GB2097114A - Solar collectors - Google Patents

Abstract

A flat plate solar radiation collector panel comprises a number of parallel lengths of an extruded EPDM rubber section which includes tubes for passage of heat exchange liquid. The lengths have engagement formations (4 and 5) at their long edges so that a mat of the engaged lengths may be assembled, and the tubes are connected to a pair of copper headers (11). The undersurface of the tube mat so formed contains no recesses or keying formations. It is secured to a base 7 of the collector panel by a cement which forms a strong bond with the base 7 and a weak bond with the mat. The panel is easy to assemble in situ and, because of the weak bond, to dismantle when required. The tube mat behaves as a single sheet and not as a plurality of separate sections so a weak bond will still retain the mat even if there are areas of failure of the bond between the cement and the mat. <IMAGE>

Description

SPECIFICATION Device for absorbing radiant heat This invention relates to a device for absorbing heat radiation and more particularly, but not exclusively, concerns flat plate solar heat collector panels.

The materials from which solar heat collectors are formed need to be resistant to extremes of temperature and to the damaging effects of long-term exposure to solar radiation. It has been proposed to absorb solar radiation in synthetic rubber tubes made of EPDM (ethylene propylene diene monomer or terpolymer) blackened by the addition of powdered graphite and to remove the absorbed heat by passage of a heat exchange fluid such as water through the tubes. One difficulty is the fixing of the EPDM tubes to external, e.g. roof, surfaces because of a lack if a suitable adhesive.

It has been proposed to overcome this difficulty by providing an extruded EPDM tube section comprising a small number oftubes, for example 5 tubes, interconnected by webs, some or all of the webs having in their underlying surface inwardly diverging recesses which may receive a settable cement applied to a substrate, the cement bonding to the substrate and setting to form a mechanical interlock between the set cement and the rubber strips.

One disadvantage of th is proposal is that, after the cement has set hard, it is by no means easy to remove the rubber strips from the substrate.

Another proposal is to construct a lattice-work mat of spaced, parallel tube strips and transverse spaced parallel bindings, and place the lattice in a bed of cement which flows around the lattice members and then sets to retain the lattice on a substrate. This proposal has the disadvantage that manual laying of the lattice is hindered by contact with the unset cement.

The present invention seeks to overcome the disadvantages of these prior proposals and accordingly provides a device for absorbing radiant heat which comprises a system of tubes constructed from a flexible material which is adapted to absorb radiant heat, which tubes carry, in use of the device, a heatexchange fluid, a base surface on which the tube system may be mounted, and a cement for securing the tube system to the base surface by forming a permanent bond with the material of the base surface and a breakable bond with the material of the tube system, wherein the tube system comprises a plurality of extruded tube strips, each of the strips having a number of the fluid carrying tubes spaced apart by interconnecting webs, the edges of each of the strips carry co-operating, mating formations to permit assembly of the tube system by interengagement of adjacent, parallel strips, and the undersurface of the assembled tube system is devoid of such recesses as would provide a mechanical interlock between any part of the said undersurface and the underlying cement.

Because the strips of the tube system are firmly connected together along their entire length so that there are no gaps between adjacent strips at locations intermediate their ends, the tube system behaves as a single sheet and so can be retained adequately on the substrate with a relatively weak bond between the cement and the rubber, and can tolerate unintended local failure of the bond, rather in the manner that failure of the adhesive bond between a wallpaper and a wall can be tolerated in the middle of a strip of wallpaper far more readily than failure of the bond adjacent one of the long edges of a strip of wallpaper.

It will be convenient to provide a zone of reduced thickness at the point where each web joins each fluid-conducting tube, so that the webs may be peeled back from the tubes at opposed ends of the tube system to permit connection of individual tubes of the tube system to manifolds or headers at each end of the tube system.

Preferably the tube system will be of EPDM rubber and the mating formations will be of male and female nature so that each strip has one long edge with a male formation and the other, opposed, long edge with a corresponding female formation.

One clear advantage of a breakable, i.e. weak, bond between the cement and the tube system is that an individual tube strip of the system can readily be removed, for example if it is damaged, and replaced with another tube strip, even after years of use of the panel when the cement is likely to have become so hard that release of a mechanical interlock between the tube system and the cement is achieved only with great difficulty.

For a better understanding of the invention, reference will now be made, by way of example, to the accompanying drawings, in which: Figure lisa plan view from above of a solar heat collector panel, a central section of the panel having been omitted from the drawing, and a glazing panel having been partly cut away, for clarity; and Figure 2 is a vertical section of the panel in the plane I-I of Figure 1.

The illustrated panel comprises five parallel and interlinked lengths 1 of an extruded EPDM tube section which comprises seven tubes 2 for passage of a heat-exchange fluid. The tubes 2 are connected by webs 3 which can be peeled back from the tubes 2 at tear lines (not shown) of reduced material thickness where the webs 3 join the external surfaces of the tubes 2.

As best seen in Figure 2, one long edge of each tube section length 1 has an upstanding edge 4 which provides a male formation for engagement with a correspondingly shaped female formation 5 at a long edge of an adjacent length. By engagement of these male/female formations 4 and 5 a single tube mat made up of five interengaged tube section lengths is provided.

The mat is laid on a layer of settable cement 6 previously spread on an insulating base block 7 within four insulating wall blocks 8 of the panel the whole being supported by, and within, a framework of an aluminium alloy section 9 and sheet 10. The cement forms a strong, permanent bond with the base 7 but only a weak, breakable bond with the undersurface of the tube mat. It is to be noted (see Figure 2) that the tube mat undersurface contains no recesses of keying formations with which the set cement can form a mechanical interlock.

Heat exchange fluid is conveyed to and from the tube mat by means of a pair of copper header pipes 11 which are each provided with a line of 35 stub branch pipes 12 over each of which is fitted one of the EPDM tubes. For added safety a clip 13 may be used to secure each rubber tube 2 to its associated stub pipe 12.

Instead of a clip 13 an internally threaded nut 14 on each of the tubes 2 may be used to secure the tubes 2 onto the stub pipes 12. Only one of these nuts 14 is shown in Figure 1, purely as an example. The shape ofthethread isto be determined in accordance with the nature of the material of the tubes 2.

Instead of stub pipes 12, the header pipes 11 can be provided with orifices (of which only an exemplary one is shown in Figure 1) having wall surfaces 15 adapted for reception of the tubes 2 within the orifices. Such a means of connection is described in our co-pending British Patent Application No.

8107650.

The copper header pipes 11 may extend through both side walls 8 of the panel, as shown in Figure 1, protected by rubber grommets 16 fitted within orifices in the framework 9, and the ends of the header pipes 11 connected to further solar panels or blanked off, as appropriate. It may be, however, that one header end is blanked off within the panel, and connections to the header pipes made through the base 7 or end walls of the panel rather than through a side wall.

A glazing panel 17 is sandwiched between the wall surfaces 8 and a top flange 18 of the framework 9 by a rubber sealing strip 19 which maintains the panel interior hermetically sealed. The choice of material for the glazing panel 17 is one with which those skilled in the art are familiar and is made with due allowance for the damaging effects of ultra-violet light to which solar panels are particularly suspect.

It has been found that a product of the Dunlop Company of Great Britain is suitable for use as the cement 6. The product is identifed by the manufacturer's reference DP 1700 and is a synthetic rubber compound which cures on use. The insulating blocks are of polyurethane foam faced with aluminium foil.

Claims (2)

1. A device for absorbing radiant heat which comprises a system oftubes constructed from a flexible material which is adapted to absorb radiant heat, which tubes carry, in use ofthe device, a heatexchange fluid, a base surface on which the tube system may be mounted, and a cement for securing the tube system to the base surface by forming a permanent bond with the material of the base surface and a breakable bond with the material of the tube system, wherein the tube system comprises a plurality of extruded tube strips, each of the strips having a number of the fluid carrying tubes spaced apart by inter-connecting webs, the edges of each of the strips carry co-operating, mating formations to permit assembly of the tube system by interengagement of adjacent, parallel strips, and the undersurface of the assembled tube system is devoid of such recesses as would provide a mechanical interlock between any part of the said undersurface and the underlying cement.

2. A device for absorbing radiant heat substantially as hereinbefore described with reference to the accompanying drawings.