JPH0760018B2 - Control method for multiple water heaters - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an operation control method for a parallel type multiple water heater in which a plurality of water heaters are connected in parallel to increase the range of hot water supply capacity.

[0002]

2. Description of the Related Art Conventionally, by connecting a plurality of water heaters in parallel, it is possible to increase the range of hot water supply capacity of each water heater (for example, the range from the minimum hot water discharge amount to the maximum hot water discharge amount). In such a parallel type multiple water heater, the number of hot water heaters to be operated is controlled when increasing or decreasing the amount of hot water discharged according to the increase or decrease in the amount of hot water consumed. For example, the one described in JP-A-64-63749 has two
In parallel type multiple water heaters that are connected with water heaters each equipped with water control valves and hot water discharge solenoid valves of one or more units, when one water heater is in operation, the amount of hot water discharged, that is, the amount of hot water consumed, increases When the maximum hot water discharge capacity of one of the water heaters is reached, 2
Open the hot water supply solenoid valve of the water heater after the third unit to start operation,
Decrease the water flow rate of the first water heater to a predetermined amount (for example, 1/2 of the water flow rate of the first water heater immediately before the second water heater starts operation is set as a predetermined amount, and The amount of water is reduced at the same time as the amount of combustion), and when two or more units are operating and the amount of hot water discharged falls below a specified value, combustion is started in the reverse order of when combustion is started. The hot water discharge solenoid valve provided in the second and subsequent hot water heaters is fully closed when the hot water heater to which the hot water discharge solenoid valve is attached stops combustion, so that When the operation switch is turned off, the valve is fully opened to ensure the amount of water used when cold water is used from the hot water tap, and to drain water.

Further, generally, after installing and constructing a water heater or repairing appliances, the maximum secondary pressure of the gas proportional control valve for controlling the gas supply amount according to the current value provided in the gas supply path. In addition, it is necessary to adjust the minimum secondary pressure. For example, as described in Japanese Patent Application Laid-Open No. 62-155434, the maximum secondary pressure setting switch or the minimum secondary pressure setting switch is operated to operate the maximum secondary pressure. Pressure supply (that is, maximum combustion) state or minimum secondary pressure supply (that is, minimum combustion) state is forcibly changed to maximum secondary pressure setting resistance or minimum 2
The secondary pressure setting resistor is being adjusted.

[0004]

However, when the above-mentioned conventional maximum secondary pressure adjusting means is applied to a plurality of water heaters of a parallel type, when the maximum secondary pressure is adjusted, the maximum combustion state is forcibly changed. In addition, since it is necessary to sufficiently increase the amount of water flow to prevent boiling, if the maximum secondary pressure adjustment operation is performed for one of the multiple water heaters and the amount of water flow is increased, the above-mentioned unit control ( When the number of water heaters is increased, other water heaters start operating and maximum combustion is being performed. The water flow rate of the water heater being adjusted is a predetermined amount (for example, adjustment just before other water heaters start operating). 1 / of the water flow rate of the water heater inside
There is a problem in that there is a risk of boiling due to a decrease in 2) (note that in the normal unit number control, as described above, when the water flow rate decreases, the supply gas amount decreases correspondingly). It is also possible to temporarily remove the connections (electric wires, signal lines, etc.) of water heaters other than the water heater that is subject to the maximum secondary pressure adjustment operation, but how many times can each water heater that constitutes a plurality of water heaters be used? However, there is a problem in that connection and disconnection may be repeated to cause erroneous connection, and the time and effort required for construction and repair of the water heater increase.

An object of the present invention is to control the number of operating units by increasing / decreasing the amount of hot water discharged, and to adjust the maximum secondary pressure of the gas proportional control valve without boiling it. To provide a device control method.

[0006]

In order to achieve the above object, a method for controlling a plurality of water heaters according to the present invention comprises at least two water heaters each provided with a gas proportional control valve, a water amount adjusting valve and a hot water discharge solenoid valve in parallel. When at least one hot water supply device is connected, the hot water supply operation is performed by opening the hot water supply solenoid valve of another hot water supply device when the requested hot water supply satisfies the predetermined increase condition. Multiple hot water heaters that increase the number of hot water heaters while controlling the number of hot water heaters by closing the hot water solenoid valve of one of the hot water heaters that are in operation when the required hot water discharge amount meets a predetermined reduction condition In the water heater, a maximum secondary pressure adjusting switch is provided corresponding to each water heater constituting the plurality of water heaters, and the maximum secondary pressure adjusting switch of any water heater is turned on to shift to the maximum secondary pressure adjusting operation. , Maximum secondary pressure adjustment switch By but a tapping solenoid valve on the water heater is opened, the tapping solenoid valve other water heater closed,
It is possible to secure a water flow rate of a predetermined amount or more and perform the maximum secondary pressure adjusting operation without fear of boiling.

[0007]

Embodiments of the present invention will be described with reference to the drawings.
In the present embodiment, three water heaters 1, 2, 3 are connected in parallel, and each water heater 1, 2, 3 has a heat exchanger 11, 12, 13 and a heat exchanger 11, respectively. Water inlets 21, 22, 23 connected to the inlet sides of 12, 13 and hot water outlets 31, 32, 33 connected to the outlet sides of the heat exchangers 11, 12, 13 and water inlets 21, 22, 23 And bypass paths 41, 42, 43 that connect the hot water passages 31, 32, 33 with each other
And burners 101, 102 for heating the heat exchangers 11, 12, 13,
It is equipped with 103 and.

In each water heater 1, 2 and 3, a bypass passage
41, 42, 43 downstream of the branch portion, that is, the heat exchangers 11, 12, 13
In the water inlets 21, 22, 23 on the inlet side, the can body water flow rate Q _K1 , Q _K2 ,
_Intake water amount sensors 51, 52, 53 for detecting Q _K3 are provided, and bypass water amount sensors 61, 62, 63 and bypass water amount Q for detecting bypass water amounts Q _B1 , Q _B2 , Q _B3 are provided in the bypass passages 41, 42, 43. Bypass valves 71, 72, 73 for adjusting _B1 , Q _B2 , Q _B3 are provided, and a hot water outlet passage 31, upstream of the junction of the bypass passages 41, 42, 43, that is, on the outlet side of the heat exchangers 11, 12, 13 is provided. 32 and 33 are provided with water flow control valves 81, 82 and 83 with an overflow prevention function, and hot water discharge valves 31, 32 and 33 are provided with hot water discharge solenoid valves 91, 92 and 93. Further, proportional control valves 111, 112, 113 are provided in the gas supply paths connected to the burners 101, 102, 103, respectively. The water inlets 21, 22, and 23 of each water heater 1, 2, and 3 are both connected to the original water supply passage 4, while the hot water outlets 31, 32, and 33 are both connected to the hot water supply passage 5 and are connected to the original water supply passage 4. An incoming water temperature sensor 6 for detecting the incoming water temperature Tc is provided.

The set temperature Ts, the water temperature Tc detected by the water temperature sensor 6, the can body water flow rates Q _K1 , Q _K2 , Q _K3 detected by the water flow rate sensors 51, 52 and 53, and the bypass water flow rate sensor.
And a bypass water Q _B1, Q _B2, Q _B3 detected at 61, 62, 63 and input to the controller 7, the driving control signal from the controller 7, a bypass valve 71, 72, 73, the amount of water adjusted with excessive outflow prevention It outputs to the valves 81, 82 and 83, the hot water solenoid valves 91, 92 and 93 and the proportional control valves 111, 112 and 113.

Water flow control valve 81, 82, 83 with overflow prevention function
Is the water flow rate of the can bodies of each water heater 1, 2, 3 Q _K1 , Q _K2 , Q _K3
Is the maximum flow rate Qmax ₁ , Qmax ₂ , Qma of each water heater ₁ , ₂ , 3
x ₃ or more (Q _K1 ≧ Qmax ₁ , Q _K2 ≧ Qmax ₂ , Q _K3 ≧ Q
At max ₃ ), the opening is reduced for each, and the flow rate is reduced to prevent overflow independently of each other, while the can body water flow rate Q _K1 , Q _K2 , Q _K3 is the maximum flow rate Q max ₁ , respectively. Qma
x ₂ , less than Qmax ₃ (Q _K1 <Qmax ₁ , Q _K2 <Qmax ₂ , Q _K3 <
At the time of Qmax ₃ ), the openings of the can body water flow rates Q _K1 , Q _K2 , and Q _K3 are maintained. If the water flow resistances of the water heaters 1, 2, and 3 are equal in the state where the above-mentioned overflow prevention is not performed, the can body water flow rates Q _K1 , Q _K2 , and Q _{K3 of the} water heaters 1, 2, and 3 are equal.
Are equal to each other (Q _K1 = Q _K2 = Q _K3 ).

By-pass valves 71, 72 of each water heater 1, 2, 3
Reference numeral 73 denotes a target distribution ratio (Q _K1 / Q _B1 = 1 / α ₁ , Q 1) as a distribution ratio which is a ratio of the can body water flow rate Q _K1 , Q _K2 , Q _K3 and the bypass water flow Q _B1 , Q _B2 , Q _{B3. K2} / Q _B2 = 1 / α ₂ , Q _K3
/ Q _B3 = 1 / α ₃ ), but in the present embodiment, α ₁ = α ₂ = α ₃ =
Let be α. From the set temperature Ts and the incoming water temperature Tc, the can set temperature Tks of each water heater 1, 2, 3 can be obtained by the following equation. T _KS = (1 + α) Ts −α · Tc For the purpose of preventing low temperature corrosion and boiling, the range of the can set temperature Tks is set (for example, 50
℃ ≤ Tks ≤ 80 ℃). Further, the can body set flow rate Q _KS is calculated by the following equation. Q _KS = (Gmax. × 25) / (T _KS -Tc) = Gmax ₁ / (T
_KS -Tc) where, Gmax. Maximum scale number of the water heater, Gmax ₁ is heat. Further, the total set flow rate Q _TS of each water heater is obtained by the following equation. _{Q TS = (Gmax. × 25} ) / (Ts -Tc) Further, in the flow velocity in the water passage of the water heater is likely to be eroded and becomes excessive, as well as pre-set total maximum flow Q _Tmax, the following Total minimum set flow rate Q according to the formula
_{Calculate TSmin} . _QTSmin. = (Gmin. * 25) / (Ts-Tc) where Gmin. Is the minimum number.

The controller 7 or each water heater 1,
The maximum secondary pressure adjusting switch 12 corresponding to each water heater 1, 2 and 3 is provided in the controllers (not shown) provided in 2 and 3 respectively.
1, 122, 123 and minimum secondary pressure adjustment switch 131, 132
, 133 are provided, and the maximum secondary pressure setting switch 121
, 122, 123 is turned on, the corresponding water heater 1, 2, 3 is forcibly moved to the maximum secondary pressure supply (that is, maximum combustion) state while ensuring a predetermined water flow amount, This is to adjust the maximum secondary pressure setting resistance. Regardless of the operating state of multiple water heaters, the hot water outlet solenoid valve is opened only for the water heaters that are in the adjustment operation, and the hot water outlet solenoid valves of other water heaters are fully closed. The installation locations of the maximum secondary pressure adjusting switch and the minimum secondary pressure adjusting switch are not limited to the controller 7, but may be provided in a remote controller (not shown in this embodiment) or a water heater main body. . For example, all hot water heaters 1, 2, and 3 are in hot water discharge operation (hot water solenoid valve).
91, 92, 93 open) any water heater (for example, water heater 2)
Maximum secondary pressure setting switch (maximum secondary pressure setting switch 12
When 2) is turned on, the hot water outlet solenoid valve 92 of the water heater 2 is kept open and the combustion is shifted to maximum combustion.
The hot water discharge solenoid valve (the hot water discharge solenoid valves 91, 93) is fully closed to stop the hot water discharge operation. In addition, when the two water heaters (for example, the water heaters 1 and 2) are in the hot water discharge operation (the hot water solenoid valves 91 and 92 are open and the hot water solenoid valve 93 is closed), the remaining hot water heater (the hot water heater 3) is the maximum When the secondary pressure setting switch (maximum secondary pressure setting switch 123) is turned on, the hot water supply solenoid valve (hot water supply solenoid valve 93) of the water heater (water heater 3) that starts the adjustment operation is opened to shift to maximum combustion,
The hot water discharge solenoid valves (hot water discharge solenoid valves 91, 92) of the two water heaters (water heaters 1, 2) are closed to stop the hot water discharge operation. Further, by turning on any of the minimum secondary pressure setting switches 131, 132, 133, the corresponding water heaters 1, 2, 3 are forcibly moved to the minimum secondary pressure supply (that is, minimum combustion) state. , Adjust the minimum secondary pressure setting resistance.

The control operation will be described with reference to the flow chart of FIG. When the operation switch is off, the water flow control valves 81, 82, 82 with overflow prevention function for all water heaters 1, 2, 3
83 is fully closed, hot water solenoid valves 91, 92, 93 and bypass valve
71, 72, 73 can be opened to use cold water in the hot water tap. When the operation switch is turned on and the maximum secondary pressure adjusting switch 121 of the water heater 1 is turned on, only the hot water outlet solenoid valve 91 of the water heater 1 is opened, and the hot water solenoid valves of the other water heaters 2 and 3 are opened.
92 and 93 are fully closed, and only the water heater 1 shifts to the maximum secondary pressure adjusting operation, forcibly performing maximum combustion and the proportional control valve 111.
Adjust the maximum secondary pressure of. At this time, the hot water supply solenoid valves 92 and 93 of the water heaters 2 and 3 are fully closed, and the number of units is not controlled. Therefore, a sufficient water flow amount of the water heater 1 is secured and there is no fear of boiling.

Next, the maximum secondary pressure adjusting switch of the water heater 1
When 121 is turned off and the maximum secondary pressure adjusting switch 122 of the water heater 2 is turned on, only the hot water solenoid valve 92 of the hot water heater 2 is opened, and the hot water solenoid valves 91, 93 of the other hot water heaters 1, 3 are opened. Is fully closed, and only the water heater 2 shifts to the maximum secondary pressure adjusting operation, forcibly performing maximum combustion to adjust the maximum secondary pressure of the proportional control valve 112. Further, when the maximum secondary pressure adjusting switches 121 and 122 of the water heaters 1 and 2 are off and the maximum secondary pressure adjusting switch 123 of the water heater 3 is turned on, the hot water supply solenoid valve of the water heater 3 is turned on.
Only 93 is opened, the hot water outlet solenoid valves 91 and 92 of the other water heaters 1 and 2 are fully closed, and only the water heater 3 shifts to the maximum secondary pressure adjusting operation, forcibly performing maximum combustion and proportional control. Max 2 of valve 113
Adjust the next pressure.

When the maximum secondary pressure setting switches 121, 122, 123 of all the water heaters 1, 2, 3 are turned off, the normal number control is performed, and the hot water outlet solenoid valve 91 of the water heater 1 is fully opened. ,
The water flow control valve 81 with overflow prevention function and the bypass valve 71 are opened to start the hot water supply operation of the water heater 1, and the other water heaters 2, 3
The hot water supply solenoid valves 92 and 93 are fully closed, that is, the hot water heaters 2 and 3 are stopped.

When only the hot water supply device 1 is in the hot water discharge operation, the overflow prevention water amount adjusting valve 81 prevents overflow, and the can body water flow rate Q _K1 becomes equal to the can body set flow rate Q _KS. With the target distribution ratio (Q _K / Q _B = 1 / α),
Hot water at the set temperature Ts is being discharged. When the amount of hot water discharge increases and at least one of the following increasing conditions is satisfied, the hot water discharge solenoid valve 92 of the water heater 2 is opened and the hot water discharge operation of the water heater 2 is started. [Increase condition] The can body water flow rate Q _K1 becomes 90% or more of the above can body set flow rate Q _KS (Q _K1 ≧ 0.9 · Q _KS ). The sum of the can body water flow rate Q _K1 and the bypass water flow rate Q _B1 is 90% or more of the above total set flow rate Q _TS {(Q _K1 + Q _B1 ) ≧ 0.9
・ Q _TS }. The sum of the can body water flow rate Q _K1 and the bypass water flow rate Q _B1 is 90% or more of the above total maximum flow rate Q _Tmax {(Q _K1 + Q _B1 ) ≧ 0.
9 · Q _Tmax }.

In the water quantity adjusting valve 82 with the overflow preventing function of the water heater 2 which has started the hot water discharge operation, the can body water flow rate Q _K1 of the water heater 1 is a preset K times the can body set flow rate Q _KS (for example, K = 0.5
The opening is adjusted so that Hot water heater 2 at this time
The can body set flow rate Q _KS2 of Q _KS2 is Q _KS2 = Q _K2 − (Q _KS · K−Q _K1 ).

When the amount of hot water discharged further increases, the water flow rate adjusting valve 82 with overflow prevention function of the water heater 2 is opened so that the can body water flow rate Q _{K1 of} the water heater 1 does not exceed K times the set body flow rate Q _KS. The degree is adjusted, and the amount of hot water discharged from the water heater 2 increases.
In this state, when at least any one of the above-mentioned increasing conditions is satisfied in the water heater 2, the hot water supply solenoid valve of the water heater 3
93 is opened, the hot water supply operation of the water heater 3 is started, and at this time point, the water amount adjusting valve 82 with the overflow prevention function of the water heater 2 shifts to the overflow prevention operation. At this time, the water flow rate adjusting valve 83 with the overflow prevention function of the water heater 3 is opened so that the can body water flow rate Q _K2 of the water heater 2 becomes K times the can body set flow rate Q _KS (K = 0.5). Adjusted. The can body set flow rate Q _KS3 of the water heater 3 at this time is Q _KS3 = Q _K3 − (Q _KS · K−Q _K2 ).

Next, reduction control in which the amount of hot water discharged is reduced and the number of operating units is reduced will be described. When the water heater 3 satisfies at least one of the following reduction conditions (the water flow rate of the can body Q _{K2 in the} water heater 2 is K times the set body flow rate Q _KS ), the hot water of the water heater 3 is discharged. The solenoid valve 93 is closed, and the water flow rate adjusting valve 82 with overflow prevention function of the water heater 2 is set to the preset flow rate Q _KS of the can body water flow rate Q _{K1 of} the water heater 1 from the overflow prevention opening. The opening is adjusted to double (K = 0.5).

[Reduction condition] The water flow rate Q _K3 is the minimum required water flow rate M of the water heater 3
It decreases below the sum of OQ _K and the water flow rate of a given body q _K (for example, 0.5 l / min.) (Q _K3 ≦ MOQ _K + q _K ). The sum of the can body water flow rate Q _K3 and the bypass water flow rate Q _B3 decreases below the sum of the total minimum required water flow rate MOQ _{T of the} water heater 3 and the predetermined total required water flow rate q _T (eg, 1 l / min.). {(Q _K3 + Q _B3 ) ≦ (MOQ _T + q _T )}. The sum of the can body through water Q _K3 and the bypass water Q _B3 is the total minimum setting of the water heater 3 flow Q _Tsmin. And a predetermined total set flow rate q _TS (e.g., 1l / min.) Decreases below the sum of the { (Q _K3 + Q _B3 ) ≦ (Q _TSmin. + Q _TS )}.

Furthermore, when the amount of hot water discharged decreases and the water heater 2 satisfies at least one of the above-mentioned reduction conditions (water heater 1
In this case, the can body water flow rate Q _K1 is ensured to be K times the can body set flow rate Q _KS ), and the hot water supply solenoid valve 92 of the water heater 2 is closed, and the water flow control valve 81 with the overflow prevention function 81 of the water heater 1 is closed. Continues the overflow prevention operation.

As described above, when the number of operating water heaters is increased, by controlling the flow rate of the water heater that starts the latest operation, the can body water flow rate Q _K of the water heater that has started operation before that is controlled. Maintaining a predetermined value or more (for example, controlling the flow rate of the water heater 3 to keep the can body water flow rate Q _K2 of the water heater 2 at least K times the can body set flow rate Q _KS ) to prevent deterioration of the hot water discharge characteristics. To do. Further, in the case of reducing the number of operating water heaters, when stopping the operation of the water heater that has recently started operation, by controlling the flow rate of the water heater that has started operation before that,
The can body water flow rate Q _K of the water heater that has started operation in front of the table is maintained at a predetermined value or more (for example, when the water heater 3 is stopped, the flow rate of the water heater 2 is controlled to control the water heater 1). Can body water flow Q
_K1 is kept at K times or more of the set value Q _KS of the can body), and the deterioration of the tapping property is prevented. As mentioned above, 1
When the maximum secondary pressure setting switch of any water heater is turned on while any number of water heaters from one to three are in hot water discharge operation, only that water heater shifts to maximum combustion and other water heaters The secondary solenoid valve is fully closed to adjust the maximum secondary pressure.

In the above embodiment, the target distribution ratio α was set to be the same in all the water heaters, but they are all different (α
Naturally, ₁ ≠ α ₂ ≠ α ₃ ).
Further, in the above embodiment, the can body water flow rate Q _K or the total flow rate (that is, Q
_The number of units is controlled based on the fluctuation of ( _K + Q _B ).
The number of units may be controlled based on the fluctuation of the can body water flow rate Q _K or the total flow rate (that is, Q _K + Q _B ) of an arbitrary water heater. Furthermore, in the above-mentioned embodiment, a plurality of water heaters in which water heaters having bypass paths are connected in parallel have been described, but it goes without saying that a plurality of water heaters including water heaters not having a bypass path may be used. In that case, the condition for increasing the number of water is the can body water flow rate Q _K Immediate total water flow rate Q
_{Since T} (Q _K = Q _T ), the can body water flow rate Q _K or the total water flow rate Q _T is greater than or equal to the maximum flow rate set value A, which is a times the maximum flow rate. The body water flow rate Q _K or the total water flow rate Q _T is equal to or less than the minimum flow rate set value B which is b times the minimum flow rate.

As described above, in the method of controlling a plurality of water heaters according to the present invention, when any one of the individual water heaters constituting the plurality of water heaters is turned on, the maximum secondary pressure adjusting switch is turned on. Regardless of whether or not the hot water supply device of the hot water supply device is in the hot water discharge operation, the hot water supply solenoid valve of the hot water supply device is opened and the hot water discharge solenoid valves of the other water supply devices are closed. A large amount of water is supplied by operating the hot water supply, etc., and while confirming the operation of each water heater and the number-of-units control operation, turning on the maximum secondary pressure adjustment switch of any water heater causes boiling due to the large flow rate. Since the maximum secondary pressure of the gas proportional control valve can be adjusted without fear, a trial run switch is not required.

[0023]

Since the present invention is constructed as described above, it has the following effects. When any one of the individual water heaters constituting the plurality of water heaters is turned on, the maximum secondary pressure adjustment switch is turned on, regardless of whether the water heater or another water heater is in the tapping operation. Open the hot water solenoid valve of the water heater and close the hot water solenoid valve of the other water heaters.
Turn on the maximum secondary pressure adjustment switch of any water heater while confirming the operation of each water heater and the number of units control operation by flowing a large amount of water by operating all the water heaters that compose multiple water heaters. Thus, the maximum secondary pressure of the gas proportional control valve can be adjusted without fear of boiling due to the large flow rate. Also, when the maximum secondary pressure adjustment switch of a water heater that is not burning is turned on, the hot water outlet solenoid valve of that hot water heater is opened, and the hot water outlet solenoid valves of other hot water heaters are closed. The maximum secondary pressure of all water heaters can be adjusted.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a parallel type multiple water heater to which a method for controlling multiple water heaters of the present invention is applied.

FIG. 2 is a flowchart of a method for controlling multiple water heaters according to the present invention.

[Explanation of symbols]

1, 2, 3 water heater, 4 yuan water supply channel, 5 hot water supply channel, 6
Inlet temperature sensor 7 Controller 11, 12, 13 Heat exchanger, 21, 22, 23 Inlet channel, 31, 32,
33 Hot water outlet 41, 42, 43 Bypass passage, 51, 52, 53 Inlet water flow sensor 61, 62, 63 Bypass water flow sensor, 71, 72, 73 Bypass valve 81, 82, 83 Overflow prevention water flow control valve, 91 , 92, 93
Solenoid valve 121, 122, 123 Maximum secondary pressure setting switch 131, 132, 133 Minimum secondary pressure setting switch

Claims (1)

[Claims] 1. A plurality of water heaters comprising at least two water heaters connected in parallel, each of which has a gas proportional control valve and a hot water discharge solenoid valve, and which controls the number of operating water heaters in accordance with the required amount of hot water discharge. A maximum secondary pressure adjusting switch corresponding to each water heater constituting the water heater is provided, and when the maximum secondary pressure adjusting switch of any water heater is turned on, the hot water outlet solenoid valve of that water heater is opened and the other A method for controlling a plurality of water heaters, characterized in that a hot water discharge solenoid valve of the water heater is closed.