SOLAR ENERGY COLLECTOR SYSTEM

Abstract: A solar collector system comprising a plurality of single ended absorber tubes (43) and a manifold (40) which provides for fluid circulation to extract heat from the tubes and which may be formed of plastic. Substantially no channelling is provided in the absorber tubes. Each absorber tube is positioned such that the open end of the tube is located at the same level or at a higher level tan the closed end.

Description: -I- SGLAR ENERGY COLLECTOR SYSTEM. BACKGROUND. This invention relates to a solar energy collector system which comprises a plurality of single-ended absorber tubes and a manifold which provides for fluid passage into and from the tubes. Various systems of the type to which the present invention relates are well known and they typically comprise an array of glass absorber tubes which are close coupled by way of distributors or branch pipes to a metal manifold. Each absorber tube comprises an inner glass tube which has one open end and the other end closed an outer glass tube which surrounds the inner tube, an evacuated space located between and defined by the walls of the two tubes, and a solar selective surface on the inner tube. Fluid is caused to pass through the manifold and, via the distributor pipes, into and from the open end of the absorber tubes. Parts of the manifold and distributors which are situated outside the absorber tubes are invariably encased in a thermally insulating material such as foamed plastic to minimize heat losses from the manifold and distributors. Whilst resident in the absorber tubes, the fluid is exposed to heat energy which is transmitted through the inner wall of the absorb¬ er tubes as a result of solar radiation impinging on the solar selective surface coating. I* 1 al of the known prior art collector systems which use single-ended absorber tubes, provision is made for channelling of the heat exchange fluid into and from the absorber tubes via glass or metal tubes or partitions. That is, the fluid is directed into and is conveyed along substantially the full length of each absorber tube in a stream which is kept separate from the outflowing stream. In the case where there is temporarily no fluid or no fluid flow within the absorber tubes, the absorber tubes can reach temperatures in excess of 200°C, thus high melting point materials such as glass or metal must be used for the channelling devices. However, it has now been determined that, somewhat surprisingly and contrary to all previous assumptions, it-is not essential that the fluid be channelled along the length of the absorber tubes. It has been determined that, if the absorber tubes are coupled to the manifold and are inclined at the horizontal, or at an angle below the horizontal with the closed end of the tubes being located at a level.below that of the open ends which are coupled to the manifold, channelling of the fluid within the absorber tubes is not necessary. SUMMARY OF THE INVENTION. The present invention provides a solar energy collector system which comprises a plurality of single- ended absorber tubes, a manifold which is connectable in a fluid flow circuit, and distributor elements coupling an open end of respective ones of the absorber tubes in fluid passage communication with the manifold. Each absorber tube is inclined at the horizontal, or at an angle below the horizontal with the open end of the tube being located at a level above that of the closed end of the tube, and no channelling means are provided within the absorber tubes for effecting streaming of fluid which is at any one time resident in the tubes. In addition to its simplicity, an advantage of the present invention is that for particular embodiments of the inven¬ tion, in which no part of the manifold and distributor elements protude into the absorber tubes, and therefore no part of the manifold and distributor elements are subject to high temperatures, the manifold and distributor elements may be made entirely from low melting point materials, such as plastics and foamed plastics rather than from metal or glass as used in prior art manifolds. The manifold and distributor elements may be enclosed in thermally insulating material, but if thermally insulating material such as plastics and foamed plastics are used in construction of the manifold and distributor elements, a thermally insulating enclosure may be unnecessary. The distributor elements may be constructed with ports to provide for admission and emission of separate (inflowing and outflowing) streams of fluid, but no conduits or partitions or the like extend along a substantial part of the length of the absorber tubes to effect channelling of the fluid when it is resident within the tubes. BRIEF DESCRIPTION OF THE DRAWINGS. The invention will be more fully understood from the following description which is given with reference to the accompanying drawings wherein: Figure 1 shows a sectional end-elevation view of a prior art absorber tube which incorporates means for channelling fluid through the tube, Figure 1A shows a perspective view of the channelling means of Figure 1 , and channelling means being shown removed from the absorber tube, Figure 2 shows a side elevation view of a second prior art absorber tube/manifold arrangement which incorporates means for channelling fluid through the tube, Figure 3 shows a side elevation view of a third prior art absorber tube/manifold arrangement which incorporates means for channelling fluid through the tube, Figure shows a perspective (partly schematic) view of a solar collector system to which the present invent¬ ion relates, Figure 5 shows a side elevation view of absorber tubes coupled to a manifold in accordance with a first method of the present invention, Figure 6 shows a side elevation view of absorber tubes coupled to a manifold in accordance v/ith a second method of the present invention, Figure 7 shows a side elevation view of absorber tubes coupled to a manifold in accordance with a third method of the present invention, Figure 8 shows a side elevation view of absorber tubes coupled to a ma -n4i-fold in accordance with a fourth method of the present invention, Figure 9 shows a side elevation view of absorber tubes coupled to a manifold in accordance with a fifth method of the present invention, and Figure 10 shows a side elevation view of absorber tubes coupled to a manifold in accordance v/ith a sixth method of the present invention. DETAILED DESCRIPTION. As shovm in Figures 1 and 1A, one prior art collector system comprises a twin-pipe manifold 11A to which a U-tube 11B is connected for channelling heat exchange fluid through a single-ended glass absorber tube 12. The heat exchange fluid does not actually contact the absorber tube 12 but one leg of the U-tube 11B is maintained in thermal contact v/ith the inner wall of the absorber tube by a resilient metal retaining sleeve 13« In the second prior art arrangement, as illustrated in Figure 2, heat exchange fluid is conveyed out from a glass absorber tube 1^ by way of a glass conduit 15 and into a manifold distributor 1 . The glass conduit 15 functions to channel the outflowing fluid along substant¬ ially the full length of the absorber tube, so that the inflowing and outflowing streams are kept separate. The inflowing stream is directed into the absorber tube 11+ from the manifold distributor 16 and passes along the annulus between the glass conduit 15 and the inner wall of the absorber tube lit. After passing along substantially the full length of the absorber tube, the heat exchange fluid channels into the glass conduit 15 to be conveyed from the absorber tube. A similar arrangement is employed in the prior art system, as shown in Figure 3 of the drawings. Thus, a divided manifold " header pipe 17 is coupled to an absorber tube 18 by divided distributor pipes 19, and a partition 20 extends for substantially the full length of the absorber tubes from the distributor pipes 19. The partition 20 extends diametrically across each absorber tube and.pr -osvi-des for separate (semi-circular) channels for the inflowing and outflowing streams of heat exchange fluid. A significant feature of all prior art solar collector systems, as typified by the arrangementsshown in Figures 1 to 3, is that the heat exchange fluid is actually channelled along substantially the full length of the absorber tubes so that the inflowing and outflowing fluid streams are effectively separated. However, as hereinbefore mentioned, the present invention is directed to a system which does not provide for channelling of the inflowing and outflowing streams along a significant portion of the length of the absorber tubes, and arrangements which embody the invention are illustrated in Figures 1+ to 10 of the drawings. As shown in Figure , the solar collector system comprises a manifold 1+0 through which heat exchange fluid is pumped by a pump 1+1. Depending upon the type of installation, a constant supply of the heat exchange fluid may be recirculated through the system, with the heat being extracted from the fluid at a heat exchanger 1+2, or fresh fluid may be directed from a source and through the solar collector system to points of usage of the fluid. The latter system would be used in domestic plumbing situations. A plurality of single-ended absorber tubes 1 are close coupled to the manifold 0 by way of distributor elements , and the absorber tubes are inclined horizontally or at an angle θ below the horizontal. The angle 0 preferably is less than 60 and the closed end of each absorber tube is disposed at a level below that of the open end of the tube which couples with the * associated distributor element. Various methods of coupling the absorber tubes 1+3 to the distributor elements are shovm in Figures 5 to10. As shownin Figure 5, the manifold Z+0 comprises a single header pipe, and distributor elements or branches 44 project outwardly from the header pipe. The distributor elements 44 project into the open ends of the absorber tubes 43 and 0-rings 5 are provided to effect a fluid tight seal between the distributor elements and t " e open ends of the absorber tubes. Fluid passes along the manifold 40 in the direction indicated by the arrow and heat is exchanged between such fluid and that which is resident at any one time in the absorber tubes 43. Also, a proportion of the fluid which is contained within the absorber tubes may migrate into the manifold 40 to mix with the through flowing fluid and make-up fluid will then enter the absorber tubes from the manifold. The heat exchange fluid may be pumped through the manifold or, in some applications of the system, if the manifold is connected into an appropriate fluid circuit usually containing a fluid storage tank above the level of the manifold, the fluid may be induced to flow through the system by a thermo-syphoning action. A particular advantage of the embodiment shovm in Figure 5 is that the absorber tubes are connected in series, but due to the absence of partitioning within the absorber tubes, the manifold and distributor elements exhibit minimal impedance to fluid flow. In an alternative embodiment, as shovm in Figure 6, the manifold 40 is constituted by a number of series connected pipes, and the distributor elements 44 are ported to direct fluid into and from the absorber tubes 43. In this case, the heat exchange fluid is actually directed into the absorber tubes 43 by one of the ports 46 and then flows from the tube by way of the other port 46A. The inlet and outlet ports 46 and 46A are separated i by the greatest possible distance and, although not shown in the drawings, a partition may be provided between the ports and extend into the absorber tubes for a distance corresponding approximately to 20 per cent of the length of the absorber tubes. 0-rings 45 are provided to effect a fluid tight seal between the distributor elements and the open ends of the absorber tubes. The further embodiment which is illustrated in Figure 7 of the drawings is similar to that shown in Figure 6, but the manifold 40 is constituted by two parallel pipes 47 and 48. Heat exchange fluid is directed into respective ones of the absorber tubes from the pipe 47, by way of the connecting pipes 47A and the inlet port 46, and outflowing fluid is directed into the pipe 48 by way of the connecting pipes 48A and the outlet ports 46A. In the embodiment shown in Figure 7, the impedances of connecting pipes 47A, 48A and inlet/outlet ports 46, 46A respectively, may be adjusted to equalize flow into each parallel connected absorber tube in the solar energy collector system and in addition may be adjusted to minimize loss rate of fluid from the collector system should one or more of the glass absorber tubes break. The arrangements shown in Figures 8 and 9 are similar to those shown in Figures 5 and 6, v/ith the only significant difference being in the coupling arrangement between the distributor elements 44 and the absorber tubes 43 * I the embodiments shovm in Figures 8"and 9, the distributor elements h are constructed to locate about (rather than within) the absorber tubes. The distributor elements may be similarly constructed in the embodiment shown in Figure 7. The further embodiment which is illustrated in Figure 10 of the drawings is similar to the embodiment shown in Figure 5 of the drawings, but consists of a manifold 40 with distributor elements 44 and absorber tubes 43 being disposed on opposite sides of the manifold rather than on a single side,- the absorber tubes " b ieing horizontal or inclined at angles 6 v/ith the horizon- tal. In this embodiment the manifold 40 is generally inclined at an angle to horizontal. A particular advantage of the embodiment shown in Figure 10 is that tv/ice the number of absorber tubes, and thus tv/ice the total solar collector area may be obtained for a given length of manifold. Further embodiments incorporating distributor elements and absorber tubes on opposite sides of the manifold may be "similarly constructed by modifications of the embodiments shown in Figures 6 and 7 of the drawings. As in the case of the embodiments mentioned hereinbefore, the distributor elements may be constructed to locate either about or within the absorber tubes. Figure 10 of the drav/ings shows distributor elements 44 locating about the absorber tubes 43 Each of the particular embodiments described hereinbefore may be comprised of metals such as copper, aluminium or steel. In each of the particular embodiments in which the distributor elements are constructed to locate about rather than within the absorber tubes, no part of the manifold or distributor elements protude inside the absorber tubes. low melting point materials such as plastics or foamed plastics may therefore be used for construction of the manifold and distributor elements in these particular embodiments. Variations and modifications may be made in respect of the invention as above described and as set forth in the following statement of claims.

Claims: STATEMENT OF CLAIMS. The claims defining the invention are as follows: 1._ A solar energy collector system comprising a plural¬ it of single-ended absorber tubes, a manifold which is connectable in a fluid flow circuit, and distributor elements coupling an open end of respective ones of the absorber* tubes in fluid passage communication with the manifold; each absorber tube being inclined at the horizontal, or at an angle below the horizontal with the open end of the tube being located at a level above that of the closed end of the tube, and no channelling means being provided within the absorber tubes for effecting streaming of fluid which is at any one time resident in the tubes. 2. The solar energy collector of claim 1 in which the manifold consists of a single headerpipe and the distributor elements contain a single port for fluid exchange between manifold and absorber tubes. 3i The solar energy collector of claim 1 in which the manifold consists of a number of series connected pipes and the distributor elements are ported to direct fluid into and from the absorber tubes. 4. The solar energy collector of claim 1 in which the manifold consists of two parallel pipes for fluid inlet and fluid outlet and the distributor elements are ported to direct fluid into and from the absorber tubes. 5. The solar energy collector of claim 1 in which the distributor elements are disposed on opposite sides of the manifold. 6. The solar energy collector of claim 1 in which the distributor elements project into the open ends of the absorber tubes and 0-rings effect fluid tight seals between distributor elements and the open ends of the absorber tubes. 7. The solar energy collector of claim 1 in which the distributor elements locate about the absorber tubes and 0-rings effect fluid tight seals between distributor elements and the open ends of the absorber tubes. 8. The solar energy collector of claim 1 in which the^δ ^^ . - to- manifold and/or distributor elements are comprised of copper. 9- The solar energy collector of claim 1 in which the manifold and/or distributor elements are comprised of c aluminium. 10. The solar energy collector of claim 1 in which the manifold and/or distributor elements are comprised of steel. 11. The solar energy collector of claim 1 in which the 10 manifold and/or distributor are comprised of plastic and/or foamed plastic. 12. The solar energy collector of claim 1 in which the fluid flowing in the circuit is essentially water. 13. The solar energy collector system of claim 1 in 15 which fluid is pumped through the manifold. 14. The solar energy collector system of claim 1 in v/hich fluid is induced to flow through the manifold by thermo-syphon action.

Inventors: HARDING GEOFFREY LESTER, WINDOW BRIAN, HARDING, GEOFFREY, LESTER, WINDOW, BRIAN
Applicants: HARDING GEOFFREY LESTER, WINDOW BRIAN, HARDING, GEOFFREY, LESTER, WINDOW, BRIAN
Application year: 1983
Main classification: F24J3
IPC codes: F24J2