CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of Japan Application No. 2021-048358, filed on Mar. 23, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND
Technical Field

The disclosure relates to control of a hot water supply apparatus, and more particularly to control in which deposition of scale is suppressed.

Related Art

Conventionally, if hard water containing a large amount of calcium or the like is used in a hot water supply apparatus as tap water supplied to the hot water supply apparatus, calcium (scale) is deposited and may adhere to and accumulate in a housing. As a result, heat exchange between the housing and the water in the housing is hindered, excessive thermal stress is applied in the housing, and thermal fatigue failure may finally occur.

As a countermeasure against adhesion of scale to the housing, for example, Japanese Patent Laid-Open No. 2014-88976 (Patent Document 1) discloses a “hot water supply apparatus able to suppress deposition of scale in a heat exchanger”. This hot water supply apparatus includes: “a combustion burner (5); a blower fan (51); a heat exchanger (31) heated by combustion exhaust generated by combustion of the combustion burner (5); a water supply pipe (1) supplying water to a pipeline (3) of the heat exchanger (31); a hot water outflow pipe (2), performing heat exchange on the water in the pipeline (3) by the heat exchanger (31), heating the water and then discharging hot water; a drainpipe (42) branched from the hot water outflow pipe (2); an on-off valve (43) provided at the drainpipe (42); and a control part (14) that, when a hot water outflow operation is stopped and combustion of the combustion burner (5) is stopped, performs a heat exchanger cooling operation in which the on-off valve (43) is opened and water is passed from the water supply pipe (1) to the drainpipe (42) through the pipeline (3)” (see the abstract). According to this hot water supply apparatus, “after the hot water outflow operation, since the temperature of the heat exchanger can be lowered at an early stage by performing the heat exchanger cooling operation in which the water is passed from the water supply pipe into the pipeline of the heat exchanger, an inconvenience can be prevented in which high-temperature hot water and water may remain stored in the pipeline and post-boiling may occur. Accordingly, deposition of scale in the pipeline of the heat exchanger can be suppressed” (see paragraph [0018]).

Japanese Patent Laid-Open No. 2001-50589 (Patent Document 2) discloses a technique of “preventing boiling of hot water at an outlet side of a heat exchanger of a water heater and generation of condensed water at the heat exchanger at low cost”. In this technique, “in the case where a set temperature Ts of a water heater is higher than a high temperature set temperature THS, when a hot water outflow temperature To is higher than the set temperature Ts, an inner body control temperature TNDS is set lower by a high temperature regulation temperature ΔThn obtained according to the hot water outflow temperature To and the set temperature Ts, when the hot water outflow temperature To is lower than the set temperature Ts, the inner body control temperature TNDS is set higher by a high temperature regulation temperature ΔTh and equal to or lower than a boiling prevention temperature TF defined so that the hot water does not boil due to heating of a heat exchanger 30, and combustion of a burner is controlled so that an inner body temperature reaches the set inner body control temperature” (see the abstract).

PATENT DOCUMENTS

Patent Document 1: Japanese Patent Laid-open No. 2014-88976

Patent Document 2: Japanese Patent Laid-open No. 2001-50589

According to the technique disclosed in Patent Document 1, since scale adhesion is suppressed after hot water outflow is stopped, there is a possibility that the effect may be low in terms of suppressing scale adhesion during use of the hot water supply apparatus. Since the heat exchanger (housing) is cooled by a cooling operation by passage of water or the like, there is a risk that a housing temperature may be lowered more than necessary. Further, when a pipe is cooled by passing water, there is also a risk that the pipe may be rapidly cooled and its durability may deteriorate due to heat shock.

SUMMARY

According to an embodiment, a hot water supply apparatus is provided. The hot water supply apparatus includes: a burner; a housing, including a heat exchanger heated by the burner; a water supply channel, supplying water to an inlet of the housing; a hot water outflow channel, to which hot water is supplied from an outlet of the housing; a bypass channel, bypassing the housing and connected to the water supply channel and the hot water outflow channel; a first temperature sensor, detecting a temperature of the water supplied to the housing; a second temperature sensor, detecting a temperature of the hot water at the outlet of the housing; a third temperature sensor, detecting a temperature of the hot water supplied from the hot water supply apparatus after the bypass channel and the hot water outflow channel join; and a control device, controlling operation of the hot water supply apparatus. The control device receives input of a set value of the temperature of the hot water supplied from the hot water supply apparatus, determines a combustion level of the burner based on the set value and amount of the hot water supplied from the hot water supply apparatus, and controls a combustion operation performed by the burner in accordance with a maximum temperature of the housing predetermined according to the combustion level.

According to another embodiment, a method executed by a computer for controlling a hot water supply apparatus is provided. The method includes the following. Input of a set value of a temperature of hot water supplied from a hot water supply apparatus is received, in which the hot water supply apparatus includes a burner, and a housing including a heat exchanger heated by the burner. A combustion level of the burner is determined based on the set value and amount of the hot water supplied from the hot water supply apparatus. A combustion operation performed by the burner is controlled in accordance with a maximum temperature of the housing predetermined according to the combustion level.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an outline of a configuration of a hot water supply apparatus according to an embodiment.

FIG. 2 is a block diagram illustrating an example of a hardware configuration of a control device 110.

FIG. 3 is a graph illustrating a relationship between number (hot water supply capacity) of a hot water supply apparatus 100 and temperature of a housing 102.

FIG. 4 is a diagram illustrating an example of information set through an operation panel 112 according to an embodiment.

FIG. 5 is a diagram illustrating a mode of data storage in a memory 220 of the hot water supply apparatus 100 according to an embodiment.

FIG. 6 is a diagram illustrating a mode of data storage in the memory 220 according to another aspect.

FIG. 7 is a flowchart illustrating a part of processing executed by a CPU 210 of the hot water supply apparatus 100 according to an embodiment.

DESCRIPTION OF THE EMBODIMENTS

The disclosure discloses a technique in which deposition of scale is suppressed during use of a hot water supply apparatus according to an aspect.

According to an embodiment, a hot water supply apparatus is provided. The hot water supply apparatus includes: a burner; a housing, including a heat exchanger heated by the burner; a water supply channel, supplying water to an inlet of the housing; a hot water outflow channel, to which hot water is supplied from an outlet of the housing; a bypass channel, bypassing the housing and connected to the water supply channel and the hot water outflow channel; a first temperature sensor, detecting a temperature of the water supplied to the housing; a second temperature sensor, detecting a temperature of the hot water at the outlet of the housing; a third temperature sensor, detecting a temperature of the hot water supplied from the hot water supply apparatus after the bypass channel and the hot water outflow channel join; and a control device, controlling operation of the hot water supply apparatus. The control device receives input of a set value of the temperature of the hot water supplied from the hot water supply apparatus, determines a combustion level of the burner based on the set value and amount of the hot water supplied from the hot water supply apparatus, and controls a combustion operation performed by the burner in accordance with a maximum temperature of the housing predetermined according to the combustion level.

In the hot water supply apparatus according to another aspect, the burner burns at multiple combustion levels. The maximum temperature is set for each combustion level.

In the hot water supply apparatus according to another aspect, the maximum temperature of the housing when the combustion level of the burner is minimum is lower than the maximum temperature of the housing when the combustion level of the burner is maximum.

In the hot water supply apparatus according to another aspect, in response to the combustion level being equal to or less than a preset combustion level, the maximum temperature of the housing when the set value is lower than a predetermined temperature is lower than the maximum temperature of the housing when the set value is higher than the predetermined temperature.

In the hot water supply apparatus according to another aspect, the control device further detects that scale adheres inside the heat exchanger based on the temperature at the outlet of the housing, and, based on the detection that the scale adheres inside the heat exchanger, causes the hot water supply apparatus to perform a predetermined operation.

In the hot water supply apparatus according to still another aspect, the maximum temperature of the housing is able to be changed based on any one of the temperature of the water supplied to the housing, the temperature of the hot water delivered from the housing, the temperature of the hot water supplied from the hot water supply apparatus, the set value, and a hot water supply capacity required for the hot water supply apparatus.

According to another embodiment, a method executed by a computer for controlling a hot water supply apparatus is provided. The method includes the following. Input of a set value of a temperature of hot water supplied from a hot water supply apparatus is received, in which the hot water supply apparatus includes a burner, and a housing including a heat exchanger heated by the burner. A combustion level of the burner is determined based on the set value and amount of the hot water supplied from the hot water supply apparatus. A combustion operation performed by the burner is controlled in accordance with a maximum temperature of the housing predetermined according to the combustion level.

In the method according to another aspect, the burner burns at multiple combustion levels, and the maximum temperature is set for each combustion level.

In the method according to another aspect, the maximum temperature of the housing when the combustion level of the burner is minimum is lower than the maximum temperature of the housing when the combustion level of the burner is maximum.

In the method according to another aspect, in response to the combustion level being equal to or less than a preset combustion level, the maximum temperature of the housing when the set value is lower than a predetermined temperature is lower than the maximum temperature of the housing when the set value is higher than the predetermined temperature.

The method according to another aspect further includes the following. It is detected that scale adheres inside the heat exchanger based on the temperature at the outlet of the housing. Based on the detection that the scale adheres inside the heat exchanger, the hot water supply apparatus is caused to perform a predetermined operation.

In the method according to still another aspect, the maximum temperature of the housing is able to be changed based on any one of a temperature of water supplied to the housing, a temperature of hot water delivered from the housing, the temperature of the hot water supplied from the hot water supply apparatus, the set value, and a hot water supply capacity required for the hot water supply apparatus.

According to still another embodiment, a program for causing a computer to execute a method for controlling a hot water supply apparatus is provided. The program causes the computer to execute the following. Input of a set value of a temperature of hot water supplied from a hot water supply apparatus is received, in which the hot water supply apparatus includes a burner, and a housing including a heat exchanger heated by the burner. A combustion level of the burner is determined based on the set value and amount of the hot water supplied from the hot water supply apparatus. A combustion operation performed by the burner is controlled in accordance with a maximum temperature of the housing predetermined according to the combustion level.

In the program according to another aspect, the burner burns at multiple combustion levels. The maximum temperature is set for each combustion level.

In the program according to another aspect, the maximum temperature of the housing when the combustion level of the burner is minimum is lower than the maximum temperature of the housing when the combustion level of the burner is maximum.

In the program according to another aspect, in response to the combustion level being equal to or less than a preset combustion level, the maximum temperature of the housing when the set value is lower than a predetermined temperature is lower than the maximum temperature of the housing when the set value is higher than the predetermined temperature.

According to another aspect, the program further causes the computer to execute the following. It is detected that scale adheres inside the heat exchanger based on the temperature at the outlet of the housing. Based on the detection that the scale adheres inside the heat exchanger, the hot water supply apparatus is caused to perform a predetermined operation.

In the program according to still another aspect, the maximum temperature of the housing is able to be changed based on any one of a temperature of water supplied to the housing, a temperature of hot water delivered from the housing, the temperature of the hot water supplied from the hot water supply apparatus, the set value, and a hot water supply capacity required for the hot water supply apparatus.

The above as well as other objects, features, aspects and advantages of the disclosure will become apparent from the following detailed description of the disclosure which is understood in connection with the accompanying drawings.

Embodiments of the disclosure are hereinafter described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals, and they also have the same names and functions. Accordingly, detailed description thereof will not be repeated.

Referring to FIG. 1, a configuration of a hot water supply apparatus 100 is described. FIG. 1 is a diagram illustrating an outline of a configuration of a hot water supply apparatus according to an embodiment.

The hot water supply apparatus 100 includes a case 101, a housing 102, a heat exchanger 103, a burner 104, a blower fan 105, a gas valve 106, a spark plug 107, a spark plug 107, a motor 109, a control device 110, a display part 111, an operation panel 112, a flow sensor 113, a flow regulating valve 114, a first temperature sensor 141, a second temperature sensor 142, a third temperature sensor 143, pipes 180a, 180b, 180c, and a gas pipe 190. Arrows in FIG. 1 indicate a direction in which a fluid flows. The fluid may include hot water, water, and a cleaning solution used in a cleaning mode in which the hot water supply apparatus 100 is operated in order to remove scale adhering inside the heat exchanger 103.

The housing 102, the control device 110, the display part 111, the flow sensor 113, the flow regulating valve 114, and the pipes 180a, 180b and 180c are disposed in the case 101. The heat exchanger 103, the burner 104 and the blower fan 105 are disposed in the housing 102. The housing 102 is provided with an exhaust port 102a and an intake port (not illustrated).

The heat exchanger 103 heats the fluid including hot water and water by heat from the burner 104. Specifically, the heat exchanger 103 is configured to exchange heat with combustion gas generated by the burner 104. In the example of FIG. 1, the heat exchanger 103 has a fin-and-tube structure having multiple plate-shaped fins and a heat transfer tube penetrating the multiple fins. The heat exchanger 103 is not limited to the fin-and-tube type. In FIG. 1, each part including the heat exchanger 103 and the pipes 180a, 180b and 180c constitutes a “hot water supply circuit”. The burner 104 corresponds to an embodiment of a “heating part” that heats the hot water supply circuit.

The burner 104 generates the combustion gas by burning fuel gas. In an aspect, the burner 104 is composed of multiple combustion devices. According to the temperature and amount of hot water required, the multiple combustion devices are ignited in accordance with a preset combustion level. It can be said that the combustion level corresponds to a so-called “combustion stage number” required for the hot water supply apparatus 100. For example, the combustion level may be defined from 1 to 6 and the burner 104 may be composed of twenty combustion devices. As an example of this case, at the combustion level “1”, three combustion devices are operated; at the combustion level “2”, five combustion devices are operated; at the combustion level “3”, ten combustion devices are operated; at the combustion level “4”, thirteen combustion devices are operated; at the combustion level “5”, fifteen combustion devices are operated; and at the combustion level “6”, twenty combustion devices are operated. The number of combustion levels is not limited to six, and may be less than six or more than six.

The burner 104 is connected to the gas pipe 190. The gas valve 106 is provided at the gas pipe 190. The spark plug 107 is disposed above the burner 104. When the spark plug 107 creates an ignition spark between targets provided on the burner 104, a flame is generated in a fuel-air mixture ejected from the burner 104.

The blower fan 105 supplies the burner 104 with the air required for combustion. The blower fan 105 is driven by the motor 109 and is configured to be rotatable. The blower fan 105 introduces the air from the intake port into the housing 102, and discharges the air used for combustion out of the housing 102 from the exhaust port 102a.

The first temperature sensor 141 is disposed at the pipe 180a and detects a temperature of the water supplied to the hot water supply apparatus 100. The second temperature sensor 142 is disposed at an outlet of the heat exchanger 103, and detects an outlet temperature (hereinafter also referred to as “housing temperature”) being a temperature of hot water immediately after the hot water is discharged from the outlet of the heat exchanger 103. The third temperature sensor 143 detects a temperature of the hot water obtained by mixing the hot water delivered from the pipe 180b with the water delivered from the pipe 180c. In an aspect, the first temperature sensor 141, the second temperature sensor 142 and the third temperature sensor 143 are composed of a so-called negative temperature coefficient (NTC) thermistor having a characteristic that an electric resistance value decreases in response to a temperature rise.

In an aspect, the control device 110 is able to detect the occurrence of scale blockage in the heat exchanger 103 by using the housing temperature detected by the second temperature sensor 142. As an example, when scale adheres inside a pipe of the heat exchanger 103, normal heat transfer of the heat exchanger 103 is impaired and heat transfer efficiency is lowered. As a result, the amount of heat held by the heat exchanger 103 increases, and a post-boiling temperature when a hot water supply operation is stopped rises. Accordingly, it can be presumed that the higher the housing temperature detected by the second temperature sensor 142, the larger the amount of scale adhered. Therefore, in an embodiment, the control device 110 compares a temperature detected by the second temperature sensor 142 with a predetermined threshold. If the temperature detected exceeds the threshold, the control device 110 may determine a degree of scale blockage (the amount of scale adhered) according to a degree of the temperature detected exceeding the threshold.

When detecting the scale blockage, the control device 110 notifies that scale adheres to the heat exchanger 103. For example, the control device 110 displays on the display part 111 the fact that scale adheres to the heat exchanger 103. As an example, in the case where the display part 111 includes a red light emitting device, the control device 110 turns on the red light emitting device. In another aspect, if the operation panel 112 includes a monitor, the control device 110 displays on the monitor a message indicating that scale adheres to the heat exchanger 103.

When detecting the adhesion of scale, the control device 110, automatically or based on a user's operation on the hot water supply apparatus 100, switches an operation mode of the hot water supply apparatus 100 to the cleaning mode of the heat exchanger 103, delivers the cleaning solution prepared in advance to the heat exchanger 103, cleans the heat exchanger 103 and removes the scale. When the cleaning of the heat exchanger 103 is completed, the control device 110 may switch the operation mode of the hot water supply apparatus 100 to a normal mode and resume operation of the hot water supply apparatus 100.

In an aspect, the second temperature sensor 142 may be attached to the pipe 180b downstream of the heat exchanger 103 that is for hot water outflow, or may be attached to the heat transfer tube in the heat exchanger 103. As another method for detecting the occurrence of scale blockage, in addition to the second temperature sensor 142 that detects the housing temperature, for example, a configuration of detecting a decrease in a flow rate of hot water and water due to the scale blockage downstream of the heat exchanger 103 may be adopted.

The pipes 180a, 180b and 180c are configured to flow the above fluid via the heat exchanger 103. Specifically, the pipe 180a is a pipe for water supply, the pipe 180b is a pipe for hot water outflow, and the pipe 180c is a pipe for bypassing.

The pipe 180a is connected to a water supply side of the heat exchanger 103 and supplies a fluid (such as water) from the pipe inlet 122A to the heat exchanger 103 (more specifically, the heat transfer tube).

The pipe 180b is connected to a hot water outflow side of the heat exchanger 103 and delivers the fluid from the heat exchanger 103 outside through a pipe outlet 123A.

The pipe 180c forms a bypass flow path between the pipe 180a and the pipe 180b. More specifically, the pipe 180c is connected to the pipe 180a and the pipe 180b, respectively, so as to bypass the fluid supplied from the pipe inlet 122A to the pipe 180a and guide the fluid to the pipe 180b. A bypass flow regulating valve 115 is connected to the pipe 180c. The bypass flow regulating valve 115 adjusts a flow rate or the like of the fluid in the pipe 180c.

The flow regulating valve 114 is provided on a downstream side of a junction of the pipe 180b and the pipe 180c, that is, between the junction and the pipe outlet 123A. The flow regulating valve 114 adjusts the amount of the fluid (for example, hot water) delivered from the pipe outlet 123A. The flow regulating valve 114 and the bypass flow regulating valve 115 also function as shut-off valves by being completely shut off. An opening degree of each of the flow regulating valve 114 and the bypass flow regulating valve 115 is adjusted by, for example, a stepping motor.

The display part 111 is controlled by the control device 110 to display information. The displayed information includes a set temperature, current temperature (for example, hot water temperature), an error in the case where the occurrence of scale blockage is detected, information about the scale cleaning mode, or the like. In the example of FIG. 1, the display part 111 is configured separately from the operation panel 112. However, in another aspect, the operation panel 112 that is able to remotely operate the hot water supply apparatus 100 may include the display part 111. In still another aspect, a speaker for outputting information or a warning by voice may be provided.

The control device 110 outputs, to each part, electric power supplied to the hot water supply apparatus 100 via a power plug (not illustrated). The control device 110 controls operation of a constituent device of the hot water supply apparatus 100 by executing a program stored in a memory. For example, the control device 110 controls operation (combustion)/stop of the burner 104 and the amount of gas supplied to the burner 104 as well as controls operation/stop of the blower fan 105 and a fan rotation speed during operation.

In another aspect, the control device 110 may output an error to the display part 111 when the occurrence of scale blockage is detected. In this case, after outputting the error, the control device 110 controls each unit so as to prohibit a combustion operation of the burner 104. Further, when a starting operation for starting the cleaning mode for the hot water supply apparatus 100 is received, the control device 110 controls each unit so as to start the cleaning mode for cleaning the inside of the heat exchanger 103 with the cleaning solution. When the cleaning mode is ended, the control device 110 is able to delete a history of error notification and cancel the prohibition of the combustion operation of the burner 104. A configuration of the control device 110 will be described later.

[Hardware Configuration of Control Device]

Referring to FIG. 2, a configuration of the control device 110 is described. FIG. 2 is a block diagram illustrating an example of a hardware configuration of the control device 110. The control device 110 is typically composed of a microcomputer. The control device 110 includes a central processing unit (CPU) 210, a memory 220, an input/output circuit 230, and an electronic circuit 240. The CPU 210, the memory 220, and the input/output circuit 230 are able to exchange signals with each other via a bus 250. The electronic circuit 240 is configured to execute predetermined arithmetic processing by dedicated hardware. The electronic circuit 240 is able to transmit and receive signals to and from the CPU 210 and the input/output circuit 230.

The control device 110 is electrically connected to the spark plug 107, the motor 109, the second temperature sensor 142, the flow sensor 113, the display part 111, and the operation panel 112.

The CPU 210 receives input of an output signal (detection value) from each sensor including the second temperature sensor 142 through the input/output circuit 230. Further, the CPU 210 receives input of a signal indicating an operation instruction given to the operation panel 112 through the input/output circuit 230. The operation instruction includes, for example, an on/off operation on an operation switch of the hot water supply apparatus 100, a hot water supply set temperature, and various time reservation settings (also referred to as “timer settings”). The CPU 210 controls operation of each component including the spark plug 107 and the motor 109 so that the hot water supply apparatus 100 operates in accordance with the operation instruction.

The CPU 210 may output information indicating a state of the hot water supply apparatus 100 via the display part 111. The display part 111 includes a liquid crystal monitor, an organic electroluminescence (EL) monitor, a lamp or the like. In another aspect, the CPU 210 may notify the state of the hot water supply apparatus using voice or melody or the like by using a speaker (not illustrated).

[Relationship Between Hot Water Supply Capacity and Housing Temperature]

Referring to FIG. 3, a relationship between hot water supply capacity and housing temperature is described. FIG. 3 is a graph illustrating a relationship between a number (hot water supply capacity) of the hot water supply apparatus 100 and a temperature of the housing 102. In an aspect, a maximum temperature of the housing 102 may have a linear relationship with the hot water supply capacity. For example, in the case where the number (hot water supply capacity) required for the hot water supply apparatus 100 is 40, the maximum temperature of the housing 102 is about 80° C. (=176° F.). On the other hand, in the case where the number (hot water supply capacity) is 70, the maximum temperature of the housing 102 is about 70° C. (=158° F.).

However, the hot water supply set temperature designated for the hot water supply apparatus 100 does not always require a maximum number (hot water supply capacity). In that case, a change in the temperature of the housing 102 may cause a change in thermal stress.

Therefore, according to an embodiment, the maximum temperature of the housing 102 may be controlled according to the hot water supply set temperature and the combustion level (so-called combustion stage number) of the hot water supply apparatus 100. For example, in an aspect, temperature control of the housing 102 is performed as follows.

In the case where the set temperature is equal to or lower than 120° F. (=about 49° C.), for the combustion levels 1 to 4, the maximum temperature of the housing 102 may be set to 140° F. (=60° C.). For the combustion levels 5 and 6, the maximum temperature may be set to 176° F. (=80° C.).

In the case where the set temperature is higher than 120° F. (=about 49° C.) and equal to or lower than 140° F. (=about 60° C.), for the combustion levels 1 to 4, the maximum temperature of the housing 102 may be set to 158° F. (=70° C.). For the combustion levels 5 and 6, the maximum temperature may be set to 176° F. (=80° C.).

In the case where the set temperature is higher than 140° F. (=about 60° C.), for the combustion levels 1 to 6, the maximum temperature of the housing 102 may be set to 176° F. (=80° C.).

[Temperature Setting]

Referring to FIG. 4, temperature setting of the hot water supply apparatus 100 is described. FIG. 4 is a diagram illustrating an example of information set through the operation panel 112 according to an embodiment. The operation panel 112 includes, for example, a touch panel. The touch panel displays setting information of the hot water supply apparatus 100, and receives operation input by the user of the operation panel 112.

For example, as illustrated in a state (A), in an aspect, the operation panel 112 indicates 60° C. (that is, 140° F.) as the set temperature of the hot water supply apparatus 100. When the user presses a “Confirm” button after setting the temperature to 60° C., information indicating that the set temperature is 60° C. (=140° F.) is written in the memory 220. After that, the CPU 210 adjusts the combustion performed by the burner 104 based on the set temperature.

After that, when the user presses a “Down” button, the operation panel 112 may display 45° C. (that is, 113° F.), as illustrated as a state (B). When the user presses the “Confirm” button, information indicating that the set temperature is 45° C. is written in the memory 220. After that, the CPU 210 suppresses the combustion performed by the burner 104 based on the set temperature, and supplies hot water at 45° C. by adjusting the amount of water flowing through the pipe 180c as necessary.

[Data Structure]

Referring to FIG. 5 and FIG. 6, a data structure in the hot water supply apparatus 100 is described. FIG. 5 is a diagram illustrating a mode of data storage in the memory 220 of the hot water supply apparatus 100 according to an embodiment. FIG. 6 is a diagram illustrating a mode of data storage in the memory 220 according to another aspect.

As illustrated in FIG. 5, in an aspect, the memory 220 holds a table 510. The table 510 defines a maximum temperature of a housing predetermined for each combustion level of the hot water supply apparatus 100. In the table 510, the maximum temperature of the housing 102 is set to a constant value.

In contrast, according to an embodiment, the hot water supply apparatus 100 may use data as defined in a table 520 instead of the data defined in the table 510. For example, in the case where the set temperature of the hot water supply apparatus 100 is set higher than 120° F. (=49° C.) and equal to or lower than 140° F. (=60° C.), the CPU 210 controls the combustion performed by the burner 104 based on the data in the table 520.

That is, the table 520 defines the maximum temperature in two stages according to the combustion level. More specifically, the maximum temperature of the housing 102 is switched between the combustion level “4” and the combustion level “5”. Accordingly, in the case where the amount of hot water required for the hot water supply apparatus 100 can be supplied at the combustion level “4”, the maximum temperature of the housing 102 is controlled as 70° C. (=158° F.). After that, if the combustion level “6” is required for supplying hot water as a result of the fact that the user further turns on a faucet (not illustrated) and the amount of hot water used is increased, the maximum temperature of the housing 102 is controlled as 80° C. (=176° F.). That is, an upper limit temperature used in controlling the housing 102 is raised.

In an aspect, at the combustion level (combustion stage number) in a low range (for example, combustion level “1” to combustion level “4”), since thermal load on a fin pipe (not illustrated) or a fin (not illustrated) also increases, scale may easily occur. However, according to the settings shown in the table 520, since the maximum temperature of the housing 102 in that range is lowered more than the maximum temperature of the housing 102 at the combustion level in a high range (for example, combustion levels “5” and “6”), the occurrence of scale can be suppressed.

Referring to FIG. 6, the user of the hot water supply apparatus 100 may lower the set temperature to 49° C. In this case, the CPU 210 may use data defined in a table 610 instead of the data in the table 520. That is, in the table 610, the maximum temperature of the housing 102 is set to 60° C. (=140° F.) for the combustion level “1” to the combustion level “4”. For the combustion levels “5” and “6”, the maximum temperature of the housing 102 remains at 80° C. (=176° F.).

Accordingly, if the amount of hot water used by the user of the hot water supply apparatus 100 can be supplied in the range of the combustion levels “1” to “4”, the maximum temperature of the housing 102 is 60° C. (=140° F.). In an aspect, in the hot water supply apparatus 100, by mixing the hot water flowing through the pipe 180a with the water flowing through the pipe 180c, so-called bypass mixing control can be performed. Thus, in the case where the set temperature is low (for example, in the case where the set temperature is equal to or lower than 49° C. (=120° F.)), the hot water supply apparatus is able to control the temperature of hot water delivered by the bypass mixing control even if the temperature of the housing 102 is not maintained at a high temperature. After that, when the amount of hot water required is increased and the combustion level rises to “5” or “6”, the maximum temperature of the housing 102 may be set to 80° C. (=176° F.).

In this way, by changing the maximum temperature of the housing 102 according to a set value (hot water supply set temperature) for the hot water supply apparatus 100, if the hot water supply set temperature is low, the maximum temperature of the housing 102 is also lowered, and unnecessary combustion is suppressed. As a result, since the thermal stress generated in the housing 102 is reduced, deterioration of durability of the housing 102 can be suppressed.

[Control Structure]

Referring to FIG. 7, a control structure of the hot water supply apparatus 100 is described. FIG. 7 is a flowchart illustrating a part of processing executed by the CPU 210 of the hot water supply apparatus 100 according to an embodiment.

In step S710, the CPU 210 detects that the hot water supply apparatus 100 is powered on.

In step S720, based on an operation signal from the operation panel 112, the CPU 210 reads a hot water supply set temperature (for example, the table 510, the table 520 or the table 610) from the memory 220.

In step S730, the CPU 210 sets the maximum temperature of the housing 102 in a first pattern. More specifically, the CPU 210 sets the maximum temperature of the housing 102 to 60° C. (=140° F.) for the combustion levels “1” to “4”, and sets the maximum temperature of the housing 102 to 80° C. (=176° F.) for the combustion levels “5” and “6”.

In step S740, the CPU 210 sets the maximum temperature of the housing 102 in a second pattern. More specifically, the CPU 210 sets the maximum temperature of the housing 102 to 70° C. (=158° F.) for the combustion levels “1” to “4”, and sets the maximum temperature of the housing 102 to 80° C. (=176° F.) for the combustion levels “5” and “6”.

In step S750, the CPU 210 sets the maximum temperature of the housing 102 in a third pattern. More specifically, the CPU 210 sets the maximum temperature of the housing 102 to 80° C. (=176° F.) for the combustion levels “1” to “4”, and similarly sets the maximum temperature of the housing 102 to 80° C. (=176° F.) for the combustion levels “5” and “6”.

In step S760, the CPU 210 determines whether a change in the hot water supply set temperature has been detected. For example, the user may operate the operation panel 112 and change the hot water supply set temperature during use of the hot water supply apparatus 100. If a signal of a new set temperature is received from the operation panel 112, the CPU 210 may determine that a change has occurred in the hot water supply set temperature. If determining that a change in the hot water supply set temperature has been detected (YES in step S760), the CPU 210 returns the control to step S720. If not (NO in step S760), the CPU 210 switches the control to step S770.

In step S770, the CPU 210 determines whether an instruction to end operation of the hot water supply apparatus 100 has been given. For example, in the case where the user presses a stop button (not illustrated) in the operation panel 112, the CPU 210 determines that an instruction to end operation of the hot water supply apparatus 100 has been given. If determining that an instruction to end operation of the hot water supply apparatus 100 has been given (YES in step S770), the CPU 210 ends operation of the hot water supply apparatus 100. If not (NO in step S770), the CPU 210 switches the control to step S780.

In step S780, the CPU 210 continues a combustion operation of the hot water supply apparatus 100. In an aspect, when detecting that scale adheres inside the heat exchanger 103, the CPU 210 switches the operation mode of the hot water supply apparatus 100 to the cleaning mode and starts cleaning of the heat exchanger 103. When the cleaning the heat exchanger 103 is ended, the CPU 210 switches the operation mode to the normal mode. After that, the CPU 210 returns the control to step S760.

Some of the technical features disclosed above can be summarized as follows.

(1) In an aspect, the CPU 210 receives input of a set value of a temperature of hot water supplied from the hot water supply apparatus 100. The CPU 21 determines a combustion level of the burner 104 based on the set value and amount of the hot water supplied from the hot water supply apparatus 100. The amount of the hot water may correspond to a so-called required number. The CPU 210 controls a combustion operation performed by the burner 104 in accordance with a maximum temperature of the housing 102 predetermined according to the combustion level.

(2) In an aspect, the burner 104 is able to burn at multiple combustion levels. The maximum temperature is set for each combustion level. The CPU 210 controls the combustion operation performed by the burner 104 in accordance with the maximum temperature set for each of the combustion level.

(3) In an aspect, the maximum temperature of the housing 102 when the combustion level of the burner 104 is minimum is lower than the maximum temperature of the housing 102 when the combustion level of the burner 104 is maximum.

(4) In an aspect, in response to the combustion level being equal to or less than a preset combustion level, the maximum temperature of the housing 102 when the set value is lower than a predetermined temperature is lower than the maximum temperature of the housing 102 when the set value is higher than the predetermined temperature.

(5) In an aspect, the CPU 210 further detects that scale adheres inside the heat exchanger 103 based on a temperature at an outlet of the housing 102. Based on the detection that the scale adheres inside the heat exchanger 103, the CPU 210 causes the hot water supply apparatus 100 to perform a predetermined operation.

(6) In an aspect, the maximum temperature of the housing 102 is able to be changed based on any one of the temperature of the water supplied to the housing 102, the temperature of the hot water delivered from the housing 102, the temperature of the hot water supplied from the hot water supply apparatus 100, the set value, and the hot water supply capacity required for the hot water supply apparatus 100.

As described above, according to the disclosure in the present specification, in the hot water supply apparatus 100, an upper limit (maximum temperature) of the set temperature of the housing 102 can be changed according to the hot water supply capacity (so-called number) or the combustion level (so-called combustion stage number). By doing so, the set temperature of the housing 102 is not set higher than necessary. Accordingly, at the hot water supply capacity or the combustion level at which the housing 102 is frequently used, adhesion of scale can be suppressed. Since the maximum temperature is set according to the hot water supply capacity or the combustion level, adhesion of scale to the heat exchanger during use of the hot water supply apparatus 100 can be suppressed without reducing a maximum supply amount of the hot water supply apparatus 100.

Although there may be a case of being independently set as a use mode of the hot water supply apparatus 100, the hot water supply apparatus 100 may not always be used at a maximum hot water supply capacity. According to the hot water supply apparatus 100 according to the present embodiment, the maximum temperature of the housing 102 is not reduced all over the range of the hot water supply capacity, and is reduced at the combustion level (combustion stage number) at which a maximum flow rate of water does not decrease. Accordingly, adhesion of scale can be suppressed while specifications of the hot water supply apparatus 100 are maintained.

Since the housing 102 is not heated more than necessary, the thermal stress generated in the housing 102 is reduced. As a result, the durability of the housing 102 can be improved. For example, if the maximum temperature of the housing 102 is lowered by about 10 degrees, the durability of the housing 102 may become two or three times the durability of the housing 102 in the case where the maximum temperature is not lowered.

The hot water supply apparatus 100 according to the above embodiments has been illustrated as an example of a hot water supply apparatus switchable in the hot water supply capacity or the combustion level. However, in another aspect, the disclosed technical features are also applicable to a non-switchable hot water supply apparatus. In this case, the hot water supply apparatus according to another aspect may have a configuration in which the hot water supply capacity itself can be improved or reduced.

The embodiments disclosed herein are examples in all aspects and should not be interpreted as limitations. The scope of the disclosure is defined by claims instead of the above descriptions, and it is intended to include all modifications within the scope of the claims and the equivalents thereof.

INDUSTRIAL APPLICABILITY

The disclosed technical features are applicable to a commercial or household hot water supply apparatus, combination boiler or the like.