JP2637913B2 - Hot water control device for bathtub - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot water control device for a bath tub for controlling hot water supply to a bath tub, and more particularly to a hot water control system based on remote detection of a water amount by utilizing a temperature rise caused by heating the hot water in the bath tub. It relates to a control device.

[0002]

2. Description of the Related Art In an automatic bath, detection of the amount of water in a bathtub is indispensable when controlling the amount of water in the bathtub.
In order to detect the amount of water, a water level detection device, such as a pressure switch or a water level switch, for directly detecting the water level in the bathtub was required.

[0003]

By the way, a method of transferring hot water heated on the side of the appliance body provided with heating means and the like to the bathtub side by using a pump has been adopted for the automatic bath kettle. Some have a reheating function that returns the hot water in the bathtub to the appliance body side and reheats it. In such an automatic bath kettle, there is a case where the appliance main body on which the heating means is installed is separated from the bathtub, for example, the appliance main body is installed on the first floor side of a house, and the bathtub is installed on the second floor side. In such a case, the control signal line connecting the water level detecting device installed in the bathtub to the control device for controlling the instrument body and the installation position of the control device are complicated, which requires time and effort.

[0004] In addition, there is an automatic bath kettle in which the amount of water to be supplied to the bathtub is optimized by measuring the amount of water on the side of the appliance body for detecting the water level at the bathtub side. Such a bath can supply an appropriate amount of water to the volume of the bathtub. However, since the water level in the bathtub is calculated indirectly by the appliance body, naturally the amount of water reduced by bathing etc. Cannot be detected on the instrument body side.

[0005] In any of the baths, a water level detecting device must be installed, and wiring for that is necessary.

[0006] Therefore, in such a bath kettle, it is impossible to automatically add an appropriate amount of water, and there is no control function. There was an inconvenience of having to make up for it.

Therefore, the present invention provides a bathtub hot water supply control apparatus which realizes automatic control of hot water supply to a bathtub by remotely detecting the amount of hot water in the bathtub from a rise in the temperature of the hot water in the bathtub by the heating means. The purpose is to provide.

[0008]

As shown in FIG. 1, the bath water control device of the present invention is connected to a bath (20) for storing hot water (water 4c) and a circulation port provided in the bath. Then, the hot water is supplied to the outside of the bath tub, and the hot water is supplied to the hot tub by returning the hot water to the inside of the bath tub. )
A separating means (hopper 48) installed between the water channel and the reheating circuit to separate the water from the hot water on the bathtub side; A first heat exchanger (heat exchanger 28) for heating water, a second heat exchanger (heat exchanger 22 for additional heating) for heating the hot water in the bathtub through the additional heating circuit, Heating means for heating the second heat exchanger (burner 24 for reheating), and hot water in the bath tub installed in the reheating circuit and pressure-fed into the bath via the reheating circuit. A pump (56) for stirring the hot and cold water in the bathtub, a water flow detecting means (water flow sensor 62) provided in the additional heating circuit, and detecting a flow of the hot water circulated by the operation of the pump; The clean water provided from the separation means is provided to the recirculation path. Water injection valve to or cut off from the (additionally fired-pouring switching valve 50), the temperature detecting means for detecting the hot water temperature in the bathtub is installed in add-fired circulating path (temperature sensor 70), pouring selectively setting the operation and Tsui焚operation, when the pouring operation, the said on waterways through the water injection valve is opened and additionally fired circulation path perform pouring in the bath,
For add-fired operation, the hot water in said bathtub through the add-fired circulation path by operating the pump with circulating the add-fired circulating roadside, said control means for heating the hot water to circulate with a heating means (hot water supply control apparatus And a main unit 72), the pump being driven prior to the start of the pouring or reheating operation, and the pouring if the water flow detecting means does not detect the water flow. performed pouring the operation proceeds to operation, is shifted to the add-fired operation when the water flow detecting means detects the water flow, the hot water in the bathtub to the add-fired circulating path within the bath by circulating the The hot water is pumped, and the hot water in the bath is stirred by the hot water, and the temperature of the hot water in the bath is detected by the temperature detecting means. Hot water Time required to the increase in the hot water detection temperature slightly higher than the set temperature from the temperature by heating,
The amount of heat added to the heat exchanger by the heating means,
With respect to the heat amount added to the heat exchanger by the heating means, the heat exchanger, the reheating cycle and the heat efficiency obtained by the heat amount added to the hot water through the bathtub in the bathtub with reference to the heat efficiency . The remaining water amount is calculated, the remaining water amount is compared with the set water amount, the shortage amount is calculated, and then the operation is shifted to the pouring operation, and the shortage water amount is switched from the clean water side by switching the water injection valve. Is supplied to the bathtub through the additional heating circuit, and the amount of hot water in the bathtub is controlled to a set water amount, and then the temperature of the hot water in the bathtub is detected. If the temperature is lower than the set temperature, and wherein the raising boiling until more set temperature to the second heat exchanger.

In the hot water supply control device for a bathtub, the heat
Efficiency η is determined by setting the amount of water poured into the bathtub as Q₀And said
Driving a pump through the reheating circuit in the bathtub
The detected temperature of hot water detected after stirring the hot water is T1, a bathtub.
The set temperature of hot and cold water in the inside is T2,
When the heat exchanger is boiled, the heat exchanger is provided with the heating means.
The amount of heat added from
Time to reach constant temperature is t₀Where η = Q₀× (T2−T1) / S × t₀  It is characterized by what was obtained from.

[0010]

The bath water control device detects the amount of water using hot water as a medium, calculates the amount of water shortage with respect to the set water amount, supplies the amount of water shortage as warm water from the clean water side, and performs the detection based on the temperature detection again. By performing heating,
The water volume and temperature in the bathtub are controlled to set values. These controls will be described in order.

First, the amount of water in the bathtub is detected. That is, the hot and cold water in the bathtub can be circulated through the reheating circuit. That is, the hot and cold water in the bathtub is drawn out to the additional firing circuit, and is then sent to the bathtub side by pressure. As a result, the hot and cold water in the bathtub is stirred. Further, the hot and cold water in the bathtub is heated by the second heating means on the side of the additional heating circulation path.

As a result of this heating, the temperature of the hot and cold water in the bathtub becomes
If the temperature rises by the specific temperature ΔT, the specific temperature ΔT
When the t the heating time required to rise, the amount of heat obtained by adding the thermal efficiency of the system in heating capacity of the heating means as the amount of heat applied to the hot water and N _0, the water amount Q in the bathtub, Q = N ₀ · t / ΔT (1) From this equation (1), the amount of water Q in the bathtub is calculated indirectly. In this case, it is also possible to calculate the amount of water Q in the bathtub by measuring the rising temperature ΔT of the hot water at the unit time t. This water amount Q represents the current water amount in the bathtub.

Next, the amount of water shortage in the bathtub is calculated. Comparing the current water Q and tub set water amount _{Q 0,} these differences moisture deficiency Delta] Q becomes, i.e., the moisture deficiency Delta] Q is given by _{ΔQ = Q 0 -Q ··· (2} ).

Next, hot water, that is, hot water is supplied from the water supply side with respect to the shortage water amount ΔQ. This hot water supply control is a supply of a required amount of clean water from the clean water channel and heating of the clean water. That is,
A water injection valve is provided as means for switching the supply of clean water, that is, hot water, from the clean water channel to the reheating circuit. When supplying clean water, the water supply valve is opened and clean water is supplied to the bathtub through the reheating circuit. In this case, the supply amount of the clean water is detected through the water amount detecting means. Therefore, it is detected that the shortage water amount ΔQ has been supplied to the bathtub through the additional heating circuit, and based on the detection result, the water injection valve is switched to shut off the upper water channel side.

Then, in response to the supply of the clean water, the first heating means is operated to heat the clean water. The clean water is heated and supplied to the reheating circuit. As a result, hot water is supplied to the bathtub for the amount of water shortage.

Next, the temperature of hot and cold water in the bathtub is detected. That is, the detection is performed by the temperature detection means on the side of the reheating circuit. Even if hot water is supplied from the clean water side, the hot water in the bath tub may not reach the set temperature due to mixing with the hot water in the current bath tub or the hot water in the reheating circuit.

Next, the hot water in the bathtub is heated. This heats the hot and cold water in the bathtub to the set temperature, that is, the optimum temperature by the second heating means on the circulation path side. As a result, the hot and cold water in the bathtub is controlled to the set water amount and the set temperature.

As a result of such processing, the hot water control apparatus for a bath tub according to the present invention circulates through the circulation path to stir the hot water in the bath tub, and also heats the hot water in the bath tub by a heating means. Detect and calculate the current water amount in the bathtub based on it, calculate the difference between this water amount and the set water amount, that is, calculate the shortage amount, supply the shortage amount from the upper water channel to the bathtub through the circulation path, and After controlling the water amount to the set water amount, the temperature of the hot water in the bathtub is detected again, and the bath is heated by the heating means. As a result, the hot and cold water in the bathtub is controlled to the set water amount and the set temperature as quickly as possible.

The thermal efficiency referred to when calculating the amount of residual water in the bathtub contributes to accurate calculation of the amount of water by calculating using the above equation.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments shown in the drawings.

FIG. 1 shows an embodiment of a bath water control apparatus according to the present invention. Water 4a as tap water supplied from a water supply or the like passes through a hot water supply water flow switch 26 provided in the water supply channel 11, whereby the water flow is electrically detected, and Dw1 is obtained by the hot water supply water flow switch 26. Indicates the hot water flow detection signal. The water 4a is heated by the first heat exchanger 28 and the hot water supply burner 30.

The hot water supply burner 30 is provided with a combustion gas 32.
Cv1 is supplied via a base valve 34 and a hot water supply valve 36 whose opening and closing are controlled electrically, and Cv1 is an opening / closing control signal of the base valve 34, Cv2
Represents an open / close control signal for the hot water supply valve 36. Hot water supply burner 30
Is supplied by an igniter 38 that is electrically ignited as ignition means, and Sf1 represents the ignition signal. The presence or absence of ignition of the gas 32 is determined by a flame detector 4 called a flame rod for electrically detecting the presence or absence of a flame.
0 is detected, and Df1 represents an ignition detection signal.

The hot water 4b as the tap water heated by passing through the heat exchanger 28 is provided as hot water temperature detecting means, and is provided with a hot water temperature sensor 42 constituted by a thermistor for electrically detecting the hot water temperature. And its temperature is detected. At1 represents the hot water supply temperature detection signal. The hot water 4b that has passed through the hot water supply temperature sensor 42 is guided to a hot water supply / hot water switch valve 44 that electrically switches the hot water supply / hot water supply direction, and is supplied to the hot water supply port 46a by a hot water supply / hot water switch signal Sh1. The supply and the pouring to the bathtub 20 b are switched. That is, the hot water / pour switching valve 44 is
A water injection valve for supplying clean water to the circulation path side is configured.

The flow rate of the hot water 4b guided to the pouring side b via the hot water / pour switching valve 44 is detected by a flow rate sensor 47 for electrically detecting the flow rate, and Dm represents a flow rate detection signal. Hot water 4b that has passed through this flow sensor 47
Is a hopper 4 as a separation means for separating and shutting off the water supply side.
After passing through 8, it is guided to the additional heating / pouring switching valve 50 for electrically switching the hot water supply direction, and is switched to the additional heating / pouring side in accordance with the additional heating / pouring switching signal Sh <b> 2.

In this case, on the pouring side c, the hot water 4b is supplied from a pipe 52 directly connected to the bathtub 20 via a pump 56 for electrically circulating water to the bathtub 20 in the direction indicated by the arrow B. Supplied. Dr represents a pump drive signal for driving the pump 56.

On the additional heating side d, the additional heating and pouring switching valve 5 is provided.
0, the pouring is prohibited, and the water 4c as hot water in the bathtub 20 for reheating the bathtub 20 is reheated in the direction shown by the arrow A through the circulation port 54 in the bathtub 20. A pump 56 circulates the pressure by a pump 56 in a reheating circuit 60 as a circulation path including a reheating side passage of the pouring switch valve 50. That is, the supplementary heating / pouring water switching valve 50 constitutes a water pouring valve for supplying clean water to the circulation path side similarly to the hot water supply / pouring water switching valve 44. Then, as a result of pumping the water 4c toward the bathtub 20 by the pump 56, a water flow is generated in the bathtub 20, and as a result, stirring is performed.

[0027] The water 4c passing through the additional firing circulation line 60 is
Dw2 is detected by a water flow sensor 62 as a water flow detection means for electrically detecting the presence or absence of a water flow, and Dw2 represents the detection signal.

A reheating heat exchanger 22 as a second heat exchanger is installed in the reheating circuit 60, and the water 4 c in the bathtub 20 is heated by the combustion of the reheating burner 24. In this case, the combustion gas 32 is supplied to the reburning burner 24 via a reburning gas valve 64 whose opening and closing are controlled electrically.
Opening / closing of the supplementary gas valve 64 is controlled by an opening / closing control signal Cv3. The gas 32 supplied to the reburning burner 24 is
As in the case of the hot water supply burner 30, it is ignited by an igniter 66 that is electrically ignited as ignition means, and Sf2
Represents the ignition signal. The presence or absence of ignition of the gas 32 is detected by a flame detector 68 that electrically detects the presence or absence of a flame.
f2 represents an ignition detection signal.

Then, the bathtub 20 heated by reheating is used.
The internal water 4c is detected by a temperature sensor 70 composed of a thermistor or the like for electrically detecting the water temperature on the side of the additional heating circulation pipe 60, and At2 represents the temperature detection signal.

The heating system for the water 4a, the system for supplying the hot water 4b to the bathtub 20, or the reheating circuit of the water 4c in the bathtub 20 are controlled by a hot water supply control device for heating, supplying or reheating shown in FIG. Controlled.

This hot water supply control device is composed of a main device 72 and a remote controller 74. The main device 72 is installed on the appliance body side where the heat exchangers 22 and 28 are installed. Numeral 74 is installed in the bathtub 20 in a bathroom or the like that can be adjusted as desired by a bather.

Digital data of the hot water supply water flow detection signal Dw1, the hot water supply side ignition detection signal Df1, the hot water supply side water flow rate detection signal Dm, the additional heating water flow detection signal Dw2, and the additional heating ignition detection signal Df2 are supplied to the input circuit 721. After that, it is taken into the central processing unit (CPU) 722. Further, since the hot water supply temperature detection signal At1 and the additional heating temperature detection signal At2 are analog signals, the multiplexer 72 provided at the input unit is used.
The signals are alternately added to the analog-to-digital conversion circuit 723 by the self-division by 4 and are subjected to analog-to-digital conversion.

The CPU 722 performs arithmetic processing according to a heating, supply or reheating control program written in a write-only storage element (ROM) 725. In addition, the various types of data and data on the arithmetic processing are written to a storage element (RAM) 726 that can be freely written and read.

A command for heating, supply or reheating control is performed by operating a switch of a remote controller 74, and the command signal is applied to a remote control transmission / reception circuit 727, and the CPU
It is taken in.

The hot water supply side ignition signal Sf1, the open / close control signal Cv1, the hot water supply side open / close control signal Cv2, the additional heating side open / close control signal Cv3, the additional heating side ignition signal Sf2, which are various control outputs as the calculation results of the CPU 722. The pouring switch signal Sh1, the additional heating / pouring switch signal Sh2, and the pump drive signal Dr are added to the control target from the output circuit 728, respectively.

In the bath water control device, the bath tub 2
The water amount control at the time of additional firing within 0 will be described in the order of steps.

(A) The hot water supply / pour-in switching valve 44 is switched to the hot water supply side a, and the additional heating / pouring-in switching valve 50 is switched to the additional heating side d, and the additional heating mode is set with the additional heating circulation line 60 as a closed loop. I do.

(B) After setting the reheating mode, the pump 56 is driven to set the temperature of the water 4c in the bathtub 20 to a uniform temperature T. In that case, the water temperature T of the bathtub 20 is detected by the temperature sensor 70.

(C) The temperature of the water in the bathtub 20 is kept at a constant temperature T.
After that, the main valve 34 and the reheating gas valve 64 are opened, and the ignition signal Sf2 is given to the igniter 66 to cause a current to flow to discharge and ignite the reheating burner 24.

(D) While the water 4c is circulated by the pump 56, the temperature of the water 4c in the bathtub 20 is evenly increased by a temperature ΔT slightly higher than the appropriate temperature T by reburning combustion, and The required time t to ΔT is measured and written in the RAM 726.

(E) Assuming that the reburning combustion capacity N by the combustion of the reburning burner 24 is measured in advance and stored in the ROM 725, the water amount Q in the bathtub 20 becomes CP
In U722, Q = N · t / ΔT is calculated from equation (1). For example, when ΔT = 1 ° C., the water amount Q in the bathtub 20 is Q = N · t.

The calculation of the amount of water Q in the bathtub 20 is as follows.
The temperature rise ΔT may be detected for a certain time t, and the temperature rise ΔT may be stored in the RAM 726 and calculated from the equation (1).

[0043] (f) The lack of water in advance, the setting water _{Q 0} from the volume of the tub 20 is determined, it is placed by setting the remote controller 74, and its set water amount _{Q 0,} in the bathtub 20 From the detected water amount Q, the difference water amount ΔQ is calculated by the equation (2).

(G) Therefore, the hot water 4 having the difference water amount ΔQ
b in order to supply b into the bathtub 20.
The hot water 4 b is supplied into the bathtub 20 by switching the pouring side b and the reheating / pouring switching valve 50 to the pouring side c.

(H) Next, the hot water supply / pour switching valve 44 is switched to the hot water supply side a and the additional heating / pouring switching valve 50 is switched to the additional heating side d to boil the hot water 4b in the bathtub 20 to the appropriate temperature T. To complete the pouring and reheating to the appropriate water volume and temperature.

When the heat retention and hot water control are performed by using the steps (a) to (h), the pouring into the bathtub 20 and the reheating are automatically repeated at regular time intervals. Thereby, optimal control for keeping the water amount Q and the temperature T in the bathtub 20 constant can be performed.

Further, the boiling time t due to the reheating combustion measured in the step (d) is influenced by the thermal efficiency. Factors that reduce the thermal efficiency include the material of the bathtub, the reheating piping, the outside air temperature and the equipment. There is an error in the inherent gas pressure set value. Therefore, the thermal efficiency η is calculated by the following equation using the following formula: η = Q ₀ × (T 2 −T 1) / S × t ₀ (3)
6, and the value is updated each time additional heating is performed. However, Q ₀ is set water (= Note hot water amount), T1 uniform temperature of the water supplied to the tub 20 at the pouring operation, T2 is boiling up uniform temperature (= boiling up set temperature), t ₀ is boiling The ascending time, S is the reheating input capacity, that is, the reheating burner 24
Is the amount of heat added to the reheating heat exchanger 22 by the combustion of.

In this case, the reheating input capacity S is set to R
The reheating combustion capacity N is stored in the OM 725, and is given by the product of the reheating input capacity S and the thermal efficiency η (N = S · η).

In the detection and control of the amount of water in the bathtub 20, when the water level hw is lower than the circulation port 54 in the bathtub 20, as shown in FIG. Since the water does not circulate in the circulation line 60, it can be determined from the water flow detection signal Dw2 of the water flow sensor 62. In this case, the mode does not shift to the reheating mode.

In this case, the hot water supply / pour switching valve 44 is switched to the pouring side b, and the additional heating / pour switching valve 50 is switched to the pouring side c, which corresponds to 1/2 of the set appropriate water level hw ₀ of the bathtub 20. After the water level is raised above the circulation port 54 by supplying the amount of water to be supplied, the operations of the steps (a) to (h) are performed, which corresponds to １ ／ of the set appropriate water level hw ₀ of the bathtub 20. If the water flow sensor 62 does not detect the water flow even when the water amount is supplied, the water supply unit further supplies （(= ×× １ ／) of the set appropriate water level hw ₀ . Still, when the water flow sensor 62 does not detect the water flow, １ ／ of the set appropriate water level hw ₀ (= １ ／ × 1)
/ 2 x 1/2). Such a supply operation is tried sequentially until the water flow sensor 62 detects a water flow.

[0051]

As described above, according to the present invention, without installing a water amount detector or a signal line on the bathtub side,
Using the heating by the existing heating means, the amount of water is calculated remotely from the rise in the temperature of the hot water in the bathtub, the amount of water shortage with respect to the set amount of water is calculated, and the clean water corresponding to this amount of water shortage is heated to warm water. Meanwhile, hot water can be supplied to the bathtub from the waterway side through the circulation path, and after controlling the water amount in the bathtub to the set water amount, reheating is performed based on the temperature detection to heat the hot water in the bathtub. Even when the main unit and the bathtub are far apart, the bathtub water volume and the bathwater temperature in the bathtub can be controlled with high accuracy, and the bather can remove the hot water in the bathtub without having to add the necessary hot water. It is possible to quickly control and optimize the optimum water amount and temperature.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a hot water control apparatus for a bathtub according to the present invention.

FIG. 2 is a block diagram illustrating a hot water supply control unit of the hot tub control device of the bathtub illustrated in FIG. 1;

FIG. 3 is a diagram showing a relationship between a circulation port of a bathtub and a water level.

[Explanation of symbols]

 4c Water (hot water) 11 Upper waterway 20 Bath tub 22 Heat exchanger for additional heating (second heating means) 24 Burner for additional heating (heating means) 28 Heat exchanger (first heating means) 44 Switching between hot water supply and hot water supply Valve (water injection valve) 47 Water flow rate sensor (flow rate detection means) 48 Hopper (separation means) 50 Reheating / pour-in switching valve (water injection valve) 60 Reheating circulation line (circulation path) 62 Water flow sensor 70 Temperature sensor (temperature) Detecting means) 72 Main device (control means)

Claims (2)

(57) [Claims] 1. A reheating circuit comprising a bath for storing hot water, a pipe connected to a circulation port provided in the bath for guiding the hot water out of the bath, and returning the hot water to the inside of the bath. A water channel for guiding clean water to a reheating circuit, separating means provided between the clean water channel and the reheat circuit to separate the clean water and the hot water on the bathtub side, A first heat exchanger installed on the side to heat the clean water, a second heat exchanger to heat the hot water in the bathtub through the reheating circuit, and heating the second heat exchanger A heating unit that is installed in the reheating circuit and a pump that pumps the hot water in the bathtub into the bathtub through the reheating circuit and agitates the hot water in the bathtub; A water flow provided in a circulation path and circulated by the operation of the pump is detected. A flow detection means, a water injection valve provided in the reheating circuit, for supplying or shutting off the clean water from the separation means side to the reheating circuit side, and the bathtub provided in the reheating circuit. temperature detecting means for detecting the hot water temperature of the inner, selectively setting the pouring operation and Tsui焚operation, when the pouring operation, and the upper water passage through the water injection valve and said add-fired circulating path opened to thereby perform poured into the bathtub, when the add-fired operation,
By operating the pump to circulate the hot and cold water in the bathtub through the reheating circuit to the reheating circuit side,
Control means for heating the hot and cold water circulated by the heating means, comprising: a hot water control apparatus for a bath tub, wherein the pump is driven prior to the start of pouring or reheating operation, and the water flow detecting means detects the water flow. If not detected performs pouring transitions to the pouring operation, when the water flow detecting means detects the water flow is shifted to the add-fired operation, the add-fired circulating passage the hot water in the bathtub Circulating the water in the bathtub, pumping the hot water in the bathtub to stir the hot water in the bathtub, detecting the temperature of the hot water in the bathtub by the temperature detecting means, and operating the heating means. the second slightly higher temperature than the set temperature hot water from the heating to the hot water detection temperature inside the tub through the heat exchanger
The time required for raising, the amount of heat applied to the second heat exchanger by the heating means, and the amount of heat applied to the second heat exchanger by the
The remaining water amount in the bathtub is calculated by referring to the heat efficiency of the heat exchanger, the heat efficiency obtained by the amount of heat added to the hot water through the reheating circuit and the bathtub, and the remaining water amount is compared with a set water amount. After the shortage amount is calculated, the operation is shifted to the pouring operation, and the bathtub is passed through the reheating circuit while heating the shortage amount from the clean water side by the first heat exchanger by switching the water injection valve. After controlling the amount of hot water in the bathtub to the set water amount, the temperature of the hot water in the bathtub is detected, and when the temperature is lower than the set temperature, the water is heated to the set temperature by the second heat exchanger. A hot and cold water control device for a bathtub. 2. The thermal efficiency η is defined as a set amount of water poured into the bathtub Q _O , a temperature of the hot water detected after the pump is driven and the hot water in the bathtub is stirred through the additional heating circuit. T1, the set temperature of hot and cold water in the bathtub is T2, and the amount of heat applied from the heating means to the second heat exchanger when boiling the second heat exchanger to the set temperature T2 is S. when the time from the temperature T1 to reach the set temperature and _{t O, η = Q O ×} (T2-T1) / S × hot water bath of claim 1, wherein a obtained from t _O Control device.