Fuel cell system

Abstract

A fuel cell system (11) comprises: a fuel cell (16); an external water flow path (81) through which externally supplied water flows; a first heat exchange section (13) that is positioned either proximate to the outer side of the fuel cell or inside the fuel cell, to allow the water from the external water flow path to collect heat generated by the fuel cell; a hot-water supply flow path (12) that supplies heated water to the outside; a first heat exchange flow path (82) that is connected to the external water flow path and passes through the first heat exchange section; and a first water flow path (83) that connects the external water flow path and the hot-water supply flow path. The hot-water supply flow path, the first heat exchange flow path, and the first water flow path converge in a converging section (70) which is configured such that water vapor inside the first heat exchange flow path can be liquified to flow through the hot-water supply flow path.

Description

fuel cell system CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Japanese Patent Application No. 2022-130781 (filed August 18, 2022), the entire disclosure of which is incorporated herein by reference.

[0002] The present disclosure relates to fuel cell systems.

[0003] BACKGROUND ART A domestic cogeneration system is known that generates electricity using a fuel cell, recovers heat emitted from the fuel cell, and uses the recovered heat to heat and supply city water (see Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2002-298863

[0005] (1) A fuel cell system according to one embodiment of the present disclosure includes a fuel cell; an external water flow path through which water supplied from the outside flows; a first heat exchange unit located close to the outside of the fuel cell or located inside the fuel cell, which causes water from the external water flow path to recover heat generated by the fuel cell; a hot water supply flow path that supplies heated water to the outside; a first heat exchange flow path connected to the external water flow path and passing through the first heat exchange unit; and a first water flow path that connects the external water flow path and the hot water supply flow path, and the junction where the hot water supply flow path, the first heat exchange flow path, and the first water flow path converge is configured so that water vapor inside the first heat exchange flow path is liquefied and flows through the hot water supply flow path.

[0006] (2) As one embodiment of the present disclosure, in (1), the confluence section has a water storage section for storing water, a water inlet connected to the first water flow path, and a water outlet connected to the hot water supply flow path, and is configured so that at least a portion of the first heat exchange flow path is inside the water storage section.

[0007] (3) As one embodiment of the present disclosure, in (1) or (2), a bypass flow path is provided that connects the external water flow path and the first water flow path.

[0008] (4) As one embodiment of the present disclosure, in any one of (1) to (3), a second water flow path is provided that connects the hot water supply flow path to the upstream side of the connection part of the external water flow path with the first water flow path.

[0009] (5) As an embodiment of the present disclosure, in any one of (1) to (4), the external water flow path has a second heat exchange portion that exchanges heat with exhaust gas discharged from the fuel cell.

[0010] (6) As an embodiment of the present disclosure, in any one of (1) to (5), the water heater further includes a cooling / heating device that heats or cools water flowing through the hot water supply passage.

[0011] (7) As an embodiment of the present disclosure, in (4), a third water flow path between the first water flow path and the second water flow path, connecting the external water flow path and the hot water supply flow path, and a cooling / heating device for heating or cooling water flowing through the third water flow path. The external water flow path may further include a second heat exchanger for exchanging heat with exhaust gas discharged from the fuel cell.

[0012] (8) A fuel cell system according to an embodiment of the present disclosure comprises: a fuel cell; an external water flow path through which water supplied from the outside flows; a first heat exchange unit located adjacent to the outside of the fuel cell or located inside the fuel cell, and causing water from the external water flow path to recover heat generated by the fuel cell; a hot water supply flow path that supplies heated water to the outside; a first heat exchange flow path connected to the external water flow path and passing through the first heat exchange unit; a first water flow path connecting the external water flow path and the hot water supply flow path; a bypass flow path connecting the external water flow path and the first water flow path; a second water flow path connecting the hot water supply flow path to the upstream side of the connection part of the external water flow path with the first water flow path; a third water flow path located between the first water flow path and the second water flow path, and connecting the external water flow path and the hot water supply flow path; and a control device. The junction where the hot water supply flow path, the first heat exchange flow path, and the first water flow path join is configured so that water vapor inside the first heat exchange flow path is liquefied and flows through the hot water supply flow path, and the control device controls water from the external water flow path to flow through at least one of the first heat exchange flow path, the bypass flow path, the first water flow path, the second water flow path, and the third water flow path depending on the operation of the fuel cell and the demand for hot water supply.

[0013] (9) As one embodiment of the present disclosure, in (8), when the fuel cell is stopped, the control device controls at least one of the first water flow path, the second water flow path, and the third water flow path to allow water to flow in response to a request for hot water supply.

[0014] (10) As one embodiment of the present disclosure, in (8) or (9), a cooling and heating device is provided that heats or cools the water flowing through the hot water supply flow path or the water flowing through the third water flow path, and the control device controls the cooling and heating device to heat according to the temperature of the heated water supplied to the outside when the fuel cell is operating or stopped and there is a continuous demand for hot water supply.

[0015] (11) As one embodiment of the present disclosure, in any of (8) to (10), the fuel cell has a cooling and heating device that heats or cools the water flowing through the hot water supply flow path or the water flowing through the third water flow path, and the control device controls the bypass flow path so that water flows when the fuel cell is operating and there is no demand for hot water supply, controls the water from the hot water supply flow path so that it flows through the second water flow path or the third water flow path to the external water flow path, and controls the cooling and heating device so that it cools.

[0016] (12) As an embodiment of the present disclosure, in any one of (8) to (11), when the fuel cell is operating and there is a demand for hot water supply, the control device controls the first heat exchange flow path to allow water to flow, and controls the second water flow path or the third water flow path as necessary to allow water to flow.

[0017] FIG. 1 is a schematic configuration diagram of a fuel cell system according to an embodiment of the present disclosure. FIG. 2 is a structural diagram schematically showing the internal configuration of a fuel cell. FIG. 3 is a diagram schematically showing the configuration of a junction section. FIG. 4 is a diagram for explaining control performed by a control device. FIG. 5 is a diagram for explaining control performed by a control device. FIG. 6 is a diagram for explaining control performed by a control device. FIG. 7 is a diagram for explaining control performed by a control device. FIG. 8 is a diagram for explaining control performed by a control device. FIG. 9 is a schematic configuration diagram of a fuel cell system according to an embodiment of the present disclosure.

[0018] Hereinafter, a fuel cell system according to an embodiment of the present disclosure will be described with reference to the drawings. In each drawing, identical or corresponding parts are designated by the same reference numerals. In the following description of the embodiment, the description of identical or corresponding parts will be omitted or simplified as appropriate. Furthermore, the drawings are schematic. The dimensional ratios and the like in the drawings do not necessarily correspond to the actual ones.

[0019] 1, a fuel cell system 11 according to one embodiment of the present disclosure includes a plurality of flow paths through which water flows, a heat exchange unit, a fuel cell 16, a cooling / heating device 22, and a control device 35. The fuel cell system 11 is installed in, for example, a home.

[0020] The fuel cell 16 may include a reformer and a cell stack. The fuel cell 16 may be a fuel cell module containing the reformer and the cell stack within a housing. The reformer generates fuel such as hydrogen by causing a steam reforming reaction between gas supplied as raw fuel and water. The cell stack is, for example, a solid oxide fuel cell (SOFC) and generates electricity through an electrochemical reaction using an oxidizer such as oxygen contained in the air and fuel produced by the reformer. The fuel cell 16 generates heat during power generation operation. The cell stack also generates water through the electrochemical reaction. Unreacted fuel and unreacted oxidant discharged from the cell stack are combusted to provide energy for the steam reforming reaction in the reformer. The water discharged from the cell stack is discharged from the fuel cell 16 in a high-temperature gaseous state along with combustion gases resulting from the combustion of the unreacted fuel and unreacted oxidant. The heat generated during power generation operation and the heat of combustion are recovered using a heat transfer medium as heat generated by the fuel cell 16. Here, the cell stack may be a polymer electrolyte fuel cell (PEFC), in which case the configuration of the reformer and other components of the fuel cell 16 may be changed as appropriate.

[0021] The exhaust gas discharged from the fuel cell 16 may contain combustion gas and gaseous water. The exhaust gas discharged from the fuel cell 16 may be heat exchanged with a heat medium using the second heat exchange unit 14 described below. The exhaust gas cooled by the heat exchange may be separated into gaseous exhaust gas and condensed liquid water by a gas-liquid separator. The separated exhaust gas may be discharged outside the fuel cell system 11. The separated water may be sent to the fuel cell 16 as water to be used in the steam reforming reaction.

[0022] The fuel cell system 11 of this embodiment has multiple flow paths through which water flows, including an external water flow path 81, a hot water supply flow path 12, a first heat exchange flow path 82, a first water flow path 83, a bypass flow path 44, and a second water flow path 84.

[0023] The external water flow path 81 is a flow path through which water supplied from outside the fuel cell system 11 flows. A temperature sensor 55 for measuring the temperature of the water that enters the external water flow path 81 may be provided. A flow rate sensor 62 for measuring the amount of water that enters the external water flow path 81 may also be provided. A first flow rate adjustment valve 43 for adjusting the amount of water supplied may also be provided in the external water flow path 81. A temperature sensor 51 for measuring the temperature of the water after passing through a second heat exchanger 14 (described later) may also be provided in the external water flow path 81.

[0024] The hot water supply flow path 12 is a flow path that supplies heated water (hot water) to the outside. A temperature sensor 56 that measures the temperature of the water at the outlet of the hot water supply flow path 12 may be provided. In addition, a temperature sensor 54 that measures the temperature of the water upstream of the position of the cooling / heating device 22 may be provided.

[0025] The first heat exchange passage 82 is connected to the external water passage 81 and is a passage that passes through the first heat exchange section 13, which will be described later.

[0026] The first water flow path 83 is a flow path that connects the external water flow path 81 and the hot water supply flow path 12. The first water flow path 83 may be provided with a second flow rate adjustment valve 45 that adjusts the amount of water supplied from the external water flow path 81.

[0027] The bypass flow path 44 is a flow path that connects the external water flow path 81 and the first water flow path 83. The bypass flow path 44 and the first heat exchange flow path 82 may be connected to the external water flow path 81 by a three-way valve 31.

[0028] The second water flow path 84 is a flow path that connects the upstream side of the connection part of the external water flow path 81 with the first water flow path 83 to the hot water supply flow path 12. More specifically, the second water flow path 84 may be connected to the hot water supply flow path 12 on the downstream side of the cooling / heating device 22. The second water flow path 84 may be provided with a third flow rate adjustment valve 46 that adjusts the amount of water passing through the second water flow path 84.

[0029] In the fuel cell system 11, water from the hot water supply flow path 12 may pass through the second water flow path 84 and enter the external water flow path 81 to be circulated. A circulation pump 40 may be provided in the external water flow path 81 to increase the pressure of the water so as to circulate it.

[0030] The fuel cell system 11 according to this embodiment has a first heat exchanger 13 and a second heat exchanger 14 as heat exchangers.

[0031] The first heat exchange unit 13 may be located close to the outside of the fuel cell 16 (outside the casing 29) or inside the fuel cell 16 (inside the casing 29). When the fuel cell 16 is a PEFC, the first heat exchange unit 13 may be located close to a reformer constituting the fuel cell 16. When the first heat exchange unit 13 is located close to the outside of the fuel cell 16, it may be located so as to be in contact with the outside of the fuel cell 16. When the first heat exchange unit 13 is located inside the fuel cell 16, it may be located around at least one of the reformer 26 and the cell stack 27. In such a configuration, the first heat exchange unit 13 may be located around at least one of the reformer 26 and the cell stack 27 without any thermal insulation therebetween. 2, the first heat exchange unit 13 may be formed by providing a conduit 25 through which a medium passes around at least one of a reformer 26 and a cell stack 27 without an intervening insulating material. In the present disclosure, an insulating material is a material that prevents heat transfer, and may be, for example, a fiber-based insulating material such as glass wool, or a foam-based insulating material such as a resin foam. The fuel cell 16 may be configured such that a packing 28 made of an insulating material is located closer to the reformer 26 or the cell stack 27 than the conduit 25.

[0032] The pipe 25 for the heat medium in the first heat exchange unit 13 may be provided inside a housing 29 that surrounds at least one of the reformer 26 and the cell stack 27. In a configuration in which the pipe 25 is provided inside the housing 29, a heat insulating material 30 may be located between the pipe 25 and the housing 29. As another example, the pipe 25 may be located close to the outside of the housing 29 within a range that allows heat transfer from at least one of the reformer 26 and the cell stack 27.

[0033] The first heat exchange unit 13 recovers heat generated in the fuel cell 16 using water from the external water flow path 81. More specifically, the heat is recovered as follows: The outer surface of the pipe 25 is heated by radiation from the reformer 26 or the cell stack 27 or by convection of the surrounding gas. The first heat exchange unit 13 recovers heat by transferring heat from the outer surface to the heat medium (water) as it flows through the pipe 25.

[0034] The second heat exchange unit 14 exchanges heat with the exhaust gas discharged from the fuel cell 16 in the external water flow path 81. That is, the second heat exchange unit 14 heats the outer surface of the external water flow path 81 with the heat of the exhaust gas, and transfers the heat of the outer surface to the heat medium (water) when the heat medium flows through the external water flow path 81.

[0035] The cooling / heating device 22 is provided near the hot water supply flow path 12 and heats or cools the water flowing through the hot water supply flow path 12. The cooling / heating device 22 is a burner. As another example, the cooling / heating device 22 may be an electric heater or the like. The cooling / heating device 22 may have a fuel injection line for supplying gas fuel and an air supply line for forcibly drawing in outside air using a blower. The cooling / heating device 22 mixes the gas fuel and outside air at an ignition port and burns them. The water is heated by the combustion in the cooling / heating device 22. The cooling / heating device 22 can also cool the water by generating wind using a blower.

[0036] The junction 70 is a portion where the hot water supply flow path 12, the first heat exchange flow path 82, and the first water flow path 83 converge. The junction 70 is configured so that water vapor inside the first heat exchange flow path 82 is liquefied and flows through the hot water supply flow path 12. The junction 70 functions as a steam trap. In this embodiment, the junction 70 is configured as shown in FIG. 3 . The junction 70 has a water storage section 72 that stores water, a water inlet 73 connected to the first water flow path 83, and a water outlet 74 connected to the hot water supply flow path 12. At least a portion of the first heat exchange flow path 82 is configured to be inside the water storage section 72. Water remaining in the first heat exchange flow path 82 may be heated by the heat of the fuel cell 16 and turned into water vapor, but the water is cooled and liquefied by the water in the water storage section 72 of the junction 70. In the past, water vapor was generated in the pipes, causing the hot water supply operation to stop, but the fuel cell system 11 according to this embodiment can improve operational reliability by liquefying the water vapor at the junction 70. Here, the supply of water to the water storage unit 72 may be controlled so as to be executed when water vapor is likely to be generated.

[0037] The fuel cell system 11 may further include an expansion tank 71. The expansion tank 71 is a tank for absorbing expansion water, and is provided, for example, in the external water flow path 81. The expansion tank 71 reduces the effects of pressure fluctuations on water hammer and the hot water supply flow rate.

[0038] The control device 35 includes one or more processors and memories. The processor may include a general-purpose processor that loads a specific program to execute a specific function, and a dedicated processor specialized for a specific process. The dedicated processor may include an application-specific integrated circuit (ASIC). The processor may include a programmable logic device (PLD). The PLD may include a field-programmable gate array (FPGA). The control device 35 may be either a system-on-a-chip (SoC) or a system in a package (SiP) in which one or more processors work together. The control device 35 may control components of the fuel cell system 11, such as the cooling / heating device 22, the three-way valve 31, the circulation pump 40, the first flow control valve 43, the second flow control valve 45, and the third flow control valve 46. The control device 35 may acquire information on the operation of the fuel cell system 11, such as the operating status of the fuel cell 16 and requests for hot water supply. The control device 35 may also acquire detection data from the temperature sensor 51, the temperature sensor 54, the temperature sensor 55, the temperature sensor 56, the flow rate sensor 62, and the like.

[0039] The control device 35 controls the water from the external water flow path 81 to flow through at least one of the first heat exchange flow path 82, the bypass flow path 44, the first water flow path 83, and the second water flow path 84, depending on the operation of the fuel cell 16 and the demand for hot water supply. An example of the control will be described below with reference to the drawings. In Figures 4 to 8, arrows indicate the flow of water.

[0040] As shown in FIG. 4 , when the fuel cell 16 is operating or stopped and there is a continuous demand for hot water, the control device 35 controls the cooling / heating device 22 to heat according to the temperature of the heated water supplied to the outside. The control device 35 controls the three-way valve 31 so that water from the external water flow path 81 flows through the first heat exchange flow path 82 and is heated in the first heat exchange unit 13. For example, when the temperature detected by the temperature sensor 56 is lower than a predetermined temperature (e.g., 40° C.), the control device 35 activates the cooling / heating device 22 to heat the water. The control device 35 may adjust the heating intensity of the cooling / heating device 22 based on the temperatures detected by the temperature sensors 54 and 56, for example. The control device 35 also controls the opening degree of the three-way valve 31. The control device 35 may adjust the amount of water that flows through the first heat exchange flow path 82 and is heated in the first heat exchange section 13, and the amount of water that flows from the bypass flow path 44 through the first water flow path 83 and merges at the junction section 70, based on, for example, the operating state of the fuel cell 16 and the temperature detected by the temperature sensor 54.

[0041] As shown in Fig. 5, when the fuel cell 16 is operating and there is no demand for hot water supply, the control device 35 controls the bypass flow path 44 so that water flows, and controls the water from the hot water supply flow path 12 to flow through the second water flow path 84 to the external water flow path 81. The control device 35 switches the three-way valve 31 so that water flows into the bypass flow path 44. The control device 35 also controls the cooling / heating device 22 so that it cools. The control device 35 cools the water by generating air using the blower of the cooling / heating device 22. The control device 35 operates the circulation pump 40 to circulate the water.

[0042] When the fuel cell 16 is stopped, the control device 35 controls the cooling / heating device 22 to heat water by allowing water to flow through the first water flow path 83 or the second water flow path 84 depending on the demand for hot water. Figure 6 shows a case where the fuel cell 16 is stopped after the state shown in Figure 5. Because there is a possibility that the water remaining in the first heat exchange path 82 will be heated and turned into steam, the control device 35 controls the second flow control valve 45 to supply water to the water storage section 72 of the junction section 70.

[0043] Figure 7 shows a case where the fuel cell 16 resumes operation after the state shown in Figure 6 and a request for hot water supply is made. When the fuel cell 16 is operating and a request for hot water supply is made, the control device 35 controls the first heat exchange flow path 82 so that water flows. Furthermore, the control device 35 controls the second water flow path 84 so that water flows as needed to adjust the temperature. This allows hot water to be supplied at an appropriate temperature.

[0044] 8 shows a case where hot water supply is requested without the fuel cell 16 restarting operation. When the fuel cell 16 is stopped and hot water supply is requested, the control device 35 controls the second flow control valve 45 to allow water to flow through the first water flow path 83. The control device 35 then activates the cooling / heating device 22 to heat the water. The control device 35 may control the third flow control valve 46 to allow water to flow through the second water flow path 84 so that hot water can be supplied at an appropriate temperature.

[0045] In the fuel cell system 11 according to this embodiment configured as described above, even if the water remaining in the piping is vaporized, the water is liquefied and flows through the hot water supply flow path 12. Therefore, the fuel cell system 11 according to this embodiment can improve reliability without stopping operation due to water vaporization or the like.

[0046] 9, a fuel cell system 11 according to a second embodiment of the present disclosure further includes a third water flow path 85 as a plurality of water flow paths. Description of the same components as those in the fuel cell system 11 according to the first embodiment will be omitted.

[0047] The third water flow path 85 is located between the first water flow path 83 and the second water flow path 84, and connects the external water flow path 81 and the hot water supply flow path 12. In this embodiment, the cooling / heating device 22 is provided near the third water flow path 85, and heats or cools the water flowing through the third water flow path 85. The third water flow path 85 may be provided with a fourth flow rate adjustment valve 47 that adjusts the amount of water passing through the third water flow path 85.

[0048] In this embodiment, when the fuel cell 16 is operating and there is no demand for hot water supply, the control device 35 controls the bypass flow path 44 so that water flows, and controls the water from the hot water supply flow path 12 to flow through the third water flow path 85 to the external water flow path 81. The control device 35 switches the three-way valve 31 so that water flows into the bypass flow path 44. The control device 35 also controls the cooling / heating device 22 so that it cools. The control device 35 cools the water by generating air using the blower of the cooling / heating device 22. The control device 35 operates the circulation pump 40 to circulate the water.

[0049] In this embodiment, when the fuel cell 16 is stopped, the control device 35 controls at least one of the first water flow path 83, the second water flow path 84, and the third water flow path 85 to allow water to flow in response to a request for hot water supply.

[0050] In this embodiment, when the fuel cell 16 restarts operation after being shut down and there is a demand for hot water supply, the control device 35 controls the first heat exchange flow path 82 so that water flows. Furthermore, the control device 35 controls the third water flow path 85 so that water flows as needed for temperature adjustment. This allows hot water to be supplied at an appropriate temperature.

[0051] In the fuel cell system 11 according to this embodiment configured as described above, even if the water remaining in the piping is vaporized, the water is liquefied and flows through the hot water supply flow path 12. Therefore, the fuel cell system 11 according to this embodiment can improve reliability without stopping operation due to water vaporization or the like.

[0052] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art could make various modifications or alterations based on the present disclosure. Therefore, it should be noted that these modifications or alterations are included in the scope of the present disclosure. For example, the functions included in each component can be rearranged so as not to cause logical inconsistencies, and multiple components can be combined or divided into one.

[0053] Furthermore, embodiments of the present disclosure are not limited to the specific configurations of any of the above-described embodiments, but rather extend to any and all novel features or combinations thereof described in the present disclosure, or any and all novel method or process steps or combinations thereof described.

[0054] In this disclosure, descriptions such as "first" and "second" are identifiers for distinguishing the configuration. In this disclosure, configurations distinguished by descriptions such as "first" and "second" can have their numbers exchanged. The exchange of identifiers is performed simultaneously. The configurations remain distinguished even after the exchange of identifiers. Identifiers may be deleted. A configuration from which an identifier has been deleted is distinguished by a symbol. The descriptions of identifiers such as "first" and "second" in this disclosure should not be used solely to interpret the order of the configurations or to justify the existence of an identifier with a smaller number.

[0055] REFERENCE SIGNS LIST 11 fuel cell system 12 hot water supply flow path 13 first heat exchange section 14 second heat exchange section 16 fuel cell 22 cooling / heating device 25 pipe line 26 reformer 27 cell stack 28 packing 29 housing 30 heat insulating material 31 three-way valve 35 control device 40 circulation pump 43 first flow control valve 44 bypass flow path 45 second flow control valve 46 third flow control valve 47 fourth flow control valve 51, 54, 55, 56 temperature sensor 62 flow sensor 70 confluence section 71 expansion tank 72 water storage section 73 water inlet 74 water outlet 81 external water flow path 82 first heat exchange flow path 83 first water flow path 84 second water flow path 85 third water flow path

Claims

1. A fuel cell; an external water flow path through which water supplied from the outside flows; a first heat exchange unit located adjacent to the outside of the fuel cell or located inside the fuel cell, and causing water from the external water flow path to recover heat generated in the fuel cell; a hot water supply passage for supplying heated water to the outside; a first heat exchange flow path connected to the external water flow path and passing through the first heat exchange section; A first water flow path connecting the external water flow path and the hot water supply flow path, A fuel cell system, wherein a junction where the hot water supply flow path, the first heat exchange flow path, and the first water flow path join is configured so that water vapor inside the first heat exchange flow path is liquefied and flows through the hot water supply flow path.

2. 2. The fuel cell system of claim 1, wherein the confluence section has a water storage section for storing water, a water inlet connected to the first water flow path, and a water outlet connected to the hot water supply flow path, and is configured such that at least a portion of the first heat exchange flow path is inside the water storage section.

3. 3. The fuel cell system according to claim 1, further comprising a bypass flow passage connecting the external water flow passage and the first water flow passage.

4. 3 . The fuel cell system according to claim 1 , further comprising a second water flow passage connecting the hot water supply flow passage to an upstream side of a connection portion of the external water flow passage with the first water flow passage. 4 .

5. 3. The fuel cell system according to claim 1, further comprising a second heat exchanger in the external water flow passage for exchanging heat with exhaust gas discharged from the fuel cell.

6. 3. The fuel cell system according to claim 1, further comprising a cooling / heating device for heating or cooling the water flowing through the hot water supply passage.

7. a third water flow path between the first water flow path and the second water flow path, the third water flow path connecting the external water flow path and the hot water supply flow path; The fuel cell system according to claim 4 , further comprising a cooling / heating device that heats or cools the water flowing through the third water flow path.

8. A fuel cell; an external water flow path through which water supplied from the outside flows; a first heat exchange unit located adjacent to the outside of the fuel cell or located inside the fuel cell, and causing water from the external water flow path to recover heat generated in the fuel cell; a hot water supply passage for supplying heated water to the outside; a first heat exchange flow path connected to the external water flow path and passing through the first heat exchange section; A first water flow path connecting the external water flow path and the hot water supply flow path; a bypass flow path connecting the external water flow path and the first water flow path; A second water flow path connecting the upstream side of the external water flow path relative to a connection portion with the first water flow path and the hot water supply flow path; a third water flow path between the first water flow path and the second water flow path, the third water flow path connecting the external water flow path and the hot water supply flow path; A control device, a junction portion where the hot water supply passage, the first heat exchange passage, and the first water passage join together is configured so that water vapor inside the first heat exchange passage is liquefied and flows through the hot water supply passage, A fuel cell system, wherein the control device controls water from the external water flow path to flow through at least one of the first heat exchange flow path, the bypass flow path, the first water flow path, the second water flow path, and the third water flow path in accordance with the operation of the fuel cell and the demand for hot water supply.

9. 9. The fuel cell system of claim 8, wherein the control device controls at least one of the first water flow path, the second water flow path, and the third water flow path to allow water to flow in response to a request for hot water supply when the fuel cell is stopped.

10. A cooling / heating device that heats or cools the water flowing through the hot water supply flow path or the water flowing through the third water flow path, 10. The fuel cell system according to claim 8 or 9, wherein the control device controls the cooling and heating device to heat in accordance with the temperature of heated water supplied to the outside when the fuel cell is operating or stopped and there is a continuous demand for hot water supply.

11. A cooling / heating device that heats or cools the water flowing through the hot water supply flow path or the water flowing through the third water flow path, 10. The fuel cell system of claim 8 or 9, wherein, when the fuel cell is operating and there is no demand for hot water supply, the control device controls the bypass flow path to allow water to flow, controls the water from the hot water supply flow path to flow through the second water flow path or the third water flow path to the external water flow path, and controls the cooling and heating device to cool.

12. 9. The fuel cell system of claim 8, wherein the control device controls the first heat exchange flow path to allow water to flow when the fuel cell is operating and there is a demand for hot water supply, and controls the second water flow path or the third water flow path as necessary to allow water to flow.