrigerant circuit diagram of a switching circuit in a refrigerant circuit system according to a third modification. [Figure 9A] FIG. 11 is a schematic diagram of a heat medium circuit in a refrigerant circuit system according to a fourth modified example. [Figure 9B] FIG. 11 is a schematic diagram of a heat medium circuit in a refrigerant circuit system according to a fifth modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. <Refrigerant circuit system configuration> FIG. 1 is a refrigerant circuit diagram showing an example of the configuration of a refrigerant circuit system according to the present embodiment. The refrigerant circuit system 1 according to the present embodiment is, for example, a hot water supply system. The hot water supply system supplies hot water to an object. The object in the present embodiment includes a hot water supply object such as a faucet, a shower, and a bath, and a heating device using hot water. The refrigerant circuit system 1 according to the present embodiment is composed of, for example, an outdoor unit 10 installed outdoors and an indoor unit 20 installed indoors. The outdoor unit 10 includes a low-side circuit 30, a part of which is connected to the indoor unit 20. The indoor unit 20 includes a high-side circuit 40 and a heat medium circuit 50. The refrigerant circuit system 1 according to the present embodiment may include a control unit 100 (see FIG. 7A). A natural refrigerant, for example, is used as the first refrigerant filled in the high-temperature side circuit 40 and the second refrigerant filled in the low-temperature side circuit 30. The low-temperature side circuit 30 is filled with, for example, carbon dioxide, and the high-temperature side circuit 40 is filled with, for example, propane.

[0008] The low stage side circuit 30 includes a low stage side compressor 51, a low stage side heat source heat exchanger 52, a four-way switching valve 53, a first expansion valve 54, shutoff valves 61, 62, 63, 64, a first cock 65, a second cock 66, a cascade heat exchanger 67, and a low stage side utilization heat exchanger 68. The low stage side circuit 30 also includes a switching circuit 80 that causes the refrigerant to flow to the cascade heat exchanger 67 without flowing to the low stage side utilization heat exchanger 68. The low stage side circuit 30 may further include a second expansion valve 55, a receiver tank 56, and check valves 57, 58, 59, 60. The low-side circuit 30 is not limited to the above-mentioned configuration. For example, the low-side circuit 30 may be configured to include a filter, a heat sink, an oil separator, etc. Also, the low-side circuit 30 may be configured to include a high-pressure switch as a pressure sensor or a protective detector.

[0009] The low-stage side compressor 51 draws in refrigerant from the suction side and discharges the compressed refrigerant from the discharge side. The low-stage side compressor 51 may be provided with an accumulator on its suction side that separates the refrigerant into gas and liquid. The low-stage side compressor 51 has its discharge side connected to the first port (P1) of the four-way switching valve 53, and its suction side connected to the third port (P3) of the four-way switching valve 53. The low-side heat source heat exchanger 52 exchanges heat between the refrigerant and the outside air. The low-side heat source heat exchanger 52 functions as an evaporator during heating operation. The low-side heat source heat exchanger 52 may be configured to include an outdoor fan.

[0010] The four-way switching valve 53 has a first port (P1), a second port (P2), a third port (P3), and a fourth port (P4), and can switch between a state in which the first port (P1) and the second port (P2) communicate with each other and the third port (P3) and the fourth port (P4) communicate with each other and a state in which the first port (P1) and the fourth port (P4) communicate with each other and the second port (P2) and the third port (P3) communicate with each other. During heating operation, the four-way switching valve 53 is in a state in which the first port (P1) and the second port (P2) communicate with each other and the third port (P3) and the fourth port (P4) communicate with each other.

[0011] The first expansion valve 54 and the second expansion valve 55 are an example of a low-temperature side expansion mechanism. They are configured to be variable in opening degree and have a function of lowering the pressure of the refrigerant circulating in the low-temperature side circuit 30 and expanding the refrigerant. The receiver tank 56 is a tank that stores the liquid refrigerant that has been condensed and turned into a liquid in the cascade heat exchanger 67. The low-temperature side circuit 30 may have a configuration including a pipe that connects the receiver tank 56 and the low-temperature side compressor 51.

[0012] The check valves 57, 58, 59, and 60 are valves for preventing the refrigerant from flowing backward, and determine the direction in which the refrigerant flows. The flow of the refrigerant will be described in detail later. The shutoff valves 61, 62, 63, and 64 serve to connect the piping of the outdoor unit 10 and the piping of the indoor unit 20.

[0013] The cascade heat exchanger 67 exchanges heat between the low-temperature side circuit 30 and the high-temperature side circuit 40. The cascade heat exchanger 67 has a flow path connected to the low-temperature side circuit 30 and a flow path connected to the high-temperature side circuit 40. The cascade heat exchanger 67 is, for example, a double-pipe heat exchanger in which two pipes of different diameters are combined in an inner and outer double layer. The cascade heat exchanger 67 may also be another type of heat exchanger, such as a plate heat exchanger. During heating operation, the cascade heat exchanger 67 functions as a condenser in the low-temperature side circuit 30 and as an evaporator in the high-temperature side circuit 40.

[0014] The low-temperature side heat exchanger 68 exchanges heat between the low-temperature side circuit 30 and the heat medium circuit 50. The low-temperature side heat exchanger 68 has a flow path connected to the low-temperature side circuit 30 and a flow path connected to the heat medium circuit 50. During heating operation, the low-temperature side heat exchanger 68 works as a condenser. The heat medium flowing through the heat medium circuit 50 is warmed by removing heat from the second refrigerant flowing through the low-temperature side circuit 30, thereby fulfilling the heating function. The low-temperature side heat exchanger 68 is a water heat exchanger, but is not limited to this, and may be configured as an air heat exchanger, for example.

[0015] The low-temperature side circuit 30 has a bypass flow path 811. The bypass flow path 811 connects a flow path that connects the low-temperature side utilization heat exchanger 68 and the cascade heat exchanger 67 to a flow path that connects the low-temperature side utilization heat exchanger 68 and the low-temperature side compressor 51. The first cock 65 and the second cock 66 have a function of switching whether or not the second refrigerant is flowed to the low stage side heat exchanger 68 by opening and closing them. The first cock 65 is disposed on a flow path connecting the low stage side heat exchanger 68 and the low stage side compressor 51, and the second cock 66 is disposed on a bypass flow path 811. When the refrigerant is flowed to the low stage side heat exchanger 68, the first cock 65 is opened and the second cock 66 is closed. On the other hand, when the refrigerant is not flowed to the low stage side heat exchanger 68 but is flowed to the cascade heat exchanger 67 through the bypass flow path 811, the first cock 65 is closed and the second cock 66 is opened. The opening and closing of the first cock 65 and the second cock 66 is controlled by, for example, the control unit 100 (see FIG. 7A) according to a switching condition described later.

[0016] The high-temperature side circuit 40 includes a cascade heat exchanger 67 , a high-temperature side compressor 69 , a high-temperature side utilization heat exchanger 70 , and a high-temperature side expansion mechanism 71 . The high-temperature side circuit 40 is not limited to the above-mentioned configuration. For example, the high-temperature side circuit 40 may be configured to include a filter, a heat sink, an oil separator, etc. Also, the high-temperature side circuit 40 may be configured to include a high-pressure switch as a pressure sensor or a protective detector.

[0017] The high-stage compressor 69 draws in refrigerant from its suction side and discharges the compressed refrigerant from its discharge side. The high-stage compressor 69 may be provided with an accumulator on its suction side that separates the refrigerant into gas and liquid. The high-stage compressor 69 has its discharge side connected to the high-stage utilization heat exchanger 70 and its suction side connected to the cascade heat exchanger 67.

[0018] The high-temperature side heat exchanger 70 exchanges heat between the high-temperature side circuit 40 and the heat medium circuit 50. During heating operation, the high-temperature side heat exchanger 70 works as a condenser. The heat medium flowing through the heat medium circuit 50 is warmed by removing heat from the refrigerant flowing through the high-temperature side circuit 40, thereby fulfilling the heating function. The high-temperature side heat exchanger 70 is a water heat exchanger, but is not limited to this, and may be configured as, for example, an air heat exchanger. The high-temperature side expansion mechanism 71 has a function of lowering the pressure of the refrigerant circulating in the high-temperature side circuit 40 and expanding the refrigerant. The high-temperature side expansion mechanism 71 is, for example, a capillary tube. Since the flow path of the capillary tube is narrow, resistance is generated in the flow of the refrigerant, and the pressure drops. The high-temperature side circuit 40 may also be configured to have an expansion valve instead of a capillary tube.

[0019] FIG. 7A is a block diagram showing an example of the configuration of the main devices according to this embodiment. The control unit 100 is, for example, a controller 100. The controller 100 is a device that controls the operation of the hot water supply system. The controller 100 includes an MCU (Micro Control Unit), an electric circuit, and an electronic circuit. The MCU includes a CPU (Central Processing Unit) 101, a memory 102, and a communication interface (communication I / F) 103. The memory 102 stores various programs to be executed by the CPU 101. The controller 100 may be configured as one physically independent element, or may be configured as two or more physically separated elements. The controller 100 controls the low-stage side circuit 30 and the high-stage side circuit 40. Specifically, the controller 100 controls the low-stage side compressor 51, the high-stage side compressor 69, the four-way switching valve 53, the first expansion valve 54, and the second expansion valve 55.

[0020] The heat medium circuit 50 exchanges heat with the low-side circuit 30 and the high-side circuit 40 via a low-side utilization heat exchanger 68 and a high-side utilization heat exchanger 70, and provides functions using heat exchange. The heat medium circuit 50 is filled with, for example, water, seawater, lake water, or brine such as antifreeze as the heat medium. Alternatively, antifreeze such as tetra-n-butylammonium bromide hydrate (TBAB), silicone oil, or ethylene glycol may be filled as the heat medium. An example of the configuration of the heat medium circuit 50 will be described with reference to Fig. 2. Fig. 2 is a heat medium circuit diagram showing an example of the configuration of the heat medium circuit 50 according to this embodiment. The heat medium circuit 50 includes, in addition to the low-temperature side heat exchanger 68 and the high-temperature side heat exchanger 70, for example, a three-way cock 81, a tank 82, a heat exchanger 83, a pump 84, and heat medium pipes 85 to 89. The three-way cock 81 may be replaced with, for example, a T-pipe.

[0021] The heat medium flowing through the heat medium piping 85 of the heat medium circuit 50 is given a driving force by the pump 84 and circulates inside the heat medium piping 85. The heat medium flowing through the heat medium piping 85 passes through the low stage side utilization heat exchanger 68 and the high stage side utilization heat exchanger 70, during which it is warmed by heat exchange with the refrigerant flowing through the low stage side circuit 30 and the high stage side circuit 40. Here, the heat medium flows through the low stage side utilization heat exchanger 68 and then into the high stage side utilization heat exchanger 70. The hot water coming out of the high stage side utilization heat exchanger 70 is sent by the three-way cock 81 to the tank 82 or the heat medium piping 86 depending on its purpose.

[0022] When heating is used, the three-way cock 81 sends hot water to the heat medium piping 86. The heat medium piping 86 is connected to each room that uses heating, and performs the heating function in each room. The water that has been used for heating and cooled returns through the heat medium piping 89. The water that returns from the heat medium piping 89 enters the low-temperature side heat exchanger 68 and the high-temperature side heat exchanger 70, where it is warmed by heat exchange, and sent back to each room.

[0023] When hot water is used, the three-way cock 81 sends hot water to the tank 82. Water is stored in the tank 82, and heat exchanger 83 exchanges heat between the water flowing through the heat medium piping 85 and the water stored in the tank 82. The water stored in the tank 82 is heated by the heat exchanger 83 and sent to the heat medium piping 87, and used to supply hot water for showers, etc. Meanwhile, the water flowing through the heat medium piping 85 is cooled by the heat exchanger 83, enters the low-side utilization heat exchanger 68 and the high-side utilization heat exchanger 70, is heated by heat exchange, and is sent back to the tank 82. When the water stored in the tank 82 is used, city water or the like is replenished from the heat medium piping 88.

[0024] The refrigerant circuit system 1 according to the present embodiment can switch between the first cycle and the second cycle by using the switching circuit 80. The switching circuit 80 switches between the first cycle and the second cycle by using the first cock 65, the second cock 66, and the bypass passage 811. When the first cycle is used, the low stage side circuit 30 closes the first cock 65 and opens the second cock 66 to flow the second refrigerant to the cascade heat exchanger 67 without flowing the refrigerant to the low stage side utilization heat exchanger 68. When the second cycle is used, the first cock 65 is closed and the second cock 66 is opened to flow the second refrigerant to the low stage side utilization heat exchanger 68, and heat exchange is performed in the low stage side utilization heat exchanger 68. The first cycle, the second cycle and the switching conditions therebetween are described below.

[0025] <First Cycle> Next, the operation of the refrigerant circuit system 1 during heating operation in the first cycle according to this embodiment will be described with reference to Fig. 3 and Fig. 4. Fig. 3 is a refrigerant circuit diagram showing the flow of refrigerant during heating operation in the first cycle according to this embodiment. Fig. 4 is a pressure-specific enthalpy diagram during heating operation in the first cycle, where (a) is a pressure-specific enthalpy diagram in the high-temperature side circuit 40, and (b) is a pressure-specific enthalpy diagram in the low-temperature side circuit 30.

[0026] When the first cycle is used, the first cock 65 is closed and the second cock 66 is open. During heating operation, the four-way switching valve 53 of the low-temperature side circuit 30 is in a state where the first port (P1) and the second port (P2) are communicated with each other and the third port (P3) and the fourth port (P4) are communicated with each other.

[0027] When the first cycle is used, the second refrigerant circulates along the arrows shown in Fig. 3. More specifically, in the low-stage side circuit 30, the refrigerant is first compressed from a low-pressure state (see point 91 in Fig. 3 and Fig. 4(b)) by the low-stage side compressor 51. The compressed refrigerant passes through the four-way switching valve 53, the stop valve 63, the stop valve 64, and the second cock 66, and enters the cascade heat exchanger 67. When the first cycle is used, no refrigerant flows through the low-stage side utilization heat exchanger 68 and no heat exchange takes place, so the state of the refrigerant does not change between points 92 and 93 in Fig. 3 (see points 92, 93 in Fig. 4(b)). The cascade heat exchanger 67 functions as a condenser in the low-temperature side circuit 30, and the refrigerant is cooled by heat exchange with the high-temperature side circuit 40 (see point 94 in FIG. 3 and FIG. 4(b)).

[0028] The refrigerant leaving the cascade heat exchanger 67 passes through the shutoff valve 62, the shutoff valve 61, the check valve 60, and the second expansion valve 55, and enters the receiver tank 56. The refrigerant leaving the receiver tank 56 passes through the first expansion valve 54 and the check valve 57, and enters the low-side heat source heat exchanger 52. The refrigerant is decompressed when passing through the second expansion valve 55 and the first expansion valve 54 (see point 95 in Figures 3 and 4(b)). The low-side heat source heat exchanger 52 functions as an evaporator, and the refrigerant is heated by heat exchange with the outside air (see point 91 in FIG. 3 and FIG. 4(b)). The refrigerant leaving the low-side heat source heat exchanger 52 passes through the four-way switching valve 53 and enters the low-side compressor 51 again. In this manner, the refrigerant is circulated in the low-side circuit 30.

[0029] In the high-temperature side circuit 40, the first refrigerant circulates along the arrows shown in Fig. 3. The refrigerant is first compressed from a low-pressure state (see point 96 in Fig. 3 and Fig. 4(a)) by the high-temperature side compressor 69 (see point 97 in Fig. 3 and Fig. 4(a)). The compressed refrigerant enters the high-temperature side utilization heat exchanger 70. The high-temperature side utilization heat exchanger 70 functions as a condenser, and the refrigerant flowing through the high-temperature side circuit 40 loses heat to the heat medium flowing through the heat medium circuit 50, and is cooled (see point 98 in Fig. 3 and Fig. 4(a)).

[0030] Next, the refrigerant passes through the high-side expansion mechanism 71 and is depressurized in the process (see point 99 in Figures 3 and 4(a)). The depressurized refrigerant enters the cascade heat exchanger 67. The cascade heat exchanger 67 functions as an evaporator in the high-side circuit 40, and the refrigerant is heated by heat exchange with the low-side circuit 30 (see point 96 in Figures 3 and 4(a)). The refrigerant leaving the cascade heat exchanger 67 enters the high-side compressor 69 again. In this manner, the refrigerant is circulated in the high-side circuit 40.

[0031] When the first cycle is used, the heat medium flowing through the heat medium circuit 50 is warmed by heat exchange with the refrigerant flowing through the high-temperature side circuit 40 via the high-temperature side heat exchanger 70. On the other hand, when the first cycle is used, no heat exchange is performed in the low-temperature side heat exchanger 68.

[0032] <Second Cycle> Next, the operation of the refrigerant circuit system 1 during heating operation in the second cycle according to this embodiment will be described with reference to Fig. 5 and Fig. 6. Fig. 5 is a refrigerant circuit diagram showing the flow of refrigerant during heating operation in the second cycle according to this embodiment. Fig. 6 is a pressure-specific enthalpy diagram during heating operation in the second cycle, where (a) is a pressure-specific enthalpy diagram in the high-side circuit 40, and (b) is a pressure-specific enthalpy diagram in the low-side circuit 30. When the second cycle is used, the first cock 65 is open and the second cock 66 is closed. During heating operation, the four-way switching valve 53 is in a state where the first port (P1) and the second port (P2) communicate with each other and the third port (P3) and the fourth port (P4) communicate with each other.

[0033] When the second cycle is used, the refrigerant circulates along the arrows shown in FIG. 5. More specifically, in the low-stage side circuit 30, the refrigerant is first compressed from a low-pressure state (see point 91 in FIG. 5 and FIG. 6(b)) by the low-stage side compressor 51 (see point 92 in FIG. 5 and FIG. 6(b)). The compressed refrigerant passes through the four-way switching valve 53, the stop valve 63, the stop valve 64, and the first cock 65, and enters the low-stage side utilization heat exchanger 68. The low-stage side utilization heat exchanger 68 functions as a condenser, and the refrigerant flowing through the low-stage side circuit 30 loses heat to the heat medium flowing through the heat medium circuit 50, and is cooled (see point 93 in FIG. 5 and FIG. 6(b)). The refrigerant leaving the low-stage side utilization heat exchanger 68 enters the cascade heat exchanger 67. The cascade heat exchanger 67 functions as a condenser in the low-temperature side circuit 30, and the refrigerant is cooled by heat exchange with the high-temperature side circuit 40 (see point 94 in FIG. 5 and FIG. 6(b)).

[0034] The refrigerant leaving the cascade heat exchanger 67 passes through the shutoff valve 62, the shutoff valve 61, the check valve 60, and the second expansion valve 55, and enters the receiver tank 56. The refrigerant leaving the receiver tank 56 passes through the first expansion valve 54 and the check valve 57, and enters the low-side heat source heat exchanger 52. The refrigerant is decompressed when passing through the second expansion valve 55 and the first expansion valve 54 (see point 95 in Figures 5 and 6(b)). The low-side heat source heat exchanger 52 functions as an evaporator, and the refrigerant is heated by heat exchange with the outside air (see point 91 in Fig. 5 and Fig. 6(b)). The refrigerant leaving the low-side heat source heat exchanger 52 passes through the four-way switching valve 53 and enters the low-side compressor 51 again. In this manner, the refrigerant is circulated in the low-side circuit 30.

[0035] In addition, in the high-temperature side circuit 40 when the second cycle is used, the flow of refrigerant and the pressure-specific enthalpy diagram during heating operation are the same as those when the first cycle is used. When the second cycle is in use, the heat medium flowing through the heat medium circuit 50 is warmed by exchanging heat with the refrigerant flowing through the low-side circuit 30 and the high-side circuit 40 via the low-side utilization heat exchanger 68 and the high-side utilization heat exchanger 70, respectively.

[0036] <Switching conditions> For example, when a flammable refrigerant such as propane is used in the high-temperature side circuit 40, the amount of the refrigerant charged is limited. Therefore, in the first cycle, the heating capacity is limited only by heat exchange via the high-temperature side heat exchanger 70. On the other hand, in the second cycle, both the low-temperature side heat exchanger 68 and the high-temperature side heat exchanger 70 are used for heat exchange, and the heat medium flowing through the heat medium circuit 50 is warmed. When the second cycle is used, heat exchange is also performed in the low-temperature side heat exchanger 68, so that it is possible to provide a higher heating capacity than when the first cycle is used.

[0037] In the second cycle, the refrigerant flowing through the low-temperature side circuit 30 is cooled in the low-temperature side utilization heat exchanger 68, and is further cooled in the cascade heat exchanger 67. This makes it possible to obtain a higher specific enthalpy than when the first cycle is used, thereby improving the refrigeration effect. On the other hand, in the second cycle, it is necessary to increase the pressure to ensure the outlet hot water temperature (first heat transfer medium temperature), and therefore the compressor speed must be increased. In contrast, in the first cycle, it is not necessary to set the pressure as high as when using the second cycle, and efficient operation is possible.

[0038] For these reasons, it is desirable to perform highly efficient operation using the first cycle when the required heating capacity is small, and to switch to the second cycle to ensure sufficient heating capacity when the required heating capacity is large. The switching between the first cycle and the second cycle in the refrigerant circuit system 1 according to the present embodiment will be described below.

[0039] <<Switching from 1st cycle to 2nd cycle during heating operation>> In the refrigerant circuit system 1 according to this embodiment, switching from heating operation using the first cycle to heating operation using the second cycle is performed, for example, when the control unit 100 determines that the required heating capacity will not be reached. When switching from the first cycle to the second cycle, the first tap 65 is opened and the second tap 66 is closed. The required heating capacity is determined by the control unit 100 based on three factors: the outlet water temperature (target outlet water temperature) set by the user, the current inlet water temperature, and the water flow rate.

[0040] The case where it is determined that the required heating capacity is not reached is, for example, when the rotation speed of the high-temperature side compressor 69 is equal to or exceeds the upper limit or a certain threshold value, and the pump command value that controls the water flow rate is also equal to or below a certain threshold value, but the outlet hot water temperature does not reach the target value. The outlet hot water temperature is the temperature of the water supplied from the tank 82 to the heat medium pipe 87. An example of the flow of switching from the first cycle to the second cycle during heating operation will be described with reference to Fig. 7B. Fig. 7B is a flowchart of switching from the first cycle to the second cycle during heating operation, in which (a) shows an example in which the upper limit value of the rotation speed of the high-side compressor 69 is used, and (b) shows an example in which the threshold value of the rotation speed of the high-side compressor 69 is used.

[0041] FIG. 7B(a) will be described. In Fig. 7B(a), first, an operation using the first cycle is performed (step 1001). The control unit 100 judges whether the rotation speed of the high-side compressor 69 is equal to or higher than the upper limit (step 1002). If the rotation speed is equal to or lower than the upper limit (NO in step 1002), the process returns to step 1001 and an operation using the first cycle is performed. If the rotation speed is equal to or greater than the upper limit (YES in step 1002), the control unit 100 determines whether or not the pump command value that controls the water flow rate is equal to or less than the threshold value (step 1003). If the pump command value is equal to or greater than the threshold value (NO in step 1003), the process returns to step 1001 and operation using the first cycle is performed.

[0042] If the pump command value is equal to or less than the threshold value (YES in step 1003), the control unit 100 determines whether the outlet hot water temperature has reached the target value (step 1004). If the outlet hot water temperature has not reached the target value (NO in step 1004), the process returns to step 1001 and operation using the first cycle is performed. If the outlet heated water temperature has reached the target value (YES in step 1004), the control unit 100 switches to operation using the second cycle (step 1005).

[0043] Next, FIG. 7B(b) will be described. In Fig. 7B(b), first, an operation using the first cycle is performed (step 1011). The control unit 100 judges whether the rotation speed of the high-temperature side compressor 69 is equal to or higher than a threshold value (step 1012). If the rotation speed is equal to or lower than the threshold value (NO in step 1012), the process returns to step 1011 and an operation using the first cycle is performed. If the rotation speed is equal to or greater than the threshold (YES in step 1012), the control unit 100 determines whether or not the pump command value that controls the water flow rate is equal to or less than the threshold (step 1013). If the pump command value is equal to or greater than the threshold (NO in step 1013), the process returns to step 1011 and operation using the first cycle is performed.

[0044] If the pump command value is equal to or less than the threshold value (YES in step 1013), the control unit 100 determines whether the outlet hot water temperature has reached the target value (step 1014). If the outlet hot water temperature has not reached the target value (NO in step 1014), the process returns to step 1011 and operation using the first cycle is performed. If the outlet heated water temperature has reached the target value (YES in step 1014), the control unit 100 switches to operation using the second cycle (step 1015).

[0045] The rotation speed of the high-side compressor 69 being the upper limit means that the compressor rotates at a speed equal to or higher than the upper limit rotation speed of the compressor that can be continuously operated and is set for each compressor. The rotation speed of the high-side compressor 69 is equal to or higher than a certain threshold value, for example, when the high-side compressor 69 rotates at a speed equal to or higher than 75% of its rotation capacity. The pump command value that controls the water flow rate is equal to or lower than a certain threshold value, for example, when the output value is equal to or lower than 50%. The outlet temperature does not reach the target value, for example, when the target value is 55°C and the outlet temperature only reaches 50°C. In such a case, it is determined that the heating capacity required to set the outlet temperature to the target value cannot be reached by using the first cycle, and the first cycle is switched to the second cycle.

[0046] The above-mentioned thresholds of the rotation speed of the high-temperature side compressor 69 and the pump command value are merely examples, and are not limited to these. For example, each threshold that is a reference for switching the refrigeration cycle may be configured to be changeable. By switching between the first cycle and the second cycle according to the above-mentioned switching conditions, the refrigeration cycle can be switched based on the rotation speed of the high-temperature side compressor 69, the pump command value, and the outlet hot water temperature.

[0047] Furthermore, when it is determined that the required heating capacity will not be reached, it refers to, for example, when the rotation speed of high-temperature side compressor 69 is equal to or higher than the upper limit or a certain threshold value, and the heating capacity estimated from the inlet water temperature, the outlet hot water temperature, and the pump command value has not reached the target capacity, and it is determined that the heating capacity has not improved for a certain period of time. When using the first cycle, if the heating capacity has not reached the target capacity and has not improved for a certain period of time despite the high-temperature side compressor 69 operating at a rotation speed equal to or higher than the upper limit or a certain threshold value, it is determined that the required heating capacity will not be reached in the first cycle. For example, if the high-temperature side compressor 69 is rotating at 100% of its rotational capacity and the heating capacity estimated from the inlet water temperature, outlet water temperature, and pump command value does not reach the target capacity for five minutes, a switch from the first cycle to the second cycle is performed.

[0048] The rotation speed and duration of the high-temperature side compressor 69 described above are merely examples, and are not limited to these. By switching between the first cycle and the second cycle according to the above switching conditions, it is possible to switch to the refrigeration cycle when it is determined that the required heating capacity cannot be reached in the first cycle. Also, by switching when it is determined that the heating capacity has not improved for a certain period of time, it is possible to prevent switching to the refrigeration cycle before the heating capacity has reached its full potential.

[0049] Furthermore, control unit 100 may switch from heating operation using the first cycle to heating operation using the second cycle, for example, when the current rotation speed of high-temperature side compressor 69 is at the upper limit and the current heating capacity does not reach the required heating capacity, or the current outlet hot water temperature does not reach the target outlet hot water temperature. The current heating capacity is determined by control unit 100 based on the current outlet hot water temperature, the current inlet water temperature, and the water flow rate. The switching may be controlled based on the temperature of another portion, for example, based on the temperature of the heat medium supplied from the heat medium pipe 86. The temperature is measured, for example, by a thermometer (not shown).

[0050] The pump command value used to determine whether to switch from the first cycle to the second cycle may be changed by setting the heat medium pipe length. The heat medium pipe length is the length of the heat medium pipes 86, 87 (see FIG. 2) that send the heat medium flowing through the heat medium circuit 50 to each room that uses heating or hot water. Even if the pump command value is the same, the water flow rate cannot be made uniform if the heat medium pipe lengths are different. Even if the pump 84 (see FIG. 2) is used with the same pump command value, the amount of water that can flow varies depending on the heat medium pipe length.

[0051] When estimating the heating capacity from the pump command value, if the amount of water that can flow varies depending on the heat medium pipe length, the heating capacity cannot be accurately estimated. Therefore, in order to reduce errors in estimating the heating capacity, for example, the control unit 100 accepts input of the heat medium pipe length and changes the pump command value according to the heat medium pipe length setting. For example, if the pump command value is 40% when the heat medium piping length is 15 m, the pump command value can be set to 70% when the heat medium piping length is 30 m, thereby correcting the difference in water volume due to differences in heat medium piping length. With this configuration, water can flow at the same flow rate even when the heat transfer medium piping lengths are different.

[0052] <<Switching from 2nd cycle to 1st cycle during heating operation>> In refrigerant circuit system 1 according to this embodiment, for example, the control unit can switch from heating operation using the second cycle to heating operation using the first cycle when the current heating capacity reaches the required heating capacity, or the current hot water outlet temperature reaches the target hot water outlet temperature, and the current rotation speed of high-temperature side compressor 69 has a margin above the upper limit of the rotation speed of high-temperature side compressor 69. When switching from the second cycle to the first cycle, first cock 65 is closed and second cock 66 is opened. When the rotation speed of the high-side compressor 69 has a margin relative to the upper limit, it means, for example, that the current rotation speed of the high-side compressor 69 is less than 90% of the upper limit rotation speed of the high-side compressor.

[0053] An example of the flow of switching from the second cycle to the first cycle during heating operation will be described with reference to Fig. 7C. Fig. 7C is a flow chart of switching from the second cycle to the first cycle during heating operation, where (a) shows an example when the required heating capacity is used, and (b) shows an example when the target hot water outlet temperature is used.

[0054] FIG. 7C(a) will be described. In Fig. 7C(a), first, an operation using the second cycle is performed (step 2001). The control unit 100 judges whether or not the current heating capacity has reached the required heating capacity (step 2002). If the current heating capacity has not reached the required heating capacity (NO in step 2002), the process returns to step 2001 and an operation using the second cycle is performed.

[0055] If the current heating capacity has reached the required heating capacity (YES in step 2002), the control unit 100 determines whether the current rotation speed of the high-side compressor 69 has a margin with respect to the upper limit of the rotation speed of the high-side compressor 69 (step 2003). If there is no margin with respect to the upper limit (NO in step 2003), the process returns to step 2001 and operation using the second cycle is performed. If there is a margin for the upper limit value (YES in step 2003), the control unit 100 switches to operation using the first cycle (step 2004).

[0056] Next, FIG. 7C(b) will be described. In Fig. 7C(b), first, operation using the second cycle is performed (step 2011). Control unit 100 determines whether the current outlet hot water temperature has reached the target outlet hot water temperature (step 2012). If the current outlet hot water temperature has not reached the target outlet hot water temperature (NO in step 2012), the process returns to step 2011 and operation using the second cycle is performed.

[0057] If the current hot water outlet temperature has reached the target hot water outlet temperature (YES in step 2012), the control unit 100 determines whether the current rotation speed of the high-temperature side compressor 69 has a margin relative to the upper limit of the rotation speed of the high-temperature side compressor 69 (step 2013). If there is no margin relative to the upper limit (NO in step 2013), the process returns to step 2011 and operation using the second cycle is performed. If there is a margin for the upper limit value (YES in step 2013), the control unit 100 switches to operation using the first cycle (step 2014).

[0058] <<Refrigerant circuit system 1 startup>> FIG. 7D is a flowchart at the start-up of the refrigerant circuit system according to the present embodiment. When starting up the refrigerant circuit system 1 according to this embodiment, the control unit determines whether to perform heating operation using the first cycle or heating operation using the second cycle based on the switching determination capability. The switching determination capability is an index for determining whether to use the first cycle or the second cycle during heating operation, and is determined by the control unit 100 based on the target hot water outlet temperature and the outside air temperature. 7D, when the switching determination capacity exceeds the required heating capacity (YES in step 3001), the control unit 100 starts operation of the refrigerant circuit system 1 in the first cycle (step 3002). On the other hand, when the switching determination capacity is lower than the required heating capacity (NO in step 3001), the control unit 100 starts operation of the refrigerant circuit system 1 in the second cycle (step 3003).

[0059] <<Control steps of refrigerant circuit system 1>> The control flow of the refrigerant circuit system 1 according to the present embodiment includes, for example, a first step in which the user sets the hot water outlet temperature, a second step in which the control unit 100 calculates the required heating capacity and the switching judgment capacity, and a third step in which it is judged whether to perform a heating operation using the first cycle or a heating operation using the second cycle based on the calculated switching judgment capacity. If the heating operation using the first cycle is performed in the third step, a fourth step is performed to switch to a heating operation using the second cycle if (1) the current rotation speed of the high-temperature side compressor 69 is at the upper limit value and (2) the current heating capacity does not reach the required heating capacity or (3) the current hot water outlet temperature does not reach the target hot water outlet temperature. If the heating operation using the second cycle is performed in the third step, a fifth step is performed to switch to a heating operation using the first cycle if (1) the current rotation speed of the high-temperature side compressor 69 has a margin for the upper limit value of the rotation speed of the high-temperature side compressor 69 and (2) the current heating capacity reaches the required heating capacity or (3) the current hot water outlet temperature reaches the target hot water outlet temperature. For example, when a heating operation using the first cycle is currently being performed, the control unit 100 may periodically determine whether any of the conditions (1) to (3) apply: (1) whether the current rotation speed of the high-temperature side compressor 69 is at the upper limit, (2) whether the current heating capacity has not reached the required heating capacity, or (3) whether the current hot water outlet temperature has not reached the target hot water outlet temperature. Also, for example, when a heating operation using the second cycle is currently being performed, the control unit 100 may periodically determine whether any of the conditions (1) to (3) apply: (1) whether the current rotation speed of the high-temperature side compressor 69 has a margin relative to the upper limit of the rotation speed of the high-temperature side compressor 69, (2) whether the current heating capacity has reached the required heating capacity, or (3) whether the current hot water outlet temperature has reached the target hot water outlet temperature.

[0060] Also, when an abnormality occurs in the high-stage side circuit 40, the heating operation may be performed only with the low-stage side circuit 30. An abnormality is an event that makes it impossible to operate using the high-stage side circuit 40, such as a failure of the high-stage side compressor 69. Also, even in the case of a minor failure that does not prevent operation, the heating operation may be performed only with the low-stage side circuit 30. With this configuration, even if the high temperature side circuit 40 cannot be used, a certain degree of heating capacity can be ensured using only the low temperature side circuit 30.

[0061] Also, a configuration may be adopted in which an abnormality report is issued when an abnormality occurs in the high-temperature side circuit 40. The user who receives the abnormality report can understand the situation in which the high-temperature side circuit 40 cannot be used, and can quickly take action. With this configuration, the occurrence of an abnormality can be confirmed even when not in the field, and the user can also make the decision to perform heating operation using only the low-temperature side circuit.

[0062] In this embodiment, the high temperature side circuit 40 is installed indoors. When propane is used as the refrigerant filled in the high temperature side circuit 40 and the circuit is installed indoors, there is no restriction on the floor area of ​​the room in which the equipment is installed if the amount of refrigerant is 152 g or less according to IEC60335-2-40 Ed.7, but if the amount of refrigerant exceeds 152 g, the floor area of ​​the room in which the equipment is installed is restricted and safety measures must be taken in case of leakage. In the present invention, the heat exchanger volume can be reduced by suppressing the maximum heating capacity in the first cycle, and the amount of refrigerant can be reduced, and when the heating capacity is insufficient, the system switches to the second cycle and ensures heating capacity on the low-temperature side circuit 30 side, thereby expanding the maximum heating capacity. By suppressing the amount of refrigerant in this way, it becomes possible to install the high-temperature side circuit 40 filled with propane indoors where only a certain amount of ventilation is possible.

[0063] <Effects> The refrigerant circuit system of the present disclosure is a two-stage refrigerant circuit system in which a high-stage side circuit (40) using a first refrigerant and a low-stage side circuit (30) using a second refrigerant are connected via a cascade heat exchanger (67), the high-stage side circuit 40 includes a high-stage side compressor 69, a high-stage side utilization heat exchanger 70, and a high-stage side expansion mechanism 71, the low-stage side circuit 30 includes a low-stage side compressor 51, a low-stage side utilization heat exchanger 68, a first expansion valve 54, a second expansion valve 55, and a low-stage side heat source heat exchanger 52, and has a switching circuit 80 between a first cycle in which refrigerant flows from the low-stage side compressor 51 to the cascade heat exchanger 67, and a second cycle in which refrigerant flowed from the low-stage side compressor 51 to the low-stage side utilization heat exchanger 68 flows to the cascade heat exchanger 67. In this case, the refrigeration cycle can be switched depending on the required heating capacity. Here, in the refrigerant circuit system of the present disclosure, the high temperature side utilization heat exchanger 70 and the low temperature side utilization heat exchanger 68 are water heat exchangers, and the refrigerant circuit system further includes a heat medium circuit 50 including heat medium pipes 85, 86, 87, 89, a pump 84, and a tank 82. Here, in the refrigerant circuit system of the present disclosure, the low-temperature side circuit (30) further includes a bypass flow path (811), a first cock (65), and a second cock (66). Here, the refrigerant circuit system 1 of the present disclosure switches to the second cycle when it is determined that the required heating capacity will not be reached during heating operation using the first cycle. In this case, the refrigeration cycle can be switched by comparing the current heating capacity with the required heating capacity. In the refrigerant circuit system of the present disclosure, the required heating capacity is determined based on three factors: the outlet water temperature (target outlet water temperature) set by the user, the current inlet water temperature, and the water flow rate. Here, the refrigerant circuit system 1 of the present disclosure switches to the second cycle when the rotation speed of the high-side compressor 69 is equal to or higher than an upper limit or a certain threshold value, and the pump command value for controlling the heat medium flow rate is equal to or lower than a certain threshold value, but the first heat medium temperature from the heat medium pipe 87 has not reached a target value. In this case, the refrigeration cycle can be switched based on the rotation speed of the high-side compressor 69, the pump command value, and the outlet hot water temperature. Furthermore, the refrigerant circuit system 1 of the present disclosure switches to the second cycle when it is determined that the rotation speed of the high-temperature side compressor 69 is equal to or higher than an upper limit or a certain threshold, the heating capacity estimated from the inlet water temperature, the outlet hot water temperature, and the pump command value has not reached a target capacity, and the heating capacity has not increased for a certain period of time. In this case, it is possible to prevent switching to the refrigeration cycle before the heating capacity has reached its maximum. In addition, in the refrigerant circuit system 1 of the present disclosure, the pump command value used to determine whether to switch from the first cycle to the second cycle is changed depending on the heat medium pipe length setting. In this case, even if the heat medium pipe length is different, water can be made to flow at the same flow rate. Furthermore, in the refrigerant circuit system 1 of the present disclosure, when an abnormality occurs in the high-temperature side circuit 40, the heating operation is performed only by the low-temperature side circuit 30. In this case, even if the high-temperature side circuit 40 cannot be used, a certain degree of heating capacity can be ensured only by the low-temperature side circuit 30. Furthermore, the refrigerant circuit system 1 of the present disclosure issues an abnormality report when an abnormality occurs in the high-temperature side circuit 40. In this case, the occurrence of the abnormality can be confirmed even when not in the field, and the user can also make a decision to perform heating operation using only the low-temperature side circuit 30. In the refrigerant circuit system 1 of the present disclosure, the high-temperature side circuit 40 is provided indoors. In this case, even if a flammable refrigerant is used in the high-temperature side circuit, the regulation on the amount of flammable refrigerant to be charged can be satisfied, and the refrigerant circuit system can be installed indoors where only a certain level of ventilation is possible. Moreover, the refrigerant circuit system 1 of the present disclosure uses natural refrigerants for both of the above-mentioned two types of refrigerants. Moreover, the refrigerant circuit system 1 of the present disclosure uses propane in the high-temperature side circuit 40 and carbon dioxide in the low-temperature side circuit 30. In the refrigerant circuit system 1 of the present disclosure, in the heat medium circuit 50, the heat medium supplied from the pump 84 flows in the order of the low-temperature side utilization heat exchanger 68 and the high-temperature side utilization heat exchanger 70. In this case, the refrigeration cycle can be switched according to the required heating capacity by switching the switching circuit 80 without switching the flow path on the heat medium circuit 50 side. The refrigerant circuit system of the present disclosure further includes a four-way selector valve (53), and switches between a heating operation and a cooling operation by switching the four-way selector valve (53).

[0064] <Modification> Modifications of the refrigerant circuit system 1 of the present disclosure will now be described. The following modifications can be combined as appropriate.

[0065] <Variation 1> In the refrigerant circuit system 1 of the present disclosure described above, in the bypass flow path 811 of the low-side circuit 30, the first cock 65 is arranged on the flow path connecting the low-side utilization heat exchanger 68 and the low-side compressor 51, but this is not limited to this embodiment. Fig. 8A is a schematic refrigerant circuit diagram of a switching circuit in a refrigerant circuit system according to Modification 1. As shown in Fig. 8A, a first cock 65 is disposed on a flow path connecting a low-temperature side utilization heat exchanger 68 and a cascade heat exchanger 67 (see Fig. 1).

[0066] <Variation 2> FIG. 8B is a schematic refrigerant circuit diagram of a switching circuit in a refrigerant circuit system according to Modification 2. As shown in FIG. In the refrigerant circuit system 1 of the present disclosure, in the bypass flow passage 811 of the low stage side circuit 30, the first cock 65 and the second cock 66 are used to switch whether or not the second refrigerant is caused to flow to the low stage side utilization heat exchanger 68. In contrast, as shown in Fig. 8B, in the refrigerant circuit system 1 of the second modification, a three-way valve 812 is disposed at a location where one end of the bypass flow passage 811 is connected to a flow passage that connects the low stage side utilization heat exchanger 68 and the low stage side compressor 51 (see Fig. 1).

[0067] <Variation 3> FIG. 8C is a schematic refrigerant circuit diagram of a switching circuit in a refrigerant circuit system according to Modification 3. As shown in FIG. As shown in FIG. 8C, in the refrigerant circuit system 1 of the third modified example, a three-way valve 813 is disposed at a point where one end of the bypass flow path 811 is connected to a flow path connecting the low-temperature side utilization heat exchanger 68 and the cascade heat exchanger 67 (see FIG. 1).

[0068] <Modification 4> FIG. 9A is a schematic diagram of a heat medium circuit in a refrigerant circuit system according to a fourth modification. In the heat medium circuit 50 of the refrigerant circuit system 1 of the present disclosure, the heat medium passes through the low stage side heat exchanger 68 and then flows into the high stage side heat exchanger 70, but is not limited to such an embodiment. As shown in Fig. 9A, in the heat medium circuit 50 of the fourth modification, the heat medium passes through the high stage side heat exchanger 70 and then flows into the low stage side heat exchanger 68.

[0069] <Variation 5> FIG. 9B is a schematic diagram of a heat medium circuit in a refrigerant circuit system according to the fifth modification. As shown in FIG. 9B, in the heat medium circuit 50 according to the fifth modification, the heat medium circulates independently through the low-temperature side heat utilization heat exchanger 68 and the high-temperature side heat utilization heat exchanger 70.

[0070] Although the embodiments have been described above, the technical scope of the present disclosure is not limited to the scope of the above-described embodiments. It is clear from the claims that the technical scope of the present disclosure also includes combinations of two or more of the above-described embodiments, and modifications or improvements to the above-described embodiments. [Explanation of symbols]

[0071] Reference Signs List 1... refrigerant circuit system, 10... outdoor unit, 20... indoor unit, 30... low-stage side circuit, 40... high-stage side circuit, 50... heat medium circuit, 51... low-stage side compressor, 52... low-stage side heat source heat exchanger, 53... four-way switching valve, 54... first expansion valve, 55... second expansion valve, 67... cascade heat exchanger, 68... low-stage side utilization heat exchanger, 69... high-stage side compressor, 70... high-stage side utilization heat exchanger, 71... high-stage side expansion mechanism, 80... switching circuit

Claims

1. a high-stage side circuit (40) including a high-stage side compressor (69), a high-stage side utilization heat exchanger (70), and a high-stage side expansion mechanism (71), and using a first refrigerant; a low-side circuit (30) including a low-side compressor (51), a low-side utilization heat exchanger (68), a low-side expansion mechanism (54, 55), and a low-side heat source heat exchanger (52), and using a second refrigerant; a cascade heat exchanger (67) for exchanging heat between the low-side circuit (30) and the high-side circuit (40); the first refrigerant is propane; The second refrigerant is carbon dioxide. The high temperature side circuit (40) is arranged indoors.

2. 2. The refrigerant circuit system according to claim 1, wherein a charging amount of the first refrigerant is 152 g or less.

3. The refrigerant circuit system according to claim 1 or 2, wherein the low-temperature side circuit (30) further comprises a bypass flow path (811).

4. 4. The refrigerant circuit system according to claim 3, wherein the bypass passage (811) causes the first refrigerant to flow through the cascade heat exchanger (67) without flowing through the low-temperature side heat utilization heat exchanger (68).

5. 3. The refrigerant circuit system according to claim 1, further comprising a mode in which operation is performed using only the low-temperature side circuit (30).

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