water heater

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

Technical Field

[0001] The present disclosure relates to a water heater.

Background Art

[0002] The water supply device of Patent Document 1 includes a heat exchanger, a water inlet pipe connected to the heat exchanger for supplying tap water, a hot water outlet pipe connected to the heat exchanger for discharging heated hot water, and a bypass pipe connected between the water inlet pipe and the hot water outlet pipe for bypassing the heat exchanger. Further, the water supply device includes a mixing motor capable of controlling the flow rate flowing through the bypass pipe, an inner cylinder thermistor for detecting the inner cylinder temperature, and a controller for controlling the operation of the mixing motor according to the inner cylinder temperature obtained by the inner cylinder thermistor. In this water supply device, the controller decreases the flow rate flowing through the bypass pipe by the mixing motor according to the decrease gradient of the inner cylinder temperature obtained by the inner cylinder thermistor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A water heater provided with a bypass pipe enables water to be supplied to a heat exchanger heated by combustion exhaust generated by the combustion of gas in a gas burner by a water inlet pipe, while enabling water to be bypassed by a bypass pipe connected between the water inlet pipe and the hot water outlet pipe. 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 by adjusting this mixing degree, the temperature of the hot water supplied from the hot water outlet pipe can be adjusted.

[0005] In this type of water heater, if ignition occurs before the entire heat exchanger is sufficiently heated, immediately after ignition, a large proportion of the combustion heat supplied to the heat exchanger is transferred to the "parts that do not contribute much to heat transfer to the hot water." Therefore, compared to when the entire heat exchanger is sufficiently heated, it is more difficult to efficiently raise the temperature of the hot water passing through the heat exchanger.

[0006] One of the purposes of this disclosure is to provide a technology that can efficiently raise the temperature of the hot water passing through the heat exchanger in a water heater equipped with a bypass pipe. [Means for solving the problem]

[0007] One of the disclosed items is a water heater, A gas burner that burns gas and supplies exhaust gas produced by the combustion of the gas, A heat exchanger comprising heat transfer tubes heated by the exhaust supplied from the gas burner, An inlet for introducing water and an inlet pipe provided between the heat transfer tube, which supplies water to the heat transfer tube, A hot water outlet pipe connected to the downstream side of the heat transfer tube and carrying hot water supplied from the heat transfer tube, A bypass pipe that forms a bypass path for water branching from the inlet pipe and is connected to the outlet pipe, and which can allow water to flow to the outlet pipe via the bypass path, A bypass valve that adjusts the amount of water flowing from the inlet pipe to the outlet pipe via the bypass pipe, A control device for controlling the bypass valve, It has, When the sum of the aforementioned water flow rate and the amount of supply water supplied from the inlet pipe to the heat exchanger side rather than the bypass pipe is defined as the total water flow rate, and the ratio of the aforementioned water flow rate to the total water flow rate is defined as the bypass rate, the bypass rate is adjusted by the adjustment of the water flow rate by the bypass valve. The control device performs bypass increase control to set the bypass ratio to a predetermined value or higher during a predetermined initial period after the combustion of the gas burner has started, and then performs normal control to adjust the bypass ratio based on the target temperature after the initial period has elapsed. [Effects of the Invention]

[0008] The technology described herein can efficiently raise the temperature of the hot water passing through the heat exchanger in a water heater equipped with a bypass pipe. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is an explanatory diagram illustrating a water heater according to the first embodiment. [Figure 2] Figure 2 is a flowchart illustrating the flow of hot water supply control performed by a water heater according to the first embodiment. [Modes for carrying out the invention]

[0010] Embodiments of the present disclosure are listed and illustrated below. The features illustrated below may be combined in any non-consistent way.

[0011] [1] A gas burner that burns gas and supplies exhaust gas produced by the combustion of the gas, A heat exchanger comprising heat transfer tubes heated by the exhaust supplied from the gas burner, An inlet for introducing water and an inlet pipe provided between the heat transfer tube, which supplies water to the heat transfer tube, A hot water outlet pipe connected to the downstream side of the heat transfer tube and carrying hot water supplied from the heat transfer tube, A bypass pipe that forms a bypass path for water branching from the inlet pipe and is connected to the outlet pipe, and which can allow water to flow to the outlet pipe via the bypass path, A bypass valve that adjusts the amount of water flowing from the inlet pipe to the outlet pipe via the bypass pipe, A control device for controlling the bypass valve, It has, When the sum of the aforementioned water flow rate and the amount of supply water supplied from the inlet pipe to the heat exchanger side rather than the bypass pipe is defined as the total water flow rate, and the ratio of the aforementioned water flow rate to the total water flow rate is defined as the bypass rate, the bypass rate is adjusted by the adjustment of the water flow rate by the bypass valve. The control device performs bypass increase control to set the bypass ratio to a predetermined value or higher during a predetermined initial period after the combustion of the gas burner has started, and then performs normal control to adjust the bypass ratio based on the target temperature after the initial period has elapsed. Control of the bypass valve Water heater.

[0012] The water heater described in [1] above controls the bypass valve so that the bypass rate in the relatively early period after the gas burner combustion starts (a predetermined initial period) is higher than the bypass rate after the initial period has elapsed. Therefore, in this water heater, the amount of water supplied to the heat exchanger is relatively suppressed during the initial period, and the heating of the heat exchanger is promoted, so the heat exchanger heats up quickly. Therefore, this water heater can shorten the "period in which it is difficult to efficiently raise the temperature of the hot water passing through the heat exchanger," and can efficiently raise the temperature of the hot water passing through the heat exchanger in a water heater equipped with a bypass pipe.

[0013] [2] The control device performs bypass suppression control such that the bypass rate is lower than the bypass rate during the initial period for at least a portion of the period from when the combustion of the gas burner starts until the start of the initial period. The water heater described in [1].

[0014] The water heater described in [2] can reduce the bypass ratio relatively lower before the above initial period (the period of increasing the bypass ratio relatively) after the combustion of the gas burner starts, and can increase the amount of hot water passing through the heat exchanger. Therefore, in the above water heater, even if there are foreign substances in the heat transfer tubes of the heat exchanger immediately after the start of combustion, the foreign substances are likely to flow due to the relatively large amount of hot water supplied. Therefore, in this water heater, it is easy to perform control to suppress the amount of water supplied to the heat exchanger (control to increase the bypass ratio relatively) in a state where there is no blockage of foreign substances in the heat exchanger.

[0015] (3) The end point of the above initial period is the time when a predetermined fixed time has elapsed since the ignition of the gas burner. The water heater according to (1) or (2).

[0016] The water heater described in [3] can easily set the end timing of the control to suppress the amount of water supplied to the heat exchanger (control to increase the bypass ratio relatively) without performing complicated calculations, and the end timing is not likely to vary in each hot water supply operation repeated in daily use.

[0017] (4) 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 the outside of the water heater, and the target temperature. The water heater according to any one of (1) to (3).

[0018] The water heater described in [4] can stably and easily promote the heating of the heat exchanger by maintaining the bypass ratio at a fixed ratio during the initial period, and can set the bypass ratio by reflecting 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 after the initial period has elapsed, and can perform hot water temperature control according to the situation.

[0019] (5) It includes a plurality of burner units each including one or more of the above gas burners. The control device performs control to select the burner unit to be burned, and during the initial period, burns the burner unit with the largest number of gas burners among the multiple burner units. A water heater listed in any one of the following four categories: [1] through [4].

[0020] The water heater described in [5] above can heat the entire heat exchanger earlier during the initial period, and can further shorten the period during which it is difficult to efficiently raise the temperature of the hot water passing through the heat exchanger.

[0021] <First Embodiment> Figure 1 illustrates a water heater 1 according to the first embodiment. The water heater 1 shown in Figure 1 is configured as a bypass mixing type water heater. In the water heater 1, a combustion chamber 2 equipped with an air intake fan 3 is provided inside the appliance body. The combustion chamber 2 is an appliance that has a space for burning gas inside. Air is supplied to the combustion chamber 2 by the air intake fan 3, and fuel gas is supplied via a gas pipe 8.

[0022] Multiple burner units 4, each equipped with a gas burner 4A, are provided inside the combustion chamber 2. The multiple burner units 4 have different combustion capabilities. Specifically, the number of gas burners 4A differs for each burner unit 4. Each gas burner 4A operates to burn a gas mixture and supply exhaust gas produced by the combustion of the gas mixture. The gas mixture burned by the gas burner 4A is a mixture of fuel gas supplied via the gas pipe 8 and primary air from the air intake fan 3.

[0023] The gas pipe 8 leading to the gas burner 4A comprises a common pipe 8A that forms a common path, and multiple branch pipes 8B that branch off from the common pipe 8A to each burner unit 4. The common pipe 8A is equipped with a main solenoid valve 9 and a gas proportional valve 10. Each branch pipe 8B is equipped with a switching solenoid valve 11, 11... The opening degree or switching of each of the main solenoid valve 9, the gas proportional valve 10, and the switching solenoid valves 11, 11... is controlled by a controller 12 acting 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 ignite the gas.

[0024] The heat exchanger 5 is a device that is heated by the combustion of a gas burner 4A and performs heat exchange. The heat exchanger 5 is equipped with heat transfer tubes 5A that are heated by the exhaust (combustion exhaust) supplied from the gas burner 4A. An inlet pipe 6 is connected to one end of the heat transfer tubes 5A, and a hot water outlet pipe 7 is connected to the other end. When water flows from the inlet pipe 6 into the heat transfer tubes 5A, the water flows through the heat transfer tubes 5A and out to the hot water outlet pipe 7.

[0025] The water inlet pipe 6 is installed between the water inlet, which introduces water from a water pipe located outside the water heater 1, and the heat transfer tube 5A of the heat exchanger 5, and is a pipe that supplies the water introduced from the water inlet to the heat transfer tube 5A. The downstream end of the water inlet pipe 6 is connected to the upstream end of the heat transfer tube 5A.

[0026] The hot water outlet pipe 7 is connected to the downstream end of the heat transfer pipe 5A and is routed to carry 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 carries hot water from the heat transfer pipe 5A to the hot water tap 20 when the hot water tap 20 is open (an open state in which hot water can be discharged).

[0027] The bypass pipe 16 is a pipe installed between the inlet pipe 6 and the outlet pipe 7, and is a pipe that can carry water in a way that bypasses the heat exchanger 5. One end of the bypass pipe 16 is connected to the inlet pipe 6 and the other end is connected to the outlet pipe 7, so as to form a bypass path for water branching off from the inlet pipe 6. The bypass pipe 16 is configured, for example, to carry water introduced from the inlet pipe 6 toward the outlet pipe 7 when the hot water tap 20 is open and the bypass valve 19 is open.

[0028] Upstream of the connection point between the inlet pipe 6 and the bypass pipe 16, a water flow sensor 17 for detecting the amount of water flowing throughout the entire fixture and a water flow rate adjustment device 18 are provided. In the example shown in Figure 1, the water flow sensor 17 is installed in the inlet pipe 6 between the water inlet and the connection point, and detects the amount of water flowing through this section (i.e., the amount of water introduced into the inlet pipe 6 from the outside). The controller 12 determines the amount of water at the location where the water flow sensor 17 is installed (i.e., the amount of water introduced into the inlet pipe 6 from the outside) based on the information provided by the water flow sensor 17. The water flow rate adjustment device 18 is installed in the inlet pipe 6 between the water inlet and the connection point, and adjusts the amount of water flowing through this section. Specifically, the water flow rate adjustment device 18 has a valve body interposed in the inlet pipe 6, and the opening degree of the valve body is adjustable. The controller 12 controls the water flow rate adjustment device 18 to adjust the amount of water at its position, specifically by controlling the opening degree of the valve body of the water flow rate adjustment device 18, thereby adjusting the amount of water flowing through the inlet pipe 6.

[0029] The bypass valve 19 is a valve that adjusts the amount of water (flow rate) that flows from the inlet pipe 6 to the outlet pipe 7 via the bypass pipe 16, and for example, it has a valve body and a drive device. In the example in Figure 1, the bypass valve 19 is installed near the connection point with the inlet pipe 6 in the bypass pipe 16 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 is an example of a control device and controls the bypass valve 19 to adjust the amount of water at the location of the bypass valve 19, and specifically controls the opening degree of the valve body of the bypass valve 19 to adjust the amount of water flowing from the inlet pipe 6 to the bypass pipe 16.

[0030] A first thermistor 21 is provided in the hot water outlet pipe 7 downstream of the connection point with the bypass pipe 16 (towards the hot water tap 20). The first thermistor 21 detects the temperature of the hot water at the location where the first thermistor 21 is installed in the hot water outlet pipe 7 (the position between the connection point 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 just before it is discharged from the hot water tap 20. The temperature detected by the first thermistor 21 is an example of the hot water outlet temperature.

[0031] A second thermistor 22 is provided in the outlet pipe 7 upstream of the connection point with the bypass pipe 16 (on the heat exchanger 5 side). The second thermistor 22 detects the temperature of the hot water at the location where the second thermistor 22 is installed in the outlet pipe 7 (the location between the connection point between the heat transfer pipe 5A and 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 outlet pipe 7.

[0032] In the inlet pipe 6, a third thermistor 23 is provided upstream of the connection point with the bypass pipe 16. The third thermistor 23 detects the water temperature at the location where it is installed in the inlet pipe 6 (the location between the water inlet and the connection point 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 inlet pipe 6 from the water inlet. The temperature detected by the third thermistor 23 is 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.

[0033] The controller 12 is a control device capable of performing various types of control, and includes, 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 types of information, a communication device for communicating with each device, and other interfaces. The controller 12 is, for example, capable of communicating with the remote controller 24. The remote controller 24 is a device that a user can operate from the outside, and for example, is an operating device that can set the set temperature, etc. The remote controller 24 can provide various types of information to the controller 12 and can obtain various types of information from the controller 12.

[0034] Next, we will explain water flow control. The controller 12 can control the hot water supply in the manner shown in Figure 2. Controller 12 starts the control shown in Figure 2 when the start condition is met. The start condition is, for example, that power is supplied to Controller 12 from a power supply device (not shown), or that the power-on state is maintained after the end of the control shown in Figure 2. Other start conditions may also be used.

[0035] When the controller 12 starts the hot water supply control shown in Figure 2, it first determines in step S1 whether or not water flow has been detected. For example, if the controller 12 determines in step S1 that the amount of water detected by the water volume sensor 17 has exceeded a threshold, it makes an affirmative determination (a Yes determination) and proceeds to step S2. On the other hand, if the controller 12 determines in step S1 that the amount of water detected by the water volume sensor 17 has not exceeded a threshold, it makes a negative determination (a No determination) and terminates the hot water supply control shown in Figure 2. If the controller 12 terminates the hot water supply control shown in Figure 2 by making a negative determination (a No determination) in step S1, it starts the hot water supply control shown in Figure 2 again after a predetermined short time and makes the determination in step S1.

[0036] If 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 intake fan 3 to perform pre-purging, 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 activates 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, for example, the controller 12 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.

[0037] After ignition is performed by the ignition control in step S2, the controller 12 proceeds to step S3 and performs bypass suppression control to reduce the amount of water flowing through the bypass pipe 16. Bypass suppression control is a control that suppresses the bypass ratio more than the bypass increase control described later. The bypass ratio is the ratio of the amount of water flowing through 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 inlet pipe 6 beyond the bypass pipe 16, and the "water flow rate," which is the amount of water flowing through the bypass pipe 16, is the total water amount Wt. In the following explanation, the supply water amount is W1, the water flow rate 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 that flows from the bypass valve 19 to the hot water outlet pipe 7 in the bypass pipe 16. The water flow rate W2 is determined by the formula W2 = Wt - W1. Wt is the sum of the supply water rate W1 and the water flow rate W2, so Wt = W1 + W2. The bypass ratio B is determined by the formula B = W2 / Wt.

[0038] When the controller 12 performs bypass suppression control in step S3, for example, it blocks the path with the bypass valve 19, thereby setting the water flow rate through the bypass pipe 16 to 0 and the bypass ratio to 0. In this example, during bypass suppression control, the supply water amount W1 and the total water amount Wt (inlet water amount) are the same, and all the water that flows into the inlet pipe 6 from the outside flows to the heat transfer pipe 5A. After the controller 12 starts bypass suppression control in step S3, it determines in step S4 whether the elapsed time since ignition has reached the threshold T1. If it determines that the elapsed time since ignition has not reached the threshold T1, it returns to step S3 and continues bypass suppression control. On the other hand, if the controller 12 determines in step S4 that the elapsed time since ignition has reached the threshold T1, it proceeds to step S5 and performs bypass increase control. In other words, the controller 12 continues bypass suppression control for at least the period from the time of ignition until time T1, and when time T1 has elapsed from the time of ignition, it terminates the bypass suppression control and starts bypass increase control.

[0039] As described above, the controller 12 controls the bypass valve 19 to lower the bypass rate B to a lower level than the bypass rate B during the initial period for at least a portion of the period (preferably the entire period) from the start of combustion of the gas burner 4A in step S2 until the start of the initial period (when time T1 has elapsed from the ignition time). The period from the ignition of the gas burner 4A in step S2 until 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 after the pre-control period and is the period during which the bypass increase control described later is performed.

[0040] Furthermore, bypass suppression control may be performed even 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 (for example, 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 furthermore, the bypass rate may be maintained at 0 until Yes is determined in step S4.

[0041] When the controller 12 performs bypass increase control in step S5, for example, it opens the path with the bypass valve 19 and adjusts the opening degree of the bypass valve 19 so that the bypass ratio B becomes a predetermined fixed ratio. The bypass increase control is a control that increases the bypass ratio during a partial period or the entire period of the normal control described later. After starting the bypass increase control in step S5, the controller 12 determines whether or not the elapsed time after ignition has reached the threshold value T2 in step S6. If it is determined that the elapsed time after ignition has not reached the threshold value T2, the process returns to step S5 to continue the bypass increase control. On the other hand, when 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 to perform normal control. In this example, T1 < T2. That is, the controller 12 continues the bypass increase control from the time when the time T1 has elapsed since the ignition time until the time T2 has elapsed, and when the time T2 has elapsed since the ignition time, the bypass increase control is terminated and the normal control is started. The value of the fixed ratio is not particularly limited, and for example, it may be 0.3, and it may be slightly larger or smaller than this value.

[0042] In this way, the controller 12 controls the bypass valve 19 so that the bypass ratio B during the above initial period after the combustion of the gas burner 4A starts is higher than the bypass ratio B during the normal period after the above initial period has elapsed. The above initial period is the period during which the above bypass increase control is performed, and specifically, it is the period from the time when the time T1 has elapsed since ignition until the time T2 has elapsed. That is, the end point of the above 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 above normal period is the period during which the normal control described later is performed, and it is the period from the time when the time T2 has elapsed since ignition until the water flow is not detected in step S8.

[0043] In this embodiment, each of the multiple burner units 4 is provided with one or more gas burners, and the number of gas burners 4A differs among the multiple burner units 4. When the controller 12 performs bypass suppression control in step S3 and bypass increase control in step S5, it is desirable to perform bypass suppression control and bypass increase control so that only the burner unit 4 with the largest number of gas burners 4A among the multiple burner units 4 is burned, and the other burner units 4 are not burned. In this way, 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, the entire heat exchanger 5 can be heated more quickly.

[0044] When the controller 12 performs normal control in step S7, it sets the bypass rate 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, according to the following equation 1. In equation 1, B is the bypass rate, Q (kcal / h) is the amount of heating 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 the value detected by the water volume sensor 17, and the inlet water temperature T3 is the value detected by the thermistor 23. The target temperature Tt may be a temperature set by operating the remote controller 24, a predetermined fixed temperature, or a temperature set in the control. In any case, the target temperature Tt is a value set as the target temperature of the water flowing through the hot water outlet pipe 7 when normal control is performed. Thermal efficiency η is an index in which 1 is set when the efficiency is 100% and 0 is set when the efficiency is 0%. Thermal efficiency η may be a predetermined fixed value, or a thermal efficiency may be prepared for each combination of burning units among the multiple burner units 4, and calculations may be performed to use the thermal efficiency corresponding to the combustion combination in normal control. The heating amount Q may be calculated by a known method to determine how much heating is being performed based on the gas supply amount to each of the multiple burner units 4 and the unit currently burning in the multiple burner units 4. The gas supply amount 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, and the switching solenoid valves 11, 11...

[0045] B=1-(Q×η / (Wt×(Tt-T3))) (Math. 1)

[0046] Thus, after the initial period described above has elapsed, the controller 12 determines the bypass ratio B based on the temperature of the water flowing through the inlet pipe 6 (inlet water temperature T3), the total water volume Wt (inlet water volume), which is the amount of water flowing into the 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 and controlling to that bypass ratio B" at predetermined short intervals until the water flow state is no longer detected in step S8 (specifically, for example, until the amount of water detected by the water volume sensor 17 falls below a threshold).

[0047] 3. Examples of effects The water heater 1 controls the bypass valve 19 so that the bypass rate in the relatively early period (a predetermined initial period) after the combustion of the gas burner 4A has started is higher than the bypass rate after the initial period has elapsed. Therefore, in this water heater 1, the amount of water supplied to the heat exchanger 5 is relatively suppressed during the initial period, and the heating of the heat exchanger 5 is promoted. As a result, this water heater 1 can shorten the "period in which it is difficult to efficiently raise the temperature of the hot water passing through the heat exchanger 5," and can efficiently raise the temperature of the hot water passing through the heat exchanger 5 in a water heater 1 equipped with a bypass pipe 16.

[0048] By performing the control shown in step S3 of Figure 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 start of combustion of the gas burner 4A, 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 tubes 5A of the heat exchanger 5 immediately after the start of combustion, the foreign matter is easily flushed out by the relatively large amount of hot water supplied. Thus, 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 there is no blockage of foreign matter in the heat exchanger 5.

[0049] The water heater 1 allows for easy setting of the termination timing of the control that reduces the amount of water supplied to the heat exchanger 5 (control that relatively increases the bypass rate) based on time, without requiring complex calculations, and the termination timing is less likely to vary in each hot water supply operation that is repeated during daily use.

[0050] During the initial period, the water heater 1 maintains a fixed bypass ratio B, thereby stably and easily promoting the heating of the heat exchanger 5. After the initial period, the bypass ratio B is set to reflect the temperature of the water flowing through the inlet pipe 6 (inlet temperature T3), the total amount of water Wt flowing into the inlet pipe 6 from the outside, and the target temperature Tt, allowing for hot water temperature control according to the situation.

[0051] The water heater 1 can heat the entire heat exchanger 5 more quickly during the initial period described above, and can further shorten the period during which it is difficult to efficiently raise the temperature of the hot water passing through the heat exchanger 5.

[0052] <Other Embodiments> The present invention is not limited to the embodiments described above and in the drawings. For example, any combination of the features of the embodiments described above or below is possible as long as it does not contradict each other. Furthermore, any feature of the embodiments described above or below may be omitted unless explicitly stated as essential. In addition, the embodiments described above may be modified as follows.

[0053] The embodiments described above are merely examples and can be modified as appropriate. For example, the water heater 1 may be configured to supply hot water to the bathtub via a path branching off from the hot water outlet pipe.

[0054] In the embodiments described above, bypass suppression control was performed to set the bypass ratio to 0. However, bypass suppression control only requires that the bypass ratio be smaller than that in the case of bypass increase control, and may be a value slightly greater than 0, for example.

[0055] In the above-described embodiments, the bypass ratio is set to a fixed ratio in the bypass increase control, but the bypass ratio may be slightly changed. For example, in the bypass increase control, the bypass ratio may be gradually increased or decreased within a high bypass ratio range. Alternatively, the bypass ratio may be set to a first bypass ratio from the ignition time to time T1 to time Ta, and a second bypass ratio from time Ta to time T2. In this case, T1 < Ta < T2. Of course, other modification methods may also be used.

[0056] The normal control of the above-described embodiments is merely an example. For example, the bypass ratio may be calculated using another arithmetic expression for setting the bypass ratio based on the total water amount Wt, the target temperature Tt, and the inlet water temperature T3. As the normal control, for example, the normal control may be performed so as to determine the bypass ratio by the method disclosed in Japanese Patent Application Laid-Open No. 2013-245895. Alternatively, during normal control, combustion stage switching control as disclosed in Japanese Patent Application Laid-Open Nos. 2016-173212, 2018-200123, and 2018-200123 may be performed. In any case, it is sufficient that the bypass ratio during the bypass increase control is larger than the bypass ratio during a partial period of the normal control. Desirably, the bypass ratio during the bypass increase control is larger than the bypass ratio during the entire period of the normal control.

[0057] It should be considered that all aspects of the embodiments disclosed this time are illustrative and not restrictive. The scope of the present invention is not limited to the embodiments disclosed this time, and it is intended that all modifications within the scope indicated by the claims or within the scope equivalent to the claims are included.

Explanation of Reference Numerals

[0058] [ 1: Water heater <[ 4A: Gas burner 5: Heat exchanger [[ID=?1]]5A: Heat transfer tube 6: Inlet water pipe 7: Outlet water pipe 12: Controller (control device) 16: Bypass pipe 19: Bypass valve

Claims

1. A gas burner that burns gas and supplies exhaust gas produced by the combustion of the gas, A heat exchanger comprising heat transfer tubes heated by the exhaust supplied from the gas burner, An inlet for introducing water and an inlet pipe provided between the heat transfer tube, which supplies water to the heat transfer tube, A hot water outlet pipe connected to the downstream side of the heat transfer tube and carrying hot water supplied from the heat transfer tube, A bypass pipe that forms a bypass path for water branching from the inlet pipe and is connected to the outlet pipe, and which can allow water to flow to the outlet pipe via the bypass path, A bypass valve that adjusts the amount of water flowing from the inlet pipe to the outlet pipe via the bypass pipe, A control device for controlling the bypass valve, It has, When the sum of the aforementioned water flow rate and the amount of supply water supplied from the inlet pipe to the heat exchanger side rather than the bypass pipe is defined as the total water flow rate, and the ratio of the aforementioned water flow rate to the total water flow rate is defined as the bypass rate, the bypass rate is adjusted by the adjustment of the water flow rate by the bypass valve. The control device performs bypass increase control to set the bypass ratio to a predetermined value or higher during a predetermined initial period after the combustion of the gas burner has started, normal control to adjust the bypass ratio based on the target temperature after the initial period has elapsed, and bypass suppression control to lower the bypass ratio to a lower level than the bypass ratio during the initial period for at least a portion of the period from the start of combustion of the gas burner to the start of the initial period. Water heater.

2. The end of the initial period is the time when a predetermined period of time has elapsed since the ignition of the gas burner. The water heater according to claim 1.

3. The control device performs the bypass increase control 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 to adjust the bypass ratio based on the temperature of the water flowing through the inlet pipe, the amount of water flowing into the inlet pipe from outside the water heater, and the target temperature. The water heater according to claim 1.

4. A plurality of burner units comprising one or more of the gas burners, The control device performs control to select the burner unit to be burned, and during the initial period, burns the burner unit with the largest number of gas burners among the multiple burner units. The water heater according to claim 1.

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