JP7538525B2 - Hot water supply equipment - Google Patents

Description

This disclosure relates to a water heater.

Conventionally, water heating devices that control the combustion amount range of a burner group are known. For example, the water heating device of Patent Document 1 includes a burner group, a combustion amount adjustment means, and a combustion amount range switching means. The combustion amount adjustment means adjusts the amount of fuel supplied to the burner group. The combustion amount range switching means switches the number of burners to which fuel is supplied.

JP 2017-198416 A

In the water heating device of Patent Document 1, when the time elapsed since the start of combustion of the burner group exceeds a predetermined time, even if the required heating amount becomes higher than the upper switchover combustion amount, the device operates to maintain operation in the current combustion range without switching the combustion range of the burner group until this state continues for a predetermined time. The water heating device of Patent Document 1 attempts to suppress the occurrence of hunting by such operation, but there is a risk that hunting cannot be sufficiently suppressed. Also, not limited to this example, in water heating devices that perform some kind of limiting operation during combustion control, there is a risk that stable hot water heating operation cannot be maintained if the limiting operation is not performed appropriately.

Therefore, in order to solve at least one of the above problems, the present disclosure provides a water heating device that can perform a limiting operation that makes it easier to maintain stable hot water heating operation.

The hot water supply device according to the present disclosure includes:
A hot water supply device having a gas burner with a plurality of ranges defined as a gas combustion range,
A water inlet pipe into which water flows from the outside of the hot water supply device;
A hot water outlet pipe that flows hot water to the outside of the hot water supply device;
A flow rate detection unit that detects an inlet water flow rate, which is the flow rate of water flowing through the water inlet pipe;
an inlet water temperature detection unit for detecting an inlet water temperature, which is the temperature of water flowing through the water inlet pipe;
A hot water outlet temperature detection unit detects a hot water outlet temperature, which is the temperature of the hot water flowing through the hot water outlet pipe;
A hot water outlet temperature setting unit that sets the temperature of the hot water flowing through the hot water outlet pipe;
a control unit that calculates a control amount for determining a combustion amount of the gas burner based on the inlet water flow rate, the inlet water temperature, a set temperature set by the outlet water temperature setting unit, and the outlet water temperature;
a switching unit that switches a combustion range of the gas in the gas burner to one of the plurality of ranges based on a calculation result by the control unit;
Equipped with
The switching unit performs a limiting operation including prohibiting switching of the combustion range of the gas when a predetermined limiting condition is satisfied,
The limiting condition is a case where a predetermined condition is satisfied in the calculation of the controlled variable by the control unit, and a condition for switching the combustion range among the plurality of ranges in a predetermined order is established.

The hot water supply device according to the present disclosure includes:
A hot water supply device having a gas burner with a plurality of ranges defined as a gas combustion range,
A water inlet pipe into which water flows from the outside of the hot water supply device;
A hot water outlet pipe that flows hot water to the outside of the hot water supply device;
A flow rate detection unit that detects an inlet water flow rate, which is the flow rate of water flowing through the water inlet pipe;
an inlet water temperature detection unit for detecting an inlet water temperature, which is the temperature of water flowing through the water inlet pipe;
A hot water outlet temperature detection unit detects a hot water outlet temperature, which is the temperature of the hot water flowing through the hot water outlet pipe;
A hot water outlet temperature setting unit that sets the temperature of the hot water flowing through the hot water outlet pipe;
a control unit that calculates a feedforward control amount based on the inlet water flow rate, the inlet water temperature, and a set temperature set by the outlet water temperature setting unit, calculates a feedback control amount according to a predetermined feedback calculation method, and calculates a control amount for determining a combustion amount in the gas burner based on the sum of the feedforward control amount and the feedback control amount;
Equipped with
The control unit is
The calculation of the control amount is repeated, and the combustion amount is determined each time the control amount is calculated;
When a predetermined limiting condition is established, the combustion amount is limited so that the combustion amount is set to the upper limit value when the control amount exceeds a predetermined upper limit value, or the combustion amount is set to the lower limit value when the control amount is below a predetermined lower limit value;
When calculating the current control amount when the restriction condition is met, an increase/decrease value for bringing the hot water temperature closer to the set temperature is calculated according to the feedback calculation method based on the set temperature and the hot water outlet temperature, and even if the combustion amount was limited in the previous determination of the combustion amount, the current feedback control amount is calculated based on the value obtained by adding a standard control amount based on the previous feedback control amount and the increase/decrease value.

The water heater disclosed herein can perform limiting operations that make it easier to maintain stable water heating operation.

FIG. 1 is an explanatory diagram conceptually illustrating the configuration of a water heater according to a first embodiment. FIG. 2 is a diagram showing the relationship between the combustion amount of the first gas burner and the rotation speed of the fan in the hot water supply apparatus of FIG. FIG. 3 is a flowchart showing a flow of combustion control performed in the hot water supply apparatus of FIG. FIG. 4 is a flowchart showing a flow of combustion control performed in the water heater of the second embodiment. FIG. 5 is a graph illustrating a simulation result of a water heating apparatus according to another example. FIG. 6 is a graph illustrating a simulation result of the water heating apparatus of the first embodiment.

Below, embodiments of the present disclosure are listed and exemplified. Note that the features [1] to [10] exemplified below may be combined in any manner as long as they are not inconsistent.

[1] A hot water supply device having a gas burner with multiple ranges defined as gas combustion ranges,
A water inlet pipe into which water flows from the outside of the hot water supply device;
A hot water outlet pipe that flows hot water to the outside of the hot water supply device;
A flow rate detection unit that detects an inlet water flow rate, which is the flow rate of water flowing through the water inlet pipe;
an inlet water temperature detection unit for detecting an inlet water temperature, which is the temperature of water flowing through the water inlet pipe;
A hot water outlet temperature detection unit detects a hot water outlet temperature, which is the temperature of the hot water flowing through the hot water outlet pipe;
A hot water outlet temperature setting unit that sets the temperature of the hot water flowing through the hot water outlet pipe;
a control unit that calculates a control amount for determining a combustion amount of the gas burner based on the inlet water flow rate, the inlet water temperature, a set temperature set by the outlet water temperature setting unit, and the outlet water temperature;
a switching unit that switches a combustion range of the gas in the gas burner to one of the plurality of ranges based on a calculation result by the control unit;
Equipped with
The switching unit performs a limiting operation including prohibiting switching of the combustion range of the gas when a predetermined limiting condition is satisfied,
The water heating apparatus, wherein the limiting condition is a case where a predetermined condition is satisfied in the calculation of the control amount by the control unit, and a condition for switching the combustion range among the plurality of ranges in a predetermined order is established.

The water heating device of [1] can perform a restriction operation, including prohibiting switching of the gas combustion range, when a predetermined condition is satisfied in the calculation of a control amount for determining the combustion amount of the gas burner, and a condition for switching the combustion range among multiple ranges in a predetermined order is established. In other words, the water heating device can determine whether or not to prohibit switching of the gas combustion range based on the calculation status of the control amount and the switching status of the combustion range. Therefore, this water heating device can more reliably prevent switching restrictions that deviate significantly from the calculation status of the control amount or from the switching status of the combustion range. Therefore, this water heating device can perform a restriction operation that makes it easier to prevent instability of the hot water heating operation due to hunting under unstable conditions, and to maintain stable hot water heating operation.

[2] In the hot water supply device described in [1], the multiple ranges include at least a first range and a second range that is wider than the first range. The limiting condition includes a case where, when the calculation result satisfies the predetermined condition, a condition for switching the combustion range of the gas in the gas burner to the first range, the second range, and the first range in that order is satisfied, or a condition for switching to the second range, the first range, and the second range in that order is satisfied. When the limiting condition is satisfied, the switching unit performs the limiting operation to prohibit switching from one of the first range and the second range to the other.

The water heater of [2] is able to grasp conditions in which hunting may occur, at least between the first range and the second range in which the amount of combustion is greater than that of the first range, and more reliably suppress the occurrence of hunting.

[3] In the hot water supply device described in [1] or [2], the control unit calculates a feedforward control amount based on the inlet water flow rate, the inlet water temperature, and the set temperature, calculates a feedback control amount based on the set temperature and the outlet hot water temperature, and calculates the control amount based on the sum of the feedforward control amount and the feedback control amount. Furthermore, when the limiting condition is met, the control unit limits the combustion amount so that the combustion amount is set to the upper limit value when the control amount exceeds a predetermined upper limit value, or the combustion amount is set to the lower limit value when the control amount falls below a predetermined lower limit value.

The water heater of [3] is based on a control system that calculates a control amount based on the sum of a feedforward control amount and a feedback control amount, and determines the combustion amount based on this control amount. When a limiting condition is met, the combustion amount can be restricted so as to prevent it from exceeding an upper limit or falling below a lower limit.

[4] In the hot water supply device described in [3], the control unit repeatedly calculates the control amount and determines the combustion amount each time the control amount is calculated. Furthermore, when the control unit calculates the current control amount when the limiting condition is satisfied, the control unit calculates an increase or decrease value for bringing the outlet hot water temperature closer to the set temperature based on the difference between the set temperature and the outlet hot water temperature according to a predetermined feedback calculation method, and calculates the current feedback control amount based on the sum of the standard control amount based on the previous feedback control amount and the increase or decrease value, even if the combustion amount was limited in the previous determination of the combustion amount.

In the water heating device of [4], when repeatedly calculating the control amount, the current control amount is calculated by calculating an increase/decrease value for bringing the outlet temperature closer to the set temperature based on the set temperature and the outlet temperature according to a feedback calculation method, and the current feedback control amount is calculated based on the sum of a reference control amount based on the previous feedback control amount and the increase/decrease value. Therefore, by using a reference control amount reflecting the previous feedback control amount and increasing/decreasing this reference control amount by an increase/decrease value based on the outlet temperature, the current feedback control amount can be calculated more appropriately. Moreover, even if the combustion amount was limited in the previous combustion amount determination, the current feedback control amount can be calculated using the previous feedback control amount, so the current feedback control amount can be calculated more appropriately while preventing the previous feedback control amount from being excessively limited by the combustion amount limit.

[5] A hot water supply device having a gas burner with multiple ranges defined as gas combustion ranges,
A water inlet pipe into which water flows from the outside of the hot water supply device;
A hot water outlet pipe that flows hot water to the outside of the hot water supply device;
A flow rate detection unit that detects an inlet water flow rate, which is the flow rate of water flowing through the water inlet pipe;
an inlet water temperature detection unit for detecting an inlet water temperature, which is the temperature of water flowing through the water inlet pipe;
A hot water outlet temperature detection unit detects a hot water outlet temperature, which is the temperature of the hot water flowing through the hot water outlet pipe;
A hot water outlet temperature setting unit that sets the temperature of the hot water flowing through the hot water outlet pipe;
a control unit that calculates a feedforward control amount based on the inlet water flow rate, the inlet water temperature, and a set temperature set by the outlet water temperature setting unit, calculates a feedback control amount according to a predetermined feedback calculation method, and calculates a control amount for determining a combustion amount in the gas burner based on the sum of the feedforward control amount and the feedback control amount;
Equipped with
The control unit is
The calculation of the control amount is repeated, and the combustion amount is determined each time the control amount is calculated;
When a predetermined limiting condition is established, the combustion amount is limited so that the combustion amount is set to the upper limit value when the control amount exceeds a predetermined upper limit value, or the combustion amount is set to the lower limit value when the control amount is below a predetermined lower limit value;
This water heating device calculates, when the restriction condition is met and the current control amount is calculated, an increase/decrease value for bringing the outlet hot water temperature closer to the set temperature is calculated in accordance with the feedback calculation method based on the set temperature and the outlet hot water temperature, and even if the combustion amount was limited in the previous determination of the combustion amount, the current feedback control amount is calculated based on the value obtained by adding a standard control amount based on the previous feedback control amount and the increase/decrease value.

The water heater of [5] is based on the assumption that the control amount is calculated based on the sum of the feedforward control amount and the feedback control amount, and the combustion amount is determined based on this control amount. When the limiting condition is met, the combustion amount can be restricted so as to be prevented from exceeding the upper limit or falling below the lower limit. Furthermore, in the repeated calculation of the control amount, when the current control amount is calculated, an increase/decrease value for bringing the hot water outlet temperature closer to the set temperature is calculated according to a feedback calculation method based on the set temperature and the hot water outlet temperature, and the current feedback control amount can be calculated based on the sum of the standard control amount based on the previous feedback control amount and the increase/decrease value. Therefore, the current feedback control amount can be calculated more appropriately by using the standard control amount reflecting the previous feedback control amount and increasing/decreasing this standard control amount by the increase/decrease value based on the hot water outlet temperature. Moreover, even if the combustion amount was limited in the previous determination of the combustion amount, the current feedback control amount can be calculated using the previous feedback control amount, so that the current feedback control amount can be calculated more appropriately while preventing the previous feedback control amount from being excessively limited by the limit on the combustion amount.

[6] In the hot water supply device described in [4] or [5], when the limiting condition is satisfied, the control unit performs a process of calculating a correction value by correcting the feedback control amount so that the control amount is equal to or less than the second upper limit value when the control amount exceeds a second upper limit value that is greater than the upper limit value, or a process of calculating a correction value by correcting the feedback control amount so that the control amount is equal to or greater than the second lower limit value when the control amount falls below a second lower limit value that is less than the lower limit value. Furthermore, when the correction value was calculated when the combustion amount was calculated last time, the control unit determines the standard control amount based on the correction value instead of the previous feedback control amount when calculating the control amount this time, and when the control amount was greater than the upper limit value and less than the second upper limit value when the combustion amount was calculated last time, or when the control amount was less than the lower limit value and greater than the second lower limit value, the control unit determines the standard control amount based on the previous feedback control amount when calculating the control amount this time.

In the water heating device of [6], when a correction value was calculated when the previous combustion amount was calculated (i.e., when the previous control amount deviates from the second upper limit value that is greater than the upper limit value or the second lower limit value that is smaller than the lower limit value), the reference control amount can be determined based on the correction value instead of the previous feedback control amount when calculating the current control amount. In other words, when the previous feedback control amount obtained by the calculation is a value that determines the combustion amount so that it deviates significantly from the upper limit value and the lower limit value, the previous feedback control amount is not used as is when calculating the current feedback control amount in calculating the current combustion amount, but the correction value can be used instead to calculate the current feedback control amount. Moreover, the correction value is a value obtained by "calculating a correction value obtained by correcting the feedback control amount so that the control amount is equal to or less than the second upper limit value when the control amount exceeds the second upper limit value that is greater than the upper limit value, or calculating a correction value obtained by correcting the feedback control amount so that the control amount is equal to or more than the second lower limit value when the control amount falls below the second lower limit value that is smaller than the lower limit value", so that the restriction can be prevented from becoming an excessive value. On the other hand, if the control amount is greater than the upper limit and less than the second upper limit, or is less than the lower limit and greater than the second lower limit, the reference control amount can be determined based on the feedback control amount from the previous time when the control amount is calculated. In other words, even if the combustion amount is limited based on the upper limit or lower limit when the combustion amount is calculated from the previous time, if the second upper limit or the second lower limit has not been reached, the reference control amount can be determined using the previous feedback control amount (unlimited value) rather than a limited value such as a correction value, and the current feedback control amount can be calculated. Therefore, when the combustion amount is repeatedly calculated, it is possible to suppress a decrease in tracking ability or responsiveness caused by repeated feedback calculations in which the "previous feedback control amount" is limited.

[7] In the water heating device described in any one of [1] to [6], the control unit calculates a feedforward control amount of the combustion amount in the gas burner based on the inlet water flow rate, the inlet water temperature, and the set temperature, and the limiting condition includes a condition in which the feedforward control amount satisfies a predetermined stability condition.

The water heater of [7] can perform limiting operations when the feedforward control amount is stable, making it easier to avoid performing limiting operations in situations where the feedforward control is unstable.

[8] In the water heating device described in [7], the predetermined stability condition is when the absolute value of the difference between the maximum and minimum values when the control unit calculates the feedforward control amount multiple times falls within a limited range.

The water heater of [8] can more appropriately evaluate whether the feedforward control amount is stable, and can more reliably avoid limiting operations in situations where the feedforward control is unstable.

[9] In the water heater described in [7] or [8], the control unit calculates a feedback control amount of the combustion amount in the gas burner based on the set temperature and the hot water outlet temperature, and the predetermined stable condition includes a condition in which the sum of the feedforward control amount and the feedback control amount is within a predetermined range.

The water heater of [9] can perform limiting operation when the feedforward control amount and the feedback control amount are stable, so it is easier to more reliably avoid performing limiting operation in situations where the control amount is unstable.

[10] In the hot water supply device described in any one of [1] to [9], the switching unit starts the limiting operation in response to the establishment of the limiting condition, and then cancels the execution of the limiting operation when the termination condition is established.

After starting the limiting operation, the water heater in [10] can continue the limiting operation until the end condition is met, and can cancel the limiting operation when the end condition is met.

First Embodiment
A first embodiment is described below with reference to FIGS.
(Configuration of hot water supply device 1)
The hot water supply device 1 shown in FIG. 1 has a function of heating tap water supplied from the outside and discharging hot water. The hot water supply device 1 includes a first gas burner 2, a water inlet pipe 4, a hot water outlet pipe 6, a heat exchanger 8, a first connecting pipe 15, a fan 31, and the like. The first gas burner 2 is configured as a burner group having a plurality of burners. The water inlet pipe 4 is configured as a pipe into which water flows from the outside of the hot water supply device 1 (water inlet 16), and the hot water outlet pipe 6 is configured as a pipe through which hot water flows to the outside through the hot water outlet 18. The heat exchanger 8 includes a hot water supply side heat transfer pipe section 11 interposed between the water inlet pipe 4 and the hot water outlet pipe 6, and is a part that functions to transfer heat generated by combustion in the first gas burner 2 to the water passing through the inside of the hot water supply side heat transfer pipe section 11. The fan 31 supplies combustion air to the first gas burner 2.

The first gas burner 2 comprises a first burner group 30A, a second burner group 30B, and a third burner group 30C. Fuel gas is supplied to each burner group 30A-30C via a gas supply pipe 32. The gas supply pipe 32 is provided with, in order from the upstream side, a main gas solenoid valve 33, a gas proportional valve 34, and switching gas solenoid valves 35A, 35B, and 35C. When the main gas solenoid valve 33 is opened, fuel gas is supplied to each burner group 30A-30C, and when the main gas solenoid valve 33 is closed, the supply of fuel gas to each burner group 30A-30C is cut off. The gas proportional valve 34 adjusts the amount of fuel gas supplied to each burner group 30A-30C. The switching gas solenoid valves 35A, 35B, and 35C are provided corresponding to the first burner group 30A, the second burner group 30B, and the third burner group 30C, respectively. The switching gas solenoid valves 35A, 35B, and 35C function to adjust the amount of combustion of the first gas burner 2 by adjusting the amount of fuel supplied to the first gas burner 2. When the switching gas solenoid valves 35A, 35B, and 35C are opened, fuel gas is supplied to the corresponding first burner group 30A, the second burner group 30B, and the third burner group 30C. When the switching gas solenoid valves 35A, 35B, and 35C are closed, the supply of fuel gas to the corresponding first burner group 30A, the second burner group 30B, and the third burner group 30C is cut off. By switching the opening or closing of each of the switching gas solenoid valves 35A, 35B, and 35C, the combustion ranges of the first burner group 30A, the second burner group 30B, and the third burner group 30C can be switched.

The hot water supply device 1 can switch the combustion range of the first gas burner 2 to three stages. The first range R1, which has the lowest combustion amount (smallest combustion range), is a combustion range in which the first burner group 30A is burned and the second burner group 30B and the third burner group 30C are not burned. The second range R2, which has a higher combustion amount than the first range R1 (larger combustion range than the first range R1), is a combustion range in which the first burner group 30A and the second burner group 30B are burned and the third burner group 30C is not burned. The third range R3, which has a higher combustion amount than the second range R2 (larger combustion range than the second range R2), is a combustion range in which the first burner group 30A, the second burner group 30B, and the third burner group 30C are all burned.

As shown in FIG. 2, the maximum combustion amount Q1max (upper limit of the first range R1) in the first range R1 is higher than the minimum combustion amount Q2min (lower limit of the second range R2) in the second range R2. The maximum combustion amount Q2max (upper limit of the second range R2) in the second range R2 is higher than the minimum combustion amount Q3min (lower limit of the third range R3) in the third range R3. As shown in FIG. 2, the rotation speed of the fan 31 is preset according to the combustion range and the combustion amount within that combustion range. The controller 28 rotates the fan 31 at the set rotation speed based on the combustion range and the combustion amount. The unit of combustion amount is, for example, kcal/h.

As shown in FIG. 1, the water heater 1 is provided with a spark plug 36 for igniting the first gas burner 2 near the first gas burner 2. The water heater 1 is provided with an igniter (not shown) that applies a high voltage to the spark plug 36 to generate a spark discharge.

As shown in FIG. 1, the water heater 1 is provided with an inlet water temperature sensor 41, a flow rate sensor 42, a water volume adjustment valve 43, and an outlet water temperature sensor 44. The inlet water temperature sensor 41 detects the temperature of the water flowing through the inlet water pipe 4 (inlet water temperature). The inlet water temperature sensor 41 corresponds to an example of an inlet water temperature detection unit. The flow rate sensor 42 detects the flow rate of the water flowing through the inlet water pipe 4 (inlet water flow rate). The flow rate sensor 42 corresponds to an example of a flow rate detection unit. When hot water is not being supplied to the bathtub 20 in the water heater 1 (when the solenoid valve in the path from the outlet water pipe 6 to the bathtub 20 is shut off), the inlet water flow rate corresponds to the outlet water flow rate from the outlet water pipe 6. The water volume adjustment valve 43 adjusts the flow rate of water supplied to the inlet water pipe 4. The outlet water temperature sensor 44 detects the temperature of the hot water supplied from the outlet water pipe 6 (outlet water temperature). The outlet water temperature sensor 44 corresponds to an example of an outlet water temperature detection unit.

The heat exchanger 8 transfers the heat of the combustion exhaust generated by the combustion of gas in the first gas burner 2 to the water passing through the heat exchanger 8. The heat exchanger 8 includes a primary heat exchanger 9 and a secondary heat exchanger 10, with the primary heat exchanger 9 being arranged upstream of the combustion exhaust path of the first gas burner 2, and the secondary heat exchanger 10 being arranged downstream of the combustion exhaust path. The hot water supply side heat transfer pipe section 11 includes a first heat transfer pipe section 12 and a third heat transfer pipe section 13, with the first heat transfer pipe section 12 being provided in the secondary heat exchanger 10, and the third heat transfer pipe section 13 being provided in the primary heat exchanger 9. The first heat transfer pipe section 12 of the secondary heat exchanger 10 is connected to the downstream side of the water inlet pipe 4, and the first connecting pipe 15 is connected to the downstream side of the first heat transfer pipe section 12. The third heat transfer pipe section 13 of the primary heat exchanger 9 is connected to the downstream side of the first connecting pipe 15, and the outlet pipe 6 is connected to the downstream side of the third heat transfer pipe section 13.

The heat exchanger 8 functions to recover sensible heat from the combustion exhaust gas by the primary heat exchanger 9, and then recover latent heat by the secondary heat exchanger 10. Specifically, the primary heat exchanger 9 transfers the combustion heat contained in the combustion exhaust gas generated by the first gas burner 2 to the water passing through the third heat transfer tube section 13, and exchanges heat by transferring the thermal energy of the sensible heat to the passing water. In addition, the secondary heat exchanger 10 transfers the combustion heat of the combustion exhaust gas generated by the first gas burner 2 after it passes through the primary heat exchanger 9 to the water passing through the first heat transfer tube section 12, and exchanges heat by transferring the thermal energy of the latent heat to the passing water.

The hot water supply device 1 also includes a second gas burner 102, a forward pipe 104, a return pipe 106, a second connecting pipe 115, etc., and has the function of reheating the bath using the above-mentioned heat exchanger 8. The second gas burner 102 (bath burner) is a part that burns combustion gas to generate combustion exhaust (exhaust gas). The forward pipe 104 is a path that guides water from the bathtub 20 side to the heat exchanger 8 via the inlet 116. The return pipe 106 is a path that guides water from the heat exchanger 8 to the bathtub 20 side via the outlet 118. The above-mentioned heat exchanger 8 includes a bath-side heat transfer pipe section 111 interposed between the forward pipe 104 and the return pipe 106, and functions to transfer heat generated by combustion in the second gas burner 102 to the water passing through the inside of the bath-side heat transfer pipe section 111.

The bath side heat transfer pipe section 111 includes a second heat transfer pipe section 112 and a fourth heat transfer pipe section 113, the second heat transfer pipe section 112 being provided in the secondary heat exchanger 10, and the fourth heat transfer pipe section 113 being provided in the primary heat exchanger 9. The second heat transfer pipe section 112 of the secondary heat exchanger 10 is connected to the downstream side of the forward piping 104, and the second connecting pipe 115 is connected to the downstream side of the second heat transfer pipe section 112. The fourth heat transfer pipe section 113 of the primary heat exchanger 9 is connected to the downstream side of the second connecting pipe 115, and the return piping 106 is connected to the downstream side of this heat transfer pipe section.

The above-mentioned primary heat exchanger 9 transfers the combustion heat contained in the combustion exhaust gas generated by the second gas burner 102 to the water passing through the fourth heat transfer tube section 113, and exchanges heat by transferring the thermal energy of sensible heat to the passing water. The secondary heat exchanger 10 transfers the combustion heat generated by the combustion exhaust gas generated by the second gas burner 102 after it passes through the primary heat exchanger 9 to the water passing through the second heat transfer tube section 112, and exchanges heat by transferring the thermal energy of latent heat to the passing water.

The hot water supply device 1 also includes a drain pipe 22 and a neutralizer 24. The upstream side of the drain pipe 22 is connected to a drain joint 26 (see FIG. 3) of the secondary heat exchanger 10, and the downstream side is connected to the neutralizer 24. The drain generated by the recovery of latent heat in the secondary heat exchanger 10 is discharged to the outside of the secondary heat exchanger 10 via the drain joint 26 and sent to the neutralizer 24 through the drain pipe 22.

The hot water supply device 1 also includes a controller 28 as a control device. The controller 28 is configured, for example, as a known microcomputer or the like, and is configured to be able to acquire signals from various sensors provided in the hot water supply device 1, and is configured to be able to control various actuators provided in the hot water supply device 1. For example, when the hot water supply device 1 detects water flow in the water inlet pipe 4 by a water flow sensor (not shown), the first gas burner 2 is operated to generate hot water. As another example, when the hot water supply device 1 detects water flow in the outflow pipe 104 by a water flow sensor (not shown), the second gas burner 102 is operated to reheat the bath. The hot water supply device 1 includes a hot water supply remote control (remote controller) (not shown). The controller 28 corresponds to an example of a "hot water outlet temperature setting unit" and functions to set the temperature (set temperature, target temperature) of the hot water flowing through the hot water outlet pipe 6 based on the user's operation on the operation unit such as the hot water supply remote control (for example, an operation to input a desired hot water outlet temperature, etc.). The controller 28 (outlet hot water temperature setting unit) has the function of storing the set outlet hot water temperature when the set temperature is input through the operation unit or other information input.

The controller 28 corresponds to an example of a "control unit" and functions to calculate a control amount for controlling the combustion amount of the first gas burner 2 based on the inlet water flow rate (hereinafter also referred to as inlet water amount) W, the inlet water temperature Ti, the set temperature Ts, and the outlet hot water temperature To. The unit of the inlet water flow rate (inlet water amount) W is, for example, 1/min. The unit of the inlet water temperature Ti is, for example, °C. The unit of the set temperature Ts is, for example, °C. The unit of the outlet hot water temperature To is, for example, °C. The unit of the control amount is, for example, kcal/h. If the control amount calculated in the nth calculation is _Fn (kcal/h), the control amount _Fn can be determined by _Fn = FF + _FBn . FF is the feedforward control amount, and _FBn is the feedback control amount calculated in the nth calculation. The unit of the feedforward control amount is, for example, kcal/h. The unit of the feedback control amount is, for example, kcal/h. In this embodiment, the controller 28 (control unit) repeatedly calculates the control amount, and determines the combustion amount based on the control amount every time the control amount is calculated. For example, when the control amount _Fn is calculated in the nth calculation, the combustion amount _Qn based on the nth calculation is determined based on the control amount _Fn .

The controller 28 corresponds to an example of a "switching unit" and functions to determine the combustion amount based on the calculation result of the control amount, and to switch the combustion range to which fuel is supplied in the first gas burner 2 between multiple ranges based on the determined combustion amount. The method of determining the combustion amount based on the control amount will be described in detail later. Specifically, the controller 28 controls the switching gas solenoid valves 35A, 35B, and 35C to switch the burner group to which fuel is supplied among the burner groups 30A to 30C, thereby switching the combustion range of the first gas burner 2 to one of the first range R1, the second range R2, and the third range R3. For example, the controller 28 can switch the combustion range of the first gas burner 2 from one of the first range R1 and the second range R2 to the other by controlling the switching gas solenoid valves 35A, 35B, and 35C, and can switch the combustion range of the first gas burner 2 from one of the second range R2 and the third range R3 to the other.

If the combustion amount calculated periodically and repeatedly while the first gas burner 2 continues to burn in the first range R1 continues to be equal to or less than the maximum combustion amount Q1max (upper limit value of the first range R1), the controller 28 controls the first gas burner 2 to burn at the calculated combustion amount while maintaining the combustion range of the first gas burner 2 in the first range R1. If the calculated combustion amount exceeds the maximum combustion amount Q1max (upper limit value of the first range R1) while the first gas burner 2 continues to burn in the first range R1, the controller 28 switches the combustion range from the first range R1 to the second range R2 unless a predetermined limiting condition is satisfied.

If the combustion amount calculated periodically and repeatedly while the first gas burner 2 continues to burn in the second range R2 is equal to or less than the maximum combustion amount Q2max (upper limit value of the second range R2) and equal to or more than the minimum combustion amount Q2min (lower limit value of the second range R2), the controller 28 controls the first gas burner 2 to burn at the calculated combustion amount while maintaining the combustion range of the first gas burner 2 in the second range R2. If the combustion amount calculated while the first gas burner 2 continues to burn in the second range R2 exceeds the maximum combustion amount Q2max (upper limit value of the second range R2), the controller 28 switches the combustion range from the second range R2 to the third range R3 unless a predetermined limiting condition is satisfied. If the combustion amount calculated while the first gas burner 2 continues to burn in the second range R2 falls below the minimum combustion amount Q2min (the lower limit of the second range R2), the controller 28 switches the combustion range from the second range R2 to the first range R1 unless a predetermined limiting condition is met.

If the combustion amount calculated repeatedly while the first gas burner 2 continues to burn in the third range R3 is equal to or greater than the minimum combustion amount Q3min (lower limit value of the third range R3), the controller 28 controls the first gas burner 2 to burn at the calculated combustion amount while maintaining the combustion range of the first gas burner 2 in the third range R3. If the combustion amount calculated while the first gas burner 2 continues to burn in the third range R3 falls below the minimum combustion amount Q3min (lower limit value of the third range R3), the controller 28 switches the combustion range from the third range R3 to the second range R2 unless a predetermined limiting condition is satisfied.

In this way, when the first gas burner 2 is burning in a predetermined combustion range, if the combustion amount calculated periodically and repeatedly is equal to or less than the upper limit value and equal to or greater than the lower limit value of the combustion range, the controller 28 controls the first gas burner 2 to burn at the calculated combustion amount while maintaining the combustion range of the first gas burner 2 in the combustion range. If the combustion amount calculated when the first gas burner 2 continues to burn in the combustion range exceeds the upper limit value of the combustion range, the controller 28 switches the range of gas combustion from the combustion range to a combustion range one step larger than the combustion range if the predetermined limiting condition is not met. If the combustion amount calculated when the first gas burner 2 continues to burn in the combustion range falls below the lower limit value of the combustion range, the controller 28 switches the range of gas combustion from the combustion range to a combustion range one step smaller than the combustion range if the predetermined limiting condition is not met. It is also possible that a lower limit value is not set for any of the combustion ranges (e.g., the first range R1), and in this case, it is sufficient that the lower limit value is always set or higher during combustion in this combustion range (e.g., the first range R1). It is also possible that an upper limit value is not set for any of the combustion ranges (e.g., the third range R3), and in this case, it is sufficient that the upper limit value is always set or lower during combustion in this combustion range (e.g., the third range R3).

The controller 28 corresponds to an example of a "feedforward control unit." The controller 28 functions to calculate a feedforward control amount FF based on the inlet water flow rate (inlet water amount) W, the inlet water temperature Ti, and the set temperature Ts. The feedforward calculation for determining the feedforward control amount FF can be performed based on a known method disclosed in, for example, JP 09-113031 A, or it may be calculated using the formula 1 described below. In the representative example described below, the feedforward control amount FF is calculated using the formula 1.

In Equation 1, FF is the feedforward control amount. Ts is the set temperature, Ti is the inlet water temperature, and W is the inlet water amount. η is the thermal efficiency, which is a predetermined known value. The unit of thermal efficiency is, for example, (%). The number "60" in Equation 1 is a coefficient, and may be replaced with another fixed value A.

The controller 28 corresponds to an example of a "feedback control unit" and calculates a feedback control amount FB _n based on the set temperature Ts and the outlet hot water temperature To detected by the outlet hot water temperature sensor 44. Specifically, based on the deviation (Ts-To) between the set temperature Ts and the outlet hot water temperature To, the feedback control amount is calculated so as to reduce the deviation (Ts-To). The feedback calculation for determining the feedback control amount may be a known PI calculation, a PD calculation, or a PID calculation. For example, the feedback calculation may be performed by a known method disclosed in JP-A-8-14540 or the like, or may be calculated by the formulas 2 and 3 described below. In a representative example described below, the feedback control amount FB _n in the nth calculation is calculated by the formulas 2 and 3.

In the formula 2, FB _n is the feedback control amount calculated by the feedback calculation in the n-th calculation. FB _n-1 is the feedback control amount calculated by the feedback calculation in the n-1-th calculation. If the predetermined correction condition is not satisfied in the n-1-th calculation (if the correction value α _n-1 described below is not calculated), FB _n-1 is the feedback control amount calculated by the feedback calculation in the n-1-th calculation. If the predetermined correction condition is satisfied in the n-1-th calculation (if the correction value α _n-1 described below is calculated), FB _n-1 is replaced with the correction value α _n-1 as in the formula 4. The calculation method of the correction condition and the correction value will be described later. Wper is the water volume change rate (%) when comparing the water inflow volume at the n-1-th calculation with the water inflow volume at the n-th calculation, and is a value indicating the ratio of the water inflow volume at the n-th calculation to the water inflow volume at the n-1-th calculation. The value of FB _n-1 ×Wper corresponds to an example of a reference control amount. Kp is a proportional gain, Kd is a differential gain, and Ki is an integral gain. ΔFB is a PID calculation value calculated by a PID calculation with Ts-To as the deviation, and corresponds to an example of an increase or decrease value. A known method can be used for the PID calculation with Ts-To as the deviation. When calculating the current control amount F _n in the nth calculation, the controller 28 (control unit) calculates an increase or decrease value ΔFB for bringing the outlet hot water temperature To closer to the set temperature Ts based on the difference between the set temperature Ts and the outlet hot water temperature To according to a predetermined feedback calculation method (for example, a feedback calculation method using Equation 3). Then, the controller 28 (control unit) calculates the current feedback control amount FB n based on the standard control amount (FB _n-1 ×Wper) based on the previous feedback control amount FB n _{-1 and} the increase or decrease value ΔFB according to the above formula 2. In the representative example described below, the sum of the reference control amount (FB _n-1 × Wper) and the increase/decrease value ΔFB is set to the current feedback control amount FB _n , but the current feedback control amount FB _n may be determined by correcting the sum by multiplying it by a predetermined coefficient or adding another sum.

(Combustion control of hot water supply device)
The following description relates to combustion control by water heating apparatus 1. The control in Fig. 3 is control executed by controller 28 in water heating apparatus 1. When an ignition operation is performed, water heating apparatus 1 ignites first gas burner 2 to start combustion, thereby starting the combustion control described in Figs. 2 and 3.

When a predetermined limiting condition is met, the controller 28 performs a limiting operation, including prohibiting switching of the combustion range. The limiting operation may include other controls than prohibiting switching of the combustion range. For example, the limiting operation may include controls such as prohibiting a change in the set temperature, and may include controls such as prohibiting combustion at a combustion amount that exceeds an upper limit value set for the current combustion range, or prohibiting combustion at a combustion amount that is below a lower limit value set for the current combustion range.

When a predetermined limiting condition is met, for example, "when the calculation result of the control amount satisfies a predetermined condition, a condition for switching the combustion range among multiple ranges in a predetermined order is met." When a predetermined condition is met, for example, "when the feedforward control amount satisfies a predetermined stability condition." When a limiting condition is met, for example, when the calculation result of the control amount (feedforward control amount) satisfies a predetermined condition, a condition for switching the combustion range in the first gas burner 2 to the first range R1, the second range R2, and the first range R1 is met, or when a condition for switching to the second range R2, the first range R1, and the second range R2 is met. Alternatively, the limiting condition may be satisfied when the calculation result of the control amount (feedforward control amount) satisfies a predetermined condition, and the condition for switching the combustion range of the first gas burner 2 to the second range R2, the third range R3, and the second range R2 in that order is satisfied, or when the condition for switching to the third range R3, the second range R2, and the third range R3 in that order is satisfied.

In the control of Fig. 3, first, in step S11, the controller 28 judges whether the feedforward control amount is in a stable state. That is, the controller 28 judges whether the calculated feedforward control amount FF satisfies a stability condition. The stability condition is satisfied when the maximum and minimum values of the feedforward control amount FF sampled multiple times are within a limit range determined based on the average value of the most recent multiple samplings. The stability condition is satisfied, for example, when the following formula (1) is satisfied. As described above, the controller 28 calculates the feedforward control amount FF, which is a factor for determining the combustion amount in the first gas burner 2, based on the inlet water flow rate (inlet water amount) W, the inlet water temperature Ti, and the set temperature Ts in each period. Specifically, the controller 28 calculates (samples) the feedforward control amount FF at a predetermined period (e.g., a period of 100 milliseconds), and each time the controller 28 calculates the feedforward control amount FF, it specifies the feedforward control amount (FFdate) for a most recent predetermined number of times (e.g., the most recent 10 times), specifies the maximum value (maximum value of FFdate) and the minimum value (minimum value of FFdate) from among the feedforward control amounts (FFdate) for the predetermined number of times, and calculates the average value of the remaining feedforward control amounts (FFdate) by subtracting the maximum value and the minimum value from the feedforward control amounts (FFdate) for the predetermined number of times as the average value of FFdate (first data).The controller 28 then determines whether or not the following formula (1) is satisfied for the feedforward control amount (FFdate) for the most recent predetermined number of times.
| Maximum value of FFdate - Minimum value of FFdate | < Average value of FFdate × 10% ... (1)

That is, the controller 28 determines that the stability condition is satisfied when the absolute value of the difference between the maximum value (maximum value of FFdate) and the minimum value (minimum value of FFdate) of the feedforward control amount of the most recent predetermined number of times (for example, the feedforward control amount FF calculated for the past 10 times) is smaller than 10% of the average value of the FFdate, and determines that the stability condition is not satisfied when the absolute value is not smaller than 10% of the average value of the FFdate. When the stability condition is satisfied, this corresponds to an example of a case where the calculation result of the control amount satisfies the predetermined condition, and when the stability condition is not satisfied, this corresponds to an example of a case where the calculation result of the control amount does not satisfy the predetermined condition. When the controller 28 determines that the formula (1) does not hold (No in step S11), it repeats the process of step S11 until it determines that the formula (1) holds. On the other hand, when the controller 28 determines that the formula (1) holds (Yes in step S11), it proceeds to step S12.

In the representative example described above, the case where formula (1) is satisfied corresponds to an example of a case where the stability condition is satisfied, and the case where formula (1) is not satisfied corresponds to an example of a case where the stability condition is not satisfied, but this is not a limitation. For example, the stability condition may be satisfied when |maximum value of FFdate - minimum value of FFdate| is equal to or less than a predetermined value, and the stability condition may not be satisfied when this is not the case. Alternatively, the stability condition may be satisfied when the variance or standard deviation of the feedforward control amount for the above-mentioned predetermined number of times satisfies a predetermined numerical condition, and the stability condition may not be satisfied when this is not the case.

In step S12, the controller 28 determines whether the combustion range of the first gas burner 2 changes between specific combustion ranges. In the following description, "change between specific combustion ranges" refers to, for example, the combustion range of the first gas burner 2 switching between the first range R1, the second range R2, and the first range R1, or the second range R2, the first range R1, and the second range R2. However, this is not limited to this example, and the combustion range of the first gas burner 2 may be switched between the second range R2, the third range R3, and the second range R2, or the third range R3, the second range R2, and the third range R3. Alternatively, the combustion range of the first gas burner 2 may be switched between the first range R1, the second range R2, the first range R1, and the second range R2, or the second range R2, the first range R1, the second range R2, and the first range R1. In addition, the determination of whether the combustion range of the first gas burner 2 has changed between specific combustion ranges may be made by determining whether the combustion range has changed between specific combustion ranges within a specified time.

If the controller 28 determines that the combustion range of the first gas burner 2 has not changed between specific combustion ranges (No in step S12), it performs the process of step S11 again. On the other hand, if the controller 28 determines that the combustion range of the first gas burner 2 has changed between specific combustion ranges (Yes in step S12), it proceeds to step S13.

In step S13, the controller 28 records the latest feedforward control amount FF (the last calculated current feedforward control amount (current feedforward control amount) FF) and the most recent predetermined number of feedforward control amounts (for example, the last 10 feedforward control amounts (FFdate) including the current feedforward control amount).

In the next step S14, the controller 28 prohibits the combustion range of the first gas burner 2 from switching between specific combustion ranges. Specifically, when the current combustion range is either the first range R1 or the second range R2, if the limiting condition is satisfied, the controller 28 performs a limiting operation to prohibit the combustion range in the first gas burner 2 from switching from one of the first range R1 and the second range R2 to the other. Such a limiting operation is also performed when the condition for switching from one of the first range R1 and the second range R2 to the other is satisfied under normal circumstances. For example, even if the calculated combustion amount during combustion in the first range R1 becomes equal to or greater than the upper limit value of the first range R1, switching to the second range R2 is prohibited. Similarly, even if the calculated combustion amount during combustion in the second range R2 becomes equal to or less than the lower limit value of the second range R2, switching to the second range R2 is prohibited. This allows the water heater 1 to prevent hunting from occurring when switching the combustion range. When performing the process of step S14, the controller 28 continues the control to prohibit switching of the combustion range until the next termination condition is met.

In step S14, the controller 28 starts control to limit the amount of combustion in addition to the control to prohibit switching of the combustion range. If the controller 28 starts control to limit the amount of combustion in the processing of step S14, the controller 28 continues the control to limit the amount of combustion until the next time the termination condition is satisfied.

The controller 28 (controller) repeatedly calculates the control amount _Fn at least while the hot water supply operation is being performed, and determines the combustion amount _Qn each time the control amount _Fn is calculated. Specifically, the controller 28 (controller) calculates the control amount _Fn in each period, and in a period in which a predetermined limiting condition (a limiting condition for the combustion amount) is satisfied, the controller 28 (controller) does not use the control amount _Fn calculated in that period as the combustion amount as it is, but uses a value obtained by limiting the control amount _Fn calculated in that period using a predetermined limiting method as the combustion amount.

In a period in which the predetermined limiting condition is satisfied, the controller 28 determines the sum of the feedforward control amount FF and the feedback control amount _FBn as the control amount _Fn , and determines this control amount _Fn as the combustion amount _Qn . On the other hand, in a period in which the predetermined limiting condition is satisfied, if the control amount _Fn obtained by calculation exceeds a predetermined upper limit value (upper limit value of the current combustion range), the controller 28 determines the combustion amount _Qn in a form that limits the combustion amount _Qn to the above-mentioned upper limit value (upper limit value of the current combustion range). Similarly, in a period in which the predetermined limiting condition is satisfied, if the control amount _Fn obtained by calculation falls below a predetermined lower limit value (lower limit value of the current combustion range), the controller 28 determines the combustion amount _Qn in a form that limits the combustion amount _Qn to the above-mentioned lower limit value (lower limit value of the current combustion range). In other words, in a period in which the above-mentioned predetermined limiting condition is satisfied, the controller 28 determines the combustion amount by correcting the feedback control amount so that the sum of the feedforward control amount FF and the feedback control amount _FBn calculated in that period is equal to or less than a predetermined upper limit value or equal to or more than a predetermined lower limit value. By performing such control, in a period in which the above-mentioned limiting condition (combustion amount limiting condition) is satisfied, the combustion amount is limited to be equal to or less than the upper limit value or equal to or less than the lower limit value. On the other hand, in a period in which the above-mentioned limiting condition (combustion amount limiting condition) is not satisfied, the controller 28 (control unit) can use the control amount _Fn calculated in that period as the combustion amount _Qn as it is.

Furthermore, in this embodiment, in a cycle in which the above-mentioned limiting condition (combustion amount limiting condition) is satisfied, a process is performed to calculate a correction value by correcting the feedback control amount so that the control amount is equal to or less than the second upper limit value when the calculated control amount exceeds a second upper limit value (a second upper limit value greater than the upper limit value of the current combustion range) that is greater than the upper limit value (the upper limit value of the current combustion range). In this case, the correction value is a value obtained by subtracting the calculated previous feedforward control amount from the second upper limit value (a second upper limit value greater than the upper limit value of the current combustion range). In the case where the control amount calculated in the previous calculation is F _n-1 , the upper limit value is Ma1, and the second upper limit value is Mb1, the correction value α _n-1 obtained when Mb1>Ma1 and F _n-1 >Mb1 can be Mb1-FF _n-1 =α _n-1 . _{FF n-1} is the feedforward control amount FF calculated when the previous control amount F _n-1 is calculated.

Similarly, in a cycle in which the above-mentioned limiting condition (combustion amount limiting condition) is satisfied, when the calculated control amount falls below a second lower limit (a second lower limit value smaller than the lower limit value of the current combustion range) that is smaller than the lower limit value (the lower limit value of the current combustion range), a correction value is calculated by correcting the feedback control amount so that the control amount is equal to or greater than the second lower limit value. In this case, the correction value is a value obtained by subtracting the previous calculated feedforward control amount from the second lower limit (a second lower limit value smaller than the lower limit value of the current combustion range). In the case where the control amount calculated in the previous calculation is F _n-1 , the lower limit value is Mc1, and the second lower limit value is Md1, the correction value α _n-1 obtained when Md1<Mc1 and F _n-1 <Md1 can be Md1-FF _n-1 =α _n-1 . _{FF n-1} is the feedforward control amount FF calculated when the previous control amount F _n-1 is calculated.

In either case, if such a correction value α _n-1 was calculated when calculating the previous combustion amount Q _n-1 , the correction value α _n-1 is used instead of the previous feedback control amount FB _n-1 in equation 3 when calculating the current control amount F _n (FF+FB _n ), and the reference control amount (α _n-1 ×Wper) is determined based on this correction value α _n-1 . For example, if the correction value obtained as described above by correcting the previous feedback control amount FB _n-1 is α _n-1 , the current feedback control amount FB _n is calculated based on the following equation 4.

For example, when the combustion range of the first gas burner 2 is the first range R1, the controller 28 prohibits control to switch the combustion range from the first range R1 to the second range R2 if the above-mentioned limiting condition is satisfied. At the same time, the controller 28 determines the combustion amount by reducing the feedback control amount so that the control amount (the sum of the feedforward control amount and the feedback control amount) is equal to or less than 100% (the upper limit value in the first range R1) of the maximum value of the combustion amount in the first range R1 (maximum combustion amount Q1max). That is, in this case, when the control amount is less than the upper limit value in the first range R1, the control amount is the combustion amount, and when the control amount is equal to or more than the upper limit value in the first range R1, the upper limit value in the first range R1 (the maximum value of the combustion amount in the first range R1) is the combustion amount. In this case, when the combustion range of the first gas burner 2 is the first range R1, the water heater 1 can prohibit switching of the combustion range from the first range R1 to the second range R2, and further, when the calculated control amount exceeds the upper limit value in the first range R1, the combustion amount can be limited to the upper limit value in the first range R1. Furthermore, when the control amount (the sum of the feedforward control amount and the feedback control amount) exceeds the second upper limit value in the first range R1 (for example, a value of 110% of the maximum value of the combustion amount in the first range R1 (maximum combustion amount Q1max)), the controller 28 can determine a correction value based on this value (the second upper limit value in the first range R1), and can use this correction value as α _n-1 instead of FB _n-1 when calculating the combustion amount next time.

Also, for example, when the combustion range of the first gas burner 2 is the second range R2, if the above-mentioned limiting condition is satisfied, the controller 28 prohibits control to switch the combustion range from the second range R2 to the first range R1. At the same time, if the control amount (the sum of the feedforward control amount and the feedback control amount) is smaller than 100% (the lower limit value in the second range R2) of the minimum value of the combustion amount in the second range R2 (the minimum combustion amount Q2min), the controller 28 increases the feedback control amount to determine the combustion amount so that it is greater than or equal to this minimum value. That is, in this case, if the control amount is equal to or less than the lower limit value in the second range R2, the lower limit value in the second range R2 (the minimum value of the combustion amount in the second range R2) is set as the combustion amount. In this case, the water heater 1 can prohibit the combustion range of the first gas burner 2 from being switched from the second range R2 to the first range R1, and can limit the combustion amount to the lower limit value in the second range R2 when the calculated control amount falls below the lower limit value in the second range R2. Furthermore, when the control amount (the sum of the feedforward control amount and the feedback control amount) falls below the second lower limit value in the second range R2 (a value that is 90% of the minimum value of the combustion amount in the second range R2 (minimum combustion amount Q2min)), the controller 28 can determine a correction value based on this value (the second lower limit value in the second range R2), and can use this correction value as α _n-1 instead of FB _n-1 when calculating the combustion amount next time.

In this way, when the limiting condition is met and a limiting operation is performed that includes prohibiting switching of the combustion range, a control amount that would cause switching of the combustion range is not required. Therefore, the water heater 1 limits the feedback control amount so that the sum of the feedforward control amount and the feedback control amount is less than a predetermined upper limit value or exceeds a predetermined lower limit value. This makes it possible to suppress control that would cause a large change in the amount of combustion associated with switching of the combustion range.

Furthermore, if a correction value α _n-1 was calculated when the previous combustion amount was calculated, then when the current control amount is calculated, a reference control amount can be determined based on the correction value α _n-1 instead of the previous feedback control amount FB _n-1. Therefore, if the previous feedback control amount FB _n-1 obtained by calculation is a value that is determined to significantly deviate from the upper limit and lower limit values, then when calculating the current feedback control amount FB _n in calculating the current combustion amount, the previous feedback control amount FB _n-1 is not used as is, but instead the correction value α _n-1 can be used to calculate the current feedback control amount FB _n . Moreover, the correction value α _n-1 is a value obtained by "a process of calculating a correction value obtained by correcting the feedback control amount so that the control amount is equal to or less than the second upper limit value when the control amount exceeds a second upper limit value that is greater than the upper limit value, or a process of calculating a correction value obtained by correcting the feedback control amount so that the control amount is equal to or greater than the second lower limit value when the control amount falls below a second lower limit value that is smaller than the lower limit value," so that a leeway can be provided compared to the case where the control amount is restricted based on the upper limit value or the lower limit value, and it is possible to prevent the restriction value from becoming excessively excessive.

After step S14, in the following step S15, the controller 28 determines whether the outlet hot water temperature (the temperature of the hot water supplied from the hot water outlet pipe 6) detected by the outlet hot water temperature sensor 44 is stable. For example, the controller 28 determines whether the outlet hot water temperature has been maintained for 30 seconds without changing by more than ±0.5°C. If the controller 28 determines that the outlet hot water temperature is stable (Yes in step S15), it proceeds to step S16. On the other hand, if the controller 28 determines that the outlet hot water temperature is not stable (No in step S15), it proceeds to step S18, which will be described later.

In step S16, the controller 28 determines whether the following formula (2) is satisfied.
|Outlet temperature - Set temperature| > Allowable temperature difference ... (2)

That is, the controller 28 judges whether the absolute value of the difference between the hot water temperature detected by the hot water temperature sensor 44 and the set hot water temperature is greater than a predetermined allowable temperature difference. The allowable temperature difference is a predetermined fixed value, for example, 3°C. When the controller 28 judges that the above formula (2) is satisfied, the controller 28 switches the combustion range of the first gas burner 2 to a specific combustion range. For example, when the controller 28 judges that the hot water temperature is lower than the set temperature by 3°C or more, the controller 28 switches the combustion range of the first gas burner 2 from the first range R1 to the second range R2. For example, when the controller 28 judges that the hot water temperature is higher than the set temperature by 3°C or more, the controller 28 switches the combustion range of the first gas burner 2 from the second range R2 to the first range R1. After step S16, the controller 28 performs step S14 again. On the other hand, when the controller 28 judges that the above formula (2) is not satisfied, the controller 28 proceeds to step S18 described later. For example, if the controller 28 determines that the difference between the outlet hot water temperature and the set temperature is less than 3°C, it proceeds to step S18.

After starting the limiting operation in response to the establishment of the limiting condition (after step S14), the controller 28 cancels the execution of the limiting operation when the end condition (the following formula (3)) is established. First, in step S18, the controller 28 determines whether the following formula (3) is satisfied.
|Latest feedforward control amount - FFdate|>Allowable FF value change amount ... (3)

That is, the controller 28 judges whether the absolute value of the difference between the latest calculated feedforward control amount (predetermined feedforward control value) and the FFdate (corresponding to the "second data") recorded in step S13 is greater than a predetermined allowable FF value change amount (predetermined allowable change amount). The FF value change amount is, for example, the average value of the past 10 calculated FFdates (FFdates calculated in step S11). If the controller 28 judges that the above formula (3) is not satisfied, it performs step S15 again. On the other hand, if the controller 28 judges that the above formula (3) is satisfied, it performs step S19.

In step S19, the controller 28 releases the prohibition state of switching the combustion range of the first gas burner 2 set in step S14. That is, the controller 28 permits, for example, the combustion range of the first gas burner 2 to be switched from the first range R1 to the second range R2, and from the second range R2 to the first range R1. After step S19, the controller 28 performs step S11 again. Note that the control shown in FIG. 3 continues, for example, until the first gas burner 2 is extinguished.

(Effects of this configuration)
In the above-mentioned water heating device 1, as a condition for performing a limiting operation including prohibition of switching of the combustion range, it is necessary that the control amount for controlling the combustion amount of the first gas burner 2 calculated by the controller 28 satisfies a predetermined condition. Therefore, the water heating device 1 can determine whether or not to perform a limiting operation based on the control amount for controlling the combustion amount of the first gas burner 2. In addition, as a condition for performing a limiting operation, the water heating device 1 is configured to require that the combustion range is switched in a predetermined order among a plurality of ranges. Therefore, the water heating device 1 can perform a limiting operation when the combustion range is switched in a predetermined order. In this way, the water heating device 1 can grasp a state in which the occurrence of hunting can be predicted and determine whether or not to perform a limiting operation based on the control actually performed. Therefore, the water heating device 1 can more reliably suppress the occurrence of hunting.

In the above-described hot water supply device 1, the limiting condition is when the calculation result satisfies a predetermined condition, and the condition for switching the combustion range in the order of first range R1, second range R2, and first range R1 is met, or when the condition for switching in the order of second range R2, first range R1, and second range R2 is met. When the limiting condition is met, the controller 28 performs a limiting operation to prohibit switching from one of the first range R1 and the second range R2 to the other. This makes it possible to grasp a state in which the occurrence of hunting may be suspected at least between the first range R1 and the second range R2, which has a greater amount of combustion than the first range R1, and to more reliably suppress the occurrence of hunting.

In the above-mentioned water heating device 1, the restriction condition is when the condition for switching the combustion range in a predetermined order is met when the feedforward control amount satisfies a predetermined stability condition. In this way, by setting the feedforward control amount to satisfy the predetermined stability condition when it reaches a desired value, it is possible to prohibit switching of the combustion range in a state where there are few external factors such as a sudden change in the inlet water temperature.

In the above-mentioned water heating device 1, the specified stable condition is when the maximum and minimum values obtained by sampling the feedforward control amount multiple times are within a limit range that is determined based on the average value of the multiple samplings. This makes it possible to determine whether the specified stable condition is met based on the values of the multiple samplings of the feedforward control amount. Therefore, the water heating device 1 can more accurately determine whether the feedforward control amount is stable.

In the above-mentioned water heating device 1, the specified stable condition is when the sum of the feedforward control amount and the feedback control amount is within a specified range. This allows the satisfaction of the specified stable condition to be determined based on the feedback control amount of the combustion amount as well. Therefore, in a configuration that uses feedback control of the combustion amount, the water heating device 1 can more accurately determine the satisfaction of the limiting condition.

In the hot water supply device 1 described above, the controller 28 starts the limiting operation in response to the establishment of the limiting condition, and then cancels the execution of the limiting operation when the end condition is established. This makes it possible to cancel the execution of the limiting operation when the execution of the limiting operation is not necessary after the limiting operation has started. In other words, in a situation where the combustion range needs to be switched (such as when the combustion range is switched in response to a change in the set temperature), the combustion range can be appropriately switched.

As described above, in the hot water supply device 1, the controller 28 (controller) periodically and repeatedly calculates the control amount _Fn at a predetermined period, and determines the combustion amount each time the control amount _Fn is calculated. Specifically, the controller 28 (controller) calculates the control amount _Fn based on the sum of the feedforward control amount FF and the feedback control amount _FBn , and performs control to determine the combustion amount based on this control amount _Fn . When the limiting condition is not satisfied, the controller 28 (controller) sets the control amount _Fn to the combustion amount. On the other hand, when the limiting condition is satisfied, the controller 28 (controller) restricts the combustion amount so as to prevent it from exceeding the upper limit value or falling below the lower limit value. That is, when the control amount _Fn exceeds the upper limit value, the controller 28 (controller) sets the upper limit value to the combustion amount, and when the control amount _Fn falls below the lower limit value, the controller 28 (controller) sets the lower limit value to the combustion amount. More specifically, in repeatedly calculating the control amount _Fn , the controller 28 (control unit) calculates an increase/decrease value ΔFB for bringing the outlet hot water temperature To closer to the set temperature Ts according to a feedback calculation method based on the set temperature Ts and the outlet hot water temperature To, and calculates the current feedback control amount _FBn based on a value (ΔFB+FBn- ₁ ×Wper) obtained by adding a reference control amount (FBn-1×Wper) based on the previous feedback control amount FBn _-1 and the increase/decrease value _ΔFB . Thus, by using the reference control amount (FBn _{-1 ×} Wper) reflecting the previous feedback control amount FBn _-1 , and increasing or decreasing this reference control amount (FBn _-1 ×Wper) by the increase/decrease value ΔFB based on the outlet hot water temperature To, the current feedback control amount _Fn can be calculated more appropriately. Moreover, even if the combustion amount was limited in the previous determination of the combustion amount, the current feedback control amount FB n can be calculated using the previous feedback control amount FB _n-1 as long as the previous control amount F _{n-1 does} not significantly deviate from the upper limit or lower limit. This makes it possible to more appropriately calculate the current feedback control amount FB _n while preventing the previous feedback control amount FB _n-1 from being excessively limited due to the limitation on the combustion amount.

On the other hand, when the correction value α _n-1 was calculated when the previous combustion amount was calculated (i.e., when the previous control amount F _n-1 deviates from the second upper limit value that is greater than the upper limit value or the second lower limit value that is smaller than the lower limit value), the controller 28 (control unit) can determine the reference control amount based on the correction value α _{n-1 instead} of the previous feedback control amount FB _{n-1 when calculating the current control amount. In other words, when the previous feedback control amount FB n-1} obtained by calculation is a value that determines the combustion amount so that it deviates significantly from the upper limit value and the lower limit value, when calculating the current feedback control amount FB _n in calculating the current combustion amount, the previous feedback control amount FB _n-1 is not used as it is, but the correction value α _n-1 can be used instead to calculate the current feedback control amount FB _n . Moreover, the correction value α _n-1 is a value obtained by "calculating a correction value in which the feedback control amount is corrected so that the control amount is equal to or less than the second upper limit value when the control amount exceeds the second upper limit value that is greater than the upper limit value, or calculating a correction value in which the feedback control amount is corrected so that the control amount is equal to or more than the second lower limit value when the control amount falls below the second lower limit value that is less than the lower limit value", so that it is possible to prevent the limit from becoming too excessive. On the other hand, when the control amount is greater than the upper limit value and smaller than the second upper limit value when the previous combustion amount is calculated, or when the control amount is smaller than the lower limit value and larger than the second lower limit value, the reference control amount can be determined based on the previous feedback control amount when the current control amount is calculated. In other words, even when the combustion amount is limited based on the upper limit value or the lower limit value when the previous combustion amount is calculated, if the second upper limit value or the second lower limit value has not been reached, the reference control amount can be determined using the previous feedback control amount (unlimited value) in the calculation of the current control amount, rather than a limited value like the correction value, and the current feedback control amount can be calculated. Therefore, when repeatedly calculating the combustion amount, it is possible to suppress a decrease in tracking ability or responsiveness caused by repeated feedback calculations in which the "previous feedback control amount" is limited.

FIG. 5 shows an example in which the correction value is not calculated by the formula 4, and when the control amount deviates so as to exceed the upper limit, the feedback control amount is reduced to correct the control amount to the upper limit, and the corrected control amount is set as the combustion amount. When the feedback control amount is corrected in this way, the corrected feedback control amount is used as the "previous feedback control amount" when calculating the next control amount. On the other hand, FIG. 6 shows the simulation result related to the above-mentioned first embodiment. In the example of FIG. 5, when the outlet hot water temperature decreases in response to a change in the inflow water amount, the feedback calculation is performed so that the control amount is excessively suppressed as in the times Ta, Tb, and Tc of FIG. 5, so it takes time to correct the decrease in the outlet hot water temperature as in the times T11, T12, and T13. In contrast, in the example of FIG. 6 related to the first embodiment, when the outlet hot water temperature decreases in response to a change in the inflow water amount, the control amount fluctuates as in the times Tx, Ty, and Tz, but the current control amount is determined so that the previous feedback calculation value is used as is unless the control amount deviates significantly from the upper limit. Furthermore, even if the controlled variable deviates excessively from the upper limit, the correction value α _n-1 is determined with a certain margin from the upper limit, so that the controlled variable can be prevented from being excessively suppressed when calculating the current controlled variable, and specifically, the upper limit and the combustion amount match after time ta, as shown in Figure 6. This makes it possible to suppress the time required to correct the decrease in the outlet hot water temperature, such as times T21, T22, and T23.

Second Embodiment
The following description relates to the water heater 1 of the second embodiment. The water heater 1 of the second embodiment differs from the first embodiment in the condition for prohibiting switching of the combustion range of the first gas burner 2, but other configurations are the same as those of the first embodiment. Therefore, in the following description, the same configurations as those of the first embodiment will be described using the same reference numerals, and detailed description will be omitted.

(Combustion control of hot water supply device)
The following description relates to the combustion control by the water heating apparatus 1. The combustion control of the second embodiment differs from that of the first embodiment in that step S21 is added between step S12 and step S13, as shown in Fig. 4. The control shown in Fig. 4 is executed by the controller 28 in the water heating apparatus 1. The water heating apparatus 1 starts the combustion control shown in Fig. 4 by igniting the first gas burner 2 to start combustion.

Steps S11 and S12 are performed in the same manner as in the first embodiment. Step S12 is followed by step S21. The controller 28 calculates a feedback control amount for the combustion amount in the first gas burner 2 based on the set temperature and the outlet water temperature. The stable condition is when the sum of the feedforward control amount and the feedback control amount is within a predetermined range. In step S21, the controller 28 determines whether the following formula (4) is satisfied.
Lower limit value<feedforward control amount+feedback control amount<upper limit value (4) That is, it is determined whether the sum of the feedforward control amount and the feedback control amount is greater than a predetermined lower limit value and less than a predetermined upper limit value. Here, the lower limit value is a predetermined value (e.g., Q2min×90%) that is less than the minimum value (minimum combustion amount Q2min) of the second range R2. The upper limit value is a predetermined value (e.g., Q2max×110%) that is greater than the maximum value (maximum combustion amount Q1max) of the first range R1. After step S21, the controller 28 performs steps S13 to S19 in the same manner as in the first embodiment.

In the above-mentioned water heating device 1, the predetermined stable condition is when the sum of the feedforward control amount and the feedback control amount is within a predetermined range. This allows the success or failure of the predetermined stable condition to be determined based on the feedback control amount of the combustion amount as well. Therefore, in a configuration using feedback control of the combustion amount, the water heating device 1 can more accurately determine the success or failure of the limiting condition. In particular, as an additional condition, it is necessary that the combustion amount is greater than a predetermined lower limit value that is smaller than the minimum value of the second range R2 (minimum combustion amount Q2min) and smaller than a predetermined upper limit value that is greater than the maximum value of the first range R1 (maximum combustion amount Q1max). In this way, the water heating device 1 limits the combustion amount to a range between a predetermined lower limit value that is smaller than the minimum value of the second range R2 (minimum combustion amount Q2min) and a predetermined upper limit value that is greater than the maximum value of the first range R1 (maximum combustion amount Q1max). This allows the water heating device 1 to perform control that is limited to the change in the combustion range between the first range R1 and the second range R2.

<Other embodiments>
The present disclosure 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. In addition, any feature of the above or later described embodiments can be omitted unless it is clearly stated as essential. Furthermore, the above-mentioned embodiment may be modified as follows.

In the combustion control of the first embodiment described above, the controller 28 controls switching between the first range R1 and the second range R2 to prevent hunting between the first range R1 and the second range R2. However, the controller 28 may also control switching between the second range R2 and the third range R3 to prevent hunting between the second range R2 and the third range R3. This configuration can also be applied to switching between any combustion ranges, even if the first gas burner 2 of the water heater 1 is configured to have two or four or more combustion ranges.

In the above description of the first embodiment, the case where the feedforward control amount satisfies a predetermined stable condition in step S11 of the combustion control is exemplified as "a case where a predetermined condition is satisfied in the calculation of the control amount by the control unit". However, "a case where a predetermined condition is satisfied in the calculation of the control amount by the control unit" is not limited to this. For example, "a case where a predetermined condition is satisfied in the calculation of the control amount by the control unit" may be a case where a control amount (such as a feedback control amount) for controlling a combustion amount other than the feedforward control amount becomes a predetermined value. Alternatively, "a case where a predetermined condition is satisfied in the calculation of the control amount by the control unit" may be a case where the most recent multiple control amounts in step S11 are all within a predetermined range, or the absolute values of the differences between the maximum and minimum values of the most recent multiple control amounts in step S11 are all within a predetermined range, or the change in the amount of water inflow within a recent predetermined time in step S11 may be within a certain range.

In the above description of the first embodiment, in step S11 of the combustion control, formula (1) is given as an example of the stability condition. However, the stability condition is not limited to this. For example, the stability condition may be that the latest feedforward control amount is a value within a predetermined range (for example, that the difference between the latest feedforward control amount and the average value of the previous multiple feedforward control amounts is less than a certain value).

In the above description of the combustion control of the first embodiment, the release condition for the prohibition state of switching of the combustion range is exemplified in step S18. However, the release condition for the prohibition state of switching of the combustion range may be other conditions. For example, the release condition for the prohibition state of switching of the combustion range may be that the first gas burner 2 is extinguished, or that the set temperature is changed by the hot water supply remote control.
In addition, the condition for releasing the prohibition state of switching of the combustion range may be that the flow rate of water detected by the flow sensor 42 satisfies a predetermined flow rate condition (specifically, that the following formula (5) is satisfied).
Wst-D<water flow rate<Wst+D (5) where Wst is the water flow rate at the time step S14 is executed, for example, and D is the larger of Wst×20% or 1 L/min.
The condition for canceling the inhibition of switching of the combustion range may be to satisfy the following formula (6).
|Outlet temperature - Set temperature|>10℃ ... (6)

In the combustion control of the first embodiment described above, in step S15, the controller 28 determines that the outlet hot water temperature is stable if the outlet hot water temperature is maintained at a temperature that does not change by more than ±0.5°C for 30 seconds. However, the controller 28 may determine that the outlet hot water temperature is stable if 120 seconds have passed since step S14 was executed.

In the above embodiment, when the correction value α _n-1 was calculated when the previous combustion amount was calculated, the reference control amount was determined based on the correction value α _n-1 instead of the previous feedback control amount FB _n-1 when the current control amount F _n was calculated, but this determination is not necessary. Specifically, for example, the correction value α _n-1 may not be calculated, and the previous feedback control amount FB _n-1 may always be used when the current control amount F _n is calculated. Alternatively, when the combustion amount is limited so that the combustion amount is set to the upper limit when the control amount exceeds a predetermined upper limit, or the combustion amount is set to the lower limit when the control amount falls below a predetermined lower limit, the feedback control amount calculated by the feedback calculation method may be increased or decreased to limit such a combustion amount. In this method, when such a combustion amount is limited when the previous combustion amount was calculated, the feedback control amount increased or decreased when the previous combustion amount was calculated may be used when the current control amount is calculated, instead of the feedback control amount calculated by the previous feedback calculation.

In the above embodiment, the inlet water temperature sensor 41 corresponds to an example of the inlet water temperature detection unit, and the inlet water temperature is directly detected by the inlet water temperature sensor 41, but other configurations may be used as long as the inlet water temperature can be grasped. For example, the controller 28 may calculate the inlet water temperature based on the outlet water temperature detected by the outlet water temperature sensor 44, the inlet water volume detected by the flow rate sensor 42, and the combustion volume of the first gas burner 2. In this case, the outlet water temperature sensor 44 and the controller 28 correspond to an example of the inlet water temperature detection unit. If the controller 28 can grasp the inlet water volume and the combustion volume, it can estimate the flow rate of water passing through the heat exchanger 8 and the amount of heat transfer given to this water, and calculate the rising temperature of the water when passing through the heat exchanger 8. Therefore, the inlet water temperature can be calculated based on this rising temperature and the outlet water temperature. In addition, various other known methods may be used as long as the configuration can calculate the inlet water temperature.

1...Hot water supply device 2...First gas burner (gas burner)
4...water inlet pipe 6...hot water outlet pipe 28...controller (switching unit, control unit, hot water outlet temperature setting unit)
30A: First burner group 30B: Second burner group 30C: Third burner group 35A, 35B, 35C: Switching gas solenoid valve (combustion amount adjustment unit)
41...Inlet water temperature sensor (inlet water temperature detection unit)
42...Flow rate sensor (flow rate detection unit)
44...Outlet hot water temperature sensor (outlet hot water temperature detection unit)

Claims (10)

A hot water supply device having a gas burner with a plurality of ranges defined as a gas combustion range,
A water inlet pipe into which water flows from the outside of the hot water supply device;
A hot water outlet pipe that flows hot water to the outside of the hot water supply device;
A flow rate detection unit that detects an inlet water flow rate, which is the flow rate of water flowing through the water inlet pipe;
an inlet water temperature detection unit for detecting an inlet water temperature, which is the temperature of water flowing through the water inlet pipe;
A hot water outlet temperature detection unit detects a hot water outlet temperature, which is the temperature of the hot water flowing through the hot water outlet pipe;
A hot water outlet temperature setting unit that sets the temperature of the hot water flowing through the hot water outlet pipe;
a control unit that calculates a control amount for determining a combustion amount of the gas burner based on the inlet water flow rate, the inlet water temperature, a set temperature set by the outlet water temperature setting unit, and the outlet water temperature;
a switching unit that switches a combustion range of the gas in the gas burner to one of the plurality of ranges based on a calculation result by the control unit;
Equipped with
The switching unit performs a limiting operation including prohibiting switching of the combustion range of the gas when a predetermined limiting condition is satisfied,
The water heating apparatus, wherein the limiting condition is a case where a predetermined condition is satisfied in the calculation of the control amount by the control unit, and a condition for switching the combustion range among the plurality of ranges in a predetermined order is established. The plurality of ranges includes at least a first range and a second range that is wider than the first range,
the limiting condition includes a case where, when the calculation result satisfies the predetermined condition, a condition for switching the combustion range of the gas in the gas burner from the first range to the second range to the first range in that order is satisfied, or a condition for switching from the second range to the first range to the second range in that order is satisfied,
The hot water supply device according to claim 1 , wherein the switching unit performs the limiting operation to prohibit switching from one of the first range and the second range to the other when the limiting condition is met. The control unit is
calculating a feedforward control amount based on the inlet water flow rate, the inlet water temperature, and the set temperature, calculating a feedback control amount based on the set temperature and the outlet hot water temperature, and calculating the control amount based on the sum of the feedforward control amount and the feedback control amount;
3. The hot water supply device according to claim 1, wherein, when the limiting condition is satisfied, the combustion amount is limited so that the combustion amount is set to the upper limit value when the control amount exceeds a predetermined upper limit value, or the combustion amount is set to the lower limit value when the control amount is below a predetermined lower limit value. The control unit is
The calculation of the control amount is repeated, and the combustion amount is determined each time the control amount is calculated;
The water heating device of claim 3, wherein when the restriction condition is met and the current control amount is calculated, an increase/decrease value for bringing the outlet temperature closer to the set temperature is calculated based on the difference between the set temperature and the outlet temperature in accordance with a predetermined feedback calculation method, and even if the combustion amount was restricted in the previous determination of the combustion amount, the current feedback control amount is calculated based on the sum of a standard control amount based on the previous feedback control amount and the increase/decrease value. A hot water supply device having a gas burner with a plurality of ranges defined as a gas combustion range,
A water inlet pipe into which water flows from the outside of the hot water supply device;
A hot water outlet pipe that flows hot water to the outside of the hot water supply device;
A flow rate detection unit that detects an inlet water flow rate, which is the flow rate of water flowing through the water inlet pipe;
an inlet water temperature detection unit for detecting an inlet water temperature, which is the temperature of water flowing through the water inlet pipe;
A hot water outlet temperature detection unit detects a hot water outlet temperature, which is the temperature of the hot water flowing through the hot water outlet pipe;
A hot water outlet temperature setting unit that sets the temperature of the hot water flowing through the hot water outlet pipe;
a control unit that calculates a feedforward control amount based on the inlet water flow rate, the inlet water temperature, and a set temperature set by the outlet water temperature setting unit, calculates a feedback control amount according to a predetermined feedback calculation method, and calculates a control amount for determining a combustion amount in the gas burner based on the sum of the feedforward control amount and the feedback control amount;
Equipped with
The control unit is
The calculation of the control amount is repeated, and the combustion amount is determined each time the control amount is calculated;
When a predetermined limiting condition is established, the combustion amount is limited so that the combustion amount is set to the upper limit value when the control amount exceeds a predetermined upper limit value, or the combustion amount is set to the lower limit value when the control amount is below a predetermined lower limit value;
This water heating device calculates the current control amount when the restriction condition is met, based on the set temperature and the hot water outlet temperature, an increase or decrease value for bringing the hot water outlet temperature closer to the set temperature in accordance with the feedback calculation method, and even if the combustion amount was limited in the previous determination of the combustion amount, the current feedback control amount is calculated based on the value obtained by adding a standard control amount based on the previous feedback control amount and the increase or decrease value. When the limiting condition is satisfied, a process of calculating a correction value by correcting the feedback control amount so that the control amount is equal to or less than the second upper limit value when the control amount exceeds a second upper limit value that is greater than the upper limit value, or a process of calculating a correction value by correcting the feedback control amount so that the control amount is equal to or more than the second lower limit value when the control amount falls below a second lower limit value that is smaller than the lower limit value,
When the correction value is calculated in the previous calculation of the combustion amount, the reference control amount is determined based on the correction value in place of the previous feedback control amount in the current calculation of the control amount;
6. The water heating device of claim 4, wherein when the control amount was greater than the upper limit value and smaller than the second upper limit value when the combustion amount was calculated last time, or when the control amount was smaller than the lower limit value and greater than the second lower limit value, when the control amount is calculated this time, the standard control amount is determined based on the previous feedback control amount. the control unit calculates a feedforward control amount of a combustion amount in the gas burner based on the inlet water flow rate, the inlet water temperature, and the set temperature,
The hot water supply apparatus according to claim 1 , wherein the restriction condition includes a condition that the feedforward controlled variable satisfies a predetermined stability condition. The hot water supply device according to claim 7 , wherein the predetermined stability condition is that an absolute value of a difference between a maximum value and a minimum value when the control unit calculates the feedforward control amount a plurality of times falls within a limited range. The control unit calculates a feedback control amount of a combustion amount in the gas burner based on the set temperature and the tap temperature,
The hot water supply apparatus according to claim 7 or 8, wherein the predetermined stability condition includes a condition that a sum of the feedforward control amount and the feedback control amount is within a predetermined range. The hot water supply device according to claim 1 or 2, wherein the switching unit starts the limiting operation in response to satisfaction of the limiting condition, and then cancels the execution of the limiting operation when an end condition is satisfied.

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