Abstract:
In a heat collector comprising a linear tubular heat collector member defining an internal passage for conducting fluid a reflector having a reflecting surface partly surrounding the heat collector member and a heat insulating member provided in association with the reflector. The insulating member is typically directly attached to the reflector. The heat insulating member improves the thermal efficiency of the heat collector.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to a radiation heat collector typically employed to collect solar heat to fluid media such as water.  
         BACKGROUND OF THE INVENTION  
         [0002]    Conventionally, various forms of solar heat collectors have been proposed. Typically, a solar heat collector comprises a tubular heat collector member for conducting water that is to be heated, and a reflector for converging incident solar light upon the heat collector member. The reflector may consist of sheet metal having a reflective surface which is formed into a per se known CPC (compound parabolic concentrator) shape and reinforced by a plurality of ribs. The CPC is given as a combination of a pair of parabolic segments at an angle which is joined by an involute curve. The CPC allows an incident solar ray to efficiently converge upon the heat collector member placed in a bottom part thereof over a wide range of incident angle. For details of the CPC, reference should be made to U.S. Pat. No. 4,002,499 issued Jan. 11, 1977 to R. Winston.  
           [0003]    However, because the CPC surface has a relatively complex profile, it was difficult to form sheet metal into the desired shape, and the material for the reflector was required to have a significant thickness to ensure an adequate rigidity and maintain the original shape. Therefore, the manufacturing cost was high, and the reflector was undesirably heavy. Because such a solar heat collector is a consumer item, and typically placed on a roof, such disadvantages are highly detrimental for the market acceptability.  
           [0004]    Furthermore, the thermal efficiency of a solar heat collector is highly crucial in making the solar heat collector acceptable in the market because it has to compete with other forms of heat sources such as gas and electricity. Heat insulation for the collected heat is an important factor in determining the thermal efficiency, but again it has to be accomplished without substantially increasing the cost and weight of the solar heat collector.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    In view of such problems of the prior art and recognitions by the inventors, a primary object of the present invention is to provide a radiation heat collector which can improve the thermal efficiency by favorably insulating the collected heat.  
           [0006]    A second object of the present invention is to provide a radiation heat collector which is light in weight.  
           [0007]    A third object of the present invention is to provide a radiation heat collector which is economical to manufacture.  
           [0008]    A fourth object of the present invention is to provide a radiation heat collector which is provided with a reflector which can be given with a precise surface profile, and can maintain it during use.  
           [0009]    According to the present invention, such objects can be accomplished by providing a heat collector, comprising: a linear tubular heat collector member defining an internal passage for conducting fluid; a reflector having a reflecting surface partly surrounding the heat collector member; and a heat insulating member provided in association with the reflector. The insulating member is typically directly attached to the reflector. The heat insulating member improves the thermal efficiency of the heat collector.  
           [0010]    The insulating member make take the form of a substantially transparent module cover which covers an open end of the reflector. The cover allows the radiation input freely while preventing the dissipation of the heat collected in the heat collector member.  
           [0011]    Alternatively or additionally, the insulating member may comprise a thermally insulating layer attached to a backside of the reflector. It is advantageous to make use of a part of the reflector as the insulating member. For instance, the reflector may comprise a support member defining a surface profile for a reflective surface, and a reflective layer formed over the surface profile to define a reflective surface, the support member serving as the thermally insulating layer. Alternatively, the reflector may comprise a stamp formed or roll formed sheet metal defining a reflective surface, and a support member supporting the stamp formed sheet metal from backside thereof, the support member serving as the thermally insulating layer.  
           [0012]    The reflector may also comprise a stamp formed or roll formed sheet metal defining a reflective surface, and a plurality of ribs formed on a back side thereof for reinforcement. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    Now the present invention is described in the following with reference to the appended drawings, in which:  
         [0014]    [0014]FIG. 1 is a perspective view of a heat collector embodying the present invention;  
         [0015]    [0015]FIG. 2 is a cross sectional view showing one of the heat collector modules;  
         [0016]    [0016]FIG. 3 is a perspective view of a second embodiment of the present invention;  
         [0017]    [0017]FIG. 4 is a cross sectional view showing one of the heat collector modules of the heat collector illustrated in FIG. 3;  
         [0018]    [0018]FIG. 5 is a cross sectional view of the heat collector illustrated in FIG. 3;  
         [0019]    [0019]FIG. 6 is a perspective view of a third embodiment of the present invention; and  
         [0020]    [0020]FIG. 7 is a cross sectional view showing one of the heat collector modules of the heat collector illustrated in FIG. 6. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    [0021]FIG. 1 generally illustrates a radiation heat collector in the form of a solar water heater embodying the present invention. This heat collector comprises a casing  1  in the form of a box having an open top end, and a plurality of heat collector modules  2  placed one next to another inside the casing  1 . Each heat collector module  2  comprises a heat collector member  3  consisting of a tubular member, and a reflector  4  for reflecting solar light onto the heat collector member  3 . The tubular heat collector members  3  are connected to one another in series via a connecting pipe  3   a , and one end of the serial connection is connected to a cool water source via a pump or the like while the other end thereof is connected to a user of hot water such as a storage tank and a radiator. If desired, the tubular heat collector members  3  may also be connected to one another in parallel. It is also possible to combine serial and parallel connections as desired.  
         [0022]    The open end of the casing  1  may be closed by a sheet or a plurality of sheets of glass or other transparent material  5  to thermally insulate the interior of the casing  1 . It has been proven to be advantageous to use a double glass pane, optionally having an evacuated intermediate layer. If desired, the interior of the casing  1  may be evacuated for an improved thermal insulation.  
         [0023]    Referring to FIG. 2, each reflector  4  is formed by molding plastic material such as foamed urethane or the like having a high level of thermal insulation, and is provided with a reflective surface  4   a  defined by a reflective layer  6 . The reflective layer  6  may be formed by any one of a number of known methods including, not exclusively, plating, ion plating and other physical or chemical film forming processes, and coating. According to this arrangement, the reproducibility and stability of the shape of the reflective surface can be ensured more easily and more economically than the more conventional arrangement using stamp formed sheet metal to form the reflector. The surface contour of the reflective surface  4   a  is determined by the surface profile of the underlying surface of the main body of the reflector  4  made of thermally insulating material.  
         [0024]    The reflective surface  4   a  of each reflector  4  is formed as a per se known CPC (compound parabolic concentrator) shape. The CPC is given as a combination of a pair of parabolic segments (side segments)  4   b  at angle θ which is joined by an involute curve (bottom segment)  4   c.  The bottom segment  4   c  is provided with a central ridge  4   d.  The CPC allows an incident solar ray to efficiently converge upon the heat collector member  3  placed in a bottom part thereof over a wide range of incident angle. For details of the CPC, reference should be made to U.S. Pat. No. 4,002,499 issued Jan. 11, 1977 to R. Winston. The central ridge  4   d  in the bottom part of each reflector  4  ideally touches the heat collector member  3 , but in practice is spaced from the heat collector member  3  so that the loss of heat from the heat collector member  3  due to such a contact may be avoided.  
         [0025]    Each reflector  4  was shaped like a trough defining a CPC reflective surface in the illustrated embodiment, but the reflective surface  4   a  may consist of a simple parabolic surface or any approximately parabolic surface. Because each reflector is thermally insulated, dissipation of heat via the casing  1  can be minimized, and the fabrication process is simplified because no separate thermal insulation material is required.  
         [0026]    FIGS.  3  to  5  show a second embodiment of the present invention. This heat collector comprises a casing  11  in the form of a box having an open top end, and a plurality of heat collector modules  12  placed one next to another inside the casing  11 . Each heat collector module  12  comprises a heat collector member  13  consisting of a tubular member, and a reflector  14  for reflecting solar light onto the heat collector member  13 . The tubular heat collector members  13  are connected to one another in series via a connecting pipe  13   a,  and one end of the serial connection is connected to a cool water source via a pump or the like while the other end thereof is connected to a user of hot water such as a storage tank and a radiator.  
         [0027]    The open end of the casing  11  is closed by a cover  15  consisting of glass or other substantially transparent material. Thus, the interior of the casing  11  is entirely enclosed. The reflectors  14  of the heat collector modules  12  may each consist of stamp formed or roll formed sheet metal having a reflective surface which is formed into a per se known CPC (compound parabolic concentrator) shape and reinforced by a plurality of ribs  14   a.    
         [0028]    As best shown in FIG. 4, the open upper end of each heat collector module  12  is closed by a planar module cover  17  made of glass or other substantially transparent material, and the interior of each heat collector module  12  is entirely enclosed. This prevents heat from dissipating out of the heat collector module  13 .  
         [0029]    As best shown in FIG. 5, a layer of thermally insulating material  16  consisting foamed plastic, mineral fibers and other known thermally insulating material is placed in a bottom part of the casing  11 , and each heat collector module  12  is snugly received in the complementary recesses formed on the surface of the thermally insulating layer  16 .  
         [0030]    [0030]FIGS. 6 and 7 show a third embodiment of the present invention. In this case, no casing is used, and a plurality of heat collector modules  22  are arranged in parallel to one another with their end portions aligned along either side. A pair of connecting pipe covers  25   a  and  25   b  are arranged on either side of the heat collector module assembly. Each heat collector module  23  comprises a tubular heat collector member  23  and a reflector  24  for reflecting solar light onto the heat collector member  23 . The heat collector modules  22 , more specifically the reflectors  24 , are each attached to the connecting pipe covers  25   a  and  25   b  at either end thereof so that these connecting pipe covers  25   a  and  25   b  retain the shape of the entire assembly.  
         [0031]    The tubular heat collector members  13  are connected to one another in series via a connecting pipe  23   a,  and one end of the serial connection is connected to a cool water source via a pump or the like while the other end thereof is connected to a user of hot water such as a storage tank and a radiator.  
         [0032]    Each reflector  24  is formed by stamp forming or roll forming sheet metal, and its back side is attached, via a bonding agent or the like, to a complementary surface of a support member  26  formed by molded plastic material such as foamed urethane or the like having a high level of thermal insulation and capability to retain the shape of the reflector  24 . The reflective surface  24   a  of each reflector  24  is formed as a per se known CPC (compound parabolic concentrator) shape. As best shown in FIG. 7, the open upper end of each heat collector module  22  is closed by a planar module cover  27  made of glass or other substantially transparent material, and the interior of each heat collector module  22  is entirely enclosed. This prevents heat from dissipating out of the heat collector module  22 .  
         [0033]    The interior of each connecting pipe cover  25   a  and  25   b  is appropriately insulated by using foamed plastic, mineral fibers or the like. The connecting pipe covers  25   a  and  25   b  have the additional function of protecting the connecting pipes  23  from external influences such as moisture and impacts.  
         [0034]    Although the present invention has been described in terms of a preferred embodiment thereof, it is obvious to a person skilled in the art that various alterations and modifications are possible without departing from the scope of the present invention which is set forth in the appended claims.