GB2483457A

GB2483457A - Roof structure for collecting solar energy for heat exchange.

Info

Publication number: GB2483457A
Application number: GB1014892.2A
Authority: GB
Inventors: Roger Alfred Bullivant; Chris Wood
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-09-08
Filing date: 2010-09-08
Publication date: 2012-03-14
Also published as: GB201014892D0

Abstract

The roof structure 10 comprises a metal cladding layer, preferably made from tiles 12, a support structure 14 and a metal backing layer 16 in contact with the lower portion of cladding layer and mounted to the support structure and including at least one pipe 18 for heat exchange fluid. The backing member is preferably a plate member. The backing layer may be in contact with between 50% and 75% of the cladding layer. The support structure may comprise a series of battens 20 which the backing layer preferably spans between. The backing member may comprise a sheet which defines a number of channels 36 parallel to each other for receiving the pipes. The heat exchange pipe may be connected to heat exchangers located within ground piles or bore holes for heat exchange with the ground.

Description

A

Improvements in or relating to roof structu The present invention relates to improvements in or relating to roof structures.

Many proposals have been made for roof structures for various purposes. In some examples, roof structures are intended to collect solar energy in order to improve the energy efficiency of the building on which the roof is constructed.

In examples of the present invention, there is provided a roof structure comprising: a cladding layer; a support structure on which the cladding layer is supported; the structure further comprising at least one backing member supported on the support structure underneath the cladding layer and including at least one pipe for heat exchange fluid, the backing member consisting of or including a body of metal, and the cladding layer being wholly or substantially of metal, and at least part of the area of the cladding layer being in surface contact with the backing member.

The cladding layer may be formed of tiles. The or each tile may be wholly or substantially of metal.

The backing member may be a plate member which is wholly or substantially of metal. The backing member may comprise a substrate carrying a metal surface layer.

The cladding layer and backing member may be formed to provide surface contact over at least 50% or at least 75% of the surface of the cladding layer.

The cladding layer and/or the backing member may be formed of a material having a thermal conductivity greater than 1 OW/mK, such as 20W/mK or above, and/or a specific heat capacity below 500J/kgK.

The structure may further comprise fixings securing the cladding layer to the support structure. The fixings may secure the cladding layer by penetrating the cladding layer and support structure. The fixings may penetrate the cladding layer and the backing member to secure the cladding layer and the backing member to the support structure and in surface contact with each other. The surface contact between the cladding layer and the backing member may be provided at least in the vicinity of the fixings.

The structure may further comprise thermally conductive filler material interposed between the cladding layer and the backing member other than in the region of surface contact therebetween, the filler material promoting thermal conduction from the cladding layer to the backing member. The filler material may be wholly or substantially metal and may be pliable.

The support structure may include a plurality of elongate battens spaced apart and extending across the roof. The or each backing member may span between adjacent battens.

The or each backing member may comprise a sheet formed to provide one or more channels for receiving heat exchange pipes. The or each backing member may comprise a plurality of parallel channels for securing heat exchange pipes.

The heat exchange pipes may be connected to transfer collected heat into the ground. The heat exchange pipes may be connected to heat exchangers within ground piles or within bore holes, for heat exchange with the ground.

Example embodiments of the present invention will now be described in more detail, by way of example only, and with reference to the accompanying drawings, in which: Fig. 1 is a section through part of a roof structure and Figs. 1 a and 1 b are detailed partial views of alternative structures; Fig. 2 is a schematic view of a tile of the roof structure of Fig. 1; Fig. 3 is a perspective view of a backing plate of the roof structure of Fig. 1; Fig. 4 is a perspective view of the roof structure of Fig. 1, during construction; and Fig. 5 is a highly schematic diagram of a building incorporating the roof structure and ground piles.

Overview Referring to the drawings, Fig. 1 shows a roof structure 10 comprising a cladding layer in the form of a plurality of tiles 12. A support structure 14 is also provided, on which the tiles 12 are supported. The structure 10 further comprises several backing members in the form of plates 16 supported on the support structure 14 underneath the tiles 12. The backing plate 16 include pipes 18 for heat exchange fluid.

The backing plates 16 consist of or include a body of metal. All or at least some of the tiles 12 are wholly or substantially of metal. In addition, as will be described, at least part of the area of each of the tiles 12 is in surface contact with one of the backing plates 16.

Support structure The support structure 14 includes parallel rafters 20, only one of which is visible in Fig. 1, which extend up the roof to define the pitch (slope) of the roof structure 10. The rafters 20 may be timber. Conventional insulation material (not shown) may be provided between the rafters 20.

Battens 22 are secured to the rafters 20 by nails 24. The battens 22 run horizontally across the roof, therefore being parallel to each other and spaced apart up the roof structure 1 a Tiles One of the tiles 12 is illustrated in Figure 2. The tile 12 is made of sheet metal, such as steel, which may be coated in conventional manner, such as with an aluminium-zinc alloy. Consequently, the tile 12 has a low thermal mass and a high thermal conductivity. The low thermal mass results in the tile 12 heating up relatively quickly, when exposed to solar radiation. The high thermal conductivity results in any captured heat being distributed quickly across the tile 12, so that the tile 12 will heat up in a generally uniform manner when exposed to solar radiation.

The tile 12 has a main portion 26 which is generally planar and rectangular. The top edge of the portion 26 carries a securing lip 28. An upper hook portion 30 stands above the portion 26, close to the upper edge of the tile 12, but spaced from the upper edge.

The lower edge of the tile 12 is formed as a lower hook portion 32, which is complementary in shape to the upper hook portion 30, so that the lower hook portion 32 of one tile 12 can hook with the upper hook portion 30 of another tile 12, in order to secure together the two tiles. This condition can be seen in Fig. 1, in which each tile 12 has its, lower hook portion 32 locked to the upper hook portion 30 of a tile below, and has its upper hook portion 30 engaged by the lower hook portion 32 of a tile above. In addition, each tile 12 is secured to the battens 22 by means of further nails 34 which secure the tiles 12 to the battens 22 by penetrating the securing lip 28 of the tiles 12, and the battens 22 of the support structure 14.

The upper surface of the main portion 26 may be finished in many different ways, particularly for aesthetic reasons. For example, the upper surface may be coated with an aggregate or other material in order for the tile 12 to have the appearance of a conventional clay or concrete tile, slate or other conventional building material, once installed in the finished roof structure 10.

Although the cladding layer is described above as formed from discrete tiles 12, other alternatives could be used. For example, the cladding layer may be formed from a continuous sheet of material, such as a sheet installed from rolls, and which may be embossed, printed, coated or otherwise treated for aesthetic effect.

Backing plate One of the backing plates 16 is illustrated in Fig. 3. The backing plate 16 is made of a strip of sheet metal, such as steel. Consequently, the backing plate 16 has a low thermal mass and a high thermal conductivity. The low thermal mass results in the backing plate 16 heating up relatively quickly, when exposed to heat. The high thermal conductivity results in any captured heat being distributed quickly across the backing plate 16, so that the backing plate 16 will heat up in a generally uniform manner.

The backing plate 16 is formed with a plurality of parallel channels 36 running along the length of the strip. In this case, three parallel channels 36 are illustrated. Each of the channels 36 houses a heat exchanger pipe 18. The pipes 18 are in close contact with the channels 36, in order to provide good thermal contact between the material of the backing plate 16 and the heat exchanger fluid carried within the pipes 18. The pipes 18 may be of polyethylene, conventional for thermal heating applications and having advantageous properties of durability, easy use, low cost, light weight and low thermal expansion.

The backing plate 16 is thus long in the direction of the pipes 18, so that it may is extend parallel with the battens 22 and be secured to them in a manner which can be understood from Fig. 1. In Fig. 1, it can be seen that the further nails 34, used to secure the tiles 12 to the battens 22, also penetrate the upper and lower edges of the backing plates 16 to secure the backing plates 16 to the battens 22.

Each backing plate 16 spans between adjacent battens 22. This positions the heat exchanger pipes 18 parallel with the battens 22. The pipes 18 are formed as respective lengths of a single uninterrupted pipe which curves back at each end of the roof structure 10, to connect the pipes 18 together. Manifolds or other connecting pipework (not shown) can be provided, preferably at a position accessible for maintenance, in order to connect the heat exchanger fluid to other systems.

Although the backing members are described above as backing plates in the form of strip sheet metal, other alternatives could be used. For example, instead of a plate member which is wholly or substantially of metal, the backing member may comprise a substrate primarily to provide support, structural integrity etc. and carrying a metal surface layer for surface contact with the cladding layer, for the reasons described.

Qoptact between tiles and backinqplates Returning again to Figure 1, it can be seen that by virtue of the penetration of the further nails 34 through the securing lip 28 of the tiles 12, and through the backing plate 16 near their upper and lower edges, the tiles 12 and the backing plates 16 are secured to the support structure 14. Moreover, the tiles 12 are secured with surface contact between the tiles 12 and the backing plate 16. That is, the action of the further nails 34 in pressing the tiles 12 toward the battens 22, also presses the tiles 12 against the backing plate 16, ensuring that surface contact exists between the tiles 12 and the backing plate 16, at least in the vicinity of the further nails 34. The degree to which surface contact is provided can be changed by changing the spacing of the nails 34. Thus, placing the nails 34 more closely together will tend to increase the degree to which surface contact is provided.

Additional surface contact may arise between the tiles 12 and the backing plates 16, particularly if either of these components is slightly curved, rather than being flat. In a further alternative, illustrated in Fig. 1 a, each backing plate 16 is formed with a step 37 which results in the cladding layer and backing member being in surface contact over a much greater part of their area. For example, it is envisaged that the cladding layer and backing member may be formed in this or similar manner to provide surface contact over at least 50%, or at least 75% of the surface of the cladding layer.

In a further example (Fig. 1 b), the thermal performance of the structure 10 can be enhanced by the provision of thermally conductive filler material 38 interposed between the cladding layer 12 and the backing members 16, other than in the regions of surface contact between those components. The filler material 38 is intended to promote thermal conduction from the cladding layer 12 to the backing member 16. The filler material 38 may be wholly or substantially metal and may be pliable. For example metal ribbon, pads of woven or entangled wires or other structures could be used.

Construction of the roof structure The sequence for constructing the roof structure 10 can now be described briefly, particularly with reference to Fig. 4.

After the rafters 20 and battens 22 have been installed (neither of which are visible in Fig. 4), the backing plates 16 are installed over the battens 22, held in place by additional nails (not visible).

The pipes 18 are then laid into the channels 36 as a single run of flexible pipe, to form the required heat exchange circuit. This minimises or removes the need for access for maintenance after installation.

The tiles 12 are then laid on top of the backing plate 16 and pipes 18. This is done from the bottom edge of the roof, up toward the apex. Each row of tiles 12 is connected to the tiles of the row below by locking the lower hook portion 32 to the upper hook portion 30 of the row below, thereby securing the lower edge of the tile 12 to the structure 10. The securing lip 28 is then used to secure the upper edge of the tile 12 by driving further nails 34 through the securing lip 28 and through the backing plate 16, as has been described above. This secures each row of tiles 12 to the structure 10 and also creates the surface contact between the tiles 12 and the backing plate 16, discussed above.

Performance The roof structure 10 can be used to capture heat from solar radiation by circulating heat exchange fluids through the pipes 18. As the roof structure 10 is heated by solar radiation, so the heat can be transferred to the heat exchange fluid and conveyed away to another location by flow of the fluid through the pipes 18.

We have found that the features of the roof structure 10, described above, are beneficial in providing heat exchange in this manner. In our understanding, various features contribute to this. The low thermal mass and the high thermal conductivity of the tiles 12 and of the backing plates 16, by virtue of their metal construction, results in the tiles 12 heating up quickly in the sunlight. This quickly puts the tiles 12 in a position to allow heat transfer to the exchange fluid. The provision of surface contact between the tiles 12 and the backing plates 16 provides good thermal contact between these components, thus allowing heat to pass from the tiles 12 into the backing plates 16. Again, the low thermal mass and a high thermal conductivity of the backing plate 16 tends to distribute this heat quickly throughout the backing plate 16, thereby making the heat available to the pipes 18.

By contrast, some other types of structure for recovering solar energy from a roof may require high temperatures in order to operate (such as the elevated temperature of a hot water tank), or may have high thermal masses (such as systems using concrete, clay or slate tiles). In cases which use high thermal masses, a significant delay may occur between the onset of sunlight, and the necessary operating temperature being achieved. Indeed, if the sunlight is intermittent (such as on a cloudy day), it may even be found that the sun has once again been obscured before the necessary operating temperature has been achieved.

These performance differences can be further explained by reference to typical values for various properties of the materials. For example, the thermal conductivity of steel will depend on the grade of steel, but will typically lie in the range of 1 0-50W/mK, and the specific heat capacity will typically be less than 500J/kgK, such as 490J/kgK. If the density of material is assumed to be in the region of 8,000kg/m3, the thermal diffusivity of the material will typically be in the range from about 4 x 1 06m2/s to 12 x 1 06m2/s. By contrast, the thermal conductivity of concrete is typically lower by a factor of 10 or more (less than 1W/mK) and the specific heat capacity may be nearly double that of steel (around 800J/kgK). The density of concrete may be less than 2,000kg/m3, giving a typical value for thermal diffusivity of concrete of around 0.5 x 106m2/s. Thus, the thermal diffusivity of concrete is typically lower than that of steel by a factor of or more.

Substances with high thermal diffusivity will rapidly adjust their temperature to that of their surroundings, because they can conduct heat quickly in comparison with their volumetric heat capacity (density/specific heat capacity). Thus, the relatively high thermal conductivity of steel (or other metals), combined with the lower specific heat capacity will result in a greater elevation of temperature for the same amount of input energy from sunlight, ambient air etc., and hence a greater ability to effect heat transfer along a temperature gradient, as compared to a material such as concrete. These differences are further enhanced by differences in the masses of material involved. A roof made of steel tiles may have a weight in the region of 6kg/m2, whereas the typical weight of a concrete tile roof may be around 10 times greater (70 or BOkg/m2). Thus, there is a much greater mass of concrete for energy to disperse through, as compared to the low thermal mass of a metal tile, and therefore temperature elevation and heat transfer along a temperature gradient will be much worse in concrete, clay or slate tiles, than in metal tiles of the type described above. We therefore prefer to form the cladding layer from a material with a thermal conductivity of at least 10W/rn K. We prefer to form the cladding layer from a material with specific heat capacity below 500J/kgK.

We have found that the structure 10 allows heat transfer to the heat exchange fluid to begin quickly, when thermal radiation is received by the tiles 12, particularly if the heat transfer takes place at a temperature around the ambient temperature, rather than at an elevated temperature such as the temperature which would be required for heating a hot water tank. The use of metal tiles 12 is also expected to enable the capture of heat from ambient air, as long as the air temperature is above the temperature of the fluid in the pipes 18.

Consequently, we envisage that the roof structure 10 described above can be particularly beneficial for collecting solar radiation for storage in the ground. This is illustrated very simply in Fig. 5. Thus, energy collected through the roof structure 10 during relatively warm periods, such as the summer, can be stored in the ground 40 beneath a building 42, in order to maintain a bank of energy 44 within the ground 40, from which energy can be drawn during relatively cold months, such as the winter. In this example, the building 42 is supported on piles 46 and only some of the piles 46 incorporate heat exchangers. These allow heat to be drawn from the ground 40 by a heat pump, for use within the building, at 48, such as for heating the building during the winter. We have found that if heat is drawn from the ground in this way, without any provision for replenishment, average ground temperature will reduce steadily, resulting in less efficient operation of the ground heat pump. However, heat transfer into the ground during summer months, for replenishment, can take place at relatively low temperatures, i.e. at ground temperature. Consequently, the structure 10 is expected to be beneficial for these purposes in that it can collect solar energy efficiently (by virtue of the low thermal mass and high thermal conductivity of the components) even at ambient temperatures or other relatively low temperatures, allowing the heat energy stored in the ground 40 to be replenished for use during the following winter. In this way, heat is captured at relatively low temperature (the temperature of ambient air and/or the temperature of tiles heated by sunlight) and stored in the ground at relatively low temperature. Thus, relatively low grade (low temperature) heat is captured and stored in a low grade (low temperature) form. However, the stored energy can be recovered by a heat pump and converted to higher grade heat, such as higher temperature heat for use in space heating, water heating etc. We envisage that this use of low grade heat will significantly enhance the overall efficiency of the system. For example, heat can be captured as soon as the temperature in the roof structure 10 is greater than the temperature of the heat exchange fluid in the pipes 18, which will in turn be at or slightly above the ground temperature. This contrasts with a high grade energy capture system, such as a solar hot water system, in which the heat exchange fluid must be at a temperature higher than the hot water tank, in order to further heat the water, so that the roof structure 10 would need to achieve much higher temperature in order to capture any heat to the hot water system, as compared with the temperature required to capture heat for storage in the ground.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

CLAIMS1. A roof structure comprising: a cladding layer; a support structure on which the cladding layer is supported; the structure further comprising at least one backing member supported on the support structure underneath the cladding layer and including at least one pipe for heat exchange fluid, the backing member consisting of or including a body of metal, and the cladding layer being wholly or substantially of metal, and at least part of the area of the cladding layer being in surface contact with the backing member.
2. A structure according to claim 1, wherein the cladding layer is formed of tiles.
3. A structure according to claim 2, wherein the or each tile is wholly or substantially of metal.
4. A structure according to any preceding claim, wherein the backing member is a plate member which is wholly or substantially of metal. S..

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5. A structure according to any preceding claim, wherein the backing member comprises a substrate carrying a metal surface layer. * *5 * * S

*.:.
6. A structure according to any preceding claim, wherein the cladding layer and backing member are formed to provide surface contact over at least 50% or at least 75% of the surface of the cladding layer.
7. A structure according to any preceding claim, wherein the cladding layer and/or the backing member are formed of a material having a thermal conductivity greater than 10W/rn K, such as 20W/rn K or above, and/or a specific heat capacity below 500J/kgK.
8. A structure according to any preceding claim, wherein the structure further comprises fixings securing the cladding layer to the support structure.
9. A structure according to claim 8, wherein the fixings secure the cladding layer by penetrating the cladding layer and support structure.
10. A structure according to claim 8 or 9, wherein the fixings penetrate the cladding layer and the backing member to secure the cladding layer and the backing member to the support structure and in surface contact with each other.
11. A structure according to claim 10, wherein the surface contact between the cladding layer and the backing member is provided at least in the vicinity of the fixings.
12. A structure according to any preceding claim, further comprising thermally conductive filler material interposed between the cladding layer and the backing member other than in the region of surface contact therebetween, the filler material promoting thermal conduction from the cladding layer to the backing member. n

*. 25
13. A structure according to claim 12, wherein the filler material is wholly or substantially metal and/or is pliable. * ** *
14. A structure according to any preceding claim, wherein the support structure includes a plurality of elongate battens spaced apart and extending across the roof.
15. A structure according to claim 14, wherein the or each backing member spans between adjacent battens.
16. A structure according to any preceding claim, wherein the or each backing member comprises a sheet formed to provide one or more channels for receiving heat exchange pipes.
17. A structure according to claim 16, wherein the or each backing member comprises a plurality of parallel channels for securing heat exchange pipes.
18. A structure according to any preceding claim, wherein the or each heat exchange pipe is connected to transfer collected heat into the ground.
19. A structure according to claim 18, wherein the or each heat exchange pipe is connected to heat exchangers within ground piles or within bore holes, for heat exchange with the ground.
20. A roof structure substantially as described above, with reference to the accompanying drawings.
21. Any novel subject matter or combination including novel subject mailer disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims. to a * * , .-I r * * * * *