GB2097455A

GB2097455A - Electrically heatable hollow glazing panels

Info

Publication number: GB2097455A
Application number: GB8112615A
Authority: GB
Original assignee: Glaverbel Belgium SA
Current assignee: AGC Glass Europe SA
Priority date: 1981-04-23
Filing date: 1981-04-23
Publication date: 1982-11-03

Abstract

In order to simplify the connection of current supply leads to an electrically heatable hollow glazing panel 1 comprising at least two sheets 2, 3 of glazing material held in spaced relation by intervening marginal space members 4, 5, the panel includes a said sheet 2 which has electrical resistance heating means 7 extending between marginal portions of a face thereof which is interior of the panel 1 and in conductive contact (via an optional bus strip 6) with a said spacer member 4 at each such marginal portion, each such member 4 being connected to an electrical lead-in wire or terminal 12 and being electrically conductive, whereby such spacer members are electrically connected in series via said heating means. <IMAGE>

Description

SPECIFICATION Electrically heatable hollow glazing panels The present invention relates to electrically heatable hollow glazing panels comprising at least two sheets of glazing material held in spaced relation by intervening marginal spacing members.

If a heating element of such a panel is deposited on an outer face of the panel, it is apt to be damaged, for example by abrasion or atmospheric corrosion and it may be undesirable for reasons of safety.

It has accordingly been proposed to apply such a heating element to a face of a sheet which will be interior of the finished panel. This gives rise to a problem of making electrical connections between the heating element within the panel and a source of heating current.

It is an object of the present invention to provide a remedy for this problem.

According to the present invention, there is provided an electrically heatable hollow glazing panel comprising at least two sheets of glazing material held in spaced relation by intervening marginal spacing members, characterised in that the panel includes a said sheet which has electrical resistance heating means extending between marginal portions of a face thereof which is interior of the panel and in conductive contact with a said spacer member at each such marginal portion, each such member being electrically conductive, whereby such spacer members are electrically connected in series via said heating means.

Thus, in the manufacture of a panel according to the invention, supply of heating current to the heating means may be made by connecting wires to their associated spacer members, so that the problem referred to above is remedied. Previous solutions to that problem have in general entailed leading a current supply wire either past or through a spacer member which presents inconveniences in manufacture and makes it difficult to seal the panel if this is desired as it usually is.

In some embodiments of the invention, said electrical resistance heating means is constituted by a ladder-like array of heating elements, e.g.

wires. In such a case, spacer members at margins of the panel can themselves serve as terminals for the heating means. Preferably however, said heating means extends between electrically conductive bus strips deposited on such marginal portions and each in conductive contact with a said spacer member. This improves current flow between the heating means and the spacer members. Such heating means may be constituted for example by wires as aforesaid or by conductive enamel strips which extend in parallel between the bus strips, but preferably, said heating means is constituted by a transparent electrically conductive coating. The adoption of this preferred optional feature is of considerable practical advantage in the performance of the present invention. Panels according to the invention are particularly useful for the display of goods for sale and other articles.It will readily be appreciated that a ladder-like or other grid type array of heating elements could be optically intrusive and that a transparent coating type of heating element will enable the display to be viewed in a more acceptable manner. Preferably, said transparent coating is a coating which reduces the emissivity of the coated sheet in respect of long wavelength infra red radiation (i.e.

wavelengths greater than 5 yam), since the use of such a coating reduces radiant heat transfer across the panel.

There are many conductive materials which can be used to form a transparent coating. The coating may be formed as a thin metal film e.g. of gold, silver, copper, or aluminium which is deposited on the sheet. However metal coatings as such also have a marked effect on the visible light transmissivity of the coated sheet, and accordingly it is preferred that the coating should be of a metal compound such as an oxide which may be doped to improve is conductivity. Doped tin oxide coatings are particularly preferred since they can be arranged to have low emissivities (e.g. in the range 0.2 to 0.1) for long wavelength infra red radiation while allowing a high proportion (e.g.

80% or more) of incident visible light to pass.

Preferably, said spacer members in conductive contact with said bus strips are each assembled in touching relationship with their respective bus strip. This is usually sufficient to give an adequate electrical connection. Alternatively, or in addition, and in order to ensure a good electrical contact, it is preferred that each said bus strip is connected to its associated spacer member by a soldered wire connection.

Preferably, said electrical resistance heating means is spaced apart from spacer members or portions of spacer members which lead between said marginal portions. This helps to ensure that all the heating current applied flows through the heating means.

In order to avoid current flow between the spacer members at said opposed side margins via any other spacer members, it is preferred that said spacer members are interconnected via connector pieces of insulating material.

The panel as a whole may simply be clamped together, but it is preferred that said spacer members are glued to said sheets.

An electrical lead-in-wire or terminal is preferably connected to a spacer member at each said opposed margin. This can easily be done before or after assembly of the panel by riveting said wires or terminals to said spacers, but the connections are preferably made after assembly of the panel since it is easier to assemble the panel without the connectors.

The said heating means may comprise one or more loop type heating elements extending between portions of the same side margin of the panel, but preferably, said heating means extends between opposed side margins of the panel.

The invention includes a refrigerated compartment having a wall or wall portion formed by a panel as herein defined.

In supermarkets and other food stores, frozen food for sale is often displayed in open refrigerated compartments. This entails the expenditure of more energy for maintaining the compartment at a low temperature than would be necessary for a closed compartment, but it has been felt desirable to accept this disadvantage in order that the foodstuffs may be visible to the customer. By making use of a refrigerated compartment embodying this invention, foodstuffs in a closed compartment can be viewed through the glazing panel. The panel itself is heatable in order that the tendency for atmospheric moisture to condense and subsequently freeze thereon is reduced so that the panel can be kept substantially free of ice thus maintaining its light transmitting properties.

It is especially suitable for a said panel to form a door for such a refrigerated compartment, for example, an openable lid of a floor mounted chesttype refrigerated compartment.

Advantageously, the sheet bearing said heating means is spaced from the sheet which bounds the interior of the compartment, since it is desirable that the heatable sheet should not be on the side of the refrigerated compartment. That is to say, the heat source of the panel should be kept away from the cold source of the refrigerator.

It is especially preferred that said heating means be constituted by an infra red reflecting conductive coating which faces the interior of the compartment. This entails reduced emission of infra red radiation towards the interior of the compartment.

The interior space of the panel serves to insulate the exterior sheet from the interior of the compartment, and this coupled with any heating effect of the panel is or can be sufficient to maintain the exterior sheet of the panel above the dew-point so that no condensation forms on the exterior surface of the panel. When the compartment is opened, the interior sheet of the panel will be exposed to ambient atmosphere and because of its low temperature, moisture will tend to condense thereon. However the rate at which moisture does condense on that sheet will be reduced because it is heated by the heating means of the panel.When the compartment is again closed, that sheet will tend to form the warmest portion of the compartment wall so that any moisture present in the atmosphere within the compartment will preferentially condense on another wall or on any contents of the compartment, and indeed any condensation remaining on that sheet of the panel will tend to evaporate and recondense on a colder surface within the compartment.

Preferred embodiments of the present invention will now be described by way of example with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a detail plan view of a corner of a first embodiment of heatable panel according to the invention; Figure 2 is a sectional view along the line Il-Il of Figure 1; and Figures 3 and 4 are plan views of a second and a third embodiment of panel according to the invention.

In Figures 1 and 2, an electrically heatable hollow glazing panel 1 comprises two sheets 2, 3 of glazing material secured by intervening marginal spacer members such as 4, 5. One sheet 2 of the panel 1 has electrically conductive bus strips such as 6 deposited on opposed side margins of a face thereof which is interior of the panel. Electrical resistance heating means 7 extend between the bus strips. Each bus strip 6 is in conductive contact with a spacer member 4 which leads along one of those opposed side margins of the panel 1, and each such spacer member 4 is electrically conductive. In this way the spacer members such as 4 which lead along those opposed side margins of the panel are electrically connected in series via the heating means 7.

In the embodiment illustrated in Figures 1 and 2, the electrical resistance heating means 7 is constituted by a transparent electrically conductive coating which is of a type designed to reduce the emissivity of the coated sheet 2 in respect of infra red radiation having wave-lengths greater than 5 ,um.

There are many materials which can be used to form such a transparent coating, as is well known in the art, the most usual coating material probably being SnO2 which contains a doping agent (for example fluorine ions or antimony ions) to enhance its conductivity.

The actual resistance of the heating means 7 to be adopted in any given practical situation will of course depend on the required heat output and the available power supply. Such resistance can be selected by varying the thickness of the coating or the proportion of doping agent used.

In a specific case where a rectangular panel measuring 55 cm by 85 cm is designed for use as a door of a refrigerated compartment, with the bus strips leading along its shorter margins, it is usually desirable for the resistivity of the coating 7 to be between 16 and 23 7.

In the embodiment illustrated in Figures 1 and 2, it will be noted (from Figure 1) that the conductive coating 7 is spaced apart from the spacer member 5 which leads between the opposed side margins of the sheet 2 on which the bus strips such as 6 are deposited, so that any current fed to the other spacer members such as 4 flows only through the heating means 7.

From Figure 2 it will be noted that the spacer member 4 in conductive contact with the bus strip 6 is assembled in touching relationship with that bus strip to provide the necessary electrical connection. Further electrical contact between the bus strip 6 and the spacer member 4 is provided by a wire connection 8 soldered to the spacer member 4 and a portion 9 of the bus strip 6.

The illustrated spacer members 4, 5 are of hollow section and they are interconnected at the corners of the panel 1 by connector pieces such as 10 made from insulating material which can be plugged into the ends of the spacer strips. The spacer members 4, 5 (and the connector pieces 10) are secured to the sheets 2, 3 by layers of glue 11.

An electrical lead in terminal 12 is connected to the spacer member 4 by a rivet 13.

The panel illustrated in Figures 1 and 2 is designed to form a door for a refrigerated compartment, and in use would normally be mounted so that the sheet 3 bounds the interior of the compartment, the sheet 2 bearing the heating means thus being spaced from the interior of the compartment, and the infra red reflecting conductive coating 7 which constitutes the heating means would therefore face the interior of the compartment.

The glazing material used to form the sheets 2, 3 is preferably glass, and such glass is preferably tempered, either thermally or chemically, in order to increase its resistance to breakage.

In modifications of this embodiment, the spacer member 4 is not in direct touching relationship with the bus strip 6, because a glue layer 11 extends between them and/or because they are not in register. In this case the sole conductive contact is provided by the connection 8.

Figure 3 shows an alternative embodiment of the invention which may for example be used to form a heatable window of a railway carriage. The panel 14 illustrated in Figure 3 comprises two generally rectangular sheets of glass 1 5, 1 6 having rounded corners which are secured together by two generally U-shaped spacer members 1 7, 1 8. As illustrated, the ends of the two spacer members 17, 18 are interconnected half way up the vertical sides of the panel by insulating connector pieces 1 9, 20.

The upper and lower horizontal margins of one of the sheets 1 5, 16 bear bus strips 21, 22 respectively between which extends an electrical resistance heater 23, for example constituted by a doped tin oxide coating. It will be rioted that in this embodiment the heater 23 is spaced from the vertically leading portions of the spacer members 17,18.

When the invention is embodied in a window of a railway carriage, or indeed any other heated or heatable compartment, the panel would normally be installed with the coated sheet to the inside of the compartment so that the coating faces outwards.

In Figure 4, an electrically heatable hollow glazing panel 23 comprises two glass sheets 24, 25 held in spaced relation by five straight spacer members 26 to 30. Spacer members 26, 27, 28 lead along substantially the full length of the top, left hand and bottom side margins respectively of the panel and are joined at the corners of the panel to insulating corner connector pieces 31.

The other spacer members 29, 30, themselves joined together by an insulating connector piece 32 lead between the corner connector pieces 31 at the right hand side of the panel so that each of these spacers 29, 30 leads along a portion of the right hand side margin of the panel. A loop-wise deposited heating element 33 extends between bus strips 34, 35 respectively in electrical contact with those latter spacer members 29, 30. The heating element is suitably of doped tin oxide and is deposited on one of the glass sheets.

The bus strips are suitably formed by metallic deposits, e.g. of copper and/or by a conductive enamel.

Claims

1. An electrically heatable hollow glazing panel comprising at least two sheets of glazing material held in spaced relation by intervening marginal spacer members, characterised in that the panel includes a said sheet which has electrical resistance heating means extending between marginal portions of a face thereof which is interior of the panel and in conductive contact with a said spacer member at each such marginal portion, each such member being electrically conductive, whereby such spacer members are electrically connected in series only via said heating means.

2. A hollow glazing panel according to Claim 1, wherein said heating means extends between electrically conductive bus strips deposited on said marginal portions and each in conductive contact with a said spacer member.

3. A hollow glazing panel according to Claim 2, characterised in that said electrical resistance heating means is constituted by a transparent electrically conductive coating.

4. A hollow glazing panel according to Claim 3, characterised in that said transparent coating is a coating which reduces the emissivity of the coated sheet in respect of long wavelength infra red radiation.

5. A hollow glazing panel according to any of Claims 2 to 4, characterised in that said spacer members in conductive contact with said bus strips are each assembled in touching relationship with their respective bus strip.

6. A hollow glazing panel according to any of Claims 2 to 5, characterised in that each bus strip is connected to its associated spacer member by a soldered wire connection.

7. A hollow glazing panel according to any preceding claim, characterised in that said electrical resistance heating means is spaced apart from spacer members or portions of spacer members which lead between said marginal portions.

8. A hollow glazing panel according to any preceding claim, characterised in that said spacer members are interconnected via connector pieces of insulating material.

9. A hollow glazing panel according to any preceding claim, characterised in that said spacer members are glued to said sheets.

10. A hollow glazing panel according to any preceding claim, characterised in that said wires or terminals are riveted to said spacers.

10. A hollow glazing panel according to any preceding claim, characterised in that an electrical lead-in wire or terminal is connected to a spacer member at each said opposed sheet margin.

11. A hollow glazing panel according to Claim 1 0. characterised in that said wires or terminals are riveted to said spacers.

12. A hollow glazing panel according to any preceding claim, characterised in that said heating means extends between opposed side margins of the panel.

13. A hollow glazing panel according to Claim 1 and substantially as herein described.

14. A refrigerated compartment having a wall or wall portion formed by a panel according to any preceding claim.

15. A refrigerated compartment according to Claim 14, characterised in that said panel forms a door for the compartment.

16. A refrigerated compartment according to Claim 14 or 1 5, characterised in that the sheet bearing said heating means is spaced from the sheet which bounds the interior of the compartment.

17. A refrigerated compartment according to any of Claims 14 to 16, characterised in that said heating means is constituted by an infra red reflecting conductive coating which faces the interior of the compartment.

New claims or amendments to claims filed on 2nd October, 1981.

Superseded claims 1, 10 and

11.

New or amended claims 1 and 10 appendant claims renumbered and appendancies corrected.

1. An electrically heatable hollow glazing panel comprising at least two sheets of glazing material held in spaced relation by intervening marginal spacer members, characterised in that the panel includes a said sheet which has electrical resistance heating means extending between marginal portions of a face thereof which is interior of the panel and in conductive contact with a said spacer member at each such marginal portion, each such member being connected to an electrical lead-in wire or terminal and being electrically conductive, whereby such spacer members are electrically connected in series only via said heating means.