Refrigerating device

Abstract

The invention provides a refrigeration device capable of switching between single-stage operation and two-stage operation. The refrigeration device can restrain heat leakage from a utilization side device to a refrigerant circuit side through a heat exchanger which does not enable refrigerant to flow and does not work as the heat exchanger. The present invention is provided with: a high-stage-side refrigerant circuit (2) in which a high-stage-side heat medium heat exchanger (11) that exchanges heat with a heat medium and a stepped heat exchanger (13) are connected in this order by refrigerant piping; a low-stage-side refrigerant circuit (3) in which the stepped heat exchanger (13), a low-stage-side heat medium heat exchanger (24) that is connected in parallel with the stepped heat exchanger (13) and exchanges heat with the heat medium, and the low-stage-side heat exchanger (22) are connected in this order by refrigerant piping; and a control unit (5) that controls the high-stage-side refrigerant circuit (2) and the low-stage-side refrigerant circuit (3), the control unit (5) being capable of switching between a single-stage operation and a second-stage operation, the low-stage-side heat medium heat exchanger (24) being provided with low-stage-side shutoff means (40, 41), and the high-stage-side heat medium heat exchanger (11) being provided with high-stage-side shutoff means (42, 43).

Description

Technical Field

[0001] The present invention relates to a refrigeration device capable of switching between a single-stage operation using one refrigerant circuit and a two-stage operation using two refrigerant circuits using a stepped heat exchanger. Background Art

[0002] The current two-stage refrigeration device has: a high-temperature side refrigerant circuit; a low-temperature side refrigerant circuit; and a stepped heat exchanger (intermediate heat exchanger) shared by the high-temperature side refrigerant circuit and the low-temperature side refrigerant circuit. The stepped heat exchanger acts as an evaporator for the high-temperature side refrigerant circulating in the high-temperature side refrigerant circuit, and acts as a condenser for the low-temperature side refrigerant circulating in the low-temperature side refrigerant circuit. That is, the high-temperature side refrigerant and the low-temperature side refrigerant are heat exchanged in the stepped heat exchanger, and the cooling tank (a box that stores the object to be cooled) is cooled by the low-stage side refrigerant circulating in the low-temperature side refrigerant circuit. In this way, the two-stage refrigeration device exchanges heat between the refrigerant circulating in the high-temperature side refrigerant circuit and the refrigerant circulating in the low-temperature side refrigerant circuit in the stepped heat exchanger, so that the cooling tank can be cooled to a lower temperature compared to a refrigeration device that performs a normal single-stage operation, thereby improving the cooling capacity.

[0003] In this way, the two-stage refrigeration system can improve the cooling capacity. On the other hand, the two refrigerant circuits, the high-temperature side refrigerant circuit and the low-temperature side refrigerant circuit, are operated, so more energy is consumed. Therefore, when a large cooling capacity is not required, single-stage operation is sometimes suitable.

[0004] Therefore, Patent Document 1 discloses a cooling device that switches between single-stage operation and two-stage operation according to changes in required capacity and temperature, thereby achieving improved operation efficiency.

[0005] The refrigeration device disclosed in Patent Document 1 is provided with: a low-temperature side refrigerant circuit, which has a low-temperature side condenser and a low-temperature side evaporator, and the low-temperature side evaporator absorbs heat from the circulating low-temperature side refrigerant; and a high-temperature side refrigerant circuit, which has a high-temperature side condenser, a high-temperature side first evaporator and a high-temperature side second evaporator, and the high-temperature side first evaporator or the high-temperature side second evaporator absorbs heat from the circulating high-temperature side refrigerant. In addition, a stepped heat exchanger is formed to act as a low-temperature side condenser and a high-temperature side second evaporator. The refrigeration device can perform a single-stage operation, that is, the high-temperature side refrigerant is circulated to the high-temperature side first evaporator, and the object to be cooled is cooled in the high-temperature side first evaporator. In addition, the refrigeration device can perform a two-stage operation, that is, the high-temperature side refrigerant is circulated to the high-temperature side second evaporator, and the low-temperature side refrigerant is circulated to the low-temperature side refrigerant circuit, the high-temperature side refrigerant and the low-temperature side refrigerant are heat exchanged in the stepped heat exchanger, and the object to be cooled is cooled in the low-temperature side evaporator. Furthermore, the operation can be switched between the single-stage operation and the two-stage operation.

[0006] Patent Document 1: Japanese Patent Application Publication No. 2009-2610 Summary of the invention

[0007] However, regarding the two-stage refrigeration device disclosed in Patent Document 1, in the case of single-stage operation, the cooling tank side as the utilization side instrument absorbs heat from the low-temperature side refrigerant circuit side through the low-temperature side evaporator of the low-temperature side refrigerant circuit that is stopped. In addition, in the case of two-stage operation, the cooling tank side as the utilization side instrument also absorbs heat from the high-temperature side refrigerant circuit side through the high-temperature side first evaporator in a state where the refrigerant is not flowing and does not function as an evaporator (heat exchanger). Therefore, there is a problem of insufficient heat exchange between the refrigerant of the utilization side instrument and the object to be cooled.

[0008] In view of the above problems, an object of the present invention is to provide a refrigeration device which can switch between single-stage operation and two-stage operation and can suppress heat leakage from the utilization side instrument to the refrigerant circuit side through the heat exchanger in a state where the refrigerant is not flowing and not functioning as a heat exchanger.

[0009] One embodiment of the present invention is a refrigeration device comprising: a high-level refrigerant circuit, which uses refrigerant piping to sequentially connect a high-level compressor, a high-level heat medium heat exchanger for performing heat exchange with a heat medium, a high-level pressure reducing mechanism, and a stepped heat exchanger so that the high-level refrigerant circulates; a low-level refrigerant circuit, which uses refrigerant piping to sequentially connect a low-level compressor, a stepped heat exchanger, a low-level heat medium heat exchanger connected in parallel with the stepped heat exchanger for performing heat exchange with the heat medium, a low-level pressure reducing mechanism, and a low-level heat exchanger so that the low-level refrigerant circulates; and a control unit, which controls the high-level refrigerant circuit and the low-level refrigerant circuit, and the control unit is capable of performing single-stage operation and two-stage operation. Switching, in single-stage operation, the high-level side refrigerant is not circulated in the high-level side refrigerant circuit, but the low-level side refrigerant is circulated in the low-level side refrigerant circuit, and the heat medium is heated in the low-level side heat medium heat exchanger. In two-stage operation, the high-level side refrigerant is circulated in the high-level side refrigerant circuit, and the low-level side refrigerant is circulated in the low-level side refrigerant circuit, and the high-level side refrigerant and the low-level side refrigerant are heat exchanged in the step heat exchanger and the heat medium is heated in the high-level side heat medium heat exchanger. A low-level side cut-off unit for cutting off the flow of the low-level side refrigerant to the low-level side heat medium heat exchanger is provided in the low-level side refrigerant circuit, and a high-level side cut-off unit for cutting off the flow of the high-level side refrigerant to the high-level side heat medium heat exchanger is provided in the high-level side refrigerant circuit.

[0010] Effects of the Invention

[0011] According to the present invention, a refrigeration device can be provided that can switch between single-stage operation and two-stage operation and can suppress heat leakage from a user-side device to a refrigerant circuit side via a heat exchanger in a state where no refrigerant flows and the heat exchanger does not function as a heat exchanger. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a refrigerant circuit diagram of the two-stage refrigeration system according to the first embodiment of the present invention.

[0013] Figure 2 This is a control flow chart of the two-stage refrigeration system according to the first embodiment of the present invention.

[0014] Figure 3 This is a refrigerant circuit diagram of a two-stage refrigeration system according to a second embodiment of the present invention.

[0015] Figure 4 This is a control flow chart of the two-stage refrigeration system according to the second embodiment of the present invention.

[0016] Figure 5 This is a refrigerant circuit diagram of a two-stage refrigeration system according to a third embodiment of the present invention. DETAILED DESCRIPTION

[0017] 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 the embodiment.

[0018] Figure 1 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.

[0019] Example

[0020] Reference Figure 1 The two-stage refrigeration device 1 of this embodiment is described. The two-stage refrigeration device 1 is a refrigeration device that can be used for cooling operation when the high-stage side heat medium heat exchanger 11 is used as an evaporator, and can be used for heating operation when the high-stage side heat medium heat exchanger 11 is used as a condenser. In this embodiment, a two-stage refrigeration device for heating operation is described. The two-stage refrigeration device 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, and the control unit 5 controls the two-stage refrigeration device 1.

[0021] The high-stage refrigerant circuit 2 sequentially connects a high-stage compressor 10, a high-stage heat medium heat exchanger 11 for performing heat exchange with a heat medium such as air or water, a high-stage expansion valve 12 as a high-stage pressure reducing mechanism, and a stepped heat exchanger 13 by using a refrigerant pipe 6, so that the high-stage refrigerant circulates. In the present embodiment, the high-stage heat medium heat exchanger 11 is a heat exchanger for performing 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 for performing heat exchange between the high-stage refrigerant and the low-stage refrigerant flowing in the low-stage refrigerant circuit 3. In addition, in the present embodiment, the high-stage heat medium heat exchanger 11 is a heat exchanger for performing heat exchange between the high-stage refrigerant and the heat medium flowing in the heat medium circuit 4, but it may be a heat exchanger for performing heat exchange with air as a heat medium sent by 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.

[0022] In the high-stage refrigerant circuit 2, a high-stage four-way valve 14 for switching the high-stage refrigerant discharged from the high-stage compressor 10 to flow to the high-stage heat medium heat exchanger 11 side or to flow 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 medium heat exchanger 11 side by 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 medium heat exchanger 11, the high-stage expansion valve 12, and the step heat exchanger 13 and is sucked into the high-stage compressor 10.

[0023] In the high-stage refrigerant circuit 2, a high-stage first stop valve 42 is provided on the upstream side of the high-stage heat medium heat exchanger 11 (the upstream side of the refrigerant flow during heating), and a high-stage second stop valve 43 is provided on the downstream side of the high-stage heat medium heat exchanger 11 (the downstream side of the refrigerant flow during heating). The high-stage first stop valve 42 and the high-stage second stop valve 43 are the high-stage shutoff means in the present invention. The high-stage first stop valve 42 shuts off the inflow of the high-stage refrigerant from the upstream side of the high-stage heat medium heat exchanger 11. The high-stage second stop valve 43 shuts off the inflow of the high-stage refrigerant from the downstream side of the high-stage heat medium heat exchanger 11.

[0024] The low-stage refrigerant circuit 3 has a first circulation path 23 and a second circulation path 26. The first circulation path 23 connects 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 a low-stage pressure reducing mechanism, and the low-stage heat exchanger 22 that absorbs heat from the outside air in sequence by using the refrigerant piping 6, so that the low-stage refrigerant circulates. 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 solid arrows in the low-stage refrigerant circuit 3 indicate the flow of the low-stage refrigerant.

[0025] The low-stage refrigerant circuit 3 uses a refrigerant pipe provided with a low-stage heat medium heat exchanger 24 and a low-stage second expansion valve 25 for heat exchange with the heat medium, so that the refrigerant pipe connecting the low-stage four-way valve 27 and the step heat exchanger 13 described later and the refrigerant pipe connecting the low-stage first expansion valve 21 and the low-stage heat exchanger 22 are connected. Here, the low-stage second expansion valve 25 is a low-stage second pressure reducing mechanism. That is, the step heat exchanger 13 and the low-stage heat medium heat exchanger 24 are connected in parallel between the low-stage four-way valve 27 located on the upstream side and the low-stage heat exchanger 22 located on the downstream side during heating operation. The second circulation path 26 connects the low-stage compressor 20, the low-stage heat medium heat exchanger 24, the low-stage second expansion valve 25 and the low-stage heat exchanger 22 in sequence by using a refrigerant pipe, so that the low-stage refrigerant circulates.

[0026] In the low-stage refrigerant circuit 3, the low-stage four-way valve 27 is connected to the discharge side of the low-stage compressor 20. The low-stage four-way valve 27 switches 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 medium heat exchanger 24 side or to flow to the low-stage heat exchanger 22 side. In this embodiment, the 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 medium 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 low-stage heat exchanger 22 and is sucked into the low-stage compressor 20. The low-stage refrigerant discharged from the low-stage compressor 20 flows through the low-stage heat medium heat exchanger 24 , the low-stage second expansion valve 25 , and the low-stage heat exchanger 22 , and is sucked into the low-stage compressor 20 .

[0027] In the low-stage refrigerant circuit 3, a low-stage first stop valve 40 is provided on the upstream side of the low-stage heat medium heat exchanger 24 (the upstream side of the refrigerant flow during heating), and a low-stage second stop valve 41 is provided on the downstream side of the low-stage heat medium heat exchanger 24 (the downstream side of the refrigerant flow during heating). The low-stage first stop valve 40 and the low-stage second stop valve 41 are the low-stage cut-off means in the present invention. The low-stage first stop valve 40 cuts off the inflow of the low-stage refrigerant from the upstream side of the low-stage heat medium heat exchanger 24. The low-stage second stop valve 41 cuts off the inflow of the low-stage refrigerant from the downstream side of the low-stage heat medium heat exchanger 24.

[0028] In the low-pressure refrigerant circuit 3 , the low-pressure compressor 20 , the low-pressure heat exchanger 22 , and the low-pressure four-way valve 27 are commonly used in the first circulation path 23 and the second circulation path 26 .

[0029] The heat medium circuit 4 sequentially connects the circulation pump 30, the utilization side heat exchanger 31 for performing heat exchange between the indoor air and the heat medium, the low-stage heat medium heat exchanger 24, and the high-stage heat medium heat exchanger 11 by using the pipe 32, so that water as the heat medium circulates. In addition, antifreeze can be used as the heat medium instead of water. In the utilization side heat exchanger 31, the water as the heat medium performs heat exchange with the indoor air, and the air that performs heat exchange with the water as the heat medium is used for heating. The high-stage heat medium heat exchanger 11 is a heat exchanger that performs heat exchange between the water as the heat medium and the high-stage refrigerant flowing in the high-stage refrigerant circuit 2. The low-stage heat medium heat exchanger 24 is a heat exchanger that performs heat exchange between the water as the heat medium and the low-stage refrigerant flowing in the low-stage refrigerant circuit 3. The arrows in the heat medium circuit 4 indicate the flow of water as the heat medium.

[0030] The two-stage refrigeration device 1 is a refrigeration device that utilizes the latent heat change of the high-stage refrigerant in the high-stage refrigerant circuit 2 and the latent heat change of the low-stage refrigerant in the low-stage refrigerant circuit 3, and utilizes the sensible heat change of the heat medium (water) in the heat medium circuit 4. In addition, in the present embodiment, the high-stage refrigerant in the high-stage refrigerant circuit 2 and the low-stage refrigerant in the low-stage refrigerant circuit 3 are the same refrigerant, but they are not necessarily the same, and for example, they may be the low-stage refrigerant having a lower boiling point than the high-stage refrigerant. In addition, a refrigerant that can utilize the latent heat change in the heat medium circuit may also be utilized. In this case, the circulation pump 30 of the heat medium circuit 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 heat medium heat exchanger 24.

[0031] In addition, the secondary refrigeration device 1 has a high-stage heat exchange heat medium inlet temperature sensor 46 and a high-stage heat exchange refrigerant inlet temperature sensor 47. The high-stage heat exchange heat medium inlet temperature sensor 46 measures the temperature of the heat medium in the heat medium circuit 4 when it flows into the high-stage heat medium heat exchanger 11. The high-stage heat exchange refrigerant inlet temperature sensor 47 measures the temperature of the high-stage refrigerant discharged from the high-stage compressor 10 in the high-stage refrigerant circuit 2 and flowing into the high-stage heat medium heat exchanger 11.

[0032] Furthermore, the two-stage refrigeration device 1 has a low-stage heat exchange heat medium inlet temperature sensor 48 and a low-stage heat exchange refrigerant inlet temperature sensor 49. The low-stage heat exchange heat medium inlet temperature sensor 48 measures the temperature of the heat medium in the heat medium circuit 4 when it flows into the low-stage heat medium heat exchanger 24. The low-stage heat exchange refrigerant inlet temperature sensor 49 measures the temperature of the low-stage refrigerant discharged from the low-stage compressor 20 in the low-stage refrigerant circuit 3 and flowing into the low-stage heat medium heat exchanger 24.

[0033] In this way, the temperature sensors are installed at four locations in the two-stage refrigeration device 1, but any type of temperature sensor may be used.

[0034] In the two-stage refrigeration device 1, the low-stage refrigerant, which is compressed by the low-stage compressor 20 of the low-stage refrigerant circuit 3 and becomes a high-temperature and high-pressure gas-phase refrigerant, dissipates heat to the high-stage refrigerant in the stepped heat exchanger 13 and becomes a high-temperature and high-pressure liquid-phase refrigerant, and becomes a low-temperature and low-pressure gas-liquid two-phase refrigerant in the low-stage first expansion valve 21. The low-stage refrigerant, which has become a low-temperature and low-pressure gas-liquid two-phase refrigerant, absorbs heat from the outside air in the low-stage heat exchanger 22 and becomes a low-temperature and low-pressure gas-phase refrigerant. The low-stage refrigerant, which has become a low-temperature and low-pressure gas-phase refrigerant, is compressed again by the low-stage compressor 20.

[0035] In the high-stage refrigerant circuit 2, the low-temperature and low-pressure high-stage refrigerant that absorbs heat from the low-stage refrigerant in the stepped heat exchanger 13 is compressed by the high-stage compressor 10 to become a high-temperature and high-pressure gas-phase refrigerant. The high-stage refrigerant that has become a high-temperature and high-pressure gas-phase refrigerant dissipates heat to the water, which is the heat medium circulating in the heat medium circuit 4 via the high-stage heat medium heat exchanger 11, and generates high-temperature warm water. The high-stage refrigerant dissipates heat to the water in the high-stage heat medium heat exchanger 11 and becomes a high-temperature and high-pressure liquid-phase refrigerant, and the high-stage refrigerant becomes a low-temperature and low-pressure gas-liquid two-phase refrigerant in the high-stage expansion valve 12. The high-stage refrigerant that has become a low-temperature and low-pressure gas-liquid two-phase refrigerant absorbs heat from the low-stage refrigerant in the stepped heat exchanger 13 and becomes a low-temperature and low-pressure gas-phase refrigerant, and is compressed again by the high-stage compressor 10. In addition, regarding the two-stage refrigeration device 1, the low-temperature and low-pressure low-stage refrigerant that absorbs heat from the outside air in the low-stage heat exchanger 22 of the low-stage refrigerant circuit 3 is compressed by the low-stage compressor 20 to become a high-temperature and high-pressure gas-phase refrigerant. The low-stage refrigerant that has become a high-temperature and high-pressure gas-phase refrigerant dissipates heat to the water of the heat medium circulating in the heat medium circuit 4 in the low-stage heat medium heat exchanger 24. Therefore, in the low-stage refrigerant circuit 3, heat is dissipated to the water of the heat medium circulating in the heat medium circuit 4 via the low-stage heat medium heat exchanger 24 to generate warm water.

[0036] The control unit 5 switches between single-stage operation and two-stage operation. In the single-stage operation, the operation of the high-stage compressor 10 is stopped in the high-stage refrigerant circuit 2 and the high-stage refrigerant is not circulated. In addition, the low-stage compressor 20 is operated in the low-stage refrigerant circuit 3 to circulate the low-stage refrigerant, and the heat medium is heated in the low-stage heat medium heat exchanger 24. Regarding the two-stage operation, the high-stage compressor 10 is operated in the high-stage refrigerant circuit 2 to circulate the high-stage refrigerant, and in addition, the low-stage compressor 20 is operated in the low-stage refrigerant circuit 3 to circulate the low-stage refrigerant. The two-stage operation is an operation in which the high-stage refrigerant and the low-stage refrigerant are heat-exchanged in the stepped heat exchanger 13, and the high-stage refrigerant and the heat medium are heat-exchanged in the high-stage heat medium heat exchanger 11 to heat the heat medium.

[0037] The control unit 5 closes the high-stage first stop valve 42 and the high-stage second stop valve 43 in the case of single-stage operation to cut off the flow of the high-stage refrigerant into the high-stage heat medium heat exchanger 11. In the case of two-stage operation, the low-stage first stop valve 40 and the low-stage second stop valve 41 are closed to cut off the flow of the low-stage refrigerant into the low-stage heat medium heat exchanger 24.

[0038] Here, regarding the prior art two-stage refrigeration device which is not provided with the first high-stage stop valve 42 and the second high-stage stop valve 43 and the first low-stage stop valve 40 and the second low-stage stop valve 41, if single-stage operation and two-stage operation are performed, there are the following problems.

[0039] That is, in the case of single-stage operation, in the heat medium circuit 4, the temperature of the high-stage refrigerant may be lowered and lower than the temperature of the low-stage refrigerant by stopping the operation of the high-stage compressor 10. In this case, the heat medium that absorbs heat from the low-stage refrigerant in the low-stage heat medium heat exchanger 24 and becomes high temperature dissipates heat to the high-stage refrigerant in the high-stage heat medium heat exchanger 11. That is, the heat medium absorbs heat from the high-stage refrigerant circuit 2. Therefore, the effect of improving the operation efficiency cannot be fully achieved.

[0040] In the case of two-stage operation, when the heating target temperature of the heat medium in the heat medium circuit 4 is high, the temperature of the low-stage refrigerant passing through the low-stage heat medium heat exchanger 24 of the low-stage refrigerant circuit 3 is sometimes lower than the temperature of the heat medium. In this case, the heat medium passing through the utilization side heat exchanger 31 of the heat medium circuit 4 exchanges heat with the low-stage refrigerant whose temperature is lower than that of the heat medium in the low-stage heat medium heat exchanger 24, so the heat medium dissipates heat to the low-stage refrigerant circuit 3 side (heat leakage), and the effect of improving the operation efficiency cannot be fully exerted.

[0041] However, in the present embodiment, in the case of single-stage operation, the control unit 5 closes the high-stage side first stop valve 42 and the high-stage side second stop valve 43 to cut off the flow of the high-stage side refrigerant into the high-stage side heat medium heat exchanger 11. Therefore, the heat medium that absorbs heat from the low-stage side refrigerant and becomes high temperature in the low-stage side heat medium heat exchanger 24 does not exchange heat with all of the high-stage side refrigerant that has not reached a high temperature due to non-operation, but exchanges heat only with the high-stage side refrigerant of the low-stage side heat medium heat exchanger 24 accumulated between the high-stage side first stop valve 42 and the high-stage side second stop valve 43. Therefore, heat leakage from the heat medium circuit 4 side to the high-stage side refrigerant circuit 2 side can be reduced.

[0042] In addition, in the present embodiment, in the case of two-stage operation, the control unit 5 closes the low-stage first stop valve 40 and the low-stage second stop valve 41 to cut off the flow of the low-stage refrigerant into the low-stage heat medium heat exchanger 24. Therefore, the heat medium passing through the utilization side heat exchanger 31 of the heat medium circuit 4 does not perform heat exchange with all of the low-stage refrigerant having a lower temperature than the heat medium of the low-stage refrigerant circuit 3, but performs heat exchange with only the low-stage refrigerant accumulated in the low-stage heat medium heat exchanger 24 between the low-stage first stop valve 40 and the low-stage second stop valve 41. Therefore, heat leakage from the heat medium circuit 4 side to the low-stage refrigerant circuit 3 side can be reduced.

[0043] Next, use Figure 1 Describes the defrosting operation. Figure 1 In the figure, the arrows shown by the dotted lines indicate the flow of the low-stage refrigerant in the defrosting operation. The defrosting operation is performed as follows. For example, as the defrosting start condition, it is set that the heating operation is continuously performed for 3 hours when the outside air temperature is less than or equal to 5°C, and the temperature of the low-stage heat exchanger 22 is less than or equal to -15°C. Moreover, if the defrosting start condition is met, the control unit 5 switches the low-stage four-way valve 27 to the so-called refrigeration cycle side in the low-stage refrigerant circuit 3. That is, it is switched so that the low-stage refrigerant discharged from the low-stage compressor 20 flows to the low-stage heat exchanger 22 side. The low-stage first expansion valve 21 becomes fully opened, and the low-stage first stop valve 40 and the low-stage second stop valve 41 become closed. In the high-stage refrigerant circuit 2, the operation of the high-stage compressor 10 is stopped, and the high-stage first stop valve 42 and the high-stage second stop valve 43 are closed.

[0044] By the defrosting operation, the low-stage refrigerant discharged from the low-stage compressor 20 flows into the low-stage heat exchanger 22 and melts the frost attached to the low-stage heat exchanger 22. The low-stage refrigerant flowing out of the low-stage heat exchanger 22 flows into the stepped heat exchanger 13 and returns to the suction side of the low-stage compressor 20 via the low-stage four-way valve 27. In the defrosting operation of the present embodiment, in the low-stage refrigerant circuit 3, the low-stage first stop valve 40 and the low-stage second stop valve 41 are closed, so that the low-stage refrigerant that passes through the low-stage heat exchanger 22 and is cooled for defrosting does not flow into the low-stage heat medium heat exchanger 24. Therefore, the high-temperature heat medium flowing in the heat medium circuit 4 does not exchange heat with the cooled low-stage refrigerant, so that the temperature change of the heat medium can be reduced.

[0045] In addition, in the defrosting operation of the present embodiment, the high-stage side first stop valve 42 and the high-stage side second stop valve 43 are closed in the high-stage side refrigerant circuit 2. Therefore, the high-stage side refrigerant that exchanges heat with the low-stage side refrigerant that has passed through the low-stage side heat exchanger 22 and cooled for defrosting in the stepped heat exchanger 13 does not flow into the high-stage side heat medium heat exchanger 11, so the high-temperature heat medium flowing in the heat medium circuit 4 does not exchange heat with the high-stage side refrigerant, thereby reducing the temperature change of the heat medium.

[0046] Next, refer to Figure 2 The control flowchart shown here explains the control during the heating operation of the two-stage refrigeration device 1 according to the present embodiment.

[0047] When starting the two-stage refrigeration device 1, the control unit 5 first performs a startup control based on the two-stage operation (ST1). In the startup control, the high-stage compressor 10 and the low-stage compressor 20 are increased in a step-by-step manner to a specified rotation speed (pre-set fixed values, respectively specified for different models). The openings of the high-stage expansion valve 12, the low-stage first expansion valve 21, and the low-stage second expansion valve 25 are maintained at a specified initial opening (pre-set fixed values, respectively specified for different models). The control unit 5 closes the low-stage first stop valve 40 and the low-stage second stop valve 41, and opens the high-stage first stop valve 42 and the high-stage second stop valve 43. Moreover, in the startup control of the control unit 5, the high-stage refrigerant is circulated in the high-stage refrigerant circuit 2, and the low-stage refrigerant is circulated in the first circulation path 23 of the low-stage refrigerant circuit 3. The low-stage refrigerant is not circulated in the second circulation path 26 of the low-stage refrigerant circuit 3. In addition, in Figure 2 In the flowchart, the description of starting the circulation pump 30 is omitted, and the circulation pump 30 is started at the time when the operation of the secondary refrigeration device 1 is started.

[0048] Next, it is determined whether the high-side compressor 10 and the low-side compressor 20 have reached the specified speed (ST2). When the high-side compressor 10 and the low-side compressor 20 have reached the specified speed (YES of ST2), the normal heating operation (ST3) is entered. When the high-side compressor 10 and the low-side compressor 20 have not reached the specified speed (NO of ST2), the startup control is continued. Regarding the normal heating operation (ST3), the high-side compressor 10 and the low-side compressor 20 are controlled to a speed corresponding to the requested capacity. The high-side expansion valve 12, the low-side first expansion valve 21, and the low-side second expansion valve 25 are controlled by the target discharge temperature control. In the target discharge temperature control of the high-side expansion valve 12, the discharge temperature is detected by a temperature sensor (not shown) that detects the temperature of the refrigerant on the discharge side of the high-side compressor 10, and the opening of the high-side expansion valve 12 is controlled in such a way that its detected value is close to the calculated value that changes according to the operating state, that is, the target discharge temperature. In the target discharge temperature control of the low-stage first expansion valve 21, the discharge temperature is detected by a temperature sensor (not shown) that detects the temperature of the refrigerant on the discharge side of the low-stage compressor 20, and the opening of the low-stage first expansion valve 21 is controlled so that the detected value approaches the target discharge temperature, which is a calculated value that changes according to the operating state. The low-stage first stop valve 40 and the low-stage second stop valve 41 are kept in a closed state, and the high-stage first stop valve 42 and the high-stage second stop valve 43 are kept in an open state.

[0049] Next, it is determined whether the heating target temperature of the heat medium is greater than or equal to the specified value (ST4), which is the heat medium target temperature set according to the user's setting value and the air conditioning load. Regarding the specified value, the minimum value of the heat medium temperature that cannot be reached in the single-stage operation is set in advance through experiments, etc. When the heat medium target temperature is greater than or equal to the specified value (YES of ST4), the first stop valve 40 on the low-stage side and the second stop valve 41 on the low-stage side remain in a closed state, and the first stop valve 42 on the high-stage side and the second stop valve 43 on the high-stage side remain in an open state (ST5). That is, the two-stage operation is continued. When the heat medium target temperature is less than the specified value (NO of ST4), it is switched to single-stage operation. Regarding the single-stage operation, the high-stage compressor 10 is stopped and the high-stage expansion valve 12 is closed. In addition, the first stop valve 40 on the low-stage side and the second stop valve 41 on the low-stage side are opened, and the first stop valve 42 on the high-stage side and the second stop valve 43 on the high-stage side are closed (ST9).

[0050] In addition, in the present embodiment, in step ST4, it is determined whether the target temperature of the heat medium is greater than or equal to the specified value. However, instead of determining whether the target temperature of the heat medium is greater than or equal to the specified value, it is also possible to determine whether the temperature of the heat medium is higher than the temperature of the high-stage side refrigerant flowing into the high-stage side heat medium heat exchanger 11. Specifically, when the temperature of the heat medium measured by the high-stage side heat exchange heat medium inlet temperature sensor 46 is higher than the temperature of the high-stage side refrigerant flowing into the high-stage side heat medium heat exchanger 11 measured by the high-stage side heat exchange refrigerant inlet temperature sensor 47, the process proceeds to step ST5 and continues the two-stage operation. On the other hand, when the temperature of the heat medium measured by the high-stage side heat exchange heat medium inlet temperature sensor 46 is less than or equal to the temperature of the high-stage side refrigerant flowing into the high-stage side heat medium heat exchanger 11 measured by the high-stage side heat exchange refrigerant inlet temperature sensor 47, the process proceeds to step ST9 and switches to the single-stage operation.

[0051] After the processing of the two-stage operation (ST5) or the single-stage operation (ST9) is finished, it is determined whether the defrost start condition is met (ST6). When the defrost start condition is met (YES of ST6), the defrost operation is performed (ST7). When the defrost start condition is not met (No of ST6), the process returns to the step before ST3, and the normal heating operation in the two-stage operation is continued. Regarding the defrost operation, the low-stage four-way valve 27 is switched to the refrigeration cycle side. That is, the low-stage refrigerant discharged from the low-stage compressor 20 flows to the low-stage heat exchanger 22 side. The low-stage compressor 20 is operated at a specified speed, the low-stage first expansion valve 21 becomes fully opened, and the low-stage first stop valve 40 and the low-stage second stop valve 41 become closed. In the high-stage refrigerant circuit 2, the operation of the high-stage compressor 10 is stopped, the high-stage expansion valve 12 becomes closed, and the high-stage first stop valve 42 and the high-stage second stop valve 43 are also closed.

[0052] Through the defrosting operation, the low-stage refrigerant discharged from the low-stage compressor 20 and reaching a high temperature flows into the low-stage heat exchanger 22, and melts the frost attached to the low-stage heat exchanger 22. The low-stage refrigerant flowing out of the low-stage heat exchanger 22 flows into the stepped heat exchanger 13, and returns to the suction side of the low-stage compressor 20 via the low-stage four-way valve 27. In the defrosting operation of the present embodiment, in the low-stage refrigerant circuit 3, the low-stage first stop valve 40 and the low-stage second stop valve 41 are closed, so the low-stage refrigerant does not pass through the low-stage heat medium heat exchanger 24.

[0053] Next, it is determined whether the defrosting is completed (ST8). The completion of the defrosting is determined, for example, based on whether the defrosting operation time has passed a predetermined time or whether the temperature of the low-stage heat exchanger 22 has reached a predetermined temperature. If the defrosting is completed (YES in ST8), the process returns to the normal heating operation before step ST3 and performs the two-stage operation. If the defrosting is not completed (NO in ST8), the defrosting operation is continued.

[0054] Next, use Figure 3 A two-stage refrigeration system 50 according to the second embodiment will be described. Figure 3 A refrigerant circuit diagram of a two-stage refrigeration device 50 according to the second embodiment is shown. The difference between the two-stage refrigeration device 1 according to the first embodiment and the two-stage refrigeration device 50 according to the second embodiment is that a first step heat exchange stop valve 44 and a second step heat exchange stop valve 45 are provided in the step heat exchanger 13 of the low-stage refrigerant circuit 3 of the two-stage refrigeration device 50, and the other structures are the same. Figure 3 In the present invention, the same reference numerals are given to the same structures as those of the two-stage refrigeration system 1 according to the first embodiment. In addition, the description of the same structures as those of the two-stage refrigeration system 1 according to the first embodiment will be omitted.

[0055] In the low-stage refrigerant circuit 3, a first step heat exchange stop valve 44 is provided on the upstream side of the step heat exchanger 13 (the upstream side of the refrigerant flow during heating), and a second step heat exchange stop valve 45 is provided on the downstream side of the step heat exchanger 13 (the downstream side of the refrigerant flow during heating). The first step heat exchange stop valve 44 and the second step heat exchange stop valve 45 are the step heat exchanger side cut-off units in the present invention. The first step heat exchange stop valve 44 cuts off the flow of the low-stage refrigerant from the upstream side to the step heat exchanger 13. The second step heat exchange stop valve 45 cuts off the flow of the low-stage refrigerant from the downstream side to the step heat exchanger 13.

[0056] In the present embodiment, in the case of single-stage operation, the control unit 5 stops the high-stage compressor 10, closes the high-stage first stop valve 42 and the high-stage second stop valve 43, and cuts off the flow of the high-stage refrigerant from the upstream side and the downstream side to the high-stage heat medium heat exchanger 11. In addition, the step heat exchange first stop valve 44 and the step heat exchange second stop valve 45 are closed to cut off the flow of the low-stage refrigerant from the upstream side and the downstream side to the step heat exchanger 13. In this way, the step heat exchange first stop valve 44 and the step heat exchange second stop valve 45 are closed, so that the low-stage refrigerant compressed by the low-stage compressor 20 and becomes high temperature does not exchange heat with the high-stage refrigerant that does not become high temperature due to non-operation. Therefore, heat leakage from the low-stage refrigerant circuit 3 side to the high-stage refrigerant circuit 2 side can be reduced. In addition, in the present embodiment, the high-stage side first stop valve 42 and the high-stage side second stop valve 43 are closed at the same time as the high-stage side compressor 10 stops, but the high-stage side first stop valve 42 and the high-stage side second stop valve 43 may be closed after the high-stage side compressor 10 stops for a certain time (for example, 5 minutes). Even if the heat medium target temperature is lower than the specified value, the temperature of the heat medium may be lower than the temperature of the high-stage side refrigerant flowing into the high-stage side heat medium heat exchanger 11 just after the high-stage side compressor 10 stops. In this case, the heat medium can absorb heat from the high-stage side refrigerant, so by performing such a process, it is possible to suppress a sharp drop in heating capacity when switching from two-stage operation to single-stage operation.

[0057] In addition, in the present embodiment, in the low-stage refrigerant circuit 3, a first step heat exchange stop valve 44 is provided on the upstream side of the step heat exchanger 13 (the upstream side of the refrigerant flow during heating), and a second step heat exchange stop valve 45 is provided on the downstream side of the step heat exchanger 13 (the downstream side of the refrigerant flow during heating), but it is not necessarily limited to this. That is, for example, the first step heat exchange stop valve 44 and the second step heat exchange stop valve 45 are not provided in the low-stage refrigerant circuit 3. On the other hand, in the high-stage refrigerant circuit 2, a first step heat exchange stop valve may be provided on the upstream side of the step heat exchanger 13 (the upstream side of the refrigerant flow during heating), and a second step heat exchange stop valve may be provided on the downstream side of the step heat exchanger 13 (the downstream side of the refrigerant flow during heating). In addition, a first step heat exchange stop valve 44 and a second step heat exchange stop valve 45 are provided in the low-stage refrigerant circuit 3. On this basis, a first step heat exchange stop valve 44 and a second step heat exchange stop valve 45 may be provided in the high-stage refrigerant circuit 2 at the upstream side of the step heat exchanger 13 (the upstream side of the refrigerant flow during heating) and a second step heat exchange stop valve may be provided at the downstream side of the step heat exchanger 13 (the downstream side of the refrigerant flow during heating).

[0058] Next, use Figure 3Describes the defrosting operation. Figure 3 In the figure, the arrows shown by the dotted lines indicate the flow of the low-stage refrigerant in the defrosting operation. The defrosting operation is performed as follows. For example, as the defrosting start condition, it is set that the heating operation is continuously performed for 3 hours when the outside air temperature is less than or equal to 5°C, and the temperature of the low-stage heat exchanger 22 is less than or equal to -15°C. Moreover, if the defrosting start condition is met, the control unit 5 switches the low-stage four-way valve 27 to the so-called refrigeration cycle side in the low-stage refrigerant circuit 3. That is, the low-stage refrigerant discharged from the low-stage compressor 20 is switched to flow to the low-stage heat exchanger 22 side. The low-stage first expansion valve 21 becomes fully opened, and the low-stage first stop valve 40 and the low-stage second stop valve 41 become closed. In the high-stage refrigerant circuit 2, the operation of the high-stage compressor 10 is stopped, the high-stage first stop valve 42 and the high-stage second stop valve 43 are closed, and the step heat exchange first stop valve 44 and the step heat exchange second stop valve 45 are opened.

[0059] By the defrosting operation, the low-stage refrigerant discharged from the low-stage compressor 20 flows into the low-stage heat exchanger 22, and melts the frost attached to the low-stage heat exchanger 22. The low-stage refrigerant flowing out of the low-stage heat exchanger 22 flows into the stepped heat exchanger 13, and returns to the suction side of the low-stage compressor 20 via the low-stage four-way valve 27. In the defrosting operation of the present embodiment, in the low-stage refrigerant circuit 3, the low-stage first stop valve 40 and the low-stage second stop valve 41 are closed, so the low-stage refrigerant that passes through the low-stage heat exchanger 22 and is cooled for defrosting does not flow into the low-stage heat medium heat exchanger 24. Therefore, the high-temperature heat medium flowing in the heat medium circuit 4 does not exchange heat with the cooled low-stage refrigerant, so that the temperature change of the heat medium can be reduced.

[0060] In addition, in the defrosting operation of the present embodiment, the high-stage side first stop valve 42 and the high-stage side second stop valve 43 are closed in the high-stage side refrigerant circuit 2. Therefore, the low-stage side refrigerant that passes through the low-stage side heat exchanger 22 and is cooled for defrosting and the high-stage side refrigerant that has undergone heat exchange in the step heat exchanger 13 do not flow into the high-stage side heat medium heat exchanger 11. Therefore, the high-temperature heat medium flowing in the heat medium circuit 4 does not undergo heat exchange with the high-stage side refrigerant, so that the temperature change of the heat medium can be reduced. In addition, the step heat exchange first stop valve 44 and the step heat exchange second stop valve 45 are opened. Therefore, the low-stage side refrigerant that passes through the low-stage side heat exchanger 22 and becomes low temperature in order to melt the attached frost can absorb heat from the high-stage side refrigerant that has not yet become low temperature when passing through the step heat exchanger 13. Therefore, such a low-stage side refrigerant can be used for defrosting the low-stage side heat exchanger 22.

[0061] Next, refer to Figure 4 The control flowchart shown in the figure explains the control during the heating operation of the two-stage refrigeration device 50 according to the present embodiment.

[0062] When the control unit 5 starts the two-stage refrigeration device 50, it first performs a startup control based on the two-stage operation (ST10). In the startup control, the high-stage compressor 10 and the low-stage compressor 20 are increased stepwise to a specified rotation speed (pre-set fixed value, respectively specified for different models). The control unit 5 maintains the opening of the high-stage expansion valve 12, the low-stage first expansion valve 21, and the low-stage second expansion valve 25 at a specified initial opening (pre-set fixed value, respectively specified for different models). The low-stage first stop valve 40 and the low-stage second stop valve 41 are closed, the high-stage first stop valve 42 and the high-stage second stop valve 43 are opened, and the step-type heat exchange first stop valve 44 and the step-type heat exchange second stop valve 45 are opened. Moreover, in the startup control of the control unit 5, the high-stage refrigerant is circulated in the high-stage refrigerant circuit 2, and the low-stage refrigerant is circulated in the first circulation path 23 of the low-stage refrigerant circuit 3. The low-pressure side refrigerant is not allowed to circulate in the second circulation path 26 of the low-pressure side refrigerant circuit 3. Figure 4 In the flowchart, the description of starting the circulation pump 30 is omitted, and the circulation pump 30 is started at the time point when the operation of the secondary refrigeration device 50 is started.

[0063] Next, it is determined whether the high-side compressor 10 and the low-side compressor 20 have reached a specified speed (ST11). When the high-side compressor 10 and the low-side compressor 20 have reached the specified speed (YES of ST11), the normal heating operation is entered (ST12). When the high-side compressor 10 and the low-side compressor 20 have not reached the specified speed (NO of ST11), the startup control is continued. Regarding the normal heating operation (ST12), the high-side compressor 10 and the low-side compressor 20 are controlled to a speed corresponding to the requested capacity. The high-side expansion valve 12, the low-side first expansion valve 21, and the low-side second expansion valve 25 are controlled by the target discharge temperature control. In the target discharge temperature control of the high-side expansion valve 12, the discharge temperature is detected by a temperature sensor (not shown) that detects the temperature of the refrigerant on the discharge side of the high-side compressor 10, and the opening of the high-side expansion valve 12 is controlled in such a way that its detected value is close to the calculated value that changes according to the operating state, that is, the target discharge temperature. In the target discharge temperature control of the low-stage side first expansion valve 21, the discharge temperature is detected by a temperature sensor (not shown) that detects the temperature of the refrigerant on the discharge side of the low-stage compressor 20, and the opening degree of the low-stage side first expansion valve 21 is controlled in such a way that the detected value approaches the calculated value that changes according to the operating state, that is, the target discharge temperature. The low-stage side first stop valve 40 and the low-stage side second stop valve 41 are kept in a closed state, the high-stage side first stop valve 42 and the high-stage side second stop valve 43 are kept in an open state, and the step heat exchange first stop valve 44 and the step heat exchange second stop valve 45 are also kept in an open state.

[0064] Next, it is determined whether the heating target temperature of the heat medium is greater than or equal to the specified value (ST13). Regarding the specified value, the minimum value of the heat medium temperature that cannot be reached in the single-stage operation is set in advance through experiments, etc. When the heat medium target temperature is greater than or equal to the specified value (YES of ST13), the first stop valve 40 on the low-stage side and the second stop valve 41 on the low-stage side remain in a closed state, the first stop valve 42 on the high-stage side and the second stop valve 43 on the high-stage side remain in an open state, and the first stop valve 44 and the second stop valve 45 of the step heat exchanger also remain in an open state (ST14). That is, the two-stage operation is continued. When the heat medium target temperature is less than the specified value (NO of ST13), it is switched to single-stage operation. Regarding the single-stage operation, the high-stage side compressor 10 is stopped, the high-stage side expansion valve 12 is closed, and the first stop valve 40 on the low-stage side and the second stop valve 41 on the low-stage side are opened. In addition, the high-stage side first stop valve 42 and the high-stage side second stop valve 43 are closed, and the step heat exchange first stop valve 44 and the step heat exchange second stop valve 45 are closed (ST18).

[0065] In addition, in the present embodiment, in step ST13, it is determined whether the heat medium target temperature is greater than or equal to a specified value. However, instead of determining whether the heat medium target temperature is greater than or equal to a specified value, it is also possible to determine whether the temperature of the heat medium is higher than the temperature of the high-stage side refrigerant flowing into the high-stage side heat medium heat exchanger 11. In the case where the temperature of the heat medium measured by the high-stage side heat exchange heat medium inlet temperature sensor 46 is higher than the temperature of the high-stage side refrigerant flowing into the high-stage side heat medium heat exchanger 11 measured by the high-stage side heat exchange refrigerant inlet temperature sensor 47, the process proceeds to step ST14 and the two-stage operation is continued. On the other hand, in the case where the temperature of the heat medium measured by the high-stage side heat exchange heat medium inlet temperature sensor 46 is less than or equal to the temperature of the high-stage side refrigerant flowing into the high-stage side heat medium heat exchanger 11 measured by the high-stage side heat exchange refrigerant inlet temperature sensor 47, the process proceeds to step ST18 and switches to the single-stage operation.

[0066] After finishing the processing of the two-stage operation (ST14) or the single-stage operation (ST18), determine whether the defrost start condition is met (ST15). When the defrost start condition is met (YES of ST15), the defrost operation is performed (ST16). When the defrost start condition is not met (No of ST15), return to the step before ST12, and continue the normal heating operation in the two-stage operation. Regarding the defrost operation, the low-stage four-way valve 27 is switched to the refrigeration cycle side. That is, it is switched so that the low-stage refrigerant discharged from the low-stage compressor 20 flows to the low-stage heat exchanger 22 side. The low-stage compressor 20 is operated at a specified speed, the low-stage first expansion valve 21 becomes fully opened, and the low-stage first stop valve 40 and the low-stage second stop valve 41 become closed. The step heat exchanger first stop valve 44 and the step heat exchanger second stop valve 45 are opened. In the high-stage refrigerant circuit 2, the operation of the high-stage compressor 10 is stopped, the high-stage expansion valve 12 is closed, and the first high-stage stop valve 42 and the second high-stage stop valve 43 are also closed.

[0067] By the defrosting operation, the high-temperature low-stage refrigerant discharged from the low-stage compressor 20 flows into the low-stage heat exchanger 22, and melts the frost attached to the low-stage heat exchanger 22. The low-stage refrigerant flowing out of the low-stage heat exchanger 22 flows into the stepped heat exchanger 13, and returns to the suction side of the low-stage compressor 20 via the low-stage four-way valve 27. In the defrosting operation of the present embodiment, the low-stage first stop valve 40 and the low-stage second stop valve 41 are closed in the low-stage refrigerant circuit 3. Therefore, the low-stage refrigerant that passes through the low-stage heat exchanger 22 and is cooled for defrosting does not flow into the low-stage heat medium heat exchanger 24. Therefore, the high-temperature heat medium flowing in the heat medium circuit 4 does not exchange heat with the cooled low-stage refrigerant, so that the temperature change of the heat medium can be reduced. On the other hand, the first step heat exchange stop valve 44 and the second step heat exchange stop valve 45 are opened, so that the low-temperature low-stage refrigerant passing through the low-stage heat exchanger 22 to melt the attached frost can absorb heat from the high-stage refrigerant that has not yet become low temperature when passing through the step heat exchanger 13. Therefore, this low-stage refrigerant can be used for defrosting the low-stage heat exchanger 22.

[0068] Next, it is determined whether the defrosting is completed (ST17). The completion of the defrosting is determined, for example, based on whether the defrosting operation time has passed a predetermined time or whether the temperature of the low-stage heat exchanger 22 has reached a predetermined temperature. If the defrosting is completed (YES in ST17), the process returns to the normal heating operation before ST12 and performs the two-stage operation. If the defrosting is not completed (NO in ST17), the defrosting operation is continued.

[0069] Next, use Figure 5 A two-stage refrigeration system 60 according to the third embodiment will be described. Figure 5 A refrigerant circuit diagram showing a two-stage refrigeration device 60 according to the third embodiment. The differences between the two-stage refrigeration device 1 according to the first embodiment and the two-stage refrigeration device 60 according to the third embodiment are as follows. That is, the two-stage refrigeration device 1 according to the first embodiment is shown to be used for heating operation, and the two-stage refrigeration device 60 according to the third embodiment is shown to be used for cooling operation. Figure 5 In the present invention, the same reference numerals are given to the same structures as those of the two-stage refrigeration system 1 according to the first embodiment. In addition, the description of the same structures as those of the two-stage refrigeration system 1 according to the first embodiment will be omitted.

[0070] The high-stage refrigerant circuit 2 sequentially connects a high-stage compressor 10, a stepped heat exchanger 13, a high-stage expansion valve 12 as a high-stage pressure reducing mechanism, and a high-stage heat medium heat exchanger 11 for heat exchange with a heat medium such as air or water, by using a refrigerant pipe 6, so that the high-stage refrigerant circulates. In the present embodiment, the high-stage heat medium heat exchanger 11 is a heat exchanger for 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 for heat exchange between the high-stage refrigerant and the low-stage refrigerant flowing in the low-stage refrigerant circuit 3. In addition, in the present embodiment, the high-stage heat medium heat exchanger 11 is a heat exchanger for heat exchange between the high-stage refrigerant and the heat medium flowing in the heat medium circuit 4. However, for example, it may be a heat exchanger for heat exchange with air as a heat medium sent by a blower not shown. The arrows in the high-stage refrigerant circuit 2 indicate the flow of the high-stage refrigerant during cooling operation.

[0071] In the high-stage refrigerant circuit 2, the high-stage four-way valve 14 is connected to the discharge side of the high-stage compressor 10. The high-stage four-way valve 14 switches the high-stage refrigerant discharged from the high-stage compressor 10 to flow to the high-stage heat medium heat exchanger 11 side or to the stepped heat exchanger 13 side. In the present embodiment, the case (refrigeration operation) in which the high-stage refrigerant discharged from the high-stage compressor 10 flows to the stepped heat exchanger 13 side by 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 stepped heat exchanger 13, the high-stage expansion valve 12, and the high-stage heat medium heat exchanger 11, and is sucked into the high-stage compressor 10.

[0072] In the high-stage refrigerant circuit 2, a high-stage second stop valve 43 is provided on the upstream side of the high-stage heat medium heat exchanger 11 (the upstream side of the refrigerant flow during cooling), and a high-stage first stop valve 42 is provided on the downstream side of the high-stage heat medium heat exchanger 11 (the downstream side of the refrigerant flow during cooling). The high-stage first stop valve 42 and the high-stage second stop valve 43 are the high-stage shutoff means in the present invention. The high-stage second stop valve 43 shuts off the inflow of the high-stage refrigerant from the upstream side of the high-stage heat medium heat exchanger 11. The high-stage first stop valve 42 shuts off the inflow of the high-stage refrigerant from the downstream side of the high-stage heat medium heat exchanger 11.

[0073] The low-stage refrigerant circuit 3 has a first circulation path 23 and a second circulation path 26. The first circulation path 23 connects the low-stage compressor 20, the low-stage heat exchanger 22 that dissipates heat to the outside air, the low-stage first expansion valve 21 as a low-stage pressure reducing mechanism, and the stepped heat exchanger 13 connected to the high-stage refrigerant circuit 2 in sequence by the refrigerant piping 6, so that the low-stage refrigerant circulates. 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 solid arrows in the low-stage refrigerant circuit 3 indicate the flow of the low-stage refrigerant.

[0074] The low-stage refrigerant circuit 3 uses a refrigerant pipe provided with a low-stage heat medium heat exchanger 24 and a low-stage second expansion valve 25 for heat exchange with the heat medium, so that the refrigerant pipe connecting the low-stage four-way valve 27 and the step heat exchanger 13 described later and the refrigerant pipe connecting the low-stage first expansion valve 21 and the low-stage heat exchanger 22 are connected. Here, the low-stage second expansion valve 25 is a low-stage second pressure reducing mechanism. That is, during heating operation, the step heat exchanger 13 and the low-stage heat medium heat exchanger 24 are connected in parallel between the low-stage four-way valve 27 located on the upstream side and the low-stage heat exchanger 22 located on the downstream side. The second circulation path 26 connects the low-stage compressor 20, the low-stage heat exchanger 22, the low-stage second expansion valve 25 and the low-stage heat medium heat exchanger 24 in sequence by using the refrigerant pipe, so that the low-stage refrigerant circulates.

[0075] In the low-stage refrigerant circuit 3, the low-stage four-way valve 27 is connected to the discharge side of the low-stage compressor 20. The low-stage four-way valve 27 switches 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 medium heat exchanger 24 side or to flow to the low-stage heat exchanger 22 side. In this embodiment, the case (cooling operation) in which the low-stage refrigerant discharged from the low-stage compressor 20 flows to the low-stage heat exchanger 22 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 low-stage heat exchanger 22, the low-stage first expansion valve 21, and the stepped heat exchanger 13 and is sucked into the low-stage compressor 20. The low-stage refrigerant discharged from the low-stage compressor 20 flows through the low-stage heat exchanger 22 , the low-stage second expansion valve 25 , and the low-stage heat medium heat exchanger 24 , and is sucked into the low-stage compressor 20 .

[0076] In the low-stage refrigerant circuit 3, a low-stage second stop valve 41 is provided on the upstream side of the low-stage heat medium heat exchanger 24 (the upstream side of the refrigerant flow during cooling), and a low-stage first stop valve 40 is provided on the downstream side of the low-stage heat medium heat exchanger 24 (the downstream side of the refrigerant flow during cooling). The low-stage first stop valve 40 and the low-stage second stop valve 41 are the low-stage cutoff means in the present invention. The low-stage second stop valve 41 cuts off the inflow of the low-stage refrigerant from the upstream side of the low-stage heat medium heat exchanger 24. The low-stage first stop valve 40 cuts off the inflow of the low-stage refrigerant from the downstream side of the low-stage heat medium heat exchanger 24.

[0077] Regarding the two-stage refrigeration device 60, the low-stage refrigerant compressed by the low-stage compressor 20 of the low-stage refrigerant circuit 3 becomes a high-temperature and high-pressure gas-phase refrigerant, dissipates heat to the outside air in the low-stage heat exchanger 22 to become a high-temperature and high-pressure liquid-phase refrigerant, and becomes a low-temperature and low-pressure gas-liquid two-phase refrigerant in the low-stage first expansion valve 21. The low-stage refrigerant that becomes a low-temperature and low-pressure gas-liquid two-phase refrigerant absorbs heat from the high-stage refrigerant circulating in the high-stage refrigerant circuit 2 through the stepped heat exchanger 13, thereby becoming a low-temperature and low-pressure gas-phase refrigerant. The high-stage refrigerant that becomes a high-temperature and high-pressure gas-phase refrigerant compressed by the high-stage compressor 10 of the high-stage refrigerant circuit 2 dissipates heat to the low-stage refrigerant in the stepped heat exchanger 13 to become a high-temperature and high-pressure liquid-phase refrigerant, and becomes a low-temperature and low-pressure gas-liquid two-phase refrigerant in the high-stage expansion valve 12. The high-stage refrigerant, which has become a low-temperature and low-pressure gas-liquid two-phase refrigerant, absorbs heat from the heat medium, i.e., water, circulating in the heat medium circuit 4, via the high-stage heat medium heat exchanger 11 to form low-temperature cold water. In addition, regarding the two-stage refrigeration device 1, the low-stage refrigerant, which has become a high-temperature and high-pressure liquid-phase refrigerant by dissipating heat to the outside air in the low-stage heat exchanger 22, is converted into a low-temperature and low-pressure gas-liquid two-phase refrigerant by the low-stage second expansion valve 25. The low-stage refrigerant, which has become a low-temperature and low-pressure gas-liquid two-phase refrigerant, absorbs heat from the heat medium, i.e., water, circulating in the heat medium circuit 4, via the low-stage heat medium heat exchanger 24 to generate low-temperature cold water.

[0078] The control unit 5 switches between single-stage operation and two-stage operation. Regarding the single-stage operation, the operation of the high-stage compressor 10 is stopped in the high-stage refrigerant circuit 2 and the high-stage refrigerant is not circulated. In addition, the low-stage compressor 20 is operated in the low-stage refrigerant circuit 3 to circulate the low-stage refrigerant, and the heat medium is cooled in the low-stage heat medium heat exchanger 24. On the other hand, regarding the two-stage operation, the high-stage compressor 10 is operated in the high-stage refrigerant circuit 2 to circulate the high-stage refrigerant, and in addition, the low-stage compressor 20 is operated in the low-stage refrigerant circuit 3 to circulate the low-stage refrigerant. The two-stage operation is an operation in which the high-stage refrigerant and the low-stage refrigerant are heat-exchanged in the stepped heat exchanger 13, and the high-stage refrigerant and the heat medium are heat-exchanged in the high-stage heat medium heat exchanger 11 to cool the heat medium.

[0079] In the case of single-stage operation, the control unit 5 closes the high-stage side first stop valve 42 and the high-stage side second stop valve 43 to cut off the flow of the high-stage side refrigerant into the high-stage side heat medium heat exchanger 11. In the case of two-stage operation, the low-stage side first stop valve 40 and the low-stage side second stop valve 41 are closed to cut off the flow of the low-stage side refrigerant into the low-stage side heat medium heat exchanger 24.

[0080] Here, regarding the prior art two-stage refrigeration device which is not provided with the first high-stage stop valve 42 and the second high-stage stop valve 43 and the first low-stage stop valve 40 and the second low-stage stop valve 41, if single-stage operation and two-stage operation are performed, there are the following problems.

[0081] That is, in the case of single-stage operation, in the heat medium circuit 4, the high-stage refrigerant stops the operation of the high-stage compressor 10 and causes the temperature to rise, sometimes exceeding the temperature of the low-stage refrigerant. The heat medium that has become low-temperature by dissipating heat to the low-stage refrigerant in the low-stage heat medium heat exchanger 24 absorbs heat from the high-stage refrigerant in the high-stage heat medium heat exchanger 11. That is, the heat medium dissipates heat to the high-stage refrigerant circuit 2 side (heat leakage), and the effect of improving the operation efficiency cannot be fully exerted.

[0082] On the other hand, in the case of two-stage operation, when the cooling target temperature of the heat medium in the heat medium circuit 4 is low, the temperature of the low-stage refrigerant passing through the low-stage heat medium heat exchanger 24 of the low-stage refrigerant circuit 3 may be higher than the temperature of the heat medium. In this case, if the heat medium passing through the utilization side heat exchanger 31 of the heat medium circuit 4 exchanges heat with the low-stage refrigerant having a higher temperature than the heat medium in the low-stage heat medium heat exchanger 24, the heat medium absorbs heat from the low-stage refrigerant circuit 3 side, and the effect of improving the operation efficiency cannot be fully exerted.

[0083] However, in the present embodiment, the control unit 5 closes the high-stage side first stop valve 42 and the high-stage side second stop valve 43 in the case of single-stage operation, and cuts off the flow of the high-stage side refrigerant into the high-stage side heat medium heat exchanger 11. Therefore, the heat medium that has become low-temperature by dissipating heat to the low-stage side refrigerant in the low-stage side heat medium heat exchanger 24 does not exchange heat with all of the high-stage side refrigerant that has not reached a low temperature due to non-operation, but exchanges heat only with the high-stage side refrigerant accumulated between the high-stage side first stop valve 42 and the high-stage side second stop valve 43. Therefore, the amount of heat absorbed by the heat medium from the high-stage side refrigerant circuit 2 side can be reduced.

[0084] In addition, in the present embodiment, in the case of two-stage operation, the control unit 5 closes the low-stage first stop valve 40 and the low-stage second stop valve 41 to cut off the flow of the low-stage refrigerant into the low-stage heat medium heat exchanger 24. Therefore, the heat medium passing through the utilization side heat exchanger 31 of the heat medium circuit 4 does not perform heat exchange with all of the low-stage refrigerant having a higher temperature than the heat medium of the low-stage refrigerant circuit 3, but performs heat exchange with only the low-stage refrigerant of the low-stage heat medium heat exchanger 24 accumulated between the low-stage first stop valve 40 and the low-stage second stop valve 41. Therefore, the amount of heat absorbed by the heat medium from the low-stage refrigerant circuit 3 side can be reduced.

[0085] In the above-mentioned embodiment, the low-stage side heat medium heat exchanger 24 is provided with the low-stage side first stop valve 40 and the low-stage side second stop valve 41. However, it is not necessary to provide the low-stage side first stop valve 40 and the low-stage side second stop valve 41, and either the low-stage side first stop valve 40 or the low-stage side second stop valve 41 may be provided. However, it is preferred to provide the low-stage side first stop valve 40 and the low-stage side second stop valve 41. By providing the low-stage side first stop valve 40 and the low-stage side second stop valve 41, it is possible to reduce heat leakage between the low-stage side refrigerant circuit 3 side and the heat medium circuit 4. The same is true for the high-stage side heat medium heat exchanger 11 and the stepped heat exchanger 13.

[0086] In addition, in the above-mentioned embodiment, a two-stage device is described, but it is not limited to a two-stage device, and a multi-stage device of three or more stages may be used.

[0087] The above description is made with reference to a limited number of embodiments, but the scope of rights is not limited thereto, and changes based on the above disclosed embodiments are self-evident to those skilled in the art.

[0088] Description of the label

[0089] 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 medium heat exchanger, 12…High-stage expansion valve, 13…Step heat exchanger, 14…High-stage four-way valve, 20…Low-stage compressor, 21…Low-stage 1st expansion valve, 22…Low-stage heat exchanger, 23…1st circulation path, 24…Low-stage heat medium heat exchanger 、25…Second expansion valve on low-stage side、26…Second circulation path、27…Four-way valve on low-stage side、28…Heat exchanger on low-stage side、30…Circulation pump、31…Heat exchanger on utilization side、32…Pipe、40…First stop valve on low-stage side、41…Second stop valve on low-stage side、42…First stop valve on high-stage side、43…Second stop valve on high-stage side、44…First stop valve for step-type heat exchange、45…Second stop valve for step-type heat exchange、50…Second-stage refrigeration device、60…Second-stage refrigeration device

Claims

1. A refrigeration device, characterized in that: The refrigeration device comprises: A high-stage refrigerant circuit, which circulates the high-stage refrigerant, connects the high-stage compressor, the high-stage heat medium heat exchanger for performing heat exchange between the high-stage refrigerant and the heat medium, the high-stage pressure reducing mechanism, and the stepped heat exchanger in sequence by refrigerant piping; a low-stage refrigerant circuit that circulates the low-stage refrigerant and sequentially connects the low-stage compressor, the stepped heat exchanger, a low-stage heat medium heat exchanger that is connected in parallel with the stepped heat exchanger to exchange heat between the low-stage refrigerant and the heat medium, a low-stage pressure reducing mechanism, and the low-stage heat exchanger by using refrigerant piping; and a control unit that controls the high-pressure side refrigerant circuit and the low-pressure side refrigerant circuit, The control unit is capable of switching between single-stage operation and two-stage operation. In the single-stage operation, the high-stage refrigerant is not circulated in the high-stage refrigerant circuit, but the low-stage refrigerant is circulated in the low-stage refrigerant circuit, and the heat medium is heated in the low-stage heat medium heat exchanger. In the two-stage operation, the high-stage refrigerant is circulated in the high-stage refrigerant circuit, and the low-stage refrigerant is circulated in the low-stage refrigerant circuit, the high-stage refrigerant and the low-stage refrigerant are heat-exchanged in the stepped heat exchanger, and the heat medium is heated in the high-stage heat medium heat exchanger. The low-stage refrigerant circuit is provided with a low-stage shutoff unit for shutting off the flow of the low-stage refrigerant into the low-stage heat medium heat exchanger. The high-stage-side refrigerant circuit is provided with a high-stage-side shutoff unit that shuts off the flow of the high-stage-side refrigerant into the high-stage-side heat medium heat exchanger.

2. The refrigeration device according to claim 1, characterized in that: The refrigeration device has a heat medium circuit that connects a circulation pump, a utilization side heat exchanger, the low-stage heat medium heat exchanger, and the high-stage heat medium heat exchanger in sequence by piping so that the heat medium circulates. The control unit controls the heat medium circuit.

3. The refrigeration device according to claim 1 or 2, characterized in that: The control unit cuts off the flow of the low-stage refrigerant into the low-stage heat medium heat exchanger by the low-stage cutoff unit when the heating target temperature of the heat medium is greater than or equal to a predetermined value during the two-stage operation. During the two-stage operation, when the heating target temperature of the heat medium is lower than a predetermined value, the two-stage operation is switched to the single-stage operation, and the high-stage-side shutoff unit shuts off the high-stage-side refrigerant from flowing into the high-stage-side heat medium heat exchanger.

4. The refrigeration device according to claim 1 or 2, characterized in that: The control unit, in the single-stage operation, cuts off the flow of the high-stage refrigerant into the high-stage heat medium heat exchanger by the high-stage cutoff unit when the temperature of the heat medium flowing into the high-stage heat medium heat exchanger is higher than the temperature of the high-stage refrigerant flowing into the high-stage heat medium heat exchanger. In the two-stage operation, when the temperature of the heat medium flowing into the low-stage heat medium heat exchanger is higher than the temperature of the low-stage refrigerant flowing into the low-stage heat medium heat exchanger, the low-stage cutoff unit is used to cut off the flow of the low-stage refrigerant into the low-stage heat medium heat exchanger.

5. The refrigeration device according to claim 1 or 2, characterized in that: The control unit blocks the flow of the high-stage refrigerant into the high-stage heat medium heat exchanger by the high-stage shutoff unit when the high-stage compressor is stopped for a period of time equal to or longer than a predetermined period of time.

6. The refrigeration device according to claim 1 or 2, characterized in that: A low-stage four-way valve is provided in the low-stage refrigerant circuit, and the low-stage four-way valve is connected to the discharge side of the low-stage compressor, and switches the low-stage refrigerant discharged from the low-stage compressor to flow to the stepped heat exchanger side and the low-stage heat medium heat exchanger side or to flow to the low-stage heat exchanger side. When a predetermined defrosting start condition is met, the control unit switches the low-stage four-way valve so that the low-stage refrigerant discharged from the low-stage compressor flows into the low-stage heat exchanger. The low-stage side cutoff unit cuts off the flow of the low-stage side refrigerant into the low-stage side heat medium heat exchanger, The high-stage-side shutoff unit shuts off the flow of the high-stage-side refrigerant into the high-stage-side heat medium heat exchanger.

7. The refrigeration device according to claim 1 or 2, characterized in that: A step heat exchanger side cut-off unit for cutting off the flow of at least either the low-stage side refrigerant or the high-stage side refrigerant into the step heat exchanger is arranged in the low-stage side refrigerant circuit or the high-stage side refrigerant circuit, and the step heat exchanger side cut-off unit is used to cut off the flow of refrigerant during the single-stage operation.

8. A refrigeration device, characterized in that: The refrigeration device comprises: A high-side refrigerant circuit, which uses refrigerant piping to sequentially connect a high-side compressor, a stepped heat exchanger, a high-side pressure reducing mechanism, and a high-side heat medium heat exchanger for heat exchange with a heat medium, so that the high-side refrigerant circulates; A low-stage refrigerant circuit, which sequentially connects a low-stage compressor, a low-stage heat exchanger, a low-stage pressure reducing mechanism, the stepped heat exchanger, and a low-stage heat medium heat exchanger connected in parallel with the stepped heat exchanger to perform heat exchange with the heat medium by using a refrigerant piping, so that the low-stage refrigerant circulates; as well as a control unit that controls the high-pressure side refrigerant circuit and the low-pressure side refrigerant circuit, The control unit is capable of switching between single-stage operation and two-stage operation. In the single-stage operation, the high-stage refrigerant is not circulated in the high-stage refrigerant circuit, but the low-stage refrigerant is circulated in the low-stage refrigerant circuit, and the heat medium is cooled in the low-stage heat medium heat exchanger. In the two-stage operation, the high-stage refrigerant is circulated in the high-stage refrigerant circuit, and the low-stage refrigerant is circulated in the low-stage refrigerant circuit, the high-stage refrigerant and the low-stage refrigerant are heat exchanged in the stepped heat exchanger, and the heat medium is cooled in the high-stage heat medium heat exchanger. The low-stage refrigerant circuit is provided with a low-stage shutoff unit for shutting off the flow of the low-stage refrigerant into the low-stage heat medium heat exchanger. The high-stage-side refrigerant circuit is provided with a high-stage-side shutoff unit that shuts off the flow of the high-stage-side refrigerant into the high-stage-side heat medium heat exchanger.

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