Domestic hot water storage tank with immersed heating element

Abstract

The invention relates to a domestic hot water storage tank (1) comprising an inlet (2) for introducing water into the tank (1), an outlet (3) for removing hot water from the tank (1), and a heating element intended to be immersed in the water of the tank (1) in order to heat the water present in the lower part of the tank (1) in the installed position. According to the invention, the heating element comprises at least one electrically insulated, resistive flexible wire, the ends (10a, 10b) of which extend from the tank (1) for connection to an external power supply, and at least a portion of whose length, situated between the ends (10a, 10b), is intended to rest by gravity at the bottom of the tank (1) in said installed position, forming a random cluster (12). Figure for the abstract: Fig. 3

Description

Title of the invention: Domestic hot water storage tank with immersed heating element Technical field

[0001] The present invention relates to the general field of domestic hot water storage tanks, and more specifically to a domestic hot water storage tank comprising an inlet connection for bringing water into the tank, an outlet connection for bringing hot water contained in the tank out and a heating element intended to be immersed in the water in the tank in order to heat the water present in the lower part of the tank in the installed position. Technological background

[0002] Such tanks are used for example in electric water heaters.

[0003] [Fig.l] schematically illustrates a known tank 1 for an electric water heater, particularly suitable for a so-called "over-sink" installation. The tank 1, generally made of steel with an enameled internal wall, has an inlet connection 2 for bringing cold water under pressure into the tank 1, and an outlet connection 3 for bringing heated water contained in the tank 1 out. In such a configuration, the cold water enters the interior of the tank 1 through an inlet pipe 4 carried by the inlet connection 2 and extending in the axis of this inlet connection 2. The water contained in the tank 1 is heated by an electric heating element 5.The heating temperature is regulated by means of one or more thermostats housed in a glove finger 6 extending through an opening made in the tank 1, to heat the water according to a set temperature (for example between 60 and 65°C to allow an actual outlet temperature of approximately 40°C to be obtained if the outlet water is mixed via a mixer tap with cold water). At the request of a user at a draw-off point (sink or washbasin tap, shower, bathtub, etc.), the heated water can leave the tank 1 through an outlet pipe 7 carried by the outlet connection 3 and extending axially to the outlet connection 3.

[0004] An electric water heater mostly works by accumulation, that is to say that it does not heat the water continuously, but accumulates a quantity of hot water for daily needs and operates according to the principle of stratification. More precisely, cold water under pressure enters the tank as it empties to meet domestic hot water needs. The cold water that enters is heated by the heating element or any alternative energy supply and gradually rises to the top of the tank. Indeed, like air, hot water has a lower density than cold water. It is therefore lighter and naturally gains height. On the other hand, cold water, which is naturally denser, remains at the bottom of the tank. It is this physical principle which is the origin of the name stratification.

[0005] In the case of the “over-sink” configuration of [Fig.l], the inlet pipe 4 extends only into the lower internal part of the tank 1, and has a stamped upper part to prevent any vertical entry of cold water, and an intermediate portion provided with lateral orifices guaranteeing a substantially horizontal penetration of the cold water into the tank. Such an intermediate portion is commonly called a “jet breaker” because it will “break” the pressure of the water injected into the bottom of the tank and thus preserve the natural distribution of the layers of water according to their temperature. Conversely, the outlet pipe 4 is much longer so as to take the heated water from the upper internal part of the tank 1.

[0006] For a so-called "under-sink" configuration, illustrated schematically in [Fig.2], we find the same components as those detailed above. However, taking into account the position of the inlet 2 and outlet 3 tappings in the upper part of the tank 1, and to respect the phenomenon of water stratification, the inlet pipe 4 is here much longer so that its intermediate part carrying the lateral orifices and its stamped end are placed in the lower part of the tank 1. The outlet pipe is on the other hand very short so as to take the hot water located in the upper part of the tank 1.

[0007] In both of the above configurations, it is known to further equip the tank 1 with an anode 8 for protecting the tank 1 against corrosion which extends longitudinally inside the tank 1. The protective anode forms a cathodic protection which may be sacrificial, for example made of magnesium alloy or aluminum alloy. Alternatively, the protective anode may be permanent. In the latter case, an imposed electric current flows through the protective anode. Alternatively, the protective anode may be of the combined type with an imposed current anode around which a sacrificial anode is arranged.

[0008] In the embodiments illustrated in Figures 1 and 2, the electric heating element 5, the glove finger 6 containing the thermostat(s) and the protective anode 8 extend into the tank 1 through a corresponding opening passing through the external wall of the tank 1, and are carried by the same flange 9, itself removably fixed to the tank 1, on the periphery of the opening. More precisely, the protective anode 8 extends close to and parallel to the glove finger 6 and to a portion of the heating element 5, and substantially horizontally when the tank is installed.

[0009] In both configurations above, the heating element is constituted by a shielded electrical resistance 5 immersed in the water of the tank 1.

[0010] The use of a shielded electrical resistor has a number of of disadvantages:

[0011] First of all, this type of resistance has a high surface power density (expressed in Watts per square meter), which results in a high temperature of the resistance wall which is in contact with the water. The shielded electrical resistance is sensitive in particular to the quality of the water and its lifespan is short. In addition, since the aim is to heat mainly the water contained at the bottom of the tank, it is necessary, as visible in Figures 1 and 2, to give the shielded electrical resistance 5 a relatively complex elbow L shape, the number of elbows of which depends on the desired heating power. This elbow L shape makes it complex to position the heating element carried by the flange 9 inside the tank, especially in the case of a compact tank.In fact, the tank 1 is generally made by assembling two bottoms 1a, 1b and possibly an intermediate shell 1c whose dimension varies according to the tank capacity that is desired. Consequently, the more compact the tank (for example for a capacity of 5 liters), the more difficult it is to install the armored resistance inside the tank. When the flange 9 also carries the corrosion protection anode, as illustrated in figures 1 and 2, the installation of the elbow armored resistance is impossible if this anode is too long.

[0012] To increase the life of the heating element, it has already been proposed to replace the shielded electric heating resistor with a steatite resistor placed inside a sealed sheath made of enamelled steel, the whole being immersed in water, and for example carried by the flange 9. This type of heating element is however very expensive and bulky, which does not allow its use in the case of a compact tank.

[0013] Other solutions consist of heating the water from the outside of the tank. In particular, solutions are known which consist of covering the tank with a heating blanket comprising, inside a flexible envelope, a mesh of resistive electric wires. Given the very low surface power density of the electric wires, these solutions do not allow for the significant heating powers and therefore heating speeds required in certain markets. They are also very expensive. Other solutions consist of using the principle of induction heating via heating coils which directly heat the tank. The latter must be made of ferritic steel. In addition to the excessively high cost, the electric fields can have an uncontrolled impact on the lifespan of the enameled tank.Moreover, all solutions aimed at heating the water from the outside of the tank are less efficient than solutions with an immersed heating element. Summary of the invention

[0014] The present invention aims to overcome the drawbacks of known solutions.

[0015] This object is achieved in accordance with the present invention, which relates to a domestic hot water storage tank comprising an inlet tapping for bringing water into the tank, an outlet tapping for bringing out hot water contained in the tank and a heating element intended to be immersed in the water of the tank in order to heat the water present in the lower part of the tank in the installed position, characterized in that said heating element comprises at least one electrically insulated resistive flexible wire, the ends of which exit the tank for connection to an external power supply, and at least a portion of length located between the ends of which is intended to rest by gravitation at the bottom of the tank in said installed position, forming a random pile.

[0016] In one possible embodiment, the heating element comprises a plurality of flexible resistive wires, the ends of which exit the tank for connection to an external power supply, each wire being electrically insulated and having at least a portion of length between its ends intended to rest by gravitation at the bottom of the tank in said installed position, forming with the other wires said random cluster.

[0017] Said at least one wire preferably comprises a metal core, and an electrically insulating sheath, surrounding said core.

[0018] In one possible embodiment, the tank further comprises an anode for protecting the tank against corrosion, said anode extending longitudinally inside the tank.

[0019] In one possible embodiment, the tank further comprises an element removably attached to the tank to seal an opening passing through the wall of the tank, the ends of said at least one wire or of said plurality of wires exiting the tank at the opening and said element.

[0020] The protective anode is preferably carried by said element.

[0021] In one possible embodiment, the inlet tapping and the outlet tapping are located in the lower part of the tank in the installed position. Alternatively, the inlet tapping and the outlet tapping are located in the upper part of the tank in the installed position.

[0022] In one possible embodiment, the element is located in the lower part of the tank in the installed position. The element can then serve as a drain plug.

[0023] In another possible embodiment, the element is located in the upper part of the tank in the installed position.

[0024] In one possible embodiment, the element is a flange located on a side wall of the tank in the installed position. Brief description of the figures

[0025] The description which follows with reference to the attached drawings, given as examples non-limiting, will make it clear what the invention consists of and how it can be implemented. In the attached figures:

[0026] [Fig.l] [Fig.l], already written above, schematically illustrates a part of a known tank for an electric water heater, particularly adapted to a so-called “on-sink” configuration;

[0027] [Fig.2] [Fig.2], already written above, schematically illustrates part of a another known tank for water heaters, particularly suitable for a so-called “under-sink” configuration;

[0028] [Fig.3] [Fig.3] illustrates a modification made to the water heater tank of the [Fig.l], in accordance with a first embodiment of the present invention;

[0029] [Fig.4] [Fig.4] illustrates a modification made to the water heater tank of the [Fig.2], in accordance with another embodiment of the present invention;

[0030] [Fig.5] [Fig.5] gives comparative tests illustrating the gains of the invention. Description of embodiment(s)

[0031] In the figures, identical or equivalent elements will bear the same reference signs. The various diagrams are not to scale. In certain figures, certain elements, including the tank, have been deliberately shown in dotted lines in order to facilitate understanding of the figures and to show parts internal to the tank.

[0032] [Fig. 3] illustrates a first embodiment of a tank according to the invention for an electric water heater, particularly suitable for a so-called “on-sink” configuration.

[0033] We thus find the elements already described with reference to [Fig.l], namely: - a tank 1, preferably made of steel, and preferably enamelled on its internal wall; - an inlet connection 2 and an outlet connection 3, preferably welded to the external wall of the tank 1 in the lower part of this tank, at the level of corresponding openings made in this external wall; and - an inlet rod 4 carried by the inlet tapping 2 so as to extend axially to the inlet tapping and inside the tank 1, and an outlet rod 7 carried by the outlet tapping 3 so as to extend axially to the inlet tapping and inside the tank 1.

[0034] The inlet and outlet connections are for example also made of steel.

[0035] In this non-limiting example, the inlet tapping 2 and the outlet tapping 3 are located in the lower part of the tank when the latter is in the installed position, and oriented so that the inlet rod 4 and the outlet rod 7 extend substantially parallel to the interior of the tank 1.

[0036] The tank 1 further comprises a heating element intended to be immersed in the water of the tank 1 in order to heat the water present in the lower part of the tank 1 in the installed position. According to the invention, this heating element is constituted, in the example shown, of two flexible resistive wires, each electrically insulated, and whose ends 10a, 10b on the one hand, and 11a, 11b on the other hand, come out of the tank 1 for connection to an external electrical supply (not shown). The tank 1 is also shown in the installed position, a position in which it can be seen that the portion of length located between the ends 10a, 10b or 11a, 11b rests by gravitation at the bottom of the tank 1, forming a random cluster 12.

[0037] Each flexible resistive wire mainly and preferably comprises a core made of a metal wire resistant to the passage of current, and an electrically insulating sheath, for example made of silicone, surrounding the core.

[0038] As the wires are immersed in the water of the tank and this water is likely to be drunk by a user, the material of the sheath is preferably chosen to meet the requirements of existing health and potability standards relating to electrically insulating materials authorized for food contact.

[0039] In an alternative embodiment not shown, the heating element may consist of a single flexible resistive wire, a portion of the length of which is intended to rest by gravity at the bottom of the tank when the latter is in the installed position. An advantage of providing a plurality of wires lies in the fact that it is possible in particular to regulate different power levels, or even to use several phases of the external power supply.

[0040] By using a substantial length of wires which forms the random cluster 12, the tests have shown that it is possible to obtain a volumetric power density (capacity of the cluster to transmit energy, at a given volume) sufficient to heat the water in the lower part of the tank.

[0041] [Fig.5] gives comparative tests obtained with a wire (in accordance with the invention), with a conventional copper shielded resistance of power equal to 350 Watts, with a conventional copper shielded resistance of power equal to 2500 Watts, with a known steatite resistance of power equal to 2400 Watts.

[0042] In the example of [Fig.5], the wire used has a diameter of 3 millimeters and a linear power of 57 W / m, which makes it possible to obtain a power density of 8064 W / L. Of course, other power density values ​​can be obtained with other wires. The choice of wire is made according to normative constraints, design constraints and / or cost. As a non-limiting example, a wire with an external diameter (including the sheath) of between 2 and 7 millimeters will preferably be chosen. The necessary length of the wire forming the cluster will depend directly on the desired power (for example, typically between 200 and 3500 Watts in the non-limiting case of domestic water heaters). The power density is calculated by dividing the power of the wire (in W) by the occupied volume. The occupied volume can be modeled in 3D, or calculated experimentally. For a wire of length L and diameter D, the occupied volume V is given by the following equation: V=7tL(§) 2

[0043] It should be noted that the wire is preferably chosen so that the volume occupied is as small as possible.

[0044] In the example shown in [Fig. 3], the tank 1 comprises a plug 13 removably attached to the tank 1 to seal an opening passing through the wall of the tank 1. Given its position in the lower part, the plug 13 can advantageously serve as a drain plug. As can be seen in this figure, the ends 10a, 10b on the one hand, and 11a, 11b on the other hand, for the two flexible wires, exit the tank 1 at the opening and the drain plug 13. In a variant not shown, it is also possible to provide for the plug 13 to carry a glove finger comprising one or more thermostats allowing temperature measurement for the purposes of temperature regulation by a regulation circuit external to the tank.

[0045] The tank 1 preferably further comprises an anode for protecting the tank 1 against corrosion (not shown), for example a sacrificial anode made of magnesium alloy or aluminum alloy, arranged so as to extend longitudinally inside the tank 1. In one possible embodiment, the anode for protecting against corrosion may be carried by the plug 13. Alternatively, it may be envisaged that the protective anode is carried in the axial extension of the inlet pipe 4.

[0046] In the example shown in [Fig. 3], the inlet tapping 2, the outlet tapping 3 and the plug 13 through which the ends of the flexible wire(s) exit, are located in the lower part of the tank 1 in the installed position. Other arrangements are of course possible without departing from the scope of the present invention. In another embodiment not shown, the ends of the flexible wire(s) may exit at an element other than the plug 13, for example a flange, removably fixed to the tank 1, on the periphery of an opening passing through the wall of the tank 1. The flange may be similar to the flange 9 of [Fig. 1], fixed laterally on the tank and carrying the ends of the flexible wire(s) (instead of the shielded resistor 5 of [Fig. 1]), or even a glove finger containing one or more thermostats and / or a protective anode.

[0047] [Fig.4] illustrates another embodiment of a tank according to the invention for a water heater, particularly suitable for a so-called “under-sink” configuration.

[0048] Unlike the “on sink” configuration seen previously, the inlet tapping 2 and the outlet tapping 3 of the tank are here located in the upper part of the tank 1 when the tank is in the installed position. The inlet pipe 4 still has a part 41 forming a jet breaker with lateral openings. However, in order to respect the stratification phenomenon, the inlet pipe 4 is much longer so that this part 41 forming a jet breaker is found in the lower part of the interior of the tank 1.

[0049] Just as in the embodiment described above with reference to [Fig. 3], the heating element is constituted, in the example shown in [Fig. 4], of two flexible resistive wires, each electrically insulated, and whose ends 10a, 10b on the one hand, and 11a, 11b on the other hand, come out of the tank 1 for connection to an external electrical power supply (not shown). The tank 1 is also shown in the installed position, a position in which it can be seen that the portion of length located between the ends 10a, 10b or 11a, 11b rests by gravitation at the bottom of the tank 1, forming a random cluster 12.

[0050] In an alternative embodiment not shown, the heating element may consist of a single flexible resistive wire, a portion of the length of which is intended to rest by gravity at the bottom of the tank when the latter is in the installed position.

[0051] Here again, the tank 1 comprises a plug 13 removably attached to the tank 1 to seal an opening passing through the wall of the tank 1. As can be seen in this figure, the ends 10a, 10b on the one hand, and 11a, 11b on the other hand, for the two flexible wires exit the tank 1 at the opening and the plug 13. In a variant not shown, it is also possible to provide for the plug 13 to carry a glove finger comprising one or more thermostats allowing temperature measurement for the purposes of temperature regulation by a regulation circuit external to the tank.

[0052] The tank 1 preferably further comprises an anode for protecting the tank 1 against corrosion (not shown), for example a sacrificial anode made of magnesium alloy or aluminum alloy, arranged so as to extend longitudinally inside the tank 1. In one possible embodiment, the anode for protecting against corrosion may be carried by the plug 13. As a variant, it may be envisaged that the protective anode is carried in the axial extension of the outlet pipe.

[0053] In the example shown in [Fig. 4], the inlet tapping 2, the outlet tapping 3 and the drain plug 13 through which the ends of the flexible wire(s) exit, are located in the upper part of the tank 1 in the installed position. Other arrangements are of course possible without departing from the scope of the present invention. For example, in another embodiment not shown, the ends of the flexible wire(s) may exit at an element other than the plug 13, for example a flange, removably fixed to the tank 1, on the periphery of an opening passing through the wall of the tank 1. The flange may be similar to the flange 9 of [Fig. 2], fixed laterally rattling on the tank and carrying the ends of the flexible wire(s) (instead of the shielded resistor 5 of [Fig.l]), or even a glove finger containing one or more thermostats and / or a protective anode.

[0054] Whatever the embodiment, the present invention has numerous advantages:

[0055] Thus, the wire(s) constituting the heating element are immersed, which constitutes, as we saw in the introduction, a more effective solution than heating from the outside of the tank.

[0056] Furthermore, the wire(s) constituting the heating element having a low surface power density, they are less sensitive to the quality of the water. This increases the lifespan of the heating element compared to those of known solutions of immersed heating element.

[0057] Furthermore, the power volume density offered by the random wire cluster is much greater than the power volume density of a sheath containing a steatite resistor. This results in a gain in space requirement.

[0058] Furthermore, in the embodiments illustrated in Figures 3 and 4, it is no longer necessary to provide a large flange. Indeed, only a small element, for example the drain plug, can be used here to allow the ends of the wire (or wires) constituting the heating element to exit the tank to be connected to an external power supply. In the embodiments for which the plug 13 also carries the temperature probes and / or a corrosion protection anode, or those for which the protection anode is carried by the inlet or outlet rod, the need to use the flange 9 and to have a corresponding opening on the tank bottom 1b as illustrated in Figures 1 and 2 is eliminated. The two tank bottoms 1 and 1b can thus be identical, which further reduces manufacturing costs.

[0059] Finally, all assembly operations are considerably simplified.

[0060] Although the preceding detailed description has only been made in the context of tanks for electric water heaters, the present invention applies to any storage tank comprising a heating element intended to be immersed in the water of the tank.

Claims

Claims

1. Domestic hot water storage tank (1) comprising an inlet connection (2) for bringing water into the tank (1), an outlet connection (3) for bringing hot water contained in the tank (1) out and a heating element intended to be immersed in the water of the tank (1) in order to heat the water present in the lower part of the tank (1) in the installed position, characterized in that said heating element consists of at least one electrically insulated resistive flexible wire, the ends (10a, 10b) of which exit from the tank (1) for connection to an external power supply, and at least a portion of length located between the ends (10a, 10b) of which is intended to rest by gravitation at the bottom of the tank (1) in said installed position, forming a random pile (12).

2. Tank (1) according to claim 1, in which the heating element is made up of a plurality of flexible resistive wires, the ends (10a, 10b, 11a, 11b) of which exit from the tank (1) for connection to an external power supply, each wire being electrically insulated and having at least a portion of length between its ends (10a, 10b; 11a, 11b) intended to rest by gravitation at the bottom of the tank (1) in said installed position, forming with the other wires said random cluster (12).

3. Tank (1) according to any one of the preceding claims, in which said at least one wire comprises a metal core, and an electrically insulating sheath, surrounding said core.

4. Tank (1) according to any one of the preceding claims, further comprising an anode for protecting the tank (1) against corrosion, said anode extending longitudinally inside the tank (1).

5. Tank (1) according to any one of the preceding claims, further comprising an element (13) removably fixed to the tank (1) to seal an opening passing through the wall of the tank (1), the ends (10a, 10b; 11a, 11b) of said at least one wire or of said plurality of wires exiting the tank (1) at the opening and said element (13).

6. Tank (1) according to the combination of claims 4 and 5 in which the protective anode is carried by said element (13).

7. Tank (1) according to any one of claims 5 or 6, in

8.

9.

10.

11. in which the inlet tapping (2) and the outlet tapping (3) are located in the lower part of the tank (1) in the installed position. Tank (1) according to any one of claims 5 or 6, in which the inlet tapping (2) and the outlet tapping (3) are located in the upper part of the tank (1) in the installed position. Tank (1) according to any one of claims 5 to 8, wherein said element is a flange located on a side wall of the tank (1) in the installed position. Tank (1) according to claim 7, in which said element (13) is located in the lower part of the tank (1) in the installed position, and forms a drain plug. Tank (1) according to claim 8, wherein said element (13) is located in the upper part of the tank (1) in the installed position.

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