JP2024092319A - Water heater - Google Patents

Abstract

To provide a water heater which makes it easier to quickly bring the outlet temperature of hot water flowing into a tapping pipe from a heat exchanger closer to a target temperature in the heating initial stage, and can easily stabilize the tapping temperature in a period after the heating initial stage.SOLUTION: In a water heater 1, a control device 12 calculates an offset bypass rate Bof by multiplying a value which is obtained by subtracting an outlet temperature Tb detected by a second thermistor (outlet temperature detection part) from a preset target temperature by a coefficient G, adjusts a bypass valve 19 so as to increase a bypass rate B as the offset bypass rate Bof is higher, and performs adjustment control to bring a tapping temperature Tr closer to a set temperature Tt. In a heating initial stage after the start of combustion of a gas burner 4A, the control device 12 performs first adjustment control for calculating the offset bypass rate by using a first coefficient G1, and after the heating initial stage, performs second adjustment control using a second coefficient G2 as the coefficient. The control device 12 determines the coefficient G by using a decision method for determining the second coefficient G2 to be lower than the first coefficient G1 constantly or when a prescribed condition is established.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 adjust the degree of heating of the heat exchanger and the degree of heating of the hot and cold water flowing through the heat exchanger by adjusting the ratio (bypass ratio) of the "amount of water flowing through the bypass pipe" to the "total amount of water, which is the sum of the amount of water flowing through the bypass pipe and the amount of water flowing through the heat exchanger." For example, the higher the bypass ratio, the easier the heat exchanger will heat up, and the smaller the bypass ratio, the more difficult it will be to heat up the heat exchanger.

In this type of water heater, if the rate at which the bypass rate increases or decreases is increased, the rate at which the hot water passing through the heat exchanger is heated can be significantly changed, but there is a problem in that overshooting or undershooting the target temperature is likely to become significant. On the other hand, if the rate at which the bypass rate increases or decreases is reduced, overshooting or undershooting the target temperature is likely to be suppressed, but it may take longer for the hot water temperature to approach the target temperature.

One of the objectives of this disclosure is to provide a technology that makes it easier to bring the outlet temperature of hot water flowing from the heat exchanger into the hot water outlet pipe closer to the target temperature more quickly during the initial heating period, and makes it easier to stabilize the outlet temperature during the period after the initial heating period.

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;
An outlet temperature detection unit that detects an outlet temperature of hot water flowing from the heat exchanger to the hot water outlet pipe at a first position;
a hot water outlet temperature detection unit that detects a hot water outlet temperature at a second position downstream of the first position in the hot water outlet pipe;
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 includes:
calculating an offset bypass ratio by multiplying a value obtained by subtracting the outlet temperature detected by the outlet temperature detection unit from a predetermined target temperature by a coefficient;
The bypass valve is adjusted so that the bypass ratio is increased as the offset bypass ratio is increased, and adjustment control is performed so that the outlet hot water temperature approaches a set temperature.
At an initial stage of heating after the start of combustion of the gas burner, a first adjustment control is performed to calculate the offset bypass ratio by using a first coefficient as the coefficient;
After the initial heating period, a second adjustment control is performed to calculate the offset bypass ratio using a second coefficient as the coefficient, and the coefficient is determined by a determination method that always determines the second coefficient to be lower than the first coefficient, or when a specified condition is satisfied.

The technology disclosed herein makes it easier to more quickly bring the outlet temperature of hot water flowing from the heat exchanger into the hot water outlet pipe closer to the target temperature during the initial heating period, and makes it easier to stabilize the outlet temperature during the period after the initial heating period.

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. FIG. 3 is a flow chart illustrating a normal control flow in the hot water discharge control illustrated in FIG. FIG. 4 is a flowchart illustrating a flow of a differential FB bypass rate calculation in the normal control illustrated in FIG. FIG. 5 is a table showing the correspondence relationship between the water volume and the coefficient (first coefficient) when the elapsed time tp is equal to or shorter than the reference time. FIG. 6 is a table showing the correspondence between the water volume and the coefficient when the elapsed time tp exceeds the reference time. FIG. 7 is a graph showing the correspondence relationship between the amount of water and the coefficient. FIG. 8 is a graph showing the transition of each value over time in Reference Example 1 to which the first embodiment of the invention is not applied. FIG. 9 is a graph showing the transition of each value over time in Reference Example 2 to which the invention of the first embodiment is not applied. FIG. 10 is a graph showing the transition of each value over time in an example to which the first embodiment of the invention is applied.

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;
An outlet temperature detection unit that detects an outlet temperature of hot water flowing from the heat exchanger to the hot water outlet pipe at a first position;
a hot water outlet temperature detection unit that detects a hot water outlet temperature at a second position downstream of the first position in the hot water outlet pipe;
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 includes:
calculating an offset bypass ratio by multiplying a value obtained by subtracting the outlet temperature detected by the outlet temperature detection unit from a predetermined target temperature by a coefficient;
The bypass valve is adjusted so that the bypass ratio is increased as the offset bypass ratio is increased, and adjustment control is performed so that the outlet hot water temperature approaches a set temperature.
At an initial stage of heating after the start of combustion of the gas burner, a first adjustment control is performed to calculate the offset bypass ratio by using a first coefficient as the coefficient;
After the initial heating period, a second adjustment control is performed to calculate the offset bypass ratio using a second coefficient as the coefficient, and the coefficient is determined by a determination method that always determines the second coefficient to be lower than the first coefficient, or when a specified condition is satisfied.

The water heater of [1] above can set the offset bypass rate higher in the early heating stage to promote heating of the heat exchanger. Thus, the water heater can raise the temperature of the heat exchanger early in the early heating stage to suppress the generation of drainage. On the other hand, the water heater can set the offset bypass rate relatively low in the period after the early heating stage to gradually approach the target temperature. Thus, the water heater can suppress a sudden and large change in the outlet temperature near the target temperature after the outlet temperature has risen to a certain extent, and can easily suppress the hunting phenomenon in which the outlet temperature repeatedly rises and falls near the target temperature.

[2] The water heater according to [1], wherein the control device determines the coefficient using a determination method in which the second coefficient is set to be lower than the first coefficient when the set temperature is lower than a threshold temperature.

When the set temperature is relatively small, if a method is used in which the outlet temperature is changed suddenly after the heat exchanger temperature has risen to a certain level, the outlet temperature is more likely to rise above the target temperature. However, as in the water heater described in [2] above, if the outlet temperature is prevented from changing suddenly and significantly after the heat exchanger temperature has risen to a certain level, it becomes easier to prevent the outlet temperature from rising too far above the target temperature when the set temperature is relatively small.

[3] A water flow detection unit for detecting the amount of water passing through the device,
The control device, regardless of whether the first coefficient or the second coefficient is determined as the coefficient, increases the coefficient as the water flow rate detected by the water flow detection unit increases,
The water heater described in [1] or [2], wherein the determination method is such that, regardless of the value of the water flow detected by the water volume detection unit, the second coefficient determined based on the value is lower than the first coefficient determined based on the value.

In the water heater of [3] above, in the initial heating stage, heating is adjusted to match the water volume so that the greater the water volume, the greater the degree of heating of the heat exchanger is adjusted, and the offset bypass rate can be set to a larger value for any water volume to promote heating of the heat exchanger. On the other hand, this water heater also adjusts heating to match the water volume in the period after the initial heating stage so that the greater the water volume, the greater the degree of heating of the heat exchanger is adjusted, but when the second coefficient is used, the offset bypass rate can be set to a smaller value for any water volume, preventing the outlet temperature from changing rapidly and significantly around the target temperature.

First Embodiment
1. Overview of the water heater Fig. 1 illustrates a water heater 1 according to a first embodiment. The water heater 1 shown 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 in which a space for burning gas is configured. 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 plurality of 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 burner 4A functions to burn the gas and supply exhaust gas generated by the combustion of the gas.

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 control device 12. Reference numeral 13 denotes an igniter, reference numeral 14 denotes an ignition electrode, and reference numeral 15 denotes a flame rod. The control device 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 a water inlet that introduces water from a water pipe (not shown) provided 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 is a pipe that 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, and allows water to flow to the hot water outlet pipe 7 via the bypass path. The bypass pipe 16 is configured to, for example, allow water introduced from the water inlet pipe 6 to flow toward the hot water outlet pipe 7 when the bypass valve 19 is open while the hot water tap 20 is open.

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 at a location between the water inlet and the connection position, and detects the amount of water flowing through this location (i.e., the amount of water introduced into the water inlet pipe 6 from the outside). The control device 12 grasps the amount of water at the location 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 at a location between the water inlet and the connection position, and adjusts the amount of water flowing through this location. 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 control device 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 water flow rate regulator 18 to adjust the opening degree of the valve body, 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 (water flow rate) that flows 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 control device 12 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 degree 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 hot water outlet temperature. The hot water outlet temperature is represented as Tr.

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. The temperature detected by the second thermistor 22 is also referred to as the outlet temperature Tb.

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. In the following description, the inlet water temperature is represented as Ti. The temperatures detected by the first thermistor 21, the second thermistor 22, and the third thermistor 23 are provided to the control device 12.

The control device 12 is a control device capable of performing various types of control, 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 types of information, a communication device for communicating with each device, and other interfaces. The control device 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 types of information to the control device 12, and can obtain various types of information from the control device 12.

2. Overview of Water Flow Control Next, the water flow control will be described.
The control device 12 performs hot water discharge control in the flow shown in Fig. 2, and controls the bypass valve 19, etc. The control device 12 starts the control of Fig. 2 when a start condition is met. The start condition is, for example, that the supply of power to the control device 12 from a power supply device (not shown) has started, or that the power-on state is maintained after the control of Fig. 2 has ended. Other start conditions may also be used.

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

When the control device 12 advances the process to step S2, it performs ignition control. When the control device 12 performs ignition control in step S2, it 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 the control device 12 performs ignition control in step S2, for example, it ignites only one of the multiple burner units 4, and in step S2, it 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 control device 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 "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, to the "passing water amount", which is the amount of water flowing through the bypass pipe 16, when the total water amount Wt is 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. 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 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, and Wt = W1 + W2. The bypass rate B is determined by the formula B = W2/Wt.

When the control device 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. Therefore, 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 water inlet pipe 6 from the outside flows to the heat transfer pipe 5A. After starting the bypass suppression control in step S3, the control device 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 control device 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 control device 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 control device 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 to burn in step S2 until 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 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 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 control device 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 in the normal control described later. After starting the bypass increase control in step S5, the control device 12 determines whether the elapsed time after ignition has reached the threshold value T2 in step S6, 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 continues. On the other hand, if the control device 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. This normal control is repeated until the water flow is not detected (i.e., until the result of step S8 becomes Yes). The normal control will be described in detail later. In this example, T1<T2. In other words, the control device 12 continues the bypass increase control from the time T1 after the ignition point until the time T2 has passed, and when the time T2 has passed from the ignition point, the control device 12 ends the bypass increase control and starts normal control. The value of the fixed ratio is not particularly limited, and may be, for example, 0.3, or may be slightly larger or smaller than this value.

In this way, the control device 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, 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.

3. Details of Normal Control When performing normal control in step S7, the control device 12 performs mixing control, which will be described later, at predetermined time intervals (for example, every 0.25 seconds) and can adjust the bypass rate at predetermined time intervals.

Specifically, the control device 12 performs mixing control in the flow shown in FIG. 3, and continues the control of FIG. 3 while the normal control of step S7 continues (from the time when a Yes decision is made in step S6 until a Yes decision is made in step S8). When the control device 12 ends the normal control of step S7, that is, when a Yes decision is made in step S8, it ends the control of FIG. 3 and ends the control of FIG. 2.

When the control device 12 starts the control of FIG. 3 by determining Yes in step S6, it determines in step S11 whether a predetermined time (e.g., 0.25 seconds) has elapsed since the start of the control of FIG. 3 or the end of the previous step S16, and if it determines that the predetermined time has elapsed, it proceeds to step S12.

When the process proceeds to step S12, the control device 12 calculates the FF bypass rate in step S12. The control device 12 calculates this FF bypass rate, for example, by the following formula (1). The FF bypass rate is represented as Bff. The inner cavity target temperature may be, for example, a predetermined fixed value, or may be an updated value determined according to the set temperature, etc. The inner cavity target temperature is represented as Ta. The set temperature is a target temperature of hot water discharged from the tap, and is a set value that can be set by the user operating the remote controller 24. The set temperature 12 is stored in the control device 12, for example, so that it can be updated. The set temperature is represented as Tt. Ti is the inlet water temperature described above. Formula (1) is a formula for calculating the FF bypass rate Bff based on the inner cavity target temperature Ta, the set temperature Tt, and the inlet water temperature Ti.
Bff = (Ta - Tt) / (Ta - Ti) (1)

After calculating the FF bypass ratio Bff in step S12, the control device 12 advances the process to step S13, where it calculates an offset bypass ratio. The offset bypass ratio is represented as Bof. The control device 12 calculates this offset bypass ratio, for example, by the following formula (2). In formula (2), Tb is the above-mentioned outlet temperature Tb. In formula (2), the larger the value of G, the faster the rate of increase of the outlet temperature Tb until it reaches the inner cavity target temperature Ta. The method of setting the coefficient G will be described later.
Bof = G × (Ta - Tb) (2)

After calculating the offset bypass ratio Bof in step S13, the control device 12 advances the process to step S14, where it calculates the FB bypass ratio. This FB bypass ratio is a correction value of the bypass ratio based on the outlet hot water temperature Tr, and is calculated by the following formula (3). α is a constant. The FB bypass ratio is represented as Bfb. Formula (3) is a formula for calculating the FB bypass ratio Bfb based on the outlet hot water temperature Tr, the set temperature Tt, the inner cavity target temperature Ta, and the inlet water temperature Ti.
Bfb=(Tr-Tt)×α/(Ta-Ti) (3)

After calculating the FB bypass rate Bfb in step S14, the control device 12 advances the process to step S15, where it calculates the differential FB bypass rate. This differential FB bypass rate is determined by a calculation method described below according to the change (slope) of the inner body temperature. The differential FB bypass rate is represented as Bd.

After calculating the differential FB bypass rate Bd in step S15, the control device 12 adds the FF bypass rate Bff, the offset bypass rate Bof, the FB bypass rate Bfb, and the differential FB bypass rate Bd calculated in steps S12 to S15 to calculate the target bypass rate Bt. Hereinafter, the target bypass rate is represented as Bt. The target bypass rate Bt is determined by the formula Bt = Bff + Bof + Bfb + Bd.

When calculating the differential FB bypass rate Bd in step S15, the control device 12 performs the calculation according to the flow shown in FIG. 4, for example. When the control device 12 starts the processing of step S15, it first calculates the gradient of the inner body temperature in step S20 of FIG. 4. This gradient is obtained by calculating the difference between the detected inner body temperature and the previous inner body temperature stored in the previous control. The inner body temperature obtained in this way is stored in S11 as the previous inner body temperature to be used next time.

Next, in S22, it is determined whether the gradient of the inner body temperature obtained in S20 exceeds -0.1°C, i.e., whether there is no downward trend. If the gradient exceeds -0.1°C, it is determined that there is no downward trend, and in S23, the gradient of the inner body temperature is set to 0. On the other hand, if the gradient does not exceed -0.1°C, it is determined that there is a downward trend, and in S24, the current differential FB bypass rate is calculated by the following formula (4).
This time's differential FB bypass rate = inner body temperature gradient x 30 / (inner body target temperature - inlet water temperature) (4)

In the judgment in S25, the control device 12 judges whether or not the previous differential FB bypass rate calculated and stored last time is lower than the current differential FB bypass rate obtained in S14. If the previous differential FB bypass rate is not lower than the current differential FB bypass rate, in S27, the current differential FB bypass rate is set as the differential FB bypass rate Bd, and this is stored as the previous differential FB bypass rate to be used next time. On the other hand, if the previous differential FB bypass rate is lower than the current differential FB bypass rate, in S26, the differential FB bypass rate is corrected by the following formula (5). This is to obtain a smoothed differential FB bypass rate using the previous differential FB bypass rate and the current differential FB bypass rate.
Differential FB bypass rate Bd = (previous differential FB bypass rate × m + current differential FB bypass rate × n) / (m + n) (where m > n) (5)
The differential FB bypass ratio obtained in S24 or S26 in this manner is used to calculate the target bypass ratio in Fig. 2. The method of determining the differential FB bypass ratio Bd described above with reference to Fig. 4 is merely an example, and the above-mentioned method may be slightly modified, or the differential FB bypass ratio Bd may be calculated by another method.

4. Method of Setting the Coefficient G In the representative example shown in FIG. 1, the position where the second thermistor 22, which corresponds to an example of an outlet temperature detector, detects the temperature is the first position. The second thermistor 22 detects the temperature of the hot water flowing from the heat exchanger 5 into the hot water outlet pipe 7 as the outlet temperature at the first position. In the representative example, the position where the first thermistor 21, which corresponds to an example of an outlet temperature detector, detects the temperature is the second position. The first thermistor 21 detects the temperature of the hot water flowing through the hot water outlet pipe 7 at the second position downstream of the first position in the hot water outlet pipe 7 as the outlet temperature. In the representative example, the water volume Wt detected by the water volume sensor 17 corresponds to an example of the total water volume. The total water volume Wt is the sum of the water flow volume W2, which is the amount of water flowing through the bypass pipe 16, and the water supply volume W1, which is the amount of water supplied to the heat exchanger 5 side of the bypass pipe 16 in the water inlet pipe 6. The bypass ratio B is the ratio (W2/Wt) of the flow rate W2 to the total water volume Wt.

In the water heater 1, the control device 12 adjusts the bypass valve 19 to adjust the water flow rate W2, and thus adjusts the bypass ratio B. The control device 12 calculates the target bypass ratio Bt every short period of time, and adjusts the bypass ratio B to the target bypass ratio Bt by setting the opening degree of each bypass valve 19 to the opening degree that results in the new target bypass ratio Bt each time the target bypass ratio Bt is calculated (each time step S16 in FIG. 3 is executed).

When the control device 12 calculates the offset bypass ratio Bof in step S13, as described above, it calculates the offset bypass ratio Bof by the calculation formula Bof = G x (Ta - Tb) based on the inner cavity target temperature Ta and the outlet temperature Tb at the time of execution of step S13. That is, the control device 12 calculates the offset bypass ratio Bof by multiplying the value (Ta - Tb) obtained by subtracting the outlet temperature Tb detected by the second thermistor 22 (outlet temperature detection unit) from the predetermined target temperature (inner cavity target temperature Ta) by the coefficient G. Then, the control device 12 determines the coefficient G used in the calculation in step S13 based on the set temperature Tt at the time of execution of step S13, the total water volume Wt, and the elapsed time tp from the start of combustion at the start of execution of step S13, using the following method. The elapsed time tp is the elapsed time from the start of combustion of the gas burner 4A to the start of execution of step S13.

In a representative example, the time tp elapsed until the start of step S13 is equal to or less than a predetermined reference time, which is the initial heating period, and the time tp elapsed until the start of step S13 is equal to or less than the reference time, which is the period after the initial heating period. When executing the process of step S13, if the time tp elapsed until the start of the process is equal to or less than the reference time, the control device 12 uses the first coefficient G1 calculated by the first coefficient determination method as the coefficient G. If the time tp elapsed until the start of step S13 exceeds the reference time and the set temperature Tt at the start of step S13 is less than the threshold temperature Tth, the control device 12 uses the second coefficient G2 calculated by the second coefficient determination method as the coefficient G. Even if the time tp elapsed until the start of step S13 exceeds the reference time, if the set temperature Tt at the start of step S13 is equal to or greater than the threshold temperature Tth, the control device 12 uses the first coefficient G1 calculated by the first coefficient determination method as the coefficient G.

In a typical example, the first condition is satisfied when the elapsed time tp until the start of the processing of step S13 is less than the reference time, or when the elapsed time tp until the start of the processing of step S13 exceeds the reference time and the set temperature Tt at the start of the processing of step S13 is equal to or greater than the threshold temperature Tth. The second condition is satisfied when the elapsed time tp until the start of the processing of step S13 exceeds the reference time and the set temperature Tt at the start of the processing of step S13 is less than the threshold temperature Tth. FIG. 5 is a table showing the correspondence between the amount of water and the coefficient when the elapsed time tp is less than the reference time. The left table in FIG. 6 is a table showing the correspondence between the amount of water and the coefficient when the elapsed time tp exceeds the reference time and the set temperature Tt is less than the threshold temperature Tth. The right table in FIG. 6 is a table showing the correspondence between the amount of water and the coefficient when the elapsed time tp exceeds the reference time and the set temperature Tt is equal to or greater than the threshold temperature Tth.

As shown in Figures 5, 6 and 7, when the first condition is satisfied, the control device 12 determines the first coefficient G1 by the first coefficient determination method and uses this first coefficient G1 as the coefficient G. Specifically, when the first condition is satisfied and the total water volume Wt is less than X1, the first coefficient G1 is set to Ga1, and when the total water volume Wt is X3 or more, the first coefficient G1 is set to Ga3. When the first condition is satisfied and the total water volume Wt is X1 or more and less than X2, the first coefficient G1 is set to a value determined by a linear equation passing through two points (X1, Ga1) and (X2, Ga2). Specifically, when the water volume is X, the first coefficient G1 determined by G1-Ga1=((Ga2-Ga1)/(X2-X1))x(X-X1) is used as the coefficient G. When the first condition is satisfied and the total water volume Wt is equal to or greater than X2 and less than X3, the first coefficient G1 is a value calculated using a linear equation that passes through two points (X2, Ga2) and (X3, Ga3). Specifically, when the water volume is X, the first coefficient G1 calculated using G1-Ga2=((Ga3-Ga3)/(X3-X2))×(X-X2) is used as the coefficient G.

As shown in Figures 6 and 7, when the second condition is satisfied, the control device 12 determines the second coefficient G2 by the second coefficient determination method, and uses this second coefficient G2 as the coefficient G. Specifically, when the second condition is satisfied and the total water volume Wt is less than X1, the second coefficient G2 is set to Gb1, and when the total water volume Wt is X3 or more, the second coefficient G2 is set to Gb3. When the second condition is satisfied and the total water volume Wt is X1 or more and less than X2, the second coefficient G2 is set to a value determined by a linear equation passing through two points (X1, Gb1) and (X2, Gb2). Specifically, when the water volume is X, the second coefficient G2 determined by G2-Gb1=((Gb2-Gb1)/(X2-X1))x(X-X1) is used as the coefficient G. When the second condition is satisfied and the total water volume Wt is equal to or greater than X2 and less than X3, the second coefficient G2 is a value calculated using a linear equation that passes through two points (X2, Gb2) and (X3, Gb3). Specifically, when the water volume is X, the first coefficient G1 calculated using G2-Gb2=((Gb3-Gb3)/(X3-X2))×(X-X2) is used as the coefficient G.

In the above formula, Ga1<Ga2<Ga3. Also, Gb1<Gb2<Gb3. Furthermore, Ga1>Gb1, Ga2>Gb2, and Ga3>Gb3. Specifically, Ga1>Gb3. Ga1 is, for example, 0.025, Ga2 is, for example, 0.06, and Ga3 is, for example, 0.08. Gb1 is, for example, 0.005, Gb2 is, for example, 0.012, and Gb3 is, for example, 0.016. X1 is, for example, 2 (L/min), X2 is, for example, 10 (L/min), and X3 is, for example, 15 (L/min). The threshold temperature Tth is, for example, 125 degrees Fahrenheit.

In this way, the control device 12 determines the coefficient G by the above-mentioned method, adjusts the bypass valve 19 so that the bypass ratio B increases as the offset bypass ratio Bof increases, and performs adjustment control so that the tap temperature Tr approaches the set temperature Tt. Then, as described above, the control device 12 performs a first adjustment control to calculate the offset bypass ratio Bof using the first coefficient G1 calculated by the first coefficient determination method as the coefficient G during the initial heating period after the start of combustion of the gas burner 4A, and performs a second adjustment control to calculate the offset bypass ratio Bof using the second coefficient G2 calculated by the second coefficient determination method as the coefficient G during the period after the initial heating period. Then, when a predetermined condition is met, specifically, when the set temperature Tt is less than the threshold temperature, the coefficient G is determined by a determination method that determines the second coefficient G2 to be lower than the first coefficient G1.

3. Example of effect The water heater 1 can set the offset bypass ratio Bof larger in the initial heating stage to promote the heating of the heat exchanger 5. Therefore, the water heater 1 can raise the temperature of the heat exchanger 5 early in the initial heating stage to suppress the generation of drainage. On the other hand, the water heater 1 can set the offset bypass ratio Bof relatively low in the period after the initial heating stage to gradually approach the target temperature (inner cavity target temperature Ta). Therefore, the water heater 1 can suppress the outlet temperature Tb from changing suddenly and significantly around the target temperature Ta after the outlet temperature Tb has risen to a certain degree, and can easily suppress the hunting phenomenon in which the outlet temperature Tb repeatedly rises and falls around the target temperature Ta.

Figure 8 shows an example of an experimental result when hot water supply operation is performed using only the first coefficient determination method without using the second coefficient determination method, where the inlet water temperature is 25 degrees Celsius, the set temperature Tt is 100 degrees Fahrenheit, and the total water volume Wt is 3 (L/min). Figure 9 shows an example of an experimental result when hot water supply operation is performed using only the first coefficient determination method without using the second coefficient determination method, where the inlet water temperature is 25 degrees Celsius, the set temperature Tt is 100 degrees Fahrenheit, and the total water volume Wt is 10 (L/min). As in Figures 8 and 9, when the second coefficient determination method is not used, the inner cavity temperature (outlet temperature Tb) repeatedly rises and falls, making it difficult to stabilize the outlet hot water temperature. On the other hand, Figure 10 shows an example of the application of the present invention, where the inlet water temperature is 25 degrees Celsius, the set temperature Tt is 100 degrees Fahrenheit, and the total water volume Wt is 10 (L/min). As shown in FIG. 10, when the present invention is applied, the inner cavity temperature (outlet temperature Tb) tends to rise quickly, and the inner cavity temperature (outlet temperature Tb) and the tap water temperature Tr tend to stabilize after a certain amount of time.

In the water heater 1, the control device 12 determines the coefficient G by a determination method in which the second coefficient G2 is set lower than the first coefficient G1 when the set temperature Tt is less than the threshold temperature Tth. When the set temperature Tt is relatively small, if a method is used in which the outlet temperature Tb is changed suddenly after the temperature of the heat exchanger 5 has risen to a certain degree, the outlet temperature Tb is more likely to rise more significantly beyond the target temperature Ta. However, as in the water heater 1, if the outlet temperature Tb is prevented from changing suddenly and significantly after the temperature of the heat exchanger 5 has risen to a certain degree, it becomes easier to prevent the outlet temperature Tb from rising too much beyond the target temperature Ta when the set temperature Tt is relatively small.

In the initial heating stage, the water heater 1 performs heating according to the amount of water so that the greater the amount of water, the greater the degree of heating of the heat exchanger 5 is adjusted, and for any amount of water, the offset bypass rate Bof can be set to a larger value to promote heating of the heat exchanger 5. On the other hand, in the period after the initial heating stage, the water heater 1 also performs heating according to the amount of water so that the greater the amount of water, the greater the degree of heating of the heat exchanger 5 is adjusted, but when the second coefficient G2 is used, the offset bypass rate Bof can be set to a smaller value for any amount of water, and a sudden and large change in the outlet temperature Tb near the target temperature Ta can be suppressed.

<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, the target bypass rate Bt during normal control is calculated by the formula Bt = Bff + Bof + Bfb + Bd, but this is not limited to this example, and some of Bff, Bfb, and Bd may be omitted, some of the calculation methods for these may be changed, or correction values may be added.

In the embodiment described above, the bypass suppression control of S3 and the bypass increase control of S5 in FIG. 2 are performed, but either or both of these controls may be omitted. For example, the processing of step S7 may be performed after step S2 in FIG. 2, the control of step S7 may be performed if the answer to step S4 is Yes, and the controls of steps S3 and S4 in FIG. 2 may be omitted.

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: Hot water outlet pipe 12: Control device 16: Bypass pipe 19: Bypass valve 21: First thermistor (Hot water outlet temperature detection unit)
22: Second thermistor (outlet temperature detection section)

Claims (3)

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;
An outlet temperature detection unit that detects an outlet temperature of hot water flowing from the heat exchanger to the hot water outlet pipe at a first position;
a hot water outlet temperature detection unit that detects a hot water outlet temperature at a second position downstream of the first position in the hot water outlet pipe;
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 includes:
calculating an offset bypass ratio by multiplying a value obtained by subtracting the outlet temperature detected by the outlet temperature detection unit from a predetermined target temperature by a coefficient;
The bypass valve is adjusted so that the bypass ratio is increased as the offset bypass ratio is increased, and adjustment control is performed so that the outlet hot water temperature approaches a set temperature.
At an initial stage of heating after the start of combustion of the gas burner, a first adjustment control is performed to calculate the offset bypass ratio by using a first coefficient as the coefficient;
After the initial heating period, a second adjustment control is performed to calculate the offset bypass ratio using a second coefficient as the coefficient, and the coefficient is determined by a determination method that always determines the second coefficient to be lower than the first coefficient, or when a specified condition is satisfied. The water heater according to claim 1 , wherein the control device determines the coefficient by a determination method in which the second coefficient is set to be lower than the first coefficient when the set temperature is lower than a threshold temperature. A water flow detection unit detects the amount of water passing through the water flow passage.
The control device, regardless of whether the first coefficient or the second coefficient is determined as the coefficient, increases the coefficient as the water flow rate detected by the water flow detection unit increases,
The water heater of claim 1 or claim 2, wherein the determination method is such that, regardless of the value of the water flow detected by the water volume detection unit, the second coefficient determined based on the value is lower than the first coefficient determined based on the value.

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