Hot water production system for buildings

Abstract

In a system (1) for hot water preparation for buildings, in particular for households, with a water tank (2) which has a first area (6) for storing hot water with a hot water draw-off connection (7) and a second area (8) for storing cold water with a cold water inlet connection (9), wherein the first and the second area (6, 8) are in flow connection with one another and the water tank (2) is designed for a water pressure of at least 7 bar and for a water temperature of at least 70°C, and with a heating device (3) for heating the cold water, the water tank (2) is made of plastic and the heating device (3) is detachably connected to the water tank (2).

Description

[0001] The invention relates to a system for hot water preparation for buildings, in particular for households, comprising a water tank which has a first area for storing hot water with a hot water draw-off connection and a second area for storing cold water with a cold water inlet connection, wherein the first and the second area are in flow connection with one another and the water tank is designed for a water pressure of at least 7 bar and for a water temperature of at least 70° C, and comprising a heating device for heating the cold water.

[0002] In such systems, it is common practice to apply the heating energy to the outer surface of the water tank and heat the cold water through the water tank wall. A spiral heat transfer channel is mounted on the metal wall of the water tank, and heat transfer fluid is conducted through the channel. Since metal is a good heat conductor, the heat can be transferred from the heat transfer fluid in the channel to the cold water in the water tank.

[0003] In contrast, the object of the invention is to improve a generic system in such a way that its assembly, maintenance and repair are simplified and, in addition, its operating costs are reduced.

[0004] According to the invention, this object is achieved by the commonality of the features of claim 1.

[0005] The measures according to the invention considerably reduce the effort required for installation, inspections and any maintenance, as well as the operating costs of a system for hot water preparation for buildings. Since the water tank is made of plastic and the heating device is detachably attached to it, it is possible to attach the heating device to the water tank only once it has reached its final destination. Its assembly weight is considerably reduced compared to a metal water tank with an integrated heating device, making it easier to transport, particularly by hand, to its destination in a home or building, where it can also be correctly positioned and aligned. Furthermore, a plastic water tank is much more durable than a metal water tank, and therefore costs for replacing it are incurred at much longer intervals.In the event of damage, the heater can be removed from the water tank and replaced or repaired separately. This eliminates the need to replace the water tank if the heater is irreparably damaged.

[0006] The plastic is preferably fiber-reinforced, especially glass-fiber-reinforced. This increases the strength of the plastic, so that the compressive strength of the water tank can be increased while maintaining the same wall thickness, or the wall thickness can be reduced for a given compressive strength of the water tank. This allows for a further reduction in the weight of the water tank.

[0007] In an advantageous embodiment of the invention, the heating device comprises a heat exchanger arranged within the water tank in its second region. The heat exchanger is in direct contact with the cold water to be heated, so that the cold water is heated extremely effectively. Due to the effective heat exchange between the heat exchanger arranged in the water tank and the cold water, the required amount of heat transfer medium passing through the heat exchanger can be kept relatively low.

[0008] The heat exchanger is preferably a double-walled heat exchanger. This complies with health regulations that allow the use of coolant as a heat transfer medium to heat the water in the water tank. With a double-walled heat exchanger arranged in the water tank, a system according to the invention can be operated in a house or apartment, for example, using the natural fluid R290 propane as the heat transfer medium, where EN378 permits no more than 150g of propane. A fluorine-containing fluid, such as R134a, or a natural fluid, such as R744, can also be used as the heat-transfer coolant.

[0009] In a favorable development of the invention, the water tank has an opening in its wall surrounding the second region for the passage of the heat exchanger. The opening is enclosed by an opening edge formed as a flange projecting onto the outside of the water tank and enclosing the opening. The heat exchanger is connected to the flange in a watertight manner by means of a clamp connection. These measures allow the heat exchanger to be easily inserted into and removed from the water tank. Using the flange and the clamp connection, the heat exchanger can be quickly and securely attached to the water tank in a pressure-tight and watertight manner.

[0010] Preferably, the flange is a section of an annular plastic insert with a circumferential fastening section that engages behind the water tank wall in the edge area of the opening and is attached there to the inner surface of the water tank wall. The flange can thus be attached to the water tank in a pressure-tight and watertight manner with relatively little technical effort.

[0011] Preferably, the plastic insert has a circumferential steel casing on its outer circumferential surface facing away from the opening, which extends perpendicular to the circumferential direction along the underside of the flange and into the water tank between the water tank wall and the engaging fastening section over a predetermined partial length of the fastening section. Such a steel casing serves to reinforce the plastic insert and increases the bending and shear strength for horizontal loads, for example, in the event of lateral impacts against the flange, as well as the compressive strength of the underside of the flange for applying the clamping force by the clamp connection.

[0012] Advantageously, the clamp connection comprises a cover that covers the opening and rests on the flange, clamping it watertight. The heat exchanger comprises a heat transfer medium inlet and a heat transfer medium outlet that extend through the cover and are connected to it in a detachable and watertight manner, for example, by means of a nut / locknut connection with seals. In this way, the heat exchanger arranged in the water tank, including the heat transfer medium inlet and heat transfer medium outlet, can be attached to the water tank without major technical effort.

[0013] In a preferred embodiment of the invention, the lid is formed from two superimposed plates, one facing the water tank and the other facing away from the water tank. With the plastic plate, the inner surface of the water tank that comes into contact with the water is made entirely of plastic. The metal plate, however, has no contact with the water in the water tank. The material and thickness of the metal plate are selected so that the lid has sufficient strength against the pressure prevailing in the water tank, for example, against a water pressure of at least 7 bar.

[0014] The clamping connection advantageously has an open clamping ring which has an opening of a predetermined width along its circumference, wherein the opening is bridged by a clamping device which is fastened to the clamping ring on both sides of the opening and by tightening which the opening width and thus the inner diameter of the clamping ring can be reduced, wherein the clamping ring has a cross-section perpendicular to the circumferential direction with a section in the shape of a V which is open towards the interior of the ring and which is designed to jointly encompass the outer edge regions of the cover and flange and to press them together when the clamping device is tightened. In this way, a clamping connection which is watertight and pressure-resistant can be produced in a simple manner.

[0015] The V-shaped cross-sectional section preferably has two side walls with facing inner surfaces, which are inclined such that the V-shaped cross-sectional section widens toward the inside of the ring. The underside of the flange facing the water tank and the top side of the cover facing away from the water tank are inclined toward each other toward their outer edges and rest against the inner surfaces of the side walls of the V-shaped cross-sectional section. This structural design of the clamp connection minimizes the technical complexity both for its manufacture and for the watertight attachment of the heat exchanger to the water tank (using the seals).

[0016] In an advantageous embodiment of the invention, the heating device is designed as a heat transfer circuit which has an expansion valve, an evaporator and a compressor in the flow direction of the heat transfer medium after the heat exchanger,

[0017] A coolant, such as propane R290, is preferably used as the heat transfer medium.

[0018] In a further advantageous embodiment of the invention, the system has a first heat transfer circuit with a first heat transfer medium and a second heat transfer circuit with a second heat transfer medium, wherein the first heat transfer circuit has the heat exchanger and the second heat transfer circuit has, in the flow direction of the second heat transfer medium outside the water tank, one after the other an expansion valve, an evaporator and a compressor and both heat transfer circuits are connected to a second heat exchanger, also arranged outside the water tank, for transferring heat from the second heat transfer medium to the first heat transfer medium.

[0019] In this embodiment, water is preferably used as the first heat carrier and a coolant, for example a glycol-water mixture, as the second heat carrier.

[0020] Furthermore, a pump is interposed in the drain line from the first heat exchanger located in the second area - the cold water area - of the water tank to the second heat exchanger.

[0021] In yet another advantageous embodiment of the invention, the system has a water circuit and a heat transfer medium circuit with a heat transfer medium, wherein the water circuit has the water tank and a cold water extraction line for extracting cold water from the water tank and a hot water supply line for supplying hot water to the water tank, and the heat transfer medium circuit has, in the flow direction of the heat transfer medium, an expansion valve, an evaporator and a compressor outside the water tank one after the other, and both circuits are connected to a heat exchanger, also arranged outside the water tank, for transferring heat from the heat transfer medium to the water.

[0022] The invention will be explained in more detail by way of example with reference to the drawings. They show: Figure 1 is a schematic representation of a first embodiment of a system according to the invention; Figure 2 is a similar representation to Figure 1 a second embodiment of a system according to the invention; Figure 3 in a similar representation to Figure 1 a third embodiment of a system according to the invention; Figure 4 in a similar representation to Figure 1 a fourth embodiment of a system according to the invention; Figure 5 in a similar representation to Figure 1 a fifth embodiment of a system according to the invention; Figure 6 a vertical section along line AA in Figure 7 through a section of the water tank, with a heat exchanger of the heating device arranged in the water tank and with the opening for passing through and fastening this heat exchanger; and Figure 7 a bottom view of the water tank from Figure 6, on a reduced scale.

[0023] The Figures 1 to 5 The illustrated embodiments of systems 1 according to the invention for providing hot water for buildings, in particular for households, have a water tank 2 and a heating device 3 for heating cold water.

[0024] In the illustrated embodiments, the water tank 2 is a vertically arranged cylinder with a dome-shaped upper end cap 4 and a dome-shaped lower end cap 5. The water tank 2 is made of glass fiber reinforced plastic and designed for a water pressure of at least 7 bar and a water temperature of at least 70° C. It has a first, upper region 6 for storing hot water with a hot water draw-off connection 7 in the upper end cap 4 and a second, lower region 8 for storing cold water with a cold water inlet connection 9 in the lower end cap 5. The first and the second region are in flow connection with one another.

[0025] In the Figures 1 to 3In the illustrated embodiments, an opening 10 is further formed in the lower cover 5, through which a first heat exchanger 11, 11a of the heating device 3 can be inserted into the water tank 2 for assembly and can also be removed again for disassembly. The first heat exchanger 11, 11a is arranged in the second area 8, ie in the cold water area, in the assembled state. In the case of Figures 1 and 2 For safety reasons, it is designed as a double-walled condenser, since in these cases the condenser is flowed through by a coolant as a heat transfer medium. Figure 3 11a is designed as a single-walled condenser, since in this case water flows through the condenser as the (first) heat transfer medium. In all three cases, the heat exchanger or condenser 11, 11a has a heat transfer medium inlet 12 and a heat transfer medium outlet 13 (see Figure 6), which extend through the opening 10 to the outside of the water tank 2. It is also possible to exchange the heat transfer medium inlet and the heat transfer medium outlet.

[0026] As from Figure 6 As can be seen, this opening 10 is enclosed by an opening edge 14, which is designed as a flange 15 projecting onto the outside of the water tank 2 and enclosing the opening 10. The flange 15 is a section of an annular plastic insert 16, which has a circumferential fastening section 17 that engages behind the water tank wall 18 in the edge region of the opening 10 and is fastened there to the inner surface 19 of the water tank wall 18 in a watertight and pressure-tight manner. The fastening can be effected, for example, by gluing or by melting the abutting surfaces of the water tank wall 18 and the fastening section 17.

[0027] The plastic insert 16 has a circumferential steel casing 22 on its outer peripheral surface 21 facing away from the opening 10. This casing extends perpendicular to the circumferential direction along the flange underside 23 and then further into the water tank 2 between the water tank wall 18 and the engaging fastening section 17 over a predetermined partial length of the fastening section 17 and ends before the fastening section 17 is attached to the water tank wall 18.

[0028] The opening 10 is covered by a cover 24, which rests on the flange 15 and is clamped thereto in a watertight manner. The heat transfer fluid inlet 12 and the heat transfer fluid outlet 13 of the heat exchanger 11, 11a arranged in the water tank 2 extend through the cover 24 and are detachably connected thereto, for example, each by means of a nut / locknut connection 20 including seals for watertight sealing. In this way, the heat exchanger 11, 11a arranged in the water tank 2 is detachably connected to the cover 24 by means of the nut / locknut connections 20. The cover 24, in turn, is detachably connected to the flange 15 by means of a clamp connection 25.

[0029] As can be seen from the Figures 1-3 As can be seen in Figures 1 and 2 (and also 4 to 7), the cold water inlet connection 9 can also extend through the cover 24. This can be achieved by means of a conventional wall duct.

[0030] The lid 24 is formed from two superimposed plates. A plastic plate 26 faces the water tank 2, so that the entire inner surface 19 of the water tank 2 that comes into contact with the water in the water tank 2 is made of plastic and meets sanitary requirements. The side of the lid 24 facing away from the water tank 2 forms a metal plate 27. This ensures the sufficient strength of the lid 24 and is designed to absorb the water pressure prevailing in the water tank 2.

[0031] The lid 24 is clamped to the flange 15 by means of a clamp connection 25, which ensures a watertight connection between the lid 24 and the flange 15 at the pressure and temperature present in the water tank 2.

[0032] In the Figures 6 and 71 shows such a clamping connection 25. It has an open clamping ring 28 which has an opening of a predetermined width along its circumference. This opening is bridged by a clamping device 29 which is fastened to the clamping ring 28 on both sides of the opening. The clamping device 29 can, for example, be in the form of a screw 30 which is rotatably mounted in a screw nut on one side of the opening and on the other, opposite side of the opening, the underside of the screw head of which rests against a stop which is fastened to the clamping ring 28 in a shear- and bend-resistant manner. If the screw 30 is screwed into the screw nut to tighten the clamping device 29, the distance between the screw head and the screw nut shortens, with the screw head pressing against the stop and thus reducing the opening width and thus the inner diameter of the clamping ring 28.

[0033] Perpendicular to the circumferential direction, the clamping ring 28 has a cross-section with a section 31 in the shape of a V open towards the inside of the ring, which is designed to encompass the outer edge regions 32, 33 of the cover 24 and the flange 15 together and to press them together when the clamping device 29 is tightened.

[0034] The V-shaped cross-sectional section 31 has two side walls with mutually facing inner surfaces 34, 35, which are inclined such that the V-shaped cross-sectional section 31 widens towards the inside of the ring

[0035] The upper side of the lid 24 facing away from the water tank 2, in the illustrated embodiment the upper side of the metal plate 27, and the underside 23 of the flange 15 facing the water tank 2 with its steel casing 22 run towards each other at an incline towards their outer edges 36, 37 and rest on the inner surfaces 34, 35 of the side walls.

[0036] When the clamping device 29 is tightened as described above, the inclined surfaces 34, 35 of the V-shaped cross-sectional section 31 slide along the inclined surfaces of the cover 24, i.e., the metal plate 27, and the underside of the flange 15 or the steel casing 22 present there, and thus press the cover 24 onto the flange 15.

[0037] In the Figures 1 and 2In the exemplary embodiments of systems 1 according to the invention shown, the heating device 3 is formed from a heat transfer medium circuit which has the double-walled heat exchanger 11 arranged in the second region 8, i.e. in the cold water region, of the water tank 2 and, outside the water tank 2 in the flow direction of the heat transfer medium, an expansion valve E, an evaporator 38 and a compressor C after this heat exchanger 11. The heat transfer medium cooled in the heat exchanger 11 thus flows out of the water tank 2 via a drain line 13, 39 to the expansion valve E, and from the compressor C the reheated heat transfer medium flows back to the heat exchanger 11 arranged in the water tank 2 via a return line 12, 40.

[0038] In Figure 1an example of a so-called monobloc system is shown, in which the expansion valve E, the evaporator 38 and the compressor C are arranged above the water tank 2 and are housed together with the water tank 2 in a housing (not shown).

[0039] In Figure 2 a so-called split system is shown, in which the expansion valve E, the evaporator 38 and the compressor C are housed separately from the housing 45 of the water tank 2 in a separate housing 41, which is arranged, for example, laterally next to the water tank 2.

[0040] In the Figure 3In the exemplary embodiment of the system 1 according to the invention shown, the heating device 3 is formed from a first heat transfer medium circuit 42 with a first heat transfer medium and a second heat transfer medium circuit 43 with a second heat transfer medium. The first heat transfer medium circuit 42 has the single-walled heat exchanger 11a arranged in the second region 8, i.e. in the cold water region, of the water tank 2. The second heat transfer medium circuit 43 is arranged completely outside the water tank 2 and has, in succession in the flow direction of the second heat transfer medium, an expansion valve E, an evaporator 38 and a compressor C. Both heat transfer medium circuits 42, 43 are connected to a second heat exchanger 44a arranged outside the water tank 2 for transferring heat from the second heat transfer medium to the first heat transfer medium.The second heat exchanger 44a can be single-walled, since the first heat transfer circuit 42 with the first heat exchanger 11a is also interposed between it 44a and the water tank 2. A pump P is arranged in the first heat transfer circuit 42 in the drain line 13, 39 from the first heat exchanger 11a to the second heat exchanger 44a.

[0041] This embodiment is in Figure 3 shown as a split system, with a second housing 46 arranged laterally next to a housing 45 for the water tank 2 for the second heat exchanger 44a, the pump P and the second heat transfer circuit 43. A design as a monobloc system is also possible.

[0042] In the Figures 4 and 5In the illustrated embodiments of systems 1 according to the invention, the heating device 3 each has a water circuit 47 and a heat transfer medium circuit 48 with a heat transfer medium. The water circuit 47 includes the water tank 2 and a cold water extraction line 49 for extracting cold water from the water tank 2, as well as a hot water supply line 50 for supplying hot water to the water tank 2. The heat transfer medium circuit 48 includes, in the flow direction of the heat transfer medium outside the water tank 2, an expansion valve E, an evaporator 38, and a compressor C. Both circuits 47, 48 are connected to a heat exchanger 44, which is also arranged outside the water tank 2 and is double-walled for safety reasons, for transferring heat from the heat transfer medium to the water. A pump P is arranged in the cold water extraction line 49 outside the water tank 2.

[0043] In Figure 4An embodiment is shown in which the heat transfer circuit 48 is arranged laterally next to the water tank 2 and the cold water extraction line 49 passes through a cover 24 which covers an opening 10 in the lower cover 5. The cover 24 can be designed in the same way as in connection with the Figure 6 described cover 24 (without the heat exchanger located in the water tank). The hot water supply line 50 passes directly through the upper cover cap.

[0044] This embodiment can, as in Figure 4 shown as a split system - similar to the design according to Figure 3 - with separate housings 45, 46.

[0045] At the Figure 5In the embodiment shown, the heat transfer circuit 48 is arranged above the water tank 2 and both the hot water supply line 50 and the cold water extraction line 49 pass through the upper cover cap 4. The cold water extraction line 49 passes through the first area 6, ie the hot water area, of the water tank 2 and opens into the second area 8 of the water tank 2, ie the cold water area.

[0046] This design is suitable as a monobloc system. List of reference symbols

[0047] 1 System for providing hot water for buildings 2 Water tank 3 Heating device 4 Upper cover 5 Lower cover 6 First, upper section for storing hot water 7 Hot water draw-off connection 8 Second, lower section for storing cold water 9 Cold water inlet connection 10 Opening in the lower cover 11, 11a First heat exchanger 12 Heat transfer medium inlet of the first heat exchanger 13 Heat transfer medium outlet of the first heat exchanger 14 Opening edge of opening 10 15 Flange 6 Plastic insert 17 Fastening section 18 Water tank wall 19 Inner surface of the water tank wall 20 Nut / lock nut connection 21 Outer peripheral surface of the plastic insert 22 Steel jacket 23 Flange base 24 Cover 25 Clamp connection 26 Plastic plate 27 Metal plate 28 Clamp ring 29Clamping device 30Screw 31V-shaped cross-sectional section 32Outer edge area of the cover 33Outer edge area of the flange 34,35inclined surfaces of the V-shaped cross-sectional section 36outer edge of the metal plate of the cover 37outer edge of the flange underside 38evaporator 39drain line (with heat carrier drain 13 of the first heat exchanger) 40return line (with heat carrier inlet 12 of the first heat exchanger) 41housing for expansion valve E, evaporator 38 and compressor C 42first heat carrier circuit 43second heat carrier circuit 44, 44asecond heat exchanger 45housing for the water tank 46housing for the second heat exchanger 44a / 44, the pump P and the second heat carrier circuit 43 / the heat carrier circuit 48 47water circuit 48heat carrier circuit 49cold water extraction line 50hot water supply line , CCompressor EExpansion valve PPump

Claims

1. Installation (1) for hot water preparation for buildings, in particular for households, with - a water tank (2) which has a first area (6) for storing hot water with a hot water draw-off connection (7) and a second area (8) for storing cold water with a cold water inlet connection (9), wherein the first and the second area (6, 8) are in flow connection with each other and the water tank (2) is designed for a water pressure of at least 7 bar and for a water temperature of at least 70°C, and with - a heating device (3) for heating the cold water, characterized in that the water tank (2) is made of plastic and the heating device (3) is detachably connected to the water tank (2).

2. Plant (1) according to claim 1, characterized in that the plastic is fiber-reinforced, in particular glass-fiber-reinforced.

3. Plant (1) according to claim 1 or 2, characterized in thatthe heating device (3) has a heat exchanger (11, 11a) which is arranged within the water tank (2) in its second region (8).

4. Plant (1) according to claim 3, characterized in that the heat exchanger (11) is a double-walled heat exchanger.

5. Plant (1) according to claim 3 or 4, characterized in that the water tank (2) has an opening (10) in its wall (18) surrounding the second region (8) for the heat exchanger (11, 11a) to pass through, the opening (10) being enclosed by an opening edge (14) which is designed as a flange (15) projecting onto the outside of the water tank (2) and enclosing the opening (10), and the heat exchanger (11, 11a) is connected to the flange (15) in a watertight manner by means of a clamping connection (25).

6. Plant (1) according to claim 5, characterized in thatthe flange (15) is a section of an annular plastic insert (16) which has a circumferential fastening section (17) which engages behind the water tank wall (18) in the edge region of the opening (10) and is fastened there to the inner surface (19) of the water tank wall (18).

7. Plant (1) according to claim 6, characterized in that the plastic insert (16) has, on its outer circumferential surface (21) facing away from the opening (10), a circumferential steel casing (22) which extends at right angles to the circumferential direction along the underside of the flange (23) and into the water tank (2) between the water tank wall (18) and the engaging fastening section (17) over a predetermined partial length of the fastening section (17).

8. Plant (1) according to one of claims 5 to 7, characterized in thatthe clamping connection (25) has a cover (24) which covers the opening (10) and rests on the flange (15) and is clamped to the latter (15) in a watertight manner, wherein the heat exchanger (11, 11a) has a heat transfer medium inlet (12) and a heat transfer medium outlet (13) which extend through the cover (24) and are detachably connected to the latter (24).

9. Plant (1) according to claim 8, characterized in that the lid (24) is formed from two superimposed plates (26, 27), with a plastic plate (26) facing the water tank (2) and a metal plate (27) facing away from the water tank (2).

10. Annex (1) according to claim 8 or 9, characterized in thatthe clamping connection (25) has an open clamping ring (28) which has an opening of a predetermined width along its circumference, the opening being bridged by a clamping device (29) which is fastened to the clamping ring (28) on both sides of the opening and by clamping which (29) the opening width and thus the inner diameter of the clamping ring (28) can be reduced, the clamping ring (28) having a cross-section perpendicular to the circumferential direction with a section (31) in the shape of a V which is open towards the inside of the ring and which is designed to jointly encompass the outer edge regions of the cover (24) and the flange (15) and to press them together when the clamping device (29) is tightened.

11. Annex (1) according to claim 10, characterized in thatthe V-shaped cross-sectional section (31) has two side walls with mutually facing inner surfaces which are inclined (34, 35) such that the V-shaped cross-sectional section (31) widens towards the inside of the ring, and that the underside (23) of the flange (15) facing the water tank (2) and the upper side of the cover (24) facing away from the water tank (2) run towards each other at an inclination towards their outer edges (37, 36) and bear against the inner surfaces of the side walls of the V-shaped cross-sectional section (31).

12. Plant (1) according to one of claims 3 to 11, characterized in that the heating device (3) is designed as a heat transfer medium circuit which, in the flow direction of the heat transfer medium after the heat exchanger (11) outside the water tank (2), has an expansion valve (E), an evaporator (38) and a compressor (C).

13. Plant (1) according to one of claims 3 to 11, characterized bya first heat transfer circuit (42) with a first heat transfer medium and a second heat transfer circuit (43) with a second heat transfer medium, wherein the first heat transfer circuit (42) has the heat exchanger (11a) and the second heat transfer circuit (43) has, in the flow direction of the second heat transfer medium outside the water tank (2), one after the other an expansion valve (E), an evaporator (38) and a compressor (C) has and both heat carrier circuits (42, 43) are connected to a second heat exchanger (44a), also arranged outside the water tank (2), for transferring heat from the second heat carrier to the first heat carrier, 14. Plant (1) according to claim 1 or 2, characterized bya water circuit (47) and a heat transfer medium circuit (48) with a heat transfer medium, wherein the water circuit (47) has the water tank (2) and a cold water extraction line (49) for extracting cold water from the water tank (2) and a hot water supply line (50) for supplying hot water to the water tank (2), and the heat transfer medium circuit (48) has, in the flow direction of the heat transfer medium outside the water tank (2), one after the other, an expansion valve (E), an evaporator (38) and a compressor (C), and both circuits (47, 48) are connected to a heat exchanger (44) likewise arranged outside the water tank (2) for transferring heat from the heat transfer medium to the water.

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