EP0812522A1

EP0812522A1 - Electric heating element of the convection or convection-radiation type

Info

Publication number: EP0812522A1
Application number: EP96905895A
Authority: EP
Inventors: Jacques Fremaux; André Giraud
Original assignee: Generale d'Innovation et de Developpement COGIDEV Cie
Current assignee: Saint Gobain Vitrage SA
Priority date: 1995-03-01
Filing date: 1996-03-01
Publication date: 1997-12-17
Also published as: FR2731311B1; CA2213835A1; WO1996027271A1; JPH11505662A; FR2731311A1

Abstract

These heating elements, which are transparent, take a minimum of space and have a good efficiency, are comprised of a heating body consisting of at least one tempered glass plate covered with a thin electroconducting layer, and associated to one or a plurality of surfaces configured like transparent, complementary layers or plates, providing for the definition and control of the mode of heat transfer from the heating element to the environment and/or providing for the electric insulation. There is disclosed a wall convector comprising two protection plates (4, 6) made of thermally and mechanically resistant glass, the wall plate (4) comprising an infrared reflecting layer (4a) and an intermediary heating plate (5) with a thin electroconducting layer (5a) facing the layer (4a); said plates are spaced apart by a distance sufficiently large so that the convection does not bring in any exagerated overheating of air, and sufficiently small so that the convection does not bring in perturbation phenomena due to descending draughts.

Description

ELECTRIC HEATING ELEMENT OF THE CONVECTION OR CONVECTION AND RADIATION TYPE.

The present invention relates to electric heating elements of the convection or convection and radiation type.

Domestic electric heating is today not only widely used but encouraged and many devices are used to achieve it.

They generally use the principle of the Joule effect to create a source of heat thanks to a fall of potential in a resistance, managed by the law of Ohm. The heat thus produced is then transferred by various processes.

The most widely used is convection transfer. The air located in the vicinity of the heated resistor sees its temperature increase, therefore its density decrease. It tends to rise; an ascending current is established and the hot air is replaced by cold air which in turn heats up and, the phenomenon of thermo-siphon initiated, it continues. The device produced in this transfer mode is a convector.

Another way of transferring the energy produced at the level of the electrical resistance is the radiation emitted by this one and which is propagated through the part, The radiated energy is in first approximation proportional to the fourth power of the temperature Kelvin like demonstrated by Stephan and Boltzmann. The corresponding device is a radiant panel.

Finally, it happens that the transfer takes place from the resistance by conduction in a fluid which in turn heats an envelope, which transfers its calories to the ambient air by the different transfer methods described. This process is used in traditional central heating where water, steam, an oil are the heat transfer fluids. These devices are generally (and incorrectly) called radiators. These various devices have drawbacks, which, acceptable in certain cases, can be serious in many uses.

First, they often harm the general aesthetics of the rooms in which they are installed.

The luminous heating elements, which are at the base of the functioning of certain devices, more or less visible, more or less complicated (twisted wires, coated wires, etc.), surrounded by support and protective parts, can constitute particularly unsightly assemblies. .

The non-luminous resistive elements, generally used for convectors, are enclosed in housings or covers comprising openings in the lower part, in the upper part, sometimes laterally, are opaque and bulky and often do not fit in well with the surrounding decor. Sometimes even (heating historic monuments for example), they can be downright unacceptable.

Secondly, these current devices also suffer from yield losses linked to their very structure. Thus, when it comes to wall convectors, they transmit a significant part of the heat to the wall against which they are placed which dissipates it by conduction towards the outside. This loss is all the higher as the concern not to exceed a maximum temperature on the external wall of the convector leads to limiting the transfer of the resistance to the air which passes through the convector. Other phenomena can limit the efficiency or the use of current heaters. Thus, the radiant effect of current metal convectors is limited by the fact that the external wall of the convector which closes the duct in which the air circulates must be kept at a low temperature and opposes by its opacity the transmission of radiation. infrared produced by the hot resistance. Or, the panels radiant heaters can only reach a good radiation temperature if they are placed in inaccessible places, such as ceilings, which is unfavorable for heating a high ceiling volume as found in duplex apartments with mezzanine.

Finally, the increased demands on the concept of comfort, which require minimizing thermal jolts, that is to say the variations in room temperature between two successive switches on of the heating device are not, in most cases, satisfied with current devices.

The present invention relates to heating elements which do not have the drawbacks indicated by the prior art.

They comprise a heating body composed of at least one plate of thermal glass ent and mechanically resistant, covered with a thin transparent electrically conductive layer, which acts as a resistance in which the electricity which passes through it is transformed into heat by the Joule effect; said heating body being associated with one or more surfaces, in the form of layers or plates, transparent, complementary, parallel or almost parallel to the heating plate (s), which, by their properties and / or their arrangements in relation to the heating plate (s), makes it possible to define and control, according to the chosen use, the mode of transfer of heat from the heating element to the environment and / or to provide electrical insulation, the various plates being arranged so as to allow air circulation between them.

In the case of the apparatuses according to the present invention, formed from plates spaced apart from each other, which are not joined together by any closed frame, thus allowing the entry of air through the lower part and laterally, the air flows at lower temperature and convective flow air flow is greater for better thermal regulation of the room.

The heating elements according to the invention ensure, as will be indicated below, good transparency, very good performance, minimum space requirement and compliance of the device with the safety requirements and standards in force.

To understand the functioning, according to the invention, of these complementary transparent surfaces, it is advisable to recall some of the properties of the transparent layers, for example deposited on the surface of a glass.

Either a glass plate coated with a layer of

300 nm (3000 Å) of doped tin oxide. It has: (a) a conductivity of approximately 30 Ω / D and if a potential difference is established between two opposite sides of a rectangular plate, the layer behaves like an electrical resistance whose value depends on the ratio of the dimensions of the sides of the rectangle and which heats up by Joule effect, and, by conduction, also heats the glass plate. Thus, a square of such a layered glass, connected to a 220 V electric power supply network, would dissipate a power of 1613 Watts, whatever the dimensions of the square. It appears that the thermal performance depends only on the surface and the ratio of dimensions

(length and width) of the plate. The choice of power, for a given coated glass, is obtained by the ratio of the dimensions of the plate and the choice of temperature by the product of the dimensions of the plate. By setting the power and the temperature, it is easy to calculate the dimensions.

The surface of the glass, on the side opposite the layer, is considered to be insulating. Its surface resistance is of the order of 10 ¹² Ω / D (1000 billion Ω / D);

(b) a surface emissivity on the layer side of 0.15 and on the opposite side of 0.9. A hot plate emits radiation proportional to the emissivity and which will be asymmetrical and in the proportions of 0.9 to 0.15, ie 6. According to

Kirchoff, the radiation emitted can only be done on the lengths where the glass plate has an absorption band. It is located on lengths greater than 5 μm. Only wavelengths between 5 and 20 μm are carriers of appreciable energy, which can be calculated by Planc's law. They correspond to physiological wavelengths, that is to say those which provide a feeling of comfort and well-being.

(c) Infrared reflectivity of 85% on the layer side and 4% on the opposite side. The whole glass and layer remains transparent to light. The authors of the present invention thus had the idea of using these properties to orient the direction of emission on one side or the other of the heating plate, to reflect, or, on the contrary, to let pass radiation. In addition, an additional glass plate or a transparent insulating layer can be used to prevent access to the heating plate and thus burn or receive an electric shock, while maintaining the transparency of the element. of heating. Incidentally, decorative effects can be found using the color or light effects that these plates or layers allow.

Thus, according to the present invention, heating elements as varied as wall or mobile convectors are proposed, baseboards or heating strips, wall or mobile radiant panels, mixed elements wall or mobile radiant convectors, mobile or removable heating partitions, for modular spaces, tumble dryers, etc.

To further deepen the understanding, according to the invention, of the operation of a heating appliance, let us examine an embodiment in the form of a wall convector. The calories are provided by the Joule effect in a heating body consisting of a glass plate, coated on one side with a transparent electrically conductive layer positioned towards the wall. This arrangement makes it possible to minimize the thermal radiation towards the wall because of the low emissivity of the layer. In front of this first plate I, and separated, for example, by 15 mm, is placed a glass plate II thermally and mechanically resistant, the object of which is: (a) to define a space where convection, air flowing from bottom to top;

(b) prevent users from touching the hot plate I, the temperature of which can thus be brought to 120 "C;

(c) to prevent users from touching the electric plate by touching the plate I. For this purpose, either the plate I is of smaller size than the plate II, or, what is even better, the conductive layer is limited to a smaller surface than that of the plate I; (d) blocking the infrared radiation emitted by the plate I towards the plate II by a reflective layer of the infrared deposited on the plate II opposite the face I or re-emitting towards the part after absorption by the glass of the plate II part of the radiation emitted if the plate II does not include an infrared reflecting layer.

In the two options mentioned above, the temperature of plate II does not exceed 60 "C.

Against the wall, a few millimeters from it, is placed between the wall and the plate I, a plate III spaced from the plate I, for example by 15 mm. This plate consists of a glass, coated, on the side furthest from the wall, with an infrared reflecting layer, the role of which is: (a) to delimit a second space between the plates I and

III where air heated by plate I circulates; (b) to send back to the plate I, the infrared radiation which it had emitted, so that the wall is protected and thus the losses are very reduced. The efficiency of such a convector is greatly improved compared to traditional convectors: the exchange surface between the air and the heating body is maximum and corresponds to twice the surface of the convector due to the double compartmentalisation of the space. convection. The air flow, important at a lower temperature than in conventional devices, meets modern requirements for thermal comfort in the home; losses were minimized by controlling the radiation emitted by the heater. The aesthetics of this device is provided either by the transparency of its components, or by elements of color or decor, benefiting from the specific qualities of the "glass" material - transparency, reflections, colors, etc. - which can be brought by plate II and of which a wide range exists among glassmakers or glassmakers.

For other applications, the choice and the arrangement of the complementary transparent surfaces which accompany the heating plate may be different. Thus, to constitute a transparent heating partition, for example in landscaped offices, there is a large heating surface, which makes it possible to maintain a low energy dissipation per unit of surface and the surface temperature remains low. The energy emitted in the form of radiation is this time usable on either side of the partition, and there is therefore no need to provide the means to reflect it towards the heating body.

It is therefore sufficient to protect the heating plate, thermally and mechanically resistant, against the possibility of untimely electrical contacts. This can be done by placing a second glass plate against the conductive layer, possibly separated by an interval of air or with a transparent polymer sheet or else to cover the conductive layer with a second transparent, insulating layer, compatible with the temperature of the heating body, such as the layers of silica, chromium oxide, oxide titanium or silicone.

Another application for assessing the versatility and efficiency of the device according to the invention relates to a radiant panel.

The base is always a transparent, thermally resistant heating plate, coated with a thin electrically conductive layer facing the wall which supports the panel. As indicated above, the radiation emitted by the plate brought to a temperature for example of 120-130 ° C. is asymmetrical. It is much higher (more than 4 times) towards the room than towards the wall. However, to minimize losses by transmission to the wall, another transparent surface is interposed between the latter and the heating plate, constituted for example by a glass plate covered with an infrared reflecting layer (this may be a glass with a tin oxide layer identical to that used for the heating plate). In this use as a radiant panel, intended to transmit heat directly to the room and to its inhabitants, it may not be advantageous to let part of the heat dissipate by convection. You can do this on the geometry (distance between the two plates, closing the upper part) or on the position (radiant panels placed against the ceiling).

The three preceding illustrations having shown the variety of possible applications of the invention, we will now endeavor to describe its components and practical embodiments.

As the heating plate, a glass plate is used coated on one of its faces with a thin transparent electrically conductive layer with low emissivity and reflecting the infrared. There are several kinds, including those based on tin oxide doped with antimony or fluorine, or indium oxide doped with tin, deposited under a thickness of a few hundred nanometers, and whose surface conductivity can range from a few Ω / D to a few hundred d 'Ω / D. We can cite the use of commonly marketed glasses, with a conductivity of 35 Ω / D or 50 Ω / D, manufactured by the Saint-Gobain-Vitrage Company and marketed under the names EKO and EKO Plus respectively, or K-Glass of 30 Ω / D from the Pilkinton Company, or Thermoplus-comfort of 40 Ω / D from Glaverbel.

However, these glasses must be tempered for use according to the present invention, in order to make the plates resistant to the significant thermal shocks to which they will be subjected. Such glasses, in the non-toughened state, are marketed for the production of glazing allowing sunlight to penetrate and, on the contrary, reflecting infrared radiation of longer wavelengths; not emitting these wavelengths, this glazing is favorable for energy savings. Likewise, such non-toughened glasses are sometimes used in the structure of certain windshields, designed to ensure defrosting by the Joule effect at low temperature.

To constitute the complementary transparent surface (s) which have the purpose of defining and orienting the heat fluxes coming from the heating plate (s) or ensuring other functions, the following nonlimiting examples may be cited: to reflect infrared radiation: the low-emissivity layers already mentioned have this property; we can also cite thin metallic layers (silver or copper for example); all these layers are optionally protected by a transparent overcoat (silica, transparent polymers); to provide electrical insulation: simple glass plates or transparent layers (silica, chromium oxide, titanium oxide, silicone, transparent polymers); to provide mechanical protection: tempered glass plates or plates of transparent polymers or laminated composites glass - plastic material (s) (glass-PVB; glass-polyurethane for example); to ensure decorative effects: plates of transparent glass or polymers, colored or engraved, or printed, or enamelled, or coated with layers or films themselves decorative.

Of course, some of these plates can simultaneously perform several of the functions mentioned.

To these basic components, there are additional components, such as the means for fixing the plates relative to one another and relative to the walls concerned, or alternatively switches and thermostats of models comparable to those used for current appliances, chosen in aesthetic harmony with the heating elements previously defined.

The current arrives via two strongly conducting lines (screen-printed or glued), located in intimate contact with the electroconductive layer, on two opposite edges of the latter. Complementary lines of the same type can be deposited within this interval, allowing then, by an appropriate connection, to connect in series the resistances represented by the surfaces delimited on the conductive layer. For some of these heating elements, it may be advantageous to control the operations by an automatic presence detector. This could be the case for example for radiant panels intended to warm the public in certain places open to the outside, such as shopping malls, waiting rooms, displays, etc. The present invention will be further illustrated by the following examples.

Example 1: CONVECTOR

This type of device, in principle, has been described above. It can be a wall convector, or even a mobile convector, which can in this case be a backup heater.

Such an apparatus comprises the following succession of plates arranged facing one another: - a first protective plate, made of thermally and mechanically resistant glass; a heating plate, the electrically conductive thin layer of which faces towards said first protective plate; - If necessary, a second heating plate whose thin electrically conductive layer is turned on the same side as the previous one; or else several other heating plates, the thin electrically conductive layers of which are turned on the same side as the previous one; a second protective plate, made of thermally and mechanically resistant glass; each of the protective plates may include, on the side facing the neighboring heating plate, an infrared reflecting layer, and the various plates being spaced apart from one another by a sufficiently large distance so that the convection does not bring about an exaggerated overheating of air, and weak enough so that convection does not bring disturbances by downdrafts.

In the case of a wall convector, if the first protective plate is that placed opposite the wall, it is advantageous that it comprises, on the side opposite the wall, an infrared reflecting layer, facing the thin electrically conductive layer from the neighboring heating plate. In practice, in most cases, the distance between two neighboring plates would therefore be between 5 and 25 mm.

The plates making up the convector are generally arranged vertically, their spacing therefore being constant; they can also (at least one of them) be inclined relative to the vertical plane so that the spacing between two plates increases from bottom to top, this geometrical arrangement being favorable for the regulation of the heat transfer which heats the air.

Furthermore, it is advantageously possible to provide that at least one protective plate of the convector overflows from the heating plate (s) all around its periphery, or that all the plates of the convector are of the same dimension, the live part of the conductive layers of the heating plates being limited to a smaller area than that of the plates themselves.

A particular embodiment of a wall convector will now be described with reference to Figures 1 and 2 of the accompanying drawing: Figure 1 is a front view of this convector; and Figure 2 is, on a larger scale, a partial sectional view along II-II of Figure 1.

We can see in these Figures 1 and 2 that there is shown by 1, as a whole, a transparent convector mounted against a wall 2 at a conventional distance from the ground 3.

In the mounting position, the convector 1 comprises three rectangular plates 4, 5 and 6, substantially parallel to one another and to the wall 2, made of the same glass with a 6 mm EKO type layer from the Saint-Gobain Company, this thin layer being designated respectively 4a, 5a and 6a.

The plate 4, closest to the wall, is arranged so that its layer 4a is turned away from the wall 2.

The plate 5 has a length shorter than that of the plate 4 and it is arranged relative to the plate 4 so that, in the direction of the length, the latter overflows by an equal distance on both sides, and that, in the direction of the height, it overflows at the lower part by a distance substantially equal to the aforementioned distance, and, at the top, a slightly greater distance. The plate 5 is also arranged so that its layer 5a _. either turned towards layer 4a.

As for the plate 6, it is identical to the plate 4, except that it is of lesser height, and it is arranged opposite the latter so as to project from the plate 5 by an equal distance over the whole around. The layer 6a is turned towards the plate 5.

Along the two vertical edges of the plate 5, on the side of the layer 5a., Are arranged two thin conductive strips 7a _. , 7b, which constitute current supply buses to said layer 5a. At the lower part of each strip 7a, 7b, a wire 8a, 8b respectively for connection to the network is welded. These wires 8a, 8b, although visible in the drawing, are relatively hidden from view.

Two decorative insulating strips 9a, 9b respectively can be arranged along the two horizontal edges of the plate 5, also on the layer 5a. These optional bands 9a, 9b, with the bands 7a, 7b, outline the slightly darker periphery of a rectangle, thus improving the aesthetic appearance.

For mounting the convector 1, four holes are made in each of the plates 4, 5 and 6. The holes are made in the four corners of the plate 5, and those of the plates 4 and 6 in the opposite locations to observe the relative positioning plates, the latter being further apart from each other and the plate 4 being separated from the wall 2 as described below.

Four sleeves 10 are screwed into the wall 2, according to the spacing of the holes made in the plates, these sleeves 10 receiving screws 11 on the projecting part of which is screwed a cylindrical piece 12 for holding plates 4, 5 and 6. Each piece 12 has, at its end coming to be placed against the wall 2, a flange 13 constituting the spacer between the wall 2 and the plate 4. Once the latter applied against the flanges 13, rings 14 are successively put in place playing the role of spacers between the plates 4 and 5, the plate 5, rings 15 playing the role of spacers between the plates 5 and 6 , the plate 6, then cabochons 16 for holding the latter, whose rods are screwed into the end parts of the parts 12 and whose heads can have a decorative role.

A shelf 17 can be fixed to the wall 2, perpendicular to the latter coming to bear on the upper edge of the plate 4.

In the convector 1, the plate 4 is a thermal protection plate, the plate 5, the heating plate, and the plate 6, a mechanical and thermal protection plate as well as decorative, if it is chosen from a glass having a decorative effect. . It is possible, instead of a plate 6 coated with a layer 6a, to use an uncoated plate 6, in which case this will have a role of mechanical protection only, and possibly a decorative role depending on the choice of glass. 4, 4 and 4 mm thick plates can be used. The distance between two successive plates can be 20 mm, in which case the total size of the plates in depth is 52 mm.

Furthermore, the heating plate 5 could be replaced by two heating plates of the same type, with the electrically conductive layers always turned towards the side of the plate 6. In this case, a distance of 15 mm can be provided between two successive plates, the total overall dimensions of the plates then being 61 mm. Also, it is possible, by the choice of spacer rings 14 and 15 of suitable shapes, to mount for example the heating plate or plates 5 and the plate 6 in an inclined position relative to the vertical plane so that the spacing between an inclined plate and the vertical plane increases from bottom to top. It is thus possible to provide an angle of inclination of less than 20 'between the plates. Powered by a normal distribution network voltage, the layer 5a dissipates by the Joule effect an energy which heats the plate 5 and brings it to a temperature T ₅ . As indicated above, it can be considered without great error that the two faces of the plate 5 are at the same temperature ₅ . The energy radiated by the face 5a is low and is reflected by the face 4a of the plate 4, reflecting the infrared. The energy radiated by the plate 4 is low, the latter does not heat up by radiation. The energy radiated by the face opposite to the layer 5a corresponds approximately to that of a black body. It is reflected by the face 6a of the plate 6. The temperatures T ₄ and T ₆ depend only on a convective exchange caused by the hot air which circulates between the plates 4 and 5, and 5 and 6. The system is managed by the temperature T ₅ (therefore the power of the convector) and the spacings between the plates.

The electrical resistance R of the rectangular glass plate 5 is as follows:

or a is the height of the plate or length of each of the current collectors 7a, 7b; - b is the length of the plate or distance between the two current collectors 7a, 7b; and

Rc is the ohmic surface resistance. For a given electrical supply voltage of this resistor R, the electrical power is: u ^< (V)

(W)

(Ω)

U being fixed (220 Volts), to choose a power, or to determine a range of powers, we calculate R, then we adjust the ratio b / a to obtain R. Another parameter intervenes, namely the power load per unit of surface (S), which conditions the surface temperature of the plate:

P _(W) _ P _(W) _ u ² o -

S (dm ² ) axb Rc xb ²

S therefore only depends on b; b being fixed, the desired electrical power will provide a.

If we aim to offer convectors with a power range of 500 to 2000 W while remaining in the range of 10 to 20 W / dm ² , in particular from 10 to 13 W / dm ^2, for the load S , one can conceive, by having glasses with layers of the trade whose resistances are

35 Ω / D and 50 Ω / D approximately, a vertical heating element with three plates (high powers from 5000 to 2000 W) or a horizontal heating element with three plates (low powers from 500 to 1000 W) or with four plates, two of which heating (powers greater than 1000 W). The dimensions a and b of the heating plates are for example such that S <1 m ² ; 0.5 <b / a <1.5; and 8 <b <12 dm.

The surface temperature of the protective plate 6 is limited to 60 ° C. The spacing of the plates, which can be varied between 10 and 20 mm for example, allows the temperature of the air circulating between the plates to be adjusted.

In the case of two heating plates in parallel, combinations of two heating plates of different powers are possible. Example 2: HEATING PLINTH / HEATING BAND

Such an apparatus comprises two heating plates arranged facing each other with their thin electrically conductive layers arranged face to face, one serving as an infrared reflecting plate for the other, a protective plate made of thermally or mechanically resistant glass that can be arranged opposite of the outdoor heating plate.

In Figure 3 of the accompanying drawing, there is shown schematically ent, in vertical section, a heating baseboard 18, composed of two heating plates 19, 20 whose layers 19a, 20a are arranged opposite and mounted in parallel, a protective plate 21 being, where appropriate, placed opposite one of the two plates 19, 20. If the height a of the plinth is fixed at 1 dm, b / a being much greater than 1, in particular between 8 and 10 dm , a power density of 15 W / dm leads to a power of 250 W with a layer of 46.5 Ω / D, and a power density of 10 W / dm ² leads to a power of 200 W, with a layer 38.7 Ω / D. For 6 = 15 W / dm ² , the surface temperature of around 110 ° C requires a structure with three glass plates (18; 19; 20). For δ = 10 W / dm ² , the surface temperature of approximately 80 ° C allows a structure with two glass plates (18, 19), advantageous for the bulk in thickness. The second plate serves as both a heating plate and a reflective plate.

The increase in the dimension a (strip) makes it possible to reach greater powers with the commercial layers of little different values of 35 Ω / D and 50 Ω / D.

For a = 3 dm, with power densities of 15 W / dm ² and 10 W / dm ² . we obtain respectively 360 W and 225 W for Rc = 50 Ω / D and 430 W and 350 W for Rc = 35 Ω / D. Example 3: SUPPORTED RADIANT PANEL

This device, in principle, has been described above.

It comprises a protective plate of thermally and mechanically resistant glass, placed facing the support wall, and comprising on the side opposite the latter, an infrared reflecting layer, and, facing the latter, a heating plate. the electrically conductive thin layer of which faces the protective glass plate, the two plates being spaced apart sufficiently far that the convection does not bring about an exaggerated overheating of the air, and sufficiently weak so that the convection does not brings no phenomenon of disturbance by downdrafts. In Figure 4 of the accompanying drawing, there is shown schematically ent, in vertical section, a radiant panel 22, composed of a heating plate 23 coated with a thin electrically conductive layer 23a, and, disposed opposite the latter, a protective glass plate 24, which is coated with a thin reflective layer of infrared 24a _. .

The plate 23 can have the following dimensions: 7 <b <8.5 dm; 1/3 <b / a <1; the density δ being of the order of 20 W / dm ² , for a power of 1000 to 2000 W. The conductive layer 23a is also at low emissivity; from the point of view of the radiation emitted by the glass, the behavior of the two faces of the plate 23 is asymmetrical, and the radiated energies are proportional to the emissivity. The small thickness of the glass means that the gradient in the thickness is very small and that it can be assumed that the glass is isothermal. The temperature of the glass for a value of δ of 20 W / dm * is around 120-130 ° C., from which it follows that the energy radiated by the face on the layer side 23a (ε = 0.2) is of the order of 300 W / m ² and the energy radiated by the opposite face (ε = 0.9) is around 1300 W / m ² . At the above temperatures, the wavelength which emits the most energy is equivalent to 7.3 μm. The practical width of the spectral range is between 3.65 μm and 32.85 μm, which corresponds to the absorption band of the glass, therefore of emission according to Kirchoff's law. The low emissivity layer 23a at these wavelengths tends to minimize the energy radiated on the layer side. A temperature variation of the order of 10 ° C does little to modify the distribution of the radiation.

To improve the performance of the radiant panel 23 alone, it is necessary to reflect the radiated energy emitted by the layer 23a. So placed next to the layer 23a, the plate 24 of coated glass, the layer 24a of which is turned towards the layer 23a and which will reflect the infrared. Depending on the spacing between the plates 23 and 24, it is possible to generate convection between them. The heating element 22, as shown in FIG. 4, is thus obtained, both radiant and convector if the plates 23 and 24 are arranged vertically. The panel 22 can also be placed against a ceiling.

The present invention also makes it possible to produce heated partitions. Such partitions may include a heating plate, the electrically conductive thin layer of which is protected by a glass plate placed opposite it, with an air gap, the two plates being spaced apart by a sufficiently large distance that the convection does not bring an exaggerated overheating of the air, and weak enough so that convection does not bring disturbance phenomena by downdrafts.

It is understood that the embodiments described above are in no way limiting and may give rise to any desirable modification, without departing from the scope of the invention.

Claims

1 - Electric heating element, characterized in that it comprises a heating body composed of at least one thermally and mechanically resistant glass plate, covered with a transparent electroconductive layer which acts as a resistance in which the electricity which the crosspiece is transformed into heat by the Joule effect; said heating body being associated with one or more surfaces in the form of layers or plates, transparent, complementary, parallel or almost parallel to the heating plate (s), which, by their properties and / or their arrangement in relation to the heating plate (s) makes it possible to define and control, depending on the use chosen, the mode of transfer of heat from the heating element to the environment and / or to provide electrical insulation, the various plates being arranged so as to allow air circulation between them.

2 - Heating element according to claim 1, characterized in that the thin transparent electroconductive layer, with low emissivity and reflecting the infrared, is a layer of tin oxide doped with antimony or fluorine, or d indium oxide doped with tin, deposited under a thickness of a few hundred nanometers, and whose surface conductivity ranges from a few Ω / D to a few hundred Ω / D.

3 - Heating element according to one of claims 1 and 2, characterized in that it comprises at least one complementary transparent surface capable of reflecting infrared radiation and chosen in particular from transparent low-emissivity layers of the type of those defined to claim 2; and thin metallic layers; said layers being optionally protected by a transparent over-layer, in particular made of silica or a transparent polymer.

4 - Heating element according to one of claims 1 to 3, characterized in that it comprises at least one complementary transparent surface capable of providing electrical insulation and chosen in particular from glass plates or transparent layers, in particular of silica, chromium oxide, titanium oxide, silicone, or a transparent polymer .

5 - Heating element according to one of claims 1 to 4, characterized in that it comprises at least one complementary transparent surface capable of providing mechanical protection and chosen in particular from tempered glass, transparent polymer or laminated composite glass - plastic material (s).

6 - Heating element according to one of claims 1 to 5, characterized in that it comprises at least one complementary transparent surface capable of ensuring a decorative effect and chosen in particular from glass plates or transparent polymers, colored or engraved, or printed, or enameled, or coated with layers or films themselves decorative.

7 - Heating element according to one of claims 1 to 6, characterized in that the arrival of the current takes place via two strongly conductive lines, located in intimate contact with the electrically conductive layer, on two edges opposite of this, complementary lines of the same type can be deposited within this interval, then making it possible to connect in series the resistances represented by the surfaces delimited on the conductive layer.

8 - Heating element according to one of claims 1 to 7, consisting of a convector (1), characterized in that it comprises the following succession of plates arranged opposite one another: a first protective plate (4), made of thermally and mechanically resistant glass; a heating plate (5) whose thin electrically conductive layer (5a.) faces towards said first protective plate (4); if necessary, a second heating plate whose thin electrically conductive layer is turned on the same side as the previous one; or else several other heating plates whose thin electrically conductive layers are turned on the same side as the previous one; a second protective plate (6), made of thermally and mechanically resistant glass; each of said protective plates (4; 6) possibly comprising, on the side facing the neighboring heating plate, a layer (4a; 6a) reflecting the infrared, and the various plates (4; 5; 6) being spaced apart from one another 'A distance large enough so that the convection does not bring excessive overheating of the air, and small enough so that the convection does not bring disturbance phenomena by downdrafts.

9 - Heating element according to claim 8, characterized in that the distance between two adjacent plates (4 and 5; 5 and 6) is between 5 and 25 mm. 10 - Heating element according to one of claims 8 and 9, characterized in that the plates (4; 5; 6) are arranged vertically or inclined relative to the vertical plane so that the spacing between two plates respectively either constant or increases from bottom to top.

11 - Heating element according to one of claims 8 to 10, characterized in that at least one protective plate (6) projects from the heating plate (s) (5) over its entire periphery. 12 - Heating element according to one of claims 8 to 10, characterized in that all the plates of the convector are of the same dimension, the part under tension of the conductive layers of the heating plates being limited to a smaller area than that actual plates.

13 - Heating element according to one of claims 1 to 7, in the form of a plinth heater (18) or a heating strip, characterized in that it comprises two heating plates (19; 20) arranged opposite with their thin electrically conductive layers (19a; 20a _. ) arranged face to face, l one serving as an infrared reflecting plate for the other, a protective plate (21) made of thermally or mechanically resistant glass or a decorative glass plate which can be arranged opposite the external heating plate (20). 14 - Heating element according to one of claims 1 to 7, consisting of a radiant panel (22), characterized in that it comprises a protective plate (24) of thermally and mechanically resistant glass, arranged opposite of the support wall, and comprising on the side opposite the latter, a layer (24a) reflecting the infrared, and, facing the latter, a heating plate (23) including the thin electrically conductive layer (23a ) is turned towards the protective glass plate (24), the two plates being separated by a distance large enough so that the convection does not bring about an excessive overheating of the air, and sufficiently weak so that the convection does not bring no phenomenon of disturbance by downdrafts.

15 - Heating element according to one of claims 1 to 7, consisting of a heating partition, characterized in that it comprises a heating plate whose thin electrically conductive layer is protected by a glass plate placed opposite of the latter with an air gap, said plates being spaced apart by a distance large enough so that the convection does not bring about an excessive overheating of the air, and sufficiently low so that the convection does not bring any phenomena of disturbance by downdrafts.