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You are an expert at summarizing long articles. Proceed to summarize the following text: 
TECHNICAL FIELD 
       [0001]    The present invention relates to a window having an integral solar heat collector. 
       BACKGROUND OF THE INVENTION 
       [0002]    Windows may incorporate a transparent solar collector and thereby offer a more pleasing architectural aesthetic than opaque solar heat collectors. These windows typically include two glass sheets between which either air or a liquid is received—the latter being described in GB2450474. A problem experienced with these liquid-circulating transparent collectors has been the necessity for connecting the window to a remote heat exchanger in which the energy-absorbing fluid piped from the collector transfers heat energy to some other fluid for utilisation. This has involved an undesirably large amount of plumbing, pump and pipe fittings, together with the additional volume of heat absorbing fluid required to fill such plumbing, as well as the labour and materials in the piping and assembly thereof. It also has involved excessive opportunity for leakage, property damage and loss of comparatively expensive energy-absorbing working fluid, say when a transparent pane is broken. It is an object of the present invention to overcome or substantially ameliorate the above disadvantages or more generally to provide an improved heat absorbing window. 
       DISCLOSURE OF THE INVENTION 
       [0003]    According to one aspect of the present invention there is provided a heat-absorbing window assembly comprising: 
         [0000]    first and second transparent panes separated from one another to provide a first passageway therebetween for receiving a working fluid;
 
a frame in which a periphery of the panes is secured;
 
a heat exchanger secured in the frame, the heat exchanger having a second passageway therein for the working fluid and a third passageway therein for a service fluid;
 
and conduit means coupling the first and second passageways to make a working fluid circuit in the frame by which heat energy absorbed by the working fluid in the first passageway is supplied to the heat exchanger.
 
         [0004]    Preferably the frame includes elongate upper and lower members in which opposing upper and lower ends of the first passageway are received, and the second and third passageways extend longitudinally within the upper member. 
         [0005]    Preferably inlet and outlet ports proximate opposing ends of the third passageway extend through openings in the frame proximate opposing ends of the upper member. 
         [0006]    Preferably the conduit means comprise upper and lower headers extending adjacent upper and lower ends of the first passageway respectively, longitudinally spaced openings in the upper and lower headers providing fluid communication between each header and its respective end of the first passageway, and a first and second conduit connecting the second passageway to the upper and lower headers respectively. 
         [0007]    Preferably the window further comprises a tank within the frame for providing an expansion space. Preferably the tank is mounted in the upper member and connected to the first conduit. 
         [0008]    Preferably the second and third passageways are coaxial, most preferably the third passageway is annular in cross section and surrounds the second passageway. 
         [0009]    Preferably the third passageway is provided in a tubular member surrounded by thermal insulation and received within the upper frame member. 
         [0010]    Preferably the service fluid flows through the third passageway in a direction opposite the flow of the working fluid through the second passageway. 
         [0011]    This invention provides a heat-absorbing window assembly which is effective and efficient in operational use, and which may be economically constructed. The heat-absorbing window has a compact working circuit all located within the window frame, which minimizes the amount of working fluid in the system. This also reduces the flow friction and heat losses in the circuit, and results in better heat transfer characteristics. Pumping energy is eliminated in the recirculating liquid flow, which is self regulated as the higher buoyant force induces higher flow resistance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: 
           [0013]      FIG. 1  is a schematic front sectional view of a heat absorbing window according to an exemplary embodiment of the invention, and 
           [0014]      FIG. 2  is a schematic section along line AA of  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    A heat-absorbing window includes elongate upper and lower members  10 ,  11  and side members  12 ,  13  formed of metal or a rigid polymer. The members  10 - 13  are hollow, having an elongate open mouth in which the edges of first and second panes  14 ,  15  of transparent glass or polymer are received. The members  10 - 14  are connected by joints (not shown) at their ends to form a rectangular window frame  16 . In use the frame  16  is fastened in an architectural opening and may be fixed in position, or optionally it may be mounted by hinges or rails for pivoting or sliding movement. The frame is mounted upright in the orientation shown in the drawings, but may be inclined upwardly as when mounted in a pitched roof to provide a skylight, or when a hinged window is opened. 
         [0016]    The first and second panes  14 ,  15  are flat, rectangular and parallel, being spaced apart to define a first passageway  17  therebetween. The long edges of the panes  14 ,  15  received in the side members  12 ,  13  are sealed closed, while the short edges are connected to upper and lower distribution headers  18 ,  19 . To improve the heat absorption of the working fluid, the surface of the inner transparent pane  14  (the pane that bounds the indoor space) can be applied with a layer of reflective film (not shown), subjecting the first passageway  17  to a reflected radiation on its path back to the ambient environment. This reflective layer also advantageously also reduces the space heat gain within the building. To extend the functionality of the window, the outer transparent pane  15  can be a photovoltaic glazing of which the solar cells (not shown) can be cooled by the fluid flow in the first passageway  17 , and the electricity generated is used to support other building activities. 
         [0017]    The headers  18 ,  19  are received in the upper and lower members  10 ,  11  respectively and comprise like tubular members with longitudinally spaced openings in their walls that communicate with upper and lower edges of the first passageway  17 . The end  20  of the upper header  18  is closed, and the opposing end  21  is connected by a conduit  22  to a second passageway  23  formed in a copper tube  24 . The end  25  of the lower header  19  is connected by a conduit  26  to the second passageway  23 , while the opposing end  27  is connected via a shut-off valve  28  to a charging and discharging port  29 . For draining, the lower header  19  slopes towards the end  27 . The patterns of openings in the headers  18 ,  19  for connection to the first passageway  17  are arranged to produce a uniform upward flow of fluid across the full width of the first passage  17 . The cross-section of the distribution headers  18 ,  19  may alternatively be rectangular, or may vary in shape or size along its length. 
         [0018]    The copper tube  24  and the second passageway  23  defined by it form part of a narrow elongate heat exchanger  30  mounted in the upper member  10 , which also includes an outer tube  31  coaxial with the tube  24  to define a third passageway  32  which is annular in cross section. The third passageway  32  is substantially coextensive with the second passageway  23  and includes inlet and outlet ports  33 ,  34  proximate opposing ends of the third passageway  32  that extend through openings in the frame proximate opposing ends of the upper member  10 . The heat exchanger  30  is fixed in the upper frame member  10  by means of pipe fittings  38  fixed at opposing ends of the hollow member or outer tube  31  and extending through respective apertures in the frame member  10 . The fittings  38  thus serve both to mechanically mount the heat exchanger  30  and to provide a fluid connection to the inlet and outlet ports  33 ,  34 . In alternative embodiments (not shown) one or other of the tubes  24 ,  31  may be integral with the upper frame member  10 . 
         [0019]    A tank  35  is mounted within the frame for providing an expansion space. As illustrated, the tank  35  is mounted in the upper member  10  and connected to the conduit  22 . An air vent (not shown) is provided for venting air from the system. For air venting the heat exchanger  30  and upper header  18  are sloped upward toward the tank  35 , the connection to the conduit  22  thereby being at the highest point in the circuit. 
         [0020]    The window frame  16  is filled with thermal insulation material  36  such as polyurethane foam, surrounding the heat exchanger  30 , the conduits  22 ,  26  and the periphery of the panes  14 ,  15 . 
         [0021]    The first passageway  17 , headers  18 ,  19  and conduits  22 ,  26  are filled with a working fluid such as a transparent fluid such as water or alcohol, or a mixture of water and alcohol. Optionally the working fluid can be another pure or mixed transparent liquid, or semi-transparent (coloured) liquid to alter the optical properties, in particular the solar transmittance of the glazing in the visible range. Solar radiation absorption elevates the temperature of the working fluid, and induces a natural circulation flow as a result of the thermosyphon effect. Referring to  FIG. 1 , the working fluid flows in an anti-clockwise circuit up through the first passageway and through the heat exchanger  30 , returning via the conduit  26  to the first passageway. 
         [0022]    A service fluid, as for providing a hot water service in a building, is connected to flow between the inlet and outlet  33 ,  34  in counter-flow to the working fluid in the heat exchanger  30 . In the case of a hinged window, the inlet and outlet  33 ,  34  are connected via two flexible hoses to the service fluid pipework inside the building structure. A plurality of heat-absorbing windows can be connected together by the service fluid pipework, either in parallel or, series, or a combination thereof, in order to maximize the heat collecting capacity. Additionally a phase-change-material can be applied at the flow channel  31  of the heat exchanger  30 . This additional heat storage helps to stabilize the working temperature of the service fluid and thus further improve the overall heat exchange performance. When the working fluid has been drained out, the window air circulation through the first passageway provides a limited amount of heat exchange capability. 
         [0023]    Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof. For instance, a refrigerant could be used as the working fluid such that the first passageway  17  will behave as an evaporator and the heat exchanger will behave as a condenser. Alternatively, to enhance thermal comfort in winter a hot service fluid could be directed to the heat exchanger and a pump may be mounted to the frame for circulating the working fluid.

Summary:
A window with an integral solar heat-absorber is provided in a compact, low-cost package. Two transparent panes are separated from one another to provide a first passageway for receiving a working fluid. The periphery of the panes is secured in a frame in which a heat exchanger is also secured, the heat exchanger having a second passageway for the working fluid and a third passageway for a service fluid. The first and second passageways are coupled to make a working fluid circuit.