EP2902714A1

EP2902714A1 - Hot-water supply system

Info

Publication number: EP2902714A1
Application number: EP12885365.2A
Authority: EP
Inventors: Tomoyoshi Obayashi
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2012-09-28
Filing date: 2012-09-28
Publication date: 2015-08-05
Anticipated expiration: 2032-09-28
Also published as: JP6033321B2; JPWO2014049814A1; WO2014049814A1; EP2902714A4; EP2902714B1

Abstract

[Object] To prevent a variation in pressure inside a water distributing pipe while achieving instant hot water supply.

[Solution] A hot water supply system includes a hot water storage tank that stores hot water, a hot water supply pipe through which the hot water in the hot water storage tank is supplied to a hot water outlet terminal, a circulation pipe through which the hot water flowing through the hot water supply pipe is returned to the hot water storage tank, and a circulating pump disposed in the hot water supply pipe. The circulation pipe is connected to the hot water supply pipe and the hot water storage tank. The circulating pump is configured to draw by suction the hot water in the hot water storage tank and discharge the hot water toward the hot water outlet terminal and the circulation pipe.

Description

Technical Field

The present invention relates to a hot water supply system capable of instantly supplying hot water to a hot water outlet terminal, such as a faucet or a shower.

Background Art

A typical heat pump hot water supply device includes a refrigeration cycle including a compressor, a radiator, an expansion valve, and a heat absorber which are sequentially connected to each other by refrigerant pipes. In the hot water supply device, heat is exchanged between water and a refrigerant, such as carbon dioxide, to generate hot water. The hot water generated by the hot water supply device is supplied from a hot water storage tank through a hot water supply pipe to a hot water outlet terminal, such as a faucet or a shower.
For business purposes in, for example, commercial facilities such as hotels, hot water supply pipes are very long in terms of characteristics of the facilities. In such a facility, therefore, a person who wants to use hot water may fail to immediately use hot water. Hot water supply systems have recently been proposed to allow instant supply of hot water (refer to, for example, Patent Literatures 1 and 2). In each system disclosed in Patent Literatures 1 and 2, a hot water storage tank is connected to a hot water supply pipe, and the hot water supply pipe is connected to passages individually branching from the hot water supply pipe to a hot water outlet terminal and a circulation pipe. Hot water flowing through the hot water supply pipe is returned to the hot water storage tank through the circulation pipe. The circulation of hot water through the hot water supply pipe and the circulation pipe allows hot water stored in the hot water storage tank to be instantly available via the hot water outlet terminal.

Citation List

Patent Literature

Patent Literature 1: Japanese Patent No. 4943258 (p. 12, Fig. 1)
Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2012-32078 (p. 13, Fig. 12)

Summary of Invention

Technical Problem

In each hot water supply system disclosed in Patent Literatures 1 and 2, however, a circulating pump is disposed in the circulation pipe through which hot water is returned to the hot water storage tank, and is located downstream of a point at which the circulation pipe branches off from the hot water supply pipe extending to the hot water outlet terminal. If water (clean water) supplied through a water distributing pipe to a facility in which the hot water supply system is installed is stopped due to a power supply interruption or the like, the circulating pump in an ON state will take in water accumulated in the water distributing pipe through a mixing faucet, thus causing a variation in pressure inside the water distributing pipe.
The present invention has been made to solve the above-described disadvantage, and aims to provide a hot water supply system capable of reducing a variation in pressure inside a water distributing pipe while achieving instant hot water supply.

Solution to Problem

The present invention provides a hot water supply system including a hot water storage tank, a hot water supply pipe, a circulation pipe, and a circulation pump. The hot water storage tank stores hot water. The hot water supply pipe supplies the hot water in the hot water storage tank to a hot water outlet terminal. The circulation pipe is connected to the hot water supply pipe and the hot water storage tank, and returns, to the hot water storage tank, the hot water flowing through the hot water supply pipe. The circulating pump is disposed in the hot water supply pipe. The circulating pump draws by suction the hot water in the hot water storage tank and discharges the hot water toward the hot water outlet terminal and the circulation pipe. Advantageous Effects of Invention
In the hot water supply system according to the present invention, since the circulating pump is disposed upstream of the hot water outlet terminal in the direction in which hot water flows, it applies a pressure for hot water discharge to the hot water outlet terminal. For example, even if water supply is cut off, the circulating pump draws by suction no water in a water distributing pipe connected to the hot water outlet terminal. Advantageously, the system reliably prevents a variation in pressure inside the water distributing pipe while achieving instant hot water supply. Brief Description of Drawings

[Fig. 1] Fig. 1 is a schematic diagram illustrating a hot water supply system according to Embodiment 1 of the present invention.
[Fig. 2] Fig. 2 is a graph illustrating a pressure distribution in a circulation circuit in Embodiment 1 of the present invention.
[Fig. 3] Fig. 3 is a schematic diagram illustrating a conventional hot water supply system.
[Fig. 4] Fig. 4 is a graph illustrating a variation in pressure inside a water distributing pipe during water supply cutoff in each of the hot water supply system of Fig. 1 and the hot water supply system of Fig. 3.

Description of Embodiments

Embodiment

1

Fig. 1 is a schematic diagram illustrating a hot water supply system according to Embodiment 1 of the present invention. A hot water supply system 100 shown in Fig. 1 includes, for example, a hot water supply device 1, a hot water storage tank 2, a hot water supply pipe 11, a circulating pump 12, and a circulation pipe 14. The hot water supply device 1 is implemented in a heat pump hot water supply device that uses, for example, carbon dioxide as a refrigerant, and connected to the hot water storage tank 2 via connecting pipes 3a and 3b. The hot water supply device 1 heats low-temperature water, stored in a lower portion of the hot water storage tank 2 and supplied from the hot water storage tank 2 through the connecting pipe 3a, and then supplies the heated water or hot water to the hot water storage tank 2 through the connecting pipe 3b.
The hot water storage tank 2, which is connected to the hot water supply device 1 by the connecting pipes 3a and 3b, stores hot water supplied from the hot water supply device 1. The lower portion of the hot water storage tank 2 is connected to a water distributing pipe (clean water distributing pipe) 41 via a feed pipe 4, a check valve 6, and a pressure reducer 7. For example, when hot water is consumed in any of hot water outlet terminals 22, and the amount of hot water stored in the hot water storage tank 2 becomes equal to or less than a predetermined amount, water is supplied from the water distributing pipe 41 to the hot water storage tank 2 through the feed pipe 4, the check valve 6, and the pressure reducer 7.
When the hot water in the hot water storage tank 2 reaches a predetermined temperature or below, low-temperature water is supplied from the lower portion of the hot water storage tank 2 to the hot water supply device 1 through the connecting pipe 3a. The water is heated to a high temperature by the hot water supply device 1 and the high-temperature hot water is again supplied to the hot water storage tank 2 through the connecting pipe 3b. The hot water supply device 1 and the hot water storage tank 2 form a heat source circuit which circulates low-temperature water and high-temperature hot water.
The pressure reducer 7 has a predetermined preset value. When water discharged from the pressure reducer 7 has a pressure lower than the set value, a valve included in the pressure reducer 7 is operated to be open. On the other hand, when water discharged from the pressure reducer 7 reaches a pressure equal to or higher than the set value, the valve in the pressure reducer 7 is operated to be closed. The set value of the pressure reducer 7 can be externally changed. To save water, the set value need only be lowered to reduce the amount of water fed to the hot water storage tank 2. Although the pressure in the hot water storage tank 2 lowers with a decrease in set value, the circulating pump 12 can provide a pressure high enough to supply hot water to the hot water outlet terminals 22. Consequently, hot water can be stably supplied to the hot water outlet terminals 22.
When hot water is used in any of the hot water outlet terminals 22, the pressure in the hot water storage tank 2 lowers, and the pressure at a discharge outlet of the pressure reducer 7 also lowers. This generates a difference between the pressure in the water distributing pipe 41 and that at the discharge outlet of the pressure reducer 7 (the latter pressure is on the side of the hot water storage tank). In this case as well, the valve in the pressure reducer 7 is opened so that the pressure at the discharge outlet of the pressure reducer 7 reaches the set value. Consequently, water is supplied from the water distributing pipe 41 and the feed pipe 4 to the pressure reducer 7, so that the pressure at the discharge outlet of the pressure reducer 7 rises. When the pressure reaches the set value or more, the valve in the pressure reducer 7 is closed to stop water feed to the hot water storage tank 2.
The hot water supply pipe 11 is connected to the upper portion of the hot water storage tank 2. Hot water in the hot water storage tank 2 is supplied through the hot water supply pipe 11 to the hot water outlet terminals 22. The circulating pump 12 is disposed in the hot water supply pipe 11. The circulating pump 12 draws hot water by suction from the hot water storage tank 2 through the hot water supply pipe 11, and discharges it toward the hot water outlet terminals 22. The operation of the circulating pump 12 is controlled by a circulation controller 33.
The circulating pump 12 is connected in parallel with a check valve 13. The check valve 13 permits hot water to flow only in the direction from the hot water storage tank 2 to the hot water outlet terminals 22. If the circulating pump 12 is stopped or broken, or if the circulating pump 12 used is a small-capacity pump that keeps the pump power low, hot water will pass through the check valve 13 depending on the pressure in the hot water storage tank 2 and be supplied to the hot water outlet terminals 22.
The circulating pump 12 and the check valve 13 are spaced apart from the hot water storage tank 2 by a distance smaller than that by which the circulating pump 12 and the check valve 13 are spaced apart from the hot water outlet terminals 22. In particular, the circulating pump 12 and the check valve 13 are preferably arranged near the hot water storage tank 2. That is, the pressure at a suction inlet 12a of the circulating pump 12 is reduced in proportion to the length of the pipe between the hot water storage tank 2 and the circulating pump 12. If this pressure reduction generates bubbles (cavitation), the circulating pump 12 may break or reduce in life due to factors associated with the bubbles. The suction inlet 12a of the circulating pump 12 in the hot water supply pipe 11 is therefore set on the side of the hot water storage tank 2, thus preventing the circulating pump 12 from breaking.
The hot water supply pipe 11 is connected to passages individually branching from the hot water supply pipe 11 to the hot water outlet terminals 22 and the circulation pipe 14. Each hot water outlet terminal 22 is implemented using, for example, a shower or a faucet, and is connected to the hot water supply pipe 11 with a corresponding one of mixing faucets 21. Each mixing faucet 21 is connected to the hot water supply pipe 11, and also connected to the water distributing pipe 41 via a check valve 8, a pressure reducer 9, and a feed pipe 5. The mixing faucet 21 mixes hot water supplied from the hot water supply pipe 11 and water supplied from the water distributing pipe 41, so that hot water with an optimum temperature is provided by the hot water outlet terminal 22. In the hot water supply system 100, the hot water supply pipe 11, the circulating pump 12, the check valve 13, the mixing faucets 21, and the hot water outlet terminals 22 form a hot water circuit with the above-mentioned arrangement.
The circulation pipe 14 branches from the hot water supply pipe 11 and connects to the lower portion of the hot water storage tank 2. Hot water discharged from the circulating pump 12 is returned through the circulation pipe 14 to the hot water storage tank 2. With the above-mentioned arrangement, in the hot water supply system 100, the hot water storage tank 2, the hot water supply pipe 11, the circulating pump 12, the check valve 13, and the circulation pipe 14 form a circulation circuit 10 through which hot water is returned to the central or lower portion of the hot water storage tank 2.
The hot water supply system 100 further includes a pressure detecting unit 31, a temperature detecting unit 32, and the circulation controller 33. The pressure detecting unit 31 detects the pressure of hot water flowing through the circulation circuit 10. The pressure detecting unit 31 is disposed on, for example, the hot water supply pipe 11. The circulation controller 33 activates the circulating pump 12 when a pressure P detected by the pressure detecting unit 31 becomes equal to or less than a preset pressure Pref. The activation of the circulating pump 12 enables supply of a large amount of hot water without any increase in pressure inside the hot water storage tank 2. If the pressure P is above the set pressure, the circulation controller 33 stops the circulating pump 12.
The temperature detecting unit 32 detects a temperature T of hot water circulated through the circulation circuit 10. The circulation controller 33 stops the operation of the circulating pump 12 when the temperature T detected by the temperature detecting unit 32 becomes equal to or more than a preset temperature Tref. This prevents wasteful heat radiation from hot water caused by circulation through the circulation circuit 10. Thus, the system efficiently achieves instant hot water supply to instantly supply high-temperature hot water.
Fig. 2 is a graph illustrating the pressure at each position in the hot water supply system 100 shown in Fig. 1. The flow of hot water in the hot water supply system 100 will now be described with reference to Figs. 1 and 2. As illustrated in Fig. 2, assume that the pressure in the hot water storage tank 2 is kept at a predetermined pressure, and the circulating pump 12 is operated under the control of the circulation controller 33, as described above. Hot water is drawn by suction into the suction inlet 12a of the circulating pump 12 from the upper portion of the hot water storage tank 2. The pressure at the suction inlet 12a is reduced in proportion to the length of the pipe between the hot water storage tank 2 and the circulating pump 12.
The hot water drawn by suction through the suction inlet 12a of the circulating pump 12 is discharged from a discharge outlet 12b of the circulating pump 12 toward the hot water outlet terminals 22. The hot water is also discharged from the check valve 13. At this time, the operation of the circulating pump 12 increases the pressure inside the hot water supply pipe 11. The hot water flowing through the hot water supply pipe 11 is divided into streams flowing to the hot water outlet terminals 22 and a stream flowing to the circulation pipe 14. The amount of hot water stream flowing to the circulation pipe 14 depends on the amount of hot water used in the hot water outlet terminals 22. The hot water flowing through the circulation pipe 14 is returned to the hot water storage tank 2.
As described above, the circulating pump 12 disposed in the hot water supply pipe 11 prevents a variation in pressure inside the water distributing pipe 41 if water supply through the water distributing pipe 41 is cut off due to, for example, the stop of a pressure pump 40. That is, in a conventional hot water supply system 200 as illustrated in Fig. 3, a circulating pump 212 is disposed in a circulation pipe 14. In this system, therefore, the circulating pump 212 draws by suction hot water through a suction inlet 212a on the side of a hot water supply pipe 11 and hot water outlet terminals 22. When water supply is cut off in the above-described way in this system, the circulating pump 212 will draw water by suction not only from a feed pipe 5 through mixing faucets 21, but also from a water distributing pipe 41 through a check valve 8. Disadvantageously, this will cause a variation in pressure not only in the feed pipe 5 but also in the water distributing pipe 41.
Fig. 4 is a graph illustrating a variation in pressure inside the water distributing pipe 41 during water supply cutoff in each of the hot water supply system 100 of Fig. 1 and the conventional hot water supply system 200 of Fig. 3. Referring to Fig. 4, assume that the pressure pump 40 disposed upstream of the water distributing pipe 41 in the direction in which water flows allows the water distributing pipe 41 to be filled with water at all times and to maintain a high pressure state. The water in the water distributing pipe 41 is supplied to the hot water outlet terminals 22 through the check valve 8, the pressure reducer 9, and the feed pipe 5. When the circulating pump 12 (212) is OFF as illustrated in Fig. 4 during water supply cutoff caused by, for example, an interruption of power supply to the pressure pump 40, the high pressure state is maintained without any significant variation in pressure.
On the other hand, when the circulating pump 12 (212) is ON during the water supply cutoff, water is supplied to the hot water outlet terminals 22 only by a residual pressure in the feed pipe 5, and the residual pressure in the feed pipe 5 falls upon the use of the water in the hot water outlet terminals 22. In the conventional hot water supply system 200 shown in Fig. 3, since the suction inlet 212a of the circulating pump 212 is connected to the passages extending to the hot water outlet terminals 22, the circulating pump 212 draws water by suction not only from the feed pipe 5 but also from the water distributing pipe 41 through the mixing faucets 21, the check valve 8, and the pressure reducer 9. Consequently, a variation in pressure inside the water distributing pipe 41 is significantly greater than a reduction in pressure inside the water distributing pipe 41 caused by power supply cutoff.
In the hot water supply system 100 of Fig. 1, the hot water outlet terminals 22 are connected to the passages extending to the discharge outlet 12b of the circulating pump 12. When the circulating pump 12 is operated upon water supply cutoff caused by stopping the pressure pump 40, hot water discharged from the circulating pump 12 will apply a discharge pressure to the feed pipe 5 through the hot water supply pipe 11 and the mixing faucets 21. The check valve 8, which is disposed in the feed pipe 5, interrupts water pressurized by the circulating pump 12. Consequently, a variation in pressure inside the water distributing pipe 41 can be minimized in the hot water supply system 100 in which the circulation of hot water through the circulation circuit 10 by the circulating pump 12 enables hot water in the hot water circuit to be maintained at a high temperature and accordingly achieves instant hot water supply. In other words, the circulating pump 12 is disposed in the hot water supply pipe 11 located upstream of the hot water outlet terminals 22 in the direction in which hot water flows, thus allowing a variation in pressure inside the feed pipe 5 to be minimized even when water supply is cut off by power supply cutoff or the like.
When a large amount of hot water is used in any hot water outlet terminal 22, the pressure at the suction inlet of the circulating pump 12 is reduced in proportion to the distance or length of the pipe between the hot water storage tank 2 and the circulating pump 12. Since the pressure reduction generates bubbles, the circulating pump 12 is disposed in the hot water supply pipe 11 on the side of the hot water storage tank 2. This can prevent the pump from being broken by bubbles.
In the conventional hot water supply system 200 of Fig. 3, the pressure in the hot water supply pipe 11 has to be high enough to prevent the above-described cavitation. Additionally, the pressure in the hot water storage tank 2 has to be high enough to supply a large amount of hot water. The hot water storage tank 2 accordingly needs a high strength. Disadvantageously, this results in an increase in cost. On the other hand, the installation of the circulating pump 12 near the hot water storage tank 2, as illustrated in Fig. 1, prevents generation of a negative pressure at the suction inlet 12a of the circulating pump 12 even when the pressure in the hot water storage tank 2 is set low. This prevents cavitation and enables stable circulation of hot water.
When the pressure detected by the pressure detecting unit 31, which is disposed on the side of the discharge outlet 12b of the circulating pump 12, lowers to the preset value or below, the circulation controller 33 operates the circulating pump 12. This allows the supply of a large amount of hot water without any increase in pressure inside the hot water storage tank 2.
Controlling the operation of the circulating pump 12 based on a temperature detected by the temperature detecting unit 32 prevents wasteful heat radiation from hot water caused by circulation through the circulation circuit 10. Thus, the system efficiently achieves instant hot water supply to instantly supply high-temperature hot water.
The pressure reducer 7, including the valve switched to be open or closed based on the set value which can be externally changed, is disposed in the feed pipe 4 connected to the hot water storage tank 2. This allows intentional supply of a small amount of hot water (water saving).
The present invention is not limited to Embodiment 1 described above. For example, although Fig. 1 illustrates the arrangement of the single hot water storage tank 2, a plurality of hot water storage tanks 2 may be arranged in parallel or in series.
Although Fig. 1 illustrates the arrangement of the circulating pump 12 and the check valve 13 separated from the hot water storage tank 2, the circulating pump 12 and the check valve 13 may be integrated with the hot water storage tank 2. This facilitates installation as well as suppression of the above-described bubbles. Furthermore, the diameter of the pipe connecting the hot water storage tank 2 and the circulating pump 12 can be reduced.
In Fig. 1, the pressure detecting unit 31 and the temperature detecting unit 32 need only be arranged in either the hot water supply pipe 11 or the circulation pipe 14 in the circulation circuit 10. The arrangement of these units is not limited to that in Embodiment 1 described above.

Reference Signs List

1 hot water supply device 2 hot water storage tank 3a, 3b connecting pipe 4, 5 feed pipe 6 check valve 7 pressure reducer 8 check valve 9 pressure reducer 10 circulation circuit 11 hot water supply pipe 12, 212 circulating pump 12a, 212a suction inlet 12b, 212b discharge outlet 13 check valve 14 circulation pipe 15 feed pipe 21 mixing faucet 22 hot water outlet terminal 31 pressure detecting unit 32 temperature detecting unit 33 circulation controller 40 pressure pump 41 water distributing pipe 100, 200 hot water supply system P pressure Pref set pressure T temperature Tref set temperature

Claims

A hot water supply system comprising:
a hot water storage tank configured to store hot water;

a hot water supply pipe configured to supply the hot water in the hot water storage tank to a hot water outlet terminal;

a circulation pipe connected to the hot water supply pipe and the hot water storage tank, and configured to return, to the hot water storage tank, the hot water flowing through the hot water supply pipe; and

a circulating pump disposed in the hot water supply pipe, and configured to draw by suction the hot water in the hot water storage tank and discharge the hot water toward the hot water outlet terminal and the circulation pipe.
The hot water supply system of claim 1, further comprising:
a check valve parallelly connected to the circulating pump.
The hot water supply system of claim 1 or 2, wherein the circulating pump is spaced apart from the hot water storage tank by a distance smaller than a distance by which the circulating pump is spaced apart from the hot water outlet terminal.
The hot water supply system of any one of claims 1 to 3, further comprising:
a pressure detecting unit configured to detect a pressure in the circulation pipe; and

a circulation controller configured to activate the circulating pump when a pressure detected by the pressure detecting unit reaches not more than a preset pressure.
The hot water supply system of any one of claims 1 to 4, further comprising:
a temperature detecting unit configured to detect a temperature in the circulation pipe; and

a circulation controller configured to stop the circulating pump when a temperature detected by the temperature detecting unit reaches not less than a preset temperature.
The hot water supply system of any one of claims 1 to 5, further comprising:
a feed pipe configured to supply water to the hot water storage tank; and

a pressure reducer disposed in the feed pipe, the pressure reducer having a variable pressure reduction value.