NL9201921A - MULTIPLE GLASS PANEL, IN PARTICULAR FOR SOLAR COLLECTORS. - Google Patents

Description

Multiple glazing panel, especially for solar collectors.

The invention relates to a multiple glazing panel provided with glass plates spaced by the ribs of at least one metal spacer interposed between and soldered to the or each pair of successive glass plates.

Such glazing panels are well known and are usually used for glazing building window openings and for other purposes where a greater degree of heat insulation is required than that which can be provided by a single sheet of glass.

Such units are usually manufactured by metallizing the edges of glass plates, usually with a layer of copper, and soldering spacers to such metallized edges.

However, we have found that such a manufacturing process results in the formation of a panel that has unsatisfactory properties when used in certain conditions, especially when a high degree of thermal insulation is required.

The present invention aims to provide a new form of a multiple glazing panel which offers very good thermal insulation and which, at least in some embodiments, can be used in conditions where a typically known panel would not be suitable.

In accordance with the present invention, a multiple glazing panel is provided with glass plates spaced by the ribs of at least one metal spacer interposed between and soldered to the or each pair of successive glass plates, characterized in that the spacers are soldered to with the edges of the glass plates by strips of conductive enamel deposited on those edges, that the or at least one space between the plates has been evacuated and that such space between the plates is one or more includes additional spacers arranged to maintain the spacing between the plates against differential pressure across the glass plates.

Since such a panel is provided with a vacuum-drawn space located between the plates, heat transfer through the panel due to gas convection currents is practically prevented and the panel accordingly has good insulating properties. Furthermore, such good insulation properties are retained due to the very good and durable sealing, which is applied by soldering the spacer (s) to the enamel strips on the glass plates. We have found that applying an enamel strip to a glass plate does not create micro-cracks in the glass, which are often caused by spraying a metallizing coating on a glass plate, as is done in the manufacture of brazed multiple glazing panels with conventional construction. Also, such enamel deposition is often less porous than a metalized coating. The advantage of using enamel strips, as opposed to a metalized strip, is the fact that the bond between the enamel and the glass is stronger and more resistant to stresses to which the panel will be exposed in use, with the result that the seal and consequently the low gas pressure in a space between the plates and vacuum-sucked can be maintained for a longer period of time. Such stresses may result from, for example, fluctuations in atmospheric pressure, wind and daily or other temperature fluctuations to which the panel may be exposed.

In addition, such stresses acting on the spacer / plate connections are relieved to some extent by the presence of the additional spacers within the vacuum-drawn space located between the plates. As mentioned, such additional spacers maintain the spacing between the plates, with the result that dimpled bending of the plates due to vacuum suction of the space therebetween, which causes stress on the joints between the metal spacer and the glass, becomes substantially appearance. In addition, arbitrary additional temporary forces, for example as a result of wind gusts to which the panel can be exposed, will not load these connections to the extent that they would be loaded in the absence of the extra spacer (s). This is because such an arbitrary voltage will be transmitted through the additional spacer (s), so that the relative orientation of the two glass plates will remain substantially unchanged from the metal spacer at the edges. In a particular case, a gust of wind could dent a panel so that it would move on its edge in a few arc minutes. But both plates would be dented equally so that the edge spacer that keeps them apart would be less bending than if one plate could be dented independently of the other, and stresses acting on the spacer joints would be reduced .

In most preferred embodiments of the invention, the or at least one such spacer is in the form of an airgel block.

Airgel is an oxide-based foam material that contains up to 98% by volume of pores. Airgel therefore has a low density, so that it only contributes little to the weight of a panel, and moreover it has a very low heat conductivity, so that the panel has good insulating properties. Provided the airgel is kept dry, blocks of that material may have sufficient structural compressive strength to act as spacers for the intended purposes. The compression resistance of airgel varies according to its density, which may range from about 0.08 g / cm3 to about 3 3 0.4 g / cm: for a density of 0.1 g / cm, the compression resistance is about 0.15 MPa, for a density of 0.2 g / cm3, the compression resistance is about 0.15 MPa, and for a density of 0.3 g / cm3, the compression resistance is about 0.3 MPa. Airgel usually has a Young's modulus in the order of 106 to 107 N / m2. However, it is important to protect the airgel from moisture, since its structure is very vulnerable to moisture attack. This is accomplished by attaching the spacers to the edges of the glass plates by conductive enamel strips to seal the space between the plates containing the airgel spacer (s).

Aerogels can be formed from oxides of various materials, for example, aluminum, zircon, tin and tungsten, but the perhaps most common airgel is formed from silicon dioxide. Of course, an airgel may comprise a mixture of oxides, for example, a silica airgel may contain additives of other oxides, for example, aluminum, tellurium, germanium or other materials, to give the airgel to be formed with specific desirable properties.

Silicon dioxide-based aerogels can be made in the form of blocks, for example with a thickness of up to 3 cm, which blocks have very good transparency despite the foam structure of the airgel. Obviously, the edges of the blocks would be visible in the finished panel. If it is desirable to prevent this, such a space between the plates can be filled substantially with airgel in the form of a single plate.

If the panel is expected to be exposed to reasonably higher temperatures during use, then it will be clearly desirable to use a thermally degradable organic adhesive to hold an additional spacer in place in the appropriate space between the plates. avoid. A suitable size of such an additional spacer can be relied upon so that it is simply held in place by the forces applied thereto by its adjacent glass plates due to the vacuum suction of the space between the plates. This also has the advantage that the intensity of the contact between the additional spacer and the glass plates is not improperly increased, which could have a detrimental effect on the heat insulation properties of the panel. However, if it is desirable to provide a connection between such an additional spacer and the glass, such an additional spacer, for example, from silica-based airgel, may be bonded to a glass plate using a solvent-free, fusible bond material, such as a powdered silicone resin. Alternatively, such an airgel can be molded on-site on a glass plate so that it is bonded directly to it without the need for an organic adhesive: this could also help reduce problems related to manipulating the airgel before it enters the panel is brought.

Preferably, a preparative solder coating is applied to the conductive enamel. We have found that a consistent, high-quality solder joint is more easily accomplished, particularly in mass fabrication, when a spacer is soldered onto a conductive enamel strip provided with a preparatory solder coating.

Of course, a reliable attachment of the spacers to the glass plates by soldering will only last as long as the panel is not exposed to temperatures higher than the melting point (solidus temperature) of the solder used. A specific use provided for panels in accordance with this invention is as insulating covers for solar collectors. A solar collector equipped with a panel according to this invention can reach a temperature of up to 180 ° C. Solders conventionally used in the multiple glazing industry have a melting point of about 170 ° C. It is preferred that the solder used has a melting point of at least 200 ° C. So-called silver solders can be used.

It will be noted that when a panel in accordance with the present invention is used as a solar collector cover, it will undergo a daily temperature cycle much greater than that to which a conventional double glazing panel in a window of a building is used during use. exposed. Indeed, a panel used in this manner according to the present invention can be exposed to a daily thermal stress cycle that is greater than that to which a conventional double glazing panel is subjected even during manufacture. Particularly in this context, the use of enamel strips deposited on the glass plates offers particularly important advantages in terms of the useful life of the panel.

It will also be appreciated that the metal of the spacers should withstand the temperatures to which the panel will be exposed. Preferably, the metal of the or each spacer has a melting point above 250 ° C.

Preferably, the metal of the or each spacer comprises copper or a copper alloy. Such metals have good corrosion resistance and melting points satisfactory for their intended purposes and good compressive strength so that they can be made thin enough to be flexible enough to absorb curvature stresses and thus their connections to the glass to relieve tension.

Advantageously, the or each spacer comprises a rib running between a pair of substantially parallel flanges and attached to the enamel strips by means of those flanges. This makes a larger area of a spacer available for connection to the enamel and thus promotes the reliable formation of a firm and durable connection.

In some such preferred embodiments of the invention, the rib and flanges of the or each such spacer are made of different metals. This allows the metals used to form the rib and flanges to be selected for the specific function that part of the spacer is to perform.

In particular, this allows the metals to be selected so that the metal from which such a flange is made has a thermal linear expansion coefficient between that of the metal of the rib and of the conductive enamel to which such a flange is attached. This has the advantage that stresses due to different thermal expansion or shrinkage are spread so that such stresses are more easily absorbed without breaking the joint.

Preferably, the or any space of the panel located between the plates comprises a desiccant. This helps to keep the space between the plates dry, in order to reduce any chance of internal corrosion of the metal spacer (s), as well as any chance of condensation inside the panel, and it also helps, when additional airgel spacers are used to keep such airgel dry.

In some preferred embodiments of the invention, at least one glass plate side is coated, which modifies the electromagnetic radiation properties of that plate. In such embodiments, the use of a conductive enamel strip has the further advantage over a metallized strip that the enamel can be applied on top of the coating. A copper metallized strip cannot be applied to certain specifically targeted coatings as it will not hold well: the use of a conductive enamel strip removes the need to remove such coating on the strip area. A coating can be used to give the coated sheet any of different properties as desired.

In some such embodiments, a coating is applied which reduces the emissivity of the coated side to infrared radiation with wavelengths greater than 3000 nm. This provides an improved greenhouse effect, since little of the energy of the solar spectrum is radiated at such wavelengths, while a very large portion of the energy radiated by bodies that are not very hot has such wavelengths.

In addition, or additionally, it is preferable that a coating is applied which reduces the reflectivity of the coated side with respect to total solar radiation. This increases the portion of the total solar radiation that will be emitted from the panel.

In some preferred embodiments of the invention, each glass sheet consists of a sheet of glass which has an absorbance of up to 5.5% of the total solar radiant energy, calculated for a sheet having a thickness of 4 mm. This also increases the portion of the total solar radiation that will be emitted from the panel. This can be achieved by using glass of a special composition and with a low absorbency. Ordinary soda-lime glass has an absorbance of about 10% of the total solar radiation energy for a plate with a thickness of 4 mm.

The invention also relates to a solar collector provided with a heat-absorbing medium covered by a panel according to any one of the claims related thereto.

Preferred embodiments of the invention will now be described by way of example with reference to the accompanying schematic drawing, in which: - Fig. 1 is a cross-sectional detail through an embodiment of a panel according to this invention, and - Fig. 2 is a detail of a cross section through a solar collector, in which a second embodiment of such a panel is included.

Fig. 1 shows a finished panel intended for use to cover a solar collector and shown in the upward direction in which it will be applied before use.

At the top thereof, which side would be oriented towards the sun during use, a first glass plate 1 is provided with an optical coating 2, which is designed to decrease the reflectivity of total energy of that side with respect to solar radiation. Such a coating can for example consist of a coating of magnesium fluoride, which is applied with a thickness of a quarter wavelength or can consist of a multilayer coating.

Around the edge of its side which is not coated, a layer of a conductive enamel 3 is deposited, which is covered with a tin layer 4 of a solder with a melting point above 200 ° C. A suitable solder alloy with a melting point of 221 ° C contains 96 wt% tin and 4 wt% silver. Suitable enamel compositions are known per se, for example, as used to form the conductive elements of vehicle window heating. A suitable composition for the enamel is marketed by Degussa AG of Frankfort, Federal Republic of Germany, under their designation "SP 627". That conductive enamel contains about 65% silver.

A second glass plate 5, provided with an optical coating 6 of doped tin oxide, which reduces the emissivity of the coated side with regard to infrared radiation with wavelengths greater than 3000 nm, is also provided with an edge-applied strip of conductive enamel 3, which is again tinned with brazing 4. That second enamel strip 3 is also deposited on the uncoated side of its respective plate.

A metal spacer is placed over the tinned enamel strip on the second glass plate 5 and is spot soldered along its length to hold it in place. As shown, the spacer consists of two flanges 7, which are attached to a rib 8 by means of metal connections 9. These connections 9 can be made by welding, brazing with brass or brazing. The rib 8 is suitably formed of copper covered with a tin / lead alloy to enhance its corrosion resistance. The flanges 7 are suitably made of a metal with a linear thermal expansion coefficient that lies between the respective linear thermal expansion coefficients of copper and the enamel used.

The open top box, which is formed by the second plate 5 and the spacer, is then substantially filled with one or more blocks of airgel 10, which will serve as additional spacers after assembly of the panel, then the first plate 1 placed on the second plate 5 so that the tinned enamel strip contacts the exposed flange 7 of the spacer, and the edges of the assembly are heated to melt the solder 4 for joining the panel together.

This heating is done in an appropriate manner by generating eddy currents in the conductive enamel, the spacer and the solder layers 4.

More detailed information on a suitable soldering technique can be found in British Patent Specification 2,122,057.

After joining and cooling the panel, the inner space thereof is vacuumed to an internal pressure of between 10 Pa and 10 kPa. Any tendency of the glass plates of the panel to dent due to pressure differentials thereon is resisted by the airgel 10, which is tightly received within the space between the plates. The tight pick-up also serves to hold the airgel 10 in place within the space between the plates.

In a specific practical embodiment, the airgel layer 10 has a thickness of 2 cm. Such a panel may have a solar transmissivity of at least 70% and a thermal transmittance K of less than 0.6 Wm-2 * K-1.

In a variant, a perforated desiccant-containing sleeve is attached to a spacer rib 8 within the space between the plates along one edge of the panel.

In a second variant, the airgel is formed on site on one of the glass plates, again tightly received, so that it cannot move within the final space between the plates.

In a third variant, the glass of soda-lime glass used, which has an iron content of less than 0.04%, is calculated as Fe203, so that it has a solar absorption capacity of about 2.2%, calculated for a plate with a thickness of 4 mm.

In a fourth variant, the glass plates are thermally tempered, for example by subjecting them to a suitable cooling scheme after firing the enamel strips 3.

In a fifth variant, an optional protective element is fitted around the edges of the panel. Such a protective element can be formed by reactive injection molding to fill the channel of the spacer 7,8 and to provide lips which extend over the edges of the glass plates 1, 5 around their peripheries.

Fig. 2 shows a second embodiment of the panel according to the invention, which panel is mounted on a solar collector.

In Fig. 2, the panel comprises two plates 11, 12 of low iron thermally tempered glass, each of which has a thickness of 4 mm, which are connected to each other by means of a spacer 13, which is soldered to the previously enamelled strips 14 deposited on the edges of the glass plates. The second glass plate 12 is provided with a coating 15 of tin oxide with an optically low emissivity, on which coating the associated enamel strip is deposited. In this embodiment, the enamel consists of a paste containing 50% by weight of silver, 3% by weight of glass frit (lead borosilicate), 41% by weight of volatiles (perpineol and dibutyl phthalate) and 6% by weight of ethyl cellulose.

As illustrated, the spacer 13 is a unitary member of the channel portion. In a variant of this or the previous embodiment, the spacer simply consists of a flat rib extending between the glass plates.

Before assembling the panel, a number of spaced blocks of airgel, such as the block indicated by the reference numeral 16, are distributed over the surface of the second glass plate. The airgel used to form the blocks has a density of about 0.2 g / cm3, giving it a compression resistance of about 0.15 MPa, and the size and spacing of the blocks is chosen taking them into account , as well as expected stresses in the finished panel.

After soldering and cooling, this panel is also vacuumed and the resulting differential pressure across the glass plates 11, 12 presses those plates against the airgel blocks, which are thus held in place and serve as spacers, which resist further indentation of the plates. Deformation of the plates due to such pressure differences can be minimized by appropriately dimensioning airgel blocks 16 and spacer 13. The thickness of the airgel blocks is adjusted to the width of the rib of the spacer, or vice versa, so that the airgel blocks are tightly received between the glass plates.

The finished panel is mounted in a frame 17, by means of which it is spaced above the energy absorbing surface 18 of a solar collector.

Padding strips of rock wool or glass wool can be interposed between the frame 17 and the panel to protect the edges of the panel from chipping and to accommodate differences in thermal expansion, if desired.

Claims (15)

Multiple glazing panel, provided with glass plates, which are spaced apart by the ribs of at least one metal spacer interposed between and soldered to the or each pair of successive glass plates, characterized in that the spacers are soldered to the edges of the glass plates by means of strips of conductive enamel deposited on said edges, that the or at least one space located between the plates is vacuum-drawn and that such space located between the plates comprises one or more additional spacing members, which are arranged to maintain the distance between the plates against pressure differences across the glass plates. The panel of claim 1, wherein the or at least one additional spacer consists of an airgel block. Panel according to claim 1 or 2, wherein said conductive enamel is provided with a preparatory solder coating. Panel according to any of the preceding claims, wherein the solder used has a melting point of at least 200 ° C. Panel according to any of the preceding claims, wherein the metal of the or each said spacer has a melting point above 250 ° C. Panel according to any of the preceding claims, wherein the metal of the or each said spacer comprises copper or a copper alloy. Panel according to any of the preceding claims, wherein the or each said spacer is provided with a rib running between a pair of substantially parallel flanges and secured to the enamel strips by means of those flanges. The panel of claim 7, wherein the rib and flanges of the or each such spacer are made of different metals. The panel of claim 8, wherein the metal from which such a flange is made has a thermal linear expansion coefficient between that of the metal of the rib and of the conductive enamel to which such a flange is attached. Panel according to any one of the preceding claims, wherein the or each space of the panel located between the plates comprises a dehydrating agent. Panel according to any of the preceding claims, wherein at least one glass plate side is provided with a coating which changes the transmission properties of said plate with respect to electromagnetic radiation. The panel of claim 11, wherein a coating is applied which reduces the emissivity of the coated side to infrared radiation with wavelengths greater than 3000 nm. Panel as claimed in claim 11 or 12, wherein a coating is applied, which reduces the reflectivity of the coated side with regard to total solar radiation. Panel according to any one of the preceding claims, wherein each glass plate consists of a glass plate with a total solar radiation energy absorption capacity of at most 5.5%, calculated for a plate with a thickness of 4 mm. Solar collector provided with a heat-absorbing medium, covered by a panel according to any one of the preceding claims.