Abstract:
In a radiation heat collector, comprising: a linear tubular heat collector member defining an internal passage for conducting fluid and a reflector having a reflecting surface partly surrounding the heat collector member, the reflector is rotatably supported around the heat collector member so that the angular position can be changed at will so as to optimize the orientation of the reflector for the given location, inclination of the solar collector, time of the year and time of the day.

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. However, the sun changes its position during the day, and the daily motion of the sun changes according to the time of the year. Also, the motion of the sun depends on the latitude of the location. A solar heat collector using a reflector provides a relatively high efficiency, but its efficiency drops sharply if the incident angle of the solar light with respect to the solar heat collector is improper.  
           [0003]    Therefore, there has been a considerable difficulty in achieving a designed efficiency due to the failure to aim the solar heat collector in an optimum direction. Even if the solar heat collector is aimed in an optimum direction at one point of time, the efficiency may drop sharply in a different point of time.  
           [0004]    Another problem in the conventional solar heat collector is its incapability to shut off the solar input. If there is no demand for hot water, the water held inside the heat collector member will boil to an excessive extent, and the resulting rise in the internal pressure may cause an adverse effect on the seals of various parts and may even affect the overall integrity of the solar heat collector. When the heat collector member is heated by the sun under a dry condition, the resulting rise in the temperature of the heat collector member may even damage the various components of the solar heat collector.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    In view of such problems of the prior art, a primary object of the present invention is to provide a radiation heat collector which can maintain a high efficiency without regard to the incident angle of the incident radiation heat.  
           [0006]    A second object of the present invention is to provide a radiation heat collector which can shut off radiation heat input when desired.  
           [0007]    A third object of the present invention is to provide a radiation heat collector which is easy to install.  
           [0008]    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; and a reflector having a reflecting surface partly surrounding the heat collector member; the reflector being rotatably supported around the heat collector member. Thereby, the angular position can be changed at will so as to optimize the orientation of the reflector for the given location, inclination of the solar collector, time of the year and time of the day.  
           [0009]    The reflector may be directed in an optimum fashion by using a powered actuator for rotating the reflector, and a controller for operating the powered actuator according to a predicted motion of the sun.  
           [0010]    When the incident radiation is desired to be shut off, the reflector may be adapted to be turned to an angular position at which the reflector is located substantially above the heat collector member. This position is also beneficial for protecting the heat collector member from external influences such as hail.  
           [0011]    For practical purposes, a plurality of heat collector members may be arranged in a mutually parallel relationship, and connected to one another in series via connecting pipes. It is also possible to combine both serial and parallel connections of the heat collector members to suit the particular need. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    Now the present invention is described in the following with reference to the appended drawings, in which:  
         [0013]    [0013]FIG. 1 is a perspective view of a heat collector embodying the present invention;  
         [0014]    [0014]FIG. 2 is a partly broken-away fragmentary side view of the heat collector of FIG. 1;  
         [0015]    [0015]FIG. 3 is a fragmentary sectional taken along line III-III of FIG. 2;  
         [0016]    [0016]FIG. 4 is a cross sectional view showing one of the heat collector modules; and  
         [0017]    [0017]FIGS. 5 and 6 are views similar to FIG. 2 showing the mode of operation of the heat collector. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    [0018]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.  
         [0019]    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.  
         [0020]    Referring to FIGS. 2 and 3, the reflector  4  of each heat collector module  2  is rotatably supported by bearings  6  around the heat collector member  3  (point  0  in FIG. 2). The bearings  6  may be either slide bearings or roller bearings. This arrangement eliminates the need for a pivot shaft or the like, and simplifies the overall structure. The adjacent heat collector modules  2  are spaced from each other so as to avoid any interference between the reflectors  4 . A pinion  7  is centrally attached to an end of each reflector  4 , and meshes with a common rack  8 . The rack  8  is supported by rollers  11  so as to be linearly moveable, and has one end which projects out of the casing  1  and is fitted with a handle  9 . Thus, the reflector  4  of each heat collector module  2  can be rotated to a desired angle by operating the handle  9  toward and away from the casing  1 . Alternatively or additionally, a powered actuator such as an electric motor  10  may be used as shown by the imaginary lines in FIG. 1. In this case, the output shaft of the electric motor  10  may be fitted with a pinion which meshes with the rack  8 . If desired, the electric motor  10  may be connected to a controller  12  which can determine the orientation of the reflectors  4  according to the latitude of the location, angular position of the heat collector, time (season) of the year and time of the day so that the reflectors  4  may be directed to the optimum direction at all times.  
         [0021]    The reflectors  4  of the heat collector modules  2  may each 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. The central ridge  4   a  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.  
         [0022]    The mode of operation of this heat collector is described in the following. Suppose that the heat collector is placed at a 30 degree angle relative to the horizontal plane by taking into account the latitude of the location. The heat collector in this case is adapted to rotate each reflector by 30 degrees from its neutral position in either direction by actuating the rack  8  and pinions  7 . The electric motor is controlled so as to direct each reflector  4  to the sun at all times. If the reflectors  4  are placed too close to one another, each reflector may prevent the sun ray from reaching the adjacent reflectors. However, by suitably spacing the reflectors  4  from one another, it is possible to allow each reflector to receive a same amount of light without regard to the position of the sun, and ensure a stable heat collection over a long period of time.  
         [0023]    When there is no need for collecting heat due to the absence of any demand for hot water, for instance, the reflectors  4  may be rotated to a position to cover the heat collector members  3  or to surround the heat collector members  3  with their reflective surfaces. If necessary, the back side or convex side of each reflector may be given with a reflective surface to optimize the shielding of the incident sun light. This prevents excessive boiling of the water or excessive heating of the heat collector members  3 . Excessive boiling of the water may have an adverse effect on seal members and integrity of the entire assembly. Similarly, excessive heating of the heat collector member under a dry condition may cause an adverse effect on the material of the various components. Also, when sunlight is not available or at night, covering the heat collector members  3  with the reflectors  4  reduces the radiation loss of heat by reflecting back the thermal radiation from the heat collector members  3  onto themselves. Additionally, the reflectors  4  may be used for covering the heat collector members  3  to protect them from external influences such as hail.  
         [0024]    When a controller  12  is used in association with the electric motor  10 , the motor  10  may be controlled so as to direct the reflectors  4  to the optimum position at all times by taking into account the latitude of the location, installed angle of the solar collector, time of the year or season and time of the day. Typically, the controller  12  is programmed so as to control the motor  10  according to the predicted motion of the sun.  
         [0025]    In the above described embodiment, the reflectors  4  were turned by using an arrangement including a pinion attached to each reflector and a rack, but other arrangements are also possible. For instance, the pinions attached to the adjacent reflectors may be meshed directly to each other to synchronize the motion of the reflectors. Alternatively, a chain, belt or linkage may be employed to achieve the same purpose. The actuator may also consist of a linear motor, hydraulic actuator or the like.  
         [0026]    Each reflector was shaped like a trough defining a CPC reflective surface in the illustrated embodiment, but the reflective surface may consist of a simple parabolic surface or any approximately parabolic surface. In this case, the advantage of turning the reflectors is even greater because a parabolic reflective surface is known to be affected by the failure to squarely face the sunlight more severely than the CPC reflective surface.  
         [0027]    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.