Refrigeration system and method for controlling refrigeration system

Abstract

To provide a refrigeration system capable of maintaining a desired temperature inside a refrigeration warehouse while reducing both initial and running costs, and a method for controlling the refrigeration system.SOLUTION: A refrigeration system according to one embodiment of the present invention comprises: a first freezer that suctions air in a refrigeration warehouse as a first refrigerant, and cools the inside of the refrigeration warehouse by supplying the first refrigerant into the refrigeration warehouse again; a second freezer that has an evaporator provided in the refrigeration warehouse using carbon dioxide as a second refrigerant, and cools the inside of the refrigeration warehouse by exchanging heat between the evaporator and the air in the refrigeration warehouse; and a control unit that controls the operations of the first freezer and the second freezer. The control unit controls the operations of the first freezer and the second freezer so that the temperature in the refrigeration warehouse is maintained at a steady temperature higher than the triple point of carbon dioxide.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a refrigeration system and a method for controlling the refrigeration system.

Background Art

[0002] For example, for storing fish such as tuna and bonito, it is necessary to maintain the inside of the cold storage warehouse at an ultra-low temperature (below -50°C). In recent years, as a refrigeration system for maintaining the inside of the cold storage warehouse in an ultra-low temperature state, a configuration that employs a refrigerator using air as a refrigerant (air refrigerator) is known (see, for example, Patent Document 1 below). Air is non-toxic and non-flammable, and has an ODP (ozone depletion potential) and a GWP (global warming potential) of zero. Therefore, it is considered that by adopting an air refrigerator, a refrigeration system that has little impact on the surrounding environment and the global environment can be provided.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in an air refrigerator, the heat exchange efficiency for a certain output is constant regardless of the temperature range. In other words, since an air refrigerator performs sensible heat cooling by a gas cycle that remains in a single phase as a gas, the change in enthalpy due to a temperature change is smaller compared to a refrigerant such as freon that performs cooling by latent heat of vaporization. Therefore, in an air refrigerator, the heat exchange efficiency tends to be low when cooling from a high temperature range to a low temperature range. Therefore, for example, when the temperature inside the cold storage warehouse rises due to a sudden load fluctuation inside the cold storage warehouse, the power required for cooling increases, resulting in an increase in running costs. In addition, when installing a plurality of air refrigerators to withstand sudden load fluctuations inside the cold storage warehouse, there is a problem that the initial cost increases.

[0005] The present invention provides a refrigeration system and a control method for the refrigeration system that can maintain a desired temperature in a refrigerated warehouse while suppressing both initial cost and running cost.

Means for Solving the Problems

[0006] In order to solve the above problems, the present invention adopts the following aspects. A refrigeration system according to an aspect of the present invention includes a first refrigerator that takes in air in a refrigerated warehouse as a first refrigerant and cools the inside of the refrigerated warehouse by supplying the taken-in first refrigerant back into the refrigerated warehouse; a second refrigerator that has an evaporator provided in the refrigerated warehouse with carbon dioxide as a second refrigerant and cools the inside of the refrigerated warehouse by performing heat exchange between the evaporator and the air in the refrigerated warehouse; and a control unit that controls the operations of the first refrigerator and the second refrigerator, wherein the control unit controls the operations of the first refrigerator and the second refrigerator so that the temperature in the refrigerated warehouse is maintained at a steady temperature higher than the triple point of carbon dioxide.

[0007] According to this aspect, it is possible to maintain the temperature in the refrigerated warehouse at a steady temperature while controlling the operations of both the first refrigerator and the second refrigerator. In this case, for example, in a high-temperature range where the heat exchange efficiency of the first refrigerator is low, by operating the second refrigerator, the running cost can be suppressed compared to the case where the first refrigerator is continuously operated all the time. Further, by using the second refrigerator as a part of the refrigeration system, compared with the case where a refrigeration system is realized only by a plurality of first refrigerators, the initial cost can be suppressed and an efficient cooling operation can be performed against a rapid load fluctuation in the refrigerated warehouse. As a result, it is possible to maintain the inside of the refrigerated warehouse at a desired temperature (steady temperature) while suppressing both the initial cost and the running cost.

[0008] Moreover, since the first refrigerator and the second refrigerator are controlled so that the temperature in the refrigerated warehouse is maintained at a steady temperature higher than the triple point of carbon dioxide, it is possible to suppress the phase change of the second refrigerant in the evaporator into a solid (dry ice formation). As a result, a highly reliable refrigeration system can be provided over a long period of time.

[0009] In the refrigeration system according to the above aspect, when a temperature higher than the steady temperature is set as the operation determination temperature, the control unit operates the second refrigerator with the first refrigerator stopped when the temperature in the refrigerated warehouse is higher than the operation determination temperature, and operates the first refrigerator with the second refrigerator stopped when the temperature in the refrigerated warehouse is higher than the steady temperature and equal to or lower than the operation determination temperature. This is preferable. According to this aspect, when the temperature in the refrigerated warehouse is higher than the operation determination temperature, by operating only the refrigerator with excellent heat exchange efficiency in each temperature range where the temperature is equal to or higher than the operation determination temperature, the running cost can be suppressed.

[0010] In the refrigeration system according to the above aspect, when a temperature higher than the steady temperature is set as the operation determination temperature, the control unit operates both the first refrigerator and the second refrigerator when the temperature in the refrigerated warehouse is higher than the operation determination temperature, and operates the first refrigerator with the second refrigerator stopped when the temperature in the refrigerated warehouse is higher than the steady temperature and equal to or lower than the operation determination temperature. This is preferable. According to this configuration, when the temperature in the refrigerated warehouse exceeds the operation determination temperature, by operating both the first refrigerator and the second refrigerator, the inside of the refrigerated warehouse can be quickly restored to a steady state (the temperature followability can be improved).

[0011] In the refrigeration system according to the above aspect, it is preferable that the control unit stops the operations of both the first refrigerator and the second refrigerator when the temperature in the refrigerated warehouse reaches the steady temperature. According to this aspect, it is possible to suppress the temperature in the refrigerated warehouse from reaching the triple point of carbon dioxide while suppressing the running cost.

[0012] In the refrigeration system according to the above aspect, it is preferable that the second refrigerator includes a high-stage cycle provided outside the refrigerated warehouse with ammonia as a high-stage refrigerant, and a low-stage cycle using the second refrigerant as a low-stage refrigerant. According to this aspect, refrigerants with different boiling points can be used in their respective optimal temperature ranges, so that stable operation is possible while suppressing running costs. In this case, since the high-stage cycle is provided outside the refrigerated warehouse, even if ammonia leaks from the high-stage cycle, it can be prevented from entering the refrigerated warehouse.

[0013] A control method for a refrigeration system according to an aspect of the present invention includes a first refrigerator that takes in air in a refrigerated warehouse as a first refrigerant and cools the inside of the refrigerated warehouse by supplying the taken-in first refrigerant back into the refrigerated warehouse, a second refrigerator that has an evaporator provided in the refrigerated warehouse with carbon dioxide as a second refrigerant and cools the inside of the refrigerated warehouse by performing heat exchange between the evaporator and the air in the refrigerated warehouse, and a control unit that controls the operations of the first refrigerator and the second refrigerator. The control unit controls the operations of the first refrigerator and the second refrigerator so that the temperature in the refrigerated warehouse is maintained at a steady temperature higher than the triple point of carbon dioxide.

Effect of the Invention

[0014] According to each of the above aspects, both the initial cost and the running cost can be suppressed, and the temperature inside the refrigerated warehouse can be maintained at a desired temperature.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0016] Next, embodiments of the present invention will be described with reference to the drawings. In the embodiments and modifications described below, corresponding configurations may be denoted by the same reference numerals and description thereof may be omitted. In the following description, expressions indicating relative or absolute arrangements such as "parallel", "orthogonal", "center", "coaxial", etc. not only strictly represent such arrangements, but also represent states in which they are relatively displaced with tolerances and angles or distances that can obtain the same function. Further, in the present embodiment, "opposite" includes not only the case where the orthogonal directions (normal directions) of two surfaces coincide with each other, but also the case where the orthogonal directions intersect each other.

[0017] (First Embodiment) [Refrigeration Device 1] FIG. 1 is a schematic configuration diagram of the refrigeration device 1. The refrigeration device 1 shown in FIG. 1 is an ultra-low temperature refrigeration device 1 used for storing fish such as tuna and bonito (hereinafter referred to as refrigeration objects). The refrigeration device 1 includes a refrigerated warehouse 10 and a refrigeration system 11.

[0018] <Refrigerated Warehouse 10> The refrigerated warehouse 10 has an entrance / exit (not shown) through which objects to be frozen are carried in and out, and stores the carried-in objects to be frozen within a predetermined temperature range. Inside the refrigerated warehouse 10, an in-warehouse temperature sensor 12 for detecting the temperature inside the refrigerated warehouse 10 (the in-warehouse temperature T) is provided. It is preferable that the in-warehouse temperature sensor 12 is provided at a position where the temperature is likely to rise inside the refrigerated warehouse 10. In the illustrated example, the in-warehouse temperature sensor 12 is provided at the upper part inside the refrigerated warehouse 10.

[0019] <Refrigeration system 11> The refrigeration system 11 includes an air refrigerating machine (first refrigerating machine) 20, a binary refrigerating machine (second refrigerating machine) 50, and a control unit 100.

[0020] <Air refrigerating machine 20> The air refrigerating machine 20 takes in the air inside the refrigerated warehouse 10 as a refrigerant (first refrigerant), and cools the inside of the refrigerated warehouse 10 by circulating the air between the inside of the refrigerated warehouse 10 so as to supply the taken-in air back into the refrigerated warehouse 10. Specifically, the air refrigerating machine 20 includes a defroster 21, a cold heat recovery heat exchanger 22, a compressor 23, a primary cooler 24, and an expander 25. The defroster 21, the cold heat recovery heat exchanger 22, the compressor 23, the primary cooler 24, and the expander 25 are provided in order in the air flow direction on the air flow path 26. The upstream end of the air flow path 26 is connected to an intake port 31 provided in the refrigerated warehouse 10. On the other hand, the downstream end of the air flow path 26 is connected to an outlet port 32 provided in the refrigerated warehouse 10. The intake port 31 and the outlet port 32 are each provided near the ceiling of the refrigerated warehouse 10. However, the outlet port 32 may be provided near the ceiling of the refrigerated warehouse 10, and the intake port 31 may be provided near the floor surface of the refrigerated warehouse 10.

[0021] The defroster 21 has the air flowing into the air flow path 26 through the intake port 31 introduced therein. The defroster 21 removes the frost contained in the air taken in from inside the refrigerated warehouse 10, thereby suppressing the inflow of frost to the compressor 23 on the air flow path 26 and preventing damage to the compressor 23.

[0022] The cold and heat recovery heat exchanger 22 includes a low-temperature side flow path 22a into which the air that has passed through the defroster 21 is introduced, and a high-temperature side flow path 22b into which the air that has passed through the primary cooler 24 is introduced. The cold and heat recovery heat exchanger 22 heats the air flowing through the low-temperature side flow path 22a (cools the air flowing through the high-temperature side flow path 22b) by performing heat exchange between the low-temperature side flow path 22a and the high-temperature side flow path 22b.

[0023] The compressor 23 is provided on the air flow path 26 on the downstream side of the low-temperature side flow path 22a. The air that has passed through the cold and heat recovery heat exchanger 22 (low-temperature side flow path 22a) is introduced into the compressor 23. The compressor 23 compresses the air introduced into the compressor 23 to make it high-temperature and high-pressure air. The primary cooler 24 is provided on the air flow path 26 on the downstream side of the compressor 23. The primary cooler 24 cools the air by performing heat exchange between the air that has passed through the compressor 23 and the cooling water that has passed through the cooling water circuit 35. Note that the air that has passed through the primary cooler 24 is further cooled by being heat-exchanged with the air that has passed through the low-temperature side flow path 22a in the process of passing through the high-temperature side flow path 22b as described above.

[0024] The expander 25 is provided on the air flow path 26 on the downstream side of the high-temperature side flow path 22b. The expander 25 reduces the pressure of the air that has passed through the high-temperature side flow path 22b to make it low-temperature and low-pressure air. Note that the air that has passed through the expander 25 is supplied into the refrigerated warehouse 10 through the discharge port 32.

[0025] <Binary refrigerator 50> The binary refrigerator 50 includes a high-stage cycle 60 and a low-stage cycle 70. The binary refrigerator 50 cools the refrigerant circulating in the low-stage cycle 70 by performing heat exchange between the refrigerant (for example, ammonia (NH3)) circulating in the high-stage cycle 60 and the refrigerant (carbon dioxide (CO2)) circulating in the low-stage cycle 70. In the following description, the refrigerant flowing in the high-stage cycle 60 is referred to as the high-stage refrigerant, and the refrigerant flowing in the low-stage cycle 70 is referred to as the low-stage refrigerant (second refrigerant). Further, for the binary refrigerator 50, it is sufficient that carbon dioxide is used at least for the low-stage refrigerant. That is, if the boiling point of the high-stage refrigerant is higher than that of the low-stage refrigerant, a refrigerant other than ammonia may be used.

[0026] The high-stage cycle 60 includes a high-stage compressor 61, a high-stage oil separator 62, a high-stage condenser 63, a high-stage expansion valve 64, and a cascade condenser 65. The high-stage compressor 61, the high-stage oil separator 62, the high-stage condenser 63, the high-stage expansion valve 64, and the cascade condenser 65 (high-stage circuit 65a) are provided in order in the flow direction of the high-stage refrigerant on the high-stage flow path 66. All the devices constituting the high-stage cycle 60 are installed outside the refrigerated warehouse 10.

[0027] The high-stage compressor 61 compresses the low-pressure gas-phase high-stage refrigerant introduced into the high-stage compressor 61 to obtain a high-temperature and high-pressure gas-phase high-stage refrigerant. The high-stage oil separator 62 is provided on the high-stage flow path 66 on the downstream side of the high-stage compressor 61. The high-stage oil separator 62 separates the lubricating oil of the high-stage compressor 61 discharged from the high-stage compressor 61 together with the gas-phase high-stage refrigerant from the gas-phase high-stage refrigerant that has passed through the high-stage compressor 61.

[0028] The high-stage condenser 63 is provided on the high-stage flow path 66 on the downstream side of the high-stage oil separator 62. The high-stage condenser 63 releases heat from the high-temperature and high-pressure gas-phase high-stage refrigerant sent from the high-stage compressor 61 by performing heat exchange between the high-stage refrigerant and the cooling water, and converts the high-stage refrigerant into a high-pressure liquid-phase high-stage refrigerant.

[0029] The high-stage expansion valve 64 is provided on the high-stage flow path 66 on the downstream side of the high-stage condenser 63. The high-stage expansion valve 64 reduces the pressure of the high-pressure liquid-phase high-stage refrigerant fed from the high-stage condenser 63, turning the high-pressure liquid-phase high-stage refrigerant into a high-stage refrigerant in a low-temperature and low-pressure gas-liquid mixed state.

[0030] The cascade condenser 65 includes a high-stage circuit 65a through which the high-stage refrigerant passes and a low-stage circuit 65b through which the low-stage refrigerant passes. The high-stage circuit 65a is provided on the high-stage flow path 66. The high-stage refrigerant that has passed through the high-stage expansion valve 64 is introduced into the high-stage circuit 65a. Other configurations of the cascade condenser 65 such as the low-stage circuit 65b will be described later.

[0031] The low-stage cycle 70 includes a low-stage compressor 71, a low-stage oil separator 72, a cascade condenser 65, a receiver 73, a pump 78, a low-stage expansion valve 74, and a low-stage evaporator 75. The low-stage compressor 71, the low-stage oil separator 72, the cascade condenser 65 (low-stage circuit 65b), the receiver 73, the pump 78, the low-stage expansion valve 74, and the low-stage evaporator 75 are provided in order in the flow direction of the low-stage refrigerant on the low-stage flow path 76. Among the devices constituting the low-stage cycle 70, devices other than the low-stage evaporator 75 are installed outside the refrigerated warehouse 10.

[0032] The low-stage compressor 71 compresses the low-pressure gas-phase low-stage refrigerant introduced into the low-stage compressor 71 to make it a high-temperature and high-pressure gas-phase low-stage refrigerant. The low-stage oil separator 72 is provided on the low-stage flow path 76 on the downstream side of the low-stage compressor 71. The low-stage oil separator 72 separates the lubricating oil of the low-stage compressor 71 discharged from the low-stage compressor 71 together with the gas-phase low-stage refrigerant from the gas-phase low-stage refrigerant that has passed through the low-stage compressor 71.

[0033] The low-stage circuit 65b of the cascade condenser 65 is provided between the low-stage oil separator 72 and the receiver 73 on the low-stage flow path 76. The cascade condenser 65 performs heat exchange between the high-temperature and high-pressure vapor-phase low-stage refrigerant that has passed through the low-stage compressor 71 and the low-temperature and low-pressure high-stage refrigerant that has passed through the high-stage expansion valve 64, and converts the high-temperature and high-pressure vapor-phase low-stage refrigerant into a high-pressure liquid-phase low-stage refrigerant.

[0034] The receiver 73 stores the liquid-phase low-stage refrigerant that has passed through the cascade condenser 65. The pump 78 sends out the low-stage refrigerant toward the downstream side. The low-stage expansion valve 74 is provided on the low-stage flow path 76 on the downstream side of the receiver 73. The low-stage expansion valve 74 reduces the pressure of the high-pressure liquid-phase low-stage refrigerant sent from the receiver 73 and converts the high-pressure liquid-phase low-stage refrigerant into a low-temperature and low-pressure gas-liquid mixed state low-stage refrigerant.

[0035] The low-stage evaporator 75 is provided in the refrigerated warehouse 10. Specifically, a pedestal 15 that stands up from the floor surface is installed in the refrigerated warehouse 10. The pedestal 15 extends to near the ceiling of the refrigerated warehouse 10. Therefore, the low-stage evaporator 75 is arranged near the ceiling of the refrigerated warehouse 10 while being supported by the pedestal 15. In the present embodiment, the vicinity of the ceiling refers to the range from the central part in the entire height direction of the refrigerated warehouse 10 to the ceiling. However, the installation location of the low-stage evaporator 75 can be selected at any position within the refrigerated warehouse 10. Further, the low-stage evaporator 75 may be suspended from the ceiling of the refrigerated warehouse 10.

[0036] The low-stage evaporator 75 is provided between the low-stage compressor 71 and the low-stage expansion valve 74 on the low-stage flow path 76. The low-stage evaporator 75 includes an evaporator circuit 75a through which the low-stage refrigerant passes. In the low-stage evaporator 75, in the process of the low-stage refrigerant passing through the evaporator circuit 75a, the air in the refrigerated warehouse 10 and the low-stage refrigerant are heat-exchanged, and the air in the refrigerated warehouse 10 is cooled by the latent heat of vaporization when the low-stage refrigerant vaporizes. Note that a circuit temperature sensor 80 for detecting the supply temperature of the low-stage refrigerant to the evaporator circuit 75a is provided at the upstream end of the evaporator circuit 75a.

[0037] <Control Unit 100> The control unit 100 comprehensively controls the operation of the refrigeration system 11. The control unit 100 is realized by a hardware processor such as a CPU executing a computer program (software) stored in the storage unit 110. Based on the temperature T inside the refrigerated warehouse 10 detected by the in-warehouse temperature sensor 12, the control unit 100 switches between the operation of the air refrigeration machine 20 and the binary refrigeration machine 50 to maintain the in-warehouse temperature T at the steady temperature Ta. Note that the steady temperature Ta is a temperature suitable for storing the object to be refrigerated and is the temperature maintained when the sealed state inside the refrigerated warehouse 10 continues. In the present embodiment, the steady temperature Ta is set to a temperature near the triple point (for example, -55°C) within a range not lower than the triple point of carbon dioxide (-56.6°C).

[0038] The control unit 100 includes a storage unit 110, an acquisition unit 111, a determination unit 112, and a processing unit 113. The storage unit 110 stores information necessary for the processing performed by the refrigeration system 11. For example, the storage unit 110 stores a table of the operation patterns of the refrigeration machines 20 and 50 set based on the detection results of the in-warehouse temperature sensor 12. The storage unit 110 may be realized by an EEPROM, ROM, RAM, etc., or may be realized by an HDD, flash memory, etc.

[0039] The acquisition unit 111 acquires the in-warehouse temperature T based on the detection result of the in-warehouse temperature sensor 12.

[0040] The determination unit 112 determines the state inside the refrigerated warehouse 10 based on the information acquired by the acquisition unit 111 and the information stored in the storage unit 110. Specifically, the determination unit 112 determines whether the internal temperature T acquired by the acquisition unit 111 is higher than the operation determination temperature Tb. Further, the determination unit 112 determines whether the internal temperature T is equal to or lower than the operation determination temperature Tb. The operation determination temperature Tb is a temperature at which re-cooling inside the refrigerated warehouse 10 becomes necessary due to load fluctuations inside the refrigerated warehouse 10 (for example, when the loading and unloading of frozen objects into and out of the refrigerated warehouse 10 is frequently performed, or when outside air enters the refrigerated warehouse 10 in summer), and is set higher than the steady temperature Ta. In the present embodiment, the operation determination temperature Tb is, for example, a branching point at which the superiority and inferiority of the heat exchange efficiency of the air-cooled refrigerator 20 and the heat exchange efficiency of the binary refrigerator 50 are reversed, and is set to -50°C. That is, in the temperature range (high temperature range) where the internal temperature T is higher than the operation determination temperature Tb, the heat exchange efficiency of the binary refrigerator 50 is higher than that of the air-cooled refrigerator 20, and in the temperature range (low temperature range) where the internal temperature T is lower than the operation determination temperature Tb, the heat exchange efficiency of the air-cooled refrigerator 20 is higher than that of the binary refrigerator 50.

[0041] The processing unit 113 outputs an operation signal to the air-cooled refrigerator 20 and the binary refrigerator 50 based on the determination result of the determination unit 112. Specifically, when the determination unit 112 determines that the internal temperature T is higher than the operation determination temperature Tb, the processing unit 113 operates only the binary refrigerator 50 with the air-cooled refrigerator 20 stopped (high temperature range operation mode). Further, when the determination unit 112 determines that the internal temperature T is higher than the steady temperature Ta but equal to or lower than the operation determination temperature Tb, the processing unit 113 operates only the air-cooled refrigerator 20 with the binary refrigerator 50 stopped (low temperature range operation mode). When the determination unit 112 determines that the internal temperature T is equal to the steady temperature Ta, the processing unit 113 stops both the air-cooled refrigerator 20 and the binary refrigerator 50 (steady mode).

[0042] [Control Method of Refrigeration System 11] FIG. 2 is a flowchart for explaining the control method of the refrigeration system 11. FIG. 3 is a time chart for explaining the control method of the refrigeration system 11. Hereinafter, when the inside of the refrigerated warehouse 10 is maintained in a steady state (a state where the temperature T inside the warehouse is equal to the steady temperature Ta), a control method when a load fluctuation (temperature drop) occurs inside the refrigerated warehouse 10 due to some cause will be explained.

[0043] In step S11, the operations of both the air-cooled refrigerator 20 and the binary refrigerator 50 are stopped, and the inside of the refrigerated warehouse 10 is maintained in a steady state (steady mode). In this case, the temperature T inside the warehouse is maintained higher than the triple point of carbon dioxide, and the dry-ice formation of the low-pressure refrigerant in the evaporator circuit 75a is suppressed. Also, the inside of the refrigerated warehouse 10 is maintained in a state suitable for the object to be refrigerated.

[0044] In step S12, it is determined whether the temperature T inside the warehouse is higher than the operation determination temperature Tb. If the determination result in step S12 is "NO", it is determined that although the temperature T inside the warehouse is higher than the steady temperature Ta, it is below the operation determination temperature Tb, and step S12 is repeated. That is, when the determination result in step S12 is "NO", although the temperature T inside the warehouse has an increasing trend from the steady temperature Ta but has not yet exceeded the operation determination temperature Tb, the steady mode is maintained. On the other hand, if the determination result in step S12 is "YES", it is determined that the temperature T inside the warehouse is higher than the operation determination temperature Tb, and the process proceeds to step S13. In this case, it is determined that the steady state inside the refrigerated warehouse 10 is disrupted due to a load fluctuation inside the refrigerated warehouse 10, and the inside of the refrigerated warehouse 10 has reached a high-temperature region.

[0045] In step S13, in order to return the inside of the refrigerated warehouse 10 from the high-temperature region to the steady state, only the binary refrigerator 50 is operated while the air-cooled refrigerator 20 is stopped (high-temperature region operation mode). Thereby, the inside of the refrigerated warehouse 10 is cooled by the binary refrigerator 50. Note that the high-temperature region operation mode continues until the temperature T inside the warehouse reaches the operation determination temperature Tb.

[0046] In step S14, it is determined whether the temperature T inside the warehouse is less than or equal to the operation determination temperature Tb. When the determination result of step S14 is "NO" (when the temperature T inside the warehouse is higher than the operation determination temperature Tb), the high-temperature range operation mode is continued. When the determination result of step S14 is "YES" (when the temperature T inside the warehouse is less than or equal to the operation determination temperature Tb and higher than the steady temperature Ta), the process proceeds to step S15. That is, when the determination result of step S14 is "YES", it is determined that the temperature T inside the warehouse has returned from the high-temperature range to the low-temperature range by the high-temperature range operation mode in step S13.

[0047] In step S15, in order to return the temperature T inside the warehouse from the low-temperature range to the steady state, the binary refrigerator 50 is stopped and only the air refrigerator 20 is operated (low-temperature range operation mode). Thereby, the inside of the refrigerated warehouse 10 is cooled by the air refrigerator 20.

[0048] In step S16, it is determined whether the temperature T inside the warehouse is lower than the operation determination temperature Tb. When the determination result of step S16 is "NO" (when the temperature T inside the warehouse is higher than the operation determination temperature Tb), the process returns to step S13. That is, when a large load fluctuation occurs inside the refrigerated warehouse 10 during the low-temperature range operation mode, etc., the temperature T inside the warehouse may become higher than the operation determination temperature Tb. In such a case, the process returns to step S13 and the high-temperature range operation mode is performed again to control the temperature T inside the warehouse to return to the low-temperature range. Thereby, it is possible to cope with sudden load fluctuations in the low-temperature range operation mode. On the other hand, when the determination result of step S16 is "YES" (when the temperature T inside the warehouse is less than or equal to the operation determination temperature Tb), it is determined that the temperature T inside the warehouse is maintained in the low-temperature range, and the process proceeds to step S17.

[0049] In step S17, it is determined whether the temperature T inside the warehouse has reached the steady temperature Ta. When the determination result of step S17 is "NO", the low-temperature range operation mode is continued.

[0050] On the other hand, if the determination result in step S17 is "YES", it is determined that the temperature inside the warehouse T has reached the steady temperature Ta, and the process proceeds to step S18. In this case, it can be determined that the inside of the refrigerated warehouse 10 has returned to a steady state.

[0051] After that, in step S18, the operations of both the air refrigerating machine 20 and the binary refrigerating machine 50 are stopped. Thus, this routine ends.

[0052] In the refrigeration system 11 of this embodiment, an air refrigerating machine (first refrigerating machine) 20 that uses air as a refrigerant (first refrigerant) and a binary refrigerating machine (second refrigerating machine) 50 that has a low-temperature evaporator (evaporator) 75 provided inside the refrigerated warehouse 10 using carbon dioxide as a refrigerant (second refrigerant) are provided, and the operations of the air refrigerating machine 20 and the binary refrigerating machine 50 are controlled so that the temperature (temperature T inside the warehouse) inside the refrigerated warehouse 10 is maintained at a steady temperature Ta higher than the triple point of carbon dioxide. According to this configuration, the temperature inside the refrigerated warehouse 10 can be maintained at the steady temperature Ta while switching the operations of the air refrigerating machine 20 and the binary refrigerating machine 50. In this case, for example, in a high-temperature range where the heat exchange efficiency of the air refrigerating machine 20 is low, by operating the binary refrigerating machine 50, the running cost can be suppressed compared to the case where the air refrigerating machine 20 is continuously operated all the time. Further, by using the binary refrigerating machine 50 as a part of the refrigeration system 11, the initial cost is suppressed and the refrigerated warehouse 10 can withstand a rapid load fluctuation inside compared to the case where the refrigeration system 11 is realized only by a plurality of air refrigerating machines 20. As a result, both the initial cost and the running cost can be suppressed, and the inside of the refrigerated warehouse 10 can be maintained at a desired temperature (steady temperature Ta).

[0053] Moreover, regarding the binary refrigerator 50, by using carbon dioxide as the refrigerant introduced into the low-stage evaporator 75, even if the low-stage refrigerant leaks in the refrigerated warehouse 10, it is easy to ensure the safety in the refrigerated warehouse 10. Moreover, since the air refrigerator 20 and the binary refrigerator 50 are controlled so that the temperature in the refrigerated warehouse 10 is maintained at a temperature higher than the triple point of carbon dioxide, it is possible to suppress the dry-ice formation of the low-stage refrigerant in the low-stage evaporator 75. As a result, a refrigeration system 11 with excellent reliability can be provided over a long period of time.

[0054] In the refrigeration system 11 of the present embodiment, the binary refrigerator 50 is configured to include a high-stage cycle 60 using ammonia as a high-stage refrigerant and a low-stage cycle 70 using carbon dioxide as a low-stage refrigerant. According to this configuration, refrigerants with different boiling points can be used in their respective optimal temperature ranges, so that the running cost can be suppressed and stable operation can be achieved. In this case, since the high-stage cycle 60 is provided outside the refrigerated warehouse 10, even if ammonia leaks from the high-stage cycle 60, it can be suppressed from entering the refrigerated warehouse 10.

[0055] In the refrigeration system 11 of the present embodiment, when the temperature T inside the warehouse is higher than the operation determination temperature Tb, the control unit 100 operates the binary refrigerator 50 while stopping the air refrigerator 20, while when the temperature T inside the warehouse is higher than the steady temperature Ta and equal to or lower than the operation determination temperature Tb, the control unit 100 operates the air refrigerator 20 while stopping the binary refrigerator 50. According to this configuration, when the temperature T inside the warehouse is higher than the operation determination temperature Tb or lower than the operation determination temperature Tb, by operating only the refrigerator with excellent heat exchange efficiency in each temperature range, the running cost can be suppressed.

[0056] In the refrigeration system 11 of the present embodiment, the control unit 100 is configured to stop the operations of both the air refrigerator 20 and the binary refrigerator 50 when the temperature inside the refrigerated warehouse 10 reaches the steady temperature Ta. According to this configuration, while suppressing the running cost, it is possible to suppress the temperature inside the refrigerated warehouse 10 from reaching the triple point of carbon dioxide.

[0057] (Second Embodiment) FIG. 4 is a flowchart for explaining a control method of the refrigeration system 11 according to the second embodiment. FIG. 5 is a time chart for explaining a control method of the refrigeration system 11 according to the second embodiment. As shown in FIGS. 4 and 5, in the refrigeration system 11 of the present embodiment, in the high-temperature region operation mode of step S14, both the air refrigerating machine 20 and the binary refrigerating machine 50 are operating.

[0058] According to this configuration, when the indoor temperature T exceeds the operation determination temperature Tb, by operating both the air refrigerating machine 20 and the binary refrigerating machine 50, the inside of the refrigerated warehouse 10 can be quickly restored to a steady state (the temperature followability can be enhanced).

[0059] (Third Embodiment) In the above-described embodiment, the configuration in which the air refrigerating machine 20 and the binary refrigerating machine 50 are switched and operated based only on the indoor temperature T has been described, but the present invention is not limited to this configuration. In the third embodiment, in addition to the indoor temperature T, for example, based on an ON / OFF schedule predetermined according to the time zone shown in FIG. 6, the air refrigerating machine 20 and the binary refrigerating machine 50 are operated, which is different from the above-described embodiment. In the schedule shown in FIG. 6, “ON” indicates a time zone in which the corresponding refrigerating machine is operable, and “OFF” indicates a time zone in which the corresponding refrigerating machine is inoperable.

[0060] For example, when the air refrigerating machine 20 is in the “ON” state and the binary refrigerating machine 50 is in the “OFF” state from 22:00 to 8:00, even if the indoor temperature T is higher than the operation determination temperature Tb (high-temperature region), the binary refrigerating machine 50 does not operate. That is, even when the indoor temperature T is higher than the operation determination temperature Tb, both the binary refrigerating machine 50 and the air refrigerating machine 20 do not operate. On one hand, for example, when the air-cooled chiller 20 is in the "OFF" state and the binary chiller 50 is in the "ON" state from 8:00 to 17:00, even if the indoor temperature T is higher than the steady temperature Ta and below the operation determination temperature Tb (low temperature range), the air-cooled chiller 20 does not operate. That is, even when the indoor temperature T is below the operation determination temperature Tb, both the binary chiller 50 and the air-cooled chiller 20 are not allowed to operate.

[0061] In this way, in this embodiment, in addition to the indoor temperature T, the operation determination of each chiller 20, 50 is also carried out according to the ON / OFF schedule determined in advance according to the time zone. Thus, for example, according to the time zone where the electricity consumption and load fluctuations around the time are likely to occur, the final operation determination of each chiller 20, 50 can be made. As a result, further reduction of the running cost can be achieved.

[0062] (Other Modification Examples) As described above, the preferred embodiments of the present invention have been described, but the present invention is not limited to these embodiments. Additions, omissions, substitutions, and other changes of the configuration are possible without departing from the spirit of the present invention. The present invention is not limited by the above description and is limited only by the appended claims. In the above-described embodiment, the configuration in which the refrigeration system 11 according to the present invention is used in the refrigeration device 1 for storing fish has been described, but it is not limited to this configuration. The refrigeration system 11 can be adopted in various technical fields such as for foods other than fish and for medical use. In the above-described embodiment, the case where the binary chiller 50 is adopted as the second chiller has been described, but it is not limited to this configuration. The second chiller can adopt various chillers as long as it uses at least carbon dioxide as the refrigerant. Also, the second chiller may be an indirect expansion type or a direct expansion type. In the above-described embodiments, the configuration for maintaining the internal temperature T at the steady temperature Ta by the on and off operations of the air refrigerator 20 and the binary refrigerator 50 has been described, but the configuration is not limited thereto. A configuration for maintaining the internal temperature T at the steady temperature Ta by adjusting the outputs of the air refrigerator 20 and the binary refrigerator 50 may also be used.

[0063] In the above-described embodiments, the configuration for maintaining the inside of the refrigerated warehouse 10 in a steady state based on the detection result by the internal temperature sensor 12 provided in the evaporator circuit 75a has been described, but the configuration is not limited thereto. For example, the inside of the refrigerated warehouse 10 may be maintained in a steady state based on the detection result by the circuit temperature sensor 80. By controlling the operations of the air refrigerator 20 and the binary refrigerator 50 based on the supply temperature of the low-stage refrigerant detected by the circuit temperature sensor 80, it is possible to reliably suppress the low-stage refrigerant from becoming dry ice. In the above-described embodiments, the configuration for stopping the air refrigerator 20 when the internal temperature T reaches the steady temperature Ta has been described, but the configuration is not limited thereto. When the internal temperature T reaches the steady temperature Ta, it can be appropriately adjusted, such as reducing the output of the air refrigerator 20. In the above-described embodiments, the case where one air refrigerator 20 and one binary refrigerator 50 are installed has been described, but the configuration is not limited thereto. As long as at least one air refrigerator 20 and at least one binary refrigerator 50 are installed, a configuration in which a plurality of any of the refrigerators are installed may also be used.

[0064] In addition, within the scope not departing from the gist of the present invention, it is possible to appropriately replace the components in the above-described embodiments with well-known components, and the above-described various modification examples may also be appropriately combined.

Explanation of Reference Numerals

[0065] 10: Refrigerated warehouse 11: Refrigeration system 20: Air refrigerator (first refrigerator) 50: Binary refrigerator (second refrigerator) 60: High-stage cycle 70: Low-stage cycle 100: Control Unit T: Temperature inside the warehouse Ta: Steady temperature Tb: Operating judgment temperature

Claims

1. A first refrigerator that takes in the air inside the refrigerated warehouse as a first refrigerant and cools the inside of the refrigerated warehouse by supplying the taken-in first refrigerant back into the refrigerated warehouse, A second refrigerator that has an evaporator provided inside the refrigerated warehouse using carbon dioxide as a second refrigerant and cools the inside of the refrigerated warehouse by performing heat exchange between the evaporator and the air inside the refrigerated warehouse, A control unit that controls the operations of the first refrigerator and the second refrigerator, and The control unit controls the operations of the first refrigerator and the second refrigerator so that the temperature inside the refrigerated warehouse is maintained at a steady temperature higher than the triple point of carbon dioxide. A refrigeration system.

2. When a temperature higher than the steady temperature is set as an operation determination temperature, The control unit, When the temperature inside the refrigerated warehouse is higher than the operation determination temperature, operates the second refrigerator with the first refrigerator stopped, The refrigeration system according to claim 1, wherein when the temperature inside the refrigerated warehouse is higher than the steady temperature and equal to or lower than the operation determination temperature, the first refrigerator is operated with the second refrigerator stopped.

3. When a temperature higher than the steady temperature is set as an operation determination temperature, The control unit, When the temperature inside the refrigerated warehouse is higher than the operation determination temperature, operates both the first refrigerator and the second refrigerator, The refrigeration system according to claim 1, wherein when the temperature inside the refrigerated warehouse is higher than the steady temperature and equal to or lower than the operation determination temperature, the first refrigerator is operated with the second refrigerator stopped.

4. The control unit stops the operations of both the first refrigerator and the second refrigerator when the temperature inside the refrigerated warehouse reaches the steady temperature. The refrigeration system according to claim 2 or claim 3.

5. The second refrigerator, Has a high-stage cycle provided outside the refrigerated warehouse using ammonia as a high-stage refrigerant, And a low-stage cycle using the second refrigerant as a low-stage refrigerant. The refrigeration system according to any one of claims 1 to 3.

6. A first refrigerator that takes in the air inside the refrigerated warehouse as a first refrigerant and cools the inside of the refrigerated warehouse by supplying the taken-in first refrigerant back into the refrigerated warehouse, A second refrigerator that has an evaporator provided inside the refrigerated warehouse using carbon dioxide as a second refrigerant and cools the inside of the refrigerated warehouse by performing heat exchange between the evaporator and the air inside the refrigerated warehouse, A control method for a refrigeration system including a control unit that controls operations of the first refrigerator and the second refrigerator, comprising: The control unit controls operations of the first refrigerator and the second refrigerator so that the temperature in the refrigerated warehouse is maintained at a steady temperature higher than the triple point of carbon dioxide.

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