Fuel cell waste heat utilization system

Abstract

This system provides a fuel cell waste heat utilization system that effectively transfers heat without disrupting the temperature stratification of the hot water storage tank. [Solution] The first fuel cell unit located in the first dwelling unit and the second fuel cell unit located in the second dwelling unit are each equipped with a fuel cell N, a hot water storage tank T for storing hot water heated by the waste heat of the fuel cell N, a temperature sensor S for detecting the temperature of the hot water in the hot water storage tank T, a control unit H4 for controlling the supply and discharge of hot water in the hot water storage tank T, and a determination unit H2. The control unit H4 of the first fuel cell unit and the second fuel cell unit perform heat exchange control to supply hot water from the first hot water storage tank T to the second hot water storage tank T through the hot water pipe 31. In the heat exchange control, if the value obtained by subtracting the temperature detected by the third temperature sensor 33 from the temperature detected by the second temperature sensor S1 is greater than or equal to a preset value, the control unit H4 is configured not to supply hot water to the upper part of the second hot water storage tank.

Description

Technical Field

[0001] The present invention relates to a fuel cell waste heat utilization system.

Background Art

[0002] Conventionally, a fuel cell (a reforming type fuel cell system) is known which generates hydrogen from carbohydrates contained in fuels such as city gas and kerosene by a reformer and performs power generation by chemically reacting the generated hydrogen with air.

[0003] In a household fuel cell, since heat is generated together with power generation, a hot water supply unit can be configured by effectively using the heat energy to improve energy efficiency. Since a fuel cell with a large output generates a large amount of waste heat, it is important to effectively utilize this waste heat from the viewpoint of energy efficiency. As a general use destination of the waste heat of a fuel cell, there is a case where the waste heat is accumulated as hot water in a hot water storage tank and used for hot water supply.

[0004] From the viewpoint of effective utilization of heat, a system for heat exchange among a plurality of households is also known. Among them, there are a method of directly sending hot water from a hot water storage tank to a hot water storage tank (for example, see Patent Document 1) and a method of providing a heat exchanger in a hot water storage tank and heating the water in the hot water storage tank through the heat exchanger (for example, see Patent Document 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] When heat is exchanged with other units, heat loss occurs in the piping as water is sent through the pipes to the other units' hot water storage tanks. If the water whose temperature has dropped due to heat loss is sent to the other units' hot water storage tanks, it will be like pouring low-temperature water (e.g., 40°C) into a high-temperature water (e.g., 60°C), which may disrupt the temperature stratification of the hot water storage tank and result in inefficient heat exchange.

[0007] This invention has been made in view of the above-mentioned problems, and its purpose is to provide a fuel cell waste heat utilization system that effectively transfers heat without disrupting the temperature stratification of the hot water storage tank. [Means for solving the problem]

[0008] The characteristic configuration of the fuel cell waste heat utilization system of the present invention is a first fuel cell unit having a first fuel cell located in a first dwelling unit that generates electricity by supplying fuel, a first hot water storage tank that stores hot water heated by the waste heat of the first fuel cell, a first temperature sensor that detects the temperature of the hot water at the bottom of the first hot water storage tank, a first control unit that controls the supply and discharge of hot water in the first hot water storage tank, and a first determination unit that determines whether the amount of heat in the first hot water storage tank can be transferred to other dwelling units based on the temperature detected by the first temperature sensor, and a second unit located in a second dwelling unit that supplies fuel A second fuel cell that generates more electricity, a second hot water storage tank that stores hot water heated by the waste heat of the second fuel cell, a second temperature sensor that detects the temperature of the hot water at the top of the second hot water storage tank, a second control unit that controls the supply and discharge of hot water in the second hot water storage tank, a second heat quantity detection unit that detects the amount of heat in the second hot water storage tank, a second determination unit that determines whether the amount of heat in the second hot water storage tank is insufficient to meet the demand of the second dwelling based on the amount of heat in the second hot water storage tank detected by the heat quantity detection unit, and a circuit connecting the top and bottom of the second hot water storage tank. The system comprises a second fuel cell unit having a heat exchanger for heat dissipation that exchanges heat from the hot water to a heat dissipation circuit connected to a heating waste heat utilization terminal, a hot water pipe communicating the upper part of the first hot water storage tank, the upper part of the second hot water storage tank, and the heat exchanger for heat dissipation, and a third temperature sensor that detects the temperature of the hot water passing through the hot water pipe near the second tank, wherein the first determination unit determines that the amount of heat in the first hot water storage tank is transferable, and the second determination unit determines that the amount of heat in the second hot water storage tank is insufficient to meet the demand of the second dwelling unit. When determined by the above, the first control unit and the second control unit are configured to perform heat exchange control to supply hot water from the first hot water storage tank to at least one of the second hot water storage tank and the heat exchanger for heat dissipation through the hot water supply pipe. In the heat exchange control, if the value obtained by subtracting the temperature detected by the third temperature sensor from the temperature detected by the second temperature sensor is greater than or equal to a preset value, the first control unit and the second control unit are configured not to supply hot water from the first hot water storage tank to the upper part of the second hot water storage tank through the hot water supply pipe.

[0009] According to the above-described configuration, the first hot water storage tank installed in the first dwelling unit, the second hot water storage tank installed in the second dwelling unit, and the heat exchanger for heat dissipation are connected via a hot water supply pipe. Furthermore, the system is configured to allow the exchange of hot and cold water between the first hot water storage tank, the second hot water storage tank, and the heat exchanger for heat dissipation. Therefore, when the first hot water storage tank is full, it becomes possible to supply hot water to at least one of the second hot water storage tank and the heat exchanger for heat dissipation, thereby sharing the heat. Consequently, when hot water is supplied from the first hot water storage tank to the second hot water storage tank, if the temperature of the hot water has decreased due to heat dissipation in the supply pipe and flows into the upper part of the second hot water storage tank, disrupting the temperature stratification within the second hot water storage tank, the supply of hot water from the first hot water storage tank to the upper part of the second hot water storage tank is stopped, and instead, hot water is supplied to the heat exchanger for heat dissipation, etc., to exchange heat, thereby suppressing the disruption of the temperature stratification within the second hot water storage tank.

[0010] A further characteristic feature of the fuel cell waste heat utilization system of the present invention is that, in the heat exchange control, if the value obtained by subtracting the temperature detected by the third temperature sensor from the temperature detected by the second temperature sensor is less than a preset value, the first control unit and the second control unit are configured to supply the hot water in the first hot water storage tank only to the upper part of the second hot water storage tank through the hot water supply pipe.

[0011] According to the above characteristic configuration, when transferring heat from the first hot water storage tank, if supplying hot water to the upper part of the second hot water storage tank does not disrupt the temperature stratification within the second hot water storage tank, then it becomes possible to transfer heat only to the second hot water storage tank.

[0012] A further characteristic configuration of the fuel cell waste heat utilization system of the present invention is that the first fuel cell unit is equipped with a first prediction unit that calculates the estimated required heat amount in the first hot water storage tank within a preset time, and a first heat quantity detection unit that detects the heat amount in the first hot water storage tank, and the first determination unit is configured to determine whether or not the heat amount in the first hot water storage tank can be shared with other dwelling units based on the heat amount in the first hot water storage tank detected by the first heat quantity detection unit and the estimated required heat amount calculated by the first prediction unit.

[0013] According to the above feature configuration, the estimated amount of heat required for use in the first dwelling unit is calculated. Therefore, the first determination unit can accurately determine whether or not the amount of heat in the first hot water storage tank can be shared with other dwelling units.

[0014] A further characteristic configuration of the fuel cell waste heat utilization system of the present invention is that the second fuel cell unit is equipped with a second prediction unit that calculates the estimated required heat amount in the second hot water storage tank within a preset time, and the second determination unit is configured to determine whether the heat amount in the second hot water storage tank is insufficient for the demand in the second dwelling unit, based on the heat amount in the second hot water storage tank detected by the second heat amount detection unit and the estimated required heat amount calculated by the second prediction unit.

[0015] According to the above feature configuration, the estimated required heat amount for use in the second dwelling unit is calculated. Therefore, the second determination unit can accurately determine whether or not there is insufficient heat in the first hot water storage tank.

[0016] A further characteristic configuration of the fuel cell waste heat utilization system of the present invention is that a water supply channel branching from the hot water supply pipe is provided, communicating with the upper part of the first hot water storage tank and the central and lower parts of the second hot water storage tank; the second hot water storage tank is provided with a water supply temperature sensor provided near the water supply inlet, which is the connection point between the second hot water storage tank and the water supply channel; and a storage unit that stores the usage history of the waste heat utilization terminal in the second dwelling unit; and in the heat exchange control, if the value obtained by subtracting the temperature detected by the third temperature sensor from the temperature detected by the second temperature sensor is equal to or greater than the preset value, Furthermore, the system is configured such that, if the second determination unit determines from the usage history recorded in the storage unit that there is no plan to use heating in the second dwelling unit, and the difference between the temperature detected by the third temperature sensor and the temperature detected by the central temperature sensor of the water supply temperature sensor is less than or equal to a set value, hot water is supplied to the central water outlet of the water supply unit; and if the temperature detected by the central temperature sensor of the water supply temperature sensor is lower than the temperature detected by the third temperature sensor and the difference is greater than or equal to a set value, hot water is supplied to the lower water outlet of the water supply unit.

[0017] According to the above-described configuration, when heat is transferred from the first hot water storage tank to the second hot water storage tank, if the temperature difference between the temperature of the hot water supplied from the first hot water storage tank detected by the third temperature sensor and the temperature of the hot water in the upper part of the second hot water storage tank is greater than or equal to a preset value, and there are no plans to use heating in the second dwelling unit, then hot water can be supplied from the first hot water storage tank to the central or lower part of the second hot water storage tank, and heat can be transferred from the first hot water storage tank without disrupting the temperature stratification of the second hot water storage tank.

[0018] A further characteristic feature of the fuel cell waste heat utilization system of the present invention is that it is equipped with a storage unit that stores the usage history of the waste heat utilization terminal in the second dwelling unit, and in the heat exchange control, when the value obtained by subtracting the temperature detected by the third temperature sensor from the temperature detected by the second temperature sensor is equal to or greater than the preset value, and when the second determination unit determines from the usage history stored in the storage unit that there is a plan to use heating in the second dwelling unit, it is configured to supply hot water to the heat exchanger for heat dissipation.

[0019] According to the above configuration, when heat is transferred from the first hot water storage tank to the second hot water storage tank, if the temperature difference between the temperature of the hot water supplied from the first hot water storage tank detected by the third temperature sensor and the temperature of the hot water at the top of the second hot water storage tank is greater than or equal to the set value, and heating is planned to be used in the second dwelling unit, then hot water can be supplied from the first hot water storage tank to the heat exchanger for heat dissipation, and heat can be transferred from the first hot water storage tank without disrupting the temperature stratification of the second hot water storage tank.

[0020] A further characteristic configuration of the fuel cell waste heat utilization system of the present invention is that it is equipped with a storage unit that stores the usage history of the waste heat utilization terminal in the second dwelling unit, a second prediction unit that predicts the usage time period of the waste heat utilization terminal based on the usage history stored in the storage unit, and a second control unit that sets the pre-heating operation start time to a set time before the start time of the usage time period and executes pre-heating operation at a temperature lower than the heating set temperature.

[0021] According to the above-described configuration, when hot water is supplied to a heat exchanger after heat has been released through the hot water pipe and its temperature has dropped, even if the temperature of the hot water is low and the heating operation is performed at a temperature below the set temperature, a pre-heating operation at a temperature lower than the heating set temperature can be performed, and the hot water can be effectively utilized even if the temperature drops in the hot water pipe during heat exchange.

[0022] A further characteristic configuration of the fuel cell waste heat utilization system of the present invention is provided with a return path connected from the heat exchanger for heat dissipation to the lower part of the first hot water storage tank. When heat transfer is performed from the first hot water storage tank to the heat exchanger for heat dissipation through a hot water pipe, the hot water and steam heat-exchanged in the heat exchanger for heat dissipation are configured to return from the heat exchanger for heat dissipation through the return path to the lower part of the first hot water storage tank.

[0023] According to the above characteristic configuration, by performing heat transfer from the first hot water storage tank to the heat exchanger for heating in the second household, the amount of water in the first hot water storage tank decreases, but the amount of water in the first hot water storage tank can be maintained by returning it from the heat exchanger for heating to the first hot water storage tank.

Brief Description of the Drawings

[0024] [Figure 1] It is a block diagram showing a fuel cell system. [Figure 2] It is a diagram showing the transfer of hot water and steam from the first hot water storage tank to the second hot water storage tank. [Figure 3] It is a flowchart showing determination control and the like for performing heat transfer control. [Figure 4] It is a diagram showing the estimated required consumption of the amount of heat consumed per day in a household.

Modes for Carrying Out the Invention

[0025] 〔Embodiment〕 Hereinafter, an embodiment of the fuel cell waste heat utilization system of the present invention will be described based on the drawings.

[0026] (Overall Configuration of Fuel Cell) As shown in Figure 1, the fuel cell unit 1 is equipped with a power generation module M and a hot water storage tank T. The power generation module M is a module with a fuel cell N as its core, and the fuel cell N generates electricity by supplying hydrogen. High-temperature heat is emitted from the fuel cell N. Therefore, in the waste heat recovery heat exchanger K, the waste heat from the fuel cell N heats the hot water, and this hot water is stored in the hot water storage tank T. The hot water stored in the hot water storage tank T is supplied as hot water for kitchens, bathrooms, washbasins, etc. in the dwelling. In addition, the hot water stored in the hot water storage tank T is used as a heat source for waste heat utilization terminals D (e.g., floor heating panels, bath reheating, bathroom dryers, bathroom heaters, etc.). Waste heat utilization terminals D correspond to "waste heat utilization terminals".

[0027] As shown in Figure 1, the indoor distribution board 3 is connected to a power supply line 2 for the power load 100, a power receiving line 4A from a power company or other power source 4, and a power transmission line 5 from the fuel cell N.

[0028] The fuel cell N in this embodiment is a polymer electrolyte fuel cell, configured to generate electricity using hydrogen as fuel and receiving oxygen. Hydrogen is supplied from a hydrogen supply source G. Alternatively, a raw material gas containing hydrocarbons such as city gas may be supplied from the hydrogen supply source G, and the fuel cell N may have a configuration in which the raw material gas is reformed in a reformer to produce hydrogen.

[0029] A power converter 6 is installed in the transmission line 5 from the fuel cell N. The power converter 6 is equipped with an inverter for grid connection and adjusts the power generated by the fuel cell N to the same voltage and frequency as the power supplied from the power source 4. Therefore, the power from the power source 4 and the power generated by the fuel cell N are supplied to the power load 100.

[0030] A heat recovery heat exchanger K is installed in the power generation module M. The heat recovery heat exchanger K recovers waste heat from the fuel cell N. The hot water heated in the heat recovery heat exchanger K creates a temperature stratification of the hot water in the hot water storage tank T.

[0031] The fuel cell unit 1 of this embodiment is equipped with a control unit H4. The control unit H4 controls the entire control system of the fuel cell unit 1, including the operation of the fuel cell N. A remote control R is connected to the control unit H4. The remote control R is equipped with a power generation remote control R1 and a temperature control remote control R2. The power generation remote control R1 issues commands to start and stop the operation of the fuel cell N. The temperature control remote control R2 issues various commands such as commands to start and stop floor heating operation, setting target temperatures for hot water supply, and commands for hot water supply to the bath. Thus, the control unit H4 is configured to control the operation of the fuel cell unit 1 based on commands from the remote control R.

[0032] (Fuel cell cooling configuration) A fuel cell N consists of multiple cells C stacked on top of each other. A solid polymer electrolyte membrane is formed in each cell C, sandwiched between a fuel electrode and an oxygen electrode. As the fuel cell N generates electricity, the cells C generate heat. To cool the cells C, a cooling section 7 is placed between two adjacent cells C. The cooling section 7 has a cooling water channel. Cooling water circulation paths 8 are connected to the inlet and outlet of the cooling water channel. The material used to make up the cooling water channel is a conductive and porous material, such as a carbon plate.

[0033] The cooling water circulation path 8 is equipped with a cooling water circulation pump 10 for circulating the cooling water, a water tank 11 for storing the cooling water, a water treatment device 12, and a waste heat recovery heat exchanger K. When cooling water flows through the cooling water passage of the cooling section 7, the cooling water is supplied to the solid polymer electrolyte membrane through the fuel electrode. This promotes heat exchange between the cooling water and the solid polymer electrolyte membrane, and the temperature of cell C is cooled to an appropriate temperature (e.g., 80°C).

[0034] In the cooling water circulation path 8, a waste heat recovery heat exchanger K is provided downstream of the cooling section 7. The cooling water, whose temperature has risen as it passes through the cooling section 7, flows into the waste heat recovery heat exchanger K. In other words, the heat from the cells C recovered in the cooling section 7 is recovered (supplied) by the waste heat recovery heat exchanger K as waste heat from the fuel cell N.

[0035] A water treatment device 12 is installed downstream of the water tank 11 in the cooling water circulation path 8. The cooling water supplied from the water tank 11 may contain electrolytes and impurities that do not dissolve in water. Therefore, the cooling water supplied from the water tank 11 is purified by the water treatment device 12. The water treatment device 12 is equipped with, for example, an adsorbent capable of adsorbing organic matter present in the cooling water, and an ion exchange resin capable of removing ions dissolved in the cooling water.

[0036] (Hot water storage configuration in a hot water storage tank) As described above, the waste heat from the fuel cell N is recovered (supplied) by the waste heat recovery heat exchanger K. The recovered waste heat from the fuel cell N is stored in the hot water in the hot water storage tank T. As shown in Figure 1, a hot water circulation path 13 is connected to the bottom and top of the hot water storage tank T. A heat storage circulation pump 14 and the waste heat recovery heat exchanger K are provided in the middle of the hot water circulation path 13. The hot water circulation path 13 has a forward path 13a connecting the bottom of the hot water storage tank T and the waste heat recovery heat exchanger K, and a return path 13b connecting the waste heat recovery heat exchanger K and the top of the hot water storage tank T. The heat storage circulation pump 14 is provided in the forward path 13a.

[0037] The heat storage circulation pump 14 draws hot water from the bottom of the hot water storage tank T into the supply path 13a, and the hot water is returned to the top of the hot water storage tank T via the waste heat recovery heat exchanger K. In the waste heat recovery heat exchanger K, the cooling water in the cooling water circulation path 8 is cooled, and the hot water in the hot water flow circulation path 13 is heated. In other words, the hot water in the hot water storage tank T is drawn in from the bottom of the hot water storage tank T, heated by the waste heat of the fuel cell N, and then circulates through the hot water flow circulation path 13, returning to the top of the hot water storage tank T. As a result, a temperature stratification is formed inside the hot water storage tank T, with the temperature increasing towards the top.

[0038] A chilled water sensor 15 is provided upstream of the heat storage circulation pump 14 in the outbound path 13a. The chilled water sensor 15 detects the temperature of the hot water drawn in from the bottom of the hot water storage tank T. In addition, a hot water sensor 16 is provided in the return path 13b. The hot water sensor 16 detects the temperature of the hot water heated in the heat recovery heat exchanger K.

[0039] The temperature detected by the hot water sensor 16 is the temperature of the high-temperature layer in the temperature stratification inside the hot water storage tank T. The control unit H4 uses the temperature detected by the cold water sensor 15 as feedforward information and controls the rotation speed of the heat storage circulation pump 14 so that the temperature detected by the hot water sensor 16 reaches the target temperature (for example, 60°C). Note that different target temperatures may be automatically set depending on the season, such as summer, winter, or the transitional season. Alternatively, the target temperature may be manually set by the user operating the remote control R.

[0040] A hot water outlet passage 17 is connected to the top of the hot water storage tank T. The hot water stored in the hot water storage tank T is supplied through the hot water outlet passage 17 to hot water consumption points (kitchen, washbasin, bath, etc.) such as hot water taps 18.

[0041] A water supply channel 19 is connected to the bottom of the hot water storage tank T. The water supply channel 19 is a water source such as a municipal water supply. When the hot water stored in the hot water storage tank T is discharged to the outlet channel 17, water is supplied to the bottom of the hot water storage tank T from the water supply channel 19. At this time, the flow of hot water to the hot water tap 18 etc. through the outlet channel 17 is carried out using the water supply pressure in the water supply channel 19. In other words, when the hot water tap 18 etc. is opened, the hot water in the hot water storage tank T is pushed out by the water supply pressure in the water supply channel 19 to the outlet channel 17 connected to the top of the hot water storage tank T and discharged to the hot water tap 18 etc.

[0042] In this embodiment, an auxiliary heat source unit 20 is provided in the middle of the hot water outlet path 17. If the temperature of the hot water supplied from the hot water storage tank T is lower than the required temperature of the hot water consumption point, the hot water is heated by the auxiliary heat source unit 20.

[0043] The hot water storage tank T is equipped with three temperature sensors S for detecting the temperature of the stored hot water: an upper temperature sensor S1, an upper / lower central temperature sensor S2, and a lower temperature sensor S3. The upper temperature sensor S1 is located at the top of the hot water storage tank T. The upper / lower central temperature sensor S2 is located at the upper / lower central part of the hot water storage tank T. The lower temperature sensor S3 is located at the bottom of the hot water storage tank T. The lower temperature sensor S3 is located above the bottom of the hot water storage tank T. Based on the detection information from the temperature sensors S, the control unit H4 can detect the temperature of the hot water in the hot water storage tank T across the upper and lower parts. The temperature sensors S correspond to the "first temperature sensor," the "second temperature sensor," the "first heat quantity detection unit," and the "second heat quantity detection unit."

[0044] A hot water consumption circuit 24 is connected to the upper and lower parts of the hot water storage tank T. A consumption circulation pump 25 and a heat exchanger 23 are provided in the middle of the hot water consumption circuit 24. As shown in Figure 1, the hot water consumption circuit 24 has a hot water supply passage 24a connecting the upper part of the hot water storage tank T to the heat exchanger 23, a return passage 24b connected to the lower part of the hot water storage tank T, and a return passage 24c connecting the heat exchanger 23 to the return passage 24b. In other words, each hot water storage tank T is connected to the return passage 24c via the return passage 24b. A consumption circulation pump 25 is provided in the hot water supply passage 24a. When the consumption circulation pump 25 is driven, hot water is drawn from the upper part of the hot water storage tank T to the hot water supply passage 24a by the consumption circulation pump 25, and the hot water is returned to the lower part of the hot water storage tank T via the heat exchanger 23. A shut-off valve 34 is provided in the middle of the return path 24b.

[0045] A heat transfer medium circulation path 26 is connected to the heat exchanger 23. A heat transfer medium circulation pump 27 is installed in the middle of the heat transfer medium circulation path 26. The heat transfer medium between the heat exchanger 23 and the waste heat utilization terminal D circulates in the heat transfer medium circulation path 26. In the heat exchanger 23, the hot water in the hot water storage tank T is cooled, and the heat transfer medium in the heat transfer medium circulation path 26 is heated.

[0046] A flow sensor 28 is provided in the hot and cold water supply path 24a. A return temperature detection sensor 29 is provided in the return path 24b. The flow sensor 28 detects the flow rate (flow rate per unit time) of the hot and cold water flowing through the hot and cold water consumption circuit 24. The return temperature detection sensor 29 detects the temperature of the hot and cold water flowing through the return path 24b.

[0047] Furthermore, the control unit H4 is configured to perform a hot water consumption process that controls the operation of the consumption circulation pump 25 by circulating hot water through the hot water consumption circuit 24 at a set target flow rate, and when performing the hot water consumption process, it is also configured to perform a heating circulation process that circulates the heat medium through the heat medium circulation path 26.

[0048] When the underfloor heating, bath reheating, bathroom heating, etc. are operated, the control unit H4 activates the consumption circulation pump 25 and the heat transfer medium circulation pump 27 of the waste heat utilization terminal D. In addition, the control unit H4 controls the operation (rotation speed) of the consumption circulation pump 25 based on the detection result of the flow sensor 28 in order to circulate hot water in the hot water consumption circuit 24 at a set target flow rate. As a result, the heat energy of the hot water stored in the hot water storage tank T is consumed.

[0049] A drain channel 21 is connected to the upper and lower center of the hot water storage tank T. A drain valve 22 is provided in the drain channel 21 to open and close it. The drain valve 22 discharges the hot water from the hot water storage tank T.

[0050] (A system that supplies hot water from a storage tank to other dwelling units.) As described above, the waste heat from the fuel cell N is stored in the hot water in the hot water storage tank T, and the hot water in the hot water storage tank T is used as hot water for supply and as a heat source for the waste heat utilization terminal D. However, if the hot water supply and the waste heat utilization terminal D are not used much while the fuel cell N is operating continuously, not only the hot water in the upper part of the hot water storage tank T but also the hot water in the lower part of the hot water storage tank T will become hot. When the hot water at the bottom of the hot water storage tank T becomes hot, this hot water flows into the waste heat recovery heat exchanger K, making it impossible to cool the cooling water in the cooling water circulation path 8. As a result, the cells C of the fuel cell N cannot be properly cooled, which may lead to problems such as the fuel cell N failing. This problem becomes particularly apparent during the summer months when the demand for hot water is low.

[0051] One possible solution to this problem is to install a radiator in the supply path 13a of the hot and cold water circulation path 13. However, radiators tend to occupy a large area, making them difficult to adopt in dwellings where space conservation is required.

[0052] As another means of solving the above problem, this embodiment is configured to allow the hot water from the hot water storage tank T to be shared with other dwelling units. As shown in Figures 1 and 2, a fusion passage 30 is connected to the top of the hot water storage tank T1, and the fusion passage 30 is connected to a hot water supply pipe 31. In other words, each hot water storage tank T is connected to the hot water supply pipe 31 via the fusion passage 30. A hot water temperature sensor 33 is also provided at the connection point between the fusion passage 30 and the hot water supply pipe 31.

[0053] A three-way valve 32 is provided in the melting passage 30. The melting passage 30 has a melting passage 30a that branches off from the three-way valve 32a and connects from the hot water supply pipe 31 to the upper part of the hot water storage tank T, a melting passage 30b that connects from the hot water supply pipe 31 to the hot water consumption circuit 24, and a melting passage 30c that branches off from the melting passage 30b and connects to the upper and lower central part and the lower part of the hot water storage tank T, with a three-way valve 32b provided in the middle of the melting passage 30b. An upper and lower central temperature sensor S2 and a lower temperature sensor S3 are provided near the water inlet 37, which is the connection point between the melting passage 30c and the hot water storage tank T. The upper and lower central temperature sensor S2 corresponds to the "water supply temperature sensor".

[0054] A supply pump 35 is provided in the melting passage 30a. When the supply pump 35 is driven, it draws hot water from the top of the hot water storage tank T into the melting passage 30, and the hot water is supplied to other dwelling units via the hot water supply pipe 31.

[0055] A supply flow sensor 36 is provided in the melting passage 30b. The supply flow sensor 36 detects the flow rate (flow rate per unit time) of hot water flowing through the melting passage 30b. The control unit H4 then executes a hot water supply process that controls the operation of the supply pump 35 in a manner that circulates hot water through the melting passage 30 at a set target flow rate, and is configured to also execute a heating circulation process that circulates the heat medium through the heat medium circulation passage 26 when executing the hot water supply process.

[0056] (A system that supplies hot water from a storage tank to other dwelling units.) The fuel cell waste heat utilization system is a diagram showing the transfer of hot water from storage tank T1 to storage tank T2, and includes a fuel cell unit 1 (first fuel cell unit) located in the first dwelling unit, which has a first fuel cell that generates electricity when fuel is supplied, a storage tank T1 (first storage tank) that stores hot water heated by the waste heat of the first fuel cell, a lower temperature sensor S3 (first temperature sensor) that detects the temperature of the hot water at the bottom of the storage tank T1, a control unit H4 (first control unit) that controls the supply and discharge of hot water in the storage tank T1, and a determination unit H2 (first determination unit) that determines whether the amount of heat in the storage tank T1 can be transferred to another dwelling unit based on the temperature detected by the lower temperature sensor S3, and a second fuel cell located in the second dwelling unit that generates electricity when fuel is supplied, a storage tank T2 (second storage tank) that stores hot water heated by the waste heat of the second fuel cell, and an upper temperature sensor that detects the temperature of the hot water at the top of the storage tank T2. The fuel cell unit 1 (second fuel cell unit) includes: a sensor S1 (second temperature sensor); a control unit H4 (second control unit) that controls the supply and discharge of hot water in the hot water storage tank T2; a temperature sensor S (second heat quantity detection unit) that detects the amount of heat in the hot water storage tank T2; a determination unit H2 (second determination unit) that determines whether the amount of heat in the hot water storage tank T2 is insufficient for the demand in the second dwelling based on the amount of heat in the hot water storage tank T2 detected by the temperature sensor S; and a heat exchanger 23 for heat dissipation that performs heat exchange from the hot water passing through a circuit connecting the top and bottom of the hot water storage tank T2 to a heat dissipation circuit connected to a heating waste heat utilization terminal; a hot water passage pipe 31 that communicates the top of the hot water storage tank T1, the top of the hot water storage tank T2, and the heat exchanger 23; and a hot water temperature sensor 33 (third temperature sensor) that is positioned at the connection between the melting passage 30 connected to the hot water storage tank T2 and the hot water passage pipe 31 and detects the temperature of the hot water passing through the hot water passage pipe 31. Figure 2 is a schematic diagram of a fuel cell waste heat utilization system, omitting the first fuel cell, second fuel cell, control unit H4, and determination unit H2 from the above configuration.

[0057] As shown in Figure 2, the upper part of the hot water storage tank T1 is connected to the hot water storage tank T2 and heat exchanger 23 of another dwelling unit via a fusion passage 30 and a hot water supply pipe 31 to which the fusion passage 30 is connected. The lower part of the hot water storage tank T1 and the lower part of the hot water storage tank T2 and the heat exchanger 23 are connected via return passages 24b and 24c, respectively. When hot water is to be exchanged from the hot water storage tank T1 to another dwelling unit, the supply pump 35 of the fusion passage 30 connected to the hot water storage tank T1 is driven, supplying hot water to the hot water storage tank T2 and heat exchanger 23 of the other dwelling unit. After supplying the hot water, it is returned to the lower part of the hot water storage tank T1 from the lower part of the hot water storage tank T2 or from the heat exchanger 23 via return passages 24b and 24c.

[0058] The operation of the fuel cell waste heat utilization system is described below. Figure 3 is a flowchart showing the decision control and other steps for performing heat exchange control. When the lower temperature sensor S3 detects a temperature above a preset level (e.g., 40°C or higher) (Step #01: Yes), the prediction unit H1 calculates the estimated required heat amount in the hot water storage tank T within a preset first set time (e.g., within 6 hours). The memory unit H3 records the start time of use and the amount of hot and cold water used by the waste heat utilization terminal D for the past week, on an hourly basis. The prediction unit H1 calculates the estimated required heat amount to be used in the dwelling within the first set time based on the past usage history of the waste heat utilization terminal D stored in the memory unit H3 (Step #02). Figure 4 shows the amount of hot water supplied to the bath and the estimated daily required heat amount used by the waste heat utilization terminal D for each time period. Note that Figure 4 may also show the amount of hot water supplied to the bath and the usage history of the waste heat utilization terminal D stored in the memory unit H3. Furthermore, the prediction unit H1 calculates the total amount of heat that will be generated within the first set time by the waste heat from the fuel cell N. (Step #03) The prediction unit H1 corresponds to the "first prediction unit" and the "second prediction unit".

[0059] The determination unit H2 (first determination unit) determines whether the heat in the hot water storage tank T (first hot water storage tank T1) can be shared with other dwelling units based on the total heating amount calculated from the current heat storage amount of the hot water storage tank T calculated from the temperature detected by the temperature sensor S (first heat quantity detection unit) and the waste heat of the fuel cell N, and the estimated required heat amount calculated by the prediction unit H1 (first prediction unit) (step #04). If the determination in step #4 is Yes, the control unit H4 transmits information indicating that heat can be shared to the control unit H4 of the fuel cell unit 1 of the other dwelling unit, and proceeds to step #5. If the determination in step #4 is No, the heat in the hot water storage tank T (first hot water storage tank T1) is used in the dwelling unit itself (step #06).

[0060] If the amount of heat in the hot water storage tank T (first hot water storage tank T1) can be shared with other dwelling units (Step #04: Yes), the control unit H4 (first control unit) determines whether or not it is necessary to share heat with other dwelling units (Step #05). In other words, in Step #04, the control unit H4 (first control unit) determines whether or not it has received information from the control unit H4 of the fuel cell unit 1 of the other dwelling unit indicating that there is a need to share heat.

[0061] If the determination in step #05 is Yes, the control unit H4 of the fuel cell unit 1 of the other dwelling unit described later starts heat exchange control (step #13). If the determination in step #05 is No, the control unit H4 (first control unit) executes control to open the drain valve 22 of the drain channel 21 (step #07). As a result, hot water is drained from the hot water storage tank T to the outside. Due to the control in step #07, cold water is supplied from the water supply channel 19 to the bottom of the hot water storage tank T. This allows the cold water to flow to the waste heat recovery heat exchanger K, and the cells C of the fuel cell N can be properly cooled.

[0062] If the temperature detected by the lower temperature sensor S3 is below a preset temperature (e.g., 40°C) (Step #01: No), the prediction unit H1 calculates the estimated amount of heat required in the hot water storage tank T within a preset second time period (e.g., within 1 hour). In other words, the prediction unit H1 calculates the estimated amount of heat required to be consumed in the dwelling within that second time period based on past performance data stored in the memory unit H3 (Step #08). The prediction unit H1 also calculates the total amount of heat that will be generated by the waste heat from the fuel cell N to heat the hot water in the hot water storage tank T within that second time period (Step #09).

[0063] The determination unit H2 (second determination unit) determines whether the amount of heat in the hot water storage tank T (second hot water storage tank T2) is insufficient to meet the demand of the dwelling unit (second dwelling unit) based on the temperature detected by the temperature sensor S (second heat quantity detection unit), the total amount of heat generated by the waste heat of the fuel cell N, and the estimated required heat amount calculated by the prediction unit H1 (second prediction unit) (step #10). If the determination in step #10 is Yes, the control unit H4 (second control unit) transmits information indicating the need for heat exchange to the control unit H4 of the fuel cell unit 1 of the other dwelling unit.

[0064] If the amount of heat in the hot water storage tank T (second hot water storage tank T2) is insufficient to meet the demand of the dwelling unit (second dwelling unit) (Step #10: Yes), the control unit H4 (second control unit) determines whether there is a hot water storage tank T that can provide heat to the other dwelling unit (Step #11). In other words, in Step #11, the control unit H4 (second control unit) determines whether it has received information from the control unit H4 of the fuel cell unit 1 of the other dwelling unit indicating that heat exchange is possible.

[0065] If the amount of heat in the hot water storage tank T (second hot water storage tank T2) is sufficient to meet the demand of the dwelling unit (second dwelling unit) (Step #10: No), or if there is no other hot water storage tank T that can provide heat to other dwelling units (Step #11: No), then normal operation will continue (Step #12).

[0066] If the control unit H4 (second control unit) determines that heat exchange is possible from another dwelling unit (step #11: Yes), the supply of hot and cold water is started from the hot water storage tank T (first hot water storage tank T1) of the other dwelling unit that can exchange heat through the hot water supply pipe 31 (step #13). The control unit H4 (second control unit) then determines whether the value obtained by subtracting the temperature detected by the hot water supply temperature sensor 33 (third temperature sensor) at the connection between the hot water supply pipe 31 and the melting passage 30 from the temperature detected by the upper temperature sensor S1 (second temperature sensor) of the hot water storage tank T is equal to or greater than a preset temperature (for example, 10°C or higher) (step #14). If the determination in step #14 is Yes, the control unit H4 (second control unit) executes control to open the three-way valve 32a so that hot and cold water flows only through the melting passage 30b. As a result, if the temperature of the hot water used for circulation drops due to heat dissipation as it passes through the hot water supply pipe 31, the supply of hot water to the upper part of the hot water storage tank T (second hot water storage tank T2) is stopped, thereby preventing the collapse of the temperature stratification inside the hot water storage tank T (second hot water storage tank T2).

[0067] If the determination in step #14 is No, the control unit H4 (second control unit) controls the three-way valve 32a to open in a direction that allows hot water to flow only into the melting passage 30a (step #16). In other words, if the temperature difference of the supplied hot water is smaller than a preset value, hot water can be supplied to the upper part of the hot water storage tank T without disrupting the temperature stratification. The prediction unit H1 (second prediction unit) predicts the usage time periods for the floor heating panel and bathroom heating among the waste heat utilization terminals D, based on the usage history of the waste heat utilization terminals D stored in the memory unit H3. The control unit H4 (second control unit) determines whether or not to use heating within a preset time (for example, within 30 minutes) based on the heating usage time period predicted by the prediction unit H1 (second prediction unit) (step #15).

[0068] If it is determined that there is a planned use of floor heating panels or bathroom heating among the waste heat utilization terminals D (Step #15: Yes), the control unit H4 (second control unit) executes control to open the three-way valve 32 so that hot water flows only through the melting passage 30b (Step #17). As a result, hot water is supplied directly to the heat exchanger 23 for heat dissipation from the hot water storage tank T of other dwelling units. Furthermore, as a result of the control in Step #17, the control unit H4 (second control unit) executes control to start a pre-heating operation at a temperature lower than the heating set temperature, with a pre-heating operation start time set at a preset time (for example, 30 minutes before) from the heating usage time period predicted by the prediction unit H1 (second prediction unit).

[0069] The hot water that has undergone heat exchange in the heat dissipation heat exchanger 23 is returned via the return path 24c to the bottom of the hot water storage tank T of the other dwelling unit that supplied the hot water (step #18).

[0070] If the determination in step #15 is No, the control unit H4 (second control unit) executes control to open the three-way valve 32 so that hot water flows only into the melting passage 30c (step #19). If the difference between the temperature detected by the hot water temperature sensor 33 (third temperature sensor) and the temperature of the upper and lower central temperature sensor S2 inside the hot water storage tank T (second hot water storage tank T2) is less than or equal to a preset temperature, the control unit H4 (second control unit) executes control to supply hot water to the central water outlet 37a, which is the connection point between the central part of the hot water storage tank (second hot water storage tank T2) and the melting passage 30c. If the temperature of the upper and lower central temperature sensor S2 inside the hot water storage tank T (second hot water storage tank T2) is lower than the temperature detected by the hot water temperature sensor 33 (third temperature sensor), and the difference is greater than or equal to a preset temperature, the control unit H4 (second control unit) executes control to supply hot water to the lower water outlet 37b, which is the connection point between the lower part of the hot water storage tank (second hot water storage tank T2) and the melting passage 30c.

[0071] In the hot water storage tank T of the other dwelling units that receive hot and cold water, the lower part of the hot water storage tank T is replenished with cold water from the water supply channel 19 by the control in steps #16 and #19.

[0072] Thus, when supplying hot water from the hot water storage tank T (first hot water storage tank T1) of one fuel cell unit 1 to the hot water storage tank T (second hot water storage tank T2) of the other fuel cell unit 1, the control unit H4 (first control unit) of one fuel cell unit 1 and the control unit H4 (second control unit) of the other fuel cell unit 1 are configured to perform a transfer control to supply the hot water in the first hot water storage tank T1 to the second hot water storage tank T2 and the heat exchanger 23 for heat dissipation through the hot water supply pipe 31. One fuel cell unit 1 corresponds to the "first fuel cell unit". The other fuel cell unit 1 corresponds to the "second fuel cell unit".

[0073] In other words, when the first hot water storage tank is full, it becomes possible to supply hot water to at least one of the second hot water storage tank and the heat exchanger for heat dissipation, thereby sharing the heat. As a result, when hot water is supplied from the first hot water storage tank to the second hot water storage tank, if the temperature of the hot water decreases due to heat dissipation in the hot water pipe and flows into the upper part of the second hot water storage tank, causing the temperature stratification inside the second hot water storage tank to collapse, the supply of hot water from the first hot water storage tank to the upper part of the second hot water storage tank will not be stopped, and instead, hot water will be supplied to the heat exchanger for heat dissipation, etc., to exchange heat and prevent the temperature stratification inside the second hot water storage tank from collapsing.

[0074] (Another embodiment) The present invention is not limited to the configurations exemplified in the embodiments described above, and other representative embodiments of the present invention are described below.

[0075] (1) The forward path 13a of the hot water circulation path 13 may have parallel paths, one that branches off to the radiator and one that does not branch off to the radiator. In this case, when the temperature of the hot water flowing through the forward path 13a rises above a predetermined temperature, the hot water may flow into the radiator before flowing into the heat recovery heat exchanger K.

[0076] (2) In the above embodiment, when heat is exchanged, if the difference in the temperature of the exchanged hot water detected by the hot water temperature sensor 33 (third temperature sensor) with respect to the upper temperature sensor S1 (second temperature sensor) of the hot water storage tank T (second hot water storage tank T2) is less than a preset value, the hot water is supplied only to the upper part of the hot water storage tank T (second hot water storage tank T2). The embodiment is not limited to this, and the heat may be exchanged to the heat exchanger through the heat exchange passage 30b.

[0077] (3) In the embodiments described above, a polymer electrolyte fuel cell was used as an example of fuel cell N, but the same can be implemented when, for example, a solid oxide fuel cell is used as fuel cell N. Also, although numerical values ​​such as temperature were given as examples, these can be changed.

[0078] Furthermore, the configurations disclosed in the above embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with configurations disclosed in other embodiments, as long as no inconsistencies arise. Moreover, the embodiments disclosed herein are illustrative, and the embodiments of the present invention are not limited thereto, and can be modified as appropriate without departing from the object of the present invention. [Industrial applicability]

[0079] This invention is applicable to fuel cell waste heat utilization systems. [Explanation of Symbols]

[0080] 1: Fuel cell unit (First fuel cell unit, Second fuel cell unit) 23: Heat exchanger for heat radiation 26: Heat medium circulation path (heat radiation circuit) 30: Flexible path 31:Hot water pipe 32: Three-way valve 33: Hot water temperature sensor (third temperature sensor) 34: Shut-off valve 37: Water inlet D: Heat dissipation terminal H1: Prediction unit (First prediction unit, Second prediction unit) H2: Judgment part (first judgment part, second judgment part) H3: Storage section H4: Control Unit (First Control Unit, Second Control Unit) N: Fuel cell (first fuel cell, second fuel cell) S: Temperature sensor (first temperature sensor, second temperature sensor, first heat quantity detection unit, second heat quantity detection unit) T: Hot water storage tanks (first hot water storage tank, second hot water storage tank) T1: First hot water storage tank T2: Second hot water storage tank

Claims

1. A first fuel cell unit comprising: a first fuel cell located in a first dwelling unit that generates electricity by supplying fuel; a first hot water storage tank that stores hot water heated by the waste heat of the first fuel cell; a first temperature sensor that detects the temperature of the hot water at the bottom of the first hot water storage tank; a first control unit that controls the supply and discharge of hot water in the first hot water storage tank; and a first determination unit that determines whether the amount of heat in the first hot water storage tank can be transferred to other dwelling units based on the temperature detected by the first temperature sensor; A second fuel cell unit comprising: a second fuel cell located in the second dwelling unit that generates electricity by supplying fuel; a second hot water storage tank that stores hot water heated by the waste heat of the second fuel cell; a second temperature sensor that detects the temperature of the hot water at the top of the second hot water storage tank; a second control unit that controls the supply and discharge of hot water in the second hot water storage tank; a second heat quantity detection unit that detects the amount of heat in the second hot water storage tank; a second determination unit that determines whether the amount of heat in the second hot water storage tank is insufficient to meet the demand in the second dwelling unit based on the amount of heat in the second hot water storage tank detected by the second heat quantity detection unit; and a heat exchanger for heat dissipation that exchanges heat from the hot water passing through a circuit connecting the top and bottom of the second hot water storage tank to a heat dissipation circuit connected to a waste heat utilization terminal. The system includes a hot water pipe connecting the upper part of the first hot water storage tank, the upper part of the second hot water storage tank, and the heat exchanger for heat dissipation, and a third temperature sensor for detecting the temperature of the hot water passing through the hot water pipe near the second hot water storage tank. When the first determination unit determines that the amount of heat in the first hot water storage tank is transferable, and the second determination unit determines that the amount of heat in the second hot water storage tank is insufficient to meet the demand of the second dwelling unit, the first control unit and the second control unit are configured to perform heat transfer control, which involves supplying hot water from the first hot water storage tank to at least one of the second hot water storage tank and the heat exchanger for heat dissipation through the hot water supply pipe. In the heat exchange control described above, if the value obtained by subtracting the temperature detected by the third temperature sensor from the temperature detected by the second temperature sensor is greater than or equal to a preset value, the first control unit and the second control unit are configured not to supply the hot water in the first hot water storage tank to the upper part of the second hot water storage tank through the hot water supply pipe in the fuel cell waste heat utilization system.

2. In the heat exchange control, if the value obtained by subtracting the temperature detected by the third temperature sensor from the temperature detected by the second temperature sensor is less than the preset value, the first control unit and the second control unit are configured to supply the hot water in the first hot water storage tank only to the upper part of the second hot water storage tank through the hot water supply pipe, as described in claim 1.

3. The first fuel cell unit is equipped with a first prediction unit that calculates the estimated required heat amount in the first hot water storage tank within a preset time, and a first heat amount detection unit that detects the heat amount in the first hot water storage tank. The fuel cell waste heat utilization system according to claim 1, wherein the first determination unit is configured to determine whether or not the heat in the first hot water storage tank can be shared with other dwelling units based on the heat amount in the first hot water storage tank detected by the first heat amount detection unit and the estimated required heat amount calculated by the first prediction unit.

4. The second fuel cell unit is equipped with a second prediction unit that calculates the estimated required amount of heat in the second hot water storage tank within a preset time period. The fuel cell waste heat utilization system according to claim 1, wherein the second determination unit is configured to determine whether the amount of heat in the second hot water storage tank is insufficient for the demand in the second dwelling unit, based on the amount of heat in the second hot water storage tank detected by the second heat quantity detection unit and the estimated required heat amount calculated by the second prediction unit.

5. The first hot water storage tank is provided with a water supply channel branched from the hot water supply pipe, which communicates with the upper part of the first hot water storage tank and the central and lower parts of the second hot water storage tank. The second hot water storage tank is provided with a water supply temperature sensor located near the water outlet, which is the connection point between the second hot water storage tank and the water supply channel, and a storage unit that stores the usage history of the waste heat utilization terminal in the second dwelling unit. In the heat exchange control, if the value obtained by subtracting the temperature detected by the third temperature sensor from the temperature detected by the second temperature sensor is greater than or equal to the preset value, and the second determination unit records the data in the storage unit. The fuel cell waste heat utilization system according to claim 1, which is configured such that, if it is determined from the usage history that there is no plan to use heating in the second dwelling unit, and the difference between the temperature detected by the third temperature sensor and the temperature detected by the central temperature sensor of the water supply temperature sensor is less than or equal to a preset value, hot water is supplied to the central water inlet of the water supply channel, and if the temperature detected by the central temperature sensor of the water supply temperature sensor is lower than the temperature detected by the third temperature sensor and the difference is greater than or equal to a preset value, hot water is supplied to the lower water inlet of the water supply channel.

6. The fuel cell waste heat utilization system according to claim 1, further comprising a storage unit for storing the usage history of the waste heat utilization terminal in the second dwelling unit, and configured such that, in the heat exchange control, when the value obtained by subtracting the temperature detected by the third temperature sensor from the temperature detected by the second temperature sensor is equal to or greater than the preset value, and the second determination unit determines from the usage history stored in the storage unit that there is a plan to use heating in the second dwelling unit, hot water is supplied to the heat exchanger for heat dissipation.

7. The fuel cell waste heat utilization system according to claim 4, further comprising a storage unit for storing the usage history of the waste heat utilization terminal in the second dwelling unit, a second prediction unit for predicting the usage time period of the waste heat utilization terminal from the usage history stored in the storage unit, and a second control unit configured to start preheating operation at a temperature lower than the heating set temperature, with the preheating operation start time set to a preheating operation start time before the set start time of the usage time period.

8. A return path is provided from the heat exchanger for heat dissipation to the lower part of the first hot water storage tank. The fuel cell waste heat utilization system according to claim 1, wherein when heat is transferred from the first hot water storage tank to the heat dissipation heat exchanger through the hot water supply pipe, the hot water that has undergone heat exchange in the heat dissipation heat exchanger is configured to return from the heat dissipation heat exchanger to the lower part of the first hot water storage tank through the return path.

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