GB1576717A

GB1576717A - Solar radiation collectors

Info

Publication number: GB1576717A
Application number: GB26395/76A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-06-17
Filing date: 1977-06-17
Publication date: 1980-10-15

Description

(54) IMPROVEMENTS IN AND RELATING TO SOLAR RADIATION COLLECTORS (71) I, GRAHAM BRUCE KENT, a British subject, of Goldtrieve House, 54 Over Road, Almondsbury, Bristol, BS12 4BW, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to solar heat collectors, and particularly to solar radiation absorber elements of the type designed to extract useful heat from incident thermal radiation such as solar radiation.

Solar radiation collecting devices are known in which water or some other heat exchange liquid is circulated through internal ducts in a heat exchanger which has surfaces exposed to incident sunlight. An object of the present invention is to provide a radiant heat collector of high eff- ciency and economic construction.

According to the present invention there is provided an extruded metal solar radiation absorber element for use in a solar heat collector, the absorber element having at least one longitudinally extending internal duct and two external lateral fins extending longitudinally on opposite sides of the duct, each fin tapering in thickness from the portion adjacent the duct to its outer edge, one face of the fins being intended for exposure to solar radiation to be absorbed, and the opposite face of the fins being protected from heat loss by adjacent thermally insulating material.

The provision of external lateral fins of tapering thickness leads to efficient transfer of heat by conduction across the width of the fins to the internal duct, in which a heat exchange fluid would flow in use of the absorber element. Extrusion of the element is facilitated by the fact that the fins are longitudinally extending.

Preferably the outer edges of the two fins are disposed in a common plane spaced from the axis of the longitudinally extending duct. The median lines of the cross sections of the fins are preferably inclined to each other at an obtuse angle at the roots of the fins. The cross section of each fin may, moreover, have a curved median line, so that the two fins present in cross section a dihedral or "gull wing" configuration the convexly curved surfaces of which are exposed to radiation in use of the absorber element.

To enhance the heat transfer to fluid circulated through the internal duct the latter is preferably formed with a number of longitudinally extending inwardly projecting ribs, which increase the surface area of the duct.

These ribs are conveniently formed during the extrusion of the element.

A solar radiation collecting panel such as a roof-mounted solar panel may be made from a number of absorber elements according to the invention. For this purpose the absorber elements would be mounted sideby-side with the outer edges of the fins of neighbouring elements parallel to each other and coplanar with the outer edges of the fins of the other absorber elements, the internal ducts of the absorber elements being interconnected at opposite ends by respective manifolds.

In such a solar radiation collecting panel the surfaces of the absorber elements opposite the surfaces exposed to incident solar radiation are thermally insulated. The absorber elements are preferably arranged with the longitudinal axes of their ducts coplanar and located behind the outer edges of the fins with respect to the direction of incident radiation. The absorber elements would normally be housed in an enclosure covered by a light transmitting panel or winddw through which radiant heat impinges on heat collecting surfaces of the absorber elements.

By manufacture the solar radiation absorber elements themselves and the components of the enclosure from aluminium or aluminium alloy extrusions it is possible to assemble the panel easily and economically from a small number of component parts.

A solar radiation collecting panel according to the invention may be connected in a water or other liquid circulation system according to the practical application for which the panel is used. The circulation system would normally include an electrically operated circulating pump controlled thermostatically in response to the exposed surface temperature of the heat absorbed elements so that the circulating pump operates only when this surface temperature exceeds that of the water or other heat storage liquid in a storage tank forming part of the circulation system. This enables the system to be shut down automatically, for example at night, or in the absence of solar radiation, preventing heat loss from the heat collecting panel by re-radiation.

The invention will be further described, by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic perspective view of a solar radiation collecting panel according to one embodiment of the invention; Figure 2 is a diagrammatic transverse cross section through part of a solar radiation collecting panel according to one embodiment of the invention, and Figure 3 is a diagrammatic longitudinal cross section through part of the solar radiation collecting panel shown in Figure 2.

The drawings illustrate a solar radiation collecting panel adapted to be mounted on the roof of a building and comprising a number of (in the illustrated example, three) extruded aluminium or aluminium alloy radiation absorber elements 1 mounted in an enclosure 2 formed by extruded aluminium frame sections and covered on its upper surface by a glass window 3.

Each solar radiation absorber element 1 comprises an elongate element extruded with a longitudinally extending internal duct 4 (Figure 2) and two external lateral fins 5 extending longitudinally on opposite sides of the duct. Each fin tapers in thickness from the root portion adjacent the duct to its outer edge. It will be seen from Figure 2 that the outer edges of the two fins 5 of each absorber element 1 are disposed in a common plane spaced from and disposed in front of the axis of the longitudinally extending duct 4 with respect to the direction of incident solar radiation, indicated by arrows R in Figures 2 and 3.

Furthermore, the median lines of the cross sections of the fins 5 are curved, the convex surfaces of the fins 5 facing in the direction of incident radiation R, and these median lines are inclined to each other at an obtuse angle, in this example about 1600, at the roots of the fins 5.

Each solar radiation absorber element 1 is extruded with an internal duct 4 of noncircular cross section to give a high surface area of the duct 4 relative to its cross sectional area. In the illustrated example the duct 4 is extruded with a number of longitudinally extending inwardly projecting ribs 6.

The solar radiation absorber elements 1 are assembled in the panel side-by-side with the outer edges of the fins 5 of the neighbouring elements 1 parallel to each other and separated by a narrow gap sufficient to allow for thermal expansion of the elements in use. The outer edges of the fins 5 of the elements 1 are coplanar and line in a plane disposed above the plane containing the longitudinal axes of the internal ducts 4 of the absorber elements 1.

The absorber elements 1 are supported within the enclosure by mounting bolts 7, preferably of insulating material such as plastics, which engage a T-section cross member 8 extending transversely across the bottom of the enclosure (Figure 3). The absorber elements 1 have a backing 9 of thermally insulating material such as polystyrene foam interposed between the individual elements 1 and the supporting cross members 8.

Prior to assembly of the absorber elements 1 in the panel the ribs 6 of the internal duct 4 of each absorber element 1 are drilled out at each end of the duct 4 for a short length defining a smooth-bored end passage 10 (Figure 3) into which a connector spigot 11 is inserted. The connector spigot 11 has an external resilient O-ring 12 which forms a sliding seal with the smooth-bored end section 10. The connector spigots 11 have internal through bores which establish communication between the respective ducts 4 and transversely extending manifolds 13, 14 into which the respective spigots 11 are force-fitted to make fluid tight connections therewith. The sliding seal connections between the absorber elements 1 and the manifolds 13, 14 permit expansion and contraction of the collector elements without imposing undesirable strain on the assembly as a whole. The spigots 11 may alternatively be welded, screwed or otherwise connected to the manifolds 13, 14.

The manifolds 13 and 14 are connected to respective inlets and outlets for a heat exchange fluid such as water which, in use of the solar heat collecting panel, is circulated through the ducts 4 of the absorber elements 1 via the manifold 13, the spigots 11, and the manifold 14. In flowing through the internal ducts 4 of the absorber elements 1 the fluid picks up heat which has been transferred by conduction to the walls of the ducts 4 from the fins 5.' 5 To enhance the radiation collecting effi ciency of the fins 5 the exposed surfaces of the latter may be suitably plated, and preferably have a blackened surface to enhance their heat absorption coefficient.

The graded profile of the fins 5 of each heat collector element ensures a low tem peratnre gradient across - the width of each fin 5 in use of the heat collecting panel, with a minimum mass of metal consistent with sufficient mechanical strength and feasability of extrusion. This in turn ensures a minimum thermal capacity of the absorber element while maximising the heat transfer from the fins to the internal duct of the absorber element.

The inlet and outlet manifolds 13, 14 are connected in a closed circulation system (not shown) for water or other heat exchange fluid including a pump and an external heat exchanger. The heat exchanger may be located within a heat storage vessel such as a water tank. The circulation pump is driven by an electric motor (not shown) which is controlled by a differential electronic temperature control switch responsive to the temperature sensed at the exposed surfaces of the heat absorber elements 1 to switch off the circulation pump when this temperature is less than that of the liquid in the heat exchanger or the thermal storage vessel.

In an alternative embodiment of the invention, not shown, the internal ducts 4 of the solar radiation absorber elements 1 may constitute evaporator sections of respective heat pipes the condenser sections of which are located in an external heat exchanger, each heat pipe having sealed within it a quantity of a suitable liquid of low boiling point which is evaporated by the solar heat collected at the absorber elements 1 and condensed at the external heat exchanger to impart heat thereto.

In some practical applications of the invention the solar radiation collecting panel may include or be in heat exchange relationship with the evaporator of a heat pump.

Such an arrangement yields heat at a higher temperature than the temperature of circulating refrigerant in the evaporator and, therefore, at a higher temperature than the solar panel itself.

The low volume of fluid contained in the internal ducts of the panel, compared with that contained in most solar panels, ensures a rapid transient response of the panel, for example when exposed to a brief burst of solar radiation.

For some practical applications, such as, for example. the heating of swimming pools, where a large quantity of water is to be heated by a relatively small amount, the solar radiation absorber elements according to the invention may be exposed directly to solar radiation without the necessity for a surrounding enclosure or for a light trans mitting window.

Apart from the fact that the solar radiation collector elements are easily extruded in aluminium in any desired length, these elements have sufficient strength and rigidity to form part of the structure of the roof or roof cladding of a building, so that they are ideally suited for the incorporation of a solar heat collecting facility in a building under construction, apart from their use in a solar heat collecting panel for installation on an existing roof or wall of a building.

The relatively slim cross sectional thickness of the solar radiation absorber elements makes them compatible -with contemporary roofing materials and avoids the unsightly appearance commonly associated with most types of solar panel.

WHAT I CLAIM IS: 1. An extruded metal solar radiation absorber element for use in a solar heat collector, the absorber element having at least one longitudinally extending internal duct and two external lateral fins extending longitudinally on opposite sides of the duct, each fin tapering in thickness from the portion adjacent the duct to its outer edge, one face of the fins being intended for exposure to solar radiation to be absorbed, and the opposite face of the fins being protected from heat loss by adjacent thermally insulating material.

2. A radiation absorber element as claimed in Claim 1, in which the outer edges of the two fins are disposed in a common plane spaced from the axis of the longitudinally extending duct.

3. A radiation absorber element as claimed in Claim 2, in which the median lines of the cross sections of the fins are inclined to each other at an obtuse angle at the roots of the fins.

4. A radiation absorber element as claimed in any one of the preceding claims, in which the internal duct is formed with a number of longitudinally extending inwardly projecting ribs to enhance the surface area of the duct.

5. A radiation absorber element as claimed in any one of the preceding claims, extruded in aluminium or aluminium alloy.

6. A solar radiation absorber element as claimed in any one of claims 1 to 5, in which the internal duct communicates with a primary heat exchanger in a closed circuit for refrigerant fluid in which the internal duct of the collector acts as the evaporator section and the primary heat exchanger as the condenser section of a heat pump.

7. A solar radiation collecting panel com

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Claims

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1 the fluid picks up heat which has been transferred by conduction to the walls of the ducts 4 from the fins 5.' 5 To enhance the radiation collecting effi ciency of the fins 5 the exposed surfaces of the latter may be suitably plated, and preferably have a blackened surface to enhance their heat absorption coefficient.

7. A solar radiation collecting panel com

prising a number of absorber elements according to any of claims 1 to 6 mounted side by side with the outer edges of the fins of neighbouring elements parallel to each other and coplanar with the outer edges of the fins of the other absorber elements, the internal ducts of the absorber elements being interconnected at opposite ends by respective manifolds.

8. A solar radiation collecting panel as claimed in claim 7, in which the collector elements are backed by a covering of thermally insulating material on the said opposite face of the lateral fins.

9. A solar radiation collecting panel as claimed in Claim 7, made up of radiation absorber elements according to Claim 2, in which the collectors are arranged with the longitudinal axes of their ducts coplanar and behind the outer edges of the fins with respect to the direction of incident radiation.

10. A solar radiation collecting panel as claimed in claim 7, claim 8 or claim 9, in which the absorber elements are housed in an enclosure covered by a light transmitting panel or window through which incident radiation impinges on heat collecting surfaces of the absorber elements.

11. A solar radiation collecting panel as claimed in any of Claims 7 to 10, in which the internal ducts of the absorber elements communicate with the manifolds through respective hollow connector spigots which have sliding seal connections with opposite ends of the respective internal ducts of the absorber elements.

12. A solar radiation absorber element or a solar radiation collecting panel equipped therewith, substantially as herein described with reference to and as shown in the accompanying drawings.