JP2024090834A - Water heater - Google Patents

Abstract

To efficiently increase the temperature of hot water passing a heat exchanger, in a water heater which includes a bypass pipe.SOLUTION: A water heater 1 includes a gas burner 4A, a heat exchanger 5, a water inlet pipe 6, a hot water tapping pipe 7 and a bypass pipe 16. Furthermore, the water heater 1 includes: a bypass valve 19 for adjusting a passing water amount W2 flowing in the hot water tapping pipe 7 via the bypass pipe 16 from the water inlet pipe 6; and a controller 12 (control device) for controlling the bypass valve 19. In the water heater 1, in the case where the sum of the passing water amount W2 and a water supply amount W1 supplied further to the heat exchanger side than the bypass pipe 16 in the water inlet pipe 6 is defined as a total water amount Wt, and a ratio of the passing water amount W2 with respect to the total water amount Wt is defined as a bypass rate B, the bypass rate B is adjusted by the passing water amount W2 being adjusted by the bypass valve 19. The controller 2 (control device) performs bypass increase control for setting the bypass rate B equal to or higher than a predetermined value in a predetermined initial period after the combustion of the gas burner 4A is started, and after the initial period has elapsed, performs normal control for adjusting the bypass rate B based on a target temperature.SELECTED DRAWING: Figure 1

Description

This disclosure relates to a water heater.

The hot water supply device of Patent Document 1 includes a heat exchanger, a water inlet pipe connected to the heat exchanger to supply tap water, a hot water outlet pipe connected to the heat exchanger to supply heated hot water, and a bypass pipe connected between the water inlet pipe and the hot water outlet pipe to bypass the heat exchanger. The hot water supply device further includes a mixing motor capable of controlling the flow rate through the bypass pipe, an inner body thermistor that detects the inner body temperature, and a controller that controls the operation of the mixing motor according to the inner body temperature obtained by the inner body thermistor. In this hot water supply device, the controller reduces the flow rate through the bypass pipe by the mixing motor according to the gradient of the decrease in the inner body temperature obtained by the inner body thermistor.

JP 2013-245895 A

A water heater equipped with a bypass pipe can supply water through a water inlet pipe to a heat exchanger that is heated by exhaust gas generated by burning gas in a gas burner, while the bypass pipe connected between the water inlet pipe and the hot water outlet pipe allows water to be bypassed. With this configuration, water from the bypass pipe can be mixed with the hot water supplied from the heat exchanger to the hot water outlet pipe, and the temperature of the hot water supplied from the hot water outlet pipe can be adjusted by adjusting the degree of mixing.

In this type of water heater, if the heat exchanger is not fully warmed up when it is ignited, immediately after ignition, a large proportion of the combustion heat supplied to the heat exchanger is transferred to "parts that are less likely to contribute to heat transfer to the hot water," making it more difficult to efficiently raise the temperature of the hot water passing through the heat exchanger compared to when the entire heat exchanger is fully warmed up.

One of the objectives of this disclosure is to provide a technology that can efficiently increase the temperature of hot water passing through a heat exchanger in a water heater equipped with a bypass pipe.

The water heater according to the present disclosure is
a gas burner for burning a gas and supplying exhaust gas generated by the burning of the gas;
a heat exchanger including a heat transfer tube heated by the exhaust gas supplied from the gas burner;
a water inlet pipe provided between a water inlet for introducing water and the heat transfer tube and supplying water to the heat transfer tube;
A hot water outlet pipe connected to the downstream side of the heat transfer tube and through which hot water supplied from the heat transfer tube flows;
a bypass pipe which constitutes a bypass path for water branching off from the water inlet pipe and is connected to the hot water outlet pipe, and which allows water to flow to the hot water outlet pipe via the bypass path;
a bypass valve for adjusting the amount of water flowing from the water inlet pipe through the bypass pipe to the hot water outlet pipe;
A control device for controlling the bypass valve;
having
The bypass valve adjusts the water flow rate and the bypass ratio when the sum of the water flow rate and the water supply rate supplied to the heat exchanger side from the bypass pipe in the water inlet pipe is defined as a total water amount, and the ratio of the water flow rate to the total water amount is defined as a bypass ratio.
The control device performs bypass increase control to set the bypass ratio higher than a predetermined value during a predetermined initial period after combustion of the gas burner begins, and performs normal control to adjust the bypass ratio based on a target temperature after the initial period has elapsed.

The technology disclosed herein can efficiently increase the temperature of hot water passing through a heat exchanger in a water heater equipped with a bypass pipe.

FIG. 1 is an explanatory diagram that illustrates a schematic diagram of a water heater according to a first embodiment. FIG. 2 is a flowchart illustrating the flow of hot water discharge control performed in the water heater according to the first embodiment.

Below, embodiments of the present disclosure are listed and exemplified. Note that the features exemplified below may be combined in any compatible combination.

[1] A gas burner that burns gas and supplies exhaust gas generated by the combustion of the gas;
a heat exchanger including a heat transfer tube heated by the exhaust gas supplied from the gas burner;
a water inlet pipe provided between a water inlet for introducing water and the heat transfer tube and supplying water to the heat transfer tube;
A hot water outlet pipe connected to the downstream side of the heat transfer tube and through which hot water supplied from the heat transfer tube flows;
a bypass pipe which constitutes a bypass path for water branching off from the water inlet pipe and is connected to the hot water outlet pipe, and which allows water to flow to the hot water outlet pipe via the bypass path;
a bypass valve for adjusting the amount of water flowing from the water inlet pipe through the bypass pipe to the hot water outlet pipe;
A control device for controlling the bypass valve;
having
The bypass valve adjusts the water flow rate and the bypass ratio when the sum of the water flow rate and the water supply rate supplied to the heat exchanger side from the bypass pipe in the water inlet pipe is defined as a total water amount, and the ratio of the water flow rate to the total water amount is defined as a bypass ratio.
The control device controls the bypass valve to perform bypass increase control, which sets the bypass ratio higher than a predetermined value during a predetermined initial period after combustion of the gas burner begins, and to perform normal control, which adjusts the bypass ratio based on a target temperature after the initial period has elapsed.

The water heater of [1] above controls the bypass valve so that the bypass ratio in a relatively early period (a specified initial period) after the gas burner starts to burn is higher than the bypass ratio after the initial period has elapsed. Thus, in this water heater, the amount of water supplied to the heat exchanger in the initial period is relatively reduced, promoting heating of the heat exchanger, and the heat exchanger tends to warm up quickly. Thus, this water heater can shorten the "period during which it is difficult to efficiently increase the temperature of hot and cold water passing through the heat exchanger," and can efficiently increase the temperature of hot and cold water passing through the heat exchanger in a water heater equipped with a bypass pipe.

[2] The water heater described in [1], wherein the control device performs bypass suppression control to make the bypass ratio lower than the bypass ratio in the initial period during at least a portion of the period from when combustion of the gas burner begins to when the initial period begins.

The water heater of [2] above can increase the amount of hot and cold water passing through the heat exchanger by relatively lowering the bypass rate before the initial period (the period during which the bypass rate is relatively increased) after the gas burner starts to burn. Therefore, in the water heater described above, even if foreign matter is present in the heat transfer tube of the heat exchanger immediately after combustion starts, the foreign matter is likely to be washed away by the relatively large amount of hot and cold water supplied. Therefore, in this water heater, it is easy to perform control to reduce the amount of water supplied to the heat exchanger (control to relatively increase the bypass rate) when the heat exchanger is not clogged with foreign matter.

[3] The water heater according to [1] or [2], wherein the end point of the initial period is a point when a predetermined fixed time has elapsed since the ignition of the gas burner.

The water heater described in [3] above can easily set the end timing of the control that reduces the amount of water supplied to the heat exchanger (control that relatively increases the bypass rate) without performing complex calculations, and the end timing is less likely to vary during each hot water supply operation that is repeated during daily use.

[4] A water heater described in any one of [1] to [3], wherein the control device performs the bypass increase control so as to maintain the bypass ratio at a predetermined fixed ratio during the initial period, and after the initial period has elapsed, performs the normal control so as to adjust the bypass ratio based on the temperature of the water flowing through the water inlet pipe, the amount of water flowing into the water inlet pipe from outside the water heater, and a target temperature.

The water heater described above in [4] maintains the bypass ratio at a fixed ratio during the initial period, thereby stably and easily promoting heating of the heat exchanger, and after the initial period has elapsed, the bypass ratio is set to reflect the temperature of the water flowing through the water inlet pipe, the amount of water flowing into the water inlet pipe from the outside, and the target temperature, making it possible to control the outlet water temperature according to the situation.

[5] A plurality of burner units each having one or more of the gas burners are provided,
The water heater described in any one of [1] to [4], wherein the control device performs control to select the burner unit to be burned, and burns the burner unit having the largest number of gas burners among the multiple burner units during the initial period.

The water heater described above in [5] can heat up the entire heat exchanger more quickly during the initial period, further shortening the "period during which it is difficult to efficiently raise the temperature of hot water passing through the heat exchanger."

First Embodiment
Fig. 1 illustrates a water heater 1 according to a first embodiment. The water heater 1 illustrated in Fig. 1 is configured as a bypass mixing type water heater. In the water heater 1, a combustion chamber 2 equipped with an air supply fan 3 is provided in the appliance body. The combustion chamber 2 is an appliance configured with a space inside for burning gas. Air is supplied to the combustion chamber 2 by the air supply fan 3, and fuel gas is supplied via a gas pipe 8.

A plurality of burner units 4 each equipped with a gas burner 4A are provided inside the combustion chamber 2. The burner units 4 have different combustion capacities. Specifically, the number of gas burners 4A differs from one another for each burner unit 4. Each gas burner 4A operates to burn a mixed gas and supply exhaust gas generated by the combustion of the mixed gas. The mixed gas burned by the gas burner 4A is a mixture of fuel gas supplied via a gas pipe 8 and primary air from the air supply fan 3.

The gas pipe 8 leading to the gas burner 4A includes a common pipe 8A forming a common path, and multiple branch pipes 8B branching off from the common pipe 8A to each burner unit 4. The common pipe 8A is provided with a main solenoid valve 9 and a gas proportional valve 10. Each branch pipe 8B is provided with a switching solenoid valve 11, 11.... The opening degree or opening/closing of each of the main solenoid valve 9, gas proportional valve 10, and switching solenoid valves 11, 11... is controlled by a controller 12 as a control device. Reference numeral 13 denotes an igniter, reference numeral 14 denotes an ignition electrode, and reference numeral 15 denotes a flame rod. The controller 12 can operate the igniter 13 and the ignition electrode 14 to cause ignition.

The heat exchanger 5 is a device that is heated by the combustion of the gas burner 4A and performs heat exchange. The heat exchanger 5 is equipped with a heat transfer tube 5A that is heated by the exhaust (combustion exhaust) supplied from the gas burner 4A. A water inlet tube 6 is connected to one end of the heat transfer tube 5A, and a hot water outlet tube 7 is connected to the other end. When water flows from the water inlet tube 6 into the heat transfer tube 5A, the water flows through the heat transfer tube 5A and out to the hot water outlet tube 7.

The water inlet pipe 6 is provided between the water inlet, which introduces water from a water pipe installed outside the water heater 1, and the heat transfer pipe 5A of the heat exchanger 5, and is a pipe that supplies the water introduced from the water inlet to the heat transfer pipe 5A. The downstream end of the water inlet pipe 6 is connected to the upstream end of the heat transfer pipe 5A.

The hot water outlet pipe 7 is connected to the downstream end of the heat transfer pipe 5A and is arranged to flow the hot water supplied from the heat transfer pipe 5A. One end of the hot water outlet pipe 7 is connected to the heat transfer pipe 5A, and the other end is connected to the hot water tap 20. The hot water outlet pipe 7 flows hot water from the heat transfer pipe 5A to the hot water tap 20, for example, when the hot water tap 20 is open (an open state in which hot water can be discharged).

The bypass pipe 16 is a pipe provided between the water inlet pipe 6 and the hot water outlet pipe 7, and is a pipe that allows water to flow so as to bypass the heat exchanger 5. The bypass pipe 16 has one end connected to the water inlet pipe 6 and the other end connected to the hot water outlet pipe 7 so as to form a bypass path for water branching off from the water inlet pipe 6. The bypass pipe 16 is configured to allow water introduced from the water inlet pipe 6 to flow toward the hot water outlet pipe 7 when the hot water tap 20 is open and the bypass valve 19 is open, for example.

A water flow sensor 17 that detects the amount of water flowing through the entire appliance and a water flow rate regulator 18 are provided upstream of the connection position of the bypass pipe 16 in the water inlet pipe 6. In the example of FIG. 1, the water flow rate sensor 17 is provided in the water inlet pipe 6 between the water inlet and the connection position, and detects the amount of water flowing through this portion (i.e., the amount of water introduced into the water inlet pipe 6 from the outside). The controller 12 grasps the amount of water at the position where the water flow rate sensor 17 is provided (i.e., the amount of water introduced into the water inlet pipe 6 from the outside) based on information provided by the water flow rate sensor 17. The water flow rate regulator 18 is provided in the water inlet pipe 6 between the water inlet and the connection position, and adjusts the amount of water flowing through this portion. Specifically, the water flow rate regulator 18 has a valve body interposed in the water inlet pipe 6, and the opening degree of the valve body is adjustable. The controller 12 controls the water flow rate regulator 18 to adjust the amount of water at the position of the water flow rate regulator 18, specifically, by controlling the valve of the water flow rate regulator 18 to adjust the opening degree, thereby adjusting the amount of water flowing through the water inlet pipe 6.

The bypass valve 19 is a valve that adjusts the amount of water (flow rate) flowing from the water inlet pipe 6 through the bypass pipe 16 to the hot water outlet pipe 7, and includes, for example, a valve body and a drive device. In the example of FIG. 1, the bypass valve 19 is provided near the connection position of the bypass pipe 16 with the water inlet pipe 6, and operates as a bypass water flow rate adjustment device that adjusts the amount of water flowing through the bypass pipe 16. The controller 12 corresponds to an example of a control device, and controls the bypass valve 19 to adjust the amount of water at the position of the bypass valve 19, and specifically, adjusts the amount of water flowing from the water inlet pipe 6 to the bypass pipe 16 by controlling the opening of the valve body of the bypass valve 19.

A first thermistor 21 is provided on the hot water outlet pipe 7 downstream (hot water tap 20 side) of the connection with the bypass pipe 16. The first thermistor 21 detects the temperature of the hot water at the position where the first thermistor 21 is provided on the hot water outlet pipe 7 (the position between the connection with the bypass pipe 16 and the hot water tap 20). The temperature detected by the first thermistor 21 is the temperature of the hot water immediately before it is released from the hot water tap 20. The temperature detected by the first thermistor 21 corresponds to an example of the outlet hot water temperature.

A second thermistor 22 is provided on the hot water outlet pipe 7 upstream (towards the heat exchanger 5) of the connection with the bypass pipe 16. The second thermistor 22 detects the temperature of the hot water at the position where the second thermistor 22 is provided on the hot water outlet pipe 7 (the position between the heat transfer pipe 5A and the connection with the bypass pipe 16). The temperature detected by the second thermistor 22 is the temperature of the hot water immediately after it flows out of the heat transfer pipe 5A in the hot water outlet pipe 7.

A third thermistor 23 is provided in the water inlet pipe 6 upstream of the connection with the bypass pipe 16. The third thermistor 23 detects the temperature of the water at the position where the third thermistor 23 is provided in the water inlet pipe 6 (the position between the water inlet and the connection with the bypass pipe 16). The temperature detected by the third thermistor 23 is the temperature of the water immediately after it is introduced into the water inlet pipe 6 from the water inlet. The temperature detected by the third thermistor 23 corresponds to an example of the inlet water temperature. The temperatures detected by the first thermistor 21, the second thermistor 22, and the third thermistor 23 are provided to the controller 12.

The controller 12 is a control device capable of performing various controls, and is equipped with, for example, an information processing device such as a microcomputer having information processing functions and various calculation functions, a storage device such as a semiconductor memory capable of storing various information, a communication device for communicating with each device, and other interfaces. The controller 12 is capable of communicating with, for example, a remote controller 24. The remote controller 24 is a device that can be operated by a user from the outside, and is, for example, an operating device capable of setting and operating the set temperature, etc. The remote controller 24 can provide various information to the controller 12 and obtain various information from the controller 12.

Next, the water flow control will be described.
The controller 12 can control the pouring of water in the manner shown in FIG.
The controller 12 starts the control of Fig. 2 when a start condition is met. The start condition is, for example, that the supply of power from a power supply device (not shown) to the controller 12 has started, or that the power-on state has been maintained after the control of Fig. 2 has ended, or other start conditions may be used.

When the controller 12 starts the hot water discharge control of FIG. 2, it first judges in step S1 whether or not water flow has been detected. For example, when the controller 12 judges in step S1 that the amount of water detected by the water volume sensor 17 has exceeded the threshold, it makes a positive judgment (Yes judgment) and proceeds to step S2. On the other hand, when the controller 12 judges in step S1 that the amount of water detected by the water volume sensor 17 has not exceeded the threshold, it makes a negative judgment (No judgment) and ends the hot water discharge control of FIG. 2. When the controller 12 makes a negative judgment (No judgment) in step S1 and ends the hot water discharge control of FIG. 2, it starts the hot water discharge control of FIG. 2 again after a predetermined short time and makes the judgment of step S1.

When the process proceeds to step S2, the controller 12 performs ignition control. When performing ignition control in step S2, the controller 12 rotates the air supply fan 3 to perform pre-purge, opens the main solenoid valve 9, the switching solenoid valve 11, and the gas proportional valve 10 to supply gas to the gas burner 4A, and operates the igniter 13 to ignite the gas burner 4A. The ignition of the gas burner 4A is confirmed by the flame rod 15. When performing ignition control in step S2, the controller 12, for example, ignites only one of the multiple burner units 4, and in step S2, opens the switching solenoid valve 11 provided in the branch pipe 8B that supplies gas to the burner unit 4 to be ignited.

After ignition is performed by the ignition control in step S2, the controller 12 advances the process to step S3 and performs bypass suppression control to suppress the amount of water flowing through the bypass pipe 16. The bypass suppression control is a control that suppresses the bypass ratio more than the bypass increase control described below. The bypass ratio is the ratio of the above-mentioned water flow rate to the total water amount Wt, where the sum of the "supply water amount" which is the amount of water supplied to the heat exchanger 5 side from the bypass pipe 16 in the inlet pipe 6 and the "passing water amount" which is the amount of water flowing through the bypass pipe 16 is the total water amount Wt. In the following description, the supply water amount is W1, the passing water amount is W2, and the inlet water amount which is the amount of water entering from the water inlet is the total water amount Wt. The supply water amount W1 is the amount of water supplied to the heat exchanger 5 side from the position where the bypass pipe 16 is connected in the inlet pipe 6 (specifically, the end position of the bypass pipe 16 on the inlet pipe 6 side). The water flow rate W2 is the amount of water flowing in the bypass pipe 16 from the bypass valve 19 to the hot water outlet pipe 7. The water flow rate W2 is determined by the formula W2 = Wt - W1. Wt is the sum of the water supply rate W1 and the water flow rate W2, and Wt = W1 + W2. The bypass ratio B is determined by the formula B = W2/Wt.

When the controller 12 performs the bypass suppression control in step S3, for example, by blocking the path with the bypass valve 19, the water flow rate of the bypass pipe 16 is set to 0, and the bypass rate is set to 0. In this example, during the bypass suppression control, the supply water amount W1 and the total water amount Wt (inlet water amount) are the same, and all of the water that flows into the inlet pipe 6 from the outside flows into the heat transfer pipe 5A. After starting the bypass suppression control in step S3, the controller 12 determines in step S4 whether the elapsed time after ignition has reached the threshold value T1, and if it is determined that the elapsed time after ignition has not reached the threshold value T1, the process returns to step S3 and the bypass suppression control is continued. On the other hand, if the controller 12 determines in step S4 that the elapsed time after ignition has reached the threshold value T1, the process proceeds to step S5 and the bypass increase control is performed. In other words, the controller 12 continues the bypass suppression control at least from the ignition point to the time T1, and if the time T1 has elapsed from the ignition point, the bypass suppression control is terminated and the bypass increase control is started.

As described above, the controller 12 controls the bypass valve 19 so that the bypass ratio B is lower than the bypass ratio B in the initial period during at least a portion (preferably the entire period) from when the gas burner 4A starts burning in step S2 to the start of the initial period (when time T1 has elapsed since the ignition point). The period from when the gas burner 4A is ignited in step S2 to when time T1 has elapsed (the period during which bypass suppression control is performed) is also called the "pre-control period." The initial period is the period following the pre-control period, and is the period during which bypass increase control, described below, is performed.

Note that bypass suppression control may also be performed before ignition control is performed in step S2. For example, the bypass rate of the bypass pipe 16 may be set to 0 before ignition control is performed in step S2 (e.g., before water flow is detected in step S1), and the bypass rate may be maintained at 0 before and after ignition control is performed in step S2, and further, the bypass rate may be maintained at 0 until the determination in step S4 is Yes.

When the controller 12 performs the bypass increase control in step S5, for example, the bypass valve 19 opens the path and adjusts the opening of the bypass valve 19 so that the bypass ratio B is a predetermined fixed ratio. The bypass increase control is a control that increases the bypass ratio more than a part or all of the period of the normal control described later. After starting the bypass increase control in step S5, the controller 12 determines in step S6 whether the elapsed time after ignition has reached the threshold value T2, and if it determines that the elapsed time after ignition has not reached the threshold value T2, the process returns to step S5 and the bypass increase control is continued. On the other hand, if the controller 12 determines in step S6 that the elapsed time after ignition has reached the threshold value T2, the process proceeds to step S7 and the normal control is performed. Note that in this example, T1<T2. That is, the controller 12 continues the bypass increase control from the time when the time T1 has elapsed from the ignition point until the time T2 has elapsed, and if the time T2 has elapsed from the ignition point, the bypass increase control is terminated and the normal control is started. The value of the fixed ratio is not particularly limited and may be, for example, 0.3, or it may be slightly larger or smaller than this value.

In this way, the controller 12 controls the bypass valve 19 so that the bypass rate B during the initial period after the gas burner 4A starts to burn is higher than the bypass rate B during the normal period after the initial period has elapsed. The initial period is the period during which the bypass increase control described above is performed, and more specifically, is the period from when time T1 has elapsed since ignition until time T2 has elapsed. In other words, the end of the initial period is the time when a predetermined fixed time T2 has elapsed since the ignition of the gas burner 4A in step S2. The normal period is the period during which normal control, which will be described later, is performed, and is the period from when time T2 has elapsed since ignition until water flow is not detected in step S8.

In this embodiment, each of the burner units 4 is provided with one or more gas burners, and the number of gas burners 4A differs from one another. When the controller 12 performs the bypass suppression control in step S3 and the bypass increase control in step S5, it is desirable to perform control to select the burner unit 4 to be burned so that only the burner unit 4 with the largest number of gas burners 4A among the multiple burner units 4 is burned, and to perform the bypass suppression control and the bypass increase control so that the other burner units 4 are not burned. In this way, the entire heat exchanger 5 can be heated more quickly by burning the burner unit 4 with the largest number of gas burners 4A among the multiple burner units 4 during the pre-control period and the initial period.

When the controller 12 performs normal control in step S7, it sets the bypass ratio B based on the inlet water temperature T3, which is the temperature detected by the third thermistor 23, and the inlet water volume (total water volume Wt), which is the water volume detected by the water volume sensor 17, using the following formula 1. In formula 1, B is the bypass ratio, Q (Kcal/h) is the amount of heat generated by the burner unit 4, T3 (°C) is the inlet water temperature, Tt (°C) is the target temperature, Wt (L/h) is the total water volume (inlet water volume), and η is the thermal efficiency. The total water volume Wt is specifically a value detected by the water volume sensor 17, and the inlet water temperature T3 is a value detected by the thermistor 23. The target temperature Tt may be a temperature set by operating the remote controller 24, may be a predetermined fixed temperature, or may be a temperature set in the control. In any case, the target temperature Tt is a value determined as the target temperature of the water flowing through the hot water outlet pipe 7 when normal control is performed. The thermal efficiency η is an index in which an efficiency of 100% is set to 1 and an efficiency of 0% is set to 0. The thermal efficiency η may be set to a predetermined fixed value, or a thermal efficiency may be prepared for each combination of units that are burning among the multiple burner units 4, and calculations may be performed to use the thermal efficiency corresponding to the combination of combustion in normal control. The amount of heat Q may be calculated by a known method to determine the amount of heat that is being applied based on the amount of gas supplied to each of the multiple burner units 4 and the units that are burning in the multiple burner units 4. The amount of gas supplied to each of the multiple burner units 4 is determined by the opening degree of the main solenoid valve 9, the gas proportional valve 10, the switching solenoid valves 11, 11, etc.

B = 1 - (Q x η / (Wt x (Tt - T3))) ... (Equation 1)

In this way, after the above-mentioned initial period has elapsed, the controller 12 determines the bypass ratio B based on the temperature of the water flowing through the water inlet pipe 6 (inlet water temperature T3), the total water volume Wt (inlet water volume), which is the volume of water flowing into the water inlet pipe 6 from the outside, and the target temperature Tt, and controls the bypass valve 19 to achieve the determined bypass ratio B. After the initial period has elapsed, the controller 12 performs the "operation of calculating the bypass ratio B by calculation and controlling to the bypass ratio B" at predetermined short intervals until the water flow state is not detected in step S8 (specifically, for example, until the water volume detected by the water volume sensor 17 falls below the threshold value).

3. Example of effect The water heater 1 controls the bypass valve 19 so that the bypass ratio at a relatively early time (a specified initial period) after the start of combustion of the gas burner 4A is higher than the bypass ratio after the initial period has elapsed. Thus, in this water heater 1, the amount of water supplied to the heat exchanger 5 during the initial period is relatively reduced, and heating of the heat exchanger 5 is promoted. Thus, this water heater 1 can shorten the "period during which it is difficult to efficiently increase the temperature of hot water passing through the heat exchanger 5," and can efficiently increase the temperature of hot water passing through the heat exchanger 5 in the water heater 1 equipped with the bypass pipe 16.

By performing the control of step S3 in FIG. 2, the water heater 1 can relatively lower the bypass rate before the initial period (the period during which the bypass rate is relatively increased) after the gas burner 4A starts to burn, thereby increasing the amount of hot water passing through the heat exchanger 5. Therefore, in the water heater 1, even if foreign matter is present in the heat transfer tube 5A of the heat exchanger 5 immediately after the start of combustion, the foreign matter is likely to be washed away by the relatively large amount of hot water supplied. Therefore, in this water heater 1, control to reduce the amount of water supplied to the heat exchanger 5 (control to relatively increase the bypass rate) is easily performed when the heat exchanger 5 is not clogged with foreign matter.

The water heater 1 can easily set the end timing of the control that reduces the amount of water supplied to the heat exchanger 5 (control that relatively increases the bypass rate) by time without performing complex calculations, and the end timing is less likely to vary during each hot water supply operation that is repeated during daily use.

During the initial period, the water heater 1 maintains the bypass rate B at a fixed ratio, thereby stably and easily promoting the heating of the heat exchanger 5, and after the initial period has elapsed, the bypass rate B is set to reflect the temperature of the water flowing through the water inlet pipe 6 (inlet water temperature T3), the total amount of water Wt flowing into the water inlet pipe 6 from the outside, and the target temperature Tt, making it possible to control the outlet water temperature according to the situation.

The water heater 1 can heat the entire heat exchanger 5 more quickly during the initial period, further shortening the "period during which it is difficult to efficiently raise the temperature of the hot water passing through the heat exchanger 5."

<Other embodiments>
The present invention is not limited to the embodiments described above and in the drawings. For example, the features of the above or later described embodiments can be combined in any combination within a range that does not contradict. Furthermore, any feature of the above or later described embodiments can be omitted unless it is clearly stated as essential. Furthermore, the above described embodiments may be modified as follows.

The above-described embodiment is merely an example, and the design can be modified as appropriate. For example, the water heater 1 may be configured to supply hot water to the bathtub through a path branching off from the hot water outlet pipe.

In the embodiment described above, bypass suppression control was performed to set the bypass ratio to 0, but the bypass suppression control only needs to set the bypass ratio to a smaller value than that of bypass increase control, and may be, for example, a value slightly larger than 0.

In the embodiment described above, the bypass ratio is a fixed ratio in the bypass increase control, but the bypass ratio may be changed slightly. For example, in the bypass increase control, the bypass ratio may be increased or decreased gradually within a high bypass ratio range. Alternatively, the bypass ratio may be set to a first bypass ratio from time T1 to time Ta after the ignition point in time, and to a second bypass ratio from time Ta to time T2. In this case, T1<Ta<T2. Of course, other methods of change may be used.

The normal control in the above-described embodiment is merely an example, and the bypass ratio may be calculated using another calculation formula that sets the bypass ratio based on the total water volume Wt, the target temperature Tt, and the inlet water temperature T3. As the normal control, for example, normal control may be performed so as to determine the bypass ratio by the method disclosed in JP 2013-245895 A. Alternatively, during normal control, combustion stage switching control such as that disclosed in JP 2016-173212 A, JP 2018-200123 A, and JP 2018-200123 A may be performed. In any case, it is sufficient that the bypass ratio during bypass increase control is greater than the bypass ratio during a portion of the normal control period, and preferably, the bypass ratio during bypass increase control is greater than the bypass ratio during the entire normal control period.

The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is not limited to the embodiments disclosed herein, but is intended to include all modifications within the scope of the claims or within the scope equivalent to the claims.

1: Water heater 4A: Gas burner 5: Heat exchanger 5A: Heat transfer pipe 6: Water inlet pipe 7: Water outlet pipe 12: Controller (control device)
16: Bypass pipe 19: Bypass valve

Claims (5)

a gas burner for burning a gas and supplying exhaust gas generated by the burning of the gas;
a heat exchanger including a heat transfer tube heated by the exhaust gas supplied from the gas burner;
a water inlet pipe provided between a water inlet for introducing water and the heat transfer tube and supplying water to the heat transfer tube;
A hot water outlet pipe connected to the downstream side of the heat transfer tube and through which hot water supplied from the heat transfer tube flows;
a bypass pipe which constitutes a bypass path for water branching off from the water inlet pipe and is connected to the hot water outlet pipe, and which allows water to flow to the hot water outlet pipe via the bypass path;
a bypass valve for adjusting the amount of water flowing from the water inlet pipe through the bypass pipe to the hot water outlet pipe;
A control device for controlling the bypass valve;
having
The bypass valve adjusts the water flow rate and the bypass ratio when the sum of the water flow rate and the water supply rate supplied to the heat exchanger side from the bypass pipe in the water inlet pipe is defined as a total water amount, and the ratio of the water flow rate to the total water amount is defined as a bypass ratio.
The control device performs bypass increase control to set the bypass ratio higher than a predetermined value during a predetermined initial period after combustion of the gas burner begins, and performs normal control to adjust the bypass ratio based on a target temperature after the initial period has elapsed. The water heater according to claim 1 , wherein the control device performs bypass suppression control to make the bypass ratio lower than the bypass ratio in the initial period during at least a portion of a period from when the gas burner starts combustion to a start point of the initial period. The water heater according to claim 1 or 2, wherein the end point of the initial period is a point when a predetermined fixed time has elapsed since the ignition of the gas burner. The water heater described in claim 1 or claim 2, wherein the control device performs the bypass increase control so as to maintain the bypass ratio at a predetermined fixed ratio during the initial period, and performs the normal control so as to adjust the bypass ratio after the initial period has elapsed based on the temperature of the water flowing through the water inlet pipe, the amount of water flowing into the water inlet pipe from outside the water heater, and a target temperature. A burner unit including one or more of the gas burners is provided,
3. The water heater according to claim 1, wherein the control device performs control to select the burner unit to be combusted, and combusts the burner unit having the largest number of gas burners among the plurality of burner units during the initial period.

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