COMBUSTION APPARATUS

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Japan application serial no. 2020-124994, filed on Jul. 22, 2020. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND
Technical Field

The disclosure relates to a combustion apparatus.

Description of Related Art

Japanese Patent Laid-Open No. H09-170813A (Patent Document 1) discloses a forced air supply type hot water dispenser including a gas burner, a heat exchanger that is heated by the gas burner to convert cold water into hot water, and an air supply fan that supplies combustion air for the gas burner to a combustion chamber. In Patent Document 1, after the hot water supply is stopped, the air supply fan is continuously operated for a certain period of time to perform post-purge. As a result, post-boiling due to the temperature rise around the heat exchanger after the hot water supply is stopped is suppressed, and unexpected high-temperature water is prevented from being output when the hot water is re-supplied during intermittent use.

RELATED ART
Patent Document

[Patent Document 1] Japanese Patent Laid-open No. H09-170813A

SUMMARY
Technical Problem

However, during the application of intermittent combustion with repeated combustion and non-combustion periods of the burner, while performing the post-purge described above each time the combustion period is ended can prevent unexpected high-temperature hot water from being output when the next combustion period starts, the temperature drop of hot water is accelerated by cooling the heat exchanger after the combustion is stopped, so the non-combustion period until the start of the next combustion period may be shortened. As a result, the cycle length corresponding to the sum of each combustion period and non-combustion period is shortened, and the ignition and extinguishing of the burner are frequently repeated.

Since thermal stress is frequently applied to equipment such as the heat exchanger when the burner is ignited and extinguished, there is a concern that fatigue failure of the equipment will be increased and a problem will occur in the equipment durability.

The disclosure has been made to solve such a problem, and the disclosure provides a combustion apparatus capable of suppressing frequent switching between a combustion period and a non-combustion period when intermittent combustion is applied.

Solution to the Problem

According to an aspect of the disclosure, a combustion apparatus includes a combustion part for burning a fuel, a blower fan that blows an air to the combustion part, an ignition device for igniting the combustion part, and a control part that controls operations of the combustion part, the blower fan, and the ignition device. The control part is configured to selectively perform a continuous combustion in which the combustion part is operated to burn continuously and an intermittent combustion in which a combustion period and a non-combustion period of the combustion part are repeatedly provided. When the continuous combustion is stopped, the control part extinguishes the combustion part and operates the blower fan to perform a scavenging operation. When the combustion period in the intermittent combustion is ended, the control part extinguishes the combustion part and operates the blower fan to perform a scavenging operation in the non-combustion period. A total air blowing amount of the blower fan in the scavenging operation during the non-combustion period is set to be less than a total air blowing amount of the blower fan in the scavenging operation when the continuous combustion is stopped.

Effects

According to the disclosure, it is possible to provide a combustion apparatus capable of suppressing frequent switching between a combustion period and a non-combustion period when intermittent combustion is applied.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of a hot water supplier to which a combustion apparatus according to an embodiment of the disclosure is applied.

FIG. 2 is a mode transition diagram of the hot water supplier.

FIG. 3 is a functional block diagram of the temperature control in the combustion mode of the hot water supplier by the controller.

FIG. 4 is a conceptual diagram showing an example of the basic control operation in the intermittent combustion.

FIG. 5 is a flowchart for explaining the scavenging operation when the transition from the continuous combustion to the combustion standby mode is performed.

FIG. 6 is a diagram for explaining the scavenging operation when the transition from the continuous combustion to the combustion standby mode is performed.

FIG. 7 is a flowchart for explaining an embodiment of the scavenging operation in the intermittent combustion.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the disclosure will be described in detail with reference to the drawings. Further, in the following, the same or corresponding parts in the drawings will be designated by the same reference numerals, and the descriptions will not be repeated in principle.

[Configuration of Hot Water Supplier]

FIG. 1 is a schematic configuration diagram of a hot water supplier to which a combustion apparatus according to an embodiment of the disclosure is applied.

With reference to FIG. 1, a hot water supplier 100 includes a combustion can body 25 (hereinafter also simply referred to as the “can body”) in which a heat exchanger 39, a burner 31 and the like are housed, a gas valve 30, a blower fan 36, a venturi mixer 38, a water inlet pipe 50, a can body pipe 52, a hot water outlet pipe 54, a bypass valve 60, and a controller 80.

The water inlet pipe 50 is connected to the can body pipe 52 and a bypass pipe 58 via the bypass valve 60. Low temperature water such as tap water is supplied to the water inlet pipe 50. The low-temperature water in the water inlet pipe 50 is distributed to the can body pipe 52 and the bypass pipe 58 via the bypass valve 60.

The can body pipe 52 is connected to the heat exchanger 39. Low-temperature water introduced from the water inlet pipe 50 into the can body pipe 52 is heated by passing through the heat exchanger 39 by the heat amount generated by the burner 31.

The gas valve 30 is disposed in a gas supply pipe to the burner 31. Though not shown, the gas valve 30 includes a solenoid valve having a function of turning on and off the supply of fuel gas to the burner 31 and a gas proportional valve that controls the gas flow rate of the gas supply pipe according to the opening degree. The heat amount generated by the burner 31 can be controlled by the gas flow rate of the gas supply pipe.

The burner 31 is configured to be capable of controlling the heat amount generated not only by adjusting the gas flow rate but also by switching control of the number of combustion capacity stages (hereinafter also simply referred to as “the number of combustion stages”). Though not shown, the burner 31 has a plurality of combustion nozzles capable of individually supplying fuel by a gas on-off switching valve (capacity switching valve). The number of combustion nozzles to be operated for combustion can be selectively changed and adjusted by controlling and switching the on and off of each capacity switching valve by the controller 80. For example, a plurality of combustion nozzles are divided into a plurality of groups, and fuel gas can be selectively supplied to the plurality of groups by the on-off switching of the capacity switching valve. As a result, the number of combustion stages can be switched to a plurality of stages. In addition, the heat amount generated can be varied by varying the flow rate of gas supplied to the combustion nozzles of each stage. By continuous variable control of the generation capacity, the heating capacity of the combustion apparatus can be varied. The burner 31 corresponds to an embodiment of the “combustion part.”

The venturi mixer 38 mixes the fuel gas supplied from the gas supply pipe with the combustion air. Hereinafter, the fuel gas mixed with the combustion air is also referred to as the “mixed gas.” The mixed gas is supplied to the burner 31 by the blower fan 36 via a mixing chamber 34.

The air blowing amount of the blower fan 36 is controlled so that the air-fuel ratio with the amount of gas supplied from the burner 31 as a whole becomes a predetermined value (for example, the stoichiometric air-fuel ratio). Since the air blowing amount of the blower fan 36 is proportional to the fan rotation speed, the rotation speed of the blower fan 36 is controlled according to the target rotation speed set according to the change in the supply gas amount. The blower fan 36 is provided with a rotation speed sensor 37 for detecting the fan rotation speed.

When an ignition device 32 is operated by the controller 80, a high frequency voltage is applied to a spark plug 33 to generate a spark in the spark plug 33. When the mixed gas is ignited by this spark, the fuel gas is burned and a flame is generated. A flame detection device 35 is configured by a thermocouple or the like for detecting a flame. The controller 80 detects that the burner 31 has been ignited by comparing the output voltage of the thermocouple with a threshold value.

The combustion heat generated by the flame of the burner 31 is provided to the heat exchanger 39 in the can body 25. The heat exchanger 39 heats the passing low-temperature water by heat exchange with the combustion heat. As a result, high-temperature water heated by the heat exchanger 39 is output to the hot water outlet pipe 54. An exhaust duct 40 for discharging the exhaust gas after combustion is provided on the downstream side of the can body 25 in the flow direction of the combustion gas.

The bypass pipe 58 and the hot water outlet pipe 54 are connected at a confluence point 56. Therefore, from the hot water supplier 100, hot water at an appropriate temperature adjusted by mixing the high-temperature water output from the can body 25 and the low-temperature water from the bypass pipe 58 is supplied to a hot water tap 70 or a predetermined hot water supply destination such as a bath pouring circuit (not shown).

The bypass valve 60 controls the ratio of the flow rate of the can body pipe 52 to the flow rate of the bypass pipe 58 by controlling the valve opening degree according to a control command from the controller 80. The flow rate ratio k of the bypass valve 60 is defined by k=q2/q1 by using the ratio of the can body flow rate q1 from the water inlet pipe 50 to the can body pipe 52 to the bypass flow rate q2 from the water inlet pipe 50 to the bypass pipe 58. The controller 80 has acquired a correspondence relationship between the opening degree of the bypass valve 60 and the flow rate ratio k in advance and, in the outlet hot water temperature control described later, sets the opening degree of the bypass valve 60 for realizing the desired flow rate ratio k by using the correspondence relationship.

A temperature sensor 62 is disposed in the can body pipe 52 and detects the temperature of the low-temperature water (hereinafter also referred to as the “inlet water temperature Tw”). A temperature sensor 64 is disposed in a section on the upstream side (the heat exchanger 39 side) of the hot water outlet pipe 54 with respect to the confluence point 56 and detects the temperature of the high-temperature water (hereinafter also referred to as the “can body temperature Tb”). A temperature sensor 66 is disposed in a section on the downstream side of the hot water outlet pipe 54 with respect to the confluence point 56 and detects the outlet hot water temperature Th after the high-temperature water and the low-temperature water is mixed. A flow rate sensor 68 is disposed in the can body pipe 52 and detects the can body flow rate q1.

The controller 80 can be configured by, for example, a microcomputer. The controller 80 receives a detection value of each sensor and a user operation and generates a control command to each device in order to control the overall operation of the hot water supplier 100. The user operation includes an operation on/off command for the hot water supplier 100 and a command for the set value of the outlet hot water temperature (outlet hot water target temperature Tr*), which are input by operating an operation switch provided on a remote controller (not shown).

[Operation Mode of Hot Water Supplier]

FIG. 2 is a mode transition diagram of the hot water supplier 100.

As shown in FIG. 2, the operation mode of the hot water supplier 100 includes an “operation off mode,” an “operation on mode,” and a “combustion mode.” The operation off mode corresponds to the power off state of the hot water supplier 100. When the operation switch (SW) is turned on in the operation off mode, the hot water supplier 100 transitions to the operation on mode.

In the operation on mode, the fuel supply to the burner 31 is cut off, and the combustion of the burner 31 is continuously stopped. In this state, combustion stands by until the minimum operating flow rate (MOQ) is detected. Hereinafter, the state in which the flow rate in the hot water supplier 100 exceeds the MOQ is also referred to as the “MOQ on,” and the state in which the flow rate does not exceed the MOQ is also referred to as the “MOQ off.”

When the MOQ on is detected in the operation on mode, the combustion mode is started. In the combustion mode, the gas valve 30 is opened and fuel gas is supplied to the burner 31. Hereinafter, the operation on mode is also referred to as the “combustion standby mode.”

In the combustion mode, a required heat generation amount Qrq for the burner 31 is set by the temperature control for controlling the outlet hot water temperature Th to the outlet hot water target temperature Tr*, and the operation state (the number of combustion stages and the gas flow rate) of the burner 31 is controlled according to the required heat generation amount Qrq. In the temperature control of the combustion mode, one of “continuous combustion,” in which the combustion period of the burner 31 is continuously provided, and “intermittent combustion,” in which the combustion period and the non-combustion period of the burner 31 are repeatedly provided, is applied. The temperature control in the combustion mode will be described later.

In the combustion mode, when the MOQ off is detected, the operation mode transitions to the operation on mode (the combustion standby mode). As a result, the combustion of the burner 31 is continuously stopped.

When the operation SW is turned off in the combustion standby mode or the combustion mode, the hot water supplier 100 transitions to the operation off mode. When the operation SW is turned off in the combustion mode, the combustion of the burner 31 is also stopped.

[Temperature Control in Combustion Mode]

FIG. 3 is a functional block diagram of the temperature control in the combustion mode of the hot water supplier 100 by the controller 80. The function of each block in FIG. 3 can be realized by software processing in which the controller 80 executes a program stored in advance. Alternatively, it is also possible to realize a part or all of each block by hardware processing using a dedicated electronic circuit.

With reference to FIG. 3, the controller 80 has a can body temperature control part 810 and a flow rate ratio control part 820. The can body temperature control part 810 includes a required heat amount calculation part 812, a burner control part 814, and a fan control part 816.

The required heat amount calculation part 812 calculates the required heat generation amount Qrq for the burner 31 based on the can body flow rate q1 (the flow rate sensor 68), the inlet water temperature Tw (the temperature sensor 62), the can body temperature Tb (the temperature sensor 64), and the target temperature Tb* of the can body temperature Tb.

The burner control part 814 determines the operation state (the number of combustion stages, the gas flow rate and the like) of the burner 31 for controlling the heat amount generated by the burner 31 according to the required heat generation amount Qrq from the required heat amount calculation part 812. Then, a control command to the burner 31 and the gas valve 30 is generated according to the determined operation state of the burner 31. Further, the burner control part 814 determines the target fan rotation speed Fr* of the blower fan 36 according to the determined operation state of the burner 31.

The fan control part 816 sets the target fan rotation speed Fr* of the blower fan 36 according to the required heat generation amount Qrq from the burner control part 814. Then, a control command to the blower fan 36 is generated according to the set target fan rotation speed Fr*.

The flow rate ratio control part 820 generates a control command to the bypass valve 60 for controlling the outlet hot water temperature Th to the outlet hot water target temperature Tr* based on the outlet hot water target temperature Tr* and the temperature (Tb, Th, Tw) detected by the temperature sensors 62 to 66.

With reference back to FIG. 2, in the combustion mode, the burner 31 generates a heat amount according to the required heat generation amount Qrq by selectively applying the continuous combustion and the intermittent combustion.

When the combustion standby mode is transitioned to the combustion mode, the ignition control of the burner 31 is first performed. In the ignition control, the burner 31 is ignited by operating the ignition device 32 in a state where the gas valve 30 is controlled according to a predetermined ignition condition. When the ignition of the burner 31 is detected based on the output of the flame detection device 35, the continuous combustion or the intermittent combustion is started depending on the magnitude of the required heat generation amount Qrq.

In the continuous combustion, the burner 31 is operated to burn continuously in an operation state set according to the required heat generation amount Qrq. The maximum heat generation amount in the continuous combustion is the heat generation amount in a state where the number of combustion stages is maximized and the gas flow rate is maximized. In addition, the minimum heat generation amount Q1 in the continuous combustion corresponds to the heat generation amount when the number of combustion stages is minimized and the gas flow rate is set to the lower limit value at which a stable combustion state can be ensured. That is, the minimum heat generation amount Q1 corresponds to the lower limit value of the heat generation amount range in the continuous combustion.

Therefore, the burner control part 814 controls the burner 31 so that the continuous combustion is applied when the required heat generation amount Qrq is greater than or equal to Q1, while the intermittent combustion is applied when the required heat generation amount Qrq is less than Q1. In this way, it is possible to deal with even the case where the required heat generation amount Qrq is less than Q1. Therefore, when Qrq <Q1 after the ignition control or during the continuous combustion, the intermittent combustion is applied, and the combustion mode is continued.

In the intermittent combustion, the combustion of the burner 31 in the operation state that generates the minimum heat generation amount Q1 is intermittently performed. That is, the burner 31 is extinguished and reignited so that a combustion period Ton for generating the minimum heat generation amount Q1 and a non-combustion period Toff in which the combustion is temporarily stopped are repeatedly provided.

When the required heat generation amount Qrq rises during the intermittent combustion and Qrq>Q1* is established, the transition from the intermittent combustion to the continuous combustion is performed. The determination value Q1* at this time is preferably set greater than Q1 in order to avoid hunting.

On the other hand, during the intermittent combustion, when the required heat generation amount Qrq further decreases and becomes less than a predetermined lower limit value Q2, the combustion mode is ended and the transition to the combustion standby mode is performed.

Further, in each of the continuous combustion and the intermittent combustion, the transition to the combustion standby mode is performed also when the MOQ off is detected. After the transition to the combustion standby mode, the combustion of the burner 31 is stopped until the combustion mode is started again.

FIG. 4 is a conceptual diagram showing an example of the basic control operation in the intermittent combustion.

With reference to FIG. 4, during the intermittent combustion, the combustion period (corresponding to Ton in the figure) and the non-combustion period (corresponding to Toff in the figure) are switched according to the comparison between the can body temperature Tb (the temperature sensor 64) and the target temperature range of the can body temperature Tb. The upper limit value TH of the target temperature range of the can body temperature Tb is set to a temperature α ° C. higher than the target temperature Tb* in the temperature control (TH=Tb*+α). The lower limit value TL of the target temperature range is set to a temperature β° C. lower than the target temperature Tb* (TL=Tb*−β). α and β are constants. Further, α and β may have the same value or different values.

In the operation example of FIG. 4, at the time t1 during the combustion period, in response to the case where Tb>TH, the burner 31 is extinguished, and the non-combustion period is started. When the non-combustion period is started, the combustion of the burner 31 is stopped, so that the can body temperature Tb gradually decreases. At the time t3 during this non-combustion period, when Tb<TL, the combustion period is started, and the burner 31 is reignited. After that, the non-combustion period is started at the time t5 and the time t7 when Tb>TH, while the combustion period is started at the time t6 and the time t8 when Tb<TL.

In this way, the combustion period and the non-combustion period of the burner 31 are repeatedly provided in accordance with the transition of the can body temperature Tb.

As shown in FIG. 4, during the application of the intermittent combustion, at the start of the combustion period, an ignition operation for reigniting the burner 31 is performed. When the ignition operation is started, the burner control part 814 (FIG. 3) operates the ignition device 32. The ignition device 32 applies a high frequency voltage to the spark plug 33. When the high frequency voltage is applied, a spark is generated in the spark plug 33, and this spark ignites the mixed gas from the burner 31 to ignite the burner 31. When the burner control part 814 detects that the burner 31 has been ignited based on the comparison between the output voltage from the flame detection device 35 and the threshold value, the burner control part 814 stops the ignition device 32 and transitions from the ignition operation to the combustion operation.

Further, if the ignition is not detected within a predetermined set time, the burner control part 814 stops the ignition device 32 and then re-operates the ignition device 32. The burner control part 814 repeatedly operates the ignition device 32 until the ignition is detected. In the case where the ignition is not detected and it cannot be transitioned to the combustion operation even after the operation is repeated for a predetermined number of times, the burner control part 814 ends the ignition operation. In this case, the hot water supplier 100 transitions from the combustion mode to the combustion standby mode.

At the start of the non-combustion period, after extinguishing the burner 31, a scavenging operation is performed for discharging (scavenging) the combustion exhaust gas and the unburned mixed gas lingering in the vicinity of the burner 31 through the exhaust duct 40. When the scavenging operation is started, the fan control part 816 (FIG. 3) operates the blower fan 36. Effective scavenging can be performed by increasing the rotation speed of the blower fan 36 during the scavenging operation to be greater than the fan rotation speed during the ignition operation and the combustion operation.

Further, the scavenging operation is performed even after the combustion of the burner 31 is stopped when the hot water supplier 100 transitions from the combustion mode to the combustion standby mode. That is, the scavenging operation is performed when the MOQ off is detected in the continuous combustion and the transition to the combustion standby mode is performed.

FIG. 5 is a flowchart for explaining the scavenging operation when the transition from the continuous combustion to the combustion standby mode is performed. The control process according to the flowchart shown in FIG. 5 can be performed by the controller 80 during the application of the continuous combustion.

With reference to FIG. 5, the controller 80 determines in step S01 whether the continuous combustion is in progress. When the continuous combustion is in progress (when YES is determined in S01), the controller 80 determines in step S02 whether the MOQ off is detected. When the continuous combustion is not in progress (when NO is determined in S01), the controller 80 does not perform the process after S02.

When the MOQ off is detected during the continuous combustion (when YES is determined in S02), the controller 80 proceeds the process to S03, extinguishes the burner 31, and stops the combustion of the burner 31. Subsequently, the controller 80 proceeds the process to steps S04 to S08 to perform the scavenging operation in accordance with the predetermined scavenging condition. The scavenging condition includes a condition that defines the rotation speed of the blower fan 36 and the operation time of the blower fan 36.

FIG. 6 is a diagram for explaining the scavenging operation when the transition from the continuous combustion to the combustion standby mode is performed. FIG. 6 shows an example of the fan rotation speed Fc and the operation time Ts of the blower fan 36 during the scavenging operation.

With reference to FIG. 6, the scavenging operation includes a first scavenging operation and a second scavenging operation. In the first scavenging operation, the blower fan 36 is operated at a fan rotation speed Fc1 for a time Ts1. The fan rotation speed Fc1 is, for example, 6000 rpm, and the operation time Ts1 is, for example, 5 seconds. In the second scavenging operation, the blower fan 36 is operated at a fan rotation speed Fc2 for a time Ts2. The fan rotation speed Fc2 is, for example, 3000 rpm, and the operation time Ts2 is, for example, 30 seconds. In the example of FIG. 6, it is set that Fc1>Fc2 and Ts1<Ts2, but the magnitude relationship between Fc1 and Fc2 and the magnitude relationship between Ts1 and Ts2 are not limited to thereto.

The first scavenging operation is mainly performed for discharging the combustion exhaust gas and the unburned mixed gas lingering in the vicinity of the burner 31. In particular, this is because if the unburned mixed gas lingers, when the burner 31 is reignited, a flame propagates through this mixed gas, which may cause a phenomenon of explosive ignition with loud noise, the so-called explosive welding. The fan rotation speed Fc1 of the first scavenging operation is preferably set to be greater than the fan rotation speed during the continuous combustion in order to efficiently discharge the combustion exhaust gas and the unburned mixed gas.

The second scavenging operation is mainly performed for removing the residual heat of the heat exchanger 39 and the like after the combustion is stopped, and for discharging air with moist present in the can body 25. That is, the second scavenging operation corresponds to the post-purge. By performing the post-purge, it is possible to suppress post-boiling due to the residual heat of the heat exchanger 39 after the combustion is stopped, and to prevent temporary high-temperature water from being provided when hot water is re-delivered.

As described above, since the second scavenging operation does not aim at discharging the lingering gas as in the first scavenging operation, the fan rotation speed Fc2 may be set to be less than or equal to the fan rotation speed Fc1 of the first scavenging operation. Further, unlike the first scavenging operation, the second scavenging operation mainly aims at cooling the heat exchanger 39 and the like. Therefore, the operation time Ts2 may be set longer than the operation time Ts1 of the first scavenging operation in consideration of the heat capacity of the heat exchanger 39 and the like.

With reference back to FIG. 5, when the scavenging operation is started, the controller 80 first performs the first scavenging operation in step S04. In step S04, the controller 80 sets the target fan rotation speed Fr* of the blower fan 36 to Fc1, and controls the blower fan 36 so that the fan rotation speed Fc detected by the rotation speed sensor 37 matches the target fan rotation speed Fr*. Further, when the first scavenging operation is started, the controller 80 activates a timer to start measuring the operation time of the first scavenging operation. Assuming the timer value Ts=0 at the start of the first scavenging operation, the timer value Ts is automatically increased according to the operation time.

During the first scavenging operation, the controller 80 compares the timer value Ts with the preset operation time Ts1 in step S05. When Ts<Ts1 (when NO is determined in S05), the controller 80 returns to S04 and continues the first scavenging operation. As a result, the first scavenging operation is continuously performed until the timer value Ts reaches Ts1.

When the timer value Ts reaches the operation time Ts1 (when YES is determined in S05), the controller 80 ends the first scavenging operation and clears the timer value Ts. Further, the controller 80 proceeds the process to step S06 and performs the second scavenging operation. In step S06, the controller 80 sets the target fan rotation speed Fr* of the blower fan 36 to Fc2, and controls the blower fan 36 so that the fan rotation speed Fc detected by the rotation speed sensor 37 matches the target fan rotation speed Fr*. Further, when the second scavenging operation is started, the controller 80 re-activates the timer and starts measuring the operation time of the second scavenging operation. Assuming the timer value Ts=0 at the start of the second scavenging operation, the timer value Ts is automatically increased according to the operation time.

During the second scavenging operation, the controller 80 compares the timer value Ts with the preset operation time Ts2 in step S07. When Ts<Ts2 (when NO is determined in S07), the controller 80 returns to S06 and continues the second scavenging operation. As a result, the second scavenging operation is continuously performed until the timer value Ts reaches Ts2.

When the timer value Ts reaches the operation time Ts2 (when YES is determined in S07), the controller 80 ends the scavenging operation in step S08 and clears the timer value Ts. Further, the controller 80 proceeds the process to step S09 and ends the continuous combustion. As a result, the transition to the combustion standby mode is performed, and the combustion of the burner 31 is continuously stopped.

As described above, by performing the scavenging operation after the burner 31 is extinguished, it is possible to prevent the occurrence of explosive welding when the burner 31 is reignited and to suppress the post-boiling in the heat exchanger 39 after the combustion is stopped.

However, if it is configured that the above-described scavenging operation is performed every time the combustion period is ended during the application of the intermittent combustion, though it is possible to prevent the occurrence of explosive welding when the next combustion period starts, during the non-combustion period, there is a concern that the heat exchanger 39 after the combustion is stopped is unnecessarily cooled. Since the low-temperature water keeps passing through the heat exchanger 39 even during the non-combustion period, the occurrence of post-boiling in the heat exchanger 39 is suppressed.

According to this, in the operation example shown in FIG. 4, the decrease of the can body temperature Tb during the non-combustion period is accelerated, and as a result, the elapsed time from the start of the non-combustion period to the time when Tb<TL (time Toff in FIG. 4) is shortened. Then, as the non-combustion period is shortened, the cycle length (Ton+Toff) corresponding to the sum of each combustion period and non-combustion period is also shortened.

When the cycle length in the intermittent combustion is shortened, since the combustion period and the non-combustion period are frequently switched, the number of ignitions of the burner 31 increases. As a result, thermal stress is frequently applied to equipment such as the heat exchanger 39 as the burner 31 is repeatedly ignited and extinguished, which may increase fatigue failure of the equipment and cause a problem in the equipment durability. In addition, there is a concern that the consumption of fuel gas may increase due to unnecessary combustion of the burner 31. Therefore, it is necessary to suppress the cooling of the heat exchanger 39 during the non-combustion period and suppress the shortening of the non-combustion period.

Therefore, in the combustion apparatus according to the embodiment, the scavenging operation performed during the non-combustion period of the intermittent combustion is configured to reduce the total air blowing amount, which is the total value of the air blowing amount of the blower fan 36, compared with the scavenging operation performed when the continuous combustion is stopped.

Specifically, the total air blowing amount of the blower fan 36 can be estimated by multiplying the air blowing amount per unit time of the blower fan 36 and the operation time of the blower fan 36. Further, since the air blowing amount per unit time of the blower fan 36 is proportional to the fan rotation speed, in the following description, the total air blowing amount shall be calculated by the product of the fan rotation speed and the operation time of the blower fan 36 (the fan rotation speed×the operation time).

In the operation example of FIG. 6, the total air blowing amount in the first scavenging operation is indicated by the product (Fc1×Ts1) of the fan rotation speed Fc1 and the operation time Ts1. The total air blowing amount in the second scavenging operation is indicated by the product of the fan rotation speed Fc2 and the operation time Ts2 (Fc2×Ts2). Further, the total air blowing amount of the scavenging operation performed when the normal combustion is stopped can be indicated by the total value (Fc1×Ts1+Fc2×Ts2) of the total air blowing amount of the first scavenging operation (Fc1×Ts1) and the total air blowing amount of the second scavenging operation (Fc2×Ts2).

On the other hand, the total air blowing amount in the scavenging operation during the non-combustion period is set to a value less than the above-described total value (Fc1×Ts1+Fc2×Ts2). The hatched region in FIG. 6 illustrates the scavenging operation during the non-combustion period. In the example of FIG. 6, the blower fan 36 is operated at the fan rotation speed Fc2 for a time Ts1 #during the non-combustion period. This time Ts1 #is longer than Ts1 and shorter than Ts2 (Ts1<Ts1 #<Ts2). The area of the hatched region in FIG. 6 corresponds to the total air blowing amount in the scavenging operation during the non-combustion period.

As described above, during the non-combustion period, the cooling of the heat exchanger 39 can be suppressed by reducing the total air blowing amount of the blower fan 36 as compared with the case after the continuous combustion is stopped. Therefore, the rate of decrease of the can body temperature Tb during the non-combustion period can be slow, and the shortening of the non-combustion period can be suppressed. As a result, since it is possible to prevent frequent switching between the combustion period and the non-combustion period, the equipment durability can be improved, and wasteful consumption of fuel gas can be suppressed.

Further, during the application of the intermittent combustion, since the fluctuation cycle of the can body temperature Tb becomes longer as the cycle length (Ton+Toff) corresponding to the sum of each combustion period and non-combustion period becomes longer, the stability of the outlet hot water temperature Th can be improved.

However, even in the scavenging operation during the non-combustion period, it is necessary to ensure the prevention of explosive welding when the burner 31 is reignited. Therefore, the total air blowing amount in the scavenging operation during the non-combustion period is at least greater than or equal to the total air blowing amount in the first scavenging operation (Fc1×Ts1).

For such an embodiment, it is possible to exemplify a configuration in which only the first scavenging operation shown in FIG. 6 is performed and the second scavenging operation is not performed during the non-combustion period. According to this, when the combustion period is ended during the application of the intermittent combustion and the burner 31 is extinguished for the start of the non-combustion period, the controller 80 operates the blower fan 36 at the fan rotation speed Fc1 for the time Ts1, and then stops the blower fan 36.

FIG. 7 is a flowchart for explaining an embodiment of the scavenging operation in the intermittent combustion. The control process according to the flowchart shown in FIG. 7 can be performed by the controller 80 during the application of the intermittent combustion.

Further, in the flowchart shown in FIG. 7, the process of steps S02 to S08 shows the control process when transitioning from the intermittent combustion to the combustion standby mode, and is the same as the control process when transitioning from the continuous combustion to the combustion standby mode shown in FIG. 5. Therefore, the description of the process of S02 to S08 will be omitted.

With reference to FIG. 7, the controller 80 determines in step S01A whether the intermittent combustion is in progress. When the intermittent combustion is not in progress (when NO is determined in S01A), the controller 80 does not perform the process after S02.

On the other hand, when the intermittent combustion is in progress (when YES is determined in S01A), the controller 80 determines in step S02 whether the MOQ off is detected. When the MOQ off is detected during the intermittent combustion (when YES is determined in S02), the controller 80 proceeds the process to S03, extinguishes the burner 31, and stops the combustion of the burner 31. Subsequently, the controller 80 performs the scavenging operation according to steps S04 to S08. When the scavenging operation is ended (step S08), the controller 80 proceeds the process to step S09A and ends the intermittent combustion. As a result, the transition to the combustion standby mode is performed, and the combustion of the burner 31 is continuously stopped.

On the other hand, if the MOQ off is not detected during the intermittent combustion (when NO is determined in S02), the controller 80 proceeds the process to step S10 and switches the combustion period and the non-combustion period according to the comparison between the can body temperature Tb (the temperature sensor 64) and the target temperature range of the can body temperature Tb.

During the intermittent combustion, the controller 80 determines in step S10 whether the combustion period is in progress. When the combustion period is not in progress (when NO is determined in S10), the controller 80 does not perform the process after S11. On the other hand, when the combustion period is in progress (when YES is determined in S10), the controller 80 proceeds the process to step S11 and compares the can body temperature Tb and the upper limit value TH of the target temperature range. When Tb≤TH (when NO is determined in S10), the controller 80 does not perform the process after S11.

On the other hand, when Tb>TH (when YES is determined in S11), the controller 80 extinguishes the burner 31 in order to start the non-combustion period in step S12. During the non-combustion period, the controller 80 proceeds the process to steps S13 to S15 to perform the scavenging operation according to the predetermined scavenging condition.

Specifically, the controller 80 performs the first scavenging operation in step S13. In step S13, the controller 80 sets the target fan rotation speed Fr* of the blower fan 36 to Fc1, and controls the blower fan 36 so that the fan rotation speed Fc detected by the rotation speed sensor 37 matches the target fan rotation speed Fr*. Further, when the first scavenging operation is started, the controller 80 activates a timer to start measuring the operation time of the first scavenging operation. Assuming the timer value Ts=0 at the start of the first scavenging operation, the timer value Ts is automatically increased according to the operation time.

During the first scavenging operation, the controller 80 compares the timer value Ts with the preset operation time Ts1 in step S14. When Ts<Ts1 (when NO is determined in S14), the controller 80 returns to S13 and continues the first scavenging operation. As a result, the first scavenging operation is continuously performed until the timer value Ts reaches Ts1. When the timer value Ts reaches the operation time Ts1 (when YES is determined in S14), the controller 80 ends the scavenging operation in S15 and clears the timer value Ts.

During the non-combustion period, the controller 80 compares the can body temperature Tb with the lower limit value TL of the target temperature range in step S16. When Tb≥TL (when NO is determined in S16), the controller 80 does not perform the process in S17, and the non-combustion period is continued. On the other hand, when Tb<TL (when YES is determined in S16), the controller 80 proceeds the process to step S17 and reignites the burner 31 in order to start the combustion period. According to the above procedure, the combustion period and the non-combustion period of the burner 31 are repeatedly provided in accordance with the transition of the can body temperature Tb, and the first scavenging operation is performed during the non-combustion period. When the MOQ off is detected during the intermittent combustion (when YES is determined in S02), the controller 80 proceeds the process to steps S03 to S09A, extinguishes the burner 31, and performs the first and second scavenging operations.

For another embodiment of the scavenging operation in the intermittent combustion, as illustrated in FIG. 6, it is possible to exemplify a configuration in which, on condition that the total air blowing amount of the blower fan 36 is greater than or equal to the total air blowing amount in the first scavenging operation (Fc1×Ts1) and less than the total value (Fc1×Ts1+Fc2×Ts2) of the total air blowing amount of the first scavenging operation (Fc1×Ts1) and the total air blowing amount of the second scavenging operation (Fc2×Ts2), the fan rotation speed Fc of the blower fan 36 is set to a rotation speed less than Fc1 and the time Ts1 #is set to a time longer than Ts1. In addition, the embodiment of the scavenging operation is not limited to these embodiments, and may be set as desired according to the heat capacity of the heat exchanger 39 and the like under the above conditions.

As described above, according to the combustion apparatus according to the embodiments, the total air blowing amount of the blower fan in the scavenging operation during the non-combustion period is set to be less than the total air blowing amount of the blower fan in the scavenging operation when the normal combustion is stopped, whereby during the non-combustion period, the cooling of the heat exchanger can be suppressed as compared with the case after the continuous combustion is stopped. According to this, the rate of decrease of the can body temperature during the non-combustion period can be slow, and the shortening of the non-combustion period can be suppressed, so frequent switching between the combustion period and the non-combustion period can be prevented. As a result, the equipment durability can be improved, and wasteful consumption of fuel gas can be suppressed.

Further, during the application of the intermittent combustion, since the fluctuation cycle of the can body temperature Tb becomes longer as the cycle length corresponding to the sum of each combustion period and non-combustion period becomes longer, the stability of the outlet hot water temperature Th can be improved.

Further, in the above-described embodiments, the control operation in the combustion apparatus to which the continuous combustion and the intermittent combustion are selectively applied in the combustion mode has been described, but the control operation in the intermittent combustion according to the embodiment can also be applied to a combustion apparatus to which only intermittent combustion is applied in the combustion mode. In this case, the total air blowing amount of the blower fan in the scavenging operation during the non-combustion period is set to be less than the total air blowing amount of the blower fan in the scavenging operation when the intermittent combustion is stopped, whereby the same effect as that of the above-described embodiments can be obtained. For example, according to the control process according to the flowchart shown in FIG. 7, it may be configured that when the intermittent combustion is stopped, the first scavenging operation and the second scavenging operation are performed, while during the non-combustion period, only the first scavenging operation is performed, and the second scavenging operation is not performed.

Further, in the above-described embodiments, an example in which the combustion part is configured by the burner 31 using gas as fuel is shown, but the energy source for heating can be any energy source. Further, in the above-described embodiments, an example in which the combustion apparatus is applied to the bypass mixing type hot water supplier controlled by the bypass valve 60 is described, but the combustion apparatus according to the embodiments may be applied to a hot water supplier having a configuration other than the bypass mixing type.

It should be considered that the embodiments disclosed herein are exemplary in all aspects and are not restrictive. The scope of the disclosure is shown by the scope of claims rather than the above description, and it is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

COMBUSTION APPARATUS

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