Fuel cell system and fuel cell system operating method

Abstract

To suppress a rapid temperature change of hot water supplied from a backup heat source machine unit in a fuel cell system in which communication between a fuel cell unit and the backup heat source machine unit is not performed.SOLUTION: A fuel cell system 10 includes: a fuel cell unit 12 provided with a fuel cell module for generating power; a hot-water storage tank 48 that stores hot water heated by heat exchange in the fuel cell unit 12; a temperature adjustment unit 111A that is provided in the fuel cell unit 12, uses heat of the hot water stored in the hot-water storage tank 48, and adjusts temperature of hot water delivered from the fuel cell unit 12 to a hot-water output target temperature T0; and a target temperature switching unit 111B that switches the hot-water output target temperature T0 from a normal hot-water output target temperature T1 to a low-temperature hot-water output target temperature T2 that is lower than the normal hot-water output target temperature T1 when temperature of the hot water stored in the hot-water storage tank 48 becomes equal to or less than a switching temperature TC that is higher than the hot-water output target temperature T0.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a fuel cell system and a method for operating the fuel cell system, and more particularly to a fuel cell system which is a cogeneration system equipped with a hot water storage tank and has a backup heat source unit (BB) for heating hot water, and a method for operating the fuel cell system. [Background technology]

[0002] A cogeneration fuel cell system has been proposed that generates electricity using a fuel cell unit and supplies hot water using the exhaust heat of the fuel cell unit. In this fuel cell system, hot water heated by the exhaust heat of the fuel cell unit is stored in a hot water storage tank. In addition, a hot water supply unit having an auxiliary heat source is provided, and when the temperature of the hot water stored in the hot water storage tank is lower than a desired temperature, the hot water supply unit heats the hot water from the hot water storage tank.

[0003] However, when the temperature of the hot water stored in the hot water storage tank drops, it is difficult to rapidly heat it using the auxiliary heat source. Therefore, in Patent Document 1, when the temperature of the upper layer of the hot water storage tank falls below a temperature (T+β) that is β higher than the set temperature T, a heat shortage is predicted and the auxiliary heat source is activated. By communicating between a control device on the fuel cell unit side where the hot water storage tank is provided and a control device on the hot water supply unit side having the auxiliary heat source, it is possible to transmit temperature information from the fuel cell unit side to the auxiliary heat source side and activate the auxiliary heat source in advance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-91613 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, when communication is not possible between the control device on the fuel cell unit side and the control device on the hot water supply unit (backup heat source unit) side equipped with an auxiliary heat source, such as when a fuel cell unit is additionally installed (retrofitted) to an existing heat source unit, it may not be possible to transmit temperature information of the hot water tank to the backup heat source unit side, resulting in a situation in which it is difficult for the backup heat source unit side to follow temperature changes on the hot water storage tank side. Even when the control device on the fuel cell unit side cannot communicate with the control device on the backup heat source unit side, it is necessary to suppress sudden temperature changes in the hot water supplied from the backup heat source unit.

[0006] The present invention has been made in consideration of the above circumstances, and has an object to suppress a sudden change in temperature of hot water supplied from a backup heat source unit in a fuel cell system in which communication between the fuel cell unit and the backup heat source unit is not performed. [Means for solving the problem]

[0007] The fuel cell system of the first embodiment comprises a fuel cell unit having a fuel cell module that generates electricity, a hot water storage tank that stores hot water heated by heat exchange in the fuel cell unit, a temperature adjustment unit provided in the fuel cell unit that uses the heat of the hot water stored in the hot water storage tank to adjust the temperature of the hot water discharged from the fuel cell unit to a target hot water outlet temperature, a target temperature switching unit that switches the target hot water outlet temperature from a normal hot water outlet target temperature to a low-temperature hot water outlet target temperature lower than the normal hot water outlet temperature when the temperature of the hot water stored in the hot water storage tank falls below a switching temperature higher than the target hot water outlet temperature, and a heat source unit that is not in communication with the fuel cell unit and is capable of heating the hot water discharged from the fuel cell unit using heat generated by gas combustion.

[0008] The fuel cell system according to the first aspect includes a fuel cell unit, a hot water tank, and a heat source unit. The hot water tank stores hot water heated by heat exchange in the fuel cell unit. The heat source unit heats the hot water sent from the fuel cell unit using heat generated by gas combustion.

[0009] The temperature of the hot water delivered from the fuel cell unit is adjusted to the target hot water outlet temperature by the temperature adjustment unit using the heat of the hot water stored in the hot water storage tank. Here, since the heat source unit is not in communication with the fuel cell unit, even if there is a change in the temperature of the hot water delivered from the fuel cell unit, it cannot follow the temperature change at the beginning of the change, and heats the hot water from the fuel cell unit at a specified combustion number. Therefore, if the temperature of the hot water stored in the hot water storage tank drops and the temperature adjustment unit can no longer adjust it to the normal hot water outlet target temperature, there is a possibility that the temperature of the hot water supplied to the user from the heat source unit will suddenly drop.

[0010] Therefore, when the temperature of the hot water stored in the hot water storage tank falls below a predetermined switching temperature, the target hot water outlet temperature, which is the adjustment target of the temperature adjustment unit, is switched by the target temperature switching unit from the normal hot water outlet target temperature to a low-temperature hot water outlet target temperature lower than the normal hot water outlet target temperature. As a result, the temperature of the hot water supplied to the heat source unit is lowered from the point when the temperature of the hot water stored in the hot water storage tank falls below the switching temperature higher than the hot water outlet target temperature. Then, the heat source unit performs heating corresponding to the low-temperature hot water outlet target temperature from the normal hot water outlet target temperature. As a result, the speed of the temperature drop of the hot water stored in the hot water storage tank is suppressed. Furthermore, the heat source unit can suppress the change in the hot water supply temperature to the user to about the temperature difference between the normal hot water outlet target temperature and the low-temperature hot water outlet target temperature. In this way, it is possible to suppress a sudden change in the temperature of the hot water supplied to the user without obtaining hot water temperature information of the hot water storage tank in the heat source unit.

[0011] In the fuel cell system according to the second aspect, the switching temperature is set to a temperature that is α° C. higher than the normal target hot water outlet temperature.

[0012] Here, "a temperature α°C higher than the normal target hot water outlet temperature" means that the temperature is higher than the normal target hot water outlet temperature. By setting the switching temperature in this manner, the temperature of the hot water supplied to the heat source unit is lowered before the target hot water outlet temperature can no longer be maintained at the normal target hot water outlet temperature, and the heat source unit can start heating according to the hot water temperature.

[0013] In the fuel cell system according to a third aspect, the low temperature target hot water outlet temperature is set at a temperature β degrees Celsius lower than the normal target hot water outlet temperature, and a relationship of α>β is established.

[0014] By setting the low-temperature target hot water outlet temperature in this manner, the temperature of the hot water supplied to the heat source unit is reduced by less than α° C. Therefore, the heat source unit only needs to control the heating to follow small temperature changes, and can suppress sudden temperature changes in the hot water supplied to the user without obtaining hot water temperature information from the hot water storage tank.

[0015] In a fuel cell system of a fourth aspect, a second switching temperature lower than the switching temperature is set, and the target temperature switching unit switches the hot water outlet target temperature from the low temperature hot water outlet target temperature to a second low temperature hot water outlet target temperature lower than the low temperature hot water outlet target temperature when the temperature of the hot water stored in the hot water storage tank becomes lower than the second switching temperature.

[0016] In the fuel cell system according to the fourth aspect, when the temperature of the hot water stored in the hot water tank falls to or below a second switching temperature that is lower than the switching temperature, the target hot water outlet temperature is switched from the low-temperature target hot water outlet temperature to an even lower second-low-temperature target hot water outlet temperature. Therefore, the target hot water outlet temperature can be lowered in multiple stages, and the heat source unit can make the temperature change of the hot water supplied to the user gentle without obtaining information on the hot water temperature in the hot water tank.

[0017] In the fuel cell system according to a fifth aspect, the target hot water outlet temperature is maintained constant when the temperature of the hot water stored in the hot water storage tank is higher than the switching temperature.

[0018] In this way, by maintaining the target hot water outlet temperature constant, the heat source unit reduces the opportunities for control in response to changes in the temperature of the hot water supplied from the fuel cell unit, and sudden changes in the temperature of the hot water supplied to the user from the heat source unit can be suppressed.

[0019] A fuel cell system operating method according to a sixth aspect of the present invention stores hot water heated by exhaust heat from a fuel cell module that generates electricity in a hot water storage tank in a fuel cell unit, and uses the heat of the hot water stored in the hot water storage tank to adjust the temperature of the hot water discharged from the fuel cell unit to a target hot water outlet temperature.When the temperature of the hot water stored in the hot water storage tank falls below a predetermined switching temperature that is higher than a normal hot water outlet target temperature, the temperature of the hot water discharged from the fuel cell unit is switched from the normal hot water outlet target temperature to a low-temperature hot water outlet target temperature that is lower than the normal hot water outlet target temperature.The hot water discharged from the fuel cell unit can be heated using heat from gas combustion, and is discharged to a heat source unit that is not in communication with the fuel cell unit.

[0020] The temperature of the hot water discharged from the fuel cell unit is adjusted to the low-temperature hot water outlet target temperature by utilizing the heat of the hot water stored in the hot water storage tank. Here, since the heat source unit does not communicate with the fuel cell unit, even if there is a change in the temperature of the hot water discharged from the fuel cell unit, it cannot follow the temperature change at the beginning of the change, and heats the hot water discharged from the fuel cell unit at a specified combustion number. Therefore, if the temperature of the hot water stored in the hot water storage tank drops and it can no longer be adjusted to the normal hot water outlet target temperature, there is a possibility that the temperature of the hot water supplied to the user from the heat source unit will suddenly drop.

[0021] Therefore, when the temperature of the hot water stored in the hot water storage tank falls below a predetermined switching temperature, the adjustment is switched so that the temperature of the hot water discharged from the fuel cell unit is changed from the normal hot water outlet target temperature to a low-temperature hot water outlet target temperature that is lower than the normal hot water outlet target temperature. As a result, the temperature of the hot water supplied to the heat source unit is lowered from the point in time when the temperature of the hot water stored in the hot water storage tank falls below the switching temperature. Then, the heat source unit performs heating corresponding to the low-temperature hot water outlet target temperature from the normal hot water outlet target temperature. As a result, the speed of the temperature drop of the hot water stored in the hot water storage tank is suppressed. Furthermore, the heat source unit can suppress the change in the hot water supply temperature to the user to about the temperature difference between the normal hot water outlet target temperature and the low-temperature hot water outlet target temperature. In this way, it is possible to suppress a sudden change in the temperature of the hot water supplied to the user without obtaining hot water temperature information from the hot water storage tank in the heat source unit.

[0022] In the fuel cell system operating method of the seventh aspect, the switching temperature is set to a temperature α degrees Celsius higher than the normal hot water outlet target temperature, and the low temperature hot water outlet target temperature is set to a temperature β degrees Celsius lower than the normal hot water outlet target temperature, such that the relationship is α>β.

[0023] Here, "a temperature α°C higher than the normal hot water outlet target temperature" means a temperature higher than the normal hot water outlet target temperature. By setting the switching temperature and the low temperature hot water outlet target temperature in this manner, the temperature reduction of the hot water supplied to the heat source unit is smaller than α°C. Therefore, the heat source unit only needs to control the heating to follow small temperature changes, and can suppress sudden temperature changes in the hot water supplied to the user without obtaining hot water temperature information from the hot water storage tank.

[0024] In an eighth aspect of the fuel cell system operating method, a second switching temperature lower than the switching temperature is set, and when the temperature of the hot water stored in the hot water storage tank becomes lower than the second switching temperature, the hot water outlet target temperature is switched from the low-temperature hot water outlet target temperature to a second low-temperature hot water outlet target temperature lower than the low-temperature hot water outlet target temperature.

[0025] In the fuel cell system operating method according to the eighth aspect, when the temperature of the hot water stored in the hot water storage tank falls to or below a second switching temperature that is lower than the switching temperature, the temperature of the hot water discharged from the fuel cell unit is switched from the low-temperature hot water outlet target temperature to an even lower second low-temperature hot water outlet target temperature. Therefore, the temperature of the hot water discharged from the fuel cell unit can be lowered in multiple stages, and the heat source unit can make the temperature change of the hot water supplied to the user gentle without obtaining hot water temperature information in the hot water storage tank.

[0026] In a fuel cell system operating method according to a ninth aspect, the target hot water outlet temperature is maintained constant when the temperature of the hot water stored in the hot water storage tank is higher than the switching temperature.

[0027] In this way, by maintaining the target hot water outlet temperature constant, the heat source unit reduces the opportunities for control in response to changes in the temperature of the hot water supplied from the fuel cell unit, and sudden changes in the temperature of the hot water supplied to the user from the heat source unit can be suppressed. Effect of the Invention

[0028] As described above in detail, according to the present invention, even when communication between the fuel cell unit and the backup heat source unit is not performed, a sudden change in temperature of the hot water supplied from the backup heat source unit can be suppressed. [Brief description of the drawings]

[0029] [Figure 1] 1 is a diagram showing an example of the configuration of a fuel cell system according to a first embodiment. [Diagram 2] 2 is a block diagram showing an example of an electrical configuration of an FC control unit according to the first embodiment. FIG. [Diagram 3] FIG. 2 is a block diagram showing an example of an electrical configuration of a BB control unit according to the first embodiment. [Figure 4] 2 is a block diagram showing an example of the functional configuration of an FC control unit according to the first embodiment. FIG. [Diagram 5]5 is a flowchart showing an example of the flow of a target heated water outlet temperature adjustment process according to the first embodiment. [Figure 6] 5 is a flowchart showing an example of the flow of a temperature adjustment process in the target hot water outlet temperature adjustment process according to the first embodiment. [Figure 7] 5 is a flowchart showing an example of the flow of a temperature adjustment process of a hot water temperature adjustment process according to the first embodiment. [Figure 8] 13 is a flowchart showing an example of the flow of a second target heated water outlet temperature adjustment process according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

[0031] [First embodiment] FIG. 1 is a diagram showing an example of the configuration of a fuel cell system 10 according to a first embodiment. As shown in FIG. 1, a fuel cell system 10 according to this embodiment is roughly divided into two units: a fuel cell unit 12 and a hot water supply unit 14, which is an example of a heat source unit.

[0032] The fuel cell unit 12 generates power using fuel gas and water. It also includes a hot water storage tank 48, which stores hot water as a heat transfer medium for recovering heat generated by power generation through heat exchange. The hot water supply unit 14 heats the clean water heated by the fuel cell unit 12 to a target temperature and supplies the heated water. As an example, an open tank is used as the hot water storage tank 48, but a pressurized tank may also be used.

[0033] The hot water tank 48 may be provided in the same housing as the fuel cell module 20, or in a housing separate from the fuel cell module 20. When the hot water tank 48 is provided in a housing separate from the fuel cell module 20, devices such as a mixing valve 72 and clean water heat exchanger 54, which will be described later, may be provided in the housing on the fuel cell module 20 side, or in the housing on the hot water tank 48 side.

[0034] The fuel cell unit 12 includes a fuel cell module 20, which is an example of a fuel cell that generates electricity. The fuel cell module 20 includes a reformer, a burner, and a fuel cell stack as its main components inside a housing. The fuel cell module 20 is supplied with raw material gas, oxidant gas (air), reforming water, etc. from supply paths (not shown).

[0035] The reformer provided in this fuel cell module 20 reforms the raw material gas with reforming water to generate hydrogen.

[0036] In this reformer, the raw material gas supplied is heated by the heat of combustion from a burner (not shown) and a fuel gas containing hydrogen gas is generated by an endothermic reaction. This fuel gas is supplied to the fuel electrode of the fuel cell stack in the fuel cell module 20.

[0037] The fuel cell stack is, for example, a solid oxide fuel cell stack, and has a plurality of stacked fuel cell units. Each fuel cell unit has an electrolyte layer, and a fuel electrode and a cathode that are stacked on the front and back sides of the electrolyte layer, respectively.

[0038] Oxidizing gas (external air) is supplied to the air electrode. At the air electrode, oxygen in the oxidizing gas reacts with electrons to generate oxygen ions, as shown in formula (1) below. These oxygen ions pass through the electrolyte layer and reach the fuel electrode.

[0039] (Air electrode reaction) 1 / 2O2+2e - →O 2- (1)

[0040] Meanwhile, at the fuel electrode, oxygen ions that have passed through the electrolyte layer react with hydrogen and carbon monoxide in the fuel gas, producing water (water vapor), carbon dioxide, and electrons, as shown in the following formulas (2) and (3). The electrons produced at the fuel electrode reach the air electrode through an external circuit. Electricity is generated in each fuel cell as the electrons move from the fuel electrode to the air electrode in this manner. Furthermore, each fuel cell generates heat as a result of the above reactions during power generation.

[0041] (Anode reaction) H2+O 2- →H2O+2e - (2) CO+O 2- →CO2+2e - (3)

[0042] The fuel electrode exhaust gas discharged from the fuel electrode and the air electrode exhaust gas discharged from the air electrode are supplied to the burner as burner gas. The burner exhaust gas generated by combustion in the burner is discharged to the exhaust heat exchanger 36 through the exhaust path 34.

[0043] An exhaust heat exchanger 36 is provided in the exhaust path 34, and the downstream side of the exhaust heat exchanger 36 is connected to the exhaust gas flow path 30. The combustion exhaust gas from the fuel cell module 20 is cooled by heat exchange with a heat transfer medium 50 (described later) in the exhaust heat exchanger 36, and then exhausted. Note that water vapor contained in the combustion exhaust gas can be condensed and separated into water and gas, and the water can be reused as reforming water.

[0044] A heat recovery circuit 42 that circulates a heat transfer medium 50 between the exhaust heat exchanger 36 and a hot water storage tank 48 is connected to the exhaust heat exchanger 36. A heat recovery pump 44 is provided in a first flow path 42a, which is one flow path of the heat recovery circuit 42 that connects the exhaust heat exchanger 36 and the hot water storage tank 48. The upstream side of the heat recovery pump 44 of the first flow path 42a is connected to the hot water storage tank 48. Hot water is stored in the hot water storage tank 48 as a heat transfer medium. The top of the hot water storage tank 48 is open to the atmosphere. In addition, a tank temperature sensor 52 that measures the temperature of the hot water in the upper part of the hot water storage tank 48 is provided in the hot water storage tank 48.

[0045] The first flow path 42a is connected to the lower part of the hot water storage tank 48, and the hot water stored in the lower part of the hot water storage tank 48 is preferentially sent to the exhaust heat exchanger 36. The hot water supplied from the hot water storage tank 48 to the first flow path 42a of the heat recovery circuit 42 is sent to the exhaust heat exchanger 36 by the heat recovery pump 44.

[0046] The hot water sent from the hot water storage tank 48 to the exhaust heat exchanger 36 via the first flow path 42a is returned to the hot water storage tank 48 via the second flow path 42e, which is the other flow path of the heat recovery circuit 42. The second flow path 42e is connected to the top of the hot water storage tank 48. The heat of the combustion exhaust gas from the fuel cell module 20 is transferred to the heat transfer medium 50 by the exhaust heat exchanger 36, and the heat transfer medium 50 heated by this heat is returned to the top of the hot water storage tank 48. As a result, the hot water in the hot water storage tank 48 is heated by the heat generated in the fuel cell module 20.

[0047] The hot water stored in the hot water storage tank 48 is supplied to a clean water heat exchanger 54 provided in the fuel cell unit 12 via a heat supply circuit 58 that is different from the heat recovery circuit 42. The hot water in the hot water storage tank 48 is returned to the hot water storage tank 48 via the clean water heat exchanger 54 provided in the heat supply circuit 58.

[0048] A heat supply pump 56 is provided in a first flow path 58a upstream of the clean water heat exchanger 54 of the heat supply circulation path 58. The heat supply pump 56 operates when the heat of the hot water in the hot water storage tank 48 is used to heat the clean water or the like.

[0049] The upstream end of the first flow path 58a is connected to the top of the hot water tank 48, and hot water stored in the top of the hot water tank 48 is sent to the first flow path 58a. The tank temperature sensor 52 is disposed at a height near the connection part of the first flow path 58a with the hot water tank 48. The tank temperature sensor 52 detects the temperature of the top of the hot water stored in the hot water tank 48 (hereinafter referred to as "tank hot water temperature information TT"). The downstream end of the first flow path 58a is connected to the clean water heat exchanger 54, and the hot water stored in the top of the hot water tank 48 is supplied to the clean water heat exchanger 54. The second flow path 58e on the downstream side of the heat supply circulation path 58 is connected to the bottom of the hot water tank 48, and the hot water from which heat has been removed by the clean water heat exchanger 54 is returned to the bottom side of the hot water tank 48.

[0050] An inflow passage 60 having an inflow-side branch point 60a is connected to the clean water heat exchanger 54. The inflow passage 60 is connected to an inlet pipe joint 62. The inlet pipe joint 62 is connected to a water supply pipe 64, for example, a water pipe, and clean water is supplied to the inflow passage 60.

[0051] The clean water heat exchanger 54 is connected to an outlet passage 66 through which the clean water from the inlet passage 60 flows out after heat exchange.

[0052] A mixing valve 72 is provided downstream of the outflow branch point 66a of the outflow passage 66. The mixing valve 72 is connected to the inflow branch point 60a via a bypass passage 74. The mixing valve 72 is a valve that mixes clean water from the inflow passage 60 and hot water from the clean water heat exchanger 54, and adjusts the mixing ratio of the clean water from the inflow passage 60 and the hot water from the clean water heat exchanger 54 so that the outflow temperature becomes a predetermined hot water outlet target temperature T0. The mixing valve 72 is connected to an FC control unit 110, which will be described later.

[0053] The temperature of the hot water flowing out from mixing valve 72 corresponds to outlet hot water temperature information TD measured by outlet hot water thermometer 67, which will be described later. Target outlet hot water temperature T0 is set lower than a requested hot water temperature that is arbitrarily set by the user. Also, target outlet hot water temperature T0 is set higher than the temperature of clean water supplied from water supply pipe 64. In this way, by setting target outlet hot water temperature T0 higher than the clean water temperature, the exhaust heat of fuel cell unit 12 can be effectively used for preheating.

[0054] A flow meter 65 and an outlet hot water thermometer 67 are provided on the outlet path 66 downstream of the mixing valve 72. The flow meter 65 measures the flow rate of the hot water flowing out from the mixing valve 72. The outlet hot water thermometer 67 measures the temperature of the hot water flowing out from the mixing valve 72. The flow meter 65 and the outlet hot water thermometer 67 are connected to the FC control unit 110 described below, and the flow meter 65 transmits the measured hot water flow rate (hereinafter referred to as the "outlet hot water flow rate RF") to the FC control unit 110, and the outlet hot water thermometer 67 transmits the measured outlet hot water temperature information TD to the FC control unit 110.

[0055] The downstream side of the outflow path 66 from the flow meter 65 and the outlet hot water thermometer 67 is connected to an outlet joint 76 , and the outlet joint 76 is connected to a water inlet joint 80 of the hot water supply unit 14 via an outlet pipe 78 .

[0056] A gas supply pipe 24 is connected to the gas joint 82 of the hot water supply unit 14, and city gas is supplied from the gas supply pipe 24 to a burner 150 of the hot water supply unit 14. Hot water passing through a heat exchanger 154 is heated by the combustion heat of the burner 150.

[0057] In this embodiment, the minimum number of burners 150 is designated as G0. The minimum number here refers to the combustion number when burner 150 of hot water supply unit 14 is continuously driven and combusted with the heating power of burner 150 set to the minimum.

[0058] A hot water supply pipe 86 is connected to the hot water supply joint 84 of the hot water supply unit 14, and the hot water supply pipe 86 is routed to a hot water supply location where hot water is used.

[0059] A water inlet passage 152 is connected to the water inlet joint 80 of the hot water supply unit 14, and the water inlet passage 152 is connected to a heat exchanger 154. The heat exchanger 154 is connected to the hot water supply joint 84 via a hot water supply passage 158 having a mixing valve 156, and the mixing valve 156 is connected to a water inlet side branch point 152a of the water inlet passage 152 via a bypass passage 160. In addition, a BB flow meter 53 is provided between the water inlet joint 80 and the water inlet side branch point 152a.

[0060] The BB flow meter 53 measures the flow rate of hot water (BB flow rate information RB) supplied from the fuel cell unit 12 to the hot water supply unit 14 via the hot water outlet pipe 78. The BB flow meter 53 is connected to the BB control unit 170, which will be described later, and outputs the measured BB flow rate information RB to the BB control unit 170.

[0061] Mixing valve 156 is a valve that mixes hot water from water inlet 152 and hot water from heat exchanger 154, and adjusts the mixing ratio of the hot water from water inlet 152 and the hot water from heat exchanger 154 according to the temperature required by the user. Mixing valve 156 is provided with a hot water supply thermometer 157 that measures the temperature of the hot water sent out from mixing valve 156 (hereinafter referred to as "hot water supply temperature information TS"). Hot water supply thermometer 157 is connected to BB control unit 170, which will be described later, and outputs hot water supply temperature information TS to BB control unit 170.

[0062] In addition, the hot water supply unit 14 is provided with heating pipes for heating and bath pipes for reheating the bath, each of which constitutes a circulation path, and the hot water in the circulation path is heated by heat exchange in the heat exchanger 154. These heating pipes and bath pipes are not shown in the figure.

[0063] The hot water supply unit 14 functions as a backup heat source device that heats the hot water heated by the fuel cell unit 12 and the water flowing through the heating pipes and bath pipes as needed.

[0064] The fuel cell unit 12 is provided with an FC control unit 110 as a controller. The operation of the fuel cell unit 12 is controlled by the FC control unit 110. A remote control device 51 is also connected to the FC control unit 110. The remote control device 51 accepts operation input from the user, and displays various types of information about the fuel cell unit 12, such as status information, error information, etc.

[0065] FIG. 2 is a block diagram showing an example of the electrical configuration of the FC control unit 110 according to the first embodiment.

[0066] As shown in FIG. 2, the FC control unit 110 of this embodiment includes a CPU (Central Processing Unit) 111, a ROM (Read Only Memory) 112, a RAM (Random Access Memory) 113, an input / output interface (I / O) 114, a memory unit 115, and an external interface (hereinafter referred to as "external I / F") 116.

[0067] The CPU 111, the ROM 112, the RAM 113, and the I / O 114 are connected to each other via a bus. The I / O 114 is connected to various functional units including a storage unit 115 and an external I / F 116. These functional units are capable of communicating with the CPU 111 via the I / O 114.

[0068] For example, a hard disk drive (HDD), a solid state drive (SSD), a flash memory, etc. are used as the storage unit 115. A control program 115A for controlling the operation of the fuel cell unit 12 is stored in the storage unit 115. The control program 115A may be stored in the ROM 112.

[0069] The control program 115A may be pre-installed in the FC control unit 110, for example. The control program 115A may be realized by storing it in a non-volatile storage medium or distributing it via a network and appropriately installing it in the FC control unit 110. Note that examples of non-volatile storage media include a CD-ROM (Compact Disc Read Only Memory), a magneto-optical disk, a HDD, a DVD-ROM (Digital Versatile Disc Read Only Memory), a flash memory, a memory card, and the like.

[0070] In this embodiment, a program for adjusting the target hot water outlet temperature is stored as part of control program 115A. In addition, data used in the target hot water outlet temperature adjustment process is stored, including the normal target hot water outlet temperature T1, the low-temperature target hot water outlet temperature T2, and the switching temperature TC.

[0071] The target water outlet temperature adjustment process adjusts the water outlet temperature information TD, which is the temperature of the water measured by the outlet water thermometer 67, so that it is within the target water outlet range TR (T0±γ°C), which is the temperature band above and below the target water outlet temperature T0, and when the tank water temperature information TT falls below the switching temperature TC, switches the target water outlet temperature T0 from the normal target water outlet temperature T1 to the low-temperature target water outlet temperature T2.

[0072] Here, the switching temperature TC is set to a temperature higher than the set target hot water outlet temperature T0. In this embodiment, the normal hot water outlet target temperature T1 is set as the initial value of the target hot water outlet temperature T0, and a temperature α°C higher than the normal hot water outlet target temperature T1 is set as the switching temperature TC. The low-temperature hot water outlet target temperature T2 is set to a temperature β°C lower than the normal hot water outlet target temperature T1. The temperature difference α°C between the switching temperature TC and the normal hot water outlet target temperature T1 is set to be larger than the temperature difference β°C between the normal hot water outlet target temperature T1 and the low-temperature hot water outlet target temperature T2.

[0073] For example, remote control device 51, tank temperature sensor 52, flow meter 65, outlet hot water thermometer 67, mixing valve 72, heat recovery pump 44, and heat supply pump 56 are connected to external I / F 116. These remote control device 51, tank temperature sensor 52, flow meter 65, outlet hot water thermometer 67, mixing valve 72, heat recovery pump 44, and heat supply pump 56 are connected to CPU 111 via external I / F 116 so as to be able to communicate with each other.

[0074] 3 is a block diagram showing an example of the electrical configuration of the BB control unit 170 according to the first embodiment. The BB control unit 170 is not connected to the FC control unit 110 and is not in communication with the FC control unit 110.

[0075] As shown in FIG. 3, the BB control unit 170 of this embodiment, like the FC control unit 110, has a CPU 171, a ROM 172, a RAM 173, an input / output interface (I / O) 174, a memory unit 175, and an external interface (hereinafter referred to as "external I / F") 176.

[0076] The CPU 171, the ROM 172, the RAM 173, and the I / O 174 are connected to each other via a bus. The I / O 174 is connected to various functional units including a storage unit 175 and an external I / F 176. These functional units are capable of communicating with the CPU 171 via the I / O 174.

[0077] Storage unit 175 stores control program 175A for controlling the operation of hot water supply unit 14. This control program 175A may be stored in ROM 172. A program for hot water supply temperature adjustment processing is stored as part of control program 175A. The hot water supply temperature adjustment processing adjusts the temperature of hot water supplied from hot water supply unit 14 to the user. Storage unit 175 also stores the hot water temperature requested by the user (hereinafter referred to as "requested temperature information TU"). The user can set an arbitrary temperature as the requested temperature information TU from an input unit not shown, and can change it at any time.

[0078] For example, a hot water thermometer 157, a mixing valve 156, and a BB flowmeter 53 are connected to the external I / F 176. The hot water thermometer 157, the mixing valve 156, and the BB flowmeter 53 are connected to the CPU 171 via the external I / F 176 so as to be able to communicate with each other.

[0079] Fig. 4 is a block diagram showing an example of a functional configuration of the FC control unit 110 according to the first embodiment. The CPU 111 of the FC control unit 110 according to this embodiment writes a control program 115A stored in a storage unit 115 into a RAM 113 and executes the program, thereby functioning as each unit shown in Fig. 4. As shown in Fig. 4, the CPU 111 of the FC control unit 110 according to this embodiment functions as a temperature adjustment unit 111A and a target temperature switching unit 111B.

[0080] Temperature adjustment unit 111A adjusts the temperature of hot water supplied from fuel cell unit 12 to hot water supply unit 14 to target hot water outlet temperature T0. Target temperature switching unit 111B switches target hot water outlet temperature T0 from normal target hot water outlet temperature T1 to low-temperature target hot water outlet temperature T2 when tank hot water temperature information TT becomes equal to or lower than switching temperature TC.

[0081] Next, the operation of the FC control unit 110 according to the first embodiment will be described with reference to FIGS.

[0082] 5 is a flowchart showing the target hot water outlet temperature adjustment process of the control program 115A according to the first embodiment. As described above, in the fuel cell unit 12, the hot water in the hot water storage tank 48 is heated by the exhaust heat generated by the power generation in the fuel cell module 20, so the temperature of the hot water stored in the hot water storage tank 48 changes. Therefore, the target hot water outlet temperature adjustment process is executed while the fuel cell unit 12 is in operation. The target hot water outlet temperature T0 is set to the normal target hot water outlet temperature T1 as an initial value.

[0083] First, in step S12, tank hot water temperature information TT detected by tank temperature sensor 52 is obtained. In step S14, it is determined whether the obtained tank hot water temperature information TT is equal to or lower than switching temperature TC. If the determination in step S14 is positive, in step S16, target hot water outlet temperature T0 is switched to low-temperature target hot water outlet temperature T2. If the determination in step S14 is negative, in step S18, target hot water outlet temperature T0 is switched to normal target hot water outlet temperature T1.

[0084] After steps S16 and S18, in step S20, a temperature adjustment process is executed. In the temperature adjustment process, as shown in FIG. 6, in step S22, outlet hot water temperature information TD measured by outlet hot water thermometer 67 is acquired. In step S24, it is determined whether or not the outlet hot water temperature information TD is within the target hot water outlet range TR. If the determination in step S24 is negative, in step S26, the opening degree of mixing valve 72 is adjusted, and the process returns to step S24. The adjustment of the opening degree of mixing valve 72 is repeated until the outlet hot water temperature information TD is within the target hot water outlet range TR, and so-called feedback control is executed. If the determination in step S24 is positive, the temperature adjustment process is terminated, and the process returns to step S12 in FIG. 5.

[0085] Then, in the case where there is a hot water supply request from the user, CPU 171 of hot water supply unit 14 executes the hot water supply temperature adjustment process shown in FIG.

[0086] In step S40, requested temperature information TU is acquired, in step S41, hot water temperature information TS is acquired, and in step S42, BB flow rate information RB is acquired. In step S44, based on the acquired requested temperature information TU, hot water temperature information TS, and BB flow rate information RB, burner output control processing is executed in step S44, and mixing valve opening adjustment processing is executed in step S46. The burner output control processing and mixing valve opening adjustment processing are executed by determining the output of burner 150 and determining the opening of mixing valve 156 so that hot water temperature information TS approaches requested temperature information TU.

[0087] In step S48, it is determined whether hot water supply has ended. The end of hot water supply can be detected when the BB flow rate information RB becomes 0. If the determination in step S48 is negative, the process returns to step S40 and the above process is repeated. If the determination in step S48 is positive, the hot water supply temperature adjustment process is terminated.

[0088] In this manner, in the fuel cell unit 12 of the present embodiment, the temperature of the hot water supplied to the hot water supply unit 14 is adjusted to within the target hot water outlet range TR close to the target hot water outlet temperature T0. In this manner, by maintaining the target hot water outlet temperature T0 within a constant range, the hot water supply unit 14 reduces the opportunities for control in response to changes in the temperature of the hot water supplied from the fuel cell unit 12. Therefore, even if the hot water supply unit 14 is not in communication with the fuel cell unit 12, abrupt changes in the temperature of the hot water supplied from the hot water supply unit 14 to the user can be suppressed.

[0089] Furthermore, when the tank hot water temperature information TT falls below the switching temperature TC, the target hot water outlet temperature T0 is switched from the normal hot water outlet target temperature T1 to the low-temperature hot water outlet target temperature T2. This switching causes the temperature of the hot water supplied to hot water supply unit 14 to drop from the point at which the temperature of the hot water stored in the hot water storage tank falls below the switching temperature TC, which is higher than the normal hot water outlet target temperature T1. This reduces the amount of heat transferred from the hot water stored in hot water storage tank 48 to the clean water, even when hot water is being supplied continuously for a relatively long period of time (for example, when storing hot water in a bathtub), and makes it possible to suppress the rate at which the temperature of the hot water in hot water storage tank 48 drops.

[0090] Meanwhile, hot water supply unit 14 processes the hot water supplied from fuel cell unit 12 to the required temperature through a hot water supply temperature adjustment process. When the hot water supplied from fuel cell unit 12 is changed from normal hot water outlet target temperature T1 to low temperature hot water outlet target temperature T2, heating is performed in response to this change. As a result, hot water supply unit 14 can suppress the change in the hot water supply temperature to the user at the beginning of the change to about β°C, the temperature difference between normal hot water outlet target temperature T1 and low temperature hot water outlet target temperature T2. This allows hot water supply unit 14 to suppress sudden changes in the temperature of the hot water supplied to the user without obtaining hot water temperature information from the hot water storage tank.

[0091] In this embodiment, the temperature difference β°C between the normal hot water outlet target temperature T1 and the low temperature hot water outlet target temperature T2 is set to be smaller than the temperature difference α°C between the switching temperature TC and the normal hot water outlet target temperature T1, but it does not necessarily have to be set in this manner. By setting α°C > β°C as in this embodiment, the range of temperature change can be reduced.

[0092] [Second embodiment] Next, a second embodiment of the present invention will be described. In this embodiment, the same parts as those in the first embodiment are given the same reference numerals, and detailed descriptions thereof will be omitted.

[0093] In this embodiment, the configuration of the fuel cell system 10 is similar to that of the first embodiment (see Figs. 1 to 4). In this embodiment, there are multiple switching temperatures for switching the target hot water outlet temperature T0, and a low temperature target hot water outlet temperature is set corresponding to each switching temperature.

[0094] In this embodiment, a program for a second target hot water outlet temperature adjustment process is stored as part of control program 115A. In addition, data used in the second target hot water outlet temperature adjustment process is stored, including normal target hot water outlet temperature T1, first low temperature target hot water outlet temperature T2-1, second low temperature target hot water outlet temperature T2-2, first switching temperature TC-1, and second switching temperature TC-2.

[0095] The second target water outlet temperature adjustment process adjusts the water outlet temperature information TD, which is the temperature of the water measured by the outlet water thermometer 67, so that it is within the target water outlet range TR, which is the temperature range above and below the target water outlet temperature T0, and when the tank water temperature information TT becomes equal to or below the first switching temperature TC-1, switches the target water outlet temperature T0 from the normal water outlet target temperature T1 to the first low-temperature water outlet target temperature T2-1, and when the tank water temperature information TT becomes equal to or below the second switching temperature TC-2, switches the target water outlet temperature T0 from the low-temperature water outlet target temperature T2-1 to the second low-temperature water outlet target temperature T2-2.

[0096] Here, the first switching temperature TC-1 is set to a temperature higher than the set hot water outlet target temperature T0. In this embodiment, the normal hot water outlet target temperature T1 is set as the initial value of the hot water outlet target temperature T0, and a temperature α°C higher than the normal hot water outlet target temperature T1 is set as the first switching temperature TC-1. The low temperature hot water outlet target temperature T2-1 is set to a temperature β°C lower than the normal hot water outlet target temperature T1. The temperature difference α°C between the first switching temperature TC-1 and the normal hot water outlet target temperature T1 is set to be larger than the temperature difference β°C between the normal hot water outlet target temperature T1 and the first low temperature hot water outlet target temperature T2-1.

[0097] The second switching temperature TC-2 is set to a temperature α°C higher than the first low-temperature target water outlet temperature T2-1, and the second low-temperature target water outlet temperature T2-2 is set to a temperature β°C lower than the first low-temperature target water outlet temperature T2-1. The second switching temperature TC-2 is set to a temperature lower than the first switching temperature TC-1 and higher than the normal target water outlet temperature T1.

[0098] Temperature adjustment unit 111A adjusts the temperature of hot water supplied from fuel cell unit 12 to hot water supply unit 14 to target hot water outlet temperature T0. Target temperature switching unit 111B switches target hot water outlet temperature T0 from normal hot water outlet target temperature T1 to first low-temperature hot water outlet target temperature T2-1 when tank hot water temperature information TT becomes a first switching temperature TC-1, and switches target hot water outlet temperature T0 from first low-temperature hot water outlet target temperature T2-1 to second low-temperature hot water outlet target temperature T2-2 when tank hot water temperature information TT becomes a second switching temperature TC-2.

[0099] Next, the operation of the FC control unit 110 according to the second embodiment will be described with reference to FIG.

[0100] 8 is a flowchart showing the second target hot water outlet temperature adjustment process of the control program 115A according to the second embodiment. The second target hot water outlet temperature adjustment process is executed while the fuel cell unit 12 is in operation. The target hot water outlet temperature T0 is set to the normal target hot water outlet temperature T1 as an initial value.

[0101] First, in step S12, tank hot water temperature information TT detected by tank temperature sensor 52 is obtained. In step S34, it is determined whether the obtained tank hot water temperature information TT is equal to or lower than first switching temperature TC-1. If the determination in step S34 is negative, in step S18, the target hot water outlet temperature T0 is switched to the normal target hot water outlet temperature T1.

[0102] If the determination in step S34 is positive, then in step S36 it is determined whether the acquired tank hot water temperature information TT is equal to or lower than the second switching temperature TC-2. If the determination in step S36 is negative, then in step S37 the target hot water outlet temperature T0 is switched to the first low-temperature target hot water outlet temperature T2-1. If the determination in step S36 is positive, then in step S38 the target hot water outlet temperature T0 is switched to the second low-temperature target hot water outlet temperature T2-2.

[0103] After steps S18, S37, and S38, a temperature adjustment process is executed in step S20 (see FIG. 5).

[0104] In this embodiment, when the temperature of the hot water stored in the hot water storage tank 48 falls to or below a second switching temperature TC-2 that is lower than the first switching temperature TC-1, the temperature of the hot water delivered from the fuel cell unit 12 is switched from the first low-temperature hot water outlet target temperature T2-1 to an even lower second low-temperature hot water outlet target temperature T2-2. Therefore, the temperature of the hot water delivered from the fuel cell unit 12 can be lowered in multiple stages (two stages), and the hot water supply unit 14 can make the temperature change of the hot water supplied to the user more gradual.

[0105] In this embodiment, the target water outlet temperature T0 is lowered in two stages, but the target water outlet temperature T0 may be lowered in three stages, four stages or more.

[0106] In the first and second embodiments described above, when the flow rate of hot water supplied from fuel cell unit 12 to hot water supply unit 14 falls below a predetermined switching flow rate R0, control may be performed to lower the target hot water outlet temperature T0. In this case, the switching flow rate R0 can be detected based on the flow rate (hot water outlet flow rate R1) measured by flow meter 65. [Explanation of symbols]

[0107] 10. Fuel Cell System 12 Fuel Cell Unit 14 Hot water unit (heat source unit) 20 Fuel Cell Module 48 Hot Water Tank 52 Tank temperature sensor 67 Outlet water thermometer 110 FC control section 111A Temperature adjustment section 111B Target temperature switching section T0 Target temperature T1 Normal target temperature T2 Low temperature tapping target temperature T2-1 First low-temperature tapping target temperature T2-2 Second low-temperature tapping target temperature TC switching temperature TC-1 1st switching temperature TC-2 2nd switching temperature

Claims

1. a fuel cell unit provided with a fuel cell module for generating electricity; a hot water storage tank for storing hot water heated by heat exchange in the fuel cell unit; a temperature sensor provided in the fuel cell unit for measuring the temperature of the hot water stored in the hot water storage tank; a temperature adjusting unit provided in the fuel cell unit, which adjusts the temperature of the hot water discharged from the fuel cell unit to a target hot water outlet temperature by utilizing the heat of the hot water stored in the hot water storage tank; a target temperature switching unit that switches the target hot water outlet temperature from a normal target hot water outlet temperature to a low-temperature target hot water outlet temperature that is lower than the normal target hot water outlet temperature when the temperature of the hot water stored in the hot water storage tank becomes equal to or lower than a switching temperature that is higher than the target hot water outlet temperature based on the temperature measured by the temperature sensor; a heat source unit that is not in communication with the fuel cell unit, the temperature adjustment unit, and the target temperature switching unit and that is capable of heating hot water sent from the fuel cell unit using heat generated by combustion of gas; A fuel cell system comprising:

2. The switching temperature is set to a temperature α°C higher than the normal target temperature. The fuel cell system according to claim 1 .

3. The low temperature target temperature is set at a temperature β°C lower than the normal target temperature, and the relationship is α>β. The fuel cell system according to claim 2 .

4. A second switching temperature is set which is lower than the switching temperature; When the temperature of the hot water stored in the hot water storage tank becomes equal to or lower than the second switching temperature, the target temperature switching unit switches the target hot water outlet temperature from the low-temperature target hot water outlet temperature to a second low-temperature target hot water outlet temperature that is lower than the low-temperature target hot water outlet temperature. The fuel cell system according to any one of claims 1 to 3.

5. The normal hot water outlet target temperature is maintained constant when the temperature of the hot water stored in the hot water storage tank is higher than the switching temperature. The fuel cell system according to any one of claims 1 to 4.

6. In the fuel cell unit, hot water heated by exhaust heat from the fuel cell module which generates electricity is stored in a hot water storage tank; a temperature adjustment unit adjusts the temperature of the hot water discharged from the fuel cell unit to a target hot water outlet temperature by utilizing the heat of the hot water stored in the hot water storage tank, and when the temperature of the hot water stored in the hot water storage tank measured by a temperature sensor falls below a predetermined switching temperature higher than a normal hot water outlet target temperature, a target temperature switching unit switches the adjustment so that the temperature of the hot water discharged from the fuel cell unit changes from the normal hot water outlet target temperature to a low-temperature hot water outlet target temperature lower than the normal hot water outlet target temperature; The hot water delivered from the fuel cell unit can be heated using heat generated by the combustion of gas, and the hot water is delivered to a heat source unit that is not in communication with the fuel cell unit, the temperature adjustment unit, and the target temperature switching unit. A method for operating a fuel cell system.

7. The switching temperature is set to a temperature α°C higher than the normal target temperature, The low temperature target temperature is set to a temperature β°C lower than the normal target temperature, The relationship is said to be α>β. The method for operating a fuel cell system according to claim 6.

8. A second switching temperature is set which is lower than the switching temperature; When the temperature of the hot water stored in the hot water storage tank becomes equal to or lower than the second switching temperature, the target hot water outlet temperature is switched from the low temperature target hot water outlet temperature to a second low temperature target hot water outlet temperature that is lower than the low temperature target hot water outlet temperature. The method for operating a fuel cell system according to claim 6 or 7.

9. The normal hot water outlet target temperature is maintained constant when the temperature of the hot water stored in the hot water storage tank is higher than the switching temperature. The method for operating a fuel cell system according to any one of claims 6 to 8.

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