Abstract:
A system of passively heating water using solar energy and an absorber formed from two identical halves of molded darkened glass that are fused together. The absorber is essentially a plurality of black glass struts that are sandwiched between two black glass surfaces. The struts act as baffle plates and define cells. Water is carried through the system via the thermosiphoning effect.

Description:
BACKGROUND 
     (1) Field 
     The present invention relates generally to heating water using solar energy and, more particularly, to an absorber formed from two identical halves of darkened glass that are fused together. 
     (2) Related Art 
     Small-scale solar water heating systems are typically constructed of an insulating housing, including a window which permits solar radiation to enter the housing, and a solar collector. Solar collectors are also known as “absorbers”. Solar water heaters are generally categorized as active or passive. Active heaters pump water from a reservoir, such as a tank or pool, to the solar collector where the water is heated, then onto the desired destination. These systems require various controllers, including water flow controllers, since a relatively small volume of water resides in the solar collector, and this water, if overheated, could easily damage or destroy the delicate collector. Pool heaters and flat panel water heaters commonly seen on roofs are usually active solar heaters. As of the date of filing this application, a typical active solar water heater designed to meet most of the water heating the needs of a family of four costs approximately $7,000US to $9,000US fully installed in the US. In the San Francisco Bay Area, the annual energy expenditure for “conventionally” heating water for a family of four is approximately $400US. 
     Passive water heaters are generally less structurally sophisticated insofar as they lack pumping and precise water flow controllers. Instead, water is moved via the thermosiphoning effect through a large solar collector which also serves as a storage tank, then onto the desired location. A very simple version of this is found in many tropical locations, such as southern China, where uninsulated black tanks are often placed on roofs to simultaneously store and heat water. Without insulation, however, the hot water must be consumed during the solar day. As of the filing date of this application, more sophisticated passive water heaters, which are generally capable meeting heated water needs of a family of four in the US, cost approximately $7,000US installed in the Bay Area. 
     Many potential consumers consider solar heating systems to be cost prohibitive. This hurdle to ownership is compounded because the projected financial break-even point for solar heating systems is in the decades. Accordingly, solar heating systems are generally considered to be environmentally friendly but financially unfriendly investments. This is unfortunate given the myriad of problems associated with the consumption of non-renewable energy sources. 
     Copper is widely considered the material of choice in solar water heating systems. It is bendable, can be soldered and brazed, undergoes minimal corrosion, and does not pose water-related toxicity concerns. However, copper is quite expensive, trading as a commodity in the $2.00 to $4.00US range in the three years prior to filing this application. In short, the cost of copper is a major hurdle to solar heating system ownership for many consumers. In some solar heaters, aluminum may be used in place of part of the copper to reduce cost, but this adds substantially to assembly costs. The other major cost contributor to solar heating systems is the labor associated with manufacturing. Typically systems include a multitude of delicate parts that must be assembled with precision because sloppy assembly will lead to leaks and system failure. 
     Thus, there remains a need for a new and improved solar water heating system that is economically feasible for consumers. Ideally this system would be relatively simple and inexpensive to manufacture, be constructed of environmentally friendly and inexpensive materials, and not be any more difficult to install than already known solar water heating systems. This new and improved solar water heating system should also perform as well as current systems with respect to temperature and availability of water, longevity of system and aesthetics. 
     SUMMARY OF THE INVENTIONS 
     The present invention is directed to heating water using solar energy and, more particularly, to an absorber formed from two identical halves of molded darkened glass that are fused together. 
     Accordingly, one aspect of the present inventions is to provide a passive system for solar heating water that is affordable for most consumers and will pay for itself in under 10 years. 
     Another aspect of the present invention is to construct the system using environmentally friendly materials that are readily available. 
     Yet another aspect of the present invention is to provide a system that is as reliable, efficacious, aesthetically pleasing and easy to install as other, much more expensive systems. 
     Still another aspect of the present invention is to facilitate water&#39;s capture of solar energy with cells formed of darkened glass, and facilitate movement of that water via the thermosiphoning effect. 
     Another aspect of the present invention is to teach a method of forming a monolithic glass absorber of two identical sides that are easy to manufacture and assemble. 
     These and other aspects of the present inventions will become apparent to those skilled in the art after a reading of the following description of the preferred embodiment when considered with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a perspective view of the exterior of the system; 
         FIG. 2  is a side cross-sectional view of the interior in one embodiment of the system, as taken along line  2 - 2  of  FIG. 1 ; 
         FIG. 3  is a schematic top cross-sectional view of the absorber in one embodiment of the system; 
         FIG. 4  is a schematic side cross-sectional view of a portion of absorbers in one embodiment; 
         FIG. 5  is a schematic top cross-sectional view of the interior of absorbers in one embodiment; 
         FIG. 6  is a schematic perspective view of the exterior of the absorber in situ with the inlet and outlet connectors attached; 
         FIG. 7  is a cross-sectional view demonstrating attachment of absorber to inlet connector to copper tubing; 
         FIG. 8  is a schematic side view of two molded glass halves fused together; and 
         FIG. 9  is a schematic top cross-sectional view of the interior of the absorbers in the preferred embodiment, schematically showing the side cross-sectional views of the absorber baffles extending therefrom as  FIG. 9   a.    
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description, like reference characters designate like or corresponding parts throughout several views. 
     Referring now to the drawings in general and  FIG. 1  in particular, it will be understood that the illustrations are for the purpose of describing a preferred embodiment of the invention and are not intended to limit the invention thereto. As best seen in  FIG. 1 , system  10  includes housing  30  with housing top portion  37  oriented upwardly and housing bottom portion  38  oriented downwardly. This orientation coincides with how system  10  is intended to be mounted in situ, for example on a slanted roof, although nearly horizontal mounting would also work so long as outlet  45  is oriented on absorber upper portion  25  and inlet  40  is oriented on absorber lower portion  26 , as shown in  FIG. 6 . Outlet sleeve  24  preferably extends through housing top portion  37 . The preferred size of system  10  is approximately 4′×8′×8″. 
       FIG. 2  is a not-to-scale cross-sectional view taken along reference lines  2 - 2  of  FIG. 1 , depicting the orientation of absorber  20  within housing  30 , and various structures associated therewith. Starting outwardly, outer pane  32  would be exposed directly to sunlight and the environment in situ, and is separated from inner pane  33  by an air gap  39  which is preferably approximately 1 to 2 inches thick. Outer pane  32  and inner pane  33  are preferably made of tempered glass, but standard glass or weather and UV resistant plastic such as SABIC Innovative Plastics&#39; LEXAN® (polycarbonate) would also be suitable. Preferably panes  32  and  33  are approximately ⅛ to ¼ inches thick. Panes  32  and  33  are preferably held in position by pane supports  34 . Continuing inwardly, inner pane  33  is separated from upper surface  27  of absorber  20  by about 1 inch of space  18 . Struts  21  connect upper surface  27  to lower surface  28  of absorber  20 , best shown in  FIG. 4 , and define cells  22 , which are best illustrated in  FIGS. 3-5 . Struts  21  provide integrity by preventing distortion of absorber surfaces  27  and  28  due to water pressure, while also contributing to the structural integrity of the system. Turning back to  FIG. 2 , optionally beneath lower surface  28  is at least one spacer  35  to help prevent the unwanted escape of heat from absorber  20 . Beneath lower surface  28  (and optionally spacers  35 ) is insulation  36 . Preferably insulation  36  is an approximately 1 to 2 inches thick layer of polyisocyanurate, but other insulators such as high temperature fiberglass would be suitable as well. Insulation  36  is adjacent housing  30 . Optionally, side perimeter insulation foam  44  abuts edges of absorber. 
     Upper surface  27 , lower surface  28  and struts  21  are all comprised substantially of glass. Glass is a very unlikely material for an absorber given its reputation as an insulator, but the inventor has unexpectedly discovered that it makes an excellent absorber. Specifically, it is inert, does not corrode, can withstand extremely high temperatures and fluctuations, and does not impart impurities or taste to water. Moreover, glass manufacturing methods are well known and easily adapted to the present invention, glass is very inexpensive (as low as $5/ton at time of filing for post-consumer scrap glass), and not susceptible to commodity price spikes. Preferably the glass is post-consumer glass containing a black pigment so it exhibits a transparency value of less than 10%, however other non-clear glass would also be suitable. Alternatively, it is possible to coat the glass with a darkening agent. Used herein, “darkened glass” shall generically refer to glass that is pigmented, non-clear, coated with a darkening agent, and/or combinations thereof. The preferred pigment is iron oxide (Fe 2 O 3 ) but copper oxide, manganese oxide, nickel oxide and other metal oxides and mixtures thereof are also suitable. Iron Oxide is sometimes produced as a waste product from other industrial processes, and thus is advantageously economical and “green”. An acceptable black pigmented glass could be created by combining approximately 90% scrap soda lime glass with about 7% iron oxide plus several percent of other metal oxides such as copper, manganese, or nickel oxides. In some applications of this absorber, it may be more appropriate to utilize thermal shock resistant borosilicate glass or types of glass other than recycled soda lime container glass. 
     Cells  22  can be square, cylindrical or hexagonal, as shown in  FIGS. 3-5  respectively, noting that  FIG. 4  is in cross-section. Cells  22  are substantially bordered by struts  21 , with gaps  19  permitting the flow of water between cells, as necessary to achieve the thermosiphoning effect. Although not shown, struts  21  of cylindrical cells have holes through which water flows horizontally between cells. In other words, gaps  19  are defined by struts  21  for cylindrical cells, while gaps  19  for square and hexagonal cells  22  are defined by the space between struts  21 . 
       FIG. 9  depicts the preferred embodiment and includes baffles  16  substantially perpendicular to struts  21 . In this embodiment cells  22  are cylindrical and longitudinally separated by struts  21  which define gaps  19  (not shown). Baffles  16  define slots  17 , which facilitate emptying of system  10  when desired for cleaning, winterizing, etc. Preferably slots traverse baffles vertically all the way from top to bottom, as shown in  FIG. 9   a.    
     Cells  22  are preferably approximately ½ to approximately 10 inches wide, with approximately 1 to approximately 6 inches being more preferred and approximately 2 to approximately 4 inches being most preferred. Struts  21  are preferably approximately ⅛ to approximately 1 inch thick, with approximately ¼ to approximately ¾ inches being more preferred and approximately ⅜ to approximately ½ inches being most preferred. Preferably upper surface  27  is a texturized surface  15 , as shown in  FIG. 4 , to trap sunlight. Texturizing could be introduced after the absorber is formed, or preferably during the molding process itself. Although  FIG. 4  shows only upper surface  27  texturized, it should be understood that texturized surface  15  would likewise be on lower surface  28  if texturizing were created during the molding process since both halves would be identical. Preferably struts  21  are approximately ½ to approximately 10 inches tall (measured from absorber upper potion  25  and absorber lower portion  26 , best shown in  FIG. 2 ), more preferably approximately 1 to approximately 6 inches tall and most preferably approximately 2 to approximately 4 inches. Preferably the outer glass thickness of absorber upper potion  25  and absorber lower portion  26  are approximately 1/16 to approximately 1 inch thick, with approximately ⅛ to approximately ⅝ inches being more preferred and approximately ¼ to approximately ⅜ inches being most preferred. 
       FIG. 6  schematically depicts absorber  20  placed on a roof (without an outer insulating housing) with absorber upper portion  25  oriented upwardly, absorber lower portion  26  oriented downwardly, inlet connector  42  joined to inlet  40 , and outlet connector  43  joined to outlet  45 . As shown in  FIG. 7 , inlet connector  42  is a not an integral part of absorber  20 . Rather inlet connector  42  (and outlet connector  43 ) slips into lip  41  of absorber  20 . Connectors  42  and  43  are preferably made of glass of exactly the same composition of glass in absorber  20 , and can be affixed to absorber  20  by fusion, adhesives and other conventional methods which would be long lasting and maintain integrity in the environment. As set forth in  FIG. 7 , flange  46  abuts the end of copper tubing  49 , and is preferably secured with o-ring  48  and clamp  47 . Flared channel  31 , as best shown in  FIG. 7 , and downwardly sloping bottom  29 , as best shown in  FIG. 6 , collectively assist in achieving complete drainage in the event the system requires manual draining for severe weather, maintenance, etc. It should be noted that the aforementioned description regarding inlet connector  42  and associated attachments and features may apply likewise to outlet connector  43 , but detailed discussion of the latter have been omitted for conciseness. In situ, copper tubing  49  connected to inlet is connected to the water main, and the outlet is connected to indoor plumbing. Water is moved through system  10  when hot water tap is turned on in the building. 
     Housing  30  is essentially a “rectangular box” with one of the sides comprising at least one pane of glass (outer pane  32 ), and preferably lined on non-paned interior sides with insulation  36 . The non-paned sides of housing  30  may be constructed of wood, metal, plastic, alloys, fiberglass, polymers, or combinations thereof, but anodized aluminum is the preferred material. Housing top portion  37  and housing bottom portion  38  preferably define apertures through which structures associated with inlet  40  and outlet  45  (such as, for example, inlet connector  42 , outlet connector  43 , flange  46 , lip  41 ) may protrude through so to connect absorber  20  with copper tubing  49   
     As discussed above, the present invention is much more economical than other solar water heating systems currently available because the primary material used in its construction is glass, as opposed to copper. However, the novel manufacturing method also lowers the price of the system because the present invention does not include the complicated and labor intensive interconnection of vessels and tubes found in known systems, but rather a monolithic absorber which is comprised of two identical molded glass pieces that have been fused together to form an effective absorber. Specifically, as depicted in  FIG. 8 , molded glass half  60  is joined to an identical molded glass half  60  and fused along intersection plane  62 . Each glass half  60  individually comprises “half struts” connected to a “surface”, thereby defining “half cells” (with 5 sides for square cell embodiment), and “half gaps” associated therewith. The “surface” ultimately becomes upper surface  27  or lower surface  28 , depending on whether molded glass half  60  becomes a “top” or “bottom”. Corresponding parts must be aligned with precision prior to fusing to ensure, for example, “half struts” and “half gaps” are properly abutted one to another to permit desired thermosiphoning effect. 
     Molding and joining diagonally bisected halves to achieve offset inlet and outlet sleeves  23  and  24 , as shown in  FIG. 8 , is preferred because it facilitates drainage. However, it would alternatively be possible to mold and join two depth-, length- or width-bisected halves to form monolithic absorber  20 . 
     It should be understood that there is no functionality associated with using darkened glass (versus clear glass) to construct molded glass half  60  that will ultimately be the “bottom half”. However, using darkened glass for both halves (“top half” and “bottom half”) is preferable for ease of manufacturing, particularly given the almost negligible price associated with darkening the glass. Also, by manufacturing both top and bottom halves using glass with exactly the same composition, the final product contains a uniform coefficient of thermal expansion, in order to reduce stress during thermal cycles, both in the manufacturing process and in water heating. 
     Certain modifications and improvements will occur to those skilled in the art upon a reading of the foregoing description. By way of example, it is possible to use the novel glass absorber without the insulating housing as a pool water heater in place of less-durable plastic which is typically used for this application. Also it is possible to use the novel glass absorber panels as a building-integrated roofing material for heating or pre-heating water, or for removing heat from roofs in hot climates. Also, it is possible to use the glass absorbers in low volume active collectors. It should be understood that all such modifications and improvements have been deleted herein for the sake of conciseness and readability but are properly within the scope of the following claims.