Water heating system and water heater

Abstract

A water heating system may include: a plurality of water heaters connected in parallel to each other; and a connection controller. The connection controller may be configured to: select one or more of the plurality of water heaters as active water heaters and a remainder of the plurality of water heaters as inactive water heaters; send an activation instruction to the controllers of the active water heaters; and send a stop instruction to the controllers of the inactive water heaters. The connection controller may be configured to: increase or decrease a number of the active water heaters based on a maximum flow rate of a valve and a detected flow rate in each of the active water heaters; and when increasing the number of the active water heaters, select a next active water heater from the inactive water heaters that have not sent an error signal.

Description

REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Japanese Patent Application No. 2024-116955 filed on Jul. 22, 2024. The entire content of the priority application is incorporated herein by reference.BACKGROUND ART

[0002] A water heating system is known in which a plurality of water heaters connected in parallel with each other is connected to a connecting unit. The connecting unit has three flow rate levels set for water heaters, namely “low”, “medium”, and “high”, and when a frow rate of one of operating water heaters increases to the “high” level, the connecting unit activates one of water heaters that is not operating. Further, when the flow rate of one of the operating water heaters decreases to the “low” level, the connecting unit shuts this water heater down. That is, the connecting unit adjusts how many water heaters are to be operated (i.e., increases or decreases a number thereof) according to the flow rates of the operating water heaters. Further, the operating water heaters perform thermal power adjustment to heat water based on a hot water temperature detected by a temperature sensor installed in an outlet pipe.SUMMARY

[0003] Since conventional technology is on premise that all water heaters have substantially same maximum flow rate, how many water heaters to be operated can appropriately be increased or decreased based on the flow rates of the operating water heaters. However, in this type of water heaters, a heating capacity of a heating unit may be decreased by decreasing a maximum flow rate of the water heater when an error related to the heating unit occurs. In a water heating system with such water heaters, the maximum flow rates of the water heaters may differ from each other. In this case, the aforementioned premise may not stand true in the water heating system, and the system may not be able to appropriately increase or decrease the number of operating water heaters. The description herein provides a technique that can appropriately increase or decrease a number of active water heater in a water heating system that includes water heaters configured to decrease its maximum flow rate when an error related to a heating unit occurs.

[0004] In an aspect of the present teachings, a water heating system may comprise: a plurality of water heaters connected in parallel to each other; and a connection controller configured to control the plurality of water heaters. In that case, each of the plurality of water heaters may comprise: a heating unit configured to heat water; a flow rate sensor configured to detect a flow rate of the water flowing into the water heater; a valve configured to limit the flow rate of the water flowing into the water heater to a limit flow rate or lower; and a controller configured to communicate with the connection controller. The controller may be configured to: start heating the water with the heating unit when a detected flow rate detected by the flow rate sensor increases to an ignition flow rate while the heating unit is not heating the water; adjust a heating capacity of the heating unit so that a temperature of the water heated by the heating unit approaches a hot water setting temperature while the heating unit is heating the water; and stop heating the water with the heating unit when the detected flow rate falls to an extinguishing flow rate while the heating unit is heating the water. The connection controller may be configured to: select one or more of the plurality of water heaters as active water heaters and a remainder of the plurality of water heaters as inactive water heaters; send an activation instruction to the controllers of the active water heaters; and send a stop instruction to the controllers of the inactive water heaters. Each of the controllers may be configured to: in a case of receiving the activation instruction from the connection controller, control the valve so that the limit flow rate becomes a maximum flow rate; in a case of receiving the stop instruction from the connection controller, control the valve so that the limit flow rate matches zero; and when an error related to the heating unit occurs, reduce the heating capacity of the heating unit by lowering the maximum flow rate, and send an error signal indicating an occurrence of the error to the connection controller. The connection controller may be configured to: increase or decrease a number of the active water heaters based on the maximum flow rate of the valve and the detected flow rate in each of the active water heaters; and when increasing the number of the active water heaters, select a next active water heater from among one or more water heaters that have not sent an error signal among the inactive water heaters.

[0005] According to the above configuration, if a water heater sending an error signal exists among the inactive water heaters, the connection controller does not select that water heater as the next active water heater. That is, in the above configuration, a water heater of which maximum flow rate is decreased due to the occurrence of the error is excluded from a selection of the next active water heater from among the inactive water heaters. As such, the number of active water heaters can be increased or decreased appropriately in the water heating system that comprises the water heaters that are configured to decrease the maximum flow rate in the event of error occurrence in their heating units. The term “one or more water heaters that have not sent an error signal” herein includes both one or more water heaters that have not sent an error signal in the past and one or more water heaters that had sent an error signal in the past but have not sent an error signal in recent time period.

[0006] In the second aspect of the technology disclosed herein according to the first aspect, each of the plurality of water heaters may further comprise a water temperature sensor configured to detect the temperature of the water flowing into the water heater. In that case, each of the controllers may be configured to adjust the heating capacity of the heating unit based on the hot water setting temperature, the detected flow rate, and a detected temperature detected by the water temperature sensor.

[0007] According to the above configuration, a heat quantity to be given to the water at the flow rate flowing into the water heater can be calculated based on the detected flow rate and a difference between the hot water setting temperature and the detected temperature. Due to this, the heating capacity of the heating unit can be adjusted based on the calculated heat quantity.

[0008] In a third aspect of the technology disclosed herein according to the first or second aspect, each of the heating units may comprise a gas burner.

[0009] According to the above configuration, for example, when an error related to the gas burner occurs, thermal power of the gas burner can be decreased by setting the maximum flow rate to a smaller value.

[0010] In a fourth aspect of the technology disclosed herein according to any one of the first to third aspects, the error related to the heating unit may include a temperature of a predetermined part of the water heater in which the heating unit is incorporated exceeding a threshold temperature. In that case, each of the controllers may be configured to: when the error occurs, decrease the maximum flow rate in steps without sending the error signal to the connection controller; and when the maximum flow rate falls to a threshold flow rate, send the error signal to the connection controller.

[0011] If the temperature of the predetermined part in the water heater exceeds the threshold temperature due to heat generated by the heating unit, a damage may occur in the predetermined part. According to the above configuration, even if the temperature of the predetermined part exceeds the threshold temperature, the error signal is not sent to the connection controller until the maximum flow rate of the water heater becomes lower than the threshold flow rate, and the maximum flow rate is decreased in steps in the meantime. Due to this, by lowering the temperature of the predetermined part of this malfunctioning water heater in steps, a damage that could occur in the predetermined part can be suppressed while still leaving this water heater, of which temperature of the predetermined part has exceeded the threshold temperature, as a candidate that could be selected as an active water heater.

[0012] In a fifth aspect of the technology disclosed herein according to any one of the first to fourth aspects, each of the plurality of water heaters may comprise a first memory configured to store error information indicating that the error is occurring. In that case, each of the controllers may be configured to continuously send the error signal to the connection controller while the error information is stored in the first memory. The connection controller may be configured to, when increasing the number of active water heaters, select a next active water heater from among one or more water heaters that have not sent the error signal in recent time period among the inactive water heaters.

[0013] According to the above configuration, the connection controller can select a water heater that have not sent an error signal in recent time period as the active water heaters.

[0014] In a sixth aspect of the technology disclosed herein according to the fifth aspect, each of the controllers may be configured to, when the error is resolved, delete the error information stored in the first memory.

[0015] According to the above configuration, when the error is resolved, the water heater stops sending the error signal. Due to this, the connection controller can select the water heater for which the error has been resolved as an active water heater.

[0016] In a seventh aspect of the technology disclosed herein according to any one of the first to sixth aspects, each of the controllers may be configured to further send identification information for identifying the water heater together with the error signal to the connection controller. In that case, the connection controller may comprise a second memory configured to store the identification information received from the controller in association with error occurrence information indicating that the error is occurring in the water heater, and the connection controller may be configured to, when increasing the number of active water heaters, select a next active water heater from among one or more water heaters of which identification information is not stored in the second memory in association with the error occurrence information among the inactive water heaters.

[0017] According to the above configuration, the connection controller can select an active water heater based on the identification information stored in association with the error occurrence information in the second memory.

[0018] In an eighth aspect of the technology disclosed herein according to the seventh aspect, each of the controllers may be configured to, when the error is resolved, further send an error resolving signal indicating that the error has been resolved together with the identification information to the connection controller. In that case, the connection controller may be configured to, when receiving the error resolving signal and the identification information, delete at least one of the error occurrence information and the identification information stored in association with the error occurrence information in the second memory.

[0019] According to the above configuration, when the error in the water heater is resolved, at least one of the error occurrence information and the identification information stored in association with the error occurrence information is deleted from the second memory. Due to this, the connection controller can select the water heater for which the error has been resolved as an active water heater.

[0020] In a ninth aspect of the technology disclosed herein according to any one of the first to eighth aspects, the connection controller may be configured to, when receiving the error signal from at least one of the active water heaters, send the stop instruction to the at least one of the active water heaters and select a new active water heater from among the inactive water heaters.

[0021] According to the above configuration, when an error occurs in an active water heater, this active water heater can be stopped and a new active water heater can be selected.

[0022] In a tenth aspect of the technology disclosed herein according to any one of the first to ninth aspects, the water heating system may further comprise a notification unit configured to notify a user of the occurrence of the error.

[0023] According to the above configuration, the user can be made aware that an error has occurred in the water heater.

[0024] In an eleventh aspect of the technology disclosed herein according to any one of the first to tenth aspects, the connection controller may be configured to: determine one of multiple flow rate levels set in multiple stages for the detected flow rate in each of the active water heaters; and increase or decrease the number of the active water heaters based on the respective numbers of the active water heaters of the respective determined flow rate levels.

[0025] When an error related to the heating unit occurs in an active water heater and the maximum flow rate of the active water heater is decreased, the detected flow rate of this active water heater would also be decreased. Due to this, the flow rate level of the detected flow rate of the active water heater of which maximum flow rate has been decreased due to the occurrence of the error related to the heating unit cannot be properly determined. Due to this, when the error related to the heating unit occurs and the maximum flow rate of the active water heater becomes small, the number of the active water heaters for each flow rate level cannot be properly calculated. According to the water heating system disclosed herein, the water heater of which maximum flow rate has been decreased due to the occurrence of the error related to the heating unit is not selected as an active water heater. As such, the number of active water heaters for each flow rate level can be calculated appropriately. Due to this, the number of active water heaters can appropriately be increased or decreased based on the number of the active water heaters for each flow rate level.

[0026] In a twelfth aspect of the technology disclosed herein according to any one of the first to eleventh aspects, the connection controller may be composed of one or more of the controllers of the plurality of water heaters.

[0027] According to the above configuration, for example, a configuration of the water heating system can be simplified compared to a configuration having a connection controller separate from the water heaters.

[0028] Also, the present teachings further discloses a water heater configured to constitute the above-described water heating system. The water heater, which constitutes one of a plurality of water heaters connected in parallel to each other, wherein the plurality of water heaters constitute a water heater set, may comprise: a heating unit configured to heat water; a flow rate sensor configured to detect a flow rate of the water flowing into the water heater; a valve configured to limit the flow rate of the water flowing into the water heater to a limit flow rate or lower; and a controller configured to communicate with one or more other water heaters of the water heater set. In that case, the controller may be configured to selectively execute a primary process and a subordinate process subordinate to the primary process. The subordinate process may comprise: starting to heat the water with the heating unit when a detected flow rate detected by the flow rate sensor increases to an ignition flow rate while the heating unit is not heating the water; adjusting a heating capacity of the heating unit so that a temperature of the water heated by the heating unit approaches a hot water setting temperature while the heating unit is heating the water; and stopping to heat the water with the heating unit when the detected flow rate falls to an extinguishing flow rate while the heating unit is heating the water. The primary process may comprise: selecting one or more of water heaters in the water heater set as active water heaters and a remainder of the plurality of water heaters in the water heater set as inactive water heaters; sending an activation instruction to controllers of the active water heaters; and sending a stop instruction to controllers of the inactive water heaters. The subordinate process may comprise: controlling the valve so that the limit flow rate becomes a maximum flow rate in a case of receiving the activation instruction from a water heater executing the primary process; controlling the valve so that the limit flow rate matches zero in a case of receiving the stop instruction from the water heater executing the primary process; and when an error related to the heating unit occurs, reducing the heating capacity of the heating unit by lowering the maximum flow rate, and sending an error signal indicating an occurrence of the error to the water heater executing the primary process. The primary process may comprise: increasing or decreasing a number of the active water heaters based on the maximum flow rate of the valve and the detected flow rate in each of the active water heaters; and when increasing the number of active water heaters, selecting a next active water heater from among one or more water heaters that have not sent an error signal among the inactive water heaters.

[0029] A connection controller constituting the above water heating system, a non-transitory computer-readable storage medium storing a computer program for the connection controller, and a method of controlling the connection controller are also novel and useful.BRIEF DESCRIPTION OF DRAWINGS

[0030] FIG. 1 shows a schematic diagram of a water heating system 100 according to an embodiment.

[0031] FIG. 2 shows a schematic diagram of a water heater 10A.

[0032] FIG. 3 shows a configurational diagram of the water heating system 100.

[0033] FIG. 4 shows a flowchart of a heating process.

[0034] FIG. 5 shows a flowchart of an error resolution process.

[0035] FIG. 6 shows a flowchart of an active water heater selection process.

[0036] FIG. 7 shows a flowchart of an error notification process.

[0037] FIG. 8 shows a flowchart of an error notification terminating process.DESCRIPTION

[0038] Representative, non-limiting examples of the present disclosure will now be described in further detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing aspects of the present teachings and is not intended to limit the scope of the present disclosure. Furthermore, each of the additional features and teachings disclosed below may be utilized separately or in conjunction with other features and teachings to provide improved a water heating system, as well as a water heater, and methods for using and manufacturing the same.

[0039] Moreover, combinations of features and steps disclosed in the following detailed description may not be necessary to practice the present disclosure in the broadest sense, and are instead taught merely to particularly describe representative examples of the present disclosure. Furthermore, various features of the above-described and below-described representative examples, as well as the various independent and dependent claims, may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings.

[0040] All features disclosed in the description and / or the claims are intended to be disclosed separately and independently from each other for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter, independent of the compositions of the features in the embodiments and / or the claims. In addition, all value ranges or indications of groups of entities are intended to disclose every possible intermediate value or intermediate entity for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter.EMBODIMENT(Configuration of Water Heating System 100)

[0041] As shown in FIG. 1, a water heating system 100 of an embodiment comprises a plurality of water heaters 10A to 10D, a plurality of faucets 2, a hot water supply pipe 4, a water supply pipe 6, and a remote controller 50. The plurality of water heaters 10A to 10D is connected in parallel to the water supply pipe 6 and the hot water supply pipe 4. In the water heating system 100, water is supplied to the plurality of water heaters 10A to 10D through the water supply pipe 6. The plurality of water heaters 10 A to 10D is configured to heat the supplied water to produce hot water. The hot water produced by the plurality of water heaters 10A to 10D is supplied to a user through the hot water supply pipe 4 and the plurality of faucets 2. The water (not ‘hot water’) mentioned herein includes cold water and hot water, in other words, the water of various temperatures may flow therein.(Configuration of Water Heater 10A)

[0042] Referring to FIG. 2, a structure of the water heater 10A among the plurality of water heaters 10A to 10D will be described. Each of the water heaters 10A to 10D has a similar structure. The water heater 10A comprises a water passage pipe 12, a heating medium pipe 14, a heat exchanger 15, an air supply duct 17, an exhaust duct 18, a heating unit 20, and a controller 40.

[0043] An upstream end of the water passage pipe 12 is connected to the water supply pipe 6 (see FIG. 1). Water is supplied to the water passage pipe 12 from the water supply pipe 6. The water passage pipe 12 comprises a water temperature sensor 30, a flow rate sensor 32, a water volume servo 34, a bypass channel 35, a hot water temperature sensor 36, and a bypass servo 38. The water temperature sensor 30, the flow rate sensor 32, and the water volume servo 34 are located upstream of the heat exchanger 15, whereas the hot water temperature sensor 36 and the bypass servo 38 are located downstream of the heat exchanger 15. A downstream end of the water passage pipe 12 is connected to the hot water supply pipe 4 (see FIG. 1).

[0044] The water temperature sensor 30 detects a temperature of the water flowing from the water supply pipe 6 into the water passage pipe 12. The flow rate sensor 32 detects a flow rate of the water flowing from the water supply pipe 6 into the water passage pipe 12. The water volume servo 34 is a so-called servo valve, which limits the flow rate of the water flowing into the water passage pipe 12. The water volume servo 34 is configured to switch between an open state that allows a waterflow from the water supply pipe 6 into the water passage pipe 12 and a closed state that blocks the waterflow from the water supply pipe 6 into the water passage pipe 12. A limit flow rate, which is the flow rate of water flowing from the water supply pipe 6 into the water passage pipe 12, changes according to an opening degree of the water volume servo 34. The bypass channel 35 provides a path for the water to bypass the heat exchanger 15 in the water passage pipe 12. The bypass servo 38 controls a volume of water that flows into the bypass channel 35. The hot water temperature sensor 36 detects a temperature of hot water flowing out of the water passage pipe 12 into the hot water supply pipe 4.

[0045] The heating medium pipe 14 is a closed circuit that circulates heating medium between the heat exchanger 15 and the heating unit 20 in the water heater 10A. The heating medium pipe 14 comprises a pump 16. The pump 16 circulates the heating medium within the heating medium pipe 14. In the present embodiment, the heating medium is water or antifreeze fluid. In a variant, the heating medium pipe 14 may be connected to the heating medium pipes 14 of other water heaters 10B to 10D, for example. The heat exchanger 15 exchanges heat between the heating medium and the water. The heat exchanger 15 causes the heating medium having a high temperature flowing from the heating unit 20 to dissipate heat and lower its temperature, while the water in the water passage pipe 12 is thereby heated to a higher temperature, and hot water is produced.

[0046] The heating unit 20 comprises a gas burner 22, a sensible heat exchanger 24, and a latent heat exchanger 26. The gas burner 22 burns fuel gas (e.g., city gas) supplied from a fuel supply source that is not shown. The sensible heat exchanger 24 exchanges heat between combustion gas burned by the gas burner 22 and the heating medium flowing in the heating medium pipe 14. The latent heat exchanger 26 recovers latent heat of the combustion gas after the heat exchange with the heating medium in the sensible heat exchanger 24, and uses the latent heat to heat the heating medium. By heating the heating medium in the heating medium pipe 14 by both the sensible heat exchanger 24 and the latent heat exchanger 26, energy efficiency can be improved compared to a configuration in which the heating medium is heated only by the sensible heat exchanger 24, for example. Furthermore, by recovering heat from the combustion gas by both the sensible heat exchanger 24 and the latent heat exchanger 26, a temperature in the exhaust duct 18 described below can be decreased compared to, for example, a configuration in which heat is recovered from the combustion gas only by the sensible heat exchanger 24. In a variant, the heating unit 20 may heat the heating medium in the heating medium pipe 14 by an electric heater instead of the gas burner 22. Alternatively, the heating unit 20 may not comprise the latent heat exchanger 26, and may heat the heating medium using only the sensible heat exchanger 24. Alternatively, the water heater 10A may not comprise the heating medium pipe 14, the heat exchanger 15, and the pump 16, and may be configured such that the water passage pipe 12 extends through the heating unit 20 and the water in the water passage pipe 12 is directly heated by the gas burner 22.

[0047] The air supply duct 17 is disposed at a top portion of the water heater 10A, and communicates inside of the water heater 10A with outside. The air supply duct 17 draws air S1 from the outside into the water heater 10A by using a fan (not shown). This enables the gas burner 22 in the heating unit 20 to burn the fuel gas. The exhaust duct 18 is located adjacent to the air supply duct 17 and connects the inside of the water heater 10A with the outside. The exhaust duct 18 is connected to the heating unit 20. In the heating unit 20, the combustion gas produced by the gas burner 22 flows through the latent heat exchanger 26 and the sensible heat exchanger 24, thereby becomes exhaust gas E1, and is discharged to the outside of the water heater 10A through the exhaust duct 18. The exhaust duct 18 comprises an exhaust temperature sensor 19 that detects a temperature of the exhaust gas E1 in the exhaust duct 18.(Configuration of Remote Controller 50)

[0048] The remote controller 50 shown in FIG. 1 is mounted inside user's home (not shown). The remote controller 50 is operated by a user to control the plurality of water heaters 10A to 10D. As shown in FIG. 3, the remote controller 50 comprises an operation unit 51, a display unit 52, a communication I / F 53, and a controller 54. The operation unit 51 receives various inputs from the user. The operation unit 51 receives a user's operation to turn on power of the water heating system 100. The operation unit 51 also receives a user's input of a hot water temperature setting, which is a hot water temperature to be achieved at the faucets 2. The display unit 52 displays various information about the plurality of water heaters 10A to 10D. The communication I / F (abbreviation of interface) 53 is an I / F for communication with each of the water heaters 10A to 10D. The controller 54 is a computer with a CPU and memory.

[0049] As shown in FIG. 3, the water heater 10A further comprises a communication I / F 13. The communication I / F 13 is an I / F for communication with the communication I / Fs of other water heaters 10B to 10D (not shown) and the communication I / F 53 of the remote controller 50. In the present embodiment, each of the water heaters 10A to 10D and the remote controller 50 are connected to each other for wired communication. In a variant, each of the water heaters 10A to 10D and the remote controller 50 may be connected to each other wirelessly.

[0050] The water heater 10A is assigned an ID “01”. Similarly, an ID “02” is assigned to the water heater 10B, an ID “03” is assigned to the water heater 10C, and an ID “04” is assigned to the water heater 10D. Each of the IDs “01” to “04” is information for identifying a water heater. Each of the IDs “01” to “04” is assigned by a primary unit described below when each water heater 10A to 10D is connected.

[0051] The water heaters 10A to 10D of the embodiment are used in connection to each other. In other words, the plurality of water heaters 10A to 10D each operate as individual water heaters while working in cooperation with each other to supply hot water to the plurality of faucets 2. When the power of the water heating system 100 is turned on at the remote controller 50, all of the connected water heaters 10A to 10D are turned on. In the water heating system 100, when a hot water setting temperature is entered at the remote controller 50 and the hot water supply pipe 4 is opened by a faucet 2, hot water heated to the hot water setting temperature is supplied from the faucet 2.

[0052] For example, if a flow rate of hot water supplied from the faucet 2 is relatively small, the water volume servo 34 of one water heater (e.g., 10A) is opened and the water volume servos 34 of the other water heaters 10B to 10D are closed. As a result, only the water heater 10A heats the water and supplies the hot water to the faucet 2. If the flow rate of the hot water supplied to the faucet 2 is relatively high, a number of water heaters to be activated is increased. For example, the water volume servos 34 of two water heaters (e.g., 10A and 10B) are opened and the water volume servos 34 of the other water heaters 10C and 10D are closed. Due to this, a relatively high flow rate of hot water can be supplied to the faucet 2 using the two water heaters 10A and 10B.

[0053] Thus, when the water heaters 10A to 10D are used in connection together, energy consumption can be decreased, for example, when supplying a comparatively small flow rate of hot water to the faucet 2 as compared to a system with a single water heater having a large heating capacity equaling a sum of heating capacities of the water heaters 10A to 10D, for example. Furthermore, since various heating capacities can be achieved by connecting the water heaters 10A to 10D of the same type, versatility of the water heaters 10A to 10D can be improved.

[0054] When the water heaters 10A to 10D are used in connection to each other, a water heater selected from these water heaters 10A to 10D operates as a “primary unit”. In addition, the plurality of water heaters 10A to 10D also operates as “subordinate units”. Here, the “primary unit” is the water heater that primarily manages the entire water heating system 100. In contrast, the “subordinate units” are water heaters that operate subordinately to the primary unit. The water heater 10A is capable of operating as the “primary unit” and also as the “subordinate unit”. That is, in the present embodiment, the water heater 10A can selectively perform primary unit processing based on its operation as the primary unit and a subordinate unit processing based on its operation as the subordinate unit. Due to this, the configuration of the water heating system 100 can be simplified as compared for example to a system with a consolidated controller that manages the entire water heating system 100 separately from each of the water heaters 10A to 10D.

[0055] The water heater 10A executes, as the primary unit processing, for example, an active water heater selection process (see FIG. 6) to select a water heater to be activated (as an active water heater) from among the water heaters 10A to 10D. The water heaters 10A to 10D are configured to execute, as the subordinate unit processing, for example, a heating process (see FIG. 4) to heat the water in response to receiving an activation instruction from the primary unit. Hereinbelow, the water heater selected as the primary unit may simply be termed the “primary unit” and the water heaters selected as the subordinate units may simply be termed the “subordinate units”.

[0056] The water heater 10A may be selected as the primary unit by the user, for example, when connecting the water heaters 10A to 10D. The water heater 10A may also be automatically selected as the primary unit based on information such as unique serial numbers assigned to the water heaters 10A to 10D. In other words, the water heater 10A is not set as the primary unit at the time of its manufacture, and may be selected as the primary unit after it has been connected with the other water heaters 10B to 10D.(Configuration of Controller 40)

[0057] As shown in FIG. 3, the controller 40 of the water heater 10A is a computer with a CPU 42 and a memory 44. The controller 40 is electrically connected to respective units and modules of the water heater 10A. The controller 40 receives, for example, values detected from each of the sensors 30, 32, 36, 19 for example. Further, the controller 40 also controls operations of the pump 16, the gas burner 22, the water volume servo 34, and the bypass servo 38, for example.

[0058] The memory 44 comprises volatile and non-volatile memories. The memory 44 stores a program 46, a primary unit flag F1, an ignition flow rate L1, a correction value L2, an extinguishing flow rate L3, a threshold temperature Tth1, a threshold flow rate Lth1, a water heater table Ta1, a determination formula table Ta2, and a condition table Ta3. Each of the information is stored in the memory 44 in advance at the time of manufacture of the water heater 10A. In a variant, each of the information may be downloaded a posteriori via the Internet from a server provided by a vendor of the water heater 10A, for example, or installed a posteriori via a medium.

[0059] The controller 40 executes various processes according to the program 46 stored in the memory 44. For example, the controller 40 executes a thermal power adjustment process (see S22 in FIG. 4) to adjust thermal power of the gas burner 22 in the heating unit 20. In the thermal power adjustment process, the controller 40 calculates a required heat quantity by multiplying a detected flow rate detected by the flow rate sensor 32 to a difference between the hot water setting temperature received from the remote controller 50 and a detected temperature detected by the water temperature sensor 30, and adjusts the thermal power of the gas burner 22 according to the calculated required heat quantity. As a result, a temperature of the hot water heated by the heating unit 20 approaches the hot water setting temperature. In addition, the controller 40 executes each of the processes shown in FIGS. 4 to 8.

[0060] The primary unit flag F1 is information indicating that the water heater 10A is selected as the primary unit in the water heating system 100. The primary unit flag F1 is stored in the memory 44, for example, in response to the water heater 10A being selected by the user or a setup service provider. When the primary unit flag F1 is stored in the memory 44, the controller 40 recognizes that it has been selected as the primary unit and executes the primary unit processing shown, for example, in FIGS. 6 to 8. When the primary unit flag F1 is not stored in the memory 44, the controller 40 recognizes that it is selected as a subordinate unit, and executes a subordinate unit processing shown in FIGS. 4 and 5, for example. Here, the controller 40 can execute the subordinate unit processing even if the primary unit flag F1 is stored in the memory 44, i.e., even if it is selected as the primary unit.

[0061] The ignition flow rate L1 is a flow rate used to determine a timing to ignite the gas burner 22 in the heating unit 20. For example, if the water volume servo 34 is fully open but the faucet 2 is closed, the water stagnates in the water passage pipe 12. If the gas burner 22 is ignited in this state, the temperature of the water stagnant in the water passage pipe 12 could become too high. For this reason, the gas burner 22 is ignited when the faucet 2 is opened and a flow rate of L1 or more is detected by the flow rate sensor 32.

[0062] The correction value L2 is used to calculate a minimum flow rate L4 described below based on the ignition flow rate L1.

[0063] The extinguishing flow rate L3 is a flow rate used to determine a timing to extinguish the gas burner 22 in the heating unit 20. When the faucet 2 is closed, the flow rate of the water in the water passage pipe 12 decreases to the extinguishing flow rate L3 or below. Due to this, the gas burner 22 is extinguished in response to the closing of the faucet 2 and the detection of a flow rate falling to the extinguishing flow rate L3 or below. The extinguishing flow rate L3 is set to a value that is smaller than the ignition flow rate L1. Due to this, the gas burner 22 can be suppressed from being repeatedly ignited and extinguished too frequently. However, the extinguishing flow rate L3 may be at a same value as the ignition flow rate L1.

[0064] The threshold temperature Tth1 corresponds to an exhaust temperature detected by the exhaust temperature sensor 19. The threshold temperature Tth1 is a temperature to determine, for example, that the exhaust duct 18 may be damaged by a temperature rise of the exhaust gas E1 in the exhaust duct 18. The threshold temperature Tth1 is set according to materials of the exhaust duct 18 and peripheral members of the exhaust duct 18. For example, when the peripheral members of the exhaust duct 18 contain resin, the threshold temperature Tth1 is set comparatively low. This can prevent the resin of the peripheral members from melting. Thus, the temperature of the exhaust gas E1 produced by combustion of the gas burner 22 (i.e., the exhaust temperature) must be kept at or below the threshold temperature Tth1. Here, as mentioned earlier, the thermal power of the gas burner 22 is adjusted according to the required heat quantity calculated by a product of the detected flow rate and the difference between the hot water setting temperature and the detected temperature. Further, when the maximum flow rate becomes smaller, i.e., when the opening degree of the water volume servo 34 becomes smaller, the detected flow rate, which is the flow rate of the hot water flowing from the water supply pipe 6 into the water passage pipe 12, also becomes smaller. Due to this, for example, the thermal power of the gas burner 22 at a first maximum flow rate is smaller than the thermal power of the gas burner 22 at a second maximum flow rate, which is larger than the first maximum flow rate. In the water heater 10A, when the exhaust temperature increases to the threshold temperature Tth1, a process of decreasing the maximum flow rate is executed by decreasing the opening degree of the water volume servo 34. Due to this, the thermal power of the gas burner 22 is decreased, and thus the exhaust temperature can be lowered.

[0065] The threshold flow rate Lth1 corresponds to a detected flow rate detected by the flow rate sensor 32. The threshold flow rate Lth1 is a value used in the heating process described below, and represents a lower limit value of the maximum flow rate.

[0066] The water heater table Ta1 is information used by the primary unit to manage each of the water heaters 10A to 10D. Due to this, the water heater table Ta1 is stored in the memory 44 of the primary unit (i.e., water heater 10A) and not in the memories 44 of the other water heaters 10B to 10D. The primary unit retrieves various information from each of the water heaters 10B to 10D at a timing when it is connected to the other water heaters 10B to 10D, and stores the information in the water heater table Ta1. In addition to the water heater 10A, the water heater table Ta1 stores a valve status, the maximum flow rate, the detected flow rate, and status information for the other water heaters 10B to 10D that are connected. The valve status indicates either “open”, indicating that the water volume servo 34 is fully open, or “closed”, indicating that it is fully closed. The valve status may further indicate, for example, “50%” indicating that the water volume servo 34 is only half open. The maximum flow rate indicates the flow rate of water that can currently be supplied to the water heaters 10A to 10D. The detected flow rate indicates the flow rate that the flow rate sensor 32 currently detects. The status information indicates either “error”, indicating that an error is occurring in the water heater, and “normal”, indicating that no error is occurring. In the present embodiment, the error includes, for example, the exhaust temperature detected by the exhaust temperature sensor 19 located in the exhaust duct 18 becoming the threshold temperature Tth1 described above or higher. In a variant, the error may be a blockage of the exhaust duct 18, overheating of the heating unit 20, or overheating of a housing (reference sign not given) of the water heater 10A. Further, the water heater table Ta1 may, for example, store only the valve statuses of the water heaters 10A to 10D.

[0067] The determination formula table Ta2 stores determination formulas for determining a flow rate level of the detected flow rate. The flow rate levels include “small,”“medium,” and “large”. In the present embodiment, the flow rate level is determined to be “small” when the detected flow rate is at the minimum flow rate L4 or below. The minimum flow rate L4 is a flow rate obtained by adding the correction value L2 to the ignition flow rate L1 described above. Further, when the detected flow rate is greater than the minimum flow rate L4 and equal to or less than an upper limit flow rate L5, the flow rate level is determined to be “medium”. The upper limit flow rate L5 is a predetermined value that is set based on the maximum flow rate. In the present embodiment, the upper limit flow rate L5 is 90% of the maximum flow rate. That is, the upper limit flow rate L5 is a value set based on the maximum flow rate. When the detected flow rate is higher than the upper limit flow rate L5, the flow rate level is determined to be “large”.

[0068] The condition table Ta3 stores an increase condition for increasing a number of active water heaters by selecting water heater(s) from among inactive water heaters, and a decrease condition for decreasing the number of active water heaters by stopping operation of the active water heaters. An “inactive water heater” herein is a water heater among the plurality of water heaters 10A to 10D that is not operating. More specifically, a water heater of which valve status as described above indicates “closed” is an inactive water heater. Contrary to this, an “active water heater” is a water heater among the plurality of water heaters 10A to 10D that is operating. More specifically, a water heater of which valve status indicates “open” is an active water heater. In the present embodiment, the increase condition is satisfied when a number of active water heaters of which flow rate level is “large” among the active water heaters exceeds a number of active water heaters of which flow rate level is “small”. In this case, an active water heater is selected from among the inactive water heaters, and the water volume servo 34 of that water heater is opened. As a result, the number of active water heaters is increased. Further, the decrease condition is satisfied when the number of the active water heaters of which flow rate level is “small” exceeds the number of active water heaters of which flow rate level is “large” among the active water heaters. In this case, a water heater to be stopped (inactive water heater) is selected from among the active water heaters, and the water volume servo 34 of that water heater is closed. As a result, the number of active water heaters is decreased. Although not shown, if the number of active water heaters at flow rate level “small” is equal to the number of active water heaters at flow rate level “large”, the number of active water heaters is maintained. Thus, in the present embodiment, the number of active water heaters is increased or decreased based on the condition table Ta3, which is based on the number of active water heaters for each flow rate level “small,”“medium”, and “large”.

[0069] Here, specific examples of the increase and decrease conditions will be explained. First, Case C1 in which no error is occurring in the water heaters will be explained. As an example, a case under a state in which only the water heater 10A with ID “01” is selected as the active water heater, where the maximum flow rate Lm1 of the water heater 10A is 10 L / min, the detected flow rate Ld1 is 9.6 L / min, and the minimum flow rate L4 is 3.0 L / min will be described, for example. The detected flow rate of 9.6 L / min exceeds the upper limit flow rate L5 (9.0 L / min, i.e., 90% of the maximum flow rate of 10 L / min). Due to this, based on the determination formula table Ta2, the detected flow rate Ld1 of the water heater 10A is determined to be at flow rate level “large”. In this case, the number of active water heaters at flow rate level “large” (i.e., 1 unit) becomes larger than the number of active water heaters at flow rate level “small” (i.e., 0 unit), and the increase condition is satisfied.

[0070] Due to this, a water heater (e.g., 10B) to be the next active water heater is selected, and the water volume servo 34 of this water heater 10B is opened. As a result, the 9.6 L / min water that has flowed into the water heater 10A alone is distributed to the two water heaters 10A and 10B. As a result, the detected flow rate of each water heater 10A and 10B decreases to about 4.8 L / min, which is about half of 9.6 L / min. In this case, since the detected flow rate of each of the active water heaters 10A and 10B is greater than the minimum flow rate L4 (3.0 L / min) and equal to or less than the upper limit flow rate L5 (9.0 L / min), both of the detected flow rates are determined to be at flow rate level “medium”. This means that the number of water heaters at flow rate level “small” (i.e., 0 units) is equal to the number of water heaters at flow rate level “large” (i.e., 0 units), and since neither the increase condition nor the decrease condition is satisfied, operation of each water heater 10A and 10B is continued.

[0071] Next, Case C2 in which an error occurs in the water heater 10A will be described. In this case, for example, an error is occurring in the water heater 10A under the state in which only the water heater 10A with ID “01” is selected as the active water heater. Due to this, in this case, instead of the information enclosed by a dashed line of Case C1, information enclosed by a dashed line of Case C2, shown to the right of the water heater table Ta1, is stored in the water heater table Ta1. Although details will be described below with reference to FIG. 4, when, for example, the exhaust temperature of exhaust gas E1 detected by the exhaust temperature sensor 19 becomes the threshold temperature Tth1 or higher, the maximum flow rate of the water heater 10A is decreased from Lm1 (10 L / min) to Lm2 (6 L / min).

[0072] When the maximum flow rate Lm2 is set at 6 L / min, for example, and the detected flow rate Ld2 of the water heater 10A becomes 5.6 L / min, the detected flow rate Ld2 exceeds the upper limit flow rate L5 (5.4 L / min, or 90% of the maximum flow rate Lm2) and the detected flow rate Ld2 is determined to be at flow rate level “large”. In this case, as in the aforementioned example, the number of water heaters at flow rate level “large” (i.e., 1 unit) is greater than the number of water heaters at flow rate level “small” (i.e., 0 unit), and thus the water heater 10B is selected as the next active water heater. In Case C2, the detected flow rate of the water heater 10B decreases to about 2.8 L / min, which is about half of 5.6 L / min. This is less than the minimum flow rate L4 (3.0 L / min) described above. Due to this, the detected flow rates of the water heaters 10A and 10B are both determined to be at flow rate level “small”. As a result, the number of active water heaters at flow rate level “small” (i.e., 2 units) becomes larger than the number of active water heaters at flow rate level “large” (i.e., 0 units). In this case, since the decrease condition is satisfied, one (e.g., 10B) of the water heaters 10A and 10B is selected as an inactive water heater and the operation of that water heater is stopped. In other words, in this case, the water volume servo 34 of the water heater 10B selected as the inactive water heater is closed.

[0073] When the water volume servo 34 of the water heater 10B is closed, the flow rate of water flowing into the water heater 10B becomes zero. The water that was flowing into the water heater 10B flows back into the water heater 10A, where the water volume servo 34 is continuously open. Due to this, the detected flow rate Ld2 of the water heater 10A rises again to 5.6 L / min. In this case, as described above, the detected flow rate Ld2 of the water heater 10A is determined to be at flow rate level “large,” the increase condition is satisfied, 10B is again selected as the next active water heater, for example, and the water volume servo 34 of this water heater is opened. However, when the water that was flowing into the water heater 10A is divided into multiple flows as described above, the detected flow rate of each of the water heaters 10A and 10B falls below the minimum flow rate L4, the decrease condition is satisfied, and the water volume servo 34 of one of the water heaters 10A and 10B (for example, 10B) is closed. In this configuration that decreases the maximum flow rate when an error occurs, if the maximum flow rate is decreased to twice the minimum flow rate L4 or less, the number of active water heaters may increase, and when the water is divided into multiple flows, the detected flow rate may become the minimum flow rate L4 or less, and the increase or decrease of the number of active water heaters may be repeated frequently. The following describes processes executed in the water heating system 100 of the embodiment to appropriately calculate the number of active water heaters and appropriately increase or decrease the number of active water heaters in the configuration that decreases the maximum flow rate when an error occurs.(Heating Process)

[0074] Referring to FIG. 4, a heating process executed by the controllers 40 (i.e., CPUs 42) of the water heaters 10A to 10D will be described. The heating process is a process in which each water heater 10A to 10D heats the water supplied from the water supply pipe 6 (see FIG. 1), and is a subordinate process commonly executed by the water heaters 10A to 10D. The controller 40 of each of the water heaters 10A to 10D executes the process of FIG. 4 in response to receiving the aforementioned activation instruction from the primary unit (e.g., 10A).

[0075] In S2, the controller 40 fully opens the water volume servo 34. Due to this, when the faucet 2 is operated by the user and the hot water supply pipe 4 is opened, the water from the water supply pipe 6 is enabled to flow into the water passage pipe 12.

[0076] In S10, the controller 40 monitors the detected flow rate of the flow rate sensor 32 increases to the ignition flow rate L1 in the memory 44. If the detected flow rate increases to the ignition flow rate L1 (YES in S10), the controller 40 proceeds to S20.

[0077] In S20, the controller 40 ignites the gas burner 22. This starts heating of the water in the water passage pipe 12.

[0078] In S22, the controller 40 executes the thermal power adjustment process. As described above, in the thermal power adjustment process, the thermal power of the gas burner 22 is adjusted according to the required heat quantity calculated by multiplying the detected flow rate to the difference between the hot water setting temperature and the detected temperature. Due to this, the temperature of the water heated by the gas burner 22 approaches the hot water setting temperature inputted by the user to the remote controller 50.

[0079] In S30, the controller 40 monitors that the detected flow rate falls to the extinguishing flow rate L3 in the memory 44. If the detected flow rate falls to the extinguishing flow rate L3 (YES in S30), the controller 40 proceeds to S60. If the detected flow rate exceeds the extinguishing flow rate L3 (NO in S30), the controller 40 proceeds to S40.

[0080] In S40, the controller 40 determines whether the exhaust temperature detected by the exhaust temperature sensor 19 is equal to or higher than the threshold temperature Tth1 in the memory 44. If the exhaust temperature is less than the threshold temperature Tth1 (NO in S40), the controller 40 returns to S22 and executes the thermal power adjustment process again in S22. If the exhaust temperature is equal to or higher than the threshold temperature Tth1 (YES in S40), the controller 40 proceeds to S42.

[0081] In S42, the controller 40 decreases the maximum flow rate by decreasing the opening degree of the water volume servo 34. Here, the controller 40 decreases the maximum flow rate in steps according to a difference between the exhaust temperature and the threshold temperature Tth1. Specifically, the controller 40 decreases the maximum flow rate by a first flow rate amount when the difference between the exhaust temperature and the threshold temperature Tth1 exceeds a predetermined value. Further, if the difference between the exhaust temperature and the threshold temperature Tth1 does not exceed the predetermined value, the controller 40 decreases the maximum flow rate by a second flow rate amount, which is smaller than the first flow rate amount. In a variant, the controller 40 may decrease the maximum flow rate by a flow rate amount proportional to the difference between the exhaust temperature and the threshold temperature Tth1, or it may decrease the maximum flow rate by a predetermined set flow rate amount regardless of the difference between the exhaust temperature and the threshold temperature Tth1.

[0082] In S50, the controller 40 determines whether the maximum flow rate is equal to or less than the threshold flow rate Lth1 in the memory 44. If the maximum flow rate exceeds the threshold flow rate Lth1 (NO in S50), the controller 40 returns to S22 and again executes the thermal power adjustment process. When the maximum flow rate is decreased by the process in S42, that is, when the opening degree of the water volume servo 34 is decreased, the flow rate of the water flowing into the water passage pipe 12 (that is, the detected flow rate) decreases. As mentioned earlier, when the detected flow rate decreases, the exhaust temperature decreases because the thermal power of the gas burner 22 is decreased. When the exhaust temperature is higher than the threshold temperature Tth1 (YES in S40), the controller 40 repeats the processes from S22 to S42 until the maximum flow rate falls to the threshold flow rate Lth1. Due to this, the controller 40 decreases the maximum flow rate in steps until the maximum flow rate falls to the threshold flow rate Lth1, and the exhaust temperature can be decreased in steps. Thus, the exhaust temperature can be suppressed from continuing to exceed the threshold temperature Tth1. Here, the exhaust temperature can be decreased to a lower temperature when the threshold flow rate Lth1 is smaller. However, if, for example, the threshold flow rate Lth1 becomes too small, the increase or decrease in the number of active water heaters will be repeated frequently, as in the specific example described above. Due to this, in the present embodiment, a value obtained by adding a predetermined correction value to a flow rate obtained by doubling the minimum flow rate L4 is used as the threshold flow rate Lth1. Due to this, as in the aforementioned specific example, the maximum flow rate Lm2 does not become twice the minimum flow rate L4 or less. As such, even if the number of active water heaters increases and the water is divided into multiple flows, the increase or decrease in the number of active water heaters can be suppressed from being repeated frequently. When the maximum flow rate is equal to or less than the threshold flow rate Lth1 (YES in S50), the controller 40 proceeds to S52.

[0083] In S52, the controller 40 stores error information in the memory 44. The error information indicates that an error is occurring in the water heater (e.g., 10A) in which the controller 40 is located.

[0084] In S54, the controller 40 continuously sends an error signal to the primary unit. Due to this, the controller 40 can inform the primary unit that an error is occurring in the water heater in which the controller 40 is located. If an error occurs in the water heater 10A selected as the primary unit, the controller 40 of the water heater 10A sends an error signal to itself. That is, in this case, the error signal is sent and received within a control board of the controller 40 of the water heater 10A. Due to this, the controller 40 of the water heater 10A can acknowledge that an error is occurring in itself.

[0085] In S56, the controller 40 receives a stop signal from the primary unit that received the error signal.

[0086] In S60, the controller 40 extinguishes the gas burner 22. This stops the heating of the water in the water passage pipe 12.

[0087] In S62, the controller 40 fully closes the water volume servo 34. Due to this, the flow rate of water flowing into the water heater 10A becomes zero. After S62, the process of FIG. 4 is terminated.(Error Resolution Process)

[0088] With reference to FIG. 5, an error resolution process executed by the controller 40 will be described. The error resolution process is executed when the error is resolved in the water heater in which the error has occurred. Hereafter, the water heater in which the error occurred may be termed an “abnormal water heater”. The controller 40 of the abnormal water heater executes the process of FIG. 5 in response to receiving a resolution operation acceptance signal from the remote controller 50. The resolution operation acceptance signal is sent to the abnormal water heater by the remote controller 50 when, for example, a repairman cleans the exhaust duct 18 of the water heater in which the error occurred and thereafter performs an error resolution operation indicating that the error has been resolved using the operation unit 51 of the remote controller 50. In an initial stage of FIG. 5, the controller 40 continues to send the error signal (see S54 in FIG. 4). A method of sending the resolution operation acceptance signal is not limited to transmission from the remote controller 50, and various methods may be used.

[0089] In S70, the controller 40 deletes the error information in the memory 44 stored in S52 of FIG. 4.

[0090] In S72, the controller 40 stops sending the error signal to the primary unit that it started sending in S54 of FIG. 4. That is, the controller 40 continuously sends the error signal to the primary unit until the error information is deleted in S70.

[0091] In S80, the controller 40 sends its ID and the error resolution signal to the primary unit. This informs the primary unit that the error has been resolved. After S80, the process of FIG. 5 is terminated.(Active Water Heater Selection Process)

[0092] Referring to FIG. 6, an active water heater selection process executed by the controller 40 will be described. The active water heater selection process is a process of selecting active water heater(s), and is one of the primary unit processing described above. For example, the controller 40 executes a process shown in FIG. 6 in response to the water heating system 100 being turned on by the remote controller 50. If the primary unit flag F1 (see FIG. 3) is stored in its own memory 44, the controller 40 continues the process of FIG. 6 while the water heating system 100 is turned on.

[0093] In S90, the controller 40 selects a water heater to be the active water heater. The controller 40 selects water heaters in a predetermined order (e.g., in an order of IDs “01” to “04”) among the plurality of water heaters 10A to 10D. Hereinbelow, the water heater selected in S90 may be termed “target water heater” and the ID of the target water heater may be termed “target ID”.

[0094] In S100, the controller 40 determines whether the status information stored in the water heater table Ta1 associated with the target ID of the target water heater selected in S90 is “error”, or whether an error signal (see S70 in FIG. 5) has so far been received from the target water heater together with the target ID. If at least one of the following is satisfied: either the status information of the target water heater is “error” or an error signal has been received from the target water heater (YES in S100), the controller 40 determines that an error is occurring in the target water heater and returns to S90 to select another water heater as the target water heater. As above, the controller 40 determines whether or not an error is occurring in the target water heater based on both the condition that the status information is “error” and the condition that an error signal has been received from the target water heater. Due to this, even if communication between the primary unit and the subordinate unit becomes interruptive and an error signal is not properly received from the subordinate unit, for example, it is still possible to determine that an error is occurring in the target water heater based on the status information in the memory 44. In a variant, in S100, the controller 40 may determine that an error is occurring in the target water heater based on either the status information of the target water heater being “error” or an error signal having been received from the target water heater. The controller 40 repeats the process of S90 and S100 until a target water heater that is not experiencing an error is selected. If the status information of the target water heater is “normal” and no error signal is received from this target water heater (NO in S100), the controller 40 determines that the target water heater is normal and proceeds to S102.

[0095] In S102, the controller 40 sends the activation instruction to the target water heater. That is, the target water heater is selected as an active water heater. Due to this, the active water heater executes the heating process shown in FIG. 4.

[0096] In S104, the controller 40 obtains the detected flow rate from the active water heater that sent the activation instruction in S102.

[0097] In S106, the controller 40 identifies the flow rate level of the detected flow rate of the active water heater obtained in S104 by using the determination formula table Ta2 in the memory 44.

[0098] In S110, the controller 40 determines whether the increase condition is satisfied based on the flow rate level identified in S106 and the condition table Ta3 in the memory 44. If the increase condition is satisfied (YES in S110), the controller 40 returns to S90 and selects a new target water heater. Due to this, the process of S100 described above is executed for that target water heater, and a new normal target water heater is identified, and the number of active water heaters can thus be increased. If the increase condition is not satisfied (NO in S110), the controller 40 proceeds to S120.

[0099] In S120, the controller 40 determines whether there are two or more active water heaters based on the water heater table Ta1 in the memory 44. Specifically, the controller 40 determines whether there are two or more water heaters of which valve status in the water heater table Ta1 indicates “open”. If there is only one active water heater (NO in S120), the controller 40 returns to S104 and again obtains the detected flow rates from the activated water heaters. That is, when there is only one active water heater, the controller 40 repeats the process from S104 to S110 until the increase condition is satisfied. If there are two or more active water heaters (YES in S120), the controller 40 proceeds to S130.

[0100] In S130, the controller 40 determines whether the decrease condition is satisfied based on the flow rate level identified in S106 and the condition table Ta3 in the memory 44. If the decrease condition is not satisfied (NO in S130), the controller 40 returns to S104 and again obtains the detected flow rates of the active water heaters. If the decrease condition is satisfied (YES in S130), the controller 40 proceeds to S132.

[0101] In S132, the controller 40 identifies the active water heaters to which a stop instruction is to be sent based on a pre-stored order (e.g., in an order of longest to shortest actual operation time) among the plurality of active water heaters, and sends the stop instruction to the identified active water heater. Due to this, the active water heater extinguishes the gas burner 22 (S60 in FIG. 4) and fully closes the water volume servo 34 (S62). Due to this, the number of active water heaters is decreased.(Error Notification Process)

[0102] Referring to FIG. 7, an error notification process executed by the controller 40 is described. The error notification process is a primary unit processing that is executed in parallel with the aforementioned active water heater selection process of FIG. 6. The error notification process is a process of notifying, if an error has occurred in an active water heater, the occurrence of the error and stopping the operation of this active water heater in which the error is occurring. The controller 40 executes a process of FIG. 7 in response to receiving an error signal (S54 in FIG. 4) from the abnormal water heater described above.

[0103] In S140, the controller 40 sends a notification instruction to the remote controller 50. The notification instruction is an instruction to the remote controller 50 to display an error occurrence screen on the display unit 52 of the remote controller 50 and to output an alarm sound. The error occurrence screen includes an error code indicating that the exhaust temperature of the abnormal water heater exceeds the threshold temperature Tth1, and the ID of the abnormal water heater. Due to this, the user can recognize which of the plurality of water heaters 10A to 10D is the abnormal water heater, in addition to the fact that an error has occurred in the water heater.

[0104] In S150, the controller 40 sends a stop signal to the abnormal water heater (S56 in FIG. 4). As a result, the controller 40 of the abnormal water heater extinguishes the gas burner 22 (S60 in FIG. 4) and fully closes the water volume servo 34 (S62 in FIG. 4). Due to this, the operation of the abnormal water heater is stopped, and the next active water heater is selected from among the inactive water heaters in the process described in FIG. 6.(Error Notification Terminating Process)

[0105] Referring to FIG. 8, an error notification terminating process executed by the controller 40 will be described. Similar to the error notification process shown in FIG. 7, the error notification terminating process is also primary unit processing that is executed in parallel with the active water heater selection process shown in FIG. 6. The error notification terminating process is a process for changing the abnormal water heater to be selectable as an active water heater when the error is resolved in the abnormal water heater. The controller 40 executes a process shown in FIG. 8 in response to receiving the ID and the error resolution signal from the abnormal water heater (S80 in FIG. 5).

[0106] In S160, the controller 40 changes the status information stored in association with the ID of the received abnormal water heater from “error” to “normal” based on the water heater table Ta1. That is, the controller 40 deletes the status information indicating the error stored in association with the ID of the abnormal water heater. Due to this, the controller 40 can recognize that the error of the abnormal water heater has been resolved (S100 in FIG. 6). As a result, the controller 40 is enabled to select the abnormal water heater as the next active water heater in the subsequent active water heater selection process (see FIG. 6).

[0107] In S170, the controller 40 sends a notification stop instruction to the remote controller 50. The notification stop instruction is an instruction to the remote controller 50 to stop displaying the error occurrence screen and outputting the alarm sound described above. By doing so, the user can recognize that the error of the abnormal water heater has been resolved. After S170, the process in FIG. 8 is terminated.(Effects of Embodiment)

[0108] Thus, in the water heating system 100 of the embodiment, when the target water heater sends an error signal, that is, when an error is occurring in the target water heater (YES in S100 of FIG. 6), this target water heater is not selected as the active water heater. Due to this, the water heater of which maximum flow rate has been decreased is not selected as the active water heater. That is, among the inactive water heaters, the water heater of which maximum flow rate has been decreased is excluded from the selection of an active water heater. Due to this, the water heating system 100 can appropriately calculate the number of active water heaters for each flow rate level despite the presence of differences between the maximum flow rates for the respective water heaters, and thus can suitably increase or decrease the number of active water heaters.

[0109] Further, in the water heating system 100 of the embodiment, the water heater 10A can continue to operate by decreasing the maximum flow rate (S42) and thermal power (S22) even if the exhaust temperature becomes the threshold temperature Tth1 or higher (YES in S40 of FIG. 4). However, if the maximum flow rate of the water heater 10A is decreased to the threshold flow rate Lth1 (YES in S50 of FIG. 4), the primary unit does not select the water heater 10A as an active water heater (S100 in FIG. 6). As such, even when an error has occurred, the water heating system 100 can appropriately increase or decrease the number of active water heaters by excluding the water heater 10A from the selection of active water heater while allowing individual operation of the water heater 10A.(Corresponding Relationships)

[0110] The controller 40 that executes the processes in FIGS. 6, 7, and 8, i.e., the controller 40 that executes the primary unit processing, is an example of “connection controller”, and the controller 40 that executes the processes in FIGS. 4 and 5, i.e., the controller 40 that executes the subordinate unit processing, is an example of “controller”. The exhaust duct 18 is an example of “predetermined part”. The status information “error” is an example of “error occurrence information”.(Variant 1)

[0111] The water heating system 100 may further comprise a connection controller separate from the plurality of water heaters 10A to 10D and that manages the entire water heating system 100. In that case, the controllers 40 of the water heaters 10A to 10D may perform only the subordinate unit processing of FIGS. 4 and 5, and the connection controller may perform the primary unit processing of FIGS. 6 to 8.(Variant 2)

[0112] The formula for determining the flow rate level “large” may include, for example, the difference between the maximum flow rate and the detected flow rate being less than a predetermined threshold, instead of the detected flow rate exceeding the upper limit flow rate L5 (90% of the maximum flow rate).(Variant 3)

[0113] In the process of S22 of FIG. 4, the controller 40 may, for example, calculate a heat quantity that will additionally be required by using the product of the detected flow rate and the difference between the hot water setting temperature and the hot water temperature detected by the hot water temperature sensor 36, and adjust the thermal power of the gas burner 22 so that the hot water temperature approaches the hot water setting temperature, instead of calculating the required heat quantity by the product of the detected flow rate and the difference between the hot water setting temperature and the detected temperature and adjusting the thermal power of the gas burner 22 so that the temperature of heated water approaches the hot water setting temperature. In another variation, the controller 40 may adjust the thermal power of the gas burner 22 so that the hot water temperature approaches the hot water setting temperature by using both the difference between the hot water setting temperature and the detected temperature as well as the difference between the hot water setting temperature and the hot water temperature.(Variant 4)

[0114] The plurality of water heaters 10A to 10D may each comprise a heat exchanger temperature sensor configured to detect a temperature around the sensible heat exchanger 24, for example, instead of or in addition to the exhaust temperature sensor 19. In that case, the controller 40 may compare the detected temperature of the heat exchanger temperature sensor with a threshold temperature in S40 of FIG. 4, and if the detected temperature of the heat exchanger temperature sensor is equal to or higher than the threshold temperature (YES in S40), the process may proceed to S42. Due to this, a temperature of the area around the sensible heat exchanger 24 can be suppressed from exceeding beyond the threshold temperature. In this variant, the area around the sensible heat exchanger 24 is an example of “predetermined part”. In a yet another variant, the plurality of water heaters 10A to 10D may each comprise a heat exchanger temperature sensor configured to detect a temperature around the latent heat exchanger 26. In this variation, the area around the latent heat exchanger 26 is an example of “predetermined part”.

Claims

1. A water heating system comprising:a plurality of water heaters connected in parallel to each other; anda connection controller configured to control the plurality of water heaters,wherein each of the plurality of water heaters comprises:a heating unit configured to heat water;a flow rate sensor configured to detect a flow rate of the water flowing into the water heater;a valve configured to limit the flow rate of the water flowing into the water heater to a limit flow rate or lower; anda controller configured to communicate with the connection controller,wherein the controller is configured to:start heating the water with the heating unit when a detected flow rate detected by the flow rate sensor increases to an ignition flow rate while the heating unit is not heating the water;adjust a heating capacity of the heating unit so that a temperature of the water heated by the heating unit approaches a hot water setting temperature while the heating unit is heating the water; andstop heating the water with the heating unit when the detected flow rate falls to an extinguishing flow rate while the heating unit is heating the water,wherein the connection controller is configured to:select one or more of the plurality of water heaters as active water heaters and a remainder of the plurality of water heaters as inactive water heaters;send an activation instruction to the controllers of the active water heaters; andsend a stop instruction to the controllers of the inactive water heaters,wherein each of the controllers is configured to:in a case of receiving the activation instruction from the connection controller, control the valve so that the limit flow rate becomes a maximum flow rate;in a case of receiving the stop instruction from the connection controller, control the valve so that the limit flow rate matches zero; andwhen an error related to the heating unit occurs, reduce the heating capacity of the heating unit by lowering the maximum flow rate, and send an error signal indicating an occurrence of the error to the connection controller, andwherein the connection controller is configured to:increase or decrease a number of the active water heaters based on the maximum flow rate of the valve and the detected flow rate in each of the active water heaters; andwhen increasing the number of the active water heaters, select a next active water heater from among one or more water heaters that have not sent an error signal among the inactive water heaters.

2. The water heating system according to claim 1, wherein each of the plurality of water heaters further comprises a water temperature sensor configured to detect the temperature of the water flowing into the water heater, andwherein each of the controllers is configured to adjust the heating capacity of the heating unit based on the hot water setting temperature, the detected flow rate, and a detected temperature detected by the water temperature sensor.

3. The water heating system according to claim 1, wherein each of the heating units comprises a gas burner.

4. The water heating system according to claim 1, wherein the error related to the heating unit includes a temperature of a predetermined part of the water heater in which the heating unit is incorporated exceeding a threshold temperature, andwherein each of the controllers is configured to:when the error occurs, decrease the maximum flow rate in steps without sending the error signal to the connection controller; andwhen the maximum flow rate falls to a threshold flow rate, send the error signal to the connection controller.

5. The water heating system according to claim 1, wherein each of the plurality of water heaters comprises a first memory configured to store error information indicating that the error is occurring,each of the controllers is configured to continuously send the error signal to the connection controller while the error information is stored in the first memory, andwherein the connection controller is configured to, when increasing the number of active water heaters, select a next active water heater from among one or more water heaters that have not sent the error signal in recent time period among the inactive water heaters.

6. The water heating system according to claim 5, wherein each of the controllers is configured to, when the error is resolved, delete the error information stored in the first memory.

7. The water heating system according to claim 1, wherein each of the controllers is configured to further send identification information for identifying the water heater together with the error signal to the connection controller,wherein the connection controller comprises a second memory configured to store the identification information received from the controller in association with error occurrence information indicating that the error is occurring in the water heater, andwherein the connection controller is configured to, when increasing the number of active water heaters, select a next active water heater from among one or more water heaters of which identification information is not stored in the second memory in association with the error occurrence information among the inactive water heaters.

8. The water heating system according to claim 7, wherein each of the controllers is configured to, when the error is resolved, further send an error resolving signal indicating that the error has been resolved together with the identification information to the connection controller, andwherein the connection controller is configured to, when receiving the error resolving signal and the identification information, delete at least one of the error occurrence information and the identification information stored in association with the error occurrence information in the second memory.

9. The water heating system according to claim 1, wherein the connection controller is configured to, when receiving the error signal from at least one of the active water heaters, send the stop instruction to the at least one of the active water heaters and select a new active water heater from among the inactive water heaters.

10. The water heating system according to claim 1, wherein the water heating system further comprises a notification unit configured to notify a user of the occurrence of the error.

11. The water heating system according to claim 1, wherein the connection controller is configured to:determine one of multiple flow rate levels set in multiple stages for the detected flow rate in each of the active water heaters; andincrease or decrease the number of the active water heaters based on the respective numbers of the active water heaters of the respective determined flow rate levels.

12. The water heating system according to claim 1, wherein the connection controller is composed of one or more of the controllers of the plurality of water heaters.

13. A water heater, which constitutes one of a plurality of water heaters connected in parallel to each other, wherein the plurality of water heaters constitute a water heater set, the water heater comprising:a heating unit configured to heat water;a flow rate sensor configured to detect a flow rate of the water flowing into the water heater;a valve configured to limit the flow rate of the water flowing into the water heater to a limit flow rate or lower; anda controller configured to communicate with one or more other water heaters of the water heater set,wherein the controller is configured to selectively execute a primary process and a subordinate process subordinate to the primary process;the subordinate process comprises:starting to heat the water with the heating unit when a detected flow rate detected by the flow rate sensor increases to an ignition flow rate while the heating unit is not heating the water;adjusting a heating capacity of the heating unit so that a temperature of the water heated by the heating unit approaches a hot water setting temperature while the heating unit is heating the water; andstopping to heat the water with the heating unit when the detected flow rate falls to an extinguishing flow rate while the heating unit is heating the water,wherein the primary process comprises:selecting one or more of water heaters in the water heater set as active water heaters and a remainder of the plurality of water heaters in the water heater set as inactive water heaters;sending an activation instruction to controllers of the active water heaters; andsending a stop instruction to controllers of the inactive water heaters,wherein the subordinate process comprises:controlling the valve so that the limit flow rate becomes a maximum flow rate in a case of receiving the activation instruction from a water heater executing the primary process;controlling the valve so that the limit flow rate matches zero in a case of receiving the stop instruction from the water heater executing the primary process; andwhen an error related to the heating unit occurs, reducing the heating capacity of the heating unit by lowering the maximum flow rate, and sending an error signal indicating an occurrence of the error to the water heater executing the primary process, andwherein the primary process comprises:increasing or decreasing a number of the active water heaters based on the maximum flow rate of the valve and the detected flow rate in each of the active water heaters; andwhen increasing the number of active water heaters, selecting a next active water heater from among one or more water heaters that have not sent an error signal among the inactive water heaters.

14. The water heating system according to claim 2,wherein each of the heating units comprises a gas burner,wherein the error related to the heating unit includes a temperature of a predetermined part of the water heater in which the heating unit is incorporated exceeding a threshold temperature, andwherein each of the controllers is configured to:when the error occurs, decrease the maximum flow rate in steps without sending the error signal to the connection controller; andwhen the maximum flow rate falls to a threshold flow rate, send the error signal to the connection controller,wherein each of the plurality of water heaters comprises a first memory configured to store error information indicating that the error is occurring,each of the controllers is configured to continuously send the error signal to the connection controller while the error information is stored in the first memory, andwherein the connection controller is configured to, when increasing the number of active water heaters, select a next active water heater from among one or more water heaters that have not sent the error signal in recent time period among the inactive water heaters,wherein each of the controllers is configured to, when the error is resolved, delete the error information stored in the first memory,wherein each of the controllers is configured to further send identification information for identifying the water heater together with the error signal to the connection controller,wherein the connection controller comprises a second memory configured to store the identification information received from the controller in association with error occurrence information indicating that the error is occurring in the water heater, andwherein the connection controller is configured to, when increasing the number of active water heaters, select a next active water heater from among one or more water heaters of which identification information is not stored in the second memory in association with the error occurrence information among the inactive water heaters,wherein each of the controllers is configured to, when the error is resolved, further send an error resolving signal indicating that the error has been resolved together with the identification information to the connection controller, andwherein the connection controller is configured to, when receiving the error resolving signal and the identification information, delete at least one of the error occurrence information and the identification information stored in association with the error occurrence information in the second memory,wherein the connection controller is configured to, when receiving the error signal from at least one of the active water heaters, send the stop instruction to the at least one of the active water heaters and select a new active water heater from among the inactive water heaters,wherein the water heating system further comprises a notification unit configured to notify a user of the occurrence of the error,wherein the connection controller is configured to:determine one of multiple flow rate levels set in multiple stages for the detected flow rate in each of the active water heaters; andincrease or decrease the number of the active water heaters based on the respective numbers of the active water heaters of the respective determined flow rate levels,wherein the connection controller is composed of one or more of the controllers of the plurality of water heaters.

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