Heat Storage Apparatus, Air Conditioning Apparatus, And Heat Storage Method

Abstract

A disclosure describes a heat storage apparatus to store heat generated by a heat generator via a medium includes: a first circuit closed to circulate the medium therethrough in a direction; a heat exchanger to exchange the heat; a heat storage tank including a phase change material to exchange heat with the medium; a first measurement unit to measure a temperature of the medium; a cooling unit to cool the medium when the temperature of the medium is higher than a predetermined target temperature and to set the temperature of the medium to be approximately equal to the target temperature; a count unit to count an elapsed time from when the phase change material exchanges heat with the medium and starts a phase change; and a determination unit to determine whether the phase change material is allowed to be supercooled or not based on the elapsed time.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2012-187601, filed on Aug. 28, 2012, the entire contents of which are incorporated herein by reference.

FIELD

[0002] This embodiment relates to a heat storage apparatus including a phase change material, and to an air conditioning apparatus and a heat storage method.

BACKGROUND

[0003] For warm-up of an internal combustion engine or a transmission (heat generator), the following technique is known: exhaust heat from a heat generator is stored in a phase change material via a medium. When heated, the phase change material stores heat by a phase change from a solid phase to a liquid phase. The phase change material in the liquid phase is put into a supercooled state in which the state of the liquid phase is kept even when a temperature thereof is lowered. The phase change material put into the supercooled state is nucleated by application of a mechanical stimulation, a voltage, or the like and changes in phase from the liquid phase to the solid phase. At this time, the phase change material radiates the heat stored in the process of the phase change from the solid phase to the liquid phase. When the phase of the phase change material is changed from the solid phase to the liquid phase, if even a part of the phase change material remains in the solid phase, the whole phase change material is restored to the solid phase in the case where the temperature of the phase change material is lowered. Thus, the phase change material is not allowed to be put into the supercooled state. For that reason, in the case where the phase change material is used for warm-up, it is necessary for the phase change material to be in the supercooled state. Therefore, at a stage of heat storage, it is necessary to determine whether the phase of the whole phase change material is completely changed from the solid phase to the liquid phase, that is, whether the phase change material is allowed to be supercooled or not in the case where the temperature of the phase change material is lowered.

[0004] On the other hand, Japanese Patent Application Laid-open No. 2009-236433 relates to a technique in which whether the phase change material is allowed to be supercooled or not is determined based on the temperature of a medium. However, depending on an operational status of the heat generator, the temperature of the medium successively changes. Therefore, in such a case of being based on the temperature of a medium, it is difficult to easily determine whether the phase change material is allowed to be supercooled or not. It should be noted that the entire contents of Japanese Patent Application Laid-open No. 2009-236433 is incorporated herein by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 is a block diagram showing a heat storage apparatus according to a first embodiment;

[0006] FIG. 2 is a block diagram showing a control device according to the first, embodiment;

[0007] FIG. 3 is a flowchart showing an operation of the heat storage apparatus according to the first embodiment;

[0008] FIG. 4 is a block diagram showing a control device according to a first modified example;

[0009] FIGS. 5A, 5B, and 5C are exemplary graphs of simulation results according to the first modified example;

[0010] FIG. 6 is a block diagram showing a heat storage apparatus according to a second modified example;

[0011] FIG. 7 is at block diagram showing a control device according to the second modified example;

[0012] FIG. 8 is a block diagram showing a heat storage apparatus according to a second embodiment;

[0013] FIGS. 9A, 9B, and 9C are exemplary graphs of simulation results according to the second embodiment;

[0014] FIG. 10 is a block diagram showing an air conditioning apparatus according to a third embodiment; and

[0015] FIG. 11 is a block diagram showing a control device according to the third embodiment.

[0016] FIG. 12 is a block diagram showing the control device of FIG. 8

DETAILED DESCRIPTION

[0017] In view of the above circumstances, according to an embodiment, a heat storage apparatus configured to store heat generated by a heat generator via a medium includes: a first circuit closed to circulate the medium therethrough in a direction; a heat exchanger that is provided at a part of the first circuit and is configured to exchange the heat generated by the heat generator with the medium; a heat storage tank that is provided downstream of the direction in which the medium circulates, with respect to the heat exchanger of the first circuit, and includes a phase change material to exchange heat with the medium storing the heat generated by the heat generator; a first measurement unit configured to measure a temperature of the medium that passes from the heat exchanger to the heat storage tank; a cooling unit that is configured to cool the medium when the measured temperature of the medium is higher than a predetermined target temperature, and to set the temperature of the medium that passes from the heat exchanger to the heat storage tank to be approximately equal to the target temperature; a count unit configured to count an elapsed time from when the phase change material exchanges heat with the medium and starts a phase chance from a solid phase to a liquid phase; and a determination unit configured to determine whether the phase change material is allowed to be supercooled or not based on the elapsed time.

[0018] According to an embodiment, an air conditioning apparatus including the heat storage apparatus described above includes: a nucleating device configured to nucleate the phase change material; a second bypass circuit that is connected to the first circuit at a second branch point and is configured to bypass the heat storage tank; a second control valve configured to switch a flew path of the medium to one of the first circuit and the second bypass circuit at the second branch point; and a second control unit configured to control, when the determination unit determines that the phase change material is allowed to be supercooled, switching of the second control valve to switch the flow path of the medium to the second bypass circuit.

[0019] According to an embodiment, a heat storage method for one of a heat storage apparatus and an air conditioning apparatus that include a medium, a first circuit closed to circulate the medium therethrough in a direction, a heat exchanger that is provided at a part, of the first circuit and is configured to exchange heat generated by a heat generator with the medium, and a heat storage tank that is provided downstream of the direction in which the medium circulates, with respect to the heat exchanger of the first circuit, and includes a phase change material to exchange heat with the medium storing the heat generated by the heat generator, includes: circulating the medium; measuring a temperature of the medium that passes from the heat exchanger to the heat storage tank; cooling the medium when the measured temperature of the medium is higher than a predetermined target temperature, and setting the temperature of the medium that passes from the heat exchanger to the heat storage tank to be approximately equal to the target temperature; counting an elapsed time from when the phase change material exchanges heat with the medium and starting a phase change from a solid phase to a liquid phase; and determining, by a determination unit, whether the phase change material is allowed to be supercooled or not based on the elapsed time.

[0020] According to an aspect of embodiments, a heat storage apparatus, an air conditioning apparatus, and a heat storage method that are capable of easily determining whether a phase change material is allowed to be supercooled or not are provided.

[0021] Hereinafter, an embodiment will be described.

FIRST EMBODIMENT

[0022] FIG. 1 is a block diagram showing a heat storage apparatus according to a first embodiment. In this embodiment, the heat storage apparatus can be used for an in-vehicle air conditioning apparatus of an electric vehicle (EV) (hereinafter, referred to as vehicle) including, for example, a storage battery, a motor, an inverter, and an electronic control unit (ECU) that controls those components. For example, a heat storage apparatus is provided near a motor or an inverter of an electric vehicle including an air conditioning apparatus. Heat (waste heat) radiated from the motor, the inverter, and the like is stored in the heat storage apparatus in advance. Thus, when a warm-up operation of the air conditioning apparatus is required, the heat stored in the heat storage apparatus can be used.

[0023] A heat storage apparatus 1000 of FIG. 1 includes a first circuit 101. A medium used for heat exchange circulates through the first circuit 101. The medium is liquid or gas capable of transporting heat obtained by heat exchange. In this embodiment, water is used as the medium, for example. Further, the heat storage apparatus 1000 includes a heat exchanger 15 and a heat storage tank 20. The heat exchanger 15 exchanges, with the medium, the heat generated by a heat generator 10 capable of operating (generating heat) and not operating (generating no heat) and gives the heat to the medium. The heat storage tank 20 includes a phase change material 25 that exchanges heat with the medium, which has exchanged heat with the heat generator 10, and receives the heat from the medium. Here, the heat generator 10 is a device that generates heat in the vehicle. For example, the heat generator 10 is a storage battery, a motor, or an inverter. Additionally, the heat storage apparatus 1000 includes a cooling unit 30 and a first measurement unit 130. The cooling unit 30 regulates the temperature of the medium to be approximately a target temperature. The first measurement unit 130 measures the temperature of the medium before the medium passes through the heat storage tank 20.

[0024] The first circuit 101 is a pipe that connects the heat exchanger 15, the heat storage tank 20, and the cooling unit 30 to one another in a loop. The medium circulates through the pipe. Specifically, in FIG. 1, the first circuit 101 connects the heat exchanger 15 and the heat storage tank 20 to each other, the heat storage tank 20 and the cooling unit 30 to each other, and the cooling unit 30 and the heat exchanger 15 to each other. It should be noted that in order to allow heat exchange between the medium and the heat generator 10 and between the medium and the phase change material 25, the first circuit 101 is desirably made of a metal material (for example, copper) having excellent thermal conductivity in a portion where heat is exchanged. Further, in order to suppress heat radiation from the surface of the pipe, a resin member or the like having excellent heat resistance and heat insulating properties can be used in portions other than the above-mentioned portion.

[0025] The medium sequentially passes through the heat exchanger 15, the heat storage tank 20, and the cooling unit 30 to circulate through the first circuit 101 while repeating heat exchange with the heat generator 10 and the heat storage rank 20. In other words, the medium passes through the cooling unit 30 and thereafter passes through the heat exchanger 15 by circulating through the first circuit 101. The medium is driven by a pump or the like not shown in the figure.

[0026] The phase change material 25 is a material that is capable of changing its phase between a solid phase and a liquid phase by heat exchange and can be put into a supercooled state in the liquid phase. Further, the phase change material 25 is a material that nucleates and changes its phase to the solid phase by receiving an impact or an input of voltage application or the like when being in the supercooled state. In this embodiment, a sodium acetate hydrate is used, for the phase change material 25, for example.

[0027] The heat generator 10 is provided near the heat exchanger 15, for example, in contact with the heat exchanger 15. The heat generator 10 gives heat to the medium circulating through, the first circuit 101, via the heat exchanger 15. The heat is generated to the outside by the heat generator 10 operating when the vehicle is driven.

[0028] The heat storage tank 20 is a container that is provided downstream of the heat exchanger 15 of the first circuit 101 and contains the phase change material 25. Here, the term "downstream" is defined with reference to a direction in which the medium within the first circuit 101 flows. The heat storage tank 20 connects a pipe (not shown) to the first circuit 101. The pipe penetrates through the container. In the heat storage tank 20, when the medium, which has exchanged heat with the heat generator 10, passes through the pipe, the phase change material 25 receives the heat of the medium by heat exchange. It should be noted that the pipe penetrating through the container is assumed to be a part of the first circuit 101. In other words, the first circuit 101 passes through the heat storage tank 20.

[0029] The cooling unit 30 includes a radiator 31 and a fan 32 opposed to the radiator 31. The radiator 31 is connected to the first circuit 101. The radiator 31 receives heat from the medium that, passes through the radiator 31, and radiates the heat to the outside, thus cooling the medium. The fan 32 rotates to generate airflow toward the radiator 31, thus cooling the radiator 31. A first control unit 41 to be described later controls the rotating speed of the fan 32 to regulate an air volume of the airflow that is generated by the fan 32 and applied to the radiator 31. Therefore, through the regulation of the air volume of the airflow applied to the radiator 31, a surface temperature of the radiator 31 is lowered and the temperature of the medium passing through the radiator 31 is lowered.

[0030] Further, the cooling unit 30 includes a first bypass circuit 102 and a first control valve 103. The first bypass circuit 102 is connected to the first circuit 101 via the first control valve 103 at a branch point A and connected to the first circuit 101 at a branch point B to bypass the radiator 31. The first control valve 103 switches a flow path of the medium, which has passed through the first circuit 101 and reached the first control valve 103, to one of the first circuit 101 and the first bypass circuit 102. Here, a state in which the flow path of the medium is switched to (or maintained to be) the first circuit 101 is defined as a "first control valve OFF", and a state in which the flow path of the medium is switched to (or maintained to be) the first bypass circuit 102 is defined as a "first control valve ON".

[0031] The first measurement unit 130 is a temperature sensor provided between the heat exchanger 15 and the heat storage tank 20. The first measurement unit 130 measures a temperature (hereinafter, referred to as first temperature) of the medium passing from the heat exchanger 15 to the heat storage tank 20. Specifically, the first measurement unit 130 measures a first temperature of the medium after the medium receives heat by heat exchange with the heat generator 10 and before the medium gives the heat to the phase change material 25 by heat exchange with the phase change material 25.

[0032] Additionally, the heat storage apparatus 1000 of FIG. 1 includes a control device 200 and a storage device 300. It should be noted that an arithmetic processing unit such as a central processing unit (CPU) and a micro processing unit (MPU) is used as the control device 200. Further, a recording medium such as a memory and a hard disk drive (HDD) is used as the storage device 300.

[0033] FIG. 2 is a block diagram showing the control device 200 of FIG. 1.

[0034] The control device 200 of FIG. 2 includes an instruction unit 40, a first control unit 41, a count unit 42, and a determination unit 43 as logic modules. The instruction unit 40 controls the operation of the heat generator 10. The first control unit 41 controls the cooling unit 30 to cool the medium in the case where the first temperature is higher than a target temperature. The count unit 42 counts an elapsed time from when the phase change material 25 starts to change its phase from the solid phase to the liquid phase. The determination unit 43 determines whether the phase change material 25 finishes the phase change to the liquid phase based on the elapsed time counted by the count unit 42.

[0035] The instruction unit 40 controls the operation of the heat generator 10 based on an instruction from a driver who drives the vehicle. In other words, the instruction unit controls the heat generator 10 to be activated or deactivated. The heat storage apparatus 1000 stores heat generated by the heat generator 10 during a period of time from when the instruction unit 40 controls the heat generator 10 to be activated to when the instruction unit 40 controls the heat generator 10 to be deactivated.

[0036] The first control unit 41 compares the first temperature of the medium, which is measured by the first measurement unit 130, and the target temperature with each other, and controls the rpm of the fan 32 to indirectly control the air volume of the airflow applied to the radiator 31. Further, the first control unit 41 controls switching between ON and OFF of the first control valve 103. Here, the target temperature can be determined in advance and stored in the storage device 300. It should be noted that the target temperature is a fixed value that can be defined within the range equal to or higher than a melting point of the phase change material 25 and equal to or lower than a heatproof temperature of a device constituting the vehicle (for example, semiconductor device of inverter).

[0037] For example, the first control unit 41 switches the first control valve 103 to be Ob in the case where the first temperature of the medium is lower than the target temperature. At this time, the medium bypasses the radiator 31 by passing through the first bypass circuit 102. The medium passing through the first, bypass circuit 102 obtains heat from the heat generator 10 without being cooled and thus the temperature thereof is rising. On the other hand, in the case where the first temperature of the medium falls within a predetermined range with reference to the target temperature, the first control unit 41 controls the rpm of the fan 32 in accordance with a difference between the first temperature of the medium and the target temperature by using algorithms such as proportional (P) control, proportional integral (PI) control, and proportional integral derivative (PID) control. Also by storing a table in which the rpm of the fan 32 and the difference between the first temperature of the medium and the target temperature are associated with each other in the storage device 300 in advance, the first control unit 41 can control the rpm of the fan 32 by referring to the table.

[0038] The count unit 42 counts an elapsed time from when the phase change material 25 exchanges heat with the medium having the first temperature and starts the phase change from the solid phase to the liquid phase until the instruction unit 40 controls the heat generator 10 to be deactivated. At this time, a heat quantity (hereinafter, referred to as first heat quantity), which is required by a phase change material 25 by the time the phase change material 25 starts the phase change from the solid phase to the liquid phase, is investigated in advance by experiments or simulations, for example. The phase change material 25 in this case has the same type and volume as the phase change material 25 included in the heat storage tank 20. Then, the heat quantity thus obtained is stored in the storage device 300. Then, a heat quantity (hereinafter, referred to as second heat quantity) given to the phase change material 25 is estimated based on a time history of the first temperature of the medium, which is measured by the first measurement unit 130. A time point at which the estimated second heat quantity reaches the first heat quantity stored in the storage device 300 is set as a starting point of the phase change from the solid phase to the liquid phase. The count unit 42 counts the elapsed time from the starting point.

[0039] The determination unit 43 compares the elapsed time counted by the count unit 42 and a time (first time) with each other. The time (first time) is in the range from the start to the end of the phase change from the solid phase to the liquid phase in the case where the phase change material 25 constantly exchanges heat with the medium having the target temperature during the phase change from the solid phase to the liquid phase. In the case where the elapsed time is the first time or longer, the determination unit 43 determines that the phase change material 25 finishes the phase change to the liquid phase. In other words, the determination unit 43 determines that the phase change material 25 is allowed to be supercooled. On the other hand, in the case where the elapsed time is shorter than the first time, the determination unit 43 determines that the phase change material 25 does not finish the phase change to the liquid phase. In other words, the determination unit 43 determines that the phase change material 25 is not allowed to be supercooled. It should be noted that the determination unit 43 performs determination at a timing at which the instruction unit 40 controls the heat generator 10 to be deactivated, for example. The determination unit 43 stores a determination result in the storage device 300.

[0040] It should be noted that as the above-mentioned first time, in the case where a phase change material 25 constantly exchanges heat with the medium having the target temperature during the phase change from the solid phase to the liquid phase, the phase change material 25 in this case having the same type and volume as the phase change material 25 included in the heat storage tank 20, a first time from the start to the end of the phase change from the solid phase to the liquid phase can be investigated, in advance by experiments or simulations, for example, and then, the first time thus obtained can be stored in the storage device 300. In other words, in the case where the phase change material 25 exchanges heat with the medium having the first temperature over the first time or longer with reference to the first time, it is possible to estimate that the phase change material 25 stores heat of an enough heat quantity to completely change the phase to the liquid phase.

[0041] When the instruction unit 40 controls the heat generator 10 to be activated based on an instruction from the driver, the display device 400 refers to the determination result stored in the storage device 300 to display the determination result. In other words, with display, the driver can recognize the determination result, that is, a heat storage state of the phase change material 25.

[0042] FIG. 3 is a flowchart showing an operation of the heat storage apparatus 1000. It should be noted that the operation of the phase change material 25 from the solid phase state is shown in FIG. 3.

[0043] In Step 1001, the instruction unit 40 controls the heat generator 10 to be activated according to an instruction of the driver.

[0044] In Step 1002, the first measurement unit 130 measures the first temperature of the medium.

[0045] In Step 1003, the first control unit 41 controls the cooling unit 30 to lower the temperature of the medium in the case where the first temperature is higher than the target temperature. Further, in the case where the first temperature is lower than the target temperature, the temperature of the medium is raised by the heat of the heat generator 10 without being cooled. Thus, the temperature of the medium is regulated to or approximately a target temperature. It should be noted that even if the temperature of the medium at this time does not definitely coincide with the target temperature, the temperature of the medium only needs to be regulated to fall within an allowable range that is determined in advance, for example. It is desirable to set the allowable range to .+-.2.degree. C. of the target temperature, for example. Alternatively, it is desirable to set the allowable range to .+-.1.degree. C. of the target temperature when represented in the ratio with respect to the target temperature with reference to an absolute temperature.

[0046] The operation in Step 1002 and Step 1003 is continued until the instruction unit 40 controls the heat generator 10 to be deactivated in Step 1006 to be described later, for example.

[0047] In the case where the phase change material 25 starts the phase change in Step 1004, the count unit 42 starts to count an elapsed time from this time point in Step 1005.

[0048] In Step 1006, when the driver finishes driving the vehicle, the instruction unit 40 controls the heat generator 10 to be deactivated according to an instruction from the driver (for example, operation of turning off ignition key).

[0049] In Step 1007, the count unit 42 finishes counting the elapsed time. A timing at which the count is finished may be the same timing as Step 1006. Otherwise, the timing may be any timing after the Step 1006 in consideration of residual heat of the heat generator 10.

[0050] In Step 1008, in the case where the phase change material 25 constantly exchanges heat with the medium having the target temperature during the phase change from the solid phase to the liquid phase, a first time (threshold value) from the start to the end of the phase change from the solid phase to the liquid phase is obtained from the storage device 300 so that the threshold value and the elapsed time are compared with each other.

[0051] In Step 1009, in the case where the elapsed time is the threshold value or more, the determination unit 43 determines that the phase change material 25 is allowed to be supercooled. For example, simultaneously with the determination, a determination result is recorded in the storage device 300.

[0052] In Step 1010, in the case where the elapsed time is smaller than the threshold value, the determination unit 43 determines that the phase change material 25 is not allowed to be supercooled. For example, simultaneously with the determination, a determination result is recorded in the storage device 300.

[0053] In Step 1011, when the driver starts to drive the vehicle, the instruction unit 40 controls the heat generator 10 to be activated according to an instruction from the driver (for example, operation of turning on ignition key).

[0054] In Step 1012, the display device 400 displays the determination result stored in the storage device 300.

[0055] According to the heat storage apparatus 1000 of this embodiment, the temperature of the medium that exchanges heat with the phase change material is constant, and thus a temperature difference between the temperature of the medium and a melting point of the phase change material and a heat transfer coefficient between the medium and the phase change material are constant. Therefore, the temperature of the medium can be eliminated from parameters used in the determination, and whether the phase change material 25 is allowed to be supercooled or not can be easily determined based on only a simple index of the elapsed time.

[0056] Further, the temperature of the medium before passing through the heat storage tank 20 is set to be a constant temperature, and accordingly the phase change material 25 can store heat at a constant heat transfer quantity (heat storage capability) during the phase change. Therefore, by experiments, simulations, or the like performed in advance under the same conditions, the first temperature (threshold value) can be set easily.

[0057] It should be noted that in the case where the heat generator 10 is a motor and includes a water jacket that penetrates through the motor, for example, the water jacket can be connected to the first circuit 101. At this time, the heat generator 10 gives heat, which is generated to the outside when the medium passes through the water jacket, to the medium by heat exchange. In this case, the water jacket is assumed to be the heat exchanger 15.

FIRST MODIFIED EXAMPLE

[0058] FIG. 4 is a block diagram showing a control device 200 according to a first modified example. In this modified example, the control device 200 is different from the control device 200 of FIG. 2 in that the control device 200 in this modified example includes an estimation unit 44 as a logic module.

[0059] The estimation unit 44 estimates an estimation value of a heat storage quantity based on the elapsed time counted by the count unit 42. Specifically, the heat storage quantity is a quantity of heat stored by the phase change material 25 after the phase change material 25 exchanges heat with the medium having the target temperature and starts to change its phase from the solid phase to the liquid phase. For example, the estimation unit 44 estimates the heat storage quantity by integrating a difference between the first temperature measured by the first measurement unit 130 and the melting point of the phase change material 25.

[0060] The determination unit 43 compares the estimation value of the heat storage quantity, which is estimated by the estimation unit 44, and a maximal value of the heat storage quantity with each other. The heat storage quantity is a quantity of heat that can be stored by the phase change material 25 from the start to the end of the phase change from the solid phase to the liquid phase in the case where the phase change material 25 constantly exchanges heat with the medium having the target temperature during the phase change from the solid phase to the liquid phase. In the case where the estimation value of the heat storage quantity is the maximal value of the heat storage quantity or larger, the determination unit 43 determines that the phase change material 25 finishes the phase change to the liquid phase. In other words, the determination unit 43 determines that the phase change material 25 is allowed to be supercooled. On the other hand, in the case where the estimation value of the heat storage quantity is smaller than the maximal value of the heat storage quantity, the determination unit 43 determines that the phase change material 25 does not finish the phase change to the liquid phase. In other words, the determination unit 43 determines that the phase change material 25 is not allowed to be supercooled. The determination unit 43 stores a determination result in the storage device 300.

[0061] It should be noted that as the above-mentioned maximal value of the heat storage quantity, in the case where a phase change material 25 constantly exchanges heat with the medium having the target temperature during the phase change from the solid phase to the liquid phase, the phase change material 25 in this case having the same type and volume as the phase change material 25 included in the heat storage tank 20, a maximal value of a quantity of heat that can be stored by the phase change material 25 from the start to the end of the phase change from the solid phase to the liquid phase can be investigated in advance by experiments or simulations, for example, and then, the maximal value thus obtained can be stored in the storage device 300.

[0062] FIGS. 5A, 5B, and 5C are exemplary graphs of simulation results for describing an action or the heat storage apparatus 1000. As shown in FIG. 5A, a case where the first temperature of the medium from time T1 to time T2 is constant will be discussed. Further, as shown in FIG. 5B, it is assumed that the phase change material 25 starts the phase change from the solid phase to the liquid phase at time T1 and finishes the phase change at time T2.

[0063] At this time, FIG. 5C shows a time history of a heat transfer quantity of heat that transfers from the phase change material 25 to the medium from time T1 to time T2.

[0064] According to this modified example, the temperature of the medium before passing through the heat storage tank 20 is set to be a constant temperature, and accordingly the phase change material 25 can store heat at a constant heat transfer quantity during the phase change. Therefore, by experiments, simulations, or the like performed in advance under the same conditions, the maximal value of the heat storage quantity can be set easily. Further, in addition to a simple index of the elapsed time, whether the phase change material 25 is allowed to be supercooled or not can be easily determined based on the temperature of the medium, which has been regulated by the cooling unit 30, that is, based on a constant temperature of the medium.

SECOND MODIFIED EXAMPLE

[0065] FIG. 6 is a block diagram showing a heat storage apparatus 1000 according to a second modified example. Further, FIG. 7 is a block diagram showing a control device 200 according to the second modified example. In this modified example, the heat storage apparatus 1000 is different from the heat storage apparatus 1000 of FIG. 1 in that the heat storage apparatus 1000 in this modified example includes a heating unit 150. Further, the control device 200 is different from the control device 200 of FIG. 2 in that the control device 200 in this modified example includes an estimation unit 44.

[0066] The estimation unit 44 estimates an estimation value of a heat storage quantity based on the elapsed time counted by the count unit 42. Specifically, the heat storage quantity is a quantity of heat stored by the phase change material 25 after the phase change material 25 exchanges heat with the medium having the target temperature and starts to change its phase from the solid phase to the liquid phase. Further, in the case where the determination unit 43 determines that the phase change material 25 is not allowed to be supercooled, the estimation unit 44 calculates a difference between a maximal value of the heat storage quantity and the estimation value of the heat storage quantity at a time point of the determination by the determination unit 43. The heat storage quantity is a quantity of heat that can be stored by the phase change material 25 from the state to the end of the phase change from the solid phase to the liquid phase in the case where a phase change material 25 constantly exchanges heat with the medium having the target temperature during the phase change from the solid phase to the liquid phase.

[0067] The heating unit 150 is a heater provided near the heat storage tank 20. The heating unit 150 gives a heat quantity corresponding to the difference calculated by the estimation unit 44 to the phase change material 25.

[0068] At a time point at which the heating unit 150 gives a heat quantity corresponding to the difference to the phase change material 25, the determination unit 43 determines that the phase change material 25 is allowed to be supercooled. The determination unit 43 stores a determination result to the storage device 300.

[0069] According to this modified example, at a time point at which the operation of the heat generator 10 is stopped, even when the phase change material 25 is not in a state allowed to be supercooled, it is possible to completely change the phase of the phase change material 25 to the liquid phase when a sufficient heat quantity is given to the phase change material 23. In other words, it is possible to put the phase change material 25 into a supercooled state.

[0070] Although the example in which the heating unit 150 is provided near the heat storage tank 20 has been described here, the following configuration may be provided. For example, the heating unit 150 is provided at a part of the first circuit 101 so that the medium is heated and thus a heat quantity is indirectly given to the phase change material 25.

SECOND EMBODIMENT

[0071] FIG. 8 is a block diagram showing a heat storage apparatus 1000 according to a second embodiment. FIG. 12 is a block diagram showing the control device of FIG. 8 In this embodiment, the heat storage apparatus 1500 is different from the heat storage apparatus 1000 of FIG. 1 in that the heat storage apparatus 1500 includes a second measurement unit 140.

[0072] The second measurement unit 140 is a temperature sensor provided between the heat storage tank 20 and the cooling unit 30. The second measurement unit 140 measures a temperature (hereinafter, referred to as second temperature) of a medium after the medium passes through the heat storage tank 20 but before through the cooling unit 30, the medium passing through the first circuit 101. Specifically, the second measurement unit 140 measures a second temperature of the medium after the medium gives heat to the phase change material 25 by heat exchange and before the temperature thereof is lowered by the cooling unit 30.

[0073] The count unit 42 counts an elapsed time starting from a time point at which the second temperature measured by the second measurement unit 140 is put to be constant. In other words, the second temperature of the mediums having passed through the heat storage tank 20 can be considered to be approximate to the temperature of the phase change material 25. Therefore, the time point at which the second temperature is put to be constant can be considered as a time point at which the phase change material 25 starts to change its phase from the solid phase to the liquid phase.

[0074] It should be noted that the term "constant" herein means that an absolute value of a change rate (K/s) of the second temperature is equal to or smaller than a threshold value defined beforehand. In other words, the count unit 42 can count an elapsed time starting from a time point at which the absolute value of the change rate (K/s) of the second temperature first reaches the threshold value defined beforehand.

[0075] FIGS. 9A, 9B, and 9C are exemplary graphs of simulation results for describing an action of the heat storage apparatus 1500. As shown in FIG. 9A, a case where the first temperature of the medium from time T1 to time T2 is constant will be discussed. Further, as shown in FIG. 9B, it is assumed that the phase change material 25 starts the phase change from the solid phase to the liquid phase at time T1 and finishes the phase change at time T2.

[0076] At this time, FIG. 9C shows an absolute value of a change rate of the second temperature. Accordingly, it is found that the absolute value of the change rate of the second temperature is equal to or smaller than the threshold value (for example, 0.001) during a period of time from time T1 when the phase change material 25 starts the phase change to time T2 when the phase change material 25 finishes the phase change.

[0077] According to the heat storage apparatus 1500 in this embodiment, the temperature of the phase change material is not directly measured and the second temperature of the medium that is close to the temperature of the phase change material 25 is measured, which makes it possible to highly accurately estimate, based on the second temperature, a timing at which the phase change material 25 starts to change its phase from the solid phase to the liquid phase. Accordingly, whether the phase change material 25 is allowed to be supercooled or not can be determined highly accurately based on a more correct elapsed time.

THIRD EMBODIMENT

[0078] FIG. 10 is a block diagram showing an air conditioning apparatus 2000 according to a third embodiment. Further, FIG. 11 is a block diagram showing a control device 200 of FIG. 10. The air conditioning apparatus 2000 of FIG. 10 includes the heat storage apparatus 1000 of FIG. 1. The same configurations as those of the heat storage apparatus 1000 of FIG. 1 and the control device 200 of FIG. 2 are denoted by the same reference numerals, and detailed descriptions thereof will be omitted.

[0079] The air conditioning apparatus 2000 of FIG. 10 includes a nucleating device 160, a second bypass circuit 112, and a second control valve 113. Additionally, the air conditioning apparatus 2000 includes an air conditioning unit 170 and a second circuit 111 that connects the air conditioning unit 170 and the heat storage tank 20 to each other in a loop and causes a medium to pass through the second circuit 111. The control device 200 of FIG. 11 includes a second control unit 45 as a logic module.

[0080] The nucleating device 160 is a device for giving a trigger such as an impact or an input of voltage application to the phase change material 25 to cause the phase change material 25 to nucleate. In the case where the storage device 300 stores information that the supercooling is allowed, the operation of the nucleating device 160 is controlled by the instruction unit 40 based on an instruction from a driver who drives a vehicle.

[0081] The second bypass circuit 112 is connected to the first circuit 101 via the second control valve 113 at a branch point C and connected to the first circuit 101 at a branch point D to bypass the heat storage tank 20.

[0082] The second control valve 113 switches a flow path of the medium, which has passed through the first circuit 101 and reached the second control valve 113, to one of the first circuit 101 and the second bypass circuit 112. Here, a state in which the flow path of the medium is switched to (or maintained to be) the first circuit 101 is defined as a "second control valve OFF", and a state in which the flow path of the medium is switched to (or maintained to be) the second bypass circuit 112 is defined as a "second control valve ON".

[0083] The air conditioning unit 170 regulates an air temperature or humidity in the vehicle. Here, a general heat pump system including a compressor, a condenser, an evaporator, and the like is used as the air conditioning unit 170, and detailed descriptions thereof will be omitted.

[0084] The second control unit 45 controls the switching of the second control valve 113 to be turned on at a timing at which the instruction unit 40 controls the nucleating device 160. Accordingly, heat of the phase change material 25 that radiates the heat by nucleating is not transmitted to the medium in the first circuit 101. Therefore, heat can be efficiently transmitted to the medium in the second circuit 111.

[0085] It should be noted that a seat, a wheel, and the like, through which the second circuit 111 passes, may be used as the air conditioning unit 170. In this case, a high-temperature medium passing through the second circuit can directly warm the seat, the wheel, and the like.

[0086] The heat storage apparatus, the air conditioning apparatus, and the heat storage method according to at least one of the embodiments described above allows a highly accurate determination as to whether the phase change material is allowed to be supercooled or not.

[0087] While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of the other forms; furthermore, various omissions, substitutions and changes in the form the methods and systems described herein may be made without departing from the sprit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

Claims

1. A heat storage apparatus, configured to store heat generated by a heat generator via a medium, comprising: a first circuit closed to circulate the medium therethrough in a direction; a heat exchanger that is provided at a part of the first circuit and is configured to exchange the heat generated by the heat generator with the medium; a heat storage tank that is provided downstream of the direction in which the medium circulates, with respect to the heat exchanger of the first circuit, and includes a phase change material to exchange heat with the medium storing the heat generated by the heat generator; a first measurement unit configured to measure a temperature of the medium that passes from the heat exchanger to the heat storage tank; a cooling unit, that is configured to cool the medium when the measured temperature of the medium is higher than a predetermined target temperature, and to set the temperature of the medium that passes from the heat exchanger to the heat storage tank to be approximately equal to the target temperature; a count unit configured to count an elapsed time from when the phase change material exchanges heat with the medium and starts a phase change from a solid phase to a liquid phase; and a determination unit configured to determine whether the phase change material is allowed to be supercooled or not based on the elapsed time.

2. The heat storage apparatus according to claim 1, further comprising a storage unit configured to store a first time from a start of the phase change of the phase change material to an end of the phase change in a case where the phase change material exchanges heat with the medium having the target temperature, wherein the determination unit is configured to compare the first time and the elapsed time with each other and to determine whether the phase change material is allowed to be supercooled or not.

3. The heat storage apparatus according to claim 1, further comprising: a storage unit configured to store a first heat storage quantity of heat that can be stored from a start of the phase change of the phase change material to an end of the phase change in a case where the phase change material exchanges heat with the medium having the target temperature; and an estimation unit configured to estimate an estimation value of a heat storage quantity of the heat stored from the start of the phase change of the phase change material, using the temperature of the medium measured by the first measurement unit and the elapsed time, wherein the determination unit is configured to compare the first heat storage quantity and the estimation value of the heat storage quantity with each other and to determine whether the phase change material is allowed to be supercooled or not.

4. The heat storage apparatus according to claim 1, further comprising a second measurement unit configured to measure a second temperature of the medium after the medium passes through the heat storage tank, wherein the count unit is configured to count an elapsed time starting from a time point from which the second temperature stays constant.

5. The heat storage apparatus according to claim 1, further comprising a heating unit configured to apply heat to the phase change material, wherein the heating unit is configured to heat, when the determination unit determines that the phase change material is not allowed to be supercooled, one of the phase change material and the medium.

6. The heat storage apparatus according to claim 1, wherein the cooling unit includes a radiator that is connected to the first circuit, and a fan that is opposed to the radiator, and the heat storage apparatus further comprises a first control unit configured to control a rotating speed of the fan.

7. The heat storage apparatus according to claim 1, wherein the cooling unit includes a first bypass circuit that is connected to the first circuit at a first branch point and is configured to bypass the radiator, and a first control valve configured to switch a flow path of the medium to one of the first circuit and the first bypass circuit at the first branch point, and the heat storage apparatus further comprises a first control unit configured to control switching of the first control valve.

8. The heat storage apparatus according to claim 1, wherein the heat generator includes at least one of a motor, an inverter, and a battery.

9. An air conditioning apparatus, comprising: a heat storage apparatus configured to store heat generated by a heat generator via a medium, the heat storage apparatus including a first circuit closed to circulate the medium therethrough in a direction, a heat exchanger that is provided at a part of the first circuit and is configured to exchange the heat generated by the heat generator with the medium, a heat storage tank that is provided downstream of the direction in which the medium circulates, with respect to the heat exchanger of the first circuit, and includes a phase change material to exchange heat with the medium storing the heat generated by the heat generator, a first measurement unit configured to measure a temperature of the medium that passes from the heat exchanger to the heat storage tank, a cooling unit that is configured to cool the medium when the measured temperature of the medium is higher than a predetermined target temperature, and to set the temperature of the medium that passes from the heat exchanger to the heat storage tank to be approximately equal to the target temperature, a count unit configured to count an elapsed time from when the phase change material exchanges heat with the medium and starts a phase change from a solid phase to a liquid phase, and a determination unit configured to determine whether the phase change material is allowed to be supercooled, or not based on the elapsed time; a nucleating device configured to nucleate the phase change material; a second bypass circuit that is connected to the first circuit at a second branch point and is configured to bypass the heat storage tank; a second control valve configured to switch a flow path of the medium to one of the first circuit and the second bypass circuit at the second branch point; and a second control unit configured to control, when the determination unit determines that the phase change material is allowed to be supercooled, switching of the second control valve to switch the flow path of the medium to the second bypass circuit.

10. A heat storage method for one of a heat storage apparatus and an air conditioning apparatus including a medium, a first circuit closed to circulate the medium therethrough in a direction, a heat exchanger that is provided at a part of the first circuit and is configured to exchange heat generated by a heat generator with the medium, a heat storage tank that is provided downstream of the direction in which the medium circulates, with respect to the heat exchanger of the first circuit, and includes a phase change material to exchange heat with the medium storing the heat generated by the heat generator, the heat storage method comprising: circulating the medium; measuring a temperature of the medium that passes from the heat exchanger to the heat storage tank; cooling the medium when the measured temperature of the medium is higher than a predetermined target temperature, and setting the temperature of the medium that passes from the heat exchanger to the heat storage tank to be approximately equal to the target temperature; counting an elapsed time from when the phase change material exchanges heat with the medium and starting a phase change from a solid phase to a liquid phase; and determining, by a determination unit, whether the phase change material is allowed to be supercooled or not based on the elapsed time.

11. The heat storage method according to claim 10, further comprising: storing a first time from a start of the phase change of the phase change material to an end of the phase change in a case where the phase change material exchanges heat with the medium having the target temperature; and comparing the first time and the elapsed time with each other and determining whether the phase change material is allowed to be supercooled or not.

12. The heat storage method according to claim 10, further comprising: storing a first heat storage quantity of heat that can be stored from a start of the phase change of the phase change material to an end of the phase change in a case where the phase change material exchanges heat with the medium having the target temperature; estimating an estimation value of a heat storage quantity of the heat stored from the start of the phase change of the phase change material, using the measured temperature of the medium and the elapsed time; and comparing the first heat storage quantity and the estimation value of the heat storage quantity with each other and determining whether the phase change material is allowed to be supercooled or not.

13. The heat storage method according to claim 10, further comprising: measuring a second temperature of the medium after the medium passes through the heat storage tank; and counting an elapsed time from a time point from which the second temperature stays constant.

14. The heat storage method according to claim 10, further comprising heating one of the phase change material and the medium by a heating unit configured to apply heat to the phase change material, when it is determined that the phase change material is not allowed to be supercooled.

15. The heat storage method according to claim 10, further comprising controlling a rotating speed of a fan that is opposed to a radiator connected to the first circuit.

16. The heat storage method according to claim 10, further comprising control switching of a first control valve that is configured to switch a flow path of the medium to one of the first circuit and a first bypass circuit at a first branch point, the first bypass circuit being connected to the first circuit at the first branch point and being configured to bypass a radiator.