DE202011109063U1 - Absorber holder with temperature-independent convection suppression for rear-panel insulated solar collectors - Google Patents

Abstract

Holding device in the housing (1) of a solar collector with film insulation on the back (4) for fastening and stationary stabilization of a flat absorber or the heat exchanger (3) thermally connected thereto, characterized in that it consists of at least one inner support (6), d , H. a support that is not arranged on the edge of the absorber or heat exchanger.

Description

Problem, subject of the invention

Conventional flat solar panels (flat panels) differ only slightly in their construction. They consist of a housing, which is usually made of Al or an Al alloy, recently also made of plastic, and in which a mostly selectively coated, planar absorber is installed parallel to the rear wall of the housing. The absorber is connected to a device (usually tubes) for heat transfer to a fluid and is usually delimited from the environment by an air gap and a glass plate to reduce thermal losses. On the absorber back of the solar panel is usually provided with a thermal insulation to keep the thermal losses low. The rear thermal insulation is usually made of mineral or rock wool, which represents a not inconsiderable cost factor in the collector, is difficult to handle and requires a high weight of the panels. In addition, the insulating effect of such materials depends strongly on the environmental conditions. Through the heating and cooling processes during the day and at night, the pressure fluctuates in a flat collector, so that it interacts with the ambient air and moist air can get into the interior of the collector. If the water vapor condenses in the insulation - which often happens - it is moistened. The water that is thus stored in the insulating material greatly reduces the collector efficiency, as the heat losses on the back increase due to the higher thermal conductivity of the damp insulation material [1, 2, 3]. In addition, this increases the collector weight. The reduced efficiency leads to a reduction of the solar yield and requires an additional heating effort, which usually has to be covered by the use of fossil fuels.

The invention relates to a rear insulation concept for flat-plate collectors based on a film insulation, which replaces the mineral wool and optimizes the moisture content of the collector with low weight and low production costs. It also provides the absorber with a stable mechanical bearing while minimizing thermal bridges that would lead to thermal losses. In addition, it prevents the slack of the film caused by thermal expansion at higher operating temperatures, so that a high level of functional reliability is ensured and also the convective backside thermal losses are reliably minimized.

Prior art, previous work

To reduce the back collector losses and to improve the moisture balance, various concepts have been developed that solve individual problems but also create new ones, so that the efficiency, reliability and production costs of the collectors could not be optimized at the same time.

In DE 20 2005 007 474 U1 a solution of the moisture problem is given, which is based on that the conventional rear insulation, z. As mineral wool, is replaced by one or more films, so that no materials are used, which could act as a moisture storage. This has the ideal consequence that the thermal conductivity of the rear insulation at ambient temperature compared to wet mineral wool is reduced by about a factor of 4, namely from about 0.1 Wm ^-1 K ^-1 (moderately moist mineral wool [1]) to about. 0.025 Wm ^-1 K ^-1 , (static air at 25 ° C). With the same collector height, this results in lower heat losses to the rear.

Such a backside film insulation offers an average of about the same insulating effect as the mineral wool in the dry state while reducing the weight and manufacturing costs of flat-plate collectors [4]. However, it also leads to variations in the insulation effect by the development of different convection patterns in the collector, depending on temperatures, geometry and inclination angle of the collector. It must also be provided against slack at higher operating temperatures usually a complicated clamping device for the film. Also, the absorber can no longer be stored on the mineral wool, so that in practice the safe operation of collectors with back film insulation can not be readily ensured. While in conventional flat plate collectors the stiffnesses of the absorber and the heat exchanger are insignificant due to the flat support on the insulating material, they play an important role in the film insulation. Depending on the design of the heat exchanger (serpentine absorber, harp absorber or meander absorber), the collector design may decrease DE 20 2005 007 474 U1 Due to the high temperatures that are reached during operation of the solar collector, come to the sag of the absorber or the heat exchanger itself. As a result, it can be detached, for example, from the suspension on the collector housing. In addition, the thermal losses on the now reduced air gap between the absorber and the film increase greatly, so that the sag would also affect the efficiency of the solar collector. In addition, the film can even be destroyed by the overheating associated with the sag of the absorber.

Due to the large thermal expansion of the usually made of plastic film at higher absorber or collector temperatures, however, the distance between the absorber and film - even with the use of a jig - so far enlarge that the convection can not be suppressed and the film u. U. even applied to the housing.

The increased toughness of the air due to increased temperatures and the higher buoyancy forces further promote the formation of convection, so that in this case the rear heat losses of the collector rise sharply and its efficiency decreases.

DE 20 2008 001 864 U1 and DE 20 2008 010 263 U1 describe dam variants for collector housings made of plastic, with the help of which both the moisture problem and the temperature-dependent gap widths can be avoided. In both concepts, however, other heat losses are accepted. In addition to the gap width, the formation of convection is also dependent on the so-called overflow length, ie on the distance over which a flow can absorb thermal energy. Larger overflow lengths promote the formation of convective flows. At the in DE 20 2005 007 474 U1 The concept described is the overflow equal to the entire collector or absorber length, which leads to increased heat losses on the back. At the in DE 20 2008 001 864 U1 proposed solution thermal bridges are inserted, which u in suitable for Konvektionsunterdrückung dimensioning of the air chambers. U. transport a significant portion of the heat generated in the absorber to the rear wall and thus also increase the losses. In addition, both inventions generally require new collectors, since conventional flat plate collectors are typically manufactured with metallic housings.

literature

• [1] Fabian Ochs, Hans Müller-Steinhagen, Thermal conductivity of insulation materials In: VDI Heat Atlas (2nd Ed.), Springer, 2010, ISBN 978-3-540-77876-9 ,
• [2] Ole Holck, Svend Svendsen, Stefan Brunold, Ueli Frei, Michael Köhl, Markus Heck, Henk Oversloot: Solar collector design with respect to moisture problems. Solar Energy 75 (2003) 269-276 ,
• [3] Michael Köhl, Volker Kübler, Markus Heck: Optimization of the micro-climate in solar collectors. Solar Energy Materials & Solar Cells 91 (2007) 721-726 ,
• [4] Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU), Program Solarthermie2000plus, Dr. Ing. Thomas Beikircher, ZAE Bayern, Final Report on Project 0329280A, High-efficiency flat plate collector with foil insulation and overheating protection for operating temperatures of 70-100 ° C, 2010 ,

Object of the invention

The Durchfeuchtungsproblematik the rear thermal insulation of conventional flat-plate collectors (see above) should be avoided by the substitution of mineral / rock wool by a film between the absorber and the rear wall of the housing. At the same time, the thermal efficiency and reliability of this Dämmvariante of solar panels should be improved at all temperatures possible in real operation. In addition, the invention is to allow a lighter and cheaper construction compared to ordinary collectors. In addition, the inventive rear insulation should be retrofitted in conventional flat panels by replacing the conventional mineral or stone wool insulation or by supplementing existing rear film divides.

Task solution, description of the invention

The present invention solves the problems indicated above based on the in DE 20 2005 007 474 U1 specified rear foil insulation of a flat collector. Consequently, compared to conventional collectors, a similar weight saving as in DE 20 2005 007 474 U1 achieved. The absorber or its associated heat exchanger is held in the present invention by at least one inner support in position (claim 1). To fix the absorber or heat exchanger on the edge additional external supports can be used, which are mounted directly inside the frame of the collector housing (claim 2), so that can be dispensed with a conventional suspension. The outer supports can also be designed as a circumferential second frame (claim 3). They insulate the side walls of the housing against the heat loss through the convection flow and at the same time serve to clamp the film (claim 4), if this is not attached directly to the collector housing. By means of the inner support / supports ensures that absorber and heat exchanger and the thus also supported film (claim 5) even when heated not sag beyond a tolerable level. An elaborate clamping mechanism for the film can therefore be dispensed with. In addition, eliminates the Durchfeuchtungsproblematik if the supports are not used materials that absorb moisture to a significant extent can, or their volume is negligible compared to that of ordinary mineral wool insulation in flat plates. Consequently, back heat losses compared to conventional collectors - as in DE 20 2005 007 474 U1 described - regardless of the environmental conditions reduced, but now at all possible temperatures in operation. In particular, this relates to the higher, that is above 80 ° C, absorber temperatures at which the expansion of the film would otherwise lead to slack, which could be prevented only by a very complex clamping mechanism.

The back losses are further minimized by the invention by suppressing the formation of convection by small overflow lengths. The overflow length is the distance along which a flow can absorb thermal energy. To shorten this, is / are the inner / inner support / supports, which is installed between the collector rear wall and absorber or heat exchanger (s), designed as a wall / walls (claim 6), which is perpendicular or at least not parallel to that direction / run, in which otherwise a convective flow would occur (claim 7). In order to impede the formation of convection even further, the support walls can also be performed rib-like (claim 8).

The supports can be designed for good mechanical strength as a solid body (claim 9) or better than hollow profiles (claim 10) in order to minimize the thermal losses by heat conduction to a minimum.

By comparison to DE 20 2008 001 864 U1 and DE 20 2008 010 263 U1 significantly longer length of the supports described here but their thermal bridge function is already greatly reduced anyway. The greater length is due to the fact that in the film insulation both the absorber or heat exchanger and film as well as between the film and the collector back wall, the minimum distance to avoid heat conduction must be maintained in the air gap (see above). At the double rear wall off DE 20 2008 001 864 U1 and DE 20 2008 010 263 U1 The braces bridge this distance only once.

The holder is fixed or floating with the absorber or heat exchanger, the film and the collector housing connected (claims 11-16). By a movable connection, the thermal expansion of the components is not hindered, while still a sagging of absorber or heat exchanger and film and the associated increase in heat transfer from the absorber to the collector back wall are avoided by the support / supports. So that the film can not be damaged, the surfaces of the inner supports are particularly smooth or perform in conjunction with the film slidably (claim 17).

As materials for the holder are plastics (claim 18) or other substances with low thermal conductivity (claim 19) in question, and also used in conventional collectors mineral or rock wool (claim 20), z. B. are used as insulating filler of plastic hollow sections. Thus, the rear thermal losses are kept low by heat conduction. The almost inevitable in a floating connection of support and film gap in the support can reduce the heat conduction from the absorber or heat exchanger on the support to the collector housing again.

For simple retrofitting existing, conventionally insulated flat plate collectors, the entire holder with the film can also be assembled into one component (claim 21). Thus, the mineral or rock wool can be easily replaced with an optimized film insulation, since the surface storage of the absorber is replaced on the mineral wool according to the invention by supports. A firm connection between absorber or heat exchanger and absorber holder and between the holder and the collector housing can be realized by screwing, gluing, clamping, riveting, punching, pressing, welding or other form-fitting connections (claim 22).

To illustrate the invention, the description 3 illustrations are attached. Show it;

: Perspective view of a rear foil-insulated flat collector with inner support walls according to the invention and conventional absorber / heat exchanger suspension and Folieneinspannung the collector housing.

: Sectional view of a rear-foil-insulated flat collector with inner and outer support walls according to the invention. By way of example, here an absorber / heat exchanger suspension is shown via the headers of the heat exchanger.

: Sectional view of an alternative embodiment of the outer support, again as a hollow profile with absorber / heat exchanger suspension and Folieneinspannung

LIST OF REFERENCE NUMBERS

1

collector housing

2

Transparent cover

3

Absorber with heat exchanger

4

foil

5

Folieneinspannung

6

Inner support

7

Outer support

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 202005007474 U1 [0004, 0005, 0008, 0011, 0011, 0011]
• DE 202008001864 U1 [0008, 0008, 0014, 0014]
• DE 202008010263 U1 [0008, 0014, 0014]

Cited non-patent literature

• Fabian Ochs, Hans Müller-Steinhagen, Thermal conductivity of insulation materials In: VDI Heat Atlas (2nd Ed.), Springer, 2010, ISBN 978-3-540-77876-9 [0009]
• Ole Holck, Svend Svendsen, Stefan Brunold, Ueli Frei, Michael Köhl, Markus Heck, Henk Oversloot: Solar collector design with respect to moisture problems. Solar Energy 75 (2003) 269-276 [0009]
• Michael Köhl, Volker Kübler, Markus Heck: Optimization of the micro-climate in solar collectors. Solar Energy Materials & Solar Cells 91 (2007) 721-726 [0009]
• Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU), Program Solarthermie2000plus, Dr. Ing. Thomas Beikircher, ZAE Bayern, Final report on project 0329280A, High-efficiency flat collector with foil insulation and overheating protection for operating temperatures of 70-100 ° C, 2010 [0009]

Claims (22)

Holding device in the housing ( 1 ) of a solar collector with rear foil insulation ( 4 ) for fixing and stationary stabilization of a flat absorber or the thermally attached thereto heat exchanger ( 3 ), characterized in that it consists of at least one inner support ( 6 ), ie a support which is not arranged on the edge of the absorber or heat exchanger. Holding device according to one of the preceding claims, characterized in that it additionally comprises two outer supports, ie supports adjoining directly to the housing frame ( 7 ) consists. Holding device according to claim 2, characterized in that the outer supports are designed as part of a circulating or partially circulating frame within the collector housing. Holding device according to one or more of the preceding claims, characterized in that the film, which is used for rear-side thermal insulation of the collector, is firmly clamped in the outer supports ( 5 ). Holding device according to claim 1, characterized in that the inner / inner support / supports also supports the film used for the rear thermal insulation of the collector. Holding device according to claim 5, characterized in that the inner / inner support / supports divide the rear space between the absorber or heat exchanger and film, and between the film and collector housing in two or more chambers, z. B. by the execution as walls. Holding device according to claim 6, characterized in that the inner / inner support wall / support walls is not parallel, but preferably perpendicular to that direction runs / run, in which would form a convective flow without this wall / walls in real operation of the solar collector. Holding device according to one or more of the preceding claims, characterized in that it is designed like a rib and thus acts konvektionsunterdrückend. Holding device according to one or more of the preceding claims, characterized in that the supports are designed in solid construction. Holding device according to one or more of the preceding claims, characterized in that the supports are designed as hollow profiles. Holding device according to one or more of the preceding claims, characterized in that it is firmly connected to the absorber or heat exchanger. Holding device according to one or more of claims 1-10, characterized in that it is connected in a floating manner with the absorber or heat exchanger. Holding device according to one or more of the preceding claims, characterized in that it is firmly connected to the collector housing. Holding device according to one or more of claims 1-12, characterized in that it is floatingly connected to the collector housing. Holding device according to one or more of the preceding claims, characterized in that it is firmly connected to the film. Holding device according to one or more of claims 1-14, characterized in that it is floatingly connected to the film. Holding device according to claim 16, characterized in that the surface of the supports is smooth and slidable in cooperation with the film. Holding device according to one or more of the preceding claims, characterized in that it consists of one or more plastics such. As PU, XPS, ABS, PA, PC, PET, PVDF, EP Hgw (glass fabric 7 epoxy), EPDM, TPX, PSU, PES, PEI or fluoropolymers consists. Holding device according to one or more of claims 1-17, characterized in that it consists of a material with low thermal conductivity, ie less than 1 Wm ^-1 K ^-1 at room temperature. Holding device according to one or more of claims 1-17, characterized in that the inner / inner and / or outer / outer support / supports consist at least partially of mineral or rock wool. Holding device according to one or more of the preceding claims, characterized in that all the components of the back Collector insulation, ie outer and inner supports and the film, are designed as a coherent collector component. Holding device according to one or more of the preceding claims, characterized in that it is firmly connected to the absorber or heat exchanger and / or with the collector housing by screws, clamps, gluing, riveting, punching, pressing, welding or other form-fitting connections.

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