Flat Plate Solar Collector

This invention relates in general to solar energy collection and, more particularly, to a collector of generally flat plate character for transference of solar heat to liquids.

The present invention contemplates the provision of a relatively elongated generally flat collector having a coextensive compartment subdivided into a plurality of discrete channels each internally containing a multiplicity of insulators for developing tortuous liquid flow from the normally upper end to the lower end of said collector whereby water flowing therethrough is subjected to solar heat transmitted through an upper plate for absorbing such heat with consequent temperature elevation so that the water discharged from said collector may be utilized from any of a multitude of purposes by reason of the received energy.

Therefore, it is an object of the present invention to provide a collector for solar heat which is of markedly simple construction, being comprised of a limited number of inexpensive durable components, and which may be easily used by the average individual.

It is another object of the present invention to provide a solar heat collector of the type generally stated which may be of any predetermined size for co-ordination with the area available for presentation of the collector and for the ultimate purpose of the absorbed energy.

It is a further object of the present invention to provide a solar heat collector of the type stated which incorporates a body designed for facile disposition upon a sun-exposed inclined surface permitting of gravitational liquid flow therethrough for heat absorption and, hence, temperature elevation during such flow.

It is a further object of the present invention to provide a solar heat collector of the type stated which is uniquely constructed so as to be of relatively light weight for facile handling; which may be disposed in compact form for ease of transportability, as well as storage in limited space.

It is a still further object of the present invention to provide a solar heat collector of the type stated which in operation does not require the services of an attendant; which through its unique construction is resistant to breakdown and is, hence, fully reliable in usage; which is formed of sturdy elements so as to resist damage from environmental conditions so as to be useful throughout the range of normally encountered weather conditions.

FIG. 1 is a perspective view, in partial fragment, of a flat plate solar collector constructed in accordance with and embodying the present invention illustrating said collector in operative position upon a roof.

FIG. 2 is an enlarged fragmentary plan view of the upper left hand corner of the collector shown in FIG. 1 as generally within the zone defined by line 2--2.

FIG. 3 is a vertical transverse sectional view taken on the line 3--3 of FIG. 2.

FIG. 4 is a vertical transverse sectional view taken on the line 4--4 of FIG. 2.

FIG. 5 is a transverse sectional view taken on the line 5--5 of FIG. 3.

FIG. 6 is a vertical transverse sectional view taken on the line 6--6 of FIG. 1.

Referring now by reference characters to the drawings which illustrate the preferred embodiment of the present invention, A generally designates a collector of solar energy which may be considered as of the flat plate type for disposition upon a suitable sun-exposed surface, such as, desirably, the roof 1 of a building 2, wherein roof 1 is inclined at a suitable angle to promote gravitational flow of heat absorbing liquid, such as water. Collector A may be considered as constituting a relatively flat container having a body b for flow therealong of water received at the upper end thereof and discharged at the opposite or lower end thereof, all as will be more fully described hereinbelow.

Collector A embodies a lower or base plate 3, of sheetlike character, which is adapted to be disposed upon roof 1, or other support surface, being suitably rigidly engageable thereto as by any selected means, such as by bonding, by glutinous materials, by tacking, by tacking strips, by welding strips, or the like. If desired, said lower plate 3, in lieu of direct securement upon roof 1, may be mounted upon a sheet of flexible insulation (See FIG. 3) such as, for instance, polyurethane, and having thickness as in the order of 1/2inch. Alternatively collector A may be mounted on rigid insulation secured to the mounting surface. Insulation mounting 4 is not of extreme criticality, but has proved useful wherein the roof surface has been uneven and the like, and where heat transfer through the roof is to be minimized. Lower plate 3 is formed of synthetic material and is designed for high heat absorptivity, being of dark coloration, such as black, throughout its extent. Mounting 4 is an optional element that may prevent extremely limited heat loss to roof 1 and which may enhance stabilization of lower plate 3 in operative position.

Lower plate 3 is preferably formed of plastic material, such as polyvinyl fluoride, polyethylene, polycarbonate, and KELVAR*, being relatively thin and flexible, permitting ease of workability, but possessing the requisite properties for resisting destruction through high temperatures as in the order of 300.degree. F. or exceedingly low temperatures, such as freezing, whereby said lower plate 3 is substantially proof against the usual range of weather conditions encountered over extended periods of time. Said lower plate 3 is inert to mildew and similar fungus-like growths so as to be of enhanced durability. Lower plate 3 may also be constructed of a material that is etched, embossed or otherwise roughened to provide a raised portion in such a way as to present greater surface area and to impede the flow thereover, thus enhancing the transfer of heat from said lower plate 3 to the liquid flowing over it, all as will be more fully discussed hereinbelow.

Spacedly above, aligned with, and in opposed relationship to, lower plate 3 is a top plate 5 which in addition to being transmissible so as to allow solar radiation to pass therethrough to the interior of collector body b, also serves as a protector for collector A to shield same against disruptive atmospheric conditions as developed through high winds, storms, etc., as well as having the capability of withstanding damage through high temperatures as within the order of 300.degree. F. as well as low temperatures so that brittleness, aging, cracking and the like is obviated. Top plate 5, further has the characteristic that, while transmitting solar radiation in the inward direction, it tends to block the radiation of the longer heat waves generated by lower, absorbing, plate 3. Top plate 5 which is thus transparent and basically non-heat absorptive, is also desirably of flexible sheet character being relatively thin for maximum heat transmissivity, as of infrared radiation, yet of sufficient strength to avoid rupture through subjection to hail and like missiles, whether naturally inspired or otherwise. It has been found that material suitable for top plate 5 may be from the class consisting of polyvinyl fluoride, polyethylene polyester, fiberglas, reinforced plastics, teflon, and fluorinated ethylene propylene. Top plate 5 in addition to being highly durable and tough also is substantially impervious to ultra violet light.

Upper and lower plate 5,3, respectively, are suitably connected along their marginal portions with their main or central portions being in vertically spaced-apart, substantially planar parallel relationship, to complete the basic formation of collector body b with the definition of an intervening coextensive chamber c therebetween.

Admittedly there are numerous expedients whereby upper and lower plates 5,3 may be integrated or united to provide a leak proof integrity at all zones of jointure, whether seams, overlaps, or the like. For purposes of example only, lower plate 3 is shown in the drawings as having upwardly and inwardly turned lateral portions, as at 6, overlapping the underlying portion of the marginal zone of top plate 5, as at 7 (see FIG. 3) and being mutually affixed, as by adhesives, chemicals or the like. It is, of course, evident that any other type of suitable means may be used for effecting the desired mutual securement of upper and lower plates 5,3, as for example, heat welding, chemicals, solvents, tapes, etc., whereby upper and lower plates 5,3 are integrated for developing liquid proof chamber c. It is manifest that the maximum area of upper plate 5 will be unrestricted by optimum exposure to the sun's heat.

Provided within chamber c is a multitude of insulators 8 which are of the bubble or pocket type, being popularly referred to as a bubble pack, and may have a generally hemispherical configuration, being formed for integration on the undersurface of top plate 5 with the normally open upper ends thereof directed against the undersurface of top plate 5 to develop closed pockets. Such insulators 8, being preferably of like size, are customarily vacuum-formed by well known techniques and extend between upper and lower plates 5,3 with the bottom portions thereof being secured, as by an adhesive, to the confronting upper surface of plate 3, as at 9, thereby conducing to integration of collector body b. The lower point of contact should encompass a reasonably small area, so that liquid flow will have the greatest possible area of surface to flow over, from which to absorb heat. Insulators 8 are dimensioned in conformity with the dimensions of the particular collector A, as if such insulators 8 are of a relatively excessive size, as related to the collector, the same will cause the creation of convection currents developing undesired heat transfer; while on the other hand, if such insulators 8 are of too limited volume, the same are insufficient for insulation purposes. The determination of the size of insulators 8 is well within the capacity of one having normal skill in the art; a range of 3/8 inch to 1/2 inch diameter has been found to be suitable. As will be seen in the drawings and more particularly FIG. 2, insulators 8 are arranged in a generally staggered or altenating pattern wherein discrete but tortuous channels, as indicated generally at 10 by arrows, are formed so that water flowing from the upper end of collector A to the lower end will be caused to flow around the insulators 8 and thus necessarily follow a path of a twisting nature which will have the recognized purpose of generally lengthening the time of flow of liquid from the upper end to the lower end of collector body b so as to accord a relatively enhanced period for heat absorption and completely wetting the heat absorbing surface.

As is best indicated in FIGS. 1 and 2, collector body b is lengthwise divided into a multiplicity of channels extending the full length of collector body b and which may be of varying width, as indicated at 11, 12, 13, and which channels are developed by heat sealing or otherwise securing upper and lower plates 5,3 along lines of securement, as broadly indicated at 11', 12', 13', which latter distinctly demarcate the interior of chamber c into the preselected number of such discrete channels. Such channels, as exemplified by 11, 12 13, are coextensive with collector A so that as will be shown, water entering the upper end of one channel will be prevented from flowing laterally into an adjacent channel and thereby be constricted to flow within but a single channel. Channels 11, 12, 13 are shown as being of different width, but such is merely for expository purposes since the channels may be of any desired width commensurate with the overall dimension of collector A and the nature of the surface supporting same. In actual practice, a width of about 3 inches to 4 inches has been found to be most efficient. But with an underlying support surface which is not of an even character so that a transverse slope is encountered, the channels 11, 12, 13 and the like prevent, as will be shown more fully hereinbelow, the liquid to be heated from flowing to one side of collector A with expectedly imperfect and unsatisfactory heat absorption; with a substantial portion of the collector body b being unused. Thus, the generalization of collector body b assures of substantially even distribution of the liquid to receive the heat to be distributed through the entire collector so that maximum efficiency is assured.

At its upper end collector body b is snugly received within a downwardly opening recess 14 provided at the lower end of a casing 15 extending transversely of collector A and being coextensive therewith; said casing 15 forming a substantially enclosed chamber d for receiving a liquid manifold, 16, which projects through an opening, as at 17, in one side wall of casing 15 for connection to a liquid supply pipe, indicated at 18, which suitably leads from a convenient source of liquid. The opposite end of manifold 16 is closed but throughout the extent of manifold 16 within casing 15 there are provided a multiplicity of branch conduits 19 which are spaced-apart throughout the length of manifold 16 for directing flow from said manifold and into the various collector channels 11, 12, 13, as the case may be. Depending upon the width of the particular channel being serviced manifold 16 will in such zone contain a commensurate number of such branches 19. Manifold 16 may be considered of the balancing type and might merely comprise, if desired, a plastic hose having spaced-apart perforations (not shown) on lieu of branches 19 and could contain piercing elements so as to engage the hose intimately with the collector body b which elements would have the function of maintaining the manifold and the collector body b in desired mutual securement and with assurance of the perforations opening into what might normally be the closed end of collector body b. Thus, there are admittedly numerous manners in which to provide a liquid manifold for introducing water or the like into the collector body channels and that illustrated is for purposes of basic clarification only.

At its lower end collector body b is similarly received within what might be considered the normally upper open end 20 of a lower casing 21 being coextensive with collector body b, but which casing 21 is provided interiorly with a continuous chamber 22 to constitute a manifold into which liquid will flow from each of the collector channel bodies 11, 12, 13, etc. (see FIG. 6). In its lower end portion, casing 21 incorporates a relatively short downwardly extending outlet 23 which may be engaged, as by threading, to a discharge pipe 24 leading to a warm water reservoir, a heat exchanger, motor, or the like. Thus, after having traversed collector body b water flowing from inlet manifold 16 is discharged from collector A through discharge pipe 24 for collection or immediate purposeful usage as the case may be. A pressure relief valve (not shown) may be provided in the lower end manifold so that in the event of blockage of the drain, relief from hydrostatic pressure will be provided in order to prevent bursting of collector A should a head of liquid be built up therewithin. Such valve might take the form of a spring loaded valve or a safety panel designed, to open, below the bursting strength of collector A.

From the foregoing the operation of solar collector A should be readily apparent. Water or other heat absorbing liquid is fed into the body b of collector A from its source via inlet manifold 16 and branch conduits 19 for flow through gravity by reason of the angulation of the roof 1 supporting collector A within the tortuous, insulator-developed paths 10 within the various channels 11, 12, 13, etc. It is, of course, understood that the liquid source will have sufficient pressure so as to overcome any adverse gravitational effect developed through any transverse angulation of roof 1 so that the liquid will be directed to all of the various channels in order that the entirety of collector A may at all times be in effective, economic use. The water flowing within collector A is subjected to solar energy transmitted through top plate 5, which energy will be substantially absorbed by the highly heat absorbably lower plate 5. Accordingly, the liquid will be continuously receiving heat from the heated lower plate as well as some limited heat passing through chamber c toward said lower plate 5. Insulators 8 thus serve to restrict the zones for heat conduction while the insulator and the top plate 5 tend to prevent re-radiation of the lower frequency heat generated at the lower absorbing plate 3; and thereby conduce to the most efficient utilization of solar heat transmitted through top plate 5. Accordingly, as the water travels along collector body b it will gradually be elevated in temperature so that when flowing into casing 21 and thence outwardly through discharge pipe 24 it will have reached a substantial temperature level when considered in terms of the temperature of the water being fed to said collector A. Although there may be some initial pressure from any pump at the water source, such is inconsequential for driving water through collector A as such pressure is merely adequate to assure of overcoming any adverse transverse roof slope as the water moving through collector A should be considered as flowing solely under gravitational effect.

It is particularly interesting to observe that collector A is uniquely constructed to prevent any loss of heat through re-radiation as top plate 5 permits transmission of infrared heat, which is of relatively short wave form, into chamber c, while being impervious to relatively long waves so that the short waved heat which passes into collector A will not be lost as by re-radiation if the same were of long wave character. This particular condition has been more popularly referred to as the "greenhouse effect" in that collector A while being transparent to sun radiation is opaque to heat re-radiation.

It is obvious that the present invention would operate upon roofs and other supporting members of varying degree of angularity with respect to the vertical.

The dimensions of collector A are indeed optional depending upon the support surface available and the quantity of liquid which can be efficiently threated. As shown above by reason of the nature of the materials of construction the body of collector A is generally flexible and, hence, capable of being rolled upon itself so as to be compressed into a relatively compact entity for ready transportability, storage in minimum space, and facility of handling for disposing same in, and removing same from, operative condition. While the preferred embodiment is preferably fabricated of flexible materials adapted to be rolled for tranporting, as well as for conforming to the mounting surface, it is contemplated that more rigid materials might also be used if desired.

Considerable experimentation has been effected with the present invention to establish its reliability and absolute feasibility for the intended purpose. Purely exemplary is the fact that experiments have demonstrated that with an outdoor temperature of 73.degree. F. and a water inlet temperature of 70.degree. F., water moving once through the collector will attain a temperature of 80.degree. F. with an overcast sky, and a sun angle at 50.degree. from the normal plane of collector A. To attain such results a collector having a dimension of approximately 80 feet in length, and with a top and bottom layer having an exposed width of between 3 to 3-1/2 feet was adequate thereby demonstrating the highly efficient nature of the present invention. In obtaining the foregoing results it was determined that the flow of water was at a rate of 225 pounds of water per hour and with such latter being multiplied by the 10.degree. rise in temperature would evidence a production of 2250 BTU per hour. It was further discovered that with water being caused to flow at a rate more rapid than 225 pounds per hour, an increased portion of the surface of collector A was covered resulting in a relatively greater degree of heat transfer and, accordingly, a higher energy availability in the discharged water.

Therefore, from the foregoing the uniqueness of the present invention is most apparent and with the lack of costly personnel attendance being obvious. The structure is uncomplicated and with a total absence of moving parts assures of longevity of usage in a most reliable and economical fashion.