Two-stage refrigeration device

Abstract

In a two-stage refrigerating apparatus, a two-stage refrigerating apparatus capable of suppressing a decrease in heating capacity caused by deterioration of startup operation due to rapid startup operation is provided. 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 passage (23) that exchanges heat with the high-stage side refrigerant at a stepped heat exchanger (13) and a second circulation passage (26) that exchanges heat with a heat medium at a low-stage side heat exchanger (24), and a heat medium circuit (4) that circulates a heat medium that exchanges heat with the high-stage side refrigerant at a high-stage side heat exchanger (11) and exchanges heat with the low-stage side refrigerant at the low-stage side heat exchanger (24) are provided. The heat medium circuit (4) has a first heat medium circulation passage (35) that circulates the heat medium at the high-stage side heat exchanger (11) and the low-stage side heat exchanger (24), and a second heat medium circulation passage (36) that circulates the heat medium at the high-stage side heat exchanger (11).

Description

TECHNICAL FIELD

[0001] The present application relates to a two-stage refrigeration device, and particularly to a two-stage refrigeration device capable of suppressing a decrease in heating capacity. BACKGROUND

[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 stepped heat exchanger (intermediate heat exchanger) in common. Moreover, the refrigerant circulating in the high-stage refrigerant circuit and the refrigerant circulating in the low-stage refrigerant circuit are caused to exchange heat in the stepped heat exchanger, and the high-temperature side refrigerant circulating in the high-stage refrigerant circuit is used to heat water to generate hot water.

[0003] Such a two-stage refrigeration device has a possibility that the high-stage refrigerant circuit and the low-stage refrigerant circuit become unbalanced from the time of startup to the time of stable state due to differences in refrigerant characteristics, temperature conditions at startup, and the like, and the compressor of the low-stage refrigerant circuit reaches a protective stop. Therefore, regarding the two-stage refrigeration device disclosed in Patent Literature 1, the ratio of the rotational speed of the compressor of the high-stage refrigeration circuit during startup operation (hereinafter, referred to as "startup operation") to the rotational speed of the compressor of the low-stage refrigeration circuit is set to be greater than the ratio at the time of stable operation. This is to prevent a protective stop caused by excessive high pressure of the low-stage refrigeration circuit during startup operation.

[0004] Patent Literature 1: Japanese Patent Application Publication No. 2013-213590 SUMMARY

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

[0006] In view of the above-described problems, an object of the present application is to provide a two-stage refrigeration device capable of suppressing a decrease in heating capacity caused by rapidly performing startup operation, regarding a two-stage refrigeration device.

[0007] One embodiment of the present application is a two-stage refrigeration device including: a high-stage refrigerant circuit that connects, in order, a high-stage compressor, a high-stage heat exchanger, a high-stage pressure-reducing mechanism, and a stepped heat exchanger with refrigerant pipes, so that a high-stage refrigerant circulates; a low-stage refrigerant circuit that has a first circulation passage that connects, in order, a low-stage compressor, the stepped heat exchanger, a low-stage first pressure-reducing mechanism, and a heat-source-side heat exchanger with refrigerant pipes, so that a low-stage refrigerant circulates, and that exchanges heat between the high-stage refrigerant and the low-stage refrigerant in the stepped heat exchanger, and a second circulation passage that connects, with refrigerant pipes, between the low-stage compressor and the stepped heat exchanger and between the low-stage first pressure-reducing mechanism and the heat-source-side heat exchanger in the first circulation passage, and that connects, in order, the low-stage compressor, a low-stage heat exchanger, a low-stage second pressure-reducing mechanism, and the heat-source-side heat exchanger with refrigerant pipes, so that the low-stage refrigerant circulates; a heat medium circuit that has a first heat medium circulation passage that connects, in order, a first circulation pump, a utilization-side heat exchanger, the low-stage heat exchanger, and the high-stage heat exchanger with pipes, so that a heat medium circulates, and that exchanges heat between the high-stage refrigerant and the heat medium in the high-stage heat exchanger and between the low-stage refrigerant and the heat medium in the low-stage heat exchanger, and a second heat medium circulation passage that has a first bypass passage that connects, with pipes, between the utilization-side heat exchanger and the low-stage heat exchanger and between the low-stage heat exchanger and the high-stage heat exchanger in the first heat medium circulation passage, and that connects, in order, the first circulation pump, the utilization-side heat exchanger, the first bypass passage, and the high-stage heat exchanger with pipes, so that the heat medium circulates; a first switching unit that exchanges heat between the high-stage refrigerant and the low-stage refrigerant in the stepped heat exchanger, and that switches, in the heat medium circuit, between causing the heat medium to flow in the first heat medium circulation passage and causing the heat medium to flow in the second heat medium circulation passage; and a control unit that 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 application, a two-stage refrigeration device that can suppress a decrease in heating capacity caused by rapid startup operation can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1A FIG. 1 is a refrigerant circuit diagram of a two-stage refrigeration device according to an embodiment of the present application.

[0011] Figure 1B FIG. 1 is a refrigerant circuit diagram of a two-stage refrigeration device according to an embodiment of the present application.

[0012] Figure 1C is a view showing the flow of refrigerant in the second operation mode of the two-stage refrigeration device to which the embodiment of the present application relates.

[0013] Figure 2 is a control block diagram of the two-stage refrigeration device to which the embodiment of the present application relates.

[0014] Figure 3 is a control flowchart of the two-stage refrigeration device to which the embodiment of the present application relates.

[0015] Figure 4A is a refrigerant circuit diagram of the two-stage refrigeration device to which the other embodiment of the present application relates.

[0016] Figure 4B is a view showing the flow of refrigerant in the first operation mode of the two-stage refrigeration device to which the other embodiment of the present application relates.

[0017] Figure 4C is a view showing the flow of refrigerant in the second operation mode of the two-stage refrigeration device to which the other embodiment of the present application relates.

[0018] Figure 5 is a control block diagram of the two-stage refrigeration device to which the other embodiment of the present application relates.

[0019] Figure 6 is a control flowchart of the two-stage refrigeration device to which the other embodiment of the present application relates. DETAILED DESCRIPTION

[0020] Hereinafter, the embodiment of the two-stage refrigeration device to which the present application relates will be described in detail based on the drawings. Moreover, the present application is not limited by this embodiment.

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

[0022] EMBODIMENT

[0023] REFERENCE Figures 1A-1C The two-stage refrigeration device 1 of the present embodiment will be described. Figure 1Ais a refrigerant circuit diagram of the two-stage refrigerating apparatus 1 of the present embodiment. The two-stage refrigerating apparatus 1 is a refrigerating apparatus that can be used for a cooling operation in a case where the utilization-side heat exchanger 31 is used as an evaporator, and can be used for a hot-water generating operation or a heating operation in a case where the utilization-side heat exchanger 31 is used as a condenser. Hereinafter, the hot-water generating operation and the heating operation will be sometimes collectively referred to as a heating operation. In the present embodiment, the two-stage refrigerating apparatus for the heating operation will be described. The two-stage refrigerating apparatus 1 has a high-stage side refrigerant circuit 2, a low-stage side refrigerant circuit 3, a heat medium circuit 4, and a control unit 5. The control unit 5 includes a storage unit that stores data such as a target temperature, software for control, and the like, and controls the two-stage refrigerating apparatus 1.

[0024] The high-stage side refrigerant circuit 2 connects, in order, the high-stage side compressor 10, the high-stage side heat exchanger 11, the high-stage side expansion valve 12 as a high-stage side pressure reducing mechanism, and the stepped heat exchanger 13 by means of the refrigerant pipe 6, and circulates the high-stage side refrigerant. In the present embodiment, the high-stage side heat exchanger 11 is a heat exchanger that exchanges heat between the high-stage side refrigerant and the heat medium flowing in the heat medium circuit 4. The stepped heat exchanger 13 is a heat exchanger that exchanges heat between the high-stage side refrigerant and the low-stage side refrigerant flowing in the low-stage side refrigerant circuit 3. Further, if the high-stage side heat exchanger 11 and the stepped heat exchanger 13 are heat exchangers that can exchange heat between liquids, they can be, for example, plate heat exchangers or double-pipe heat exchangers. In addition, in the present embodiment, the high-stage side heat exchanger 11 is a heat exchanger that exchanges heat between the high-stage side refrigerant and the heat medium flowing in the heat medium circuit 4, and can be, for example, a heat exchanger that exchanges heat with air as the heat medium via a non-illustrated air blower. The arrow of the high-stage side refrigerant circuit 2 indicates the flow of the high-stage side refrigerant at the time of the heating operation.

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

[0026] The low-stage side refrigerant circuit 3 has a first circulation passage 23 and a second circulation passage 26. With respect to the first circulation passage 23, the low-stage side refrigerant circuit 3 is connected between the low-stage side compressor 20 and the stepped heat exchanger 13, between the low-stage side first expansion valve 21 and the heat-source side heat exchanger 22, and the low-stage side refrigerant is circulated by the refrigerant pipe 6 in this order. The heat-source side heat exchanger 22 is a heat exchanger that exchanges heat between the low-stage side refrigerant and outside air. The heat-source side heat exchanger 22 is provided with a condensing temperature detection sensor 22a that detects the condensing temperature of the low-stage side refrigerant flowing in the heat-source side heat exchanger 22. The stepped heat exchanger 13 is a heat exchanger that exchanges heat between the low-stage side refrigerant and the high-stage side refrigerant circuit 2. The stepped heat exchanger 13 is provided with a condensing temperature detection sensor 13a that detects the condensing temperature (refrigerant condensing temperature) of the low-stage side refrigerant flowing in the stepped heat exchanger 13, and an outlet temperature detection sensor 13b that detects the outlet temperature of the low-stage side refrigerant. The arrows of the low-stage side refrigerant circuit 3 indicate the flow of the low-stage side refrigerant.

[0027] The low-stage side refrigerant circuit 3 has a second circulation passage 26 that circulates the low-stage side refrigerant. The second circulation passage 26 connects the low-stage side compressor 20 and the stepped heat exchanger 13, and the low-stage side first expansion valve 21 and the heat-source side heat exchanger 22, by the refrigerant pipe provided with the low-stage side heat exchanger 24 and the low-stage side second expansion valve 25, and connects the low-stage side compressor 20, the low-stage side heat exchanger 24, the low-stage side second expansion valve 25, and the heat-source side heat exchanger 22 in this order by the refrigerant pipe. The low-stage side heat exchanger 24 is a heat exchanger that exchanges heat between the low-stage side refrigerant and the heat medium circuit 4, and has a first heat storage portion that has a heat storage material. The low-stage side heat exchanger 24 is provided with a condensing temperature detection sensor 24a that detects the condensing temperature of the low-stage side refrigerant flowing in the low-stage side heat exchanger 24, and an outlet temperature detection sensor 24b that detects the outlet temperature of the low-stage side refrigerant. Further, a heat medium return temperature detection sensor 24c that detects the heat medium return temperature, which is the temperature of the heat medium flowing in the low-stage side heat exchanger 24 as the heat medium flowing in the heat medium circuit 4, is provided. If the low-stage side heat exchanger 24 is a heat exchanger that exchanges heat between liquids, it can be, for example, a plate heat exchanger or a double-pipe heat exchanger.

[0028] In the low-stage refrigerant circuit 3, the low-stage four-way valve 27, which switches the flow of the low-stage refrigerant discharged from the low-stage compressor 20 to the step-type heat exchanger 13 side and the low-stage heat exchanger 24 side or 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 where the low-stage four-way valve 27 is used to cause the low-stage refrigerant discharged from the low-stage compressor 20 to flow to the step-type heat exchanger 13 side and the low-stage heat exchanger 24 side (heating operation) will be described. In this case, in the low-stage refrigerant circuit 3, the low-stage refrigerant discharged from the low-stage compressor 20 is caused to flow through the step-type heat exchanger 13, the low-stage first expansion valve 21, and the heat-source side heat exchanger 22 and is then sucked into the low-stage compressor 20. In addition, the low-stage refrigerant discharged from the low-stage compressor 20 is caused to flow through the low-stage heat exchanger 24, the low-stage second expansion valve 25, and the heat-source side heat exchanger 22 and is then sucked into the low-stage compressor 20.

[0029] In the low-stage refrigerant circuit 3, the low-stage compressor 20, the heat-source side heat exchanger 22, and the low-stage four-way valve 27 are common to the first circulation passage 23 and the second circulation passage 26.

[0030] The heat medium circuit 4 connects, in order, the first circulation pump 30, the utilization side heat exchanger 31, the low-stage heat exchanger 24, and the high-stage heat exchanger 11 by a pipe 32 and circulates water as a heat medium. In addition, instead of water, a non-freezing solution can be used as the heat medium. The utilization side heat exchanger 31 is provided in an indoor unit not shown that is provided in a room, and indoor air is caused to flow into the utilization side heat exchanger 31 by an air current generated by a blower fan not shown. The water as a heat medium and the air in the room in which the indoor unit is provided are caused to exchange heat in the utilization side heat exchanger 31, and the air that has exchanged heat with the water as a heat medium is used for heating. The high-stage heat exchanger 11 is a heat exchanger that causes the water as a heat medium and the high-stage refrigerant flowing in the high-stage refrigerant circuit 2 to exchange heat. The low-stage heat exchanger 24 is a heat exchanger that causes the water as a heat medium and the low-stage refrigerant flowing in the low-stage refrigerant circuit 3 to exchange heat. The arrow of the heat medium circuit 4 indicates the flow of the water as a heat medium.

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

[0032] The two-stage freezing device 1 has a first operation mode in which the heat medium flows in the first heat medium circulation passage 35, and a second operation mode in which the heat medium does not flow in the low-stage-side heat exchanger 24 and flows in the second heat medium circulation passage 36. Figure 1B represents a state in which the heat medium is circulated in the first heat medium circulation passage 35 according to the first operation mode. Figure 1C represents a state in which the heat medium is circulated in the second heat medium circulation passage 36 according to the second operation mode. The first operation mode is a heating operation in which heat absorbed from the outside air by the heat source-side heat exchanger 22 of the low-stage-side refrigerant circuit 3 is released to the air in the room 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 operation mode is an operation in which the heat medium does not flow in the low-stage-side heat exchanger 24 and flows in the second heat medium circulation passage 36. The second operation mode is performed when the temperature of the heat medium flowing out from the utilization-side heat exchanger 31 and flowing into the low-stage-side heat exchanger 24, that is, 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, which is measured by the condensation temperature detection sensor 24a.

[0033] The two-stage freezing device 1 is a freezing device that utilizes the latent heat of the high-stage side refrigerant of the high-stage side refrigerant circuit 2, the latent heat of the low-stage side refrigerant of the low-stage side 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 side refrigerant of the high-stage side refrigerant circuit 2 and the low-stage side refrigerant of the low-stage side refrigerant circuit 3 are the same refrigerant, but need not be the same, and can be, for example, a low-stage side refrigerant having a lower boiling point than the high-stage side refrigerant. In addition, a refrigerant that can change the latent heat to 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 provided as a pressure reducing mechanism in the path between the utilization side heat exchanger 31 and the low-stage side heat exchanger 24.

[0034] Regarding the two-stage freezing device 1, the low-stage side refrigerant, which is a low-temperature and low-pressure gas-phase refrigerant, is compressed to a high-temperature and high-pressure gas-phase refrigerant in the low-stage side compressor 20 with heat absorption from the outside air by the heat source side heat exchanger 22 of the low-stage side refrigerant circuit 3. Further, 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 to become 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 to a high-temperature and high-pressure gas-phase refrigerant in the high-stage side compressor 10. The high-temperature and high-pressure gas-phase refrigerant releases heat to the water that is the heat medium circulating in the heat medium circuit 4 in the high-stage side heat exchanger 11 to generate hot water. In addition, the low-stage side refrigerant, which is a low-temperature and low-pressure gas-phase refrigerant, is compressed to a high-temperature and high-pressure gas-phase refrigerant in the low-stage side compressor 20 with heat absorption from the outside air by the heat source side heat exchanger 22 of the low-stage side refrigerant circuit 3. The high-temperature and high-pressure gas-phase refrigerant releases heat to the water that is the heat medium circulating in the heat medium circuit 4 in the low-stage side heat exchanger 24. Thus, the low-stage side refrigerant circulating in the low-stage side refrigerant circuit 3 can be condensed using the water that is the heat medium circulating in the heat medium circuit 4.

[0035] Regarding the two-stage freezing device of the related art, the ratio (R1 / R2) of the rotation speed (R1) of the compressor of the high-stage side refrigeration circuit during startup operation to the rotation speed (R2) of the compressor of the low-stage side refrigeration circuit is set to be higher than the ratio during stable operation. Thus, the low-stage side refrigeration circuit is suppressed from not being condensed and generating high pressure excess to cause the compressor of the low-stage side refrigeration circuit to become a protection stop state. However, in the related art, the rotation speed of the compressor of the low-stage side refrigeration circuit during startup operation is limited, and thus in the startup operation, time is taken until sufficient heating capacity is exerted. On the other hand, the two-stage freezing device 1 of the present embodiment has the high-stage side refrigerant circuit 2 and the low-stage side refrigerant circuit 3 having the first circulation passage 23 and the second circulation passage 26. Further, in the first operation mode, as described above, the rotation speed of the compressor of the low-stage side refrigeration circuit is not limited during startup operation, and thus the low-stage side refrigeration circuit is not suppressed from not being condensed and generating high pressure excess to cause the compressor of the low-stage side refrigeration circuit to become a protection stop state. Thus, the low-stage side refrigeration circuit can be condensed and the low-stage side refrigeration circuit can exert sufficient heating capacity during startup operation. Figure 1BAs shown, in the high-side heat exchanger 11 of the high-side refrigerant circuit 2 and the low-side heat exchanger 24 of the second circulation path 26 of the low-side refrigerant circuit 3, the low-side refrigerant and the circulating heat medium in the heat medium circuit 4 exchange heat. This allows the low-side refrigerant circulating in the low-side refrigerant circuit 3 to directly exchange heat and condense with the circulating heat medium in the heat medium circuit 4, thus suppressing the compressor's protective shutdown in the low-side refrigeration circuit and enabling rapid start-up.

[0036] On the other hand, if the first operating mode continues, the air that has exchanged heat with the heat medium in the utilization side heat exchanger 31 will be heated. Therefore, the temperature of the heat medium flowing out of the utilization side heat exchanger 31 and into the low-level side heat exchanger 24 (heat medium return temperature) 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. A greater amount of uncondensed gaseous refrigerant is distributed in the low-level side heat exchanger 24, where a greater amount of liquid-phase low-level side refrigerant was originally distributed, causing the liquid-phase low-level side refrigerant to excessively linger in other paths of the low-level side refrigeration circuit (e.g., an accumulator not shown on the suction side of the low-level side compressor 20). Therefore, liquid compression may occur in the low-level side compressor 20. In addition, the refrigerant on the lower side can be condensed in the lower side heat exchanger 24, so if the speed of the lower side compressor 20 is increased, the reliability of the lower side compressor 20 may decrease.

[0037] However, the secondary refrigeration unit 1 of this embodiment has a second operating mode in which the heat medium does not flow into the low-level heat exchanger 24 but flows in the second heat medium circulation path 36. The second operating mode operates as follows: Figure 1C As shown, when the return temperature of the heat medium is high and close to the condensation temperature of the low-side refrigerant, the heat medium does not flow in the low-side heat exchanger 24, but instead circulates in the second heat medium circulation path 36. By operating in the second mode, the high-temperature heat medium is prevented from flowing into the low-side heat exchanger 24, so the low-side refrigerant exchanges heat with the surrounding air via the low-side heat exchanger 24 and the refrigerant piping 6. This prevents the low-side refrigerant flowing into the low-side heat exchanger 24 from condensing, thus allowing the low-side heat exchanger 24 to function as a condenser without increasing the speed of the low-side compressor 20. Furthermore, since the secondary refrigeration unit 1 of this embodiment has a second operating mode, it is preferable that the low-side heat exchanger 24 is a dual-tube heat exchanger with an outer peripheral flow path and an inner peripheral flow path, and that the low-side refrigerant flows in the outer peripheral flow path while water, as the heat medium, flows in the inner peripheral flow path. This facilitates heat dissipation and condensation of the low-side refrigerant.

[0038] Next, the control of the two-stage freezing device 1 according to the present embodiment will be described with reference to the control flowchart shown in Fig. 6. Figure 2 The control unit 5 has a first supercooling degree calculating unit 45, a second supercooling degree calculating unit 46, and a storage unit 47. The first supercooling degree calculating unit 45 calculates the supercooling degree of the low-stage side refrigerant of the stepped heat exchanger 13. The second supercooling degree calculating unit 46 calculates the supercooling degree of the low-stage side refrigerant of the low-stage side heat exchanger 24. Further, the storage unit 47 stores, for example, data such as a target temperature, software for control, a program for calculating the supercooling degree, and the like. The condensing temperature of the low-stage side refrigerant flowing in the stepped heat exchanger 13 measured by the condensing temperature detecting sensor 13a and the outlet temperature of the low-stage side refrigerant flowing in the stepped heat exchanger 13 measured by the outlet temperature detecting sensor 13b are input to the first supercooling degree calculating unit 45. The condensing temperature of the low-stage side refrigerant flowing in the low-stage side heat exchanger 24 measured by the condensing temperature detecting sensor 24a and the outlet temperature of the low-stage side refrigerant flowing in the low-stage side heat exchanger 24 measured by the outlet temperature detecting sensor 24b are input to the second supercooling degree calculating unit 46. Further, 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 of the first circulating 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 conditioning space and the set temperature specified by the user) when the heating operation using the utilization side heat exchanger 31 is performed, and the target heat medium temperature is set to a larger value as the air conditioning load is larger.

[0039] Further, the heat medium return temperature measured by the heat medium return temperature detecting sensor 24c and the condensing temperature of the heat source side heat exchanger 22 measured by the condensing temperature detecting sensor 22a are input to the control unit 5. The control of the first three-way valve 34 is performed based on the heat medium return temperature and the condensing temperature of the heat source side heat exchanger 22 input to the control unit 5.

[0040] The control unit 5 determines the rotation speeds of the high-stage side compressor 10 and the low-stage side compressor 20 based on the target heat medium temperature. Further, the control of the low-stage side first expansion valve 21 is performed based on the supercooling degree of the low-stage side refrigerant of the stepped heat exchanger 13 calculated by the first supercooling degree calculating unit 45. Further, the control of the low-stage side second expansion valve 25 is performed based on the supercooling degree of the low-stage side refrigerant of the low-stage side heat exchanger 24 calculated by the second supercooling degree calculating unit 46.

[0041] Next, the control of the two-stage freezing device 1 according to the present embodiment will be described with reference to the control flowchart shown in Fig. 6. Figure 3 The control of the two-stage freezing device 1 according to the present embodiment will be described with reference to the control flowchart shown in Fig. 6.

[0042] The control portion first starts the first operation mode (ST1). In the first operation mode, the first three-way valve 34 is switched in a manner such that the heat medium flows in the first heat medium circulation path 35. Next, the first circulation pump 30 is started (ST2). Next, a start-up operation is performed (ST3). With the start-up operation, the high-stage side compressor 10 and the low-stage side compressor 20 are started, the opening degrees of the high-stage side expansion valve 12, the low-stage side first expansion valve 21, and the low-stage side second expansion valve 25 are maintained at predetermined initial opening degrees, and the high-stage side refrigerant is circulated in the high-stage side refrigerant circuit 2. In addition, the low-stage side refrigerant is circulated in the first circulation path 23 and the second circulation path 26 of the low-stage side refrigerant circuit 3. Here, the initial opening degrees are the opening degrees of the high-stage side expansion valve 12, the low-stage side first expansion valve 21, and the low-stage side second expansion valve 25 from the start of the operation of the two-stage freezing device 1 until the high-stage side refrigerant circuit 2 and the low-stage side refrigerant circuit 3 stabilize. The initial opening degrees are determined in accordance with the performance of the high-stage side compressor 10 and the low-stage side compressor 20 and are set in advance.

[0043] Next, if a prescribed time elapses, the startup operation is ended (ST4). The prescribed time is, for example, 10 minutes. The prescribed time is a minimum time required until the secondary refrigeration device 1 becomes a stable operation state converging according to a load, and is determined in advance based on experiments or the like. After the startup operation is ended, the normal operation is switched (ST5). In the normal operation, the low-side first expansion valve 21 and the low-side second expansion valve 25 are controlled in such a manner that the low-side refrigerant at the outlet of the stepped heat exchanger 13 and the low-side refrigerant at the outlet of the low-side heat exchanger 24 respectively reach prescribed supercooling degrees. Here, the prescribed supercooling degrees are fixed values set in advance, and are set to values of 1 deg or more in order not to cause the low-side refrigerant in a two-phase state to flow into each expansion valve. In addition, with respect to the high-side expansion valve 12, suction superheat control is performed in which the suction superheat degree of the high-side compressor 10 is controlled to a target value. The target value is a fixed value set in advance, and is set to a value of 1 deg or more in order to cause the high-side refrigerant suctioned into the high-side compressor 10 to become an appropriate refrigerant state. Furthermore, instead of the suction superheat control with respect to the high-side expansion valve 12, target discharge temperature control or supercooling degree control can be performed. Next, it is determined whether or not the heat medium return temperature after flowing out from the utilization-side heat exchanger 31 is lower than a prescribed value (first prescribed temperature) (ST6). The prescribed value (first prescribed temperature) is a variable, and is, for example, a temperature 2°C lower than the condensation temperature of the low-side refrigerant. Alternatively, with respect to the condition of step ST6, it can be determined whether or not the difference between the heat medium return temperature after flowing out from the utilization-side heat exchanger 31 and the condensation temperature of the low-side refrigerant suctioned into the low-side heat exchanger 24, which is detected by the condensation temperature detection sensor 24a of the low-side refrigerant circuit 3, is 2°C or more. The second prescribed temperature is a value such that, if lower than the value, the low-side refrigerant does not condense in the low-side heat exchanger 24, and it is likely that liquid compression occurs in the low-side compressor 20. In a case where the heat medium return temperature is not lower than the prescribed value (No of ST6), the second operation mode is started (ST7). With respect to the second operation mode, the first three-way valve 34 is switched in such a manner that the heat medium flows in the second heat medium circulation passage 36. In a case where the heat medium return temperature is not lower than the prescribed value, high-temperature high-pressure low-side refrigerant in a gas phase state passing through the low-side heat exchanger 24 cannot be radiated in some cases. However, by performing the second operation mode, the high-temperature heat medium is not caused to flow into the low-side heat exchanger 24. Therefore, the low-side refrigerant suctioned into the low-side heat exchanger 24 is radiated by exchanging heat with the surrounding air via the low-side heat exchanger 24 and the refrigerant pipe 6, and thus it is possible to suppress the low-side refrigerant from not condensing. Next, target supercooling degree control is performed in such a manner that the supercooling degree of the low-side refrigerant at the outlet of the low-side heat exchanger 24 reaches a target supercooling degree (ST8).If the target supercooling degree control is performed, the opening degree of the low-stage second expansion valve 25 is controlled in the closing direction, finally closed, or opened with a slight degree in a manner such that supercooling is achieved. The target supercooling degree control is the control of the low-stage second expansion valve 25 via the second supercooling degree calculation unit 46.

[0044] Next, it is determined whether a defrosting start condition is satisfied (ST9). The defrosting start condition is, for example, a case where the heating operation is continued for 3 hours while the outside air temperature is less than or equal to 5°C, or a case where the temperature detected by the condensing temperature detection sensor 22a of the heat source-side heat exchanger 22 is less than or equal to -15°C. In a case where the defrosting start condition is satisfied (Yes in ST9), the low-stage four-way valve 27 is switched to the so-called refrigeration cycle side to start the defrosting operation (ST14), and the defrosting operation is ended after a prescribed time elapses (ST15). The prescribed time is a time set in advance, and is a time (for example, 10 minutes) sufficient for the frost adhering to the heat source-side heat exchanger 22 to be melted by the defrosting operation. On the other hand, in a case where the defrosting start condition is not satisfied (No in ST9), it is determined whether the heat medium return temperature is lower than a prescribed value (ST10). In a case where the heat medium return temperature is not lower than the prescribed value (No in ST10), the target supercooling degree control is continued before returning to ST9. In a case where the heat medium return temperature is lower than the prescribed value (Yes in ST10), the first operation mode is switched (ST11). Regarding the first operation mode, the first three-way valve 34 is switched in a manner such that the heat medium flows in the first heat medium circulation path 35. As a result, the low-stage second expansion valve 25, which is controlled by the target supercooling degree control, is controlled in the opening direction from the closed or slightly opened state (ST12). After the first operation mode is switched, if the target supercooling degree control is performed, the low-stage refrigerant in the high-temperature and high-pressure gaseous phase that passes through the low-stage heat exchanger 24 can be radiated and condensed. Therefore, the opening degree of the low-stage second expansion valve 25 is controlled in the opening direction in a manner such that the supercooling degree of the low-stage refrigerant after passing through the low-stage heat exchanger 24 reaches the target supercooling degree. The target supercooling degree control is the control of the low-stage second expansion valve 25 via the second supercooling degree calculation unit 46. The target supercooling degree control is continued before returning to ST6.

[0045] In the case where the heat medium return temperature is lower than the prescribed value (Yes in ST6), it is determined whether a defrosting start condition is satisfied (ST13). The defrosting start condition is determined on the basis of the outside air temperature and the temperature detected by the condensing temperature detection sensor 22a of the heat source side heat exchanger 22. In the case where the defrosting start condition is satisfied (Yes in ST13), the defrosting operation is started (ST14), and after a prescribed time elapses, the defrosting operation is ended (ST15). On the other hand, in the case where the defrosting start condition is not satisfied (No in ST13), the process returns to before ST6 and it is determined whether the heat medium return temperature is lower than the prescribed value (ST6).

[0046] Next, the operation of the secondary refrigeration device 50 will be described with reference to Figures 4A-4C The secondary refrigeration device 50 according to another embodiment will be described. Figure 4A is a refrigerant circuit diagram of the secondary refrigeration device 50 according to another embodiment. Figure 4B is a view showing the flow of refrigerant in the first operation mode of the secondary refrigeration device 50 according to another embodiment of the present application. In addition, Figure 4C is a view showing the flow of refrigerant in the second operation mode of the secondary refrigeration device 50 according to another embodiment of the present application. The secondary refrigeration device 1 according to the first embodiment and the secondary refrigeration device 50 according to another embodiment differ in the following point. That is, the second bypass passage 37 is provided, which has one end connected to the pipe 32 between the first three-way valve 34 and the low-stage side heat exchanger 24 and the other end connected to the pipe 32 between the low-stage side heat exchanger 24 and the other end of the first bypass passage 33. Other structures are the same. Therefore, detailed description of the structures common to the secondary refrigeration device 1 according to the first embodiment will be omitted. In addition, the same reference numerals are used for the same structures.

[0047] The secondary refrigeration device 50 is a refrigeration device that can be used for the refrigeration operation in the case where the utilization side heat exchanger 31 is used as an evaporator and for the hot water generation operation or the heating operation in the case where the utilization side heat exchanger 31 is used as a condenser. Hereinafter, the hot water generation operation and the heating operation will be collectively referred to as the heating operation. In the present embodiment, the secondary refrigeration device for the heating operation will be described.

[0048] The two-stage freezing device 50 has a high-stage side refrigerant circuit 2, a low-stage side refrigerant circuit 3, a heat medium circuit 4, and a control section 5 that controls the two-stage freezing device 50. The heat medium circuit 4 has a first bypass passage 33 and a second bypass passage 37. With respect to the first bypass passage 33, one end is connected to a pipe 32 between the utilization side heat exchanger 31 and the low-stage side heat exchanger 24, and the other end is connected to a pipe between the low-stage side heat exchanger 24 and the high-stage side heat exchanger 11. With respect to the second bypass passage 37, one end is connected to the pipe 32 between the first three-way valve 34 and the low-stage side heat exchanger 24, and the other end is connected to the pipe 32 between the low-stage side 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 that is a second switching unit is provided at the other end of the second bypass passage 37. Further, a heat storage section 39 (corresponding to a second heat storage section) having a heat storage material, a second circulation pump 40, and a stop valve 41 are provided from the other end toward the one end of the second bypass passage 37. The second three-way valve 38 switches the flow of water as a heat medium in the first heat medium circulation passage 35 and the flow in the third heat medium circulation passage 42. The heat storage section 39 stores heat taken from the low-stage side refrigerant by the low-stage side heat exchanger 24 via water as a heat medium. In addition, a temperature detection sensor 39a that detects the temperature of the heat storage section 39 is provided in the heat storage section 39. The second circulation pump 40 causes water as a heat medium to flow from the other end toward the one end of the second bypass passage 37. The stop valve 41 is a valve that causes water as a heat medium to flow from the other end toward the one end of the second bypass passage 37 and does not cause it to flow from the one end toward the other end.

[0050] The two-stage freezing device 50 has a first operation mode in which the heat medium flows in the first heat medium circulation passage 35, and a second operation mode in which the heat medium flows in the second heat medium circulation passage 36 and the third heat medium circulation passage 42. With respect to the first operation mode, the heat source side heat exchanger 22 of the low-stage side refrigerant circuit 3 takes heat from the outside air, and the heat taken 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 side refrigerant circuit 3. Further, it is an operation for radiating heat from the heat medium of the heat medium circuit 4 after taking heat to the air in the room. With respect to the second operation mode, it is an operation in which the heat source side heat exchanger 22 of the low-stage side refrigerant circuit 3 takes heat from the outside air, and radiates heat from the heat medium of the heat medium circuit 4 to the air in the room via the high-stage side refrigerant circuit 2. In addition, with respect to the second operation mode, it is an operation in which the heat source side heat exchanger 22 of the low-stage side refrigerant circuit 3 takes heat from the outside air, and accumulates the heat taken from the outside air in the heat storage section 39 of the heat medium circuit 4.

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

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

[0053] Further, the heat medium return temperature detected by the heat medium return temperature detection sensor 24c, the condensing temperature of the heat source side heat exchanger 22 detected by the condensing temperature detection sensor 22a, and the temperature of the heat storage portion 39 detected by the temperature detection sensor 39a are input to the control portion 5. The control of the first three-way valve 34, the second three-way valve 38, and the second circulating pump 40 is performed based on the heat medium return temperature, the temperature of the heat source side heat exchanger 22, and the temperature of the heat storage portion 39 input to the control portion 5. That is, in order to prevent the heat medium return temperature from being higher than the condensing temperature of the low-stage side refrigerant flowing into the heat source side heat exchanger 22, the heat medium is radiated by the heat storage portion 39.

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

[0055] With respect to the two-stage freezing device 50 of the present embodiment, the heat accumulated in the heat storage portion 39 in the second operation mode is used for a defrosting operation for removing frost adhering to the heat source side heat exchanger 22. The defrosting operation is performed in the following manner. 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 switching is performed in such a manner that the low-stage side refrigerant discharged from the low-stage side compressor 20 flows to the heat source side heat exchanger 22 side, 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 evaporators. The low-stage side first expansion valve 21 and the low-stage side second expansion valve 25 are set to an opening degree close to full opening. 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 part of the low-stage side refrigerant flowing out from 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 circulating passage 42 in which the heat storage portion 39 is provided. The remaining low-stage side refrigerant flowing out from 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 in which the high-stage side compressor 10 is stopped. The low-stage side refrigerant after the heat absorption flows into the heat source side heat exchanger 22 again via the low-stage side compressor 20 and melts the frost.

[0056] Reference Signs List Figure 6The control flowchart shown explains the control of the two-stage freezing device 50 according to the present embodiment.

[0057] The control unit first starts the first operation mode (ST21). With the first operation mode, the first three-way valve 34 is switched in a manner that causes the heat medium to flow in the first heat medium circulation path 35. Next, the first circulation pump 30 is activated (ST22). Next, the activation operation is performed (ST23). With the activation operation, the high-stage side compressor 10 and the low-stage side compressor 20 are activated, and the opening degrees of the high-stage side expansion valve 12, the low-stage side first expansion valve 21, and the low-stage side second expansion valve 25 are maintained at predetermined initial opening degrees. Thereby, the high-stage side refrigerant is circulated in the high-stage side refrigerant circuit 2, and the low-stage side refrigerant is circulated in the first circulation path 23 and the second circulation path 26 of the low-stage side refrigerant circuit 3. The initial opening degrees are the opening degrees of the high-stage side expansion valve 12, the low-stage side first expansion valve 21, and the low-stage side second expansion valve 25 from when the two-stage freezing device 50 starts operation until the high-stage side refrigerant circuit 2 and the low-stage side refrigerant circuit 3 stabilize. The initial opening degrees are determined in accordance with the performance of the high-stage side compressor 10 and the low-stage side compressor 20, and are set in advance.

[0058] Next, if a prescribed time elapses, the startup operation is ended (ST24). The prescribed time is, for example, 10 minutes. The prescribed time is a minimum time required until the secondary refrigerant device 50 becomes a stable operation state converging according to a load, and is determined in advance according to experiments and the like. After the startup operation is ended, the normal operation is switched (ST25). Regarding the normal operation, the low-side first expansion valve 21 and the low-side second expansion valve 25 are controlled in such a manner that the low-side refrigerant at the outlet of the stepped heat exchanger 13 and the low-side refrigerant at the outlet of the low-side heat exchanger 24 reach a prescribed subcooling degree. The prescribed subcooling degree is a fixed value set in advance in such a manner that the low-side refrigerant in a two-phase state does not flow into each expansion valve, and is set to a value of at least 1 deg or more. In addition, the high-side expansion valve 12 performs suction superheat control that controls the suction superheat degree of the high-side compressor 10 to a target value. The target value is a fixed value set in advance in such a manner that the high-side refrigerant sucked into the high-side compressor 10 becomes an appropriate refrigerant state, and is set to a value of 1 deg or more. Further, the high-side expansion valve 12 can perform target discharge temperature control or subcooling degree control without performing the suction superheat control. Next, it is determined whether or not the heat medium return temperature after flowing out from the utilization-side heat exchanger 31 is lower than a prescribed value (first prescribed temperature) (ST26). The prescribed value (first prescribed temperature) is a variable, and is, for example, a temperature that is 2°C lower than the condensation temperature of the low-side refrigerant. Alternatively, regarding the condition of step ST26, it can be determined whether or not the difference between the heat medium return temperature after flowing out from the utilization-side heat exchanger 31 and the condensation temperature of the low-side refrigerant flowing into the low-side heat exchanger 24 measured by the condensation temperature detection sensor 24a of the low-side refrigerant circuit 3 is 2 deg or more. The second prescribed temperature is a value such that, if lower than the value, the low-side refrigerant does not condense in the low-side heat exchanger 24, and it is likely that liquid compression occurs in the low-side compressor 20. In the case where the heat medium return temperature is not lower than the prescribed value (No of 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 in such a manner that the heat medium flows in the second heat medium circulation passage 36, and the heat quantity sucked from the outside air is accumulated in the heat storage portion 39 of the heat medium circuit 4. The second operation mode is performed for a prescribed time to complete the heat storage into the heat storage portion 39 (ST28). Next, target subcooling degree control is performed in such a manner that the subcooling degree of the low-side refrigerant at the outlet of the low-side heat exchanger 24 reaches a target subcooling degree (ST29). If the target subcooling degree control is performed, the low-side second expansion valve 25 is controlled in the closing direction in such a manner that the opening degree is realized to achieve subcooling, and is finally closed or opened with a slight degree. The target subcooling degree control is control of the low-side second expansion valve 25 performed by the second subcooling degree calculation unit 46.

[0059] Next, it is determined whether a defrost start condition is satisfied (ST30). The defrost start condition is, for example, a case where the heating operation is continued for 3 hours while the outside air temperature is less than or equal to 5°C, or a case where the temperature detected by the condenser temperature detection sensor 22a of the heat source-side heat exchanger 22 is less than or equal to -15°C. In a case where the defrost start condition is satisfied (Yes in ST30), the low-stage four-way valve 27 is switched to the so-called refrigeration cycle side to start the defrost operation (ST35), and the defrost operation is ended after a prescribed time elapses (ST36). The prescribed time is a time set in advance and is a time (for example, 10 minutes) sufficient for the frost adhering to the heat source-side heat exchanger 22 to be melted by the defrost operation. On the other hand, in a case where the defrost start condition is not satisfied (No in ST30), it is determined whether the heat medium return temperature is lower than a prescribed value (ST31). In a case where the heat medium return temperature is not lower than the prescribed value (No in ST31), the target subcooling degree control is continued until before step ST30. In a case where the heat medium return temperature is lower than the prescribed value (Yes in ST31), the first operation mode is switched (ST32). In the first operation mode, the first three-way valve 34 is switched in such a manner that the heat medium flows in the first heat medium circulation path 35. As a result, the low-stage second expansion valve 25 is controlled in the opening direction from the closed or slightly open state by the target subcooling degree control (ST33). If the target subcooling degree control is performed after the first operation mode is switched, the high-temperature and high-pressure gas-phase low-stage refrigerant passing through the low-stage heat exchanger 24 can be cooled and condensed. Therefore, the low-stage second expansion valve 25 is controlled in the opening direction in such a manner that the subcooling degree of the low-stage refrigerant passing through the low-stage heat exchanger 24 after that reaches the target subcooling degree. The target subcooling degree control is the control of the low-stage second expansion valve 25 performed by the second subcooling degree calculation unit 46. The target subcooling degree control is continued until before step ST26.

[0060] In the case where the heat medium return temperature is lower than the prescribed value (Yes in ST26), it is judged whether a defrost start condition is satisfied (ST34). The defrost start condition is a condition related to the above-mentioned outside air temperature, and a temperature detected by the condensing temperature detection sensor 22a based on the heat source side heat exchanger 22. In the case where the defrost start condition is satisfied (Yes in ST34), it is judged whether the heat storage temperature of the heat storage portion 39 is higher than a prescribed value (ST37). The prescribed value is a temperature which is prescribed in advance by a test or the like, and judged to be able to obtain a sufficient heat storage amount which can be used for the defrost operation. In the case where the heat storage temperature of the heat storage portion 39 is higher than the prescribed value (Yes in ST37), the defrost operation is started (ST35), and after a prescribed time elapses, the defrost operation is ended (ST36). On the other hand, in the case where the heat storage temperature of the heat storage portion 39 is not higher than the prescribed 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 in such a manner that the heat medium flows in the second heat medium circulation path, and the heat amount sucked from the outside air is stored in the heat storage portion 39 of the heat medium circuit 4. The second operation mode is performed for a prescribed time, and the heat storage to the heat storage portion 39 is completed (ST39). Next, the defrost operation is started (ST35), and after a prescribed time elapses, the defrost operation is ended (ST36).

[0061] The above description has been made with reference to a limited number of embodiments, and the scope of the right is not limited thereto. It will be obvious to a person skilled in the art that changes based on the above-described embodiments are obvious.

[0062] Explanation of reference numerals

[0063] 1…two-stage freezing device, 2…high-stage side refrigerant circuit, 3…low-stage side refrigerant circuit, 4…heat medium circuit, 5…control unit, 6…refrigerant pipe, 10…high-stage side compressor, 11…high-stage side heat exchanger, 12…high-stage side expansion valve, 13…cascade heat exchanger, 13a…condensation temperature detection sensor, 13b…outlet temperature detection sensor, 14…high-stage side four-way valve, 20…low-stage side compressor, 21…low-stage side 1st expansion valve, 22…heat source side heat exchanger, 22a…condensation temperature detection sensor, 23…1st circulation path, 24…low-stage side heat exchanger, 24a…condensation temperature detection sensor, 24b…outlet temperature detection sensor, 24c…heat medium return temperature detection sensor, 25…low-stage side 2nd expansion valve, 26…2nd circulation path, 27…low-stage side four-way valve, 30…1st circulation pump, 31…use side heat exchanger, 32…pipe, 33…1st bypass path, 34…1st three-way valve, 35…1st heat medium circulation path, 36…2nd heat medium circulation path, 37…2nd bypass path, 38…2nd three-way valve, 39…heat storage unit, 39a…temperature detection sensor, 40…2nd circulation pump, 41…shut-off valve, 42…3rd heat medium circulation path, 45…1st supercooling degree calculation unit, 46…2nd supercooling degree calculation unit, 47…storage unit, 50…two-stage freezing device

Claims

1. A two-stage refrigeration device characterized by comprising: a high-stage side refrigerant circuit that connects, in order, a high-stage side compressor, a high-stage side heat exchanger, a high-stage side pressure reducing mechanism, and a stepped heat exchanger with refrigerant piping, so that a high-stage side refrigerant circulates; a low-stage side refrigerant circuit that has a first circulation path that connects, in order, a low-stage side compressor, the stepped heat exchanger, a low-stage side first pressure reducing mechanism, and a heat source side heat exchanger with refrigerant piping, so that a low-stage side refrigerant circulates, and a second circulation path that connects, with refrigerant piping, between the low-stage side compressor and the stepped heat exchanger and between the low-stage side first pressure reducing mechanism and the heat source side heat exchanger in the first circulation path, and connects, in order, the low-stage side compressor, a low-stage side second pressure reducing mechanism, and the heat source side heat exchanger with refrigerant piping, so that the low-stage side refrigerant circulates; a heat medium circuit that has a first heat medium circulation path that connects, in order, a first circulation pump, a utilization side heat exchanger, the low-stage side heat exchanger, and the high-stage side heat exchanger with piping, so that a heat medium circulates, the high-stage side refrigerant and the heat medium exchange heat at the high-stage side heat exchanger, and the low-stage side refrigerant and the heat medium exchange heat at the low-stage side heat exchanger, and a second heat medium circulation path that has a first bypass path that connects, between the utilization side heat exchanger and the low-stage side heat exchanger and between the low-stage side heat exchanger and the high-stage side heat exchanger in the first heat medium circulation path, and connects, in order, the first circulation pump, the utilization side heat exchanger, the first bypass path, and the high-stage side heat exchanger with piping, so that the heat medium circulates; the high-stage side refrigerant and the low-stage side refrigerant exchange heat at the stepped heat exchanger, a first switching unit that switches, in the heat medium circuit, so that the heat medium flows in the first heat medium circulation path or in the second heat medium circulation path; and a control unit that controls the high-stage side refrigerant circuit, the low-stage side refrigerant circuit, and the heat medium circuit.

2. The two-stage refrigeration device according to claim 1, characterized in that: at the time of starting the two-stage refrigeration device, the control unit starts the high-stage side compressor, the low-stage 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 two-stage refrigeration device according to claim 2, characterized in that: ​ In a case where the temperature of the heat medium passing through the utilization-side heat exchanger exceeds a first prescribed temperature, or a case where the difference between the temperature of the heat medium passing through the utilization-side heat exchanger and the refrigerant condensation temperature of the low-stage-side heat exchanger of the low-stage-side refrigerant circuit is less than a second prescribed temperature, the control section switches the first switching unit in such a manner that the heat medium flows in the second heat medium circulation path.

4. The two-stage refrigerating apparatus according to claim 1, wherein A four-way valve is provided in the low-stage-side refrigerant circuit, and is connected to the discharge side of the low-stage-side compressor, and switches the flow of the low-stage-side refrigerant discharged from the low-stage-side compressor to the stepped heat exchanger side and the low-stage-side heat exchanger side, or to the heat-source-side heat exchanger side.

5. The two-stage refrigerating apparatus according to claim 4, wherein The low-stage-side heat exchanger has a first heat storage portion having a heat storage material.

6. The two-stage refrigerating apparatus according to claim 5, wherein In a case where the temperature of the heat storage material is greater than or equal to a prescribed temperature, the control section switches the four-way valve to the heat-source-side heat exchanger side, and performs a defrosting operation using the heat stored in the heat storage material.

7. The two-stage refrigerating apparatus according to claim 1, wherein The two-stage refrigerating apparatus has: a third heat medium circulation path in which a second bypass path provided with a second circulation pump, a second heat storage portion having a heat storage material, and a shutoff valve are connected in parallel to the first bypass path in the heat medium circuit, and the second circulation pump, the shutoff valve, the low-stage-side heat exchanger, and the second heat storage portion are connected in order by a refrigerant pipe so that the heat medium circulates; a second switching unit that switches the flow of the heat medium in the first heat medium circulation path or in the third heat medium circulation path in the heat medium circuit; and a four-way valve that is connected to the discharge side of the low-stage-side compressor in the low-stage-side refrigerant circuit, and switches the flow of the low-stage-side refrigerant discharged from the low-stage-side compressor to the stepped heat exchanger side and the low-stage-side heat exchanger side, or to the heat-source-side heat exchanger side.

8. The two-stage refrigerating apparatus according to claim 7, wherein At the start of the two-stage refrigerating apparatus, the control section starts the high-stage-side compressor, the low-stage-side compressor, and the first circulation pump, and switches the first switching unit and the second switching unit in such a manner that the heat medium flows in the first heat medium circulation path.

9. The two-stage refrigerating apparatus according to claim 8, wherein In a case where the temperature of the heat medium passing through the utilization-side heat exchanger exceeds a first prescribed temperature, or a case where the difference between the temperature of the heat medium passing through the utilization-side heat exchanger and the refrigerant condensing temperature of the low-stage-side heat exchanger of the low-stage-side refrigerant circuit is less than a second prescribed temperature, the control section switches the first switching unit so that the heat medium flows in the second heat medium circulation path, and switches the second switching unit so that the heat medium flows in the third heat medium circulation path.

10. The two-stage refrigeration device according to claim 9, wherein In a case where the temperature of the heat storage material is greater than or equal to a prescribed temperature, the control section switches the four-way valve to the heat-source-side heat exchanger side, and performs a defrosting operation using the heat stored in the heat storage material.

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