HEATING MEDIUM CIRCULATION APPARATUS

Abstract

A heating medium circulation apparatus promptly detects an overheating abnormality of a heating medium caused by insufficient circulation. The heating medium is pumped by a pump in a predetermined direction in a closed-loop circuit connecting a heater and a heat dissipator. An outgoing temperature and a return temperature of the heating medium flowing out of and into the heater are detected. When a heat dissipation-based operation starts, the pump is activated, and heating is started. Heating is temporarily stopped when the outgoing temperature reaches a heating stop temperature. Heating is resumed when the outgoing temperature falls below a heating resumption temperature. An additional condition that the difference between the outgoing and return temperatures is less than a determination value can be added to the condition for resuming heating. An overheating abnormality is detected when the additional condition remains unsatisfied until a determination time elapses after heating is stopped.

Claims

1. A heating medium circulation apparatus for circulating a heating medium between a heater configured to heat the heating medium and a heat dissipator configured to dissipate heat from the heating medium, the apparatus comprising: a circulation circuit being a closed-loop circuit connecting the heater and the heat dissipator; a circulation pump configured to pump the heating medium in the circulation circuit in a predetermined direction; an outgoing temperature sensor configured to detect a temperature of the heating medium flowing out of the heater; a return temperature sensor configured to detect a temperature of the heating medium flowing into the heater; a heating controller configured to control heating in the heater; and an overheating abnormality detector configured to detect an overheating abnormality, the overheating abnormality being local overheating of the heating medium caused by insufficient circulation of the heating medium in the circulation circuit, wherein 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, and 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 in the heater when a heating stop condition is satisfied, and the heating stop condition is that the temperature detected by the outgoing temperature sensor reaches a heating stop temperature, the heating controller resumes the heating in the heater when a heating resumption condition is satisfied, the heating resumption condition is that the temperature detected by the outgoing temperature sensor or the temperature detected by the return temperature sensor decreases to a heating resumption temperature, the heating controller is configured to add an additional condition to the heating resumption condition, and the additional condition is that a temperature difference between the temperature detected by the outgoing temperature sensor and the temperature detected by the return temperature sensor is less than a determination value, and the overheating abnormality detector detects the overheating abnormality when a detection condition is satisfied, and the detection condition is that the additional condition, when added to the heating resumption condition, remains unsatisfied until a predetermined determination time elapses from a time at which the heating in the heater is stopped in response to the heating stop condition being satisfied.

2. The heating medium circulation apparatus according to claim 1, wherein the detection condition includes a further condition that an increasing gradient being a rate of increase per unit time of the temperature detected by the outgoing temperature sensor is higher than or equal to a predetermined determination gradient, and the overheating abnormality detector detects the overheating abnormality when the detection condition including the further condition is satisfied.

3. The heating medium circulation apparatus according to claim 2, wherein the heating controller adds the additional condition to the heating resumption condition in response to the increasing gradient of the temperature detected by the outgoing temperature sensor being higher than or equal to the determination gradient.

4. The heating medium circulation apparatus according to claim 1, wherein the detection condition includes a further condition that the temperature detected by the outgoing temperature sensor remains higher than an abnormality determination temperature for at least a specified time after the heating in the heater is stopped in response to the heating stop condition being satisfied, the abnormality determination temperature is higher than the heating stop temperature, and the overheating abnormality detector detects the overheating abnormality when the detection condition including the further condition is satisfied.

5. The heating medium circulation apparatus according to claim 4, wherein the heating controller adds the additional condition to the heating resumption condition in response to the temperature detected by the outgoing temperature sensor remaining higher than the abnormality determination temperature for at least the specified time after the heating in the heater is stopped in response to the heating stop condition being satisfied.

6. The heating medium circulation apparatus according to claim 2, wherein the detection condition includes a further condition that the temperature detected by the outgoing temperature sensor remains higher than an abnormality determination temperature for at least a specified time after the heating in the heater is stopped in response to the heating stop condition being satisfied, the abnormality determination temperature is higher than the heating stop temperature, and the overheating abnormality detector detects the overheating abnormality when the detection condition including the further condition is satisfied.

7. The heating medium circulation apparatus according to claim 6, wherein the heating controller adds the additional condition to the heating resumption condition in response to the temperature detected by the outgoing temperature sensor remaining higher than the abnormality determination temperature for at least the specified time after the heating in the heater is stopped in response to the heating stop condition being satisfied.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 is a diagram of a space and water heating apparatus 1 as an example use of a heating medium circulation apparatus.

[0019] 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.

[0020] 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.

[0021] FIG. 4 is a flowchart of the first half of a combustion control process in a first modification performed by the controller 40.

[0022] FIG. 5 is a flowchart of the second half of the combustion control process in the first modification performed by the controller 40.

[0023] FIG. 6 is a flowchart of the first half of a combustion control process in a second modification performed by the controller 40.

[0024] 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

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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 and the temperature detected by the return temperature sensor 24. Before this technique is described in detail, the phenomenon that is typical of an overheating abnormality is described first.

[0043] 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.

[0044] 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 a combustion stop condition that the outgoing temperature reaches a predetermined combustion stop temperature is satisfied, the combustion in the burner 3 is temporarily stopped (extinguished). This causes the outgoing temperature to stop increasing and then decrease. Then, when a combustion resumption condition that the outgoing temperature decreases to a predetermined combustion resumption temperature lower than the combustion stop temperature is satisfied, 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 stop condition in the present embodiment corresponds to a heating stop condition 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. The combustion resumption condition in the present embodiment corresponds to a heating resumption condition in one or more aspects of the present invention.

[0045] Thus, the combustion in the burner 3 is temporarily stopped (extinguished) when the outgoing temperature reaches the combustion stop temperature (when the combustion stop condition is satisfied), and is resumed (ignited) when the outgoing temperature decreases to the combustion resumption temperature (when the combustion resumption condition is satisfied). 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. As the outgoing temperature decreases, the temperature detected by the return temperature sensor 24 (return temperature) increases, with the temperature difference between the outgoing temperature and the return temperature decreasing. Thus, the combustion resumption condition for resuming the combustion in the burner 3 may be that the return temperature decreases to the combustion resumption temperature, rather than the outgoing temperature decreasing to the combustion resumption temperature.

[0046] 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). When the combustion stop condition is satisfied 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.

[0047] 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 may cause 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.

[0048] When the combustion resumption condition is satisfied upon the outgoing temperature decreasing 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, satisfying the combustion stop condition. The combustion in the burner 3 is thus temporarily stopped again (extinguished). 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.

[0049] In some embodiments, the combustion in the burner 3 may be resumed based on the return temperature, in place of the outgoing temperature, as described above. In this case, the return temperature does not substantially 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 resumption condition is satisfied. The combustion in the burner 3 is thus resumed after a predetermined wait time elapses from the time at which the combustion in the burner 3 is stopped. In this manner, during an overheating abnormality, the heating medium does not circulate sufficiently in the circulation circuit and thus the temperature of the heating medium cannot be uniform across the circulation circuit when the combustion in the burner 3 is stopped, unlike in the normal state. The return temperature thus does not substantially increase, with the temperature difference between the outgoing temperature and the return temperature not easily reduced. Thus, an overheating abnormality is likely to be occurring due to insufficient circulation of the heating medium when the temperature difference between the outgoing temperature and the return temperature remains more than or equal to a determination value until a predetermined determination time elapses from the time at which the combustion in the burner 3 is stopped in response to the combustion stop condition being satisfied. Using this as the detection condition thus allows prompt detection of an overheating abnormality.

[0050] 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).

[0051] The determination is then performed as to whether the combustion stop condition is satisfied (STEP 3). As described above, in the combustion control for the burner 3 in the present embodiment, the combustion stop condition is that the temperature detected by the outgoing temperature sensor 25 (outgoing temperature) reaches the predetermined combustion stop temperature. When the combustion stop condition is not yet satisfied (No in STEP 3), the determination in STEP 3 is repeated at predetermined intervals.

[0052] When the combustion stop condition is satisfied (Yes in STEP 3), the combustion in the burner 3 is temporarily stopped (STEP 4). A determination timer is then activated (STEP 5). The determination timer measures the time elapsed from the time at which the combustion in the burner 3 is stopped in response to the combustion stop condition being satisfied.

[0053] After the determination timer is activated, the determination is performed as to whether the combustion resumption condition is satisfied (STEP 6). In the combustion control for the burner 3 in the present embodiment, the combustion resumption condition can include an additional condition, in addition to the condition that the outgoing temperature decreases to the predetermined combustion resumption temperature. The additional condition is that the temperature difference between the outgoing temperature and the return temperature is less than the predetermined determination value. While the combustion in the burner 3 is stopped, the outgoing temperature may or may not be higher than the return temperature. The heating medium circulating in the circulation circuit may cause the return temperature to exceed the outgoing temperature. In some embodiments, the combustion resumption condition may be that the return temperature, in place of the outgoing temperature, decreases to the combustion resumption temperature.

[0054] When the combustion resumption condition with the additional condition is not yet satisfied (No in STEP 6), the determination is performed as to whether the predetermined determination time has elapsed on the determination timer (STEP 7). When the determination time has not elapsed on the determination timer (No in STEP 7), the processing returns to STEP 6. The determination is performed again as to whether the combustion resumption condition with the additional condition is satisfied (STEP 6). As described above, during an overheating abnormality, the heating medium does not circulate sufficiently in the circulation circuit and thus the return temperature does not substantially increase, although the outgoing temperature may decrease to the combustion resumption temperature some time after the combustion in the burner 3 is stopped. The temperature difference between the outgoing temperature and the return temperature is thus not easily reduced below the determination value. In contrast, while the heating medium in the circulation circuit is circulating, the outgoing temperature decreases to the combustion resumption temperature when the combustion in the burner 3 is stopped. The circulation also causes the temperature of the heating medium to be uniform across the circulation circuit, thus causing the temperature difference between the outgoing temperature and the return temperature to be less than the determination value.

[0055] When the combustion resumption condition with the additional condition is satisfied before the determination time elapses on the determination timer (Yes in STEP 6), the heating medium in the circulation circuit is determined to be circulating, with a low likelihood of an overheating abnormality occurring. The determination timer is thus stopped (STEP 8), and the determination for an overheating abnormality is temporarily stopped. When the combustion in the burner 3 is resumed (STEP 9), the processing returns to STEP 3, and the subsequent processing described above is performed again.

[0056] When the determination time has elapsed on the determination timer without the combustion resumption condition with the additional condition being satisfied (Yes in STEP 7), the additional condition remains unsatisfied (the temperature difference between the outgoing temperature and the return temperature remains more than or equal to the determination value). Thus, an overheating abnormality is likely to be occurring due to insufficient circulation of the heating medium in the circulation circuit. Thus, an overheating abnormality is detected (STEP 10). A notification about the overheating abnormality is then provided (STEP 11). 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.

[0057] 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. 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. The combustion resumption condition is that the outgoing temperature decreases to the combustion resumption temperature. Such control is repeatedly performed. The combustion resumption condition can also include the additional condition that the temperature difference between the outgoing temperature and the temperature detected by the return temperature sensor 24 (return temperature) is less than the determination value. The detection condition for detecting an overheating abnormality is that the additional condition remains unsatisfied until the predetermined determination time elapses from the time at which the combustion in the burner 3 is stopped in response to the combustion stop condition being satisfied.

[0058] As described above, during an overheating abnormality, the heating medium does not circulate sufficiently in the circulation circuit and thus the temperature of the heating medium cannot be uniform across the circulation circuit when the combustion in the burner 3 is stopped, unlike in the normal state. The return temperature thus does not substantially increase, with the temperature difference between the outgoing temperature and the return temperature not easily reduced. Thus, an overheating abnormality is likely to be occurring when the temperature difference between the outgoing temperature and the return temperature remains more than or equal to the determination value (the additional condition remains unsatisfied) until the determination time elapses from the time at which the combustion in the burner 3 is stopped. Using this as the detection condition thus allows prompt detection of an overheating abnormality. With the additional condition added to the combustion resumption condition, the combustion in the burner 3 is not resumed simply by the outgoing temperature decreasing to the combustion resumption temperature before the determination time elapses. Instead, the determination as to whether the temperature of the heating medium is uniform across the circulation circuit can be continued until the determination time elapses while the combustion in the burner 3 remains stopped.

[0059] 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.

[0060] 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 increasing gradient, or the rate of increase per unit time, of the outgoing temperature is higher than or equal to a determination gradient (STEP 23).

[0061] The determination gradient in the first modification is higher than the upper limit of increasing gradients of the outgoing temperature determined experimentally while the heating medium in the circulation circuit is circulating. In the normal state in which the heating medium is circulating in the circulation circuit with no overheating abnormality, the circulating heating medium is gradually heated while passing through the first heat exchanger 15. Thus, the outgoing temperature of the heating medium detected by the outgoing temperature sensor 25 when the heating medium flows out of the first heat exchanger 15 has an increasing gradient lower than the determination gradient. In contrast, during an overheating abnormality, the insufficient circulation of the heating medium may cause the heating medium in the first heat exchanger 15 to overheat, expand thermally (partly boil), and overflow the first heat exchanger 15 as described above. The outgoing temperature of the overflowing heating medium detected by the outgoing temperature sensor 25 may thus have an increasing gradient higher than the determination gradient (refer to FIG. 2B). In the space and water heating apparatus 1 according to the first modification, the determination gradient differs between the space heating operation and the hot-water supply operation. The determination gradient for the current operation mode (the space heating operation or the hot-water supply operation) is used. In the hot-water supply operation in which hot water is to be supplied promptly at a set temperature, the combustion level of the burner 3 tends to be higher and the outgoing temperature tends to increase more easily than in the space heating operation. The determination gradient is thus higher in the hot-water supply operation than in the space heating operation.

[0062] When the increasing gradient of the outgoing temperature is not higher than or equal to the determination gradient (No in STEP 23), the determination is performed as to whether the combustion stop condition is satisfied (whether the outgoing temperature has reached the combustion stop temperature, STEP 24). When the combustion stop condition is not yet satisfied (No in STEP 24), the processing returns to STEP 23. The determination is performed again as to whether the increasing gradient of the outgoing temperature is higher than or equal to the determination gradient (STEP 23). The determination is also performed again as to whether the combustion stop condition is satisfied (STEP 24).

[0063] When the combustion stop condition is satisfied without the increasing gradient of the outgoing temperature being higher than or equal to the determination gradient (Yes in STEP 24), the combustion in the burner 3 is temporarily stopped (STEP 25). The determination is then performed as to whether the combustion resumption condition is satisfied (STEP 26). In the combustion control for the burner 3 in the first modification, the combustion resumption condition does not normally include the above additional condition (the condition that the temperature difference between the outgoing temperature and the return temperature is less than the determination value). Thus, the combustion resumption condition used in STEP 26 is that the outgoing temperature decreases to the combustion resumption temperature. When the combustion resumption condition is not yet satisfied (No in STEP 26), the determination in STEP 26 is repeated at predetermined intervals. When the combustion resumption condition is satisfied (Yes in STEP 26), the combustion in the burner 3 is resumed (STEP 27). The processing then returns to STEP 23. The determination is performed again as to whether the increasing gradient of the outgoing temperature is higher than or equal to the determination gradient (STEP 23).

[0064] When the increasing gradient of the outgoing temperature is higher than or equal to the determination gradient (Yes in STEP 23), then the determination is performed as to whether the combustion stop condition is satisfied (whether the outgoing temperature has reached the combustion stop temperature, STEP 28). When air or other substance enters the heating medium in the circulation circuit, the outgoing temperature may temporarily increase steeply. In this case, however, the outgoing temperature can decrease immediately without reaching the combustion stop temperature, or the outgoing temperature can remain below the combustion stop temperature with its increase less steep. Thus, when the combustion stop condition is not satisfied (No in STEP 28), the processing returns to STEP 23. The determination is performed again as to whether the increasing gradient of the outgoing temperature is higher than or equal to the determination gradient (STEP 23).

[0065] Both when the increasing gradient of the outgoing temperature is higher than or equal to the determination gradient and when the combustion stop condition is satisfied (Yes in STEP 28), the combustion in the burner 3 is temporarily stopped (STEP 29). The determination timer is then activated (STEP 30). An overheating abnormality is likely to be occurring, and thus the additional condition is added to the combustion resumption condition (STEP 31). In other words, the combustion resumption condition is that the temperature difference between the outgoing temperature and the return temperature is less than the determined value, in addition to the condition that the outgoing temperature decreases to the combustion resumption temperature.

[0066] The determination is then performed as to whether the combustion resumption condition with the additional condition is satisfied (STEP 32 in FIG. 5). When the combustion resumption condition with the additional condition is not yet satisfied (No in STEP 32), the determination is performed as to whether the predetermined 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), the processing returns to STEP 32. The determination is performed again as to whether the combustion resumption condition with the additional condition is satisfied (STEP 32).

[0067] When the combustion resumption condition with the additional condition is satisfied before the determination time elapses on the determination timer (Yes in STEP 32), an overheating abnormality is less likely to be occurring. The determination timer is thus stopped (STEP 34), and the determination for an overheating abnormality is temporarily stopped. When the combustion in the burner 3 is resumed (STEP 35), the processing returns to STEP 23, and the subsequent processing described above is performed again.

[0068] When the determination time has elapsed on the determination timer without the combustion resumption condition with the additional condition being satisfied (Yes in STEP 33), the additional condition remains unsatisfied (the temperature difference between the outgoing temperature and the return temperature remains more than or equal to the determination value). Thus, an overheating abnormality is likely to be occurring due to insufficient circulation of the heating medium in the circulation circuit. Thus, an overheating abnormality is detected (STEP 36). A notification about the overheating abnormality is then provided (STEP 37). The combustion control process in FIGS. 4 and 5 then ends.

[0069] 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 additional condition remains unsatisfied (the temperature difference between the outgoing temperature and the return temperature remains more than or equal to the determination value) until the predetermined determination time elapses from the time at which the combustion in the burner 3 is stopped. The detection condition includes a further condition that the increasing gradient, or the rate of increase per unit time, of the outgoing temperature is higher than or equal to the determination gradient.

[0070] 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 expand thermally (partly boil) and overflow the first heat exchanger 15. This may cause a steep increase in the outgoing temperature of the heating medium detected by the outgoing temperature sensor 25 that cannot occur in the normal state. Thus, an overheating abnormality is highly likely to be occurring when the increasing gradient of the outgoing temperature is higher than or equal to the determination gradient. Adding this condition to the detection condition allows more accurate detection of an overheating abnormality.

[0071] In the space and water heating apparatus 1 according to the first modification, the additional condition is added to the combustion resumption condition in response to the increasing gradient of the outgoing temperature being higher than or equal to the determination gradient. To determine whether the additional condition is satisfied (whether the temperature of the heating medium is uniform across the circulation circuit), the apparatus is to wait up to the duration of the determination time after the combustion in the burner 3 is stopped. The additional condition is added to the combustion resumption condition for detecting an overheating abnormality only when an overheating abnormality is highly likely to be occurring, including when the increasing gradient of the outgoing temperature is higher than or equal to the determination gradient. The additional condition is not added to the combustion resumption condition when an overheating abnormality is less likely to be occurring. This avoids a delay in resuming the combustion in the burner 3 to achieve convenience and comfort for the user of the space and water heating apparatus 1.

[0072] 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 combustion stop condition is satisfied (whether the outgoing temperature has reached the combustion stop temperature, STEP 53). When the combustion stop condition is not yet satisfied (No in STEP 53), the determination in STEP 53 is repeated at predetermined intervals.

[0073] When the combustion stop condition is satisfied (Yes in STEP 53), the combustion in the burner 3 is temporarily stopped (STEP 54). The determination timer is then activated (STEP 55). 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 56). During an overheating abnormality, although the combustion in the burner 3 is temporarily stopped when the combustion stop condition is satisfied 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 second modification is set longer than the duration of the outgoing temperature taken to eliminate detection noise. When air or other substance enters the heating medium in the circulation circuit, the outgoing temperature can also reach the combustion stop temperature (the combustion stop condition can be satisfied) 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.

[0074] 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 56), an overheating abnormality is less likely to be occurring. The determination timer is thus stopped (STEP 57), and the determination for an overheating abnormality is temporarily stopped. The determination is then performed as to whether the combustion resumption condition is satisfied (STEP 58). In the combustion control for the burner 3 in the second modification, the combustion resumption condition does not normally include the above additional condition (the condition that the temperature difference between the outgoing temperature and the return temperature is less than the determination value), as in the first modification described above. Thus, the combustion resumption condition used in STEP 58 is that the outgoing temperature decreases to the combustion resumption temperature. When the combustion resumption condition is not yet satisfied (No in STEP 58), the determination in STEP 58 is repeated at predetermined intervals. When the combustion resumption condition is satisfied (Yes in STEP 58), the combustion in the burner 3 is resumed (STEP 59). The processing then returns to STEP 53. The determination is performed again as to whether the combustion stop condition is satisfied (STEP 53).

[0075] In contrast, when the outgoing temperature has remained higher than the abnormality determination temperature for at least the specified time (Yes in STEP 56), an overheating abnormality is highly likely to be occurring. The additional conditional is thus added to the combustion resumption condition (STEP 60). In other words, the combustion resumption condition is that the temperature difference between the outgoing temperature and the return temperature is less than the determined value, in addition to the condition that the outgoing temperature decreases to the combustion resumption temperature.

[0076] The determination is then performed as to whether the combustion resumption condition with the additional condition is satisfied (STEP 61 in FIG. 7). When the combustion resumption condition with the additional condition is not yet satisfied (No in STEP 61), the determination is performed as to whether the predetermined determination time has elapsed on the determination timer (STEP 62). When the determination time has not elapsed on the determination timer (No in STEP 62), the processing returns to STEP 61. The determination is performed again as to whether the combustion resumption condition with the additional condition is satisfied (STEP 61).

[0077] When the combustion resumption condition with the additional condition is satisfied before the determination time elapses on the determination timer (Yes in STEP 61), an overheating abnormality is less likely to be occurring. The determination timer is thus stopped (STEP 63), and the determination for an overheating abnormality is temporarily stopped. When the combustion in the burner 3 is resumed (STEP 64), the processing returns to STEP 53, and the subsequent processing described above is performed again.

[0078] When the determination time has elapsed on the determination timer without the combustion resumption condition with the additional condition being satisfied (Yes in STEP 62), the additional condition remains unsatisfied (the temperature difference between the outgoing temperature and the return temperature remains more than or equal to the determination value). Thus, an overheating abnormality is likely to be occurring due to insufficient circulation of the heating medium in the circulation circuit. Thus, an overheating abnormality is detected (STEP 65). A notification about the overheating abnormality is then provided (STEP 66). The combustion control process in FIGS. 6 and 7 then ends.

[0079] 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 additional condition remains unsatisfied (the temperature difference between the outgoing temperature and the return temperature remains more than or equal to the determination value) until the predetermined determination time elapses from the time at which the combustion in the burner 3 is stopped. The detection condition includes a further condition that the outgoing temperature remains higher than the abnormality determination temperature that is higher than the combustion stop temperature for at least the specified time after the combustion in the burner 3 is stopped in response to the combustion stop condition being satisfied (the outgoing temperature reaching the combustion stop temperature).

[0080] 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 when the combustion stop condition is satisfied upon the outgoing temperature 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. When air or other substance enters the heating medium in the circulation circuit, the outgoing temperature can also reach the combustion stop temperature (the combustion stop condition can be satisfied) 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. Adding this condition to the detection condition allows more accurate detection of an overheating abnormality.

[0081] In the space and water heating apparatus 1 according to the second modification, the additional condition is added to the combustion resumption condition in response to the outgoing temperature remaining higher than the abnormality determination temperature for at least the specified time after the combustion in the burner 3 is stopped in response to the combustion stop condition being satisfied. To determine whether the additional condition is satisfied (whether the temperature of the heating medium is uniform across the circulation circuit), the apparatus is to wait up to the duration of the determination time after the combustion in the burner 3 is stopped. The additional condition is added to the combustion resumption condition for detecting an overheating abnormality only when an overheating abnormality is highly likely to be occurring, including when the outgoing temperature remains higher than the abnormality determination temperature for at least the specified time. The additional condition is not added to the combustion resumption condition when an overheating abnormality is less likely to be occurring. This avoids a delay in resuming the combustion in the burner 3 to achieve convenience and comfort for the user of the space and water heating apparatus 1.

[0082] 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.

[0083] For example, the first modification and the second modification described above may be combined. More specifically, the detection condition for detecting an overheating abnormality may include three conditions (a), (b), and (c). (a) The additional condition remains unsatisfied (the temperature difference between the outgoing temperature and the return temperature remains more than or equal to the determination value) until the predetermined determination time elapses from the time at which the combustion in the burner 3 is stopped. (b) The increasing gradient, or the rate of increase per unit time, of the outgoing temperature is higher than or equal to the determination gradient. (c) The outgoing temperature remains higher than the abnormality determination temperature that is higher than the combustion stop temperature for at least the specified time after the combustion in the burner 3 is stopped in response to the combustion stop condition being satisfied (the outgoing temperature reaching the combustion stop temperature). This allows more accurate detection of an overheating abnormality. In this case, the additional condition may be added to the heating resumption condition in response to (b) being satisfied, or (c) being satisfied, or both (b) and (c) being satisfied.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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

[0089] 1 space and water heating apparatus [0090] 2 housing [0091] 3 burner [0092] 4 combustion unit [0093] 5 combustion fan [0094] 6 joint [0095] 7 air supply channel [0096] 8 gas supply channel [0097] 9 open-close valve [0098] 10 zero governor [0099] 11 spark plug [0100] 12 flame rod [0101] 13 check valve [0102] 15 first heat exchanger [0103] 16 second heat exchanger [0104] 17 exhaust duct [0105] 18 exhaust port [0106] 19 air supply port [0107] 20 panel radiator [0108] 20a pipe [0109] 20b open-close valve [0110] 21 outgoing channel [0111] 22 return channel [0112] 23 circulation pump [0113] 24 return temperature sensor [0114] 25 outgoing temperature sensor [0115] 26 bimetallic switch [0116] 27 branch channel [0117] 28 hot-water supply heat exchanger [0118] 29 three-way valve [0119] 30 water inlet channel [0120] 31 hot-water outlet channel [0121] 32 water flow sensor [0122] 33 water flow servo [0123] 34 water inlet temperature sensor [0124] 35 heat-exchanger outlet temperature sensor [0125] 36 bypass channel [0126] 37 bypass servo [0127] 38 hot-water outlet temperature sensor [0128] 40 controller [0129] 41 hot-water supply remote control [0130] 42 space-heating remote control