EP0502775A1 - Heated window for refrigerated showcase and method of manufacturing same - Google Patents

Abstract

The invention relates to a show-case/counter equipped with a glazed part (2) and in which are displayed cold or defrozen products. According to the invention, the single glazing (5) with which the show-case is equipped is provided with a reduced emissivity layer on the cold side and equipped with current supply strips (11, 12; 13, 14) making it possible to heat a part of the layer by Joule effect. The invention also proposes the process for manufacturing the glazing. <IMAGE>

Description

The invention relates to a counter display case equipped with a glazed part and in which cold or frozen products are exposed.

When products stored in a refrigerated container must remain visible as is the case in commercial premises, the container is fitted with glass parts which transform it into a refrigerated display case. There are several variations of these display cases. Some have the shape of cupboards and then, it is the door itself which is transparent, others constitute safes and it is the horizontal cover which is glazed to allow the observation of the contents. The invention relates more specifically to counter display cases. In this type of display, the showcase generally separates the public from the merchant who has sole access to the goods while the latter must be perfectly visible to customers. Consequently, it is necessary to avoid that the glazed parts of the showcases are covered with condensation.

To avoid condensation, the method that is used generally consists in maintaining the face of the glazing on the environmental side at a temperature above the dew point of the atmosphere concerned. This goal is achieved by increasing the insulation performance of the glazing and sometimes, in addition, by heating the face on the "hot" side. The simplest way to improve the thermal insulation performance of single glazing is to replace it with multiple glazing. This technique is easy to implement in the case of display cabinets or in that of display cabinets, indeed multiple glazing, consisting of two or more flat glasses mounted parallel to each other easily equip cabinet doors or lids trunk. In the case of counter display cases, for mounting reasons, the insulating glazing solution is only suitable for mixed variants which include opaque and other transparent parts. In the case of a fully glazed wall, different solutions exist: supply of heat or blowing of hot air in the lower part or localized doubling of the glazing thanks to an additional additional glazed element.

The invention sets itself the task of producing a simple glazing intended to equip a counter display case which makes it possible to limit condensation, without causing overheating, which is inexpensive to install and operate and which is easy to manufacture and to install.

The problems associated with condensation on glazing fitted to enclosures where cold or frozen products are stored have received a number of known solutions. Thus, US Pat. No. 4,382,177 relates to single or double glazing units mounted in vertical doors of refrigeration cabinets or horizontal covers of chest freezers. These glazings are covered on their face on the cold side, with a film itself covered with a thin layer reflecting the infrared radiation. A single glazing fitted in this way has improved thermal insulation properties and thus works in a similar way to that of traditional multiple insulating glazing: the insulation being improved on the cold side, the hot side is warmer and the condensations are 'produce there for a higher ambient air vapor content. However, the improvement remains modest, the temperature rises little and the difference in content humidity of the atmospheres which cause condensation in both cases, low.

In the case of a refrigerated chest, patent application EP 236 286 proposes a similar solution: infrared reflecting layer on the cold side of the glazing. This solution limits condensation on the cover when it is open, in a vertical position, following its tilting around a horizontal axis.

There are many methods for depositing thin conductive or semi-conductive layers on glass, which also have the property of having a reduced emissivity. Several means are known in particular which make it possible to pyrolyze on hot glass organic salts which transform into conductive oxides. Among these, that of patent EP 125,153 makes it possible to deposit a thin layer based on tin oxide doped with fluorine on flat glass continuously between the exit from a "float" bath and the entry into the annealing rack. This process makes it possible to have glass plates with a transparent and conductive layer of indefinite dimensions for a reduced cost price.

These practically invisible thin layers have good low-emissivity and electrical conduction properties.

The invention provides a method for avoiding condensation on a refrigerated display case equipped with a single electrically heated glazing in which the glazing has been equipped with a low-emissivity conductive layer and where it is only heated by Joule effect if the condensation conditions are met. The process uses a fog detector to control heating. The invention also relates to a device comprising a layer with reduced emissivity, current supply strips for heating the layer by Joule effect and means for determining whether the conditions of condensation are met. One of these means is a fog detector placed on the surface of the glazing, on the outside. Furthermore, Joule heating affects only part of the surface of the single glazing and, in a variant, the strips of current supply are horizontal and preferably affect the entire length of the glazing. In another variant, the current supply strips are each located in a vertical plane. Optionally, they are shorter than the dimension of the glazing in their vertical plane, then the reduced emissivity layer is advantageously interrupted between the part of the surface of the simple glazing subjected to Joule heating and the rest of the surface. This interruption most often consists of a narrow line which joins the ends of the current leads. In all cases, the reduced emissivity layer preferably belongs to the group of semiconductor oxide layers comprising tin oxide doped with fluorine or chlorine, indium oxide doped with tin, l antimony-doped tin oxide, aluminum-doped zinc oxide.

The invention also relates to the use of a monolithic glazed element equipped with a low-emissivity conductive layer in a refrigerated display case in order to avoid condensation of water vapor or, if the layer is on the internal face, this use is made in order to reduce the heating of the exposed products.

Using the techniques of the invention, refrigerated countertops are available, which are elegant, efficient, economical both in installation and in operation. They also combine the advantages of improved insulation (operating cost of refrigeration) and those of efficient defrosting.

The figures and the description which follow will make it possible to understand the operation of the invention and to discover the advantages thereof.

Figure 1 shows the counter display case of the invention.

Figure 2 is an exemplary embodiment of the glazing of the display case of the invention.

Figure 3 shows the preferred variant of the same glazing.

In supermarkets, big box stores, restaurants, there are more and more counter-windows where customers are on one side of the window without being able to touch the displayed goods while the sales staff are on the other side or have - at least - access to the displayed goods, they can identify and seize the products indicated to him by the customer who, him, was free to select what suited him. In these showcases it is particularly food products, such as meat, cheeses or pastries which are presented. Glass is therefore preferred to plastics to equip the glass parts of these display cases: its ease of cleaning, its very good scratch resistance and its price make it the material of choice for this application. Its high modulus of elasticity and its ease of forming encourage it to be used alone without framing, in a self-supporting structure.

In Figure 1 there is shown a counter display of the type in question. It includes a box 1 intended to receive in its upper part 2 the products which must be exposed. The wall 3 is made of insulating materials limiting thermal losses. In the lower part 4 of the trunk are generally grouped the cold generating systems as well as the regulation. The glass plate 5 is hot formed so as to give it a functional form of the type of that shown in FIG. 1. In the drawing, a prismatic shape is shown consisting of three planar elements 6, 7 and 8 connected by two curved zones 9, 10. The shapes are varied but they are generally prismatic with possibly a number of planar parts other than three. The glazing is generally a safety glazing of the laminated type or more commonly, toughened. The bending of such prismatic elements is advantageously carried out using the device described in French patent application No. 90.04806 filed on 13.04.1990. This process, in addition to the ease with which it makes it possible to obtain products of complicated shape with very good quality, in particular from an aesthetic point of view, avoids elongation of the glass.

In FIG. 1, the lateral elements which support the prismatic glazing at its extremities. If the counter display case is insulated and therefore has only one element such as that shown in FIG. 1, these are opaque or transparent plates which prevent the circulation of air at the ends of the display case. The connection between the side plates and the glazing is then carried out by a rigid section possibly fitted with seals. When several elements of the type of that of FIG. 1 are combined one after the other to form a counter, the vertical separation plates can be eliminated and possibly replaced by vertical retaining rods associated with seals which connect the glazing 5 to each other. In the lower part of the glazing, it is supported by a U-shaped profile fitted with an elastomer seal. Often, this is where a hinge has been provided, it allows the complete opening of the window for cleaning or for installing the goods.

To limit condensation, especially in zones 6, 9 and 7 which are most useful for viewing the goods on display, various methods have been proposed. One of them consists in placing, in the lower part of the showcase, inside, a strip of flat glass which is substantially parallel to zone 6 of the showcase and placed at a short distance from the latter. It thus plays a role similar to that of an insulating glazing and therefore makes it possible to limit the cooling of the lower part of the glazing 5 and thus to delay the onset of condensation. Another method consists in placing in the lower part of the display case 5, outside, over its entire length, a ramp for blowing dry and / or hot air. This displaces the dew point of the atmosphere in which the surface of zone 6 of the glazing is located. As more, its temperature rises thanks to the circulation of air (hot), the two phenomena delay and often prevent the formation of fogging. The other methods consist in heating, indirectly or directly the lower part of the display case, either a heating cord is placed at the foot of the glazing, or the team of resistors deposited on its surface, in the manner of what exists, on the rear glasses heated cars. This last technique which overheats the location where the resistors are to obtain an average temperature on the whole of the glazing is likely to cause localized heating of the exposed foodstuffs and, possibly, to deteriorate them.

Each of the preceding solutions has drawbacks either of an aesthetic nature in the case of the doubling glass strip (which it is moreover difficult to clean) and in that of the "heating glasses" type solution, or else they are bothersome for the public, such as blowing air, or even, what is more serious, the methods adopted detract from the main function of a refrigerated counter display case, which is the preservation of the food presented. This is the case with all the methods which heat the glazing to a temperature markedly higher than its natural equilibrium temperature in its function as a wall thermally separating two atmospheres, one cold, the other hot. The heated wall radiates thermal energy (infrared) which is absorbed by the food and warms it.

The invention proposes to make use of a semiconductor layer with reduced emissivity, particularly based on doped metal oxides such as tin oxide doped with fluorine or indium oxide doped with tin (ITO ) the role of a thermal insulator to which one can add at will that of heating element. In this way, condensation is avoided thanks to a two-step action, firstly maintaining the external surface of the display case at a temperature higher than it would be without the layer, then, if necessary, that is to say if the moisture content of the ambient atmosphere requires it, heating of this same surface to a higher temperature. Among the different methods for depositing semiconductor layers on glass, some produce layers which have a particular type of brittleness - this is the case, for example, very thick layers. When, during the treatment of the coated glass, to heat it, bend it, soak it, the surface of the glass which carries the layer is caused to lengthen, then the layer can crack which disrupts electrical conduction. It is essential, when using such layers, to avoid allowing stretching of the support surface of the layer. From this point of view, the method of hanging the glass from French patent application 90.04806 guarantees that such stretching will not occur. In the same way one will avoid producing a bending in which the layer would be on the convex side.

Figures 2 and 3 concretely show the conditions for implementing the invention.

In FIG. 2, we see an example of glazing with a layer, curved and then tempered so as to constitute the front face of a counter-display case, the basic glass used is a float glass 6 mm thick. On leaving the float bath, before annealing in the drying room, it underwent a pyrolysis treatment of a powder of an organometallic compound of tin and fluorine according to the method of European patent EP 125 153 B. The characteristics of this layer are for example, a thickness of 200 nm and a sufacic resistance of 50 ohms per square. After cutting the glass rectangle to the desired dimensions and after mechanical treatment of the edges, two layers of current supply 11 and 12 were deposited on the layer side, parallel to the longest side of the rectangle. 'A silver-based paste, suitable for good adhesion to the conductive layer and allowing the soldering of the supply conductors, for example, the reference ES 574 804/01 from the company DEGUSSA. Once cooked, the strips 11, 12 have a width of 3 mm and a thickness of 20 μm, these two quantities being linked to the intensity of the current which it is intended to pass through the conductor. After the silver paste has dried, it is covered with a protective layer made of enamel from the same manufacturer with the reference: VR-HPC series. Only the locations intended to receive the electrical connections at least at one of the ends of the strips 11, 12, do not benefit from this protection. This second layer of enamel protrudes from the first by about 1 mm on each side. The distance between the electrodes is, for example, 40 cm, which allows using a voltage of 24 volts, to have a 72 watts of electrical power per square meter.

When a showcase counter consists of several elements identical to that of FIG. 2 placed end to end, an electrical connection can be established between successive plates, at the electrodes 11, 12, by means of H-shaped jumpers equipped springs the connections are greatly simplified. Likewise, the metal parts which are often used to support the vertical parts of the counter display cabinets in the connection zone of two neighboring glazings advantageously serve to connect the electrodes to the current source.

After depositing the pasta intended, after cooking, to form enamels, the plate is carried in a vertical oven, where it is supported by supports for example of the type described in French patent application No. 90-04806. After heating, a press bends and immediately upon leaving the press, quenching is carried out by blowing air jets.

During the development of the techniques of the invention, tests were carried out. This involved measuring the comparative efficiency of a traditional display case such as that of FIG. 1, equipped with a simple tempered glass and a display case according to the invention like that of FIG. 2 with a layer of 50 ohms. per square in four cases: without heating, with 30 W / m² (distance between electrodes, 62 cm at 24 volts), 72 W / m² (40 cm) and 200 W / m² (24cm).

The comparison was carried out with laminated glazing fitted with a heating interlayer film, the power of which was adjusted by varying the supply voltage.

The glazing was installed in a display case where food products were exposed to 6 ° C while the atmosphere of the room was 20 ° C. The results are summarized in the following table, we see the temperatures reached by the exterior surface of the glazing:

We see on these examples that the temperature rise goes from 1.5 ° C (without electrical supply) to 18.4 ° C (with 200 W / m²).

The examples of hardened single-glazing coated with a semiconductor layer of the SnO₂ type doped with fluorine which is obtained by pyrolysis of powdery organometallic compounds are not limiting of the means of the invention. We have already seen that the semiconductor layers based on ITO are suitable as well. Likewise, the pyrolysis of powder can be replaced by the pyrolysis of liquids. But all conductive, low-emitting and rather transparent layers are suitable. This is the case, for example, with layers of ITO deposited on cold glass, in a subsequent phase, by sputtering techniques such as those described in European patent application EP 350 362 A. Likewise, placing it on a glazing of traditional display case like that of FIG. 1, of a low-emissive conductive film, insofar as the glazing thus equipped reproduces the characteristics of the invention, is part of the techniques thereof.

In a variant of the glazing in FIG. 2, it has been fitted with a not shown fog detector. It allows the glazing to be heated only when the need arises. Several systems have been proposed, they are intended to equip the heated rear glasses of automobiles. These are, for example, conductive enamel pellets deposited on the external face of the display case, at the place where condensation occurs first, that is to say preferably, in the middle, in the lower part. The pastille includes two comb-shaped electrodes whose teeth are inserted. Electronics connected to the electrodes are sensitive to variations in electrical conduction linked to the moisture content of the glass surface. It controls the switching on of the heating. Such a device is described for example in patent FR 2 127 059. Associated with the glazing of the invention, it makes it possible to have a very efficient and very energy-efficient system. Furthermore, the fact of limiting the temperature rise to the strict minimum which is added to the low emission of infrared radiation from the glazing unit of the invention to the foodstuffs exposed in the refrigerated display case guarantees that these will not deteriorate not due to excessive local heating.

The glazing in Figure 2 is very effective, however, the electrode 12 which crosses the field of vision of the observer who looks at the products exposed in the window can be considered unsightly, even annoying. This is why the preferred form of the invention which is shown in FIG. 3 does not include this horizontal electrode. Instead, two electrodes 13 and 14 have been placed which are parallel to the short sides of the glazing, situated in vertical planes, their length is limited to the area which must be heated. In the figure, only two electrodes have been shown. However, given the value of the surface resistance of the conductive layer (generally between 50 and 10 ohms per square) and according to the surface power desired, while taking into account the acceptable electrical voltage (maximum 24 or possibly 48 volts ), it may be necessary to add one or more intermediate electrodes. The electrodes are identical in all respects to those described on the occasion of the variant shown in FIG. 2.

If the technique of depositing the thin conductive low-emissive and transparent layer allows partial deposition on the surface of the glass, it may be advantageous to limit the deposition of the layer to the surface between the electrodes. In this case the layer would only cover zone 15 and would be limited by a line of suitable shape connecting the ends of the electrodes 13, 14 such as for example line 16.

• Dépôt de poudre de zinc à partir d'une suspension dans un solvant et selon la ligne à traiter. Le dépôt se fait par serigraphie.
• Séchage du dépôt
• Pulvérisation d'acide chlorhydrique sur le dépôt de zinc : l'hydrogène naissant détruit la couche.

When the layer is continuous and also covers the area 17 in the upper part of the glazing, there can be significant localized heating around the ends of the electrodes 13, 14. There are indeed numerous lines of current coming from these points and which irradiate not only in zone 15 but also in a significant part of zone 17. This phenomenon can be considered as annoying by users. In this case, the invention proposes to suppress the electrical conduction of the layer on a narrow strip between the zones 15 and 17. A technique commonly used to remove the layers of semiconductor oxides consists in treating the layer with nascent hydrogen. The process steps are:

• Deposit of zinc powder from a suspension in a solvent and according to the line to be treated. The deposit is made by screen printing.
• Drying of the deposit
• Spraying hydrochloric acid on the zinc deposit: the nascent hydrogen destroys the layer.

Another technique which can be used to create a narrow insulating strip between zones 15 and 17 is the electro-erosion method described in European patent EP 15 4 572 B. It is also obviously possible to provide, before the layer is deposited on the glass, the deposition of a mask, such as for example a mask based on iron oxide in suspension deposited by screen printing, which will prevent contact of the layer with the glass and can be removed later.

It is thus possible to interrupt the conductive layer in a practically invisible manner and then the creation of hot spots at the ends of the electrodes is avoided.

Thanks to the techniques which have just been described, and as the results of the measurements show, the invention makes it possible to produce glazings intended to equip refrigerated display cases where condensation is practically impossible, this result being obtained avoiding the usual disadvantages such as: discomfort of vision for the barge who looks at the goods, unnecessary heating of the products displayed, high cost of installation or operation ...

Claims (14)

Method for avoiding condensation on a refrigerated display case equipped with a single electrically heated glazing, characterized in that the glazing is equipped with a low-emissivity conductive layer and that it is only heated by Joule effect if the condensation conditions are met. Method according to claim 1, characterized in that it uses a fog detector to control the heating. Device for preventing condensation on simple glazing fitted to a refrigerated display case, characterized in that it comprises a layer with reduced emissivity, current supply strips making it possible to heat the layer by Joule effect and means for determining whether the conditions condensation are combined. Device according to claim 3, characterized in that it comprises, on the surface of the glazing, on the outside, a fog detector. Device according to claim 2 or 3, characterized in that the Joule heating affects only part of the surface of the single glazing. Device according to claim 5 characterized in that the current supply strips are horizontal. Device according to claim 6 characterized in that the current supply strips affect the entire length of the glazing. Device according to Claim 5, characterized in that the current supply strips are each located in a vertical plane. Device according to Claim 8, characterized in that the current supply strips are shorter than the dimension of the glazing in their vertical plane. Device according to Claim 9, characterized in that the layer with reduced emissivity is interrupted between the part of the surface of the simple glazing subjected to heating by the Joule effect and the rest of the surface. Device according to claim 10 characterized in that the interruption consists of a narrow line which joins the ends of the current leads. Device according to one of Claims 3 to 11, characterized in that the layer with reduced emissivity belongs to the group of layers of semiconductor oxides comprising tin oxide doped with fluorine or chlorine, indium oxide doped with tin, tin oxide doped with antimony, zinc oxide doped with aluminum. Use in a refrigerated display case of a monolithic glazed element fitted with a low-emissivity conductive layer in order to avoid condensation of water vapor. Use in a refrigerated display case of a monolithic glazed element fitted on its internal face with a low-emissivity conductive layer in order to reduce the heating of the exposed products.

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