Fuel cell system

Abstract

To provide a fuel cell system capable of quickly boiling water.SOLUTION: A fuel cell system comprises a hot water storage tank 8 storing hot water, a power generation unit M that operates with supply of fuel gas, a waste heat recovery heat exchange unit N that recovers waste heat from the power generation unit M, a circulation path 9 for the flow of hot water, that connects the bottom of the hot water storage tank 8 to an upper part of the hot water storage tank 8, a circulation pump 10 that circulates hot water through the circulation path 9, an anti-freezing heater 13 that can heat the hot water flowing through the circulation path 9, and an operation control unit 28. When the power generation unit M is operating, the operation control unit 28 causes the waste heat recovery heat exchange unit N and the anti-freeze heater 13 to heat the hot water flowing through the circulation path 9 in such a manner that the temperature of the hot water stored in the hot water storage tank 8 reaches a target temperature.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel cell system. [Background technology]

[0002] Patent document 1 discloses a cogeneration system that is equipped with an anti-freeze heater that heats the hot water flowing through a circulation path, and when the power generation unit is stopped and anti-freeze operation conditions are met, such as the outside air temperature dropping below a set temperature, the anti-freeze heater and circulation pump are activated to heat the hot water flowing through the circulation path.

[0003] Patent Document 2 discloses a hot water storage type hot water supply system that performs a sterilization operation in which all of the hot water in a hot water storage tank is boiled to a sterilization temperature at which Legionella bacteria are killed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-32321 [Patent Document 2] Japanese Patent Publication No. 2022-165691 Summary of the Invention [Problem to be solved by the invention]

[0005] In the cogeneration system described in Patent Document 1, when the power generation unit is operating, heat from the heat exchanger is transferred to the hot water circulating in the heat exchanger so that the temperature of the hot water supplied to the hot water tank reaches a target temperature. As a result, the hot water that has absorbed the heat circulates in the pipes. However, depending on the state of the hot water tank and the amount of hot water used, it may be necessary to boil the water quickly.

[0006] Furthermore, in the hot water storage type hot water supply system described in Patent Document 2, the hot water in the hot water storage tank cannot be used while the sterilization operation is being performed. However, it is desired that the time during which the hot water storage tank cannot be used be as short as possible.

[0007] An object of the present invention is to provide a fuel cell system that can quickly boil water. [Means for solving the problem]

[0008] The characteristic configuration of a fuel cell system for achieving the above-mentioned objective comprises a hot water storage tank for storing hot water, a power generation unit that operates by supplying fuel gas, a waste heat recovery heat exchange unit that recovers waste heat from the power generation unit, a circulation path for the flow of hot water connecting the bottom of the hot water storage tank to the top of the hot water storage tank, a circulation pump that circulates hot water through the circulation path, an anti-freeze heater that can heat the hot water flowing through the circulation path, and an operation control unit, wherein when the power generation unit is operating, the operation control unit heats the hot water flowing through the circulation path using the waste heat recovery heat exchange unit and the anti-freeze heater so that the temperature of the hot water stored in the hot water storage tank reaches a target temperature.

[0009] According to the above-mentioned characteristic configuration, since the hot water is heated by both the exhaust heat recovery heat exchanger and the anti-freeze heater, the time required to boil the hot water is shorter than in a configuration in which the hot water is heated only by the exhaust heat recovery heat exchanger. Therefore, the hot water can be boiled more quickly.

[0010] Another characteristic feature of the fuel cell system of the present invention is that it further comprises a sensor for detecting the state of the hot water tank, and the operation control unit activates the anti-freeze heater depending on the state of the hot water tank detected by the sensor.

[0011] According to the above characteristic configuration, the operation control unit operates the anti-freeze heater when it is necessary to quickly boil water according to the state of the hot water tank. In other words, when it is not necessary to quickly boil water, the anti-freeze heater is not operated. This prevents the anti-freeze heater from being operated unnecessarily, and prevents unnecessary increases in power consumption.

[0012] Another characteristic configuration of the fuel cell system of the present invention is that the sensor detects the temperature of the hot water stored in the hot water storage tank, and the operation control unit activates the anti-freeze heater when it determines that the temperature of the hot water stored in the hot water storage tank is below a first threshold value.

[0013] When the temperature of the hot water in the hot water tank is low, the hot water needs to be boiled. According to the above characteristic configuration, the operation control unit activates the anti-freeze heater when the hot water needs to be boiled quickly. As a result, the hot water is heated by both the exhaust heat recovery heat exchange unit and the anti-freeze heater, so the time it takes to boil the hot water is shortened.

[0014] Another characteristic configuration of the fuel cell system of the present invention is that the sensor detects the amount of hot water stored in the hot water storage tank, and the operation control unit activates the anti-freeze heater when it determines that the amount of hot water stored in the hot water storage tank is less than or equal to a second threshold value.

[0015] When the amount of hot water in the hot water tank is low, the hot water needs to be boiled. According to the above characteristic configuration, the operation control unit activates the anti-freeze heater when the hot water needs to be boiled quickly. As a result, the hot water is heated by both the exhaust heat recovery heat exchange unit and the anti-freeze heater, so the time it takes to boil the hot water is shortened.

[0016] Another characteristic feature of the fuel cell system of the present invention is that it further comprises an acquisition unit that acquires past outside temperatures, seasons, dates, and past amounts of hot and cold water used, and the operation control unit activates the antifreeze heater according to a target day whose past outside temperatures, seasons, or dates are similar to the current day.

[0017] The trends in hot and cold water usage on the current day are similar to those on a target day with a similar past outside temperature, season, or date to the current day. In other words, by referring to the past hot and cold water usage linked to the target day, the hot and cold water usage on the current day can be predicted. According to the above characteristic configuration, the anti-freeze heater is activated when it is predicted that hot and cold water needs to be boiled quickly based on the past hot and cold water usage. In other words, when it is predicted that hot and cold water does not need to be boiled quickly, the anti-freeze heater is not activated. This prevents the anti-freeze heater from being operated unnecessarily, and therefore prevents unnecessarily high power usage.

[0018] Another characteristic feature of the fuel cell system of the present invention is that the operation control unit activates the anti-freeze heater when it determines that the current time corresponds to a time period during which hot water is continuously being used on the target day.

[0019] The time periods during which hot water is continuously used on the target day are time periods during which hot water usage is high. Furthermore, the trends in the amount of hot water used on the current day and the target day are similar. In other words, the time periods on the current day corresponding to the time periods during which hot water is continuously used on the target day are predicted to have high hot water usage. According to the above characteristic configuration, the operation control unit activates the anti-freeze heater when it determines that the current time is a time period during which hot water usage is predicted to be high. As a result, the hot water is heated by both the exhaust heat recovery heat exchange unit and the anti-freeze heater, thereby shortening the time it takes to boil the water.

[0020] Another characteristic feature of the fuel cell system of the present invention is that it further includes an identification unit that identifies a first time period, which is a time period during which the amount of hot water and cold water used within a specified period on the target day exceeds a certain amount, and the operation control unit activates the anti-freeze heater when it determines that the current time corresponds to the first time period.

[0021] On the target day, the first time slot is a time slot during which hot and cold water usage is high. Furthermore, the trends in hot and cold water usage on the current day and the target day are similar. In other words, the time slot on the target day corresponding to the first time slot is predicted to have high hot and cold water usage. According to the above characteristic configuration, the operation control unit activates the anti-freeze heater when it determines that the current time is a time slot during which hot and cold water usage is predicted to be high. As a result, the hot water is heated by both the exhaust heat recovery heat exchange unit and the anti-freeze heater, thereby shortening the time it takes to boil the water.

[0022] Another characteristic feature of the fuel cell system of the present invention is that it further includes a sensor that detects the temperature of the hot water stored in the hot water storage tank, and the operation control unit activates the anti-freeze heater when it determines that the current time corresponds to the first time zone and that the temperature of the hot water detected by the sensor is below a third threshold value.

[0023] According to the above characteristic configuration, when the operation control unit determines that the current time is a time period when hot water usage is predicted to be high and the hot water temperature in the hot water storage tank is low, the operation control unit activates the anti-freeze heater. As a result, the hot water is heated by both the exhaust heat recovery heat exchange unit and the anti-freeze heater, shortening the time it takes to boil the hot water.

[0024] Another characteristic feature of the fuel cell system of the present invention is that it further includes an identification unit that identifies a first time period, which is a time period on the target day when the amount of hot water usage within a specified period exceeds a certain amount, and the operation control unit activates the anti-freeze heater when it determines that, when the power generation unit is started, no hot water has been drawn from the hot water storage tank for a certain period of time or more since the power generation unit was stopped, and that the current time corresponds to the first time period.

[0025] Sterilization operation is required if hot water is not drawn from the hot water storage tank for a certain period of time or longer after the power generation unit is stopped. Furthermore, during sterilization operation, the target temperature at which the hot water is boiled is higher than during normal operation. In other words, the time it takes to boil the water is longer than during normal operation. According to the above characteristic configuration, when the power generation unit is started, the operation control unit activates the anti-freeze heater if it determines that sterilization operation is required and that the current time is a time period when hot water usage is predicted to be high. As a result, the hot water is heated by both the exhaust heat recovery heat exchange unit and the anti-freeze heater, shortening the time it takes to boil the water.

[0026] Another characteristic feature of the fuel cell system of the present invention is that it further includes a sensor that detects the amount of hot water stored in the hot water storage tank, and when the operation control unit determines that the total amount of hot water currently being used exceeds the total amount of hot water used on the target day, it prohibits the operation of the anti-freeze heater.

[0027] If the total amount of hot and cold water currently used exceeds the total amount of hot and cold water used on the target day, it is predicted that the amount of hot and cold water used will be low from then on. According to the above characteristic configuration, the operation control unit prohibits the operation of the anti-freeze heater when it predicts that the amount of hot and cold water used will be low. This prevents the anti-freeze heater from being operated unnecessarily, so that power consumption does not increase unnecessarily.

[0028] Another characteristic feature of the fuel cell system according to the present invention is that the circulation path is connected to the exhaust heat recovery heat exchanger via the antifreeze heater.

[0029] According to the above characteristic configuration, hot water can be heated more efficiently than when the circulation path is divided into a path in which an anti-freeze heater is installed and a path in which an exhaust heat recovery heat exchange unit is installed. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 1 is a diagram showing a fuel cell system. [Figure 2] 10 is a flowchart illustrating an example of processing by an operation control unit. [Figure 3] 10 is a flowchart showing another example of processing by the operation control unit. [Figure 4] FIG. 10 is a diagram showing an example of hot and cold water usage on a target day. [Figure 5] FIG. 10 is a diagram showing an example of the amount of hot and cold water used on a day. [Figure 6] FIG. 10 is a diagram illustrating another example of a fuel cell system. DETAILED DESCRIPTION OF THE INVENTION

[0031] A fuel cell system according to an embodiment of the present invention will now be described with reference to the drawings. As shown in Figure 1, an indoor distribution panel 3 is connected to a plurality of power supply lines 2 to an electrical load 1, a commercial power transmission line 4A from a commercial power source 4 that supplies commercial power, and a power transmission line 5 from a fuel cell power generation module M (corresponding to the power generation unit).

[0032] A power conversion unit 6 having an inverter and the like is provided on the power transmission line 5 from the fuel cell power generation module M. The power conversion unit 6 adjusts the power generated from the fuel cell power generation module M. Specifically, the power conversion unit 6 adjusts the power generated from the fuel cell power generation module M to the same voltage and frequency as the power supplied from the commercial power source 4.

[0033] Commercial power from a commercial power source 4 and power generated by the fuel cell power generation module M are supplied to a plurality of electrical loads 1 via a power supply line 2 .

[0034] As shown in FIG. 1, the fuel cell system includes a system casing K. The system casing K includes a fuel cell power generation module M, a sealed hot water storage tank 8 for storing hot water, a waste heat recovery heat exchanger N for recovering heat from exhaust gas discharged from the fuel cell power generation module M as waste heat, a circulation path 9 for flowing hot water that connects the bottom and top of the hot water storage tank 8, a circulation pump 10 that circulates the hot water through the circulation path 9, an operation control unit 28, and an anti-freeze heater 13 that heats the hot water flowing through the circulation path 9. The circulation path 9 is connected from the bottom of the hot water storage tank 8 to the top of the hot water storage tank 8 via the waste heat recovery heat exchanger N. Hot water taken out from the bottom of the hot water storage tank 8 is returned to the top of the hot water storage tank 8 through the circulation path 9 by the circulation pump 10.

[0035] The fuel cell system includes a remote controller R that transmits various types of information to the operation control unit .

[0036] When the fuel cell power generation module M is in operation, the operation control unit 28 causes the exhaust heat recovery heat exchange unit N to heat the hot water flowing through the circulation path 9 so that the hot water stored in the hot water storage tank 8 reaches a first target temperature T1 (corresponding to the target temperature). The first target temperature T1 is, for example, approximately 65°C. However, the first target temperature T1 can be set arbitrarily by manually operating the remote control R. Furthermore, the first target temperature T1 may be automatically set to a different temperature depending on the season, such as summer, winter, or intermediate season.

[0037] The hot water stored in the hot water tank 8 is discharged to a hot water consumption point such as a hot water tap through a hot water outlet passage 11 connected to the top of the hot water tank 8. In addition, cold water is supplied to the hot water tank 8 from a water supply source such as a tap water line through a water supply passage 12 connected to the bottom of the hot water tank 8.

[0038] 1, the circulation path 9 is connected to the exhaust heat recovery heat exchanger N via an antifreeze heater 13. The circulation path 9 has an outgoing path 9a that connects the bottom of the hot water storage tank 8 with the antifreeze heater 13 and the exhaust heat recovery heat exchanger N, and a returning path 9b that connects the exhaust heat recovery heat exchanger N with the upper part of the hot water storage tank 8.

[0039] On the outbound path 9a, from the upstream side in the direction in which the hot water flows, there are provided a circulation pump 10, an anti-freeze heater 13, and a radiator 14 that cools the hot water flowing through the circulation path 9 in this order. The radiator 14 cools the hot water circulating through the circulation path 9 when the hot water that has reached the first target temperature T1 is stored in the entire hot water storage tank 8 (full storage), etc.

[0040] A pump drive circuit 10A of the circulation pump 10 and a heater drive circuit 13A of the antifreeze heater 13 can be supplied with commercial power from a commercial power source 4 or power from a power conversion unit 6.

[0041] [Sensor] As shown in Figure 1, the fuel cell system includes a cold water side sensor 15 that detects the temperature of hot water taken out from the bottom of the hot water storage tank 8, a hot water side sensor 16 (corresponding to a sensor) that detects the temperature of hot water heated by the exhaust heat recovery heat exchange section N, a hot water storage tank temperature sensor 17a (corresponding to a sensor) that detects the temperature of hot water stored in the hot water storage tank 8, a hot water storage tank water volume sensor 17b (corresponding to a sensor) that detects the amount of hot water stored in the hot water storage tank 8, and a hot water outlet sensor 33 (corresponding to a sensor) that detects the amount of hot water dispensed from the hot water storage tank 8.

[0042] The cold water side sensor 15, the hot water side sensor 16, and the hot water tank temperature sensor 17a are temperature sensors. The cold water side sensor 15 is provided upstream of the circulation pump 10 on the outbound path 9a. The hot water side sensor 16 is provided on the return path 9b. Multiple hot water tank temperature sensors 17a are provided at predetermined intervals in the vertical direction of the hot water storage tank 8. In this embodiment, five hot water tank temperature sensors 17a are provided in the hot water storage tank 8. However, this is not limited to this, and the number of hot water tank temperature sensors 17a can be any number. The temperatures detected by the cold water side sensor 15, the hot water side sensor 16, and the hot water storage tank temperature sensor 17a are output to the operation control unit 28.

[0043] The hot water tank water level sensor 17b and the hot water outlet sensor 33 are water level sensors. The hot water tank water level sensor 17b is provided in the return path 9b. The hot water tank water level sensor 17b detects the flow rate of hot water flowing through the return path 9b per unit time. The hot water outlet sensor 33 is provided in the hot water outlet path 11. The hot water outlet sensor 33 detects the flow rate of hot water flowing through the hot water outlet path 11 per unit time. The amounts of hot water detected by the hot water tank water level sensor 17b and the hot water outlet sensor 33 are output to the operation control unit 28.

[0044] In other words, the hot water tank temperature sensor 17a and the hot water tank water volume sensor 17b detect the state of the hot water tank 8. The state of the hot water tank 8 includes the amount of hot water stored in the hot water tank 8 or the temperature of the hot water.

[0045] Alternatively, the temperature of the hot water stored in the hot water storage tank 8 may be detected by the hot water side sensor 16. The temperature of the hot water stored in the hot water storage tank 8 may be calculated by converting the heat quantity of the hot water accumulated in the hot water storage tank 8 detected by the hot water storage tank temperature sensor 17a.

[0046] The amount of hot water stored in hot water storage tank 8 may be calculated based on the amount of hot water detected by hot water outlet sensor 33. Specifically, the amount of hot water stored in hot water storage tank 8 is calculated by subtracting the amount of hot water dispensed from hot water storage tank 8 from the amount of hot water in hot water storage tank 8 when it is full. In other words, hot water side sensor 16 and hot water outlet sensor 33 detect the state of hot water storage tank 8.

[0047] The amount of hot and cold water used is detected based on a signal input from the hot water discharge sensor 33. The detected amount of hot and cold water used is stored in the operation control unit 28 in association with the time when the hot water was discharged.

[0048] The circulation path 9 has a bypass path 9c that connects the flow path portion of the outgoing path 9a between the chilled water side sensor 15 and the circulation pump 10 with the return path 9b. Also, a bypass valve 18 is provided in the flow path portion of the outgoing path 9a between the chilled water side sensor 15 and the circulation pump 10.

[0049] A mixing valve 19 is provided in the hot water outlet path 11. The mixing valve 19 mixes hot water (cold water) supplied from a branch path 12A branching off from the water supply path 12 with hot water (hot water) flowing through the hot water outlet path 11. By mixing the hot water (cold water) from the branch path 12A with the hot water (hot water) flowing through the hot water outlet path 11, hot water is dispensed at a set hot water temperature that is preset by the remote control R. The set hot water temperature is, for example, about 40°C. However, the set hot water temperature can be set arbitrarily by manually operating the remote control R.

[0050] An instantaneous hot water heater D, which operates on fuel gas such as city gas, processes and dispenses hot water from a hot water outlet passage 11. A cold water passage 20 is provided that supplies hot water (cold water) from branch passage 12A to a location downstream of mixing valve 19 in hot water outlet passage 11. An on-off valve 20A that opens and closes cold water passage 20 is provided in cold water passage 20. When the hot water in hot water storage tank 8 cannot be used due to a sterilization operation of hot water storage tank 8, cold water passage 20 is opened by on-off valve 20A, and hot water (cold water) from cold water passage 20 is supplied to water heater D and heated. As a result, hot water at the set hot water supply temperature can be dispensed even during a sterilization operation of hot water storage tank 8.

[0051] The fuel cell power generation module M comprises a reforming treatment section 22 to which fuel gas such as city gas is supplied through a fuel gas supply path 21, a cell stack 23 comprising a plurality of solid oxide fuel cell cells, and a high-temperature container 24 that houses the reforming treatment section 22 and the cell stack 23.

[0052] The reforming unit 22 performs steam reforming on the fuel gas to generate a reformed gas with a high hydrogen content. The generated reformed gas is supplied to the cell stack 23. The reforming unit 22 is supplied with steam in addition to the fuel gas.

[0053] Air (oxygen-containing gas) is supplied to the interior of the high-temperature container 24. The cell stack 23 generates electricity by passing the reformed gas through the fuel electrode and passing the air (oxygen-containing gas) supplied to the interior of the high-temperature container 24 through the oxygen electrode.

[0054] The reformed gas that has passed through the fuel electrode is combusted using the air (oxygen-containing gas) that has passed through the oxygen electrode and the air (oxygen-containing gas) supplied to the inside of the high-temperature container 24. The reforming processing unit 22 is heated by this combustion heat. An exhaust gas passage 25 is provided through which exhaust gas obtained by burning the reformed gas is discharged from the high-temperature container 24. The exhaust gas passage 25 passes through an exhaust heat recovery heat exchanger N. The exhaust heat recovery heat exchanger N can recover the exhaust heat of the exhaust gas obtained by burning the reformed gas that has passed through the fuel electrode.

[0055] A fuel gas supply valve 26 that opens and closes the fuel gas supply path 21 to turn on and off the supply of fuel gas, and a pressure sensor 27 that detects the supply pressure of fuel gas are provided in the fuel gas supply path 21. The supply pressure of fuel gas detected by the pressure sensor 27 is output to an operation control unit 28.

[0056] [Operation control unit] The operation control unit 28 includes a memory such as a HDD or nonvolatile RAM, and a CPU. The programs stored in the memory are executed by the CPU. As shown in FIG. 1, the operation control unit 28 includes an acquisition unit 29 and an identification unit 30.

[0057] When an operation command is input from the remote control R, the operation control unit 28 performs a predetermined startup procedure (such as opening the fuel gas supply valve 26) to operate the fuel cell power generation module M. In other words, the fuel cell power generation module M operates when fuel gas is supplied. Furthermore, when an operation stop command is input from the remote control R, the operation control unit 28 performs a predetermined stop procedure (such as closing the fuel gas supply valve 26) to stop the fuel cell power generation module M. When the fuel cell power generation module M is stopped, the operation control unit 28 measures the elapsed time since the fuel cell power generation module M was stopped.

[0058] When the operation control unit 28 determines that the anti-freeze conditions are met while the fuel cell power generation module M is stopped and the anti-freeze heater 13 is stopped, it activates the anti-freeze heater 13 and the circulation pump 10 (anti-freeze operation).

[0059] The fuel cell system is equipped with an outside air temperature sensor that detects the outside air temperature. The anti-freeze condition is that the outside air temperature detected by the outside air temperature sensor is lower than a set temperature. When the operation control unit 28 determines that the anti-freeze condition is met, it activates the anti-freeze heater 13 and the circulation pump 10. The set temperature is, for example, about 3°C. However, the set temperature is not limited to this and can be set arbitrarily.

[0060] The operation control unit 28 operates the heater drive circuit 13A to drive the antifreeze heater 13 at the rated output. The operation control unit 28 also operates the pump drive circuit 10A to drive the circulation pump 10 at a drive output (pump output) of about 60% of the rated output.

[0061] The operation control unit 28 is capable of communicating information with external devices via an information communication line 31. The acquisition unit 29 acquires past weather information, seasons, dates, and past amounts of hot and cold water used from an external device or an information providing server 32. The acquisition unit 29 also acquires weather information for the current day, which is the day to which the current time belongs, from the external device or the information providing server 32. The weather information includes the outside temperature, humidity, weather, etc. in the area where the system casing K is installed. The acquisition unit 29 acquires the outside temperature over time. In other words, the acquisition unit 29 acquires the outside temperature, humidity, and weather for each time period.

[0062] The past amount of hot water usage is data relating to the past amount of hot water used that was dispensed from the hot water storage tank 8. In this embodiment, the operation control unit 28 transmits data relating to the amount of hot water usage for each time period for one day to an external device or information providing server 32. This is not a limitation, and the interval at which the operation control unit 28 transmits data to the external device or information providing server 32 can be set arbitrarily. For example, the operation control unit 28 may transmit data for each time period for one week to the external device or information providing server 32.

[0063] The external device or information providing server 32 updates and stores the past amounts of hot and cold water used based on the data sent from the operation control unit 28. The external device or information providing server 32 stores, for example, the amounts of hot and cold water used over the past three years.

[0064] The identifying unit 30 identifies a target date that is a date whose past outdoor temperature, season, or date is similar to the current day's outdoor temperature, season, or date, based on the past outdoor temperature, season, or date.

[0065] In this embodiment, a date similar to the current day's outdoor temperature is a past date whose minimum temperature is within a range of ±2°C of the predicted minimum temperature of the current day. The range of dates similar to the current day's outdoor temperature is not limited to this, and can be set arbitrarily. For example, a date similar to the current day's outdoor temperature may be a past date whose average temperature is within a range of ±2°C of the predicted average temperature of the current day.

[0066] In this embodiment, a date similar to the current date is a past date within a range of ±15 days from the current date in a different year. The range of dates similar to the current date can be set arbitrarily. For example, a date similar to the current date may be a past date in the same month as the current date in a different year.

[0067] As shown in Figure 4, the identification unit 30 identifies a first time period A1, which is a time period during which the amount of hot water and cold water used within a specified period exceeds a certain amount θ1, and a second time period A2, which is a time period during which the amount of hot water and cold water used within a specified period is equal to or less than the certain amount θ1, on the target day.

[0068] The fixed amount θ1 is the amount of hot water that corresponds to the capacity of the hot water tank 8. The fixed amount θ1 is, for example, about 26 L. However, the fixed amount θ1 is not limited to this, and may be smaller or larger than 26 L.

[0069] The predetermined period corresponds to the time it takes for a certain amount θ1 of hot water stored in hot water storage tank 8 to be fully stored by exhaust heat recovery heat exchange section N. The predetermined period is, for example, about four hours.

[0070] The amount of hot water used in first time slot A1 exceeds the capacity of hot water tank 8. In other words, the amount of hot water used in first time slot A1 exceeds the amount of hot water stored in hot water tank 8 at the current time.

[0071] [Switching to heat recovery promotion mode] When the fuel cell power generation module M is in operation, the operation control unit 28 can heat the hot water stored in the hot water storage tank 8 not only by the exhaust heat recovery heat exchange unit N, but also by both the exhaust heat recovery heat exchange unit N and the anti-freeze heater 13, and the hot water flowing through the circulation path 9.

[0072] The processing of the operation control unit 28 will be described with reference to the flowchart in Fig. 2. The operation control unit 28 continuously executes this flowchart at predetermined timings. The steps described below may be performed in any order, or multiple steps may be performed simultaneously, as long as no contradictions arise.

[0073] The operation control unit 28 determines whether the fuel cell power generation module M is in an operating state (step #01). The processing of step #01 is repeated until it is determined that the fuel cell power generation module M is in an operating state (step #01: No).

[0074] Whether the fuel cell power generation module M is in an operating state is determined based on the fuel gas supply pressure input from the pressure sensor 27. However, the operation control unit 28 may also determine whether the fuel cell power generation module M is in an operating state based on the open / closed state of the fuel gas supply valve 26.

[0075] When it is determined that the fuel cell power generation module M is in an operating state (Step #01: Yes), the operation control unit 28 determines whether the hot water tank 8 is full (Step #02). The processing of Step #02 is repeated until it is determined that the hot water tank 8 is not full (Step #02: Yes).

[0076] If it is determined that the hot water tank 8 is not full (step #02: No), the acquisition unit 29 acquires the outside temperature and the amount of hot water used in the past (step #03). In addition, the identification unit 30 identifies a target date in the past (step #04).

[0077] The operation control unit 28 determines whether the fuel cell system satisfies any of the following heat recovery promotion conditions. If any of the following heat recovery promotion conditions is satisfied, the operation control unit 28 activates the anti-freeze heater 13 and the circulation pump 10. In other words, if any of the heat recovery promotion conditions is satisfied, the operation control unit 28 automatically switches the fuel cell system to a heat recovery promotion mode in which the hot water flowing through the circulation path 9 is heated by both the exhaust heat recovery heat exchange unit N and the anti-freeze heater 13. On the other hand, if all of the heat recovery promotion conditions are not satisfied, the operation control unit 28 heats the hot water flowing through the circulation path 9 by the exhaust heat recovery heat exchange unit N.

[0078] In the accelerated heat recovery mode, the operation control unit 28 operates the antifreeze heater 13 even when the fuel cell power generation module M is in an operating state and the antifreeze conditions are not satisfied.

[0079] (Heat recovery promotion condition 1) The temperature of the hot water stored in the hot water storage tank 8 is equal to or lower than the first threshold value V1. The operation control unit 28 determines whether the temperature of the hot water stored in the hot water storage tank 8 is equal to or lower than the first threshold value V1 based on the signal input from the hot water storage tank temperature sensor 17a. In this embodiment, the operation control unit 28 determines whether the temperature of the hot water input from the second-lowest hot water storage tank temperature sensor 17a among the multiple hot water storage tank temperature sensors 17a is equal to or lower than the first threshold value V1. The first threshold value V1 is approximately 25°C. However, the first threshold value V1 can be set arbitrarily.

[0080] (Heat recovery promotion condition 2) The amount of hot water stored in hot water tank 8 is equal to or less than second threshold value V2. Based on a signal input from hot water tank water level sensor 17b, operation control unit 28 determines whether the amount of hot water stored in hot water tank 8 is equal to or less than second threshold value V2. Second threshold value V2 corresponds to approximately one-third of the capacity of hot water tank 8. In this embodiment, second threshold value V2 is approximately 8.7 L. However, the second threshold value V2 is not limited to this and can be set arbitrarily.

[0081] In other words, operation control unit 28 activates antifreeze heater 13 and circulation pump 10 according to the state of hot water tank 8 detected by hot water tank temperature sensor 17a or hot water tank water level sensor 17b.

[0082] (Heat recovery promotion condition 3) Continuous use of hot water is expected. The operation control unit 28 determines whether the current time corresponds to a time period during which hot water is continuously used on the target day. The determination of whether hot water is continuously used will be described later.

[0083] (Heat recovery promotion condition 4) The current time corresponds to the first time zone A1, and the hot water temperature is equal to or lower than the third threshold V3. The operation control unit 28 determines whether the current time corresponds to the first time zone A1, and whether the hot water temperature detected by the hot water storage tank temperature sensor 17a is equal to or lower than the third threshold V3. In this embodiment, the operation control unit 28 determines whether the hot water temperature input from the second-lowest hot water storage tank temperature sensor 17a among the multiple hot water storage tank temperature sensors 17a is equal to or lower than the third threshold V3. The third threshold V3 is approximately 30°C. The third threshold V3 is not limited to this, and can be set arbitrarily.

[0084] In other words, the operation control unit 28 activates the antifreeze heater 13 and the circulation pump 10 according to the past amounts of hot and cold water used that are linked to the target day.

[0085] The operation control unit 28 determines whether the current total amount of hot and cold water usage exceeds the total amount of hot and cold water usage θ2 used on the target day (step #05). If it is determined that the current total amount of hot and cold water usage exceeds the total amount of hot and cold water usage θ2 used on the target day (step #05: Yes), the operation control unit 28 prohibits the operation of the antifreeze heater 13 (step #06).

[0086] If it is determined that the current total amount of hot and cold water usage is less than or equal to the total amount of hot and cold water usage θ2 on the target day (step #05: No), operation control unit 28 determines whether the current time corresponds to a time period during which hot and cold water is continuously used on the target day (step #07).If it is determined that the current time corresponds to a time period during which hot and cold water is continuously used on the target day (step #07: Yes), operation control unit 28 activates antifreeze heater 13 and circulation pump 10 (step #12).

[0087] If it is determined that the current time does not correspond to the time period during which hot water is continuously used on the target day (step #07: No), the operation control unit 28 determines whether the current time corresponds to the first time period A1 (step #08).

[0088] If it is determined that the current time does not correspond to the first time zone A1 (step #08: No), the operation control unit 28 prohibits the operation of the antifreeze heater 13 (step #06). In other words, the antifreeze heater 13 is not operated during a time zone in which hot and cold water usage is predicted to be low. As a result, no power is consumed by the operation of the antifreeze heater 13, so power consumption does not increase unnecessarily. However, if the heat recovery promotion condition 3 is satisfied, the operation of the antifreeze heater 13 is not prohibited by the operation control unit 28 even if it is determined that the current time does not correspond to the first time zone A1.

[0089] If it is determined that the current time corresponds to first time zone A1 (step #08: Yes), operation control unit 28 determines whether the temperature of the hot water is equal to or lower than third threshold value V3 (step #09). If it is determined that the temperature of the hot water is equal to or lower than third threshold value V3 (step #09: Yes), operation control unit 28 activates antifreeze heater 13 and circulation pump 10 (step #12). In other words, operation control unit 28 activates antifreeze heater 13 and circulation pump 10 when it is determined that the current time corresponds to first time zone A1 and that the temperature of the hot water stored in hot water storage tank 8 detected by hot water storage tank temperature sensor 17a is equal to or lower than third threshold value V3.

[0090] If it is determined that the temperature of the hot water is higher than the third threshold V3 (step #09: No), the operation control unit 28 determines whether the amount of hot water stored in the hot water storage tank 8 is equal to or less than the second threshold V2 (step #10). If it is determined that the amount of hot water stored in the hot water storage tank 8 is equal to or less than the second threshold V2 (step #10: Yes), the operation control unit 28 activates the antifreeze heater 13 and the circulation pump 10 (step #12).

[0091] If it is determined that the amount of hot water stored in the hot water storage tank 8 is greater than the second threshold value V2 (step #10: No), the operation control unit 28 determines whether the temperature of the hot water stored in the hot water storage tank 8 is equal to or lower than the first threshold value V1 (step #11). If it is determined that the temperature of the hot water stored in the hot water storage tank 8 is equal to or lower than the first threshold value V1 (step #11: Yes), the operation control unit 28 activates the antifreeze heater 13 and the circulation pump 10 (step #12).

[0092] If it is determined that the temperature of the hot water stored in the hot water tank 8 is higher than the first threshold value V1 (step #11: No), the process proceeds to step #03.

[0093] When the anti-freeze heater 13 and the circulation pump 10 are activated (step #12), the hot water flowing through the circulation path 9 is heated by both the exhaust heat recovery heat exchange unit N and the anti-freeze heater 13. The hot water flowing through the circulation path 9 is supplied to the hot water storage tank 8. The operation control unit 28 determines whether the temperature of the hot water stored in the hot water storage tank 8 has reached the first target temperature T1 (step #13). The processing of step #13 is repeated until it is determined that the temperature of the hot water has reached the first target temperature T1 (step #13: No).

[0094] If it is determined that the temperature of the hot water has reached the first target temperature T1 (step #13: Yes), the operation control unit 28 stops the operation of the antifreeze heater 13 (step #14) and ends the process normally. In this embodiment, the operation control unit 28 determines whether the temperatures of the hot water input from all of the hot water tank temperature sensors 17a have reached the first target temperature T1.

[0095] [Processing during sterilization of hot water tanks] 3, the process performed by operation control unit 28 during the sterilization operation of hot water tank 8 will be described. The steps described below may be performed in any order, or multiple steps may be performed simultaneously, as long as no contradictions arise.

[0096] When starting up the fuel cell power generation module M, the operation control unit 28 determines whether hot water has not been dispensed from the hot water storage tank 8 for a certain period of time or longer since the fuel cell power generation module M was stopped (step #21). The processing of step #21 is repeated until it is determined that hot water has not been dispensed from the hot water storage tank 8 for a certain period of time or longer (step #21: No).

[0097] Whether or not hot water is being discharged from hot water storage tank 8 is determined based on a signal input from hot water discharge sensor 33. Without being limited to this, operation control unit 28 may determine whether or not there is a change in the amount of hot water stored in hot water storage tank 8 based on a signal input from hot water storage tank water volume sensor 17b.

[0098] Whether or not a certain period of time has elapsed is measured based on the time elapsed since the fuel cell power generation module M was shut down. In this embodiment, a certain period of time or more is three days or more. However, the certain period of time is not limited to this and can be set arbitrarily.

[0099] When starting up the fuel cell power generation module M, if it is determined that hot water has not been drawn from the hot water storage tank 8 for a certain period of time or longer (step #21: Yes), the acquisition unit 29 acquires the outside temperature and the amount of hot water used in the past (step #22). In addition, the identification unit 30 identifies the target date (step #23).

[0100] The operation control unit 28 determines whether the fuel cell system satisfies the following sterilization operation promotion conditions. If the following sterilization operation promotion conditions are met, the operation control unit 28 activates the antifreeze heater 13 and the circulation pump 10. In other words, if the sterilization operation promotion conditions are met, the operation control unit 28 heats the hot water flowing through the circulation path 9 by both the exhaust heat recovery heat exchange unit N and the antifreeze heater 13. On the other hand, if the sterilization operation promotion conditions are not met, the operation control unit 28 heats the hot water flowing through the circulation path 9 by the exhaust heat recovery heat exchange unit N.

[0101] (Sterilization operation promotion condition) The current time is a time corresponding to the first time zone A1. The operation control unit 28 determines whether the current time is a time corresponding to the first time zone A1 based on the past amounts of hot and cold water used.

[0102] As described above, the hot water in hot water tank 8 cannot be used during the sterilization operation of hot water tank 8, and therefore the state of hot water tank 8 is not included in the sterilization operation promotion conditions. During the sterilization operation of hot water tank 8, operation control unit 28 activates antifreeze heater 13 and circulation pump 10 according to the past amount of hot water used linked to the target day.

[0103] The operation control unit 28 determines whether the current total amount of hot and cold water usage exceeds the total amount of hot and cold water usage θ2 used on the target day (step #24). If it is determined that the current total amount of hot and cold water usage exceeds the total amount of hot and cold water usage θ2 used on the target day (step #24: Yes), the operation control unit 28 prohibits the operation of the antifreeze heater 13 (step #25).

[0104] If it is determined that the current total amount of hot and cold water usage is equal to or less than the total amount of hot and cold water usage θ2 on the target day (step #24: No), operation control unit 28 determines whether the current time corresponds to first time slot A1 (step #26).If it is determined that the current time does not correspond to first time slot A1 (step #26: No), operation control unit 28 prohibits operation of antifreeze heater 13 (step #25).

[0105] If it is determined that the current time corresponds to the first time zone A1 (step #26: Yes), the operation control unit 28 activates the antifreeze heater 13 and the circulation pump 10 (step #27).

[0106] As described above, when the fuel cell power generation module M is started up, the operation control unit 28 operates the anti-freeze heater 13 and the circulation pump 10 if it determines that no hot water has been drawn from the hot water storage tank 8 for a certain period of time or longer since the fuel cell power generation module M was stopped, and that the current time corresponds to the first time zone A1.

[0107] When the anti-freeze heater 13 and the circulation pump 10 are activated (step #27), the hot water flowing through the circulation path 9 is heated by both the exhaust heat recovery heat exchange unit N and the anti-freeze heater 13. The hot water flowing through the circulation path 9 is supplied to the hot water storage tank 8. The operation control unit 28 determines whether the temperature of the hot water stored in the hot water storage tank 8 has reached the second target temperature T2 (corresponding to the target temperature) (step #28). The processing of step #13 is repeated until it is determined that the temperature of the hot water has reached the second target temperature T2 (step #28: No). In this embodiment, the operation control unit 28 determines whether the temperatures of the hot water input from all of the hot water storage tank temperature sensors 17a have reached the second target temperature T2.

[0108] The second target temperature T2 is preset to a temperature higher than the first target temperature T1. The second target temperature T2 can be set arbitrarily. The second target temperature T2 is, for example, approximately 75°C. Since the temperature of the hot water stored in the hot water storage tank 8 is higher than that during normal use, the hot water in the hot water storage tank 8 is sterilized.

[0109] If it is determined that the temperature of hot water has reached the second target temperature T2 (step #28: Yes), the operation control unit 28 stops the operation of the antifreeze heater 13 (step #29) and ends the process normally.

[0110] Next, an example of the amount of hot and cold water used on a target day will be explained using a specific example.

[0111] Figure 4 shows the past hot and cold water usage on the target day. As mentioned above, the past hot and cold water usage is acquired by the acquisition unit 29 from an external device or the information providing server 32. In Figure 4, time is shown on the horizontal axis. Specifically, the horizontal axis shows the time from 0:00 on the target day to 0:00 on the day following the target day. The time is divided into time slots every four hours starting from 0:00.

[0112] In Figure 4, the vertical axis shows the amount of hot water and water used on the target day. In this embodiment, the amount of hot water and water used shown in the bar graph is the amount of hot water and water used per hour. As mentioned above, the amount of hot water and water used is the amount of hot water and water dispensed from the hot water storage tank 8. In addition, the total amount of hot water and water used for the target day, θ2, is shown in the line graph.

[0113] In Figure 4, the amount of hot and cold water used for each time period is shown by a dashed line. As shown in Figure 4, the amount of hot and cold water used in the time period from 8:00 to 12:00 and the amount of hot and cold water used in the time period from 16:00 to 20:00 exceed a certain amount θ1. In other words, the identification unit 30 identifies the time period from 8:00 to 12:00 and the time period from 16:00 to 20:00 as the first time period A1.

[0114] Furthermore, in time periods other than the time period from 8:00 to 12:00 and the time period from 16:00 to 20:00, the amount of hot water and cold water used for each time period is equal to or less than a certain amount θ1. In other words, the identification unit 30 identifies time periods other than the time period from 8:00 to 12:00 and the time period from 16:00 to 20:00 as second time period A2.

[0115] As shown in Figure 4, the amount of hot water and cold water used per hour is not continuously zero during the time period from 16:00 to 20:00. In other words, the time period from 16:00 to 20:00 is a time period during which hot water and cold water is continuously used on the target day. Therefore, the operation control unit 28 determines that the time period from 16:00 to 20:00 is a time period during which hot water and cold water is continuously used on the target day.

[0116] Next, the amount of hot and cold water used on the day will be explained using a specific example. Figure 5 shows the amount of hot and cold water used on the day. As mentioned above, the amount of hot and cold water used on the day is detected based on the signal input from the hot water outlet sensor 33. In Figure 5, the vertical axis shows the amount of hot and cold water used on the day. In this embodiment, the amount of hot and cold water used shown in the bar graph is the amount of hot and cold water used per hour. The total amount of hot and cold water used on the day is shown in the line graph.

[0117] On the current day, the time slots from 8:00 to 12:00 and from 16:00 to 20:00 are time slots corresponding to the first time slot A1 on the target day. Therefore, in Figure 5, the time slots from 8:00 to 12:00 and from 16:00 to 20:00 are shown as the first time slot.

[0118] Furthermore, on the current day, time periods other than the time period from 8:00 to 12:00 and the time period from 16:00 to 20:00 correspond to the second time period A2 on the target day. Therefore, time periods other than the time period from 8:00 to 12:00 and the time period from 16:00 to 20:00 are referred to as the second time period.

[0119] As shown in Figure 5, at 20:00, the total amount of hot and cold water used for the day (the total amount of hot and cold water used for the day at the current time) exceeds the total amount of hot and cold water used for the day in question, θ2. Therefore, the operation control unit 28 prohibits the operation of the antifreeze heater 13 after 20:00. In other words, the operation control unit 28 does not switch the fuel cell system to the heat recovery promotion mode after 20:00.

[0120] Furthermore, the time period from 16:00 to 20:00 on the current day corresponds to the time period during which hot water is continuously used on the target day. In other words, in the example of Fig. 5, heat recovery promotion condition 3 is satisfied. Therefore, the operation control unit 28 switches the fuel cell system to the heat recovery promotion mode during the time period from 16:00 to 20:00.

[0121] <Another embodiment> The present invention is not limited to the above-described embodiment. For example, the following other embodiments may be used. In the other embodiments described below, the same components as those in the above-described embodiment are assigned the same numbers and symbols.

[0122] [1] In the above-described embodiment, the circulation path 9 is connected to the exhaust heat recovery heat exchanger N via the antifreeze heater 13. However, as shown in FIG. 6 , the circulation path 9 may include an outgoing path 9a connecting the bottom of the hot water tank 8 and the exhaust heat recovery heat exchanger N, a return path 9b connecting the exhaust heat recovery heat exchanger N and the upper part of the hot water tank 8, and a bypass path 9c connecting a flow path portion of the outgoing path 9a between the cold water side sensor 15 and the circulation pump 10 to the return path 9b via the antifreeze heater 13. In this case, the fuel cell system may include, as the circulation pump 10, a first circulation pump 10a provided on the outgoing path 9a and a second circulation pump 10b provided on the bypass path 9c. In this embodiment, the hot water side sensor 16 is provided downstream of the flow path portion where the return path 9b and the bypass path 9c join.

[0123] In this embodiment, the operation control unit 28 may operate the circulation pump 10 when the fuel cell system satisfies any of the heat recovery promotion conditions. Specifically, the operation control unit 28 operates the first circulation pump 10a and the second circulation pump 10b when the fuel cell system satisfies any of the heat recovery promotion conditions. In other words, the operation control unit 28 operates only the first circulation pump 10a when all of the heat recovery promotion conditions are not satisfied. In this case, the timing at which the antifreeze heater 13 operates is arbitrary. For example, the antifreeze heater 13 may be operated before the second circulation pump 10b is operated, or after the second circulation pump 10b is operated.

[0124] [2] In the above-described embodiment, the amount of hot water used is detected based on the signal input from the hot water outlet sensor 33. However, the amount of hot water used may be detected based on the amount of hot water in the hot water tank 8 input from the hot water tank water level sensor 17b.

[0125] [3] In the above-described embodiment, the past amounts of hot and cold water used are stored in an external device or the information providing server 32. However, the past amounts of hot and cold water used may be stored in the operation control unit 28. Furthermore, at least a portion of the past amounts of hot and cold water used may be stored in each of the external device, the information providing server 32, and the operation control unit 28.

[0126] [4] In the above-described embodiment, the identification unit 30 identifies the target date based on the past outside temperature and the past amount of hot and cold water used acquired by the acquisition unit 29. Without being limited to this, the identification unit 30 may be provided in the information providing server 32 or an external device. In this case, the identification unit 30 identifies the target date based on the past amount of hot and cold water used stored in the information providing server 32 or an external device. Furthermore, the acquisition unit 29 may acquire the amount of hot and cold water used on the target date identified by the identification unit 30.

[0127] [5] In the above-described embodiment, the heat recovery promotion condition 4 is that the current time corresponds to the first time slot A1 and the temperature of the hot water is equal to or lower than the third threshold value V3. However, the heat recovery promotion condition 4 may also be that the current time corresponds to the first time slot A1. In other words, the operation control unit 28 may activate the antifreeze heater 13 when it determines that the current time corresponds to the first time slot A1. In this embodiment, the antifreeze heater 13 is activated even when the temperature of the hot water is higher than the third threshold value V3.

[0128] [6] In the above-described embodiment, the operation control unit 28 activates the antifreeze heater 13 and the circulation pump 10 when the fuel cell system satisfies any of the heat recovery promotion conditions. Alternatively, the operation control unit 28 may activate the antifreeze heater 13 when the fuel cell system satisfies any of the heat recovery promotion conditions. In this case, the timing at which the circulation pump 10 operates is arbitrary. For example, the circulation pump 10 may be operated before the antifreeze heater 13 is operated, or after the antifreeze heater 13 is operated.

[0129] [7] The operation control unit 28 may switch the fuel cell system to the heat recovery promotion mode when the remote control R or other devices (for example, a mobile terminal) are manually operated. [Industrial Applicability]

[0130] The present invention can be used in a fuel cell system. [Explanation of symbols]

[0131] 8: Hot water tank 9: Circulation path 10: Circulation pump 13: Anti-freeze heater 16: Hot water sensor (sensor) 17a: Hot water tank temperature sensor (sensor) 17b: Hot water tank water level sensor (sensor) 28: Operation control unit 29: Acquisition section 30: Specific part 33: Hot water sensor (sensor) A1: 1st time slot M: Fuel cell power generation module (power generation section) N: Exhaust heat recovery heat exchange section T1: 1st target temperature (target temperature) T2: 2nd target temperature (target temperature) V1: First threshold V2: Second threshold V3: Third threshold θ1: constant amount θ2: Total amount used

Claims

1. A hot water storage tank for storing hot water; a power generation unit that operates by supplying fuel gas; a waste heat recovery heat exchange unit that recovers waste heat from the power generation unit; a circulation path for hot water flow that connects the bottom of the hot water storage tank and the upper part of the hot water storage tank; a circulation pump that circulates hot and cold water through the circulation path; an antifreeze heater capable of heating the hot water flowing through the circulation path; An operation control unit, The operation control unit is a fuel cell system that, when the power generation unit is operating, heats the hot water flowing through the circulation path using the exhaust heat recovery heat exchange unit and the anti-freeze heater so that the temperature of the hot water stored in the hot water storage tank reaches a target temperature.

2. Further provided is a sensor for detecting the state of the hot water tank; 2. The fuel cell system according to claim 1, wherein the operation control unit activates the antifreeze heater in accordance with the state of the hot water tank detected by the sensor.

3. The sensor detects the temperature of the hot water stored in the hot water tank, 3. The fuel cell system according to claim 2, wherein the operation control unit activates the antifreeze heater when it determines that the temperature of the hot water stored in the hot water tank is equal to or lower than a first threshold value.

4. The sensor detects the amount of hot water stored in the hot water storage tank, 3. The fuel cell system according to claim 2, wherein the operation control unit activates the antifreeze heater when it determines that the amount of hot water stored in the hot water storage tank is equal to or less than a second threshold value.

5. An acquisition unit for acquiring past outdoor temperatures, seasons, dates, and past amounts of hot and cold water used, 2. The fuel cell system of claim 1, wherein the operation control unit operates the antifreeze heater according to the past outside air temperature, the season, or the past usage amount linked to a target date that is similar to the current date.

6. The fuel cell system of claim 5, wherein the operation control unit activates the anti-freeze heater when it determines that the current time corresponds to a time period during which hot water is continuously used on the target day.

7. The apparatus further includes an identification unit that identifies a first time period, which is a time period during which the amount of hot water and cold water used exceeds a certain amount within a predetermined period on the target day; 6. The fuel cell system according to claim 5, wherein the operation control unit activates the antifreeze heater when it determines that the current time corresponds to the first time zone.

8. Further provided is a sensor for detecting the temperature of the hot water stored in the hot water storage tank, A fuel cell system as described in claim 7, wherein the operation control unit activates the anti-freeze heater when it determines that the current time corresponds to the first time zone and that the temperature of the hot water detected by the sensor is below a third threshold value.

9. The apparatus further includes an identification unit that identifies a first time period, which is a time period during which the amount of hot water and cold water used exceeds a certain amount within a predetermined period on the target day; The fuel cell system of claim 5, wherein the operation control unit activates the anti-freeze heater when the power generation unit is started up if it determines that no hot water has been drawn from the hot water storage tank for a certain period of time or more since the power generation unit was stopped, and that the current time corresponds to the first time zone.

10. Further provided is a sensor for detecting the amount of hot water stored in the hot water tank, The fuel cell system described in claim 5, wherein the operation control unit prohibits operation of the anti-freeze heater when it determines that the total amount of hot water and water currently used exceeds the total amount of hot water and water used on the target day.

11. 2. The fuel cell system according to claim 1, wherein the circulation path is connected to the exhaust heat recovery heat exchanger via the antifreeze heater.

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