DE2835372A1 - SUN HEATER - Google Patents

Description

L-11O97-G

UNION CARBIDE CORPORATION 270 Park Avenue, New York, N.Y. 10017, V.St.A.

Solar heater

The invention is concerned with solar heaters that convert incident solar radiation into thermal energy and the absorbed heat is transferred either to a gas, for example air, or a liquid, for example water. Devices of the type mentioned first are usually used as solar air heaters and devices of the last named type referred to as solar water heaters. The invention particularly relates to solar heaters of the one type as well as the other type where there is a heat trap between the absorber and the translucent front wall is provided.

Various proposals have already been made, a heat trap between the absorber and the front wall of a Provide flat-plate solar heating device to the heat - losses due to natural convection and radiation to reduce. An example of the use of a transparent honeycomb heat trap can be found in an essay from Holland's "Honeycomb Devices in Flat Plate Solar Collectors", Solar Energy, Volume 9, Pages 159 to 169,

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Pergamon Press (1965). A problem that arises is that in practice it may be necessary to leave a space between the honeycomb heat trap and the Provide front wall to allow different thermal expansions of the components of the heat heater. It was found, however, that the presence of such a room reduces the loss of heat by natural convection can increase to the front wall. This increased heat loss is due to the fact that natural convection currents between neighboring cells of the Form honeycomb arrangement.

Presented from the results of Edwards et al in "End-Clearance Effects on Rectangular-Honeycomb Solar Collectors" on 1975 International Solar Energy Congress and Exposition, July 28 to August 1, 1975, UCLA, Los Angeles, published in Solar Energy, Volume 18, pages 253-257, Pergamon Press (1976) it follows that this increase in heat loss can be reduced by a space between the honeycomb heat trap and the flat plate absorber instead of being provided between the heat trap and the front wall. Problematic with this proposal is, however, that the honeycomb arrangement must necessarily be provided with relatively thin walls in order to to serve as an effective heat trap, so that the honeycomb arrangement is either too flexible to be self-supporting if it is made of clear plastic, or

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the honeycomb arrangement becomes extremely fragile when made from glass. As a result, need separate funds be provided to the honeycomb assembly over its full To support the surface.

It has also been proposed a honeycomb arrangement or to provide another open cell structure in contact with the front wall so as to be used in a transpiration solar air heater a radiation trap and an air buffer device. So describes the priority Patent application P 28 23 449.3 a transpiration solar heater for gaseous media in which the cellular radiation trap at least in solid mechanical contact is kept with the front wall, so that it can also act as an air buffer layer. In The experimental work described in patent application P 28 23 449.3 has shown that a substantial improvement the thermal efficiency is achieved when the radiation trap is in firm contact with the front wall held or connected to the front wall. if on the other hand, the radiation trap is only loosely adjacent to the front wall is held, there is a problem that convection currents pass through the heat trap and come into contact with the front wall, where heat is lost can enter.

Both with flat panel solar heaters and the front

transpiration solar heaters for gaseous media, the heat trap in contact with the front wall can be supported by one or more rigid ones Rods under the heat trap made of cells or honeycombs be arranged or by providing adhesive bonds between the heat trap and the front wall will. This type of support is effective Wise the problem of a convection air flow through the heat trap. However, this is a disadvantage Support so that the rods, adhesive connections or other support elements lead to additional surfaces, from which incident sun rays are reflected or scattered in a direction leading away from the solar absorber and thus can be lost.

The present invention is directed to a novel and improved solar heater device that is those set forth above Problems with both a flat panel solar heater and a transpiration solar heater clears for gaseous media. A solar heater with a self-supporting front wall and heat trap is to be created in which the total permeability for incident solar rays is higher than with known solar heating devices where the heat traps are supported adjacent the front wall. Front wall and heat trap should have great strength, be durable, allow easy handling and economical manufacture

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allow.

The solar heater according to the invention has a housing with a translucent or transparent front wall and a radiation-absorbing collector element, which is arranged to absorb incident solar radiation passing through the front wall. The solar heater is also equipped with a heat trap, which according to the invention is integrally connected to the front wall, d. H. is formed in one piece together with this. The heat trap obtained in this way is much stronger as an unsupported cellular heat trap alone; no further support is necessary to hold the heat trap against the front wall. The ones outlined above Problems with flat plate heaters and transpiration solar heaters for gaseous media become solved in this way without supporting elements or adhesive connections or seams are required, of which incident sun rays in one of the radiation-absorbing Element away from the direction are reflected and can be lost. Because also with the Warm trap according to the invention, no adhesive bonds are present there are no problems with the aging of the adhesive, i.e. H. Discoloration, embrittlement, cracking and like that.

The combination of a one-piece heat trap

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and the front wall is in the following for the sake of simplicity referred to as "integral heat trap glazing".

The invention is described below with reference to preferred exemplary embodiments in conjunction with the drawings explained in more detail. Show it:

. ♦

Fig. 1 is a schematic sectional elevation view a typical flat panel solar heater according to the invention,

Figure 2 is a similar view for a typical one

Transpiration solar heater for gaseous Media and

Fig. 3 is a partially cut-away perspective Representation of a preferred embodiment of the one-piece combination of Front wall and heat trap.

The principles of the present invention are at both Flat panel solar heaters as well as transpiration solar heaters for gaseous media can be used, though the integral heat trap glazing in these two types fulfills slightly different functions by solar heaters. The invention is therefore independent in the following on the basis of both types of solar heating devices

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Fig. 1 shows a flat panel solar heater constructed according to the invention. The solar heater has a housing 10 with a flat radiation-absorbing collector plate 12, which is at a distance from a rear wall 14. A coil 16 or other passage arrangement for a fluid, for example air or water in the space below the flat plate absorber 12 and in contact with it. Preferably if not essential is the remaining space between the flat plate absorber 12 and the rear wall 14 are filled with an appropriate insulation 18. The housing 10 can advantageously be made of a rigid metal, for example aluminum or steel, or another rigid material be made, for example plastic or glass fibers.

The housing 10 also includes integral heat trap glazing 20, which serves as the translucent front wall of the solar heater. As illustrated, the integral heat trap glazing 20 made in one piece. It has a flat top 20a that extends from the solar heater is directed outwards, and an underside 2Ob is provided, which points inwards and which is slightly Distance above the flat plate absorber 12 is so that a small gap 22 of, for example, about 5 mm or

less is obtained. The bottom 20b is with a Variety of cellular openings equipped whose Walls are substantially perpendicular to the top 20a. The cellular ones forming the underside 20b Openings can have the shape of a honeycomb or another cell arrangement, for example a cell structure, formed by parallel ribs. The integral heat trap glazing 2O can, as in the following explained in more detail, can be manufactured in one piece by conventional molding, pressing or casting processes. The arrangement 20 is preferably made of glass or a clear plastic such as polyvinyl fluoride, Polycarbonate, fluorinated ethylene propylene, polymethyl methacrylate, aromatic polysulfones, polyethylene terephthalate, aromatic polyesters, polyvinylidene fluoride, hexafluoropropylene, chlorotrifluoroethylene and tetrafluoroethylene copolymers .

Run through while the solar heater is in operation striking sun rays the integral heat trap glazing 20; they are absorbed by the flat collector plate and converted into heat. This heat is in turn by conduction and convection to a fluid, such as air or water, transferred through the coil 16 circulates therethrough in contact with the collector plate 12.

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In this embodiment of the invention, the integral is used Worm trap glazing 20 has a dual purpose of reducing radiant heat loss from the solar heater and the formation of natural convection in the air space between the flat collector plate and to suppress the front wall. So that the cellular Underside 20b of the integral heat trap glazing 20 effectively reduce the heat loss due to radiation can, the cellular openings must be a sufficient have a high aspect ratio, as described in detail in patent application P 28 23 449.3. In the case of honeycomb arrangements, this ratio must be in the range from 2 to 10 and in the case of ribbed cell structures in the range from 4 to 2O lie. As illustrated in Fig. 1, the walls of the cell openings divide the air space between the flat collector plate and the front wall; they prevent the formation of natural convection currents. Simultaneously becomes a narrow gap 22 between the underside 20b of the glazing 20 and the flat collector plate maintained to accommodate different thermal expansions of the Allow elements of the solar heater.

Fig. 2 shows a transpiration solar heater constructed according to the invention for gaseous media. As illustrated, the device has a housing 24 with a Rear wall 26 and an inlet 28 in one side wall and an outlet 30 in the opposite side

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walled up, creating a flow path for one to be heated Gas, for example air, is formed, like this is indicated by the arrows. A porous, radiation-absorbing Collector plate 32 sits within housing 24 parallel to and at a distance from rear wall 26 in the flow path between inlet 28 and outlet 3O. The porous collector plate 32 can, for example made of a porous, dark or black fiber mat, woven or punched screen material or made of foam. While in the illustrated embodiment, the porous collector plate 32 is parallel to the back wall 26, the collector plate can also be arranged in a non-parallel relationship to the rear wall, such as this is disclosed in the patent application P 28 23 449.3. If desired, an insulation layer 34 can be adjacent the rear wall 26 and at a distance from the porous collector plate 32. The housing 24 can also be in in this case made of a rigid metal, for example aluminum or steel, or another rigid material, for example plastic or glass fibers.

The housing 24 is also provided with integral thermal leakage glazing 36, which also acts as the translucent front wall of the transpiration solar heater is used for gaseous media. The integral heat trap glazing 36 basically has the same structure

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as in Fig. 1. It has a flat top 36a and a bottom 36b, which are of a plurality of cellular Openings is formed. In this case, however, the integral heat trap glazing 36 is so in mounted on the housing so that an enlarged space 38 is created. This space 38 is used for the passage of the to be heated Gas, for example air, between the underside 36b of the heat trap glazing and the porous collector plate 32. The integral heat trap glazing can be made using the same conventional shape, Pressing or casting techniques from the same glass or Plastic materials are made as described above are mentioned.

The operation of the transpiration solar heater for gaseous media is similar in that incident solar rays pass through the integral heat trap glazing 36 and are absorbed by the porous collector plate 32 and converted into heat. In this case, however, the gas to be heated, for example air, enters via the inlet 28 in order to then follow the flow path between the inlet 28 and the outlet 30. The gas, for example air, penetrates the entire porous collector plate 32 and is heated. The heated gas then exits via space 40 under the collector plate and through outlet 30. In this embodiment the integral heat trap glazing

the dual task of reducing radiant heat loss from the solar heater and an air buffer layer to form with partitions that adjoin a forced convection flow of the gas to be heated the front wall where heat loss can occur ·. The geometric design of the integral heat trap glazing 36 in this case is basically the same as explained above, i.e. H. the aspect ratio can for honeycomb cell structures between approximately 2 and 1-O and for rib cell structures between approximately 4 'and 20 lying.

In the two embodiments shown in FIGS 2, which are shown schematically, have integral heat-trap glazing 20 and 36, for the sake of illustration only, an underside of cells with relatively thick ones Walls. It will be understood that, in order to serve as a powerful heat trap, the walls will be relatively thin; H. one Must be between approximately 0.002 and 0.5 mm thick. The thickness of the remaining upper flat part of the glazing may depend on the overall dimension the glazing and also the selected thickness of the cell walls vary. In those cases where the cell wall is very thin, the upper flat part of the glazing must be a higher proportion of the total load (i.e. dead weight, wind and snow loads, and the like) absorb and as a result be thicker. If against it

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the cell walls are comparatively thick, the upper one can flat part can be made thinner than in the case of glazing without the cellular part forming the heat trap Bottom. In general, the thickness of the flat top can vary between about 0.75 and 6.0 mm.

Fig. 3 shows the preferred embodiment of the integral Heat trap glazing. As illustrated, the integral heat trap glazing 42 has an upper planar Part 42a with a substantially flat surface and a lower cellular part 42b with cells of hexagonal cross-section. The walls of the individual cells are integrally connected to the flat upper part at 44, which leads to a continuous distribution of the material from the front wall and the heat trap without the inner surfaces, Connection seams or adhesive bonds are created from which incident sun rays are scattered or reflected can be.

The integral heat trap glazing can be made with the help of conventional molding, pressing or casting processes will. For example, the integral heat trap glazing can be used in a particularly advantageous manner corresponding to the expanded core process known from US Pat. No. 3,919,446 manufacture. Modifications and improvements of this method and of the device for carrying it out are from U.S. Patents 3,765,810, 3,919,379,

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3,919,380 and 3,919,445 are known. In this procedure can objects like integral heat trap glazing are produced 'by stretching the cross-section of a blank made of heat-deformable material in this way that from a surface of the blank emanating cavities, for example in the form of hexagonal cells, are formed will. The remaining, unstretched part of the blank forms the upper planar part of the integral Heat trap. Usually following this procedure manufactured articles with a perforated skin on the opposite of the non-stretched flat part Side provided; this skin must be removed before the article can be used as integral heat trap glazing suitable is. The perforated skin, if not removed, would be oriented so that sunbeams striking and reflected by it would be directed away from the solar absorber and be lost. The perforated skin can be removed by a electrically heated wire is passed through the cell walls immediately adjacent to the skin, or by a band saw blade that cuts in opposite directions and is equipped with a knife edge is used, as it is for the cutting of metallic honeycombs is used. To the For a better understanding of the process, reference is made to the above-mentioned patents. In addition, it goes without saying that the integral heat trap glazing can also be manufactured with the help of other processes

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- 20 - 283537. '

can, for example in the injection molding process, in which a thermally deformable material under pressure in a Mold is injected that has the desired cell shape Has.

In the illustrated embodiments, the Cell walls of the cell part of the integral thermal trap glazing 42 perpendicular to the upper planar part 42a. The invention is not limited to such a design. The cell walls can also adopt other angles, as long as only reflected from the cell walls Sun rays are not directed back to the upper level part during normal operating periods. The vorr The term "substantially perpendicular to the upper planar part", which is used horizontally, is therefore intended to also include such other angles with respect to the orientation of the cell walls include. The cell walls have been found to be at angles with respect to normal of up to about 22.5 ° can be arranged without incident sun rays being reflected away from the solar absorber, when a period of time from about three hours before to three is selected as the normal operating time Hours after the sun has reached its highest point. Regarding one For a more detailed explanation of the cell wall angle and its derivation, reference is made to patent application P 28 23 449.3 taken.

The present invention thus becomes a solar heater in the form of a flat plate heater or a perspiration heater for gaseous media with integral Thermal trap glazing created which is self-supporting and which has a high resulting permeability for incident sun rays. Furthermore, an integral heat trap glazing is used in Get solar heating devices that have a high strength-to-weight ratio, is durable, easy to handle can be and can be produced in an economical manner.

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Claims (19)

PATENT Attorney DlPL-INC. GERHaRD SCHWAN ELFENSTRASSE32 D-8000 MUNICH 83 L-11O97-G Expectations Solar heating device, characterized by a housing (10, 24) with a combination (20, 36, 42) of a translucent Front wall and a heat trap; a radiation absorbing end housed in the housing Collector element (12, 32) arranged to receive incident solar radiation passing through the front wall takes in; and a device (16, 28, 30) for passing through a fluid to be heated Medium through the housing in heat exchange with the collector element, the combination (20, 36, 42) from Front wall and heat trap is integrally formed in one piece from a translucent material, which is opposite Infrared radiation is opaque from the collector element is emitted towards the front wall. 2. Sun heater according to claim 1, characterized in that the combination (20, 36, 42) of front wall and Heat trap a substantially flat part of the surface (20a, 36a, 42a) from the housing (1O, 24) after is directed outwards, and an inner surface part (2Ob, 36b, 42b), which is inwardly towards 909807/1052 TELEPHONE: 089/6011039 CABLE: ELECTRICPATENT MUNICH ORIGINAL INSPECTED has on the housing and has a cellular structure having a plurality of cells having walls substantially perpendicular to the flat surface part are provided. 3. Sun heater according to claim 2, characterized in that the inner surface part (20b, 36b, 42b)
has transparent honeycombs. 4. Sun heater according to claim 3, characterized in that that the transparent honeycombs consist of a plurality of cells with a hexagonal cross-section. 5. Sun heater according to claim 3 or 4, characterized in that the transparent honeycombs consist of a plurality of cells which have a length / diameter ratio between approximately 2 and 10. 6. Sun heater according to one of claims 3 to 5, characterized characterized in that the transparent honeycomb consists of a plurality of cells with a wall thickness in the region , ranging from about 0.002 to about 0.5 mm. 7. Sun heater according to claim 2, characterized in that the inner surface part (2Ob ₁ 36b) has a
Has a group of transparent, parallel ribs arranged at a spacing from the beneath. 9098Ö7 / 10S2 8. Sonnenheizgerat according to claim 7, characterized in that that the transparent, mutually spaced, parallel ribs have a height / distance ratio between about 4 and 20. 9. Sonnenheizgerat according to claim 8, characterized in that the transparent, at a mutual distance arranged, parallel ribs have a wall thickness in the range of approximately O, üO2 to approximately 0.5 mm. 10. Sonnenheizgerat according to any one of the preceding claims, characterized in that as a light permeable material, glass or a clear plastic of the polyvinyl fluoride, polycarbonate, fluorinated ethylene propylene, polymethyl methacrylate, aromatic polysulfones, polyethylene terephthalate, aromatic polyester, polyvinylidene fluoride, hexafluoropropylene, chlorotrifluoroethylene and Tetraf luorathylen copolymers comprehensive group is provided. 11. Sonnenheizgerat according to one of the preceding claims, characterized in that the device for passing a fluid medium to be heated through has a closed passage (16) for circulating the fluid through the housing (10) and the passage at least in close proximity to that radiation-absorbing collector element (12) 909807/1052 is arranged. 12. Sun heater according to one of claims 1 to 1O _1, characterized in that the device for passing a to be heated, fluid medium has an inlet (28) and an outlet (30) in the housing (24) to form a flow path for the fluid are arranged, and that the radiation-absorbing collector element (32) is gas-permeable and sits in the flow path. 13. Sun heater according to claim 12, characterized in that the radiation-absorbing collector element (32) a porous, opaque mat made of pressed fibers, screen fabric, punched screen material and / or reticulated Has foam. 14. Sun heater according to claim 12 or 13, characterized in that that the radiation-absorbing collector element (32) is substantially parallel to and at a distance is arranged by the combination (36) of front wall and heat trap. 15. Sun heater according to claim 12 or 13, characterized in that that the radiation absorbing collector element is in non-parallel relation to the combination is arranged from the front wall and heat trap. 16. Sun heater according to one of the preceding claims, characterized in that the housing (10, 24) has a bottom wall (14, 26) and opposite side walls and that the combination (20,
36, 42) from the front wall and heat trap is arranged opposite and at a distance from the bottom wall. 17. Sun heater according to one of the preceding claims, characterized in that an insulation layer is adjacent to the bottom wall (14, 26) of the housing (10, 24) (18, 34) is provided. 18. Sun heater according to one of the preceding claims, characterized in that the housing (10, 24) is made of metal. 19. Sun heater according to one of claims 1 to 17, characterized characterized in that the housing (10, 24). is made of a rigid insulating material. 909807/1052