WO2001094861A1

WO2001094861A1 - A tubular-shaped heating element

Info

Publication number: WO2001094861A1
Application number: PCT/EP2001/006357
Authority: WO
Inventors: Fausto Fioroni
Original assignee: Thermowatt S.P.A.
Priority date: 2000-06-08
Filing date: 2001-06-05
Publication date: 2001-12-13
Also published as: EP1290381A1; ES2261423T3; HK1056768A1; EP1290381B1; CN1434915A; AU2001267519A1; DE60118378T2; ATE321985T1; CN1232781C; ITMO20000122A1; IT1315636B1; DE60118378D1; DK1290381T3

Abstract

This invention describes a water heating element which can be used for both boilers and electrical appliances in general. A printed electrical resistor (4, 4.1) is applied to a piece of piping (3) used to dispense hot water, using a printing technique such as, for example, screen printing. The whole created by the said two elements constitutes the essential part of a heating element (1, 1.1) which is tubular and can have different sizes and conformations and it can incorporate other means required in water heating devices.

Description

DESCRIPTION

A TABULAR-SHAPED HEATING ELEMENT

Technical field

The invention relates to a tubular-shaped heating element for use, in particular, with boilers for sanitary purposes and household electrical appliances in general.

Background Art

The heating devices currently used in the aforesaid boilers are generally the so-called 'armoured electrical resistors'. These are constituted of an resistive electric f ament immersed in a chemically inert, electrically insulating powder, which is, in its turn, pressed into a hermetically sealed metal pipe.

The optimal thermal power dispensable per unit of surface (normally called the 'thermal load') is usually approximately 8.5W/cm2 for boiler resistors and 5W/cm2 for dishwasher resistors, which are also designed to run dry during the drying phase.

It is practically impossible to vary the thermal load along the resistor.

For the power to be dispensed mainly in the areas required, it is necessary to bend the resistor itself, either in loops or in a spiral. With regards to the apparatus in which these resistors are used, it is important to make a distinction between the different types of apparatus, i.e. electrical storage heaters, the so-called "under-the-sink" electrical storage heaters, fast-acting electric boilers and instant electric boilers. Electric storage heaters are generally characterised by a flange onto which one or more electrical resistors are mounted, a thermostat sheath containing one or more temperature sensors and, possibly, an anticorrosion device constituted of a magnesium anode or a cathodic protection device electrode. The inlet pipe, which is very short, just penetrates the tank and the said pipe dispenses the cold water into the bottom of the said tank. The output pipe runs through the whole tank to draw the hot water from the highest part.

The minimum installed power in this type of boiler is approximately 1,200/1,500W.

The so-called "under-the-sink" electric storage heaters are small boilers located inside the sink unit. To make the attachment to the tap unit easier, these boilers are mounted upside down and, consequently, so that the cold water is inserted in the lower part and the hot water is drawn from the upper part, the pipe that normally acts as the inlet pipe is then attached to the output and vice-versa.

The fast-acting electric boilers are similar in construction to the storage heaters, except that they may have a smaller tank to suit the function they have to fulfil, they have a higher level of installed power and, for safety reasons, they are often of the so-called "free-discharge" kind, i.e. the water contained in the tank is at room pressure.

The instant electric boilers are characterised by a very small storage tank or by the fact that they do not have a storage tank (it is replaced by a long piece of piping which is heated by electrical resistors), by a high level of electric power (even as high as 20kW) and, for safety reasons, these too are often of the 'free-discharge' kind.

With regards to the water heating means for dishwashers, the armoured electrical resistors mentioned earlier are generally used. In certain phases of the washing programme, when immersed in water, these resistors heat the water, in other phases, when the device is dry, the said resistors proceed to dry the crockery.

The aforesaid armoured resistors have some drawbacks, a first of which is represented by the complex production process. A further drawback of this type of commonly known resistance is constituted by the distribution of the thermal power achieved with a looped or spiral-shaped resistor: all forms require costly specific equipment.

Still further drawbacks are constituted by the existence of a neutral area at the end of the resistor, which no heat can be emitted from, by the tendency for lime-scale deposit, resulting in overheating, by the water in that area boiling (noisily) and by breakage, as well as the need for large openings for inserting the unwieldy forms of the looped or spiral resistor into the boiler.

The drawbacks of the current electric storage heaters are constituted, above all, by the need for a flange, as a sealing element, and a support for at least one or more resistors, a sheath for one or more thermostat probes, and, possibly, a magnesium anode or a cathodic protection system electrode.

A further drawback of this kind of boiler is that the water must be stored at at least the usage temperature, but normally at much higher temperatures than the fast-acting boilers or even higher than the instant boilers, with a lower level of installed power but with greater heat loss and lime-scale deposits forming faster, these latter having an effect on the corrosion.

A further drawback is that it is impossible, without using a comphcated-shaped resistor, to concentrate a significant amount of the thermal power in the lower part of the tank in order to guarantee more uniform temperatures with less heat loss keeping the average temperature unchanged.

A still further drawback is constituted by the fact that with the armoured electrical resistors it is impossible to heat the water a final time when it is drawn from the device.

With regards to the fast-acting electric boilers or the current instant boilers, their most important drawbacks are constituted by the need to adopt larger electrical resistors than those used in the storage heaters, which consequently require larger flanges.

Before presenting the aims of this invention and describing the preferred embodiments and some possible variants, it is worthwhile mentioning the essential characteristics of a electrical resistor construction technique, which although a known technology, is still rarely used. The said resistors are constituted of a metal support base, generally

AISI 430 steel, capable of diffusing the thermal energy emitted and guaranteeing the adhesion of the overlaying layers even if heat expansion occurs.

The following are gradually applied to this metal support base: - one or more layers of dielectric material;

- a printed electric circuit produced through the application of a special resistive paste through an adequate printing technology, such as screen printing for example; - a further layer or layers of dielectric material.

Hereinafter the term "printed resistor" will be used to indicate the whole unit constituted of the actual printed circuit and the layers of dielectric material underneath and above it, whether the circuit was made using a screen-printing technology or any other circuit printing technology.

The thermal loads obtainable with the printed resistors obviously depend on the capacity for heat elimination but, while the there are no particular increases in the cost of producing relatively low thermal loads in relation to those generally used in the sector, these can still be extremely high (at least 18-20W/cm2). As well as for heating liquid, the printed resistors can also function dry because they can resist up to 700° C in the air (250°C at the welded points on the electric terminals). The subsequent layers can also be placed on curved surfaces.

The feeder cables are connected electrically to the printed resistive circuit at the end of the printed circuit, by welding in two points which are intentionally not covered by the second group of layers of dielectric material.

Disclosure of Invention

A first aim of this invention, in a device for heating water such as an electric boiler or a dishwasher in which it is necessary to provide electric resistive means of heating the water and, possibly, means of checking the temperature of the water and/or, possibly, electrochemical means of preventing corrosion, consists in reducing the components required to realise the aforesaid means. A second aim consists in simplifying the construction of one or more of the aforesaid heating, temperature checking and corrosion prevention means. A third aim consists in snnplifying the mounting of one or more of the aforesaid means on a device for heating water.

A fourth aim consists in limiting the lime-scale deposits that form on the aforesaid heating means.

A fifth aim consists in the possibility of emninating the support flange from one or more of the aforesaid means.

A further aim consists in the possibility of distributing the thermal power to be emitted by the aforesaid heating means better.

A still further aim, for a storage heater, consists in enabling the water to be heated fully at the moment it is drawn, using the same heating means that heat the stored water.

A still ftuiher and final aim consists in reducing the manufacturing costs.

Achieving these and other aims is possible thanks to an original use of the commonly known technique for the application of printed resistors to a metal support.

In fact, the subject of this invention, for electrical appliances in general and in particular for heating water appliances for sanitary purposes, a heating element constituted of a tubular element designed to pipe water (for sanitary purposes at least) and to whose external and/or internal surfaces are apphed one or more resistors printed in the way determined above. - Figure 1 is a section drawing of a heating element according to a preferred embodiment of the invention applied to the interior of a hot water storage tank;

- Figure 2 is a total view of the heating element as per the embodiment in the previous figure;

- Figure 3 is a section drawing, along the main axis, of the same elements shown in the previous figure;

- Figure 4 is an enlarged section drawing, at right angles to the main axis, of a general heating element; - Figure 5 is a schematic diagram of a possible variant of the invention shown in figures 2 and 3, showing the flow of water inside the heating element during the heating phase of the said water and during the drawing phase;

- Figure 6 is a schematic diagram of a further possible variant of what is shown in figure 2;

- Figure 7 shows, extremely schematically, a fast-acting boiler using heating elements according to a variant of this invention;

- Figure 8 shows a total view of the heating element according to a further embodiment of the invention. There will now follow a description of a preferred embodiment of the heating element according to the invention which can be used extremely advantageously in a storage heater.

With reference to Fig.l a heating element 1 according to the invention is shown inside the tank 2 of a storage heater. In the case given as an example, the heating element 1 is the hot water output pipe from the tank 2. As shown in figures 1 to 3, the heating element 1 is constituted of: a piece of piping 3 made of any material compatible with the printed resistor technology and with the chemical, physical and mechanical stresses to which the said piping 3 will be subjected, e.g. AISI 430 steel; a printed resistor 4 and, lastly, a pipe coupling 5. For the sake of clarity, only the actual printed circuit part of the printed resistor 4 is highhghted, although in actual fact this is hidden by the layers of dielectric material above and below it which, together with the aforesaid printed circuit constitute the printed resistors, as defined earlier. The openings 10 and 11 in the lower part and the upper part of the piping 3 are also shown.

The pipe coupling 5 is fitted with suitable connection means 6 and 7, for example, threaded bushings, to fix respectively, the said coupling 5 to both the tank 2, by means of a ring nut 8, welded to the tank 2 itself, and also to the hot water distribution system (not shown). The coupling 5 is also fitted with suitable connectors 9 for the electricity supply to the printed resistor 4, the said connectors 9 being connected electrically to the printed resistor 4 and insulated electrically from the remaining elements in a commonly known way not shown in the figure.

In figure 3, in addition to the elements already identified, there are also some openings ll.b indicated, in the upper part of the piping 3, near its inlet 3. a.

In figure 4 there are (from the inside to the outside of the heating element 1): a possible layer of material 14 on which it is difficult for lime- scale to form deposits, such as polypropylene; the piping 3 onto which the subsequent printed resistor 4 will be apphed, the said printed resistor 4 being constituted of one or more layers of a dielectric material anchored to the base of the support constituted by the piping 3; the actual resistive printed circuit and one or more external layers of a dielectric material. Last to be shown is a possible sheath 15 designed to protect the printed resistor 4 against abrasion. Figure 5, which constitutes a possible variant of the invention as indicated in figure 3, shows, with arrows, the circulation direction the water will assume during the two functioning modes of a storage heater. More precisely, on the left is the circulation triggered by convective motions during the heating phase using the heating element 1 and on the right is the direction during the phase in which the hot water is drawn. The openings 10. a and 11. a, fitted with deflectors 12 positioned towards the inside, constitute, respectively, variants of the openings 10 and 11.

Figure 6 shows a possible variant of figure 5, where the openings lO.b and ll.b are made in the piping 3 in a position with the section enlargements 13.

Figure 7 shows, mounted on a small tank 2.1, elements already shown in the previous figures: the arrows indicate the inlet and output water flow directions; although not shown in the figure, also the tank 2.1, in the same way as for the piping 3 in the previous figures, and at least for its entire cylindrical part, can constitute the support base for a printed resistor 4.1 completely identical to the printed resistor 4. The other elements indicated are identical or equivalent to those shown in the previous figures. Therefore, the fast-acting kind of boiler shown in the figure is fitted with at least two printed resistors: the aforementioned printed resistor 4.1 and the printed resistor 4 , the base element of which is constituted of a piece of piping 3 of the hot water output kind.

Figure 8 shows a heating element 1.1 according to a second embodiment of the invention which is suitable for heating water circulating in a piece of piping incorporated into a household appliance such as, for example, an instant boiler or a dishwasher. The said heating element 1.1 is fitted with one or more printed resistors 4, supported by a piece of piping 3.1 and fitted with two bushings 5.1 or equivalent means of connecting the said heating element 1.1 respectively to an input pipe for water to be heated and an output pipe for heated water. The other elements indicated are identical or equivalent to those shown in the previous figures. There will now follow a detailed description of the characteristics of the heating element 1 according to this invention.

First of all, it is obvious that the power supply to the electrical resistor 4 leads to the heating of the water stored in the storage tank 2 in a similar way to the armoured electrical resistors already in use but there are special features and advantages that will now be ghlighted.

The printed resistor 4 has been drawn in the figure indifferently, whether it is constituted of fretwork or a spiral wound around the piping 3. In actual fact, this could have any route which does not intersect itself, the route could even be irregular to vary the thermal load along the length of the heating element in the most suitable way. There could be, for example, a double spiral route with a constant pitch which begins and ends at the pair of connectors 9, or a double spiral with a variable pitch.

There may be several adjacent printed resistors 4 printed on the same insulating layer, each said resistor term ating in a respective pair of connectors 9 with a view to make it possible to modulate the thermal power emitted by inserting one or more of the said printed resistors 4. There may also be several overlaid printed resistors insulated by as many insulating layers, each said resistor terminating in a respective pair of connectors 9.

These characteristics make it possible to concentrate the distribution of the thermal power generated by the printed resistors 4 in the areas where it is most useful: for storage heaters, this is generally the lower part. Furthermore, if several printed resistors 4 are required this will not increase the overall dimensions significantly because of the aforementioned possibility of creating adjacent routes for the said printed resistors 4, or by superimposing them, as long as a layer of insulating material is placed between each said route.

An important aspect of this invention is the fact that, using the same technology, and at the same time as the printed resistors 4 are printed, electrical circuits can be printed for connecting various electrical or electronic components to the exterior of the tank electrically. These said components could be useful if mounted along the heating element, the said heating element acting as a support for the said components. The said components are welded in a commonly known way to one end of the printed electric circuits, in the most suitable position along the heating element, and insulated electrically from the surrounding environment; the other end of the said circuits terminates, with suitable electrical connectors, in position with the pipe coupling. The said components can be, for example, temperatures sensors (e.g. NTCs) to be connected to corresponding electronic thermostats; unipolar safety thermostats of the bimetallic laminar kind or those with a fuse or of another kind (which are very small in size) and in this case they can be welded on directly in series with the resistor to be monitored. Lastly, these components can be cathodic anticorrosion protection devices. The temperature sensors can also be constituted of a printed resistive track with a resistivity level dependant enough on the temperature to be measured. For this purpose, the route of the printed sensor can be constituted of a track which is long enough to increase the total resistance, thus facihtating the measuring of the resistor as a function of the temperature change.

There will now follow a description of some details or construction variants of the heating element 1 according to the invention.

During the heating phase of the water in the tank 2 of a storage heater it may be necessary to stimulate the circulation of the water inside the piping 3 to prevent the water inside this latter becoming stagnant and increasing the temperature, causing lime-scale deposits to form extremely quickly and also the water in that area to boil. If the user draws the water at that moment, this latter phenomenon could result in the user being scalded. It is possible, then, as shown in figures 1 and 3, to create openings 10 in the lower part and the piping 3. As shown in figures 5 and 6, this peraήts a continuous natural circulation inside the piping 3 during the heating phase. When the hot water is drawn, it may also be worthwhile preventing the eddy of cold water from the lower part of the boiler through the said openings. Although it has been demonstrated, in the most common applications of the invention, that one or more openings 10, constituted of 4mm holes, are sufficient to guarantee the recirculation without the cold water eddying when the water is drawn from the tank, it is still possible to envisage other suitable adaptations: for example, in figure 5 the openings 10a. are fitted with suitable deflectors 12 and in figure 6 the openings 10b. are in position with suitable section enlargements 13 which, because of the Venturi effect, cause a local pressure increase and prevent the cold water entering. In certain embodiments, however, the diameter of the heating element 1 can be made wide enough to permit a sufficiently active natural circulation inside it without any openings 10 being necessary. In other embodiments, on the contrary, the speed of the water when it is drawn from the tank is high enough or sufficiently frequent to ensure a constant washing and so prevent or remove lime-scale deposits. For this purpose, it may be advantageous, as shown in figure 4, to provide, a layer of non-stick material 14 for the lime-scale inside the piping 3, such as polypropylene.

Still during the heating phase of the water contained inside the tank 2, it may be suitable to ensure the water that rises through natural circulation inside the piping 3 is not discharged completely at the end 3. a, where, it is known, there is often an air bubble which can obstruct the circulation. For this reason, the water can still leave through the openings 11 in figure 1 or ll.b in figure 3.

In certain applications, it may be worthwhile providing an external anti-abrasion jacket for the most external layer of insulating material constituting the printed resistor 4. This can be created, as in figure 4, with a protective sheath 15 made of a suitable material, but it could also be useful to have the said protective sheath 15 made of a material designed to act as an electrode for the cathodic protection, as described in full in another patent filed at the same time, by the same applicant. Alternatively, the said protective sheath 15 can be constituted of a sacrificial metal tubular element to protect the apparatus against corrosion (in general a magnesium anode). With any commonly known means or the means described earlier, the said electrode or the said anode are suitably connected electrically to the metal tank to be protected.

With reference to figure 1, the heating element 1 permits the functioning to be flexible, which is impossible with the commonly known armoured electrical resistors. To have a high reserve, a boiler generally keeps the water at 70-75°C, while the usage temperature is generally 40° C. If little water is required and the user wishes to limit the heat loss, the storage temperature can be lowered to the usage temperature, but never below. With the heating element 1 the water can kept at slightly lower temperature than the usage temperature and it can be reheated during the drawing phase, activating the printed resistor 4. For this purpose it is necessary for the said electrical resistor 4 to be operated by a thermostat during the storage phase and by a flow sensor unit, such as a pressure switch or a flow switch, during the water-drawing phase.

In figure 1 the heating element 1 according to the invention is shown as a pipe for drawing the hot water from a storage heater but, alternatively, this can take the form of the input pipe, as in the case of the 'under-the- sink' boiler or both the inlet pipe suitably extended inside the tank, and the output pipe for a better distribution of the thermal power in the most suitable areas.

Figure 7, instead, shows a fast-acting boiler fitted with at least two printed resistors which are separated from each other physically. The first said resistor, indicated with the number 4.1 and supported by the tank 2.1, can keep the water stored at a determined temperature, regulated by a suitable thermostat. The second, indicated with the number 4 and supported by the output pipe 3 can also heat the water during the drawing phase, regulated by a suitable flow sensor, such as a pressure switch or a flow switch. jSTaturally, still with reference to figure 7, a single heating element 1 constituting the output pipe, could perform both the pre-heating function during the storage phase and the final heating function during the drawing phase as long as the said heating element 1 has the openings 11 as shown in the figure.

In the variant illustrated in figure 8, the heating element 1.1 shown constitutes, substantially, the entire water heating device. The metal base constituted by the piping 3.1 is made of any material compatible with the technology and the chemical, physical and mechanical stresses the element will be exposed to (including, in this case, the water mains pressure), for example AISI 430 steel. To limit the overall dimensions, if a significant heating surface is required, two or more heating elements can be provided of the kinds 1 or 1.1, which are parallel to each other and coaxial, as shown in figure 7 for the fast-acting boiler. Alternatively, they are connected in series in a way not shown because it is obvious. The connectors 9 for connecting the heating element 1.1 electrically can be made, as well as in position with the pipe coupling, at any point on the external surface of the said heating element 1.1. The external surface can be insulated thermally and the power can be regulated using any commonly known means used for instant electric boilers.

A heating element according to the invention can be used advantageously in a dishwasher. This is not very different from the version indicated with the number 1.1 in figure 8. The said heating element 1.1 is preferably positioned, in the dishwasher tray; the water delivered to the nozzles is made to circulate inside the pipe which gradually heats it up at each stage. For the drying phase, once the water has been drained away, the heating element functions dry. If necessary, the printed resistor 4 or 4.1 can be apphed to the internal surface of the heating element 1 or 1.1 and also the heating element 1 or 1.1 can have different shaped sections (i.e. not circular) or be curved or convex, naturally within the limits of the forms permitted by the commonly known resistor printing technology. A first advantage of the heating element 1 is that, in a storage heater, the flange can be eliminated by simply providing the following: a threaded ring nut for fixing the heating element, a welded or screwed sheath for inserting the thermostat sensors and/or the cathodic anticorrosion protection electrode and/or a threaded ring nut for inserting a magnesium anode or an electrode. It has also been shown, though, that the heating element 1 can also support, all together, the sensor units, safety thermostats and anticorrosion protection electrodes or sacrificial anodes. Therefore it is possible, in some variants, to eliminate, not only the flange, but also the other hole in the tank 2, with the exception of the hole needed for the heating element according to the invention.

In storage heaters, this invention can also permit a significant reduction in the heat loss and lime-scale formations in the tank 2.

For the sake of an example, consider a storage heater with a power of l500W. A flow of 0.07 litre/sec is required for a shower. At this rate, if the resistor is activated during the drawing phase, in practice, the said resistor only yields heat to the water that runs through the element because the heat exchange is much more active than on the outside where the water is not flowing. The result is that the temperature of the water drawn increases by approximately 5°C, allowing the water to be kept at 35°C if the usage temperature required is 40°C.

If the room temperature is 20°C, this results in a heat loss of 25% (thermal head: 35-20 = 15°C, rather than 40-20 = 20°C).

When the water is kept at a lower temperature, less lime-scale deposits form. This advantage is increased for the fast-acting boiler, i.e. those with a higher level of power, as shown in figure 7.

In general, the heating element according to the invention makes it possible to manufacture a fast-acting storage heater where the same heating element can pre-heat the water stored to the storage temperatures lower than those required and then complete the heating phase at the moment of use.

An electήcal resistor of the armoured kind for boilers usually has a thermal load, as mentioned earlier, of 8.5W/cm2 and it is subject to rapidly forming lime-scale deposits, which increase in direct proportion to the thermal load. A boiler output pipe is generally !< " in diameter (i.e. 21mm): supposing the length is 600mm and the installed power is 1500W, the heating element 1 has a thermal load of less than 4W/cm2, less than half that of the armoured resistor, and it is possible to further reduce the thermal load by increasing the pipe diameter and its surface while keeping the surface of the printed resistor route unchanged without there being any significant increase in the cost.

The heating element 1.1, preferably of the kind indicated for instant electric boilers, makes it possible to reduce the dimensions of these latter. Supposing the power is 20kW and the pipe has a diameter of %", as a thermal load of approximately 20W/cm2 is acceptable (since the water does not become stagnant, there is no risk of scaring), the length of the heating element is equal to approximately 1200mm, but, to limit the dimensions, the version produced in practice can also have two or more heating elements placed alongside or coaxially, or a pipe with a larger diameter.

Claims

1. A tubular-shaped heating element, in particular for heating apparatus for water to be used for sanitary purposes and for household electrical appliances in general, of the kind using the technology in which the printed resistor is apphed to a metal surface, the said printed resistor consisting of one or more further layers of dielectric material applied to the said metal surface, printed onto which, using for example a screen printing technique, are one or more resistive electric circuits, applied to which, in their turn, are one or more layers of dielectric material, characterised by the fact that the said heating element (1; 1.1) is constituted of at least one printed resistor (4; 4.1) on a piece of piping (3), the said piping (3) having a section which is shaped in any way to allow the water to be used for sanitary purposes at least, to pass through.

2. A heating element (1 ;1.1) according to claim 1 , characterised by the fact that one or more printed resistors (4; 4.1) can be applied to the said piping (3).

3. A heating element (1 ; 1.1) according to claims 1) or 2) characterised by the fact that each of the said printed resistors (4; 4.1) can contain one or more independent resistive electric circuits.

4. A heating element (1; 1.1) according to one or more of the previous claims characterised by the fact that the said independent resistive electric circuits can be positioned over several layers, each layer being separated from the others by one or more layers of dielectric material according to the printed electrical resistor technology.

5. A heating element (1 ; 1.1) according to one or more of the previous claims characterised by the fact that the said printed resistors (4; 4.1) can be apphed either to the external surface of the piping (3), the internal surface, or to both.

6. A heating element (1; 1.1) according to claim 1) characterised by the fact that the heating element (1; 1.1) is fitted with at least one pipe coupling (5; 5.1).

7. A heating element (1; 1.1) according to the previous claim characterised by the fact that the said one or more pipe couplings (5; 5.1) are fitted with at least some means of connection (7) to the water mains.

8. A heating element (1; 1.1) according to the previous claim characterised by the fact that the said pipe couplings (5; 5.1) are also fitted with at least one means (6) of connecting the water heating apparatus, this latter also being equipped with a suitable attachment means (8).

9. A heating element (1 ; 1.1) according to the previous claun characterised by the fact that the said suitable attachment means (8) are constituted of threaded ring nuts that are integral with the water heating apparatus.

10. A heating element (1; 1.1) according to one or more of the previous claims characterised by the fact that the said printed resistors (4; 4.1) can be apphed to the either the whole or part of the external or internal surface of the piping (3).

11. A heating element (1; 1.1) according to one or more of the previous claims characterised by the fact that each independent resistive electrical circuit that is connected to each of the said printed resistors (4; 4.1), can be connected to a corresponding pair of connectors (9) for the electrical power supply.

12. A heating element (1; 1.1) according to the previous claim characterised by the fact that the said connectors (9) are connected to the said resistive electrical circuits of the said printed resistors (4; 4.1) using means common in the printed resistor technology.

13. A heating element (1; 1.1) according to claims 11) and 12) characterised by the fact that the said connectors (9) are mounted on the said pipe couplings (5; 5.1), the said connectors (9) being insulated electrically from the said pipe couplings (5; 5.1) with commonly known means.

14. A heating element (1; 1.1) according to claims 11) and 12) characterised by the fact that the said connectors (9) are mounted at any point on the external surface of the piping (3).

15. A heating element (1; 1.1) according to one or more of the previous claims characterised by the fact that the routes of the printed resistors' (4; 4.1) resistive electrical circuits can have any form, either regular or irregular.

16. A heating element (1; 1.1) according to the previous claim characterised by the fact that the routes of the printed resistors' (4;4.1) resistive electrical circuits can be fretted or double spiral in form, the pitch of the said fretting or double spirals being either constant or variable.

17. A heating element (1; 1.1) according to one or more of the previous claims characterised by the fact that it is possible to distribute the thermal load, as required, either uniformly or differently, along the piping (3) by means of the suitably routed resistive electrical circuits of the printed resistors (4; 4.1).

18. A heating element (1; 1.1) according to one or more of the previous claims characterised by the fact that it is possible to have a protective sheath (15) which acts against the potential risk of abrasion to the printed resistor (4).

19. A heating element (1; 1.1) according to claim 18) characterised by the fact that the said protective sheath (15) can, usefully, constitute an element designed to protect the tank (2; 2.1) against the phenomenon of corrosion.

20. A heating element (1; 1.1) according to claim 19) characterised by the fact that the said element designed to protect the tank (2; 2.1) against corrosion can advantageously consist in an electrode in the form of an impressed current cathodic protection device, being the aforesaid protective sheath (15), made of the most suitable material for this additional function, such as, for example, a magnesium alloy.

21. A heating element (1; 1.1) according to claim 19) characterised by the fact that the said element designed to protect the tank (2; 2.1) against corrosion can advantageously consist in a sacrificial anode, being the aforesaid protective sheath (15), made of the most suitable material for this additional function, such as, for example, a magnesium alloy.

22. A heating element (1; 1.1) according to claims 20) or 21) characterised by the fact that the electrical connections of the said element designed to protect the tank (2; 2.1) against corrosion can be made, in part or in whole, using the means made available by the printed resistor technology.

23. A heating element (1 ; 1.1) according to one or more of the previous claims characterised by the fact that on at least one surface of the piping (3) there can be a layer of material (14) designed to make it difficult for lime-scale deposits to form, such as polypropylene.

24. A heating element (1; 1.1) according to the previous claim characterised by the fact that the said layer of material (14) is preferably apphed to the portions of the surface of the piping (3) in positions where water being heated could become stagnant.

25. A heating element (1) according to one or more of the previous claims, and designed to be used in a storage heater, characterised by the fact that the piping (3) has, in its lower part (where the water is stored at a lower temperatures) one or more openings (10; lO.a; lO.b) connecting the external surface and the internal surface of the piping (3), the said openings (10; 10. a; lO.b) having a section shaped in such a way so as to provide for the natural circulation of water inside the piping (3) during the heating phases.

26. A heating element (1) according to the previous claim characterised by the fact that the openings (lO.a; lO.b) can be equipped with means (12; 13) for obstructing the eddy of cold water during the water drawing phase.

27. A heating element (1; 1.1) according to one or more of the previous claims, and designed to be used in a storage heater, characterised by the fact that the piping (3) in the upper part, has one or more openings (11; 11.b) designed to facilitate, through natural circulation, the overflow of water from the piping (3) during the heating phases, preventing any air bubbles there may be in the inlet (3. a) becoming an obstruction.

28. A heating element (1) according to one or more of the previous claims, and designed to be used in the tank (2; 2.1) of a storage heater, characterised by the fact that the piping (3) supporting one or more printed resistors (4; 4.1) can have either a cold water inlet function or a hot water output function.

29. A heating element according to one or more of the previous claims, and designed to be used in a storage heater, characterised by the fact that one or more of the printed resistors (4.1) is supported by the external and/or internal surface of the tank (2.1).

30. A heating element (1; 1.1) according to one or more of the previous claims characterised by the fact that, using the same technology, and at the same time as the one or more printed resistors (4; 4.1) are applied, electrical circuits can be printed on the surface of the piping (3) which are designed as a useful connection for various electrical or electronic components which are advantageously mounted along the heating element (1; 1.1); the said heating element acting as a support for the said components which are welded to one end of the aforesaid printed electric circuits, in the most suitable position along the heating element (1; 1.1) and insulated electrically from the surrounding environment; the other end of the said circuits terminating, with suitable electrical connectors (9), in the most suitable position, for example at the pipe coupling (5, 5.1).

31. A heating element (1; 1.1) according to the previous claim characterised by the fact that the said electrical or electronic components can be, for example, electronic temperature sensors to be connected with corresponding electronic thermostats, or unipolar safety thermostats of a bi-metalhc laminar kind, or those with a fuse or of another kind, and also anticorrosion protection device electrodes.

32. A heating element (1;1.1) according to the previous claim characterised by the fact that, if the said components can be constituted of unipolar safety thermostats, they can be welded on directly in series with the resistive electric circuits of the printed resistors (4; 4.1) to be monitored.

33. A heating element (1; 1.1) according to one or more of the previous claims characterised by the fact that, at the same time as one or more printed resistors (4:4.1) are apphed and using the same technology, electric circuits, constituted of a track of resistive material with a resistivity level dependant enough on the temperature to be measured using normal electronic devices, can be printed onto the surface of the piping (3) in order to monitor the local temperature, the said route being therefore a temperature sensor printed using the printed resistor technology.

34. A heating element (1; 1.1) according to the previous claim characterised by the fact that the route of the printed temperature sensor can be constituted of a track long enough to increase the total resistance, thus facihtating the measuring of the resistor as a function of the temperature change.

35. A heating element (1;1.1) according to one or more of the previous claims characterised by the fact that the said printed resistors (4; 4.1) can be monitored in a commonly known way by any regulating or safety components, such as thermostats, pressure switches and flow switches.

36. A storage heater, characterised by the fact that at least one heating element (1) is used.

37. A storage heater according to the previous claim characterised by the fact that the said heating element (1) incorporates and/or supports temperature sensing means and/or safety thermostats and/or means of protection against corrosion.

38. A storage heater according to claims 36 or 37 characterised by the fact that the tank (2) has only an inlet hole for the cold water and an output hole for the hot water, there being at least one heating element (1) mounted in position with the said inlet hole or the said output hole, or both.

39. A method for regulating the temperature in a storage heater characterised by the fact that, the temperature inside the tank (2; 2.1) is kept at a first pre-set storage value and, in the drawing phase, only the water drawn is heated again to a second value which is higher than the first storage value.

40. A storage heater implementing the regulating method according to claim 39).

41. A storage heater according to claim 40), which precedes, characterised by the fact that a single heating element (1) is used both to keep the temperature of the water at a first pre-set storage value and then to reheat it to a second drawing temperature value.

42. A storage heater, in particular of the fast-acting and/or free-discharge kind, characterised by the fact that at least one or more of the printed resistors (4.1) are supported by the external and/or internal surface of the tank (2.1), it being possible that at least one further heating element (1) is present in position with the inlet or output pipe.

43. An instant boiler characterised by the fact that one or more heating elements (1.1) are used as a heating means.

44. A device for heating water and air inside a dishwasher characterised by the fact that one or more heating elements (1.1) are used as a heating means.

45. A device for heating water inside a storage heater characterised by the fact that the said device is constituted of a metal element made of a suitable material supporting a printed resistor (4).

46. A temperature sensor manufactured using the printed resistor technology constituted of a printed track of resistive material with a resistivity level dependant enough on the temperature to be measured by measuring, regulating and monitoring means normally used in household electrical appliances.

47. A support element for various electrical or electronic components such as electronic temperature sensors to be connected to the corresponding electronic thermostats, or unipolar safety thermostats of the bi-metalhc laminar kind, or those with a fuse or of another kind, and to further anticorrosion protection devices, characterised by the fact that the connecting electrical circuits of the said components are made using a printing technique according to the printed resistor technology and that the said support element, complete with the said components, is designed to be immersed in the water, as all the electrical components and all the electrical circuits are insulated in a commonly known way.