CONNECTED COMBUSTION SYSTEM

Abstract

A connected combustion system detects a failure in any of combustors connected in the system and each including a burner with its combustion state used for feedback. Each combustor includes a combustion sensor that detects the combustion state in the burner, and a detection value is used for feedback. When the detection value deviates from a predetermined normal range, at least one of a fuel gas supply or an air supply is corrected to cause the detection value to be within the normal range. The combustion state in the burner is thus adjusted. When the combustion sensor in any of the combustors has a detection value deviating from the normal range and the combustion sensor in another combustor operating simultaneously with the above combustor has a detection value within the normal range, the combustor having the detection value deviating from the normal range is determined to have a failure.

Description

BACKGROUND OF INVENTION

Field of the Invention

The present invention relates to a connected combustion system including multiple combustors connected in parallel to receive fuel gas from the same gas source.

Background Art

A known connected combustion system includes multiple combustors connected together each including a burner (e.g., Patent Literature 1). All the combustors basically have the same specifications and operate in the same manner. The combustors are connected in parallel to receive fuel gas from the same gas source. The combustion amount of each combustor is controlled based on the total amount of heat to be used in the entire connected combustion system.

A known combustor includes a combustion sensor such as a flame rod to detect the combustion state in the burner (e.g., Patent Literature 2). The detection value (e.g., the flame current) from the combustion sensor is used for feedback. When the detection value deviates from a predetermined normal range, the fuel gas supply or the air supply to the burner is corrected to cause the detection value to be within the normal range. The combustion state in the burner can thus be adjusted. The detection value from the combustion sensor can deviate from the normal range due to an individual factor that is an anomaly (failure) in a combustor caused by, for example, aging or due to a collective factor that is an anomaly (change) in the composition of fuel gas or the density of air supplied to the burner.

CITATION LIST

Patent Literature

• Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2017-62081
• Patent Literature 2: Japanese Unexamined Patent Application Publication No. Sho 63-70021

SUMMARY OF INVENTION

When the detection value from the combustion sensor deviates from the normal range, the known combustor that detects the combustion state in the burner for feedback in the above manner automatically corrects the fuel gas supply or the air supply and continues its operation (combustion in the burner) without determining whether the deviation is caused by the individual factor or the collective factor. Thus, a failure in the combustor can remain undetected.

In response to the above issue with the known technique, one or more aspects of the present invention are directed to a connected combustion system that detects a failure in any of the combustors connected in the system and each including a burner with its combustion state used for feedback.

A connected combustion system according to an aspect of the present invention has the structure below. More specifically, the connected combustion system includes a plurality of combustors and a determiner. The plurality of combustors are connected in parallel to receive fuel gas from a same gas source. Each of the plurality of combustors includes a burner and has a combustion amount controllable based on a total amount of heat to be used. Each of the plurality of combustors includes a gas regulator that regulates a supply of the fuel gas to the burner based on the combustion amount, an air regulator that regulates a supply of air to the burner based on the combustion amount, a combustion sensor that detects a combustion state in the burner, and a corrector that corrects, when the combustion sensor has a detection value deviating from a predetermined normal range, at least one of the supply of the fuel gas or the supply of the air to cause the detection value to be within the normal range. The determiner determines that a first combustor of the plurality of combustors has a failure when the combustion sensor in the first combustor has a detection value deviating from the normal range and the combustion sensor in a second combustor of the plurality of combustors operating simultaneously with the first combustor has a detection value within the normal range.

In the connected combustion system according to the above aspect of the present invention, when the first combustor has a combustion state (a detection value from the combustion sensor) deviating from the normal range and the second combustor operating simultaneously with the first combustor has a combustion state within the normal range, the deviation of the combustion state from the normal range in the first combustor is likely to result from a failure specific to the first combustor, rather than resulting from an anomaly in the fuel gas composition or in the air density. A combustor with a failure can thus be detected among the connected combustors.

In the connected combustion system according to the above aspect of the present invention, when the combustion sensor in the first combustor determined to have a failure has a detection value deviating from the normal range after correction is performed by the corrector, the first combustor may be determined to have a failure of a first level and the first combustor may be prohibited from operating. When the combustion sensor in the first combustor has a detection value within the normal range after correction is performed by the corrector, the first combustor may be determined to have a failure of a second level and the first combustor may be permitted to operate.

Thus, a combustor determined to have a failure is or is not prohibited from operating depending on the level of the failure. With a slight failure (a failure of a second level) that can be overcome by correcting either the fuel gas supply or the air supply or both, the combustor is permitted to continue operating rather than being prohibited from operating. This reduces the frequency of maintenance for the connected combustion system.

The connected combustion system according to the above aspect of the present invention may further include a storage that stores information about the first combustor determined to have the failure of the second level, and a display that displays the information stored in the storage.

The manager of the connected combustion system can refer to the display and learn about the combustor determined to have a slight failure. This allows the manager to plan the maintenance based on the displayed information or examine the displayed combustor carefully during maintenance, thus facilitating management of the connected combustion system.

In the connected combustion system according to any one of the above aspects of the present invention, when the combustion sensor in the first combustor of the connected combustors has a detection value deviating from the normal range and the combustion sensor in the second combustor operating simultaneously with the first combustor has a detection value deviating from the normal range, at least one of a composition of the fuel gas or a density of the air may be determined to have an anomaly.

In the connected combustion system according to the above aspect of the present invention, when multiple combustors have combustion states (detection values from the combustion sensors) simultaneously deviating from the normal range, the deviations are unlikely to result from failures specific to the respective combustors. The system can thus determine that the deviations result from an anomaly in the fuel gas composition (e.g., impurities in the fuel gas from the gas source) or an anomaly in the air density (e.g., an incorrect setting about the air density that depends on the altitude of the installation location).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a connected combustion system 1 according to an embodiment, showing its overall structure.

FIG. 2 is a diagram of a water heater 10 according to the present embodiment.

FIG. 3 is a flowchart of a collective operation control process performed by a system controller 7 in the connected combustion system 1 to control the operation of multiple water heaters 10.

FIG. 4 is a flowchart of an individual operation control process performed by a controller 25 in each water heater 10 to control combustion in a burner 12 under the control of the system controller 7.

FIG. 5 is a flowchart of a correction process in the present embodiment performed in the individual operation control process.

FIG. 6 is an example graph of the correlation between the resistance value and the air excess ratio.

FIG. 7 is a flowchart of an anomaly detection process performed by the system controller 7 in the present embodiment.

DETAILED DESCRIPTION

FIG. 1 is a diagram of a connected combustion system 1 according to the present embodiment, showing its overall structure. The connected combustion system 1 shown in FIG. 1 includes multiple water heaters 10 as combustors connected together, a water pipe 2 for supplying clean water to each water heater 10, a hot-water pipe 3 for discharging hot water produced in each water heater 10, and a gas pipe 4 for supplying fuel gas to each water heater 10.

The water heaters 10, which will be described later in detail with reference to another figure, basically have the same specifications, operate in the same manner, and are connected in parallel. More specifically, the water pipe 2 includes branches connected to the respective water heaters 10 to supply clean water to the water heaters 10. The hot-water pipe 3 includes branches extending from the respective water heaters 10, from which hot water flows to merge into a single stream in the hot-water pipe 3. Similarly, the gas pipe 4 includes branches connected to the respective water heaters 10 to supply fuel gas to the water heaters 10. All the water heaters 10 receive fuel gas from the same gas source.

The water pipe 2 includes a feedwater temperature sensor 5 upstream from the branch points to measure the temperature (feedwater temperature) of clean water being supplied. The hot-water pipe 3 includes an outlet flow sensor 6 downstream from the merging points to measure the flow rate of hot water being used.

The connected combustion system 1 further includes a system controller 7 that controls the entire system. The system controller 7 is connected to the water heaters 10 to allow wired or wireless communication between them, and is also electrically connected to the feedwater temperature sensor 5 and the outlet flow sensor 6. When hot water is used at the downstream end of the hot-water pipe 3, the system controller 7 controls the operation of the water heaters 10 based on, for example, the flow rate of hot water measured by the outlet flow sensor 6 and on the feedwater temperature measured by the feedwater temperature sensor 5, as described in detail later. For example, the system controller 7 varies the number of water heaters 10 for the operation performed based on the flow rate of hot water being used. More specifically, the system controller 7 adds a water heater 10 to operate for a higher flow rate of hot water. The system controller 7 includes a built-in storage 7a that stores information about the water heaters 10 (described later).

The system controller 7 is also connected to a remote control 8 to allow wired or wireless communication between them. The remote control 8 is operated by the manager of the connected combustion system 1. The remote control 8 includes an operation portion 8a and a display 8b. The operation portion 8a includes buttons for various settings (e.g., the temperature of hot water to be supplied), for activating or deactivating various functions, and for resetting. The display 8b can display, for example, the setting status or the operation status of the connected combustion system 1, and information about the water heaters 10.

FIG. 2 is a diagram of the water heater 10 according to the present embodiment. As shown in FIG. 2, the water heater 10 includes a combustion chamber 11, a burner 12 located in the combustion chamber 11 to burn fuel gas, and a combustion fan 13 that supplies combustion air to the burner 12 from below. The burner 12 receives fuel gas through the gas pipe 4. In the water heater 10, the gas pipe 4 includes a main valve 14 that opens and closes the gas pipe 4, and a proportioning valve 15 that regulates the flow rate of fuel gas in the gas pipe 4. The combustion fan 13 in the present embodiment corresponds to an air regulator in one or more aspects of the present invention. The proportioning valve 15 in the present embodiment corresponds to a gas regulator in one or more aspects of the present invention.

The combustion chamber 11 includes a spark plug 16 that ignites the burner 12 with a spark discharge, and a flame rod 17 that detects the combustion state in the burner 12. The flame rod 17 in the present embodiment corresponds to a combustion sensor in one or more aspects of the present invention.

The water heater 10 includes a heat exchanger 18 above the burner 12 and an exhaust pipe 19 connected to an upper portion of the water heater 10. High-temperature exhaust gas generated by combustion in the burner 12 flows through the heat exchanger 18 and then through the exhaust pipe 19 to outside the water heater 10. The heat exchanger 18 has an upstream end connected to the water pipe 2, and a downstream end connected to the hot-water pipe 3. In the water heater 10, the water pipe 2 includes an inlet valve 20 that opens and closes the water pipe 2, an inlet flow sensor 21 that measures the flow rate of clean water entering the water heater 10, and an inlet temperature sensor 22 that measures the temperature (incoming water temperature) of clean water entering the water heater 10.

The inlet valve 20 is opened to allow clean water to enter the water heater 10, in which the clean water is heated by heat exchange with exhaust gas from the burner 12 using the heat exchanger 18. The resulting hot water then flows to the hot-water pipe 3. In the water heater 10, the hot-water pipe 3 includes an outlet temperature sensor 23 that measures the temperature (outgoing water temperature) of hot water flowing outside the water heater 10.

Each water heater 10 further includes a controller 25 for overall control of the corresponding water heater 10. The controller 25 is electrically connected to, for example, the combustion fan 13, the main valve 14, the proportioning valve 15, the spark plug 16, the flame rod 17, the inlet valve 20, the inlet flow sensor 21, the inlet temperature sensor 22, and the outlet temperature sensor 23. The controller 25 is connected to the system controller 7 to allow communication between them. Under the control of the system controller 7, the controller 25 opens the inlet valve 20, starts combustion in the burner 12 by controlling, for example, the combustion fan 13, the main valve 14, the proportioning valve 15, and the spark plug 16, and calculates the combustion amount of the burner 12 based on the flow rate of clean water measured by the inlet flow sensor 21, the incoming water temperature measured by the inlet temperature sensor 22, or other parameters. Such processes will be described in detail later. The combustion state in the burner 12 is detected by the flame rod 17 and is maintained to be normal through feedback.

FIG. 3 is a flowchart of a collective operation control process performed by the system controller 7 in the connected combustion system 1 to control the operation of the water heaters 10. The collective operation control process is performed repeatedly at predetermined intervals after the connected combustion system 1 is powered on. As shown in FIG. 3, the collective operation control process starts with the determination as to whether any of the connected water heaters 10 (combustors) in the connected combustion system 1 is in operation (STEP 1).

When no water heater 10 is in operation (No in STEP 1), the determination is performed as to whether a start condition is satisfied (STEP 2). In the connected combustion system 1 according to the present embodiment, the start condition is determined to be satisfied when the flow rate of hot water measured by the outlet flow sensor 6 exceeds a predetermined lower limit in response to hot water being used at the downstream end of the hot-water pipe 3. At least one of the connected water heaters 10 includes the inlet valve 20 that is constantly open to allow water to flow through to the hot-water pipe 3 when the water heater 10 is not in operation. The number of such water heaters 10 depends on the lower limit of the flow rate. When the start condition is unsatisfied (No in STEP 2), the collective operation control process in FIG. 3 in this cycle is complete, and the collective operation control process in FIG. 3 is performed again in the subsequent cycle after the predetermined interval.

When the start condition is satisfied (Yes in STEP 2), the total amount of heat to be used in the entire connected combustion system 1 is calculated (STEP 3). The total amount of heat is calculated based on the flow rate of hot water measured by the outlet flow sensor 6, the feedwater temperature (the temperature of clean water) measured by the feedwater temperature sensor 5, or the set temperature of hot water input with the remote control 8. For hot water at a higher flow rate, for example, a higher total amount of heat is used. For hot water at a constant flow rate, a higher total amount of heat is used for a greater difference between the set temperature of hot water and the feedwater temperature.

After the total amount of heat to be used is calculated, water heaters 10 are selected to operate and generate the total amount of heat (STEP 4). The water heaters 10 basically have the same specifications as described above, and the number of water heaters 10 to operate is varied based on the total amount of heat to be used. For each incremental increase in the total amount of heat at a predetermined reference level, a water heater 10 to operate is added.

A start signal indicating the start of operation is then transmitted to the water heaters 10 to operate (STEP 5). The collective operation control process in FIG. 3 in this cycle is complete. The collective operation control process in FIG. 3 is performed again in the subsequent cycle after the predetermined interval. In STEP 1 in the subsequent cycle, a water heater 10 is determined to be in operation (Yes in STEP 1). The determination is then performed as to whether a stop condition is satisfied (STEP 6).

In the connected combustion system 1 according to the present embodiment, the stop condition is determined to be satisfied when the flow rate of hot water measured by the outlet flow sensor 6 on the hot-water pipe 3 decreases below the lower limit. When the stop condition is satisfied (Yes in STEP 6), a stop signal indicating the stop of operation is transmitted to the operating water heaters 10 (STEP 7). The collective operation control process in FIG. 3 in this cycle is then complete. Thus, in the collective operation control process in FIG. 3 in the subsequent cycle, no water heater 10 is determined to be in operation in STEP 1.

When the stop condition is unsatisfied (No in STEP 6), the determination is performed as to whether the total amount of heat to be used in the entire connected combustion system 1 has changed (STEP 8). For example, the total amount of heat can change in response to an increase or a decrease in the flow rate of hot water measured by the outlet flow sensor 6 or a change in the set temperature of hot water input with the remote control 8.

When the total amount of heat to be used has changed (Yes in STEP 8), the determination is performed as to whether the change in the total amount of heat involves a change in the number of water heaters 10 to operate (STEP 9). For each change (an increase or a decrease) in the total amount of heat at a predetermined reference level, a water heater 10 to operate is added or is removed.

When the number of water heaters 10 to operate has changed (Yes in STEP 9), the start signal is transmitted to the water heater 10 to be added or the stop signal is transmitted to the water heater 10 to be removed (STEP 10). Upon transmission of the start signal or the stop signal, the collective operation control process in FIG. 3 in this cycle is complete.

When the total amount of heat to be used has not changed (No in STEP 8) or when the number of water heaters 10 to operate has not changed (No in STEP 9), the collective operation control process in FIG. 3 in this cycle is complete without performing the processing in STEP 10. The collective operation control process in FIG. 3 is performed again in the subsequent cycle after the predetermined interval.

FIG. 4 is a flowchart of an individual operation control process performed by the controller 25 in each water heater 10 to control combustion in the burner 12 under the control of the system controller 7. The individual operation control process is performed repeatedly at predetermined intervals for each water heater 10 after the connected combustion system 1 is powered on. The individual operation control process starts with the determination as to whether the water heater 10 is in operation (whether the burner 12 is burning) (STEP 20).

When the water heater 10 is not in operation (No in STEP 20), the determination is performed as to whether the start signal has been received from the system controller 7 (STEP 21). As described above, the start signal indicates the start of operation. When no start signal has been received (No in STEP 21), the individual operation control process in FIG. 4 in this cycle is complete, and the individual operation control process in FIG. 4 is performed again in the subsequent cycle after the predetermined interval.

When the start signal has been received (Yes in STEP 21), the inlet valve 20 on the water pipe 2 being closed is opened to allow clean water to enter the water heater 10 (STEP 22). As described above, at least one of the connected water heaters 10 includes the inlet valve 20 that is constantly open when the water heater 10 is not in operation. The combustion amount of the burner 12 is then calculated (STEP 23). The combustion amount of the burner 12 is calculated based on the flow rate of clean water measured by the inlet flow sensor 21, the incoming water temperature (the temperature of clean water) measured by the inlet temperature sensor 22, or the set temperature of hot water input with the remote control 8. For example, the combustion amount is higher for clean water entering the water heater 10 at a higher flow rate. The combustion amount is also higher for a greater difference between the set temperature of hot water and the incoming water temperature.

Based on the calculated combustion amount of the burner 12, the fuel gas supply (the degree of opening of the proportioning valve 15) and the air supply for combustion (the speed of the combustion fan 13) are set (STEP 24). The controller 25 includes a built-in memory (not shown) that prestores the correspondence between the fuel gas supply and the air supply for each target value of the air excess ratio corresponding to the combustion amount.

Combustion in the burner 12 is then started (STEP 25). More specifically, the combustion fan 13 is rotated, the main valve 14 and the proportioning valve 15 are opened, and the spark plug 16 is turned on for ignition with a spark discharge. The speed of the combustion fan 13 corresponds to the set air supply. The degree of opening of the proportioning valve 15 corresponds to the set fuel gas supply. Upon the start of combustion in the burner 12, the individual operation control process in FIG. 4 in this cycle is complete. The individual operation control process in FIG. 4 is performed again in the subsequent cycle after the predetermined interval. In STEP 20 in the subsequent cycle, the water heater 10 is determined to be in operation (Yes in STEP 20). The determination is then performed as to whether the stop signal has been received from the system controller 7 (STEP 26).

As described above, the stop signal indicates the stop of operation. When the stop signal has been received (Yes in STEP 26), the combustion in the burner 12 is stopped (STEP 27). More specifically, the main valve 14 and the proportioning valve 15 are closed, and then the rotation of the combustion fan 13 is stopped. Further, the inlet valve 20 on the water pipe 2 is closed to stop clean water entering the water heater 10 (STEP 28), except for the water heater 10 including the inlet valve 20 that is constantly open when the water heater 10 is not in operation. The individual operation control process in FIG. 4 in this cycle is then complete. Thus, in the individual operation control process in FIG. 4 in the subsequent cycle, the water heater 10 is determined not to be in operation in STEP 20.

When no stop signal has been received (No in STEP 26), the determination is performed as to whether to change the combustion amount of the burner 12 (STEP 29). For example, the combustion amount of the burner 12 is to be changed in response to an increase or a decrease in the flow rate of clean water measured by the inlet flow sensor 21 or a deviation between the outgoing water temperature measured by the outlet temperature sensor 23 and the set temperature of hot water input with the remote control 8.

When the combustion amount of the burner 12 is to be changed (Yes in STEP 29), the fuel gas supply (the degree of opening of the proportioning valve 15) and the air supply for combustion (the speed of the combustion fan 13) are reset based on the combustion amount after the change (STEP 30). The individual operation control process in FIG. 4 in this cycle is then complete.

When the combustion amount of the burner 12 is not to be changed (No in STEP 29), the detection value from the flame rod 17 is obtained (STEP 31). The flame rod 17 is placed in a flame formed by the burner 12. A current reflecting the combustion state flows through the flame rod 17 with ions in the flame. In the water heater 10 in the present embodiment, the obtained detection value is the resistance value calculated based on the voltage across the flame rod 17 and on the current through the flame rod 17.

The determination is then performed as to whether the obtained detection value (resistance value) from the flame rod 17 is within a predetermined normal range (STEP 32). When the detection value from the flame rod 17 is within the normal range (Yes in STEP 32), the individual operation control process in FIG. 4 in this cycle is complete. When the detection value from the flame rod 17 is not within the normal range (No in STEP 32), a correction process (described later) is performed to cause the detection value to be within the normal range through feedback (STEP 33). The individual operation control process in FIG. 4 in this cycle is then complete. The individual operation control process in FIG. 4 is performed again in the subsequent cycle after the predetermined interval.

FIG. 5 is a flowchart of the correction process in the present embodiment performed in the individual operation control process. As described above, the correction process (STEP 33) is performed when the detection value from the flame rod 17 is not within the normal range. When the detection value is within the normal range, the correction process is not performed. The correction process starts with transmission of a deviation signal to the system controller 7 to indicate that the detection value from the flame rod 17 has deviated from the normal range (STEP 40).

The fuel gas supply is then corrected to cause the detection value (resistance value) from the flame rod 17 to be within the normal range (STEP 41). The controller 25 in the present embodiment corresponds to a corrector in one or more aspects of the present invention. The resistance value correlates with the air excess ratio in combustion in the burner 12, as is known.

FIG. 6 is an example graph of the correlation between the resistance value and the air excess ratio. FIG. 6 shows a positively sloped curve indicating the correlation between an air excess ratio λ on the horizontal axis and a resistance value R on the vertical axis. For the water heater 10 in the present embodiment, a target value λx of the air excess ratio λ is predetermined empirically for an appropriate combustion state in the burner 12, with an allowable range of ±a being set for the target value λx. The normal range of the resistance value R is defined to be between a resistance value Rmin corresponding to an air excess ratio λx−α and a resistance value Rmax corresponding to an air excess ratio λx+α on the curve. When the resistance value R detected by the flame rod 17 satisfies R<Rmin, then λ<λx−α. When the resistance value R satisfies R>Rmax, then λ>λx+α.

The air excess ratio λ can be expressed as λ=L/Lth, where Lth is the theoretical minimum amount of air to be used for complete combustion of fuel gas and L is the actual air supply. The air excess ratio λ can also be expressed as λ=AFR/AFRth, where AFRth is the theoretical air-fuel ratio and AFR is the actual air-fuel ratio. The fuel gas supply corrected to be lower increases the air-fuel ratio AFR and the air excess ratio λ, thus increasing the resistance value R. The fuel gas supply corrected to be higher decreases the air-fuel ratio AFR and the air excess ratio λ, thus decreasing the resistance value R.

In some embodiments, the air supply for combustion may be corrected instead of the fuel gas supply being corrected. In this case, an air supply L corrected to be higher increases the air excess ratio λ, thus increasing the resistance value R. The air supply L corrected to be lower decreases the air excess ratio λ, thus decreasing the resistance value R. In some embodiments, the fuel gas supply and the air supply for combustion may be both corrected. In this case, one of the fuel gas supply or the air supply is corrected to be higher and the other is corrected to be lower. This allows a greater change in the air excess ratio λ (and thus the resistance value R) than correcting one of the fuel gas supply or the air supply.

After the fuel gas supply is corrected in STEP 41 in the correction process in FIG. 5, the correction value is stored into the memory in the controller 25. The stored correction value is used to set the fuel gas supply subsequently. After the fuel gas supply is corrected, the detection value from the flame rod 17 is obtained again (STEP 42). The determination is then performed as to whether the obtained detection value (resistance value) is within the normal range (STEP 43).

When the detection value from the flame rod 17 is within the normal range (Yes in STEP 43), a return signal is transmitted to the system controller 7 to indicate that the detection value from the flame rod 17 has returned to the normal range (STEP 44). The correction process in FIG. 5 is then complete, and the processing returns to the individual operation control process in FIG. 4. When the detection value from the flame rod 17 is not within the normal range (No in STEP 43), the correction process in FIG. 5 is complete without performing the processing in STEP 44 (without transmitting the return signal). The processing then returns to the individual operation control process in FIG. 4.

In the individual operation control process described above, the flame rod 17 detects the combustion state in the burner 12 to determine the detection value (resistance value) that is used for feedback. When the detection value deviates from the normal range, the fuel gas supply is corrected to cause the detection value to be within the normal range. The combustion state in the burner 12 can thus be adjusted. The detection value from the flame rod 17 can deviate from the normal range due to roughly two types of factors, an individual factor and a collective factor. The individual factor refers to an anomaly (failure) in the water heater 10 caused by, for example, aging. The individual factor includes, for example, an error in the degree of opening of the proportioning valve 15 on the gas pipe 4, an error in the speed of the combustion fan 13, clogging of the exhaust pipe 19, and a decrease in the detection accuracy of the flame rod 17. The collective factor refers to an anomaly (change) in the composition of fuel gas or the density of air supplied to the burner 12. The collective factor includes, for example, impurities in the fuel gas from the gas source and an incorrect setting about the air density that depends on the installation location (altitude) of the connected combustion system 1.

When the detection value from the flame rod 17 deviates from the normal range, the individual operation control process alone can correct the fuel gas supply and continue the operation of the water heater 10 (the combustion in the burner 12) without determining whether the deviation is caused by the individual factor or the collective factor. Thus, a failure in the water heater 10 can remain undetected. Thus, in the connected combustion system 1 according to the present embodiment, the system controller 7 performs an anomaly detection process described below to detect any of the connected water heaters 10 with a failure.

FIG. 7 is a flowchart of the anomaly detection process performed by the system controller 7 in the present embodiment. The anomaly detection process is performed repeatedly at predetermined intervals after the connected combustion system 1 is powered on. As shown in FIG. 7, the anomaly detection process starts with the determination as to whether the deviation signal has been received from any of the connected water heaters 10 in the connected combustion system 1 (STEP 50). As described above, the deviation signal indicates that the detection value from the flame rod 17 deviates from the normal range.

When the flame rod 17 in a water heater 10 has a detection value deviating from the normal range, the connected combustion system 1 according to the present embodiment determines whether the water heater 10 has a failure. When no deviation signal has been received from any of the water heaters 10 (No in STEP 50), the anomaly detection process in FIG. 7 in this cycle is complete, and the anomaly detection process in FIG. 7 is performed again in the subsequent cycle after the predetermined interval.

When the deviation signal has been received from a water heater 10 (Yes in STEP 50), the determination is performed as to whether the deviation signal has been received also from another water heater 10 operating simultaneously with the above water heater 10 (STEP 51). In the connected combustion system 1, the number of water heaters 10 to operate simultaneously is varied based on the total amount of heat to be used, as described above. When no deviation signal has been received from another water heater 10 (No in STEP 51), the water heater 10 that has transmitted the deviation signal is determined to have a failure (STEP 52). The system controller 7 in the present embodiment corresponds to a determiner in one or more aspects of the present invention.

The determination is then performed as to whether the return signal has been received within a predetermined time limit from the water heater 10 determined to have a failure (STEP 53). As described above, the return signal indicates that the detection value from the flame rod 17 has returned to the normal range after the correction of the fuel gas supply. When no return signal has been received within the time limit (No in STEP 53), the detection value from the flame rod 17 still deviates from the normal range after the correction of the fuel gas supply. Thus, the water heater 10 is determined to have a serious failure (a failure of a first level) (STEP 54).

The stop signal is then transmitted to the water heater 10 determined to have a serious failure (STEP 55). In the water heater 10 that has received the stop signal, the combustion in the burner 12 is stopped as described above (refer to FIG. 4, STEP 27). The water heater 10 determined to have a serious failure is also prohibited from operating (STEP 56). This excludes the water heater 10 having a serious failure from the candidate water heaters 10 to operate (refer to FIG. 3, STEP 4).

Further, a notification about the water heater 10 determined to have a serious failure is provided (STEP 57). In the present embodiment, the notification about the water heater 10 having a serious failure is provided using the display 8b on the remote control 8. The notification may be provided in any other manner, such as using sound output from a built-in speaker (not shown) in the remote control 8. The anomaly detection process in FIG. 7 in this cycle is then complete, and the anomaly detection process in FIG. 7 is performed again in the subsequent cycle after the predetermined interval.

When the return signal has been received within the time limit from the water heater 10 determined to have a failure in STEP 53 (Yes in STEP 53), the detection value from the flame rod 17 is within the normal range after the correction of the fuel gas supply. Thus, the water heater 10 is determined to have a slight failure (a failure of a second level) (STEP 58).

Information about the water heater 10 determined to have a slight failure is then stored into the storage 7a in the system controller 7 (STEP 59). The information stored in the storage 7a is displayed for reference on the display 8b when the manager of the connected combustion system 1 operates the operation portion 8a on the remote control 8. After the information about the water heater 10 having a slight failure is stored, the anomaly detection process in FIG. 7 in this cycle is complete, and the anomaly detection process in FIG. 7 is performed again in the subsequent cycle after the predetermined interval.

The process described above is performed when no deviation signal has been received from another water heater 10 operating simultaneously with the above water heater 10 in STEP 51 (No in STEP 51). In contrast, when the deviation signal has been received also from another water heater 10 operating simultaneously with the above water heater 10 (Yes in STEP 51), the system detects a collective anomaly common to the multiple water heaters 10, or specifically, an anomaly in the composition of fuel gas or the density of air supplied to the burners 12, rather than anomalies (failures) specific to the respective water heaters 10 (STEP 60).

A notification about the detected collective anomaly is then provided (STEP 61). In the present embodiment, the notification about the collective anomaly is provided using the display 8b on the remote control 8. The notification may be provided in any other manner, such as using sound output from a speaker in the remote control 8. After the notification about the collective anomaly is provided, the anomaly detection process in FIG. 7 in this cycle is complete, and the anomaly detection process in FIG. 7 is performed again in the subsequent cycle after the predetermined interval.

In the connected combustion system 1 according to the present embodiment described above, the combustion state in the burner 12 in each of the connected water heaters 10 (combustors) is detected by the flame rod 17 and used for feedback. When the detection value (resistance value) deviates from the normal range, the fuel gas supply is corrected to cause the detection value to be within the normal range. The combustion state can thus be adjusted. When the flame rod 17 in any of the water heaters 10 has a detection value deviating from the normal range and the flame rod 17 in another water heater 10 operating simultaneously with the above water heater 10 has a detection value within the normal range, the system determines that the water heater 10 having the detection value deviating from the normal range has a failure.

When the other water heater 10 has a combustion state (a detection value from the flame rod 17) within the normal range, the deviation of the combustion state from the normal range in the above water heater 10 is likely to result from a failure specific to the water heater 10, rather than resulting from a collective anomaly in the fuel gas composition or in the air density. A water heater 10 with a failure can thus be detected among the connected water heaters 10 in the connected combustion system 1.

In the connected combustion system 1 according to the present embodiment, when the flame rod 17 in a water heater 10 has a detection value deviating from the normal range and still deviating from the normal range after the correction of the fuel gas supply, the water heater 10 is determined to have a serious failure and is prohibited from operating. When the flame rod 17 in a water heater 10 has a detection value deviating from the normal range and is then within the normal range after the correction of the fuel gas supply, the water heater 10 is determined to have a slight failure and is permitted to operate. Thus, the water heater 10 determined to have a failure is or is not prohibited from operating depending on the level of the failure. With a slight failure that can be overcome by correcting the fuel gas supply, the water heater 10 is permitted to continue operating rather than being prohibited from operating. This reduces the frequency of maintenance for the connected combustion system 1.

In the connected combustion system 1 according to the present embodiment, the storage 7a in the system controller 7 stores information about the water heater 10 determined to have a slight failure. The information stored in the storage 7a can be displayed on the display 8b on the remote control 8. The manager of the connected combustion system 1 can refer to the display 8b and learn about the water heater 10 determined to have a slight failure. This allows the manager to plan the maintenance based on the displayed information or examine the displayed water heater 10 carefully during maintenance, thus facilitating management of the connected combustion system 1.

Further, in the connected combustion system 1 according to the present embodiment, when the flame rod 17 in any of the water heaters 10 has a detection value deviating from the normal range and the flame rod 17 in another water heater 10 operating simultaneously with the above water heater 10 also has a detection value deviating from the normal range, the system determines that the fuel gas composition or the air density has a collective anomaly. When multiple water heaters 10 have combustion states (detection values from the flame rods 17) simultaneously deviating from the normal range, the deviations are unlikely to result from failures specific to the respective water heaters 10. The system can thus determine that the deviations result from an anomaly in the fuel gas composition (e.g., impurities in the fuel gas from the gas source) or an anomaly in the air density (e.g., an incorrect setting about the air density that depends on the altitude of the installation location).

The connected combustion system 1 according to the present embodiment has been 25 described. However, the present invention is not limited to the above embodiment and may be implemented in various manners without departing from the spirit and scope of the invention.

For example, in the above embodiment, the system controller 7 is connected to the controller 25 included in each water heater 10 to allow communication between them, and detects a water heater 10 having a failure based on a signal received from the controller 25. In some embodiments, the system controller 7 may be eliminated. More specifically, the controllers 25 in the water heaters 10 may be connected to one another to allow communication between them, with one water heater 10 being defined as a main water heater 10 and the other water heaters 10 being defined as sub-water heaters 10. A water heater 10 having a failure may be detected by the controller 25 in the main water heater 10, rather than by the system controller 7. When the main water heater 10 has a failure, the main water heater 10 may be redefined as a sub-water heater 10, and another sub-water heater 10 may be redefined as a main water heater 10.

In the above embodiment, the resistance value is used as the detection value from the flame rod 17. In some embodiments, the value of current (flame current value) flowing through the flame rod 17 with ions in a flame may be used as the detection value from the flame rod 17. The flame current value and the air excess ratio also have a correlation between them. Thus, the correlation can be used to correct the fuel gas supply or the air supply to cause the flame current value to be within a predetermined normal range.

In the above embodiment, the flame rod 17 is used to detect the combustion state in the burner 12. However, any detector other than the flame rod 17 may be used to detect the combustion state in the burner 12. For example, a temperature sensor that measures the temperature of a flame formed by the burner 12 may be used to detect the combustion state.

In the above embodiment, the outlet flow sensor 6 on the hot-water pipe 3 is used to measure the flow rate of hot water being used. In some embodiments, the outlet flow sensor 6 may be eliminated, and the inlet flow sensor 21 included in each of the connected water heaters 10 may be used instead. More specifically, the start condition may be determined to be satisfied when the flow rate of clean water measured by the inlet flow sensor 21 exceeds a predetermined lower limit in the water heater 10 including the constantly open inlet valve 20 (refer to FIG. 3, STEP 2). The stop condition may be determined to be satisfied when the sum of the flow rates of clean water measured by the inlet flow sensors 21 in the respective water heaters 10 decreases below the lower limit (refer to FIG. 3, STEP 6). The total amount of heat to be used may be calculated based on the sum of the flow rates of clean water measured by the inlet flow sensors 21 in the respective water heaters 10 (refer to FIG. 3, STEPs 3 and 8).

In the above embodiment, each water heater 10 directly heats clean water supplied through the water pipe 2 by heat exchange with exhaust gas from the burner 12 using the heat exchanger 18. In some embodiments, each water heater 10 may heat the clean water in any other manner such as using a circulating heating medium. More specifically, each water heater 10 may heat the heating medium by heat exchange with exhaust gas from the burner 12 using a first heat exchanger, and then heat the clean water by heat exchange with the heating medium using a second heat exchanger.

REFERENCE SIGNS LIST

• • 1 connected combustion system
  • 2 water pipe
  • 3 hot-water pipe
  • 4 gas pipe
  • 5 feedwater temperature sensor
  • 6 outlet flow sensor
  • 7 system controller
  • 7 a storage
  • 8 remote control
  • 8 a operation portion
  • 8 b display
  • 10 water heater
  • 11 combustion chamber
  • 12 burner
  • 13 combustion fan
  • 14 main valve
  • 15 proportioning valve
  • 16 spark plug
  • 17 flame rod
  • 18 heat exchanger
  • 19 exhaust pipe
  • 20 inlet valve
  • 21 inlet flow sensor
  • 22 inlet temperature sensor
  • 23 outlet temperature sensor
  • 25 controller

Claims

1. A connected combustion system, comprising: a plurality of combustors connected in parallel to receive fuel gas from a same gas source, each of the plurality of combustors including a burner and having a combustion amount controllable based on a total amount of heat to be used, each of the plurality of combustors including a gas regulator configured to regulate a supply of the fuel gas to the burner based on the combustion amount,an air regulator configured to regulate a supply of air to the burner based on the combustion amount,a combustion sensor configured to detect a combustion state in the burner, anda corrector configured to correct, when the combustion sensor has a detection value deviating from a predetermined normal range, at least one of the supply of the fuel gas or the supply of the air to cause the detection value to be within the normal range; anda determiner configured to determine that a first combustor of the plurality of combustors has a failure when the combustion sensor in the first combustor has a detection value deviating from the normal range and the combustion sensor in a second combustor of the plurality of combustors operating simultaneously with the first combustor has a detection value within the normal range.

2. The connected combustion system according to claim 1, wherein when the combustion sensor in the first combustor has a detection value deviating from the normal range after correction is performed by the corrector, the determiner determines that the first combustor has a failure of a first level and prohibits an operation of the first combustor, andwhen the combustion sensor in the first combustor has a detection value within the normal range after correction is performed by the corrector, the determiner determines that the first combustor has a failure of a second level and permits an operation of the first combustor.

3. The connected combustion system according to claim 2, further comprising: a storage configured to store information about the first combustor determined to have the failure of the second level by the determiner; anda display configured to display the information stored in the storage.

4. The connected combustion system according to claim 1, wherein when the combustion sensor in the first combustor has a detection value deviating from the normal range and the combustion sensor in the second combustor operating simultaneously with the first combustor has a detection value deviating from the normal range, the determiner determines that at least one of a composition of the fuel gas or a density of the air has an anomaly.

5. The connected combustion system according to claim 2, wherein when the combustion sensor in the first combustor has a detection value deviating from the normal range and the combustion sensor in the second combustor operating simultaneously with the first combustor has a detection value deviating from the normal range, the determiner determines that at least one of a composition of the fuel gas or a density of the air has an anomaly.

6. The connected combustion system according to claim 3, wherein when the combustion sensor in the first combustor has a detection value deviating from the normal range and the combustion sensor in the second combustor operating simultaneously with the first combustor has a detection value deviating from the normal range, the determiner determines that at least one of a composition of the fuel gas or a density of the air has an anomaly.