US20060137679A1

US20060137679A1 - Absorber for a thermal collector of a solar system and method for the production thereof

Info

Publication number: US20060137679A1
Application number: US10/545,431
Authority: US
Inventors: Frieder Flamm
Original assignee: Individual
Current assignee: Flamm GmbH
Priority date: 2003-02-19
Filing date: 2004-01-22
Publication date: 2006-06-29
Also published as: DK1606565T3; EP1606565A1; AU2004213524B2; DE502004002374D1; DE10306930B3; WO2004074749A1; ATE348988T1; CA2513822A1; ES2278299T3; EP1606565B1; AU2004213524A1; PT1606565E

Abstract

The invention relates to an absorber for a solar system comprising a pipe system for the heat transfer medium, which is disposed between two superimposed metal sheets, and a method for producing said absorber. Heat exchange between the absorber metal sheets and the pipe system is improved while production costs are reduced.

Description

The present invention relates to an absorber for a thermal collector of a solar installation having an absorber wing for light and heat conversion and a pipe system for a heat transfer medium.
Absorbers are components of solar installations Solar installations principally comprise a solar receiving surface, generally referred to as a collector, the solar loop, and the heat accumulator. The collectors are typically mounted on the roof of a house and convert the incident solar radiation into heat. Pipelines, in which a heat transfer medium, such as a water-glycol mixture, is pumped in a loop, connect the collector to the heat accumulator. The pumps are automatically switched into the solar loop via a controller when a temperature sensor signals that the temperature at the collector is higher than that in the heat accumulator. The heat of the heat transfer agent is dissipated to the accumulator water in the heat accumulator.
In the private field of use, thermal collectors are used in particular. These are collectors which absorb the incident solar radiation and convert it directly into heat. The main component of every thermal collector is the absorber. This is a metallic, dark-colored plate which is also partially made of plastic. Since the solar radiation is not transmitted by the absorber and is also hardly reflected, it is largely converted into heat which drains off via the pipe system connected to the absorber. The heat transfer agent is located in the pipe system. The absorber, with the associated pipe system, is located in a weatherproof housing having a glass cover. The air layer enclosed by the glass cover of the housing and the absorber is used as a transparent thermal insulation in the direction of the incident solar radiation. An insulating layer attached below the absorber prevents heat losses via the housing floor. The pipe system positioned below the absorber plate is typically made of a meandering, pressure-resistant copper pipe, which is connected at each end to a collection line in order to connect multiple collectors to one another.
The heat transfer between the absorber plate and the absorber pipe occurs via a linear weld seam between the top of the absorber pipe and the absorber plate. The heat transfer via the linear weld seam is not optimal. For this reason, Solvis GmbH has developed a wide soldered connection between the absorber plate and the absorber pipe that is to cause improved heat transfer. The soldered connection extends over a graduated circle on the top of the absorber pipe; the soldered connection is produced by filling up the gusset between the pipe mantle and the bottom of the absorber with solder.
In addition to the higher costs of this connection, the heat transfer between absorber plate and absorber pipe is still not optimal. In addition, the manufacturing costs of typical collectors, which are high anyway, are disadvantageous, which is largely caused by the complex absorbers.
On the basis of this related art, the present invention is based on the object of providing an absorber with an improved heat transmission between the absorber wing, in particular in form of an absorber metal sheet, and the pipe system having reduced manufacturing costs. Furthermore, the present invention is based on the object of suggesting a method for manufacturing the improved absorber.
The solution of this problem is based on the idea, to provide no separate aborber pipe, but to integrate the pipe system in the absorber wing.
In detail this object is achieved in an absorber of the type cited at the beginning, in which the pipe system (23) is positioned between two metal sheets lying one on top of another that form the absorber wing, the shape of the pipe system being introduced into at least one of the metal sheets and the metal sheets being bonded to one another.
Because the shape of the pipe system is introduced into at least one, preferably both metal sheets of the absorber wing, a significantly larger transfer area is available for the incident heat.
The metal sheets are preferably bonded to one another using an adhesive and additionally in a formfitting or stuff fitting way.
The joining of the metal sheets through an adhesive significantly reduces the manufacturing costs, since soldering or welding work for manufacturing the absorber may be completely dispensed with.
The joining of the sheets by an adhesive not only results in a significant cost reduction, but rather additionally improves the dimensional accuracy of the solar collector while simultaneously reducing the reject rate. The energy use is significantly reduced in gluing in relation to the current bonding technologies.
An adhesive from the group of silicone, epoxide, or phenol resin adhesives is preferably used as the adhesive. Thermosetting adhesives based on modified epoxide resins particularly have a high long-term resistance to changing temperatures. Furthermore, these adhesives have favorable processing conditions and strength and resistance properties for metal/metal bonds.
As already noted at the beginning, there is no circulation of the heat transfer medium in the solar loop under specific operating circumstances. In this case, temperatures of 200° C.-220° C. may occur in the absorber with appropriate solar radiation. In order to be able to compensate for strength losses of the adhesive bond occurring at these temperatures, the two metal sheets of the absorber wing are additionally bonded to one another in a formfitting or stuff fitting way. Multiple Tox points between the metal sheets have been shown to be the preferred additional bond. The Tox points are produced through clinching of the two metal sheets. This connection may be automated especially easily and therefore manufactured cost-effectively. However it is also possible, to provide welding points between the metal sheets.
Vaporization of the heat transfer medium is particularly connected to the standstill of the normal loop. This results in elevated corrosion or oxidation on the interior walls of the pipe system if the typical water-glycol mixture is used in particular.
In order to ensure sufficient stability of the absorber, the metal sheets are provided at least in the region forming the inner surfaces of the pipe system with a coating that inhibits corrosion and/or oxidation. However, the metal sheets are preferably coated completely and on both sides. Aluminum sheets are preferably anodized, while sheet steel is particularly provided with a copper or plastic coating. The coating ensures the desired longevity of the solar collectors.
A roll bond method for manufacturing evaporator plates is known from a brochure of Showa Aluminum Corporation, Osaka, Japan 1993, in which metal sheets lying one on top of another are welded to one another through hot rolling and finally cold rolled to the final thickness. The separating agent of the channel regions left out of the welding, which is applied in the screen printing method, is blown out using compressed air before the metal sheets are divided into the individual evaporator plates. This method has the disadvantage of the metal sheet thickness change during hot rolling and in the subsequent cold rolling step, since this results directly in corresponding metal sheet length changes. Problems result from this which result in a high reject rate in the following work steps. The evaporators must be manufactured from pure aluminum (Al 99.5) in order to allow the introduction of the channels.
The absorber according to the present invention does not, however, necessarily have to be made of pure aluminum and nonetheless may be manufactured easily in a large piece count. In addition, in interest of cost reduction, a method for mass production of absorbers with a low reject rate is to be suggested that requires little energy and opens up a large design freedom in regard to the design of the pipe system. These requirements are not fulfilled by the known roll bond method, so that it is less suitable for manufacturing the absorbers of collectors for solar installation.
According to the present invention, the metal sheets forming the absorber preferably are bonded to one another using an adhesive. In particular, one-component or two-component adhesives are used, which are resistant to the heat transfer medium and maintain their adhesive properties at least in the temperature range between −30° C. and +200° C.
In a preferred embodiment of the manufacturing method according to the present invention, the adhesive is not first applied after the shaping of the pipe system, but rather already to the starting material of the absorber, which is particularly strip-shaped. Strips coated in this way may be wound up like uncoated strips into a coil without sticking to one another if it is a temperature-dependent hot melt adhesive. The adhesive effect only sets in after heating to a specific temperature.
The joining of the metal sheets through an adhesive allows the use of metal sheets having the final thickness and final strength, which has advantageous effects on the dimensional accuracy of the absorber while simultaneously reducing the reject rate. The energy use is significantly reduced in gluing in relation to typical bonding technologies, such as soldering or welding. For planar application to the join surfaces, the adhesive may be rolled on using rollers or spread on using a tool similar to a doctor blade or spatula. Alternatively to the planar application, the adhesive may also be sprayed on in lines, the quantity being metered in such way that no excess adhesive penetrates into the pipe system after the joining of the metal sheets to be glued.
If the shape of the pipe system is introduced through cold shaping, particularly through deep drawing or embossing, a high cross-sectional reproduction precision and flexible arrangement of the heat transfer pipes in the metal sheets of the absorber lying one on top of another will be achieved on one side, on both sides, or on alternate sides as required.
The introduction of the pipe system through deep drawing or embossing allows the use of aluminum alloys when manufacturing absorbers instead of the pure aluminum currently used. Suitable aluminum alloys are, for example, the aluminum wrought alloys cited in the following:

- Al Mg 3
- Al Mg Si 1 or
- Al Cu Mg 1.

In an advantageous embodiment of the present invention, at least the areas of the metal sheets to be glued are subjected to a surface treatment. If aluminum sheets are used, an anodized coating is recommended, which is generated through anodic oxidation of the aluminum sheet. For sheet steel, a copper or plastic coating may be applied as a corrosion protection. Additionally or alternatively, further mechanical and/or thermal surface treatments may be performed on the areas to be glued. Mechanical surface treatments (e.g., brushing) remove contamination and roughen the surface, which may have advantageous effects on the strength of the adhesive bond for specific adhesives. The thermal surface treatment degreases the surface.
The joined metal sheets, which are cut to absorber size, are additionally bonded to one another. This additional bonding fixes the metal sheets until reaching a minimum hardness of the adhesive and unloads the adhesive bond during operation of the collector at high temperatures of the heat transfer medium. For this purpose, formfitting bonds active in the absorber plane are generated at multiple locations distributed uniformly on the absorber area using clinching (toxing), which maintain the fixing of the metal sheets required for the adhesive curing and the stabilization of the absorber under all operating conditions. The absorbers fixed in this way may leave the press for the joining procedure again immediately and, if necessary, pass through a curing furnace or cure to the required adhesive final strength under normal ambient conditions.
Depending on the adhesive used, it may be necessary for the metal sheets mechanically fixed in this way to be additionally pressed and/or heated on one another. For this purpose the plates are laid on one another with elastic intermediate layers to form a stack in order to then cure for the required time under the pressure of a press and/or the simultaneous effect of temperature.
After completing curing, any necessary post-processing follows, such as stamping, bending, flanging, and lacquering.
A production line for manufacturing an absorber according to the present invention is illustrated in a side view and a top view in FIGS. 1a, 1b.
FIG. 2 shows a schematic section through a collector having absorbers according to the present invention:
The exemplary embodiment shows a two-train production line in which two metal sheets 1 a, 1 b are processed in parallel. The strip-shaped metal sheets 1 a, 1 b, which are each uncoiled from a coil 2 a, 2 b, are, after straightening in a roller straightening machine 3 a, 3 b, fed to embossing stations 4 a, 4 b, which introduce the shape for the pipe system through embossing in both metal sheets. If the absorber pipes are only to be embossed on one side, one of the embossing stations 4 a or 4 b may be dispensed with; in this case, a flat metal sheet is joined to an embossed metal sheet.
The adhesive application is subsequently performed in both trains using a roller 5 a, 5 b positioned above the line shape in each case. Only after the adhesive is rolled on are the strip-shaped metal sheets 1 a, 1 b cut to the size of the absorber 8 to be manufactured using shears 6 a, 6 b in cutting stations 7 a, 7 b.
Subsequently, the metal sheets 1 a, 1 b, manufactured in the two parallel manufacturing trains and cut to the size of the absorbers, are joined in a compression mold 9 and fixed in their position to one another using clinching (toxing) in a formfitting bond 12 active in the metal sheet plane on at least two locations 11 a, 11 b.
The absorbers thus fixed leave the compression mold 9 again immediately and reach a curing station 13 in which they cure under the pressure of a press 14 and the simultaneous effect of temperature in batches up to the required adhesive final strength. Elastic intermediate layers 15 are located between the curing absorbers 8, which prevent damage of the absorber pipes embossed on both sides in the curing station 13. If the capacity of the curing station 13 may not absorb all absorbers 8 which may be manufactured from the two coils 2 a, 2 b, multiple curing stations may be provided to ensure a continuous production flow.
The transport of the metal sheets 1 a, 1 b between the cutting stations 7 a, 7 b, the compression mold 9, and the curing station 13 is advantageously performed automatically, for example, using conveyor means and clocked gripping and lifting devices, which are not shown in the figures for reasons of clarity.
The schematic construction of the absorber manufactured using the manufacturing train shown in FIG. 1 results from the sectional illustration of a collector shown in FIG. 2.
The flat collector, identified as a whole with 16, comprises a weatherproof housing 17 having a glass cover 18, through which the solar radiation 19 is incident on the surface 21 of the absorber 22. The preferably dark-colored surface 21 largely converts the incident solar radiation 19 into heat, which is dissipated via the pipe system 23 integrated into the absorber 22, of which only two absorber pipes are shown in cross-section. The shape of the absorber pipes is introduced through cold shaping into the metal sheets, which are bonded to one another via an adhesive layer 25. The heat transfer medium, a frostproof water-glycol mixture, circulates in the absorber pipes.
An insulation layer 24 positioned below the absorber prevents heat losses via the floor of the housing 17, while the air layer enclosed by the glass cover 18 in the absorber 22 acts as a radiation-transparent thermal insulation on the top of the absorber.

LIST OF REFERENCE NUMBERS

1 a,b metal sheets
2 a,b coil
3 a,b roller straightening machine
4 a,b embossing station
5 a,b roller
6 a,b shears
7 a,b cutting stations
8 absorber
9 compression mold
10 —
11 a,b locations
12 formfitting bond
13 curing station
14 press
15 elastic intermediate layer
16 flat collector
17 housing
18 glass cover
19 solar radiation
20 —
21 surface of collector
22 absorber
23 pipe system
24 insulation layer
25 adhesive layer

Claims

1.-18. (canceled)

19. An absorber for a thermal collector of a solar installation, comprising:

two metal sheets arranged one on top of the other forming an absorber wing for light and heat conversion, the two metal sheets defining a pipe system therebetween for conducting a heat transfer medium, wherein a shape of the pipe system is introduced into at least one of the two metal sheets;

an adhesive bonding the two metal plates to one another; and

a formfitting connection between the two metal plates, the formfitting connection being a clinched connection.

20. The absorber of claim 19, wherein said formfitting connection comprises a plurality of Tox points.

21. The absorber of claim 19, wherein said adhesive is heat resistant and impermeable to the vapor of the heat conducting medium up to at least 200° C.

22. The absorber of claim 21, wherein said adhesive is one of a silicone, epoxide resin, or phenol resin adhesive.

23. The absorber of claim 19, wherein at least regions of said two metal sheets forming interior surfaces of said pipe system are surface treated.

24. The absorber of claim 23, wherein said regions of the two metal sheets forming interior surfaces of said pipe system comprise a coating that inhibits at least one of corrosion and oxidation.

25. The absorber of claim 19, wherein a material of said two metal sheets is one of an aluminum alloy, steel, and copper.

26. The absorber of claim 24, wherein each of said two metal sheets is an anodized aluminum sheet.

27. The absorber of claim 25, wherein each of the two metal sheets is an anodized aluminum sheet.

28. The absorber of claim 24, wherein each of the two metal sheets is a steel sheet with one of a plastic or copper coating.

29. The absorber of claim 25, wherein each of said two metal sheets is a steel sheet with one of a plastic or copper coating.

30. The absorber of claim 19, wherein said two metal sheets are cold-formed to define said pipe system.

31. A method for manufacturing an absorber for a thermal collector of a solar installation, the absorber including two metal sheets arranged one on top of the other forming an absorber wing for light and heat conversion, the two metal sheets defining a pipe system therebetween for conducting a heat transfer medium, said method comprising the steps of:

cold forming at least one of two metal sheets of the absorber for introducing a shape of the pipe system;

joining the two metal sheets using an adhesive; and

generating a formfitting connection between the two metal sheets using clinching.

32. The method of claim 31, wherein the adhesive is resistant to the heat transfer medium and maintains adhesive properties within the temperature range of −30° C. to 200° C.

33. The method of claim 31, further comprising the step of straightening the two metal sheets before said step of cold forming.

34. The method of claim 31, wherein said step of cold forming comprises one of embossing or deep drawing.

35. The method of claim 31, further comprising the step of cutting the two metal sheets to a size of the absorber before said step of using the adhesive.

36. The method of claim 31, further comprising the step of cutting the two metal sheets to a size of the absorber after said step of using the adhesive.

37. The method of claim 31, wherein said step of joining includes applying temperature-dependent adhesive to each of the two metal sheets and heating the two metal sheets to a defined temperature to initiate the adhesive effect of the temperature-dependent adhesive.

38. The method of claim 31, further comprising subjecting at least the areas of the two metal sheets to be joined using adhesive to a surface treatment comprising one of a mechanical, thermal, or chemical treatment.

39. A thermal collector for a solar installation comprising an absorber including two metal sheets arranged one on top of the other forming an absorber wing for light and heat conversion, the two metal sheets defining a pipe system therebetween for conducting a heat transfer medium, wherein a shape of the pipe system is introduced into at least one of the two metal sheets, an adhesive bonding the two metal plates to one another, and a formfitting connection between the two metal plates, the formfitting connection being a clinched connection.