Hot-water supply system

A hot-water supply system 1 comprises a temperature responsive valve 61 provided in a first bypass passage 60, an orifice 31 provided in a second bypass passage 30, a flow rate sensor 24 provided in a water supply passage 11 downstream from a connection point with the second bypass passage 30, a circulating pump 33 provided in the water supply passage 11 downstream from the connection point with the second bypass passage 30, and a controller 4. The controller 40 operates the circulating pump 33 and executes circulation heating operation for operating a burner to heat the hot water circulating through a circulation circuit 80, when a flow rate detected by the flow rate sensor 24 is equal to or more than a specified flow rate.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a hot-water supply system comprising an instantaneous hot-water supply function.

Description of the Related Art

A hot-water supply system has conventionally been proposed which includes a hot water circulation circuit formed between a hot-water supplier and a mixing faucet to achieve an instantaneous hot-water supply function (for example, see Japanese Patent Laid-Open No. 8-121800 (hereinafter referred to as Patent Document 1)). In this hot-water supply system, the hot water circulation circuit is constituted by providing a bypass passage that bypasses the mixing faucet by making a water outlet passage and a hot-water outlet passage communicate with each other, the water outlet passage being branched from a water supply passage that supplies water to the hot-water supplier and being connected to a water side connection port of the mixing faucet, the hot-water outlet passage being configured to feed hot water from the hot-water supplier.

According to the configuration of the hot water supply system disclosed in Patent Document 1, it is not necessary to provide an exclusive return passage that connects a hot-water side connection port of the mixing faucet to the water supply passage of the hot-water supplier. Accordingly, construction can easily be conducted and cost of the hot-water supply system can be reduced.

In the hot-water supply system disclosed in Patent Document 1, the bypass passage bypassing the mixing faucet is equipped with a check valve configured to block water flow from the water outlet passage side to the hot-water outlet passage side, and a temperature responsive valve configured to be closed when hot-water temperature inside the bypass passage is equal to or more than a prescribed temperature.

The hot-water supply system disclosed in Patent Document 1 executes circulation heating operation to heat hot water inside the circulation circuit, which is constituted of the water supply passage, the water outlet passage, the hot-water supplier, the hot-water outlet passage, and the bypass passage, by operating a circulating pump to circulate hot water through the circulation circuit, while operating a burner in the hot-water supplier to heat a heat exchanger communicating with the water supply passage and the hot-water outlet passage.

When high-temperature hot water is fed from the hot-water supplier while the circulation heating operation is performed, the temperature responsive valve is closed and circulation of hot water in the circulation circuit is stopped, so that the high-temperature hot water is prevented from flowing to the water outlet passage side through the bypass passage. This prevents discharge of the high-temperature hot water which has flown to the water outlet passage-side, when a user opens the mixing faucet.

In the hot-water supply system disclosed in Patent Document 1, the temperature responsive valve provided in the bypass passage is closed when high-temperature hot water is fed to the hot-water outlet passage from the hot-water supplier while the circulation heating operation is performed. However, it takes a certain time for the temperature responsive valve to shift from an opened state to a closed state.

It is therefore difficult to perfectly prevent the high-temperature hot water from flowing into the water outlet passage-side during a period until the temperature responsive valve is closed after the high-temperature hot water starts to flow into the bypass passage from the hot-water outlet passage.

To overcome this difficulty, it can be considered to limit the flow rate of the hot water circulating through the circulation circuit during circulation heating operation to decrease the amount of the high-temperature hot water flowing into the water outlet passage side at the time when the temperature responsive valve is being closed. However, when the flow rate of the hot water circulating through the circulation circuit becomes less than a specified flow rate which is an operating condition of the burner, the burner fails to operate and therefore the circulation heating operation cannot be carried out.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-stated background, and it is therefore an object of the present invention to provide a hot-water supply system capable of decreasing the amount of high-temperature hot water that flows from the bypass passage into the water outlet passage side and ensuring circulation of hot water of a specified flow rate or more provided by operation of the burner when the circulation heating operation is executed.

The hot-water supply system of the present invention is a hot-water supply system including a hot-water supplier having a burner and a heat exchanger heated by the burner to instantaneously supply hot water from the hot-water supplier to a mixing faucet, the system comprising: a water supply passage configured to make a water supply system communicate with an inlet of the heat exchanger; a hot-water outlet passage configured to make an outlet of the heat exchanger communicate with a hot-water side connection port of the mixing faucet; a water outlet passage connected to the water supply passage and communicating with a water side connection port of the mixing faucet; a first bypass passage configured to bypass the mixing faucet to make the hot-water outlet passage communicate with the water outlet passage; a temperature responsive valve provided in the first bypass passage and configured to be closed to block the first bypass passage when temperature of hot water inside the first bypass passage is equal to or more than a prescribed temperature; a second bypass passage configured to make a downstream point of the water supply passage communicate with an upstream point of the hot-water outlet passage, the downstream point being downstream from a branch point branching to the water outlet passage, the upstream point being upstream from a connection point with the first bypass passage; a bypass check valve provided in the second bypass passage and configured to enable hot water to circulate from the hot-water outlet passage side to the water supply passage side while disabling the hot water from circulating from the water supply passage side to the hot-water outlet passage side; a flow rate limiting portion provided in the second bypass passage and configured to limit a flow rate of the hot water circulating through the second bypass passage; a circulating pump provided in the water supply passage downstream from a connection point with the second bypass passage or in the hot-water outlet passage upstream from a connection point with the second bypass passage and configured to circulate the hot water inside a circulation circuit including at least the water supply passage, the heat exchanger, the hot-water outlet passage, the first bypass passage, the second bypass passage, the water outlet passage, and the water supply passage; a flow rate detector configured to detect a flow rate of hot water flowing through the water supply passage downstream from the connection point with the second bypass passage; and a control unit configured to perform circulation heating operation for heating the hot water circulating through the circulation circuit by operating the circulating pump and also operating the burner when the flow rate detected by the flow rate detector is equal to or more than a specified flow rate.

According to the present invention, the hot water supplied from the hot-water supplier to the hot-water outlet passage when the circulation heating operation is executed joins the water supply passage via the first bypass passage and the second bypass passage. Accordingly, the flow rate of the hot water flowing to the first bypass passage side can easily be decreased by regulating the flow rate limited by the flow rate limiting portion provided in the second bypass passage. This makes it possible to decrease the amount of high-temperature hot water which flows from the first bypass passage to the water outlet passage during a period until the temperature responsive valve is closed after the hot water at the prescribed temperature or more circulates to the first bypass passage from the hot-water outlet passage.

Moreover, the flow rate detector detects the flow rate of the hot water flowing through the water supply passage downstream from the connection point with the second bypass passage. Accordingly, when the circulation heating operation is performed, the total flow rate of the hot water circulating through the first bypass passage and the hot water circulating through the second bypass passage is detected by the flow rate detector. This makes it possible to decrease the flow rate of the hot water in the first bypass passage and to maintain the flow rate detected by the flow rate detector to be equal to or more than the specified flow rate that enables the burner to work.

The hot-water supply system further comprises: a pump bypass passage configured to make a water inlet and a water outlet of the circulating pump communicate with each other; and a pump check valve provided in the pump bypass passage and configured to enable hot water to circulate from the water inlet side to the water outlet side of the pump while disabling the hot water from circulating from the water outlet side to the water inlet side of the pump, wherein when the flow rate detected by the flow rate detector is equal to or more than the specified flow rate while the circulation heating operation is stopped and the operation of the circulating pump is stopped, the control unit performs hot-water supply operation for operating the burner to heat water by the hot-water supplier supplied to the water supply passage from the water supply system and supplying obtained hot water to the mixing faucet through the hot-water outlet passage.

According to this configuration, when the mixing faucet is opened and water is supplied from the water supply system to the water supply passage while the circulation heating operation is stopped, and when the control unit is executing the hot-water supply operation, the water supplied to the water supply passage can be circulated from the heat exchanger to the hot-water outlet passage via the pump bypass passage side without going through the circulating pump. Therefore, it becomes possible to avoid decrease in the flow rate of the hot water supplied to the hot-water outlet caused by circulation resistance of the circulating pump.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of a hot-water supply system of the present invention will be described with reference toFIGS. 1 to 2.

With reference toFIG. 1, a hot-water supply system1of the present embodiment comprises: a hot-water supplier10; a water supply passage11connected to a water supply system2and configured to supply water to the hot-water supplier10; a water outlet passage13connected to the water supply passage11and communicating with a water side connection port50aof a mixing faucet50; a hot-water outlet passage12communicating with a hot-water side connection port50bof the mixing faucet50to supply hot water from the hot-water supplier10, a first bypass passage60bypassing the mixing faucet50and making the water outlet passage13communicate with the hot-water outlet passage12in the vicinity of the mixing faucet50; and a temperature responsive valve61provided in the first bypass passage60and configured to be closed to block the first bypass passage60when the temperature of hot water inside the first bypass passage60becomes equal to or more than a prescribed temperature (for example, 37 degrees).

The temperature responsive valve61incorporates a check valve configured to enable hot water to circulate from the hot-water outlet passage12side to the water supply passage11side while disabling the hot water from circulating from the water supply passage11side to the hot-water outlet passage12side.

The hot-water supplier10comprise: a heat exchanger21placed inside a combustion casing20, with an inlet21abeing connected to the water supply passage11and an outlet21bbeing connected to the hot-water outlet passage12; a burner22(such as a gas burner and an oil burner) placed under the heat exchanger21inside the combustion casing20and configured to heat the heat exchanger21; a hot-water supply bypass passage23bypassing the heat exchanger21and making the water supply passage11communicate with the hot-water outlet passage12; and a second bypass passage30configured to make a point Y of the water supply passage11communicate with a point U of the hot-water outlet passage12, the point Y being downstream from a branch point X branching with the water outlet passage13, the point U being upstream from a connection point Z with the first bypass passage60.

The water supply passage11is equipped with a circulating pump33configured to circulate hot water inside a circulation circuit80that includes the heat exchanger21, the hot-water supply bypass passage23, the hot-water outlet passage12, the first bypass passage60, the second bypass passage30, and the water outlet passage13. The water supply passage11is also equipped with a flow rate sensor24(equivalent to the flow rate detector of the present invention) configured to detect the flow rate of the hot water flowing in the water supply passage11downstream from a connection point with the second bypass passage30, and a supplied water temperature sensor25configured to detect the temperature of the hot water supplied from the water supply passage11to the heat exchanger21.

The circulating pump33is configured to suck hot water from the hot-water outlet passage12via the second bypass passage30, to suck hot water from the hot-water outlet passage12via the first bypass passage60and the water outlet passage13, and to deliver the sucked hot water from the water supply passage11to the heat exchanger21and to the hot-water supply bypass passage23as illustrated by arrows. As a result, the hot water circulates by a route of the circulating pump33the water supply passage11the heat exchanger21, the hot-water supply bypass passage23the hot-water outlet passage12the first bypass passage60, and the second bypass passage30the circulating pump33.

The hot-water outlet passage12is equipped with a hot-water outlet temperature sensor26configured to detect the temperature of the hot water flowing through a portion of the hot-water outlet passage12downstream from the connection point with the hot-water supply bypass passage23. The second bypass passage30is equipped with an orifice31(equivalent to the flow rate limiting portion of the present invention) configured to limit the flow rate of the hot water circulating through the second bypass passage30, and a bypass check valve32configured to enable hot water to circulate from the hot-water outlet passage12side to the water supply passage11side while disabling the hot water from circulating from the water supply passage11side to the hot-water outlet passage12side.

The hot-water supplier10comprises a pump bypass passage34bypassing the circulating pump33and communicating with the water supply passage11. The pump bypass passage34is equipped with a pump check valve35configured to enable hot water to circulate from a water inlet side to a water outlet side of the circulating pump33while disabling the hot water from circulating from the water outlet side to the water inlet side of the circulating pump33.

The hot-water supplier10further comprises a controller40(including the function of the control unit of the present invention) configured to control the overall operation of the hot-water supply system1. The controller40is connected to a remote control41configured to operate the hot-water supplier10by remote control.

The controller40is an electronic circuit unit constituted of such components as a CPU, a memory, and various interface circuits which are not illustrated. A control program of the hot-water supply system1is stored in the memory and is executed by the CPU to serve the function to control the operation of the hot-water supply system1.

The controller40receives signals such as temperature detection signals of the supplied water temperature sensor25and the hot-water outlet temperature sensor26, a flow rate detection signal of the flow rate sensor24, and a manipulate signal of the remote control41. The operation of the component elements, such as the burner22, the circulating pump33, and a display portion of the remote control41, is controlled by the control signals output from the controller40.

The user can set and cancel the instantaneous hot-water supply mode by operating the remote control41. The controller40of the hot-water supply system1monitors the flow rate detected by the flow rate sensor24. When the flow rate detected by the flow rate sensor24is equal to or more than an operation flow rate (equivalent to the specified flow rate of the present invention, e.g., 2.7 liters per minute), the controller40performs hot-water supply operation by regulating the combustion amount of the burner22so that the hot water at a hot-water preset temperature (set with the remote control41) is supplied from the hot-water outlet passage12to the mixing faucet50based on the flow rate detected by the flow rate sensor24, the temperature detected by the supplied water temperature sensor25, and the temperature detected by the hot-water outlet temperature sensor26.

When hot water is supplied to the water supply passage11, the temperature of the hot water is detected by the supplied water temperature sensor25. If the temperature is equal to or more than a value of the hot-water preset temperature+α, the controller40sets the combustion amount of the burner22to zero (combustion stopped state).

When the hot-water supply operation is executed (the circulating pump33is in OFF state), the water supplied from the water supply system2to the water supply passage11circulates not to the circulating pump33side having a relatively high circulation resistance but to the pump bypass passage34side having a low circulation resistance. This makes it possible to avoid decrease in the flow rate of the hot water supplied to the hot-water outlet passage12.

When the instantaneous hot-water supply mode is set, the controller40executes processing to retain heat of the hot water inside the circulation circuit80so that the hot water is swiftly supplied to the mixing faucet50when the mixing faucet50is opened.

Hereinafter, the processing executed by the controller40in the instantaneous hot-water supply mode will be described based on the flow chart illustrated inFIG. 2.

In STEP1ofFIG. 2, the controller40starts circulation heating operation by operating the burner22while operating the circulating pump33to heat the hot water inside the circulation circuit80. The controller40determines an ON period of the circulating pump33(a period for turning on (operating) the circulating pump33) and an OFF period (a period for turning off (stopping) the circulating pump33) in accordance with the length of the circulation circuit80(pipe length) and the presence of mounting of a heat insulator on the circulation circuit80based on the following table1.

The controller40alternately repeats the pump-ON period and the pump-OFF period in sequence. During the pump-ON period, the controller40operates the burner22to heat the hot water inside the circulation circuit80when the temperature detected by the hot-water outlet temperature sensor26becomes equal to or less than a value of a prescribed heat-retention temperature−α. When the temperature detected by the hot-water outlet temperature sensor26becomes equal to or more than a value of the heat-retention temperature+α, the controller40turns off the burner22. In this case, the controller40operates the burner22on condition that the flow rate detected by the flow rate sensor24is equal to or more than the operation flow rate (equivalent to the specified flow rate of the present invention).

In subsequent STEP2, the controller40determines whether or not the pump is in ON period. If the pump is in ON period, the processing proceeds to STEP3where the circulating pump33is turned on, and the processing proceeds to STEP4. Contrary to this, when the pump is not in ON period (the pump is in OFF period), the processing branches to STEP10where the controller40turns off the circulating pump33and returns to STEP2.

In STEP4, the controller40determines whether or not the flow rate detected by the flow rate sensor24is equal to or more than a value of a reference flow rate+β. Here, the reference flow rate is set to, for example, 9 liters per minute based on an assumed value of a flow rate of the hot water that circulates through the water supply passage11when the circulating pump33is operated with the temperature responsive valve61being closed.

The value β is an assumed value of difference between the flow rate of the hot water circulating through the water supply passage11when the circulating pump33is operated with the temperature responsive valve61being opened and the flow rate of the hot water circulating through the water supply passage11when the circulating pump33is operated with the temperature responsive valve61being closed. For example, the value β is set to 3 liters per minute.

When the flow rate detected by the flow rate sensor24is equal to or more than a value of the reference flow rate+β (when the mixing faucet50is determined to be opened) in STEP4, the processing branches to STEP20where the controller40stops the circulating pump33and executes hot-water supply operation.

When the flow rate detected by the flow rate sensor24becomes less than the operation flow rate (when it can be determined that the mixing faucet50is closed) in subsequent STEP21, the processing returns to STEP1, so that the controller40ends the hot-water supply operation and resumes the circulation heating operation.

When the flow rate detected by the flow rate sensor24is less than the value of the operation flow rate+β in STEP4, the processing proceeds to STEP5, where the controller40determines whether or not the circulating pump33continuously operates for predetermined time (set based on assumed time taken until the flow rate of the hot water circulating through the circulation circuit80is stabilized) or more. When the circulating pump33continuously operates for the predetermined time or more, the processing proceeds to STEP6. When the circulating pump33does not continuously operate for the predetermined time or more, the processing returns to STEP2.

In STEP6, the controller40checks the flow rate detected by the flow rate sensor24. Here, data of a value of a reference flow rate (an initial value is 9 liters per minute) is stored in the memory. In subsequent STEP7, the controller40corrects (updates) the reference flow rate according to following expression (1) based on the detected flow rate checked in STEP6, and the processing returns to STEP2.
{Qs−Qb(t)}×0.1+Qb(t)→Qb(t+1)  (1)
where Qs represents a detected flow rate in STEP6, Qb(t) represents a present value of the reference flow rate stored in the memory, and Qb(t+1) represents a corrected reference flow rate.

The controller40stores in the memory the reference flow rate Qb(t+1) calculated by the expression (1) as a new reference flow rate, and updates the reference flow rate accordingly.

In the circulation circuit80, the hot water fed from the heat exchanger21and the hot-water supply bypass passage23to the hot-water outlet passage12diverges to the first bypass passage60and to the second bypass passage30. Accordingly, by decreasing the flow rate of the hot water flowing through the first bypass passage60, the amount of the high-temperature hot water at a prescribed temperature or more, which flows from the first bypass passage60into the water outlet passage13until the temperature responsive valve61is closed, can be decreased.

This makes it possible to suppress the amount of the high-temperature hot water supplied from the water outlet passage13to the mixing faucet50so as to prevent excessive heat from being felt by a user when the user opens the mixing faucet50.

Moreover, the flow rate of the hot water circulating through the first bypass passage60is increased and decreased depending on the flow rate of the hot water circulating through the second bypass passage30. Accordingly, regulating the flow rate limited by the orifice31makes it possible to easily set the flow rate of the hot water circulating through the first bypass passage60while the circulating pump33is operated.

Since the flow rate sensor24is provided in a portion of the water supply passage11downstream from the connection point with the second bypass passage30, the flow rate sensor24detects the total flow rate of the hot water circulating through the first bypass passage60and the hot water circulating through the second bypass passage30. Accordingly, even when the flow rate of the hot water circulating through the first bypass passage60during the operation of the circulating pump33is decreased, the flow rate detected by the flow rate sensor24can be maintained to be equal to or more than the operation flow rate which is the operation condition of the burner22.

In the present embodiment, the hot-water supply system1comprises the pump bypass passage34bypassing the circulating pump33and communicating with the water supply passage11and the pump check valve35as illustrated inFIG. 1. However, the effect of the present invention can also be acquired when the hot-water supply system1does not comprise the pump bypass passage34nor the pump check valve35.

In the present embodiment, although the circulating pump33is provided in the water supply passage11, the circulating pump33may be provided in a portion of the hot-water outlet passage12between the connection point with the hot-water supply bypass passage23and the connection point with the second bypass passage30.