JP7603803B2 - Water heater - Google Patents

Description

This disclosure relates to a water heater equipped with a heat storage tank that stores heat generated by a heat source.

Conventionally, water heaters that use heat generated by a heat source unit to supply hot water are known. Such water heaters are configured to store heat generated by the heat source in advance in a heat storage tank unit when supplying hot water, and use the stored heat to heat the water to supply hot water. For the heat storage tank units used in water heaters, a technology is known that makes the tank cylindrical, with the main purpose of improving pressure resistance.

On the other hand, in conventional water heaters, it is desirable to miniaturize the heat storage tank unit so that it can be installed in a small space. Therefore, various heat storage tank units have been proposed to accommodate the miniaturization of heat storage tank units. For example, Patent Document 1 discloses a water heater in which the heat storage tank is formed from multiple plates, the spacing between adjacent plates is kept constant, multiple heat storage materials are placed between the plates, and a flow path section through which supply water flows between the plates is formed.

JP 2009-97825 A

However, the technology described in Patent Document 1 had the problem that if the plate portion was damaged due to corrosion or the like, there was a risk that the heat storage material would mix with the water supply.

This disclosure has been made in consideration of the problems with the above-mentioned conventional technology, and aims to provide a water heater that can prevent heat storage material from being mixed into the water supply.

The water heater according to the present disclosure includes a heating device for heating a fluid, and a heat storage tank unit for storing the fluid heated by the heating device and storing heat therein, and executes a boiling operation in which the fluid heated by the heating device is stored in the heat storage tank unit, and a hot water supply operation in which hot water is supplied by utilizing the heat stored in the heat storage tank unit, the heat storage tank unit including a heat storage section for storing the heated fluid, an upper pipe provided at an upper part of the heat storage section, a lower pipe provided at a lower part of the heat storage section, and a heat exchanger provided outside the heat storage section , the heat storage section including a first heat storage tank into which the fluid heated in the boiling operation flows, and a second heat storage tank that contains a heat storage material different from the fluid, is formed separately from the first heat storage tank, and is arranged in contact with the first heat storage tank, The heat exchanger performs heat exchange between the fluid flowing in from the first heat storage tank and the fluid flowing in from the water supply piping, and when the heated fluid flows into the heat storage section during the boiling operation, heat is stored in the second heat storage tank through heat exchange between the fluid in the first heat storage tank and the heat storage material of the second heat storage tank, and during the hot water supply operation, the fluid stored in the first heat storage tank flows into the heat exchanger from the upper piping, where its temperature is reduced, and then flows into the lower part of the first heat storage tank via the lower piping and circulates, and the first heat storage tank has a first step formed on the lower side and a second step formed on the upper side, the cut surface of which is smaller than that of the first step when cut in a horizontal plane, and the second heat storage tank is positioned so as to cover and abut against the side surface of the second step.

According to the present disclosure, the first heat storage tank constituting the heat storage unit that stores the heated fluid and the second heat storage tank that contains the heat storage material are formed separately. Therefore, even if the second heat storage tank is damaged and the heat storage material inside leaks out, it is possible to prevent the heat storage material from being mixed into the water supply.

1 is a schematic diagram showing an example of the configuration of a water heater according to a first embodiment. FIG. 2 is a perspective view showing an example of the structure of the heat storage unit in FIG. 1 . FIG. 2 is a top view showing an example of the structure of the heat storage unit in FIG. 1 . 4 is a cross-sectional view of the heat storage unit shown in FIG. 3 along the line AA. FIG. 11 is a perspective view showing an example of the structure of a heat storage section according to a second embodiment. FIG. 11 is a top view showing an example of the structure of a heat storage section according to a second embodiment. 7 is a cross-sectional view of the heat storage unit shown in FIG. 6 along the line B-B. 7 is a cross-sectional view of a modified example of the heat storage portion shown in FIG. 6 along the line BB.

The following describes embodiments of the present disclosure with reference to the drawings. The present disclosure is not limited to the following embodiments, and various modifications are possible without departing from the spirit of the present disclosure. The present disclosure also includes all combinations of possible configurations among the configurations shown in the following embodiments. In addition, in each figure, items with the same reference numerals are the same or equivalent, and this is common throughout the entire specification.

Embodiment 1.
A description will be given of a water heater according to the present embodiment 1. The water heater according to the present embodiment 1 heats a fluid using a heating device such as a heat pump during late-night hours when the unit price of electricity under a time-based contract power plan is low, stores heat, and uses the stored heat to supply hot water.

[Configuration of water heater 100]
Fig. 1 is a schematic diagram showing an example of the configuration of a water heater according to the first embodiment. As shown in Fig. 1, the water heater 100 is configured to include a heat storage tank unit 1 and a heating device 2. The heat storage tank unit 1 and the heating device 2 are connected by piping on-site. The heat storage tank unit 1 and the heating device 2 are connected by piping 3 and piping 4. In addition, a water supply pipe 5 and a hot water supply pipe 6 are connected to the heat storage tank unit 1. The water supply pipe 5 and the hot water supply pipe 6 are connected to terminals such as a shower and a faucet on-site, respectively.

(Heating device 2)
The heating device 2 is a heating means for heating the fluid supplied from the heat storage tank unit 1. For example, an electric heater, a gas boiler, a heat pump unit, or the like is used as the heating device 2. In this example, a case where a heat pump unit is used as the heating device 2 will be described.

The heating device 2 includes a compressor 21, a heating heat exchanger 22, a pressure reduction device 23, and a heat absorption heat exchanger 24. In the heating device 2, the compressor 21, the heating heat exchanger 22, the pressure reduction device 23, and the heat absorption heat exchanger 24 are connected in a ring shape by refrigerant piping, forming a refrigerant circuit in which a refrigerant such as carbon dioxide circulates.

The compressor 21 draws in low-temperature, low-pressure refrigerant, compresses it, and discharges high-temperature, high-pressure refrigerant. The compressor 21 is, for example, an inverter compressor whose capacity, which is the amount of refrigerant discharged per unit time, is controlled by changing the operating frequency.

The heating heat exchanger 22 has two flow paths formed therein: a refrigerant-side flow path through which the refrigerant circulating in the refrigerant circuit flows, and a fluid-side flow path through which the fluid circulating in the boiling circuit described below flows. The heating heat exchanger 22 exchanges heat between the refrigerant flowing in the refrigerant-side flow path and the fluid flowing in the fluid-side flow path. The heating heat exchanger 22 functions as a condenser that dissipates heat from the refrigerant to the fluid to condense the refrigerant.

The pressure reducing device 23 is, for example, an expansion valve, and reduces the pressure of the refrigerant to expand it. The pressure reducing device 23 is, for example, composed of a valve that can control the opening degree, such as an electronic expansion valve.

The endothermic heat exchanger 24 exchanges heat between the refrigerant and air supplied by a fan (not shown) installed nearby. The endothermic heat exchanger 24 evaporates the refrigerant and cools the air by the heat of vaporization. For example, a fin-and-tube type heat exchanger is used as the endothermic heat exchanger 24.

(Heat storage tank unit 1)
The heat storage tank unit 1 stores heat by storing a fluid heated by a heating device 2. The heat storage tank unit 1 includes a heat storage section 10, a heating device pump 11, a hot water supply pump 12, a heat exchanger 13, and a mixing valve 14, and is connected to a water supply pipe 5 and a hot water supply pipe 6 which are connected to external terminals.

In the heat storage tank unit 1, a boiling circuit that heats the fluid is formed by circulating the fluid through the heat storage section 10, the heating device pump 11, the heat absorption heat exchanger 24 of the heating device 2, and the heat storage section 10. In the heat storage tank unit 1, a hot water heating circuit that heats water such as city water is formed by circulating the fluid through the heat storage section 10, the heat exchanger 13, the hot water pump 12, and the heat storage section 10. Water or antifreeze is used as the fluid that circulates through the boiling circuit and the hot water heating circuit. Note that water is less expensive than antifreeze, so it is preferable to use water as the fluid.

The heat storage unit 10 stores heated fluid supplied from the heating device 2 via the piping 4. As will be described in detail later, an upper piping 33 is provided at the top of the heat storage unit 10, and a lower piping 34 is provided at the bottom of the heat storage unit 10 (see Figures 2 to 4). The heat storage unit 10 is composed of a first heat storage tank 30 and a second heat storage tank 40. The detailed configuration of the heat storage unit 10 will be described later.

The heating device pump 11 is driven by a motor (not shown) so as to send the fluid flowing out from the lower pipe 34 of the heat storage unit 10 to the heating heat exchanger 22 of the heating device 2 via the pipe 3. The hot water supply pump 12 is driven by a motor (not shown) so as to send the fluid flowing out from the upper pipe 33 of the heat storage unit 10 to the heat exchanger 13.

The heat exchanger 13 has two flow paths formed therein: a primary flow path through which the fluid flowing out of the heat storage section 10 flows, and a secondary flow path through which the fluid branched off from the water supply pipe 5 flows. The heat exchanger 13 exchanges heat between the fluids flowing through the two flow paths formed therein. The heat exchanger 13 is, for example, a plate-type heat exchanger, and is formed by processing and stacking metals such as stainless steel, aluminum, or copper into flat plates.

The mixing valve 14 is, for example, a three-way valve, and has a first inlet connected to the heat exchanger 13, a second inlet connected to a flow path branched off from the water supply pipe 5, and an outlet connected to the hot water supply pipe 6. The mixing valve 14 mixes a high-temperature fluid flowing into the first inlet with a fluid such as city water supplied through the water supply pipe 5 flowing into the second inlet, and discharges the mixed fluid from the outlet. A temperature sensor (not shown) is provided downstream of the mixing valve 14, and the mixing ratio of the fluids in the mixing valve 14 is controlled so that the temperature of the mixed fluid detected by the temperature sensor becomes the set temperature.

[Structure of heat storage section 10]
Fig. 2 is a perspective view showing an example of the structure of the heat storage unit in Fig. 1. Fig. 3 is a top view showing an example of the structure of the heat storage unit in Fig. 1. Fig. 4 is a cross-sectional view taken along line A-A of the heat storage unit shown in Fig. 3. As shown in Figs. 2 to 4, the heat storage unit 10 is composed of a first heat storage tank 30 and a second heat storage tank 40 formed separately from the first heat storage tank 30.

The first heat storage tank 30 is formed in the shape of a hollow prism having a rectangular cross-sectional shape, and is made of, for example, stainless steel. The thickness of the side wall of the first heat storage tank 30 is, for example, about 2 to 3 mm. The first heat storage tank 30 has a step in the height direction (z direction), and is formed of a first step 31 on the lower side and a second step 32 on the upper side.

The height of the first step 31 is about 1.5 to 2 times the height of the second step 32. In addition, each side of the first step 31 in the width direction (x direction) and depth direction (y direction) is formed to be about 200 mm longer than each side of the second step 32 in the same direction. In other words, the cut surface when the second step 32 is cut on a horizontal plane formed by the width direction (x direction) and depth direction (y direction) is smaller than the cut surface of the first step 31 cut on a similar horizontal plane. Furthermore, on the same side of the first step 31 and the second step 32, the distance from the side of the first step 31 to the side of the second step 32 is about 100 mm.

By forming the first step 31 and the second step 32 in this manner, when the first heat storage tank 30 is viewed from above, the intersection of the diagonals of the first step 31 and the intersection of the diagonals of the second step 32 are at the same position in the width direction (x direction) and depth direction (y direction).

An upper pipe 33 protruding upward is formed on the top surface of the first step 31. A lower pipe 34 protruding downward is formed on the bottom surface of the second step 32. The upper pipe 33 and the lower pipe 34 are formed so that the fluid stored inside the first heat storage tank 30 can flow in and out. When the first heat storage tank 30 is viewed from the top side, it is preferable that the upper pipe 33 and the lower pipe 34 are formed at approximately the same position in the width direction (x direction) and depth direction (y direction) as the intersection of the diagonal lines of the second step 32.

The second heat storage tank 40 is formed to cover and abut the side surface of the second step 32 of the first heat storage tank 30. The outer periphery of the second heat storage tank 40 is formed to have the same dimensions as the outer periphery of the first step 31 of the first heat storage tank 30. In addition, the inner periphery of the second heat storage tank 40 is formed to have the same dimensions as the outer periphery of the second step 32 of the first heat storage tank 30.

The second heat storage tank 40 is formed as a hollow prism having a rectangular cross-sectional shape made of, for example, stainless steel. The thickness of the side wall of the second heat storage tank 40 is, for example, about 2 mm, which is the same as or thinner than the side wall of the first heat storage tank 30. The height of the second heat storage tank 40 is equal to the height of the second step 32 of the first heat storage tank 30.

The first heat storage tank 30 and the second heat storage tank 40 each store a heat storage material. The first heat storage tank 30 stores water as the heat storage material. The second heat storage tank 40 stores a heat storage material different from that of the first heat storage tank 30. Specifically, the second heat storage tank 40 stores a latent heat storage material as the heat storage material. The latent heat storage material refers to a heat storage material that stores latent heat as it changes phase from solid to liquid due to melting.

In addition, examples of heat storage materials include sensible heat storage materials that are different from latent heat storage materials. Sensible heat storage materials are heat storage materials that store sensible heat by utilizing temperature changes without undergoing a phase change. The water stored in the first heat storage tank 30 does not undergo a phase change, and is therefore classified as a sensible heat storage material in this application.

The latent heat storage material may be, for example, a hydrate medium such as sodium acetate trihydrate or sodium thiosulfate pentahydrate, or an organic medium such as paraffin. An example of the melting point of sodium acetate trihydrate is 58°C, an example of the melting point of sodium thiosulfate pentahydrate is 48°C, and an example of the melting point of paraffin is 56°C. In addition, an example of the heat storage density of these latent heat storage materials in a certain temperature range is 0.54 MJ/L for sodium acetate trihydrate and 0.28 MJ/L for paraffin.

Here, sodium acetate trihydrate has a higher heat storage density than paraffin, but lacks stability in phase change due to the occurrence of a supercooling phenomenon at the melting point where the phase does not change from liquid to solid. Therefore, from the viewpoint of stability as well as heat storage density, it is preferable to select a heat storage material with a stable phase change such as paraffin as the latent heat storage material. In addition, since latent heat storage materials store more heat than sensible heat storage materials, using latent heat storage materials as the heat storage material is advantageous for miniaturizing the water heater 100.

It is preferable to configure the inner circumference of the second heat storage tank 40 so that the plate thickness is thinner than the outer circumference. This is to improve the heat transfer performance between the abutting first heat storage tank 30 and the second heat storage tank 40. The same effect can also be achieved by configuring the plate thickness of the second step 32 in the first heat storage tank 30 so that it is thinner than the plate thickness of the rest of the tank.

In addition, multiple fin-shaped plate materials may be arranged in the second heat storage tank 40 so as to extend from the inner circumference to the outer circumference. In this case, the fin-shaped plate material is preferably made of aluminum, which has a high thermal conductivity. In this way, by arranging the fin-shaped plate material in the second heat storage tank 40, the thermal conductivity between the latent heat storage materials can be improved, and the heat transfer performance between the first heat storage tank 30 and the second heat storage tank 40 can be improved.

In addition, the inner wall of the second heat storage tank 40 may be treated with a fluorine coating or other coating that makes it difficult for the paraffin latent heat storage material to adhere to it. This makes it possible to reduce the stress on the tank caused by the pressure generated by the increase in volume caused by the phase change when only a portion of the latent heat storage material located around the wall changes from solid to liquid.

1, the outlet when fluid flows out from the heat storage unit 10 to the boiling circuit, i.e., the outlet when fluid is supplied from the heat storage unit 10 to the heating device 2, is the lower pipe 34. The lower pipe 34 also serves as an inlet through which fluid flows into the heat storage unit 10 via the hot water supply heating circuit, i.e., an inlet through which the fluid that has been heat exchanged in the heat exchanger 13 flows in.

The upper pipe 33 serves as the inlet through which fluid flows into the heat storage unit 10 via the boiling circuit, i.e., the inlet through which the fluid heated by the heating device 2 flows into the heat storage unit 10. The upper pipe 33 also serves as the outlet through which fluid flows out of the heat storage unit 10 to the hot water heating circuit, i.e., the outlet through which fluid is supplied from the heat storage unit 10 to the heat exchanger 13.

In this way, the upper pipe 33 and the lower pipe 34 are components that function as an inlet and an outlet when the fluid circulates through the two circulation paths. For this reason, the upper pipe 33 and the lower pipe 34 are provided with, for example, T-shaped joints, so that the flow path branches into two.

In this example, the upper piping 33 and the lower piping 34 are shared components of the two circulation circuits, but this is not limited to this. For example, inflow and outflow piping through which fluid flows in and out may be further provided on each of the top and bottom surfaces of the first heat storage tank 30.

When the first heat storage tank 30 and the second heat storage tank 40 are combined to form the heat storage unit 10, it is preferable to place a heat conductive material such as heat conductive grease or a heat conductive sheet on the contact surface of these two tanks. This is to promote heat conduction between the first heat storage tank 30 and the second heat storage tank 40 and improve heat transfer performance.

In addition, a heat insulating material (not shown) may be arranged around the outer periphery of the heat storage unit 10. This makes it possible to suppress natural heat dissipation from the heat storage unit 10. Examples of the heat insulating material used in this case include flat vacuum insulation material, foam insulation material such as expanded polystyrene or expanded polypropylene for sealing the gaps between the vacuum insulation materials, and urethane insulation material.

Furthermore, in this example, the outer periphery of the second heat storage tank 40 is the same as the outer periphery of the first step 31, and the inner periphery of the second heat storage tank 40 is the same as the outer periphery of the second step 32, but this is not limited to this example. For example, the first heat storage tank 30 may be formed without a step, and the second heat storage tank 40 may be arranged to cover the upper side of the side of the first heat storage tank 30.

[Operation of the water heater 100]
A description will be given of the operation of the water heater 100 having the above configuration. In the water heater 100 according to the first embodiment, a boiling operation, which is a heat storage operation in the water heater 100, and a hot water supply operation, which is a hot water supply operation in the water heater 100, are performed.

(Heating operation (heat storage operation))
The boiling operation (heat storage operation) by the water heater 100 will be described. Here, a case where the fluid stored in the heat storage unit 10 is water will be described as an example. The boiling operation is an operation in which low-temperature water is boiled to a high temperature by the heating device 2, and the boiled water is stored in the heat storage unit 10. The boiling operation is mainly performed during times when electricity is cheap, such as late-night power hours, or when the amount of stored heat in the heat storage unit 10 has decreased.

When the boiling operation starts, in the heating device 2, the low-temperature, low-pressure gas refrigerant is compressed by the compressor 21 and discharged as a high-temperature, high-pressure gas refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor 21 flows into the heating heat exchanger 22, where it exchanges heat with the water flowing through the boiling circuit, condenses while releasing heat, and becomes a high-pressure liquid refrigerant that flows out of the heating heat exchanger 22.

The high-pressure liquid refrigerant flowing out of the heating heat exchanger 22 is depressurized by the pressure reducing device 23 to become a low-temperature, low-pressure, two-phase gas-liquid refrigerant. The low-temperature, low-pressure, two-phase gas-liquid refrigerant flows into the heat absorption heat exchanger 24, where it exchanges heat with air taken in by a fan (not shown), absorbs heat, evaporates, and becomes a low-pressure gas refrigerant, which is then drawn into the compressor 21.

Meanwhile, in the heat storage tank unit 1, the heating device pump 11 is driven, causing the water stored in the lower part of the first heat storage tank 30 of the heat storage section 10 to flow out from the lower piping 34. The water flowing out of the first heat storage tank 30 is sucked into the suction side of the heating device pump 11, pressurized and pumped out.

Water pumped from the heating device pump 11 flows into the heating heat exchanger 22 of the heating device 2 via piping 3. The water that flows into the heating heat exchanger 22 exchanges heat with the refrigerant flowing through the refrigerant side flow path to become high-temperature water, which flows out of the heating heat exchanger 22. The high-temperature water that flows out of the heating heat exchanger 22 flows into the upper part of the first heat storage tank 30 via piping 4 and upper piping 33.

When boiling operation is performed, the water stored in the lower part of the first heat storage tank 30 is low-temperature water at about 10°C, depending on the season. In seasons when city water is about 10°C, the temperature is about 10°C. Meanwhile, in the heating device 2, the temperature of the refrigerant discharged from the compressor 21 is about 90°C. Therefore, the water passing through the heating heat exchanger 22 during boiling operation flows into the first heat storage tank 30 in a state where its temperature has risen to about 65°C through heat exchange with the refrigerant.

The high-temperature water that flows into the first heat storage tank 30 heats the heat storage material in the second heat storage tank 40 through the wall surface of the first heat storage tank 30. In other words, the first heat storage tank 30 and the second heat storage tank 40 function as a heat exchanger.

Here, when the amount of heat stored in the heat storage material provided in the second heat storage tank 40 is small, i.e., when the temperature of the heat storage material is low, the heat of the water that flows into the first heat storage tank 30 is largely absorbed by the heat storage material of the second heat storage tank 40. Therefore, the temperature of the water that flows into the first heat storage tank 30 drops significantly.

In this way, the temperature of the heat storage material in the second heat storage tank 40 gradually increases due to the repeated flow of heated water into the first heat storage tank 30. Then, when the temperature of the heat storage material reaches close to its melting point, the amount of heat exchange between the first heat storage tank 30 and the second heat storage tank 40 decreases. Therefore, the water that flows into the first heat storage tank 30 is stored in the first heat storage tank 30 while maintaining a high temperature.

When the boiling operation is performed, high temperature water is stored at the top of the heat storage section 10, and low temperature water is stored at the bottom. Temperature stratification is also formed between the top and bottom. As the boiling operation progresses, the amount of boiling increases, the area of high temperature water becomes larger, and the temperature stratification approaches the bottom. Then, the temperature of the water stored at the bottom rises, and the inlet water temperature of the water flowing into the heating heat exchanger 22 of the heating device 2 gradually rises.

In a typical hot water heater, when the temperature of the water entering the heat pump unit, which stores the required amount of heat or acts as a heating device, rises, the performance of the heat pump unit decreases. When the performance of the heat pump unit decreases, the heating operation is stopped.

In contrast, in the water heater 100 according to the first embodiment, the temperature of the water that flows into the first heat storage tank 30 during boiling operation is reduced by heat transfer to the second heat storage tank 40. As a result, the temperature of the water flowing out of the heat storage unit 10 is lower than the temperature of water flowing out of a conventional heat storage unit relative to the amount of heat stored in the heat storage unit 10, and therefore the deterioration of the performance of the heating device 2 can be suppressed.

(Hot water supply operation (hot water supply operation))
The following describes the hot water supply operation (hot water supply action) performed by the water heater 100. The hot water supply operation is an operation for sending water (hot water) at a set hot water supply temperature from the hot water supply pipe 6 so that water (hot water) at a desired temperature can be used for showering, filling a bathtub, washing the face, and the like.

When a user commands hot water supply operation and sets the hot water supply temperature, the opening of the mixing valve 14 is adjusted so that the temperature of a temperature sensor installed downstream of the mixing valve 14 becomes the set hot water supply temperature. Then, when the user turns on the faucet or the like and city water or other water flows into the heat storage tank unit 1 from the water supply pipe 5, the hot water supply pump 12 is driven.

When the hot water supply pump 12 is driven, the water stored in the first heat storage tank 30 flows out from the upper piping 33 and flows into the primary flow path of the heat exchanger 13. The water that flows into the primary flow path of the heat exchanger 13 exchanges heat with the water flowing through the secondary flow path to become low-temperature water or medium-temperature water, and flows out of the heat exchanger 13. At this time, the water that flows out of the first heat storage tank 30 raises the temperature of the water flowing through the secondary flow path to high temperatures, for example, 40°C or higher, through heat exchange in the heat exchanger 13. The water that flows out of the heat exchanger 13 is sucked into the suction side of the hot water supply pump 12, pressurized, and sent. The water sent from the hot water supply pump 12 flows into the lower part of the first heat storage tank 30 via the lower piping 34.

Meanwhile, the water flowing in from the water supply pipe 5 is branched within the heat storage tank unit 1. At this time, one of the branched water flows into the second inlet of the mixing valve 14 via the heat exchanger 13, and the other branched water flows into the secondary flow path of the heat exchanger 13.

The water that flows into the secondary flow path of the heat exchanger 13 exchanges heat with the water flowing through the primary flow path to become high-temperature water, which then flows out of the heat exchanger 13. The water that flows out of the heat exchanger 13 flows into the first inlet of the mixing valve 14. In the mixing valve 14, the water that flows into the first inlet and the water that flows into the second inlet are mixed, and the mixed water flows out of the outlet at the set hot water temperature.

The heat storage state of the heat storage unit 10 during hot water supply operation (hot water supply operation) will be described. When the heat storage operation is completed, a temperature stratification is formed in the first heat storage tank 30 of the heat storage unit 10, with the upper part being approximately 65°C and the lower part being approximately 10°C, which is the temperature of city water. In other words, the water in the first heat storage tank 30 becomes colder from the top to the bottom, and the lowermost part is approximately the same as the inlet water temperature to the heating device 2 at the end of the heat storage operation.

Here, the initial hot water supply state is defined as a state in which the heat of the water stored in the first heat storage tank 30 is sufficiently transferred to the second heat storage tank 40, and the heat storage material in the second heat storage tank 40 changes phase to a liquid state and is maintained at 65°C.

When hot water supply operation is performed in the initial hot water supply state, the water flowing out of the upper pipe 33 of the first heat storage tank 30 is high temperature water at approximately 65°C, i.e., the highest temperature in the heat storage state. By continuing the hot water supply operation from this initial hot water supply state, the water in the first heat storage tank 30 is pushed up from the bottom to the top. Therefore, the temperature of the water in the upper part of the first heat storage tank 30 decreases as the hot water supply operation continues.

However, in the first embodiment, when the temperature of the water in the upper part of the first heat storage tank 30 drops and becomes equal to or lower than the temperature of the heat storage material in the second heat storage tank 40, the heat of the heat storage material in the second heat storage tank 40 is transferred to the water in the first heat storage tank 30. This causes the temperature of the water in the upper part of the first heat storage tank 30 to rise. Therefore, in the region of the second step 32 of the first heat storage tank 30, heat is replenished from the second heat storage tank 40 as the temperature of the water drops.

Here, the first heat storage tank 30 and the second heat storage tank 40 are formed separately. Therefore, even if the first heat storage tank 30 or the second heat storage tank 40 is damaged by corrosion and a hole is formed, the fluids in the two tanks will not mix. Therefore, in the first embodiment, it is possible to prevent the heat storage material of the second heat storage tank 40 from being mixed into the water flowing out of the first heat storage tank 30.

In this way, in the hot water heater 100 according to the first embodiment, the heat storage unit 10 that stores heat is composed of the first heat storage tank 30 and the second heat storage tank 40, and in addition to storing heat using a fluid, a latent heat storage material with a higher heat storage density than a fluid such as water is used. Therefore, when storing the same amount of heat as in the past, the heat storage unit 10 can be made smaller.

In addition, in the first embodiment, the heat stored in the first heat storage tank 30 is supplied to the second heat storage tank 40, so that the temperature of the fluid heated by the heat pump, which is the heating device 2, can be lowered. Therefore, the deterioration of the heat pump's performance can be suppressed, and the deterioration of the energy-saving performance can be suppressed.

As described above, in the hot water heater 100 according to the first embodiment, the first heat storage tank 30 and the second heat storage tank 40 constituting the heat storage unit 10 are formed separately. Therefore, even if the second heat storage tank 40 is damaged due to corrosion or the like and the heat storage material inside leaks out, it is possible to prevent the heat storage material from mixing with the fluid in the first heat storage tank 30. Furthermore, it is possible to prevent the heat storage material from mixing with the water supply.

In addition, in the hot water heater 100, the heat storage section 10 is formed of the first heat storage tank 30 and the second heat storage tank 40, and when the heated fluid flows into the first heat storage tank 30, heat is exchanged between the fluid and the heat storage material of the second heat storage tank 40, and the heat is stored in the second heat storage tank 40. As a result, the temperature of the fluid stored in the first heat storage tank 30 decreases, so that the temperature rise of the fluid supplied to the heating device 2 caused by repeated heat storage operations is suppressed while storing heat. Therefore, the deterioration of the performance of the heat pump, which is the heating device 2, can be suppressed, and the deterioration of energy-saving performance can be suppressed.

Embodiment 2.
Next, a description will be given of the present embodiment 2. The water heater 100 according to the present embodiment 2 differs from the embodiment 1 in the structure of the heat storage unit 10. In the present embodiment 2, the same reference numerals are used for the parts common to the embodiment 1, and detailed description will be omitted.

The water heater 100 according to the second embodiment is the same as the first embodiment described above, except for the structure of the heat storage section 10 provided in the heat storage tank unit 1. Therefore, the structure of the heat storage section 10 provided in the heat storage tank unit 1 of the water heater 100 will be described below.

[Structure of heat storage section 10]
Fig. 5 is a perspective view showing an example of the structure of the heat storage unit according to the second embodiment. Fig. 6 is a top view showing an example of the structure of the heat storage unit according to the second embodiment. Fig. 7 is a cross-sectional view taken along line B-B of the heat storage unit shown in Fig. 6. As shown in Figs. 5 to 7, the heat storage unit 10 is made up of a first heat storage tank 30 and a second heat storage tank 40A formed separately from the first heat storage tank 30.

The second heat storage tank 40A is formed to cover and abut the side and top surface of the second step 32 of the first heat storage tank 30. The outer periphery of the second heat storage tank 40A is formed to have the same dimensions as the outer periphery of the first step 31 of the first heat storage tank 30, as in the first embodiment. The inner periphery of the second heat storage tank 40A is formed to have the same dimensions as the outer periphery of the second step 32 of the first heat storage tank 30, as in the first embodiment.

A hole 41 penetrating in the height direction (z direction) is formed in the center of the top surface of the second heat storage tank 40 at a position corresponding to the upper piping 33 of the first heat storage tank 30. As a result, when the first heat storage tank 30 and the second heat storage tank 40 are combined, the upper piping 33 of the first heat storage tank 30 protrudes upward so as to penetrate the hole 41.

The upper surface of the second stage 32 is the area where the most heat is dissipated. Therefore, by covering it with the second heat storage tank 40 in this manner, the insulation performance is improved compared to the conventional method, and the dissipation of the stored heat can be suppressed.

[Modification of heat storage section 10]
Fig. 8 is a cross-sectional view taken along line B-B of a modified example of the heat storage unit shown in Fig. 6. As shown in Fig. 8, in the modified example of the heat storage unit 10 according to the second embodiment, the upper surface of the second step portion 32B in the first heat storage tank 30 is tapered from the center of the upper surface. In addition, the inner periphery of the upper surface of the second heat storage tank 40B is tapered so as to fit the upper surface of the second step portion 32B of the first heat storage tank 30. These tapered shapes are formed so as to be inclined at about 5° with respect to the width direction (x direction) and the depth direction (y direction).

The latent heat storage material in the second heat storage tank 40 undergoes a phase change from the upper side when it exchanges heat with the water flowing into the first heat storage tank 30. Therefore, by forming the contact surfaces on the upper surfaces of the first heat storage tank 30 and the second heat storage tank 40 in a tapered shape, it is possible to reduce stress generated in the tank.

As described above, in the hot water heater 100 according to the second embodiment, the first heat storage tank 30 is covered and abutted on the top surface of the second stage 32 in addition to the side surface of the second stage 32 by the second heat storage tank 40. This improves the insulation performance of the top surface of the second stage 32, where the most heat is dissipated, and suppresses the dissipation of stored heat.

Although the present embodiments 1 and 2 have been described above, the present disclosure is not limited to the above-mentioned embodiments 1 and 2, and various modifications and applications are possible within the scope of the gist of the present disclosure. For example, it is desirable that the second heat storage tank 40 is arranged so as to cover the upper part of the first heat storage tank 30, but this is not limited thereto, and the second heat storage tank 40 may be arranged in the middle or lower part of the first heat storage tank 30. By arranging the second heat storage tank 40 in this manner, the effects of the present embodiments 1 and 2 can be achieved.

However, the fluid in the first heat storage tank 30 is thermally stratified such that the upper part is hot and the lower part is cold, and such thermal stratification becomes even more pronounced when hot water is supplied. In addition, when supplying hot water, the fluid in the upper part of the first heat storage tank 30 is supplied to the heat exchanger 13, so it is desirable to supply heat from the second heat storage tank 40 to the upper part of the first heat storage tank 30.

In addition, in the water heater 100 of embodiments 1 and 2, the case where paraffin is used as the latent heat storage material for the second heat storage tank 40 has been described, but this is not limited to this, and other latent heat storage materials may be applied as long as they have a melting point near the heat storage temperature.

Furthermore, the heat storage material is not limited to a latent heat storage material, and a sensible heat storage material may be used. In this case, a similar effect can be achieved as long as the temperature of the fluid in the first heat storage tank 30 is high in heat storage density.

Furthermore, although the heat storage unit 10 has been described as being formed in a rectangular parallelepiped shape, this is not limited thereto, and it may be formed in a cylindrical shape, for example. By making the configuration other than the shape the same as in the first and second embodiments, the above-mentioned effects can be achieved, and although this reduces the degree of freedom in the installation space of the heat storage unit 10, it is possible to improve the pressure resistance performance.

In addition, in the first and second embodiments, the first heat storage tank 30 and the second heat storage tank 40 are described as being made of stainless steel, but this is not limited to this example. The first heat storage tank 30 and the second heat storage tank 40 may be made of a material other than stainless steel as long as the material is not corroded by the heat storage material inside. For example, materials that are not corroded by the heat storage material include iron, nickel-chromium alloys, and resins. However, it is desirable that the portions where the first heat storage tank 30 and the second heat storage tank 40 come into contact with each other be made of a material with high thermal conductivity.

1 Heat storage tank unit, 2 Heating device, 3, 4 Piping, 5 Water supply pipe, 6 Hot water supply pipe, 10 Heat storage section, 11 Heating device pump, 12 Hot water supply pump, 13 Heat exchanger, 14 Mixing valve, 21 Compressor, 22 Heating heat exchanger, 23 Pressure reducing device, 24 Heat absorption heat exchanger, 30 First heat storage tank, 31 First stage, 32, 32B Second stage, 33 Upper pipe, 34 Lower pipe, 40, 40A Second heat storage tank, 41 Hole, 100 Hot water heater.

Claims (9)

A water heater comprising a heating device that heats a fluid, and a heat storage tank unit that stores heat by storing the fluid heated by the heating device, the water heater performing a boiling operation in which the fluid heated by the heating device is stored in the heat storage tank unit, and a hot water supply operation in which hot water is supplied by utilizing the heat stored in the heat storage tank unit,
The heat storage tank unit includes:
A heat storage unit that stores the heated fluid ;
An upper pipe provided on an upper portion of the heat storage unit;
A lower pipe provided at a lower part of the heat storage unit;
A heat exchanger provided outside the heat storage unit ,
The heat storage unit is
a first heat storage tank into which the fluid heated during the boiling operation flows;
a second heat storage tank that contains a heat storage material different from the fluid, is formed separately from the first heat storage tank, and is disposed in contact with the first heat storage tank;
The heat exchanger performs heat exchange between the fluid flowing in from the first heat storage tank and a fluid flowing in from a water supply pipe,
When the fluid heated in the boiling operation flows into the heat storage section, heat is stored in the second heat storage tank by heat exchange between the fluid in the first heat storage tank and the heat storage material of the second heat storage tank,
In the hot water supply operation, the fluid stored in the first heat storage tank flows from the upper pipe into the heat exchanger, where the temperature is reduced, and then flows into the lower part of the first heat storage tank through the lower pipe and circulates,
The first heat storage tank comprises:
A first step portion formed on the lower side;
a second step portion formed on the upper side and having a cut surface smaller than that of the first step portion when cut along a horizontal plane;
The second heat storage tank comprises:
A water heater arranged to cover and abut the side surface of the second stage. The second heat storage tank comprises:
The water heater according to claim 1 , further comprising a second step portion disposed to cover and abut against an upper surface of the second step portion. 3. The hot water heater according to claim 2, wherein a contact surface between the second step portion of the first heat storage tank and the second heat storage tank on the upper surface thereof is formed in a tapered shape. The second heat storage tank comprises:
The water heater according to any one of claims 1 to 3, further comprising a latent heat storage material housed therein. The second heat storage tank comprises:
The water heater according to claim 4, wherein paraffin is contained as the latent heat storage material. The water heater according to any one of claims 1 to 5, wherein a thermally conductive material is disposed on an abutting surface between the first heat storage tank and the second heat storage tank. A water heater as described in any one of claims 1 to 6, wherein the contact surface between the first heat storage tank and the second heat storage tank is formed with a plate thickness thinner than other surfaces of the first heat storage tank and the second heat storage tank. The second heat storage tank comprises:
The water heater according to any one of claims 1 to 7, wherein fins are formed inside the water heater so as to extend from an inner periphery to an outer periphery. In the boiling operation, the fluid stored in the first heat storage tank flows out from the lower pipe, is heated by the heating device, and flows into the upper part of the first heat storage tank through the upper pipe.
The water heater according to any one of claims 1 to 8.

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