water heater

Abstract

To provide a technique that can easily suppress overshooting of a hot water supply temperature even when a combustion stage is switched to a higher level.SOLUTION: In a water heater 1, when a gas burner unit 12 is burning at a lower stage and a required input exceeds an upper limit value of a range of the lower stage during combustion, a control unit 61 performs a temporary operation of adjusting an adjustment unit so as to change the required input to a modified value lower than an intermediate value of the required input at the lower stage and supply a supply amount of gas corresponding to the modified value to the gas burner unit 12, and then performs a post-switching operation of switching a combustion stage to a stage higher than the lower stage and adjusting the adjustment unit so as to supply the supply amount of gas corresponding to the required input to the gas burner unit 12.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a water heater provided with a plurality of combustion stages. This water heater includes a burner, a heat exchanger, a water flow rate control means for controlling the water flow rate of the heat exchanger, and a temperature detection means for detecting the temperature of hot water in a hot water outlet pipe. Furthermore, this water heater includes an operation control means that performs outlet hot water temperature control to make the detected temperature obtained from the temperature detection means match a set temperature.

Prior Art Literature

Patent Literature

[0003]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] In this type of water heater, a requested input, which is a value indicating the combustion output of a gas burner unit, is calculated based on a preset set temperature, the water temperature detected by a temperature detection unit, or the like. Control is performed to burn the gas burner unit at a stage corresponding to the requested input and supply gas of a supply amount corresponding to the requested input to the gas burner unit, thereby facilitating appropriate combustion at a stage suitable for the situation. However, in this type of water heater, when the requested input rises sharply and it becomes necessary to increase the number of combustion stages, if only the number of stages is increased without changing the requested input, overshooting in which the outlet hot water temperature becomes excessively higher than the set temperature is likely to occur.

[0005] One object of the present disclosure is to provide a technique that easily suppresses overshooting of the outlet hot water temperature even when the combustion stage is switched to a higher stage.

Means for Solving the Problem

[0006] One of the disclosed items is a water heater, A gas burner unit has a gas burner for burning gas, and the combustion stage can be switched between multiple stages. A gas supply pipe that forms a path for supplying the gas to the gas burner section and is capable of supplying the gas to multiple regions of the gas burner section, An adjustment unit provided in the gas supply pipe, which switches the combustion stage by selecting the gas supply destination from among a plurality of regions of the gas burner section and adjusts the amount of gas supplied to the gas burner section, A heat exchanger comprising heat transfer tubes heated by exhaust gas generated when the gas burns in the gas burner section, An inlet for bringing in water from the outside, An inlet pipe is provided between the water inlet and the heat transfer tube, forming a path for supplying water to the heat transfer tube, A hot water outlet pipe is connected to the downstream side of the heat transfer tube and forms a path for the hot water supplied from the heat transfer tube, A temperature detection unit for detecting the temperature of the water flowing through the inlet pipe or the outlet pipe, A control unit calculates a requested input, which is a value indicating the combustion output at the gas burner section, based on a preset temperature and the temperature detected by the temperature detection unit, and controls the adjustment unit to ignite the gas burner section at a stage corresponding to the requested input and to supply the gas to the gas burner section in a supply amount corresponding to the requested input. A water heater equipped with, The range of the required input is defined in correspondence to the lower stages of the multiple combustion stages, excluding the highest stage. If the requested input exceeds the upper limit of the range for the lower stage during combustion while the gas burner is burning in the lower stage, the control unit performs a temporary operation to change the requested input to a modified value lower than the midpoint of the requested input in the lower stage and adjust the adjustment unit to supply the gas to the gas burner in an amount corresponding to the modified value. After that, the control unit performs a post-switching operation to switch the combustion stage to a stage higher than the lower stage and adjust the adjustment unit to supply the gas to the gas burner in an amount corresponding to the requested input. [Effects of the Invention]

[0007] The technology disclosed herein makes it easier to suppress overshoot in the hot water temperature even when the combustion stage changes to a higher level. [Brief explanation of the drawing]

[0008] [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. [Figure 3] Figure 3 is a graph showing the relationship between the gas supply amount (input request amount) and the target rotational speed at each combustion stage in the water heater according to the first embodiment. [Modes for carrying out the invention]

[0009] Embodiments of the present disclosure are listed and illustrated below. The features illustrated below may be combined in any non-consistent way.

[0010] [1] A gas burner section having a gas burner for burning gas, with multiple stages of combustion switching, A gas supply pipe that forms a path for supplying the gas to the gas burner section and is capable of supplying the gas to multiple regions of the gas burner section, An adjustment unit provided in the gas supply pipe, which switches the combustion stage by selecting the gas supply destination from among a plurality of regions of the gas burner section and adjusts the amount of gas supplied to the gas burner section, A heat exchanger comprising heat transfer tubes heated by exhaust gas generated when the gas burns in the gas burner section, An inlet for bringing in water from the outside, An inlet pipe is provided between the water inlet and the heat transfer tube, forming a path for supplying water to the heat transfer tube, A hot water outlet pipe is connected to the downstream side of the heat transfer tube and forms a path for the hot water supplied from the heat transfer tube, A temperature detection unit for detecting the temperature of the water flowing through the inlet pipe or the outlet pipe, A control unit calculates a requested input, which is a value indicating the combustion output at the gas burner section, based on a preset temperature and the temperature detected by the temperature detection unit, and controls the adjustment unit to ignite the gas burner section at a stage corresponding to the requested input and to supply the gas to the gas burner section in a supply amount corresponding to the requested input. A water heater equipped with, The range of the required input is defined in correspondence to the lower stages of the multiple combustion stages, excluding the highest stage. If the requested input exceeds the upper limit of the range for the lower stage while the gas burner is burning in the lower stage, the control unit performs a temporary operation to adjust the adjustment unit to change the requested input to a value lower than the midpoint of the requested input in the lower stage and to supply the gas burner with a supply amount corresponding to the changed value. Then, it performs a post-switching operation to switch the combustion stage to a stage higher than the lower stage and adjust the adjustment unit to supply the gas burner with a supply amount corresponding to the requested input. Water heater.

[0011] In the water heater of [1] above, when switching the gas burner portion from a lower combustion stage to a higher stage, a temporary operation is performed to temporarily perform combustion at a relatively low output in the lower combustion stage, and then the post-switching operation can be performed after switching to the higher stage. With this configuration, when switching from the lower stage before switching to the higher stage after switching, it is easy to suppress overshoot of the outlet hot water temperature caused by the fact that the heated water is heated even in the higher stage after switching before passing through the heat transfer tube before the switching is completed.

[0012] [2] The changed value is a lower limit value of the range of the required input associated with the lower stage The water heater according to [1].

[0013] In the water heater of [2] above, when switching from the lower stage before switching to the higher stage after switching, it becomes easier to further suppress overshoot of the outlet hot water temperature caused by the fact that the heated water is heated even in the higher stage after switching before passing through the heat transfer tube before the switching is completed.

[0014] [3] The control unit adjusts the adjustment unit to supply the gas in a supply amount corresponding to the changed value to the gas burner unit, performs the temporary operation so as to wait for a certain period of time, and then performs the post-switching operation The water heater according to [1] or [2].

[0015] In the water heater of [3] above, when switching from the lower stage before switching to the higher stage after switching, the post-switching operation can be performed after the temporary operation is performed to wait for a certain period of time with the output suppressed. Therefore, it can be reliably suppressed that a large amount of water heated during the normal operation before switching remains in the heat transfer tube when the post-switching operation is started, and it becomes easier to further suppress overshoot of the outlet hot water temperature.

[0016] <First Embodiment> The following description relates to the first embodiment. 1. Basic Configuration of Water Heater 1 The water heater 1 shown in Figure 1 is configured to supply hot water to hot water outlets such as hot water taps 2. The water heater 1 has a combustion chamber 11, and inside the combustion chamber 11 are a gas burner section 12 equipped with burner groups 12A, 12B, and 12C, a primary heat exchanger 13, a secondary heat exchanger 14, electrodes 15, an igniter 16, and a flame rod 17.

[0017] The primary heat exchanger 13 is a heat exchanger that mainly recovers sensible heat from the high-temperature exhaust generated by combustion in the burner groups 12A, 12B, and 12C. The primary heat exchanger 13 is equipped with heat transfer tubes 13A, into which water supplied from the inlet pipe 41 via the secondary heat exchanger 14 flows, and the water that has flowed through the heat transfer tubes 13A flows into the outlet pipe 43. The secondary heat exchanger 14 is a heat exchanger that mainly recovers latent heat from the exhaust whose temperature has decreased due to heat exchange in the primary heat exchanger 13. The drain pipe 18 is a pipe for discharging the drain generated in the secondary heat exchanger 14, and a neutralizer 19 is provided at the downstream end of the drain pipe 18.

[0018] The water heater 1 has a fan motor 20 and a fan 21, and the fan motor 20 rotates the fan 21 to supply air into the combustion chamber 11. An exhaust top 22 is provided at the top of the combustion chamber 11, and the structure is such that exhaust can be released to the outside of the combustion chamber 11 through the exhaust top 22. The combustion chamber 11 is equipped with an overheating prevention device 23 that forcibly stops the operation of the water heater 1 by melting it when the surrounding temperature becomes abnormally high.

[0019] The water heater 1 is equipped with a gas supply pipe 31 that serves as a gas supply route to burner groups 12A, 12B, and 12C. The gas supply pipe 31 consists of a main pipe 32 whose upstream end is connected to a gas supply source (for example, an internal city gas pipe or propane gas piping), and branch pipes 33A, 33B, and 33C that branch off from the main pipe 32. Nozzles 34A, 34B, and 34C are provided at the downstream ends of the branch pipes 33A, 33B, and 33C, and are configured to supply gas to the burner groups 12A, 12B, and 12C via each nozzle 34A, 34B, and 34C. The main pipe 32 of the gas supply pipe 31 is equipped with a main solenoid valve 35 and a gas proportional control valve 36, and the branch pipes 33A, 33B, and 33C are equipped with switching solenoid valves 37A, 37B, and 37C.

[0020] The water heater 1 includes an inlet pipe 41 that serves as the water inlet to the secondary heat exchanger 14, a hot water outlet pipe 43 that serves as the hot water outlet from the heat transfer tube 13A provided in the primary heat exchanger 13, and a bypass pipe 45 that branches off from the inlet pipe 41 midway through its flow path and connects to the hot water outlet pipe 43. The upstream end of the inlet pipe 41 is connected to a water supply source (for example, a water pipe), and along the flow path from the upstream end to the downstream end of the inlet pipe 41, in order from the upstream end, are a strainer 51 that filters the water flowing from upstream to downstream, a water flow sensor 52 that detects the amount of water flowing in the inlet pipe 41, a water flow control motor 53 that controls the amount of water flowing in the inlet pipe 41 to increase or decrease, and a thermistor 54 for detecting the temperature of the water flowing to the primary heat exchanger 13. A freeze prevention heater 55 is provided midway through the inlet path.

[0021] The outlet pipe 43 is connected at its downstream end to the hot water outlet (in this embodiment, to the location of the hot water tap 2). Along the flow path of the outlet pipe 43 from its upstream end to its downstream end, the following are provided in order from the upstream end: an inner cylinder outlet water temperature detection thermistor 56 for detecting the temperature of the hot water flowing out of the primary heat exchanger 13; an outlet water temperature detection thermistor 57 for detecting the temperature of the hot water downstream of the confluence point of the outlet pipe 43 and the bypass pipe 45; and a water drain valve with a pressure relief valve 58. The bypass pipe 45 is equipped with a bypass control motor 59 for controlling the amount of water flowing through the bypass pipe 45.

[0022] The water heater 1 is equipped with a control unit 61 and a remote controller 62 (hereinafter also referred to as the remote control 62). The control unit 61 has a built-in microcomputer equipped with a CPU, ROM, RAM, etc., and receives information from the various sensors mentioned above (flame rod 17, thermistor 54 for detecting inlet water temperature, thermistor 56 for detecting outlet water temperature, and thermistor 57 for detecting outlet water temperature, etc.), and controls the various solenoid valves mentioned above (main solenoid valve 35, gas proportional control valve 36, switching solenoid valves 37A, 37B, 37C, etc.), various motors (fan motor 20, water flow control motor 53, bypass control motor 59), igniter 16, etc.

[0023] The remote control 62 is equipped with a user interface that includes an input unit that accepts input operations from the user (for example, operations to input various information) and an output unit that displays information and outputs audio to the user. The information input from the input unit is transmitted to the control unit 61, and the output unit displays information and outputs audio based on the information transmitted from the control unit 61.

[0024] 2. Basic operation of water heater 1 In the water heater 1 configured as described above, when a user opens the hot water tap 2, the water flowing in from the water inlet proceeds to the primary heat exchanger 13 via the water flow sensor 52 and the secondary heat exchanger 14. At this time, the water flow sensor 52 outputs a signal with a frequency corresponding to the flow velocity, and when the control unit 61 detects that this signal has reached a specified frequency, the control unit 61 controls the fan motor 20 to rotate the fan 21. Based on the signal from the water flow sensor 52, the control unit 61 detects the amount of water flowing through the inlet pipe 41 (water flow rate).

[0025] After the fan 21 rotates and a pre-purge operation is performed, the igniter 16 activates and discharges from the electrode 15. Subsequently, the main solenoid valve 35 and the switching solenoid valves 37A to 37C open, the gas proportional control valve 36 enters a slow ignition operation, and the burner group 12A to 12C ignites. After ignition, the flame rod 17 detects the flame and, once combustion is confirmed, the slow ignition operation is terminated.

[0026] Once the slow ignition operation is complete, temperature control is initiated. If there is a difference between the water temperature detected by the thermistor 57 for detecting the water outlet temperature and the set temperature arbitrarily set by the user (for example, a set temperature registered in the control unit 61 after the user inputs information by operating the remote control 62), the control unit 61 determines this and controls the gas flow rate to be continuously changed by opening and closing the gas proportional control valve 36 and the switching solenoid valves 37A to 37C to maintain a constant water outlet temperature. At this time, the control unit 61 sends a signal to the fan motor 20 in response to the change in the gas flow rate by the gas proportional control valve 36, thereby maintaining a predetermined relationship between the gas flow rate and the air flow rate.

[0027] In the above-described hot water supply situation, when a user closes the hot water tap 2, the frequency signal from the water volume sensor 52 disappears, and the amount of water flowing through the inlet pipe 41 (water flow rate) falls below the threshold. Therefore, the control unit 61 closes the main solenoid valve 35 and the switching solenoid valves 37A to 37C to extinguish the fire and enters post-purge operation. After the post-purge operation timeout, the fan 21 stops.

[0028] During hot water supply, the control unit 61 calculates the combustion output (hereinafter also referred to as input) required to dispense hot water at the set temperature based on the inlet water temperature detected by the inlet water temperature detection thermistor 54, the set temperature which can be arbitrarily set by the user by operating the remote control 62, and the flow rate (amount of water flowing through the inlet pipe 41) detected by the water flow sensor 52. The control unit 61 then performs feedforward control (hereinafter referred to as FF control) corresponding to the required combustion output (input), setting the combustion stage corresponding to the required combustion output (input), as well as setting the rotation speed of the fan 21 and the opening degree of the gas proportional control valve 36.

[0029] The above-described combustion stages are switched according to the combination of which of the switching solenoid valves 37A to 37C are opened and which are closed, and in the case of the present embodiment, the combustion stages can be switched in four steps. The four combustion stages have different numerical ranges of combustible output (input) that can be handled at each stage, as shown in FIG. 2. The input for each combustion stage is determined according to the rotation speed of the fan 21 and the opening degree of the gas proportional control valve 36. In FIG. 2, the correspondence relationship between the input at each combustion stage and the rotation speed of the fan 21 is graphed.

[0030] In terms of the design of the water heater 1, for the i-th combustion stage (where i is an integer satisfying 1≤i<n, and n=4 in the present embodiment), the upper limit of input in the i-th combustion stage is set to be larger than the lower limit of combustion output in the (i+1)-th combustion stage and smaller than the upper limit of combustion output in the (i+1)-th combustion stage. Therefore, the numerical range of input that can be handled in the i-th combustion stage and the numerical range of input that can be handled in the (i+1)-th combustion stage are numerical ranges that partially overlap with each other.

[0031] In the water heater 1, a combustion stage corresponding to the required combustion output (input) is set by the above-mentioned FF control, and after the rotation speed of the fan 21 and the opening degree of the gas proportional control valve 36 are set, feedback control (hereinafter referred to as FB control) is further performed based on the temperature difference between the set temperature and the outlet hot water temperature. That is, based on the temperature difference between the set temperature and the outlet hot water temperature, the rotation speed of the fan 21 and the opening degree of the gas proportional control valve 36 are adjusted so as to reduce this temperature difference.

[0032] 3. Hot Water Supply Process The control unit 61 performs hot water supply control in a flow similar to that shown in Figure 2. After power is turned on, the control unit 61 executes the hot water supply control shown in Figure 2 and determines in step S11 whether the combustion start condition has been met. The combustion start condition may be, for example, "the amount of water detected by the water volume sensor 52 (for example, the amount of water per unit time) (hereinafter also simply referred to as "amount of water") is greater than or equal to a predetermined threshold," or it may be another condition. The control unit 61 remains in standby mode until the combustion start condition is met, and in standby mode, it repeatedly makes the "No" determination in S11.

[0033] If the control unit 61 determines in step S11 that the combustion start condition has been met (S11: Yes), it executes the ignition process in step S12 to ignite the gas burner unit 12. After the ignition process in step S12 is completed, the control unit 22A determines in step S13 whether or not the combustion end condition has been met. The combustion end condition may be, for example, "the amount of water detected by the water volume sensor 52 (for example, the amount of water per unit time) is less than a predetermined threshold," or it may be another condition (such as a predetermined operation being performed to instruct the water heater 1 to end combustion, or a predetermined stop condition being met as a condition for stopping combustion). If the control unit 61 determines in step S13 that the combustion end condition has not been met (S13: No), it calculates the gas supply amount (requested input) in step S14. The control unit 61 calculates the gas supply amount (requested input) using a known calculation method based on the amount of water (inlet water) detected by the water volume sensor 52, the set temperature set as the target temperature, and the temperature (outlet temperature) detected by the thermistor 57 at the time of execution of step S14 or immediately before execution. The method for calculating the gas supply amount (requested input) can be any calculation that brings the outlet temperature closer to the set temperature (for example, a known feedback calculation), and may be, for example, a method disclosed in Japanese Patent Application Publication No. 2010-117053, a method disclosed in Japanese Patent Application Publication No. 2018-200123, or any other known method.

[0034] In this way, in step S14, the control unit 61 calculates a gas supply amount (requested input), which is a value indicating the combustion output at the gas burner unit 12, based on a preset temperature and the temperature detected by the thermistor 57 (temperature detection unit). Furthermore, the control unit 61 also determines the target rotational speed based on the gas supply amount (requested input) calculated in the process of step S14.

[0035] In a typical example, the burner groups 12A, 12B, and 12C that make up the gas burner section 12 consist of multiple burners with different numbers from each other. Of the burner groups 12A, 12B, and 12C, burner group 12A has the most gas burners, burner group 12C has the fewest gas burners, and burner group 12B has fewer gas burners than burner group 12A but more than burner group 12C. In controlling the hot water temperature, the control unit 61 performs switching control, which switches the combustion stage of the gas burner unit 12 (hereinafter also referred to as the combustion stage or combustion phase) in four stages according to the required gas supply amount (requested input). This is done as follows: stage 1 is single combustion of only the burner group 12C, which has the fewest number of burners; stage 2 is single combustion of only the burner group 12B, which has the most number of burners; stage 3 is simultaneous combustion of burner groups 12B and 12C, which have the most number of burners; and stage 4 is simultaneous combustion of burner groups 12A and 12B, which have the most number of burners.

[0036] In a typical example, as shown in Figure 3, a correspondence between the gas supply amount (required input) and the target fan speed is defined for each combustion stage. In all of these correspondences for each combustion stage, the target speed is set to increase as the gas supply amount (required input) increases. For example, the upper limit of the required input for the first combustion stage (first upper limit) is greater than the lower limit of the required input for the second combustion stage (second lower limit), the upper limit of the required input for the second combustion stage (second upper limit) is greater than the lower limit of the required input for the third combustion stage (third lower limit), and the upper limit of the required input for the third combustion stage (third upper limit) is greater than the lower limit of the required input for the fourth combustion stage (fourth lower limit). The lower limit of the required input for the first combustion stage (first lower limit) is smaller than the lower limit of the required input for the second combustion stage (second lower limit), the lower limit of the required input for the second combustion stage (second lower limit) is smaller than the lower limit of the required input for the third combustion stage (third lower limit), and the lower limit of the required input for the third combustion stage (third lower limit) is smaller than the lower limit of the required input for the fourth combustion stage (fourth lower limit). In this way, the range of required input is defined in correspondence with the lower stages (stages 1-3) of the multiple combustion stages, excluding the maximum stage (stage 4), and a range of required input is also defined for the maximum stage (stage 4).

[0037] If the gas supply amount calculated in step S14 is within the range of the gas supply amount for the combustion stage at that time, the control unit 61 proceeds to step S16 and performs normal combustion operation. When the control unit 61 proceeds to step S16, it does not switch the combustion stage, but controls the gas proportional control valve (adjustment unit) to supply the amount of gas specified by the gas supply amount (requested input) calculated in step S14. In this case, the target rotational speed of the fan 21 is also determined based on the correspondence between the requested input and the target rotational speed, which is determined in relation to the current combustion stage. For example, if the combustion stage at step S14 is the second stage, and the gas supply amount calculated in step S14 is greater than or equal to the lower limit (second lower limit) and less than or equal to the upper limit (second upper limit) of the range of gas supply amounts for the second stage, the combustion stage is not switched from the second stage. Instead, the target rotational speed is determined based on the correspondence between the gas supply amount and the target rotational speed determined in accordance with the combustion stage (second stage) at step S14 (information such as the calculation formula showing the relationship indicated by symbol L2 in Figure 3), and the gas supply amount calculated in step S14.

[0038] In this embodiment, the gas proportional control valve 36 and the switching solenoid valves 37A, 37B, and 37C correspond to an example of the adjustment unit. The control unit 61 controls the adjustment unit to ignite the gas burner unit 12 at a stage corresponding to the gas supply amount (requested input) calculated in step S14, and to supply the gas amount corresponding to this requested input to the gas burner unit 12.

[0039] If the gas supply amount (requested input) calculated in step S14 is outside the range of the gas supply amount for the combustion stage at the time of step S14, the control unit 61 proceeds to step S17 and performs a switching combustion operation. In the switching combustion operation of step S17, the control unit 61 switches the combustion stage (number of stages) from the combustion stage at the time of step S14 to the combustion stage corresponding to the gas supply amount (requested input) calculated in step S14, and performs combustion with the above gas supply amount (requested input) at the new number of stages after the switch.

[0040] When the gas burner unit 12 is burning in a lower stage (stages 1 to 3), if the requested input calculated in step S14 exceeds the upper limit of the range of that lower stage during combustion, the control unit 61 performs a temporary operation to adjust the adjustment unit in step S17. In this operation, instead of using the requested input calculated in the most recent step S14, the control unit 61 uses a modified value lower than the midpoint of the requested input in that lower stage (specifically, the lower limit of the range of the requested input in that lower stage) and supplies the gas supply amount corresponding to the modified value to the gas burner unit 12. During this temporary operation, the control unit 61 maintains the combustion stage (lower stage) at the time of the most recent step S14 and temporarily supplies the gas supply amount of the modified value to the gas burner unit 12 for a certain period of time. After performing this temporary operation, the control unit 61 switches the combustion stage to a higher stage than the lower stage (the combustion stage in which the temporary operation was performed) and performs a post-switching operation by adjusting the adjustment unit to supply an amount of gas to the gas burner unit 12 that corresponds to the amount of gas supply (requested input) calculated in the most recent step S14.

[0041] For example, if, at the start of step S14, the gas burner unit 12 is burning at the third stage, and the requested input calculated in step S14 exceeds the upper limit of the range of requested input for the third stage (range L3 in Figure 3) and falls within the range of requested input for the fourth stage, then when performing the switching combustion operation in step S17, the control unit performs a temporary operation to adjust the adjustment unit to change the requested input to a value lower than the midpoint of the requested input for the third stage (specifically, the lower limit of the range of requested input for the third stage (third lower limit)) and supply a gas amount corresponding to that change to the gas burner unit 12. It is desirable to continue this temporary operation for a certain period of time. After performing this temporary operation for a certain period of time, the control unit 61 switches the combustion stage to the fourth stage, which is higher than the third stage, and performs a post-switching operation to adjust the adjustment unit to supply a gas amount corresponding to the requested input calculated in the most recent step S14 to the gas burner unit 12.

[0042] In the example described above, when a temporary operation is performed, a switching combustion operation is performed following the temporary operation. However, after the temporary operation and before the switching operation, an intermediate operation may be performed in which combustion occurs at the combustion stage of the temporary operation or at a combustion stage that is greater than the combustion stage of the temporary operation but smaller than the combustion stage of the switching operation, and then the system switches to the switching operation after the intermediate operation. This intermediate operation can be performed by adjusting the adjustment unit so that the gas supply amount to the gas burner unit 12 is an intermediate value (the value obtained by adding the lower limit and upper limit of the gas supply amount at that combustion stage and dividing by 2) at the combustion stage of the intermediate operation.

[0043] If the control unit 22A determines in step S13 that the combustion termination condition has been met, it proceeds to step S19, closing the main solenoid valve 35 and the switching solenoid valves 37A, 37B, and 37C, and stopping the combustion operation.

[0044] 4. Examples of effects When switching the gas burner section 12 from a lower combustion stage to a higher combustion stage, the water heater 1 can temporarily operate at a relatively lower output in the lower combustion stage before switching to the higher stage and performing the post-switch operation. This makes it easier to suppress the overshoot of the hot water temperature that occurs when switching from the lower stage before the switch to the higher stage after the switch, because the hot water heated before the switch is complete is heated again in the higher stage after the switch before it has completely passed through the heat transfer tubes.

[0045] In water heater 1, since the changed value is the lower limit of the range of required inputs associated with the lower-level stage described above, it becomes easier to suppress overshoot in the hot water temperature.

[0046] When switching from a lower setting before switching to a higher setting after switching, the water heater 1 can temporarily operate to wait for a certain period of time with reduced output before starting the post-switch operation. This ensures that a large amount of water heated during the normal operation before switching remains in the heat transfer tubes when the post-switch operation starts, making it easier to suppress overshoot in the hot water temperature.

[0047] <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.

[0048] In the above embodiment, the changed value was the lower limit of the range of required inputs associated with the lower stage immediately before the change. However, the changed value only needs to be lower than the midpoint of the range of required inputs associated with the lower stage immediately before the change (the value obtained by adding the upper and lower limits of the range of required inputs associated with the lower stage and dividing by 2). For example, the changed value may be smaller than the midpoint and slightly larger than the lower limit.

[0049] It should be noted that the embodiments disclosed herein are illustrative and not restrictive in all respects. The scope of the present invention is not limited to the embodiments disclosed herein, and is intended to include all modifications within the scope set forth in the claims or equivalents thereof. [Explanation of Symbols]

[0050] 1: Water heater 12: Gas burner section 12A: Burner 12B: Burner 12C: Burner 13:Primary heat exchanger (heat exchanger) 13A: Heat transfer tube 31: Gas supply pipe 36: Gas proportional control valve (adjustment unit) 37A: Switching Solenoid Valve (Adjustment Unit) 37B: Switching Solenoid Valve (Adjustment Unit) 37C: Switching Solenoid Valve (Adjustment Unit) 41: Inlet pipe 43: Hot water outlet pipe 54: Thermistor for detecting inlet water temperature (temperature detection unit) 56: Thermistor for detecting the water temperature at the inner cylinder outlet (temperature detection unit) 57: Thermistor for detecting hot water outlet temperature (temperature detection unit)

Claims

[Claim 1] A gas burner unit has a gas burner for burning gas, and the combustion stage can be switched between multiple stages. A gas supply pipe that forms a path for supplying the gas to the gas burner section and is capable of supplying the gas to multiple regions of the gas burner section, An adjustment unit provided in the gas supply pipe, which switches the combustion stage by selecting the gas supply destination from among a plurality of regions of the gas burner section and adjusts the amount of gas supplied to the gas burner section, A heat exchanger comprising heat transfer tubes heated by exhaust gas generated when the gas burns in the gas burner section, An inlet pipe is provided between the water inlet for introducing water from the outside and the heat transfer tube, forming a path for supplying water to the heat transfer tube, A hot water outlet pipe is connected to the downstream side of the heat transfer tube and forms a path for the hot water supplied from the heat transfer tube, A temperature detection unit for detecting the temperature of the water flowing through the inlet pipe or the outlet pipe, A control unit calculates a requested input, which is a value indicating the combustion output at the gas burner section, based on a preset temperature and the temperature detected by the temperature detection unit, and controls the adjustment unit to ignite the gas burner section at a stage corresponding to the requested input and to supply the gas to the gas burner section in a supply amount corresponding to the requested input. A water heater equipped with, The range of the required input is defined in correspondence to the lower stages of the multiple combustion stages, excluding the highest stage. If the requested input exceeds the upper limit of the range for the lower stage while the gas burner is burning in the lower stage, the control unit performs a temporary operation to adjust the adjustment unit to change the requested input to a value lower than the midpoint of the requested input in the lower stage, supply the gas to the gas burner in an amount corresponding to the changed value, and wait for a certain period of time. After that, the control unit performs a post-switching operation to switch the combustion stage to a stage higher than the lower stage and adjust the adjustment unit to supply the gas to the gas burner in an amount corresponding to the requested input. The aforementioned change value is the lower limit of the range of the requested input associated with the lower stage. After the temporary operation and before the post-switching operation, an intermediate operation is performed in which the gas is supplied in an intermediate amount for the combustion stage of the temporary operation or a combustion stage that is greater than the combustion stage of the temporary operation but smaller than the combustion stage of the post-switching operation, and then the system switches to the post-switching operation after the intermediate operation. Water heater.

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