FLUID CIRCULATION SYSTEM

Abstract

 A fluid circulation system with which situations in which inflowing high-temperature fluid causes damage to an indoor-heating device or an increase in room temperature that is not desired by a user can be reliably prevented is provided.
A fluid circulation system includes: a heat accumulating circuit in which a fluid circulates between a fluid heater and a heat storage tank; an indoor-heating circuit in which the fluid circulates between the fluid heater and an indoor-heating installation; a valve for switching between the heat accumulating circuit and the indoor-heating circuit; an outflow temperature sensor for detecting a temperature of the fluid flowing out of the fluid heater; and a controller for controlling switching between the heat accumulating circuit and the indoor-heating circuit. The controller is configured to switch, when a request to switch from the heat accumulating circuit to the indoor-heating circuit is issued during a heat accumulating operation in which the heat accumulating circuit is operated, from the heat accumulating circuit to the indoor-heating circuit on condition that the temperature of the fluid flowing out of the fluid heater is lower than a reference value.

Description

[Technical Field]

[0001] The present invention relates to a fluid circulation system.

[Background Art]

[0002] A conventional hot water heating unit is capable of performing a hot water accumulating operation for accumulating hot water in a hot water storage tank using heating means, and an indoor-heating operation for raising a room temperature by supplying hot water to an indoor-heating device such as a radiator. In this hot water heating unit, the respective operating modes are achieved by modifying a circuit through which the hot water is supplied using a flow passage switching valve (see PTL 1, for example).

[0003] Further, PTL 2 discloses a technique employed by a device that operates a circulation pump forcibly for a predetermined period when the temperature in a hot water tank falls to or below a lower limit activation temperature. In this technique, an abnormality is determined to have occurred during attachment of a pipe or the like when the temperature in the hot water tank differs from the temperature of hot water flowing into a heat pump unit by at least a predetermined value (10 deg, for example), and in this case, control for stopping the operation of the heat pump unit or the like is implemented.

[Citation List]

[Patent Literature]

[0004] 

[PTL 1] Japanese Utility Model Application Publication No. S63-129117

[PTL 2] Japanese Patent Application Publication No. 2012-47394

[Summary of Invention]

[Technical Problem]

[0005] In the hot water heating unit of PTL 1, the hot water accumulating operation is switched to the indoor-heating operation and vice versa by operating the flow passage switching valve. When a hot water accumulating circuit used during the hot water accumulating operation is switched to an indoor-heating circuit at the end of the hot water accumulating operation, high-temperature water generated during the hot water accumulating operation flows into the radiator or other indoor-heating device, and as a result, problems such as damage to the indoor-heating device and an increase in the room temperature even though the indoor-heating operation is not underway may occur.

[0006] The present invention has been designed to solve these problems, and an object thereof is to provide a fluid circulation system with which situations in which inflowing high-temperature fluid causes damage to an indoor-heating device or an increase in room temperature that is not desired by a user can be reliably prevented.

[Solution to Problem]

[0007] A fluid circulation system according to the present invention includes: a fluid heater for heating a fluid; a heat storage tank for storing the fluid; a heat accumulating circuit in which the fluid circulates between the fluid heater and the heat storage tank; an indoor-heating circuit in which the fluid circulates between the fluid heater and an indoor-heating installation; a valve for switching between the heat accumulating circuit and the indoor-heating circuit; an outflow temperature sensor for detecting a temperature of the fluid flowing out of the fluid heater; and a controller for controlling switching between the heat accumulating circuit and the indoor-heating circuit. The controller is configured to switch, when a request to switch from the heat accumulating circuit to the indoor-heating circuit is issued during a heat accumulating operation in which the heat accumulating circuit is operated, from the heat accumulating circuit to the indoor-heating circuit on condition that the temperature of the fluid flowing out of the fluid heater is lower than a reference value.

[Advantageous Effects of Invention]

[0008] With the fluid circulation system according to the present invention, situations in which inflowing high-temperature fluid causes damage to an indoor-heating device or an increase in room temperature that is not desired by a user can be reliably prevented.

[Brief Description of Drawings]

[0009] 

Fig. 1 is a view showing a configuration of a fluid circulation system according to a first embodiment of the present invention.

Fig. 2 is a view showing a circuit through which water circulates during a heat accumulating operation implemented by the fluid circulation system according to the first embodiment.

Fig. 3 is a view showing a circuit through which water circulates during an indoor-heating operation implemented by the fluid circulation system according to the first embodiment.

Fig. 4 is a flowchart showing control operations implemented by a controller of the fluid circulation system according to the first embodiment.

[Description of Embodiments]

[0010] Embodiments of the present invention will be described below with reference to the drawings. Note that identical elements in the drawings have been allocated identical reference symbols, and duplicate description thereof has been omitted. In this specification, the term "water" includes water of any temperature, from low-temperature cold water to high-temperature hot water.

First Embodiment

[0011] Fig. 1 is a view showing a configuration of a fluid circulation system according to a first embodiment of the present invention. A fluid circulation system 1 according to the first embodiment, shown in Fig. 1, is a hot water storage type hot water heating system. The fluid circulation system 1 includes a fluid heater 100, a tank unit 200, and a controller 10. The fluid heater 100 and the tank unit 200 are connected to each other via a first shared pipe 9, a second shared pipe 3, and electric wiring (not shown). In the fluid circulation system 1 according to the first embodiment, the fluid heater 100 and the tank unit 200 are provided separately, but in the present invention, the fluid heater 100 and the tank unit 200 may be formed integrally.

[0012] The fluid heater 100 according to the first embodiment is a heat pump type fluid heater. The fluid heater 100 includes a compressor 13 for compressing a refrigerant, a water-refrigerant heat exchanger 15, a decompressor 16 for decompressing the refrigerant, a low-temperature-side heat exchanger 17 (an evaporator) in which heat from a low temperature heat source (outside air, for example) is absorbed by the refrigerant, and a refrigerant pipe 14 that forms a refrigerant circuit by connecting these devices in an annular shape. The fluid heater 100 heats water by performing a heat pump cycle (refrigeration cycle) operation in the refrigerant circuit. The fluid heater 100 heats the water by implementing heat exchange between the water and the high temperature, high pressure refrigerant compressed by the compressor 13 in the water-refrigerant heat exchanger 15.

[0013] The fluid heater according to the present invention is not limited to the heat pump type fluid heater described above, and another type of fluid heater may be used. For example, the fluid heater according to the present invention may be a solar fluid heater that heats water using solar heat, or a combustion type fluid heater that heats water using combustion heat from a fuel (gas, kerosene, heavy oil, coal, and so on, for example). Further, in the first embodiment, water is used as the fluid, but the fluid according to the present invention may be a fluid other than water, such as antifreeze or brine.

[0014] A heat storage tank 2, a switching valve 6, and a circulation pump 11 are built into the tank unit 200. Water is stored in the heat storage tank 2. Temperature stratification can be realized in the heat storage tank 2 by means of a difference in the density of the water corresponding to a difference in the temperature thereof such that high-temperature water is stored on an upper side of the heat storage tank 2 and low-temperature water is stored on a lower side thereof. A feed-water pipe 18 is connected to a lower portion of the heat storage tank 2. Water supplied from a water source such as water mains is supplied into the heat storage tank 2 through the feed-water pipe 18. A hot water supply pipe 19 is connected to an upper portion of the heat storage tank 2. To supply hot water to the outside, the hot water stored in the heat storage tank 2 is pumped into the hot-water supply pipe 19.

[0015] The heat storage tank 2 includes a first water outlet 25 and a first water inlet 26. The water in the heat storage tank 2 exits the heat storage tank 2 through the first water outlet 25. Hot water heated by the fluid heater 100 enters the heat storage tank 2 through the first water inlet 26. The first water outlet 25 is located in the lower portion of the heat storage tank 2. The first water inlet 26 is located in the upper portion of the heat storage tank 2. The switching valve 6 includes a first port 6a, a second port 6b, and a third port 6c. The switching valve 6 can be switched between a condition in which the third port 6c communicates with the first port 6a while the second port 6b is closed, and a condition in which the third port 6c communicates with the second port 6b while the first port 6a is closed.

[0016] A lower pipe 8 connects the first water outlet 25 of the heat storage tank 2 to an upstream end of the first shared pipe 9. A downstream end of the first shared pipe 9 is connected to a water inlet of the water-refrigerant heat exchanger 15 of the fluid heater 100. The circulation pump 11 is connected to a midway point on the first shared pipe 9. The circulation pump 11 is preferably a pump having a variable output. A pump including a pulse width modulation control (PWM control) type DC motor, the output of which can be varied in accordance with a speed command voltage from the controller 10, for example, can be used favorably as the circulation pump 11. In the first embodiment, the circulation pump 11 is disposed in the tank unit 200, but in the present invention, the circulation pump 11 may be disposed in the fluid heater 100. The second shared pipe 3 connects a water outlet of the water-refrigerant heat exchanger 15 of the fluid heater 100 to the third port 6c of the switching valve 6. An upper pipe 4 connects the first port 6a of the switching valve 6 to the first water inlet 26 of the heat storage tank 2. In the first embodiment, the circulation pump 11 is connected to a midway point on the first shared pipe 9, but in the present invention, the circulation pump 11 may be connected to a midway point on the second shared pipe 3.

[0017] The indoor-heating installation 12 is provided on the outside of the fluid heater 100 and the tank unit 200. The indoor-heating installation 12 includes one or a plurality of indoor-heating devices 24. By passing the water heated by the fluid heater 100 through the indoor-heating device 24, the air temperature in a room is increased. At least one of an underfloor heating panel disposed under a floor, a radiator or a panel heater disposed on a wall surface of the room, and a fan convector, for example, may be used as the indoor-heating device 24. A fan convector includes a fan for circulating air through the room and a heat exchanger in which heat is exchanged between a liquid such as heated water and the air in the room, and performs heating by means of forced convection. When the indoor-heating installation 12 includes a plurality of indoor-heating devices 24, the plurality of indoor-heating devices 24 may be of the same type or different types. When the indoor-heating installation 12 includes a plurality of indoor-heating devices 24, the plurality of indoor-heating devices 24 may be connected in series, in parallel, or in both series and parallel.

[0018] The tank unit 200 is connected to the indoor-heating installation 12 via a first external pipe 22 and a second external pipe 23. The tank unit 200 includes a second water outlet 27 and a second water inlet 28. Water supplied to the indoor-heating installation 12 from the tank unit 200 exits the tank unit 200 through the second water outlet 27. A first internal pipe 5 connects the second port 6b of the switching valve 6 to the second water outlet 27 in the interior of the tank unit 200. An upstream end of the first external pipe 22 is connected to the second water outlet 27 from the outside of the tank unit 200. A downstream end of the first external pipe 22 is connected to an inlet of the indoor-heating installation 12. An upstream end of the second external pipe 23 is connected to an outlet of the indoor-heating installation 12. A downstream end of the second external pipe 23 is connected to the second water inlet 28 from the outside of the tank unit 200. A second internal pipe 7 connects the second water inlet 28 to an upstream end of the first shared pipe 9 in the interior of the tank unit 200. Water returning to the tank unit 200 from the indoor-heating installation 12 enters the tank unit 200 through the second water inlet 28.

[0019] The controller 10 is built into the tank unit 200. The controller 10 and a remote controller 21 are connected to each other to be capable of mutual communication. A user can input commands, changes to set values, and so on in relation to operations of the fluid circulation system 1 from the remote controller 21. Although not shown in the drawings, the controller 10 includes a storage unit having a ROM (a read-only memory), a RAM (a random access memory), a nonvolatile memory, and so on, a CPU (a central processing unit) that executes calculation processing on the basis of a program stored in the storage unit, and an input/output port through which external signals are input into and output from the CPU. Various actuators and sensors included in the fluid circulation system 1 are electrically connected to the controller 10. The controller 10 controls operations of the fluid circulation system 1 on the basis of detection values from the sensors, signals from the remote controller 21, and so on. Although not shown in the drawings, a display unit for displaying information such as the condition of the fluid circulation system 1, an operating unit such as a switch operated by the user, a speaker, a microphone, and so on are installed in the remote controller 21.

[0020] A plurality of temperature sensors (not shown) are mounted on the surface of the heat storage tank 2 at equal intervals in a vertical direction. By detecting a vertical direction temperature distribution within the heat storage tank 2 using these temperature sensors, the controller 10 can calculate an amount of hot water stored in the heat storage tank 2, an amount of heat stored therein, a remaining amount of hot water therein, and so on.

[0021] A flow rate sensor 30 and an outflow temperature sensor 31 are provided in the second shared pipe 3. The flow rate sensor 30 detects the flow rate of the water passing through the second shared pipe 3. The outflow temperature sensor 31 detects the temperature of the water flowing out of the fluid heater 100. The temperature of the water heated by the fluid heater 100 can be detected using the outflow temperature sensor 31. In the following description, the temperature of the water flowing out of the fluid heater 100 will be referred to as the "outflow temperature". In the first embodiment, the flow rate sensor 30 and the outflow temperature sensor 31 are installed in the tank unit 200, but in the present invention, the flow rate sensor 30 and the outflow temperature sensor 31 may be installed in the fluid heater 100.

[0022] An inflow temperature sensor 32 is provided in the first shared pipe 9. The inflow temperature sensor 32 detects the temperature of the water flowing into the fluid heater 100. The temperature of the water before being heated by the fluid heater 100 can be detected using the inflow temperature sensor 32. In the following description, the temperature of the water flowing into the fluid heater 100 will be referred to as the "inflow temperature". In the first embodiment, the inflow temperature sensor 32 is installed in the tank unit 200, but in the present invention, the inflow temperature sensor 32 may be installed in the fluid heater 100.

[0023] Next, referring to Fig. 2, a heat accumulating operation implemented by the fluid circulation system 1 will be described. Fig. 2 is a view showing a circuit through which water circulates during the heat accumulating operation implemented by the fluid circulation system 1 according to the first embodiment. Arrows in Fig. 2 show a flow direction of the water. During the heat accumulating operation, the fluid heater 100 and the circulation pump 11 are driven and the switching valve 6 is controlled to the condition in which the third port 6c communicates with the first port 6a while the second port 6b is closed. During the heat accumulating operation, the low-temperature water in the lower portion of the heat storage tank 2 is pumped to the water-refrigerant heat exchanger 15 of the fluid heater 100 through the first water outlet 25, the lower pipe 8, and the first shared pipe 9. High-temperature water obtained when the water is heated in the water-refrigerant heat exchanger 15 then flows into the upper portion of the heat storage tank 2 through the second shared pipe 3, the third port 6c and the first port 6a of the switching valve 6, the upper pipe 4, and the first water inlet 26. By circulating the water in the manner described above during the heat accumulating operation, high-temperature water is gradually stored in the interior of the heat storage tank 2 from the top toward the bottom such that the amount of heat stored in the heat storage tank 2 increases. The water circulation circuit employed during the heat accumulating operation, as described above, will be referred to hereafter as a "heat accumulating circuit".

[0024] The controller 10 starts the heat accumulating operation when the amount of remaining hot water or the amount of stored heat in the heat storage tank 2 falls to or below a preset low level. As a result of the heat accumulating operation, the amount of hot water and the amount of heat stored in the heat storage tank 2 increase, and when the amount of stored hot water and the amount of stored heat reach a preset high level, the controller 10 stops the heat accumulating operation.

[0025] Next, referring to Fig. 3, an indoor-heating operation implemented by the fluid circulation system 1 will be described. Fig. 3 is a view showing a circuit through which water circulates during the indoor-heating operation implemented by the fluid circulation system according to the first embodiment. Arrows in Fig. 3 show the flow direction of the water. During the indoor-heating operation, the fluid heater 100 and the circulation pump 11 are driven and the switching valve 6 is controlled to the condition in which the third port 6c communicates with the second port 6b while the first port 6a is closed. During the indoor-heating operation, the water heated by the water-refrigerant heat exchanger 15 of the fluid heater 100 is pumped to the indoor-heating installation 12 through the second shared pipe 3, the third port 6c and the second port 6b of the switching valve 6, the first internal pipe 5, the second water outlet 27, and the first external pipe 22. As this water passes through the indoor-heating device 24 of the indoor-heating installation 12, the water loses heat to the air in the room, the floor, and so on, and as a result, the temperature of the water decreases. This reduced-temperature water returns to the water-refrigerant heat exchanger 15 of the fluid heater 100 through the second external pipe 23, the second water inlet 28, the second internal pipe 7, and the first shared pipe 9. Having returned to the water-refrigerant heat exchanger 15, the water is reheated and recirculated. The water circulation circuit employed during the indoor-heating operation, as described above, will be referred to hereafter as a "indoor-heating circuit". In the first embodiment, the heat accumulating circuit can be switched to the indoor-heating circuit and vice versa using the switching valve 6.

[0026] An indoor remote controller (not shown) having an inbuilt room temperature sensor is provided in the room in which the indoor-heating device 24 is installed. The indoor remote controller and the controller 10 are configured to be capable of communicating with each other wirelessly. The indoor remote controller transmits information indicating the room temperature detected by the room temperature sensor to the controller 10. When the room temperature transmitted from the indoor remote controller reaches a preset target temperature during the indoor-heating operation, the controller 10 stops the indoor-heating operation. The user may instruct the controller 10 to start and stop the indoor-heating operation by operating the indoor remote control.

[0027] During the heat accumulating operation and the indoor-heating operation, the controller 10 controls the outflow temperature detected by the outflow temperature sensor 31 so as to match a target value. The controller 10 can control the outflow temperature by adjusting the output of the circulation pump 11. When the outflow temperature is higher than the target value, the controller 10 controls the outflow temperature so as to match the target value by increasing the output of the circulation pump 11 in order to increase the flow rate at which the water circulates. When the outflow temperature is lower than the target value, the controller 10 controls the outflow temperature so as to match the target value by reducing the output of the circulation pump 11 in order to reduce the flow rate at which the water circulates. The controller 10 can control the outflow temperature by adjusting the operation of the refrigerant circuit in the fluid heater 100.

[0028] During the heat accumulating operation, the controller 10 sets the target value of the outflow temperature at a first target temperature. During the indoor-heating operation, the controller 10 sets the target value of the outflow temperature at a second target temperature that is lower than the first target temperature. The first target temperature is set at a temperature within a range of approximately 60°C to 80°C, for example. The second target temperature is set at 50°C, for example. By making the first target temperature higher than the second target temperature, the amount of heat that can be stored in the heat storage tank 2 can be increased. By making the second target temperature lower than the first target temperature, the operating efficiency of the fluid heater 100 during the indoor-heating operation can be improved.

[0029] Fig. 4 is a flowchart showing control operations implemented by the controller 10 of the fluid circulation system 1 according to the first embodiment. The flowchart in Fig. 4 shows a control operation implemented in a case where a request to switch from the heat accumulating circuit to the indoor-heating circuit is issued during the heat accumulating operation. The controller 10 implements the control operation shown in Fig. 4 when the heat accumulating operation is underway.

[0030] In step S1 of Fig. 4, the controller 10 determines whether a request to switch from the heat accumulating circuit to the indoor-heating circuit has been issued. In the following description, this request will be referred to as a "circuit switch request". The circuit switch request is issued when, for example, the amount of hot water or the amount of heat stored in the heat storage tank 2 reaches a preset high level. The circuit switch request is also issued when the user prohibits the heat accumulating operation by operating the remote controller 21. To stop the heat accumulating operation when the circuit switch request has been issued, the controller 10 stops the operation of the fluid heater 100 (the compressor 13). To switch from the heat accumulating operation to the indoor-heating operation when the circuit switch request has been issued, the controller 10 controls the operations of the circulation pump 11 and the fluid heater 100 and modifies the target value of the outflow temperature from the fluid heater 100 from the first target temperature to the second target temperature.

[0031] When the circuit switch request has not been issued in step S1, the controller 10 continues the heat accumulating operation without switching from the heat accumulating circuit to the indoor-heating circuit, and then performs the determination of step S1 again. When the circuit switch request has been issued in step S1, the controller 10 advances to step S2. In step S2, the controller 10 compares the outflow temperature detected by the outflow temperature sensor 31 with a preset reference value. The reference value is preferably a temperature no higher than the first target temperature, i.e. the target value of the outflow temperature during the heat accumulating operation. The reference value is preferably a higher temperature than the second target temperature, i.e. the target value of the outflow temperature during the indoor-heating operation. The reference value is set at 60°C, for example. The reference value is a temperature at which the indoor-heating device 24 is not damaged when water at that temperature flows into the indoor-heating device 24. The reference value is a temperature at which an increase in room temperature that is not desired by the user can be prevented reliably when water at that temperature flows into the indoor-heating device 24.

[0032] When the outflow temperature detected by the outflow temperature sensor 31 is lower than the reference value in step S2, the controller 10 advances to step S3. In the first embodiment, the controller 10 advances to step S3 when the outflow temperature detected by the outflow temperature sensor 31 is lower than the reference value or equal to the reference value. For example, the controller 10 advances to step S3 in a case where the reference value is set at 60°C and the outflow temperature detected by the outflow temperature sensor 31 is 55°C.

[0033] When the outflow temperature detected by the outflow temperature sensor 31 is higher than the reference value in step S2, the controller 10 advances to step S5. In the first embodiment, the controller 10 advances to step S5 when the outflow temperature detected by the outflow temperature sensor 31 exceeds the reference value. For example, the controller 10 advances to step S5 in a case where the reference value is set at 60°C and the outflow temperature detected by the outflow temperature sensor 31 is 65°C.

[0034] In step S3, the controller 10 compares the amount of time that has elapsed following issuance of the circuit switch request with a preset wait time. The wait time is set at three minutes, for example. When the amount of time that has elapsed following issuance of the circuit switch request has not yet reached the wait time, the controller 10 returns to step S2 from step S3. When the amount of time that has elapsed following issuance of the circuit switch request has reached the wait time, the controller 10 advances from step S3 to step S4. In step S4, the controller 10 switches from the heat accumulating circuit to the indoor-heating circuit by operating the switching valve 6. The processing of the flowchart is then terminated.

[0035] As described above, when a request to switch from the heat accumulating circuit to the indoor-heating circuit is issued during the heat accumulating operation, the controller 10 executes the processing of step S2, in which the heat accumulating circuit is switched to the indoor-heating circuit on condition that the outflow temperature from the fluid heater 100 is lower than the reference value. In so doing, it is possible to prevent water at a higher temperature than the reference value from being pumped to the indoor-heating installation 12. As a result, situations in which inflowing high-temperature water (high-temperature fluid) causes damage to the indoor-heating device 24 and an increase in room temperature that is not desired by the user can be prevented from occurring reliably.

[0036] The controller 10 according to the first embodiment executes the processing of step S3, in which the heat accumulating circuit is switched to the indoor-heating circuit on condition not only that the outflow temperature from the fluid heater 100 is lower than the reference value but also that the amount of time that has elapsed following issuance of the circuit switch request has reached the wait time. In other words, in the first embodiment, the heat accumulating circuit is not switched to the indoor-heating circuit until the amount of time that has elapsed following issuance of the circuit switch request has reached the wait time, even when the outflow temperature from the fluid heater 100 is lower than the reference value. In so doing, it is possible to prevent high-temperature water from being pumped to the indoor-heating installation 12 even more reliably. As a result, situations in which inflowing high-temperature water causes damage to the indoor-heating device 24 and an increase in room temperature that is not desired by the user can be prevented even more reliably.

[0037] In step S5, the controller 10 compares the amount of time that has elapsed following issuance of the circuit switch request with a preset upper limit wait time. The upper limit wait time is longer than the wait time of step S3. For example, the upper limit wait time is set at 30 minutes. When the amount of time that has elapsed following issuance of the circuit switch request has not yet reached the upper limit wait time, the controller 10 advances from step S5 to step S7. When the amount of time that has elapsed following issuance of the circuit switch request has reached the upper limit wait time, the controller 10 advances from step S5 to step S6. In step S6, the controller 10 switches from the heat accumulating circuit to the indoor-heating circuit by operating the switching valve 6. The processing of the flowchart is then terminated.

[0038] As described above, when the amount of time that has elapsed following issuance of the circuit switch request reaches the upper limit wait time, the controller 10 switches from the heat accumulating circuit to the indoor-heating circuit in step S6 even when the outflow temperature from the fluid heater 100 is higher than the reference value. In so doing, a situation in which water at a temperature that is higher than the reference value but lower than the first target temperature flows into the heat storage tank 2 continuously for a long time can be prevented from occurring, and as a result, a reduction in the temperature in the upper portion of the heat storage tank 2 can be prevented. Further, a long delay in the start of the indoor-heating operation in a case where it is necessary to switch from the heat accumulating operation to the indoor-heating operation can be prevented.

[0039] In step S7, the controller 10 compares the inflow temperature detected by the inflow temperature sensor 32 with a preset threshold. The threshold is set at a lower temperature than the first target temperature, i.e. the target value of the outflow temperature during the heat accumulating operation. The threshold is preferably set at a value obtained by subtracting a fixed value from the first target temperature. For example, when the first target temperature is 60°C and the fixed value is 5°C, the threshold is 55°C. The threshold is used to determine whether the heat storage tank 2 is full of high-temperature water.

[0040] When the inflow temperature detected by the inflow temperature sensor 32 is lower than the threshold in step S7, the controller 10 returns to step S2. In the first embodiment, the controller 10 returns to step S2 when the inflow temperature detected by the inflow temperature sensor 32 is lower than the threshold. When the inflow temperature detected by the inflow temperature sensor 32 is higher than the threshold in step S7, the controller 10 advances to step S8. In the first embodiment, the controller 10 advances to step S8 when the inflow temperature detected by the inflow temperature sensor 32 exceeds the threshold or is equal to the threshold. For example, the controller 10 advances to step S8 when the threshold is 60°C and the inflow temperature detected by the inflow temperature sensor 32 is 55°C. In step S8, the controller 10 switches from the heat accumulating circuit to the indoor-heating circuit by operating the switching valve 6. The processing of the flowchart is then terminated.

[0041] When the inflow temperature detected by the inflow temperature sensor 32, or in other words the temperature of the water flowing out of the lower portion of the heat storage tank 2, is higher than the threshold in step S7, it can be estimated that the heat storage tank 2 is full of high-temperature water. In this case, there is nowhere in the heat accumulating circuit for heat to escape, and therefore it takes a long time for the outflow temperature from the fluid heater 100 to decrease. Hence, by switching from the heat accumulating circuit to the indoor-heating circuit immediately in step S8 in this case, a meaningless delay in the switch to the indoor-heating circuit can be prevented.

[0042] When the indoor-heating operation is implemented after switching from the heat accumulating circuit to the indoor-heating circuit in step S4, step S6, or step S8, the controller 10 controls the operations of the circulation pump 11 and the fluid heater 100 so that the outflow temperature from the fluid heater 100 matches the second target temperature. When the indoor-heating operation is not implemented after switching from the heat accumulating circuit to the indoor-heating circuit in step S4, step S6, or step S8, the controller 10 continues to operate the circulation pump 11 for a fixed time, and then stops the circulation pump 11. In the first embodiment, by continuing circulation through the indoor-heating circuit for a fixed time after stopping the heat accumulating operation, heat remaining in the fluid heater 100 can be removed, and as a result, a situation in which the water in the fluid heater 100 is at an abnormally high temperature can be prevented from occurring. Moreover, a situation in which insufficiently heated water flows into the heat storage tank 2 can be prevented from occurring, and therefore a reduction in the temperature in the upper portion of the heat storage tank 2 can be prevented.

[0043] In the first embodiment, the heat accumulating circuit is switched to the indoor-heating circuit on condition that the amount of time that has elapsed following issuance of the circuit switch request has reached the wait time, but in the present invention, the heat accumulating circuit does not have to be switched to the indoor-heating circuit on condition that the amount of time that has elapsed following issuance of the circuit switch request has reached the wait time. More specifically, in the present invention, when a request to switch from the heat accumulating circuit to the indoor-heating circuit is issued during the heat accumulating operation and the outflow temperature from the fluid heater 100 is lower than the reference value, the heat accumulating circuit may be switched to the indoor-heating circuit immediately. Likewise in this case, similar effects to those described above are obtained.

[Reference Signs List]

[0044] 

1

fluid circulation system

2

heat storage tank

3

second shared pipe

4

upper pipe

5

first internal pipe

6

switching valve

6a

first port

6b

second port

6c

third port

7

second internal pipe

8

lower pipe

9

first shared pipe

10

controller

11

circulation pump

12

indoor-heating installation

13

compressor

14

refrigerant pipe

15

water-refrigerant heat exchanger

16

decompressor

17

low-temperature-side heat exchanger

18

feed-water pipe

19

hot-water supply pipe

21

remote controller

22

first external pipe

23

second external pipe

24

indoor-heating device

25

first water outlet

26

first water inlet

27

second water outlet

28

second water inlet

30

flow rate sensor

31

outflow temperature sensor

32

inflow temperature sensor

100

fluid heater

200

tank unit

Claims

1. A fluid circulation system comprising:

a fluid heater for heating a fluid;

a heat storage tank for storing the fluid;

a heat accumulating circuit in which the fluid circulates between the fluid heater and the heat storage tank;

an indoor-heating circuit in which the fluid circulates between the fluid heater and an indoor-heating installation;

a valve for switching between the heat accumulating circuit and the indoor-heating circuit;

an outflow temperature sensor for detecting a temperature of the fluid flowing out of the fluid heater; and

a controller for controlling switching between the heat accumulating circuit and the indoor-heating circuit,

characterized in that the controller is configured to switch, when a request to switch from the heat accumulating circuit to the indoor-heating circuit is issued during a heat accumulating operation in which the heat accumulating circuit is operated, from the heat accumulating circuit to the indoor-heating circuit on condition that the temperature of the fluid flowing out of the fluid heater is lower than a reference value.

2. The fluid circulation system according to claim 1, wherein the controller is configured to switch from the heat accumulating circuit to the indoor-heating circuit on condition that an amount of time that has elapsed following issuance of the request has reached a wait time as well as on condition that the temperature of the fluid flowing out of the fluid heater is lower than the reference value.

3. The fluid circulation system according to claim 2, wherein the controller is configured to switch, once the amount of time that has elapsed following issuance of the request has reached an upper limit wait time that is longer than the wait time, from the heat accumulating circuit to the indoor-heating circuit even when the temperature of the fluid flowing out of the fluid heater is higher than the reference value.

4. The fluid circulation system according to any one of claims 1 to 3, further comprising an inflow temperature sensor for detecting a temperature of the fluid flowing into the fluid heater,
wherein when the temperature of the fluid flowing into the fluid heater is higher than a threshold, the heat accumulating circuit is switched to the indoor-heating circuit even when the temperature of the fluid flowing out of the fluid heater is higher than the reference value.

5. The fluid circulation system according to any one of claims 1 to 4, wherein the controller is configured to set a target value of the temperature of the fluid flowing out of the fluid heater at a first target temperature during the heat accumulating operation, and at a second target temperature that is lower than the first target temperature during a heating operation in which the indoor-heating circuit is operated,
the reference value being equal to or lower than the first target temperature.

Drawing