WO2006059071A1

WO2006059071A1 - Solar collector

Info

Publication number: WO2006059071A1
Application number: PCT/GB2005/004523
Authority: WO
Inventors: Ian Warner Mcgilvray
Original assignee: Ian Warner Mcgilvray
Priority date: 2004-12-01
Filing date: 2005-11-29
Publication date: 2006-06-08
Also published as: GB0426311D0

Abstract

A solar collector (1) comprising an inlet (5); an outlet (6); and a first sheet (2) and a second sheet (3) substantially flat other than any surface relief; the first and second sheet (2, 3) being n close proximity but sufficiently spaced to define one or more cavities through which fluid flows in contact with said sheets (2, 3), in use, from the inlet (5) to the outlet (6); wherein at least one of said sheets (2, 3) is a glazed sheet; wherein at least said inlet (5) or outlet (6) is formed from a plurality of mouths which span a region through which fluid is inputted and/or removed from said collector (1); and/or at least said cavity inlet (5) or outlet (6) is formed from a mouth which is substantially elongate in the cavity-spanning direction; and the first, second and any intermediate sheets (2, 3) (if present) incorporating no substantial protrusion other than any surface relief.

Description

SOLAR COLLECTOR

Field of the Invention

The invention relates to general improvements in or relating to solar collectors and in particular but not exclusively to a collector which may form an integral part of a roofing or curtain walling system. The invention also relates to systems incorporating solar collectors.

Background to the Invention and prior art known to the applicant

The closest prior art known is shown in the following documents (ordered date-wise).

I) DT 26 11 108 (1977);

2) FR 2 390 685 (1977);

3) GB 2 025 030 (1980);

4) EP 0 022 389 (1981); 5) 08 4,282,856 (1981); 6) GB 2 247 071 (1992); and 7) DE 197 05 079 (1998). These prior documents all fail to propose a solution to the problem of cross panel fluid flow for collector forming sheets without substantial protrusions. In this field, the inlet and outlet in each prior art document are single localised circular pipe mouths which limit full cross-panel flow and therefore dramatically reduce solar collection. These prior art systems prevent an)' evenly distributed flow being achieved across the cavity.

Summary of the Invention

In its broadest aspect, the invention provides a solar collector comprising an inlet; an outlet; and a first sheet and a second sheet substantially flat other than any surface relief; the first and second sheet being in close proximity but sufficiently spaced to define one or more cavities through which fluid flows in contact with said sheets, in use, from the inlet to the outlet; wherein at least one of said sheets is a glazed sheet; characterised in that at least said inlet or outlet is formed from a plurality of mouths which span a region through which fluid is inputted and/or removed from said collector; and/or at least said cavity inlet or outlet is formed from a mouth which is substantially elongate in the cavity-spanning direction; and the first, second and any intermediate sheets (if present) incorporating no substantia] protrusion other than any surface relief.

This configuration is advantageous because it allows improved collection of energy across a greater area of the solar collector as compared to the prior art localised inlet systems. This configuration will also reduce assembly complexity and manufacturing costs. There is also no need to form the sheets often made out of glass with protruding webs. Simple flat sheets may be used without undermining solar collection.

In a subsidiary aspect in accordance with the invention's broadest aspect, said mouth and/or mouths substantially spans and/or collectively substantially span one side of said collector.

In a subsidiary aspect in accordance with the invention's broadest aspect, said sheets are separated by a gap within the range 0.5mm to 1.5mm. In a subsidiary aspect in accordance with the invention's broadest aspect, the inner surface of at least one of said sheets is formed in relief and rests directly against the other sheet.

One of the advantages of this configuration is that the shape of the inner surface creates and maintains the required spacing between the sheets and thus reduces the number of components within the system. Another advantage is that the solar energy collection is increased because of the variety of angles of the surfaces at each protrusion and/or recess formed by the relief.

In a subsidiary aspect of the present invention, means are provided to maintain the internal operating pressure within said space at or below atmospheric pressure.

The advantage of such a configuration is that the sheets are maintained in their spaced relationship and unaffected by the internal pressure exerted by the circulating fluid.

In a subsidiary aspect of the present invention, the sheets are both glazed sheets and are located behind a further one or more glazed sheets.

This results in at least a triple glazed unit, which has improved thermal efficiency as compared to prior art system(s) whilst still retaining the advantages of glazed sheet fluid conduits as discussed above.

In a further subsidiary aspect of the present invention a further sheet with surface characteristics which increase solar energy collection efficiency is sandwiched between the first and second sheet.

The effect of the inclusion of such a sheet is that the fluid within the system is heated when flowing between the inlet and outlet without the need to colour either the fluid or either of the inner surfaces of the sheets encapsulating the fluid. The fluid is heated at least in part if not entirely due to its contact with this further sheet. Brief Description of the Drawings

Figures Ia, Ib, Ic and Id are schematic representations of a first embodiment showing cross-sectional views;

Figures 2a to 2d are enlarged cross-sectional views of variations of Figures Ia, Ib, Ic and I d;

Figure 3 is a cross-sectional view of a second embodiment;

Figure 4 is a cross-sectional view of a third embodiment:

Figure 5 is a cross-sectional view of a fourth embodiment;

Figure 6 is a cross-sectional view of a fifth embodiment;

Figure 7 is a block schematic representation of a system incorporating the present invention;

Figure 8 is a block schematic representation of a preferred system incorporating the present invention;

Figure 9 is a block schematic representation of a system incorporating the present invention;

Figure 10 is a block schematic representation of a system incorporating the present invention:

Figure 1 1 is a block schematic representation of how to fill/refill a system incorporating the present invention;

Figures 12a and 12b are representations of the temperature variances in known plate colleciors and the present invention respectively; Figure 13 is a block schematic representation of an array of solar collectors;

Figures 14a and 14b are another block schematic representation of an array of solar collectors;

Figure 15 illustrates different installation positions on a building i.e. roof, wall and curtain wall fixing.

Figures 16a and 16b are cross-sectional views of an embodiment integrated into roofing structures;

Figure 17 is a cross-sectional view of an enlarged view of Figures 16a and 16b;

Figures 18a and 18b are cross-sectional views of an array of collectors; and

Figures 19a shows a schematic plan view of a solar collector; whilst figure 19b shows a cross-sectional view.

Figure 19c shows a further embodiment of an inlet/outlet pipe or manifold.

Detailed Description of the Invention

'Glazed sheet^' signifies within the context of the present invention any sheet with a layer of material which is substantially transparent to solar radiation. This may for example be a plastics substantially transparent sheet; a sheet of glass; or a laminate sheet constructed from at least one transparent coating or layer and a non-transparent layer.

By the term 'increase in solar energy collection efficiency" it is to be understood that there is an overall increase in the thermal absorbency of the collection and an overall decrease in the reflection and/or radiant losses apparent within the collector. 'Coloured^" means within the context of this description of any colour (including black and even preferably black in most applications) which when used in a medium and/or as pan of or on a component of a collector increases its ability to absorb as opposed to reflecting away solar radiation. Other surface finishes of a medium and/or as part of or on a component that have similar solar absorbent properties to black are also envisaged.

'Black^' is well known to be the optimal colour which maximises solar energy collection efficiency. Other dark colours having similar properties to black are also envisaged as optimum colours for example: blues, greens, browns, purples and grey. For simplicity, the following description refers to black which the person skilled in the art may substitute for any other appropriate colour.

The fluid ma)' initially be water which may be dyed by a black substance. Alternatively a suspension may be used to achieve a blackened fluid. Any other kind of fluid may be employed if suitable including gases.

Looking at Figures I a and Ib₅ Ic and Id, it can be seen that the collector 1 is formed from two sheets 2. 3 in close proximity to each other forming a narrow gap 4 therebetween. The front sheet 3 in this embodiment is entirely transparent to solar radiation in order to allow said radiation energy to be directly captured or absorbed by the fluid (not illustrated) flowing between the sheets 2, 3. The 'back' sheet 2 acts as a back plate and may or may not be transparent. A particularly advantageous gap is comprised between 0.5 mm and 1.5 mm.

A pipe 5. 6 is bonded by seal 40 to the sheets 2, 3 forming an inlet pipe 5 and an outlet pipe 6 for the circulating fluid (see item 10 Figure 3) to circulate therebetween and across the entire surface of the collector 1. The circulating fluid enters the collector 3 via the inlet pipe 5 and is made to pass through the gap 4 between the sheets 2. 3 via apertures 7 in the inlet pipe 5 positioned such that it fills the cavity and flows from one side of the collector to the other at a rate that is essentially even throughout the cavity across the inner surfaces of the collector and into corresponding apertures in the outlet pipe 6 which then removes the heated circulating fluid from the collector. The apertures are located to substantially collectively span across the cavity to ensure that the fluid flows as a thin film across the cavity.

Figures 19 also show the inlet and/or outlet pipe 50 or manifold with a series of holes such as hole 51 in the longitudinal direction of the pipe. The series of holes or mouths may be achieved by the spaces between the meshes of a section of wall of a fibrous or porous pipe or manifold as Jong as sufficient back pressure in the pipe or manifold is achieved.

Instead of using a plurality of holes/apertures of this kind, the invention optionally envisages the use of a slit in a pipe or any other appropriate elongate mouth such as an oblong cut-out in the cavity-spanning direction such as hole 52 in figure 19c which shows a pipe 53.

A number of spacers 54 which may be for example a winding such as a rope or an elongate seal member are placed at regular intervals along the width of the collector in the direction of the flow. An edge adhesive 55 is also employed.

Radiation, convection and conduction losses from the front of the collector are reduced by means of an additional glazed sheet 8 in the form of a double glazed unit. The two glazed sheets 2, 3 and the outer glazed sheet 8 form a unit with three glazed sheets 2, 3₅ 8.

Typically the sheets 2, 3. 8 are toughened glass. Sheets 8, 3 have low iron content to achieve a high degree of heat transmission and may have finished surfaces designed to minimise radiant losses.

Looking at Figures 2a to 2d examples of how to achieve and maintain the gap 4 separating the collectors' sheets 2, 3 are illustrated and are common to all embodiments of the present invention. When discussing the size of the gap 4 between the two sheets 2, 3 in a configuration where the first and second sheet due to their relief touch each other, the specified advantageous size is the maximum separation distance between the two sheets which define the cavity. Figure 2a shows two sheets, 2a, 3a separated by spacers 9 to form a narrow gap 4 therebetween. These spacers 9 may be glass beads, batons, wire or the like. Typically, in this configuration the gap is approximately 0.8mm.

Figure 2b shows two sheets 2b. 3b each having a profiled inner surface (in other words a typical surface in relief) having a number of peaks and troughs which may or may not coincide, in use, and effectively separate sheets 2b, 3b forming the required gap therebetween when placed one atop the other.

Figure 2c shows another variant where only one sheet 2c has a profiled inner surface and Figure 2d shows another variant where each sheet has a profiled inner surface such that the peaks of one sheet coincide with the troughs of the other sheet.

Because the gap 4 between the two sheets 2, 3 which form the collector 1 is very small, approximately 0.5mm to 1.5mm, if frozen the expansion of ice crystals can be accommodated by the flexible bond 40 and spacers 9 that hold the two sheets 2, 3 together. The use of flexible silicon tubing or the like forming the inlet and outlet feed pipes 5, 6 also accommodate freezing without the need to include antifreeze within the dynamic part of the system.

Figures 3 to 6 each illustrate a single feature of the invention. A single feature will ensure that the invention works but it will not be unusual to combine one or more of these features.

As shown in Figure 3 all sheets 2, 3, 8 are transparent to solar radiation and the circulating fluid 10 may be so coloured that it absorbs the sun's energy 1 1 directly and its inherent characteristics provide an increased solar energy collection efficiency.

As shown in Figure 4₅ the 'front' glass sheet 3 may have an inner surface 12 with characteristics that improve the solar energy collection efficiency by for example, being black. The inner surface 12 is in intimate contact with the circulating fluid 10 such that the circulating fluid is heated directly by the inner surface 12 which absorbs energy 1 1 from the sun. The circulating fluid 10 may be transparent to solar radiation. Alternatively, as per Figure 5, the 'back' sheet of glass 2 may have an inner surface 13 with characteristics that improve and/or optimise SoIa₁- energy collection efficiency over conventional flat plate and/or evacuated tube collectors. This inner surface 13 is in intimate contact with the circulating fluid 10 such that the sun's rays 1 1 pass through the thin film of circulating fluid 10 prior to heating the inner surface 13 which, when so heated, heats the circulating fluid 10 directly. Again, the circulating fluid 10 may be transparent to solar radiation.

The optimal surface 12, 13 that faces towards the incoming solar radiation is one which maximises solar energy collection efficiency for example being black.

In Figure 6 the gap between the plates (previously referenced 4) contains a black sheet ] 4 that is in intimate contact with the circulating fluid 10, such that the circulating fluid 10 is heated directly by the material 14 as it absorbs energy from the sun 11. Again, the circulating fluid 10 may be transparent to solar radiation.

In common with most flat-plate collectors, the heated circulating fluid 16 leaves the collector 1 or collector array 15 and gives up its energy to water or some other medium in a storage vessel 17 as shown in Figure 7. A pump 18 ensures that the fluid 16 is circulated around the system.

The preferred configuration envisaged is for the energy to be transferred to a storage device 17 via an intermediate heat exchanger 19 to minimise the amount of fluid 16 in the dynamic section of the circuit and to simplify filling. A schematic representation of this closed system is shown in Figure 8 where an additional circulating pump or pumps 18 maintain the circulation of the fluid 16 throughout the system.

The dynamic system is arranged to operate at or at slightly less than atmospheric pressure to ensure the. distance between the front and back sheets 2, 3 is not affected by the pressure being exerted by the circulating fluid. Maintaining this pressure requirement may be achieved in several ways and will also provide sufficient volume for expansion and contraction of the circulating fluid. Examples are illustrated schematically in Figures 9 and 10.

Figure 9 shows a flexible vessel 20 connected at a point lower than the collectors 1 , 15 to accommodate changes in circulating fluid volume and to maintain the fluid held within it at atmospheric pressure. This vessel 20 ensures that the pressure at any point above this point is at a lower pressure than atmospheric pressure.

Figure 10 shows an alternative arrangement having a similar effect. A vessel 21 is connected into the circuit such that a pressure is created within the closed system that is lower than atmospheric pressure whilst at the same time accommodating circulating fluid volume changes.

There are several ways to fill the system whilst at the same time ensuring that the internal pressure remains at or just lower than atmospheric pressure. A typical example is shown in Figure 1 1.

The Collector array 1,15 is not yet connected to 22a and 22g. The flexible pipes leading from vessel A are connected to 22d and 22e.

Valve 22f is opened and all other valves are closed and degassed fluid is slowly applied to 22h. Expansion vessel 21 is filled with fluid and valve 22h is then closed. All other valves are opened. The expansion vessel is squeezed to remove trapped air from it and valve 22f is closed. Valve 22h is opened and fluid and trapped air is flushed from 22a, 22g and, after filling vessel A, it is flushed from 22i. When free from trapped air, 22a, 22g, 22b, 22d and 22e are closed to pressurise the system. The pump 18 is vented. Pump 18 is turned on and off and vented again.

When the pump is free of air, with valve 22b and 22e remaining closed, valve 22d is opened and fluid and trapped air are flushed through vessel A and out from valve 22i. The pump 18 is turned on and the pump speed is increased and decreased to remove trapped air through valve 22i. When only a few air bubbles appear in vessel A the pump is turned off and valve 22h is closed.

The collector array is connected to valves 22a and 22g. Valve 22c and 22d are open and valves 22b and 22e remain closed. Valves 22a and 22g are opened. Suction is applied to valve 22i, degassed fluid at atmospheric pressure is applied to valve 22h and valve 22h is opened slowly. Fluid and trapped air is sucked through the pump and the heat exchanger 19, through valve 22a through the collector array and out through valve 22g and 22d, vessel A and valve 22i.

When few air bubbles appeal^' in vessel A. valve 22h is closed, valve 22i is closed, the suction is disconnected and the degassed fluid supply is disconnected. Valve 22e is opened, the pump is turned on and fluid is circulated through the array at high and low speeds to flush out any remaining trapped air into vessel A. It has been found advantageous to open and close valves 22b and 22c during this operation.

When no more air bubbles appear in vessel A, valve 22b and 22f are opened and valves 22d and 22e are closed. The flexible pipes from valves 22d and 22e are disconnected. Valves 22d, 22e and 22h are sealed.

Fluid flow through the array may be controlled by means of the pump speed and valve 22c. The system is now operational.

To vent the pump 18 at any time requires the system pressure to bε increased above atmospheric pressure. To achieve this the pump is turned off, valves 22a. 22g and 22f are closed and pressurised degassed fluid is applies to valve 22h. The pump is vented.

Because the collector contains only a small volume of liquid (typically, < 1 litre/m²) the temperature of the circulating fluid within the collector can increase rapidly when the level of solar radiation increases. The low thermal inertia of the collector means that the system can store useful energy far sooner than conventional flat plate collectors. Also, because the collector contains only a minimum of fluid, when radiation levels fall and the pump is turned off, very little absorbed enei gy remaining in the collector is lost from the system.

Fluid contained in conventional flat plate collectors that have high thermal inertias heat slowly. Thus, under weather conditions that give rise to periods of brief sunny intervals, even though the level of solar radiation might be high at times, because the fluid heats slowly, the temperature of collector fluid may never reach the temperature of water in the storage cylinder and therefore no energy would be stored. By comparison, this invention would store useful energy throughout much of this period.

With flat plate and evacuated tube collectors, the energy absorbent surface 23 heated by the sun"s energy 1 1 must conduct this energy through the thickness of this material and then through the pipes 24 embedded or beneath this layer before the circulating fluid 25 within the pipes can be heated. The resultant heat gradient ensures that the surface temperature of the absorber plate 23, when heated by the sun 1 1, is ahvays greater than the circulating fluid 25 as shown in the graphical representation in Figure 12a.

Unavoidable radiant losses are minimised where the heat transfer from heated surface to circulating fluid is efficient.

In this invention, as shown in Figure 12b, the fluid 10 is heated across the entire surface area of the collector 1 and unavoidable radiant losses are thus minimised. Alternative exemplary methods of achieving this result include heating the fluid 10 directly (see figures 3, 5 and 6), maintaining the fluid 10 in intimate contact with a heated surface 12, 13, 14 (see Figures 4, 5 and 6), heat transfer occurring across an extremely thin energy absorbent layer 12 (see Figure 4) where the efficiency of heat transfer is maximised in comparison to those of flat plate and evacuated tube collectors (see Figures 12a and 12b).

Collectors 1 may be of any shape or size and the inlet and outlet pipes 5, 6 plugged together using commercially available couplings 26 to form any sized array 15 as illustrated in Figure 13 and 14. The collectors 1, 15 may be fitted to roofs, and to walls 41 where south facing roofs are unavailable or if there are design or aesthetic considerations. With wall installations, the angle may be adjusted 42 throughout the year to optimise collection efficiency as shown in Figure 15. Equally, the collectors 1, 15 may be used vertically as curtain walling.

The collector 1, 15 of the present invention has been specifically designed so that it can also serve as a roofing system and is ideally suited for integration into roofing structures where it replaces the need for conventional tiles, etc. The method of incorporation may be similar to the method used for double-glazing units on conservatories etc., and may use standard glazing bars and seals. Two options of how to best achieve this are illustrated in Figures 16a and 16b.

In Figure 16a a collector 1, 15 is positioned on top of roofing felt 27 laid onto the roof joist 28 in place of conventional roofing tiles 29 with flashing 30 placed along an upper edge of the collector 1, 15 and the adjoining roof tiles 29 to prevent the egress of rain, snow, condensation etc into the roof space. Although illustrated abutting roof tiles 29 at the upper part of the roofs¹ fall the collector 1, 15 may also be positioned to abut roof tiles 29 along a lower edge.

Figure 16b illustrates the collector 1 , 15 being located between two tile runs 29a, 29b with flashing 30a, 30b being used to prevent egress along an upper and lower edge of a collector 1. 15.

The positioning of the collector 1. 15 in this manner may be chosen due to the structure to which it is to be combined with, the amount of exposure to be gained, or a combination of each

Looking at the enlarged detail shown in Figures 17, the method of incorporation shown in Figures 16a and 16b can be better understood. Here roofing felt 27 is placed directly onto the roof joists 28 as per a standard roof construction but tins is the extent of the similarities as it is not the addition of batons and roofing tiles that follow but a sheet of plywood 31 with a 'lower stop' 32. The iower stop^" 32 positions the rigid insulation layer 33 that includes recesses that accommodate the inlet and outlet supply pipes 5. 6 of the collectors 1. A number of collectors 1 are fitted together to form an array 1 5 whereupon glazing seals - 34 and glazing bars 35 are fixed into position. For convenience of interpretation flashing and roofing tiles have not been illustrated.

Figure 18a shows a cross sectional view of the system in situ within a roofing system from a different perspective to that shown in Figure 17. Roofing felt 27 is again laid down over the joists 28, a sheet of pi}' or similar material 31 with a 'lower stop' 32 goes on next, followed by a rigid insulation layer 33 and finally the collector 1. The requisite number of collectors 1 is fitted together 26 before glazing seals 34 and glazing bars 35 are finally fixed in position and then the entire assembly is fixed in place using fixings 36.

In Figure 18b, collectors 1 complete with insulation 33 and backing 37 are positioned ^■ between glazing bars 35 and then push-fitted together to permit glazing caps 39 and glazing seals 34 to be attached between and to the collectors 1 and the glazing bars 35 before insulation strips 38 and backing, as required, are positioned and fixed in place.

Claims

1. A solar collector comprising an inlet; an outlet; and a first sheet and a second sheet substantially flat other than any surface relief; the first and second sheet being in close proximity but sufficiently spaced to define one or more cavities through which fluid flows in contact with said sheets, in use, from the inlet to the outlet; wherein at least one of said sheets is a glazed sheet; characterised in that at least said inlet or outlet is formed from a plurality of mouths which span a region through which fluid is inputted and/or removed from said collector; and/or at least said cavity inlet or outlet is formed from a mouth which is substantially elongate in the cavity-spanning direction; and the first, second and an)' intermediate sheets (if present) incorporating no substantial protrusion other than any surface relief.

2. A solar collector according to claim I₅ wherein said mouth and/or mouths substantially spans and/or collectively substantially span one side of said collector.

3. A solar collector according to either of the preceding claims, wherein said sheets are separated by a gap within the range 0.5mm to 1.5mm;

4. A solar collector according to any of the preceding claims, wherein the inner surface of at least one of said sheets is formed in relief and rests directly against the other sheet.

5. A solar collector according to any of the preceding claims, wherein the sheets are both glazed sheets and located behind one or more further glazed sheets

6. A solar collector according to any of the preceding claims, wherein a further sheet with surface characteristics which increase solar energy collection efficiency is sandwiched between the first and second sheet.

7. A solar collector substantially as herein described with reference to and/or illustrated in any appropriate combination of the accompanying text and/or Figures.