JP2001304690A - Electric water heater - Google Patents

Abstract

(57) [Summary] [Problem] To provide an electric water heater that can reduce the anxiety of running out of hot water by enabling the user to always check the remaining hot water status in detail without troublesome user's hand. I do. SOLUTION: When a first temperature sensor 1 detects a temperature lower than 45 ° C., a remaining hot water picture display “Z1” is turned off (Step S).
112), if the temperature is 45 ° C. or more and less than 60 ° C. (step S102), the remaining hot water picture display “Z1” is blinked (step S114), and if 60 ° C. or more is detected (step S103), the remaining hot water picture display “ Since "Z1" is turned on (step S115), the remaining hot water status can always be checked in detail, and the user's anxiety of running out of hot water can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric water heater for heating water in a hot water storage tank to supply hot water.

[0002]

2. Description of the Related Art Electric water heaters of this type use hot water that is used in one day by using low-cost electricity at midnight in order to comply with an electricity tariff system set by an electric power company for the purpose of equalizing electric power demand. There is a type that stores in a hot water storage tank. In this type of electric water heater, the amount of hot water stored in the hot water storage tank is limited, so if you use the hot water unplannedly, the hot water runs out. Until the hot water can not be used. In addition, when using under a contract in which power is supplied during the day, it can be boiled during the day, but it takes a considerable amount of time to boil to a usable temperature, so you can not use hot water immediately There is a problem that electricity charges are expensive because daytime electricity is set to be expensive.

[0003] In some cases, the amount of remaining hot water in the hot water storage tank is displayed on a remote controller or the like so that the amount of hot water can be used systematically while checking the remaining hot water amount. The remaining hot water amount is detected, for example, as follows.

When hot water is supplied from the upper portion of the hot water storage tank for use, hot water is simultaneously supplied from the lower portion of the hot water storage tank, and the inside of the hot water storage tank is always kept full. In addition, high-temperature hot water and water have different specific gravities, making them difficult to mix.
Separated by mixed layer. Therefore, for example, when the temperature near the temperature sensor attached to the position 100 liters from the top of the hot water storage tank changes from hot water to water, it is considered that the upper part from the temperature sensor position is hot water and the lower part is water, It is determined that the remaining hot water amount has become less than 100 liters. That is, for example, if the temperature detected by the temperature sensor is 4
When the temperature is 5 ° C or more, the remaining hot water amount is judged to be 100 liters or more,
When the temperature is lower than 45 ° C., it can be determined that the remaining hot water amount is less than 100 liters.

An example of a method for displaying the amount of remaining hot water detected in this manner will be described with reference to FIGS. FIG. 5 shows a display example of a remaining hot water amount displayed by a remote controller of a conventional electric water heater. FIG. 6 is a flowchart showing an embodiment of a conventional method for displaying the remaining hot water amount of an electric water heater.

Here, the capacity of the hot water storage tank is 370 liters, and the positions from the top of the hot water storage tank are 300 liters, 150 liters, 100 liters, and 50 liters, that is, the remaining hot water amounts are 300 liters, 150 liters, 100 liters, It is assumed that a first temperature sensor, a second temperature sensor, a third temperature sensor, and a fourth temperature sensor are respectively mounted at positions where it is possible to detect 50 liters.

In step S1 of FIG. 6, when all of the first to fourth temperature sensors detect 45 ° C. or more, it is determined that the remaining hot water amount is 300 liters or more, and step S11 is performed.
The remaining hot water picture display "Z1,""Z2,""Z3," and "Z4" are all lit and displayed as shown in the pattern "H1" in FIG. 5, and if not, the flow proceeds to step S2.

In step S2, when only the first temperature sensor detects less than 45.degree. C. and the second, third, and fourth temperature sensors detect 45.degree. Is determined to be less than
21, the remaining hot water picture displays "Z2", "Z3" and "Z4" are turned on and displayed as shown in the pattern "H2" in FIG.
If not, the process proceeds to step S3.

In step S3, the first and second temperature sensors detect a temperature lower than 45.degree.
If the temperature is not less than 100 ° C., it is determined that the remaining hot water amount is not less than 100 liters and less than 150 liters, and step S31 is performed.
The remaining hot water picture displays "Z3" and "Z4" are lit and displayed as shown in the pattern "H3" in FIG. 5, and if not, the flow proceeds to step S4.

In step S4, when the first, second, and third temperature sensors detect less than 45.degree. C. and only the fourth temperature sensor detects 45.degree. It is determined that the value is less than
Then, as shown in pattern "H4" in FIG. 5, only the remaining hot water picture display "Z4" is lit and displayed, and if not, the flow proceeds to step S5.

In step S5, when all of the first to fourth temperature sensors detect a temperature lower than 45 ° C.
It is determined that it is less than 0 liter, the process proceeds to step S51, and all the remaining hot water picture displays "Z1,""Z2,""Z3," and "Z4" are turned off as shown in the pattern "H5" in FIG.

As described above, when the temperature of the hot water in the hot water storage tank is equal to or higher than the predetermined temperature (45 ° C. in the above example), the remaining hot water is determined. The presence or absence was displayed.

[0013]

However, in the above-mentioned conventional electric water heater, even if the indication of the remaining hot water is displayed, it is not known what the actual temperature of the remaining hot water is. For example, if you have turned off the electric water heater for a few days while traveling, or if you set the water heater to a lower boiling temperature in winter, the heat in the hot water storage tank will be warmer due to heat dissipation. However, if the temperature slightly exceeds a predetermined temperature (for example, 45 ° C.), an indication that there is remaining hot water is displayed. In this case, since the temperature of the remaining hot water is low, the hot water runs out as soon as the hot water is used, and it is inconvenient that the shower or hot water beam needs to be stopped halfway.

Some conventional electric water heaters have a function of allowing a user to check the temperature of hot water in a hot water storage tank by operating a switch provided on a remote controller or the like. However, every time you try to check it, you need to operate the switch and it is troublesome.Since it is a function provided for checking the hot water temperature, you can only check the hot water temperature at the top of the hot water storage tank, It was hard to say that I could confirm the situation.
Further, in the above case, since the hot water temperature is displayed separately from the remaining hot water presence display, the entire display section becomes large, and the cost is increased.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to reduce the cost and always keep the remaining hot water in detail without bothering the user. It is an object of the present invention to provide an electric water heater that can reduce a user's fear of running out of hot water by enabling confirmation.

[0016]

In order to achieve the above object, according to the present invention, a hot water storage tank for heating and storing hot water and a temperature sensor for detecting a hot water temperature in the hot water storage tank are provided. A hot water temperature display unit for displaying a temperature detected by the temperature sensor, a remaining hot water presence / absence determining means for determining that there is remaining hot water when the temperature sensor detects a predetermined temperature or higher, and the remaining hot water presence / absence determining means The remaining hot water presence display unit that displays the result of the remaining hot water presence determined, and an electric water heater including a control unit that controls the display of the hot water temperature display unit and the remaining hot water presence display unit, the hot water temperature display unit And the remaining hot water presence display section, and the control section controls the hot water temperature display and the remaining hot water presence display at the same time. According to the above invention, since the hot water temperature display section and the remaining hot water presence / absence display section are also used, and the hot water temperature display and the remaining hot water presence / absence display are simultaneously performed, the cost is suppressed and the user's hand is troubled. It is possible to always check the remaining hot water situation in detail without having to do so, and it is possible to reduce the user's fear of running out of hot water.

According to a second aspect of the present invention, in the electric water heater according to the first aspect, when the remaining hot water presence / absence determining means determines that there is no remaining hot water, the control unit controls the remaining hot water presence display unit to turn off the light. It was decided to. According to the above invention, the display is turned off when there is no remaining hot water, so that it can be clearly confirmed that there is no remaining hot water.

According to a third aspect of the present invention, in the electric water heater according to the first or second aspect, when the remaining hot water presence / absence determining means determines that there is the remaining hot water, the level of the hot water is displayed on the hot water temperature display section. Alternatively, the display is controlled by the control unit so as to be displayed by blinking. According to the above invention, for example, when the remaining hot water temperature is high, the light is turned on, and when the remaining hot water temperature is low, the light is displayed by flashing.

According to a fourth aspect of the present invention, in the electric water heater according to the first or second aspect, when the remaining hot water presence / absence determining means determines that there is remaining hot water, the level of the hot water is indicated by the color of the hot water temperature display section. Is controlled by the control unit so as to be displayed according to the change in According to the above invention, for example, when the remaining hot water temperature is high, it is displayed in red, and when it is low, it is displayed in orange, so that not only the remaining hot water amount but also the remaining hot water temperature can always be confirmed.

According to a fifth aspect of the present invention, in the electric water heater according to the first or second aspect, when the remaining hot water presence / absence determining means determines that there is remaining hot water, the level of the hot water is indicated by the density of the hot water display. Is controlled by the control unit so as to be displayed according to the change in According to the above invention, for example, when the temperature of the remaining hot water is high, the color is displayed as dark red, and when the temperature is low, the color is displayed as light red, so that not only the amount of the remaining hot water but also the temperature of the remaining hot water can always be confirmed.

According to a sixth aspect of the present invention, in the electric water heater according to the first or second aspect, when the remaining hot water presence / absence determining means determines that there is remaining hot water, the hot water temperature is displayed on the hot water temperature display section by numerical values. Control by the control unit. According to the above invention, when there is remaining hot water, the temperature of the hot water is displayed as a numerical value, so that not only the amount of the remaining hot water but also the temperature of the remaining hot water can always be confirmed numerically.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an electric water heater showing one embodiment of the present invention.

The water in the hot water storage tank 11 is
Is boiled by using electric power at midnight by an electric heater 12 arranged below. When the hot water in the boiling water storage tank 11 is used for cooking or bathing, the same amount of water is discharged from the upper part of the hot water storage tank 11 and from the lower part of the hot water storage tank 11 at the same time. Is supplied to the hot water storage tank 11.

In the hot water storage tank 11, a first temperature sensor 1, a second temperature sensor 2, a third temperature sensor 3, and a fourth temperature sensor 4 for detecting the temperature of hot water in the hot water storage tank 11 are located at different heights. Installed. In the present embodiment, as in the conventional example, the capacity of the hot water storage tank 11 is 370 liters, and the first temperature sensor 1 has a capacity of 150 liters at a position where the capacity from the top of the hot water storage tank 11 is 300 liters. The second temperature sensor 2 is mounted at a position, the third temperature sensor means 3 is mounted at a position of 100 liters, and the fourth temperature sensor 4 is mounted at a position of 50 liters.
The temperature detected by the first temperature sensor 1 is also used to control the power supply to the electric heater 12 for boiling the hot water in the hot water storage tank 11 to a set temperature.

Remaining hot water judging means 22 for judging the presence or absence of remaining hot water at each temperature sensor mounting position based on the temperatures detected by first temperature sensor 1, second temperature sensor 2, third temperature sensor 3, and fourth temperature sensor 4. Are provided in the control unit 21. Further, the control unit 21 includes a remaining hot water presence / absence display unit 24 for displaying the result determined by the remaining hot water presence / absence determining means 22 and the first temperature sensor 1, the second temperature sensor 2, the third temperature sensor 3, and the fourth temperature sensor 4. The display unit 31 including the hot water display unit 23 for displaying the detected temperature is controlled. The display unit 31
A remote controller provided with a switch for setting the boiling water temperature of the hot water storage tank 11 is provided, and the display unit 31 generally displays the current time and the like.

Next, an example of a method for displaying the state of the remaining hot water will be described with reference to FIGS. FIG. 2 is a flowchart showing one embodiment of the remaining hot water status display method. FIG. 4 shows a display example of the remaining hot water amount on the display unit 31. here,
A method for displaying the remaining hot water picture display “Z1” in FIG. 4 will be described with reference to the flowchart in FIG.

First, in step S101, when the first temperature sensor 1 detects a temperature lower than 45.degree.
2 judges that there is no remaining hot water (step S111), and turns off the remaining hot water picture display "Z1" in FIG. 4 (step S112).

In step S101, the first temperature sensor 1
If the temperature is detected to be 45 ° C. or higher,
Determines that there is remaining hot water (step S113). Next, in step S102, the first temperature sensor 1 detects that
When a temperature lower than 0 ° C. is detected, the remaining hot water picture display “Z1” in FIG. 4 blinks (step S114).

In step S102, the first temperature sensor 1
If the detected temperature is not more than 45 ° C and less than 60 ° C,
Proceeding to step S103, when it is confirmed that the detection temperature of the first temperature sensor 1 is 60 ° C. or higher, the remaining hot water picture display “Z1” in FIG. 4 is turned on (step S115).

The remaining hot water picture display "Z2", "Z3", "Z4"
Is also displayed in the remaining hot water picture display “Z
This is the same as the method for displaying “1”. That is, when there is no remaining hot water, the remaining hot water picture display is turned off, when there is remaining hot water, the remaining hot water picture display blinks when the detected temperature is 45 ° C or higher and lower than 60 ° C,
The control unit 21 controls the display unit 31 so that the display unit 31 is turned on when the temperature is 60 ° C. or higher.

FIG. 3 shows a display pattern of remaining hot water presence / absence and hot water temperature. The above embodiment is shown in pattern A of FIG. 3, in which the remaining hot water presence and the hot water temperature are both displayed by turning off, blinking, and lighting the remaining hot water picture display. That is, the remaining hot water presence display section 24 and the hot water temperature display section 23 are also used, and the remaining hot water presence and hot water temperature are simultaneously displayed. For this reason, the remaining hot water status can always be confirmed in detail, and the user's fear of running out of hot water can be reduced.

Next, according to the actual use condition, the display unit 3
A display example of the remaining hot water status displayed in 1 will be described. When the hot water in the hot water storage tank 11 is in a state of being heated to the total set temperature, for example, 90 ° C. and the hot water is not used, all the first to fourth temperature sensors detect 60 ° C. or more. The presence / absence determining means 22 determines that there is residual hot water at the positions of all the temperature sensors. The remaining hot water picture display "Z1" is displayed by the control unit 21.
Since “Z2”, “Z3” and “Z4” are all turned on, it is possible to know that there is more than 300 liters of hot water remaining.

When hot water is used, hot water is supplied from the upper part of the hot water storage tank 11 and the same amount of water is supplied to the hot water storage tank 11 from the lower part. When about 70 liters of hot water is used, the first temperature sensor 1 detects the water temperature (for example, 15
° C), that is, below 45 ° C, the remaining hot water presence / absence determining means 22 determines that there is no remaining hot water up to the position of the first temperature sensor 1. Then, since the remaining hot water picture display “Z1” is turned off by the control unit 21, it is possible to know that the high-temperature hot water has become 150 liters or more and less than 300 liters.

When hot water is continuously used and the total amount used reaches about 220 liters, the second temperature sensor 2 in addition to the first temperature sensor 1 detects below 45 ° C.
The remaining hot water presence / absence determining means 22 determines that there is no remaining hot water up to the position of the second temperature sensor 2. Then, since "Z2" is turned off in addition to the remaining hot water picture display "Z1" by the control unit 21,
It can be known that the amount of the remaining hot water is 100 liters or more and less than 150 liters.

Further, hot water is used, and the total amount used is about 2
When the temperature reaches 70 liters, the remaining hot water presence / absence judging means 22 reaches the position of the third temperature sensor 3 because the third temperature sensor 3 in addition to the first temperature sensor 1 and the second temperature sensor 2 also detects less than 45 ° C. Judge that the remaining hot water is gone. Then, since the control unit 21 also turns off "Z3" in addition to the remaining hot water picture displays "Z1" and "Z2", it is possible to know that the high-temperature hot water has become 50 liters or more and less than 100 liters.

Further, hot water is used, and the total amount used is about 3
When the temperature reaches 20 liters, the fourth temperature sensor 4 in addition to the first temperature sensor 1, the second temperature sensor 2, and the third temperature sensor 3 also detects a temperature lower than 45 ° C. It is determined that there is no remaining hot water up to the temperature sensor 4 position. The remaining hot water picture display “Z
Since “Z4” is also turned off in addition to “1”, “Z2” and “Z3”, it is possible to know that the remaining hot water is less than 50 liters.

The display example described above is a display method substantially similar to the conventional display method. If hot water was used,
The temperature detected by the temperature sensor does not suddenly shift from a high temperature to a low temperature (water temperature). This is because the hot water and the water in the hot water storage tank 11 are vertically separated, but a mixed layer of the hot water and the water exists at the boundary. When the temperature sensor is located in the mixed layer and the detected temperature is 45 ° C. or higher and lower than 60 ° C., in the present embodiment, the control unit 21 controls the remaining hot water display to blink. This point is different from the conventional example.

As still another case, for example, when the electric water heater is turned off for a trip or the like and the user is away from home for a few days to use hot water after returning home, or by lowering the set boiling temperature of the electric water heater in winter, for example, A description will be given of a display example of the state of the remaining hot water displayed on the display unit 31 in a state where the remaining hot water in the hot water storage tank 11 is tepid due to heat radiation, such as when the temperature is set to 70 ° C. and hot water is used in the evening. .

In this case, even if there is a large amount of residual hot water, the temperature is low (for example, about 50 ° C.), but since the residual hot water temperature is 45 ° C. or higher, the conventional display simply indicates that there is residual hot water. . At this time, it can be mixed with water and used at an appropriate temperature of about 40 ° C., but when it is used for showering or bathing in a bathtub, it is likely to run out immediately after thinking that there is enough remaining hot water. In such a case, inconvenience is forced, such as forced to stop using the hot water, and the hot water accumulated in the bathtub halfway is wasted because it cannot be used for cooking. In order to solve such a problem, in the present embodiment, the remaining hot water status is displayed as follows.

When the hot water in the hot water storage tank 11 is completely warm, for example, at 50 ° C. and the hot water is unused, all of the first to fourth temperature sensors detect 50 ° C.
The remaining hot water presence / absence determining means 22 determines that there is remaining hot water at the positions of all the temperature sensors. Then, since the remaining hot water picture display "Z1,""Z2,""Z3," and "Z4" are all controlled by the control section 21 to blink, it is possible to know that the lukewarm remaining hot water is 300 liters or more.

When hot water is used, hot water is supplied from the upper portion of the hot water storage tank 11 and the same amount of water is supplied to the hot water storage tank 11 from the lower portion. When about 70 liters of hot water is used, the first temperature sensor 1 detects the water temperature (for example, 15
° C), that is, below 45 ° C, the remaining hot water presence / absence determining means 22 determines that there is no remaining hot water up to the position of the first temperature sensor 1. Then, since the remaining hot water picture display “Z1” is turned off by the control unit 21, the lukewarm remaining hot water is reduced by 150.
It is possible to know that the volume is less than 300 liters or more.

When hot water is continuously used and the total amount used reaches about 220 liters, the second temperature sensor 2 in addition to the first temperature sensor 1 detects below 45 ° C.
The remaining hot water presence / absence determining means 22 determines that there is no remaining hot water up to the position of the second temperature sensor 2. Then, since "Z2" is turned off in addition to the remaining hot water picture display "Z1" by the control unit 21,
It can be seen that the amount of remaining warm water has become 100 liters or more and less than 150 liters.

Further, hot water is used, and the total amount used is about 2
When the temperature reaches 70 liters, the remaining hot water presence / absence judging means 22 reaches the position of the third temperature sensor 3 because the third temperature sensor 3 in addition to the first temperature sensor 1 and the second temperature sensor 2 also detects less than 45 ° C. Judge that the remaining hot water is gone. Then, since the control unit 21 also turns off "Z3" in addition to the remaining hot water picture displays "Z1" and "Z2", it is possible to know that the lukewarm remaining hot water has become 50 liters or more and less than 100 liters.

Further, hot water is used, and the total amount used is about 3
When the temperature reaches 20 liters, the fourth temperature sensor 4 in addition to the first temperature sensor 1, the second temperature sensor 2, and the third temperature sensor 3 also detects a temperature lower than 45 ° C. It is determined that there is no remaining hot water up to the temperature sensor 4 position. The remaining hot water picture display “Z
Since "Z4" is also turned off in addition to "1", "Z2" and "Z3", it can be known that the lukewarm remaining hot water is less than 50 liters.

As described above, by displaying that the remaining hot water is tepid by flashing, it is possible to check the remaining hot water status in more detail than when simply displaying the presence or absence of the remaining hot water, and to allow the user to run out of hot water. Anxiety can be reduced.

In the above embodiment, no remaining hot water is turned off, lukewarm remaining hot water blinks, and high-temperature remaining hot water is turned on (pattern A in FIG. 3), but the display method is not limited to this. . Examples of other display methods are shown in patterns B to F in FIG.

Pattern B is blue when the temperature detected by the temperature sensor is lower than 45.degree.
When the temperature is above 60 ° C (with lukewarm residual hot water), orange, 6
When the temperature is 0 ° C. or more (there is high-temperature residual hot water), the display is displayed in red, and the display color changes according to the temperature detected by the temperature sensor.

The pattern C is turned off when the temperature detected by the temperature sensor is lower than 45 ° C., is displayed in a light color when the temperature is 45 ° C. or higher and lower than 60 ° C., and is displayed in a dark color when the temperature is higher than 60 ° C. The shading of a single color changes according to the temperature detected by the temperature sensor. The pattern D is an example in which the density is changed by a set of lines instead of a set of points.

Pattern E indicates "low" when the temperature detected by the temperature sensor is lower than 45 ° C, "medium" when the temperature is 45 ° C or higher and lower than 60 ° C, and “high” when the temperature is 60 ° C or higher. The character display changes according to the temperature detected by the temperature sensor.

Pattern F is “less than 45 ° C.” when the temperature detected by the temperature sensor is less than 45 ° C., and 45 ° C. or more and 60 ° C.
If it is less than 45 ° C, it is “45 ° C or more”.
0 ° C. or higher ”is displayed, and the numerical display changes according to the temperature detected by the temperature sensor.

In the above example, the temperature classification in the case where there is residual hot water is classified into two categories of “45 ° C. or more and less than 60 ° C.” and “60 ° C. or more”.
Although the stages are described, the temperature of the remaining hot water may be displayed by dividing it further finely, may be displayed linearly, or each remaining hot water picture may be displayed continuously without being divided. In this embodiment, when the hot water in the hot water storage tank 11 is used, the remaining hot water picture display is turned off sequentially from the top, but may be turned off sequentially from the bottom. The display unit 31
Various configurations such as a liquid crystal display device, a fluorescent display tube, and a light emitting diode are conceivable.

In this embodiment, an electric water heater has been described as an example, but the present invention can also be applied to a gas or oil water heater, or a combination with a heat pump or a solar water heater.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an electric water heater showing one embodiment of the present invention.

FIG. 2 is a flowchart showing an embodiment of a method for displaying the remaining hot water status of the electric water heater.

Fig. 3 Display pattern of remaining hot water and hot water temperature of the electric water heater

FIG. 4 is a display example of a remaining hot water amount of the electric water heater.

FIG. 5 is a display example of a remaining amount of hot water of a conventional electric water heater.

FIG. 6 is a flowchart showing one embodiment of a conventional method for displaying the remaining hot water amount of an electric water heater.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... 1st temperature sensor 2 ... 2nd temperature sensor 3 ... 3rd temperature sensor 4 ... 4th temperature sensor 11 ... Hot water storage tank 12 ... Electric heater 21 ... Control part 22 ... Remaining hot water presence / absence judgment means 23 ... Hot water temperature display part 24 … Remaining hot water presence display part 31… Display part

Claims (6)

[Claims] 1. A hot water storage tank for heating water to store hot water,
A temperature sensor for detecting the temperature of the hot water in the hot water storage tank, a hot water temperature display unit for displaying the temperature detected by the temperature sensor, and a remaining temperature for determining that there is remaining hot water when the temperature sensor detects a predetermined temperature or higher. A hot water presence / absence determining unit, a remaining hot water presence / absence display unit for displaying a result of the remaining hot water presence / absence determined by the remaining hot water presence / absence determining unit, and a control unit for controlling display of the hot water temperature display unit and the remaining hot water presence / absence display unit. In the electric water heater provided, the control unit controls the hot water temperature display unit and the remaining hot water presence / absence display unit, and controls the hot water temperature display and the remaining hot water presence / absence display at the same time. vessel. 2. The electric hot water as claimed in claim 1, wherein when the remaining hot water presence / absence determining means determines that there is no remaining hot water, the control unit controls the light to turn off the remaining hot water presence display unit. vessel. 3. The control section controls the hot water temperature display section to turn on or off the hot water temperature when the hot water presence / absence determining means determines that there is hot water remaining. The electric water heater according to claim 1 or 2, wherein 4. When the remaining hot water presence / absence determining means determines that there is remaining hot water, the control unit controls the hot water temperature to be displayed by a change in color of the hot water temperature display unit. The electric water heater according to claim 1 or 2, wherein 5. When the remaining hot water presence / absence determining means determines that there is residual hot water, the control unit controls the hot water temperature to be displayed by a change in shading of the hot water temperature display unit. The electric water heater according to claim 1 or 2, wherein 6. The controller according to claim 1, wherein when the remaining hot water presence / absence determining means determines that there is remaining hot water, the control unit controls the hot water temperature to be displayed as a numerical value on the hot water temperature display unit. Or the electric water heater according to claim 2.