JP7664812B2 - Fuel cell system and hot water storage unit for fuel cell system - Google Patents

Description

This invention relates to a fuel cell system that uses waste heat from a fuel cell to heat hot water and a hot water storage unit for the fuel cell system.

Conventionally, this type of fuel cell system, as described in Patent Document 1, has been provided with a first heating circuit that recovers exhaust heat from the fuel cell to heat hot water, and a second heating circuit that heats hot water using heat from a separately provided heating means (combustion heat from a gas burner), and these first and second heating circuits are connected in parallel to the hot water storage tank.

JP 2014-182923 A

In the above conventional system, the first heating circuit cannot recover much waste heat from the fuel cell, so the second heating circuit is provided to supplement the heating capacity required by the hot water user (hereinafter referred to as the required heating capacity, as appropriate). In this case, the first heating circuit and the second heating circuit are connected in parallel to the hot water storage tank as described above, so that the supply of hot water heated by the first heating circuit to the hot water storage tank and the supply of hot water heated by the second heating circuit to the hot water storage tank can be performed simultaneously in parallel.

Here, when power generation by the fuel cell is not performed for a long period of time, for example due to a long absence of the user, a circulation pump provided in the first heating circuit may be driven to prevent the proliferation of bacteria in the first heating circuit, and hot water circulation operation may be performed to circulate the hot water in the first heating circuit and the hot water in the hot water storage tank. In this case, hot water is supplied from the first heating circuit to the hot water storage tank without heating the hot water by the exhaust heat recovery of the first heating circuit from the fuel cell as described above.

In this way, when power generation is not performed and exhaust heat recovery is not performed in the first heating circuit, if there is a need for hot water supply from a user, hot water heated by the second heating circuit is supplied to the hot water storage tank. If such supply of hot water from the second heating circuit is performed simultaneously in parallel with the supply of hot water from the first heating circuit by the hot water circulation operation, depending on the flow rate of hot water on the first heating circuit side, the flow rate on the second heating circuit side may become extremely small, and adverse effects such as the heating capacity of the second heating circuit (in other words, the flow rate of hot water discharged from the second heating circuit required to raise the temperature of the hot water discharged from the first heating circuit when it merges with the first heating circuit) becoming uncontrollable may occur.

In order to solve the above problem, claim 1 of the present invention provides a fuel cell system having a hot water storage tank for storing hot water, a common supply pipe connected to the lower part of the hot water storage tank and for discharging the hot water in the hot water storage tank, a common return pipe connected to the upper part of the hot water storage tank and for returning the hot water after heating to the hot water storage tank, a heater side heating circuit having an auxiliary heater capable of heating hot water and a heater side circulation pump for circulating the hot water, a fuel cell side heating circuit having a fuel cell side circulation pump for circulating hot water that has recovered exhaust heat from a fuel cell, and control means for controlling at least the heater side circulation pump and the fuel cell side circulation pump in response to a predetermined instruction signal, The heater side heating circuit and the fuel cell side heating circuit are connected in parallel to branch off from the common return pipe, and the hot water outlet sides of the heater side heating circuit and the fuel cell side heating circuit are connected in parallel to merge into the common return pipe. When a conflict occurs between a heater operation request that instructs a heater heating operation to supply hot water heated by the auxiliary heater from the heater side heating circuit to the hot water storage tank, and a circulation operation request that instructs a hot water circulation operation to circulate the hot water in the fuel cell side heating circuit and the hot water storage tank without recovering exhaust heat from the fuel cell, the control means controls the fuel cell side circulation pump and the heater side circulation pump to give priority to the heater operation request and to perform the heater heating operation without performing the hot water circulation operation.

In addition, in claim 2, the control means outputs an operation refusal notification to the effect that the hot water circulation operation is refused when the heater heating operation is being performed based on the input of the heater operation request.

In addition, in claim 3, when the heater operation request is input while the hot water circulation operation is being performed based on the input of the circulation operation request, the control means controls the heater side circulation pump to interrupt the hot water circulation operation and perform the heater heating operation based on the heater operation request.

In addition, in claim 4, the fuel cell side circulation pump is driven at a predetermined fixed rotation speed for hot water circulation operation when the hot water circulation operation is performed.

In addition, in claim 5, the fuel cell side circulation pump is driven within a predetermined variable rotation speed range for exhaust heat recovery operation during the execution of an exhaust heat recovery operation in which hot water heated by recovering exhaust heat from the fuel cell is supplied from the fuel cell side heating circuit to the hot water storage tank, and the fixed rotation speed is a value greater than the maximum value of the variable rotation speed range.

In claim 6, the hot water supply system further includes a connection pipe connecting the hot water outlet side and the hot water inlet side of the fuel cell side heating circuit, and a switching valve that is provided at a position where the connection pipe branches off from the hot water outlet side of the fuel cell side heating circuit or at a position where the hot water inlet side of the fuel cell side heating circuit and the connection pipe join, and is switchable between a first switching position that returns the hot water flowing out from the hot water outlet side of the fuel cell side heating circuit to the hot water inlet side of the fuel cell side heating circuit via the connection pipe, and a second switching position that guides the hot water flowing out from the hot water outlet side of the fuel cell side heating circuit to the common return pipe, and the switching valve is switched to the second switching position by the control means when the hot water circulation operation starts, and is switched to the first switching position when the hot water circulation operation ends.

In addition, in order to solve the above problem, claim 7 of the present invention provides a hot water storage unit for a fuel cell system, the hot water storage unit having a hot water storage tank for storing hot water, a common supply pipe connected to the lower part of the hot water storage tank and for discharging the hot water in the hot water storage tank, a common return pipe connected to the upper part of the hot water storage tank and for returning the hot water after heating into the hot water storage tank, a heater side heating circuit having an auxiliary heater capable of heating hot water and a heater side circulation pump for circulating the hot water, and a heater side control means for controlling at least the heater side circulation pump in response to a predetermined instruction signal, the hot water inflow side of the heater side heating circuit being connected to the hot water inflow side of a fuel cell side heating circuit having a fuel cell side circulation pump for circulating hot water that has recovered exhaust heat from a fuel cell The hot water outlet side of the heater side heating circuit is connected in parallel with the hot water outlet side of the fuel cell side heating circuit so as to branch off from the common forward pipe, and the hot water outlet side of the heater side heating circuit is connected in parallel with the hot water outlet side of the fuel cell side heating circuit so as to merge into the common return pipe. In the event of a conflict between a heater operation request that instructs a heater heating operation in which hot water heated by the auxiliary heater is supplied from the heater side heating circuit to the hot water storage tank, and a circulation operation request that instructs a hot water circulation operation in which hot water in the fuel cell side heating circuit and hot water in the hot water storage tank are circulated without recovering exhaust heat from the fuel cell, the heater operation request is given priority, and the heater heating operation is performed without performing the hot water circulation operation.

According to claim 1 of this invention, the hot water in the hot water storage tank is configured to be heated using the exhaust heat of the fuel cell. That is, a fuel cell side circulation pump is provided to circulate the hot water, and a fuel cell side heating circuit is provided to recover the exhaust heat of the fuel cell, with the hot water inflow side of the fuel cell side heating circuit connected to a common forward pipe from the hot water storage tank, and the hot water outflow side of the fuel cell side heating circuit connected to a common return pipe to the hot water storage tank. As a result, the hot water in the hot water storage tank is introduced into the fuel cell side heating circuit via the common forward pipe, and is then heated using the exhaust heat of the fuel cell, and the heated hot water is returned to the hot water storage tank via the common return pipe.

According to claim 1, a heater-side heating circuit is provided that includes an auxiliary heater capable of heating hot and cold water and a heater-side circulation pump to supplement the required heating capacity. The hot and cold water inflow side of this heater-side heating circuit is connected in parallel with the hot and cold water inflow side of the fuel cell-side heating circuit so as to branch off from a common forward pipe from the hot water storage tank. The hot and cold water outflow side of the heater-side heating circuit is connected in parallel with the hot and cold water outflow side of the fuel cell-side heating circuit so as to merge into a common return pipe to the hot water storage tank. In other words, the fuel cell-side heating circuit and the heater-side heating circuit are connected in parallel with the hot water storage tank. This makes it possible to simultaneously supply hot water heated by the fuel cell-side heating circuit to the hot water storage tank and supply hot water heated by the heater-side heating circuit to the hot water storage tank.

According to claim 1, when power generation by the fuel cell is not performed for a long period of time due to a long absence of the user, etc., a circulation pump is driven to prevent the proliferation of bacteria in the fuel cell side heating circuit, and a hot water circulation operation is performed to circulate the hot water in the fuel cell side heating circuit and the hot water in the hot water storage tank. In this case, hot water is supplied to the hot water storage tank from the fuel cell side heating circuit without heating the hot water by exhaust heat recovery of the fuel cell as described above. At this time, the fuel cell side circulation pump of the fuel cell side heating circuit is controlled by the control means based on a predetermined command signal.

When power generation is not performed as described above and exhaust heat recovery is not performed by the fuel cell side heating circuit, if there is a need for hot water supply, heater heating operation is performed in which hot water heated by the heater side heating circuit is supplied to the hot water storage tank. At this time, the heater side circulation pump of the heater side heating circuit is controlled by the control means based on a specified command signal.

When the supply of hot water from this heater side heating circuit is performed simultaneously with the supply of hot water from the fuel cell side heating circuit by the hot water circulation operation, the flow rate of the heater side heating circuit may become extremely low depending on the flow rate (circulation flow rate) of the fuel cell side heating circuit, and the heating capacity of the heater side heating circuit may become uncontrollable.

According to claim 1, the control means for controlling the heater side circulation pump executes control that prioritizes heater heating operation over hot water circulation operation. Specifically, when a heater operation request instructing heater heating operation conflicts with a circulation operation request instructing hot water circulation operation, the heater operation request is prioritized, and the fuel cell side circulation pump and the heater side circulation pump are controlled so that the heater heating operation is performed without performing the hot water circulation operation.

As a result, when the heater heating operation is performed, the hot water circulation operation is not performed, so it is possible to prevent the flow rate of the heater side heating circuit from becoming extremely low due to the influence of the flow rate of the fuel cell side heating circuit as described above. As a result, it is possible to avoid the occurrence of an uncontrollable state of the heating capacity of the heater side heating circuit as described above.

According to claim 2, when heater heating operation is being performed, the control means outputs an operation refusal notification to the effect that hot water circulation operation is refused. This makes it possible to reliably avoid an uncontrollable state of the heating capacity of the heater side heating circuit due to a conflict between the two operations by not executing hot water circulation operation when heater heating operation is being performed.

According to claim 3, if a heater heating operation is instructed by a heater operation request while hot water circulation operation is being performed, the control means interrupts the hot water circulation operation and starts the heater heating operation. This makes it clear that the heater heating operation is executed with priority over the hot water circulation operation, and it is possible to reliably avoid an uncontrollable state of the heating capacity of the heater side heating circuit due to a conflict between the two operations.

According to claim 4, as described above, in the hot water circulation operation, in order to prevent the proliferation of bacteria in the fuel cell side heating circuit, hot water is circulated between the fuel cell side heating circuit and the hot water storage tank, and the hot water in the fuel cell side heating circuit is replaced. Even if bacteria are generated in the hot water in the fuel cell side heating circuit, the bacteria can be killed by supplying hot water to the hot water storage tank, which has a relatively high temperature.

According to claim 4, in response to the above, the fuel cell side circulation pump is driven at a fixed rotation speed for hot water circulation operation, which is set high in advance to achieve a relatively high flow rate, for example. This allows the hot water to be replaced quickly and reliably to kill germs.

Furthermore, according to claim 5, the fixed rotation speed when the fuel cell side circulation pump is driven during hot water circulation operation is set to a value greater than the maximum value of the predetermined rotation speed range when variably controlled during exhaust heat recovery operation. This makes it possible to replace the hot water more quickly and reliably.

According to claim 6, a connecting pipe is provided to connect the hot water outlet side and the hot water inlet side of the fuel cell side heating circuit, and a switching valve is provided at a position where the connecting pipe branches off from the hot water outlet side or at a position where the hot water inlet side of the fuel cell side heating circuit and the connecting pipe join. This switching valve can be switched between a first switching position and a second switching position under the control of a control means, and is normally switched to the first switching position. In the first switching position, the hot water flowing out from the hot water outlet side of the fuel cell side heating circuit is returned to the hot water inlet side of the fuel cell side heating circuit via the connecting pipe. In addition, in the second switching position, the hot water flowing out from the hot water outlet side of the fuel cell side heating circuit is guided to the common return pipe.

According to claim 6, the control means switches the switching valve from the first switching position to the second switching position when the hot water circulation operation starts, and returns the switching valve to the original first switching position when the hot water circulation operation ends. As a result, while the switching valve is basically switched to the first switching position, the hot water outlet side of the fuel cell side heating circuit is connected to the common return pipe during hot water circulation operation, and hot water flowing out from the hot water outlet side of the fuel cell side heating circuit can be reliably supplied into the hot water storage tank via the common return pipe.

FIG. 1 is a circuit diagram showing the overall schematic configuration of a fuel cell system according to an embodiment of the present invention. FIG. 1 is a perspective view showing a detailed structure of a heater device; A diagram explaining the operation of exhaust heat only heating operation (when the hot water temperature in the heating circuit is lower than a specified value) A diagram explaining the operation of exhaust heat only heating operation (when the hot water temperature in the heating circuit is above a specified value) A diagram explaining the operation of the heater auxiliary boiling operation Diagram explaining hot water supply operation Diagram explaining the operation of the water filling operation Diagram explaining the operation of reheating operation Diagram explaining hot water circulation operation A diagram explaining the operation of heater-only heating operation A sequence flow diagram showing a control procedure executed by a hot water supply control unit of a hot water supply unit.

Next, one embodiment of the present invention will be described with reference to Figures 1 to 11.

<Overall composition>
The overall configuration of a fuel cell system according to this embodiment is shown in schematic form in Fig. 1. In Fig. 1, this fuel cell system 1 has a hot water supply unit 100 (corresponding to a hot water storage unit for a fuel cell system) and an exhaust heat recovery unit 200.

<Hot water supply unit>
The hot water supply unit 100 has a hot water storage tank 2 for storing hot water, and a hot water tap 4 provided in the kitchen, the washroom, etc.

<Hot water storage tank and hot water outlet pipeline system>
The hot water storage tank 2 is a large-capacity tank having a capacity of, for example, 370 liters, and is connected to a hot water outlet pipe 8 at the top and a water supply pipe 9 at the bottom. In addition to the hot water outlet pipe 8 and the water supply pipe 9, a common forward pipe 10 is connected to the bottom of the hot water storage tank 2, and a common return pipe 11 is connected to the top. The hot water in the hot water storage tank 2 discharged through the common forward pipe 10 is heated by a heating circuit 400 (described later) in the exhaust heat recovery unit 200 and an auxiliary heating circuit 300 (described later) in the hot water supply unit 100, and then returned to the hot water storage tank 2 from the common return pipe 11, that is, stored by the supply of hot water from each circuit. In addition, the hot water in the hot water storage tank 2 is pushed up by the water supply from the water supply pipe 9, and the high-temperature water in the upper part of the hot water storage tank 2 is pushed out from the hot water outlet pipe 8 and supplied. In this case, the water supply pipe 9 is provided with a pressure reducing valve 46 for reducing the pressure of the water supply, and a water supply temperature sensor 49 for detecting the temperature of the water supply, and the hot water outlet pipe 8 is provided with an overpressure relief valve 45 for relieving overpressure in the hot water storage tank 2.

Multiple hot water temperature sensors 39 are arranged vertically in the hot water tank 2. In this embodiment, five hot water temperature sensors 39a, 39b, 39c, 39d, and 39e are arranged from top to bottom, and the temperature information detected by these hot water temperature sensors 39a-e is used to detect how much heat remains in the hot water tank 2, and further detects the vertical temperature distribution within the hot water tank 2.

Meanwhile, a heat exchanger 19 consisting of, for example, a stainless steel coiled pipe is provided in the hot water storage tank 2 to heat the hot water in the bathtub 6. A bath supply pipe 20 and a bath return pipe 22 equipped with a bath circulation pump 21 are connected to this heat exchanger 19, allowing the hot water in the bathtub 6 to circulate. That is, the hot water in the bathtub 6 guided through the bath return pipe 22 is heated in the heat exchanger 19 by the high-temperature water in the hot water storage tank 2, and then returned to the bathtub 6 through the bath supply pipe 20 to keep it warm or to reheat it. The bath return pipe 22 is provided with a bath temperature sensor 23 that detects the temperature of the circulating hot water in the bathtub 6.

An intermediate hot water outlet pipe 24 is connected to the intermediate position (not limited to approximately the center position in the vertical direction) of the hot water storage tank 2. This intermediate hot water outlet pipe 24 discharges hot water stored in the intermediate position (not limited to approximately the center position in the vertical direction) of the hot water storage tank 2, such as medium-temperature water whose temperature has been reduced by heat exchange with hot water from the bathtub 6 in the heat exchanger 19, or medium-temperature water whose temperature has been reduced (or increased) near the boundary layer between hot water and water.

Furthermore, at the downstream confluence position of the intermediate hot water outlet pipe 24 and the hot water outlet pipe 8, an intermediate mixing valve 25 consisting of an electric mixing valve is provided, which mixes the medium-temperature water guided from near the intermediate position of the hot water storage tank 2 via the intermediate hot water outlet pipe 24 and the high-temperature water guided via the hot water outlet pipe 8 connected to the upper end of the hot water storage tank 2. An intermediate hot water supply pipe 27 is connected downstream of this intermediate mixing valve 25, and an intermediate temperature sensor 26 is provided. The mixing ratio of the medium-temperature water and the high-temperature water in the intermediate mixing valve 25 is controlled so that the hot water temperature detected by the intermediate temperature sensor 26 becomes a mixed target temperature that is a predetermined temperature higher than the hot water supply setting temperature set by the user, for example, on a hot water supply remote control installed near the hot water tap 4 or a bath remote control installed in the bathroom.

Furthermore, at the downstream junction of the intermediate hot water supply pipe 27 and the water supply bypass pipe 29 branched off from the water supply pipe 9, a hot water supply mixing valve 28 consisting of an electric mixing valve is provided, which mixes the hot water guided from the intermediate mixing valve 25 via the intermediate hot water supply pipe 27 and the low temperature water guided from the water supply bypass pipe 29. A hot water supply pipe 30 is connected downstream of this hot water supply mixing valve 28, and a hot water supply temperature sensor 31 is provided. The mixing ratio of the hot water and the low temperature water in the hot water supply mixing valve 28 is controlled so that the hot water temperature detected by the hot water supply temperature sensor 31 becomes the hot water supply setting temperature set by the user on the hot water supply remote control or the bath remote control. The hot water supply pipe 30 is further provided with a hot water supply flow rate sensor 47 that detects the amount of hot water to be supplied.

At the downstream junction of the branch intermediate hot water supply pipe 33 branched from the intermediate hot water supply pipe 27 and the branch water supply bypass pipe 34 branched from the water supply pipe 9, a bath mixing valve 32 consisting of an electric mixing valve is provided, which mixes the hot water guided through the branch intermediate hot water supply pipe 33 and the low-temperature water guided from the branch water supply bypass pipe 34. A bath filling pipe 35 communicating with the bath return pipe 22 is connected downstream of this bath mixing valve 32, and a bath filling temperature sensor 36 is provided. The mixing ratio of the hot water and the low-temperature water in the bath mixing valve 32 is controlled so that the water temperature detected by the bath filling temperature sensor 36 becomes the bath setting temperature set by the user on the hot water supply remote control or the bath remote control. The bath filling pipe 35 is provided with a bath filling valve 37 that starts/stops filling the bathtub 6 with water, a bath flow rate sensor 38 that detects the amount of water filled in the bathtub 6, and a double check valve 48 that prevents the hot water in the bathtub 6 from flowing back.

<Waste heat recovery unit>
The exhaust heat recovery unit 200 comprises a fuel cell power generation unit 410, a hot water circulation circuit 411 that receives heat from the power generation section (heat generation section) of the fuel cell power generation unit 410 (in other words, exhaust heat from the fuel cell), a hot water circulation pump 412 provided in the hot water circulation circuit 411, a heating circuit 400 (corresponding to the fuel cell side heating circuit) for heating the hot water in the hot water storage tank 2 as described below, a circulation pump 417 (corresponding to the fuel cell side circulation pump) provided in the heating circuit 400, a water-water heat exchanger 416 that recovers exhaust heat from the fuel cell and heats the hot water by performing heat exchange between the hot water on the hot water circulation circuit 411 side and the hot water on the heating circuit 400 side, a temperature sensor 415 provided in the heating circuit 400 that detects the temperature of the hot water flowing out from the water-water heat exchanger 416, and an exhaust heat recovery control section 444 (corresponding to a control means, pump control means) that controls the operation of the circulation pump 417.

The hot water inlet side of the heating circuit 400 is connected to the common supply pipe 10 via a connecting pipe 153 outside the exhaust heat recovery unit 200 equipped with a water inlet filter 151 and a manual valve 152, a pipe 92 inside the hot water supply unit 100 connected via a connection port 91 to the hot water supply unit 100, a pipe 93, and a pipe 94.
The hot water outflow side of the heating circuit 400 is connected to the common return pipe 11 via a connecting pipe 155 outside the exhaust heat recovery unit 200 equipped with a manual valve 154, a pipe 96 inside the hot water supply unit 100 connected via a connection port 95 to the hot water supply unit 100, a hot water storage switching valve 97 (equivalent to a switching valve), and a pipe 98.

The hot water storage switching valve 97 is provided at a branching position where the connecting pipe 87 (described later) branches off from the hot water outlet side of the heating circuit 400 (or at a junction position where the hot water inlet side of the heating circuit 400 and the connecting pipe 87 join). The hot water storage switching valve 97 can be switched between a first switching position (see FIG. 3, etc., described later) in which the hot water flowing out from the hot water outlet side of the heating circuit 400 is returned to the hot water inlet side of the heating circuit 400 via the connecting pipe 87, and a second switching position (see FIG. 4, etc., described later) in which the hot water flowing out from the hot water outlet side of the heating circuit 400 is guided to the common return pipe 11.

With the above-mentioned piping configuration, when a demand for exhaust heat recovery arises due to power generation, the circulation pump 417 circulates the hot water in the hot water storage tank 2 through the water-water heat exchanger 416 via the common supply pipe 10 and the common return pipe 11. As a result, the hot water on the heating circuit 400 side is heated by receiving heat from the hot water on the hot water circulation circuit 411 side.
At this time, the circulation pump 417 is controlled by the exhaust heat recovery control unit 444. Specifically, the rotation speed of the circulation pump 417 is controlled by the exhaust heat recovery control unit 444 so that the temperature of the hot and cold water detected by the temperature sensor 415 becomes a predetermined target temperature. In addition, the heat exchange capacity of the water-water heat exchanger 416 is set to about 1.0 to 2.0 kW.

In addition, the pipes 92 and 96 are provided with sensors 89 and 88 for detecting the temperature of the hot water, respectively, and the hot water storage switching valve 97 is controlled by the hot water supply control unit 44 (corresponding to the heater side control means, control means) based on the detection results of these sensors 89 and 88. In addition, the hot water supply control unit 44 and the above-mentioned exhaust heat recovery control unit 444 correspond to the pump control means. In addition, the hot water storage switching valve 97 is connected to a connection pipe 87 (corresponding to a connection pipeline) that connects the hot water outlet pipe 96 of the heating circuit 400 to the hot water inlet pipe 92. For example, when the temperature of the hot water drawn out from the heating circuit 400 detected by the sensor 88 is lower than a predetermined value (for example, 45°C), the hot water storage switching valve 97 is switched so as to communicate the connection pipe 87 that connects the pipes 96 and 92 with the pipe 96 and to block the pipes 96 and 98 (details will be described later). As a result, the hot water discharged from the heating circuit 400 is led from pipe 96 through the connecting pipe 87 to pipe 92, where it is returned to the heating circuit 400 and reheated.

<Auxiliary heating circuit>
One of the features of this embodiment is that an auxiliary heating circuit 300 is provided in the hot water supply unit 100. That is, since the amount of exhaust heat that can be recovered from the fuel cell in the exhaust heat recovery unit 200 is by no means large compared to the amount of hot water supply load in an average home, the auxiliary heating circuit 300 is provided to compensate for the necessary heating capacity that is insufficient with the heating capacity of the exhaust heat recovery unit 200 alone.

The hot and cold water inlet side of the auxiliary heating circuit 300 is connected to the common supply pipe 10, similar to the pipe 94 communicating with the hot and cold water inlet side of the heating circuit 400. In other words, the auxiliary heating circuit 300 and the heating circuit 400 are connected in parallel to each other so as to branch off from the common supply pipe 10.
The hot water outlet side of the auxiliary heating circuit 300 is connected to the common return pipe 11, similar to the pipe 98 communicating with the hot water outlet side of the heating circuit 400. In other words, the auxiliary heating circuit 300 and the heating circuit 400 are connected in parallel to each other so as to merge into the common return pipe 11.

The auxiliary heating circuit 300 is arranged in the following order from upstream to downstream along the flow of hot water: a circulation pump 317 (corresponding to a heater side circulation pump) that circulates the hot water within the auxiliary heating circuit 300; a flow rate sensor 325 that detects the flow rate of the hot water; an inlet temperature sensor 315 that detects the inlet temperature of the hot water flowing into the heater device 301 described below; a heater device 301 (corresponding to an auxiliary heater) that heats the hot water; an outlet temperature sensor 320 that detects the outlet temperature of the hot water flowing out from the heater device 301; an orifice device 330 with a flow rate throttling function; a check valve 340; and a thermostat 345 that turns off the power to the heater device 301 if the temperature of the hot water just before it merges from the auxiliary heating circuit 300 into the common return pipe 11 becomes overheated. It is sufficient that the heater device 301 and the orifice device 330 are disposed downstream of the circulation pump 317, and the orifice device 330 may be disposed upstream of the heater device 301.

At this time, the circulation pump 317 is controlled by the hot water supply control unit 44. Specifically, the rotation speed of the circulation pump 317 is controlled by the hot water supply control unit 44 so that the hot water outlet temperature detected by the outlet temperature sensor 320 becomes a predetermined target temperature.

<Heater Device>
2 shows a detailed structure of the heater device 301. In FIG. 2, the heater device 301 includes a heater unit 302, a heater mounting plate 303 to which the heater unit 302 is attached, and mounting legs 304.

The mounting leg 304 includes a fixing member 305 for fixing the heater unit 302 to the heater mounting plate 303. The fixing member 305 includes a bolt 305a, a washer 305b, and a sleeve 305c.

The heater unit 302 is formed, for example, by bending a stainless steel pipe into a U-shape, and includes a flow pipe 306 through which hot water flows as a heat medium, an electric heater 307 also bent into a U-shape and configured, for example, as a sheath heater, and a metal cover 308 made, for example, of aluminum. In detail, the heater unit 302 is configured by embedding the flow pipe 306 in the metal cover 308 by die casting, with the flow pipe 306 disposed on the outer periphery of the U-shape of the electric heater 307. The inner diameter of the flow pipe 306 is, for example, φ7.5 [mm] in this example. In this example, the electric heater 307 has, for example, an operating voltage of 200 [V] and an output of about 3.0 [kW].

The mounting legs 304 are made of the same material as the metal cover 308, and heat from the electric heater 307 is transferred to the mounting legs 304 via the metal cover 308. The mounting legs 304 may be constructed separately from the metal cover 308 or may be constructed integrally with it, but it is preferable to construct them from a metal that easily transfers heat.

A thermostat 309 for preventing overheating is attached to the heater mounting plate 303 with a fastener such as a screw. The thermostat 309 detects whether the electric heater 307 has overheated by the heat generated by the electric heater 307 being transmitted through the heater mounting plate 303. If it is determined that the electric heater 307 has overheated, the thermostat 309 turns off the power to the electric heater 307.

<Various operations>
Next, various operations of this embodiment will be described with reference to Figures 3 to 10. Note that the arrows in each pipe indicate the direction of hot and cold water flow.

<Boiling operation>
First, the boiling operation will be described. The boiling operation in the fuel cell system 1 of this embodiment includes three types: boiling operation performed solely by the heating circuit 400 of the exhaust heat recovery unit 200 (hereinafter referred to as "exhaust heat only boiling operation"), boiling operation performed with the assistance of not only the heating circuit 400 of the exhaust heat recovery unit 200 but also the auxiliary heating circuit 300 of the hot water supply unit 100 (hereinafter referred to as "heater auxiliary boiling operation"), and boiling operation performed solely by the auxiliary heating circuit 300 of the hot water supply unit 100 (hereinafter referred to as "heater only boiling operation"). Which of these three types is performed is determined by the fuel cell power generation unit 410 of the exhaust heat recovery unit 200.

<Exhaust heat only heating operation>
The exhaust heat only boiling operation will be described with reference to Figs.
As described above, in exhaust heat only heating operation, if the temperature of hot water drawn out from heating circuit 400, as detected by sensor 88, for example, is lower than a predetermined value (for example, 45 degrees), the hot water is circulated within heating circuit 400 (and part of hot water supply unit 100) and reheated until it reaches or exceeds the predetermined value.
Specifically, as shown in FIG. 3, the hot water supply control unit 44 controls the hot water supply switching valve 97 based on an instruction from the exhaust heat recovery control unit 444 to switch the hot water storage switching valve 97 to the first switching position so as to communicate the connection pipe 87 connecting the pipes 96 and 92 with the pipe 96 and to block the pipes 96 and 98. In addition, the circulation pump 417 starts to be driven under the control of the exhaust heat recovery control unit 444. At this time, the rotation speed of the circulation pump 417 is controlled by the exhaust heat recovery control unit 444 so that the temperature of the hot water detected by the temperature sensor 415 becomes a predetermined target temperature as described above. The hot water that receives heat from the hot water on the hot water circulation circuit 411 side in the water-water heat exchanger 416 and is led from the heating circuit 400 is led from the pipe 96 to the pipe 92 via the connection pipe 87, and is returned to the heating circuit 400 again to be reheated.

When the temperature of the hot water drawn out from the heating circuit 400 is equal to or higher than a predetermined value (for example, 45 degrees), the hot water in the hot water storage tank 2 is circulated through the common forward pipe 10 and the common return pipe 11 into the water-water heat exchanger 416. Specifically, as shown in FIG. 4, the hot water storage switching valve 97 is switched to the second switching position so as to connect the pipe 96 to the pipe 98 and block the pipe 96 from the pipe 92 under the control of the hot water supply control unit 444 based on an instruction from the exhaust heat recovery control unit 444. In addition, the circulation pump 417 is driven under the control of the exhaust heat recovery control unit 444. At this time, the rotation speed of the circulation pump 417 is controlled by the exhaust heat recovery control unit 444 so that the temperature of the hot water detected by the temperature sensor 415 becomes a predetermined target temperature as described above. As a result, the low-temperature water taken out from the common forward pipe 10 connected to the lower part of the hot water storage tank 2 is introduced into the heating circuit 400 through the aforementioned route, and is heated by receiving heat from the hot water on the hot water circulation circuit 411 side in the water-water heat exchanger 416. The heated water is then returned from the heating circuit 400 to the hot water storage tank 2 through the common return pipe 11 via the aforementioned route, and as a result, high-temperature water is stored in layers starting from the top of the hot water storage tank 2. When the demand for exhaust heat recovery is eliminated or the required amount of heat is stored, the circulation pump 417 is stopped under the control of the exhaust heat recovery control unit 444, and this exhaust heat only boiling operation is terminated.

<Heater assisted boiling operation>
Next, the heater-assisted boiling operation will be described with reference to FIG. 5. When the heater-assisted boiling operation is performed, the circulation pump 417 is started to be driven as described above under the control of the exhaust heat recovery control unit 444, and the circulation pump 317 is started to be driven under the control of the hot water supply control unit 44 based on an instruction from the exhaust heat recovery control unit 444. At this time, the rotation speed of the circulation pump 317 is controlled by the hot water supply control unit 44 so that the outlet temperature of the hot water becomes a predetermined target temperature as described above, but this predetermined target temperature is the same as the target temperature when the rotation speed of the circulation pump 417 is controlled by the exhaust heat recovery control unit 444. Alternatively, the predetermined target temperature may be a temperature that is a predetermined temperature (for example, 5° C.) higher than the target temperature when the rotation speed of the circulation pump 417 is controlled by the exhaust heat recovery control unit 444. In this case, by setting the target temperature for circulation pump 317 higher than the target temperature for circulation pump 417, the flow rate in the auxiliary heating circuit 300 is suppressed compared to when the target temperature for circulation pump 317 is low, which has the effect of making it less likely to impede the flow on the heating circuit 400 side.

As described above, the low-temperature water taken out from the common supply pipe 10 connected to the bottom of the hot water storage tank 2 is introduced into the heating circuit 400 and heated in the water-water heat exchanger 416 as described above, and is also introduced into the auxiliary heating circuit 300 that is connected to branch off from the common supply pipe 10. The hot water that flows into the auxiliary heating circuit 300 is heated by the heater device 301, and then the flow rate is adjusted by being throttled in the orifice device 330. As described above, the hot water merges with the flow of hot water heated in the heating circuit 400 and is returned to the hot water storage tank 2 through the common return pipe 11.

At this time, as described above, the target temperature when controlling the rotation speed of the circulation pump 317 and the target temperature when controlling the rotation speed of the circulation pump 417 are set to be the same value by the control by the cooperation of the exhaust heat recovery control unit 444 and the hot water supply control unit 44, or the target temperature when controlling the rotation speed of the circulation pump 317 is set to a temperature that is a predetermined temperature higher than the target temperature when controlling the rotation speed of the circulation pump 417. This prevents the flow rate on the auxiliary heating circuit 300 side from being excessively large compared to the flow rate on the heating circuit 400 side. As a result, for example, the flow rate of hot water in the heating circuit 400 is controlled to about 0.2 to 0.6 [liters/minute], and the flow rate of hot water in the auxiliary heating circuit 300 is controlled to about the same value, about 0.5 to 0.8 [liters/minute].

After the above, for example, when a certain amount of heat has been stored, the circulation pump 317 is stopped first under the control of the hot water supply control unit 44 based on instructions from the exhaust heat recovery control unit 444, and heating in the auxiliary heating circuit 300 ends. After that, the operation of the circulation pump 417 is stopped under the control of the exhaust heat recovery control unit 444, and this heater-assisted boiling operation ends.

The hot water storage switching valve 97 is normally switched to the first switching position, and is switched to the second switching position at the start of boiling operation or hot water circulation operation (described later) in which exhaust heat is recovered by the heating circuit 400. The hot water storage switching valve 97 is also switched to the first switching position at the end of boiling operation or hot water circulation operation in which exhaust heat is recovered by the heating circuit 400.

The heater-only boiling operation will be explained later using Figure 10.

<Hot water operation>
Next, the hot water supply operation will be described with reference to Fig. 6. For example, when a user opens the hot water tap 4 to use hot water for washing his/her face, doing kitchen work, taking a shower, etc., the water supply from the water supply pipe 9 flows into the hot water storage tank 2. Then, the high-temperature water stored in the middle of the hot water storage tank 2 is pushed out to the intermediate mixing valve 25 side through the intermediate hot water outlet pipe 24, and is also pushed out to the intermediate mixing valve 25 side through the hot water outlet pipe 8. Then, the hot water flowing out from the intermediate mixing valve 25 flows into the hot water supply mixing valve 28 through the intermediate hot water supply pipe 27, where it is mixed with low-temperature water from the water supply bypass pipe 29 and supplied to the hot water tap 4. Then, when the user closes the hot water tap 4, the hot water supply ends.

<Bathing operation>
Next, the operation of filling the bathtub 6 with water will be described with reference to Figure 7. For example, when a user intends to fill the bathtub with water and appropriately operates the hot water supply remote control (or bath remote control), the hot water supply control unit 44 opens the water filling valve 37. Then, water supplied from the water supply pipe 9 flows into the hot water storage tank 2. As a result, as described above, the hot water in the hot water storage tank 2 is pushed out through the intermediate hot water outlet pipe 24 to the intermediate mixing valve 25 side, and is also pushed out through the hot water outlet pipe 8 to the intermediate mixing valve 25 side.

The hot water flowing out of the intermediate mixing valve 25 is then discharged into the branch intermediate hot water supply pipe 33 which branches off from the intermediate hot water supply pipe 27. The high temperature water from the branch intermediate hot water supply pipe 33 then flows into the bath mixing valve 32, where it is mixed with the low temperature water from the branch water supply bypass pipe 34, and is supplied to the bathtub 6 via the hot water filling pipe 35 and the bath return pipe 22. When the bath flow rate sensor 38 installed midway through the hot water filling pipe 35 counts a predetermined amount of hot water, the hot water supply control unit 44 closes the hot water filling valve 37, and the hot water filling operation ends.

<Reheating operation>
Next, the bath reheating operation will be explained with reference to Figure 8. For example, when a user intends to reheat the bath and operates the hot water supply remote control (or bath remote control) appropriately, the hot water supply control unit 44 drives the bath circulation pump 21 and causes the bath water in the bathtub 6 to flow into the heat exchanger 19 through the bath return pipe 22. The bath water heated by heat exchange with the high-temperature water stored in the upper part of the hot water storage tank 2 in the heat exchanger 19 flows back into the bathtub 6 through the bath supply pipe 20 (reheating operation). During this operation, when the temperature detected by the bath temperature sensor 23 reaches the bath set temperature, the hot water supply control unit 44 stops driving the bath circulation pump 21, thereby ending the reheating operation.

<Hot water circulation operation>
Next, the hot water circulation operation will be described with reference to FIG.
For example, when the fuel cell power generation unit 410 does not generate electricity for a long period of time due to a long absence of the user or the like (for example, when a predetermined continuous period of time has elapsed during which no power generation is performed), under the control of the exhaust heat recovery control unit 444, the circulation pump 417 is driven to prevent the proliferation of bacteria in the heating circuit 400, and hot water circulation operation is performed for a predetermined period of time to circulate the hot water in the heating circuit 400 and the hot water in the hot water storage tank 2. In the hot water circulation operation, hot water is supplied from the heating circuit 400 to the hot water storage tank 2 without recovering the exhaust heat from the fuel cell power generation unit 410, i.e., without heating the hot water.

Specifically, when hot water circulation operation is performed, the hot water supply control unit 44 controls the hot water supply control unit 44 based on instructions from the exhaust heat recovery control unit 444 to switch the hot water storage switching valve 97 to the second switching position so as to connect the pipes 96 and 98 and block the pipes 96 and 92. In addition, the exhaust heat recovery control unit 444 controls the circulation pump 417 to start driving. At this time, the circulation pump 417 is driven at a predetermined fixed rotation speed for hot water circulation operation. The fixed rotation speed is preferably a value (e.g., the maximum rotation speed of the circulation pump 417, e.g., 3500 [rpm]) greater than the maximum value (e.g., 3000 [rpm]) of the range of rotation speeds at which the circulation pump 417 is driven (variable rotation speed range for a predetermined exhaust heat recovery operation) during the execution of the exhaust heat only boiling operation and the heater assisted boiling operation.

As a result, the low-temperature water taken out from the common supply pipe 10 connected to the bottom of the hot water storage tank 2 is introduced into the heating circuit 400 as described above, and is returned to the hot water storage tank 2 from the heating circuit 400 via the aforementioned path without being heated.

<Heater only heating operation>
Next, the heater-only boiling operation (corresponding to the heater heating operation) will be described with reference to FIG.
Heater-only boiling operation is a boiling operation in which, when there is a need for hot water supply based on temperature information detected by the hot water temperature sensors 39a-e, hot water heated by the auxiliary heating circuit 300 is supplied to the hot water storage tank 2 when power generation is not performed by the fuel cell power generation unit 410 and exhaust heat recovery is not performed by the heating circuit 400 as described above.
In the heater-only heating operation, the circulation pump 317 of the auxiliary heating circuit 300 starts to be driven under the control of the hot water supply control unit 44 based on a predetermined command signal. At this time, the rotation speed of the circulation pump 317 is controlled by the hot water supply control unit 44 so that the outlet temperature of the hot water becomes the predetermined target temperature, as described above.

As a result, the low-temperature water taken out from the common supply pipe 10 connected to the bottom of the hot water storage tank 2 is introduced into the auxiliary heating circuit 300. The hot water that flows into the auxiliary heating circuit 300 is heated by the heater device 301 as described above, and then the flow rate is adjusted by being throttled by the orifice device 330, and the water is returned to the hot water storage tank 2 through the common return pipe 11.

<Features of the embodiment>
The greatest feature of the fuel cell system 1 of this embodiment, which has the above-described configuration and operation, is that when power generation is not being performed by the fuel cell power generation unit 410 and there is competition between hot water circulation operation and heater-only heating operation, appropriate control is performed.

<Control during conflict between hot water circulation operation and heater-only heating operation>
The control procedure executed by the hot water supply control unit 44 when the hot water circulation operation and the heater-only boiling operation compete with each other will be described with reference to the sequence flow of FIG.

First, in ST1, a flag F is initialized to 0. Note that this flag F is set to F=1 when an instruction to execute hot water circulation operation is input but the execution is rejected by the hot water supply control unit 44 (see ST13 described later).
Then, in ST2, it is determined whether or not a heater operation command (heater operation request) has been input to instruct a boiling operation in which hot water heated by the heater device 301 is supplied from the auxiliary heating circuit 300 to the hot water storage tank 2. The heater operation command is input, for example, directly from a hot water supply remote control (or a bath remote control) of the hot water supply unit 100 by a user's operation of the remote control, or is input from the hot water supply control unit 44 itself based on temperature information detected by the hot water storage temperature sensors 39a-e.
When a heater operation command is input, ST2 is determined as Yes, and in ST4, the electric heater 307 of the heater device 301 is turned ON and heater operation is started. At the same time, the operation of the circulation pump 317 is also started. As a result, hot water heated by the heater device 301 of the auxiliary heating circuit 300 is supplied to the hot water storage tank 2.

After that, when the heater operation starts as described above, in ST5, a heater operation start notification, which is a notification that the heater operation has started, is sent from the hot water supply control unit 44 to the exhaust heat recovery control unit 444.

After the heater operation start notification is sent in ST5, it is determined in ST6 whether a heater stop command has been input. The heater stop command may be input directly from a hot water supply remote control (or a bath remote control) of the hot water supply unit 100 by a user's operation of the remote control, or may be input automatically from the remote control after a predetermined time has elapsed since the heater operation command, or may be input by the hot water supply control unit 44 itself based on temperature information detected by the hot water storage temperature sensors 39a-e.
When a heater stop command is input, ST6 is judged as Yes, and in ST7, the electric heater 307 is turned off and the heater operation is stopped. At the same time, the operation of the circulation pump 317 is also stopped. As a result, the supply of hot water heated by the heater device 301 of the auxiliary heating circuit 300 to the hot water storage tank 2 is stopped.

After that, with the end of the heater operation as described above, in ST8, a heater operation stop notification, which is a notification that the heater operation has been stopped, is sent from the hot water supply control unit 44 to the exhaust heat recovery control unit 444. Then, in ST9, the hot water supply control unit 44 judges whether the flag F = 1. If the flag F = 1, that is, the execution of the hot water circulation operation is refused (see ST12 and ST13 described later), ST9 is judged as Yes, and in ST10, a circulation operation restart permission notification, which is a notification that the restart (execution) of the hot water circulation operation is permitted, is sent from the hot water supply control unit 44 to the exhaust heat recovery control unit 444. Then, the process proceeds to ST16 described later, and the subsequent processing is performed. On the other hand, in ST9, if the flag F = 0, that is, the execution of the hot water circulation operation is not refused, ST9 is judged as No, and this flow is terminated.

On the other hand, if a heater stop command has not been input in ST6, then ST6 is judged as No, and in ST11 it is judged whether or not a circulation operation command (circulation operation request) commanding hot water circulation operation has been input from the exhaust heat recovery control unit 444. If a circulation operation command has been input, ST11 is judged as Yes, and in ST12 an operation refusal notice to the effect that hot water circulation operation based on the circulation operation request will not be performed is sent from the hot water supply control unit 44 to the exhaust heat recovery control unit 444, and in ST13 the flag F is set to 1. Upon receiving this operation refusal notice, the exhaust heat recovery control unit 444 waits for hot water circulation operation.
After ST13, or if a circulation operation instruction has not been input from the exhaust heat recovery control unit 444 and ST11 is determined to be No, the process returns to ST6, and the same procedure as above is repeated.

The heater operation start notification sent in ST5 can also serve as an operation refusal notification to not perform hot water circulation operation. In that case, even if a request for hot water circulation operation occurs upon receiving the heater operation start notification in ST5, the exhaust heat recovery control unit 444 can be configured to wait for hot water circulation operation and not issue a circulation operation request until it receives the heater operation stop notification in ST8.

On the other hand, if the heater operation command has not been input in ST2, a No determination is made, and it is determined in ST14 whether or not the circulation operation command (circulation operation request) has been input from the exhaust heat recovery control unit 444. If the circulation operation request has not been input, a No determination is made in ST14, and the process returns to ST2, and the same procedure as above is repeated.
If a circulation operation request is input from the exhaust heat recovery control unit 444, ST14 is judged as Yes, and in ST15, a circulation operation permission notification, which is a notification that hot water circulation operation based on the circulation operation instruction is permitted, is sent from the hot water supply control unit 44 to the exhaust heat recovery control unit 444.

After that, in ST16, the exhaust heat recovery control unit 444, which has received the circulation operation permission notification sent in ST15, determines whether or not it has received a circulation operation start notification, which is a notification that the circulation pump 417 has started to be driven and hot water circulation operation has started. If the circulation operation start notification has not been received, ST16 is determined as No and the system waits in a loop until it is received. If the circulation operation start notification has been received, ST16 is determined as Yes, and in ST17 the hot water storage switching valve 97 is switched from the normal first switching position to the second switching position.

Then, in ST18, it is determined whether or not a circulation operation end notification has been received from the exhaust heat recovery control unit 444, which is a notification that the operation of the circulation pump 417 has been stopped and the hot water circulation operation has ended. If a circulation operation end notification has been received, ST18 is determined as Yes. In ST19, the hot water storage switching valve 97 is switched from the second switching position to the normal first switching position, and this flow ends.

On the other hand, in ST18, if the circulation operation end notification has not been received, a No determination is made, and in ST20, it is determined whether or not a heater operation instruction has been input from the exhaust heat recovery control unit 444. In ST20, if the heater operation instruction has not been input, a No determination is made, and the process returns to ST18, and the same procedure as above is repeated.
If a heater operation instruction is input from the exhaust heat recovery control unit 444, ST20 is judged as Yes, and in ST21, a request to stop circulation operation is sent from the hot water supply control unit 44 to the exhaust heat recovery control unit 444, requesting that the hot water circulation operation be stopped (not terminated but interrupted).

Then, in ST22, it is determined whether or not a circulation operation stop notification, which is a notification that hot water circulation operation has been stopped, has been received from the exhaust heat recovery control unit 444. If a circulation operation stop notification has not been received, ST22 is determined as No, and the process loops and waits until it is received. If a circulation operation stop notification has been received, ST22 is determined as Yes, and in ST23 the hot water storage switching valve 97 is switched from the second switching position to the first switching position, and in ST24 the electric heater 307 of the heater device 301 is turned ON and heater operation is started. At the same time, the operation of the circulation pump 317 is also started. As a result, hot water heated by the heater device 301 of the auxiliary heating circuit 300 is supplied to the hot water storage tank 2.

After that, in ST25, as the heater operation starts, a heater operation start notification is sent from the hot water supply control unit 44 to the exhaust heat recovery control unit 444, similar to ST5. After the heater operation start notification is sent by ST25, it is determined in ST26 whether the heater stop instruction has been input. If the heater stop instruction has not been received, ST26 is determined as No, and the process returns to ST24, where the same procedure as above is repeated.

If the heater stop command is input, ST26 is determined as Yes, and in ST27, the electric heater 307 is turned OFF and the heater operation is stopped. At the same time, the operation of the circulation pump 317 is also stopped. As a result, the supply of hot water heated by the heater device 301 of the auxiliary heating circuit 300 to the hot water storage tank 2 is stopped. After that, in ST28, a heater operation stop notification is sent from the hot water supply control unit 44 to the exhaust heat recovery control unit 444.
Thereafter, in ST29, a hot water circulation operation restart permission notice is transmitted from the hot water supply control unit 44 to the exhaust heat recovery control unit 444. Thereafter, the process proceeds to ST16, and the subsequent processes are performed.

Effects of the embodiment
In the fuel cell system 1 of the present embodiment configured as described above, the hot water in the hot water storage tank 2 is heated by exhaust heat from the fuel cell power generation unit 410. That is, a heating circuit 400 is provided that includes a circulation pump 417 for circulating hot water and recovers exhaust heat from the fuel cell power generation unit 410, the hot water inflow side of the heating circuit 400 is connected to a common supply pipe 10 from the hot water storage tank 2, and the hot water outflow side of the heating circuit 400 is connected to a common return pipe 11 to the hot water storage tank 2. As a result, the hot water in the hot water storage tank 2 is introduced into the heating circuit 400 via the common supply pipe 10, and is then heated by utilizing the exhaust heat from the fuel cell power generation unit 410, and the heated hot water is returned to the hot water storage tank 2 via the common return pipe 11.

At this time, the amount of exhaust heat that the heating circuit 400 can recover from the fuel cell is not particularly large, so in this embodiment, in order to supplement the necessary heating capacity required by the hot and cold water user side, an auxiliary heating circuit 300 is provided that is equipped with a heater device 301 capable of heating hot and cold water and a circulation pump 317. The hot and cold water inlet side of this auxiliary heating circuit 300 is connected in parallel with the hot and cold water inlet side of the heating circuit 400 so as to branch off from the common supply pipe 10 from the hot water storage tank 2.
The hot water outlet side of the auxiliary heating circuit 300 and the hot water outlet side of the heating circuit 400 are connected in parallel to each other so as to merge into a common return pipe 11 to the hot water storage tank 2. In other words, the heating circuit 400 and the auxiliary heating circuit 300 are connected in parallel to each other with respect to the hot water storage tank 2. This makes it possible to simultaneously supply hot water heated by the heating circuit 400 to the hot water storage tank 2 and supply hot water heated by the auxiliary heating circuit 300 to the hot water storage tank 2 (see FIG. 5).

In this embodiment, when power generation is not performed for a long period of time in the fuel cell power generation unit 410 of the exhaust heat recovery unit 200 due to a long absence of the user, etc., the circulation pump 417 is driven to prevent the proliferation of bacteria in the heating circuit 400, and hot water circulation operation is performed to circulate the hot water in the heating circuit 400 and the hot water in the hot water storage tank 2. In this case, hot water is supplied from the heating circuit 400 to the hot water storage tank 2 without heating the hot water by the exhaust heat recovery of the fuel cell power generation unit 410 as described above. At this time, the circulation pump 417 of the heating circuit 400 is controlled by the exhaust heat recovery control unit 444 based on a predetermined instruction signal.

When power generation is not performed and exhaust heat recovery is not performed in the heating circuit 400 as described above, if there is a need for hot water supply, a heater-only boiling operation is performed in which hot water heated by the auxiliary heating circuit 300 is supplied to the hot water storage tank 2. At this time, the circulation pump 317 of the auxiliary heating circuit 300 is controlled by the hot water supply control unit 44 based on a specified command signal.

When such a supply of hot water from the auxiliary heating circuit 300 is performed simultaneously with the supply of hot water from the heating circuit 400 by the hot water circulation operation, depending on the flow rate (circulation flow rate) of the heating circuit 400, the flow rate of the auxiliary heating circuit 300 may become extremely small, and the heating capacity of the auxiliary heating circuit 300 may become uncontrollable.

In this embodiment, the hot water supply control unit 44 that controls the circulation pump 317 executes control to prioritize the heater-only boiling operation over the hot water circulation operation. Specifically, when a heater operation request instructing the heater-only boiling operation conflicts with a circulation operation request instructing the hot water circulation operation, the heater operation request is prioritized, and the circulation pump 317 is controlled to perform the heater-only boiling operation without performing the hot water circulation operation (see ST11, ST12, and ST20, ST21 in FIG. 11).
As a result, when the heater-only heating operation is performed, the hot water circulation operation is not performed, so it is possible to prevent the flow rate of the auxiliary heating circuit 300 from becoming extremely small due to the influence of the flow rate of the heating circuit 400 as described above. As a result, it is possible to avoid the occurrence of an uncontrollable state of the heating capacity of the auxiliary heating circuit 300 as described above.

In particular, in this embodiment, when heater-only boiling operation is being performed, the hot water supply control unit 44 outputs an operation refusal notification to refuse hot water circulation operation (see ST12 in FIG. 11). This prevents hot water circulation operation from being performed when heater-only boiling operation is being performed, and reliably avoids an uncontrollable state of the heating capacity of the auxiliary heating circuit 300 caused by the conflict between the two operations.

In particular, in this embodiment, if a heater-only boiling operation is instructed by a heater operation request while hot water circulation operation is in progress, the hot water supply control unit 44 interrupts the hot water circulation operation and starts the heater-only boiling operation (see ST21 to ST24 in FIG. 11). This makes it clear that the heater-only boiling operation is executed with priority over the hot water circulation operation, and reliably avoids an uncontrollable state of the heating capacity of the auxiliary heating circuit 300 caused by a conflict between the two operations.

In addition, particularly in this embodiment, in hot water circulation operation, hot water is circulated between the heating circuit 400 and the hot water storage tank 2, and the hot water in the heating circuit 400 is replaced in order to prevent the proliferation of germs in the heating circuit 400. Even if germs grow in the hot water in the heating circuit 400, the germs can be killed by supplying hot water to the hot water storage tank 2, which has a relatively high temperature. In particular, in this embodiment, in response to the above, the circulation pump 417 is driven at a fixed rotation speed for hot water circulation operation that is set high in advance to achieve a relatively high flow rate, for example. This allows the hot water to be quickly and reliably replaced in order to kill germs.

In particular, in this embodiment, the fixed rotation speed when the circulation pump 417 is driven during hot water circulation operation is set to a value greater than the maximum value of the predetermined rotation speed range when variably controlled during boiling operation performed by the heating circuit 400. This allows the hot water to be replaced more quickly and reliably.

In this embodiment, a connection pipe 87 is provided to connect the hot water outlet side and the hot water inlet side of the heating circuit 400, and a hot water storage switching valve 97 is provided at a branching position where the connection pipe 87 branches from the hot water outlet side (or a junction position where the hot water inlet side of the heating circuit 400 and the connection pipe 87 join). This hot water storage switching valve 97 can be switched between a first switching position and a second switching position by the control of the hot water supply control unit 44, and is usually switched to the first switching position. In the first switching position, the hot water flowing out from the hot water outlet side of the heating circuit 400 is returned to the hot water inlet side of the heating circuit 400 via the connection pipe 87. In addition, in the second switching position, the hot water flowing out from the hot water outlet side of the heating circuit 400 is guided to the common return pipe 11.
According to this embodiment, the hot water supply control unit 44 switches the hot water storage switching valve 97 from the first switching position to the second switching position when the hot water circulation operation starts, and returns the hot water storage switching valve 97 to the original first switching position when the hot water circulation operation ends. As a result, while the hot water storage switching valve 97 is basically switched to the first switching position, the hot water outlet side of the heating circuit 400 and the common return pipe 11 are communicated during the hot water circulation operation, and the hot water flowing out from the hot water outlet side of the heating circuit 400 can be reliably supplied into the hot water storage tank 2 via the common return pipe 11.

The present invention is not limited to the above-described embodiment, and the configuration can be changed as appropriate without departing from the spirit of the invention. For example, the configurations described in the above-described embodiment can be combined or selected as appropriate, and part of the configuration of the above-described embodiment can be added, deleted, or replaced.

For example, in the above embodiment, an example was described in which the above operation is achieved by cooperative control of the hot water supply control unit 44 of the hot water supply unit 100 and the exhaust heat recovery control unit 444 of the exhaust heat recovery unit 200, but it may also be achieved by control by a single control means that comprehensively controls the fuel cell system 1.

REFERENCE SIGNS LIST 1 fuel cell system 2 hot water storage tank 10 common supply pipe 11 common return pipe 44 hot water supply control unit (control means, pump control means, heater side control means)
87 Connection piping (connection pipe)
97 Hot water storage switching valve (switching valve)
100 Hot water supply unit (hot water storage unit for fuel cell system)
300 Auxiliary heating circuit (heater side heating circuit)
301 Heater device (auxiliary heater)
317 Circulation pump (heater side circulation pump)
400 Heating circuit (fuel cell side heating circuit)
410 Fuel cell power generation unit 417 Circulation pump (fuel cell side circulation pump)
444 Exhaust heat recovery control unit (control means, pump control means)

Claims (7)

A hot water storage tank for storing hot water;
A common supply pipe connected to a lower portion of the hot water storage tank and for discharging hot water from the hot water storage tank;
A common return pipe connected to an upper portion of the hot water storage tank and returning the heated hot water into the hot water storage tank;
A heater-side heating circuit having an auxiliary heater capable of heating hot and cold water and a heater-side circulation pump for circulating the hot and cold water;
a fuel cell side heating circuit including a fuel cell side circulation pump for circulating hot water that has recovered exhaust heat from the fuel cell;
a control means for controlling at least the heater side circulation pump and the fuel cell side circulation pump in response to a predetermined instruction signal;
In a fuel cell system having
the hot and cold water inflow sides of the heater-side heating circuit and the fuel cell-side heating circuit are connected in parallel to each other so as to branch off from the common supply pipe;
the hot and cold water outlet sides of the heater-side heating circuit and the fuel cell-side heating circuit are connected in parallel to each other so as to merge into the common return pipe;
The control means
A fuel cell system characterized in that, when there is conflict between a heater operation request that instructs a heater heating operation in which hot water heated by the auxiliary heating heater is supplied from the heater side heating circuit to the hot water storage tank, and a circulation operation request that instructs a hot water circulation operation in which the hot water in the fuel cell side heating circuit and the hot water in the hot water storage tank are circulated without recovering exhaust heat from the fuel cell, the heater operation request is given priority, and the fuel cell side circulation pump and the heater side circulation pump are controlled to perform the heater heating operation without performing the hot water circulation operation. The control means
2. The fuel cell system according to claim 1, wherein, when the heater heating operation is being performed based on the input of the heater operation request, an operation refusal notification is output to refuse the hot water circulation operation. The control means
3. The fuel cell system according to claim 1, wherein when the heater operation request is input while the hot water circulation operation is being performed based on the input of the circulation operation request, the heater side circulation pump is controlled so as to interrupt the hot water circulation operation and perform the heater heating operation based on the heater operation request. The fuel cell side circulation pump is
4. The fuel cell system according to claim 1, wherein the fuel cell system is driven at a predetermined fixed rotation speed for the hot water circulation operation when the hot water circulation operation is performed. The fuel cell side circulation pump is
during an exhaust heat recovery operation in which hot water heated by recovering exhaust heat from the fuel cell is supplied from the fuel cell side heating circuit to the hot water storage tank, the exhaust heat recovery operation is driven within a predetermined variable rotation speed range for the exhaust heat recovery operation,
The fixed rotation speed is
5. The fuel cell system according to claim 4, wherein the value is greater than the maximum value of the variable rotation speed range. a connecting pipe connecting the hot water outlet side and the hot water inlet side of the fuel cell side heating circuit;
a switching valve that is provided at a position where the connecting pipe branches off from the hot and cold water outlet side of the fuel cell side heating circuit or at a position where the hot and cold water inlet side of the fuel cell side heating circuit and the connecting pipe join, and is switchable between a first switching position that returns the hot and cold water flowing out from the hot and cold water outlet side of the fuel cell side heating circuit to the hot and cold water inlet side of the fuel cell side heating circuit via the connecting pipe, and a second switching position that guides the hot and cold water flowing out from the hot and cold water outlet side of the fuel cell side heating circuit to the common return pipe;
and
The switching valve is controlled by the control means.
6. The fuel cell system according to claim 1, wherein the switching position is switched to the second switching position at the start of the hot water circulation operation, and is switched to the first switching position at the end of the hot water circulation operation. A hot water storage tank for storing hot water;
A common supply pipe connected to a lower portion of the hot water storage tank and for discharging hot water from the hot water storage tank;
A common return pipe connected to an upper portion of the hot water storage tank and returning the heated hot water into the hot water storage tank;
A heater-side heating circuit having an auxiliary heater capable of heating hot and cold water and a heater-side circulation pump for circulating the hot and cold water;
a heater-side control means for controlling at least the heater-side circulation pump in response to a predetermined instruction signal;
A hot water storage unit for a fuel cell system, comprising:
the hot and cold water inlet side of the heater-side heating circuit is connected in parallel with the hot and cold water inlet side of a fuel cell-side heating circuit having a fuel cell-side circulation pump for circulating hot and cold water that has recovered exhaust heat from the fuel cell so as to branch off from the common supply pipe;
the hot and cold water outlet side of the heater side heating circuit is connected in parallel with the hot and cold water outlet side of the fuel cell side heating circuit so as to merge into the common return pipe;
and,
A hot water storage unit for a fuel cell system, characterized in that when there is conflict between a heater operation request that instructs a heater heating operation in which hot water heated by the auxiliary heating heater is supplied from the heater side heating circuit to the hot water storage tank, and a circulation operation request that instructs a hot water circulation operation in which the hot water in the fuel cell side heating circuit and the hot water in the hot water storage tank are circulated without recovering exhaust heat from the fuel cell, the heater operation request is given priority, and the heater heating operation is performed without performing the hot water circulation operation.

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