Abstract:
A low-cost absorber panel for a solar hot water heating system is provided. An aluminum absorber plate, under exposure to solar radiation, makes an efficient transfer of heat to water circulating within the collector panel by direct contact with the medium in an optimized area-to-volume configuration. An innovative use of fasteners makes it possible to accommodate expansion for freezing and to allow for disassembly and maintenance. Additionally, a low-cost heat exchanger and a low-cost solar hot water system are presented using common structures.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a Continuation-in-Part of U.S. patent application Ser. No. 12/335,577, filed Dec. 16, 2008, and to which priority is herein claimed. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to solar energy collectors, and more specifically to low pressure solar hot water heater absorbers. 
       BACKGROUND OF THE INVENTION 
       [0003]    With the potential of future capacity shortages in the aging infrastructure of the electricity grid in the United States, not to mention the adverse-weather-prone supply of natural gas in the nation, solar energy represents an alternative to looming energy crisis&#39;s, as well as rising energy costs in the present. Next to space heating, water heating is the most significant factor in residential energy consumption and accounts for 13% of the household energy bill. What is needed is a solar hot water heating installation that can be accomplished on a budget by the average homeowner. 
         [0004]    Flat-plate solar collectors for water heating are present in the art. They are comprised of a heat-absorption panel in contact with circulating water and are typically housed under a transparent covering and over an insulating bed. The solar collectors are part of a system including a water supply and/or storage means, a circulation pump, and a heat-exchanger means. The heat transfer efficiency is a function of reflective, conductive, and convective heat losses, as well as the temperature differential between the absorption panel and the incident water. The convective losses are affected by the insulating bed and air envelopes, and the reflective losses depend on the reflectivity of facing surfaces, including the transparent covering. 
         [0005]    Commercially available types of flat-plate collectors are typically constructed with rows of copper riser tubes with attached copper fins exposed to radiant heat from the sun. Circulation of water through the tubing requires a pressure gradient, which is proportional to the cross-section of the tubing for a specified rate of flow. The pressure places stress on seals and soldered joints. Since the water is not in direct contact with the collector plate, some loss of conductive heat efficiency occurs. 
         [0006]    A preferred type of collector would be a low pressure system wherein the water circulates through relatively wide passageways between thinly-sandwiched absorber and companion plates and wherein the water is in direct contact with the absorber plate. This is thermally more efficient in two ways: Firstly, the water is intimate with the radiantly heated surface of the absorber plate, so conductive losses are less; and secondly, the absorber plate operates with a lower thermal gradient with respect to the environment, so convective losses are less. The passageways are sufficiently broad as to allow a 1.5 psi pressure for a 2 gpm circulation; consequently, seal integrity is less of a problem. There should be a serpentine path of water flow created by internal baffles which lengthen the contact time and create a certain amount of turbulence for the even distribution of heat. The present invention addresses a simple means for constructing such a system from readily-available materials, and costs less on a per BTU basis than the copper-tube version mentioned above. 
         [0007]    The prior art discloses different methods of construction for low pressure collectors. U.S. Pat. No. 4,103,675 to Bar-On, for example, uses an assembly of extrusions with channels therein to form passageways between inlet and outlet manifolds. The passageways do not follow a tortuous path in this case. Insufficient dwell time in contact with a radiantly heated surface might be a problem with this construction, which problem is overcome by the preferred serpentine path. Such a construction, additionally, involving welded joints, cannot be taken apart for cleaning and maintenance. Furthermore, the welding of metal parts, and particularly aluminum parts, is not a fabrication process in common usage in the home. 
         [0008]    Another method is exemplified by U.S. Pat. No. 4,182,308 to Reynolds. Reynolds teaches a construction wherein two sheets of rubber-like material are bonded along the periphery to create a water-tight interior and in alternating parallel strips with unbonded portions at the ends to create a serpentine flow path. Channels are formed by expansion of the material between the bonds when water is introduced to the system. Again, the bonded construction makes disassembly impossible, and the thermal efficiency of the elastic material is furthermore sub-optimal. Rubber, for example, has a thermal conductivity of 1.6 W/m-K, whereas the thermal conductivity of aluminum, by comparison, is 237. 
         [0009]    U.S. Pat. No. 4,315,499 to Shonerd demonstrates a third alternative for channel construction. Shonerd discloses baffles formed as a part of a base extending from sidewalls to create the flow path which alternates from one sidewall to the other. The sidewalls and the baffles are the spacers which form the narrow-depth passageways. While Shonerd uses a thermally conductive metal absorber plate over the base, and while the system is conceptually capable of disassembly, Shonerd&#39;s construction, on the other hand, does not use simplified materials readily available to the average homeowner. 
         [0010]    Weideman, in U.S. Pat. No. 4,170,223, teaches a solar collector panel having end caps which form a seal with a gasket at the periphery. In contrast to such methods as welding, soldering, or bonding, the end caps present what would appear, at first, to be a simplified means of assembling a sandwich construction of two plates. The end caps require, however, additional structure to prevent them from dislodging. The simplicity of method is undone by the complication of structure. Weidemen, furthermore, does not teach channeling to circulate water in a serpentine path. 
         [0011]    What is missing in the prior art is a simplified structure for a solar collector which is thermally-efficient, easily-maintainable, easy to fabricate, and easily convertible to a heat exchanger in a dual-use role. The key is to plan the solar collector for low-pressure operation, where the requirements for sealing are relaxed, where the physical properties of materials are not particularly critical, and where methods can be as simple as hand-tightening, for example. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    In view of the above-mentioned unfulfilled needs, the present invention embodies, but is not limited by, the following objects and advantages: 
         [0013]    A first objective of the present invention is to achieve a reduced installation cost. 
         [0014]    A second objective of the present invention is to achieve an operating pressure not exceeding 2.5 psi, and preferably, not exceeding 1.5 psi, for a circulation flow of 1.5-2.0 gpm. 
         [0015]    A third objective of the present invention is to provide an absorber plate material optimizing thermal efficiency with cost. 
         [0016]    A fourth objective of the present invention is to provide an absorber plate with a thermal conductivity exceeding that of stainless steel at 16.3 W/m-K. 
         [0017]    A fifth objective of the present invention is to provide a means for creating spacing and sealing between collector plates which is simple to construct with readily available materials. 
         [0018]    A sixth objective of the present invention is to provide a means for creating channeling and flow paths which is simple to construct with readily available materials. 
         [0019]    A seventh objective of the present invention is to provide a means for disassembling and cleaning the solar collector for easy maintenance. 
         [0020]    An eighth objective of the present invention is to provide a water-tight means for sealing having an integrated means for securely, but removably, binding the plate components into a composite. 
         [0021]    A ninth objective of the present invention is to eliminate the need for an expansion tank by providing a means for expansion to accommodate changing temperatures. 
         [0022]    A tenth objective of the present invention is to provide an apparatus usable as either an absorber panel or a heat exchanger. 
         [0023]    An eleventh objective of the present invention is to provide a solar hot water system using common architecture. 
         [0024]    These and other objects of the invention to become apparent hereinafter in accordance with the invention are realized in a low-pressure absorber panel for solar hot water systems comprised of a rectangular aluminum absorber plate combined with a matching aluminum companion plate in a sandwich-like composite. The two plates are held together with a means for binding. A means for spacing is inserted between the plates to form a boundary there around and create a water-tight internal space for a flow of water there through. Included in the internal space is a means for channeling defining a serpentine flow path. The water enters the internal space through a port in one of the absorber and companion plates and exits through another port in one of the absorber and companion plates, the two ports located so as to maximize the serpentine flow path. The water entering the internal space and moving there through under low-pressure is heated by contact with the absorber plate, which is exposed to solar radiation. The water exits the space to transfer the heat to an external system. 
         [0025]    In a preferred embodiment, the means for spacing is an elastic gasket of substantially rectangular cross-section which is arrayed along the periphery edges of the absorber and companion plates and tensioned to provide a compression seal. 
         [0026]    In another aspect of the preferred embodiment, the means for binding is an extruded clip having arms angled so as to form a narrowed opening, the extruded clip covering the elastic gasket of substantially rectangular cross-section along the length of each periphery edge, the elastic gasket compressed between the arms to form a wedge shape which resists removal of the extruded clip from the periphery edge. 
         [0027]    In still another aspect of the preferred embodiment, the means for channeling is a plurality of elastic strips of substantially rectangular cross-section. The elastic strips extend in alternation from one end or the other of the gasket at the periphery, beginning with the end closest to the entry port and ending with the end closest to the exit port, to a point short of the opposite end. The parallel channels formed thereby are connected to adjacent channels by alternating passages. The elastic strips are held in place and in compression by bolts and nuts sealed with o-rings spaced along the length thereof. 
         [0028]    In an alternative embodiment of the present invention, the means for spacing is an elastic gasket of substantially circular cross-section which is arrayed along the periphery edges of the absorber and companion plates and adjustably tensioned to provide a compression seal. In the same embodiment, the means for binding is machine screws and nuts straddling the gasket of substantially circular cross-section along the extent thereof, the machine screws optionally provided with o-ring seals for positioning in the internal space. 
         [0029]    In another alternate embodiment, a low-pressure heat exchanger is comprised of essentially the same structural elements as the low-pressure absorber panel. In the heat exchanger case, heated water is circulated to exchange heat through both the absorber and the companion plates to a host medium. 
         [0030]    In yet another alternative embodiment, a solar hot water system is comprised of at least one absorber panel and at least one heat exchanger configured as discussed above. The absorber panel and heat exchanger are connected by a means for circular fluid communication and a means for creating a circulation current to transfer radiant solar heat from the absorber panel to convective heat from the heat exchanger inside a heat-exchange vessel filled with water. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         [0031]    Various other objects, features and attendant advantages of the present invention will become fully appreciated as the same becomes better understood through the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views, and wherein: 
           [0032]      FIG. 1  is a perspective view of the assembled solar hot water heater; 
           [0033]      FIG. 2  is an exploded perspective view of the solar hot water heater; 
           [0034]      FIG. 3  is a perspective view of the absorber panel; 
           [0035]      FIG. 4  is a perspective view of the absorber panel with the absorber plate removed; 
           [0036]      FIG. 5  is a partial sectional view of the absorber panel showing the gasketing and channel; 
           [0037]      FIG. 6  is a partial cutaway plan view showing fastener and o-ring details; 
           [0038]      FIG. 7  is a partial sectional view showing fastener and o-ring detail; 
           [0039]      FIG. 8  is a partial sectional view showing the extruded clip and strip gasket of an alternative embodiment; and 
           [0040]      FIG. 9  is a schematic diagram of a solar hot water system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]    For the purposes of this description and for the claims following, the term “o-ring” can mean both toroidal and flat-shaped, and connotes compressibility such that sealing is achieved. Similarly, the term “water” is to be construed as meaning any liquid. 
         [0042]    A solar hot water heater  1  is shown in  FIGS. 1 and 2 . Solar hot water heater  1  is comprised of a frame  2 , which houses an absorber panel  10  and a transparent cover  3 , which provides an enclosure. The air space  5  within the enclosure and above the absorber panel  10  functions to reduce convective heat losses. Solar radiation  4 , passing through the transparent cover  3  and the air space  5 , is incident upon the absorber panel  10  where the radiation heats the contents therein by conduction through its absorption. Insulation material may optionally be added between frame  2  and absorber panel  10 . Coatings may also be optionally added to both the absorber panel  10  and the transparent cover  3  to respectively enhance absorption and decrease reflective losses. Such an apparatus is not only appropriate for residential use, but also for swimming pools and the general radiant heating of buildings. 
         [0043]    The assembled absorber panel  10  is best shown in  FIGS. 2 and 3 . Absorber panel  10  is comprised of absorber plate  11  and companion plate  12  joined in a thinly-spaced-apart, sandwich-like, composite. Water is introduced to absorber panel  10  from a water supply  16  (not shown) through entry port  13 , and is distributed from the absorber panel to a heat exchanger  17  ( FIG. 9 ) through exit port  14 . Entry port  13  and exit port  14  can be positioned either on the absorber plate or the companion plate. When the absorber panel is mounted at an angle to vertical, such as when mounted on a pitched roof, exit port  14  should always be elevated above entry port  13  to vent air and prevent air bubbles. 
         [0044]    In the preferred embodiment, absorber plate  11  and companion plate  12  are comprised of a 48 inch by 96 inch by 0.032 inch aluminum sheet of alloy 5052H32, or similar. 
         [0045]      FIG. 4  shows the absorber panel  10  with the absorber plate  11  removed. A means for spacing  30  is shown at the periphery edges of the exposed companion plate  12 , said means being a periphery gasket  32 , and, preferably, an elastic gasket of rectangular cross-section  31 . In an alternate embodiment ( FIGS. 6 and 7 ), periphery gasket  32  may be an elastic gasket of circular cross-section  34 . 
         [0046]    A means for channeling  40  is also shown in  FIG. 4  extending from alternating edges of periphery gasket  32 , said means being a plurality of elastic baffles of rectangular cross-section  33 . Means for spacing  30  and means for channeling  40  can be collectively described as a means for resiliently creating internal space and channels  100 . 
         [0047]    In the preferred embodiment, the elastic gasket of rectangular cross-section  31  is a butyl rubber or silicone strip measuring 5 mm by 12 mm and having a durometer in the range of 55-70. The elastic baffles of rectangular cross-section  33  may be of similar material and hardness, but reduced in size to 5 mm by 8 mm. In the alternative, the elastic gasket of circular cross-section  34  is cording of the composition of butyl rubber or silicone and measures one-quarter inch in diameter. For sealing purposes, the rectangular cross-section has greater surface contact area. The circular cross-section, however, presents a uniform height when the strip is twisted in conformance to contours. 
         [0048]    Continuing with  FIG. 4 , periphery gasket  30  creates an internal space  15  for the containment of water therein. Lengths of the elastic baffle of rectangular cross-section  33 , each length shorter than one of the periphery edges to which it is placed in parallel and extending alternately from the two periphery edges which are perpendicular to the afore-mentioned periphery edge, collectively form a system of channels  43 . Adjacent channels  43  are connected by alternating passages  42 , the passages being free spaces at the terminus of each wall section formed by the lengths of elastic baffle of rectangular cross-section  33 . The alternation of passages  42 , from one perpendicular periphery edge to the other, creates a serpentine path  41  for the flow of water through the internal space  15 .  FIG. 5  shows one of the channels  43  defined by bordering sections of elastic gasket of rectangular cross-section  31  and elastic baffle of rectangular cross-section  33 , and particularly illustrates the extreme low-aspect ratio of the channel; that is to say, the short depth to the wide breadth. Such an aspect ratio optimizes the contact surface area for heat transfer. 
         [0049]    In the preferred embodiment, a means for binding  20  comprises an extruded clip  23 , as shown in  FIG. 8 . Extruded clip  23  extends around the periphery of absorber panel  10  and overlaps the absorber plate  11  and the companion plate  12  with clip arms  24 . The corresponding means for spacing  30  is the elastic gasket of rectangular cross-section  31 . Elastic gasket of rectangular cross-section  31  is positioned between the plates and between clip arms  24 . Clip arms  24  stiffly angle toward each other so as to form a narrowed opening  25 . Clip arms  24  compress the elastic gasket of rectangular cross-section  31  there between to form a water-tight seal. The elastic gasket in envelopment by clip arms  24  and under compression there from forms a wedge shape  35  in the interior of extruded clip  23 . The wedge shape  35  cannot pass the narrowed opening  25  and thereby resists the removal of clip  23 , thus securely holding it in place. The extruded clip  23  may be removed by supplying a shear force sufficient to effectively calender the wedge. 
         [0050]    In an alternative embodiment, the means for fastening  20  comprises machine screws and nuts  21 , as shown in  FIGS. 6 and 7 . In this case, the corresponding means for spacing  30  is the elastic gasket of circular cross-section  34 . Machine screws and nuts  21 , shown in alternating positions on both sides of periphery gasket  30  in  FIG. 6 , serve both to anchor the gasket and to apply compressive force for sealing purposes. The staggered position applies the compressive force evenly around the gasket. The individually adjustable nature of each fastener makes it possible to stop any leaks which may result from the variation of materials and applied tension. In the same manner, machine screws and nuts  21  anchor the lengths of the elastic gasket of rectangular cross-section  31  forming the channels. 
         [0051]    The machine screws and nuts  21  can also provide a means for shaping surfaces and space. Because of the sheerness of the absorber and companion plates and the breadth of the channels, there will be bulging of the plates when water is moving through the channels under pressure. Through-bolted machine screws placed at selected locations intermediate the channels can be used to control the bulge, and moreover, to make allowances for both heat and freezing expansions. All machine screws traversing internal space  15  are provided with o-rings  22  to seal the perforations of that space. Because the machine screws and nuts  21  are easily removable, it is a relatively simple matter to disassemble the absorber panel for cleaning and maintenance. The machine screws of preference are one-half inch stainless steel, gauge 4-40. The o-rings are 0.45 inches in diameter with a 0.21 inch thickness. 
         [0052]    In another alternative embodiment, the heat exchanger  17  comprises the same structural elements as absorber panel  10 . In the case of heat exchanger  17 , heated water is supplied through entry port  13  and circulates to exit port  14 . The heated water transfers heat by contact with both absorber plate  11  and companion plate  12 , thereby exchanging the heat with any medium in contact with the plates. 
         [0053]    In yet another alternative embodiment, a solar hot water system  50  is comprised of at least one absorber panel  10  and at least one heat exchanger  17 . Referring to  FIG. 9 , heat exchanger  17  is submerged in a volume of water  54  inside of a heat-exchange vessel  51 . Heat-exchange vessel  51  might be a holding tank, or might also be a heat exchange tank for a swimming pool heating system. A means for providing circular fluid communication  52  connects absorber panel  10  with heat exchanger  17  through respective entry ports  13  and exit ports  14 . A means for creating a circulation current  53  transfers heat radiated onto absorber panel  10  to heat exchanger  17 , and there from, by conduction and convection, to the volume of water  54 . The means for providing circular fluid communication  52  may be plumping-supply piping or hose. The means for creating circulation current  53  may be a pump capable of operating at low pressure. 
         [0054]    The fabrication process for the absorber panel, and by extension, for the heat exchanger, is simple. It requires laying out the baffles and drilling a pattern of holes through the plates to anchor the baffles and to control bulge in the channels. With both plates in place and the gasket sandwiched between the periphery edges, the extruded clip is pressed onto and over the edges and against the resilient force of the gasket. In some cases, a mallet may be used to urge the extruded clip into position. The holes are threaded with machine screws, o-rings and nuts, as appropriate. The entry and exit ports are mounted to one or both plates. 
         [0055]    The preferred absorber panel size is thirty-two square feet. The preferred size of the heat exchanger is twenty-five square feet. 
         [0056]    It is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the preceding description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. For example, the elastic baffles may be adhesively bonded in place thereby avoiding holes in the plates. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of the description and should not be regarded as limiting.