CA1125126A - Unitary solar collector - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A unitary solar collector for transfer of thermal energy which is a synthetic thermoplastic unit. The unit has a solar-energy transmitting region and a solar-energy absorbing region. The unit is useful for heating purposes.

Description

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U~ITARY SOLAR COLLECTOR

This invention relates to synthetic-plastic, lor.~ cost c~llectors for thermal energy from solar radia~ion.
A solar collector is the essential part of e~uipment which t-znsorms solar radiant energy to some other usefu7 energy orm.
'~ 2 solax collector, energy transer is from a distant source o r2diant energy like the sun to a fluid. Broadly speaking, .
s~lzr collectors may be used with~or without radiation concen-e.D ion. In flat plate collectors which per~orm without radiation , c~c~n.ration, which are the subject of the invention, the area .
~3sorbing solar radiation is the same as the area interceptin~ soIar

-2~la.ion. Solar collectors o the rigid, ~lat plate ty~e present 2 azrticular set o problems in the transfer or collection o energy 2~d in zssociation with conduction and radiation losses. Some Q~ the ?-oblems associated with other types of solar collectors (e.g.f~inyj 2n~ solutions suggested in their manufacture and use cannot readily-be ap~li2d to collectors of the flat plate type. ,~
Conventional flat plate type collectors of solar energy ,~n~rally have a solar energy absorbing surface which m~y be ~iac~ eans or a transferring the absorbed eneFgy to a fluid, and 2n 2~v210pe transparent tb solar radiation over the solar ~ !
z~so~7~ing surface to reduce convection and radiation losses.
G-n~r~lly the 1uid which is circulated is water (often with glycol zntiLree~e added) or air.

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The principal applications of such collectors is in solar heating systems for homes and other buildings, hot water heaters, swim~ing pool heaters, heating ~ater for solar distillation and other such uses. The units can be us~d for air conditioning when operated at high temperatures in con]unction t~ith absorption-type refrigeration units.
Flat plate solar collectors are usually mounted in a stat-ionary position as an integral part of a wall or a roof structure 11, in solar house heating. A conventional collector has been described to consist of a wood or metal frame with a flat black absorber inside. Material such as fiberglass, polymer foam or sawdust is used underneath the absorbing surface for insulation and the top of the frame is covered with a thick win~ow glass.
The absorber is a black-painted metal sheet containing a plurality o~ spaced tubes for a coolant. Such flat plate collectors are described in "SOLAR ENERGY THE~L PROCESSES" by Duffie and Beck~ n, ~iley Interscience Publication, John Wiley & Sons, New York 1974 and "SOLAR ENERGY TECHMOLOGY AN~ APPLlCATIONS" by J. Richard Williams, Ann Arbor Science, 1974, pages 120-125 and pages 9 and lO, respectively.
The detailed description of the operation of each one of the components of the solar collector is a fairly complicate~ problem See General Characteristics of Flat Plate Solar Collector in the firs~ of the tl~O above-mentioned references, pages 123 and seq.
In the construction of a flat plate energy collector one seeks to maximize the various factors which influence the collector's performance. The construction of a flat plate solar energy system is thus influenced by numerous variables; adjustment to maxi.mi7,e ~ 5~

one ~ay often adversely effect another variable, thus decreasing t~e overall desirability of this system. Moreover the flat plate solar collector may not be considered as a single entity because it is mounted as an integral part of a structure such as a roof, ~hich creates new areas of problems. Typical of these is that the collector is exposed to extreme variations in temperatures and in climatic conditions which influence its mechanical ;ntegrity and stability differently from the roof structure itself.
For many years the attempts and problems to build satisfact~ry solar heater systems of various types have been reflected in the patent literature. For instance U.S. Patent No. 3~387,602 to Thomason reports shattering of a solar heat collector and .~e rapid failure of a tough plastic film when used as an inner glazir.g material in a solar heat collector.
Vario~ls types of solar panels have been disclosed in the patent literature. For instance see U.S. Pa~ent Nos.
2,3~8,476; 2,553,302; 3,077,190; 3,254,643 and 3,387,602.
Th2se patents underscore the difficulties and the various atte~pts to overcome them. For instance, Thomason in U.S. Patent ~o. 3,254,643 suggests attaching a reflective cover section to increase the intensity of available solar energy on the collector. The heat collector is of a complicated structure including insulation, sheet metal and plastic or glass. The heat collecting metal is a screen or plastic. In U.S, Patent No.

3,387,602, Thomason recommends the use of certain parts and -a~erials including fibrous materials as a solar heat collecting .

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overlayment to overcome the problems of heat expansion and contraction due to temperature changes.
. The patent to Meagher, U.S. Patent No. 3,239,000 discloses a box-like construction which includes tubular pl~stic sections;impregnated with carbon ~lack.~

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Flexible collectors are also known. In U.S. Patent No.
3,022,781, Andrassy suggests using a flexible plastic bag as a solar heater unit. Thomason in his more recent U.S. Patent No. 3,369,539 also proposes an improved solar heat collector which .is a ~lear plastic sealed bag..
It-is also noteworthy that the most recent pa~ent to issue in this field to date, U.S. Patent No. 3,859,980 to Crawford, teaches in its review of the prior art (column 1) that the prior art devices include rigid structures which have serious drawbacks such as difficulty in handling, special preparation of the roof, complicated structures, are expensive to manufacture and to install. In 1975, when the Crawford patent ~ssued, he tho-~ght best to advocate, rather than the rigid structures of .
the prior art, a flexible hea~ing unit which may be rolled or folded and may be easily placed on a roof or other suitable place of use, and unfolded into operative position. The solar heating unit whi.ch Crawford developed consists of pairs of spaced mani- 1-folds and a~plurality of tubes connected to and extending between the manifolds so that the intermediate tubes present a maximum surface to be acted on by the solar energy or for heating fluid flowin~ through them. To provide air insulating spaces 1~ 51;'~

both above and below the intermediate tubes in the unit, an envelope ror clear material, such as plastic, closes the entire ~nit and the two outermost tubes hold this plastic envelope in spaced relation. The advantage of the Crawford solar heating uni~ is its flexible and readily dismountable construction wherein no glass or other rigid transparent cover over the device is required.
An article in Plastics World in May 1973, page 32 discloses an ABS heat exchanger for a swimming pool constructed with a series of internally channeled heat exchange panels with an inlet header at one end and a collection header at the other~ -adapted with connections to the pool and the existing pumping system. Carbon black is added to improve heat absorption.
Panels constructed for swimming pool water heating are generally not suitable for use in conjunction with solar heating of homes or other buildings, as solar collector panels, especially because they lack the efficiency required of the system at higher temperatures.l 501ar collector panels available on the market consist of 1.
several components including a collector box, a cover plate - -(generally glass or plastic), an absorber plate (generally ~etal), mounted in a mounting block, a cover assembly and various necessary mounting and other assembly fixtures. The panels' construction generally includes insulation like foam. Typical solar collector panels are advertized by such manufacturers as Chamberlain as Solar Collector Panels, PPG under the name of Baseline Solar Collector and Solar Systems, ~nc. under the name i~5~

of Spectro Collector Module. A typical panel of 3 x 7 feet weighs 190 l~s. All of these panels require assembly of their components prlor to installation and their mounting into place individually to cover the desired area.
A major problem in utilizing solar energy for heating buildings and for other like applications has been the high cost per unit area of the collector panels. As can be seen from the revie~ of the prior art, the high cost of flat plate collectors is principally due to their complex and multi-component structures.
requiring substantial hand labor. These problems are further c~mplicated because the structures are not uniforml~ m~de of one material but are fabricated of metal, plastic (rigid or not)l , -wood and other type materials. These materials, of course, have differentiaL expansion and contraction due to heating and cooling which require special assembly and co~ponents .

There is thus a serious need for low cost solar energy collectors for thermal energy from solar radiation. The solar flat panel collector of the present invention is a unitary 1, structure made of a single material, a synthetic thermoplastic w'nich is a one piece structure free of the separate, auxiliary .. . .
parts and structures commonly used in the prior art collectors.
The thermal energy collector of the invention is a un;t of which the cost per unit area is remarkably lower than what has been achieved theretofore. Moreover, through a one piece structure, the collector of the invention forms with the structure to which lZ51'~76 ~ I

it is attached, such as a roof, a dimensionally stable and dynamic yet operational structure.
The objects of this inventions are manifold. One important object of the invention is to provide a flat panel sol~r collector which is adapted to be used in modular arrangements to form larger panels. Another object is to provide such a panel which alone or in conjunction with others is a~aptedsto-be affixed in mounting arrangement with or in communicat;on with the area or environment to be heated. Another object is a solar panel which is dimensionally stable and dynamic when such mounting relationship notwithstanding exposure to great variations of temperatures and climatic conditions.
Another object is a solar panel which is one type o .
material, a synthetic thermoplasticc in which certain pcrtions are solar energy collecting~and other portions are transparent or translucent to solar energy. Another object is a one piece unitary solar panel which is of great dimensional strength, of light weight, ad pted for simple installation, fabrication, of improved asthetic appearance, free of metal or other non-plastic .
components, and free of joints.
Another important object of the invention is to provide for a low cost flat panel collector which is of coextruded synthetic plastic, that is a structure which from its formation is unitary. Another object of the invention is to provide a unitary solar collector which does not require an externaL f~ame. Another ob3ect of the invention is to provide a system which can withstand - , `
freezing of water because of its-~ absence of joints and its 5~G

deformability without breakage with the expansion of freezing water: this permits its use in direct heating of potable water supplies. (Systems for solar heating which must use glycol-water mixtures are required to be separated from domestic hot water lines with a double heat exchanger). Yet another object of the invention is a solar collector which has vertical sections or fins which are capable of absorbing thermal energy. Another object of the invention is to provide a solar collector for transfer of thermal energy, which areas cooperate with an area which is transparent to solar radi-ation.
Yet another important object of the invention is the provision of a coextruded solar collector which has several layers adjacent to each other, some sandwiched in between a pair of other layers. Another object of the invention is a solar collector having provisions for channels for heat transfer fluids which can be air or liquids such as water or mixture of water with organic liquids or such organic liquids alone.
Yet another important object of the invention is a solar energy collector constructed of a coextruded, unitary, synthetic polymer which has energy absorbing channels and energy transmitting channels. Another object of the in-vention is to provide such a solar energy collector made of a W-stabilized polycarbonate, such as known under the trade marks "Lexan" or "Merlon", and a poly (methylmethacrylate), such as known under the trade mark "Plexiglas". Yet another important object of the invention is a rigid solar flat panel which is unitary and where the single material of which it is fabricated complies with preselected requirements of tensile strength, tensile modulus, elongation, impact B

1~ 5~i'6 streng~h, hardness, thermal expansion and thermal conductivity and other physical structural requirements. Another object of the .
invention is to p-~-ovide unitary solar collectors which are available in great. lengths (e.g., 30 ~eet) without joints or other discontinuities. Other objects of the invention will become apparent from the description including the drawings, wherein s~

Fig. 1 is a perspective view of the inven-tion applied to a roof structure in longitudinal alignment, partially broken away to expose interior construction details.
Fig. lA is a pérspective view of the invention applie~ to a roof structure in transverse alignment, partially bro~en away to expose interior construction details.
Fig. 2 is an isometric view of a portion of a coextruded solar collector with double window.
Fig. 3 is a partial, sectional view of a coextruded solar collector with single window. ~
Fig. 4 is a partial, sectional view of a coextruded solar collector with single window and having triangular channels.
Fig. 5 is a partial, sectional view o a coextruded solar collector having double window and an insulating air layer backin~.
Fig. 6 is a partial, isometric view of a solar collector -with coextruded foam backing.
Fi~. 7 is an enlarged, cross sectional view through a hea~er taken along line 7-7 of Fig. 1.
Fig. 8 is a partial, sectional view of a coextruded solar collector including water channels.
Fig. 9 is a partial, sectional view of a modified solar collector including circular water channels.
Fig 10 is a cross sectional view similar to Fig. 7 showing a I `
modified header construction suitable for use with an air system Fig. lOA is a partial, isometric view of the construction of Fig. 10.

~1~'5~6 Fig. ll is a view similar to Fig. lO showing a modified .eader suitable for use with a water system.
Fig. llA is a partial, isometric view of the construction or Fig. 11 Fig. 12 is a cross sectional view of another embodiment of a complete coextruded solar collector, which is symmetrical with respect to the center plane.

There follows a description of the preferred embodiments o~
the invention:
Referring now to the drawings, there is shown in Fig~ 1, a plurali~y of solar collector panels 10 which may be conveniently a~plied to the roof 12 or wall of a building by affixing the solar collector panels directly to the roof rafters 14 or to suitable '.~2l 1 framing members, or to overlays of either of these. For ?~rposes of illustration, the solar collectors 10 are arranged with their channels generally horizontally oriented as indicated by the nu~eral 16. It will be appreciated that the solar collectors 10 could also be arranged with their channels generally oriented p2r21~el to the vertical structural components o the building as illustrated in Fig. LA and as indicated by the -numeral 18. The :~orizontal and vertical orientation of the solar collectors 10 will be hereinafter more fully discussed in detail.
Generally, the solar collectors 10 are afixed to the roo-E
12 ~7ith their respective channels in aligned, continuous, juxtaposed relationship. The channels of the various solar collector panels 10 can be joined together in end to end relationship to form a plurality of aligned, continuous, fluid carrying conduits or the 1~ ~ 5~6 collectors 10 could be continuous -throughout the full extent of the roof 12. However~ this would not be necessary since an advantage is that any length one~piece panels of the invention can be manufactured, as by coextrusion. When the solar collectors lO are arranged in generally vertical relationship relative to the roof 12, horizontal headers 20 would be endwardly connected to the ends of the solar collectors lO to carry the solar heated fluid from the roof in the manner hereinafter more fully set forth. When generally horizontally arranged channels are employed by positioning the solar collectors 10 in hori~ontal alignment as illustrated in Fig. 1, generally verticalIy arranged headers 22 are provided at the roof edges to receive therein the solar heated fluid from the ends of the channels o the solar collectors to direct this fluid for its use~ul purpose in the manner hereinafter more fully explained.
In the construction of Fig. 1, the solar collector panels 10 are applied over a plywood or other sheet material backing 13 whicn is conventionally secured to the roof rafters 14. In the construction of Fig. lA, solar collector panels 10 are directly affixed to the rafters, as by brackets 49. Insulation 11 preferab1y is applied below the backing 13 between adjacent rafters 14 in the -usual manner. The panels 10 are arranged in juxtaposed relationship with the seams 19 which are defined between adjacent collectors filled with a waterproof material such as caulking. The collectors lO are firmly secured to the roof at multiple locations by employing ~steners 17 which are affixed into the roof rafters ~L3!Z~

14. Washers 15 are held by the Easteners 17 to secure adjacent pairs of solar collectors. By employing a plurality of fasteners 17 and washers 15, an extremely sturdy, element resisting exterior roof construction can be provided by the solar collectors 10.
Re~erring now to Fig. 2, a preferred embodiment of a .
coextruded solar collector 24, is illustratedl which pree'rably incorporates the basic structure of the system in a unitary member which is coextruded or duoextruded in a process whereby two or more extruders (not shown)~are joined into a common die (also not shown) so as to form an extruded shape having a plastic or different plasticsone of which is opaque and the o~her transparent to solar radiation in defined regions. It is contemplated that the solar collectors 24 will be fabricated of one piece unitary construction of width controlled by the capacity o~ the e~truder itself and of any desired length, for example, long panels of twenty feet in length or more, i desired? this bei~g a noteworthy advantage of the panels of the invention.- By utili7ing .
the extrusion process to fabricate a solar collector 24 of unitary construction, the conventional framing members and other metallic or other parts which were always necessary with prior art types o~
solar collectors can now be completely eliminated.
Generally, the solar collector system of the present invention is fabricated by the extrusion o~ a transparent covering area generally designated 26 and an integral opaque, black or dark solar radiation absorbing area adjacent thereto and generally I

llZ5~6 designated 28. The transparent covering area ~6 comprises generally an outer transparent window or panel 30 and an interior transparent window or sheet 32 which is spaced inwardly from and paralleL to the exterior window or panel 30. The transparent covering area 26 is subdivided into a plurality of parallel~
longitudinally extending channels 36 which are arranged in adjacent rows and defined one from the other by a plurality of transversely spaced, longitudinally extending transparent ribs' . _ __. . . . . , .. ... ., . . ... . . ....... . ,. ... ,.. ,.. . . ", .. __._ ,_~. ..
34. The term "transparent" as used herein means transmissive to th~
ma;or part of the solar spectral radiation; it is intended to include both optically clear windows or with translucent windo~s, i.e. those with diffuse transmission. The transparent exterior and interior windows 30 and 32 and the plurality o~ transparént ribs 34 are extruded from the same material and rom the same ~ie to form a unitary structure without the need for cutting, shaping, joining or otherwise working the material after the ,extN sion proce~s has been completed.

The opaque, black or dark colored solar radiation absorbing area 28 is integrally formed with the transparent covering area 2 and includes a solar radiation absorbing base 39 of blac~
material such as suitable polyacrylic pigmented with carbon black. The area 28 is subdivided into a plurality of parallel longitudinally extending channels 38 which are arranged in ad,jacent rows and defined one from the other by a plurality o t~ransversely spaced,longitudinally extending ribs 40. Ribs 40 are extruded of the same solar radiation absorbing material as base 3~.

~ ~ 5~v6 The black ribs function to enhance the strength and rigidity of the unitary solar collector and, since they are absorbing members, provide additionaL surface area for heating the heat-transfer fluid, which is particularly helpful when heating air.
As illustrated, the transparent covering system channels 36 may be twice as wide in their transverse dimension as channels 38 comprising in the solar radiation absorbing area 28. Trans-paren~ ribs 34 of transparent covering area 26 may be extruded coextensive with some of the black material ribs 40 of black absorbing area 28 as illustrated, or transparent ribs 34 may be laterally o~fset -~rom black material ribs 40, as may be desired. Preferably, transparent ribs 34 align over every other black material .
absorbing ribs 40 to increase the overall strength of the system. It is contemplated that channels 36 comprising the transparent covering area 26 will normally be filled with an -insulating fluid such as an insulating air layer to increase the thermal efficiency of the system. Channels 38 comprising the opaque, black or dark colored absorbing area 28 are normally filled with a heat transfer fluid which is utilized for building or other space heating purposes. Fluids such as air, water, or mixtures of water with a polyol, like ethylene glycol-water mixture or other anti-free~e solutions may be conveniently employed within channels 38.
In the embodiment illustrated in Fig 3, there is shown a very simple, basic design of a coe~truded, unitary ~lat plate solar collector 42, which is extruded into a single windo~
design. In this embodiment, a plurality of longitudinally ., ' !

extending heat transfer fluid channels 50 are de~ined between a clear ~indo~J or cover 44 and a black or opaque solar radiation ~bsorbing base 46. Preferably, a plurality of ribs ~8 are extruded of the sam2 black or opaque material as the base 46. It is contemplated that ribs 48 could also be ~abricated o~ the same. -clear plastic as the clear window 44 if so desired, ~or certain .
applications where the greater thermal eficiency o~ the black rib system as illustrated would be necessary or desirable.

Referring now to Fig. 4, there is shown a second modified singIe window, coextruded, flat plate solar collector 52 which is fabricated by coextruding and which inc~udes a clear window or cover 54 which is spaced above a black or opaque material bsse 56 a sufiicient distance to provide a plurality of longitu~.in-ally extending alternate channels 60, 62. A plurality ribs o~
black material 58 angularly extend between window 5~ and base 5 to provide.a plurality of adjacent, alternately inverted, trian~ular cross sectional shaped channels 60 and 62. In the embodiment illustrated~ ribs 58 are pre~erably abricated of black solar radia-tion-absorbing material, the same as in base 56. Under certain conditions and in certain applications, it is conceivable that certain or all ribs 58 would also be fabricated o clear plastic similar to the plastic utilized in window 54, should such a unit be require~..

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In utilizing the single window solar collector 52 of Fig. 4, several different use modes are possible. In the first mode of op2ration, the heat transfer fluid (not shown) could be transpor-ted in the alternate channels 62 with the channels 60 on each side being utilized as insulating dead air spaces. Similarly, the h~at transfer fluid (not shown) could be transported in the alternate c~annels 60 with the channels 62 being utilized as dead air spaces.
In anot'ner mode of operation, the heat transfer fluid (not shown~
c~uld be transported in both sets of adjacent channels 60 and 52 n another mode o~ operation, special manifolding (not shown) coul~
be pro~ided to enable one set of channels 60 to serve for reheating the heat transfer fluid (not shown) and the other ~e~-of adjacent alternate channels 60 could be utili7.ed for final heating of the heat transfer fluid. Special fittings (not illu~trated) would be designed for each system so that a header system would be provided which cnuld function to properly -direct the heat transfer material at the respective ends of the trizngular cross sectional channels 60 and 62 -18- `

~~5~ ,~6 Referring now to Fig. 5, there is illustrated a sectional view of a coextruded solar collector of the double window and insulating air layer backing type. This modified solar collector 64 which represents a preferred embodiment of the invention comprises generally a plurality of adjacent, longitudinally extending hea~ transfer fluid channels 76 which are defined between black base 70 and clear window 68. Heat transfer fluid channels 76 are extruded to extend the length of collector 64 in adjacent, parallel arrangement. Each channel 76 is defined from its adjacent channel 76 by rib 82 which is illustrated as being extruded from the same black plastic as black base 70. In ~, this embodiment ? a clear plastic solar radiation insulating ~
air layer 86 is extruded adjacent clear window 68 of heat transfer ~luid layer 88. Insulating air layer 86 is subdivided into a plurality of longitudinally extending channeis 74 by æpaced ribs ~0 which are fabricated of the same clear plastic as clear window 66 which defines the outer extent of inæulating air layer 86.
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As illustrated, clear plastic ribs 80 of insulating air layer 86 coincide with and register over alternate hlack plastic ribs 82 comprising the heat transfer layer 88n Heat trans~er layer 88 is defined by black ribs 82 and black base 70 and insulating air layer 86 is defined of all clear plastic including clear win~ows 66 and 68 and interconnecting ribs 80.
Second insulating air layer 90 is formed over heat transfer ~ayer base 70 and includes ~lack cover 72 which is spaced rom sol~r radiation transfer layer base 70 a sufficient distance to define second insulatin~ air layer 90. A plurality of black ribs ~' are extruded to extend between thé black base 70 of heat transf.er la~er 88.and black insulating air layer cover 72. Preferably~.blac~ .
ribs 84 register below alternate ribs 82 which de~ine channels 7 comprising heat trans~er layer 88.
~ s ill~strated, ribs 84 defining channels 78 in insulating air layer 90 do not register below the ribs 80 which define cbannels 74 of the upper insulating air layer 86 or purposes of stability;

However, it will be appreciated that ribs 84 o insulating air layer 90 could register below ribs 80 of insulating air layer 86 if desirable or necessary for any particular application. Additionally, more or fewer ribs 80, 82, 84 may be coextruded to de~ine channels 74 ? 76, 78 of all the same size, of all different sizes or of . ~
so~.e havin~ the same sizes and some o different sizes if so 11, desired for a particular application, and still ~all ~ithin the .
~eaning and scope of this invention. ~ikewise the channels can be of different shapes, as sho~m urther ~elo~. It will al~so be appreciated that clear plastic window 68 of heat transer layer 11 Z 5~ 6 88 can be fabricated i.e. coextruded of the same black plastic as ribs 82 in part and base layer 70, if so desired and still fall within the meaning and scope of this invention. As described further below it is preferred that the panel be of coextruded plastic wherein t~e solar-energy absorbing region 70,82, 72 has a higher softening temperature than the plastic of which the solar-energy transmitting region 66, 68, ' 80 is made.
Another modified coextruded solar collector 120 is illustrated in Fig. 6 which includes a plurality of insulating or solar radiation transfer layers 122, 124 which are coextrude~
to include a plurality of clear material surfaces 126, 128 or black surfaces (not illustrated) which are sub-~ivided into c'nannels 132,134 by a plurality of ribs 136,138 in the m~nner hereinbefore set forth. An insulating layer 140 is integrally formed as the bottom surface 130 of channels 134 by known proces~es to provide a solar collector 120 with its insulating-foam layer 140. ~he foam can be any synthetic plastic which is extrudable and foamable such as described further below. ', In Figs. 8 and 9, there are shown cross sectional views o~
coextruded solar collectors 156, 158 which are particularly adaptable for heating water or water-based solutions for such applications as hot water heaters, heaters for buildings, swimming pool heaters, etc. In the embodiment illustrated in Fig. 8, a unitary, coextruded structure 156 is illustrated including a clear plastic window 160 which admits solar radiation in the manner hereinbe~ore set ~orth.

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.~ plurality of clear plastic ribs 162 depend from the windo~
160 in spaced relationship to define a plurality of insulating air channels 164. The ribs 162 are coextruded and join the blac~
absorber surEace 166 in a unitary construction. A plurality o~ water carrying channels 170 are deined between the black absorber surfa'ce 166 and the base 168 by a plurality of ribs 172.
Tn the embodiment illustrated~ the base 168, the ribs 172 and'the absorber surface 166 are all fabricated of the,same or similar black plastic. As illustrated, the black plas~ic ribs .
zli~n beneath the clear plastic ribs 162. It is also within the scope of this invention to extrude the black plastic ribs 172 in ofrset relationship to the clear plastic ribs 162. The e~bodiment illustrated in Fig. 8 is,similar in construction an~ concept generally to the-embodiment illustrated in Fig. 2 with the. ' , exception that the water channels 170 are defined by a black 2bsorber 166 rather than a clear window layer 32. Additionally~
due to the increased heat carrying capacity of water over air~ ' t'ne ~ater channels 170 can be,constructed smaller than the ' .
air carrying channels 38..
.In the embodiment illustrated in Fig. 9, the unit 158 is fabricated with a top clear window 174 spaced above a black pla~ic base 176. A plurality of water carrying channels 188 are . , defined within a plurality of juxtaposed black absorber surfaces , 180 which are tangentially arranged in the coex~rusion process..
Each black absorber surface 180 is joined to the clear window ' 174 by a clear plastic rib 178. The black absorber surfaces 1.

~22- ' .

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1~0 are also joined to the base 176 by the black plastic ribs 182. The clear plastic ribs 178 and the black plastic ribs 183 serve to unify and strengthen the structure and respectively'to ad~it solar energy and to absorb solar energy. The blac~
~bsorber sur~aces 180 as shown define hollow~ cylindricaL
ch~nnels 188 ~or water carrying purposes. It will be appreciatea .hat channels of other cross sectional confi~uration may also be formed durîng the coextrusion process an~ still fall within the ~eaning and intent of this invention. The clear window 1~4, 2djacent clear plastic ribs 178 and upper portions o~ the ~lack absor~er surf,aces 188 define therebetween a plurality o. lon~itudinally,extending insulating air channels 184.
S ~'larly, the black plastic base 1767 adjacent blac~ ~lastic ~ibs 18~ and portions of the black absorber sur~aces 180 de~ine t~erebetween a plurality of juxtaposed, longitu~inally extendin~
dead air channels 18~ for back insulation purposes.
Referrinv now to Figs.10 and lOA there is.illu~tratea header 22 which is connected to the ends 150 of a plurality of solar coex~ruded collectors, for example, collectors 24, The header - -~22 m~y be extruded from a thermoplastic plastic such as polycar~,on-~te, in known manner. Header 22 is designed to provide an elongated, cylindrical header space 143 and'~n elongated -connector 145 in communication therewith through the opening 149 Connector 145 is endwardly open to slip over the ends lS0 of the , !

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s~lar collec~ors 24. A sealant 148 is used at the connector 145 for bonding and sealing the header 22 to each solar collector 24 in a su~stantially lealc-proof connection. In some cases, the same sealant may be employed to bond the header 22 directly to the roof rafters 14 or to other building construction members. A
stop 147 is extruded in the header 22 of si~e to abut against and substantially seal the ends of the insulating air channels 36 of the coextruded collectors 24. The header opening ~49 co~municates with the channels 38 to thereby admit the solar heated medium from within the solar collector 24 into the keader interior space 143. There is a small stop 150a against which the bottom edge of the collector abuts, but without blocking the channels. As illustrated in Fig. 7, the stop is, however, not 2 lways necessary.

In Figs. 11 and lLA, t~ere is illustrated a modlfied header 43 which is similar in construction to the header 22 with the exception that header space 25 is extruded to a greatly reduced cross-sectional diameter. It is contemplated that the elongated, cylindrical space 25 defined within the modified header 43 will be approximately two inches in diameter as compared to the header space 143 illustrated in Fig. 10 wherein the cross sectional diameter may be on the order of 8 inches. It is contemplated that the header space 25 will be utilized to receive water or other liquid heat transfer medium from water carrylng collectors such as illustrated in Figs. 8 and 9. In the embodiment illustrated, a solar collector 156' positions within the connector 145 and the end is cemented therein by a sealant such as the sealant 148.

~?.~5 ~ 6 In the manner similar to that illustrated in Fig. 11, the insulating air channels 164' abut against the stop 192 and are su~stantially sealed thereby. The ends of the liqui~
carrying channels 170' communicate directly with the interior 25 o~ t'ne header 43 through the header opening 194 to introduce alL.
of the solar hea~ed liquid directly into the interior space 25 defined with the header construction. The solar collector 156' is similar in construction and manufacture to the coextruded collector 1~6 and comprises a plurality of insulating air channels 164' which zre ~uxtaposed to the plurality of water carrying channels 170 F, The :insulating air channels 164' are defined outwardly by the clear ~-n~ow loO' and inwardly by the interior window 166' and the -clear-ribs 162'. T'ne water carrying channels 170t are defined ~,. the interior windot~7 166', the black absorber base 168' and the p~uraIity of transversly spaced, b~ack ribs 172~ The solar collector 156' is similar in construction and function to the solar collector 156 with the exception that the black absorber surface 1~6 of the solar collector 156 is extruded of a clear material to form the clear interior window 166'. . t Referring now to Fig. 7, there is illustrated a header 1~.7 w'nich is similar in construction to the header illustrated in Fi~. 10 with the exception that the header space 144 is shaped to a different configuration than the header space 1~3, for example, the space 144 could be substantially oval in I ~, ~ 5~

cross sec-tional configuration. An elongated connector 146 extends from the header 142 and is in communication therewith through the opPning 153. The connector 146 is endwardly open to receive therein the ends 150 of the solar collectors, for example, collectors 24. A sealant 14~ having elastomeric qualities is used to bond the connector 146 to the ends 15Q
of the collector 24 in a substantially leak-proof connection.
A stop 151 is extruded in the header 142 of size to abut aga~nst and substantially seal the ends of the insulating air channels 36 of the coextruded collectors 24. The header opening 153 communicates with the channels 38 of ~he collectors 24 to thereby admit the solar heated medium from within the .
solar collector 24 into the header interior space 144.
In Fig. 12 is shown another modification of a coextruded solar collector 200 which is similarly fabricated of unitary constructi.on. A clear window 202 defines the upper limit of the insulating air layer 216. The clear cover 204 defines the bottom limit of the layer 126 and also separates the insulating air layer 216 from the heat transfer layer 218. The black base - , 206 defines the bottom of the heat transfer layer 218. A
plurality oE clear ribs 208 extend between the window 202 and the cover 204 in paral~el, transversly spaced relationship and are extruded to extend the entire length of the collector 200. ~, A symnetrical relationship with respect to the center plane is s'nown. This facilitates coe~trusion fabrication, minimi7ing tendencies for unsymmetrical shrinkage when cooling after ext:ru~sion.

5~

Similarly, a plurality of black ribs 210 extend upwardly from ~he base 206 to the cover 204 and are arrange~l in parallel, ~ransversly spaced relationship. The ribs 210 align beneath the clear ribs 208 and the embodiment illustrated, b~t as here;n-before set forth, it will be appreciated that the collector 200 coul~
also be fabricated with some or all of the blac'~ ribs 210 transversly offset from some or all of the clear ribs 208.
T~e clear ribs 208 divide the insulating air layer into a plurality of insulating air channels 212. Similarly, the black ribs 210 subdivide the heat tran~fer layer 218 into a plurality of longitudinally extending heat transfer channels 214. In the embodiment illustrated, all of the channels 212 and the trans.~er 1.
channels 214 are illustrated to be extruded to the same cross s2ctional dimensions. Other channels 212, 214 of different cross sectional dimensions could also be extruded in the manner herein described and come within the meaning and scope of this invention. In the embodiment set forth in Fi~.12, it is contemplate~
that the lateral dimension of the collector 200 coul~ be approximately 16 inches in width and the height could be -approximately 1 to 1~ inches. Utilizing a coextrusion process, -the length of the collector 200 could be any desire~ length, ror example, 20 foot planks, which length would be governed by the size of the roof construction and the capacity of the extruders employed in the fabrication of the collector 200.
Each channel 212, 214 could be extruded to have a height and a width of between ~ inch to 5/8 of an inch. Sucll a stand~rd unit would then have a total of 64 channels, 212, 214.

~ 1 ~ 5~

The flat-panel-unit solar collector o~ the invention is -anu~actured from any suitable synthetic polymer wh;ch is an extrudable thermoplastic. Suitability of a given polymer is related to the particular application,for instance,whether the collector is to be used in different climatic con~itions (desert, tropical), solar intensity, etc., or for high or low fluid temperatures. The plastic need not ha~e overall optimum properties, such as high heat distortion temperature when suitable safeguards can be built into the system to prevent overheating i the ~low of heat-transfer medium is stopped during solar exposure; other ' ~evices can likewise be connected with the system. ~esirable -aterials properties for the light-transmitting portion include:
(1) high transmittance of solar radiation; (Z~ resistance to photo-oxidative degration and general weathering; an~ (3) ability rO be coextruded with the chosen light-absorbing material.
~esirable materials properties for the light-absorbing portion include (1) resistance to thermal distortion or deterioration under the highest temperature conditions likely to be found in use;
and (2) ability to be coextruded with the chosen lig~t-transmitting ~aterial. Other properties desired for both light-transmitting and light-absorbing- materials system are: (1) good impact resistance; (2) good low-temperature properties (particularly rreedom from brittleness); (3~ good mechanical properties(such as high tensile strength, mo~lulus of elasticity, and elongation before break); and (4) reasonable cost.

-28- ;

One thermoplastic material particularly useful for both the transmitting and absorbing portions is polycarbonate (UV-stabilized clear and black). This material has a high heat-distortion temperature. Polycarbonate is produced in the United States by Mobay Chemical Corporation (under the trade mark "Merlon") and by General Electric Company (under the trade mark "Lexan"). O-ther producers are Idemitsu Petro-chemical Company (Japan) and Teijin Chemical Ltd. (Japan).
Another material for both the transmitting and absorbing regions is poly (methyl methacrylate) or PMMA. This plastic is produced by Rohm and Haas Company (under the trade mark "Plexiglas"), by du Pont (under the trade mark "Lucite"), and by many other manufacturers. PMMA or high impact acrylics (e.g., known under the trade mark "Plexiglas DR") may be used when means for preventing overheating by accidental shut-off of flow of the heat-transfer medium are provided. A high-temperature useful candidate material for both regions is polyethersulfone; this material has a tensile strength of 4700 psi at 180C.
Other polymers which are suitable for the light-transmitting region include perfluoroalkoxy (PFA) resins;
ethylene-tetrafluoroethylene copolymer (ETFE); poly (vinyli-dene fluoride) (known under the trade mark "Kynar" PVF2);
fluorinated ethylene propylene copolymer (known under the trade mark "Teflon" FEP); and poly (ethylene-chlorotrifluoro-ethylene) (known under the trade mark "Halar" E-CTFE). For the light-absorbing region other polymers which are suitable include: polysulfone; polyaryl sulfone; polyphenylene oxide and its copolymers; polybutylene; and polypropylene, which may be modified with talc, glass microspheres, or other rein-forcing filler.

B

3 P,'~5~fJ~

By judicious selection of the mechanical, thermal~ and o2,ical properties it is possible to combine in the solar collector of the invention, the material of choice ~or the pcrticular circumstances For a tough material with best i~pact resistance and best resistance to heat distortion, a polycarbonate, especially a W- sta~ zea natural polycarbonate is desirable. Thus, a panel o the invention can be made of a polycarbonate for the solar radiation absorbing region and wit~
a poly(methacrylate) for the solar radiation trans~itting region.
'~r1en ~t 1~ ~esired ~o provide additional pro~.ection a~ainst photo-oxidative degradation, it may be advisable to overlay the p~iycarbonate with a thin layer of acrylic polymer. This may be carried out by coextruding the acrylic with the other plastic, or -lr desired by applying that thin layer by continuous lamination~
o- o.her methods. Likewise other suitable synthetic polymers ~2y be selected for co-extrusion for the ~anufacture of the sol~r collector of the invention taking into consideration their-p-operties, which are well known.
It is within the contemplation of the invention to join a .
~ection or portion of a panel which has been singly extruded, to ar.o~'ner singly extruded section or portion, to form the one p;ec panel of the invention, e.g. to join a solar energy transmitting section and a solar radiation absorbing section, or portions thereof.

~25~.~6 While reference through the specification has been mainly to carbon black as the componen~ of the coextruded collector which is the solar radiation absorbing area it is of course within the contemplation of the invention to use other materials than carbon black which are equivalent in effect. Black iron oxide pigment is an example of such a material.
hlso, the thermoplastic can be filled with inorganic materials such as glass, glass beads, glass fibers, asbestos fibers, talc, or calcium sulphate fibers or other materials whic~ have the efect to reduce the coeffecient of thermal expansion o the synthetic plastic. Indeed any of the means known or changing or modifying the physical or other properties of the plastic to bring about the desired effect in the final panel can be used providing, in accordance with the invention, that the solar panel is a single unit having the two areas described above.
Tests using a solar thermal collector of the invention using air as the fluid being heated registered an initial temperature 29C which moved rapidly at a rate of about 2.4C
per minute to reach 100C under stagnant flow conditions. The collector was an all-acrylic unit. In further experiments a collector of the invention having a double window, such as is shown in Fig~ 2 exhibited a large difference in surface temperatures between the black z~ones and the transparent zones of the fluid-heating channels. The efficiency of the system, the energy ratio of thermal collection to incident solar energy, is about 30 percent when the air is being heated to 87C; at 60C~ the efficiency is about 50 percent.

~ 55'~6 The coextruded solar collectors of the invention are useful not only for heating o~ houses and structures, but also for heating water for swimming pools. Such designs are shown in Fig. 8 and Fig. 9 wherein the water channels are represented by the black areas.
The panels of the invention can be extruded to any desired length, this in contrast to the prior art. Thus, panels of the .~idth or length of the entire roof (e.g. 50 feet) can be -anufactured. The panel of the invention may then be fastened to the rafters to become an integral part of the roo~ structure.~
Elasto~eric sealants ~e.~. polysulfide or silicone) could be ~sed between adjacent panels. UnIike the conventional panels it need not be affixed on top of the roof; that is, it could be the roof r52lf. The panels of the invention can also be used as walls or fences in vertical or in any other desired angular position ~ich i5 consistent with the desired purpose.
In accordance with the invention the following term has the following meaning:
Unit is a one-piece, unitary structure or body or article, having a continuity of structure, which does not include constructions united by such means as fasteners, or ~astening, or a plurality o interconnected pieces. The unit of the invention is a one-piece structure.

11 Z 51,~ ¦

It should be noted however that once the unit has been constructedras a single one-piece thermoplastic structure~as by simultaneous fabrication of the plastics in a continuous process, it does not preclude making provisions in that one-piece structure for another material (like metal, wood,etc.). But this is provided after the one-piece coextruded structure of the invention has been manufactured and it does not disrupt the continuity or continuum of the thermoplastic material. It is therefore contemplated that the invention as claimed include such structures. For instance provisions may be made in the structure of the invention for metal rods or tubing or brackets for a ~unctional or a decorative purpose.
From the above description it is evident that the invention provides a highly practical, low cost device for eficient use ~of thermal energy.
Extrusion of plastics is known and disclosed and so is coextrusion wherein pIastics are simultaneously coextruded, for instance in the following U.S. patents Nos. 2,747,244; 3,4617490;
3,385,917, also from such publications like Coextrusion Moves into the Big League, Modern Plastics, pages 74-77, September 1970;
~lodern Plastics, page 176, August, 1968; Modern Plastics, page ~3Q, April 196S; Modern Plastics, Tooling for Flat Coextrusion, April, 1972; The Lid's off Coextrusion, Modern Plastics, Pages 46-47, June, 1~71, and in Society of Plastic Engineers, page 48, August, 1971. This reference to literature on coextrusion does not purport to be complete, since one skilled in the art can find other such references.

Claims (34)

I CLAIM:

1. A unitary solar thermal collector panel highly effective in absorbing and transferring thermal energy and having resistance to thermal distortion, the panel being con-stituted of a coextruded, self-supporting synthetic thermoplastic integral unit and being adapted to collect and transfer solar energy which comprises (a) a first section defining a first region, the first region being adapted to allow the passage of solar radiation, the first region being divided into a plurality of first channels of which adjacent first channels are defined by first common ribs; and (b) a second section defining a second region juxtaposed from the first region, the second region being capable of absorb-ing solar radiation and transferring it to a fluid, the second region being divided into a plurality of second channels of which adjacent second channels are defined by second common ribs; and the first and second regions being defined one from the other by a common divider.

2. The panel of claim 1 wherein the first and second regions respectively, are essentially completely occupied by the said first and second channels.

3. The panel of claim 1 wherein the first channels in the first region are separated by ribs which are transparent.

4. The panel of claim 2 wherein the channels in the second region are separated by ribs which are opaque and capable of absorbing solar radiant energy.

5, The panel of claim 1 which comprises also at least one of the following additional regions: (c) a third region which is adapted to allow for the passage of solar radiation and defining a space adapted to allow for the confinement of a fluid, or (d) a fourth region which is adapted to absorb the solar radia-tion and for transferring thermal energy to a fluid and defining an area adapted to allow for the directed movement of the heated fluid within the fourth region (d), said third or fourth region (c) or (d) being positioned between the first and second regions (a) and (b) and being defined from regions (a) and (b) by a common divider.

6. The panel of claim 5 wherein the additional region is divided into a plurality of channels, which adjacent third and fourth channels are defined by third and fourth common ribs, respectively.

7. The panel of claim 1 wherein the divider is opaque to solar radiant energy.

8. The panel of claim 1 wherein the divider is capable of transmitting solar radiant energy.

9. The panel of claim 5 which comprises both a third region (c) and also a fourth region (d).

10. The panel of claim 1 wherein the solar radiation-passing region (a) is of one or more clear thermoplastic material and the solar-radiation-absorbing region (b) is of one or more pigmented thermoplastic material.

11. The panel of claim 1 which comprises a fluid confined in the first channels of the first region, which fluid is an insulating fluid.

12. The panel of claim 11 wherein the insulating fluid is air.

13. The panel of claim 1 which is a flat plate.

14. The panel of claim 1 wherein the first region is a clear polycarbonate polymer and the second region is a pigmented polycarbonate polymer.

15. The panel of claim 1 wherein the first region is a clear polycarbonate polymer and the second region is a pigmented acrylic polymer.

16. The panel of claim 2 wherein in the first region the channels are closed channels.

17. The panel of claim 1 which comprises a heat-transfer fluid in the second region.

18. The panel of claim 17 wherein the fluid is air.

19. The panel of claim 1 wherein the first and second regions are of different synthetic plastics.

20. The panel of claim 1 wherein the first region is a clear acrylic polymer and the second region is a pigmented polycarbonate polymer.

21. The panel of claim 20 wherein the polycarbonate has an overlay of a thin layer of an acrylic polymer.

22. The panel of claim 1 which comprises a coextruded foam layer adjacent to the second region (b).

23. The panel of claim 22 wherein the foam layer is of the same thermoplastic as the first and second regions.

24. A combination of the panel of claim 1 and a header which defines an interior space, one end of the first channels in the first region of the panel being in fluid-blocked relationship with respect to the header space and the same end of the second channels in the second region of the panel being in fluid-communicating relationship with the header space, the header being adapted to admit and circulate the fluid to be heated, and wherein the header comprises blocking means to block the said one end of the first channels to prevent fluid flow through the said one end into the space.

25. The combination of claim 24 wherein the header is a one piece, extruded thermoplastic.

26. The combination of claim 25 wherein the plastic of the header is polycarbonate polymer.

27. The combination of claim 24 wherein the header is adapted to be fitted over the ends of the channels of the outer and inner regions.

28. The combination of claim 24 wherein the header comprises connection means which has a first part which cooperates with the blocking means to connect the header to the section defining the first region and a second part which connects the header to the section defining the second region of the panel.

29. A combination of the solar thermal collector system of claim 24 and a structure to be heated by the system, the system being adapted to be in heat-conveying relationship with the structure, whereby the system supplies collected and transferred solar energy to the structure.

30. The combination of claim 29 wherein the structure is a building with a roof supporting structure.

31. The combination of claim 30 wherein the panels of the system cover the width or length of the roof structure.

32. The combination of claim 29 wherein the panels are at least 8 feet long.

33. The combination of claim 29 wherein the panels are adapted to be an integral part of the roof structure.

34. The combination of claim 29 and a mounting system which allows for linear, planar movement of the unit with thermal expansion, but which prevents curling out of the plane.