Secondary freezing device

Abstract

Provided is a two-stage refrigeration device capable of suppressing a decrease in heating capacity due to deterioration of start-up operation due to rapid start-up operation. The present invention is provided with: a high-stage-side refrigerant circuit (2) that circulates a high-stage-side refrigerant; a low-stage-side refrigerant circuit (3) that has a first circulation path (23) that exchanges heat with the high-stage-side refrigerant in the stepped heat exchanger (13), and a second circulation path (26) that exchanges heat with the heat medium in the low-stage-side heat exchanger (24), and that circulates the low-stage-side refrigerant; and a heat medium circuit (4) that circulates a heat medium that exchanges heat with a high-stage-side refrigerant in the high-stage-side heat exchanger (11) and exchanges heat with a low-stage-side refrigerant in the low-stage-side heat exchanger (24), the heat medium circuit (4) having: a first heat medium circulation path (35) that circulates the heat medium through the high-stage-side heat exchanger (11) and the low-stage-side heat exchanger (24); and a second heat medium circulation path (36) that circulates the heat medium through the high-stage-side heat exchanger (11).

Description

Technical Field

[0001] The present invention relates to a two-stage refrigeration device, and in particular to a two-stage refrigeration device capable of suppressing a decrease in heating capacity. Background Art

[0002] The current two-stage refrigeration device has a high-stage refrigerant circuit and a low-stage refrigerant circuit, and the high-stage refrigerant circuit and the low-stage refrigerant circuit have a common stepped heat exchanger (intermediate heat exchanger). Moreover, the refrigerant circulating in the high-stage refrigerant circuit and the refrigerant circulating in the low-stage refrigerant circuit are heat-exchanged in the stepped heat exchanger, and the high-temperature refrigerant circulating in the high-stage refrigerant circuit is used to heat water to generate hot water.

[0003] This type of two-stage refrigeration device may cause an imbalance in the time from startup to stable state due to differences in refrigerant characteristics between the high-stage refrigeration circuit and the low-stage refrigeration circuit, temperature conditions at startup, etc., causing the compressor of the low-stage refrigerant circuit to stop for protection. Therefore, with respect to the two-stage refrigeration device disclosed in Patent Document 1, the ratio of the speed of the compressor of the high-stage refrigeration circuit to the speed of the compressor of the low-stage refrigeration circuit during the period from startup to transition to stable operation of the two-stage refrigeration device (hereinafter referred to as "startup operation") is set to be greater than the ratio during stable operation. This is to prevent a protective stop caused by excessive high pressure in the low-stage refrigeration circuit during startup operation.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2013-213590 Summary of the invention

[0005] However, in the two-stage refrigeration device disclosed in Patent Document 1, the ratio of the rotation speed of the compressor of the high-stage refrigeration circuit in the startup operation to the rotation speed of the compressor of the low-stage refrigeration circuit is set to be greater than the ratio in the stable operation. Therefore, the rotation speed of the compressor of the low-stage refrigeration circuit in the startup operation is limited, and there is a problem that it takes time to fully exert the heating capacity during the startup operation.

[0006] In view of the above-mentioned problems, an object of the present invention is to provide a two-stage refrigeration device that can suppress a decrease in heating capacity due to rapid startup operation.

[0007] One embodiment of the present invention is a two-stage refrigeration device, comprising: a high-stage refrigerant circuit, which uses refrigerant piping to connect the high-stage compressor, the high-stage heat exchanger, the high-stage pressure reducing mechanism and the stepped heat exchanger in sequence, so that the high-stage refrigerant circulates; a low-stage refrigerant circuit, which has a first circulation path and a second circulation path, wherein the first circulation path uses refrigerant piping to connect the low-stage compressor, the stepped heat exchanger, the low-stage first pressure reducing mechanism and the heat source side heat exchanger in sequence, so that the low-stage refrigerant circulates, so that the high-stage refrigerant The refrigerant and the low-stage refrigerant exchange heat in the stepped heat exchanger. The second circulation path uses a refrigerant piping provided with a low-stage heat exchanger and a low-stage second pressure reducing mechanism to connect the low-stage compressor and the stepped heat exchanger, and the low-stage first pressure reducing mechanism and the heat source side heat exchanger in the first circulation path. The low-stage compressor, the low-stage heat exchanger, the low-stage second pressure reducing mechanism and the heat source side heat exchanger are connected in sequence by the refrigerant piping to circulate the low-stage refrigerant. The heat medium circuit has a first heat medium circulation The first heat medium circulation path is a heat medium circulation path, wherein the first heat medium circulation path uses a pipe to sequentially connect a first circulation pump, a utilization side heat exchanger, a low-stage side heat exchanger, and a high-stage side heat exchanger to circulate the heat medium, so that the high-stage side refrigerant and the heat medium perform heat exchange in the high-stage side heat exchanger, and the low-stage side refrigerant and the heat medium perform heat exchange in the low-stage side heat exchanger, and the second heat medium circulation path has a first bypass path, which bypasses the first heat medium circulation path between the utilization side heat exchanger and the low-stage side heat exchanger and the low-stage side heat exchanger. The heat exchanger is connected to the high-stage heat exchanger, and the first circulation pump, the utilization-side heat exchanger, the first bypass passage, and the high-stage heat exchanger are connected in sequence by piping to circulate the heat medium; the first switching unit causes the high-stage refrigerant and the low-stage refrigerant to exchange heat in the stepped heat exchanger, and in the heat medium circuit, switches the heat medium to flow in the first heat medium circulation path or in the second heat medium circulation path; and a control unit controls the high-stage refrigerant circuit, the low-stage refrigerant circuit, and the heat medium circuit.

[0008] Effects of the Invention

[0009] According to the present invention, it is possible to provide a two-stage refrigeration device that can suppress a decrease in heating capacity due to rapid startup operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1A This is a refrigerant circuit diagram of a two-stage refrigeration system according to an embodiment of the present invention.

[0011] Figure 1B It is a diagram showing the flow of the refrigerant in the first mode operation of the two-stage refrigeration system according to the embodiment of the present invention.

[0012] Figure 1C It is a diagram showing the flow of the refrigerant in the second mode operation of the two-stage refrigeration system according to the embodiment of the present invention.

[0013] Figure 2 This is a control block diagram of a two-stage refrigeration system according to an embodiment of the present invention.

[0014] Figure 3 This is a control flow chart of the two-stage refrigeration system according to the embodiment of the present invention.

[0015] Figure 4A This is a refrigerant circuit diagram of a two-stage refrigeration system according to another embodiment of the present invention.

[0016] Figure 4B It is a diagram showing the flow of the refrigerant in the first mode operation of the two-stage refrigeration system according to another embodiment of the present invention.

[0017] Figure 4C It is a diagram showing the flow of the refrigerant in the second mode operation of the two-stage refrigeration system according to another embodiment of the present invention.

[0018] Figure 5 This is a control block diagram of a two-stage refrigeration device according to another embodiment of the present invention.

[0019] Figure 6 It is a control flow chart of a two-stage refrigeration device according to another embodiment of the present invention. DETAILED DESCRIPTION

[0020] Hereinafter, an embodiment of the two-stage refrigeration system according to the present invention will be described in detail based on the drawings. However, the present invention is not limited to this embodiment.

[0021] Figure 1A This is a refrigerant circuit diagram of the two-stage refrigeration system 1 according to the present embodiment. Figure 2 This is a control block diagram of the two-stage refrigeration system 1 according to the present embodiment.

[0022] Example

[0023] Reference Figure 1A to Figure 1C A two-stage refrigeration system 1 according to this embodiment will be described. Figure 1AIt is a refrigerant circuit diagram of the two-stage refrigeration device 1 of the present embodiment. The two-stage refrigeration device 1 is a refrigeration device that can be used for cooling operation when the utilization side heat exchanger 31 is used as an evaporator, and can be used for hot water generation operation or heating operation when the utilization side heat exchanger 31 is used as a condenser. Hereinafter, the operation of generating hot water and the heating operation are sometimes collectively referred to as heating operation. In the present embodiment, a two-stage refrigeration device for heating operation is described. The two-stage refrigeration device 1 has a high-level refrigerant circuit 2, a low-level refrigerant circuit 3, a heat medium circuit 4, and a control unit 5. The control unit 5 includes a storage unit for storing data such as target temperature, control software, etc., and controls the two-stage refrigeration device 1.

[0024] The high-stage refrigerant circuit 2 sequentially connects a high-stage compressor 10, a high-stage heat exchanger 11, a high-stage expansion valve 12 as a high-stage pressure reducing mechanism, and a stepped heat exchanger 13 by means of a refrigerant pipe 6, and circulates the high-stage refrigerant. In the present embodiment, the high-stage heat exchanger 11 is a heat exchanger that performs heat exchange between the high-stage refrigerant and the heat medium flowing in the heat medium circuit 4. The stepped heat exchanger 13 is a heat exchanger that performs heat exchange between the high-stage refrigerant and the low-stage refrigerant flowing in the low-stage refrigerant circuit 3. In addition, if the high-stage heat exchanger 11 and the stepped heat exchanger 13 are heat exchangers that can perform heat exchange between liquids, they may be, for example, a plate heat exchanger or a double-tube heat exchanger. In addition, in the present embodiment, the high-stage heat exchanger 11 is a heat exchanger that performs heat exchange between the high-stage refrigerant and the heat medium flowing in the heat medium circuit 4, and may be, for example, a heat exchanger that performs heat exchange with air as a heat medium via a blower not shown. The arrows in the high-stage refrigerant circuit 2 indicate the flow of the high-stage refrigerant during the heating operation.

[0025] In the high-stage refrigerant circuit 2, a high-stage four-way valve 14 that switches the high-stage refrigerant discharged from the high-stage compressor 10 to flow to the high-stage heat exchanger 11 side or to the step heat exchanger 13 side is connected to the discharge side of the high-stage compressor 10. In the present embodiment, a case (heating operation) in which the high-stage refrigerant discharged from the high-stage compressor 10 flows to the high-stage heat exchanger 11 side using the high-stage four-way valve 14 is described. Therefore, in the high-stage refrigerant circuit 2, the high-stage refrigerant discharged from the high-stage compressor 10 flows through the high-stage heat exchanger 11, the high-stage expansion valve 12, and the step heat exchanger 13 and is sucked into the high-stage compressor 10.

[0026] The low-stage refrigerant circuit 3 has a first circulation path 23 and a second circulation path 26. With respect to the first circulation path 23, the low-stage compressor 20, the stepped heat exchanger 13 connected to the high-stage refrigerant circuit 2, the low-stage first expansion valve 21 as the low-stage first pressure reducing mechanism, and the heat source side heat exchanger 22 are connected in sequence by the refrigerant piping 6, and the low-stage refrigerant circulates. The heat source side heat exchanger 22 is a heat exchanger that performs heat exchange between the low-stage refrigerant and the outside air. The heat source side heat exchanger 22 is provided with a condensation temperature detection sensor 22a that measures the condensation temperature of the low-stage refrigerant flowing in the heat source side heat exchanger 22. In addition, the stepped heat exchanger 13 is a heat exchanger that performs heat exchange between the low-stage refrigerant and the high-stage refrigerant flowing in the high-stage refrigerant circuit 2. The stepped heat exchanger 13 is provided with a condensation temperature detection sensor 13a for measuring the condensation temperature (refrigerant condensation temperature) of the low-stage refrigerant flowing in the stepped heat exchanger 13, and an outlet temperature detection sensor 13b for measuring the outlet temperature of the low-stage refrigerant. The arrows of the low-stage refrigerant circuit 3 indicate the flow of the low-stage refrigerant.

[0027] The low-stage refrigerant circuit 3 has a second circulation path 26 for circulating the low-stage refrigerant. The second circulation path 26 connects the low-stage compressor 20 and the stepped heat exchanger 13 and the low-stage first expansion valve 21 and the heat source side heat exchanger 22 by using a refrigerant piping provided with a low-stage heat exchanger 24 and a low-stage second expansion valve 25 as a low-stage second pressure reducing mechanism, and connects the low-stage compressor 20, the low-stage heat exchanger 24, the low-stage second expansion valve 25, and the heat source side heat exchanger 22 in sequence by using a refrigerant piping. The low-stage heat exchanger 24 is a heat exchanger having a first heat storage part, and performs heat exchange between the low-stage refrigerant and the heat medium flowing in the heat medium circuit 4, and the first heat storage part has a heat storage material. The low-stage heat exchanger 24 is provided with: a condensation temperature detection sensor 24a for measuring the condensation temperature of the low-stage refrigerant flowing in the low-stage heat exchanger 24; and an outlet temperature detection sensor 24b for measuring the outlet temperature of the low-stage refrigerant. In addition, a heat medium return temperature detection sensor 24c for measuring the heat medium return temperature, which is the temperature when the heat medium flowing in the heat medium circuit 4 flows into the low-stage heat exchanger 24, is also provided. In addition, if the low-stage heat exchanger 24 is a heat exchanger capable of exchanging heat between liquids, it may be, for example, a plate heat exchanger or a double-tube heat exchanger.

[0028] In the low-stage refrigerant circuit 3, a low-stage four-way valve 27 for switching the low-stage refrigerant discharged from the low-stage compressor 20 to flow to the stepped heat exchanger 13 side and the low-stage heat exchanger 24 side, or to flow to the heat source side heat exchanger 22 side, is connected to the discharge side of the low-stage compressor 20. In the present embodiment, a case (heating operation) in which the low-stage refrigerant discharged from the low-stage compressor 20 flows to the stepped heat exchanger 13 side and the low-stage heat exchanger 24 side by using the low-stage four-way valve 27 is described. In this case, in the low-stage refrigerant circuit 3, the low-stage refrigerant discharged from the low-stage compressor 20 flows through the stepped heat exchanger 13, the low-stage first expansion valve 21, and the heat source side heat exchanger 22 and is sucked into the low-stage compressor 20. The low-stage refrigerant discharged from the low-stage compressor 20 passes through the low-stage heat exchanger 24 , the low-stage second expansion valve 25 , and the heat source-side heat exchanger 22 and is sucked into the low-stage compressor 20 .

[0029] In the low-pressure side refrigerant circuit 3 , the low-pressure side compressor 20 , the heat source side heat exchanger 22 , and the low-pressure side four-way valve 27 are structures commonly used in the first circulation path 23 and the second circulation path 26 .

[0030] The heat medium circuit 4 connects the first circulation pump 30, the utilization side heat exchanger 31, the low-stage side heat exchanger 24, and the high-stage side heat exchanger 11 in order by using the pipe 32, and circulates water as a heat medium. In addition, antifreeze can be used as a heat medium instead of water. The utilization side heat exchanger 31 is provided in an indoor unit (not shown) provided indoors, and indoor air flows into the utilization side heat exchanger 31 by using the airflow generated by the air supply fan (not shown). In the utilization side heat exchanger 31, water as a heat medium is heat-exchanged with air in the room where the indoor unit is provided, and the air heat-exchanged with water as a heat medium is used for heating. The high-stage side heat exchanger 11 is a heat exchanger that heats water as a heat medium and the high-stage side refrigerant flowing in the high-stage side refrigerant circuit 2. The low-stage side heat exchanger 24 is a heat exchanger that heats water as a heat medium and the low-stage side refrigerant flowing in the low-stage side refrigerant circuit 3. The arrows of the heat medium circuit 4 indicate the flow of water as a heat medium.

[0031] In addition, the heat medium circuit 4 is provided with a first bypass passage 33, one end of which is connected to the pipe between the use side heat exchanger 31 and the low-stage heat exchanger 24, and the other end of which is connected to the pipe between the low-stage heat exchanger 24 and the high-stage heat exchanger 11. A first three-way valve 34 (first switching means) is provided on one side of the first bypass passage 33. The first three-way valve 34 switches between the first heat medium circulation passage 35 and the second heat medium circulation passage 36. The first heat medium circulation passage 35 circulates water as a heat medium through the first circulation pump 30, the use side heat exchanger 31, the low-stage heat exchanger 24, the high-stage heat exchanger 11, and the first circulation pump 30. The second heat medium circulation passage 36 circulates water as a heat medium through the first circulation pump 30, the use side heat exchanger 31, the first bypass passage 33, the high-stage heat exchanger 11, and the first circulation pump 30.

[0032] The two-stage refrigeration system 1 has a first mode operation in which the heat medium flows through the first heat medium circulation path 35 , and a second mode operation in which the heat medium does not flow through the low-stage heat exchanger 24 but flows through the second heat medium circulation path 36 . Figure 1B This shows a state in which the heat medium is circulated in the first heat medium circulation path 35 according to the first mode operation. Figure 1C The state in which the heat medium circulates in the second heat medium circulation path 36 according to the second mode operation is shown. The first mode operation is a heating operation in which the heat absorbed from the outside air by the heat source side heat exchanger 22 of the low-stage refrigerant circuit 3 is released to the indoor air via the high-stage side heat exchanger 11 of the high-stage side refrigerant circuit 2 and the low-stage side heat exchanger 24 of the low-stage side refrigerant circuit 3. The second mode operation is an operation in which the heat medium circulates in the second heat medium circulation path 36 instead of flowing through the low-stage side heat exchanger 24. The second mode operation is performed when the temperature of the heat medium flowing out of the utilization side heat exchanger 31 and flowing into the low-stage side heat exchanger 24, i.e., the heat medium return temperature measured by the heat medium return temperature detection sensor 24c, approaches the condensation temperature of the low-stage side refrigerant flowing into the low-stage side heat exchanger 24 measured by the condensation temperature detection sensor 24a.

[0033] The two-stage refrigeration device 1 is a refrigeration device that utilizes the latent heat of the high-stage refrigerant of the high-stage refrigerant circuit 2, the latent heat of the low-stage refrigerant of the low-stage refrigerant circuit 3, and the sensible heat of the heat medium (water) of the heat medium circuit 4. In addition, in the present embodiment, the high-stage refrigerant of the high-stage refrigerant circuit 2 and the low-stage refrigerant of the low-stage refrigerant circuit 3 are the same refrigerant, but they do not need to be the same, for example, they can be set to a low-stage refrigerant with a lower boiling point than the high-stage refrigerant. In addition, a refrigerant that can use the latent heat change for the heat medium circuit can be used. In this case, the first circulation pump 30 of the heat medium circuit 4 is replaced with a compressor, and an expansion valve or the like is set as a pressure reducing mechanism in the path between the utilization side heat exchanger 31 and the low-stage heat exchanger 24.

[0034] In the two-stage refrigeration device 1, the heat source side heat exchanger 22 of the low-stage side refrigerant circuit 3 absorbs heat from the outside air, so that the low-stage side refrigerant, which is a low-temperature and low-pressure gas-phase refrigerant, is compressed in the low-stage side compressor 20 and becomes a high-temperature and high-pressure gas-phase refrigerant. Moreover, the high-temperature and high-pressure gas-phase refrigerant releases heat to the high-stage side refrigerant circulating in the high-stage side refrigerant circuit 2 in the stepped heat exchanger 13 and becomes a high-temperature and high-pressure liquid-phase refrigerant. The low-pressure high-stage side refrigerant that absorbs heat from the low-stage side refrigerant in the stepped heat exchanger 13 is compressed in the high-stage side compressor 10 and becomes a high-temperature and high-pressure gas-phase refrigerant. The high-temperature and high-pressure gas-phase refrigerant releases heat to water, which is a heat medium circulating in the heat medium circuit 4 in the high-stage side heat exchanger 11, to generate hot water. In addition, the heat source side heat exchanger 22 of the low-stage side refrigerant circuit 3 absorbs heat from the outside air, so that the low-stage side refrigerant, which is a low-temperature and low-pressure gas-phase refrigerant, is compressed in the low-stage side compressor 20 and becomes a high-temperature and high-pressure gas-phase refrigerant. This high-temperature and high-pressure gas-phase refrigerant releases heat to the water as the heat medium circulating in the heat medium circuit 4 in the low-stage heat exchanger 24. Therefore, the low-stage refrigerant circulating in the low-stage refrigerant circuit 3 can be condensed by using the water as the heat medium circulating in the heat medium circuit 4.

[0035] In the prior art two-stage refrigeration device, the ratio (R1 / R2) of the rotation speed (R1) of the compressor of the high-stage refrigeration circuit during startup operation to the rotation speed (R2) of the compressor of the low-stage refrigeration circuit is set to be higher than the ratio during stable operation. This prevents the compressor of the low-stage refrigerant circuit from being put into a protective stop state due to non-condensation and excessive high pressure in the low-stage refrigeration circuit. However, in the prior art, the rotation speed of the compressor of the low-stage refrigeration circuit during startup operation is limited, so it takes time to fully exert the heating capacity during startup operation. On the other hand, the two-stage refrigeration device 1 of the present embodiment has a high-stage refrigerant circuit 2 and a low-stage refrigerant circuit 3 having a first circulation path 23 and a second circulation path 26. Moreover, in the first mode operation, as Figure 1BAs shown, in the high-stage heat exchanger 11 of the high-stage refrigerant circuit 2 and the low-stage heat exchanger 24 of the second circulation path 26 of the low-stage refrigerant circuit 3, the low-stage refrigerant and the heat medium circulating in the heat medium circuit 4 exchange heat. In this way, the low-stage refrigerant circulating in the low-stage refrigerant circuit 3 and the heat medium circulating in the heat medium circuit 4 can be directly heat-exchanged and condensed, so that the protection stop of the compressor of the low-stage refrigeration circuit can be suppressed and the startup operation can be quickly performed.

[0036] On the other hand, if the first mode operation continues, the air that has exchanged heat with the heat medium in the utilization side heat exchanger 31 is heated. Therefore, the temperature of the heat medium (heat medium return temperature) that flows out of the utilization side heat exchanger 31 and flows into the low-level side heat exchanger 24 soon approaches the condensation temperature of the low-level side refrigerant flowing into the low-level side heat exchanger 24. In this state, the low-level side refrigerant cannot condense in the low-level side heat exchanger 24. There is a large amount of gas-phase refrigerant that was not condensed in the low-level side heat exchanger 24, which originally had a large amount of liquid-phase low-level refrigerant distributed, so that the liquid-phase low-level refrigerant is excessively retained in other paths in the low-level side refrigeration circuit (for example, an accumulator not shown in the figure provided on the suction side of the low-level side compressor 20). Therefore, liquid compression may occur in the low-level side compressor 20. Furthermore, since the low-pressure side refrigerant can be condensed in the low-pressure side heat exchanger 24 , if the rotation speed of the low-pressure side compressor 20 is increased, the reliability of the low-pressure side compressor 20 may be reduced.

[0037] However, the two-stage refrigeration system 1 of this embodiment has a second mode operation in which the heat medium does not flow into the low-stage heat exchanger 24 but flows in the second heat medium circulation path 36. The second mode operation is an operation in which Figure 1C As shown, when the heat medium return temperature of the heat medium is high temperature and close to the condensation temperature of the low-stage refrigerant, the heat medium is not allowed to flow in the low-stage heat exchanger 24, but circulates in the second heat medium circulation path 36. By performing the second mode operation, the high-temperature heat medium will not flow into the low-stage heat exchanger 24, so the low-stage refrigerant exchanges heat with the surrounding air via the low-stage heat exchanger 24 and the refrigerant pipe 6. As a result, it is possible to suppress the low-stage refrigerant flowing into the low-stage heat exchanger 24 from being unable to condense, so the low-stage heat exchanger 24 can be used as a condenser without increasing the rotation speed of the low-stage compressor 20. In addition, the two-stage refrigeration device 1 of this embodiment has a second mode operation, so it is preferred that the low-stage heat exchanger 24 is a double-tube heat exchanger having an outer peripheral flow path and an inner peripheral flow path, and is a structure in which the low-stage refrigerant flows in the outer peripheral flow path and water as a heat medium flows in the inner peripheral flow path. As a result, the low-stage refrigerant easily dissipates heat and can be easily condensed.

[0038] Next, refer to Figure 2 The control module of the two-stage refrigeration device 1 of the present embodiment is described. The control unit 5 has a first subcooling degree calculation unit 45, a second subcooling degree calculation unit 46 and a storage unit 47. The first subcooling degree calculation unit 45 calculates the subcooling degree of the low-stage side refrigerant of the step heat exchanger 13. The second subcooling degree calculation unit 46 calculates the subcooling degree of the low-stage side refrigerant of the low-stage side heat exchanger 24. In addition, the storage unit 47 stores data such as target temperature, control software, and a program for calculating the subcooling degree. The condensation temperature of the low-stage side refrigerant flowing in the step heat exchanger 13 measured by the condensation temperature detection sensor 13a and the outlet temperature of the low-stage side refrigerant flowing in the step heat exchanger 13 measured by the outlet temperature detection sensor 13b are input to the first subcooling degree calculation unit 45. The condensation temperature of the low-stage refrigerant flowing in the low-stage heat exchanger 24 measured by the condensation temperature detection sensor 24a and the outlet temperature of the low-stage refrigerant flowing in the low-stage heat exchanger 24 measured by the outlet temperature detection sensor 24b are input to the second subcooling degree calculation unit 46. In addition, the target heat medium temperature is input to the control unit 5. The target heat medium temperature is the target temperature of the water as the heat medium flowing out from the first circulation pump 30 in the heat medium circuit 4. The target heat medium temperature is changed, for example, according to the air conditioning load (the difference between the room temperature of the air-conditioned space and the set temperature specified by the user) when the heating operation using the utilization side heat exchanger 31 is performed, and the larger the air conditioning load, the larger the target heat medium temperature is set.

[0039] In addition, the heat medium return temperature measured by the heat medium return temperature detection sensor 24c and the condensation temperature of the low-stage heat exchanger 22 measured by the condensation temperature detection sensor 22a are input to the control unit 5. The first three-way valve 34 is controlled based on the heat medium return temperature and the condensation temperature of the low-stage heat exchanger 22 input to the control unit 5.

[0040] The control unit 5 determines the rotation speeds of the high-stage compressor 10 and the low-stage compressor 20 based on the target heat medium temperature. In addition, the low-stage first expansion valve 21 is controlled based on the degree of subcooling of the low-stage refrigerant of the step heat exchanger 13 calculated by the first degree of subcooling calculation unit 45. In addition, the low-stage second expansion valve 25 is controlled based on the degree of subcooling of the low-stage refrigerant of the low-stage heat exchanger 24 calculated by the second degree of subcooling calculation unit 46.

[0041] Next, refer to Figure 3 The control flowchart shown will explain the control of the two-stage refrigeration system 1 according to the present embodiment.

[0042] The control unit first starts the first operation mode (ST1). In the first operation mode, the first three-way valve 34 is switched so that the heat medium flows in the first heat medium circulation path 35. Next, the first circulation pump 30 is started (ST2). Next, the startup operation is performed (ST3). Regarding the startup operation, the high-level side compressor 10 and the low-level side compressor 20 are started, and the openings of the high-level side expansion valve 12, the low-level side first expansion valve 21, and the low-level side second expansion valve 25 are maintained at a specified initial opening, so that the high-level side refrigerant circulates in the high-level side refrigerant circuit 2. In addition, the low-level side refrigerant is circulated according to the first circulation path 23 and the second circulation path 26 of the low-level side refrigerant circuit 3. Here, the initial opening is the opening of the high-level side expansion valve 12, the low-level side first expansion valve 21, and the low-level side second expansion valve 25 after the two-stage refrigeration device 1 starts operating until the high-level side refrigerant circuit 2 and the low-level side refrigerant circuit 3 are stabilized. The initial opening degree is determined according to the performance of the high-pressure side compressor 10 and the low-pressure side compressor 20 and is set in advance.

[0043] Next, if the specified time has passed, the startup operation is terminated (ST4). The specified time is, for example, 10 minutes. The specified time is the minimum time required until the two-stage refrigeration device 1 becomes a stable operating state that converges according to the load, and is predetermined based on experiments, etc. After the startup operation is completed, it is switched to normal operation (ST5). In normal operation, the low-stage side first expansion valve 21 and the low-stage side second expansion valve 25 are controlled in such a way that the low-stage side refrigerant at the outlet of the step heat exchanger 13 and the low-stage side refrigerant at the outlet of the low-stage side heat exchanger 24 respectively reach a specified degree of subcooling. Here, the specified degree of subcooling is a predetermined fixed value, and in order to prevent the low-stage side refrigerant in a two-phase state from flowing into each expansion valve, it is set to a value greater than or equal to 1deg. In addition, with respect to the high-stage side expansion valve 12, suction superheat control is performed to control the suction superheat of the high-stage side compressor 10 to a target value. The target value is a pre-set fixed value, which is set to a value greater than or equal to 1 degree so that the high-level refrigerant sucked into the high-level compressor 10 becomes an appropriate refrigerant state. In addition, the target discharge temperature control and the subcooling control can be performed without performing the suction superheat control with respect to the high-level expansion valve 12. Next, it is determined whether the return temperature of the heat medium after flowing out of the utilization side heat exchanger 31 is lower than the specified value (the first specified temperature) (ST6). The specified value (the first specified temperature) is a variable, for example, a temperature that is 2°C lower than the condensation temperature of the low-level refrigerant. Alternatively, with respect to the condition of step ST6, it can be determined whether the difference between the return temperature of the heat medium after flowing out of the utilization side heat exchanger 31 and the condensation temperature of the low-level refrigerant flowing into the low-level heat exchanger 24 measured by the condensation temperature detection sensor 24a of the low-level refrigerant circuit 3 is greater than or equal to the second specified temperature. The second predetermined temperature is a value such that, if it is lower than this value, the low-stage refrigerant is not condensed in the low-stage heat exchanger 24, and liquid compression may occur in the low-stage compressor 20. When the heat medium return temperature is not lower than the predetermined value (No in ST6), the second operation mode (ST7) is started. Regarding the second operation mode, the first three-way valve 34 is switched so that the heat medium flows in the second heat medium circulation path 36. When the heat medium return temperature is not lower than the predetermined value, sometimes the low-stage refrigerant in the gas phase state of high temperature and high pressure passing through the low-stage heat exchanger 24 cannot dissipate heat. However, by performing the second operation mode, the high-temperature heat medium will not flow into the low-stage heat exchanger 24. Therefore, the low-stage refrigerant flowing into the low-stage heat exchanger 24 exchanges heat with the surrounding air via the low-stage heat exchanger 24 and the refrigerant pipe 6 to dissipate heat, so that the low-stage refrigerant cannot be condensed. Next, target subcooling degree control is performed so that the subcooling degree of the low-stage refrigerant at the outlet of the low-stage heat exchanger 24 reaches the target subcooling degree (ST8).If the target subcooling degree control is performed, the opening degree of the low-stage second expansion valve 25 is controlled in the closing direction so that the low-stage second expansion valve 25 can achieve subcooling, and finally closes or opens slightly. The target subcooling degree control is the control of the low-stage second expansion valve 25 performed via the second subcooling degree calculation unit 46.

[0044] Next, it is determined whether the defrost start condition is satisfied (ST9). The defrost start condition is, for example, a case where the outside temperature is less than or equal to 5°C and the heating operation is continued for 3 hours, or a case where the temperature detected by the condensation temperature detection sensor 22a of the heat source side heat exchanger 22 is less than or equal to -15°C. When the defrost start condition is satisfied (Yes of ST9), the low-stage four-way valve 27 is switched to the so-called refrigeration cycle side to start the defrost operation (ST14), and the defrost operation is terminated after a prescribed time (ST15). The prescribed time is a pre-set time, and is a sufficient time (for example, 10 minutes) for the frost attached to the heat source side heat exchanger 22 to melt by the defrost operation. On the other hand, when the defrost start condition is not satisfied (No of ST9), it is determined whether the heat medium return temperature is lower than a prescribed value (ST10). When the heat medium return temperature is not lower than a prescribed value (No of ST10), the target supercooling degree control is continued before returning to ST9. When the heat medium return temperature is lower than the specified value (Yes in ST10), the operation mode is switched to the first operation mode (ST11). With respect to the first operation mode, the first three-way valve 34 is switched so that the heat medium flows in the first heat medium circulation path 35. As a result, the opening degree of the low-stage side second expansion valve 25 is controlled in the direction of closing or opening in a slightly opened state by the target subcooling degree control (ST12). After switching to the first operation mode, if the target subcooling degree control is performed, the low-stage side refrigerant in the gas phase state of high temperature and high pressure passing through the low-stage side heat exchanger 24 can dissipate heat and condense. Therefore, the opening degree is controlled in the direction of opening the low-stage side second expansion valve 25 so that the subcooling degree of the low-stage side refrigerant after passing through the low-stage side heat exchanger 24 reaches the target subcooling degree. The target subcooling degree control is the control of the low-stage side second expansion valve 25 performed via the second subcooling degree calculation unit 46. The target subcooling degree control is continued and the process returns to before step ST6.

[0045] When the heat medium return temperature is lower than the specified value (Yes in ST6), it is determined whether the defrost start condition is satisfied (ST13). The defrost start condition is determined based on the outside air temperature and the temperature detected by the condensation temperature detection sensor 22a of the heat source side heat exchanger 22. When the defrost start condition is satisfied (Yes in ST13), the defrost operation is started (ST14), and the defrost operation is terminated after a specified time has passed (ST15). On the other hand, when the defrost start condition is not satisfied (No in ST13), the process returns to the step before ST6 and determines whether the heat medium return temperature is lower than the specified value (ST6).

[0046] Next, refer to Figure 4A to Figure 4C A two-stage refrigeration device 50 as another embodiment will be described. Figure 4A It is a refrigerant circuit diagram of a two-stage refrigeration device 50 according to another embodiment. Figure 4B : is a diagram showing the flow of the refrigerant in the first mode operation of the two-stage refrigeration device 50 according to another embodiment of the present invention. Figure 4C It is a diagram showing the flow of refrigerant in the second mode operation of the two-stage refrigeration device 50 involved in other embodiments of the present invention. The differences between the two-stage refrigeration device 1 of the initial embodiment and the two-stage refrigeration device 50 of the other embodiments are as follows. That is, a second bypass passage 37 is provided, that is, one end is connected to the pipe 32 between the first three-way valve 34 and the low-stage heat exchanger 24, and the other end is connected to the pipe 32 between the low-stage heat exchanger 24 and the other end of the first bypass passage 33. In addition, the other structures are the same. Therefore, the detailed description of the structure that is the same as the structure of the two-stage refrigeration device 1 of the initial embodiment is omitted. In addition, the same reference numerals are used for the same structure.

[0047] The secondary refrigeration device 50 is a refrigeration device that can be used for cooling operation when the utilization side heat exchanger 31 is used as an evaporator, and can be used for hot water generation operation or heating operation when the utilization side heat exchanger 31 is used as a condenser. Hereinafter, the operation of generating hot water and the heating operation are sometimes collectively referred to as the heating operation. In this embodiment, the secondary refrigeration device used for the heating operation is described.

[0048] The two-stage refrigeration device 50 includes a high-stage refrigerant circuit 2, a low-stage refrigerant circuit 3, a heat medium circuit 4, and a control unit 5. The control unit 5 controls the two-stage refrigeration device 50. The heat medium circuit 4 includes a first bypass passage 33 and a second bypass passage 37. The first bypass passage 33 has one end connected to the pipe 32 between the utilization side heat exchanger 31 and the low-stage heat exchanger 24, and the other end connected to the pipe between the low-stage heat exchanger 24 and the high-stage heat exchanger 11. The second bypass passage 37 has one end connected to the pipe 32 between the first three-way valve 34 and the low-stage heat exchanger 24, and the other end connected to the pipe 32 between the low-stage heat exchanger 24 and the other end of the first bypass passage 33.

[0049] In the second bypass passage 37, a second three-way valve 38 as a second switching unit is provided at the other end of the second bypass passage 37. Furthermore, a heat storage unit 39 (equivalent to a second heat storage unit) having a heat storage material, a second circulation pump 40, and a stop valve 41 are provided from the other end toward one end of the second bypass passage 37. The second three-way valve 38 switches between the flow of water as a heat medium in the first heat medium circulation passage 35 and the flow of water in the third heat medium circulation passage 42. The heat storage unit 39 stores heat absorbed from the low-stage refrigerant by the low-stage heat exchanger 24 via the water as a heat medium. In addition, a temperature detection sensor 39a for measuring the temperature of the heat storage unit 39 is provided in the heat storage unit 39. The second circulation pump 40 allows the water as a heat medium to flow from the other end toward one end of the second bypass passage 37. The stop valve 41 is a valve that allows the water as a heat medium to flow from the other end toward one end of the second bypass passage 37 and prevents it from flowing from one end toward the other end.

[0050] The two-stage refrigeration device 50 has a first mode operation in which the heat medium flows in the first heat medium circulation path 35, and a second mode operation in which the heat medium flows in the second heat medium circulation path 36 and the third heat medium circulation path 42. In the first mode operation, the heat source side heat exchanger 22 of the low-stage refrigerant circuit 3 absorbs heat from the outside air, and the heat absorbed from the outside air is released to the heat medium of the heat medium circuit 4 via the high-stage side heat exchanger 11 of the high-stage side refrigerant circuit 2 and the low-stage side heat exchanger 24 of the low-stage refrigerant circuit 3. In addition, it is an operation in which the heat medium of the heat medium circuit 4 after the heat absorption is dissipated to the indoor air. In the second mode operation, the operation is performed as follows, that is, the heat source side heat exchanger 22 of the low-stage refrigerant circuit 3 absorbs heat from the outside air, and the heat medium of the heat medium circuit 4 is dissipated to the indoor air via the high-stage side refrigerant circuit 2. In the second mode operation, the heat source side heat exchanger 22 of the low-pressure side refrigerant circuit 3 absorbs heat from the outside air, and the heat absorbed from the outside air is stored in the heat storage unit 39 of the heat medium circuit 4 .

[0051] The first heat medium circulation path 35 is a circulation path for circulating the heat medium through the first circulation pump 30, the utilization side heat exchanger 31, the low-stage side heat exchanger 24, the high-stage side heat exchanger 11, and the first circulation pump 30. The second heat medium circulation path 36 is a circulation path for circulating the heat medium through the first circulation pump 30, the utilization side heat exchanger 31, the first bypass path 33, the high-stage side heat exchanger 11, and the first circulation pump 30. The third heat medium circulation path 42 is a circulation path for circulating the heat medium through the second circulation pump 40 of the second bypass path 37, the stop valve 41, the low-stage side heat exchanger 24, and the second circulation pump 40.

[0052] Next, refer to Figure 5 The control module of the two-stage refrigeration device 50 of the present embodiment is described. The control unit 5 has a first subcooling degree calculation unit 45, a second subcooling degree calculation unit 46 and a storage unit 47. The first subcooling degree calculation unit 45 calculates the subcooling degree of the low-stage side refrigerant of the step heat exchanger 13. The second subcooling degree calculation unit 46 calculates the subcooling degree of the low-stage side refrigerant of the low-stage side heat exchanger 24. In addition, the storage unit 47 stores data such as target temperature, control software, and a program for calculating the subcooling degree. As described above, the condensation temperature of the low-stage side refrigerant flowing in the step heat exchanger 13 measured by the condensation temperature detection sensor 13a and the outlet temperature of the low-stage side refrigerant flowing in the step heat exchanger 13 measured by the outlet temperature detection sensor 13b are input to the first subcooling degree calculation unit 45. The condensation temperature of the low-stage refrigerant flowing in the low-stage heat exchanger 24 measured by the condensation temperature detection sensor 24a and the outlet temperature of the low-stage refrigerant flowing in the low-stage heat exchanger 24 measured by the outlet temperature detection sensor 24b are input to the second supercooling degree calculation unit 46. In addition, the target heat medium temperature is input to the control unit 5. The target heat medium temperature is the target temperature of water as the heat medium flowing out of the first circulation pump 30 in the heat medium circuit 4. The target heat medium temperature is changed, for example, according to the air conditioning load (the difference between the room temperature of the air-conditioned space and the set temperature specified by the user) when the heating operation using the utilization side heat exchanger 31 is performed, and the larger the air conditioning load, the larger the target heat medium temperature is set.

[0053] In addition, the heat medium return temperature measured by the heat medium return temperature detection sensor 24c, the condensation temperature of the low-stage heat exchanger 24 measured by the condensation temperature detection sensor 22a, and the temperature of the heat storage unit 39 measured by the temperature detection sensor 39a are input to the control unit 5. The first three-way valve 34, the second three-way valve 38, and the second circulation pump 40 are controlled based on the heat medium return temperature, the temperature of the low-stage heat exchanger 24, and the temperature of the heat storage unit 39 input to the control unit 5. That is, in order to prevent the heat medium return temperature from being higher than the condensation temperature of the low-stage refrigerant flowing into the low-stage heat exchanger 24, the heat storage unit 39 is used to dissipate heat from the heat medium.

[0054] The control unit 5 determines the rotation speeds of the high-stage compressor 10 and the low-stage compressor 20 based on the target heat medium temperature. In addition, the low-stage first expansion valve 21 is controlled via the first subcooling degree calculation unit 45 based on the condensing temperature of the high-stage refrigerant flowing in the stepped heat exchanger 13 and the outlet temperature of the high-stage refrigerant flowing in the stepped heat exchanger 13. In addition, the low-stage second expansion valve 25 is controlled via the second subcooling degree calculation unit 46 based on the condensing temperature of the low-stage refrigerant flowing in the low-stage heat exchanger 24 and the outlet temperature of the low-stage refrigerant flowing in the low-stage heat exchanger 24.

[0055] Regarding the two-stage refrigeration device 50 of the present embodiment, the heat accumulated in the heat storage unit 39 in the second mode operation is used for a defrosting operation to remove frost attached to the heat source side heat exchanger 22. The defrosting operation is performed as follows. The high-stage side compressor 10 of the high-stage side refrigerant circuit 2 is stopped, and the low-stage side four-way valve 27 of the low-stage side refrigerant circuit 3 is switched to the so-called refrigeration cycle side. That is, the low-stage side refrigerant discharged from the low-stage side compressor 20 is switched to flow to the heat source side heat exchanger 22 side, so that the heat source side heat exchanger 22 functions as a condenser, and the stepped heat exchanger 13 side and the low-stage side heat exchanger 24 function as an evaporator. The low-stage side first expansion valve 21 and the low-stage side second expansion valve 25 are set to an opening close to fully opened. The low-stage side refrigerant discharged from the low-stage side compressor 20 flows into the heat source side heat exchanger 22 and melts the frost. A portion of the low-stage refrigerant flowing out of the heat source side heat exchanger 22 flows into the low-stage side heat exchanger 24, and absorbs heat from the heat medium circulating in the third heat medium circulation path 42 provided with the heat storage unit 39. The remaining low-stage refrigerant flowing out of the heat source side heat exchanger 22 flows into the stepped heat exchanger 13, and absorbs the heat remaining in the high-stage side refrigerant circuit 2 where the high-stage side compressor 10 is stopped. The low-stage refrigerant after absorbing heat flows into the heat source side heat exchanger 22 again via the low-stage side compressor 20, and melts the frost.

[0056] Reference Figure 6The control flowchart shown in the figure explains the control of the two-stage refrigeration device 50 involved in this embodiment.

[0057] The control unit first starts the first operation mode (ST21). Regarding the first operation mode, the first three-way valve 34 is switched so that the heat medium flows in the first heat medium circulation path 35. Next, the first circulation pump 30 is started (ST22). Next, the startup operation is performed (ST23). Regarding the startup operation, the high-level side compressor 10 and the low-level side compressor 20 are started, and the openings of the high-level side expansion valve 12, the low-level side first expansion valve 21, and the low-level side second expansion valve 25 are maintained at a predetermined initial opening. Thus, the high-level side refrigerant is circulated in the high-level side refrigerant circuit 2, and the low-level side refrigerant is circulated according to the first circulation path 23 and the second circulation path 26 of the low-level side refrigerant circuit 3. The initial opening is the opening of the high-level side expansion valve 12, the low-level side first expansion valve 21, and the low-level side second expansion valve 25 after the two-stage refrigeration device 1 starts operating until the high-level side refrigerant circuit 2 and the low-level side refrigerant circuit 3 are stabilized. The initial opening degree is determined according to the performance of the high-pressure side compressor 10 and the low-pressure side compressor 20 and is set in advance.

[0058] Next, if the specified time has passed, the startup operation is terminated (ST24). The specified time is, for example, 10 minutes. The specified time is the minimum time required until the two-stage refrigeration device 1 becomes a stable operating state that converges according to the load, and is predetermined based on experiments, etc. After the startup operation is completed, it is switched to normal operation (ST25). Regarding normal operation, the low-stage side first expansion valve 21 and the low-stage side second expansion valve 25 are controlled in such a way that the low-stage side refrigerant at the outlet of the step heat exchanger 13 and the low-stage side refrigerant at the outlet of the low-stage side heat exchanger 24 reach a specified degree of subcooling. The specified degree of subcooling is a pre-set fixed value, and is set to a value at least greater than or equal to 1deg in such a way that the low-stage side refrigerant in a two-phase state does not flow into each expansion valve. In addition, the high-stage side expansion valve 12 performs suction superheat control to control the suction superheat of the high-stage side compressor 10 to a target value. The target value is a pre-set fixed value, and is set to a value greater than or equal to 1 degree in such a way that the high-level refrigerant sucked into the high-level compressor 10 becomes an appropriate refrigerant state. In addition, the high-level expansion valve 12 can perform target discharge temperature control and subcooling control without performing suction superheat control. Next, it is determined whether the return temperature of the heat medium after flowing out of the utilization side heat exchanger 31 is lower than the specified value (the first specified temperature) (ST26). The specified value (the first specified temperature) is a variable, for example, a temperature that is 2°C lower than the condensation temperature of the low-level refrigerant. Alternatively, regarding the condition of step ST26, it can be determined whether the difference between the return temperature of the heat medium after flowing out of the utilization side heat exchanger 31 and the condensation temperature of the low-level refrigerant flowing into the low-level heat exchanger 24 measured by the condensation temperature detection sensor 24a of the low-level refrigerant circuit 3 is greater than or equal to the second specified temperature. The second predetermined temperature is a value such that, if it is lower than this value, the low-stage refrigerant is not condensed in the low-stage heat exchanger 24, and liquid compression may occur in the low-stage compressor 20. When the heat medium return temperature is not lower than the predetermined value (No in ST26), the second operation mode is started (ST27). The second operation mode is an operation in which the first three-way valve 34 is switched so that the heat medium flows in the second heat medium circulation path 36, and the heat absorbed from the outside air is stored in the heat storage unit 39 of the heat medium circuit 4. The second operation mode is performed within a predetermined time to complete the heat storage in the heat storage unit 39 (ST28). Next, the target subcooling degree control is performed so that the subcooling degree of the low-stage refrigerant at the outlet of the low-stage heat exchanger 24 reaches the target subcooling degree (ST29). If the target subcooling degree control is performed, the opening degree of the low-stage second expansion valve 25 is controlled in the closing direction in a manner to achieve subcooling, and finally closed or opened slightly. The target subcooling degree control is a control of the low-stage second expansion valve 25 performed via the second subcooling degree calculation unit 46 .

[0059] Next, it is determined whether the defrost start condition is satisfied (ST30). The defrost start condition is, for example, a case where the outside temperature is less than or equal to 5°C and the heating operation is continued for 3 hours, or a case where the temperature detected by the condensation temperature detection sensor 22a of the heat source side heat exchanger 22 is less than or equal to -15°C. When the defrost start condition is satisfied (Yes of ST30), the low-stage side four-way valve 27 is switched to the so-called refrigeration cycle side to start the defrost operation (ST35), and the defrost operation is terminated after a predetermined time (ST36). The predetermined time is a pre-set time, and is a sufficient time (for example, 10 minutes) for the frost attached to the heat source side heat exchanger 22 to melt by the defrost operation. On the other hand, when the defrost start condition is not satisfied (No of ST30), it is determined whether the heat medium return temperature is lower than a predetermined value (ST31). When the heat medium return temperature is not lower than a predetermined value (No of ST31), the target supercooling degree control is continued before returning to step ST30. When the heat medium return temperature is lower than the specified value (Yes in ST31), the operation mode is switched to the first operation mode (ST32). With respect to the first operation mode, the first three-way valve 34 is switched so that the heat medium flows in the first heat medium circulation path 35. As a result, the opening degree of the low-stage side second expansion valve 25 is controlled in the direction of opening from a closed state or a slightly opened state by the target subcooling degree control (ST33). After switching to the first operation mode, if the target subcooling degree control is performed, the low-stage side refrigerant in the gas phase state of high temperature and high pressure passing through the low-stage side heat exchanger 24 can dissipate heat and condense. Therefore, the opening degree is controlled in the direction of opening the low-stage side second expansion valve 25 so that the subcooling degree of the low-stage side refrigerant after passing through the low-stage side heat exchanger 24 reaches the target subcooling degree. The target subcooling degree control is the control of the low-stage side second expansion valve 25 performed via the second subcooling degree calculation unit 46. The target subcooling degree control is continued and the process returns to before step ST26.

[0060] When the heat medium return temperature is lower than the specified value (Yes in ST26), it is determined whether the defrost start condition is satisfied (ST34). The defrost start condition is a condition related to the above-mentioned outside air temperature and the temperature detected by the condensation temperature detection sensor 22a of the heat source side heat exchanger 22. When the defrost start condition is satisfied (Yes in ST34), it is determined whether the heat storage temperature of the heat storage unit 39 is higher than the specified value (ST37). The specified value is a temperature that is determined in advance through tests and the like to be sufficient for the defrost operation. When the heat storage temperature of the heat storage unit 39 is higher than the specified value (Yes in ST37), the defrost operation is started (ST35), and the defrost operation is terminated after a specified time has passed (ST36). On the other hand, when the heat storage temperature of the heat storage unit 39 is not higher than the specified value (No in ST37), the second operation mode is started (ST38). The second operation mode is an operation in which the first three-way valve 34 is switched so that the heat medium flows in the second heat medium circulation path, and the heat absorbed from the outside air is stored in the heat storage unit 39 of the heat medium circuit 4. The second operation mode is performed for a predetermined time and the heat storage in the heat storage unit 39 is completed (ST39). Next, the defrosting operation is started (ST35), and the defrosting operation is terminated after the predetermined time has passed (ST36).

[0061] The above description is made with reference to a limited number of embodiments, the scope of rights is not limited thereto, and modifications based on the above disclosed embodiments will be apparent to those skilled in the art.

[0062] Description of the label

[0063] 1… two-stage refrigeration device, 2… high-stage refrigerant circuit, 3… low-stage refrigerant circuit, 4… heat medium circuit, 5… control unit, 6… refrigerant pipe, 10… high-stage compressor, 11… high-stage heat exchanger, 12… high-stage expansion valve, 13… step-type heat exchanger, 13a… condensation temperature detection sensor, 13b… outlet temperature detection sensor, 14… high-stage four-way valve, 20… low-stage compressor, 21… low-stage first expansion valve, 22… heat source side heat exchanger, 22a… condensation temperature detection sensor, 23… first circulation path, 24… low-stage heat exchanger, 24a… condensation temperature detection sensor, 24b… outlet temperature detection sensor , 24c…heat medium return temperature detection sensor, 25…second expansion valve on low-stage side, 26…second circulation path, 27…four-way valve on low-stage side, 30…first circulation pump, 31…heat exchanger on utilization side, 32…pipe, 33…first bypass path, 34…first three-way valve, 35…first heat medium circulation path, 36…second heat medium circulation path, 37…second bypass path, 38…second three-way valve, 39…heat storage unit, 39a…temperature detection sensor, 40…second circulation pump, 41…stop valve, 42…third heat medium circulation path, 45…first subcooling degree calculation unit, 46…second subcooling degree calculation unit, 47…storage unit, 50…secondary refrigeration device

Claims

1. A two-stage refrigeration device, characterized in that: The secondary refrigeration device has: A high-side refrigerant circuit, which uses refrigerant piping to sequentially connect a high-side compressor, a high-side heat exchanger, a high-side pressure reducing mechanism, and a stepped heat exchanger so that the high-side refrigerant circulates; A low-stage refrigerant circuit, comprising a first circulation path and a second circulation path, wherein the first circulation path connects the low-stage compressor, the stepped heat exchanger, the first low-stage pressure reducing mechanism and the heat source side heat exchanger in sequence by using a refrigerant piping so that the low-stage refrigerant circulates, and the second circulation path connects between the low-stage compressor and the stepped heat exchanger and between the first low-stage pressure reducing mechanism and the heat source side heat exchanger in the first circulation path by using a refrigerant piping provided with the low-stage heat exchanger and the second low-stage pressure reducing mechanism, and connects the low-stage compressor, the low-stage heat exchanger, the second low-stage pressure reducing mechanism and the heat source side heat exchanger in sequence by using a refrigerant piping so that the low-stage refrigerant circulates; A heat medium circuit, comprising a first heat medium circulation path and a second heat medium circulation path, wherein the first heat medium circulation path sequentially connects a first circulation pump, a utilization side heat exchanger, the low-stage side heat exchanger, and the high-stage side heat exchanger by piping to circulate the heat medium, and the high-stage side refrigerant and the heat medium perform heat exchange in the high-stage side heat exchanger, and the low-stage side refrigerant and the heat medium perform heat exchange in the low-stage side heat exchanger, and the second heat medium circulation path comprises a first bypass path, which connects the utilization side heat exchanger and the low-stage side heat exchanger and the low-stage side heat exchanger and the high-stage side heat exchanger in the first heat medium circulation path, and sequentially connects the first circulation pump, the utilization side heat exchanger, the first bypass path, and the high-stage side heat exchanger by piping to circulate the heat medium; The high-stage refrigerant and the low-stage refrigerant perform heat exchange in the stepped heat exchanger. a first switching unit for switching, in the heat medium circuit, whether the heat medium flows through a first heat medium circulation path or through a second heat medium circulation path; and A control unit controls the high-pressure side refrigerant circuit, the low-pressure side refrigerant circuit, and the heat medium circuit.

2. The secondary refrigeration device according to claim 1, characterized in that: When starting the two-stage refrigeration system, the control unit starts the high-pressure side compressor, the low-pressure side compressor, and the first circulation pump, and switches the first switching unit so that the heat medium flows in the first heat medium circulation path.

3. The secondary refrigeration device according to claim 2, characterized in that: When the temperature of the heat medium passing through the utilization side heat exchanger exceeds the first specified temperature, or when the difference between the temperature of the heat medium passing through the utilization side heat exchanger and the refrigerant condensation temperature of the low-level side heat exchanger of the low-level side refrigerant circuit is less than the second specified temperature, the control unit switches the first switching unit in such a manner that the heat medium flows in the second heat medium circulation path.

4. The secondary refrigeration device according to claim 1, characterized in that: A four-way valve is provided in the low-stage side refrigerant circuit, and the four-way valve is connected to the discharge side of the low-stage side compressor, so as to switch the low-stage side refrigerant discharged from the low-stage side compressor to flow toward the step heat exchanger side and the low-stage side heat exchanger side, or to flow toward the heat source side heat exchanger side.

5. The secondary refrigeration device according to claim 4, characterized in that: The low-stage heat exchanger includes a first heat storage unit having a heat storage material.

6. The secondary refrigeration device according to claim 5, characterized in that: When the temperature of the heat storage material is equal to or higher than a predetermined temperature, the control unit switches the four-way valve to the heat source side heat exchanger side to perform a defrosting operation using heat stored in the heat storage material.

7. The two-stage refrigeration device according to claim 1, characterized in that: The secondary refrigeration device has: a third heat medium circulation path, in which a second bypass path provided with a stop valve, a second circulation pump, and a second heat storage unit having a heat storage material is connected in parallel with the first bypass path in the heat medium circuit, and the second circulation pump, the stop valve, the low-stage heat exchanger, and the second heat storage unit are connected in sequence by a refrigerant pipe so that the heat medium circulates; a second switching unit for switching, in the heat medium circuit, whether the heat medium flows through the first heat medium circulation path or the third heat medium circulation path; as well as A four-way valve is connected to the discharge side of the low-stage side compressor in the low-stage side refrigerant circuit, and switches the low-stage side refrigerant discharged from the low-stage side compressor to flow toward the stepped heat exchanger side and the low-stage side heat exchanger side or to flow toward the heat source side heat exchanger side.

8. The secondary refrigeration device according to claim 7, characterized in that: When starting the two-stage refrigeration device, the control unit starts the high-pressure side compressor, the low-pressure side compressor, and the first circulation pump, and switches the first switching unit and the second switching unit so that the heat medium flows in the first heat medium circulation path.

9. The two-stage refrigeration device according to claim 8, characterized in that: When the temperature of the heat medium passing through the utilization side heat exchanger exceeds the first specified temperature, or when the difference between the temperature of the heat medium passing through the utilization side heat exchanger and the refrigerant condensation temperature of the low-level side heat exchanger of the low-level side refrigerant circuit is less than the second specified temperature, the control unit switches the first switching unit in a manner that causes the heat medium to flow in the second heat medium circulation path, and switches the second switching unit in a manner that causes the heat medium to flow in the third heat medium circulation path.

10. The two-stage refrigeration device according to claim 9, characterized in that: When the temperature of the heat storage material is equal to or higher than a predetermined temperature, the control unit switches the four-way valve to the heat source side heat exchanger side to perform a defrosting operation using heat stored in the heat storage material.

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