Heat storage system and heat storage method

Abstract

To provide a heat accumulation system which causes cold of a freezing machine to accumulate to achieve reduction of an average electricity charge of the freezing machine used in a freezing warehouse and low carbon or decarbonization of energy at the freezing machine which is operated by surplus power of variable renewable energy.SOLUTION: A heat accumulation system 1 includes: a freezing machine 10 which is operated by surplus power of variable renewable energy in a grid; a brine tank 20 which is connected to the freezing machine and capable of storing brine; a freezing warehouse 40 which is connected to the brine tank and freezes objects; and a liquefied gas tank 60 in which a liquefied gas is stored.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a heat storage system and a heat storage method for storing heat extracted from a refrigerator operated by surplus power of variable renewable energy.

Background Art

[0002] For example, a cold storage material used for home delivery of food is frozen and stored in a freezer warehouse. A room-temperature cold storage material is carried into a freezer warehouse cooled to a predetermined temperature by a refrigerator, frozen by the low-temperature air in the warehouse, and carried out when in use. This process of carrying in, freezing, and carrying out is constantly repeated, and thousands to tens of thousands of cold storage materials are processed in one freezer warehouse per week.

[0003] When an absorption refrigerator is used for cooling the freezer warehouse, the heat generated by the refrigerator is heat-exchanged with brine to cool an air cooler installed in the warehouse, and cold air is circulated into the warehouse using a fan (see, for example, Patent Document 1 below). When a room-temperature cold storage material is carried into the freezer warehouse, the load in the warehouse increases, so the refrigerating capacity and power consumption of the refrigerator increase.

[0004] On the other hand, it is required to effectively utilize variable renewable energy such as sunlight, wind power, and solar heat. Variable renewable energy is a promising, diverse, and important low-carbon and decarbonized domestic energy source that does not emit greenhouse gases and can be produced domestically, and thus can also contribute to energy security. In particular, in Japan where the introduction of variable renewable energy is progressing, studies on methods for storing surplus power of variable renewable energy and sector coupling for using surplus power in other fields are underway.

[0005] From the above, in a refrigerator operated by surplus power of variable renewable energy, there is a need for a heat storage system that stores the heat of the refrigerator to achieve a reduction in the average electricity cost of the refrigerator used in the freezer warehouse and the low-carbonization and decarbonization of energy.

Prior Art Documents

Patent Document

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] As a result of intensive efforts to achieve various performances required for the heat storage system described above, the inventors have invented an optimal structure.

[0008] An object of the present invention is to provide a heat storage system and a heat storage method that can achieve a reduction in the average electricity cost of a refrigerator used in a refrigerated warehouse and a reduction in carbon and decarbonization of energy by storing the cooling heat of a refrigerator operated by surplus power of variable renewable energy.

Means for Solving the Problems

[0009] The heat storage system according to the present invention for achieving the above object is a heat storage system that stores cooling heat. The heat storage system includes a refrigerator operated by surplus power of variable renewable energy in the power grid (hereinafter referred to as the grid), a brine tank connected to the refrigerator and capable of storing brine, a refrigerated warehouse connected to the brine tank and freezing an object, and a liquefied gas tank storing liquefied gas. The brine tank and the liquefied gas tank are connected by piping so that the brine in the brine tank circulates.

[0010] Further, the heat storage method according to the present invention for achieving the above object includes a refrigerator operated by surplus power of variable renewable energy in the grid, a brine tank connected to the refrigerator and capable of storing brine, a refrigerated warehouse connected to the brine tank and freezing an object, and a liquefied gas tank storing liquefied gas. The brine tank and the liquefied gas tank are connected by piping so that the brine in the brine tank circulates. It is a heat storage method for heat storage by a heat storage system. The heat storage method cools the brine in the brine tank by operating the refrigerator and stores heat in the brine. The brine in which the cold heat is stored is supplied to the liquefied gas tank and the cold heat is stored in the liquefied gas in the liquefied gas tank.

Advantages of the Invention

[0011] According to the above heat storage device and heat storage method, by operating the refrigerator using the surplus power of variable renewable energy, the brine in the brine tank can be cooled and heat can be stored in the brine. Then, the brine storing the heat can be supplied to the refrigerated warehouse to cool the inside of the refrigerated warehouse, and it is possible to achieve a reduction in the average electricity cost of the refrigerator used in the refrigerated warehouse and the decarbonization and low-carbonization of energy. Therefore, in a refrigerator operated by the surplus power of variable renewable energy, it is possible to provide a heat storage system that can store the heat of the refrigerator and achieve a reduction in the average electricity cost of the refrigerator used in the refrigerated warehouse and the decarbonization and low-carbonization of energy.

Brief Description of the Drawings

[0012]

Figure 1

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Figure 12

Mode for Carrying Out the Invention

[0013] <First Embodiment> The first embodiment of the present invention will be described with reference to FIG. 1. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted. The dimensional ratios in the drawings are exaggerated for the convenience of explanation and may be different from the actual ratios.

[0014] FIG. 1 is a schematic diagram showing a heat storage system 1 according to the first embodiment of the present invention.

[0015] The heat storage system 1 according to the first embodiment is a system for storing the cold heat generated by a refrigerator 10 that can be operated by surplus power of variable renewable energy in brine, and using the stored cold heat to cool the inside of a cold storage warehouse 40. This system is not particularly limited, but can be applied as a heat source for cold storage materials, frozen foods, refrigerated warehouses for drugs, etc., skating rinks, data centers, plant factories, aquaculture, or air conditioning in offices.

[0016] As shown in FIG. 1, the heat storage system 1 includes a refrigerator 10, a brine tank 20 that stores brine cooled by the refrigerator 10, a first pipe 30 that connects the refrigerator 10 and the brine tank 20, a refrigerated warehouse 40 where an object to be refrigerated is stored, a second pipe 50 that connects the brine tank 20 and the refrigerated warehouse 40, a liquefied gas tank 60 that stores liquefied gas, a supply line 70 that supplies the liquefied gas in the liquefied gas tank 60 to the outside, and a control unit (not shown) that controls the timing of supplying power from variable renewable energy to the refrigerator 10.

[0017] As shown in FIG. 1, the refrigerator 10 is operated by surplus power of variable renewable energy in the grid. Specifically, "operation by surplus power" means operating the refrigerator 10 in consideration of the electricity market price in the supply-demand adjustment market.

[0018] As shown in FIG. 1, the refrigerator 10 is also operated by on-site variable renewable energy. By operating the refrigerator 10 with on-site variable renewable energy in this way, more efficient power saving can be achieved.

[0019] When solar power generation is used as variable renewable energy, the refrigerator 10 uses surplus power that is likely to be generated during the day to turn on the refrigerator 10 and cool the brine in the brine tank 20. When there is no surplus power, the refrigerator 10 is turned off or the number of operating units is reduced. The on / off operation of the refrigerator 10 is performed by the control unit. In this way, the refrigerator 10 performs intermittent operation by utilizing the surplus power of variable renewable energy, so that the variable renewable energy can be effectively utilized and the power of variable renewable energy can be stored in the form of heat, contributing to the realization of carbon neutrality. Note that the control of the refrigerator is not limited to the number of operating units, and inverter control may be used.

[0020] The refrigerator 10 is not particularly limited as long as it can suitably cool the brine in the brine tank 20. From the perspective of the coefficient of performance, for example, a vapor compression refrigerator can be used. The refrigerant of the refrigerator 10 is not particularly limited, but for example, ammonia is used.

[0021] The brine tank 20 stores brine. The brine is not particularly limited, but for example, an antifreeze can be used.

[0022] As shown in FIG. 1, the first pipe 30 and the second pipe 50 are connected to the brine tank 20. The brine in the brine tank 20 circulates through the second pipe 50. A pump P1 for supplying the brine in the brine tank 20 to the refrigerated warehouse 40 via the second pipe 50 is arranged in the brine tank 20. As the pump P1, a known one can be used.

[0023] The first pipe 30 connects the refrigerator 10 and the brine tank 20. The refrigerant of the refrigerator or the brine stored in the brine tank 20 circulates through the first pipe 30.

[0024] The refrigerated warehouse 40 is where the object to be frozen is placed. An object at normal temperature is carried into the refrigerated warehouse 40 cooled to a predetermined temperature (for example, -35°C) by the brine in the brine tank 20, and the object is frozen by the low-temperature air in the refrigerated warehouse 40 and then carried out when used. In the refrigerated warehouse 40, this process of carrying in, freezing, and carrying out is repeated. When the object to be frozen is, for example, a cold storage material, thousands to tens of thousands of cold storage materials are processed in one refrigerated warehouse 40 in a week.

[0025] A thermometer T1 for measuring the temperature in the refrigerated warehouse 40 is arranged in the refrigerated warehouse 40.

[0026] The second pipe 50 connects the brine tank 20 and the refrigerated warehouse 40. The brine stored in the brine tank 20 circulates through the second pipe 50.

[0027] As shown in FIG. 1, the second pipe 50 includes a forward pipe 51 extending from the brine tank 20 toward the freezer 40 and a return pipe 52 extending from the freezer 40 toward the brine tank 20.

[0028] A thermometer T2 for measuring the temperature of the brine flowing through the forward pipe 51 is disposed in the forward pipe 51. A thermometer T3 for measuring the temperature of the brine flowing through the return pipe 52 is disposed in the return pipe 52. Since the brine supplies cold heat in the freezer 40, the temperature of the brine flowing through the return pipe 52 is generally higher than the temperature of the brine flowing through the forward pipe 51.

[0029] The liquefied gas tank 60 stores liquefied gas. Although the liquefied gas is not particularly limited herein, examples thereof include LNG (liquefied natural gas), LPG (liquefied petroleum gas), liquid hydrogen, liquid nitrogen, liquefied ammonia, and the like.

[0030] A pump P2 for supplying the liquefied gas in the liquefied gas tank 60 to the outside is disposed in the liquefied gas tank 60. A known pump can be used as the pump P2. Further, a thermometer T4 for measuring the temperature of the liquefied gas stored inside is disposed in the liquefied gas tank 60.

[0031] The supply line 70 is connected to an external spherical tank or pillow tank and a supply pipe.

[0032] The control unit controls, for example, the on / off operation of the refrigerator 10. The control unit performs control of various configurations. The control unit is, for example, a PLC.

[0033] Next, with reference to FIG. 2, a heat storage method of the heat storage system 1 according to the first embodiment will be described. FIG. 2 is a flowchart showing the heat storage method of the heat storage system 1 according to the first embodiment. Generally speaking, the heat storage method of the heat storage system 1 according to the first embodiment is a method of storing the cooling heat of the refrigerator 10 that can be operated by the surplus power of the variable renewable energy in the brine in the brine tank 20, and using the brine stored with the cooling heat to cool the refrigerated warehouse 40.

[0034] First, the control unit determines whether there is surplus power in consideration of the electricity market price in the supply-demand adjustment market (step S01).

[0035] Next, the control unit operates the refrigerator 10 using the surplus power of the variable renewable energy (step S02).

[0036] Next, the control unit stores the cooling heat in the brine in the brine tank 20 by the cooling heat of the refrigerator 10 (step S03).

[0037] Next, the control unit supplies the brine in the brine tank 20 stored with the cooling heat to the refrigerated warehouse 40 to cool the inside of the refrigerated warehouse 40 (step S04).

[0038] As described above, by supplying the brine cooled by the refrigerator 10 into the refrigerated warehouse 40, the inside of the refrigerated warehouse 40 can be cooled. Therefore, by using the stored cooling heat of the brine, power saving of the refrigerator 10 can be achieved.

[0039] Next, with reference to FIG. 3, the time evolution of various parameters of the heat storage system 1 according to the first embodiment will be described. FIG. 3 is a diagram showing the time evolution of various parameters of the heat storage system 1 according to the first embodiment. FIG. 3(A) shows the time evolution of the output of variable renewable energy. FIG. 3(B) shows the time evolution of the temperature of the brine measured by the thermometers T2 and T3. FIG. 3(C) shows the time evolution of the temperature in the refrigerated warehouse 40 measured by the thermometer T1. FIG. 3(D) shows the time evolution of the power consumption (corresponding to the number of operating units) of the refrigerator 10. Note that the specific numbers described below are not limited to these and are merely examples.

[0040] As shown in FIGS. 3(A) and 3(D), the refrigerator 10 is operated using the surplus power of renewable energy. Here, for example, a case will be described in which the surplus power of renewable energy is generated during the unloading to loading of the heat storage material and not generated during the loading to unloading of the heat storage material.

[0041] During the unloading to loading of the heat storage material, as shown in FIG. 3(D), assume that the surplus power of renewable energy is used to operate, for example, seven units of the refrigerator 10. At this time, among the seven units of the refrigerator 10, the cooling capacity of five units of the refrigerator 10 is used for cooling the brine in the brine tank 20, and the cooling capacity of two units of the refrigerator 10 is used for cooling the intrusion heat into the refrigerated warehouse 40. As a result, as shown in FIG. 3(B), during the unloading to loading of the heat storage material, the temperature of the brine measured by the thermometers T2 and T3 decreases.

[0042] On the other hand, during the period from loading to unloading the cold storage material, as shown in Fig. 3(D), for example, using on-site renewable energy, two refrigerators 10 are operated. Assume that the cooling capacity of the two refrigerators 10 is used to cool the heat intrusion into the refrigerated warehouse 40. The cooling of the loaded cold storage material is performed using the cooling capacity stored in the brine in the brine tank 20. Note that the temperature inside the refrigerated warehouse 40 is maintained at, for example, -35°C as shown in Fig. 3(C). In this way, the brine with stored cooling capacity can be supplied to the refrigerated warehouse 40 to cool the inside of the refrigerated warehouse 40, achieving a reduction in the average electricity cost of the refrigerator 10 used in the refrigerated warehouse 40 and low-carbonization and decarbonization of energy.

[0043] Next, referring to Fig. 4, the time evolution of various parameters in the comparative example will be described. Fig. 4 is a diagram showing the time evolution of various parameters in the comparative example. Fig. 4(A) is a diagram showing the temperature evolution of the cold storage material. Fig. 4(B) shows the time evolution of the temperature inside the refrigerated warehouse 40 measured by the thermometer T1. Fig. 4(C) shows the time evolution of the power consumption of the refrigerator 10 (corresponding to the number of operating units).

[0044] In the comparative example, the refrigerated warehouse 40 is directly cooled by the refrigerator without storing cooling capacity by the brine. Also, the refrigerator is not operated by the surplus power of the variable renewable energy, and a method of operating the refrigerator at the time of loading is adopted.

[0045] In such a comparative example, as shown in Fig. 4(C), all the refrigerators (for example, 7 units) are operated at the time of loading. At this time, for example, out of the 7 refrigerators, the cooling capacity of 5 units is used for cooling the cold storage material, and the cooling capacity of 2 units is used for cooling the heat intrusion into the refrigerated warehouse 40.

[0046] At the time of loading, by operating 7 refrigerators, as shown in Fig. 4(A), the cold storage material inside the refrigerated warehouse 40 drops from, for example, 15°C to -25°C. Also, as shown in Fig. 4(B), the temperature inside the refrigerated warehouse 40 measured by the thermometer T1 is maintained at -35°C.

[0047] Thus, in the comparative example, since the refrigerator is operated without using the surplus power of the variable renewable energy, it is impossible to achieve a reduction in the average electricity cost of the refrigerator and the decarbonization and low-carbonization of energy.

[0048] As described above, the heat storage system 1 according to the first embodiment is a heat storage system 1 that stores cold heat. The heat storage system 1 includes a refrigerator 10 operated by the surplus power of variable renewable energy in the grid, a brine tank 20 connected to the refrigerator 10 and capable of storing brine, a cold storage warehouse 40 connected to the brine tank 20 and freezing a heat storage material, and a liquefied gas tank 60 in which liquefied gas is stored. According to the heat storage system 1 configured in this way, by operating the refrigerator 10 using the surplus power of variable renewable energy, the brine in the brine tank 20 can be cooled and cold heat can be stored in the brine. Then, the brine with cold heat stored can be supplied to the cold storage warehouse 40 to cool the inside of the cold storage warehouse 40, and a reduction in the average electricity cost of the refrigerator 10 used in the cold storage warehouse 40 and the decarbonization and low-carbonization of energy can be achieved. Therefore, it is possible to provide a heat storage system 1 that can store the cold heat of the refrigerator 10 and achieve a reduction in the average electricity cost of the refrigerator 10 used in the cold storage warehouse 40 and the decarbonization and low-carbonization of energy in the refrigerator 10 operated by the surplus power of variable renewable energy.

[0049] Also, the refrigerator 10 is also operated by on-site variable renewable energy. According to the heat storage system 1 configured in this way, since the refrigerator 10 can be operated using variable renewable energy, a reduction in the average electricity cost of the refrigerator 10 and the decarbonization and low-carbonization of energy can be achieved more effectively.

[0050] Also, as described above, the heat storage method of the heat storage system 1 according to the first embodiment is a heat storage method in which a refrigerator 10 operated by surplus power of variable renewable energy in the grid, a brine tank 20 connected to the refrigerator 10 and capable of storing brine, a cold storage warehouse 40 connected to the brine tank 20 and freezing a heat storage material, and a liquefied gas tank 60 in which liquefied gas is stored are used. The heat storage method cools the brine in the brine tank 20 by operating the refrigerator 10 to store heat in the brine. According to this heat storage method, in the refrigerator 10 operated by the surplus power of variable renewable energy, the heat of the refrigerator 10 can be stored to achieve a reduction in the average electricity cost of the refrigerator 10 used in the cold storage warehouse 40 and the decarbonization and low-carbonization of energy.

[0051] <Second Embodiment> Next, with reference to FIG. 5, the configuration of the heat storage system 2 according to the second embodiment will be described. FIG. 5 is a schematic diagram showing the heat storage system 2 according to the second embodiment of the present invention.

[0052] Descriptions of parts common to the first embodiment will be omitted, and only the parts characteristic of the second embodiment will be described. Note that the same members as those in the first embodiment described above are denoted by the same reference numerals and described, and redundant descriptions are omitted. The second embodiment is different from the first embodiment in that it has a heat exchange section 90 that exchanges heat between the brine and the liquefied gas flowing from the cold storage warehouse 40 to the brine tank 20.

[0053] As shown in FIG. 5, the heat storage system 2 according to the second embodiment includes a refrigerator 10, a brine tank 20 for storing brine cooled by the refrigerator 10, a first pipe 30 connecting the refrigerator 10 and the brine tank 20, a refrigerated warehouse 40 for storing an object to be refrigerated, a second pipe 50 connecting the brine tank 20 and the refrigerated warehouse 40, a liquefied gas tank 60 for storing liquefied gas, a supply line 170 for supplying the liquefied gas in the liquefied gas tank 60 to the outside, a control unit (not shown) for controlling the timing of supplying power to the refrigerator 10 with variable renewable energy, and a heat exchange unit 90 for exchanging heat between the brine flowing from the refrigerated warehouse 40 to the brine tank 20 and the liquefied gas.

[0054] Since the configurations of the refrigerator 10, the brine tank 20, the first pipe 30, the refrigerated warehouse 40, the second pipe 50, the liquefied gas tank 60, and the control unit are the same as those of the heat storage system 1 according to the first embodiment described above, the description thereof is omitted.

[0055] Hereinafter, the configurations of the supply line 170 and the heat exchange unit 90 of the heat storage system 2 according to the second embodiment will be described.

[0056] The supply line 170 is provided with a first branch line 171 branched from the supply line 170 and a second branch line 172 branched from the supply line 170.

[0057] As shown in FIG. 5, valves 173 and 174 are provided in the supply line 170 in order from the upstream side. As shown in FIG. 5, a valve 175 is provided in the first branch line 171. As shown in FIG. 5, a valve 176 is provided in the second branch line 172.

[0058] By appropriately controlling the opening and closing of the valves 173, 174, 175, and 176 by the control unit, the amount of liquefied gas flowing through the heat exchange unit 90 and the amount of liquefied gas supplied to an external tank are adjusted.

[0059] The heat exchange unit 90 is heat-exchanged with the brine flowing through the return pipe 52 of the second pipe 50 and the liquefied gas in a liquid state flowing through the supply line 170. In the supply line 170, the liquefied gas in a liquid state that has passed through the heat exchange unit 90 transfers its cold heat to the brine, turns into a gaseous state, and the liquefied gas in a gaseous state is supplied to the outside. On the other hand, in the return pipe 52 of the second pipe 50, the brine that has passed through the heat exchange unit 90 receives cold heat from the liquefied gas in a liquid state and its temperature drops. As a result, the temperature of the brine in the brine tank 20 further decreases, thereby reducing the refrigeration load of the refrigerator 10.

[0060] Next, with reference to FIG. 6, a heat storage method of the heat storage system 2 according to the second embodiment will be described. FIG. 6 is a flowchart showing the heat storage method of the heat storage system 2 according to the second embodiment. The heat storage method of the heat storage system 2 according to the second embodiment is different from the heat storage method of the heat storage system 1 according to the first embodiment in that, in the heat exchange unit 90, the cold heat of the liquefied gas flowing through the supply line 170 is supplied to the brine flowing through the return pipe 52 of the second pipe 50.

[0061] In the heat storage method according to the second embodiment, steps S01 to S03 are performed in the same manner as in the heat storage method according to the first embodiment. Since steps S01 to S03 are the same as the above-described steps, the description is omitted.

[0062] In the heat storage method according to the second embodiment, step S13 is performed. In step S13, the control unit supplies the liquefied gas in the liquefied gas tank 60 to the outside with the valve 174 open and the valve 176 closed. At this time, in the heat exchange unit 90, the cold heat of the liquefied gas is supplied to the brine flowing through the return pipe 52 of the second pipe 50, and the brine is cooled (step S13). The valve 175 adjusts the amount of liquefied gas flowing through the heat exchanger 90 by adjusting the opening degree.

[0063] Thus, in the heat storage system 2 according to the second embodiment, in addition to being cooled by the refrigerator 10, the brine also receives the cold heat of the liquefied gas, so that the power saving of the refrigerator 10 can be performed more efficiently.

[0064] Next, with reference to FIG. 7, the time change of various parameters of the heat storage system 2 according to the second embodiment will be described. FIG. 7 is a diagram showing the time change of various parameters of the heat storage system 2 according to the second embodiment. FIG. 7(A) shows the time change of the output of the variable renewable energy. FIG. 7(B) shows the time change of the temperature of the brine measured by the thermometers T2 and T3. FIG. 7(C) shows the time change of the temperature in the freezer 40 measured by the thermometer T1. FIG. 7(D) shows the time change of the power consumption (corresponding to the number of operating units) of the refrigerator 10.

[0065] As shown in FIGS. 7(A) and 7(D), the refrigerator 10 is operated using the surplus power of the renewable energy. Here, for example, a case will be described in which the surplus power of the renewable energy is generated between the unloading and loading of the heat storage material, and is not generated between the loading and unloading of the heat storage material.

[0066] During the period from unloading to loading of the heat storage material, as shown in FIG. 7(D), for example, 7 units of the refrigerator 10 are operated using the surplus power of the renewable energy. At this time, among the 7 units of the refrigerator 10, the cooling heat of 5 units of the refrigerator 10 is used for cooling the brine in the brine tank 20, and the cooling heat of 2 units of the refrigerator 10 is used for cooling the intrusion heat into the freezer 40. As a result, as shown in FIG. 7(B), during the period from unloading to loading of the heat storage material, the temperature of the brine measured by the thermometers T2 and T3 decreases.

[0067] On the other hand, during the period from loading to unloading of the heat storage material, as shown in FIG. 7(D), the operation of the refrigerator 10 is stopped. Compared with the heat storage system 1 according to the first embodiment, since the temperature of the brine in the brine tank 20 can be lowered by the cooling heat of the liquefied gas, for example, the number of operating units of the 2 units of the refrigerator 10 that were operating can be set to 0 units.

[0068] The temperature inside the refrigerated warehouse 40 is maintained at, for example, -35°C as shown in FIG. 7(C). Further, in the heat exchange section 90, since cold heat is supplied from the liquefied gas to the brine, the temperature of the brine measured by the thermometer T3 is lower than the temperature of the brine measured by the thermometer T3 of the heat storage system 1 according to the first embodiment (see the arrow in FIG. 7(B)).

[0069] As described above, the heat storage system 2 according to the second embodiment further includes a heat exchange section 90 that exchanges heat between the brine and the liquefied gas flowing from the refrigerated warehouse 40 toward the brine tank 20. According to the heat storage system 2 configured in this way, since the temperature of the brine can be lowered by the cold heat of the liquefied gas, power saving of the refrigerator 10 can be achieved more efficiently.

[0070] <Third Embodiment> Next, with reference to FIG. 8, the configuration of the heat storage system 3 according to the third embodiment will be described. FIG. 8 is a schematic diagram showing the heat storage system 2 according to the third embodiment of the present invention.

[0071] Description of the parts common to the first and second embodiments will be omitted, and only the parts characteristic of the third embodiment will be described. Note that the same members as those in the above-described first and second embodiments are denoted by the same reference numerals and described, and redundant descriptions are omitted. The third embodiment is different from the second embodiment in that it has a third pipe 80 that connects the brine tank 20 and the liquefied gas tank 60.

[0072] As shown in Fig. 8, the heat storage system 3 according to the third embodiment includes a refrigerator 10, a brine tank 20 for storing brine cooled by the refrigerator 10, a first pipe 30 connecting the refrigerator 10 and the brine tank 20, a freezer warehouse 40 for storing objects to be frozen, a second pipe 50 connecting the brine tank 20 and the freezer warehouse 40, a liquefied gas tank 60 for storing liquefied gas, a supply line 170 for supplying the liquefied gas in the liquefied gas tank 60 to the outside, a control unit (not shown) for controlling the timing of supplying power to the refrigerator 10 with variable renewable energy, a heat exchange unit 90 for exchanging heat between the brine flowing from the freezer warehouse 40 to the brine tank 20 and the liquefied gas, and a third pipe 80 connecting the brine tank 20 and the liquefied gas tank 60.

[0073] The configurations of the refrigerator 10, the brine tank 20, the first pipe 30, the freezer warehouse 40, the second pipe 50, the liquefied gas tank 60, the supply line 170, the control unit, and the heat exchange unit 90 are the same as those of the heat storage system 1 according to the first embodiment described above, and thus the description thereof is omitted.

[0074] Hereinafter, the configuration of the third pipe 80 of the heat storage system 3 according to the third embodiment will be described. As shown in Fig. 8, the third pipe 80 connects the brine tank 20 and the liquefied gas tank 60. In the third pipe 80, the brine stored in the brine tank 20 circulates. In this way, the brine stored in the brine tank 20 can flow through the third pipe 80 to the liquefied gas tank 60, thereby supplying cold heat to the liquefied gas in the liquefied gas tank 60.

[0075] In this way, by supplying cold heat to the liquefied gas in the liquefied gas tank 60, it is possible to suppress the BOG of the liquefied gas and store cold heat in the liquefied gas.

[0076] By supplying cold heat to the liquefied gas, the liquefied gas becomes in a subcooled state, and BOG is suppressed. Hereinafter, the subcooled state will be described. The liquefied gas is usually in a saturated state at the boundary between the liquid phase and the gas phase. By cooling the liquefied gas in this saturated state with the cold heat of the brine, it becomes in a subcooled state. Since the liquefied gas in the subcooled state is completely in a liquid state, the generation of BOG can be suppressed.

[0077] Also, the cold heat of the refrigerator 10 operated by the surplus power of the variable renewable energy can be stored in the brine of the brine tank 20 and the liquefied gas in the liquefied gas tank 60. Therefore, compared with the heat storage systems 1 and 2 according to the first embodiment and the second embodiment, it is possible to more preferably achieve power saving of the refrigerator 10, reduction of the average electricity charge, and decarbonization and de-carbonization of energy.

[0078] Next, with reference to FIGS. 9 and 10, the heat storage method of the heat storage system 3 according to the third embodiment will be described. FIG. 9 is a flowchart showing the heat storage method of the heat storage system 3 according to the third embodiment. FIG. 10 is a flowchart showing a modified example of the heat storage method of the heat storage system 3 according to the third embodiment. The heat storage method of the heat storage system 3 according to the third embodiment is different from the heat storage methods according to the first embodiment and the second embodiment in that the cold heat generated by the refrigerator 10 operated by the surplus power of the variable renewable energy is also stored in the liquefied gas, and the BOG of the liquefied gas is suppressed.

[0079] In the heat storage method according to the third embodiment, steps S01 to S03 and step S13 are performed in the same manner as in the heat storage method according to the second embodiment. Since steps S01 to S03 and step S13 are the same as the above-described steps, the description thereof is omitted.

[0080] In the heat storage method according to the third embodiment, as shown in FIG. 9, step S14 is performed. In step S14, the chilled brine is supplied to the liquefied gas tank 60 via the third pipe 80, and the liquefied gas is cooled. As a result, the generation of BOG of the liquefied gas is suppressed, and the liquefied gas can also store chilled heat.

[0081] Note that, as shown in FIG. 10, with the valve 174 closed and the valve 176 open, the supply line 170 may be circulated (step S15) without supplying the subcooled liquefied gas to the outside, while maintaining the subcooling of the liquefied gas, and the heat exchange section 90 may be configured to supply chilled heat to the brine.

[0082] Next, with reference to FIGS. 11 and 12, the time evolution of various parameters of the heat storage system 3 according to the third embodiment will be described. FIGS. 11(A) and 12(A) show the time evolution of the output of the variable renewable energy. FIGS. 11(B) and 12(B) show the time evolution of the temperature of the brine measured by the thermometers T2 and T3. FIGS. 11(C) and 12(C) show the time evolution of the temperature in the freezer 40 measured by the thermometer T1. FIGS. 11(D) and 12(D) show the time evolution of the temperature of the liquefied gas measured by the thermometer T4. FIGS. 11(E) and 12(E) show the time evolution of the power consumption (corresponding to the number of operating units) of the refrigerator 10.

[0083] As shown in FIGS. 11(A) and 11(E), the refrigerator 10 is operated using the surplus power of the renewable energy. Here, for example, a case will be described in which the surplus power of the renewable energy is generated during the unloading to loading of the heat storage material and not generated during the loading to unloading of the heat storage material.

[0084] During the period from unloading to loading of the cold storage material, as shown in Fig. 11(E), using surplus power of renewable energy, for example, operate nine refrigerators 10. At this time, among the nine refrigerators 10, the cooling capacity of five refrigerators 10 is used for cooling the brine in the brine tank 20, the cooling capacity of two refrigerators 10 is used for cooling the intrusion heat into the refrigerated warehouse 40, and the cooling capacity of two refrigerators 10 is used for cooling the intrusion heat into the liquefied gas tank 60. As a result, as shown in Fig. 11(B), during the period from unloading to loading of the cold storage material, the temperature of the brine measured by the thermometers T2 and T3 decreases. Also, as shown in Fig. 11(D), the temperature of the liquefied gas measured by the thermometer T4 also decreases.

[0085] On the other hand, during the period from loading to unloading of the cold storage material, as shown in Fig. 11(E), stop the operation of the refrigerator 10. Compared with the heat storage system 2 according to the second embodiment, since the liquefied gas in the liquefied gas tank 60 can also store cooling heat, the temperature rise of the liquefied gas tank 60 due to the intrusion heat into the liquefied gas tank 60 can be suppressed, and the number of operating units of the refrigerator 10 can be zero while increasing the amount of loading in the refrigerated warehouse.

[0086] The temperature in the refrigerated warehouse 40 is maintained at, for example, -35°C as shown in Fig. 11(C). Also, in the heat exchange section 90, since the cooling capacity is supplied from the liquefied gas to the brine, the temperature of the brine measured by the thermometer T3 is lower than the temperature of the brine measured by the thermometer T3 of the heat storage system 1 according to the first embodiment (see the arrow in Fig. 11(B)). Also, as shown in Fig. 11(D), the temperature of the liquefied gas in the liquefied gas tank 60 measured by the thermometer T4 decreases due to the operation of the refrigerator 10. At this time, the temperature of the liquefied gas is maintained at a state lower than the saturation temperature, and the generation of BOG is suppressed.

[0087] In the case of the heat storage method of Fig. 10 described above, as shown in Fig. 12(D), compared with Fig. 11(D), the temperature of the liquefied gas rises (see the arrow in Fig. 12(D)), but since the state lower than the saturation temperature is maintained, while maintaining the subcooled state of the liquefied gas, in the heat exchange section 90, cooling capacity can be supplied to the brine.

[0088] Although the present invention has been described through the embodiments above, the present invention is not limited to the above-described embodiments and modifications, and various modifications can be made within the scope of the claims.

[0089] For example, in the first embodiment described above, the refrigerator 10 was operated by on-site variable renewable energy, but the refrigerator 10 may not be operated by on-site variable renewable energy.

[0090] Also, in the above-described embodiments and modifications, the cold heat stored in the heat storage system was used for cooling the refrigerated warehouse 40 and suppressing the generation of BOG. However, as the object of use of the cold heat stored in the heat storage system, it can also be used as a cold heat source for freezing and storing frozen foods, drugs, etc., refrigerated warehouses in the chilled temperature zone, refrigeration equipment, skating rinks, data centers, plant factories, aquaculture, or office air conditioning.

[0091] Also, in the heat storage system described above, cold heat may be stored in an object (for example, a cold storage material) provided in the refrigerated warehouse 40, and the refrigerated warehouse 40 may be cooled by managing the object.

Explanation of Reference Numerals

[0092] 1, 2, 3 Heat storage systems 10 Refrigerator 20 Brine tank 30 First pipe 40 Refrigerated warehouse 50 Second pipe 60 Liquefied gas tank 70, 170 Supply lines 80 Third pipe 90 Heat exchange section.

Claims

1. A heat storage system for storing heat and cold, comprising: a refrigerator operated by surplus power of variable renewable energy in the grid; a brine tank connected to the refrigerator and capable of storing brine; a refrigerated warehouse connected to the brine tank and freezing an object; a liquefied gas tank for storing liquefied gas; and a heat storage system in which the brine tank and the liquefied gas tank are connected by piping so that the brine in the brine tank circulates.

2. The heat storage system according to claim 1, wherein the refrigerator is also operated by on-site variable renewable energy.

3. The heat storage system according to claim 1 or 2, further comprising a heat exchange unit that exchanges heat between the brine and the liquefied gas flowing from the refrigerated warehouse to the brine tank.

4. A heat storage method for storing heat by a heat storage system, the heat storage system comprising: a refrigerator operated by surplus power of variable renewable energy in the grid; a brine tank connected to the refrigerator and capable of storing brine; a refrigerated warehouse connected to the brine tank and freezing an object; a liquefied gas tank for storing liquefied gas; and a heat storage system in which the brine tank and the liquefied gas tank are connected by piping so that the brine in the brine tank circulates, the method comprising: operating the refrigerator to cool the brine in the brine tank and store heat and cold in the brine; and supplying the brine in which the heat and cold are stored to the liquefied gas tank to store the cold heat in the liquefied gas in the liquefied gas tank.

5. The heat storage system further comprises a heat exchange unit that exchanges heat between the brine and the liquefied gas flowing from the refrigerated warehouse to the brine tank, and in the heat exchange unit, the brine receives cold heat from the liquefied gas. The heat storage method according to claim 4.

6. The heat storage method according to claim 4 or 5, wherein the brine in which the heat and cold are stored is supplied to the liquefied gas tank to suppress the generation of BOG of the liquefied gas in the liquefied gas tank.

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