Freezer

Abstract

To provide a freezer which performs a defrost operation of an evaporator by a gaseous refrigerant sent from a lower-stage compressor of two-staged compression freezing cycle.SOLUTION: A bypass passage 90 is provided for allowing the defrost refrigerant to flow in an evaporator 110 of a freezing cycle. When performing a defrost operation, a refrigerant outlet of a lower-stage compressor 11 is made to communicate with a refrigerant inlet of the evaporator 110 at the bypass passage 90 to perform the defrost operation by the intermediate-pressure refrigerant sent from the lower-stage compressor 11. The pressure of the defrost refrigerant is not as high as the two-stage compressed pressure in a normal cooling operation, which requires no need for high-pressure countermeasures at each part of the passage related to defrost operation and thus reducing the device cost. Further, energy saving is achieved by stopping operation of a higher-stage compressor 12 and performing a defrost operation for executing the lower-stage compressor 11.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a refrigeration system that executes a two-stage compression refrigeration cycle using carbon dioxide as a refrigerant, and particularly to defrosting of an evaporator. [Background technology]

[0002] In recent years, the use of carbon dioxide, a natural refrigerant with a low global warming potential (GWP), as a refrigerant (heat medium) for refrigeration equipment has been increasing. When using carbon dioxide as a refrigerant, in a refrigeration cycle, it is necessary to compress the carbon dioxide, which has a low critical temperature, at a high pressure ratio to create high pressure in order to increase the efficiency of the cycle. For this reason, in refrigeration cycles using carbon dioxide as a refrigerant, two-stage compression has often been adopted, in which two compressors, one for a low pressure stage and one for a high pressure stage, are provided to perform two-stage compression in order to increase pressure efficiently.

[0003] On the other hand, in a refrigeration system, if frost forms on the evaporator of the refrigeration cycle, the efficiency of heat exchange deteriorates, so frost is removed (defrosted) at an appropriate time. In addition to the general method of using a heater for such defrosting, methods such as circulating brine and so-called hot gas defrosting, in which high-temperature gas-phase refrigerant (hot gas) from the compressor is circulated through a bypass passage to the evaporator to melt the frost on the evaporator, have been proposed in recent years.

[0004] Among conventional defrosting methods in refrigeration cycles that mainly use carbon dioxide as a refrigerant, one example of a method using brine is disclosed in JP 2022-161409 A. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2022-161409 A Summary of the Invention [Problem to be solved by the invention]

[0006] The defrosting means in the conventional refrigeration cycle shown in the above-mentioned patent document has a configuration capable of performing defrosting by introducing brine heated by heat exchange with the heat of the refrigerant into an evaporator (cooling cooler).

[0007] However, the defrosting method disclosed in this patent document requires additional equipment such as a circulation pump, a brine tank, and brine piping to heat the brine for defrosting and circulate it through a flow path including an evaporator. In addition, it requires the input of external energy to operate the pump, making it unreasonable in terms of cost, etc.

[0008] In contrast, the previously commonly used defrosting method of using a heater to heat the evaporator from outside or pouring heated water onto the evaporator was easier to implement, but had problems such as wasting energy that did not contribute to the refrigeration cycle and causing the temperature to rise inside the space where the evaporator was located (such as a freezer).

[0009] In addition, there is a method called hot gas defrosting, but when the refrigerant is carbon dioxide, a high-pressure refrigerant that has undergone two-stage compression is used, which may lead to problems due to insufficient strength and durability of valves and piping provided in the bypass flow path for defrosting. In addition, if the strength and durability of the valves related to defrosting are to be sufficient, the problem of increased costs will arise.

[0010] The present invention has been made to solve the above-mentioned problems, and has an object to provide a refrigeration system in which an evaporator is defrosted with gas-phase refrigerant delivered from a low-stage compressor in a two-stage compression refrigeration cycle. [Means for solving the problem]

[0011] The refrigeration device according to the disclosure of the present invention is a refrigeration device that executes a vapor compression refrigeration cycle using carbon dioxide as a refrigerant and performs two-stage compression on the refrigerant, and is equipped with one or more low-stage side compressors that compress the gas phase refrigerant, one or more high-stage side compressors that further compress the refrigerant that has left the low-stage side compressor, a gas cooler that cools the refrigerant that has left the high-stage side compressor, an intermediate heat exchanger between the low-stage side compressor and the high-stage side compressor that cools the refrigerant that has left the low-stage side compressor by heat exchange with a predetermined cooling medium, a bypass flow path that allows the refrigerant to flow in a defrost operation state, and a second intermediate heat exchanger that exchanges heat with the refrigerant used for defrosting in a defrost operation state with another heat medium, and at least one expansion valve that expands the refrigerant to reduce its pressure, and the expansion valve an evaporator that evaporates the refrigerant leaving the refrigerant inlet and absorbs heat from the surroundings is connected from the outside to enable a refrigeration cycle to be performed, and the bypass flow path, in a defrost operation state, connects the refrigerant inlet of the low-stage side compressor to the refrigerant outlet of the intermediate second heat exchanger, connects the refrigerant outlet of the low-stage side compressor to the refrigerant inlet of the evaporator, and further connects the refrigerant outlet of the evaporator to the refrigerant inlet of the intermediate second heat exchanger, and the low-stage side compressor, in a defrost operation state, circulates refrigerant through the bypass flow path from the low-stage side compressor via the evaporator and the intermediate second heat exchanger to the low-stage side compressor, thereby progressing defrosting in the evaporator, and the intermediate second heat exchanger, in a defrost operation state, evaporates the refrigerant by heat exchange.

[0012] As described above, according to the disclosure of the present invention, a bypass flow path is provided to allow heated refrigerant for defrosting to flow to an external evaporator connected as an element of the refrigeration cycle, and when defrosting is performed, the refrigerant outlet of the low-stage compressor in the two-stage compression refrigeration cycle is connected to the refrigerant inlet of the evaporator via the bypass flow path, and defrosting is performed using intermediate-pressure gas-phase refrigerant delivered from the low-stage compressor. This prevents the pressure of the refrigerant circulated for defrosting from becoming high, as in the case of two-stage compression as in normal cooling operation, and makes it unnecessary to take high-pressure measures for each part of the flow path related to defrosting, thereby reducing the cost of the device. In addition, the cold heat contained in the refrigerant can be recovered by the other heat medium that has exchanged heat with the refrigerant in the intermediate second heat exchanger, and by utilizing this, it is possible to reduce heat loss and improve efficiency in the entire device.

[0013] Further, a refrigeration device according to the disclosure of the present invention includes at least a compressor, a gas cooler, an expansion valve, and an evaporator that executes a vapor compression refrigeration cycle using carbon dioxide as a refrigerant, and performs two-stage compression on a refrigerant. The refrigeration device further includes an intermediate heat exchanger between a low-stage compressor and a high-stage compressor that perform two-stage compression, the intermediate heat exchanger cooling the refrigerant that has left the low-stage compressor by heat exchange with a predetermined cooling medium, a bypass flow path through which the refrigerant flows in a defrost operation state, and a second intermediate heat exchanger that exchanges heat between the refrigerant used for defrosting and another heat medium in a defrost operation state, and the bypass flow path In a defrost operation state, the refrigerant inlet of the low-stage side compressor is connected to the refrigerant outlet of the intermediate second heat exchanger, the refrigerant outlet of the low-stage side compressor is connected to the refrigerant inlet of the evaporator, and further, the refrigerant outlet of the evaporator is connected to the refrigerant inlet of the intermediate second heat exchanger, and in a defrost operation state, the low-stage side compressor circulates refrigerant through a circulation path from the low-stage side compressor via the bypass flow path through the evaporator and the intermediate second heat exchanger to the low-stage side compressor, thereby progressing defrosting in the evaporator, and in a defrost operation state, the intermediate second heat exchanger evaporates the refrigerant by heat exchange.

[0014] As disclosed in the present invention, a bypass flow path is provided to allow heated refrigerant for defrosting to flow through the evaporator of the refrigeration cycle, and when defrosting is performed, the refrigerant outlet of the low-stage compressor in the two-stage compression refrigeration cycle is connected to the refrigerant inlet of the evaporator through the bypass flow path, and defrosting is performed using intermediate-pressure gas-phase refrigerant delivered from the low-stage compressor. This prevents the pressure of the refrigerant circulated for defrosting from becoming high, as in the case of two-stage compression as in normal cooling operation, and makes it unnecessary to take measures to increase pressure in each part of the flow path related to defrosting, thereby reducing the cost of the device. In addition, the cold heat contained in the refrigerant can be recovered by the other heat medium that has exchanged heat with the refrigerant in the intermediate second heat exchanger, and by utilizing this, it is possible to reduce heat loss and improve efficiency in the entire device.

[0015] Furthermore, in the refrigeration device disclosed herein, as necessary, the intermediate heat exchanger, in a defrost operation state, is connected by the bypass flow path to the refrigerant inlet of the evaporator and to the refrigerant outlet of the low-stage compressor, so as to double as the intermediate second heat exchanger included in the circulation path, and the other heat medium is used as the cooling medium.

[0016] As described above, according to the disclosure of the present invention, the intermediate heat exchanger that reduces the temperature and pressure of the refrigerant between the low-stage compressor and the high-stage compressor also serves as an intermediate second heat exchanger, and receives refrigerant that has been cooled as a result of defrosting in the evaporator during defrost operation and is used to heat the refrigerant. This makes it possible to reduce the number of heat exchangers installed in the refrigeration system, thereby enabling the system to be made smaller and less costly.

[0017] In addition, in the refrigeration apparatus disclosed herein, the low-stage compressor and the high-stage compressor can be operated independently of each other as necessary, and in the defrost operation state, the low-stage compressor included in the circulation path is operated while the high-stage compressor that is not executing the refrigeration cycle is stopped.

[0018] As described above, according to the disclosure of the present invention, when defrosting the evaporator, the low-stage compressor communicating with the bypass flow path is operated to allow refrigerant to be circulated to the evaporator, etc. through the bypass flow path, while the high-stage compressor that does not contribute to defrosting or the execution of the refrigeration cycle is stopped in operation and only the low-stage compressor is operated, thereby reducing energy consumption related to the operation of the high-stage compressor during defrosting, thereby achieving energy savings in the device and associated reduction in operating costs.

[0019] Furthermore, in the refrigeration device disclosed herein, as necessary, the evaporators are arranged in a parallel connection state to other elements of the refrigeration cycle, and the bypass flow path interconnects at least one evaporator, the low-stage side compressor, and the intermediate second heat exchanger to generate the circulation path, while an arrangement mode for maintaining the remaining evaporators, the low-stage side compressor, and the intermediate heat exchanger in a state in which a normal refrigeration cycle can be executed can be set for each evaporator, and a defrost operation state in which a portion of the refrigerant that has passed through the low-stage side compressor is circulated through the evaporator and the intermediate second heat exchanger included in the circulation path, and a normal refrigeration cycle in which the other portion of the refrigerant that has passed through the low-stage side compressor is circulated through the remaining evaporators and the intermediate heat exchanger are executed in parallel while making it possible to replace the evaporator to be defrosted by switching the arrangement mode of the bypass flow path.

[0020] Thus, according to the disclosure of the present invention, by switching the flow path for multiple evaporators and defrosting a specified evaporator while maintaining the remaining evaporators as one element of a normal refrigeration cycle, defrosting and the refrigeration cycle can be performed in parallel, thereby continuously cooling the object to be cooled using the refrigeration cycle while eliminating adverse effects such as a decrease in cooling capacity due to frost, and the impact of defrosting itself on the object to be cooled is kept small, for example defrosting is less likely to cause a rise in the temperature of the object to be cooled.

[0021] Furthermore, in the refrigeration device disclosed herein, if necessary, the same other heat medium as that used in the intermediate second heat exchanger is circulated in the gas cooler to exchange heat with the refrigerant, a flow path of the other heat medium in the intermediate second heat exchanger is connected to a flow path of the other heat medium in the gas cooler, and at least a portion of the other heat medium cooled through heat exchange in the intermediate second heat exchanger in the defrost operation state is introduced into the gas cooler to exchange heat with the refrigerant.

[0022] Thus, according to the disclosure of the present invention, by introducing another heat medium that has been cooled through heat exchange in the intermediate second heat exchanger in defrost operation into the gas cooler of the refrigeration cycle and using it for heat exchange with the refrigerant, the cold energy obtained by defrosting can be appropriately recovered and used to lower the temperature of the other heat medium, and accordingly the temperature of the refrigerant can also be lowered, thereby improving the efficiency of heat exchange.

[0023] Furthermore, in the refrigeration device disclosed in the present invention, as necessary, the gas cooler and the intermediate second heat exchanger are air-cooled heat exchangers in which the other heat medium that exchanges heat with the refrigerant is air that is forcibly ventilated by a fan, and the gas cooler is arranged so that one or more heat exchange sections through which the refrigerant and air pass are overlapped with the intermediate second heat exchanger in the air ventilation direction, and the fan for ventilating air is shared with the intermediate second heat exchanger.

[0024] Thus, according to the disclosure of the present invention, the gas cooler and the intermediate second heat exchanger are air-cooled heat exchangers in which the other heat medium that exchanges heat with the refrigerant is air, and are arranged stacked on top of each other in the air ventilation direction. Air cooled in the intermediate second heat exchanger by heat exchange with the refrigerant used for defrost and whose temperature has been reduced flows into the gas cooler, so that the gas cooler and the intermediate second heat exchanger can be constructed in a compact manner with an efficient layout, and during defrost operation, the temperature of the air flowing into the gas cooler is reduced and it is heat exchanged with the refrigerant, thereby improving cooling efficiency.

[0025] Furthermore, in the refrigeration device disclosed in the present invention, as necessary, the gas cooler is an air-cooled heat exchanger that exchanges heat between a refrigerant and air, and the intermediate second heat exchanger is an air-cooled heat exchanger in which the other heat medium that exchanges heat with the refrigerant is air, and when the temperature of the air that exchanges heat with the refrigerant in the gas cooler has risen, the bypass flow path is switched to a state in which a predetermined evaporator in a state for executing a normal refrigeration cycle, the low-stage compressor, and the intermediate second heat exchanger are interconnected, and the circulation path is generated, so that a defrost operation state is executed in parallel with the refrigeration cycle, and the air that has been cooled by heat exchange with the refrigerant in the intermediate second heat exchanger in the defrost operation state is introduced into the gas cooler.

[0026] As described above, according to the disclosure of the present invention, when the temperature of the air around the gas cooler, i.e., the air that exchanges heat with the refrigerant in the gas cooler, rises, the bypass flow path interconnects a predetermined evaporator, the low-stage compressor, and the intermediate second heat exchanger, which are in a state of executing a normal refrigeration cycle, to generate a circulation path, thereby executing a defrost operation state, and the air that has been cooled by heat exchange with the refrigerant in the intermediate second heat exchanger included in the circulation path is introduced into the gas cooler, so that even in a situation in which the temperature around the gas cooler rises and the temperature of the air that is the target of heat exchange also rises, the refrigerant temperature can be appropriately lowered to maintain the operating state of the refrigeration cycle, and cooling can be continued without difficulty. [Brief description of the drawings]

[0027] [Figure 1] 1 is a schematic system diagram of a refrigeration device according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is an explanatory diagram of a refrigerant path in a defrost operation state in the refrigeration device according to the first embodiment of the present invention. [Diagram 3] FIG. 5 is a schematic system diagram of a refrigeration device according to a second embodiment of the present invention. [Figure 4] FIG. 11 is a diagram illustrating a refrigerant path in a defrost operation state in a refrigeration device according to a second embodiment of the present invention. [Diagram 5]FIG. 11 is an explanatory diagram of an operating state of a gas cooler and an intermediate heat exchanger during cooling operation in a refrigeration device according to a third embodiment of the present invention. [Figure 6] FIG. 11 is an explanatory diagram of an operating state of a gas cooler and an intermediate heat exchanger when a cooling operation and a defrost operation are performed in parallel in a refrigeration device according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] (First embodiment of the present invention) A refrigeration device according to a first embodiment of the present invention will be described below with reference to Fig. 1 and Fig. 2. In this embodiment, an example of a refrigeration device that is a so-called condensing unit, which is used in a state where a load unit including an evaporator of a refrigeration cycle is connected to the outside, will be described.

[0029] As shown in the figures, the refrigeration device 1 according to this embodiment is configured such that, among the components that use carbon dioxide as a refrigerant to perform a two-stage compression refrigeration cycle, an evaporator 110 and an expansion valve 105 that expands the refrigerant in the upstream stage are connected from the outside, and the other components are built-in.

[0030] In detail, the refrigeration device 1 according to this embodiment includes a plurality of low-stage compressors 11 that compress a refrigerant, a plurality of high-stage compressors 12 that further compress the refrigerant that has left the low-stage compressors 11, an intermediate heat exchanger 20 that is disposed between the low-stage compressors 11 and the high-stage compressors 12 and that cools the refrigerant that has left the low-stage compressors 11, a gas cooler 30 that cools the high-temperature, high-pressure refrigerant discharged from the high-stage compressors 12 by heat exchange, expansion valves 41, 42, and 43 that expand the refrigerant to reduce its pressure, and a gas cooler 30 that expands the refrigerant by the expansion valve 42. The evaporator 110 is configured to include a receiver 50 that separates the expanded two-phase refrigerant into a gas phase refrigerant and a liquid phase refrigerant, a liquid separator 60 that performs gas-liquid separation of the refrigerant to be supplied to the high-stage compressor 12, an oil separator 70 that separates the refrigerant from refrigeration oil dissolved in the refrigerant, an economizer 80 that performs heat exchange between the refrigerant before flowing into the evaporator 110 and the refrigerant that has left the evaporator 110, and a bypass flow path 90 that allows refrigerant warmed for defrost to flow to the evaporator 110.

[0031] The evaporator 110 connected from the outside to the refrigeration device 1 according to this embodiment is a heat exchanger that exchanges heat between a refrigerant in a liquid phase at low pressure and air as a medium to be cooled that exists in a closed space including the evaporator (such as inside a freezer), evaporating the refrigerant into a gas phase by absorbing heat from the air, while lowering the temperature of the air. The heat exchanger itself is a known structure, and detailed description thereof will be omitted.

[0032] An expansion valve 105 is connected to the inlet side of the refrigerant flow passage of the evaporator 110, and the liquid-phase refrigerant that has expanded and had its pressure reduced through the expansion valve 105 flows into the evaporator 110. The expansion valve 105 is also well known, and a detailed description thereof will be omitted.

[0033] The refrigerant flow path inlet of the expansion valve 105 is connected to the liquid phase refrigerant outlet of the refrigeration device 1, and the refrigerant flow path outlet of the evaporator 110 is connected to the gas phase refrigerant inlet of the refrigeration device 1, thereby allowing refrigerant to circulate through the expansion valve 105 and the evaporator 110, allowing them to function as elements of the refrigeration cycle.

[0034] The low-stage compressor 11 is driven by an electric motor or the like, and sucks in and compresses the gas-phase refrigerant that has left the evaporator 110 and passed through the economizer 80, increases the temperature and pressure of the refrigerant, and then discharges and supplies the refrigerant to the intermediate heat exchanger 20. A plurality of low-stage compressors 11 are provided and connected in parallel to each other.

[0035] In a cooling operation state, i.e., when a normal refrigeration cycle is being performed, the low-stage compressor 11 draws in and compresses the refrigerant that has left the evaporator 110 and the economizer 80, and discharges it as an intermediate-pressure refrigerant. On the other hand, in a defrost operation state, the low-stage compressor 11 draws in and compresses the refrigerant that has evaporated in the intermediate heat exchanger 20, and discharges it as an intermediate-pressure refrigerant toward the evaporator 110 that is to be defrosted.

[0036] The mechanism of this low-stage compressor 11 as a compressor is similar to that of a known subcritical carbon dioxide compressor used as the low-stage side in a two-stage compression refrigeration cycle using carbon dioxide as a refrigerant, and so a description thereof will be omitted. The low-stage compressor 11 and the high-stage compressor 12 are driven independently of each other, so that even if one of them is stopped, the other can still be operated.

[0037] The high-stage side compressor 12 compresses the gas-phase refrigerant that has left the intermediate heat exchanger 20 and passed through the liquid separator 60 by work applied from the outside, raises the temperature and pressure of the refrigerant to or above the critical temperature and critical pressure, and then sends the refrigerant to the gas cooler 30. A plurality of high-stage side compressors 12 are provided and connected in parallel.

[0038] The mechanism of this high-stage compressor 12 as a compressor itself is similar to that of a known transcritical carbon dioxide compressor used as the high-stage side in a two-stage compression refrigeration cycle using carbon dioxide as a refrigerant, and so a description thereof will be omitted.

[0039] The intermediate heat exchanger 20 is disposed between the low-stage compressor 11 and the high-stage compressor 12, and cools the refrigerant that has left the low-stage compressor 11 by exchanging heat with a predetermined cooling medium. The intermediate heat exchanger 20 has a flow path for the refrigerant as well as a flow path for the cooling medium, which is a liquid such as cooling water, and is configured to circulate the cooling medium through this flow path to exchange heat with the refrigerant. The intermediate heat exchanger 20 also serves as a second intermediate heat exchanger, and functions as a radiator that cools the refrigerant during cooling operation, and functions as an evaporator of the refrigerant during defrost operation.

[0040] In the defrost operation state, the intermediate heat exchanger 20 has a refrigerant inlet connected to the refrigerant outlet of the evaporator 110 and a refrigerant outlet connected to the refrigerant inlet of the low-stage compressor 11 via the bypass flow path 90, and functions as a second intermediate heat exchanger to evaporate the refrigerant after flowing through the evaporator by heat exchange with the cooling medium.

[0041] The gas cooler 30 is a heat exchanger that exchanges heat between the refrigerant compressed in the high-stage compressor 12 to a high temperature and high pressure and the same cooling medium (cooling water) as the intermediate heat exchanger 20, and transfers heat from the refrigerant to the cooling medium to cool the refrigerant while increasing the temperature of the cooling medium. The configuration of the gas cooler 30 itself is similar to that of a known heat exchanger for cooling carbon dioxide, and a detailed description thereof will be omitted.

[0042] The expansion valves 41, 42, and 43 expand the refrigerant in each refrigerant flow path provided therein, thereby reducing the pressure. Among these, the expansion valve 42 expands the refrigerant that has left the gas cooler 30, thereby reducing the pressure, and the refrigerant that has passed through the expansion valve 42 is in a gas-liquid two-phase state. These expansion valves are similar to known expansion valves used in a multi-stage expansion type refrigeration cycle, and therefore a description thereof will be omitted.

[0043] The receiver 50 is a known device that separates the refrigerant in a two-phase gas-liquid state that has left the gas cooler 30 and been expanded and decompressed by the expansion valve 42 into a gas phase refrigerant and a liquid phase refrigerant, and temporarily stores the refrigerant. From this receiver 50, the gas phase refrigerant merges with the refrigerant that has left the intermediate heat exchanger 20 and then flows to the liquid separator 60, and the liquid phase refrigerant flows to the economizer 80.

[0044] The liquid separator (accumulator) 60 is a known device that mainly separates the refrigerant that leaves the intermediate heat exchanger 20 and is supplied to the high-stage side compressor 12 into gas and liquid, and protects the compressor by preventing liquid-phase refrigerant from flowing into the compressor. Only the gas-phase refrigerant separated by this liquid separator 60 is supplied to the suction side of the high-stage side compressor 12.

[0045] The gas phase refrigerant separated in the receiver 50 flows into the liquid separator 60 in a state of being expanded and reduced in pressure through the expansion valve 43 while merging with the refrigerant that has left the intermediate heat exchanger 20. In addition, a portion of the liquid phase refrigerant separated in the receiver 50 that is diverted as an injection portion flows into the liquid separator 60 in a state of being expanded and reduced in pressure through the expansion valve 41.

[0046] The oil separator 70 is a known device that is provided in the refrigerant flow path between the high-stage compressor 12 and the gas cooler 30, separates the refrigerant from the refrigeration oil dissolved in the refrigerant, and allows only the refrigerant to flow to the gas cooler 13.

[0047] The economizer 80 is a known device disposed upstream of the low-stage compressor 11 and performs heat exchange between the refrigerant before it reaches the liquid-phase refrigerant outlet of the refrigeration device 1 and the refrigerant that flows in from the gas-phase refrigerant inlet of the refrigeration device 1. The economizer 80 performs heat exchange between the refrigerants in the flow paths before and after the evaporator 110, lowering the temperature of the refrigerant before it enters the expansion valve 105 and the evaporator 110, and raising the temperature of the refrigerant after it leaves the evaporator 110. This makes the refrigerant heading to the evaporator 110 in a supercooled state, and increases the degree of superheat of the refrigerant heading to the low-stage compressor 11, leading to smoother operation of the refrigeration device 1.

[0048] The bypass flow passage 90 has a first flow passage 91 that is arranged between the refrigerant outlet of the low-stage compressor 11 and the refrigerant inlet of the evaporator to allow communication between them, a second flow passage 92 that is arranged between the refrigerant outlet of the evaporator 110 and the refrigerant inlet of the intermediate heat exchanger 20 to allow communication between them, and a third flow passage 93 that is arranged between the refrigerant outlet of the intermediate heat exchanger 20 and the refrigerant inlet of the low-stage compressor 11 to allow communication between them.

[0049] Each of the flow paths 91, 92, and 93 constituting the bypass flow path 90 is also provided with a flow path switching valve (not shown) for circulating the refrigerant through these paths instead of the normal refrigerant flow paths during the defrost operation state. In addition, the second flow path 92 is provided with an expansion valve 92a near the intermediate heat exchanger 20.

[0050] In the defrost operation state, the bypass passage 90 has a first passage 91 that does not communicate the refrigerant outlet of the low stage compressor 11 with the refrigerant inlet of the intermediate heat exchanger 20, but instead communicates with the refrigerant inlet of the evaporator 110 through the first passage 91. In addition, the third passage 93 does not communicate the refrigerant inlet of the low stage compressor 11 with the economizer 80 that leads to the refrigerant outlet of the evaporator 110, but instead communicates with the refrigerant outlet of the intermediate heat exchanger 20 through the third passage 93. In addition, the second passage 92 communicates the refrigerant outlet of the evaporator 110 with the refrigerant inlet of the intermediate heat exchanger 20 through the second passage 92.

[0051] In this way, the flow paths 91, 92, and 93 constituting the bypass flow path 90 form a refrigerant circulation path from the low-stage compressor 11 through the evaporator 110 and the intermediate heat exchanger 20 to the low-stage compressor 11 during defrost operation.

[0052] In this defrost operation state, the first flow path 91 of the bypass flow path 90 does not communicate the refrigerant inlet of the evaporator 110 with the expansion valve 105. Moreover, the second flow path 92 does not communicate the refrigerant outlet of the evaporator 110 with the economizer 80, and does not communicate the refrigerant inlet of the intermediate heat exchanger 20 with the refrigerant outlet of the low-stage compressor 11 and the first flow path 91. Furthermore, the third flow path 93 does not communicate the refrigerant outlet of the intermediate heat exchanger 20 with the flow path leading to the liquid separator 60 and the junction of this flow path with the flow path of gas phase refrigerant originating from the receiver 50.

[0053] When the low-stage compressor 11 circulates the refrigerant through the circulation path obtained by the bypass passage 90 in the defrost operation state, the low-stage compressor 11, the evaporator 110, the expansion valve 92a of the second passage 92, and the intermediate heat exchanger 20, which are included in the refrigerant circulation path, constitute a kind of heat pump cycle, and the evaporator 110 can be efficiently defrosted as a so-called hot gas defrost. In this defrost operation state, the refrigerant is heat exchanged with the cooling medium in the intermediate heat exchanger 20, and the refrigerant is evaporated while the temperature of the cooling medium is lowered.

[0054] Next, the operating state of the refrigeration system based on the above configuration will be described. It is assumed that a predetermined cooling medium is introduced into the gas cooler 13 and the intermediate heat exchanger 20, and that in a normal cooling operation state, at least in the gas cooler 13 and the intermediate heat exchanger 20, the heat exchange between the refrigerant carbon dioxide and the cooling medium can be steadily continued under the same conditions.

[0055] First, the operating state during normal cooling operation will be described. When the refrigerant that has completed heat exchange in the evaporator 110 and passed through the economizer 80 reaches the low-stage compressor 11, the low-stage compressor 11 compresses and pressurizes the refrigerant, thereby increasing the pressure and temperature of the refrigerant. Then, the gas-phase refrigerant that has left the low-stage compressor 11 is introduced into the intermediate heat exchanger 20.

[0056] In the intermediate heat exchanger 20, heat exchange occurs between the cooling medium (cooling water) introduced therein and the refrigerant, and the refrigerant is cooled by this heat exchange, lowering its temperature and pressure. The refrigerant that has passed through the intermediate heat exchanger 20 merges with the refrigerant that has passed through a gas-phase refrigerant flow path connected to the receiver 50 , and then flows into the liquid separator 60 . In the liquid separator 60, gas-liquid separation is performed on the refrigerant that has flowed therein. The gas-phase refrigerant separated from the liquid-phase component in the liquid separator 60 is supplied to the suction side of the high-stage side compressor 12.

[0057] When the gas-phase refrigerant that has passed through the liquid separator 60 reaches the high-stage compressor 12, the high-stage compressor 12 compresses and pressurizes the refrigerant, further increasing the pressure and temperature of the refrigerant. Then, the high-temperature, high-pressure gas-phase refrigerant discharged from the high-stage compressor 12 is introduced into the oil separator 70. In the oil separator 70, the refrigerant is separated from the refrigeration oil dissolved in the refrigerant, and the refrigerant flows to the gas cooler 30.

[0058] When the high-temperature, high-pressure refrigerant leaving the oil separator 70 flows into the gas cooler 30, it is cooled by heat exchange. In detail, in the gas cooler 30, heat exchange occurs between the cooling medium (cooling water) introduced therein and the refrigerant. The refrigerant is cooled by heat exchange with the cooling medium. Meanwhile, the cooling medium is heated by heat exchange in the gas cooler 30, and leaves the gas cooler 30 at an elevated temperature and is discharged to the outside of the device.

[0059] The refrigerant cooled by the gas cooler 30 passes through a refrigerant flow path to reach the expansion valve 42, and flows into the receiver 50 with its pressure reduced by the expansion valve 42 to an intermediate pressure of, for example, about 5.5 MPa.

[0060] In the receiver 50, the refrigerant in a two-phase gas-liquid state, which has been expanded and has its pressure reduced by the expansion valve 42, is separated into a gas phase refrigerant and a liquid phase refrigerant. The gas phase refrigerant is discharged to the outside of the receiver 50 through a refrigerant flow path connected to the upper part of the receiver 50. After this gas phase refrigerant discharged from the receiver 50 expands through the expansion valve 43, it merges with the refrigerant that has left the intermediate heat exchanger 20 and reaches the liquid separator 60.

[0061] The liquid phase refrigerant separated from the gas phase in the receiver 50 is sent out of the receiver 50 through a refrigerant flow path connected to the bottom of the receiver 50. The refrigerant sent out from the receiver 50 flows through two flow paths that branch off along the way. A portion of the refrigerant expands through the expansion valve 41 and flows into the liquid separator 60 for injection. The pressure of the refrigerant flowing into the liquid separator 60 is controlled by controlling the opening of the expansion valve 41. The refrigerant that has flowed into the liquid separator 60 is separated into gas and liquid in the liquid separator 60 , and only the gas phase refrigerant proceeds to the refrigerant inlet of the high-stage side compressor 12 .

[0062] Of the refrigerant sent from the receiver 50, the remaining refrigerant other than the portion that passes through the expansion valve 41 and heads to the liquid separator 60 advances to the economizer 80, where it is cooled by heat exchange with the refrigerant that has left the evaporator 110.

[0063] The refrigerant thus cooled by the economizer 80 exits from a liquid phase refrigerant outlet of the refrigeration device 1 and is sent to a load unit (such as a cooling coil or a refrigeration showcase) provided outside the refrigeration device 1 through connecting piping or the like. In the load unit, the refrigerant expands in the expansion valve 105 to reduce its pressure and temperature, and then flows into the evaporator 110. In the evaporator 110, the refrigerant absorbs heat through heat exchange with the air in the surrounding space where the object to be cooled is located, and the object to be cooled is cooled. The refrigerant after heat exchange exits the evaporator 110, enters the gas phase refrigerant inlet of the refrigeration device 1 from the load unit through connecting piping or the like, and returns to the refrigeration device 1.

[0064] In the refrigeration system 1, the refrigerant that has left the evaporator 110 flows into the economizer 80, where it exchanges heat with the refrigerant heading toward the evaporator 110. The refrigerant whose temperature has been increased by the heat exchange in the economizer 80 is sent from the economizer 80 to the suction side of the low-stage compressor 11. Thereafter, the refrigerant enters the low-stage compressor 11, and repeats the processes from compression in the low-stage compressor 11 onwards in the same manner as described above.

[0065] If a sensor on the load unit side detects significant frost on the evaporator 110, or if a predetermined amount of time has passed since the start of cooling operation or the last defrost and a situation has arisen in which frost is expected to progress, the refrigeration device 1 transitions to a defrost operation state. In the defrost operation state, the low-stage side compressor 11 is in an operating state, while the high-stage side compressor 12 is not in operation and is in a stopped state.

[0066] When the operation state is switched from the cooling operation state in which the refrigeration cycle is executed to the defrost operation state, in the bypass flow path 90, the first flow path 91 communicates the refrigerant outlet of the low stage side compressor 11 with the refrigerant inlet of the evaporator 110 without communicating it with the refrigerant inlet of the intermediate heat exchanger 20. In addition, the third flow path 93 communicates the refrigerant inlet of the low stage side compressor 11 with the refrigerant outlet of the intermediate heat exchanger 20 without communicating it with the economizer 80. In addition, the second flow path 92 communicates the refrigerant outlet of the evaporator 110 with the refrigerant inlet of the intermediate heat exchanger 20.

[0067] Thus, the flow paths 91, 92, and 93 of the bypass flow path 90 form a refrigerant circulation path from the low-stage compressor 11 through the evaporator 110 and the intermediate heat exchanger 20 to the low-stage compressor 11 (see FIG. 2).

[0068] The low-stage compressor 11, which is in an operating state, circulates the refrigerant through this circulation path. In detail, the low-stage compressor 11 compresses the refrigerant, and sends the refrigerant in a state in which its temperature and pressure are increased to the evaporator 110 through the first flow path 91 of the bypass flow path 90. In the evaporator 110, defrosting progresses due to the heat dissipation of the refrigerant, and the refrigerant also loses heat, causing its temperature to drop and condense.

[0069] The refrigerant that has left the evaporator 110 reaches the intermediate heat exchanger 20 through the second flow path 92. In the intermediate heat exchanger 20, the refrigerant, whose pressure and temperature have been reduced through the expansion valve 92a of the second flow path 92, evaporates through heat exchange with a cooling medium (cooling water). Meanwhile, the cooling medium reduces its temperature through heat exchange.

[0070] The refrigerant that leaves the intermediate heat exchanger 20 returns to the low-stage compressor 11, and thereafter, the refrigerant circulates through the bypass passage 90, passing from the low-stage compressor 11 through the evaporator 110 and the intermediate heat exchanger 20 to the low-stage compressor 11, while defrosting in the evaporator 110 progresses.

[0071] When the conditions for terminating the defrost operation are met, for example, when the sensor can no longer detect frost on the evaporator 110, or when a predetermined time has passed since the start of defrost and a situation has been reached in which completion of defrosting is expected, the defrost operation in the refrigeration device 1 ends and transitions to a normal cooling operation state.

[0072] When performing normal cooling operation in the refrigeration device 1 after the defrost operation is completed, the cooling medium whose temperature has been lowered by the defrost operation may be introduced into the gas cooler 30 by controlling the cooling medium circuit. If the cooling medium whose temperature has been lowered is used for heat exchange in the gas cooler 30, the temperature of the refrigerant at the refrigerant outlet of the gas cooler 30 can be lowered, and the efficiency can be improved, thereby making effective use of cold energy.

[0073] In this manner, in the refrigeration system according to this embodiment, a bypass flow path 90 is provided to allow the warmed refrigerant for defrosting to flow to the external evaporator 110 connected as an element of the refrigeration cycle. When defrosting is performed, the refrigerant outlet of the low-stage compressor 11 in the two-stage compression refrigeration cycle is connected to the refrigerant inlet of the evaporator 110 via the bypass flow path 90, and defrosting is performed using intermediate-pressure gas-phase refrigerant delivered from the low-stage compressor 11. Therefore, the pressure of the refrigerant circulated for defrosting does not become high as in the case of two-stage compression as in normal cooling operation, and high-pressure measures for each part of the flow path related to defrosting are not required, thereby reducing the cost of the system.

[0074] In the refrigeration device according to the above embodiment, the expansion valve 105 and the evaporator 110, which are elements of the refrigeration cycle, are attached externally as a load unit, forming a so-called condensing unit. However, this is not limited to this, and the expansion valve and the evaporator can be incorporated into the device to form an integrated refrigeration device that can complete the refrigeration cycle within a single device.

[0075] In addition, in the refrigeration device according to the embodiment, the devices connected to the intermediate heat exchanger 20 are switched between a normal cooling operation state and a defrost operation state by the bypass flow path 90, and the intermediate heat exchanger 20 is also used as a second intermediate heat exchanger, but the present invention is not limited to this. In addition to the intermediate heat exchanger, a predetermined second intermediate heat exchanger may be provided to exchange heat with another heat medium and evaporate the refrigerant that has been used for defrosting in the evaporator in the defrost operation state and has had its temperature lowered. In this case, although an extra installation space is required for the heat exchanger, the positional relationship of the heat exchanger with the evaporator and the low-stage compressor can be optimized for defrosting purposes, and the flow path for circulating the refrigerant for defrosting need not be complicated, simplifying the device structure.

[0076] (Second embodiment of the present invention) In the refrigeration device according to the first embodiment, a liquid cooling medium is used as the cooling medium for heat exchange with the refrigerant in the gas cooler 30 and the intermediate heat exchanger 20. However, this is not limited to this, and in a second embodiment, the cooling medium can also be air forcibly introduced by a fan.

[0077] In this case, the intermediate heat exchanger 22, which also serves as the intermediate second heat exchanger as in the above embodiment, and the gas cooler 32 are air-cooled heat exchangers in which the cooling medium that exchanges heat with the refrigerant is air forced through by a fan 37, as shown in Figures 3 and 4.

[0078] The intermediate heat exchanger 22 is a heat exchanger that circulates the refrigerant that has left the low-stage compressor 11 in a hollow portion isolated from the outside by a partition wall that serves as a heat transfer section, and exchanges heat between the refrigerant and air serving as a cooling medium flowing outside the partition wall via the partition wall. The configuration of the intermediate heat exchanger 22 is similar to that of a known heat exchanger such as a radiator that releases heat from a fluid to be cooled flowing inside to the surrounding air, and a detailed description thereof will be omitted.

[0079] As in the first embodiment, in the defrost operation state, the intermediate heat exchanger 22 has a refrigerant inlet connected to the refrigerant outlet of the evaporator 110 via the bypass flow path 90, and has a refrigerant outlet connected to the refrigerant inlet of the low-stage compressor 11, and serves as a second intermediate heat exchanger to evaporate the refrigerant after flowing through the evaporator by heat exchange with air, which is a cooling medium.

[0080] The gas cooler 32 is a heat exchanger that circulates the refrigerant that has left the high-stage compressor 12 and passed through the oil separator 70 in a hollow portion isolated from the outside by a partition wall serving as a heat transfer section, and exchanges heat between the refrigerant and air serving as a cooling medium flowing outside the partition wall via the partition wall. The configuration of the gas cooler 32 is also similar to that of a known heat exchanger such as a radiator that releases heat from a fluid to be cooled flowing inside to the surrounding air, and a detailed description thereof will be omitted.

[0081] A fan 37 is provided outside the gas cooler 32, and the airflow forcibly generated by the fan 37 is directed against the partition wall, thereby promoting heat exchange between the air and the refrigerant. The fan 37 is a known axial flow fan or centrifugal fan that supplies air as a cooling medium as a continuous flow toward the gas cooler 32, and a detailed description thereof will be omitted.

[0082] One or more of the gas coolers 32 are arranged overlapping with the intermediate heat exchanger 22 in the air flow direction, and the fan 37 for air ventilation is shared with the intermediate heat exchanger 22 . In this second embodiment, the configurations of each part of the refrigeration device 1 other than the intermediate heat exchanger 22 and the gas cooler 32, as well as the configurations of the external expansion valve 105 and the evaporator 110, are the same as those in the first embodiment, and therefore will not be described.

[0083] When the refrigeration system 1 is in a normal cooling operation state, the refrigerant compressed and pressurized by the low-stage compressor 11 and increased in pressure and temperature is introduced into the intermediate heat exchanger 22. The intermediate heat exchanger 22 exchanges heat between the refrigerant and air as a cooling medium forcedly ventilated by a fan 37, thereby cooling the refrigerant to lower its temperature. The refrigerant cooled by this intermediate heat exchanger 22 flows toward the liquid separator 60, as in the first embodiment.

[0084] The gas phase refrigerant separated from the liquid phase in the liquid separator 60 is compressed and pressurized in the high stage side compressor 12, and the pressure and temperature are further increased. Then, the refrigerant discharged from the high stage side compressor 12 is introduced into the gas cooler 32 after being separated from the refrigeration oil through the oil separator 70.

[0085] In the gas cooler 32, the refrigerant is cooled by heat exchange between the refrigerant and air as a cooling medium forcedly ventilated by a fan 37. The refrigerant having been cooled and lowered in temperature leaves the gas cooler 32, reaches the expansion valve 42, and flows into the receiver 50 in an expanded and reduced-pressure state.

[0086] In the receiver 50, the refrigerant in a gas-liquid two-phase state is separated into a gas-phase refrigerant and a liquid-phase refrigerant. Each process of the refrigeration cycle after this is the same as that of the first embodiment. The gas-phase refrigerant expands from the receiver 50 through the expansion valve 43, and then merges with the refrigerant that has left the intermediate heat exchanger 20 and flows into the liquid separator 60. In addition, the liquid-phase refrigerant leaves the receiver 50 and proceeds through two branched flow paths, one part of which expands through the expansion valve 41 and flows into the liquid separator 60, and the remaining part is cooled by heat exchange in the economizer 80, exits from the liquid-phase refrigerant outlet of the refrigeration device 1, and is sent to the load unit outside the refrigeration device 1. In the load unit, the refrigerant expands through the expansion valve 105 to reduce the pressure and temperature, reaches the evaporator 110, absorbs heat by heat exchange to cool the surroundings, and then exits the evaporator 110 and returns to the refrigeration device 1.

[0087] The refrigerant leaving the evaporator 110 flows into the economizer 80, where its temperature is increased by heat exchange, and then it enters the low-stage compressor 11, where the respective processes subsequent to compression are repeated in the same manner.

[0088] On the other hand, when the refrigeration system 1 is in a defrost operation state, as in the first embodiment, the low-stage compressor 11, which is in an operating state, circulates the refrigerant through the circulation path (see Figure 4) of the refrigerant from the low-stage compressor 11 via the evaporator 110 and the intermediate heat exchanger 22 to the low-stage compressor 11, and defrosting progresses in the evaporator 110.

[0089] In the intermediate heat exchanger 22, the refrigerant, which has had its pressure and temperature reduced after leaving the evaporator 110 and passing through the expansion valve 92a of the second flow path 92, exchanges heat with air forcibly ventilated by the fan 37 and evaporates, cooling the air. The refrigerant leaves the intermediate heat exchanger 20 and returns to the low-stage compressor 11, and thereafter continues to circulate in the same manner through the circulation path while defrosting in the evaporator 110 progresses, until the end of the defrost operation.

[0090] In the second embodiment, the intermediate heat exchanger 22 also serves as the second intermediate heat exchanger, but the present invention is not limited to this, and a second intermediate heat exchanger may be provided separately from the intermediate heat exchanger. In this case, air is used as a common heat medium for heat exchange with the refrigerant in the gas cooler and the second intermediate heat exchanger, while the cooling medium for heat exchange with the refrigerant in the intermediate heat exchanger may be a medium other than air.

[0091] In addition, as described above, air is used as a common cooling medium for heat exchange with the refrigerant in the gas cooler and the intermediate heat exchanger, while the heat medium for heat exchange with the refrigerant in the intermediate second heat exchanger can be a medium other than air.

[0092] In addition, in the second embodiment, the intermediate heat exchanger 22 and the gas cooler 32 are arranged so as to overlap each other and share the fan 37, but this is not limited to the above. The intermediate heat exchanger and the gas cooler may be arranged separately and each may be provided with a separate fan for ventilation.

[0093] (Third embodiment of the present invention) In the refrigeration device according to the above embodiment, only one evaporator 110 is provided, and correspondingly, the cooling cycle and the circulation path for defrosting are also provided in a single system, and the configuration is such that either the cooling operation or the defrosting operation can be exclusively performed. However, this is not limited to this, and as a third embodiment, a configuration can be provided in which multiple systems of evaporators and intermediate heat exchangers that also serve as intermediate second heat exchangers are provided, and normal cooling operation by a refrigeration cycle including a specified evaporator and defrosting operation for other evaporators that are not performing cooling operation can be performed simultaneously in parallel.

[0094] In detail, a plurality of evaporators are connected in parallel to other elements of the refrigeration cycle, and a plurality of intermediate heat exchangers that can also serve as intermediate second heat exchangers are also provided in parallel. A bypass passage interconnects at least one evaporator, a low-pressure compressor, and at least one intermediate heat exchanger to generate a circulation path. However, this bypass passage is arranged in such a manner that the remaining evaporators, the low-pressure compressor, and the remaining intermediate heat exchangers are kept in a state in which they can execute a normal refrigeration cycle.

[0095] In detail, the bypass passage communicates the refrigerant inlet of an evaporator included in the circulation path with the refrigerant outlet of the low-stage compressor, as in the first embodiment, and communicates the refrigerant outlet of the same evaporator with the refrigerant inlet of the intermediate heat exchanger. Also, the bypass passage communicates the refrigerant inlet of an intermediate heat exchanger included in the circulation path with the refrigerant outlet of the evaporator, as in the first embodiment, and communicates the refrigerant outlet of the same intermediate heat exchanger with the refrigerant inlet of the low-stage compressor. On the other hand, the bypass passage does not prevent the refrigerant from flowing from the refrigerant outlet of the low-stage compressor to the refrigerant inlets of the remaining intermediate heat exchangers. Also, the bypass passage does not prevent the refrigerant from flowing from the remaining evaporators via the economizer to the refrigerant inlets of the low-stage compressor. The arrangement of the bypass flow paths is set so that a similar circulation path is formed for each of the plurality of evaporators and intermediate heat exchangers.

[0096] In this case, a defrost operation state in which a part of the refrigerant that has passed through the low-stage compressor is circulated through the evaporator and the intermediate heat exchanger included in the predetermined circulation path, and a normal refrigeration cycle in which the other part of the refrigerant that has passed through the low-stage compressor is circulated through the remaining evaporators and the remaining intermediate heat exchangers, i.e., a normal cooling operation, can be executed in parallel. By switching the arrangement of the bypass flow path, the evaporator to be defrosted can be switched, and the defrost operation state and the cooling operation can be executed in parallel in the same manner.

[0097] As a result, the growth of frost on the evaporator can be prevented by defrosting, and the cooling target can be continuously cooled by the refrigeration cycle while eliminating adverse effects such as a decrease in cooling capacity due to frost, and the defrosting is less likely to cause a rise in the temperature of the cooling target, so that the effect of the defrosting itself on the cooling target can be reduced. Furthermore, by controlling the arrangement of the bypass flow path to switch so that defrosting is distributed and performed at a stage when the amount of frost does not become large in each evaporator, one defrosting can be completed in a short time, and operation can be continued while maintaining the cooling capacity.

[0098] In this way, when the defrost operation for a specified evaporator and the normal cooling operation by the refrigeration cycle including the other evaporators can be performed in parallel, if a structure is adopted in which a plurality of intermediate heat exchangers 23, 24 are stacked on the air-cooled gas cooler 33 using a shared fan 38 as shown in FIG. 5, the air flow paths in the gas cooler 33 and the intermediate heat exchangers 23, 24 are interconnected.

[0099] For this reason, a situation may arise in which air that has been cooled through heat exchange in one intermediate heat exchanger 23 that is included in the circulation path through the bypass flow path and is in defrost operation is introduced into the gas cooler 33 or another intermediate heat exchanger 24 that is in a state where a normal refrigeration cycle is being executed, and exchanges heat with the refrigerant (see Figure 6).

[0100] In this way, by introducing air that has been cooled through heat exchange in the intermediate heat exchanger 23 in defrost operation into the gas cooler 33 and using it for heat exchange with the refrigerant, the cold energy obtained by defrosting is appropriately recovered to lower the air temperature, and accordingly the temperature of the refrigerant is also lowered. This makes it possible to lower the refrigerant temperature without inputting energy from the outside, and improves the efficiency of the refrigeration cycle.

[0101] Furthermore, by utilizing this, when the outside air temperature, i.e., the temperature of the air as a cooling medium, is high, such as during the day in summer, a predetermined evaporator in a state in which a normal refrigeration cycle is executed, the low-stage compressor, and the intermediate heat exchanger 23 overlapping the gas cooler 33 can be actively switched to a state in which they communicate with each other to generate a circulation path by switching control of the bypass flow path, and a defrost operation state due to these can be executed in parallel with the refrigeration cycle. As a result, even in a situation in which the outside air temperature is high and the efficiency of the refrigeration cycle is reduced, the air cooled by heat exchange with the refrigerant in the intermediate heat exchanger 23 in the defrost operation state is introduced into the gas cooler 33, so that the refrigerant temperature can be appropriately lowered to maintain the operating state of the refrigeration cycle, and the refrigeration device can be operated smoothly.

[0102] As a result, even when the outside air temperature is high and the temperature difference with the refrigerant is small, making it difficult for heat exchange to proceed, it is possible to prevent the refrigerant from becoming pressurized, and it is also possible to eliminate the need for high-pressure measures that increase costs, such as the installation of a sprinkler system that uses the latent heat of vaporization to lower the air intake temperature.

[0103] In addition, an intermediate heat exchanger that also serves as the second intermediate heat exchanger may be disposed downstream of the gas cooler in the direction of ventilation by the fan. For example, during defrost operation in winter or other conditions where the air temperature is low, air whose temperature has been increased by heat exchange in the gas cooler flows into the intermediate heat exchanger in the defrost operation state, allowing the intermediate heat exchanger to stably function as an evaporator that absorbs heat from the air, and enabling the air to be effectively used as an evaporation heat source.

[0104] In the example shown in Figures 5 and 6, a part of the gas cooler 33 is located downstream of the intermediate heat exchangers 23, 24 in the ventilation direction by the fan 38, and the air cooled after heat exchange in any of the intermediate heat exchangers in the defrost operation state can be introduced into the gas cooler 33. However, in the case of a configuration in which the intermediate heat exchanger is located downstream of the gas cooler in the ventilation direction by the fan, the fan can be rotated in the opposite direction to that in the normal cooling operation, the ventilation direction by the fan can be reversed, and the cooled air after passing through the intermediate heat exchanger can be introduced into the gas cooler. [Explanation of symbols]

[0105] 1 Refrigeration equipment 11 Low stage compressor 12 High stage compressor 20, 22 Intermediate heat exchanger 23, 24 Intermediate heat exchanger 30, 32, 33 Gas cooler 37, 38 Fan 41, 42, 43 Expansion valve 50 Receiver 60 liquid separator 70 Oil Separator 80 Economizer 90 Bypass flow path 91 First Channel 92 Second flow path 92a Expansion valve 93 Third flow path 105 Expansion valve 110 Evaporator

Claims

1. In a refrigeration system that uses carbon dioxide as a refrigerant and executes a vapor compression refrigeration cycle and performs two-stage compression on the refrigerant, One or more low-stage compressors that compress a gas phase refrigerant; one or more high-stage compressors that further compress the refrigerant discharged from the low-stage compressor; a gas cooler that cools the refrigerant discharged from the high-stage compressor; an intermediate heat exchanger between the low-stage compressor and the high-stage compressor for cooling the refrigerant discharged from the low-stage compressor by heat exchange with a predetermined cooling medium; a bypass flow path through which the refrigerant flows during a defrost operation; and an intermediate second heat exchanger for exchanging heat between the refrigerant used for defrosting and another heat medium during the defrosting operation. At least one expansion valve that expands the refrigerant to reduce its pressure, and an evaporator that evaporates the refrigerant that has left the expansion valve and absorbs heat from the surroundings are connected from the outside, so that a refrigeration cycle can be performed; the bypass flow passage, in a defrost operation state, connects a refrigerant inlet of the low stage compressor to a refrigerant outlet of the intermediate second heat exchanger, connects a refrigerant outlet of the low stage compressor to a refrigerant inlet of the evaporator, and further connects a refrigerant outlet of the evaporator to a refrigerant inlet of the intermediate second heat exchanger; In a defrost operation state, the low-stage compressor circulates refrigerant through a circulation path from the low-stage compressor via the bypass flow path to the low-stage compressor via an evaporator and the intermediate second heat exchanger, thereby progressing defrosting in the evaporator, The intermediate second heat exchanger evaporates the refrigerant by heat exchange in a defrost operation state. A refrigeration device characterized by the above.

2. A refrigeration system having at least a compressor, a gas cooler, an expansion valve, and an evaporator that executes a vapor compression refrigeration cycle using carbon dioxide as a refrigerant, and performing two-stage compression of the refrigerant, an intermediate heat exchanger between a low-stage compressor and a high-stage compressor that perform two-stage compression, for cooling the refrigerant that has left the low-stage compressor by heat exchange with a predetermined cooling medium; a bypass flow path through which the refrigerant flows during a defrost operation; and an intermediate second heat exchanger for exchanging heat between the refrigerant used for defrosting and another heat medium during the defrosting operation. the bypass flow passage, in a defrost operation state, connects a refrigerant inlet of the low stage compressor to a refrigerant outlet of the intermediate second heat exchanger, connects a refrigerant outlet of the low stage compressor to a refrigerant inlet of the evaporator, and further connects a refrigerant outlet of the evaporator to a refrigerant inlet of the intermediate second heat exchanger; In a defrost operation state, the low-stage compressor circulates refrigerant through a circulation path from the low-stage compressor via the bypass flow path to the low-stage compressor via an evaporator and the intermediate second heat exchanger, thereby progressing defrosting in the evaporator, The intermediate second heat exchanger evaporates the refrigerant by heat exchange in a defrost operation state. A refrigeration device characterized by the above.

3. In the refrigeration apparatus according to claim 1 or 2, the intermediate heat exchanger is connected to a refrigerant outlet of the evaporator through the bypass passage in a defrost operation state, and is connected to a refrigerant inlet of a low-stage compressor through the bypass passage, so as to also serve as the intermediate second heat exchanger included in the circulation path; The other heat medium is used as the cooling medium. A refrigeration device characterized by the above.

4. In the refrigeration apparatus according to claim 1 or 2, The low-stage compressor and the high-stage compressor are operable independently of each other, In the defrost operation state, a low-stage compressor included in the circulation path is operated, while a high-stage compressor not performing a refrigeration cycle is stopped from operating. A refrigeration device characterized by the above.

5. In the refrigeration apparatus according to claim 1 or 2, The evaporator is provided in a plurality of units in a state of being connected in parallel with other elements of the refrigeration cycle, the bypass flow path interconnects at least one evaporator, the low-stage side compressor, and the intermediate second heat exchanger to generate the circulation path, while an arrangement mode can be set for each evaporator such that the remaining evaporator, the low-stage side compressor, and the intermediate second heat exchanger are maintained in a state in which a normal refrigeration cycle can be executed; A defrost operation state in which a part of the refrigerant that has passed through the low-stage compressor is circulated through an evaporator and a second intermediate heat exchanger included in the circulation path, and a normal refrigeration cycle in which the other part of the refrigerant that has passed through the low-stage compressor is circulated through the remaining evaporator and the intermediate heat exchanger are executed in parallel while the evaporator to be defrosted can be replaced by switching the arrangement of the bypass flow path. A refrigeration device characterized by the above.

6. In the refrigeration apparatus according to claim 1 or 2, The gas cooler is configured to circulate the other heat medium used in the intermediate second heat exchanger to exchange heat with the refrigerant, A flow path of the other heat medium in the intermediate second heat exchanger communicates with a flow path of the other heat medium in the gas cooler, At least a part of the other heat medium cooled through heat exchange in the intermediate second heat exchanger in the defrost operation state is introduced into the gas cooler and exchanges heat with the refrigerant. A refrigeration device characterized by the above.

7. 7. The refrigeration apparatus according to claim 6, The gas cooler and the intermediate second heat exchanger are air-cooled heat exchangers in which the other heat medium that exchanges heat with the refrigerant is air that is forced to circulate by a fan, The gas cooler is arranged so that one or more heat exchange sections through which the refrigerant and air pass are overlapped with the intermediate second heat exchanger in the air ventilation direction, and a fan for ventilation of air is shared with the intermediate second heat exchanger. A refrigeration device characterized by the above.

8. In the refrigeration apparatus according to claim 5, The gas cooler is an air-cooled heat exchanger that exchanges heat between a refrigerant and air, The intermediate second heat exchanger is an air-cooled heat exchanger in which the other heat medium that exchanges heat with the refrigerant is air, When the temperature of the air that exchanges heat with the refrigerant in the gas cooler is increased, the bypass flow passage is switched to a state in which a predetermined evaporator in a state in which a normal refrigeration cycle is executed, the low-stage compressor, and the intermediate second heat exchanger are mutually communicated to generate the circulation path, and a defrost operation state is executed in parallel with the refrigeration cycle; The air cooled by heat exchange with the refrigerant in the intermediate second heat exchanger in the defrost operation state is introduced into the gas cooler. A refrigeration device characterized by the above.

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