GB2097288A

GB2097288A - Solar control panel

Info

Publication number: GB2097288A
Application number: GB8113180A
Authority: GB
Original assignee: Glaverbel Belgium SA
Current assignee: AGC Glass Europe SA
Priority date: 1981-04-29
Filing date: 1981-04-29
Publication date: 1982-11-03
Also published as: BE892925A; FR2504955B1; GB2097288B; FR2504955A1

Abstract

In order to enhance the thermal insulating effect of a solar control panel comprising at least one clear glass sheet bearing a coating for solar control purposes without proportionate attenuation of the visible light transmission, the clear glass sheet 1 bears on one face an oxide coating 4 such that that coating 4 and the sheet 1 together have an energy absorption factor of at least 16% and on its opposite face a second coating 5 which has an emissivity of not more than 0.25 and which comprises at least one metal layer. The oxide coating 4 may be a mixture of cobalt, iron and chromium oxides. The second coating 5 may comprise a layer of gold, silver, copper, platinum or palladium and the metal layer may be under- or over-coated with another layer, for example an oxide layer. <IMAGE>

Description

SPECIFICATION Solar control panel This invention relates to a solar control panel comprising at least one clear glass sheet and incorporating a glass coating for solar shading purposes.

It is known to provide a glass sheet with a coating which is capable of screening off a proportion of incident solar radiation. When used as a glazing panel, the coating reduces the glare and/or the heating effect of strong sunlight at the building interior.

A said coating can be formed of one or more oxides. Oxide coatings can provide a useful shading effect while having an adequate visible light transmissivity to meet most glazing requirements. Such oxide coatings can have a fairly high abrasion resistance and they can be formed on large areas of glass with a high degree of uniformity. These potentialities of oxide coatings are well known in the art of coated glass manufacture and various oxide coatings are in actual use.

A disadvantage of such optical oxide coatings is the heating effect associated with their screening function. The solar shading afforded by such coatings is dependent mainly on their absorption of light and/or infrared radiation.

This energy absorption results in heating of the coated glass and the re-emission of energy as long wavelength infrared radiation. Some of this re-emitted energy is radiated towards the interior of the building and consequently detracts from the shading efficiency of the panel.

The adverse effects of the energy absorption by the oxide coating can be reduced by screening off the infrared radiation emitted towards the building interior. This can be done by means of a further coating, which may be applied to the same glass sheet or, if such sheet forms part of a glazing unit comprising a plurality of glass sheet, to another sheet of the panel. Unfortunately however, secondary screening by such a further coating as hitherto proposed is incompatible with performance specifications sometimes preferred by potential users. In general terms, the problem has been how to provide an adequate insulation against the heating effect of an energy-absorbing oxide coating without causing a greater attenuation of the visible light transmission than of the overall solar energy transmission and without unacceptable modifications of the apparent colour of the panel.

The present invention is based on the discovery that light-transmitting coatings consisting of or including one or more thin metal layers, when used in combination with an energy-absorbing oxide coating, can attenuate solar energy transmission in the invisible spectral range. This result can be realised without commitment to any or to any specific colour modifying effect because selection can be made from a number of metals for the metal or metal-containing coating.

According to the present invention there is provided a solar control panel which comprises at least one clear glass sheet and incorporates a glass coating for solar shading purposes, characterised in that a face of the or a said sheet bears an energy-absorbing coating which is composed of one or more oxides, the properties of this oxide coating being such that the clear glass pane and such coating together have an energy absorption factor of at least 16%, and on the opposite side of such coated sheet to such oxide coated face that sheet or a face of a second clear glass sheet bears a second coating which consists of or includes one or more metal layers and has an emissivity of not more than 0.25, the glass sheet(s) and the said coatings being composed so that when the panel is arranged with the said oxide-coated face towards the radiant energy source the luminous transmission factor of the panel is higher that its total energy transmission factor.

As used in this specification the term "luminous transmission factor" denotes a ratio of the quantity of visible transmitted light to the quantity of incident visible light, such quantities being corrected integrations of the transmitted and incident light values respectively over the whole spectral range of visible light, the integrations being corrected to compensate for the spectral distribution of the radiant energy source and for the spectral sensitivity characteristics of the human eye.

The measurements are made with a spectrophotometer and using a light source whose spectral composition is that of Illuminant D 65 as defined by the International Commission on Illumination (reference CIE 17 Section 45-15-145). This illuminant represents daylight with a colour temperature of about 6504K. The eye sensitivity correction factor applied is likewise that which is standardised by the International Commission on Illumination.

The term "total energy transmission factor" as used herein denotes the ratio of transmitted radiant energy to incident radiant solar energy. The term "energy absorption" as used herein denotes the fraction of incident radiant solar energy which is absorbed. For the determination of both of these factors use is made of a radiator whose spectral composition is that of direct sunlight at an elevation of 30t above the horizon. The spectral composition is given by Moon's Table for a mass of air equal to 2. The energy absorption factor of a coated glass pane as refered to in this specification, like the total energy transmission factor of a panel, is always measured with the face bearing the energy-absorbing coating directed towards the radiant energy source.The luminous transmission factor is not dependent on whether the face bearing said energy-absorbing coating is directed towards or away from the light source.

The invention enables the various advantageous properties of metal oxide optical coat ings to be realised in a panel which comprises one or more clear glass panes and in which the thermal insulating effect is enhanced without proportionate attenuation of the visible light transmission. The expression "clear glass" as used in this specification denotes glass of such composition that a 6 mm thick sheet of the glass has a luminous transmission factor of at least 85%.

In some embodiments of the invention, the panel comprises clear glass sheets held in spaced facing relationship, and the two said glass coatings are on opposite faces of the same glass sheet, the energy-absorbing oxide coating being on an external glass face of the panel. A multiple glazing panel having these features is particularly effective for solar control purposes. The second coating, which comprises a metal layer, would have some effect if located on the other or another sheet of the panel but the solar shading efficiency is greater if that coating is on the inside face of the sheet bearing the external oxide coating.

Such a multiple glazing unit is of course intended to be installed with the metal oxide coated face to the outside of the building.

The energy-absorbing oxide coating can be of a type known per se in the art of coated glass manufacture and having a neutral colour and a reasonably good visible light transmissivity.

For the said energy-absorbing oxide coating it is preferred to employ a coating comprising one or more metal oxides selected from: SnO2, TiO2, CoO, Foe202 and Cr203, and most preferably comprising CoO, Fe203 and Cr203. It is for example suitable to employ such a three-constituent coating wherein the cobalt iron and chromium oxides are in a ratio of 62:26:12 by weight. It is advantageous to employ a neutral colour energy absorbing coating with a favourable luminous transmission factor, formed by using a mixture of cobalt, iron and chromium oxides and a coating thickness of from 20 to 100 nm and preferably between 30 and 50 nm.

The second coating should have a relatively high visible light transmissivity. Preferably said second coating is such that that coating and the clear glass sheet to which it is applied together have a luminous transmission factor of at least 60%.

An appropriate combination of emissivity and luminous transmitting factors can easily be achieved by forming a low emissivity second coating comprising a metal layer in accordance with the invention. The required combination of properties can be achieved using any of a number of different metals. The choice of the composition of the second coating can be made having regard inter alia to the required spectral transmission characteristics of the panel.

Preferably the second coating comprises a layer of metal selected from gold, silver, copper, platinum and palladium.

The invention includes panels wherein a metal layer is the sole layer or the top layer of the second coating. Such a coating is suitable in particular if it is not necessary for the second coating to have substantial resistance to mechanical damage. This is the case for example if the second coating is at the interior of a multiple glazing unit. Production is facilitated by the omission of overcoating. However overcoating of the metal layer can afford improved optical properties as hereafter indicated and can improve the ageing resistance of the coating.

In some embodiments of the invention there is an underlayer, preferably an oxide layer, beneath the metal layer. The quality of a metal coating can often be improved by applying a suitable subbing layer to the glass.

In some embodiments of the invention the second coating comprises a metal oxide subbing layer beneath a metal layer.

The formation of the second coating by a combination of a metal layer with an oxide layer or with oxide layers, in particular an oxide overcoating, is useful not only for improving the quality of and/or for affording protection to the metal layer but also for favourably influencing the optical properties.

Because of interference effects, such a combination of layers can give a higher luminous transmission factor than a coating which consists solely of a layer of that metal and which has the same emissivity.

Advantageously the second coating comprises a metal layer in combination with at least one layer formed from zinc oxide, bismuth oxide, titanium oxide, cerium oxide, zirconium oxide or zinc sulphide. Specific layer combinations for the second coating which have given very good results in panels wherein the energy absorbing oxide coating is formed from oxides of cobalt, iron and chromium are: i) a silver layer on a zirconium oxide underlayer and ii) a copper layer on zirconium oxide underlayer.

Certain panels according to the invention, selected by way of example, will now be described with reference to the accompanying drawing which is a cross-section of a double glazing unit.

The illustrated unit comprises sheets 1, 2 of ordinary clear glass held in spaced relationship in a frame 3. The sheet 1 bears on its outer face an energy-absorbing coating 4 composed of oxides of cobalt, iron and chromium. The coating 4 and the glass sheet 1 are preferably composed so that they together have a luminous transmission factor of at least 40% and a total energy transmission factor of not more than 60% and an energy absorption factor of at least 16%.

On its opposite face sheet 1 bears coating 5 of low emissivity (emissivity of not more than 0.25) which consists of or comprises a layer of metal. The coating 5 is composed so that that coating and the glass sheet 1 together have a favourably high luminous transmission factor, this factor being preferably at least 60%.

The following are specific examples of panels according to the invention and constructed as described with reference to the drawing: Example 1 The sheets 1 and 2 were sheets of ordinary clear float glass each having a thickness of 6 mm.

The energy-absorbing coating 4 comprised 62% CoO, 26% Fe203 and 12% Cr203 and had a thickness between 35 and 45 nm. The glass sheet and such oxide coating together had an energy absorption factor of 25%.

The coating 5 was a two-layer coating comprising a layer of silver 20 nm in thickness covered by a layer of ZrO2 30 nm in thickness. That coating had a relative emissivity of about 0.05. The luminous transmission factor of the sheet together with the coating 5 was about 63%. The panel as a whole had a luminous transmission factor of 28.4% and a total energy transmission factor (measured with the coating 4 facing the radiant energy source) of 22.3%.

Example 2 The panel was the same as that according to Example 1 except that the coating 5 was a three-layer coating comprising a layer of copper 15 nm in thickness sandwiched between two layers of Zero2, the zirconium oxide underlayer being 8 nm in thickness and the zirconium oxide top layer being 26 nm in thickness.

That three-layer coating had a relative emissivity of about 0.05. The sheet 1 and the coating 5 together had a luminous transmission factor of about 60%. The panel as a whole had a luminous transmission factor of 25.6% and a total energy transmission factor (measured with the coating 4 facing the radiant energy source) of 22.7%.

Example 3 The sheets 1 and 2 where sheets of ordinary clear float glass having a thickness of 4 nm and 8 nm respectively. The oxide coating 4 was the same as in Example 1. The sheet 1 and the oxide coating 4 together had an energy absorption factor of 22%. The coating 5 was a two-layer coating comprising a layer of gold 11-12 nm in thickness on an underlayer of Bi203 1.5-2.0 nm in thickness. This coating had an emissivity of about 0.2. The luminous transmission factor of the sheet 1 together with coating 5 was about 60%. The panel 1 as a whole had a luminous transmission factor of 24. 1% and a total energy transmission factor (measured with the coating 4 facing the radiant energy source) of 23.3%. The panel was of neutral colour to ordinary observation, the gold coating having no perceptible colour modifying effect.The actual colour purity of the panel viewed in reflection was less than 3%. The term "colour purity" here refers to the colour purity of light reflected back from the sheet 1 when it is illuminated by Illuminant D65 defined by the International Commission of Illumination (reference CIE Section 45-15-145) from the side opposite said gold coating, the purity being determined in the manner therein specified.

Example 4 The panel was the same as that according to Example 3 except that the gold layer had a thickness of 15 nm. The luminous transmission factor of the panel was in this case also greater than its total energy transmission factor but a slight colouration of the panel caused by the gold layer was perceptible. The colour purity of the panel viewed in reflection, and determined as specified in Example 3, was at least 3% and the slight colouration of the panel caused by the gold layer was perceptible to ordinary observation.

In the foregoing Examples 1 to 4 sheets 1 and 2 were sheets of untempered glass. One or both sheets can be tempered if desired.

Claims

1. A solar control panel which comprises at least one clear glass sheet and incorporates a glass coating for solar shading purposes, characterised in that a face of the or a said clear glass sheet bears an energy-absorbing coating which is composed of one or more oxides, the properties of this oxide coating being such that the glass pane and such coating together have an energy absorption factor of at least 16%, and on the opposite side of such coated sheet to such oxide coated face that sheet or a face of a second clear glass sheet bears a second coating which consists of or includes one or more metal layers and has an emissivity of not more than 0.25, the glass sheet(s) and the said coatings being composed so that when the panel is arranged with the said oxide-coated face towards the radiant energy source, the luminous transmission factor of the panel is higher than its total energy transmission factor.

2. A panel according to claim 1, wherein there are glass sheets held in spaced facing relationship and the two said glass sheet coatings are on opposite faces of the same glass sheet, the energy-absorbing oxide coating being on an external glass face of the panel.

3. A panel according to claim 1 or 2, wherein said energy-absorbing coating is composed of an oxide or oxides selected from: SnO2, TiO2, CoO, Fe203 and Cr203.

4. A panel according to claim 3, wherein said oxide coating is composed of cobalt, iron and chromium oxides.

5. A panel according to claim 4, wherein the thickness of the energy-absorbing oxide coating is from 20 to 100 nm.

6. A panel according to any preceding claim, wherein said second coating is such that that coating and the clear glass sheet to which it is applied together have a luminous transmission factor of at least 60%.

7. A panel according to any preceding claim, wherein said second coating comprises a layer of gold, silver, copper, platinum or palladium.

8. A panel according to any preceding claim, wherein said second coating comprises a metal layer on a metal oxide underlayer.

9. A panel according to any preceding claim, wherein a metal layer is the sole layer or the top layer of the second coating.

10. A panel according to any preceding claim, wherein said second coating comprises a metal layer in combination with at least one layer of a metal compound selected from zinc oxide, bismuth oxide, titanium oxide, cerium oxide, zirconium oxide and zinc sulphide.

11. A panel according to claim 10, wherein said energy-absorbing metal oxide coating is formed of oxides of cobalt, iron and chromium and said second coating comprises a silver or copper layer on a zirconium oxide underlayer.

12. A solar control panel substantially according to any of the Examples 1 to 4 herein.

CLAIMS (26 Feb 1982)

1. A solar control panel which comprises at least one clear glass sheet bearing a coating for solar shading purposes, characterised in that a face of the or a said clear glass sheet bears an energy-absorbing coating which is composed of one or more oxides, the properties of this oxide coating being such that the glass sheet and such coating together have an energy absorption factor or at least 16%, and on the opposite side of such coated sheet to such oxide coated face that sheet or a face of a second clear glass sheet bears a second coating which consists of or includes one or more metal layers and has an emissivity of not more than 0.25, the glass sheet(s) and the said coating being composed so that when the panel is arranged with the said oxidecoated face towards the radiant energy source, the luminous transmission factor of the panel is higher than its total energy transmission factor.