Refrigeration system

Abstract

The present disclosure provides a refrigeration system capable of improving efficiency of an air conditioning temperature zone using carbon dioxide (R744), a natural refrigerant. The refrigeration system includes a refrigeration cycle circuit that connects an outdoor unit 10 including a low-stage compressor 11, a high-stage compressor 12, an outdoor heat exchanger 15, and a gas-liquid separator 16, an indoor unit 20 including an indoor heat exchanger 22, and a refrigeration-facility unit 30 including a refrigeration-facility heat exchanger 31, a gas refrigerant return pipe 60 is provided to send a gas refrigerant from the gas-liquid separator 16 to the high-stage compressor 12, and the gas refrigerant return pipe 60 is provided with a gas refrigerant return expansion valve 61 that controls a return amount of the gas refrigerant from the gas-liquid separator 16.

Description

Technical Field

[0001] The present disclosure relates to a refrigeration system.Background Art

[0002] Patent Literature 1 discloses a refrigeration system including a cascade heat exchanger that exchanges heat between a low-pressure side of an air-conditioning refrigerant circuit and a high-pressure of a refrigerant circuit for a refrigeration storage facility, in which, during a cooling operation of the air-conditioning refrigerant circuit, the refrigerant on the high-pressure side of the refrigerant circuit for a refrigeration storage facility flows through a cascade heat exchanger through the condenser, and during a heating operation of the air-conditioning refrigerant circuit, the refrigerant on the high-pressure side of the refrigerant circuit for a refrigeration storage facility flows through the cascade heat exchanger and then flows through the condenser.

[0003] Patent Literature 2 discloses a heat source unit and a refrigeration apparatus that prevent a situation in which a gas refrigerant in a gas-liquid separator cannot be sent to an intermediate flow path when the outside-air temperature is high. In the heat source unit and the refrigeration apparatus, when a first condition is satisfied in which an medium pressure corresponding to a pressure in the intermediate flow path is greater than a predetermined value during operations of a first compressor, a second compressor, and a third compressor, a control unit executes a first operation to increase a rotation speed of the third compressor.Citation ListPatent Literature

[0004] Patent Literature 1: Japanese Patent No. 4169638 Patent Literature 2: Japanese Patent Laid-Open No. 2022-039365 Summary of InventionTechnical Problem

[0005] A first aspect of the present disclose provides a refrigeration system capable of improving efficiency of an air conditioning temperature zone using carbon dioxide (R744), a natural refrigerant.

[0006] A second aspect of the present disclosure provides a refrigeration system including a refrigeration circuit with a simple configuration, and capable of improving a refrigeration capacity.Solution to Problem

[0007] The refrigeration system according to the first aspect of the present disclosure includes a refrigeration cycle circuit that connects an outdoor unit including a plurality of compressors, an outdoor heat exchanger, and a gas-liquid separator, an indoor unit including an indoor heat exchanger, and a refrigeration-facility unit including a refrigeration-facility heat exchanger, the plurality of compressors includes a low-stage compressor and a high-stage compressor, a gas refrigerant return pipe is provided to send a gas refrigerant from the gas-liquid separator to the high-stage compressor, and the gas refrigerant return pipe is provided with a gas refrigerant return expansion valve that controls a return amount of the gas refrigerant from the gas-liquid separator.

[0008] The present application incorporates the disclosure of Japanese Patent Application No. 2022-184006, filed on November 17, 2022 in its entirety.

[0009] The refrigeration system according to the second aspect of the present disclosure includes a refrigeration circuit provided with a plurality of compressors, a heat source-side heat exchanger, a plurality of utilization-side heat exchangers, and a gas-liquid separator, the plurality of compressors include a low-stage compressor and a high-stage compressor, the plurality of utilization-side heat exchangers includes a first utilization-side heat exchanger and a second utilization-side heat exchanger having a refrigerant evaporation temperature lower than that of the first utilization-side heat exchanger, the refrigeration circuit is provided with a switching mechanism that causes the refrigerant, which is discharged from the high-stage compressor and flows through at least one of the heat source-side heat exchanger and the first utilization-side heat exchanger, to flow to the gas-liquid separator, and a throttling mechanism is provided between the heat source-side heat exchanger, the first utilization-side heat exchanger, and the gas-liquid separator.

[0010] The present application incorporates the disclosure of Japanese Patent Application No. 2023-142103, filed on September 1, 2023 in its entirety.Advantageous Effects of Invention

[0011] According to the first aspect of the present disclosure, the return amount of the gas refrigerant from the gas-liquid separator is controlled by control of the opening degree of the gas refrigerant return expansion valve, whereby a differential pressure of the refrigerant sent to the indoor heat exchanger can be generated. Thus, it is possible to control the pressure by adding a specified value to the evaporation temperature of the indoor heat exchanger having a high evaporation temperature, and to improve efficiency of an air conditioning temperature zone using carbon dioxide (R744), a natural refrigerant with high environmental preservation characteristics.

[0012] According to the second aspect of the present disclosure, the refrigeration circuit can be provided with a simple configuration, enabling stable operation.Brief Description of Drawings

[0013] [FIG. 1] FIG. 1 is a circuit diagram of a refrigeration system according to a first embodiment showing an operation during a cooling operation. [FIG. 2] FIG. 2 is a circuit diagram of a refrigeration system according to the first embodiment showing an operation during a heating operation. [FIG. 3] FIG. 3 is a circuit diagram of the refrigeration system according to the first embodiment showing a heating operation at full capacity. [FIG. 4] FIG. 4 is a circuit diagram of the refrigeration system according to the first embodiment showing an operation when a large capacity is required in a refrigeration-facility unit and a heat quantity for heating is not required. [FIG. 5] FIG. 5 is a diagram showing a refrigeration circuit of a refrigeration system according to a second embodiment. [FIG. 6] FIG. 6 is a block diagram of the refrigeration system according to the second embodiment. [FIG. 7] FIG. 7 is a circuit diagram showing a refrigeration circuit of a refrigeration system during a heating operation according to the second embodiment. [FIG. 8] FIG. 8 is a circuit diagram showing a refrigeration circuit of a refrigeration system during a heating operation according to the second embodiment. [FIG. 9] FIG. 9 is a circuit diagram showing a refrigeration circuit of a refrigeration system during a heating operation according to the second embodiment. [FIG. 10] FIG. 10 is a p-h chart showing a state of a refrigerant in the refrigeration circuit according to the second embodiment. [FIG. 11] FIG. 11 is a flowchart showing an operation of the refrigeration system according to the second embodiment. [FIG. 12] FIG. 12 is a circuit diagram showing a refrigeration circuit of a refrigeration system according to the second embodiment in refrigerant recovery / vacuuming work. [FIG. 13] FIG. 13 is a circuit diagram showing a refrigeration circuit of a refrigeration system according to the second embodiment in refrigerant filling work. [FIG. 14] FIG. 14 is a circuit diagram showing a refrigeration circuit of a refrigeration system according to the second embodiment in a regulation operation. Description of Embodiments(Findings on which present disclosure is based)

[0014] At the time when the inventors have conceived of a refrigeration system according to a first aspect of the present disclosure, there has been a refrigeration system, in which refrigeration and freezing equipment and air conditioning equipment are combined into a single refrigeration circuit to use the exhaust heat from the refrigeration and freezing equipment for heating in the winter, in stores such as convenience stores, thereby saving energy.

[0015] In such a related art, HFC refrigerants are used as refrigerants, but there has been a demand for a changeover to low GWP refrigerants from the viewpoint of environmental preservation in recent years.

[0016] However, the low GWP refrigerants are slightly flammable or toxic, and have a problem in safety due to an increase in the refrigerant filling amount since a system becomes large in size when refrigeration circuits are fused into one. On the other hand, although carbon dioxide (R744), a natural refrigerant, is non-toxic and non-flammable, when such carbon dioxide is used in air conditioning devices, the efficiency is low in a refrigerant temperature zone of the air conditioning devices, whereby the inventors have found that the carbon dioxide refrigerant has been considered not suitable and a technique development is required, and have come up with the subject matter of the present disclosure in order to solve the problems.

[0017] The present disclosure provides the refrigeration system capable of improving efficiency of an air conditioning temperature zone using carbon dioxide (R744), a natural refrigerant.

[0018] Embodiments will be described in detail below with reference to the drawings. However, unnecessarily detailed descriptions will be avoided. For example, a detailed description of a well-known matter or a redundant description of a substantially identical structure may be avoided. This is to avoid rendering a related description unduly lengthy and to thereby facilitate understanding by those skilled in the art.

[0019] The following description and the accompanying drawings are provided to allow those skilled in the art to fully understand the present disclosure, and are not intended to limit the scope of the claims.(First Embodiment)

[0020] Hereinafter, a first embodiment corresponding to a first aspect of the present disclosure will be described with reference to the drawings.[1-1-1. Configuration of Refrigeration System]

[0021] FIG. 1 is a diagram showing a refrigeration cycle circuit of a refrigeration system 1 according to a first embodiment.

[0022] As shown in FIG. 1, the refrigeration system 1 includes an outdoor unit 10, an indoor unit 20, and a refrigeration-facility unit 30.

[0023] The indoor unit 20 performs air conditioning on an interior of a store, for example, a convenience store or a supermarket, and the refrigeration-facility unit 30 performs cooling on an interior of a refrigerating display showcase or a freezing display showcase that serves as a cooling storage facility installed in the store.

[0024] The outdoor unit 10 includes a low-stage compressor 11 and two high-stage compressors 12 and 12. The two high-stage compressors 12 are connected in parallel to the low-stage compressor 11.

[0025] An accumulator 13 is disposed between the low-stage compressor 11 and the high-stage compressor 12.

[0026] In other words, a refrigerant discharged from the low-stage compressor 11 is separated into gas and liquid by the accumulator 13, and only the gas refrigerant is sent to the high-stage compressor 12.

[0027] An oil separator 14 is connected to a discharge side of the high-stage compressor 12. An outdoor heat exchanger 15 is connected to the oil separator 14 through a refrigerant pipe 40.

[0028] A first heating pipe 41, which is connected to the refrigerant pipe 40 between the indoor unit 20 and the accumulator 13, is connected to the refrigerant pipe 40 between the oil separator 14 and the outdoor heat exchanger 15.

[0029] In addition, a first outdoor return pipe 42, which is connected to the refrigerant pipe 40 between the refrigeration-facility unit 30 and the low-stage compressor 11, is connected to the refrigerant pipe 40 between the oil separator 14 and the outdoor heat exchanger 15.

[0030] A first switching mechanism 50 is provided between the oil separator 14 and the outdoor heat exchanger 15. The first switching mechanism 50 includes a first cooling valve 51 that opens and closes the refrigerant pipe 40 between the oil separator 14 and the outdoor heat exchanger 15, a first heating valve 52 that is provided in a middle of the first heating pipe 41 to open and close the first heating pipe 41, and an outdoor refrigerant return valve 53 that is provided in a middle of the first outdoor return pipe 42 to open and close the first outdoor return pipe 42.

[0031] A gas-liquid separator 16 is connected to the outdoor heat exchanger 15 through the refrigerant pipe 40. A refrigeration-facility heat exchanger 31 of the refrigeration-facility unit 30 is connected to the gas-liquid separator 16 through the refrigerant pipe 40 and an inlet-side refrigeration-facility expansion mechanism 32. The refrigeration-facility heat exchanger 31 is connected to the low-stage compressor 11 through an outlet-side refrigeration-facility expansion mechanism 33.

[0032] A second cooling pipe 43, which is connected to the indoor heat exchanger 22 through an indoor expansion mechanism 21, is connected to the refrigerant pipe 40 between the outdoor heat exchanger 15 and the gas-liquid separator 16.

[0033] A second heating pipe 44, which is connected to the indoor heat exchanger 22, is connected to the refrigerant pipe 40 between the outdoor heat exchanger 15 and the gas-liquid separator 16.

[0034] A second outdoor return pipe 45, which is connected to the refrigerant pipe 40 between the refrigeration-facility heat exchanger 31 and the gas-liquid separator 16, is connected to the refrigerant pipe 40 between the outdoor heat exchanger 15 and the gas-liquid separator 16.

[0035] A second switching mechanism 54 is provided between the outdoor heat exchanger 15 and the gas-liquid separator 16. The second switching mechanism 54 includes a second cooling valve 55 that opens and closes the refrigerant pipe 40 between the outdoor heat exchanger 15 and the gas-liquid separator 16, a third cooling valve 56 that is provided in a middle of the second cooling pipe 43 to open and close the second cooling pipe 43, and a second heating valve 57 that is provided in a middle of the second heating pipe 44 to open and close the second heating pipe 44.

[0036] A refrigerant return expansion mechanism 58 is provided in a middle of the second outdoor return pipe 45 to control a flow rate of the second outdoor return pipe 45.

[0037] Check valves 59 are provided downstream of the second cooling valve 55, the third cooling valve 56, and the second heating valve 57, respectively.

[0038] The indoor heat exchanger 22 is connected to the high-stage compressor 12 through the refrigerant pipe 40, an on-off valve 23, and the accumulator 13.

[0039] In the present embodiment, a gas refrigerant return pipe 60 is provided to send a gas refrigerant from the gas-liquid separator 16 to a suction side of the accumulator 13. A gas refrigerant return expansion mechanism 61 is provided in a middle of the gas refrigerant return pipe 60.[1-2 Operation]

[0040] Next, an operation of the present embodiment will be described.

[0041] First, a cooling operation will be described.

[0042] During a cooling operation, as shown in FIG. 1, the first cooling valve 51 is opened, and the second cooling valve 55 and the third cooling valve 56 are opened. The first heating valve 52, the second heating valve 57, the first high load valve, the outdoor return valve, and the outdoor return expansion mechanism are closed.

[0043] In this state, the low-stage compressor 11 and each of the high-stage compressors 12 are driven, whereby the refrigerant compressed by the low-stage compressor 11 is sent to each of the high-stage compressors 12, further compressed by each of the high-stage compressor 12, and discharged toward the oil separator 14.

[0044] The refrigerant passing through the oil separator 14 is sent to the outdoor heat exchanger 15 through the first cooling valve 51, and exchanges heat with outside air in the outdoor heat exchanger 15.

[0045] The refrigerant after heat exchange is sent to the gas-liquid separator 16 through the second cooling valve 55, and sent to the indoor heat exchanger 22 through the third cooling valve 56.

[0046] The refrigerant exchanges heat with indoor air in the indoor heat exchanger 22 to cool the indoor air. The refrigerant subjected to heat exchange with the indoor air is returned to each of the high-stage compressors 12 through the accumulator 13.

[0047] On the other hand, some of the refrigerant from the gas-liquid separator 16 is sent to the refrigeration-facility heat exchanger 31 through the inlet-side refrigeration-facility expansion mechanism 32, and is subjected to heat exchange in the refrigeration-facility heat exchanger 31 to cool the refrigeration-facility unit 30. The refrigerant subjected to heat exchange in the refrigeration-facility heat exchanger 31 is returned to the low-stage compressor 11 through the inlet-side refrigeration-facility expansion mechanism 32.

[0048] Next, a heating operation will be described.

[0049] FIG. 2 is a circuit diagram of the refrigeration system 1 showing a heating operation. A flow of the refrigerant is indicated by arrows in the drawing.

[0050] As shown in FIG. 2, during the heating operation, the first heating valve 52 and the second heating valve 57 are opened, and the first cooling valve 51, the second cooling valve 55, the third cooling valve 56, and the outdoor refrigerant return valve 53 are closed.

[0051] In this state, the low-stage compressor 11 and each of the high-stage compressors 12 are driven, whereby the refrigerant compressed by the low-stage compressor 11 is sent to each of the high-stage compressors 12, further compressed by each of the high-stage compressor 12, and discharged toward the oil separator 14.

[0052] The refrigerant passing through the oil separator 14 is sent to the indoor heat exchanger 22 through the first heating valve 52, and exchanges heat with indoor air in the indoor heat exchanger 22 to heat the indoor air.

[0053] The refrigerant subjected to heat exchange in the indoor heat exchanger 22 is sent to the gas-liquid separator 16 through the second heating valve 57, is then sent to the refrigeration-facility heat exchanger 31 through the inlet-side refrigeration-facility expansion mechanism 32, and is subjected to heat exchange in the refrigeration-facility heat exchanger 31 to cool the refrigeration-facility unit 30.

[0054] The refrigerant subjected to heat exchange in the refrigeration-facility heat exchanger 31 is returned to the low-stage compressor 11 through the outlet-side refrigeration-facility expansion mechanism 33.

[0055] In other words, the refrigeration system 1 of the present disclosure is configured such that during heating, the indoor heat exchanger 22 functions as a condenser and the outdoor heat exchanger 15 is not used.

[0056] Next, a heating operation at full capacity will be described.

[0057] FIG. 3 is a circuit diagram of the refrigeration system 1 showing a heating operation at full capacity. A flow of the refrigerant is indicated by arrows in the drawing.

[0058] As shown in FIG. 3, during a heating operation at full capacity, the first heating valve 52, the second heating valve 57, the high load valve, and the high load expansion mechanism are opened, and the first cooling valve 51, the second cooling valve 55, and the third cooling valve 56 are closed.

[0059] In this state, the low-stage compressor 11 and each of the high-stage compressors 12 are driven, whereby the refrigerant compressed by the low-stage compressor 11 is sent to each of the high-stage compressors 12, further compressed by each of the high-stage compressor 12, and discharged toward the oil separator 14.

[0060] The refrigerant passing through the oil separator 14 is sent to the indoor heat exchanger 22 through the first heating valve 52, and exchanges heat with indoor air in the indoor heat exchanger 22 to heat the indoor air.

[0061] The refrigerant subjected to heat exchange in the indoor heat exchanger 22 is sent to the gas-liquid separator 16 through the second heating valve 57, and is then sent to the refrigeration-facility heat exchanger 31 through the inlet-side refrigeration-facility expansion mechanism 32. The refrigerant is subjected to heat exchange in the refrigeration-facility heat exchanger 31 to cool the refrigeration-facility unit 30, and the refrigerant subjected to heat exchange in the refrigeration-facility heat exchanger 31 is returned to the low-stage compressor 11 through the outlet-side refrigeration-facility expansion mechanism 33.

[0062] On the other hand, some of the refrigerant from the gas-liquid separator 16 is sent to the outdoor heat exchanger 15 through the refrigerant return expansion mechanism 58, subjected to heat exchange in the outdoor heat exchanger 15, and then returned to the low-stage compressor 11.

[0063] Thus, exhaust heat from the refrigeration-facility heat exchanger 31 and heat pumped up by the outdoor heat exchanger 15 can be used as heat for the indoor heat exchanger 22, thereby enabling more efficiently heating.

[0064] In this case, when an outside air temperature becomes lower than an interior temperature of the refrigeration-facility unit 30, an evaporation temperature of the refrigeration-facility unit 30 should be lowered in order to pump heat from the outdoor heat exchanger 15. When the evaporation temperature of the refrigeration-facility unit 30 is lowered, the temperature will be lower than a defined temperature, a thermal cycle will be short, and a short-cycle operation will occur, which may lead to a freezing accident of a product.

[0065] In the present embodiment, therefore, the opening degree of the outlet-side refrigeration-facility expansion mechanism 33 is controlled to balance a pressure with the refrigerant sent from the outdoor heat exchanger 15, whereby it is possible to avoid the above-described inconvenience.

[0066] Next, an operation will be described in a case where a large capacity is required in the refrigeration-facility unit 30 and a heat quantity for heating is not required.

[0067] FIG. 4 is a circuit diagram of the refrigeration system 1 showing an operation when a large capacity is required in the refrigeration-facility unit 30 and a heat quantity for heating is not required. A flow of the refrigerant is indicated by arrows in the drawing.

[0068] As shown in FIG. 4, when a large capacity is required in the refrigeration-facility unit 30 and a heat quantity for heating is not required, the first cooling valve 51, the second cooling valve 55, the first heating valve 52, and the second heating valve 57 are opened, and the refrigerant return valve and the third cooling valve 56 are closed.

[0069] In this state, the low-stage compressor 11 and each of the high-stage compressors 12 are driven, whereby the refrigerant compressed by the low-stage compressor 11 is sent to each of the high-stage compressors 12, further compressed by each of the high-stage compressor 12, and discharged toward the oil separator 14.

[0070] The refrigerant passing through the oil separator 14 is sent to the outdoor heat exchanger 15 through the first cooling valve 51, and exchanges heat with outside air in the outdoor heat exchanger 15.

[0071] The refrigerant after heat exchange is sent to the gas-liquid separator 16 through the second cooling valve 55.

[0072] On the other hand, the refrigerant passing through the oil separator 14 is sent to the indoor heat exchanger 22 through the first heating valve 52, exchanges heat with indoor air in the indoor heat exchanger 22 to heat the indoor air.

[0073] The refrigerant subjected to heat exchange in the indoor heat exchanger 22 interflows with the refrigerant sent from the outdoor heat exchanger 15 through the second heating valve 57, and is sent to the gas-liquid separator 16.

[0074] The refrigerant from the gas-liquid separator 16 is sent to the refrigeration-facility heat exchanger 31 through the inlet-side refrigeration-facility expansion mechanism 32. The refrigerant is subjected to heat exchange in the refrigeration-facility heat exchanger 31 to cool the refrigeration-facility unit 30, and the refrigerant subjected to heat exchange in the refrigeration-facility heat exchanger 31 is returned to the low-stage compressor 11 through the outlet-side refrigeration-facility expansion mechanism 33.

[0075] On the other hand, some of the refrigerant from the gas-liquid separator 16 is sent to the outdoor heat exchanger 15 through the refrigerant return expansion mechanism 58, and is returned to the low-stage compressor 11 after being subjected to heat exchange in the outdoor heat exchanger 15.

[0076] Thus, the outdoor heat exchanger 15 and the indoor heat exchanger 22 can be heated simultaneously by a heating operation capacity, and a heat quantity distribution thereof can be controlled. Furthermore, the outdoor heat exchanger 15 is heated, and thus frost adhering to the outdoor heat exchanger 15 can be removed.

[0077] In the present embodiment, the gas refrigerant return pipe 60 is provided to send the gas refrigerant from the gas-liquid separator 16 to the suction side of the accumulator 13. Then, the return amount of the gas refrigerant from the gas-liquid separator 16 is controlled by control of the opening degree of the gas refrigerant return expansion valve 61, whereby a differential pressure of the refrigerant sent to the indoor heat exchanger 22 can be generated.

[0078] Thus, it is possible to control the pressure by adding a specified value to the evaporation temperature of the indoor heat exchanger 22 having a high evaporation temperature. It is possible to improve efficiency of an air conditioning temperature zone, which is a weak point, using carbon dioxide (R744), a natural refrigerant with high environmental preservation characteristics.[1-3. Effects]

[0079] As described above, the refrigeration system according to the present embodiment includes a refrigeration cycle circuit that connects an outdoor unit 10 including a low-stage compressor 11, a high-stage compressor 12, an outdoor heat exchanger 15, and a gas-liquid separator 16, an indoor unit 20 including an indoor heat exchanger 22, and a refrigeration-facility unit 30 including a refrigeration-facility heat exchanger 31, a gas refrigerant return pipe 60 is provided to send a gas refrigerant from the gas-liquid separator 16 to the high-stage compressor 12, and the gas refrigerant return pipe 60 is provided with a gas refrigerant return expansion valve 61 that controls a return amount of the gas refrigerant from the gas-liquid separator 16.

[0080] Thus, the return amount of the gas refrigerant from the gas-liquid separator 16 is controlled by control of the opening degree of the gas refrigerant return expansion valve 61, whereby a differential pressure of the refrigerant sent to the indoor heat exchanger 22 can be generated. Therefore, it is possible to control the pressure by adding a specified value to the evaporation temperature of the indoor heat exchanger 22 having a high evaporation temperature, and to improve efficiency of an air conditioning temperature zone using carbon dioxide (R744), a natural refrigerant with high environmental preservation characteristics.

[0081] In the present embodiment, during the heating operation, the refrigeration cycle circuit is operated using the indoor heat exchanger 22 and the outdoor heat exchanger 15 as condensers and the refrigeration-facility heat exchanger 31 as an evaporator.

[0082] Thus, the flow direction on the high evaporation temperature side of the indoor heat exchanger 22 is reversed from that of the outdoor heat exchanger 15, and the heat pumped up from the outdoor heat exchanger 15 and the exhaust heat from the refrigeration-facility unit 30 are used together for the heating of the indoor heat exchanger 22. In addition, depending on conditions of the indoor heat exchanger 22, the outdoor heat exchanger 15 and the indoor heat exchanger 22 can be heated simultaneously, and the distribution of the heat amount can be controlled.

[0083] In the present embodiment, during the heating operation, the refrigeration cycle circuit is operated using the indoor heat exchanger 22 as a condenser, and the refrigeration-facility heat exchanger 31 and the outdoor heat exchanger 15 as evaporators.

[0084] Thus, the heat pumped up from the outdoor heat exchanger 15 and the exhaust heat from the refrigeration-facility heat exchanger 31 can be used together for the heating of the indoor heat exchanger 22, and when the outside air temperature becomes lower than the interior temperature of the refrigeration-facility unit 30, the pressure can be controlled to be the same. Therefore, it is possible to prevent the evaporation temperature of the refrigeration-facility unit 30 from dropping too low, and to control the temperature with high accuracy.

[0085] In the present embodiment, during the heating operation, the refrigeration cycle circuit is operated using the indoor heat exchanger 22 as a condenser, and only the refrigeration-facility heat exchanger 31 as an evaporator.

[0086] Thus, all of the exhaust heat from the refrigeration-facility unit 30 can be radiated with the indoor heat exchanger 22 having a high evaporation temperature. Therefore, the exhaust heat can be utilized without loss, and the heating operation can be performed with high efficiency.(Second Embodiment)(Findings on which present disclosure is based)

[0087] At the time when the inventors have conceived of a refrigeration system according to a second aspect of the present disclosure, there has been a refrigeration system including one refrigeration circuit that is provided with a low-stage compressor, a high-stage compressor, a plurality of utilization-side heat exchangers, and a heat source-side heat exchanger shared with these utilization-side heat exchangers, the utilization-side heat exchangers being operated in different evaporation temperature zones. Thus, the refrigeration system performs, for example, air conditioning of an air-conditioned space and cooling of the interior of the refrigeration-facility unit at the same time.

[0088] There has been known that such a refrigeration system includes a gas-liquid separator. In such a refrigeration system, the refrigerant discharged from the compressor flows into the utilization-side heat exchanger through the gas-liquid separator, thereby improving a refrigeration capacity.

[0089] In the above-described refrigeration system, the utilization-side heat exchanger is switched between a cooling operation and a heating operation. In such a refrigeration system, the inventors have found a problem that the configuration of the refrigeration circuit provided in the refrigeration system is complicated in order to flow the refrigerant, which is sent from the compressor, through the gas-liquid separator to the utilization-side heat exchanger in any of these operations, and have come to form the subject of the present disclosure to solve such a problem.

[0090] In view of the above, the present disclosure provides a refrigeration system including a refrigeration circuit with a simple configuration and capable of improving a refrigeration capacity.

[0091] Hereinafter, a second embodiment corresponding to a second aspect of the present disclosure will be described with reference to the drawings.[2-1-1. Configuration of Refrigeration System]

[0092] FIG. 5 is a circuit diagram showing a refrigeration system 101 according to a first embodiment. In FIG. 5, for the convenience of description, an opening / closing device in an open state is shown in white, and an opening / closing device in a closed state and expansion mechanism are shown in black. In FIG. 5, for the convenience of description, pipes through which a refrigerant flows are shown in thick lines, and pipes through which no refrigerant flows are shown in thin lines. In subsequent circuit diagrams, opening / closing devices and pipes are shown in the same manner as in FIG. 5.

[0093] As shown in FIG. 5, the refrigeration system 101 includes an outdoor unit 110, an indoor unit 120, and a refrigeration-facility unit 130, and these units are connected to each other by refrigerant pipes to form a refrigeration circuit 102 that functions as a flow path through which a refrigerant flows.

[0094] In the present embodiment, the refrigerant used in the refrigeration circuit 102 is, for example, refrigerant carbon dioxide (R744), a natural refrigerant that is non-flammable and non-toxic.

[0095] The indoor unit 120 includes an indoor heat exchanger 122 which is a utilization-side heat exchanger. The indoor unit 120 performs air conditioning on the interior of a store, which is an air-conditioned space, based on a setting temperature set by a user in a store such as a convenience store or a supermarket.

[0096] The refrigeration-facility unit 130 includes a refrigeration-facility heat exchanger 132 which is a utilization-side heat exchanger. The refrigeration-facility unit 130 performs cooling on an interior of a refrigerating display showcase or a freezing display showcase that serves as a cooling storage facility installed in the store, based on a setting temperature set by the user.

[0097] In the refrigeration system 101, when the setting temperature of the indoor unit 120 is set, a rotational frequency of each of the compressors and an air flow rate of blowers 118 and 128 are determined based on a temperature difference between the setting temperature and a temperature in the air-conditioned space in which the indoor unit 120 is installed. Furthermore, in the refrigeration system 101, when the setting temperature of the indoor unit 120 is set, an opening degree of a throttle valve provided in the indoor unit 120 is determined such that the degree of superheat of the refrigerant at each of an inlet side and an outlet side of the indoor heat exchanger 122 becomes a specified value. Thus, the refrigeration system 101 operates such that the air-conditioned space becomes the setting temperature.

[0098] Similarly, in the refrigeration system 101, when the setting temperature of the refrigeration-facility unit 130 is set, the rotational frequency of each of the compressors and the air flow rate of blowers 118 and 138 are determined based on a temperature difference between the setting temperature and a temperature in the interior of the showcase. Furthermore, in the refrigeration system 101, when the setting temperature of the refrigeration-facility unit 130 is set, an opening degree of a throttle valve provided in the refrigeration-facility unit 130 is determined such that the degree of superheat of the refrigerant at each of an inlet side and an outlet side of the refrigeration-facility heat exchanger 132 becomes a specified value. Thus, the refrigeration system 101 operates such that the interior of the showcase becomes the setting temperature.

[0099] Hereinafter, the operation, in which the refrigeration system 101 performs the air conditioning of the air-conditioned space and the indoor cooling of the showcase, will be referred to as a first operation mode.

[0100] The outdoor unit 110 functions as a so-called heat source device. The outdoor unit 110 is formed in such a manner that a plurality of compressors, a first switching mechanism 150, an outdoor heat exchanger 115, a second switching mechanism 154, and a gas-liquid separator 116 are sequentially connected.

[0101] The outdoor heat exchanger 115 corresponds to the "heat source-side heat exchanger" in the present disclosure.

[0102] In the present embodiment, the outdoor unit 110 is provided with a mechanism in which a low-stage compressor 111 and two high-stage compressors 112 and 112 are configured as a two-stage compressor. The two high-stage compressors 112 and 112 are both connected in series to the low-stage compressor 111. The two high-stage compressors 112 and 112 are connected in parallel to each other on a downstream side of the low-stage compressor 111.

[0103] Each of the compressors is a rotary compressor in which a compression mechanism is driven by a motor, for example. Each of the high-stage compressors 112 is driven to discharge the refrigerant at a higher discharge pressure than the low-stage compressor 111.

[0104] An accumulator 113 is disposed between the low-stage compressor 111 and the high-stage compressor 112. The accumulator 113 functions as a flow divider that distributes almost evenly oil sent from an oil separator 114 to each of the high-stage compressor 112.

[0105] The oil separator 114 is connected to a discharge side of the high-stage compressor 112. The first switching mechanism 150 is connected to the oil separator 114. In other words, the first switching mechanism 150 is connected to a discharge pipe of the high-stage compressor 112 through the oil separator 114.

[0106] The first switching mechanism 150 is a mechanism that switches the refrigerant sent from the high-stage compressor 112 in the refrigeration circuit 102 to flow through any one of a plurality of flow paths.

[0107] The first switching mechanism 150 includes a pipe 140 that connects the oil separator 114 and the outdoor heat exchanger 115. A first cooling valve 151 is provided in the pipe 140. The first cooling valve 151 is located between the high-stage compressor 112 and the outdoor heat exchanger 115 on the pipe 140. The first cooling valve 151 is an opening / closing device that opens and closes the pipe 140. In the present embodiment, the first cooling valve 151 is an opening / closing device that can be switched between an open state in which a refrigerant can flow through the pipe 140 and a closed state in which a refrigerant does not flow through the pipe 140.

[0108] On the pipe 140, one end of a first heating pipe 141 is connected between the oil separator 114 and the first cooling valve 151. A first heating valve 152 is provided in the first heating pipe 141. The first heating valve 152 is an opening / closing device that opens and closes the first heating pipe 141.

[0109] The other end of the first heating pipe 141 is connected to a pipe 171 that connects the indoor heat exchanger 122 of the indoor unit 120 and a suction side of the high-stage compressor 112. Thus, the discharge side of the high-stage compressor 112 is connected to the indoor heat exchanger 122 through the first heating pipe 141.

[0110] On the pipe 171, an on-off valve 123 is provided between the point, where the other end of the first heating pipe 141 is connected, and the accumulator 113. The on-off valve 123 is an opening / closing device that opens and closes the pipe 171.

[0111] On the pipe 140, one end of a first outdoor return pipe 142 is connected between the first cooling valve 151 and the outdoor heat exchanger 115. An outdoor refrigerant return valve 153 is provided in the first outdoor return pipe 142. The outdoor refrigerant return valve 153 is an opening / closing device that opens and closes the first outdoor return pipe 142. The other end of the first outdoor return pipe 142 is connected between a refrigeration-facility heat exchanger 132 of the refrigeration-facility unit 130 and a suction side of the low-stage compressor 111.

[0112] On the pipe 172, an outlet-side refrigeration-facility pressure regulation mechanism 133 is provided between the point, where the other end of the first outdoor return pipe 142 is connected, and the refrigeration-facility heat exchanger 132. The outlet-side refrigeration-facility pressure regulation mechanism 133 is an opening / closing device that can change the opening degree from a fully closed state to a fully open state. The outlet-side refrigeration-facility pressure regulation mechanism 133 functions as a so-called throttle valve that can change the pressure of the refrigerant flowing through the pipe 172 by regulating the opening degree.

[0113] As described above, the outdoor heat exchanger 115, the indoor heat exchanger 122, the refrigeration-facility heat exchanger 132, and the low-stage compressor 111 are connected to the first switching mechanism 150.

[0114] The first switching mechanism 150 switches the flow path of the refrigerant in the refrigeration circuit 102 by opening and closing the first cooling valve 151, the first heating valve 152, and the outdoor refrigerant return valve 153, and causes the refrigerant discharged from the high-stage compressor 112 to flow into either of the outdoor heat exchanger 115 and the indoor heat exchanger 122.

[0115] For example, when the refrigeration system 101 performs a cooling operation, the refrigerant discharged from the high-stage compressor 112 flows into the outdoor heat exchanger 115.

[0116] When the refrigeration system 101 performs a heating operation, the refrigerant discharged from the high-stage compressor 112 flows into the indoor heat exchanger 122. When the refrigeration system 101 performs a heating operation and the heat quantity for heating becomes excessive, the refrigerant discharged from the high-stage compressor 112 flows into each of the outdoor heat exchanger 115 and the indoor heat exchanger 122.

[0117] As described above, the first switching mechanism 150 includes the first cooling valve 151, the first heating valve 152, and the outdoor refrigerant return valve 153.

[0118] In the present embodiment, the first cooling valve 151, the first heating valve 152, and the outdoor refrigerant return valve 153 are motor-operated on-off valves that are opened and closed by an actuator or the like.

[0119] Therefore, the first switching mechanism 150 can switch the flow path of the refrigerant in the refrigeration circuit 102 without stopping the low-stage compressor 111 and the high-stage compressor 112. In other words, the refrigeration system 101 can switch operations related to air conditioning and cooling of the interior of the showcase without stopping the low-stage compressor 111 and the high-stage compressor 112.

[0120] In the first switching mechanism 150, the first cooling valve 151, the first heating valve 152, and the outdoor refrigerant return valve 153 may be opening / closing devices capable of regulating the opening degree from a fully closed state to a fully open state.

[0121] The first switching mechanism 150 corresponds to the "other switching mechanism" in the present disclosure.

[0122] On the pipe 140, the second switching mechanism 154 is provided on an opposite side of the first switching mechanism 150 with the outdoor heat exchanger 115 sandwiched therebetween. In other words, the second switching mechanism 154 is connected to the outdoor heat exchanger 115 through the pipe 140.

[0123] The second switching mechanism 154 connects the outdoor heat exchanger 115, the indoor heat exchanger 122, the refrigeration-facility heat exchanger 132, and the gas-liquid separator 116 to one another. The second switching mechanism 154 is a mechanism that switches the refrigerant to flow through any one of a plurality of flow paths that connect the outdoor heat exchanger 115, the indoor heat exchanger 122, the refrigeration-facility heat exchanger 132, and the gas-liquid separator 116 to one another.

[0124] The second switching mechanism 154 is formed in such a manner that end portions of first to fourth pipes 173, 174, 175, and 176 are connected at connection portions A, B, C, and D in a ring shape.

[0125] A throttling mechanism 155 is disposed in the first pipe 173. A refrigerant return expansion mechanism 158 is disposed in the second pipe 174 to control the flow rate.

[0126] A check valve 159 is disposed in the third pipe 175. A check valve 159 is disposed in the fourth pipe 176. In the present embodiment, the check valve 159 is a so-called self-acting automatic valve that is opened and closed by the flow of the refrigerant.

[0127] The throttling mechanism 155 and the refrigerant return expansion mechanism 158 are flow-rate control valves capable of changing the opening degree from a fully closed state to a fully open state. The throttling mechanism 155 can change the pressure of the refrigerant flowing through the first pipe 173 by regulating the opening degree. The refrigerant return expansion mechanism 158 can change the pressure of the refrigerant flowing through the second pipe 174 by regulating the opening degree. In other words, the throttling mechanism 155 and the refrigerant return expansion mechanism 158 are so-called throttle valves.

[0128] In the third pipe 175, the check valve 159 is disposed such that the refrigerant flows only toward the connection portion C from the connection portion B. In the fourth pipe 176, the check valve 159 is disposed such that the refrigerant flows only toward the connection portion D from the connection portion C.

[0129] Each of the throttling mechanism 155, the refrigerant return expansion mechanism 158, and the check valve 159 corresponds to a "valve body" in this disclosure.

[0130] The pipe 140, in which the outdoor heat exchanger 115 is provided, is connected to the connection portion A between the throttling mechanism 155 and the refrigerant return expansion mechanism 158.

[0131] The connection portion B between the refrigerant return expansion mechanism 158 and the check valve 159 provided in the third pipe 175 is connected to a middle part of the pipe 177 connecting the gas-liquid separator 116 and the refrigeration-facility heat exchanger 132. On the pipe 177, an inlet-side refrigeration-facility expansion mechanism 131 is provided between the point, where the connection portion B is connected, and the refrigeration-facility heat exchanger 132.

[0132] The connection portion C between the check valve 159 provided in the third pipe 175 and the check valve 159 provided in the fourth pipe 176 is connected to the indoor heat exchanger 122 through the pipe 178. In the pipe 178, an indoor expansion mechanism 121 of the indoor unit 120 is provided between one end to which the connection portion C is connected and the indoor heat exchanger 122. The indoor expansion mechanism 121 is an opening / closing device capable of changing the opening degree from a fully closed state to a fully open state. The indoor expansion mechanism 121 functions as a so-called throttle valve that can change the pressure of the refrigerant flowing through the pipe 178 by regulating the opening degree. Each of the indoor expansion mechanism 121 and the throttling mechanism 155 corresponds to a "throttling mechanism" in this disclosure.

[0133] The connection portion D between the check valve 159 provided in the fourth pipe 176 and the throttling mechanism 155 is connected to the gas-liquid separator 116 through the pipe 179.

[0134] As described above, the gas-liquid separator 116 is connected to the outdoor heat exchanger 115, the indoor heat exchanger 122, and the refrigeration-facility heat exchanger 132 through the second switching mechanism 154. Thus, when the refrigeration system 101 performs the first operation mode, the refrigerant flows into the gas-liquid separator 116 from the pipe 179, and flows out from the pipe 177. In other words, the pipe 179 functions as an inlet-side pipe of the gas-liquid separator 116, and the pipe 177 functions as an outlet-side pipe of the gas-liquid separator 116.

[0135] The second switching mechanism 154 corresponds to a "switching mechanism" in the present disclosure.

[0136] Next, the utilization-side heat exchanger provided in the refrigeration system 101 will be described.

[0137] When the indoor unit 120 performs a cooling operation, the indoor heat exchanger 122 functions as an evaporator. In the refrigeration system 101, the rotational frequency of each of the compressors and the air flow rate of blowers 118 and 128 are determined based on a temperature difference between the setting temperature of the indoor unit 120 and a temperature in the air-conditioned space in which the indoor unit 120 is installed. Furthermore, an opening degree of the indoor expansion mechanism 121 is determined such that the degree of superheat of the refrigerant at each of an inlet side and an outlet side of the indoor heat exchanger 122 becomes a specified value. Thus, the refrigeration system 101 operates such that the air-conditioned space becomes the setting temperature. In the present embodiment, an evaporation temperature zone of the indoor heat exchanger 122 is, for example, 3°C to 6°C.

[0138] The refrigeration-facility heat exchanger 132 functions as an evaporator. In the refrigeration system 101, the rotational frequency of each of the compressors and the air flow rate of blowers 118 and 138 are determined based on a temperature difference between the setting temperature of the refrigeration-facility unit 130 and a temperature of the interior of the showcase. Furthermore, an opening degree of the inlet-side refrigeration-facility expansion mechanism 131 is determined such that the degree of superheat of the refrigerant at each of an inlet side and an outlet side of the refrigeration-facility heat exchanger 132 becomes a specified value. Thus, the refrigeration system 101 operates such that the interior of the showcase becomes the setting temperature.

[0139] The refrigeration-facility unit 130 of the present embodiment can select and set, as an interior temperature zone, any one temperature zone from, for example, a refrigeration temperature zone (3°C to 6°C), a temperature zone (3°C to 8°C) slightly higher than the refrigeration temperature zone, a partial temperature zone (- 3°C to - 1°C), and a freezing temperature zone (- 20°C to - 18°C). For this reason, the evaporation temperature zone of the refrigeration-facility heat exchanger 132 is set lower than the interior temperature zone.

[0140] When the refrigeration-facility unit 130 is set to the refrigeration temperature zone, the evaporation temperature zone of the refrigeration-facility heat exchanger 132 is, for example, - 5°C to 0°C.

[0141] When the refrigeration-facility unit 130 is set to the partial temperature zone, the evaporation temperature zone of the refrigeration-facility heat exchanger 132 is, for example, - 12°C to - 8°C.

[0142] When the refrigeration-facility unit 130 is set to the freezing temperature zone, the evaporation temperature zone of the refrigeration-facility heat exchanger 132 is, for example, - 140°C to - 20°C.

[0143] In this way, the refrigeration system 101 is provided with two utilization-side heat exchangers with different evaporation temperature zones. Out of the two utilization-side heat exchangers with different evaporation temperature zones, the indoor heat exchanger 122 is connected to the inlet side of the high-stage compressor 112, and the refrigeration-facility heat exchanger 132 having a lower evaporation temperature zone than the indoor heat exchanger 122 is connected to the inlet side of the low-stage compressor 111.

[0144] The indoor heat exchanger 122 corresponds to a "first utilization-side heat exchanger" in the present disclosure, and the refrigeration-facility heat exchanger 132 corresponds to a "second utilization-side heat exchanger" in the present disclosure.

[0145] Next, the gas-liquid separator 116 will be described.

[0146] The gas-liquid separator 116 is a so-called flash tank that separates a gas-liquid two-phase refrigerant flown in into a gas refrigerant and a liquid refrigerant.

[0147] In the present embodiment, when the refrigeration system 101 performs a cooling operation, the refrigerant flowing from the outdoor heat exchanger 115 flows in the gas-liquid separator 116 through the second switching mechanism 154. During the cooling operation of the refrigeration system 101, the refrigerant flowing from the second switching mechanism 154 into the gas-liquid separator 116 is depressurized by the throttling mechanism 155.

[0148] When the refrigeration system 101 performs a heating operation, the refrigerant flowing from the indoor heat exchanger 122 flows in the gas-liquid separator 116 through the second switching mechanism 154. During the heating operation of the refrigeration system 101, the refrigerant flowing from the second switching mechanism 154 into the gas-liquid separator 116 is depressurized by the indoor expansion mechanism 121.

[0149] In this way, when the refrigeration system 101 performs the first operation mode, the refrigerant flows into the gas-liquid separator 116 through the second switching mechanism 154 in a state where the pressure is regulated by the throttling mechanism 155 or the indoor expansion mechanism 121. In other words, during the first operation mode, the refrigeration system 101 is provided with the second switching mechanism 154, and thus the pressure of the refrigerant flowing into the gas-liquid separator 116 can be regulated with a simple circuit configuration.

[0150] A gas refrigerant return pipe 160 is connected to the gas-liquid separator 116, and the gas refrigerant return pipe 160 is connected to the pipe 171 and then to the accumulator 113. A gas refrigerant flow-rate control valve 161 is connected to the gas refrigerant return pipe 160. The gas refrigerant flow-rate control valve 161 is an opening / closing device capable of changing the opening degree from a fully closed state to a fully open state. In the refrigeration system 101, flow rate of the gas refrigerant flowing through the gas refrigerant return pipe 160 is regulated by the opening degree of the gas refrigerant flow-rate control valve 161.

[0151] In the present embodiment, some of the gas refrigerant separated by the gas-liquid separator 116 are regulated in flow rate by the gas refrigerant flow-rate control valve 161, are sent to accumulator 113, and are returned to the suction side of the high-stage compressor 112.

[0152] In this way, in the gas-liquid separator 116, some of the gas refrigerant separated by the gas-liquid separator 116 are separated from the liquid refrigerant and flows out of the gas-liquid separator 116, whereby the liquid refrigerant is cooled to a saturation temperature corresponding to the pressure of the gas-liquid separator 116. In other words, the gas-liquid separator 116 in the refrigeration system 101 functions as a heat exchanger that cools the liquid refrigerant, and a refrigeration capacity of the refrigeration system 101 can be increased.

[0153] In addition, according to the refrigeration system 101, the opening degree of the gas refrigerant flow-rate control valve 161 is controlled, and the return amount of the gas refrigerant is regulated, whereby a pressure difference is generated between the front and the rear of the indoor expansion mechanism 121. In other words, it is possible to generate a differential pressure of the refrigerant between the inlet and the outlet of the indoor unit 120 in the refrigeration circuit 102 of the refrigeration system 101.

[0154] Thus, when the refrigeration system 101 performs the cooling operation in particular, the flow of the refrigerant is prevented from being stagnate. Then, in the indoor heat exchanger 122 of the refrigeration system 101 having a higher evaporation temperature of the refrigerant, it is possible to control the refrigerant flowing through the indoor heat exchanger 122 at a pressure value obtained by adding a specified pressure value to the pressure value serving as the evaporation temperature of the refrigerant.

[0155] An internal heat exchanger 164 is provided in a middle of each of the gas refrigerant return pipe 160 and the pipe 177. The internal heat exchanger 164 is a so-called economizer heat exchanger. The internal heat exchanger 164 is disposed, on the pipe 177, between the gas-liquid separator 116 and the connection portion B, and is disposed, on the gas refrigerant return pipe 160, between the gas refrigerant flow-rate control valve 161 and the accumulator 113.

[0156] The internal heat exchanger 164 houses the pipe 177 and the gas refrigerant return pipe 160 therein at the above-described position, and exchanges heat between the liquid refrigerant flowing through the pipe 177 and the gas refrigerant flowing through the gas refrigerant return pipe 160.

[0157] Therefore, in the refrigeration system 101, in the internal heat exchanger 164 the liquid refrigerant is cooled with the gas refrigerant. Then, the liquid refrigerant is more reliably brought into a supercooled state, and increases in the degree of supercooling. Thus, even when the temperature of the liquid refrigerant in the gas-liquid separator 116 does not drop to the saturation temperature in the gas-liquid separator 116, the liquid refrigerant is cooled in the internal heat exchanger 164, and thus the temperature thereof is reduced to the saturation temperature or lower. Then, the refrigeration system 101 can secure the degree of supercooling of the liquid refrigerant, and can improve the operating efficiency.

[0158] A connection pipe 166 is provided in the refrigeration circuit 102. The connection pipe 166 connects, on the pipe 177, between the internal heat exchanger 164 and the connection portion B, and connects, on the gas refrigerant return pipe 160, between the gas refrigerant flow-rate control valve 161 and the internal heat exchanger 164. Some of the liquid refrigerant, which is subjected to heat exchange with the gas refrigerant in the internal heat exchanger 164, flows through the connection pipe 166. The liquid refrigerant flowing through the connection pipe 166 is mixed with the gas refrigerant before the heat exchange with the liquid refrigerant in the internal heat exchanger 164.

[0159] In other words, the internal heat exchanger 164 exchanges heat between the liquid refrigerant and the mixed refrigerant of the liquid refrigerant, which is cooled by heat exchange with the gas refrigerant in the internal heat exchanger 164, and the gas refrigerant.

[0160] Thus, the internal heat exchanger 164 can increase the degree of supercooling of the liquid refrigerant. Therefore, the refrigeration system 101 can improve the operating efficiency.

[0161] A liquid refrigerant flow-rate control valve 165 is provided in the connection pipe 166. The liquid refrigerant flow-rate control valve 165 is an opening / closing device capable of changing the opening degree from a fully closed state to a fully open state. In the refrigeration system 101, the flow rate of the liquid refrigerant flowing through the connection pipe 166 is regulated by the opening degree of the liquid refrigerant flow-rate control valve 165.

[0162] Next, a service valve 190 will be described.

[0163] In the refrigeration system 101, a service valve 190 is provided in the pipe 172. On the pipe 172, the service valve 190 is provided between an outlet side of the refrigeration-facility heat exchanger 132 and the outlet-side refrigeration-facility pressure regulation mechanism 133. In the present embodiment, the service valve 190 is provided in the refrigeration-facility unit 130.

[0164] The service valve 190 includes three connection ports, for example, including pipe connection ports 192 and 194 and an external connection port 196. Each of the pipe connection ports 192 and 194 and the external connection port 196 is a valve body that can be opened and closed.

[0165] The pipe connection port 192 is connected to the pipe 172 located closer to the outlet-side refrigeration-facility pressure regulation mechanism 133. The pipe connection port 194 is connected to the pipe 172 located on the outlet side of the refrigeration-facility heat exchanger 132. In the present embodiment, the pipe connection ports 192 and 194 are normally opened.

[0166] The external connection port 196 is provided to allow the pipe 172 to be communicable with the outside, and is formed to allow connection of an external device. In the present embodiment, for example, a manifold gauge, a refrigerant recovery device 150, a vacuuming unit 152, and a refrigerant filling unit 154 are connected (see FIGS. 12 and 13). The external connection port 196 is closed when no external device is connected. The external connection port 196 may be manually opened and closed by a worker.

[0167] In the refrigeration system 101, since the service valve 190 is provided between the outlet side of the refrigeration-facility heat exchanger 132 and the outlet-side refrigeration-facility pressure regulation mechanism 133, connection ports for external devices can be provided without significantly changing the layout structure of the refrigeration circuit 102. In addition, since the service valve 190 is provided at a location close to the connection point between the outdoor unit 110 and the refrigeration-facility unit 130, the refrigeration system 101 can improve workability when the external device is connected to the refrigeration system 101.

[0168] The service valve 190 corresponds to a "connection port" in the present disclosure.[2-1-2. Configuration related to Control of Refrigeration System]

[0169] FIG. 6 is a block diagram of the refrigeration system 101.

[0170] As shown in FIGS. 5 and 6, the refrigeration system 101 is provided with a plurality of refrigerant pressure sensors 180. The refrigerant pressure sensors 180 are provided at predetermined locations of the refrigeration circuit 102 including the outdoor unit 110, the indoor unit 120, and the refrigeration-facility unit 130. The refrigerant pressure sensors 180 detect the pressure of the refrigerant flowing through those locations.

[0171] As shown in FIG. 5, the refrigerant pressure sensor 180 is provided, on the pipe 177, between the gas-liquid separator 116 and the internal heat exchanger 164. The refrigerant pressure sensor 180 is provided, on the gas refrigerant return pipe 160, between the gas refrigerant flow-rate control valve 161 and the accumulator 113.

[0172] Furthermore, the refrigerant pressure sensor 180 is provided, on the pipe 171, between the connection point of the pipe 171 and the first heating pipe 141, and the indoor heat exchanger 122. Furthermore, the refrigerant pressure sensor 180 is provided, on the pipe 172, between the outlet-side refrigeration-facility pressure regulation mechanism 133 and the suction side of the low-stage compressor 111.

[0173] The refrigerant pressure sensor 180 is provided on the refrigerant pipe that connects the discharge side of the high-stage compressor 112 and the oil separator 114.

[0174] As shown in FIGS. 5 and 6, the refrigeration system 101 is provided with a plurality of refrigerant temperature sensors 182. The refrigerant temperature sensors 182 are provided at predetermined locations of the refrigeration circuit 102 including the outdoor unit 110, the indoor unit 120, and the refrigeration-facility unit 130. The refrigerant temperature sensors 182 detect the temperature of the refrigerant flowing through these locations.

[0175] As shown in FIG. 5, the refrigerant temperature sensors 182 are provided on the refrigerant pipe located on the suction side and the refrigerant pipe located on the discharge side in each of the high-stage compressors 112. In addition, the refrigerant temperature sensor 182 is provided, on the pipe 172 located on the suction side of the low-stage compressor 111, between the outlet-side refrigeration-facility pressure regulation mechanism 133 and the suction side of the low-stage compressor 111.

[0176] Furthermore, the refrigerant temperature sensors 182 are provided on the refrigerant pipes connected to the inlet side and the outlet side of each of the indoor heat exchanger 122 and the refrigeration-facility heat exchanger 132.

[0177] As shown in FIG. 6, the refrigeration system 101 includes a space temperature sensor 127. The space temperature sensor 127 is disposed in the air-conditioned space of the indoor unit 120, and detects the temperature of the air-conditioned space.

[0178] The refrigeration system 101 includes an interior temperature sensor 137. The interior temperature sensor 137 is disposed inside a refrigerating display showcase or a freezing display showcase provided in the refrigeration-facility unit 130, and detects the interior temperature.

[0179] The blowers 118, 128, and 138 are provided in the outdoor unit 110, the indoor unit 120, and the refrigeration-facility unit 130, respectively. The blowers 118, 128, and 138 flow air to the outdoor heat exchanger 115, the indoor heat exchanger 122, and the refrigeration-facility heat exchanger 132, respectively, and facilitate heat exchange between the refrigerant and the air flowing through each of the outdoor heat exchanger 115, the indoor heat exchanger 122, and the refrigeration-facility heat exchanger 132.

[0180] The outdoor unit 110 includes an outdoor-unit communication portion 206 that communicates with the indoor unit 120 through a control wiring. The outdoor-unit communication portion 206 is configured with communication hardware, for example, a connector and a communication circuit that conform to a predetermined communication standard.

[0181] The outdoor unit 110 includes a control device 200. An outdoor unit I / F 205 is configured with communication hardware, for example, a connector and a communication circuit that conform to a predetermined communication standard. The outdoor unit I / F 205 communicates with the low-stage compressor 111, the high-stage compressor 112, the blower 118, the refrigerant pressure sensor 180, the refrigerant temperature sensor 182, and the outdoor-unit communication portion 206. The outdoor unit I / F 205 communicates with the first cooling valve 151, the first heating valve 152, the outdoor refrigerant return valve 153, the throttling mechanism 155, the refrigerant return expansion mechanism 158, the on-off valve 123, the gas refrigerant flow-rate control valve 161, the liquid refrigerant flow-rate control valve 165, and the service valve 190.

[0182] Furthermore, the outdoor unit I / F 205 communicates with an indoor unit I / F 215, a space temperature sensor 127, and a refrigeration-facility unit I / F 225.

[0183] The outdoor unit 110 includes the control device 200. The control device 200 includes a control unit 201 and a storage unit 203.

[0184] The control unit 201 is a processor such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit) that operates based on a program stored in advance in the storage unit 203. The control unit 201 may be configured with a single processor or may be configured with a plurality of processors. A DSP (digital signal processor) or the like may be used as the control unit 201. Furthermore, the control circuit such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), or an FPGA (Field-Programming Gate Array) can be used as the control unit 201.

[0185] The control unit 201 is capable of receiving various signals from each of portions provided in the outdoor unit 110, the indoor unit 120, and the refrigeration-facility unit 130 through the outdoor unit I / F 205.

[0186] The control unit 201 is connected, through the outdoor unit I / F 205, to each portion of the outdoor unit 110, for example, the storage unit 203 or the low-stage compressor 111, the indoor unit 120, and the refrigeration-facility unit 130 in a wired or wireless manner, and controls each portion.

[0187] The control unit 201 reads the computer program stored in the storage unit 203 and operates according to the read computer program, thereby functioning as an operation control unit 201a and a determination unit 201b.

[0188] The operation control unit 201a controls various devices such as each of the low-stage compressor 111, the high-stage compressor 112, and the opening / closing device provided in the outdoor unit 110. In addition, the operation control unit 201a transmits control signals to the indoor unit 120 and the refrigeration-facility unit 130 through the outdoor unit I / F 205 to cooperatively operate the refrigeration system 101.

[0189] The operation control unit 201a can change the rotation speed of the compression mechanism provided in each of the compressors, and can also change the discharge pressure of the refrigerant.

[0190] The operation control unit 201a can regulate the opening degree of the gas refrigerant flow-rate control valve 161, the throttling mechanism 155, the indoor expansion mechanism 121, the inlet-side refrigeration-facility expansion mechanism 131, the outlet-side refrigeration-facility pressure regulation mechanism 133, and the refrigerant return expansion mechanism 158. The operation control unit 201a can switch the opening / closing devices provided in each of the first switching mechanism 150 and the second switching mechanism 154, and the on-off valve 123 to either an open state or a closed state.

[0191] The determination unit 201b compares detection values of the refrigerant pressure sensors 180 or detection values of the refrigerant temperature sensors 182 with data such as a reference temperature or a reference pressure value included in setting data 103a stored in the storage unit 203.

[0192] The operation control unit 201a controls each unit of the refrigeration system 101 based on the determination from the determination unit 201b.

[0193] The storage unit 203 includes a memory device such as a RAM (Random Access Memory) or a ROM (Read Only Memory), a fixed disk device such as a hard disk, or a portable storage device such as a flexible disk or an optical disk. In addition, the storage unit 203 stores computer programs, databases, tables, and the like used for various operations of the refrigeration system 101. These computer programs may be installed in the storage unit 203 from a computer-readable portable recording medium using a known setup program, for example. The portable recording medium may be, for example, a semiconductor storage device including a CD-ROM (compact disc read only memory), a DVD-ROM (digital versatile disc read only memory), a USB (Universal Serial Bus) memory, or an SSD (Solid State Drive). The computer programs may be installed from a predetermined server, for example.

[0194] Furthermore, the storage unit 203 may include a volatile storage region and may form a work area for the control unit 201.

[0195] The storage unit 203 stores the setting data 203a. The setting data 203a includes data on the setting temperature of the indoor unit 120 and data on the setting temperature of the refrigeration-facility unit 130.

[0196] The setting data 203a includes data, for example, the rotation speed that is a specified value for each compressor and a reference pressure value that is a specified value indicating a differential pressure at a predetermined location in the refrigeration circuit 102.

[0197] The setting data 203a includes data related to the first operation mode. Specifically, the setting data 203a includes information on the opening / closing or the opening degree of each of the valve bodies provided in the refrigeration circuit 102 when the first operation mode is performed. The control unit 201 controls each of the units in the refrigeration circuit 102 according to the data related to the first operation mode. Thus, the refrigeration system 101 performs the first operation mode.

[0198] The setting data 203a includes a second operation mode. The second operation mode is an operation mode of the refrigeration system 101 that is performed in conjunction with the operation of an external device connected to the external connection port 196. The setting data 203a includes information on the opening / closing or the opening degree of each of the valve bodies provided in the refrigeration circuit 102 when the second operation mode is performed. The control unit 201 controls each of the units in the refrigeration circuit 102 according to the data related to the second operation mode. Thus, the refrigeration system 101 performs the second operation mode.

[0199] In the present embodiment, the setting data 203a includes, as the second operation mode, three operation modes of a refrigerant recovery / vacuuming mode, a refrigerant charging mode, and a regulation operation mode.

[0200] The outdoor unit I / F 205 includes communication hardware such as a communication interface circuit or a connector for the outdoor unit 110 to communicate with each device according to a predetermined communication protocol via a cable and the like. The outdoor unit I / F 205 sends data received from each device to the control device 200, and transmits data received from the control device 200 to each device.

[0201] The control device 200 includes an operation panel 232. Operating elements are provided on the operation panel 232. When the operating elements are operated, the control device 200 transmits a signal to the outdoor unit 110 to switch the operation mode of the refrigeration system 101 from the first operation mode to the second operation mode. In the present embodiment, according to the operation of the operation panel 232, the control device 200 switches to any one of three second operation modes of the refrigerant recovery / vacuuming mode, the refrigerant charging mode, and the regulation operation mode, and executes the switched mode.

[0202] The control device 200 is provided with a display panel 234. The display panel 234 performs a predetermined screen display according to the signal transmitted from the outdoor unit 110. In the present embodiment, the display panel 234 can display, for example, an operating status when the first operation mode or the second operation mode is executed, or the presence or absence of malfunction in each unit of the refrigeration system 101, and notify a worker of the operating status or the malfunction.

[0203] The control device 200 corresponds to a "control unit" in the present disclosure. The operation panel 232 corresponds to an "operation unit" in the present disclosure. The display panel 234 corresponds to a "display unit" in the present disclosure.

[0204] The indoor unit 120 includes an indoor-unit control device 210 and the indoor unit I / F 215. The indoor-unit control device 210 includes an indoor-unit control unit 211 and an indoor-unit storage unit 213.

[0205] Similarly to the control unit 201, the indoor-unit control unit 211 is a processor such as a CPU or an MPU. The indoor-unit control unit 211 operates according to a computer program stored in the indoor-unit storage unit 213 to control various devices such as the blower 128 mounted in the indoor unit 120. In addition, the indoor-unit control unit 211 receives signals output from various sensors such as the space temperature sensor 127 mounted in the indoor unit 120.

[0206] Similarly to the storage unit 203, the indoor-unit storage unit 213 includes a storage device such as a RAM or a ROM, and stores computer programs and the like used for various operations of the indoor unit 120.

[0207] The indoor unit I / F 215 includes communication hardware such as a communication interface circuit or a connector for the indoor unit 120 to communicate with each device. The indoor unit I / F 215 sends data received from the space temperature sensor 127 and each device to the indoor-unit control device 210, and transmits data received from the indoor-unit control device 210 to each device.

[0208] The refrigeration-facility unit 130 includes a refrigeration-facility-unit control device 220 and a refrigeration-facility unit I / F 225. The refrigeration-facility-unit control device 220 includes a refrigeration-facility-unit control unit 221 and a refrigeration-facility-unit storage unit 223.

[0209] Similarly to the control unit 201, the refrigeration-facility-unit control unit 221 is a processor such as a CPU or an MPU. The refrigeration-facility-unit control unit 221 operates according to a computer program stored in the refrigeration-facility-unit storage unit 223 to control various devices such as the blower 138 mounted in the refrigeration-facility unit 130. In addition, the refrigeration-facility-unit control unit 221 receives signals output from various sensors such as the interior temperature sensor 137 mounted in the refrigeration-facility unit 130.

[0210] Similarly to the storage unit 203, the refrigeration-facility-unit storage unit 223 includes a storage device such as a RAM or a ROM, and stores computer programs and the like used for various operations of the refrigeration-facility unit 130.

[0211] The refrigeration-facility unit I / F 225 includes communication hardware such as a communication interface circuit or a connector for the refrigeration-facility unit 130 to communicate with each device. The refrigeration-facility unit I / F 225 sends data received from the interior temperature sensor 137 and each device to the refrigeration-facility-unit control device 220, and transmits data received from the refrigeration-facility-unit control device 220 to each device.

[0212] The operation control unit 201a and the determination unit 201b may be provided not only in the control unit 201 but also in the indoor-unit control unit 211 or the refrigeration-facility-unit control unit 221. For example, the operation control unit 201a and the determination unit 201b may be provided in a processor provided in another location of the refrigeration system 101. For example, the operation control unit 201a and the determination unit 201b may be provided in a processor provided in a server device or the like provided outside the refrigeration system 101. Such a server device may be capable of controlling each unit of the refrigeration system 101 via a network constituted of, for example, a public line network, a dedicated line, other communication lines, and various communication facilities.[2-2. Operation of Refrigeration System]

[0213] Next, an operation of the present embodiment will be described.[2-2-1. Cooling Operation]

[0214] First, an operation of the refrigeration system 101 during a cooling operation will be described.

[0215] During the cooling operation, as shown in FIG. 5, the outdoor heat exchanger 115 is used as a gas cooler or a radiator, and the indoor heat exchanger 122 and the refrigeration-facility heat exchanger 132 are used as evaporators.

[0216] During the cooling operation, the control device 200 opens the first cooling valve 151 and closes the first heating valve 152 and the outdoor refrigerant return valve 153 in the first switching mechanism 150. In addition, the control device 200 opens the throttling mechanism 155 and closes the refrigerant return expansion mechanism 158 in the second switching mechanism 154.

[0217] In this state, the low-stage compressor 111 and each of the high-stage compressors 112 are driven, whereby the refrigerant compressed by the low-stage compressor 111 is sent to each of the high-stage compressors 112, further compressed by each of the high-stage compressor 112, and discharged toward the oil separator 114.

[0218] The refrigerant passing through the oil separator 114 is sent to the outdoor heat exchanger 115 through the first cooling valve 151 of the first switching mechanism 150, and exchanges heat with outside air in the outdoor heat exchanger 115.

[0219] The refrigerant after heat exchange is sent from the connection portion A of the second switching mechanism 154 through the throttling mechanism 155 to the gas-liquid separator 116. The liquid refrigerant separated in the gas-liquid separator 116 reaches the connection portion B of the second switching mechanism 154 after passing through the pipe 177 and being subjected to heat exchange with the gas refrigerant in the internal heat exchanger 164. One refrigerant branched at the connection portion B passes through the pipe 178 and is sent to the indoor heat exchanger 122 through the check valve 159 provided in the pipe 175 and the indoor expansion mechanism 121 of the indoor unit 120.

[0220] In the indoor heat exchanger 122, the refrigerant exchanges heat with the indoor air to cool the indoor air. The refrigerant subjected to heat exchange with the indoor air passes through the pipe 171, and is returned to the suction side of each of the high-stage compressors 112 through the on-off valve 123 and the accumulator 113.

[0221] The other refrigerant branched at the connection portion B is sent to the refrigeration-facility heat exchanger 132 through the inlet-side refrigeration-facility expansion mechanism 131 of the refrigeration-facility unit 130, and is subjected to heat exchange in the refrigeration-facility heat exchanger 132 to cool the refrigeration-facility unit 130. The refrigerant subjected to heat exchange in the refrigeration-facility heat exchanger 132 is returned to the low-stage compressor 111 through the outlet-side refrigeration-facility pressure regulation mechanism 133.

[0222] In the cooling operation of the above-described refrigeration system 101, the refrigerant discharged from the high-stage compressor 112 and radiating heat while maintaining the pressure at a high pressure in the outdoor heat exchanger 115 is reduced in pressure by the throttling mechanism 155 to become an intermediate pressure, and is sent to the gas-liquid separator 116.[2-2-2. Heating Operation]

[0223] Next, an operation of the refrigeration system 101 during a heating operation will be described.

[0224] FIG. 7 is a circuit diagram of the refrigeration system 101 showing a heating operation. In FIG. 7, a flow of the refrigerant is indicated by arrows in the drawing, and the refrigerant pipes through which the refrigerant flows are indicated by thick lines.

[0225] In the refrigeration system 101, the heating operation is performed, using the indoor heat exchanger 122 as a gas cooler or a radiator and the refrigeration-facility heat exchanger 132 as an evaporator.

[0226] As shown in FIG. 7, during the heating operation, the control device 200 opens the first heating valve 152 and closes the first cooling valve 151 and the outdoor refrigerant return valve 153 in the first switching mechanism 150. In addition, the control device 200 closes the throttling mechanism 155 and the refrigerant return expansion mechanism 158 in the second switching mechanism 154.

[0227] In this state, the low-stage compressor 111 and each of the high-stage compressors 112 are driven, whereby the refrigerant compressed by the low-stage compressor 111 is sent to each of the high-stage compressors 112, further compressed by each of the high-stage compressor 112, and discharged toward the oil separator 114.

[0228] The refrigerant passing through the oil separator 114 is sent to the indoor heat exchanger 122 through the first heating valve 152 of the first switching mechanism 150, and exchanges heat with indoor air in the indoor heat exchanger 122 to heat the indoor air.

[0229] The refrigerant subjected to heat exchange in the indoor heat exchanger 122 passes through the indoor expansion mechanism 121, reaches the connection portion C of the second switching mechanism 154, and is sent to the gas-liquid separator 116 through the check valve 159 and the throttling mechanism 155 provided in the pipe 176. The refrigerant separated in the gas-liquid separator 116 passes through the pipe 177, reaches the connection portion B of the second switching mechanism 154, and is sent to the refrigeration-facility heat exchanger 132 through the inlet-side refrigeration-facility expansion mechanism 131. The refrigerant exchange heat in the refrigeration-facility heat exchanger 132, and cools the refrigeration-facility unit 130.

[0230] The refrigerant subjected to heat exchange in the refrigeration-facility heat exchanger 132 passes through the pipe 172 and is returned to the suction side of the low-stage compressor 111 through the outlet-side refrigeration-facility pressure regulation mechanism 133.

[0231] In the refrigeration system 101 of the present disclosure, during the heating operation, the indoor heat exchanger 122 functions as a gas cooler or a radiator, and the outdoor heat exchanger 115 is not used. In other words, the refrigeration system 101 can perform heat exchange in the refrigeration-facility heat exchanger 132 using the refrigerant whose heat is radiated in the indoor heat exchanger 122, and thus can be operated without using the outdoor heat exchanger 115.

[0232] In the refrigeration system 101 of the present disclosure, during the heating operation, since the liquid refrigerant flows only through the refrigeration-facility unit 130, the opening degree of the gas refrigerant flow-rate control valve 161 is smaller compared to during cooling operation.[2-2-3. Heating operation when amount of heat exhausted from refrigeration-facility unit is insufficient]

[0233] Next, an operation will be described in a case where a heating operation is performed when the amount of heat exhausted from the refrigeration-facility unit 130 is insufficient.

[0234] FIG. 8 is a circuit diagram of the refrigeration system 101 showing a heating operation when the amount of heat exhausted from the refrigeration-facility unit 130 is insufficient.

[0235] As shown in FIG. 8, during a heating operation at full capacity, the control device 200 opens the first heating valve 152, the outdoor refrigerant return valve 153, and the refrigerant return expansion mechanism 158, and closes the first cooling valve 151 and the throttling mechanism 155.

[0236] In this state, the low-stage compressor 111 and each of the high-stage compressors 112 are driven, whereby the refrigerant compressed by the low-stage compressor 111 is sent to each of the high-stage compressors 112, further compressed by each of the high-stage compressor 112, and discharged toward the oil separator 114.

[0237] The refrigerant passing through the oil separator 114 is sent to the indoor heat exchanger 122 through the first heating valve 152, and exchanges heat with indoor air in the indoor heat exchanger 122 to heat the indoor air.

[0238] The refrigerant subjected to heat exchange in the indoor heat exchanger 122 is sent to the gas-liquid separator 116 through the check valve 159 provided in the pipe 176, and then sent to the refrigeration-facility heat exchanger 132 through the inlet-side refrigeration-facility expansion mechanism 131. The refrigerant, which cools the refrigeration-facility unit 130, and is subjected to heat exchange in the refrigeration-facility heat exchanger 132 is regulated through the outlet-side refrigeration-facility pressure regulation mechanism 133 to have the same pressure as that of the refrigerant which is sent from the first outdoor return pipe 142, and is returned to the low-stage compressor 111. This is an operation when the outside air temperature is lower than the interior temperature of the refrigeration-facility unit 130.

[0239] On the other hand, some of the refrigerant from the gas-liquid separator 116 are sent to the outdoor heat exchanger 115 through the refrigerant return expansion mechanism 158, and are returned to the low-stage compressor 111 after heat exchange in the outdoor heat exchanger 115.

[0240] Thus, exhaust heat from the refrigeration-facility heat exchanger 132 and heat pumped up by the outdoor heat exchanger 115 can be used as heat for the indoor heat exchanger 122, thereby increasing the heating capacity when the amount of heat exhausted from the refrigeration-facility unit 130 is insufficient.

[0241] Conventionally, when the outside air temperature is lower than the interior temperature of the refrigeration-facility unit 130, it is necessary to lower the evaporation temperature of the refrigeration-facility unit 130 in order to pump heat from the outdoor heat exchanger 115. However, when the evaporation temperature of the refrigeration-facility unit 130 is lowered, there is a concern that the temperature will be lower than the setting temperature of the refrigeration-facility unit 130.

[0242] Therefore, according to the present embodiment, the opening degree of the outlet-side refrigeration-facility pressure regulation mechanism 133 is controlled, whereby it is possible to achieve the balance of the pressure with the refrigerant sent from the outdoor heat exchanger 115, and to prevent a drop in the evaporation temperature of the refrigeration-facility unit 130.[2-2-4. Heating operation when large capacity is required in refrigeration-facility unit but heat quantity for heating is not required]

[0243] Next, an operation will be described in a case where a large capacity is required in the refrigeration-facility unit 130 but a heat quantity for heating is not required.

[0244] FIG. 9 is a circuit diagram of the refrigeration system 101 showing an operation when a large capacity is required in the refrigeration-facility unit 130 but a heat quantity for heating is not required.

[0245] As shown in FIG. 9, when a large capacity is required in the refrigeration-facility unit 130 but a heat quantity for heating is not required, the control device 200 opens the first cooling valve 151, the throttling mechanism 155, the first heating valve 152, and the check valve 159 provided in the pipe 176, and closes the refrigerant return valve and the check valve 159 provided in the pipe 175.

[0246] In this state, the low-stage compressor 111 and each of the high-stage compressors 112 are driven, whereby the refrigerant compressed by the low-stage compressor 111 is sent to each of the high-stage compressors 112, further compressed by each of the high-stage compressor 112, and discharged toward the oil separator 114.

[0247] The refrigerant passing through the oil separator 114 is sent to the outdoor heat exchanger 115 through the first cooling valve 151, and exchanges heat with outside air in the outdoor heat exchanger 115.

[0248] The refrigerant after heat exchange is sent to the gas-liquid separator 116 through the throttling mechanism 155.

[0249] The refrigerant passing through the oil separator 114 is sent to the indoor heat exchanger 122 through the first heating valve 152, exchanges heat with indoor air in the indoor heat exchanger 122 to heat the indoor air.

[0250] The refrigerant subjected to heat exchange in the indoor heat exchanger 122 interflows with the refrigerant sent from the outdoor heat exchanger 115 through the check valve 159 provided in the pipe 176, and is sent to the gas-liquid separator 116.

[0251] The refrigerant from the gas-liquid separator 116 is sent to the refrigeration-facility heat exchanger 132 through the inlet-side refrigeration-facility expansion mechanism 131. The refrigerant, which cools the refrigeration-facility unit 130, and is subjected to heat exchange in the refrigeration-facility heat exchanger 132 is returned to the low-stage compressor 111 through the outlet-side refrigeration-facility pressure regulation mechanism 133.

[0252] On the other hand, some of the refrigerant from the gas-liquid separator 116 is sent to the outdoor heat exchanger 115 through the refrigerant return expansion mechanism 158, and is returned to the low-stage compressor 111 after being subjected to heat exchange in the outdoor heat exchanger 115.

[0253] Thus, during the heating operation, the exhaust heat from the refrigeration-facility unit 130 can be radiated by the outdoor heat exchanger 115 and the indoor heat exchanger 122, whereby the cooling capacity of the refrigeration-facility unit 130 can be increased, and frost adhering to the outdoor heat exchanger 115 can be removed.

[0254] In this way, when the refrigeration system 101 perform the heating operation, the use state of the outdoor heat exchanger 115 can be switched to any one of a state of not being used, a state of being used as an evaporator, and a state of being used as a condenser, depending on the load on the indoor unit 120 and the refrigeration-facility unit 130. Therefore, the refrigeration system 101 can perform a stable heating operation depending on the load on the indoor unit 120 and the refrigeration-facility unit 130.[2-2-5. State of refrigerant in refrigeration circuit]

[0255] FIG. 10 is a p-h chart showing a state of the refrigerant in the refrigeration circuit 102. In FIG. 8, a vertical axis p represents a pressure (MPa), and a horizontal axis h represents enthalpy (kJ / kg).

[0256] Here, a refrigerant of the refrigeration system 101 during the cooling operation will be described.

[0257] On the suction side of the low-stage compressor 111, the state of the refrigerant is located at point P1 in FIG. 10. The refrigerant is a refrigerant evaporated in the refrigeration-facility heat exchanger 132, and a gas refrigerant at point P1. For the convenience of description, a pressure at point P1 is referred to as a low pressure.

[0258] When a low-pressure refrigerant is sucked into the low-stage compressor 111 and adiabatically compressed, the state of the refrigerant is located at point P2 in FIG. 10. Hereinafter, for the convenience of description, a pressure at point P2 is referred to as an intermediated pressure. In the present embodiment, a differential pressure between the low pressure and the intermediate pressure is, for example, 1.0 MPa.

[0259] Such a refrigerant is mixed with the refrigerant evaporated in the indoor heat exchanger 122 and the gas refrigerant flowing through the gas refrigerant return pipe 160. The mixed refrigerants are lowered in temperature while being maintained at an intermediate pressure, and becomes a state at point P3 in FIG. 10.

[0260] When the refrigerant in the state at point P3 is adiabatically compressed, such a refrigerant is in a state at point P4 in FIG. 10. Hereinafter, for the convenience of description, a pressure at point P4 is referred to as a high pressure.

[0261] When such a refrigerant is discharged from the high-stage compressor 112, the refrigerant radiates heat while being maintained at a high pressure in the outdoor heat exchanger 115. Therefore, the refrigerant is in a state at point P5 in FIG. 10.

[0262] The refrigerant in the state at point P5 is depressurized by the throttling mechanism 155, and is in a state at point P6 in FIG. 10. At point P6, the refrigerant has a pressure value higher than the intermediate pressure. Hereinafter, for the convenience of description, the pressure at point P2 is referred to as a medium pressure. In the present embodiment, a differential pressure between the intermediate pressure and the medium pressure and the intermediate pressure is, for example, 0.5 MPa.

[0263] As described above, even when the refrigeration system 101 performs either the cooling operation or the heating operation, the low-pressure liquid refrigerant depressurized by the throttling mechanism 155 or the indoor expansion mechanism 121 flows into the gas-liquid separator 116. Thus, when the refrigeration system 101 performs the first operation mode, the pressure of the refrigerant entering the gas-liquid separator 116 can be regulated.

[0264] The refrigerant in the state at point P6 is separated into a liquid refrigerant and a gas refrigerant by the gas-liquid separator 116. Out of these refrigerants, the gas refrigerant is discharged from the gas-liquid separator 116 through the gas refrigerant return pipe 160.

[0265] As the gas refrigerant is separated from discharged from the gas-liquid separator 116, the liquid refrigerant is cooled to a state at point P7 on a saturated liquid line, as shown in FIG. 10.

[0266] As described above, the gas refrigerant return pipe 160 is connected to the suction side of the high-stage compressor 112. In other words, the gas refrigerant is sucked by the high-stage compressor 112 and discharged from the gas-liquid separator 116. Thus, in the refrigeration system 101, the liquid refrigerant stored in the gas-liquid separator 116 is cooled to the state at point P7 on the saturated liquid line.

[0267] The refrigeration system 101 includes one low-stage compressor 111 and two high-stage compressors 112. In other words, in the refrigeration system 101, the capacity of the high-stage compressor 112 is larger than that of the low-stage compressor 111. The gas refrigerant is sucked by these high-stage compressors 112, and thus the refrigeration system 101 can cool the liquid refrigerant in the gas-liquid separator 116 to the state at point P7 on the saturated liquid line even when the outside air of the air-conditioned space or the refrigeration-facility unit 130 is high, for example, in summer.

[0268] In this way, the refrigeration system 101 can perform the first operation mode even when the ambient temperature of the utilization-side heat exchanger is high.

[0269] The liquid refrigerant exchanges heat with the gas refrigerant in the internal heat exchanger 164, and is in a state at point P8 in FIG. 10. At point P8, the liquid refrigerant is in a supercooled state. The gas refrigerant, which exchanges heat with the liquid refrigerant in the internal heat exchanger 164, is in a state at point P11 in FIG. 10.

[0270] The liquid refrigerant flowing out from the internal heat exchanger 164 branches off at the connection portion B and flows to the indoor unit 120 and the refrigeration-facility unit 130. The liquid refrigerant flowing to the indoor unit 120 is depressurized to an intermediate pressure by the indoor expansion mechanism 121, and is in a state at point P9 in FIG. 10. Thereafter, the liquid refrigerant flowing to the indoor unit 120 evaporates in the indoor heat exchanger 122, and is in the state at point P3 in FIG. 10. The refrigerant flows out from the indoor unit 120, and is sent to the suction side of the high-stage compressor 112. Similarly, the gas refrigerant flowing out from the internal heat exchanger 164 is also sent to the suction side of the high-stage compressor 112.

[0271] The liquid refrigerant flowing into the refrigeration-facility unit 130 is depressurized to an intermediate pressure by the inlet-side refrigeration-facility expansion mechanism 131, and is in a state at point P10 in FIG. 10. Thereafter, the liquid refrigerant flowing into the refrigeration-facility unit 130 evaporates in the refrigeration-facility heat exchanger 132, and is in the state at point P1 in FIG. 10. The refrigerant flows out from the refrigeration-facility unit 130 and is sent to the suction side of the low-stage compressor 111.

[0272] As shown in FIG. 10, the refrigeration system 101 of the present embodiment is a system including the refrigeration circuit 102 to perform a two-stage compression, two-stage expansion cycle.

[0273] As described above, in the refrigeration system 101, the opening degree of the gas refrigerant flow-rate control valve 161 is controlled, and the return amount of the gas refrigerant is regulated, whereby the inlet side of the indoor heat exchanger 122 becomes an intermediate pressure, and the outlet side of the indoor heat exchanger 122 becomes a middle pressure. In other words, it is possible to generate a differential pressure of the refrigerant between the inlet and the outlet of the indoor expansion mechanism 121 in the refrigeration circuit 102 of the refrigeration system 101.

[0274] Thus, in the indoor heat exchanger 122 of the refrigeration system 101 having a higher evaporation temperature of the refrigerant, it is possible to control the refrigerant flowing through the indoor heat exchanger 122 at a pressure value obtained by adding a specified pressure value to the pressure value serving as the evaporation temperature of the refrigerant.

[0275] Thus, in the refrigeration system 101, it is possible to improve efficiency of an air conditioning temperature zone using carbon dioxide (R744), a natural refrigerant with high environmental preservation characteristics, and to improve the efficiency of the entire refrigeration system.

[0276] As described above, the refrigeration system 101 can be stably perform the state change of the refrigerant shown in FIG. 10 by regulating the pressure of the refrigerant using the throttling mechanism 155, the indoor expansion mechanism 121, and the gas refrigerant flow-rate control valve 161, and regulating the temperature of the refrigerant using the gas-liquid separator 116. Therefore, the refrigeration system 101 can perform a stable operation by regulating the pressure and temperature of the refrigerant according to the load on the indoor unit 120 and the refrigeration-facility unit 130 caused by the outside air temperature or the like.

[0277] Furthermore, in the refrigeration system 101, the liquid refrigerant and the gas refrigerant separated in the gas-liquid separator 116 exchange heat with each other in the internal heat exchanger 164. Thus, the liquid refrigerant sent to the indoor unit 120 and the refrigeration-facility unit 130 is supercooled. For this reason, even when the temperature of the refrigerant fluctuates due to external heat radiation or heat capacity of the gas-liquid separator 116, or fluctuation in an operating load of the refrigeration system 101, the liquid refrigerant is prevented from rising to a temperature at which flash gas is generated, for example. Then, the refrigeration system 101 can stably evaporate the refrigerant in the indoor heat exchanger 122 and the refrigeration-facility heat exchanger 132.

[0278] Additionally, in the refrigeration system 101, some of the liquid refrigerant, which exchanges heat with the gas refrigerant in the internal heat exchanger 164, is mixed with the gas refrigerant before heat exchange with the liquid refrigerant, through the connection pipe 166. Thus, in the internal heat exchanger 164, the liquid refrigerant exchanges heat with the mixed refrigerant of the liquid refrigerant, which is cooled by heat exchange with the gas refrigerant in the internal heat exchanger 164, and the gas refrigerant. Therefore, the internal heat exchanger 164 can increase the degree of supercooling of the liquid refrigerant, and the refrigeration system 101 can improve the operating efficiency.[2-2-6. Operation of refrigeration system during cooling operation]

[0279] FIG. 11 is a flowchart showing an operation of the refrigeration system 101.

[0280] Next, an operation related to pressure control of the refrigeration system 101 during the cooling operation will be described.

[0281] As shown in FIG. 11, the determination unit 201b acquires a detection value of the refrigerant pressure sensor 180 provided on the discharge side of the indoor heat exchanger 122 and a detection value of the refrigerant pressure sensor 180 provided on the discharge side of the refrigeration-facility heat exchanger 132. The determination unit 201b calculates a differential pressure between an intermediate pressure and a low pressure from these acquired detection values. The determination unit 201b compares the calculated value with data of a reference pressure value involved in the setting data 203a stored in the storage unit 203 (step SA1).

[0282] When the calculated value is greater than the reference pressure value involved in the setting data 203a stored in the storage unit 203 (step SA1: YES), the determination unit 201b acquires a detection value of the refrigerant pressure sensor 180 provided in the pipe 177 through which the liquid refrigerant discharged from the gas-liquid separator 116 flows. The determination unit 201b calculates a differential pressure between the intermediate pressure and the medium pressure, from such a detection value and the detection value of the refrigerant pressure sensor 180 provided on the discharge side of the indoor heat exchanger 122. Then, the determination unit 201b compares the calculated value with the data of the reference pressure value involved in the setting data 203a stored in the storage unit 203 (step SA2).

[0283] When the calculated value is greater than the reference pressure value involved in the setting data 203a stored in the storage unit 203 (step SA2: YES), the operation control unit 201a drives each of the compressors and the blowers 118, 128, and 138 to become the setting temperature of the indoor unit 120 (step SA3).

[0284] In step SA1, when the calculated value of the differential pressure between the intermediate pressure and the low pressure is equal to or smaller than the reference pressure value in the setting data 203a stored in the storage unit 203 (step SA1: NO), the operation control unit 201a regulates the opening degree of the gas refrigerant flow-rate control valve 161 and the throttling mechanism 155 to increase the intermediate pressure (step SA4).

[0285] In the refrigeration system 101, the intermediate pressure increases when the opening degree of the throttling mechanism 155 increases or the opening degree of the gas refrigerant flow rate control valve 161 decreases.

[0286] Thereafter, the determination unit 201b acquires the detection value of refrigerant pressure sensor 180 provided on the discharge side of the indoor heat exchanger 122 and the detection value of the refrigerant pressure sensor 180 provided on the discharge side of the refrigeration-facility heat exchanger 132. The determination unit 201b calculates the differential pressure between the intermediate pressure and the low pressure from these acquired detection values, and compares the calculated value and the data of the reference pressure value involved in the setting data 203a stored in the storage unit 203 (step SA5).

[0287] When the calculated value of the differential pressure between the intermediate pressure and the low pressure is equal to or smaller than the reference pressure value involved in the setting data 203a stored in the storage unit 203 (step SA5: NO), the operation control unit 201a performs step SA4 again.

[0288] When both the calculated values of the differential pressure between the intermediate pressure and the low pressure are greater than the reference pressure value involved in the setting data 203a stored in the storage unit 203 (step SA1: YES), the determination unit 201b performs step SA2.

[0289] Thus, in the refrigeration system 101, a differential pressure of a predetermined value or more is generated at the low-stage compressor 111, and the suction side and the discharge side of each of the high-stage compressors 112. Therefore, in the refrigeration system 101, the occurrence of poor compression in the low-stage compressor 111 and each of the high-stage compressors 112 is prevented.

[0290] As described above, the refrigeration system 101 of the present embodiment is provided with the internal heat exchanger 164 that exchanges heat between the liquid refrigerant flowing from the gas-liquid separator 116 to the indoor heat exchanger 122 and the refrigeration-facility heat exchanger 132 and the gas refrigerant discharged from the gas-liquid separator 116. Furthermore, the gas refrigerant discharged from the gas-liquid separator 116 is mixed with some of the liquid refrigerant that exchanges heat with the gas refrigerant discharged from the gas-liquid separator 116 in the internal heat exchanger 164, through the connection pipe 166. Thus, in the refrigeration system 101, the liquid refrigerant becomes a lower temperature, leading in improving the refrigeration capacity of the indoor unit 120 through which the liquid refrigerant flows.

[0291] When the setting temperature of the indoor unit 120 is higher than the temperature of the liquid refrigerant by a predetermined value or greater, the refrigeration system 101 reduces the opening degree of the indoor expansion mechanism 121 to restrict the flow rate of the liquid refrigerant flowing to the indoor unit 120. Thus, in the refrigeration system 101, the medium pressure, which is the pressure of the refrigerant flowing out from the indoor heat exchanger 122, in other words, the refrigerant sucked into each of the high-stage compressor 112, decreases.

[0292] In step SA2, when the calculated value of the differential pressure between the intermediate pressure and the medium pressure is smaller than the reference pressure value involved in setting data 203a stored in the storage unit 203 (step SA2: NO), the operation control unit 201a reduces the rotational frequency of the high-stage compressor 112 (step SA6).

[0293] Next, the determination unit 201b determines whether the reduced rotational frequency of the high-stage compressor 112 is greater than a specified value involved in the setting data 203a stored in the storage unit 203 (step SA7).

[0294] When the rotational frequency is greater than the specified value (step SA7: YES), the determination unit 201b again acquires a detection value of the refrigerant pressure sensor 180 provided in the pipe 177 through which the liquid refrigerant discharged from the gas-liquid separator 116 flows. The determination unit 201b calculates a differential pressure between the intermediate pressure and the medium pressure, from the acquired detection value and the detection value of the refrigerant pressure sensor 180 provided on the discharge side of the indoor heat exchanger 122. The determination unit 201b compares the calculated value with the data of the reference pressure value involved in the setting data 203a stored in the storage unit 203 (step SA8).

[0295] When the calculated value is greater than the reference pressure value involved in the setting data 203a stored in the storage unit 203 (step SA8: YES), the operation control unit 201a drives each of the compressors and the blowers 118, 128, and 138 to become the setting temperature of the indoor unit 120 (step SA3). when the calculated value of the differential pressure between the intermediate pressure and the medium pressure is equal to or smaller than the reference pressure value involved in setting data 203a stored in the storage unit 203 (step SA8: NO), the operation control unit 201a again reduces the rotational frequency of the high-stage compressor 112 (step SA6).

[0296] In step SA7, when the rotational frequency of the high-stage compressor 112 is lower than the specified value (step SA7: YES), the operation control unit 201a reduces the opening degree of the liquid refrigerant flow-rate control valve 165 (step SA9). Thereafter, the operation control unit 201a drives each of the compressors and the blowers 118, 128, and 138 to become the setting temperature of the indoor unit 120 (step SA3).

[0297] As described above, the refrigeration system 101 can control the rotational frequency of the high-stage compressor 112 to maintain the differential pressure between the intermediate pressure and the low pressure at a predetermined value or less. Accordingly, the refrigeration system 101 can improve the refrigeration efficiency of the indoor unit 120 while preventing the input to the high-stage compressor 112. Therefore, the refrigeration system 101 can improve the efficiency of the cooling operation while saving energy.

[0298] When the rotational frequency becomes smaller than the specified value, the refrigeration system 101 reduces the opening degree of the liquid refrigerant flow-rate control valve 165. Thus, the refrigeration system 101 reduces the flow rate at which the liquid refrigerant subjected to heat exchange with the gas refrigerant discharged from the gas-liquid separator 116 in the internal heat exchanger 164 is mixed with the gas refrigerant discharged from the gas-liquid separator 116. Therefore, the flow rate of the liquid refrigerant sent to the indoor unit 120 is reduced, and the decrease in the medium pressure is prevented. Furthermore, the refrigeration system 101 prevents the driving of each of the high-stage compressors 112 from being stopped.

[0299] In the above-described cooling operation of the refrigeration system 101, the refrigerant discharged from the high-stage compressor 112 and radiating heat while maintaining its pressure at a high pressure in the outdoor heat exchanger 115 is depressurized to the medium pressure by the throttling mechanism 155, and is sent to the gas-liquid separator 116.

[0300] On the other hand, during the heating operation of the refrigeration system 101, the refrigerant discharged from the high-stage compressor 112 radiates heat while maintaining its pressure at a high pressure in the indoor heat exchanger 122. The refrigerant is depressurized to the medium pressure by the indoor expansion mechanism 121, and is sent to the gas-liquid separator 116.

[0301] In the heating operation of the refrigeration system 101 when the amount of heat exhausted from the refrigeration-facility unit 130 is insufficient, the refrigerant discharged from the high-stage compressor 112 and radiating heat while maintaining its pressure at a high pressure in the outdoor heat exchanger 115 is depressurized to the medium pressure by the throttling mechanism 155, and is sent to the gas-liquid separator 116. Similarly, the refrigerant discharged from the high-stage compressor 112 and radiating heat while maintaining its pressure at a high pressure in the indoor heat exchanger 122 is depressurized to the medium pressure by the indoor expansion mechanism 121, and is sent to the gas-liquid separator 116.

[0302] In the heating operation of the refrigeration system 101 when a large capacity is required in the refrigeration-facility unit 130 but a heat quantity for heating is not required, the refrigerant discharged from the high-stage compressor 112 and radiating heat while maintaining its pressure at a high pressure in the indoor heat exchanger 122 is depressurized to the medium pressure by the indoor expansion mechanism 121, and is sent to the gas-liquid separator 116. In addition, some of the liquid refrigerant flowing out from the gas-liquid separator 116 is depressurized to the low pressure from the medium pressure by the refrigerant return expansion mechanism 158, and is sent to the outdoor heat exchanger 115.

[0303] As described above, the refrigeration system 101 includes the first switching mechanism 150. Thus, the refrigeration system 101 can switch between the cooling operation and the heating operation. In addition, during the heating operation, the refrigeration system 101 includes the first switching mechanism 150, so that the outdoor heat exchanger 115 can be switched between a state of not being used as a condenser and a state of being used as a condenser depending on the surplus or deficiency of the heat quantity.

[0304] As described above, the refrigeration system 101 includes the second switching mechanism 154. Thus, in both cases where the indoor heat exchanger 122 functions as an evaporator and where the indoor heat exchanger 122 functions as a condenser, the refrigeration system 101 can send out the refrigerant, which is sent out from each of the high-stage compressors 112, to the heat exchanger functioning as an evaporator through the gas-liquid separator 116. Therefore, the refrigeration system 101 can increase the refrigeration capacity.

[0305] Specifically, when the indoor unit 120 performs the cooling operation, the refrigerant discharged from each of the high-stage compressors 112 flows into the gas-liquid separator 116 by the second switching mechanism 154, and then flows into the indoor heat exchanger 122 and the refrigeration-facility heat exchanger 132.

[0306] When the indoor unit 120 performs the heating operation, the refrigerant sent out from each of the high-stage compressors 112 flows into the gas-liquid separator 116 by the second switching mechanism 154, and then flows into the refrigeration-facility heat exchanger 132 or the outdoor heat exchanger 115 depending on the surplus or deficiency of the heat quantity for heating.

[0307] Furthermore, the refrigeration system 101 includes the first switching mechanism 150 and the second switching mechanism 154, and can switch, during the heating operation, the outdoor heat exchanger 115 among a state of not being used, a state of being used as a condenser, and a state of being used as a evaporator depending on the surplus or deficiency of the heat amount. Thus, during the heating operation, the refrigeration system 101 switches the state of the outdoor heat exchanger, so that cooling exhaust heat from the refrigeration-facility heat exchanger 132 can be used to adjust surplus or deficiency of the heat quantity for heating of the indoor unit 120.

[0308] In this way, the refrigeration system 101 includes the first switching mechanism 150 and the second switching mechanism 154, thereby capable of increasing the refrigeration capacity and adjusting the surplus or deficiency of the heat quantity for heating while preventing an increase in the number of valve bodies and opening / closing devices to be controlled. In other words, the refrigeration system 101 can increase the refrigeration capacity and adjust the surplus or deficiency of the heat quantity for heating using the refrigeration circuit 102 with a simple configuration.[2-2-7. Operation related to refrigerant recovery]

[0309] FIG. 12 is a circuit diagram showing a refrigeration circuit 102 of the refrigeration system 101 during refrigerant recovery / vacuuming work.

[0310] Next, the operation related to refrigerant recovery will be described.

[0311] A shown in FIG. 12, when a worker performs refrigerant recovery / vacuuming work on the refrigeration system 101, first, a refrigerant recovery device 150 or a vacuuming unit 152 is connected to the external connection port 196 of the service valve 190 through the connection pipe 156. The external connection port 196 is released by the worker after the connection pipe 156 is connected.

[0312] Next, the worker operates the operation panel 232 to select the refrigerant recovery / vacuuming mode. Thus, a predetermined signal is transmitted to the control device 200 from the operation panel 232. Upon receiving the signal, the control unit 201 controls all of the opening / closing devices provided in the refrigeration system 101 to be fully open. When all of the opening / closing devices are fully open, the control device 200 display, on the display panel 234, a screen indicating that the refrigeration system 101 performs the refrigerant recovery / vacuuming mode. Thereafter, the worker drives the refrigerant recovery device 150 or the vacuuming unit 152 to recover the refrigerant in the refrigeration circuit 102.[2-2-8. Operation related to refrigerant filling]

[0313] FIG. 13 is a circuit diagram showing a refrigeration circuit 102 of the refrigeration system 101 during refrigerant filling work.

[0314] Next, the operation related to refrigerant filling will be described.

[0315] As shown in FIG. 13, when a worker performs refrigerant filling work on the refrigeration system 101, first, a refrigerant filling unit 154 is connected to the external connection port 196 of the service valve 190 through the connection pipe 156. The external connection port 196 is released by the worker after the connection pipe 156 is connected.

[0316] Next, the worker operates the operation panel 232 to select the refrigerant filling mode. Thus, a predetermined signal is transmitted to the control device 200 from the operation panel 232. Upon receiving the signal, the control unit 201 controls each of the first cooling valve 151, the first heating valve 152, the outdoor refrigerant return valve 153, the on-off valve 123, the throttling mechanism 155, the refrigerant return expansion mechanism 158, the gas refrigerant flow-rate control valve 161, the liquid refrigerant flow-rate control valve 165, the indoor expansion mechanism 121, and the outlet-side refrigeration-facility pressure regulation mechanism 133 to be fully closed. Upon receiving the signal, the control unit 201 controls each of the check valves 159, which are provided in the pipes 175 and 176, and the inlet-side refrigeration-facility expansion mechanism 131 to be open. When such control of these opening / closing devices is completed, the control device 200 causes the display panel 234 to display a screen indicating that the refrigeration system 101 performs the refrigerant filling mode. Thereafter, the worker drives the refrigerant filling unit 154 to send out the refrigerant to the refrigeration circuit 102.

[0317] Thus, the refrigerant is stored in the refrigeration-facility heat exchanger 132 and the gas-liquid separator 116 in the refrigeration circuit 102.

[0318] FIG. 14 is a circuit diagram showing a refrigeration circuit 102 of the refrigeration system 101 during a regulation operation.

[0319] When the refrigeration system 101 performs a cooling operation after the refrigerant filling work, the external connection port 196 is closed by the worker as shown in FIG. 14.

[0320] Next, the worker operates the operation panel 232 to select the regulation operation mode. Thus, a predetermined signal is transmitted from the operation panel 232 to the control device 200. Upon receiving the signal, the control unit 201 controls each of the first heating valve 152, the outdoor refrigerant return valve 153, the refrigerant return expansion mechanism 158, the check valve 159 provided in the pipe 176, and the outlet-side refrigeration-facility pressure regulation mechanism 133 to be fully closed. Upon receiving the signal, the control unit 201 controls each of the first cooling valve 151, the on-off valve 123, the throttling mechanism 155, the check valve 159 provided in the pipe 176, the gas refrigerant flow-rate control valve 161, the liquid refrigerant flow-rate control valve 165, the indoor expansion mechanism 121, and the inlet-side refrigeration-facility expansion mechanism 131 to be fully open. When the control of these opening / closing devices is completed, the control device 200 causes the display panel 234 to display a screen indicating that the refrigeration system 101 performs the regulation operation mode. Thereafter, the worker drives each of the high-stage compressors 112 and the indoor unit 120 in a state of stopping the refrigeration-facility unit 130 and the low-stage compressor 111. Thus, the refrigerant is sent out to the outdoor heat exchanger 115 and the indoor heat exchanger 122 in the refrigeration circuit 102. In this case, the indoor expansion mechanism 121 opens such that the medium-pressure refrigerant flowing in from the gas-liquid separator 116 becomes a low-pressure refrigerant. Therefore, a high-pressure refrigerant, an intermediate-pressure refrigerant, and a medium-pressure refrigerant are generated in the refrigeration system 101.[2-3. Effects]

[0321] As described above, according to the present embodiment, the refrigeration system 101 includes the refrigeration circuit 102 that connects the outdoor unit 110 including the plurality of compressors, the outdoor heat exchanger 115, and the gas-liquid separator 116, the indoor unit 120 including the indoor heat exchanger 122, and the refrigeration-facility unit 130 including the refrigeration-facility heat exchanger 132.

[0322] The plurality of compressors are configured by the low-stage compressor 111 and the high-stage compressor 112, the indoor heat exchanger 122 having a high refrigerant evaporation temperature is connected to the high-stage compressor 112, and the refrigeration-facility heat exchanger 132 having a low refrigerant evaporation temperature is connected to the low-stage compressor 111.

[0323] The refrigeration circuit 102 includes the second switching mechanism 154 that causes the refrigerant discharged from the high-stage compressor 112 and flowing through at least either of the outdoor heat exchanger 115 or the indoor heat exchanger 122 to flow into the gas-liquid separator 116. The throttling mechanism 155 is provided between the outdoor heat exchanger 115 and the gas-liquid separator 116 to regulate the pressure of the refrigerant, and the indoor expansion mechanism 121 is provided between the indoor heat exchanger 122 and the gas-liquid separator 116.

[0324] Thus, the refrigeration system 101 can be formed with the refrigeration circuit 102 with a simple configuration, and can send the refrigerant to the evaporator through the gas-liquid separator 116 in both the case of performing the cooling operation and the case of performing the heating operation. Therefore, the refrigeration system 101 can improve the refrigeration capacity with a simple circuit configuration.

[0325] As in the present embodiment, the second switching mechanism 154 includes the pipes 173 to 176 that connect the outdoor heat exchanger 115, the indoor heat exchanger 122, the refrigeration-facility heat exchanger 132, and the gas-liquid separator 116 to one another. Each of the pipes 173 to 176 may be provided with the throttling mechanism 155 that regulates the flow of the refrigerant, the refrigerant return expansion mechanism 158, and the check valve 159.

[0326] Thus, in the refrigeration system 101, the refrigerant subjected to heat exchange by the gas-liquid separator 116 can be sent to any one of the outdoor heat exchanger 115, the indoor heat exchanger 122, and the refrigeration-facility heat exchanger 132 depending on the operation of the indoor unit 120 and the refrigeration-facility unit 130. Therefore, the refrigeration system 101 can increase the refrigeration capacity of the indoor unit 120 and the refrigeration-facility unit 130.

[0327] As in the present embodiment, the second switching mechanism 154 may include the check valve 159 and the throttling mechanism 155, as valve bodies.

[0328] Thus, in the refrigeration system 101, the refrigerant subjected to heat exchange by the gas-liquid separator 116 can be sent to any one of the outdoor heat exchanger 115, the indoor heat exchanger 122, and the refrigeration-facility heat exchanger 132 depending on the operation of the indoor unit 120 and the refrigeration-facility unit 130. Therefore, the refrigeration system 101 can increase the refrigeration capacity of the indoor unit 120 and the refrigeration-facility unit 130.

[0329] As in the present embodiment, the first switching mechanism 150 may be a mechanism that switches among any one of a flow path in which the refrigerant discharged from the high-stage compressor 112 flows to the outdoor heat exchanger 115, a flow path in which the refrigerant discharged from the high-stage compressor 112 flows to the indoor heat exchanger 122, and a flow path in which the refrigerant discharged from the high-stage compressor 112 flows to both the outdoor heat exchanger 115 and the indoor heat exchanger 122.

[0330] Thus, the refrigeration system 101 can include the refrigeration circuit 102 with simpler configuration. In addition, the refrigeration system 101 can switch the operation without stopping the compressor.

[0331] As in the present embodiment, the first switching mechanism 150 may be provided with the first cooling valve 151 located between the discharge side of the high-stage compressor 112 and the outdoor heat exchanger 115 and the outdoor refrigerant return valve 153 located downstream of the first cooling valve 151 and between the discharge side of the high-stage compressor 112 and the suction side of the low-stage compressor 111.

[0332] Thus, the refrigeration system 101 can switch among any one of a flow path in which the refrigerant discharged from the high-stage compressor 112 flows to the outdoor heat exchanger 115, a flow path in which the refrigerant discharged from the high-stage compressor 112 flows to the indoor heat exchanger 122, a flow path in which the refrigerant discharged from the high-stage compressor 112 flows to both the outdoor heat exchanger 115 and the indoor heat exchanger 122. Therefore, the refrigeration system 101 can include the refrigeration circuit 102 with a simpler configuration.

[0333] As in the present embodiment, the refrigeration system 101 includes the control device 200 that controls each of the units of the refrigeration circuit 102. The control device 200 includes the operation panel 232 that can be operated by the worker. The control device 200 includes, as operation modes of the refrigeration circuit 102, the first operation mode in which the refrigerant flowing through the indoor heat exchanger 122 and the refrigeration-facility heat exchanger 132 is regulated at a predetermined temperature and the second operation mode in which the operation is performed according to the operation of the external device connected to the refrigeration circuit 102. The control device 200 may switch between the first operation mode and the second operation mode according to the operation on the operation panel 232.

[0334] Thus, the refrigeration system 101 can switch between the first operation mode and the second operation mode according to the operation on the operation panel 232. Therefore, in the refrigeration system 101, the worker can easily switch between the operation modes.

[0335] As in the present embodiment, the control device 200 may include a plurality of second operation modes, and may switch between the second operation modes according to the operation on the operation panel 232.

[0336] Thus, in the refrigeration system 101, the worker can perform the work related to the refrigerant recovery / vacuuming and the refrigerant filling according to the operation on the operation panel 232. Therefore, in the refrigeration system 101, the worker can easily perform the work related to the refrigerant recovery / vacuuming and the refrigerant filling.

[0337] As in the present embodiment, the control device 200 may include a display panel 234 that displays a status of the refrigeration circuit 102 in each of the operation modes.

[0338] Thus, in the refrigeration system 101, the worker can perform the work related to the refrigerant recovery / vacuuming and the refrigerant filling according to the operation on the control device 200 while checking the status of the refrigeration system 101. Therefore, in the refrigeration system 101, the worker can easily perform the work related to the refrigerant recovery / vacuuming and the refrigerant filling.

[0339] As in the present embodiment, the service valve 190, to which the external device can be connected, may be provided between the refrigeration-facility heat exchanger 132 and the suction side of the low-stage compressor 111.

[0340] Thus, in the refrigeration system 101, the service valve 190 is provided at a location close to the connection point between the outdoor unit 110 and the refrigeration-facility unit 130. Therefore, the refrigeration system 101 can improve workability when the external device is connected to the refrigeration system 101.(Other Embodiments)

[0341] As described above, the first and second embodiments have been described as examples of techniques disclosed in the present application. However, the techniques of the present disclosure are not limited thereto, and are also applicable to embodiments where changes, replacements, additions, omissions, etc., are appropriately made. In addition, it is also possible to combine the components described in the first and second embodiments to create new embodiments.

[0342] Hereinafter, other embodiments will be described as examples.

[0343] The connection pipe 166 is provided in the refrigeration system 101 in the embodiments described above, but the connection pipe 166 may not be provided.

[0344] In the above-described embodiments, the outlet-side refrigeration-facility pressure regulation mechanism 133 and the service valve 190 are provided in the refrigeration-facility unit 130. However, the present invention is not limited thereto, and the outlet-side refrigeration-facility pressure regulation mechanism 133 and the service valve 190 may be provided in the outdoor unit 110. For example, the outlet-side refrigeration-facility pressure regulation mechanism 133 and the service valve 190 may be provided in the pipe 172 between the outdoor unit 110 and the refrigeration-facility unit 130.

[0345] In the above-described embodiments, the refrigeration system 101 includes one indoor heat exchanger 122 and one refrigeration-facility heat exchanger 132. However, the present invention is not limited thereto, and the refrigeration system 101 may include another refrigeration-facility heat exchanger 132 instead of the indoor heat exchanger 122. In other words, the refrigeration system 101 may include a plurality of refrigeration-facility units 130 without including the indoor unit 120.

[0346] In this case, the plurality of refrigeration-facility heat exchangers 132 have different evaporation temperature zones. Out of the plurality of refrigeration-facility heat exchangers 132, the refrigeration-facility heat exchanger 132 having a higher evaporation temperature zone is connected to the inlet side of the high-stage compressor 112, and the refrigeration-facility heat exchanger 132 having a lower evaporation temperature zone is connected to the inlet side of the low-stage compressor 111.

[0347] For example, when the refrigeration system 101 includes the refrigeration-facility unit 130 set to the freezing temperature zone and the refrigeration-facility unit 130 set to the refrigeration temperature zone, the refrigeration-facility heat exchanger 132 in the refrigeration-facility unit 130 set to the refrigeration temperature zone is connected to the inlet side of the high-stage compressor 112. On the other hand, the refrigeration-facility heat exchanger 132 in the refrigeration-facility unit 130 set to the freezing temperature zone is connected to the inlet side of the low-stage compressor 111.

[0348] In the above-described embodiments, a plurality of utilization-side heat exchangers connected to the inlet side of the high-stage compressor 112 may be provided in parallel in the pipes 178 and 171. Similarly, a plurality of utilization-side heat exchangers connected to the inlet side of the low-stage compressor 111 may be provided in parallel in the pipes 177 and 172.

[0349] Furthermore, for example, a plurality of indoor heat exchangers 122 may be provided in parallel to each other in the pipes 178 and 171. In this case, the indoor expansion mechanism 121 may be provided on the inlet side of each of the indoor heat exchangers 122. In this case, the refrigeration system 101 includes a plurality of indoor units 120. In this case, one or a plurality of indoor heat exchanger 122 and one or a plurality of refrigeration-facility heat exchanger 132 may be provided in parallel in the pipes 178 and 171.

[0350] A plurality of refrigeration-facility heat exchangers 132 may be provided in parallel to each other in the pipes 177 and 172. In this case, an inlet-side refrigeration-facility expansion mechanism 131 may be provided on the inlet side of each of the refrigeration-facility heat exchangers 132. In this case, at least one of the refrigeration-facility heat exchangers 132 provided in parallel in the pipes 177 and 172 may have an evaporation temperature zone different from that of the other refrigeration-facility heat exchangers 132.

[0351] The control device 200 may include a touch panel having integrally the functions of the operation panel 232 and the display panel 234.

[0352] Furthermore, for example, the control device 200 may be provided in either the indoor unit 120 or the refrigeration-facility unit 130. For example, either the operation panel 232 or the display panel 234 may be provided integrally in any one of the outdoor unit 110, the indoor unit 120, and the refrigeration-facility unit 130.

[0353] Furthermore, for example, the control device 200 may be provided integrally in an operation terminal such as a remote control provided in the indoor unit 120 or the refrigeration-facility unit 130. The remote control is a terminal that controls setting temperature of the indoor unit 120 or the refrigeration-facility unit 130 or starts up the indoor unit 120 or the refrigeration-facility unit 130.

[0354] Furthermore, for example, the control device 200 may be a communication terminal such as a smartphone or a tablet in which apps or programs are installed to transmit a predetermined signal to the outdoor unit 110 or each unit of the refrigeration system 101. In this case, the control device 200 may be capable of communicating with the outdoor unit 110 and each unit of the refrigeration system 101 via a network constituted of a public line network, a dedicated line, other communication lines, and various communication facilities. Specific aspects of such a network are not limited. The communication network may include at least one of a wireless communication circuit and a wired communication circuit.

[0355] Furthermore, for example, the control device 200 may be a server device in which apps or programs are installed to transmit a predetermined signal to the outdoor unit 110 or each unit of the refrigeration system 101. The server device may be capable of communicating with the outdoor unit 110 and each unit of the refrigeration system 101 via the above-described network.

[0356] Each unit shown in FIG. 6 is an example and not particularly limited to a specific implementation. Thus, hardware individually corresponding to each component does not necessarily need to be implemented, and functions of each component may be achieved by one processor executing a computer program. Some functions achieved by software in the above-described embodiments may be achieved by hardware, or some functions achieved by hardware may be achieved by software. Specific detailed components of other units of the outdoor unit 110, the indoor unit 120, and the refrigeration-facility unit 130 are optionally changeable without departing from the spirit of the present invention.

[0357] Step units of the operation shown in FIG. 9 are divisions according to main processing contents to facilitate understanding of operation of each unit of the refrigeration system 101, and the operation is not limited by a division scheme of processing units and their names. The division into a larger number of step units may be made in accordance with processing contents. The division may be made such that one step unit includes a larger number of processes. Moreover, orders of steps may be interchanged as appropriate without interference with the spirit of the present invention.

[0358] Note that the above-described embodiments are intended to illustrate the technology of the present disclosure, and thus various modifications, substitutions, additions, omissions, and the like can be made within the claims or equivalents thereof.(Supplementary Note)

[0359] The following techniques are disclosed according to the above-described embodiments.

[0360] (Technique 1) A refrigeration system includes a refrigeration cycle circuit that connects an outdoor unit including a plurality of compressors, an outdoor heat exchanger, and a gas-liquid separator, an indoor unit including an indoor heat exchanger, and a refrigeration-facility unit including a refrigeration-facility heat exchanger, the plurality of compressors includes a low-stage compressor and a high-stage compressor, a gas refrigerant return pipe is provided to send a gas refrigerant from the gas-liquid separator to the high-stage compressor, and the gas refrigerant return pipe is provided with a gas refrigerant return expansion valve that controls a return amount of the gas refrigerant from the gas-liquid separator.

[0361] According to the above-described configuration, the return amount of the gas refrigerant from the gas-liquid separator is controlled by control of the opening degree of the gas refrigerant return expansion valve, whereby a differential pressure of the refrigerant sent to the indoor heat exchanger can be generated. Therefore, it is possible to control the pressure by adding a specified value to the evaporation temperature of the indoor heat exchanger having a high evaporation temperature, and to improve efficiency of an air conditioning temperature zone using carbon dioxide (R744), a natural refrigerant with high environmental preservation characteristics.

[0362] (Technique 2) The refrigeration system according to Technique 1, in which during a heating operation, the refrigeration cycle circuit is operated using the indoor heat exchanger and the outdoor heat exchanger as condensers and the refrigeration-facility heat exchanger as an evaporator.

[0363] According to the above-described configuration, the flow direction on the high evaporation temperature side of the indoor heat exchanger is reversed from that of the outdoor heat exchanger, and the heat pumped up from the outdoor heat exchanger and the exhaust heat from the refrigeration-facility unit are used together for the heating of the indoor heat exchanger. In addition, depending on conditions of the indoor heat exchanger, the outdoor heat exchanger and the indoor heat exchanger can be heated simultaneously, and the distribution of the heat amount can be controlled.

[0364] (Technique 3) The refrigeration system according to Technique 1, in which during a heating operation, the refrigeration cycle circuit is operated using the indoor heat exchanger as a condenser, and the refrigeration-facility heat exchanger and the outdoor heat exchanger as evaporators.

[0365] According to the above-described configuration, the heat pumped up from the outdoor heat exchanger and the exhaust heat from the refrigeration-facility heat exchanger can be used together for the heating of the indoor heat exchanger, and when the outside air temperature becomes lower than the interior temperature of the refrigeration-facility unit, the pressure can be controlled to be the same. Therefore, it is possible to prevent the evaporation temperature of the refrigeration-facility unit from dropping too low, and to control the temperature with high accuracy.

[0366] (Technique 4) The refrigeration system according to Technique 1, in which during a heating operation, the refrigeration cycle circuit is operated using the indoor heat exchanger as a condenser, and only the refrigeration-facility heat exchanger as an evaporator.

[0367] According to the above-described configuration, all of the exhaust heat from the refrigeration-facility unit can be radiated with the indoor heat exchanger having a high evaporation temperature. Therefore, the exhaust heat can be utilized without loss, and the heating operation can be performed with high efficiency.

[0368] (Technique 5) A refrigeration system including a refrigeration circuit including a plurality of compressors, a heat source-side heat exchanger, a plurality of utilization-side heat exchangers, and a gas-liquid separator, the plurality of compressors include a low-stage compressor, and a high-stage compressor, the plurality of utilization-side heat exchangers include a first utilization-side heat exchanger, and a second utilization-side heat exchanger having a refrigerant evaporation temperature lower than that of the first utilization-side heat exchanger, the refrigeration circuit is provided with a switching mechanism that causes a refrigerant, which is discharged from the high-stage compressor and flows through at least one of the heat source-side heat exchanger and the first utilization-side heat exchanger, to flow to the gas-liquid separator, and throttling mechanisms are provided between the heat source-side heat exchanger and the gas-liquid separator and between the first utilization-side heat exchanger and the gas-liquid separator to regulate a pressure of the refrigerant.

[0369] Thus, the refrigeration system can be formed with the refrigeration circuit with a simple configuration, and can send the refrigerant to the heat exchanger functioning as an evaporator through the gas-liquid separator in both the case of performing the cooling operation and the case of performing the heating operation. Therefore, the refrigeration system can improve the refrigeration capacity with a simple circuit configuration.

[0370] (Technique 6) The refrigeration system according to Technique 5, in which the switching mechanism includes pipes that connect the heat source-side heat exchanger, the first utilization-side heat exchanger, the second utilization-side heat exchanger, and the gas-liquid separator to one another, and a valve body is provided in each of the pipes to regulate a flow of the refrigerant.

[0371] Thus, in the refrigeration system, the refrigerant subjected to heat exchange by the gas-liquid separator can be sent to any one of the heat source-side heat exchanger, the first utilization-side heat exchanger, and the second utilization-side heat exchanger. Therefore, the refrigeration system can increase the refrigeration capacity.

[0372] (Technique 7) The refrigeration system according to Technique 6, in which the switching mechanism includes, as the valve body, a check valve, and the throttling mechanism.

[0373] Thus, in the refrigeration system, the refrigerant subjected to heat exchange by the gas-liquid separator can be sent to any one of the utilization-side heat exchanger, the first utilization-side heat exchanger, and the second utilization-side heat exchanger. Therefore, the refrigeration system can increase the refrigeration capacity.

[0374] (Technique 8) The refrigeration system according to any one of Techniques 5 to 7, in which the refrigeration circuit includes another switching mechanism that switches to any one of: a flow path in which the refrigerant discharged from the high-stage compressor flows to the heat source-side heat exchanger, a flow path in which the refrigerant discharged from the high-stage compressor flows to the first utilization-side heat exchanger, and a flow path in which the refrigerant discharged from the high-stage compressor flows to both the heat source-side heat exchanger and the first utilization-side heat exchanger.

[0375] Thus, the refrigeration system can include the refrigeration circuit with simpler configuration. In addition, the refrigeration system can switch the operation without stopping the compressor.

[0376] (Technique 9) The refrigeration system according to Technique 8, in which the another switching mechanism includes a first cooling valve that is a valve body located between a discharge side of the high-stage compressor and the heat source-side heat exchanger, and an outdoor refrigerant return valve that is a valve body located downstream of the first cooling valve and between the discharge side of the high-stage compressor and a suction side of the low-stage compressor.

[0377] Thus, the refrigeration system can switch between any one of a flow path in which the refrigerant discharged from the high-stage compressor flows to the heat source-side heat exchanger, a flow path in which the refrigerant discharged from the high-stage compressor flows to the first utilization-side heat exchanger, a flow path in which the refrigerant discharged from the high-stage compressor flows to both the outdoor heat exchanger and the first utilization-side heat exchanger. Therefore, the refrigeration system can include the refrigeration circuit with a simpler configuration.

[0378] (Technique 10) The refrigeration system according to any one of Techniques 5 to 9, in which the refrigeration system further includes a control unit that controls each component of the refrigeration circuit, the control unit includes an operation portion that can be operated by a worker, the control unit includes, as operation modes of the refrigeration circuit, a first operation mode in which a refrigerant flowing through the first utilization-side heat exchanger and the second utilization-side heat exchanger is regulated at a predetermined temperature, and a second operation mode in which an operation is performed according to an operation of an external device connected to the refrigeration circuit, and the control unit switches between the first operation mode and the second operation mode according to an operation on the operation portion.

[0379] Thus, the refrigeration system can switch between the first operation mode and the second operation mode according to the operation on the operation portion. Therefore, in the refrigeration system, the worker can easily switch between the operation modes.

[0380] (Technique 11) The refrigeration system according to Technique 10, in which the control unit includes a plurality of second operation modes, and switches between the second operation modes according to the operation on the operation portion.

[0381] Thus, in the refrigeration system, the worker can perform the work related to the refrigerant recovery / vacuuming and the refrigerant filling according to the operation on the operation portion. Therefore, in the refrigeration system, the worker can easily perform the work related to the refrigerant recovery / vacuuming and the refrigerant filling.

[0382] (Technique 12) The refrigeration system according to Technique 10 or 11, in which the control unit includes a display portion that displays a status of the refrigeration circuit in each of the operation modes.

[0383] Thus, in the refrigeration system, the worker can perform the work related to the refrigerant recovery / vacuuming and the refrigerant filling according to the operation on the control unit while checking the status of the refrigeration system. Therefore, in the refrigeration system, the worker can easily perform the work related to the refrigerant recovery / vacuuming and the refrigerant filling.

[0384] (Technique 13) The refrigeration system according to any one of Techniques 5 to 12, in which a connection port is provided between the second utilization-side heat exchanger and a suction side of the low-stage compressor to be connectable to an external device.

[0385] Thus, the refrigeration system can improve workability when the external device is connected to the refrigeration system.Industrial Applicability

[0386] The first aspect of the present disclosure can be suitably used as a refrigeration system capable of improving efficiency of an air conditioning temperature zone using carbon dioxide (R744), a natural refrigerant with high environmental preservation characteristics.

[0387] A second aspect of the present disclosure can be suitably used as a refrigeration system capable of improving efficiency of an air conditioning temperature zone using a natural refrigerant, and improving the efficiency of the entire system.Reference Signs List

[0388] 1refrigeration system 10outdoor unit 11low-stage compressor 12high-stage compressor 13accumulator 14oil separator 15outdoor heat exchanger 16gas-liquid separator 20indoor unit 21indoor expansion mechanism 22indoor heat exchanger 23on-off valve 30refrigeration-facility unit 31refrigeration-facility heat exchanger 32inlet-side refrigeration-facility expansion mechanism 33outlet-side refrigeration-facility expansion mechanism 40refrigerant pipe 41first heating pipe 42first outdoor return pipe 43second cooling pipe 44second heating pipe 45second outdoor return pipe 50first switching mechanism 51first cooling valve 52first heating valve 53outdoor refrigerant return valve 54second switching mechanism 55second cooling valve 56third cooling valve 57second heating valve 58refrigerant return expansion mechanism 59check valve 60gas refrigerant return pipe 61gas refrigerant return expansion mechanism 101refrigeration system 102refrigeration circuit 110outdoor unit 111low-stage compressor 112high-stage compressor 113accumulator 114oil separator 115outdoor heat exchanger (heat source-side heat exchanger) 116gas-liquid separator 118,128, 138 blower 120indoor unit 121indoor expansion mechanism 122indoor heat exchanger (first utilization-side heat exchanger) 123on-off valve 127space temperature sensor 130refrigeration-facility unit 131inlet-side refrigeration-facility expansion mechanism 132refrigeration-facility heat exchanger (second utilization-side heat exchanger) 133outlet-side refrigeration-facility pressure regulation mechanism 137interior temperature sensor 140pipe 141first heating pipe 142first outdoor return pipe 150first switching mechanism (another switching mechanism) 151first cooling valve 152first heating valve 153outdoor refrigerant return valve 154second switching mechanism (switching mechanism) 155throttling mechanism 158refrigerant return expansion mechanism 159check valve 160gas refrigerant return pipe 161gas refrigerant flow-rate control valve 164internal heat exchanger 165liquid refrigerant flow-rate control valve 166connection pipe 171pipe 172pipe 173first pipe 174second pipe 175third pipe 176fourth pipe 177pipe 178pipe 179pipe 180refrigerant pressure sensor 182refrigerant temperature sensor 190service valve 192pipe connection port 194pipe connection port 196external connection port 200control device 201control unit 201aoperation control unit 201bdetermination unit 203storage unit 203asetting data 205outdoor unit I / F 206outdoor-unit communication portion 210indoor-unit control device 211indoor-unit control unit 213indoor-unit storage unit 215indoor unit I / F 220refrigeration-facility-unit control device 221refrigeration-facility-unit control unit 223refrigeration-facility-unit storage unit 225refrigeration-facility unit I / F 232operation panel 234display panel 250refrigerant recovery device 252vacuuming unit 254refrigerant filling unit 256connection pipe A, B, C, Dconnection portion

Claims

1. A refrigeration system comprising a refrigeration cycle circuit that connects an outdoor unit including a plurality of compressors, an outdoor heat exchanger, and a gas-liquid separator, an indoor unit including an indoor heat exchanger, and a refrigeration-facility unit including a refrigeration-facility heat exchanger, wherein the plurality of compressors includes a low-stage compressor and a high-stage compressor, a gas refrigerant return pipe is provided to send a gas refrigerant from the gas-liquid separator to the high-stage compressor, and the gas refrigerant return pipe is provided with a gas refrigerant return expansion valve that controls a return amount of the gas refrigerant from the gas-liquid separator.

2. The refrigeration system according to claim 1, wherein, during a heating operation, the refrigeration cycle circuit is operated using the indoor heat exchanger and the outdoor heat exchanger as condensers and the refrigeration-facility heat exchanger as an evaporator.

3. The refrigeration system according to claim 1, wherein, during a heating operation, the refrigeration cycle circuit is operated using the indoor heat exchanger as a condenser, and the refrigeration-facility heat exchanger and the outdoor heat exchanger as evaporators.

4. The refrigeration system according to claim 1, wherein, during a heating operation, the refrigeration cycle circuit is operated using the indoor heat exchanger as a condenser, and only the refrigeration-facility heat exchanger as an evaporator.

5. A refrigeration system comprising a refrigeration circuit including a plurality of compressors, a heat source-side heat exchanger, a plurality of utilization-side heat exchangers, and a gas-liquid separator, the plurality of compressors include a low-stage compressor, and a high-stage compressor, the plurality of utilization-side heat exchangers include a first utilization-side heat exchanger, and a second utilization-side heat exchanger having a refrigerant evaporation temperature lower than that of the first utilization-side heat exchanger, the refrigeration circuit is provided with a switching mechanism that causes a refrigerant, which is discharged from the high-stage compressor and flows through at least one of the heat source-side heat exchanger and the first utilization-side heat exchanger, to flow to the gas-liquid separator, and throttling mechanisms are provided between the heat source-side heat exchanger and the gas-liquid separator and between the first utilization-side heat exchanger and the gas-liquid separator to regulate a pressure of the refrigerant.

6. The refrigeration system according to claim 5, wherein the switching mechanism includes pipes that connect the heat source-side heat exchanger, the first utilization-side heat exchanger, the second utilization-side heat exchanger, and the gas-liquid separator to one another, and a valve body is provided in each of the pipes to regulate a flow of the refrigerant.

7. The refrigeration system according to claim 6, wherein the switching mechanism includes, as the valve body, a check valve, and the throttling mechanism.

8. The refrigeration system according to any one of claims 5 to 7, wherein the refrigeration circuit includes another switching mechanism that switches to any one of: a flow path in which the refrigerant discharged from the high-stage compressor flows to the heat source-side heat exchanger, a flow path in which the refrigerant discharged from the high-stage compressor flows to the first utilization-side heat exchanger, and a flow path in which the refrigerant discharged from the high-stage compressor flows to both the heat source-side heat exchanger and the first utilization-side heat exchanger.

9. The refrigeration system according to claim 8, wherein the another switching mechanism includes a first cooling valve that is a valve body located between a discharge side of the high-stage compressor and the heat source-side heat exchanger, and an outdoor refrigerant return valve that is a valve body located downstream of the first cooling valve and between the discharge side of the high-stage compressor and a suction side of the low-stage compressor.

10. The refrigeration system according to any one of claims 5 to 7, further comprising a control unit that controls each component of the refrigeration circuit, wherein the control unit includes an operation portion that can be operated by a worker, the control unit includes, as operation modes of the refrigeration circuit, a first operation mode in which a refrigerant flowing through the first utilization-side heat exchanger and the second utilization-side heat exchanger is regulated at a predetermined temperature, and a second operation mode in which an operation is performed according to an operation of an external device connected to the refrigeration circuit, and the control unit switch between the first operation mode and the second operation mode according to an operation on the operation portion.

11. The refrigeration system according to claim 10, wherein the control unit includes a plurality of second operation modes, and switches between the second operation modes according to the operation on the operation portion.

12. The refrigeration system according to claim 10, wherein the control unit includes a display portion that displays a status of the refrigeration circuit in each of the operation modes.

13. The refrigeration system according to any one of claims 5 to 7, wherein a connection port is provided between the second utilization-side heat exchanger and a suction side of the low-stage compressor to be connectable to an external device.

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