HEATING MEDIUM CIRCULATION APPARATUS

Description

BACKGROUND OF INVENTION

Field of the Invention

The present invention relates to a heating medium circulation apparatus for circulating a heating medium between a heater that heats the heating medium and a heat dissipator that dissipates heat from the heating medium.

Background Art

A heating medium circulation apparatus, typically used as, for example, a space heater or a water heater, circulates a heating medium between a heater that heats the heating medium and a heat dissipator that dissipates heat from the heating medium. The heating medium circulation apparatus includes a circulation circuit and a circulation pump. The circulation circuit is a closed-loop circuit connecting the heater (e.g., a heat exchanger) and the heat dissipator (e.g., space heating equipment or a hot-water supply heat exchanger). The circulation pump pumps the heating medium in the circulation circuit in a predetermined direction. In response to the start of a heat dissipation-based operation that uses heat dissipation performed by the heat dissipator (e.g., a space heating operation or a hot-water supply operation), the circulation pump is activated, and the heating in the heater is started. During the heat dissipation-based operation, the circulation pump remains active, and the heating in the heater is controlled based on the temperature of the circulating heating medium.

In such a heating medium circulation apparatus, the heating medium in the circulation circuit may undergo local overheating (hereafter, an overheating abnormality) when the heater performs heating although the heating medium is not circulating or its circulation flow is insufficient in the circulation circuit (hereafter, insufficient circulation of the heating medium). This may occur when, for example, the circulation pump malfunctions or an open-close valve in space heating equipment fails to open. To detect an overheating abnormality, a known technique uses a temperature-sensitive bimetallic switch installed in a heat exchanger as a heater (e.g., Patent Literature 1). The heat exchanger transfers heat from the exhaust gas produced by combustion in a burner to the heating medium. When insufficient circulation of the heating medium occurs in the circulation circuit, the heating medium in the heat exchanger may be overheated and also cause a temperature increase of the heat exchanger. When the temperature at the bimetallic switch in the heat exchanger reaches a threshold temperature, the bimetallic switch is activated (the contact switches from a closed state to an open state). This allows detection of an overheating abnormality.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2013-167426

SUMMARY OF INVENTION

When a bimetallic switch in the heat exchanger as a heater is used to detect an overheating abnormality as described above, the heat exchanger is often already at a high temperature by the time the bimetallic switch is activated. This may cause heat damage to the heat exchanger and its peripheral components. Techniques are thus awaited for detecting an overheating abnormality before the bimetallic switch is activated.

In response to the above issue with the known technique, one or more aspects of the present invention are directed to a heating medium circulation apparatus that can promptly detect an overheating abnormality, or specifically, local overheating of the heating medium caused by insufficient circulation of the heating medium in the circulation circuit.

A heating medium circulation apparatus according to aspects of the present invention has the structure below.

First Aspect

A heating medium circulation apparatus circulates a heating medium between a heater that heats the heating medium and a heat dissipator that dissipates heat from the heating medium. The apparatus includes a circulation circuit being a closed-loop circuit connecting the heater and the heat dissipator, a circulation pump that pumps the heating medium in the circulation circuit in a predetermined direction, an outgoing temperature sensor that detects a temperature of the heating medium flowing out of the heater, a heating controller that controls heating in the heater, and an overheating abnormality detector that detects an overheating abnormality being local overheating of the heating medium caused by insufficient circulation of the heating medium in the circulation circuit. The circulation pump is activated in response to a start of a heat dissipation-based operation and remains active during the heat dissipation-based operation. The heat dissipation-based operation is an operation using heat dissipation performed by the heat dissipator. The heating controller starts the heating in the heater in response to the start of the heat dissipation-based operation. The heating controller temporarily stops the heating when the temperature detected by the outgoing temperature sensor reaches a heating stop temperature, and resumes the heating when the temperature of the heating medium in the circulation circuit decreases to a heating resumption temperature. The overheating abnormality detector increments a stop count when the heating in the heater is stopped in response to the temperature detected by the outgoing temperature sensor reaching the heating stop temperature during the heat dissipation-based operation. The overheating abnormality detector detects the overheating abnormality when a detection condition is satisfied. The detection condition is that the stop count reaches a determination count within a predetermined determination time.

In the heating medium circulation apparatus according to the first aspect, the heating in the heater is controlled based on the temperature detected by the outgoing temperature sensor (hereafter, an outgoing temperature) and the temperature of the heating medium in the circulation circuit (that may be a temperature detected by a heating medium temperature sensor other than the outgoing temperature sensor). In such heating control, when an overheating abnormality is caused by insufficient circulation of the heating medium in the circulation circuit, the heating in the heater may be repeatedly stopped and resumed at shorter intervals than in the normal state, with sharp fluctuations in the outgoing temperature. Thus, an overheating abnormality is likely to be occurring when the heating in the heater is repeatedly stopped and resumed within the predetermined determination time and the stop count reaches the determination count. Using this as the detection condition thus allows prompt detection of an overheating abnormality.

Second Aspect

In the heating medium circulation apparatus according to the first aspect, the overheating abnormality detector increments the stop count when the heating in the heater is stopped in response to the temperature detected by the outgoing temperature sensor reaching the heating stop temperature during the heat dissipation-based operation and when the temperature detected by the outgoing temperature sensor remains higher than an abnormality determination temperature for at least a specified time after the heating is stopped. The abnormality determination temperature is higher than the heating stop temperature.

In the heating medium circulation apparatus according to the second aspect, when an overheating abnormality is caused by insufficient circulation of the heating medium in the circulation circuit, the heating medium overheated by the heater may partly boil and overflow the heater. Although the heating in the heater is temporarily stopped upon the outgoing temperature reaching the heating stop temperature, the outgoing temperature may increase further above the abnormality determination temperature and remain at such a temperature for some time. When air or other substance enters the heating medium in the circulation circuit, the outgoing temperature can also reach the heating stop temperature and cause the heating in the heater to temporarily stop. In this case, however, the outgoing temperature is less likely to increase further and can decrease immediately while the heating medium is circulating, although the outgoing temperature may possibly exceed the abnormality determination temperature. Thus, an overheating abnormality is highly likely to be occurring when the outgoing temperature remains higher than the abnormality determination temperature for at least the specified time. The stop count may thus be incremented only when this condition is satisfied. This allows more accurate detection of an overheating abnormality.

Third Aspect

The heating medium circulation apparatus according to the first aspect or the second aspect further includes a return temperature sensor that detects a temperature of the heating medium flowing into the heater. The detection condition that the stop count reaches the determination count within the determination time includes a further condition that the temperature detected by the return temperature sensor remains below a return reference temperature during a period from a return specific time point to a time at which the stop count reaches the determination count. The return specific time point is after the start of the heat dissipation-based operation. The overheating abnormality detector detects the overheating abnormality when the detection condition including the further condition is satisfied.

In the heating medium circulation apparatus according to the third aspect, during an overheating abnormality, the heating medium does not circulate sufficiently in the circulation circuit and thus the temperature detected by the return temperature sensor (hereafter, a return temperature) does not substantially increase, although the heating in the heater may be repeatedly stopped and resumed. When air or other substance enters the heating medium in the circulation circuit, the heating in the heater can also be repeatedly stopped and resumed. In this case, however, the return temperature increases at least once during the period from the return specific time point to the time at which the stop count reaches the determination count, with the heating medium in the circulation circuit circulating. Thus, the detection condition may include a further condition that the return temperature remains below the return reference temperature during the period from the return specific time point to the time at which the stop count reaches the determination count. Using this further condition allows more accurate detection of an overheating abnormality caused by insufficient circulation of the heating medium.

Fourth Aspect

In the heating medium circulation apparatus according to the third aspect, the return reference temperature is obtained by adding a return estimated increase to the temperature detected by the return temperature sensor at the return specific time point.

In the heating medium circulation apparatus according to the fourth aspect, the current heat dissipation-based operation may start not long after the previous heat dissipation-based operation ends. In this case, the heating medium in the circulation circuit may be already relatively warm at the start of the current heat dissipation-based operation. In this case as well, an overheating abnormality can be detected more accurately by determining whether an increase in the return temperature from the return specific time point is within the return estimated increase.

Fifth Aspect

In the heating medium circulation apparatus according to any one of the first to fourth aspects, the heat dissipator is a hot-water supply heat exchanger that heats, through heat exchange with the heating medium, water supplied from a water supply to produce hot water. The heating medium circulation apparatus further includes a hot-water supply temperature sensor that detects a temperature of the hot water supplied from the hot-water supply heat exchanger. The detection condition that the stop count reaches the determination count within the determination time includes a further condition that the temperature detected by the hot-water supply temperature sensor remains below a hot-water supply reference temperature during a period from a hot-water supply specific time point to a time at which the stop count reaches the determination count. The hot-water supply specific time point is after the start of the heat dissipation-based operation. The overheating abnormality detector detects the overheating abnormality when the detection condition including the further condition is satisfied.

In the heating medium circulation apparatus according to the fifth aspect, during an overheating abnormality, the heating medium does not circulate sufficiently in the circulation circuit and thus the temperature detected by the hot-water supply temperature sensor (hereafter, a hot-water supply temperature) does not substantially increase, although the heating in the heater may be repeatedly stopped and resumed. When air or other substance enters the heating medium in the circulation circuit, the heating in the heater can also be repeatedly stopped and resumed. In this case, however, the hot-water supply temperature increases at least once during the period from the hot-water supply specific time point to the time at which the stop count reaches the determination count, with the heating medium in the circulation circuit circulating. Thus, the detection condition may include a further condition that the hot-water supply temperature remains below the hot-water supply reference temperature during the period from the hot-water supply specific time point to the time at which the stop count reaches the determination count. Using this further condition allows more accurate detection of an overheating abnormality caused by insufficient circulation of the heating medium.

Sixth Aspect

In the heating medium circulation apparatus according to the fifth aspect, the hot-water supply reference temperature is obtained by adding a hot-water supply estimated increase to the temperature detected by the hot-water supply temperature sensor at the hot-water supply specific time point.

In the heating medium circulation apparatus according to the sixth aspect, the current heat dissipation-based operation (hot-water supply operation) may start not long after the previous heat dissipation-based operation ends. In this case, the heating medium in the circulation circuit (in particular, in the hot-water supply heat exchanger) may be already relatively warm at the start of the current heat dissipation-based operation. In this case as well, an overheating abnormality can be detected more accurately by determining whether an increase in the hot-water supply temperature from the hot-water supply specific time point is within the hot-water supply estimated increase.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a space and water heating apparatus 1 as an example use of a heating medium circulation apparatus.

FIGS. 2A and 2B are graphs showing a phenomenon that is typical of an overheating abnormality emerging during combustion control for a burner 3 performed by a controller 40.

FIG. 3 is a flowchart of a combustion control process in an embodiment performed by the controller 40 for the combustion control for the burner 3.

FIG. 4 is a flowchart of the first half of a combustion control process in a first modification performed by the controller 40.

FIG. 5 is a flowchart of the second half of the combustion control process in the first modification performed by the controller 40.

FIG. 6 is a flowchart of the first half of a combustion control process in a second modification performed by the controller 40.

FIG. 7 is a flowchart of the second half of the combustion control process in the second modification performed by the controller 40.

DETAILED DESCRIPTION

FIG. 1 is a diagram of a space and water heating apparatus 1 as an example use of a heating medium circulation apparatus. As illustrated, the space and water heating apparatus 1 according to the present embodiment includes a combustion unit 4 housed in a housing 2. The combustion unit 4 incorporates a burner 3 that burns a gas mixture of fuel gas and combustion air. The combustion unit 4 is connected to a combustion fan 5 to feed the gas mixture to the combustion unit 4.

The combustion fan 5 has an intake connected to a joint 6 at which an air supply channel 7 for supplying combustion air joins a gas supply channel 8 for supplying fuel gas. The gas supply channel 8 includes an open-close valve 9 that opens and closes the gas supply channel 8 and a zero governor 10 that lowers the pressure of fuel gas fed from upstream under pressure to the atmospheric pressure. The joint 6 incorporates a control valve that regulates the ratio of combustion air and fuel gas flowing into the combustion fan 5. When the combustion fan 5 is driven, the air flowing through the air supply channel 7 in the housing 2 and the fuel gas in the gas supply channel 8 downstream from the zero governor 10 are drawn into the combustion fan 5 through the joint 6 at a predetermined ratio, and the resultant gas mixture is fed to the combustion unit 4.

In the combustion unit 4, the burner 3 incorporated in the combustion unit 4 burns the gas mixture. In the illustrated example, the burner 3 ejects the gas mixture downward to generate flames downward and emits exhaust gas downward. The combustion fan 5 and the open-close valve 9 are electrically connected to a controller 40 that controls the overall operation of the space and water heating apparatus 1. The controller 40 controls the opening and closing of the open-close valve 9 and also controls the combustion level of the burner 3 by changing the rotational speed of the combustion fan 5 based on the amount of heat to be used.

The combustion unit 4 includes a spark plug 11 that produces sparks in the burner 3 through high-voltage discharge, a flame rod 12 that detects the flames (ignition) of the burner 3, and a check valve 13 that blocks a backflow from the combustion unit 4 to the combustion fan 5. The spark plug 11 and the flame rod 12 are electrically connected to the controller 40.

A first heat exchanger 15 is located below the burner 3. A second heat exchanger 16 is located below the first heat exchanger 15. The exhaust gas produced from combustion in the burner 3 is emitted downward and passes through the first heat exchanger 15 and the second heat exchanger 16 in this order. The first heat exchanger 15 recovers sensible heat from the exhaust gas, and the second heat exchanger 16 recovers latent heat from the exhaust gas.

After passing through the first heat exchanger 15 and the second heat exchanger 16, the exhaust gas flows through an exhaust duct 17 and is discharged through an exhaust port 18 protruding from the top of the housing 2. In the illustrated example, the housing 2 has an air supply port 19 at the top. The air supply port 19 allows air to be drawn into the housing 2, in which the air is supplied to the joint 6 through the air supply channel 7.

The upstream end of the first heat exchanger 15 is connected to the downstream end of the second heat exchanger 16. The downstream end of the first heat exchanger 15 is connected to the upstream end of a panel radiator 20 as space heating equipment through an outgoing channel 21. The upstream end of the second heat exchanger 16 is connected to the downstream end of the panel radiator 20 through a return channel 22. The return channel 22 includes a circulation pump 23 that pumps the heating medium toward the second heat exchanger 16 and a return temperature sensor 24 that detects the temperature of the heating medium flowing into the second heat exchanger 16 (hereafter, a return temperature). The circulation pump 23 and the return temperature sensor 24 are electrically connected to the controller 40.

The heating medium is delivered by the active circulation pump 23 to the second heat exchanger 16. In the second heat exchanger 16, the heating medium is preheated using latent heat recovered from the exhaust gas from the burner 3. The preheated heating medium is then delivered to the first heat exchanger 15. The first heat exchanger 15 heats the heating medium using sensible heat recovered from the exhaust gas from the burner 3. The resultant high-temperature heating medium is supplied to the panel radiator 20 through the outgoing channel 21. The outgoing channel 21 connected to the downstream end of the first heat exchanger 15 includes an outgoing temperature sensor 25 that detects the temperature of the heating medium flowing out of the first heat exchanger 15 (hereafter, an outgoing temperature). The outgoing temperature sensor 25 is electrically connected to the controller 40. The controller 40 determines the amount of heat to be used based on the temperature detected by the outgoing temperature sensor 25, and performs the combustion control for the burner 3. The burner 3, the first heat exchanger 15, and the second heat exchanger 16 in the present embodiment correspond to a heater in one or more aspects of the present invention. The controller 40 in the present embodiment functions as a heating controller in one or more aspects of the present invention.

The first heat exchanger 15 includes a bimetallic switch 26 that is a temperature-sensitive switch. The bimetallic switch 26 is electrically connected to the controller 40. When the temperature of the first heat exchanger 15 increases more than intended and the temperature at the bimetallic switch 26 reaches a threshold temperature, the contact of the bimetallic switch 26 switches from a closed state to an open state. This causes the open-close valve 9 on the gas supply channel 8 to close, forcibly stopping the combustion in the burner 3.

The panel radiator 20 includes a serpentine pipe 20a in a metal panel and an open-close valve 20b that opens and closes the pipe 20a. When the open-close valve 20b is open, the heating medium passes through the pipe 20a while radiating heat, thus heating the surroundings. The panel radiator 20 (space heating equipment) in the present embodiment corresponds to a heat dissipator in one or more aspects of the present invention.

The heating medium passes through the panel radiator 20, returns to the circulation pump 23 through the return channel 22, and is delivered to the second heat exchanger 16 again to circulate. The circulation pump 23 in the present embodiment is operated at a constant rotational speed to pump the heating medium. Although the space and water heating apparatus 1 according to the present embodiment uses hot water as the heating medium, the heating medium may be, for example, antifreeze (e.g., ethylene glycol) or silicone oil.

A branch channel 27 branches from the outgoing channel 21 downstream from the outgoing temperature sensor 25. The branch channel 27 is connected to the return channel 22 upstream from the circulation pump 23. The branch channel 27 includes a hot-water supply heat exchanger 28. The branch channel 27 and the return channel 22 include a three-way valve 29 at their connection. The three-way valve 29 is electrically connected to the controller 40. The three-way valve 29 can switch the circulation route of the heating medium flowing out of the first heat exchanger 15. More specifically, the three-way valve 29 can switch between a route through the panel radiator 20 (space heating equipment) (hereafter, an external circulation circuit) and a route through the hot-water supply heat exchanger 28 (hereafter, an internal circulation circuit). The external circulation circuit is a closed-loop circuit connecting the first heat exchanger 15 and the second heat exchanger 16 to the panel radiator 20 with the outgoing channel 21 and the return channel 22. The internal circulation circuit is a closed-loop circuit connecting the first heat exchanger 15 and the second heat exchanger 16 to the hot-water supply heat exchanger 28 with the outgoing channel 21, the return channel 22, and the branch channel 27. Both the external circulation circuit and the internal circulation circuit in the present embodiment correspond to a circulation circuit in one or more aspects of the present invention. The external circulation circuit and the internal circulation circuit may be hereafter simply referred to as a circulation circuit when they are not to be distinguished from each other.

The hot-water supply heat exchanger 28 is a liquid-liquid heat exchanger, to which a water inlet channel 30 and a hot-water outlet channel 31 are connected. The water inlet channel 30 carries clean water to the hot-water supply heat exchanger 28, at which the clean water is heated through heat exchange with the heating medium. The resultant hot water flows out into the hot-water outlet channel 31. The water inlet channel 30 includes a water flow sensor 32 that measures the flow rate of clean water flowing into the space and water heating apparatus 1, a water flow servo 33 that adjusts the flow rate of clean water, and a water inlet temperature sensor 34 that detects the temperature of clean water. The hot-water outlet channel 31 includes a heat-exchanger outlet temperature sensor 35 that detects the temperature of the hot water immediately after flowing out of the hot-water supply heat exchanger 28. The water flow sensor 32, the water flow servo 33, the water inlet temperature sensor 34, and the heat-exchanger outlet temperature sensor 35 are electrically connected to the controller 40. The hot-water supply heat exchanger 28 in the present embodiment corresponds to the heat dissipator in one or more aspects of the present invention.

The space and water heating apparatus 1 according to the present embodiment includes a bypass channel 36 connecting a section of the water inlet channel 30 downstream from the water inlet temperature sensor 34 and a section of the hot-water outlet channel 31 downstream from the heat-exchanger outlet temperature sensor 35. The clean water flowing into the space and water heating apparatus 1 can partly flow through the bypass channel 36 without flowing to the hot-water supply heat exchanger 28, with the remaining clean water flowing to the hot-water supply heat exchanger 28. The water heated by the hot-water supply heat exchanger 28 mixes with the clean water passing through the bypass channel 36, and then flows out of the space and water heating apparatus 1. The bypass channel 36 and the hot-water outlet channel 31 include a bypass servo 37 at their connection. The bypass servo 37 is electrically connected to the controller 40. The bypass servo 37 can change the mixing ratio between the water heated by the hot-water supply heat exchanger 28 and the clean water passing through the bypass channel 36.

The hot-water outlet channel 31 includes a hot-water outlet temperature sensor 38 downstream from the bypass servo 37 to detect the temperature of the hot water flowing out of the space and water heating apparatus 1. The hot-water outlet temperature sensor 38 is electrically connected to the controller 40. As described above, the clean water in the water inlet channel 30 can partly flow into the hot-water outlet channel 31 through the bypass channel 36 without flowing through the hot-water supply heat exchanger 28. Thus, the temperature detected by the hot-water outlet temperature sensor 38 is lower than the temperature detected by the heat-exchanger outlet temperature sensor 35. The bypass servo 37 can adjust the mixing ratio to reduce temperature fluctuations of the hot water flowing out of the space and water heating apparatus 1.

The controller 40 is also connected to a hot-water supply remote control 41 and a space-heating remote control 42. The user can operate the hot-water supply remote control 41 to turn on or off the hot-water supply operation or set the hot-water supply temperature. The user can also operate the space-heating remote control 42 to provide an instruction to start or stop the space heating operation or set the temperature for space heating. The space heating operation in which the heating medium is circulated in the external circulation circuit (the panel radiator 20) and the hot-water supply operation in which the heating medium is circulated in the internal circulation circuit (the hot-water supply heat exchanger 28) in the present embodiment correspond to a heat dissipation-based operation in one or more aspects of the present invention.

In the space and water heating apparatus 1 described above, the heating medium may undergo local overheating (hereafter, an overheating abnormality) in the first heat exchanger 15 in the circulation circuit. This may occur when the burner 3 performs heating although the heating medium is not circulating or its circulation flow is insufficient in any of the external circulation circuit and the internal circulation circuit (hereafter, insufficient circulation of the heating medium) due to a malfunction of the circulation pump 23. The overheating abnormality may be caused by factors other than a malfunction of the circulation pump 23. For example, the overheating abnormality may occur when the open-close valve 20b in the panel radiator 20 (space heating equipment) is not open during the space heating operation in which the heating medium is circulated in the external circulation circuit. The overheating abnormality may also occur when the three-way valve 29 is stuck in the state of circulation for the external circulation circuit while the open-close valve 20b in the panel radiator 20 is closed, although the hot-water supply operation in which the heating medium is circulated in the internal circulation circuit is being performed. To detect the circulation (flow) of the heating medium in the circulation circuit, a flow sensor may be installed in the circulation circuit. However, a flow sensor typically produces a large pressure loss. The space and water heating apparatus 1 according to the present embodiment thus does not include a flow sensor to reduce a pressure loss in the circulation circuit.

When an overheating abnormality occurs, the heating medium in the first heat exchanger 15 may be overheated and also cause a temperature increase of the first heat exchanger 15. This may cause the temperature at the bimetallic switch 26 to reach a threshold temperature, thus activating the bimetallic switch 26 (switching the contact from a closed state to an open state). An overheating abnormality can be detected in response to this activation. The combustion in the burner 3 is then forcibly stopped by cutting the fuel gas supply. Typically, the threshold temperature at which the bimetallic switch 26 is activated is relatively high. The first heat exchanger 15 is thus often already at a high temperature by the time the bimetallic switch 26 is activated. This may cause heat damage to the first heat exchanger 15 and its peripheral components. The space and water heating apparatus 1 according to the present embodiment can detect an overheating abnormality before the bimetallic switch 26 is activated by identifying a phenomenon that is typical of an overheating abnormality emerging during the combustion control for the burner 3 performed by the controller 40 based on the temperature detected by the outgoing temperature sensor 25. Before this technique is described in detail, the phenomenon that is typical of an overheating abnormality is described first.

FIGS. 2A and 2B are graphs showing a phenomenon that is typical of an overheating abnormality emerging during the combustion control for the burner 3 performed by the controller 40. The graphs in FIGS. 2A and 2B each show changes in the outgoing temperature of the heating medium (the temperature detected by the outgoing temperature sensor 25) in the combustion control for the burner 3, with the horizontal axis indicating time and the vertical axis indicating temperature. FIG. 2A shows example changes in the outgoing temperature of the heating medium in the normal state, in which the heating medium is circulating in the circulation circuit with no overheating abnormality.

As illustrated, after the combustion in the burner 3 is started (ignited), the temperature (outgoing temperature) of the heating medium flowing out of the first heat exchanger 15 increases through heat exchange with the exhaust gas from the burner 3. When the outgoing temperature reaches a predetermined combustion stop temperature, the combustion in the burner 3 is temporarily stopped (extinguished). This causes the outgoing temperature to stop increasing and then decrease. Then, when the outgoing temperature decreases to a predetermined combustion resumption temperature lower than the combustion stop temperature, the combustion in the burner 3 is resumed (ignited). This causes the outgoing temperature, which has been decreasing, to start increasing again. The combustion stop temperature in the present embodiment corresponds to a heating stop temperature in one or more aspects of the present invention. The combustion resumption temperature in the present embodiment corresponds to a heating resumption temperature in one or more aspects of the present invention.

Thus, the combustion in the burner 3 is temporarily stopped (extinguished) when the outgoing temperature reaches the combustion stop temperature, and is resumed (ignited) when the outgoing temperature decreases to the combustion resumption temperature. Such control is repeatedly performed by the controller 40. While the combustion in the burner 3 is temporarily stopped, the circulation pump 23 remains active and continues circulating the heating medium, causing the temperature of the heating medium to be uniform across the circulation circuit. Thus, the return temperature of the heating medium (the temperature detected by the return temperature sensor 24) may be used in place of the outgoing temperature. More specifically, the combustion in the burner 3 may be resumed in response to the return temperature decreasing to the combustion resumption temperature.

FIG. 2B shows example changes in the outgoing temperature of the heating medium while the heating medium in the circulation circuit is not circulating and an overheating abnormality is occurring. When the combustion in the burner 3 is started (ignited) while the heating medium in the circulation circuit is not circulating, the heating medium overheated in the first heat exchanger 15 reaches a high temperature and expands thermally (partly boils). The high-temperature heating medium overflows the first heat exchanger 15 into the outgoing channel 21 and reaches the outgoing temperature sensor 25. This causes a steep increase in the temperature detected by the outgoing temperature sensor 25 (outgoing temperature). Upon the outgoing temperature reaching the combustion stop temperature, the combustion in the burner 3 is temporarily stopped (extinguished). However, with the heating medium overheated in the first heat exchanger 15 and already at a high temperature (or partly boiling), the outgoing temperature may increase further above an abnormality determination temperature that is higher than the combustion stop temperature.

Some time after the combustion in the burner 3 is stopped, the heating medium in the first heat exchanger 15 stops expanding thermally (boiling). A lower-temperature heating medium is drawn back from a downstream portion of the outgoing channel 21 (adjacent to the panel radiator 20) toward the first heat exchanger 15 to reach the outgoing temperature sensor 25. This causes a steep decrease in the outgoing temperature. The space and water heating apparatus 1 may include an overpressure relief device (not shown) installed on the outgoing channel 21 outside the housing 2. The overpressure relief device is activated when the pressure in the circulation circuit increases with the heating medium overheated in the first heat exchanger 15 and expanding thermally (partly boiling). When the overpressure relief device is activated, the heating medium is released and flows in the outgoing channel 21 toward the overpressure relief device. This may cause a steep decrease in the outgoing temperature detected by the outgoing temperature sensor 25.

When the outgoing temperature decreases to the combustion resumption temperature, the combustion in the burner 3 is resumed (ignited). The heating medium in the first heat exchanger 15 is then overheated, causing the outgoing temperature to increase steeply again and to shortly reach the combustion stop temperature. The combustion in the burner 3 is thus temporarily stopped again (extinguished). In some embodiments, the combustion in the burner 3 may be resumed based on the return temperature, in place of the outgoing temperature. In this case, the return temperature does not increase while the heating medium in the circulation circuit is not circulating. When the return temperature is lower than the combustion resumption temperature, the combustion in the burner 3 is resumed after a predetermined wait time elapses from the time at which the combustion in the burner 3 is stopped. Thus, during an overheating abnormality, the combustion in the burner 3 may be repeatedly stopped (extinguished) and resumed (ignited) at shorter intervals than in the normal state, with sharp fluctuations in the outgoing temperature. Thus, an overheating abnormality is likely to be occurring when the number of times the combustion in the burner 3 is stopped reaches a determination count within a predetermined determination time. Using this as the detection condition thus allows prompt detection of an overheating abnormality.

FIG. 3 is a flowchart of a combustion control process in the present embodiment performed by the controller 40 for the combustion control for the burner 3. The combustion control process starts when the space heating operation or the hot-water supply operation starts, and continues until the space heating operation or the hot-water supply operation ends. As illustrated, in response to the start of the combustion control process, the circulation pump 23 is activated (STEP 1), and the combustion of a gas mixture in the burner 3 is started (STEP 2).

The determination is then performed as to whether the temperature detected by the outgoing temperature sensor 25 (outgoing temperature) is higher than or equal to the predetermined combustion stop temperature (STEP 3). As described above, in the combustion control for the burner 3 in the present embodiment, the condition for temporarily stopping the combustion in the burner 3 (hereafter, a combustion stop condition) is that the outgoing temperature reaches the combustion stop temperature. When the outgoing temperature is not yet higher than or equal to the combustion stop temperature (No in STEP 3), the determination in STEP 3 is repeated at predetermined intervals.

When the outgoing temperature is higher than or equal to the combustion stop temperature (Yes in STEP 3), the combustion stop condition is satisfied. The combustion in the burner 3 is thus temporarily stopped (STEP 4). The determination is then performed as to whether a determination timer is active (STEP 5). The determination timer measures the time elapsed from the time at which the combustion is stopped for the first time. When the determination timer is not yet active (No in STEP 5), the determination timer is to start measuring the time from the immediately preceding stop of combustion. The determination timer is thus activated (STEP 6).

After the determination timer is activated, the number of times the combustion in the burner 3 is stopped (hereafter, a stop count) is incremented by one to count the number (STEP 7). The determination is performed as to whether the stop count after the increment has reached a predetermined determination count (STEP 8). When the stop count has not reached the determination count (No in STEP 8), the determination is performed as to whether a predetermined determination time has elapsed on the determination timer (STEP 9).

When the determination time has not elapsed on the determination timer (No in STEP 9), then the determination is performed as to whether the outgoing temperature (the temperature detected by the outgoing temperature sensor 25) is lower than the predetermined combustion resumption temperature (STEP 12). As described above, in the combustion control for the burner 3 in the present embodiment, the condition for resuming the combustion in the burner 3 (hereafter, a combustion resumption condition) is that the outgoing temperature decreases to the combustion resumption temperature. In some embodiments, the combustion resumption condition may be that the return temperature (the temperature detected by the return temperature sensor 24), in place of the outgoing temperature, decreases to the combustion resumption temperature.

When the outgoing temperature is not yet lower than the combustion resumption temperature (No in STEP 12), the processing returns to STEP 9. The determination is performed again as to whether the determination time has elapsed on the determination timer (STEP 9). The determination is also performed again as to whether the outgoing temperature is lower than the combustion resumption temperature (STEP 12). When the outgoing temperature is lower than the combustion resumption temperature (Yes in STEP 12), the combustion resumption condition is satisfied. The combustion in the burner 3 is thus resumed (STEP 13). The processing then returns to STEP 3, and the subsequent processing described above is performed again. More specifically, when the outgoing temperature is higher than or equal to the combustion stop temperature (Yes in STEP 3), the combustion in the burner 3 is temporarily stopped again (STEP 4). When the determination timer is already active (Yes in STEP 5), the processing in STEP 6 is skipped. The stop count is then incremented by one (STEP 7). The determination is then performed as to whether the stop count after the increment has reached the determination count (STEP 8).

When the stop count has not reached the determination count (No in STEP 8), the determination is performed again as to whether the determination time has elapsed on the determination timer (STEP 9). The determination is also performed again as to whether the outgoing temperature is lower than the combustion resumption temperature (STEP 12). When the determination time has elapsed on the determination timer without the stop count reaching the determination count (Yes in STEP 9), the determination timer is stopped (STEP 10). The stop count is then reset (STEP 11). When the outgoing temperature falls below the combustion resumption temperature thereafter (Yes in STEP 12), the combustion in the burner 3 is resumed (STEP 13). The processing then returns to STEP 3.

When the stop count has reached the determination count before the determination time elapses on the determination timer (in other words, within the determination time) (Yes in STEP 8), the combustion in the burner 3 is repeatedly stopped and resumed at shorter intervals than in the normal state. This phenomenon is typical of an overheating abnormality. Thus, an overheating abnormality is detected (STEP 14). A notification about the overheating abnormality is then provided (STEP 15). In the present embodiment, the notification about the overheating abnormality is provided using a display (not shown) on the hot-water supply remote control 41 or the space-heating remote control 42. The notification about the overheating abnormality may be provided in any other manner, such as using sound output from a speaker (not shown) incorporated in the hot-water supply remote control 41 or the space-heating remote control 42. The combustion control process in FIG. 3 then ends. The controller 40 in the present embodiment functions as an overheating abnormality detector in one or more aspects of the present invention.

As described above, in the space and water heating apparatus 1 according to the present embodiment, in response to the start of the space heating operation or the hot-water supply operation, the circulation pump 23 is activated, and the combustion in the burner 3 is started. The combustion in the burner 3 is temporarily stopped when the combustion stop condition is satisfied, and the combustion stop condition is that the temperature detected by the outgoing temperature sensor 25 (outgoing temperature) reaches the combustion stop temperature. The combustion in the burner 3 is then resumed when the combustion resumption condition is satisfied, and the combustion resumption condition is that the outgoing temperature decreases to the combustion resumption temperature. Such control is repeatedly performed. The number of times the combustion in the burner 3 is stopped (stop count) is counted. The detection condition for detecting an overheating abnormality is that the stop count reaches the determination count within the determination time.

As described above, in the combustion control for the burner 3 based on the outgoing temperature, when an overheating abnormality is caused by insufficient circulation of the heating medium in the circulation circuit, the combustion in the burner 3 may be repeatedly stopped and resumed at shorter intervals than in the normal state, with sharp fluctuations in the outgoing temperature. Thus, an overheating abnormality is likely to be occurring when the combustion in the burner 3 is repeatedly stopped and resumed and the stop count reaches the determination count within the predetermined determination time. Using this as the detection condition thus allows prompt detection of an overheating abnormality.

The space and water heating apparatus 1 according to the above embodiment may be modified as described below. The modifications will be described focusing on the differences from the above embodiment. Like reference numerals in the modifications denote like components in the above embodiment. Such components will not be described.

FIGS. 4 and 5 are each a flowchart of a combustion control process in a first modification performed by the controller 40. Many of the steps in the combustion control process in the first modification are the same as those in the combustion control process in the above embodiment. Such steps will not be described in detail. In response to the start of the combustion control process in the first modification, the circulation pump 23 is activated (STEP 21), and the combustion in the burner 3 is started (STEP 22). The determination is then performed as to whether the outgoing temperature is higher than or equal to the combustion stop temperature (STEP 23). When the outgoing temperature is not yet higher than or equal to the combustion stop temperature (No in STEP 23), the determination in STEP 23 is repeated at predetermined intervals.

When the outgoing temperature is higher than or equal to the combustion stop temperature (Yes in STEP 23), the combustion in the burner 3 is temporarily stopped (STEP 24). The determination is then performed as to whether the determination timer is active (STEP 25). When the determination timer is not yet active (No in STEP 25), the determination timer is activated (STEP 26). The return temperature (the temperature detected by the return temperature sensor 24) is then obtained to set a return reference temperature (STEP 27). In the space and water heating apparatus 1 according to the first modification, the return reference temperature is set by adding a predetermined return estimated increase to the return temperature at a return specific time point. The return specific time point is the time at which the combustion is stopped for the first time and from which the measurement of the determination time starts. As will be described in more detail below, a condition that the return temperature remains below the return reference temperature is added to the detection condition to allow more accurate detection of an overheating abnormality. The return specific time point is not limited to the time at which the combustion is stopped for the first time, and may be any time after the start of the space heating operation or the hot-water supply operation. For example, the return specific time point may be immediately after the start of the combustion in the burner 3 in STEP 22. The return temperature may be obtained at such a return specific time point.

Subsequently, the determination is performed as to whether the outgoing temperature has remained higher than or equal to the abnormality determination temperature for at least a specified time (STEP 28). During an overheating abnormality, although the combustion in the burner 3 is temporarily stopped upon the outgoing temperature reaching the combustion stop temperature, the outgoing temperature may increase further above the abnormality determination temperature that is higher than the combustion stop temperature, as described above (refer to FIG. 2B). The specified time in the first modification is set longer than the duration of the outgoing temperature taken to eliminate detection noise. When the outgoing temperature has remained higher than the abnormality determination temperature for at least the specified time (Yes in STEP 28), the stop count is incremented by one (STEP 29). In contrast, when the outgoing temperature is lower than the abnormality determination temperature or when the outgoing temperature has not remained higher than or equal to the abnormality determination temperature for the specified time after reaching the abnormality determination temperature (No in STEP 28), the processing in STEP 29 is skipped. The stop count is thus not incremented by one.

The determination is performed as to whether the return temperature is higher than or equal to the return reference temperature (STEP 30 in FIG. 5), independently of whether the stop count has been incremented by one. As described above, the return reference temperature is obtained by adding the return estimated increase to the return temperature at the return specific time point. The return estimated increase in the first modification is set to the lower limit of increases in the return temperature determined experimentally while the heating medium in the circulation circuit is circulating. The return reference temperature may be a predetermined fixed value, unlike a value that varies with the return temperature at the return specific time point in the first modification.

When the return temperature is higher than or equal to the return reference temperature (Yes in STEP 30), a return temperature increase flag is set to ON (STEP 31). The return temperature increase flag is used for storing information indicating that the return temperature has increased above the return reference temperature. A storage area for this flag is allocated in a storage (not shown) in the controller 40. When the return temperature is not higher than or equal to the return reference temperature (No in STEP 30), the processing in STEP 31 is skipped. The return temperature increase flag is thus not set to ON.

The determination is performed as to whether the stop count has reached the determination count (STEP 32), independently of whether the return temperature increase flag has been set to ON. When the stop count has not reached the determination count (No in STEP 32), the determination is performed as to whether the determination time has elapsed on the determination timer (STEP 33). When the determination time has not elapsed on the determination timer (No in STEP 33), then the determination is performed as to whether the outgoing temperature is lower than the combustion resumption temperature (STEP 37). When the outgoing temperature is not yet lower than the combustion resumption temperature (No in STEP 37), the processing returns to STEP 33. The determination is performed again as to whether the determination time has elapsed on the determination timer (STEP 33). The determination is also performed again as to whether the outgoing temperature is lower than the combustion resumption temperature (STEP 37).

When the outgoing temperature is lower than the combustion resumption temperature (Yes in STEP 37), the combustion in the burner 3 is resumed (STEP 38). The processing then returns to STEP 23, and the subsequent processing described above is performed again. More specifically, when the outgoing temperature is higher than or equal to the combustion stop temperature (Yes in STEP 23), the combustion in the burner 3 is temporarily stopped again (STEP 24). When the determination timer is already active (Yes in STEP 25), the processing in STEPs 26 and 27 is skipped. When the outgoing temperature has remained higher than or equal to the abnormality determination temperature for at least the specified time (Yes in STEP 28), the stop count is incremented by one (STEP 29). When the return temperature is higher than or equal to the return reference temperature (Yes in STEP 30), the return temperature increase flag is set to ON (STEP 31). The determination is then performed as to whether the stop count has reached the determination count (STEP 32). When the return temperature increase flag has been already set to ON in previous processing, the return temperature increase flag is maintained in the ON state, independently of whether the return temperature is higher than or equal to the return reference temperature in the determination in STEP 30.

When the stop count has not reached the determination count (No in STEP 32), the determination is performed again as to whether the determination time has elapsed on the determination timer (STEP 33). The determination is also performed again as to whether the outgoing temperature is lower than the combustion resumption temperature (STEP 37). When the determination time has elapsed on the determination timer without the stop count reaching the determination count (Yes in STEP 33), the determination timer is stopped (STEP 34). The stop count is then reset (STEP 35), and the return temperature increase flag is set to OFF (STEP 36). When the outgoing temperature falls below the combustion resumption temperature thereafter (Yes in STEP 37), the combustion in the burner 3 is resumed (STEP 38). The processing then returns to STEP 23.

When the stop count has reached the determination count before the determination time elapses on the determination timer (in other words, within the determination time) (Yes in STEP 32), then the determination is performed as to whether the return temperature increase flag is ON (STEP 39). During an overheating abnormality, the heating medium does not circulate in the circulation circuit and thus the return temperature does not substantially increase, although the combustion in the burner 3 may be repeatedly stopped and resumed. When air or other substance enters the heating medium in the circulation circuit, the combustion in the burner 3 can also be repeatedly stopped and resumed. In this case, however, the return temperature increases at least once during the period from the return specific time point to the time at which the stop count reaches the determination count, with the heating medium in the circulation circuit circulating.

When the return temperature increase flag is ON (Yes in STEP 39), the flag indicates that the return temperature has increased above the return reference temperature. The heating medium in the circulation circuit is thus determined to be circulating, with a low likelihood of an overheating abnormality occurring. The processing thus advances to STEP 34, in which the determination timer is stopped (STEP 34). The stop count is then reset (STEP 35), and the return temperature increase flag is set to OFF (STEP 36). The subsequent processing described above is then performed again.

When the return temperature increase flag is not ON (No in STEP 39), the flag indicates that the return temperature remains below the return reference temperature during the period from the return specific time point to the time at which the stop count reaches the determination count. Thus, an overheating abnormality is highly likely to be occurring due to insufficient circulation of the heating medium in the circulation circuit. Thus, an overheating abnormality is detected (STEP 40). A notification about the overheating abnormality is then provided (STEP 41). The combustion control process in FIGS. 4 and 5 then ends.

As described above, in the space and water heating apparatus 1 according to the first modification, the detection condition for detecting an overheating abnormality is that the stop count reaches the determination count within the determination time. The stop count is incremented both when the combustion in the burner 3 is stopped in response to the outgoing temperature reaching the combustion stop temperature and when the outgoing temperature has remained higher than the abnormality determination temperature for at least the specified time after the combustion is stopped. The abnormality determination temperature is higher than the combustion stop temperature.

As described above, when an overheating abnormality is caused by insufficient circulation of the heating medium in the circulation circuit, the heating medium overheated in the first heat exchanger 15 may partly boil and overflow the first heat exchanger 15 into the outgoing channel 21. Although the combustion in the burner 3 is temporarily stopped upon the outgoing temperature (the temperature detected by the outgoing temperature sensor 25) reaching the combustion stop temperature, the outgoing temperature may increase further above the abnormality determination temperature and remain at such a temperature for some time (refer to FIG. 2B). When air or other substance enters the heating medium in the circulation circuit, the outgoing temperature can also reach the combustion stop temperature and cause the combustion in the burner 3 to stop. In this case, however, the outgoing temperature is less likely to increase further and can decrease immediately while the heating medium in the circulation circuit is circulating, although the outgoing temperature may possibly exceed the abnormality determination temperature. Thus, an overheating abnormality is highly likely to be occurring when the outgoing temperature remains higher than the abnormality determination temperature for at least the specified time. The stop count may thus be incremented only when this condition is satisfied. This allows more accurate detection of an overheating abnormality.

In the space and water heating apparatus 1 according to the first modification, the detection condition for detecting an overheating abnormality is that the stop count reaches the determination count after the combustion in the burner 3 is repeatedly stopped and resumed within the predetermined determination time. The detection condition includes a further condition that the temperature detected by the return temperature sensor 24 (return temperature) remains below the return reference temperature during the period from the return specific time point (the time at which the combustion is stopped for the first time and from which the measurement starts) to the time at which the stop count reaches the determination count. The return specific time point is after the start of the space heating operation or the hot-water supply operation.

As described above, during an overheating abnormality, the heating medium does not circulate in the circulation circuit and thus the return temperature does not substantially increase, although the combustion in the burner 3 may be repeatedly stopped and resumed. When air or other substance enters the heating medium in the circulation circuit, the combustion in the burner 3 can also be repeatedly stopped and resumed. In this case, however, the return temperature increases at least once during the period from the return specific time point to the time at which the stop count reaches the determination count, with the heating medium in the circulation circuit circulating. Thus, the detection condition may include a further condition that the return temperature remains below the return reference temperature during the period from the return specific time point to the time at which the stop count reaches the determination count. Using this further condition allows more accurate detection of an overheating abnormality caused by insufficient circulation of the heating medium.

In particular, the space and water heating apparatus 1 according to the first modification uses, as the return reference temperature, the temperature obtained by adding the return estimated increase to the return temperature (the temperature detected by the return temperature sensor 24) at the return specific time point. For example, the current space heating operation may start not long after the previous space heating operation ends. In this case, the heating medium in the circulation circuit (external circulation circuit) may be already relatively warm at the start of the current space heating operation. In this case as well, an overheating abnormality can be detected more accurately by determining whether an increase in the return temperature from the return specific time point is within the return estimated increase.

FIGS. 6 and 7 are each a flowchart of a combustion control process in a second modification performed by the controller 40. Many of the steps in the combustion control process in the second modification are the same as those in the combustion control process in the above embodiment and the first modification. Such steps will not be described in detail. In response to the start of the combustion control process in the second modification, the circulation pump 23 is activated (STEP 51), and the combustion in the burner 3 is started (STEP 52). The determination is then performed as to whether the hot-water supply operation is being performed (STEP 53).

When the hot-water supply operation is being performed (Yes in STEP 53), the temperature detected by the heat-exchanger outlet temperature sensor 35 (hereafter, a hot-water supply temperature) is obtained to set a hot-water supply reference temperature (STEP 54). In the space and water heating apparatus 1 according to the second modification, the hot-water supply reference temperature is set by adding a predetermined hot-water supply estimated increase to the hot-water supply temperature at a hot-water supply specific time point. The hot-water supply specific time point is the start time of the combustion in the burner 3 in the hot-water supply operation. As will be described in more detail below, a condition that the hot-water supply temperature remains below the hot-water supply reference temperature is added to the detection condition to allow more accurate detection of an overheating abnormality. The hot-water supply specific time point is not limited to the start time of the combustion in the burner 3 in the hot-water supply operation, and may be any time after the start of the hot-water supply operation. For example, the hot-water supply specific time point may be the time at which the combustion is stopped for the first time and from which the measurement of the determination time starts. The hot-water supply temperature may be obtained at such a hot-water supply specific time point, as in the first modification described above. The temperature detected by the hot-water outlet temperature sensor 38 may be obtained to be used as the hot-water supply temperature, in place of the temperature detected by the heat-exchanger outlet temperature sensor 35.

When the space heating operation is being performed rather than the hot-water supply operation (No in STEP 53), the processing in STEP 54 is skipped. The hot-water supply temperature is thus not obtained, and the hot-water supply reference temperature is not set. The determination is then performed as to whether the outgoing temperature is higher than or equal to the combustion stop temperature (STEP 55), independently of whether the hot-water supply operation is being performed or the space heating operation is being performed. When the outgoing temperature is not yet higher than or equal to the combustion stop temperature (No in STEP 55), the determination in STEP 55 is repeated at predetermined intervals.

When the outgoing temperature is higher than or equal to the combustion stop temperature (Yes in STEP 55), the combustion in the burner 3 is temporarily stopped (STEP 56). The determination is then performed as to whether the determination timer is active (STEP 57). When the determination timer is not yet active (No in STEP 57), the determination timer is activated (STEP 58).

Subsequently, the determination is performed as to whether the outgoing temperature has remained higher than or equal to the abnormality determination temperature for at least a specified time (STEP 59). When the outgoing temperature has remained higher than or equal to the abnormality determination temperature for at least the specified time (Yes in STEP 59), the stop count is incremented by one (STEP 60). In contrast, when the outgoing temperature is lower than the abnormality determination temperature or when the outgoing temperature has not remained higher than or equal to the abnormality determination temperature for the specified time after reaching the abnormality determination temperature (No in STEP 59), the processing in STEP 60 is skipped. The stop count is thus not incremented by one.

The determination is performed as to whether the hot-water supply operation is being performed (STEP 61 in FIG. 7), independently of whether the stop count has been incremented by one. When the hot-water supply operation is being performed (Yes in STEP 61), the determination is performed as to whether the hot-water supply temperature is higher than or equal to the hot-water supply reference temperature (STEP 62). As described above, the hot-water supply reference temperature is obtained by adding the hot-water supply estimated increase to the hot-water supply temperature at the hot-water supply specific time point. The hot-water supply estimated increase in the second modification is set to the lower limit of increases in the hot-water supply temperature determined experimentally while the heating medium in the circulation circuit (internal circulation circuit) is circulating. The hot-water supply reference temperature may be a predetermined fixed value, unlike a value that varies with the hot-water supply temperature at the hot-water supply specific time point in the second modification.

When the hot-water supply temperature is higher than or equal to the hot-water supply reference temperature (Yes in STEP 62), a hot-water supply temperature increase flag is set to ON (STEP 63). The hot-water supply temperature increase flag is used for storing information indicating that the hot-water supply temperature has increased above the hot-water supply reference temperature. A storage area for this flag is allocated in the storage (not shown) in the controller 40. When the space heating operation is being performed (No in STEP 61) or when the hot-water supply temperature is not higher than or equal to the hot-water supply reference temperature (No in STEP 62), the processing in STEP 63 is skipped. The hot-water supply temperature increase flag is thus not set to ON.

The determination is performed as to whether the stop count has reached the determination count (STEP 64), independently of whether the hot-water supply temperature increase flag has been set to ON. When the stop count has not reached the determination count (No in STEP 64), the determination is performed as to whether the determination time has elapsed on the determination timer (STEP 65). When the determination time has not elapsed on the determination timer (No in STEP 65), then the determination is performed as to whether the outgoing temperature is lower than the combustion resumption temperature (STEP 69). When the outgoing temperature is not yet lower than the combustion resumption temperature (No in STEP 69), the processing returns to STEP 65. The determination is performed again as to whether the determination time has elapsed on the determination timer (STEP 65). The determination is also performed again as to whether the outgoing temperature is lower than the combustion resumption temperature (STEP 69).

When the outgoing temperature is lower than the combustion resumption temperature (Yes in STEP 69), the combustion in the burner 3 is resumed (STEP 70). The processing then returns to STEP 55, and the subsequent processing described above is performed again. More specifically, when the outgoing temperature is higher than or equal to the combustion stop temperature (Yes in STEP 55), the combustion in the burner 3 is temporarily stopped again (STEP 56). When the determination timer is already active (Yes in STEP 57), the processing in STEP 58 is skipped. When the outgoing temperature has remained higher than or equal to the abnormality determination temperature for at least the specified time (Yes in STEP 59), the stop count is incremented by one (STEP 60). When the hot-water supply operation is being performed (Yes in STEP 61) and the hot-water supply temperature is higher than or equal to the hot-water supply reference temperature (Yes in STEP 62), the hot-water supply temperature increase flag is set to ON (STEP 63). The determination is then performed as to whether the stop count has reached the determination count (STEP 64). When the hot-water supply temperature increase flag has been already set to ON in previous processing, the hot-water supply temperature increase flag is maintained in the ON state, independently of whether the hot-water supply temperature is higher than or equal to the hot-water supply reference temperature in the determination in STEP 62.

When the stop count has not reached the determination count (No in STEP 64), the determination is performed again as to whether the determination time has elapsed on the determination timer (STEP 65). The determination is also performed again as to whether the outgoing temperature is lower than the combustion resumption temperature (STEP 69). When the determination time has elapsed on the determination timer without the stop count reaching the determination count (Yes in STEP 65), the determination timer is stopped (STEP 66). The stop count is then reset (STEP 67), and the hot-water supply temperature increase flag is set to OFF (STEP 68). When the outgoing temperature falls below the combustion resumption temperature thereafter (Yes in STEP 69), the combustion in the burner 3 is resumed (STEP 70). The processing then returns to STEP 55 again.

When the stop count has reached the determination count before the determination time elapses on the determination timer (in other words, within the determination time) (Yes in STEP 64), then the determination is performed as to whether the hot-water supply temperature increase flag is ON (STEP 71). During an overheating abnormality in the hot-water supply operation, the heating medium does not circulate in the circulation circuit (internal circulation circuit) and thus the hot-water supply temperature does not substantially increase, although the combustion in the burner 3 may be repeatedly stopped and resumed. When air or other substance enters the heating medium in the circulation circuit, the combustion in the burner 3 can also be repeatedly stopped and resumed. In this case, however, the hot-water supply temperature increases at least once during the period from the hot-water supply specific time point to the time at which the stop count reaches the determination count, with the heating medium in the internal circulation circuit circulating.

When the hot-water supply temperature increase flag is ON (Yes in STEP 71), the flag indicates that the hot-water supply temperature has increased above the hot-water supply reference temperature. The heating medium in the internal circulation circuit is thus determined to be circulating in the hot-water supply operation, with a low likelihood of an overheating abnormality occurring. The processing thus advances to STEP 66, in which the determination timer is stopped (STEP 66). The stop count is then reset (STEP 67), and the hot-water supply temperature increase flag is set to OFF (STEP 68). The subsequent processing described above is then performed again.

When the hot-water supply temperature increase flag is not ON (No in STEP 71), the flag indicates that the space heating operation is being performed or that the hot-water supply temperature remains below the hot-water supply reference temperature during the period from the hot-water supply specific time point to the time at which the stop count reaches the determination count in the hot-water supply operation. Thus, an overheating abnormality is highly likely to be occurring due to insufficient circulation of the heating medium in the internal circulation circuit. Thus, an overheating abnormality is detected (STEP 72). A notification about the overheating abnormality is then provided (STEP 73). The combustion control process in FIGS. 6 and 7 then ends.

As described above, in the space and water heating apparatus 1 according to the second modification, the detection condition for detecting an overheating abnormality is that the stop count reaches the determination count after the combustion in the burner 3 is repeatedly stopped and resumed within the predetermined determination time. The detection condition includes a further condition that the temperature detected by the heat-exchanger outlet temperature sensor 35 (hot-water supply temperature) remains below the hot-water supply reference temperature during the period from the hot-water supply specific time point (the start time of the combustion in the burner 3) after the start of the hot-water supply operation to the time at which the stop count reaches the determination count.

As described above, during an overheating abnormality in the hot-water supply operation, the heating medium does not circulate in the internal circulation circuit and thus the hot-water supply temperature does not substantially increase, although the combustion in the burner 3 may be repeatedly stopped and resumed. When air or other substance enters the heating medium in the circulation circuit (internal circulation circuit), the combustion in the burner 3 can also be repeatedly stopped and resumed. In this case, however, the hot-water supply temperature increases at least once during the period from the hot-water supply specific time point to the time at which the stop count reaches the determination count, with the heating medium in the internal circulation circuit circulating. Thus, the detection condition may include a further condition that the hot-water supply temperature remains below the hot-water supply reference temperature during the period from the hot-water supply specific time point to the time at which the stop count reaches the determination count. Using this further condition allows more accurate detection of an overheating abnormality caused by insufficient circulation of the heating medium in the hot-water supply operation.

In particular, the space and water heating apparatus 1 according to the second modification uses, as the hot-water supply reference temperature, the temperature obtained by adding the hot-water supply estimated increase to the hot-water supply temperature (the temperature detected by the heat-exchanger outlet temperature sensor 35) at the hot-water supply specific time point. For example, the current hot-water supply operation may start not long after the previous hot-water supply operation ends. In this case, the heating medium in the internal circulation circuit (in particular, in the hot-water supply heat exchanger 28) may be already relatively warm at the start of the current hot-water supply operation. In this case as well, an overheating abnormality can be detected more accurately by determining whether an increase in the hot-water supply temperature from the hot-water supply specific time point is within the hot-water supply estimated increase.

The space and water heating apparatus 1 (heating medium circulation apparatus) according to the present embodiment and the modifications has been described. However, the present invention is not limited to the above embodiment and the modifications and may be implemented in various manners without departing from the spirit and scope of the invention.

For example, in the first modification described above, the detection condition for detecting an overheating abnormality includes conditions (a), (b), and (c). (a) The combustion in the burner 3 is repeatedly stopped and resumed, and the stop count reaches the determination count within the predetermined determination time. (b) The stop count is incremented only when the outgoing temperature remains higher than the abnormality determination temperature for at least the specified time after the combustion in the burner 3 is stopped. (c) The return temperature remains below the return reference temperature during the period from the return specific time point after the start of the space heating operation or the hot-water supply operation to the time at which the stop count reaches the determination count. However, (c) may be eliminated from the detection condition among (a) to (c). In this case, the processing in STEPs 27, 30, 31, 36, and 39 may be eliminated from the combustion control process in FIGS. 4 and 5. In some embodiments, (b) may be eliminated from the detection condition among (a) to (c). In this case, the processing in STEP 28 may be eliminated from the combustion control process in FIGS. 4 and 5.

In the second modification described above, the detection condition for detecting an overheating abnormality includes conditions (a), (b), and (d). (a) The combustion in the burner 3 is repeatedly stopped and resumed, and the stop count reaches the determination count within the predetermined determination time. (b) The stop count is incremented only when the outgoing temperature remains higher than the abnormality determination temperature for at least the specified time after the combustion in the burner 3 is stopped. (d) The hot-water supply temperature remains below the hot-water supply reference temperature during the period from the hot-water supply specific time point after the start of the hot-water supply operation to the time at which the stop count reaches the determination count. However, (b) may be eliminated from the detection condition among (a), (b), and (d). In this case, the processing in STEP 59 may be eliminated from the combustion control process in FIGS. 6 and 7.

The first modification and the second modification described above may be combined. More specifically, the detection condition for detecting an overheating abnormality in the hot-water supply operation may include conditions (a), (b), (c), and (d). (a) The combustion in the burner 3 is repeatedly stopped and resumed, and the stop count reaches the determination count within the predetermined determination time. (b) The stop count is incremented only when the outgoing temperature remains higher than the abnormality determination temperature for at least the specified time after the combustion in the burner 3 is stopped. (c) The return temperature remains below the return reference temperature during the period from the return specific time point after the start of the hot-water supply operation to the time at which the stop count reaches the determination count. (d) The hot-water supply temperature remains below the hot-water supply reference temperature during the period from the hot-water supply specific time point after the start of the hot-water supply operation to the time at which the stop count reaches the determination count. This allows more accurate detection of an overheating abnormality in the hot-water supply operation.

In the above embodiment and the modifications, the heating medium circulation apparatus is used as the space and water heating apparatus 1 including the external circulation circuit for a space heating operation and the internal circulation circuit for a hot-water supply operation. However, the heating medium circulation apparatus is not limited to the space and water heating apparatus 1, and may be a space heater or a water heater including one of the external circulation circuit or the internal circulation circuit.

In the above embodiment, the panel radiator 20 is used as an example of the space heating equipment. However, the space heating equipment that dissipates heat from the heating medium is not limited to the panel radiator 20, and may be, for example, a bathroom heating and drying unit, a fan convector, or a floor heating unit.

In the above embodiment, the bypass channel 36 connects the water inlet channel 30 and the hot-water outlet channel 31, and the bypass servo 37 can change the mixing ratio between the water heated by the hot-water supply heat exchanger 28 and the clean water passing through the bypass channel 36. However, the bypass channel 36 and the bypass servo 37 may be eliminated. In this case, the heat-exchanger outlet temperature sensor 35 and the hot-water outlet temperature sensor 38 may be combined as a single temperature sensor, rather than being separate temperature sensors.

In the above embodiment, the apparatus includes the first heat exchanger 15 and the second heat exchanger 16. The circulating heating medium is preheated by the second heat exchanger 16 and then heated by the first heat exchanger 15. However, the apparatus may eliminate the second heat exchanger 16 and use the first heat exchanger 15 alone to heat the heating medium.

In the above embodiment, the burner 3 burns the gas mixture as the heater that heats the heating medium. However, the heater may have another structure, such as an electric heating unit, a heat pump, or a fuel cell.

REFERENCE SIGNS LIST

• • 1 space and water heating apparatus
  • 2 housing
  • 3 burner
  • 4 combustion unit
  • 5 combustion fan
  • 6 joint
  • 7 air supply channel
  • 8 gas supply channel
  • 9 open-close valve
  • 10 zero governor
  • 11 spark plug
  • 12 flame rod
  • 13 check valve
  • 15 first heat exchanger
  • 16 second heat exchanger
  • 17 exhaust duct
  • 18 exhaust port
  • 19 air supply port
  • 20 panel radiator
  • 20a pipe
  • 20b open-close valve
  • 21 outgoing channel
  • 22 return channel
  • 23 circulation pump
  • 24 return temperature sensor
  • 25 outgoing temperature sensor
  • 26 bimetallic switch
  • 27 branch channel
  • 28 hot-water supply heat exchanger
  • 29 three-way valve
  • 30 water inlet channel
  • 31 hot-water outlet channel
  • 32 water flow sensor
  • 33 water flow servo
  • 34 water inlet temperature sensor
  • 35 heat-exchanger outlet temperature sensor
  • 36 bypass channel
  • 37 bypass servo
  • 38 hot-water outlet temperature sensor
  • 40 controller
  • 41 hot-water supply remote control
  • 42 space-heating remote control