DE3878118T2 - HEATING WATER UNIT. - Google Patents

Description

The present invention relates to a storage type boiling water appliance or a hot water storage appliance using an electric heating element as its heat source.

Description of the related art

Hot water heating or storage devices using an electric heating element as their heat source can be divided into two types, i.e., an instantaneous type and a storage type. The instantaneous type is designed to heat water to a predetermined temperature instantaneously by means of an electric heating element of large capacity to be supplied as hot water. The storage type is designed to store hot water of a predetermined temperature in a hot water container or tank in advance and to be supplied as needed. Normally, the instantaneous type hot water devices cannot produce hot water of a satisfactory temperature unless they use an electric heating element of large capacity of 5 - 20 kW. Therefore, only storage type hot water devices are used for domestic purposes.

Typically, storage hot water appliances comprise a hot water tank encased in a thermal insulator. The lower section of the inside of the tank is connected to a water feed pipe, while the upper section is connected to a water tap via a hot water feed pipe. The lower section of the hot water tank contains an encased electric heating element. The heating element is supplied with electrical energy to heat all the water contained in the tank to e.g. 80ºC during a period when no hot water is being used, e.g. at midnight. There are two systems for supplying energy (electricity) to the heating element: a continuous power supply system and a night power supply system. In the continuous system, the energy or electricity supply to the heating element starts at any or a given time and it stops when all the water in the tank reaches a predetermined temperature.

In the night power supply system, the power supply to the heating element starts at midnight when the electrical loads (electricity consumption) are comparatively small and it is terminated when all the water in the tank reaches a predetermined temperature. For economic reasons, the night power supply system is more widely used. This system is provided with a timer or clock switch that starts operation at a predetermined time each day, for example, thereby regulating the power supply to the electric heating element. The timer switch is under the control of an electricity supplier and is not accessible to users.

However, these storage hot water appliances suffer from the following disadvantages which will be described in connection with an appliance using the continuous current supply system. When the electric heating element is activated, the water in the hot water tank is gradually heated by natural convection. The rate of rise of the water temperature depends on the efficiency of the heating element and the capacity of the tank. However, it is difficult to incorporate an electric heating element of high power into an appliance for domestic use. In order to fulfil its function as a storage type version, the appliance must have a hot water tank with a capacity of at least several hundred litres. The rate of rise of the water temperature in the tank is therefore not very high. If all the water in the tank is heated to, for example, 80ºC, the energy or Power supply to the heating element is terminated. In the case of a storage hot water appliance using the continuous power supply system, it therefore takes a long time to heat the water in the tank to the correct operating temperature of, for example, 80ºC. In addition, all the water in the tank is heated to the target temperature of 80ºC, regardless of the amount of hot water actually required. Therefore, if the amount of hot water required per day and the capacity of the tank are 100 l and 300 l respectively, energy is wasted needlessly heating 200 l of water to 80ºC. This also applies to the night-time power supply system. In a storage hot water appliance using the night-time power supply system, power is only allowed during the limited period. Therefore, to avoid a shortage of hot water during the day, the hot water tank must have a large capacity. The hot water appliance therefore requires a larger installation space and may waste electrical energy to a greater extent. In addition, the conventional hot water storage device based on the post-flow feed system stores the hot water at 80ºC in the hot water tank at midnight. During the day, the hot water can be used immediately as long as it is in the tank. However, if there is a shortage, there is no hot water available during the day.

To avoid these unfavorable conditions, an improved hot water storage device (or hot water storage boiler) is proposed. In this device, a bubble pump having an electric heating element as its heat source is connected in parallel with a hot water tank so that hot water of a predetermined temperature can be stored in the tank in a layer of a certain thickness by selectively operating the bubble pump. By means of this arrangement, a required amount of hot water of a suitable temperature, e.g. 80ºC, can be stored in the hot water tank in a short time. As a result, the demand for hot water can be met so quickly that there is no need for a hot water tank of a large capacity. and the waste of electrical energy can be limited.

The hot water appliance with the bubble pump therefore has many advantages over the appliances based on the natural convection heating system. However, with this improved hot water appliance, when the temperature of the feed water changes depending on the season, the hot water stored in the hot water tank varies accordingly. The hot water cannot therefore be used reliably. In addition, the noise of the bubbles breaking up in the bubble pump is so loud that the installation locations for the appliance are limited.

AT-B-310 316 describes a hot water appliance with a hot water tank, an upper end of which is provided with a hot water feed inlet and a lower end with a water feed inlet. A hot water feed pipe for discharging the hot water from the hot water tank to the outside is connected to the hot water feed inlet. A water feed pipe for feeding water into the hot water tank is connected to the water feed inlet. Water heating devices are arranged on the outside of the hot water tank for withdrawing water from the lower section of the interior of the tank, for heating this water and for feeding the heated water into the upper section of the hot water tank.

An object of the present invention is to provide a hot water storage device which can stabilize the temperature of the stored hot water and reduce the noise level without affecting the characteristics of a bladder pump which is connected as a heating element in parallel with a hot water tank.

The present invention relates to a hot water storage device comprising a water-containing hot water tank having an upper end provided with a hot water feed inlet and a lower end provided with a Water feed inlet, a hot water feed pipe connected to the hot water feed inlet for discharging the hot water from the tank to the outside, a water feed unit connected to the water feed inlet for introducing water into the hot water tank and a water heating device arranged outside the hot water tank or on its outside for withdrawing water from the lower section of the interior of the tank, heating the water and introducing the heated water into the upper section of the hot water tank, characterized in that the water heating device comprises a bubble pump unit with a body having a boiling chamber, (a) heating element(s) for heating the water in the boiling chamber and for generating bubbles in the water, a first connecting pipe for guiding the water from the lower section in the hot water tank to the body, a guide pipe for feeding the water fed via the first connecting pipe into the boiling chamber and for condensing bubbles by the water fed via the guide pipe, a second connecting pipe for introducing the water heated in the boiling chamber into the upper portion in the hot water tank and first and second control units arranged in the first and second connecting pipes for allowing the water to flow only from the lower portion of the hot water tank to the upper portion thereof, the guide pipe being arranged with respect to the pump body so that heat exchange takes place between the water in the boiling chamber and the water flowing through the guide pipe.

A better understanding of this invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

Fig. 1 to 8 show a hot water storage device according to an embodiment of the present invention, in detail:

Fig. 1 is a sectional view showing an outline of the device;

Fig. 2 is an enlarged sectional view of a bladder pump;

Fig. 3 is a schematic diagram of a power supply system of the device;

Fig. 4A and 4B are schematic representations of different operating states of the bubble pump;

Fig. 5 and 6 are a schematic representation of the bubble pump and a graphical representation of the relationship between the temperature changes of the inflow water and outflow water in the bubble pump, respectively;

Fig. 7 is an oscillogram showing the relationship between the respective temperatures of the inflow water and the outflow water in the bubble pump; and

Fig. 8 is a graph comparing the temperature change characteristics of the discharge water of the bubble pump according to the first embodiment and the discharge water of another bubble pump; and

Fig. 9 and 10 show a bladder pump according to another embodiment of the present invention, in detail:

Fig. 9 is a longitudinal sectional view; and

Fig. 10 is a cross-section along the line X-X in Fig. 9

A hot water storage device according to an embodiment of the present invention is described in detail below with reference to Figures 1 to 8 of the accompanying drawings.

According to Figure 1, the hot water storage device comprises a substantially cylindrical hot water container or tank 11, which is closed at both ends and extends essentially in a vertical direction. The tank 11 is covered with a heat-insulating structure 12.

A water feed inlet 13 is formed in the bottom wall of the hot water tank 11, to which one end of a water feed pipe 14 is connected. The other end of the pipe 14 is connected to a water supply, not shown, e.g. tap water. A pressure reducing valve 15 is connected to the pipe 14 (in the middle area); this serves to reduce the pressure of the water fed into the tank 11 via the pipe 14 to 1 kg/cm² or less. The upper wall of the tank 11 is provided with a hot water feed inlet 16, through which the hot water contained in the tank can be discharged or discharged to the outside. The inlet 16 is connected via a hot water feed pipe 17 to a water tap 18 in a kitchen, a bathroom or the like. Normally, the tank 11 is filled with water and is subjected to the pressure of the water supplied via the pipe 14. When the water tap 18 is opened, the water contained in the tank 11 is thus discharged to the outside via the feed inlet 16 and the feed pipe 17.

A bubble pump unit 20 extending parallel to the hot water tank 11 is embedded in the heat-insulating structure 12. According to Figures 1 and 2, the pump unit 20 comprises a pump body 27 which extends in a vertical direction. The pump body made of copper or aluminum is in the form of a cylinder, for example with a thickness of 1.5 mm, an inner diameter of 34 mm and a length of 70 mm. Openings or bores provided at the upper and lower ends of the pump body 27 are closed by upper and lower end walls 31 and 28, respectively. The lower end wall 28 is provided with an inlet 29 which is connected via a first connecting pipe 30 to a suction inlet 21 in the bottom wall of the tank 11. An outlet 32 is formed in the upper end wall 31, which is connected via a second connecting pipe 33 to a discharge inlet 22 in the upper wall of the tank 11. The tank 11, the pipe 30, the pump body 27 and the pipe 33 thus form a closed loop through which water flows.

First and second separating plates 34 and 37 are arranged inside the pump body 27, facing the lower and upper end walls 28 and 31, respectively. The interior of the body 27 is divided into three chambers by plates 34 and 37. These chambers comprise a lower valve chamber 23a defined between the wall 28 and the plate 34, an upper valve chamber 23b defined between the wall 31 and the plate 37, and a boiling chamber 67 defined between the plates 34 and 37. A first guide tube 36 is arranged inside the boiling chamber coaxially to the pump body 27, which consists, for example, of a tube made of stainless steel with an external diameter of 14 mm. The lower end of the guide tube 36 is connected in a liquid-tight manner to an opening or bore 35 formed in the first partition plate 34, while the upper end of the tube 36 extends close to the second partition plate 37. The water conducted from the hot water tank 11 via the first connecting tube 30 to the lower valve chamber 23a thus flows through the guide tube 36 and is fed into the boiling chamber 67 via an opening at the upper end or a discharge opening of the tube 36. Inside the boiling chamber there is also a second guide tube 39 made of stainless steel tubing, which is arranged coaxially to the first guide tube 36. The tube 39 has an outer diameter that is smaller than the inner diameter of the pump body 27 and an inner diameter that is larger than the outer diameter of the tube 36. The upper end of the tube 39 is attached to the underside of the second partition plate 37, communicating with the hole 38 in the plate 37. The lower end of the tube 39 extends to the position in which it overlaps the upper end portion of the tube 36. The upper end portion of the first guide tube 36 is thus inserted into the lower end portion of the second guide tube 39. Inside the second guide tube, a third partition plate 40 is attached facing the upper end of the tube 36. Several Communication holes 41 are formed in the portion of the peripheral wall of the pipe 39 located between the second and third partition plates 37 and 40. The water discharged from the discharge hole or outlet of the pipe 36 thus passes between the outer peripheral surface of the pipe 36 and the inner peripheral surface of the pipe 39 to enter the boiling chamber 67. In the boiling chamber 67, the water passes between the outer peripheral surface of the second guide pipe 39 and the inner peripheral surface of the pump body 27, being led into the hot water tank 11 via the communication holes 41, the bore 38, the upper valve chamber 23b and the second communication pipe 33.

Check valves 25 and 26 are provided in the lower and upper valve chambers 23a and 23b, respectively. The valve 25 comprises a valve seat formed by the peripheral edge of the bore 29 and a ball 42 made of a heat-resistant plastic arranged in the chamber 23a and cooperating with the valve seat. The valve 25 only allows the water to flow from the first connecting pipe 30 towards the pump body 27. Likewise, the valve 26 comprises a valve seat formed by the peripheral edge of the bore 38 and a ball 43 made of a heat-resistant plastic arranged in the chamber 23 and cooperating with the valve seat. The valve 26 only allows the water to flow from the body 27 to the second connecting pipe 33.

The bubble pump unit 20 is provided with first and second sheathed electric heaters 24a and 24b, respectively, which serve as heating means for heating the water in the boiling chamber 67. The heaters 24a and 24b, each having an output of, for example, 2 kW and 4 kW, respectively, are wound around the portions of the outer peripheral surface of the pump body 27 between the first partition plate 34 and the lower end of the second guide tube 39 and fixed by brazing.

A junction box 44 is attached to the outer surface of the heat-insulating structure. The first and second heating elements 24a and 24b are connected to power systems 45 and 46, respectively, as shown in Figure 3, through the junction box. System 45 is designed to selectively energize heating element 24a from a mains power source. In particular, system 45 is designed so that upon actuation of a push button switch 50 after turning a knob 49 of a delayed action timer switch 48 when a manual switch 47 is closed, heating element 24a can be supplied with power or with energy for a period of time set by the timer switch. System 46 is a night power supply system which allows savings in electricity charges. In particular, system 46 is a combination of a timer and switches; this system is capable of initiating power supply to electrical heating element 24b at a scheduled time, e.g., at 11 p.m. each day. Furthermore, the system 46 is designed to take an output signal S1 from a temperature sensor 51 mounted on the lower portion of the hot water tank 11 and to switch off the power supply to the heating element 24b when the temperature of the water in the lower portion of the tank 11 rises or has risen to, for example, 80ºC. In Fig. 1, the numerals 52 and 53 designate a flow control valve and a conventional float type vent valve, respectively.

The operation and application of the hot water storage device with the structure described above are explained below.

First, assume that the hot water tank 11 is filled with low-temperature water and the faucet 18 is closed. In this state, there is no water flow, so that both check valves 25 and 26 are closed and the bubble pump unit 20 is filled with the low-temperature water.

In this state, the button 49 of the timer switch 48 is operated to set a desired time limit. Then the switch 47 is closed and the Push button switch 50 is pressed. This causes the electric heating element 24a to be energized. As the heating element 24a is energized, the portion of the water in the boiling chamber 67 which is in contact with the inner surface of the pump body 27 within the heating element 24a is rapidly heated. When the temperature of the portion of the water in the chamber 67 reaches the boiling point, air bubbles 61 are generated in the manner shown in Figure 4A. As a result, the water rapidly increases in volume, thereby increasing the pressure within the boiling chamber 67. The check valve 26 is then opened so that the boiling water is discharged from the pump body 27 into the second connecting pipe 33 in the manner shown by solid arrows 62 in Figure 4A. When the bubbles 61 rise under their buoyancy and reach the level of the lower end portion of the second guide tube 39, they are cooled and condensed by the relatively cold water in the region of the lower end portion of the tube 39. As a result, the pressure inside the chamber 67 is reduced. The check valves 26 and 25 are then closed and opened respectively in the manner shown in Figure 4B, so that the cold water in the lower portion of the hot water tank 11 flows into the boiling chamber 67 via the first connecting tube 30 and the guide tubes 36 and 39. As a result, the temperature of the water in the chamber 67 continues to decrease, so that the bubbles 61 quickly disappear. The water then no longer flows in via the tube 30. The temperature of the water in the chamber 67 thus begins to rise again, so that bubbles 61 are again generated. The above-mentioned processes are then repeated within the time limit set by means of the timer switch 48. In this way, hot water or warm water of eg 80ºC is intermittently discharged from the pump body 27.

The discharged hot water is guided via the second connecting pipe 33 to be fed into the upper section of the hot water tank 11 via the discharge inlet or outlet 22. The 80ºC warm water 64 thus collects in thermally stratified in the tank 11 as shown in Fig. 1. The thickness of the thermal layer can be freely adjusted by changing the activation time of the electric heating element 24a, ie the time limit set by the timer switch 48. In the above-described case, the hot water is stored as required by the power supply system 45. In this embodiment, however, the system 46 is provided as a night power supply system which automatically supplies power to the electric heating element 24b at 11 p.m. The 80ºC warm water accumulates in the hot water tank 11 in the same way as described above.

In the hot water storage device having the bubble pump unit 20 having the described structure, even if the temperature of the water supplied to the hot water tank 11 via the water supply pipe 14 varies depending on the season or the like, the fluctuation in the temperature of the hot water supplied by the pump unit 20 can be kept relatively small, and the breaking noise of the bubbles can also be reduced. More specifically, the water is supplied to the boiling chamber 67 of the pump unit 20 via the first guide pipe 36 and the space between the first and second guide pipes 36 and 39. All of these pipes have thermal conductivity. Figure 5 illustrates in a simulated manner the flows of water and heat in the pump unit 20. As the water of temperature Tw supplied via the first connecting pipe 30 rises in the first guide pipe 36, it exchanges heat with water 66 contained in the boiling chamber 67, which boils at a temperature Ts under the influence of heat from the electric heating element 65, so that its temperature increases to Tb. When the temperature of the water between the first and second guide pipes 36 and 39 then decreases to the temperature Tb, the water exchanges heat with the water of temperature Ts rising from the chamber 67, so that its temperature increases to Tc. Water of temperature Th, which is lower than Ts, is then supplied via the upper check valve 26.

In the following, two cases are considered using Figure 6 in which the feed water temperature Tw is equal to Tw1 and Tw2 (Tw1 < Tw2).

If the temperature Tb at the feed water temperature is equal to Tb1 and Tb2 is equal to Twl or Tw2, the average temperatures Tm1 and Tm2 are Tml = (Tw1 + Tb1) /2 . . . (1) Tm2 = (Tw2 + Tb2) /2 . .. (2)

It is assumed that Tb1 - Tw1 =Δt1, Tb2 - Tw2 =Δt2, Ts - Tm1 =ΔT1 and Ts - Tm2 =ΔT2. If the amount of water flowing through the first guide tube 36 and the thermal conductivity of the tube 36 are constant and the amount of heat transferred from the water 66 in the boiling chamber 67 via the wall of the tube 36 to the water in the tube 36 is Q = k T, the heat transfer quantities for the two cases are:

qCΔt1 = kΔT1 ... (3)

qCΔt2 = kΔT2 ... (4)

where: q= flow rate (kg/s) inside the first guide tube 36 and c= specific heat (J/kg ºC) of water.

By inserting equations (1) and (2) into equations (3) and (4) we obtain:

qC(Tb1 - Tw1) = k{Ts - (Tw1 + Tb1)/2} ... (5)

qC(Tb2 - Tw2) = k{Ts - (Tw2 + Tb2)/2} ... (6)

According to equations (1) to (4) we get:

Tb2 - Tb1 = (B/A) (Tw2 - Tw1) ... (7)

Here, (B/A) is equal to {(Δt1 - 1)/2}/{(Δt1 + 1)/2} and is less than 1. Therefore, when the feed water temperature changes from Tw1 to Tw2, the change (Tb2 - Tb1) of Tb is less than (Tw2 - Tw1). Accordingly, when the feed water temperature changes, the change in the temperature of the water supplied to the boiling chamber 67 of the bubble pump unit 20 is smaller than the change in the feed water temperature, so that the temperature of the hot water supplied from the pump unit can be stabilized. In the present embodiment, the second guide tube 39 is used in combination with the first guide tube 36. Therefore, as the water fed through the pipe 36 flows downward in the pipe 39, it undergoes heat exchange with the rising flow of hot water around the pipe 39 in the boiling chamber 67, thereby further increasing its temperature to Tc. On the other hand, the rising hot water cools down to the temperature Th and is discharged from the chamber 67. Compared with the example described in connection with equation (7), therefore, the influence of the feed water temperature on the temperature of the hot water supplied by the pump unit 20 is smaller, so that the temperature of the hot water supplied can be further stabilized.

In addition, as mentioned previously, the water preheated by the heat exchange is fed into the boiling chamber 67 of the bubble pump unit 20. The cooling capacity of the preheated water is lower than that of the unheated water, and its bubble condensing ability is lower. As a result, the bubbles generated in the chamber 67 are condensed more slowly by the preheated water, so that the bursting sound of the bubbles is weaker, i.e., the generation of noise can be suppressed.

The hot water storage device is thus improved in terms of its handling performance and operability, while the degree of freedom with regard to the installation location is also increased.

Figure 7 is an oscillogram of a result of a test conducted on an experimental basis on a bubble pump having the same structure as the embodiment described above. In Figure 7, the abscissa represents the time elapsed after the start of power supply to the electric heating element. Although the feed water temperature changes from 25ºC to 45ºC, the temperature of the hot water supplied changes little. Figure 8 illustrates the test result of Figure 7 in comparison with the test result of another bubble pump. In Figure 8, the solid line represents the characteristic curve of the hot water supplied by the bubble pump unit according to the present embodiment, while the dashed line represents a characteristic curve of supplied hot water obtained when the first and second guide tubes 36 and 39 are omitted from the pump according to the described embodiment and water is fed into the boiling chamber 67 without preheating. As is apparent from Figure 8, in the present embodiment, the change in the temperature of the supplied hot water can be kept significantly smaller than the temperature of the feed water.

According to the embodiment described above, two independent electric heating elements are provided; one heating element is for a continuous power supply system, the other for a night-time power supply system. However, only one electric heating element may be used, so that electric power is supplied only from the continuous power supply system or the night-time power supply system. The power supply system in question is selected in view of the difference in electricity charges according to the time zone, the conditions of household use of hot water, etc. The arrangement of the bubble pump unit may also be changed as required.

Figures 9 and 10 illustrate a bubble pump unit 20 according to a second embodiment of the present In this pump unit, a hollow aluminum block 71 is fixed to the outer peripheral surface of the pump body 27, while sheathed electric heating elements 24a and 24b are embedded in the block in parallel to the body 27. In this second embodiment, check valves 25 and 26 are further arranged in first and second connecting pipes 30 and 33, respectively. In this case, the distal end portion of the pipe 30 extends through the lower end wall 28 of the pump body 27 into the boiling chamber 67 so as to form the first guide pipe 36.

In the first and second embodiments described above, the second guide pipe (39) may be omitted. In this case, too, the change or fluctuation in the temperature of the supplied hot water attributable to the change in the feed water temperature can be made smaller than in the case of a device without the first guide pipe 36. In addition, flap valves may be used for the check valves instead of ball valves. In addition, for the flow control function, a throttle pipe may be used instead of the flow control valve in the first connecting pipe. The flow control valve and the throttle pipe may be omitted. Depending on the change or fluctuation in the target temperature of the supplied hot water or the like, the material for the first and second guide pipes 36 and 39 may also be changed.

Claims (16)

1. Hot water storage device comprising a hot water tank (11) containing water, having an upper end provided with a hot water feed inlet (16) and a lower end provided with a water feed inlet (13), a hot water feed pipe (17) connected to the hot water feed inlet for discharging the hot water from the tank (11) to the outside, a water feed unit (14) connected to the water feed inlet for introducing water into the hot water tank, and a water heating device arranged outside the hot water tank or on its outside for drawing water from the lower portion of the interior of the tank, heating the water and introducing the heated water into the upper portion of the hot water tank (11), characterized in that the water heating device comprises a bubble pump unit (20) with a body (27) having a boiling chamber (67), (a) heating element(s) for heating the water in the boiling chamber and for generating bubbles in the water, a first connecting pipe (30) for guiding the water from the lower section in the hot water tank of the body, a guide pipe (36) for feeding the water guided via the first connecting pipe into the boiling chamber and for condensing bubbles by the water supplied via the guide pipe (360), a second connecting pipe (33) for introducing the water heated in the boiling chamber (67) into the upper section in the hot water tank and first and second control units arranged in the first and second connecting pipes (30, 33) for allowing the water to flow only from the lower section of the hot water tank to the upper section thereof, wherein the guide pipe (36) is arranged with respect to the pump body (27) so that a heat exchange between the water in the boiling chamber (67) and the water flowing through the guide tube (36). 2. Device according to claim 1, characterized in that the guide tube (36) is arranged in the boiling chamber (67) and a has a lower end communicating with the first connecting pipe (30) and an upper end opening into the boiling chamber. 3. Device according to claim 2, characterized in that the boiling chamber (67) has an upper end communicating with the second connecting tube (33) and a second end arranged close to the first connecting tube (30) and extends substantially vertically and the guide tube (36) extends into the boiling chamber in the axial direction thereof, the upper end of the guide tube being arranged close to the upper end of the boiling chamber. 4. Device according to claim 3, characterized in that the boiling chamber (67) is cylindrical and the guide tube (36) is coaxial to the boiling chamber. 5. Device according to claim 3, characterized in that the bubble pump unit (20) has a second guide tube (39) for guiding the water discharged from the upper end of the first guide tube (36) to the lower end of the boiling chamber (67), the second guide tube being arranged so that a heat exchange takes place between the water flowing through the second guide tube and the water in the boiling chamber. 6. Device according to claim 5, characterized in that the second guide tube (69 or 39) has an inner diameter which is larger than the outer diameter of the first guide tube (36) and is arranged in the boiling chamber (67) so that it encloses the upper end section of the first guide tube and is coaxial with the first guide tube, the second guide tube further has a lower end opening towards the lower end of the boiling chamber and a partition plate facing or opposite the upper end of the first guide tube, so that the water discharged from the upper end of the first guide tube is guided between the outer peripheral surface of the first guide tube and the inner peripheral surface of the second guide tube and directed downwards. 7. Device according to claim 1, characterized in that the pump body (27) has the shape of a cylinder, the inner peripheral surface of which defines the boiling chamber (67), and the heating device has first and second electrical heating elements (24a, 24b) provided on the outer surface of the pump body. 8. Device according to claim 7, characterized in that the heating device has a first power supply or feed unit (46) for activating the first electrical heating element (24b) in a predetermined manner and a second power supply unit (45) for activating the second electrical heating element (24a) in a desired manner. 9. Device according to claim 8, characterized in that the second power supply unit (45) has a timer circuit (48) for optionally setting the conduction or activation duration and the conduction or activation start time for the second electrical heating element (24a). 10. Device according to claim 8, characterized in that the first power supply unit (46) has a sensor (51) for measuring the temperature of the water in the area of the hot water tank (11) located near the water supply inlet (13), so that the power supply to the first electric heating element (24b) is initiated at a predetermined time and terminated when the water temperature measured by the sensor reaches a predetermined temperature value. 11. Device according to claim 7, characterized in that the first and second electrical heating elements (24a, 24b) are wound around the outer peripheral surface of the pump body (27) in a secured manner. 12. Device according to claim 7, characterized in that the first and second electrical heating elements (24a, 24b) each formed from a rod-shaped, coated heating element running parallel to the pump body (27). 13. Device according to claim 1, characterized in that the first control unit has a first check valve (25) which allows a flow of water only from the first connecting pipe (30) to the pump body (27), and the second control unit has a second check valve (26) which allows a flow of water only from the pump body to the second connecting pipe (33). 14. Device according to claim 13, characterized in that the first and second check valves (25, 26) are arranged in the first or second connecting pipe (30, 33). 15. Device according to claim 13, characterized in that the pump body (27) has a first valve chamber (23a) arranged between the first connecting pipe (30) and the guide pipe (36) and a second valve chamber (23b) arranged between the second connecting pipe (33) and the boiling chamber (67), the first and second check valves (25, 26) being arranged in the first and second valve chambers, respectively. 16. Device according to claim 1, further characterized by a heat-insulating device (12) covering or enveloping the tank (11), and characterized in that the bubble pump unit (20) is embedded in the heat-insulating device.