Domestic hot water storage tank with immersed heating element

Abstract

The invention relates to a domestic hot water storage tank (1) comprising an inlet connection (2) for adding water to the tank (1), an outlet connection (3) for discharging hot water contained in the tank (1) and a heating element intended to be immersed in the water in the tank (1) in order to heat the water present in the bottom portion of the tank (1) when 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 come out of the tank (1) to connect to an external electrical power supply and at least one length portion located between the ends (10a, 10b) of which is intended to rest, under the effect of gravity, at the bottom of the tank (1) when in the installed position, whereby forming a random heap (12).

Description

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 fitting for bringing water into the tank, an outlet fitting for bringing hot water contained in the tank out 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. Technological background

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

[0003] Figure 1 schematically illustrates a tank 1 commonly used in electric water heaters, particularly suited for "over-sink" installation. The tank 1, generally made of steel with an enameled inner wall, has an inlet 2 for introducing pressurized cold water into the tank 1, and an outlet 3 for expelling heated water from the tank 1. In this configuration, the cold water enters the tank 1 through an inlet pipe 4 supported by the inlet 2 and extending along the axis of this inlet 2. The water in the tank 1 is heated by an electric heating element 5.The heating temperature is regulated by one or more thermostats housed in a thermowell 6 extending through an opening in the tank 1, to heat the water according to a set temperature (for example, between 60 and 65°C to allow for an actual outlet temperature of approximately 40°C if the outlet water is mixed with cold water via a mixer tap). At the user's request at a tap (basin or sink tap, shower, bathtub, etc.), the heated water can exit the tank 1 through an outlet pipe 7 supported by the outlet fitting 3 and extending axially from the outlet fitting 3.

[0004] An electric water heater typically operates by storage, meaning it doesn't heat water continuously but accumulates a quantity of hot water for daily needs, functioning according to the principle of stratification. More specifically, cold water under pressure enters the tank as it empties to meet domestic hot water requirements. The incoming cold water is heated by the heating element or some other alternative energy source 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 rises. Conversely, cold water, being naturally denser, remains at the bottom of the tank. This physical principle is the origin of the term "stratification."

[0005] In the "over-sink" configuration shown in Figure 1, the inlet pipe 4 extends only into the lower internal portion of the tank 1. It has a stamped upper section to prevent any vertical entry of cold water, and an intermediate portion with lateral openings that ensure a nearly horizontal entry of cold water into the tank. This intermediate portion is commonly called a "jet breaker" because it reduces the pressure of the water injected into the bottom of the tank, thus preserving the natural distribution of water layers according to their temperature. Conversely, the outlet pipe 4 is much longer in order to draw the heated water from the upper internal portion of the tank 1.

[0006] For an under-sink configuration, schematically illustrated in Figure 2, the same components are used as those detailed above. However, given the position of the inlet 2 and outlet 3 connections in the upper part of the tank 1, and to account for the water stratification phenomenon, the inlet pipe 4 is much longer so that its middle section, containing the lateral openings, and its crimped end are positioned in the lower part of the tank 1. The outlet pipe, on the other hand, is very short in order to draw hot water from the upper part of the tank 1.

[0007] In both configurations above, it is known to further equip tank 1 with a protective anode 8 against corrosion, extending longitudinally inside tank 1. The protective anode forms a cathodic shield and can be sacrificial, for example made of an alloy of magnesium or aluminum alloy. Alternatively, the protective anode can be permanent. In this case, an impressed electric current flows through the protective anode. Alternatively, the protective anode can be of the type combining an impressed current anode with a sacrificial anode arranged around it.

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

[0009] In both configurations above, the heating element consists of a sheathed electrical resistance 5 immersed in the water of the tank 1.

[0010] Using a shielded electrical resistor has several disadvantages:

[0011] First, this type of heating element has a high power density (expressed in watts per square meter), resulting in a high temperature of the element's wall in contact with the water. The sheathed heating element is particularly sensitive to water quality and has a short lifespan. Furthermore, since the primary goal is to heat the water at the bottom of the tank, it is necessary, as shown in Figures 1 and 2, to give the sheathed heating element 5 a relatively complex L-shaped bend, the number of bends of which depends on the desired heating power. This L-shaped bend makes it difficult to install the heating element supported by the flange 9 inside the tank, especially in the case of a compact tank.Indeed, the tank 1 is generally made by assembling two ends 1a, 1b and possibly an intermediate shell 1c, the dimensions of which vary according to the desired tank capacity. Consequently, the more compact the tank (for example, for a 5-liter capacity), the more difficult it is to install the sheathed heating element inside the tank. When the flange 9 also carries the protective anode against the... corrosion, as illustrated in figures 1 and 2, the installation of the angled shielded resistor is impossible if this anode is too long.

[0012] To increase the lifespan of the heating element, it has already been proposed to replace the shielded electric heating element with a steatite element placed inside a sealed enamelled steel sheath, the whole thing being immersed in water, and for example supported by 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 involve heating the water from the outside of the tank. One such solution involves covering the tank with a heating blanket containing a mesh of resistive electrical wires within a flexible outer layer. However, due to the very low power density of these wires, these solutions cannot provide the high heating power and therefore the rapid heating required in some markets. They are also very expensive. Another solution uses induction heating via heating coils that directly heat the tank. The tank must be made of ferritic steel. Besides the high cost, the electric fields can have an uncontrolled impact on the lifespan of the enameled tank.Moreover, all solutions aimed at heating 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 objective is achieved in accordance with the present invention, which relates to a domestic hot water storage tank comprising an inlet for introducing water into the tank, an outlet for removing hot water from the tank, 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, characterized in that said heating element comprises at least one electrically insulated resistive flexible wire, the ends of which extend from the tank for connection to an external power supply, and at least a portion of whose length is located between the ends. intended to rest by gravity at the bottom of the tank in said installed position, forming a random mass.

[0016] In one embodiment, the heating element consists of at least one electrically insulated resistive flexible wire. The term "consists of" means that the heating element comprises only this at least one electrically insulated resistive flexible wire. In other words, this at least one electrically insulated resistive flexible wire is not contained within a sheath or tube. An external wall of this at least one electrically insulated resistive flexible wire is thus intended to be in contact with the water in the tank.

[0017] In one possible embodiment, the heating element comprises a plurality of resistive flexible 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 gravity at the bottom of the tank in said installed position, forming with the other wires said random mass.

[0018] Said at least one wire preferably comprises a metallic core and an electrical insulation sheath surrounding said core.

[0019] In one possible embodiment, the tank further comprises an anode for protecting the tank against corrosion, said anode extending longitudinally inside the tank.

[0020] In one possible embodiment, the tank further comprises an element removably fixed to the tank to seal tightly an opening 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 level of the opening and of said element.

[0021] The protective anode is preferably carried by said element.

[0022] In one possible embodiment, the inlet and outlet connections are located at the bottom of the tank in the installed position. Alternatively, the inlet and outlet connections are located at the top of the tank in the installed position.

[0023] 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.

[0024] In another possible embodiment, the element is located in the upper part of the tank in the installed position.

[0025] 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

[0026] The following description, with reference to the accompanying drawings, given by way of non-limiting examples, will clearly explain the nature of the invention and how it can be implemented. Regarding the accompanying figures:

[0027] [fig. 1] Figure 1, already written above, schematically illustrates part of a tank known for electric water heater, particularly suited to a so-called "over sink" configuration;

[0028] [fig. 2] Figure 2, already written above, schematically illustrates part of another tank known for water heater, particularly suited to a so-called "under sink" configuration;

[0029] [fig. 3] Figure 3 illustrates a modification made to the water heater tank of figure 1, in accordance with a first embodiment of the present invention;

[0030] [fig. 4] Figure 4 illustrates a modification made to the water heater tank of figure 2, according to another embodiment of the present invention;

[0031] [fig. 5] Figure 5 gives comparative tests illustrating the gains of the invention. Description of method(s) of implementation

[0032] In the figures, identical or equivalent elements will bear the same reference symbols. The various diagrams are not to scale. In some figures, certain elements, including the tank, have been intentionally represented with dashed lines to facilitate understanding of the figures and to show internal parts of the tank.

[0033] Figure 3 illustrates a first embodiment of a tank according to the invention for an electric water heater, particularly suited to a so-called "over sink" configuration.

[0034] We thus find the elements already described with reference to Figure 1, namely: - a tank 1, preferably made of steel, and preferably enameled on its wall internal ; - an inlet fitting 2 and an outlet fitting 3, preferably welded to the outer wall of the tank 1 in the lower part of this tank, at the level of corresponding openings made in this outer wall; and - an inlet pipe 4 carried by the inlet fitting 2 so as to extend axially to the inlet fitting and inside the tank 1, and an outlet pipe 7 carried by the outlet fitting 3 so as to extend axially to the inlet fitting and inside the tank 1.

[0035] The inlet and outlet fittings, for example, are also made of steel.

[0036] In this non-limiting example, the inlet spigot 2 and the outlet spigot 3 are located in the lower part of the tank when it is in the installed position, and oriented so that the inlet pipe 4 and the outlet pipe 7 extend substantially parallel inside the tank 1.

[0037] Tank 1 further includes a heating element designed to be immersed in the water of tank 1 in order to heat the water present in the lower part of tank 1 when installed. According to the invention, this heating element consists, in the example shown, of two flexible resistive wires, each electrically insulated, the ends of which 10a, 10b on the one hand, and 11a, 11b on the other, extend from tank 1 for connection to an external power supply (not shown). Tank 1 is also shown in its installed position, in which it can be seen that the portion of length located between the ends 10a, 10b or 11a, 11b rests by gravity at the bottom of tank 1, forming a random cluster 12.

[0038] Each flexible resistive wire mainly and preferably consists of a core made of a metallic wire resistant to the passage of current, and an electrical insulation sheath, for example made of silicone, surrounding the core.

[0039] As the wires are immersed in the water in the tank and this water is likely to be drunk by a user, the sheath material is preferably chosen to meet the requirements of existing health and potability standards relating to electrically insulating materials permitted for food contact.

[0040] In an alternative embodiment not shown, the heating element may consist of a single flexible resistive wire, a portion of whose length is designed to rest by gravity on the bottom of the tank when the latter is in the installed position. One advantage of having multiple wires is that it allows you to regulate different power levels, or use several phases of the external power supply.

[0041] By using a substantial length of wires which form the random cluster 12, tests have shown that one can 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.

[0042] Figure 5 shows comparative tests obtained with a wire (according to 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.

[0043] In the example shown in Figure 5, the wire used has a diameter of 3 millimeters and a linear power of 57 W / m, resulting in a specific power of 8064 W / L. Of course, other specific power values ​​can be obtained with different wires. The choice of wire is made according to regulatory requirements, design constraints, and / or cost. As a non-limiting example, a wire with an external diameter (including the sheath) between 2 and 7 millimeters is preferred. The required length of wire forming the bundle 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 specific power is calculated by dividing the wire's power (in W) by the volume occupied. The volume occupied can be modeled in 3D or calculated experimentally. For a wire of length L and diameter D, the volume occupied V is given by the following equation:

[0044] It should be noted that the wire is preferably chosen so that the volume occupied is as small as possible.

[0045] In the example shown in Figure 3, tank 1 has a plug 13 removably attached to tank 1 to seal an opening through the wall of tank 1. Given its position at the bottom, 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 On the other hand, for the two flexible wires, they exit the tank 1 at the level of the opening and the drain plug 13. In an unrepresented variant, it can also be provided that the plug 13 has a thermowell comprising one or more thermostats allowing a temperature measurement for the purpose of temperature regulation by a regulation circuit external to the tank.

[0046] The tank 1 also preferably includes an anode for protecting the tank 1 against corrosion (not shown), for example a sacrificial anode made of magnesium alloy or aluminum alloy, arranged to extend longitudinally inside the tank 1. In one possible embodiment, the corrosion protection anode can be carried by the plug 13. Alternatively, the protection anode can be carried in the axial extension of the inlet pipe 4.

[0047] In the example shown in Figure 3, the inlet fitting 2, the outlet fitting 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 its 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 attached 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 Figure 1, attached laterally to the tank and supporting the ends of the flexible wire(s) (instead of the sheathed heating element 5 of Figure 1), or even a thermowell containing one or more thermostats and / or a protective anode.

[0048] Figure 4 illustrates another embodiment of a tank according to the invention for a water heater, particularly suited to a so-called "under sink" configuration.

[0049] Unlike the "over-sink" configuration described earlier, the inlet 2 and outlet 3 of the sink are located in the upper part of the sink 1 when the sink is in the installed position. The inlet pipe 4 still has a section 41 forming a flow restrictor with lateral openings. However, to accommodate the stratification effect, the inlet pipe 4 is much longer so that this flow restrictor section 41 is located in the lower part of the inside of the sink 1.

[0050] As in the embodiment described above with reference to Figure 3, the heating element in the example shown in Figure 4 consists of two flexible resistive wires, each electrically insulated, whose ends 10a, 10b on the one hand, and 11a, 11b on the other, extend from the tank 1 for connection to an external power supply (not shown). The tank 1 is also shown in its installed position, in which the portion of length between the ends 10a, 10b or 11a, 11b can be seen resting by gravity at the bottom of the tank 1, forming a random cluster 12.

[0051] In an alternative embodiment not shown, the heating element may consist of a single flexible resistive wire, a portion of whose length is intended to rest by gravity on the bottom of the tank when the latter is in the installed position.

[0052] Here again, the tank 1 has a plug 13 removably fixed to the tank 1 to hermetically seal an opening 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 level of the opening and the plug 13. In an alternative variant not shown, the plug 13 may also be provided to have a thermowell comprising one or more thermostats allowing temperature measurement for the purpose of temperature regulation by a control circuit external to the tank.

[0053] The tank 1 also preferably includes 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 corrosion protection anode can be carried by the plug 13. Alternatively, it can be envisaged that the protection anode is carried in the axial extension of the outlet pipe.

[0054] In the example shown in Figure 4, the inlet fitting 2, the outlet fitting 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 its 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, fixed in such a way removable from tank 1, on the periphery of an opening through the wall of tank 1. The flange can be similar to flange 9 in Figure 2, fixed laterally on the tank and carrying the ends of the flexible wire(s) (instead of the sheathed resistance 5 in Figure 1), or even a thermowell containing one or more thermostats and / or a protective anode.

[0055] Regardless of the embodiment achieved, the present invention offers numerous advantages:

[0056] Thus, the wire or wires constituting the heating element are immersed, which, as we saw in the introduction, is a more efficient solution than heating from the outside of the tank.

[0057] Furthermore, since the wire(s) constituting the heating element have a low power density, they are less sensitive to water quality. This increases the lifespan of the heating element compared to known immersion heating element solutions.

[0058] Furthermore, the power density offered by the random wire bundle is much greater than the power density of a sheath containing a steatite resistor. This results in a reduction in size.

[0059] Furthermore, in the embodiments illustrated in Figures 3 and 4, a large flange is no longer required. Indeed, only a small component, such as the drain plug, can be used to allow the ends of the wire(s) constituting the heating element to exit the tank and be connected to an external power supply. In embodiments where the plug 13 also carries the temperature probes and / or a corrosion protection anode, or where the protection anode is carried by the inlet or outlet pipe, the need for the flange 9 and 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, further reducing manufacturing costs.

[0060] Finally, all assembly operations are considerably simplified.

[0061] Although the preceding detailed description was made only 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 in 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 out hot water contained in 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, characterized in that said heating element comprises 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 comprises 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 which the inlet tapping (2) and the outlet tapping (3) are located in the lower part of the tank (1) in the installed position.

8. 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.

9. A 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.

10. Tank (1) according to claim 7, wherein said element (13) is located in the lower part of the tank (1) in the installed position, and forms a drain plug.

11. 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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