WATER ELECTROLYSIS SYSTEM AND TEMPERATURE CONTROL METHOD THEREOF

Abstract

A water electrolysis system includes a water electrolyzer, a water supply pipe, a water supply pipe, a water discharge pipe, and a first and second temperature sensors. The water electrolyzer includes a water supply port and a water discharge port. The water supply pipe is connected to the water supply port. The water is to be supplied to the water electrolyzer via the water supply pipe. The water discharge pipe is connected to the water discharge port. The water is to be discharged from the water electrolyzer via the water discharge pipe. The first temperature sensor is provided at the water supply pipe between a cooling apparatus and the water supply port to detect a temperature of the water in the water supply pipe. The second temperature sensor is provided at the water discharge pipe to detect a temperature of the water in the water discharge pipe.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2016-096971, filed May 13, 2016, entitled “Water Electrolysis System and Temperature Control Method Thereof.” The contents of this application are incorporated herein by reference in their entirety.

BACKGROUND

1. Field

The present disclosure relates to a water electrolysis system and a temperature control method thereof.

Hydrogen is used in general as a fuel gas to be applied to a power generation reaction by a fuel cell. The hydrogen is produced with use of, for example, a water electrolyzer. The water electrolyzer employs a solid polymer electrolyte membrane (ion exchange membrane) in order to produce hydrogen (and oxygen) through electrolysis of water. Electrocatalyst layers are provided on both surfaces of the solid polymer electrolyte membrane to form a membrane electrode assembly. In addition, a unit cell is constructed by providing electricity suppliers on both sides of the membrane electrode assembly.

With the above configuration, a voltage is applied to both ends in a stacking direction of a cell unit in which multiple unit cells are stacked. Besides, water is supplied to the electricity supplier on the anode side. Thus, water is electrolyzed to produce hydrogen ions (protons) on the anode side of the membrane electrode assembly. These hydrogen ions permeate the solid polymer electrolyte membrane to move to the cathode side, and then couple with electrons to produce hydrogen. Meanwhile, on the anode side, oxygen produced together with hydrogen is discharged from the cell unit along with surplus water.

There may be a case where, for example, a high-pressure water electrolyzer (high differential pressure water electrolyzer) is employed as the water electrolyzer. The high-pressure water electrolyzer produces, through electrolysis of water, oxygen and hydrogen with a pressure higher than that of the oxygen. As a high-pressure water electrolyzer of this kind, a water electrolysis system and an activation method thereof disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2015-48506 are known.

This water electrolysis system includes: a water electrolyzer (high differential pressure water electrolyzer); a water supply pipe which supplies water to the water electrolyzer; and a circulation pipe which circulates the water guided out of the water electrolyzer. Connected to the water supply pipe and the circulation pipe is a gas-liquid separation apparatus which separates a gas component contained in the water guided out of the water electrolyzer. Connected to the water supply pipe are: an ion exchange apparatus which includes an ion exchange unit; a circulation pump which circulates the water; and a temperature sensor which detects a temperature of the water circulated to the water electrolyzer.

SUMMARY

According to a first aspect of the present invention, a water electrolysis system includes a water electrolyzer, a water supply pipe, and a water discharge pipe. The water electrolyzer electrolyzes water to produce oxygen and hydrogen. The water supply pipe supplies the water to a water supply port of the water electrolyzer. The water discharge pipe allows the water, subjected to electrolysis, to be discharged from a water discharge port of the water electrolyzer. The water supply pipe is provided with a cooling apparatus, and is provided with a first temperature sensor which is located between the cooling apparatus and the water supply port and which monitors a temperature of supply water supplied to the water supply port. The water discharge pipe is provided with a second temperature sensor which monitors a temperature of discharge water discharged from the water discharge port.

According to a second aspect of the present invention, a temperature control method of a water electrolysis system including a water electrolyzer which electrolyzes water to produce oxygen and hydrogen, a water supply pipe which supplies the water to a water supply port of the water electrolyzer, a water discharge pipe which allows the water, subjected to electrolysis, to be discharged from a water discharge port of the water electrolyzer, wherein the water supply pipe is provided with a cooling apparatus, and is provided with a first temperature sensor located between the cooling apparatus and the water supply port, and the water discharge pipe is provided with a second temperature sensor, the temperature control method includes the steps of causing the second temperature sensor to monitor a temperature of discharge water discharged from the water discharge port of the water electrolyzer from a time of activation of the water electrolysis system and after the temperature of the discharge water monitored by the second temperature sensor exceeds a predetermined temperature, causing the first temperature sensor to monitor a temperature of supply water supplied to the water supply port of the water electrolyzer, and starting control of the cooling apparatus to control the temperature of the supply water.

According to a third aspect of the present invention, a water electrolysis system includes a water electrolyzer, a water supply pipe, a water supply pipe, a cooling apparatus, a water discharge pipe, a first temperature sensor, and a second temperature sensor. The water electrolyzer electrolyzes water to produce oxygen and hydrogen. The water electrolyzer includes a water supply port and a water discharge port. The water supply pipe is connected to the water supply port. The water is to be supplied to the water electrolyzer via the water supply pipe. The cooling apparatus is provided in the water supply pipe. The water discharge pipe is connected to the water discharge port. The water is to be discharged from the water electrolyzer via the water discharge pipe. The first temperature sensor is provided at the water supply pipe between the cooling apparatus and the water supply port to detect a temperature of the water in the water supply pipe. The second temperature sensor is provided at the water discharge pipe to detect a temperature of the water in the water discharge pipe.

According to a fourth aspect of the present invention, a temperature control method of a water electrolysis system including a water electrolyzer to electrolyze water to produce oxygen and hydrogen, the temperature control method includes detecting a temperature of water in a water discharge pipe. The water discharge pipe is connected to the water electrolyzer. The water is discharged from the water electrolyzer via the water discharge pipe. A temperature of the water in a water supply pipe between a cooling apparatus and the water electrolyzer is detected after the temperature of the water detected in the water discharge pipe exceeds a predetermined temperature. The water supply pipe is connected to the water electrolyzer. The water is supplied to the water electrolyzer via the water supply pipe. The cooling apparatus is started to control the temperature of the water in the water supply pipe. The cooling apparatus is provided in the water supply pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings.

FIG. 1 is a schematic configuration diagram for explanation of a water electrolysis system according to an embodiment of the present disclosure.

FIG. 2 is a flowchart for explanation of a temperature control method of the water electrolysis system.

FIG. 3 is a timing diagram for explanation of the temperature control method.

DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings.

As illustrated in FIG. 1, a water electrolysis system 10 according to an embodiment of the present disclosure includes a high differential pressure water electrolyzer (water electrolyzer) 12 which produces oxygen and high-pressure hydrogen through electrolysis of water (pure water). The high-pressure hydrogen refers to hydrogen with a pressure of, for example, 1 to 80 MPa, which is higher than that of atmospheric oxygen. Note that the water electrolysis system 10 is not limited to the production of high-pressure hydrogen, but is applicable to the case of producing atmospheric hydrogen.

The high differential pressure water electrolyzer 12 has a stack of multiple water electrolysis cells 14. At both ends in a stacking direction of the stack of water electrolysis cells 14, end plates 16a and 16b are provided. Connected to the high differential pressure water electrolyzer 12 is an electrolytic power supply 18 being a direct current power supply.

The end plate 16a is provided with a water supply port 20a, while the end plate 16b is provided with a water discharge port 20b and a hydrogen outlet port 20c. A water supply pipe 22 is connected to the water supply port 20a. Connected to the water supply pipe 22 are a radiator (cooling apparatus) 24 which includes a radiator fan 23, and a circulation pump 26 which circulates water. Moreover, the water supply pipe 22 is connected to a bottom portion of an oxygen gas-liquid separation apparatus 28. Incidentally, the cooling apparatus is not limited to radiator 24. Instead, cooling equipment of various kinds may be used.

An upper portion of the oxygen gas-liquid separation apparatus 28 communicates with a blower 30 and one end portion of a water discharge pipe 32, while the other end of the water discharge pipe 32 communicates with the water discharge port 20b of the high differential pressure water electrolyzer 12. The water supply pipe 22 and the water discharge pipe 32 constitute a water circulation pipe.

Fastened to the oxygen gas-liquid separation apparatus 28 are: a pure water supply pipe 36 connected to a pure water producing unit 34; and an oxygen discharge pipe 38 for discharging oxygen (and hydrogen) separated from pure water at the oxygen gas-liquid separation apparatus 28.

One end portion of a high-pressure hydrogen pipe 42 is connected to the hydrogen outlet port 20c of the high differential pressure water electrolyzer 12. The other end portion of the high-pressure hydrogen pipe 42 is connected to a high-pressure hydrogen gas-liquid separation apparatus, though not illustrated. The high-pressure hydrogen gas-liquid separation apparatus separates water from hydrogen. Thereafter, water vapor (water) contained in the hydrogen is adsorbed at a water adsorption apparatus. As a result, a hydrogen product (dry hydrogen) is obtained.

The water electrolysis system 10 includes a controller (ECU) 44, and this controller 44 controls water electrolysis processing (operation).

The water supply pipe 22 is provided with a first temperature sensor 46 which monitors a temperature of supply water supplied to the water supply port 20a of the high differential pressure water electrolyzer 12. The water discharge pipe 32 is provided with a second temperature sensor 48 which monitors a temperature of discharge water discharged from the water discharge port 20b of the high differential pressure water electrolyzer 12. Each of the first temperature sensor 46 and the second temperature sensor 48 sends a detected temperature signal to the controller 44, and the controller 44 then controls the radiator fan 23 based on the detected temperature signal.

Hereinafter, a description is provided for the operations of the water electrolysis system 10 configured as above.

As illustrated in FIG. 1, pure water in the oxygen gas-liquid separation apparatus 28 is supplied to the water supply port 20a of the high differential pressure water electrolyzer 12 via the water supply pipe 22 under the action of the circulation pump 26. Meanwhile, a voltage is applied to the high differential pressure water electrolyzer 12 using the electrically-connected electrolytic power supply 18.

Thus, in each of the water electrolysis cells 14, pure water is electrolyzed by electricity, and hydrogen ions, electrons, and oxygen are produced. As a result, hydrogen is obtained on the cathode side through coupling between the hydrogen ions and the electrons. The hydrogen is taken out of the hydrogen outlet port 20c to the high-pressure hydrogen pipe 42.

Meanwhile, oxygen (and permeation hydrogen) generated due to the reaction and unreacted water are flowing on the anode side, and a mixture of these fluids is discharged from the water discharge port 20b to the water discharge pipe 32. The unreacted water and the oxygen and hydrogen gases are introduced to the oxygen gas-liquid separation apparatus 28 and separated from one another. After that, the water is introduced from the water supply pipe 22 to the water supply port 20a via the circulation pump 26. The oxygen and the hydrogen separated from the water are discharged from the oxygen discharge pipe 38.

A hydrogen product (dry hydrogen) in a dry state is obtained by removing the liquid water and the water vapor which are contained in the hydrogen generated in the high differential pressure water electrolyzer 12. A fuel cell electric vehicle (not illustrated) is replenished with this hydrogen product. When replenishment of the above-described hydrogen product is completed, the operation of the water electrolysis system 10 is stopped.

Next, a description is provided hereinbelow for a temperature control method according to the embodiment with reference to a flowchart illustrated in FIG. 2 and a timing diagram illustrated in FIG. 3.

First, when the activation of the water electrolysis system 10 is started, the radiator fan 23 is stopped (step S1). In the controller 44, the second temperature sensor 48 has been monitoring the temperature of discharge water (discharge water temperature) discharged from the water discharge port 20b of the high differential pressure water electrolyzer 12 since the activation of the water electrolysis system 10 (step S2). Here, when it is determined that the temperature of discharge water monitored by the second temperature sensor 48 exceeds a predetermined temperature Ta (YES at step S2), the processing proceeds to step S3.

As illustrated in FIG. 3, at the time of activation of the water electrolysis system 10, the discharge water temperature is higher than a supply water temperature because of self-heat generation by the high differential pressure water electrolyzer 12. This means that, by stopping the radiator fan 23, it is possible to rapidly increase the temperature of the high differential pressure water electrolyzer 12. After the temperature of discharge water reaches the predetermined temperature Ta, which is a control temperature for a stack outlet (water discharge port 20b), the radiator fan 23 is driven (step S3).

The predetermined temperature Ta is a temperature at which water electrolysis by the high differential pressure water electrolyzer 12 reaches a stable state. To this end, in the controller 44, the first temperature sensor 46 monitors the temperature of supply water supplied to the water supply port 20a of the high differential pressure water electrolyzer 12 (step S4). Moreover, the processing proceeds to step S5, where proportional-integral-differential (PID) control is performed based on the supply water temperature.

As illustrated in FIG. 3, in the PID control, the discharge water temperature is higher than the supply water temperature by a temperature difference ΔT because of the self-heat generation by the high differential pressure water electrolyzer 12. In light of the above, driving of the radiator fan 23 is controlled such that the supply water temperature detected by the first temperature sensor 46 is approximated to a preset stack inlet (water supply port 20a) control temperature Tb. As a result of this, the outlet temperature of the high differential pressure water electrolyzer 12 is adjusted at a constant temperature.

The stack inlet control temperature Tb is a control temperature at which to control the supply water temperature monitored by the first temperature sensor 46, the control temperature being based on estimation of the amount of heat generated in the high differential pressure water electrolyzer 12, and satisfying the condition that the discharge water temperature monitored by the second temperature sensor 48 does not exceed a discharge water temperature threshold (boost activation temperature) Tc.

In the controller 44, the second temperature sensor 48 monitors the discharge water temperature. Additionally, when it is determined that the temperature of the discharge water exceeds the discharge water temperature threshold (boost activation temperature) Tc (YES at step S6), the processing proceeds to step S7. At step S7, the radiator fan 23 is controlled at the maximum rotational rate to rapidly decrease the temperature of water supplied to the high differential pressure water electrolyzer 12. Thereby, the outlet temperature of the high differential pressure water electrolyzer 12 is cooled down to a temperature below the discharge water temperature threshold Tc. Note that the temperature of water may be decreased by increasing the flow rate of water compared to that in an ordinary state, in addition to the case of controlling the radiator fan 23 at the maximum rotational rate.

Next, the processing proceeds to step S8, where it is determined whether or not the system is to be stopped. When it is determined that the system is not to be stopped (NO at step S8), the processing returns to step S5 and the PID control is continued.

In this case, in the embodiment, the water supply pipe 22 is provided with the radiator 24. Besides, the first temperature sensor 46 and the second temperature sensor 48 are disposed upstream and downstream of the high differential pressure water electrolyzer 12, respectively. Thus, it is possible to adjust accurately and easily the temperature of water supplied to the high differential pressure water electrolyzer 12.

Also, according to the embodiment, the second temperature sensor 48 has been monitoring the temperature of discharge water discharged from the water discharge port 20b of the high differential pressure water electrolyzer 12 since the activation of the water electrolysis system 10. During that period, it is possible to avoid unnecessary cooling control by suspending the operation of the radiator fan 23 until the temperature of the high differential pressure water electrolyzer 12 increases to the predetermined temperature Ta due to the self-heat generation. This enables better improvement of the system efficiency (efficiency of water electrolysis).

Moreover, the second temperature sensor 48 is capable of preventing a situation where the temperature of the high differential pressure water electrolyzer 12 exceeds the upper limit by monitoring the outlet temperature of the high differential pressure water electrolyzer 12. Hence, it is possible to delay the deterioration of the high differential pressure water electrolyzer 12.

What is more, after water electrolysis by the high differential pressure water electrolyzer 12 reaches the stable state, the first temperature sensor 46 monitors the temperature of supply water supplied to the water supply port 20a of the high differential pressure water electrolyzer 12. Here, driving of the radiator fan 23 is controlled and the temperature of supply water is controlled.

For this reason, it is unlikely that an anomalous increase in temperature occurs after the high differential pressure water electrolyzer 12 shifts to a normal operation. Hence, if the temperature of supply water is monitored, the temperature of water is controlled more accurately. This eliminates the necessity of setting the temperature threshold at normal operation to a low value in a safe zone, making it possible to effectively improve the efficiency of water electrolysis by the high differential pressure water electrolyzer 12.

Additionally, the radiator 24 is included as the cooling apparatus. Thus, with a simple and economical configuration, it is possible to better control the temperature of the high differential pressure water electrolyzer 12.

Furthermore, the stack inlet control temperature Tb is set, which is a control temperature at which to control the supply water temperature monitored by the first temperature sensor 46, the control temperature being based on estimation of the amount of heat generated in the high differential pressure water electrolyzer 12, and satisfying the condition that the discharge water temperature monitored by the second temperature sensor 48 does not exceed a discharge water temperature threshold Tc. Thus, it is possible to delay with certainty the deterioration of the high differential pressure water electrolyzer 12 attributed to the temperature exceeding the upper limit value.

Still further, the radiator fan 23 is controlled at the maximum rotational rate when the discharge water temperature monitored by the second temperature sensor 48 exceeds the discharge water temperature threshold Tc. This makes it possible to rapidly cool down the high differential pressure water electrolyzer 12 and to delay the deterioration of the high differential pressure water electrolyzer 12.

A water electrolysis system according to the present disclosure includes a water electrolyzer, a water supply pipe, and a water discharge pipe. The water electrolyzer electrolyzes water to produce oxygen and hydrogen. The water supply pipe supplies water to a water supply port of the water electrolyzer, and the water discharge pipe allows the water, subjected to electrolysis, to be discharged from a water discharge port of the water electrolyzer.

The water supply pipe is provided with a cooling apparatus, and is provided with a first temperature sensor which is located between the cooling apparatus and the water supply port and which monitors a temperature of supply water supplied to the water supply port. The water discharge pipe is provided with a second temperature sensor which monitors a temperature of discharge water discharged from the water discharge port.

Additionally, in this water electrolysis system, it is preferable that the cooling apparatus be a radiator.

The present disclosure further relates to a temperature control method of a water electrolysis system. This temperature control method includes the step of causing a second temperature sensor to monitor a temperature of discharge water discharged from a water discharge port of a water electrolyzer from a time of activation of the water electrolysis system. This temperature control method includes the steps of, after the temperature of the discharge water monitored by the second temperature sensor exceeds a predetermined temperature, causing the first temperature sensor to monitor a temperature of supply water supplied to the water supply port of the water electrolyzer, and starting control of the cooling apparatus to control the temperature of the supply water.

Still further, it is preferable that this temperature control method include estimating an amount of heat generated in the water electrolyzer, and based on the estimation, setting a control temperature at which to control the temperature of the supply water monitored by the first temperature sensor such that the temperature of the discharge water monitored by the second temperature sensor does not exceed a discharge water temperature threshold.

Moreover, in this temperature control method, it is preferable that the cooling apparatus be a radiator.

What is more, in this temperature control method, it is preferable that a fan of the radiator be controlled at a maximum rotational rate when the temperature of the discharge water monitored by the second temperature sensor exceeds the discharge water temperature threshold.

According to the present disclosure, the water supply pipe is provided with the cooling apparatus. Besides, the first temperature sensor and the second temperature sensor are disposed upstream and downstream of the water electrolyzer, respectively. Thus, it is possible to adjust accurately and easily the temperature of water supplied to the water electrolyzer.

Also, according to the present disclosure, the second temperature sensor has been monitoring the temperature of discharge water discharged from the water discharge port of the water electrolyzer since the activation of the water electrolysis system. During that period, the cooling apparatus is suspended until the temperature of the water electrolyzer increases to the predetermined temperature due to the self-heat generation. This makes it possible to avoid unnecessary cooling control and to better improve the system efficiency. Moreover, the second temperature sensor is capable of preventing a situation where the temperature of the water electrolyzer exceeds the upper limit by monitoring the outlet temperature of the water electrolyzer. Hence, it is possible to delay the deterioration of the water electrolyzer.

What is more, after the temperature of discharge water monitored by the second temperature sensor exceeds the predetermined temperature, the first temperature sensor monitors the temperature of supply water supplied to the water supply port of the water electrolyzer, and control of the cooling apparatus is started to control the temperature of the supply water. For this reason, it is unlikely that an anomalous increase in temperature occurs after the water electrolyzer shifts to a normal operation. Hence, if the temperature of supply water is monitored, the temperature of water is controlled more accurately. This eliminates the necessity of setting the temperature threshold at normal operation to a low value in a safe zone, making it possible to effectively improve the efficiency of water electrolysis.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims

1. A water electrolysis system comprising:

a water electrolyzer which electrolyzes water to produce oxygen and hydrogen;

a water supply pipe which supplies the water to a water supply port of the water electrolyzer; and

a water discharge pipe which allows the water, subjected to electrolysis, to be discharged from a water discharge port of the water electrolyzer, wherein

the water supply pipe is provided with a cooling apparatus, and is provided with a first temperature sensor which is located between the cooling apparatus and the water supply port and which monitors a temperature of supply water supplied to the water supply port, and

the water discharge pipe is provided with a second temperature sensor which monitors a temperature of discharge water discharged from the water discharge port.

2. The water electrolysis system according to claim 1, wherein

the cooling apparatus is a radiator.

3. A temperature control method of a water electrolysis system including

a water electrolyzer which electrolyzes water to produce oxygen and hydrogen;

a water supply pipe which supplies the water to a water supply port of the water electrolyzer; and

a water discharge pipe which allows the water, subjected to electrolysis, to be discharged from a water discharge port of the water electrolyzer, wherein

the water supply pipe is provided with a cooling apparatus, and is provided with a first temperature sensor located between the cooling apparatus and the water supply port, and

the water discharge pipe is provided with a second temperature sensor, the temperature control method comprising the steps of:

causing the second temperature sensor to monitor a temperature of discharge water discharged from the water discharge port of the water electrolyzer from a time of activation of the water electrolysis system; and

after the temperature of the discharge water monitored by the second temperature sensor exceeds a predetermined temperature, causing the first temperature sensor to monitor a temperature of supply water supplied to the water supply port of the water electrolyzer, and starting control of the cooling apparatus to control the temperature of the supply water.

4. The temperature control method according to claim 3, the method further comprising

estimating an amount of heat generated in the water electrolyzer, and based on the estimation, setting a control temperature at which to control the temperature of the supply water monitored by the first temperature sensor such that the temperature of the discharge water monitored by the second temperature sensor does not exceed a discharge water temperature threshold.

5. The temperature control method according to claim 4, wherein

the cooling apparatus is a radiator.

6. The temperature control method according to claim 5, wherein

a fan of the radiator is controlled at a maximum rotational rate when the temperature of the discharge water monitored by the second temperature sensor exceeds the discharge water temperature threshold.

7. A water electrolysis system comprising:

a water electrolyzer to electrolyze water to produce oxygen and hydrogen, the water electrolyzer including a water supply port and a water discharge port;

a water supply pipe which is connected to the water supply port and via which the water is to be supplied to the water electrolyzer;

a cooling apparatus provided in the water supply pipe;

a water discharge pipe which is connected to the water discharge port and via which the water is to be discharged from the water electrolyzer;

a first temperature sensor provided at the water supply pipe between the cooling apparatus and the water supply port to detect a temperature of the water in the water supply pipe; and

a second temperature sensor provided at the water discharge pipe to detect a temperature of the water in the water discharge pipe.

8. The water electrolysis system according to claim 7, wherein

the cooling apparatus includes a radiator.

9. A temperature control method of a water electrolysis system including a water electrolyzer to electrolyze water to produce oxygen and hydrogen, the temperature control method comprising:

detecting a temperature of water in a water discharge pipe, the water discharge pipe being connected to the water electrolyzer, the water being discharged from the water electrolyzer via the water discharge pipe;

detecting a temperature of the water in a water supply pipe between a cooling apparatus and the water electrolyzer after the temperature of the water detected in the water discharge pipe exceeds a predetermined temperature, the water supply pipe being connected to the water electrolyzer, the water being supplied to the water electrolyzer via the water supply pipe; and

starting the cooling apparatus to control the temperature of the water in the water supply pipe, the cooling apparatus being provided in the water supply pipe.

10. The temperature control method according to claim 9, further comprising:

estimating an amount of heat generated in the water electrolyzer: and

setting a control temperature at which to control the temperature of the water in the water supply pipe based on the estimated amount of heat such that the temperature of the water in the water discharge pipe does not exceed a discharge water temperature threshold.

11. The temperature control method according to claim 10, wherein

the cooling apparatus includes a radiator.

12. The temperature control method according to claim 11, wherein

a fan of the radiator is controlled at a maximum rotational rate when the temperature of the water in the water discharge pipe exceeds the discharge water temperature threshold.