NZ200098A - Solar air heater with diffuse aluminium reflector - Google Patents

Description

2000 98 NEW ZEALAND PATENTS ACT, 1953 No.: Date: 200098 23 March 1982 COMPLETE SPECIFICATION IMPROVEMENTS RELATING TO SOLAR COLLECTORS I/Wetx KELVIN JOHN GOLDFINCH, an Australian citizen of 55 Cricklewood Road, Aldgate, State of South Australia, Commonwealth of Australia hereby declare the invention for which £/ we pray that a patent may be granted toxMSt/us, and the method by which it is to be performed, to be particularly described in and by the following statement: - - 1 - CfolloWed by page la) 200098 i/* ;This invention relates to solar energy collectors. ;The problem to which this invention is generally directed relates to the difficulty of collecting solar energy radiation and effecting a transfer of this to another fluid such as for instance air in an as efficient manner as is possible. ;It is well known to provide solar energy collectors in which the material surrounding Che fluid to be heated is black and heat conducting so that the fluid to be heated is heated in this direct manner. ;The collection efficiency of such collectors has been found to be generally very low and it has not always been economic to use such heat collection as compared to other forms of energy supply. ;According to this invention there is provided a solar air heater including a confining chamber with a forward side of the chamber being of a material substantially transparent to solar radiation, solar radiation absorber members arranged to extend across a collection area within the chamber, and an aluminium diffusing reflective surface which extends across an area at least as large as the collection area in the rear of the chamber, the absorber members comprising a plurality of elongate members arranged in substantially mutually parallel relationship and having separation gaps between adjacent members such that a proportion of solar radiation may pass between the members to be diffusely reflected onto rearwardly located faces of the members whereby thermal radiation from the absorber members heats air passing through the confining chamber. ;2. ;200098 ;By carefully selecting the various criteria specified, it has been found that by using black absorber faces, both the forward and rearward absorber faces are being irradiated by solar radiation and this can be distributed over a substantial absorber area and the somewhat surprising result is that collected energy can be significantly higher with respect to a given collection area than has hitherto known to be possible from other solar energy collectors. ;Preferably, the reflective surface is such that there is a high degree of reflectivity but it is an important feature that this be such as to effect a diffusing or with respect to the sizes of the absorbers some randomness of reflection direction. ;Preferably, the reflective surface can be from a substantially non-corrosive surface and can be randomly shaped so as to have a number of very small ;irregularly orientated face reduce all-up reflectivity but effect a randomness of s which to any s the dire thereby do ignificant ct ion. ;not extent ;In this way, in a particular instance, the efficiency of the solar energy collector made according to this invention has a high efficiency even when the source of the solar radiation, that is typically the sun, is not directly perpendicular to the general collection area plane. ;Indeed, with respect to a preferred embodiment, there has been shown to be an improvement in efficiency as the direction of the sun alters from a direction exactly perpendicular from the collection area plane. ;To optimize the collection efficiency, certain features have been found to be of particular use and in a preferred arrangement, the solar radiation absorber member or members comprise a plurality of elongate members, each of substantially constant cross-sectional shape along their length and each parallel one with respect to the others and each separated one with respect to those adjacent by a separation gap to allow the said significantproportion of solar radiation to bypass the members and be directed directly onto the reflective surface. ;Preferably, the shape of each of the elongate members is such that their rearward face is a^ convon* Qp/i shape in at least cross-section and their forward face is of generally convex shape.

Preferably, the relationship between the area 200998 4. of the separation'gap and that otherwise covered by the absorber member or members is that the area covered by the separation gap is substantially one quarter of the collection area.

Likewise it has been found that the relationship between the position of the absorber member or members with respect to this reflective surface is also of importance and the depth of the absorber members, that is from a forwardmost position to a rearwardmost portion is substantially -equal to the distance from the rearwardmost portion of the absorber member or members from the reflective surface.

The characteristic of the reflective surface must be such as to cause a general randomness of refLectivity without losing the degree of reflectivity necessary to provide good efficiency.

It has been found that a regular dimpling or patterning of a reflective surface will achieve sufficient diffusion of reflection provided that the size of the repeating pattern on the reflective surface is significantly smaller than the individual size of any reflective member so that in comparison to the dimensions of the width of the absorber member the pattern size is very small.

This is obviously a matter of degree and it has been found that the more random shape on a smaller individual portion of the reflective surface being independently orientated will give the better e f f i i 2 000 A preferred reflective surface comprises an alumium foil which has been first crushed and then substantially straightened to cover the reflective surface leaving however the substantially random 5 reflective, character of the surface shape.

The application has been thus far preferred to be air but there is no limitation as to the means by which the heat held should be taken and in a general form then the steps can include passing 10 a fluid along the absorber member or members so as to be generally in contact with at least substantially all of the absorbent surfaces.

The solar radiation absorber member or members are preferably of black external colour or of any 15 character such as to promote absorption in the manner of a black body.

It is believed by providing that the solar radiation either directly or through the reflection on substantially all of the absorber faces of the 20 absorber member or members that this provides the improved efficiency discovered.

If the radiation from a high temperature body falls onto a body with a much lower temperature and is re-irradiated from that lower temperature 25 body it is substantially of longer wavelength and is therefore much more likely to be entrapped within a confining body.

By substantially irradiating both the forward and rearward absorber surfaces, it is believed that 30 this generally keeps the surface temperature of 2000 .0\ the absorber members at a lower temperature and such that the heat will therefore be more likely retained within a confining body and especially by arranging for multiple reflection on the rearward 5 side against the reflective surface will also significantly assist in improving efficiency of collection.

The invention will be better understood when referred to a preferred embodiment and this will now be described with the assistance of drawings 10 in which : FIG 1 is an illustration of the first preferred embodiment shown in cross-section along the lines 1 - 1 of FIG 2, FIG 1A shows the preferred disposition of the absorber members in the said preferred embodiment as shown in FIG 1 and their relationship specifically to the reflective surface, FIG 2 is a plan view of the first preferred embodiment as shown in FIG 1, FIG 3 and FIG 4 are side and end views respectively of the first preferred embodiment, FIG 5. is a perspective view of the preferred embodiment as shown in the preceding FIG 1 to 4 inclusive, FIG 6 is a perspective view of a second preferred embodiment - this embodiment incorporating a water heating coil at an upper end pf the confining chamber, and 7.

FIG 7 is a graph showing with respect to the first preferred embodiment the incident modifier . results illustrating the way in which efficiency is improved when the angle of solar energy is other than at 90 degrees to the collection plane.

Referring to the first preferred embodiment as shown in FIGS 1 through 5 the confining chamber 1 is of rectangular proportions having sides 2 and ends 3. For the purposes of this description and throughout the specification, reference is made to a forward direction and a rearward direction which is used for the sake of convenience and is intended to relate to an expected direction of the collector panel 1 when this is in a collection position that is generally with the front face 4 adapted to first receive radiation from the source of solar energy which would normally be the sun and therefore the backface 5 being that furthest away from the source of solar energy.

Within the confining chamber 1 are a plurality of solar radiation absorber members 6 each of elongate shape and each of constant cross-section along their length and each parallel one with respect to the other and spaced apart from each other by a separation gap 7.

The members 6 each are shaped so that there are two legs 8 and 9 which are at right angles one with respect to the other each of equal length and each member 6 is arranged so that the apex of the shape 10 is forwardmost and the ends of the legs 8 and 9 in each case are rearwardmost. 2000 In this way there is a concave shape 11 on the rearward side of each,absorber member 6 and a convex shape on the forward side of each absorber member 6.

In the preferred embodiment the plurality of absorber members 6 are held in collective arrangement by baffles 12 which besides holding the absorber members 6 in their respective alignments also allow a passage 13 between an upper edge of each baffle 10 12 and the rearward facing portions of each absorber members 6 so that air can be driven therethrough but in such a manner as to promote some turbulence and therefore collecting efficiency as the air passes the respective surfaces.

The relationship between each of the absorber members 6 one with respect to the other and each with respect to the reflective surface is specifically as shown in FIG 1A which is shown to scale with respect to the preferred embodiment.

The reflective surface 14 has been found to be preferably be comprised of aluminium foil which has been first crushed and then straightened to a degree so as to generally leave a planar shape but nonetheless individual portions being very randomly 25 shaped and therefore able to effect in random direction light falling thereon or other solar radiation but effecting a diffusing of this.

The reflective surface has been extended to the sides 2 and ends 3. 000 98 The forward face of the confining chamber 1 being 4 is compris'ed of a transparent sheet material such as a high transmittable glass and this is held in convenient manner by resilient packing 15 and . 5 edging 16.

The side ends and rear face 2,3 and 5 of the confining chamber 1 are comprised of a suitable insulating material which can comprise simply of a wood composite material or it can be improved 10 by providing fibre insulation but the preferred embodiment as shown is as described.

There is a backing board 17 onto which the reflective material is directly adhered.

An air inlet 18 and an air outlet 19 are located 15 through the rearward face 5 through which air can be directed for heating.

In use the panel as shown is held in a direction so that its forwardmost face 4 is generally at right angles to the direction of the sun from where the 20 energy will be received and of course that angle will be most appropriate for the latitude of the location.

The external collector surfaces of the absorber members 6 are as black as can be effectively achieved 25 by conventional techniques and in the arrangement described and with a test procedure conducted according to the ASHRAE Standard 93/77 (Methods of testing to determine the thermal performance of solar collectors the following results were achieved. . 200098 It was first found that the incident angle modifier rises as the incidence angle increases and this is shown in FIG 7 in which the incidence angle modifier is shown as Kcc<; and the incidence angle is shown 0 so that at an incidence of 30 degrees there is an incidence angle modifier of approximately of 1.15. The latitude of the test was 38 degrees south.

For testing, the collector tilt for this latitude was 44 degrees.

An efficiency of collection based on glazed aperture area of approximately 79 percent at a zero degrees of incidence was achieved.

Referring to the second embodiment as shown in FIG 6 this illustrates a confining container 20 which has absorber members 21 held together by baffle plates 22 and in a spaced relationship to crushed and then straightened aluminium foil reflective surface material 23.

Located within the same confining chamber 20 and at an upper end thereof is a metallic coil 24 spaced above the reflective surface material 23 and having a black external coating thereon so that fluid passing through the inlet 25 and outlet 26 will be subject to an effective heating effect both by reason of direct solar radiation thereon, and by reason of heating from the air previously heated from the absorber members 21.

Claims (8)

11. 200098 WHAT t/WE CLAIM 13:

1. A solar air heater including a confining chamber with a forward side of the chamber being of a material substantially transparent to solar radiation, solar radiation absorber members arranged to extend 5. across a collection area within the chamber, and an aluminium diffusing reflective surface which extends across an area at least as large as the collection area in the rear of the chamber, the absorber members comprising a plurality of elongate members arranged in 0 substantially mutually parallel relationship and having separation gaps between adjacent members such that a proportion of solar radiation may pass between the members to be diffusely reflected onto rearwardly located faces of the members whereby thermal radiation 2 from the absorber members heats air passing through the confining chamber.

2. A solar air heater as in Claim 1 wherein the solar radiation absorber members have a black surface.

3. A solar air heater as in Claim 1 or Claim 2 wherein each elongate member has a concave rearward shape and a convex forward shape.

4. A solar air heater as in Claim 3 wherein each member includes two legs of substantially equal length and aligned in cross-section at substantially 90 degree one with respect to the other.

5. A solar air heater as in any one preceeding claim wherein the separation gaps extend over substantially one quarter of the collection area. 12. 200098

6. A solar air heater as in any one of the preceding claims wherein the depth of each member is .substantially equal to the distance of the members from the reflective surface.

7. A solar air heater according to any one of the preceding claims wherein there is further included means to effect passage of air through the confining chamber to collect heat, across the faces of the solar radiation absorber member or members.

8. A solar air heater^substantially as described in the specification with reference to and as illustrated by the accompanying drawings. {Sbl+N COiQflt^Ori Cy hia/sfeslr authorised Agents. A. J. PARK & SON, PER _f!l