Solar Collector Element

Abstract

A solar collector element including a wooden frame having longitudinal frame members and cross members which are fastened to a back panel is provided. The insulating material is inserted in the frame between the cross members. Located on top of the cross members and the insulating material is a pipe coil which has a plurality of lengths of pipe that run substantially horizontally at a small angle to each other, and each is provided with a heat-absorbing aluminium plate which, with one of its longitudinal edge portions, surrounds the respective length of pipe. The outward side of the framework is covered by a panel, preferably a corrugated panel of polycarbonate. When using solar collectors for dwelling houses, several such solar collector elements are placed adjacent to each other and connected in series, optionally so as to cover most of the height of the roof between the gutter and the ridge.

Description

FIELD OF INVENTION

The present invention relates to a sunlight or solar collector element comprising a plurality of lengths of pipe through which a heating medium is to circulate, the lengths of pipe being in contact with a heat-collecting metal plate which is to absorb solar energy and transfer it to said length of pipe and the heating medium circulating therein. The invention also relates to a sunlight or solar thermal collector for a sloping house roof comprising such solar collector elements.

BACKGROUND

To meet the world's growing energy needs, it is essential to make use of solar energy. Solar collector technology is well known in Europe, but has gained only limited ground as the price is too high. In cold countries such as Norway there is a need for greater solar collector areas, and in addition the heat storage tank must be large. The common perception of solar collector technology is that it is costly and unreliable.

The solar collectors that are sold on the European continent are expensive, but are of good quality. Usually, a solar collector of from 1-4 m² is installed on a house, and this is normally used just for heating domestic water. The heat storage tank used may contain from 50 to 300 litres. The relatively high price makes solar collector technology even less attractive in Norway because of the low outside temperature and problems with snow in the winter. An installation that is sufficiently large to produce the required output will also be disproportionately heavy.

A solar collector element as referred to above is known, for example, from JP 57006261 A. In this document the lengths of pipe run parallel between an inlet manifold and an outlet manifold. The lengths of pipe are placed relatively close together and all are in contact with one and the same metal plate, which is provided with grooves that surround portions of the outer surface of the pipes. The parallel connection means that there tends to be different water flow in the different lengths of pipe in the solar collector, which reduces the output. The lengths of pipe are usually welded to the manifolds, which results in joints that are time-consuming to make and which may be potential leakage points. In particular in large installations, there have been problems with frost damage, which means that the installation has not been able to be emptied adequately of water. This has meant that it has been necessary to use anti-freeze in the water, with the consequences this has for operating economics and the risk of pollution.

SUMMARY

The object of the present invention is to provide a solar energy collector which makes it practically and economically possible to harness solar energy also in colder latitudes. This means that the solar collector must be inexpensive to produce, must be capable of utilising the warmth of the weak winter sun, must be able to withstand being covered by snow and should also be suitable for domestic heating.

These properties are obtained according to the invention by a solar collector element of the type mentioned above, wherein the characteristic features are that the lengths of pipe are arranged basically horizontal in the mounted state of the element, that the lengths of pipe are connected in series to each other, and that a substantial part of the element is covered by a panel or sheet of basically transparent plastic material.

Since the lengths of pipe are series-connected, the water, as it circulates through the solar collector element, will come into contact with a much greater heat transferring surface than if the pipes had been parallel-connected. This means that even relatively small temperature differences between the solar energy collecting space in the element and the circulating water can be utilised even in feeble winter sunlight and misty weather. Furthermore, the basically horizontal orientation of the lengths of pipe makes it possible to utilise them for support of the external cover panel in the area between the points of support for the solar collector element on the rafters of the underlying roof on which they are mounted.

The invention also relates to a solar collector for a sloping house roof comprising aforementioned solar collector elements. The solar collector is characterised in that several elements are placed adjacent to each other so as to cover a substantial part of the height of the whole roof from gutter to ridge, that the pipe lengths of the element are connected in series, and that the elements are covered by a single plastic panel or sheet, preferably a corrugated panel of polycarbonate which is at least partly supported by the metal plates in the region of their respective length of pipe.

The solar collector elements may also be mounted on facades of building or on the ground and can form any angle to the horizontal plane.

BRIEF DESCRIPTION OF THE DRAWINGS

A number of advantageous features of the invention can be seen from the dependent claims and from the following description of the exemplary embodiments that are shown in the appended drawings, wherein

FIG. 1 is a perspective view of a house roof provided with solar collectors according to the invention;

FIG. 2 is a perspective view of the framework of a solar collector element according to the invention;

FIG. 3 shows the framework in FIG. 1 provided with lengths of pipe and metal plates;

FIG. 4 shows the element in FIG. 3 with secured lengths of pipe and metal plates;

FIG. 5 shows the element in FIG. 4 when fully mounted;

FIG. 6 shows metal plates for use in the invention.

FIG. 7 shows on a larger scale parts of a section taken along the line VII-VII in FIG. 5; and

FIG. 8 shows a section similar to that shown in FIG. 7 but taken along the line VIII-VIII in FIG. 5;

FIG. 9 shows a second embodiment of the metal plates.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a part of a sloping house roof equipped with two solar collectors 1 according to the invention. The solar collectors extend from the house gutter to its roof ridge, in the illustrated case a length of about 6 metres. The solar collector 1 comprises 10 solar collector elements of the type that will be described below, the solar collector elements being placed adjacent to each other and with their piping connected in series. The elements are covered by a single panel 2, which preferably consists of a so-called corrugated panel of polycarbonate. Such panels are commercially available with a standard size of 210×600 cm and contain air channels which run in the longitudinal direction of the panel. Such panels come in different thicknesses, and for the present purpose a panel of 6 mm in thickness has been found to be expedient. Because of the air channels, the panel has good insulating properties and can be bent a little without cracking. Such panels are otherwise largely used in greenhouses and are therefore readily available at a relatively inexpensive price.

The solar collector element according to the invention will be explained in more detail below with reference to FIGS. 2-6. FIG. 2 shows a framework 3 of a wood material that is glued and stapled to a back panel 4, which, for example, could consist of a standard sub-roof panel. By using wood, for example, Norwegian spruce, it is possible to avoid expansion problems, such as those that tend to occur in standard solar collector casings of aluminium when the temperature differences in the solar collector become large. In a solar collector according to the invention, such temperature differences may be as high as 200° C.

The framework 3 has longitudinal frame members 5 and cross members 6, the centre distance of which is 60 cm and thus corresponds to the centre distance of the rafters normally found in a sloping roof. The framework 3 can thus be positioned so that the cross members 6 lie directly above the rafters and are supported thereby. Insulating material S is placed the spaces between the cross members 6 and an inner end piece 7.

FIG. 3 shows the framework after the mounting of a pipe coil 10 comprising four lengths of pipe 11, each of which is mounted on a heat-collecting aluminium plate 12 or 13. These plates are shown in profile in FIG. 6. FIGS. 7 and 8 show their cross-section in one embodiment. The plates 12, 13 have a longitudinal edge portion 14 which is curved around the respective length of pipe 11 at an enveloping angle which exceeds 180 degrees. The longitudinal edge portion 14 in this embodiment has an extension 15 which runs backward basically parallel to the plane of the metal plate 12, 13 and is provided with a bend 16 close to its free edge to facilitate mounting of the plate 12, 13 on the length of pipe 11.

FIG. 9 shows a second embodiment of the plates 12, 13. The profile is the same as in FIG. 6, but the longitudinal edge portion 14 in this case is bent in the inverse direction of the aforementioned embodiment.

The plates 12, 13 are each fastened to the frame 3 by a single screw (not shown), thus allowing them to expand freely in both directions therefrom.

As it is difficult to obtain aluminium pipes that are sufficiently long to allow the pipe coil 10 to be made from a single pipe, the pipe coil 10 is preferably laid in two identical parts which are joined in the area 17 shown in FIG. 3. This joint can easily be made using a piece of radiator hose, which is inexpensive to purchase and withstands the mechanical stresses and temperatures that may be involved. The piece of radiator hose can also be used at the ends of the pipe coil when they are to be connected is series to adjacent solar collector elements. The distance between the lengths of pipe 11 in the pipe coil 10 is on average just about 15 cm. This means that the absorber plates 12, 13 will be of similar width and thus have a relatively large absorbing face per unit length of the lengths of pipe 11. The plates 12, 13 with the pipe coil 10 are also held in place in the framework 3 by mounting strips 18, 19, as shown in FIG. 4. The plates 12, 13 are sprayed with black, matt primer either before or after they have been secured using the strips 18, 19.

Lastly, the element 3-19 is provided with a cover panel 20, preferably a corrugated polycarbonate panel, which is clamped in place by fastenings 21 and 22. The fastening 22 also covers the connecting casing part 23 of the framework 3. The solar collector element comprising the parts 3-23 is shown in this application as an independent element. It could of course be used alone in applications which require relatively little heat, but in practice the solar collector elements will normally be placed next to each other and connected flow-wise in series, as explained in connection with FIG. 1. In such cases, the cover panel 20 will be replaced by a continuous panel 2 which covers all the solar collector elements. In roof mounting as shown in FIG. 1, such a panel 2 will provide a smooth surface without cracks or joins through which rain water could leak, and this smooth surface will help snow to slide off easily. If snow should stick to the panel 2, it could be heated slightly from its underside, so that an anti-friction layer of water is formed beneath the snow which causes the snow to slide off. The solar collector can thus in a simple manner be kept snow-free throughout the winter. With its large area, which nevertheless is relatively inexpensive in manufacture, it will be able to provide a substantial heat supplement even on cold sunny days. As the cover panel 2 is mounted on strips 18, 19 which lie on top of the pipe coil 10 and the absorber plates 12, 13, the panel will have a slight downward bend in the middle so that it comes to rest against the bent portions 14 of the plates 12, 13. The pipes 11 together with the bent plate portions 14 have a fairly large bending stiffness and also withstand substantial shear forces in the areas where they are supported by the framework cross members 6, so that the cover panel 2 has more than sufficient support for any snow load that may occur. As the solar collectors 1 are sealed outwardly and have necessary strength, they could be mounted on the rafters without any intermediate sub-roof, which further improves the economics. It will be seen that the lengths of pipe 11 in the pipe coil 10 form a small angle with each other. This means that there will be a small fall in the lengths of pipe, which in turn means that a solar collector 1 as shown in FIG. 1 could be drained completely so as to prevent frost damage if the installation is to be inoperative in the winter time. The two solar collectors 1 shown in FIG. 1 work in parallel, and water flow in the range of 1 litre per minute per square metre solar collector surface has been found to be appropriate.

It will be understood that the invention is not limited to the exemplary embodiments described above, but that it could be varied and modified by a skilled person within the scope of the claims below. Thus, for example, the pipe coil 10 could consist of a single length of pipe, or it may be composed of four lengths of pipe with a bend at one end. These lengths of pipe may then be joined to the adjacent length of pipe using a suitable connection, for example a piece of hose. Furthermore, it will be possible to use only one type of heat-absorbing metal plate instead of the two mutually inverted plates 12, 13. If just one of these is used, every other plate must be mounted so that the extended end portion 15 faces outwards, and it must then be configured so that the free end does not damage the cover panel 2, 20. The end portion 15 may optionally be bent inwards after the panel has been mounted on the length of pipe 11. Although corrugated panels of plexiglass have been found to be advantageous as cover panel material because they have good insulating effect and are supplied in large sizes which are nevertheless easy to handle, it will be understood that many other materials could be used. If the requirements of mechanical resistance allow it, a flexible material such as a glassfibre-reinforced fabric or plastic sheeting could be used. It will also be understood that the length and width of the solar collector element can be varied to be adapted to other building modules or standard sizes for the components involved.

Claims

1. A solar collector element comprising a plurality of lengths of pipe through which a heating medium is to circulate, the lengths of pipe being in contact with a heat-absorbing metal plate which is to absorb solar energy and transfer it to said lengths of pipe and the heating medium which is to circulate therein, the lengths of pipe are arranged substantially horizontal in a mounted state of the element, the lengths of pipe are each provided with a respective heat-collecting metal plate, the lengths of pipe are connected in series to each other, a substantial part of the element is covered by either a panel or sheet of a substantially transparent material, and said panel is at least partly supported by the metal plates.

2. A solar collector element according to claim 1, wherein the metal plate along one of its longitudinal edge portions is bent around the length of pipe with an enveloping angle of at least 180 degrees.

3. A solar collector element according to claim 1, wherein the lengths of pipe run at a small angle relative to one another in order to provide a continuous fall.

4. (canceled)

5. A solar collector element according to claim 1, wherein the panel is a corrugated polycarbonate panel.

6. A solar collector element according to claim 1, wherein the lengths of pipe form a continuous pipe coil, or wherein pairs of lengths of pipe form basically U-shaped portions which are connected to each other in series, or wherein the lengths of pipe are basically J-shaped pipes which are connected to each other in series.

7. A solar collector element according to claim 1, wherein the element comprises an elongate wooden frame with cross members by which the lengths of pipe are supported, insulating material being deposited between the cross members.

8. A solar collector element according to claim 1, wherein both the lengths of pipe and the metal plates are made of aluminium, the metal plates on their outward facing side being provided with a heat radiation absorbent layer, preferably a black, matt primer.

9. A solar collector element according to claim 1, wherein the element has a horizontal extent and a width of about 240 cm and 60 cm, respectively.

10. A solar collector for a sloping house roof comprising solar collector elements according to claim 1, characterised in that wherein several elements are placed adjacent to each other so as to cover a substantial part of the height of the roof from gutter to ridge, that the lengths of pipe in the elements are connected together in series, and that the elements are covered by a common flat panel preferably of corrugated polycarbonate, which is at least partly supported by the metal plates in the area of their respective length of pipe.

11. A solar collector element according to claim 2, wherein the lengths of pipe run at a small angle relative to one another in order to provide a continuous fall.

12. A solar collector element according to claim 2, wherein the panel is a corrugated polycarbonate panel.

13. A solar collector element according to claim 3, wherein the panel is a corrugated polycarbonate panel.

14. A solar collector element according to claim 2, wherein the lengths of pipe form a continuous pipe coil, or wherein pairs of lengths of pipe form basically U-shaped portions which are connected to each other in series, or wherein the lengths of pipe are basically J-shaped pipes which are connected to each other in series.

15. A solar collector element according to claim 3, wherein the lengths of pipe form a continuous pipe coil, or wherein pairs of lengths of pipe form basically U-shaped portions which are connected to each other in series, or wherein the lengths of pipe are basically J-shaped pipes which are connected to each other in series.

16. A solar collector element according to claim 5, wherein the lengths of pipe form a continuous pipe coil, or wherein pairs of lengths of pipe form basically U-shaped portions which are connected to each other in series, or wherein the lengths of pipe are basically J-shaped pipes which are connected to each other in series.

17. A solar collector element according to claim 2, wherein the element comprises an elongate wooden frame with cross members by which the lengths of pipe are supported, insulating material being deposited between the cross members.

18. A solar collector element according to claim 3, wherein the element comprises an elongate wooden frame with cross members by which the lengths of pipe are supported, insulating material being deposited between the cross members.

19. A solar collector element according to claim 5, wherein the element comprises an elongate wooden frame with cross members by which the lengths of pipe are supported, insulating material being deposited between the cross members.

20. A solar collector element according to claim 6, wherein the element comprises an elongate wooden frame with cross members by which the lengths of pipe are supported, insulating material being deposited between the cross members.