JP7295725B2 - Storage hot water heater - Google Patents

Description

The present invention relates to a hot water storage type water heater having heating means.

Conventionally, this type of hot water storage type water heater has a hot water storage tank and a heating means, and a heating return pipe leading from the lower part of the hot water storage tank to the heating means and a heating return pipe leading from the heating means to the hot water storage tank. are connected to constitute a heating circulation circuit, and a circulation pump provided in the heating circulation circuit circulates the hot water in the hot water storage tank and the heating means, and boils the water in the hot water storage tank by a boiling operation. Hot water is stored in a hot water storage tank, and the hot water in the hot water storage tank is sequentially mixed with the water supply to supply hot water at a set temperature, realizing economical hot water supply.

In addition, there is a hot water storage type water heater in which a heating bypass pipe branched from a heating return pipe is connected to a water supply pipe, and a bypass circulation route passing through the heating bypass pipe shares a part of the water supply route of the water supply pipe (for example, , Patent Document 1).

In addition, since such a heat pump type heating means cannot boil water to the desired target boiling temperature at the start of the heating operation, in the initial stage at the start of the heating operation, the number of revolutions of the circulation pump is reduced for heating. Hot water was returned to the lower part of the hot water storage tank via the bypass pipe, and after that, when the hot water could be boiled to near the target boiling temperature, the hot water was stored in the upper part of the hot water storage tank without passing through the heating bypass pipe.

JP 2007-139258 A

By the way, as in Patent Document 1, in a hot water storage type water heater in which a bypass circulation path passing through a heating bypass pipe shares a part with a water supply path of a water supply pipe, the rotation of the circulation pump is in the initial stage at the start of heating operation. When hot water is returned to the lower part of the hot water storage tank via the heating bypass pipe in a low rotation state with the number reduced, if the hot water supply operation is performed with a large hot water supply flow rate that affects this boiling operation, the bypass circulation will occur. There was a problem that the circulation of the boiling operation stopped due to the influence of the water supply pressure due to the hot water supply operation on the circulation pressure for circulating the hot water in the path.

In order to solve the above problems, the present invention provides a hot water storage tank for storing hot water, a heating means for heating the hot water in the hot water storage tank, a hot water outlet pipe connected to the upper part of the hot water storage tank, and a hot water supply pipe connected to the lower part of the hot water storage tank. a water supply pipe branched from the water supply pipe and merged with the hot water supply pipe , and when hot water supply operation is requested, high-temperature water in the hot water supply pipe and water supply in the water supply bypass pipe are mixed to supply hot water to a hot water supply destination. a hot water supply pipe for sending water, a heating supply pipe for sending the hot water from the lower part of the hot water storage tank to the heating means, a circulation pump provided in the middle of the heating supply pipe, and a hot water heated by the heating means to the hot water storage tank. a heating return pipe that branches from the heating return pipe and joins with the water supply pipe to send the hot water to the bottom of the hot water storage tank; and a heating return pipe from the heating return pipe to the heating bypass pipe. A switching valve arranged at a branch point for switching the flow of the hot water, a switching control means for controlling the switching valve, a rotational speed control means for controlling the rotational speed of the circulation pump, and the heating means. and a controller having a boiling operation control means for controlling a boiling operation in which hot water is stored in a hot water storage tank, wherein the controller includes the switching control means. The valve is opened on the side of the heating bypass pipe, and the rotational speed control means drives the rotational speed of the circulation pump to be less than a predetermined rotational speed to start the boiling operation. When the circulation pump is driven at less than a predetermined rotation speed, the switching control means closes the switching valve on the heating bypass pipe side and opens the hot water storage tank upper side, thereby performing the hot water supply operation. The switching control means closes the switching valve on the side of the heating bypass pipe and opens the upper side of the hot water storage tank when the conditions for terminating the drive at less than the predetermined rotational speed are satisfied.

The rotation speed control means controls the rotation speed of the circulation pump to be less than a predetermined rotation speed for a predetermined period of time from the start of the boiling operation, and then operates the circulation pump so that the water is heated to the target boiling temperature. The rotation speed is increased, and the rotation speed control means controls the rotation speed of the circulation pump to be less than the predetermined rotation speed when the elapsed time from the start of the boiling operation is less than a predetermined time . I did

When the temperature detected by a temperature sensor provided in the middle of the heating return pipe during the boiling operation is less than a predetermined temperature, the rotation speed control means determines that the rotation speed of the circulation pump is less than the predetermined rotation speed. I made it

According to this aspect of the invention, when the hot water supply operation is performed during the low rotation state at the start of the boiling operation, the circulation of the boiling operation is stopped. By switching from the first state on the heating bypass pipe side to the second state on the upper side of the hot water storage tank, the influence of the water supply pressure due to the hot water supply and the flow of the circulation pump due to the boiling operation is reduced, and the boiling operation is performed. It is possible to prevent the circulation of

1 is a schematic configuration diagram showing an embodiment of the present invention; FIG. 4 is a flow chart showing a first embodiment of the invention; 6 is a flow chart showing a second embodiment of the present invention;

Next, a heat pump water heater according to one embodiment of the present invention will be described with reference to the drawings.
A hot water storage tank unit 1 has a hot water storage tank 2 for storing hot water, a hot water outlet pipe 3 connected to the upper part of the hot water storage tank 2, a water supply pipe 4 connected to the lower part of the hot water storage tank 2, and hot water outlet. A hot water supply mixing valve 6 for mixing high temperature water from the pipe 3 and low temperature water from the hot water supply bypass pipe 5 branched from the water supply pipe 4, and a hot water supply pipe 7 connected downstream of the hot water supply mixing valve 6. A hot water supply temperature sensor 8 and a hot water supply flow sensor 9 for detecting a hot water supply flow rate are provided.

A heat pump unit 10 is composed of a compressor 11, a water-refrigerant heat exchanger 12 as a condenser, an electronic expansion valve 13, and an air heat exchanger 15 as an evaporator having an outdoor fan 14 and exchanging heat with air. a heat pump type heating means 16, a circulation pump 20 for circulating the hot water in the hot water storage tank 2 to the heating means 16 through a heating circulation circuit 19 consisting of a heating supply pipe 17 and a heating return pipe 18, and their driving and the heating means 16 uses carbon dioxide as a refrigerant to form a supercritical heat pump cycle. In addition, since carbon dioxide is used as a coolant, low-temperature water can be boiled up to a high temperature of about 90° C. without an electric heater.

Here, the water-refrigerant heat exchanger 12 employs a counter-flow system in which the refrigerant and hot water, which is the water to be heated, in the hot water storage tank 2 flow in opposite directions. Since the water is condensed in a critical state, the water to be heated can be efficiently heated to a high temperature. By controlling the expansion valve 13 or the compressor 11, when the inlet temperature of the water to be heated to the water-refrigerant heat exchanger 12 is a low temperature of about 5 to 20° C., the COP (energy consumption efficiency) is very good. It is possible to heat the heating water.

In addition, a switching valve 22 is provided in the middle of the heating return pipe 18, and when freezing is prevented, the switching valve 22 is switched so that the heating bypass pipe 23 connected to the water supply pipe 4 at the bottom of the hot water storage tank 2 communicates with the hot water storage tank. Freezing is prevented by circulating a short circuit using the lower part of 2. This switching valve 22 is arranged at a branch point from the heating return pipe 18 to the heating bypass pipe 23 .

In addition, when hot water that is not sufficiently heated at the initial stage of heating of the heating means 16 is circulated, hot water is not returned to the upper part of the hot water storage tank 2, but is returned to the lower part of the hot water storage tank 2 through the bypass circulation route via the heating bypass pipe 23. After that, when sufficiently heated hot water is to be circulated, the switching valve 22 is switched to the upper side of the hot water storage tank 2 .

Reference numeral 24 denotes a control device comprising a microcomputer or the like, which controls the heating control unit 21 to control the temperature of the hot water supply, such as the operation of boiling the hot water storage tank 2 by the heating circulation circuit 19, the operation of reheating the water, etc., filling the bath with hot water, reheating, and keeping warm. and other operation control.

Further, the control device 24 is provided with switching valve control means 25 for controlling the opening degree of the switching valve 22. Specifically, the switching valve control means 25 sets the switching valve 22 to the side of the heating bypass pipe 23, and A first state is switched so as to communicate with the water supply pipe 4 at the bottom of 2 and a second state is switched so that the switching valve 22 communicates with the upper side of the hot water storage tank 2 .

Further, the control device 24 is provided with rotation speed control means 26 for controlling the rotation speed of the circulation pump, and boiling operation control means 27 for controlling the boiling operation, which will be described later.

At the start of this boiling operation, the refrigerant in the heating means 16 is not sufficiently heated, and the water in the lower part of the hot water storage tank 2 flowing from the heating pipe 17 cannot be boiled to the target temperature. The number control means 26 sets the number of rotations of the circulation pump 20 to less than a predetermined number of rotations (lower than this predetermined number of rotations refers to a low rotation state, and will be referred to as a low rotation state in the text described later) to boil the water. The control means 27 drives the circulation pump 20 to perform the boiling operation. When the temperature detected by 35 or stored hot water temperature sensor 36 exceeds a predetermined temperature, rotation speed control means 26 sets the rotation speed of circulating pump 20 to a predetermined boiling rotation speed and performs a boiling operation. Further, the predetermined number of revolutions here is a number of revolutions higher than that in the low revolution state and lower than the predetermined boiling number of revolutions, and at least a number of revolutions at which the circulation of the boiling operation does not stop due to the influence of the water supply pressure due to the supply of hot water. .

Similarly to the above, when the boiling operation is started, the refrigerant in the heating means 16 is not sufficiently heated, and the water in the lower part of the hot water storage tank 2 flowing from the heating supply pipe 17 cannot be boiled to the target temperature. Therefore, the switching valve control means 25 sets the switching valve 22 to the first state, performs boiling, returns the boiled hot water to the lower portion of the hot water storage tank 2, and then reaches the termination condition of the low rotation state. Then, the switching valve 22 is set to the second state and the boiling operation is performed.

Further, the remote controller 28 has a temperature setting switch 29 for setting the set hot water supply temperature, a hot water filling switch 30 for instructing hot water filling to the bath, and a hot water filling amount 31 for setting the hot water filling amount. and a remote control unit 33 configured by a microcomputer for controlling the display unit 33 and communicating with the control device 25 .

In addition, an inlet water temperature sensor 34 is provided on the water inlet side of the water-refrigerant heat exchanger 12 of the heating circulation circuit 19 to detect the inlet water temperature, and an outlet temperature sensor 35 is provided on the outlet side to detect the temperature of the water after heating. Among a plurality of stored hot water temperature sensors 36 for detecting the temperature of stored hot water in the hot water storage tank 2 provided in the hot water storage tank 2, the uppermost stored hot water temperature sensor 36 and the outlet temperature sensor 35 Either of them continues to detect the boiling target temperature to end the boiling operation.

Reference numeral 37 denotes a relief valve communicating with the top of the hot water storage tank 2 to release air from the hot water storage tank 2 and the heating circulation circuit 19;

39 is a hot water filling valve that connects the hot water filling pipe 40 with the bathtub to supply hot water to the bathtub; 41 is a bath temperature sensor that detects the temperature of the bath supplied to the bath; It is a bath flow sensor that detects the flow rate

Next, the boiling operation will be explained.
When the amount of heat stored in the hot water decreases or when there is a request for boiling in the middle of the night, the switching valve control means 25 puts the switching valve 22 in the first state in which it communicates with the heating bypass pipe 23 side. In the second state of communication, the control device 24 drives the circulation pump 20 in the middle of the pipe connecting the hot water storage tank 2 and the heating means 16 to pump up water from the lower part of the hot water storage tank 2 and warm it with the heating means 16. The water in the hot water storage tank 2 is gradually boiled to a high temperature by continuing the operation of returning the hot water to the upper part of the hot water storage tank 2.例文帳に追加

Next, the hot water supply operation will be described.
When the hot water tap is opened, water is supplied from the water supply pipe 4, flows into the lower part of the hot water storage tank 2, passes through the water supply bypass pipe 5, and is pushed out from the upper part of the hot water storage tank 2. and adjusted so that the hot water set temperature and the temperature detected by the hot water supply temperature sensor 8 are the same, is supplied from the hot water tap.

Also, the hot water filling operation will be described.
When the hot water filling switch 30 of the remote control 28 is pushed, the control device 24 opens the hot water filling valve 39, supplies water from the water supply pipe 4, flows into the lower part of the hot water storage tank 2, passes through the water supply bypass pipe 5, and flows into the hot water storage tank. 2. The high-temperature water pushed out from the upper part and the water supply of the water supply bypass pipe 5 are mixed by the hot water supply mixing valve 6, and the hot water adjusted so that the bath set temperature and the temperature detected by the bath temperature sensor 41 are the same are supplied to the bathtub. Hot water filling is started by flowing in. Then, the flow rate is detected by the bath flow sensor 42, and when the total integrated value of the flow rate has flowed by the set amount of hot water filling, the control device 24 closes the hot water filling valve 39 to complete hot water filling. .

Next, the operation of the first embodiment when the hot water supply operation is performed during the boiling operation will be described in detail with reference to the flow chart of FIG.
When the boiling operation control means 27 starts the boiling operation (Yes in S1) due to a decrease in the stored hot water heat amount or a late-night boiling request, the switching valve control means 25 switches the switching valve 22 to the heating bypass pipe 23 side. The first state of communication is set (S2), the rotation speed control means 26 sets the rotation speed of the circulation pump 20 to the low rotation state (less than the predetermined rotation speed) (S3), and the boiling operation control means 27 controls the circulation pump. drive 20;

Then, when the hot water supply operation is not performed during this low rotation state (S4 is Yes) and the termination condition of the low rotation state is satisfied (S5 is Yes), the switching valve control means 25 switches the switching valve 22 to the hot water storage tank 2. (S6), the rotation speed control means 26 sets the rotation speed of the circulation pump 20 to a predetermined boiling rotation speed (S7), and the boiling operation control means 27 starts the boiling operation. continue.

After that, either the outlet temperature sensor 35 or the uppermost stored hot water temperature sensor 36 continues to detect the boiling target temperature (Yes in S8), thereby completing the boiling operation (S9).

Further, when the hot water supply flow sensor 9 or the bath flow sensor 42 detects the hot water supply flow rate during this low rotation state and it is determined that the hot water supply operation has been performed (S4 is No), the heating bypass pipe 23 is in the boiling operation circulation. At the position where it merges with the water supply pipe 4, the circulation is stopped due to the influence of the water supply pressure due to the hot water supply operation. A second state of communicating with the upper side is set (S10), and the water supply pressure is not affected at the position where the heating bypass pipe 23 and the water supply pipe 4 join.

After that, when the end condition of the low rotation state is satisfied (S11 is Yes), the rotation speed control means 26 sets the rotation speed of the circulation pump 20 to a predetermined boiling rotation speed (S7), and the boiling operation control means 27 Continue boiling operation.

After that, either the outlet temperature sensor 35 or the uppermost stored hot water temperature sensor 36 continues to detect the boiling target temperature (Yes in S8), and the boiling operation control means 27 completes the boiling operation ( S9).

In this way, when the hot water supply operation is performed during the low rotation state (during rotation at less than a predetermined rotation speed) at the start of the heating operation, the circulation of the heating operation stops. By switching the switching valve 22 from the first state on the side of the heating bypass pipe 23 to the second state on the upper side of the hot water storage tank 2, the control means 25 changes the water supply pressure due to the hot water supply and the flow of the circulation pump 20 due to the boiling operation. It is possible to reduce the influence of , and prevent the circulation of the boiling operation from stopping.

If the circulation of the boiling operation stops, the hot water is heated by the heating means 16, and if the heated hot water continues to stay, the outlet temperature sensor 35 detects the target boiling temperature. There is a problem that the boiling operation is completed when sufficient hot water is not stored in the hot water storage tank, and wasteful power consumption is caused by continuing to operate the heating means 16 even though the circulation by the boiling operation is not performed. Problems such as failure due to load on the means 16 and the circulation pump 20 can be solved.

Further, when the hot water supply operation is performed during the low rotation state (during rotation at less than a predetermined rotation speed) at the start of the boiling operation, the switching control means 25 switches the switching valve 22 to the first position on the heating bypass pipe 23 side. state is switched to the second state on the upper side of the hot water storage tank 2, and the switching valve 22 maintains the second state even if the hot water supply operation ends during the low rotation state after that, thereby supplying hot water in a short time. It is possible to prevent the temperature stratification in the hot water storage tank 2 from being disturbed when the start and end of the operation are repeated.

Further, the operation of the second embodiment, which is a method different from that of the first embodiment, will be described in detail based on the flow chart of FIG.
When the boiling operation control means 27 starts the boiling operation in response to a decrease in the stored hot water heat amount or a late-night time zone boiling request (Yes in S12), the switching valve control means 25 switches the switching valve 22 to the heating bypass pipe 23 side. The first state of communication is set (S13), the rotation speed control means 26 sets the rotation speed of the circulation pump 20 to the low rotation state (less than the predetermined rotation speed) (S14), and the boiling operation control means 27 controls the circulation pump. drive 20;

Then, when the hot water supply operation is not performed during this low rotation state (Yes in S15) and the conditions for ending the low rotation state are satisfied (Yes in S16), the switching valve control means 25 switches the switching valve 22 to the hot water storage tank 2. (S17), the rotation speed control means 26 sets the rotation speed of the circulation pump 20 to a predetermined boiling rotation speed (S18), and the boiling operation control means 27 starts the boiling operation. continue.

After that, either the outlet temperature sensor 35 or the uppermost stored hot water temperature sensor 36 continues to detect the boiling target temperature (Yes in S19), thereby completing the boiling operation (S20).

Further, when the hot water supply flow sensor 9 or the bath flow sensor 42 detects the hot water supply flow rate during this low rotation state and it is determined that the hot water supply operation is performed (S15 is No), the heating bypass pipe 23 during the boiling operation circulation. At the position where the water supply pipe 4 joins from the At the same time, the circulation pump 20 is controlled to a predetermined number of revolutions at which the circulation of the boiling operation does not stop due to the influence of the water supply pressure due to the hot water supply (S21), and the water supply pressure is reached at the position where the heating bypass pipe 23 and the water supply pipe 4 join. The circulating pump 20 is driven at such a rotational speed that the circulation of the boiling operation does not stop even under the influence of .

After that, when the elapsed time from the start of the boiling operation, which is one of the conditions for ending the low revolution state, has passed for a predetermined time or longer and the condition for ending is met (Yes in S22), the switching valve control means 25 switches to the switching valve. 22 is brought into communication with the upper part of the hot water storage tank 2 (S17), the rotation speed control means 26 sets the rotation speed of the circulation pump 20 to a predetermined boiling rotation speed (S18), and the boiling operation control means 27 , to continue the boiling operation.

After that, when either the outlet temperature sensor 35 or the uppermost stored hot water temperature sensor 36 continues to detect the boiling target temperature (Yes in S19), the boiling operation control means 27 completes the boiling operation ( S20).

In this way, when the hot water supply operation is performed during the low rotation state (during rotation at less than a predetermined rotation speed) at the start of the boiling operation, the rotation speed control prevents the circulation of the heating operation from stopping. Means 26 raises the number of rotations of circulation pump 20 to a predetermined number of rotations so that the circulation of the boiling operation is not stopped even if it is affected by the pressure of water supply. It is possible to reduce the influence of the operation on the flow of the circulation pump 20 and prevent the circulation of the boiling operation from stopping.

If the circulation of the boiling operation stops, the hot water is heated by the heating means 16, and if the heated hot water continues to stay, the outlet temperature sensor 35 detects the target boiling temperature. There is a problem that the boiling operation is completed when sufficient hot water is not stored in the hot water storage tank, and wasteful power consumption is caused by continuing to operate the heating means 16 even though the circulation by the boiling operation is not performed. Problems such as failure due to load on the means 16 and the circulation pump 20 can be solved.

It should be noted that the present invention is not limited to the embodiments, and it is not intended to prevent modifications within the scope of the invention. Since the water is supplied from the hot water source, the water supply pressure due to the hot water filling operation affects the circulation due to the boiling operation, which satisfies the requirements of the present invention.

Further, in the first embodiment of the present invention, when the rotation speed of the circulation pump 20 during the boiling operation is in the low rotation state (less than the predetermined rotation speed), when the hot water supply operation is performed, the switching control means 25 switches the switching valve 22 from the first state to the second state, and after switching to the second state, the switching valve 22 is not switched to the first state even when the hot water supply operation ends. When the hot water supply operation is not performed, the switching valve 22 may be switched to the first state because it is not affected by the water supply pressure.

Also in the second embodiment of the present invention, when the rotation speed of the circulation pump 20 during the boiling operation is in the low rotation state (less than the predetermined rotation speed), the rotation speed control is performed when the hot water supply operation is performed. The means 26 raises the rotation speed of the circulation pump 20 to a predetermined rotation speed, and after raising the rotation speed to the predetermined rotation speed, the rotation speed of the circulation pump 20 is kept in the low rotation state (predetermined rotation speed) even after the hot water supply operation is finished. number), but when hot water supply operation is not performed, the rotation speed of the circulation pump 20 is not affected by the water supply pressure, so even if the rotation speed of the circulation pump 20 is returned to the low rotation state (lower than the predetermined rotation speed). good.

Also, in the present invention, the heating means 16 is of a heat pump type, but the heating means 16 may be changed to a fuel cell. In addition, it is sufficient to use a heat pump or a fuel cell that takes time to raise the heating means 16 to a high temperature and keeps the rotation speed of the circulation pump 20 in a low rotation state.

Further, in the present invention, if there is a hot water supply operation during the low rotation state, the switching valve control 25 controls the switching valve 22 in the first embodiment, and the rotation speed control means 26 controls the circulation pump 20 in the second embodiment. This control is performed when the hot water supply flow rate is large enough to affect the circulation of the boiling operation when the detected value of the hot water supply flow sensor 9 or the bath flow sensor 42 is affected during the low rotation state. Each control may be executed when the hot water supply flow sensor 9 or the bath flow sensor 42 detects a hot water supply flow rate that does not affect the circulation of the boiling operation.

2 Hot water storage tank 3 Hot water outlet pipe 4 Water supply pipe 5 Hot water supply bypass pipe 6 Hot water supply mixing valve 7 Hot water supply pipe 16 Heating means 19 Heating circulation circuit 20 Circulation pump 22 Switching valve 23 Heating bypass pipe 24 Control device 25 Switching valve control means 26 Rotational speed control means 27 Boiling operation control means

Claims (3)

a hot water storage tank for storing hot water;
heating means for heating the hot water in the hot water storage tank;
a hot water outlet pipe connected to the upper part of the hot water storage tank;
a water supply pipe connected to the lower part of the hot water storage tank;
a water supply bypass pipe branched from the water supply pipe and joined with the hot water discharge pipe ;
a hot water supply pipe for mixing high-temperature water in the hot water supply pipe and water supply in the water supply bypass pipe and delivering hot water to a hot water supply destination when a hot water supply operation is requested;
a heating pipe for sending the hot water from the lower part of the hot water storage tank to the heating means;
a circulation pump provided in the middle of the heating supply pipe;
a heating return pipe for sending hot water heated by the heating means to the upper part of the hot water storage tank;
a heating bypass pipe branching from the heating return pipe and joining with the water supply pipe to send the hot water to a lower portion of the hot water storage tank;
a switching valve arranged at a branch point from the heating return pipe to the heating bypass pipe and switching the flow of the hot water;
switching control means for controlling the switching valve; rotation speed control means for controlling the rotation speed of the circulation pump; A hot water storage type hot water supply device comprising a control device having a rising operation control means,
In the control device, the switching control means opens the switching valve to the heating bypass pipe side, and the rotation speed control means drives the rotation speed of the circulation pump below a predetermined rotation speed to perform the boiling operation. start and
After that, when the hot water supply operation is performed, if the circulation pump is driven at less than a predetermined number of revolutions, the switching control means closes the switching valve on the heating bypass pipe side, and closes the switching valve on the hot water storage tank upper side. to open the
When the hot water supply operation is not performed and the end condition of driving at less than the predetermined rotational speed is satisfied, the switching control means closes the switching valve on the heating bypass pipe side and opens the hot water storage tank upper side. A hot water storage type hot water heater characterized by : The rotation speed control means controls the rotation speed of the circulation pump to be less than a predetermined rotation speed for a predetermined period of time from the start of the boiling operation, and then operates the circulation pump so that the water is heated to the target boiling temperature. increase the rpm,
The rotation speed control means controls the rotation speed of the circulation pump to be less than the predetermined rotation speed when the elapsed time from the start of the boiling operation is less than a predetermined time. The hot water storage type water heater according to claim 1 . When the temperature detected by a temperature sensor provided in the middle of the heating return pipe during the boiling operation is less than a predetermined temperature, the rotation speed control means determines that the rotation speed of the circulation pump is less than the predetermined rotation speed. 2. The hot water storage type water heater according to claim 1 , wherein

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