ES2262417A1 - Transparent solar sensor for thermal and solar applications, has flat transparent crystals joined with thermal interface material (TIM) layers defining air chambers in-between, and absorbing selective surface - Google Patents

Abstract

The sensor includes flat transparent crystals joined with TIM layers of alveolar construction, air chambers defined between TIM layers, and an absorbing selective surface. The absorbent selective surface forms a slope obtained by calculation based on the distance, width, and angle of inclination of the same surface.

Description

Transparent solar collector for applications thermal solar.

The present invention patent application consists, as indicated in its statement, in a solar collector transparent for solar thermal applications, whose new construction, conformation and design characteristics meet the mission for which it has been specifically projected, with a maximum safety and efficiency and providing numerous advantages such as will be detailed herein.

The invention relates to a solar collector thermal integrated between two insulated glazing with materials transparent, particularly for use, although not exclusively, on roofs and vertical closures of buildings.

Within the various types of collectors solar, the type of the sensor that is the object of the invention is that of a flat solar collector. Said sensors comprise one or several layers of a transparent material on the front, such like glass, through which the sun's rays hit before of reaching an absorption surface that is directly in contact with the working fluid. In bliss absorption surface, solar radiant energy is transferred towards the working fluid.

The transparent layer mentioned above allows the entry of solar radiation to the absorption surface. The main difficulty presented by the general design lies in the need to minimize radiation heat losses thermal and convection towards the environment by said part front maintaining maximum transparency to radiation solar.

Until now, on the back there was a opaque insulating material to avoid thermal losses. Is known in the art the use of transparent insulating materials (TIM) for the manufacture of the front part (or cover) of solar collectors This technique extends to all solar thermal applications including both active systems and passive systems The most practical experience with materials Transparent insulation occurs in the field of solar systems liabilities, for example in walls of isolated buildings transparent and natural lighting systems.

With reference to active solar systems, in In recent years, prototypes of flat solar collectors with transparent insulation covers in different research centers and institutions. This type of collector is an attempt to offer a cheap alternative to standard collectors available in the market for applications solar thermal in medium temperature ranges (above 100 ° C). The main technical problem that must be overcome if you want to market these prototypes is to ensure your resistance to high temperatures that occur under conditions of stagnation. When stagnation conditions occur, that is to say when the thermal fluid stops circulating coinciding with high levels of solar radiation, temperatures inside Said sensors can reach values of up to 300 ° C. Without However, there are currently no insulating materials transparent (TIM) in the market with a reasonable cost that can Withstand these temperatures.

As a consequence, the collectors they use TIM must be designed with some kind of mechanism or concept ensure that the TIM is not damaged in conditions of stagnation.

The invention presented here arises from the research and the advances made by its inventors on the application of transparent insulating materials (TIM) for collector covers in medium temperature ranges (beyond 100 ° C). The research carried out has basically been directed towards obtaining thermally optimized designs with which possible to achieve the highest possible temperatures. How result of this thermal optimization, not only have proposed cover redesigns but they have also been designed other collector elements such as opaque reverse thickness and the isolation of one side, structures that avoid thermal bridges and materials with higher thermal resistance.

The transparent solar collector for applications thermal solar object of the invention is a flat solar collector integrated in transparent transparent facade that has its front part formed by a transparent crystal, a layer of a material transparent insulator (TIM) of a thickness of 10-30 mm and alveolar structure, which is attached respectively to said glass, and a selective absorbent surface separated from the cited layer of transparent insulating material with an air chamber with a thickness preferably between 15 and 30 mm.

The absorbent surface includes a series of fins provided with selective treatment. These fins are they have a suitable distance inclined and separated from each other.

The main feature of the invention resides in the fact that on the back there is a second layer of insulating material that defines a second chamber of air disposed between it and said selective absorbent surface, preferably of a thickness between 15 and 30 mm. This TIM second layer has a thickness of between 20 and 35 mm and presents also an alveolar structure. In its furthest part of the absorbent surface, said second TIM layer is attached to a second crystal

The fins of the absorbent surface are they have an angle of approximately 45º inclined with respect to the surface of said crystals, so that the distance of separation between them is equal to the cosine product of said angle of inclination for twice the width of them.

Layers of transparent insulating material (TIM) use a thermally optimized TIM for collector covers in medium temperature ranges (beyond 100ºC) for collectors standard (with working temperatures below 100ºC).

They have an alveolar structure and have a large cell width, preferably 8 to 10 mm, for achieve maximum transmissivity of solar radiation.

Thanks to its configuration, the collector object of the invention has an improved thermal performance with respect to standard solar collectors, and has the particular ability to be used on surfaces that must be transparent for use architectural and especially in applications at temperatures of work above 50-60ºC and / or in environments cold, all at a very low cost.

When using a TIM material for a cover insulator for sensors with working temperatures in the interval of standard temperatures (below 100ºC) it is possible to reduce thermal losses in a considerably effective way. Thanks to this feature, significant improvements are obtained in the thermal efficiency

Advantageously, the transparent insulating material (TIM) has a large cell width of 8-10 mm Wide cell configuration provides greater optical performance According to the invention, the structure alveolar of said transparent insulating material (TIM) has a low material content, that is, a structure is preferable alveolar thin walls.

The transparent insulating material (TIM) has a material content corresponding to a fraction of material volume equal to or less than 1%, that is, the volume of the plastic material is 1% of the total volume of the honeycomb structure with its
cells.

According to another advantageous feature of the insulating cover of the present invention, due to the factor of cell shape (relationship between cell height and width from the cell) convection is not eliminated but reduced. The total removal of convection in cells would require some narrower cavities corresponding to a form factor of approximately 10, which would significantly reduce the optical performance and / or would make the TIM temperature at stagnation out too high.

Advantageously, the union between the material transparent insulator (TIM) and the glass is made with a suitable use of adhesive materials that make body with the TIM material. Such materials may be liquid adhesives, molten adhesives or Similar. These adhesives must be resistant to UVA and with high stability, as well as with an index of refraction as similar to glass.

The described characteristics of the material transparent insulator according to the present invention so which refers to cell size and material content, are derived of a thermal optimization of roofs with TIM for sensors with working temperatures in the average temperature range (above 100 ° C).

The cover design of the present invention ensures resistance to stagnation conditions if The material used is capable of withstanding a temperature equal to the stagnation temperature of the collector minus about 50-70ºC, depending on the design. This feature is achieved at a reasonable cost.

Another advantage that is achieved with the configuration of the front and back cover, which is described, is a great ease of use in the market sensors with small Design changes

It is described in detail below and by way of non-limiting example, a preferred embodiment of the invention from which the results will be clearer features and advantages of it. The description that follows It is given with reference to the accompanying drawing, which corresponds to a sectional view of the collector object of the present invention.

The different ones are listed below references that have been used to describe the realization Preferred of the invention:

(one)

transparent flat glass;

cap of transparent insulating material;

(3)

air chamber;

(4)

absorbent surface;

(5)

air chamber;

(6)

cap of transparent insulating material;

(7)

transparent flat glass;

(10)

fins;

(eleven)

collecting tubes;

(12)

minor tubes;

(13)

canonized aluminum profile Exterior;

(14)

aluminum insulator inside;

(D)

separation distance between fins;

(L)

fin width; Y

(?)

angle of inclination of the fins

The solar thermal collector integrated in the facade transparent isolated from the example described in accordance with the invention consists of two transparent flat crystals parallel (1, 7) 3-4 mm thick with a low iron content, although others can also be used crystals of suitable plastic materials.

Said solar thermal collector also comprises two layers (2, 6) of a transparent insulating material (TIM) of honeycomb structure respectively attached to said crystals (1, 7) by adhesive specially designed to adhere to them. The TIM layer (2) has a thickness of 15 mm and is capable of supporting up to 140 ° C, while the TIM layer (6) has a thickness of between 20 and 35 mm, depending on the applications of the solar collector thermal.

Respective air chambers are defined (3, 5) between the layers of transparent insulating material (2, 6) and a selective absorbent surface (4). This absorbent surface selective (4) presents a selective coating with an emissivity less than 7% and consists of a grid consisting of two copper collector tubes (11) and other smaller tubes (12) welded to the same.

On said smaller tubes (12) they join (of the in a manner deemed convenient) fins (10) provided with a selective treatment These fins (10) are placed inclined a angle (α) of approximately 45 ° with respect to the plane of the crystal (1, 7), depending on latitude and use, as you can Appreciate in the drawing.

The smaller tubes (12) are separated one distance (D) equal to 2 \ cdotL \ cdotcos (\ alpha), being (L) the width of the fins (10). Therefore, in the provision of said fins (10), it is fulfilled that D = 2 \ cdotL \ cdotcos45º.

The aforementioned air chambers (3, 5) arranged between the TIM structures and the absorbent surface (4) They have a thickness between 15 and 20 mm. Tests Experimental tests based on ISO standards 9806-1: 1994 (E) have confirmed that the configuration described allows to obtain a thermal efficiency of the solar collector improved, especially in applications at working temperatures in the order of 50-60ºC and / or in cold environments. This allows to guarantee the isolation of the set making possible get higher temperatures. In addition, the structure layers alveolar (2, 6) are separated from the hottest part of the cover, that is, the absorbent surface (4).

The transparent insulating material of the layers (2, 6) consists of a plastic material with honeycomb structure that It is stable in the long term, resistant to ultraviolet rays and resistant to working temperatures of up to 140ºC. In general, the maximum stable temperature of the alveolar structure layers (2, 6) corresponds to the maximum temperature that can withstand collector cover. The roof configuration is capable of resist stagnation conditions provided that the plastic of the layers (2, 6) be able to withstand a temperature equal to the collector stagnation temperature less 50-70ºC, depending on the design.

The adhesion between the structure must be taken care of alveolar of the TIM and the glass, maximizing the contact between the honeycomb structure and glass, avoiding pick-ups, of what Otherwise, multiple convection could occur between different cells of the alveolar structure, eliminating the effects of isolation. The glue must have characteristics of long-term stability, resistance to ultraviolet rays and resistance to temperatures up to 80-100ºC.

The transparent insulating material (TIM) of the layers (2, 6) have a cell width of 8-10 mm, thus providing greater optical performance.

Another characteristic of the structure Alveolar layers (2, 6) is that it has a low content in material, that is, it is an alveolar wall structure thin with a material content corresponding to a fraction of volume of material equal to or less than 1%, that is, the volume of the plastic material is 1% of the total volume of the structure alveolar with its cells.

On the other hand, the cell factor, that is, the relationship between the thickness of the layers (2, 6) of TIM material and The width of the cell is 2 to 3.5 respectively. With it significantly reduces convection in cells while maintaining a Good optical performance

With the design described can be achieved flat transparent sensors for a job of 50-60 ° C and optical performance for an incidence normal is only reduced by approximately 1-2% because when using the honeycomb structure (2) attached to the glass (one).

The sensor of the invention described in according to the figure is completed at its ends with a profile of canonized aluminum exterior (13) and an interior aluminum insulator (14).

Described sufficiently what is the present invention in correspondence with the attached drawing, is will understand that any modification of detail deemed convenient, as long as the essential characteristics of the invention summarized in the following claims are not altered.

Claims (7)

1. Transparent solar collector for solar thermal applications comprising two transparent flat crystals (1, 7), a layer (2) of a transparent insulating material (TIM) of honeycomb structure bonded respectively to said glass (1), an air chamber (3) disposed between said layer of transparent insulating material (2) and a selective absorbent surface (4), said absorbent surface (4) including a series of fins (10) arranged inclined and separated from each other a distance (D), said selective absorbent surface (4) being separated a distance (d) from said layer of material TIM (2), characterized in that it also includes a second layer of transparent insulating material (6) defining a second air chamber ( 5) disposed between it and said selective absorbent surface (4). 2. Transparent solar collector for solar thermal applications according to the first claim, characterized in that the distance (d) between said layer of insulating material (2, 6) and said selective absorbent surface (4) is between 15 and 30 mm, and wherein said fins (10) are inclined at an angle (?) relative to the surface of said crystals (1, 7), said separation distance (D) thereof being equal to the cosine product of said angle of inclination (α) of the fins (10) by twice the width (L) thereof. 3. Transparent solar collector for thermal solar applications according to the 2nd claim, characterized in that the angle of inclination (α) of the fins (10) is approximately 45 °. 4. Transparent solar collector for thermal solar applications according to the 1st claim, characterized in that said transparent insulating material (TIM) has a cell width of 8-10 mm. 5. Transparent solar collector for solar thermal applications according to the 1st claim, characterized in that the cell shape factor of the alveolar structure of said layer of transparent insulating material (2, 6) is between 2 and 3, 5. 6. Transparent solar collector for solar thermal applications according to the 1st claim, characterized in that said layers of transparent insulating material (2, 6) and said transparent flat glass (1, 7) are joined by the use of molten, liquid, or adhesive similar, with characteristics of resistance to UVA, index of refraction similar to glass and continuous adhesion. 7. Transparent solar collector for solar thermal applications according to the 1st claim, characterized in that said layer of transparent insulating material (2) located on the front of the collector has a thickness between 10 and 30 mm and in which said layer of material Transparent insulation (6) located at the rear of the sensor has a thickness between 20 and 35 mm.