Patent Publication Number: US-7902531-B2

Title: Window assembly for irradiating infrared light

Description:
FIELD OF THE INVENTION 
     The invention relates to a window assembly for irradiating infrared light. 
     BACKGROUND OF THE INVENTION 
     Methods to manage infrared radiation from the sun are widely used in buildings. For example, there are windows equipped with coatings that reflect the infrared radiation from sun in order to avoid a too high heating up of the inside of the building. Those coatings typically comprise thin metal films of copper, gold or silver, which are transparent for visible light and reflective for infrared light. A more advanced heat management is obtained by means of so called smart coatings. These coatings are based on thermochromic materials, which have reflective properties that change with temperature. In the winter these coatings are transparent for infrared light from the sun and in the summer these coatings reflect the infrared light. In this way the inside of the building is heated by the sun in the winter and not heated by the sun in the summer. Furthermore, there exist windows in buildings that are equipped with a conductive coating, such as for example indium tin oxide (ITO). By means of an electric current the window is heated thereby creating infrared radiation and thus heating the inside of the building. 
     JP-63297245 discloses far infrared radiation glass that generates and radiates intense far infrared radiation in a room to warm a room in high efficiency by forming a far infrared radiation layer on a plate glass. The disadvantage of this construction is that the same amount of heat is radiated to the outside of a building as to the inside of the building thus loosing approximately half of the infrared radiation. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide for a window assembly for irradiating infrared light into one main direction without a natural infrared source, such as the sun. The invention is defined by the independent claims. Advantageous embodiments are defined by the dependent claims. 
     This object is achieved by the window assembly according to the invention, which is characterized in that the window assembly for irradiating infrared light comprises a light guide for infrared light, which is formed by a gap between a first transparent substrate, having an exterior surface and an interior surface, which faces the light guide, and a second transparent substrate substantially parallel to the first transparent substrate and having an exterior surface and an interior surface, which faces the light guide and the interior surface of the first transparent substrate, wherein a first and a second reflective layer, that are both substantially reflective for infrared light, extend over the interior surfaces of respectively the first and the second transparent substrate and wherein the second reflective layer is provided with an opening through which at least part of the infrared light exits the light guide. In this way the infrared light leaves the light guide in one main direction through the opening of the second reflective layer and through the second transparent substrate, thereby generating heat in one main direction only. 
     An embodiment of the window assembly according to the invention further comprises an infrared light source for directing infrared light into the light guide. An advantage of this embodiment is that more heat is created because of the use of an infrared light source for generating the infrared light. Another advantage is that heat is generated without applying a natural infrared source, such as the sun. 
     An embodiment of the window assembly according to the invention further comprises means for directing the infrared light from the infrared light source into the light guide in a direction that is not parallel to the interior surfaces of the first and second transparent substrate. In this way the infrared light is directed to the reflective first and/or second reflective layer and will eventually exit the light guide via the opening in the second reflective layer. In a further embodiment of the window assembly according to the invention, the directing means comprises a parabolic reflector partially surrounding the infrared light source. The parabolic reflector or mirror collimates the infrared light to such an extent that the infrared light from the infrared light source is directed into the light guide. In an advantageous embodiment according to the invention, the parabolic reflector is movable around the infrared light source. This provides for a simple way of directing the infrared light such that it will be reflected on the first and/or second reflective layer. 
     In an embodiment of the window assembly according to the invention a further reflector for infrared light is located in the light guide in the proximity of the infrared light source. This provides for a redirection of the infrared light from the infrared light source into the direction of the first and/or second reflective layers. 
     An embodiment of the window assembly according to the invention, further comprises a reflector located on the second transparent substrate for redirecting the exiting infrared light. This provides for a way to redirect the infrared light that exits through the opening of the second reflective layer into a preferred direction. In a further embodiment according to the invention, the reflector for infrared light is located on the exterior surface of the second transparent substrate. In this way the reflector is easier to adapt, move or remove when not in use. In an advantageous embodiment according to the invention, the reflector is transparent for visible light. 
     In an embodiment of the window assembly according to the invention the infrared light source is located outside the light guide and faces the exterior surface of the first transparent substrate or the exterior surface of the second transparent substrate. This allows for a simple maintenance of the infrared light source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects of the invention will be further elucidated and described with reference to the drawings, in which: 
         FIG. 1  is a schematic cross-sectional view of a first embodiment of a window assembly according to the invention; 
         FIG. 2  is a schematic cross-sectional view of a second embodiment of a window assembly according to the invention; 
         FIG. 3  is a schematic cross-sectional view of a third embodiment of a window assembly according to the invention; and 
         FIG. 4  is a schematic cross-sectional view of a fourth embodiment of a window assembly according to the invention. 
     
    
    
     The figures are not drawn to scale. In general, identical components are denoted by the same reference numerals in the figures. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1  is a schematic cross-sectional view of a first embodiment of a window assembly according to the invention. In this first embodiment a window assembly  100  comprises a first window pane  2  that is placed parallel to a second window pane  3  wherein the first window pane  2  and the second window pane  3  are separated by a light guide  5 , which is formed by a gap between the first window pane  2  and the second window pane  3 . The first window pane  2  and the second window pane  3  are both transparent for visible light and infrared light, and are made of, for example, glass, preferably of insulating glass. The surface of the first window pane  2  that faces the light guide  5  is coated with a first reflective layer  12 , and the surface of the second window pane  3  that faces the light guide  5  is coated with a second reflective layer  13 . The first reflective layer  12  and the second reflective layer  13  are both reflective for infrared light. Preferably, the first reflective layer  12  and the second reflective layer  13  are both transparent for visible light. An infrared light source  1  is, in this embodiment, located inside the light guide  5  and radiates infrared light L into the remainder of the light guide  5 . The infrared light L is reflected on the surface of the first reflective layer  12  and on the surface of the second reflective layer  13 . To enable the infrared light L to exit the light guide  5 , the second reflective layer  13  is provided with openings  21 . As is shown in  FIG. 1 , the infrared light L exits the light guide  5  via at least one of the openings  21  in the second reflective layer  13 . The opening  21  is transparent for infrared light and for visible light. The size and density of the openings  21  determines the amount of infrared light L that exits the light guide  5 . Preferably the openings  21  are small enough that they are hardly visible and distributed in such a way that there is a uniform heating, and the openings  21  are large enough to let a substantial part of the infrared light L exit the second window pane  3  before the bottom or end of the light guide  5  is reached. The advantage of this construction is that the infrared light L leaves the light guide  5  only in directions that are mainly oriented downward, which is the main direction into which the infrared light L is radiated into the remainder of the light guide  5  by the infrared light source  1 , and to one side, which in this case is the side of the second window pane  3 . So, the window assembly  100  behaves as a directional source for the infrared light L. 
     The reflective layers  12  and  13  are, for example, coated with an indium-tin-oxide (ITO) layer, which is an electrically conductive material that is able to generate heat in case a current or a voltage is applied. Another example of a material, that may be applied for the first reflective layer  12  and the second reflecting layer  13 , is copper, gold or silver. To protect these metal layers against corrosion and to increase the transmittance of visible light, the metal coating may be sandwiched between dielectric coating layers such as TiO 2 , Bi 2 O 3  and/or ZnO. Also combinations of these layers are possible. The light guide  5  is, for example, filled with air, because the absorption of the infrared light L in air is relatively low. It is also possible to apply another material, which has a sufficiently low absorption, like quartz. Preferably the light guide  5  is filled with an inert gas, to lower the absorption of the infrared light L in the light guide  5  further. 
     The infrared light source  1  is, for example, an infrared lamp or a LED (Light Emitting Diode) source. The window assembly according to the invention should mimic the heat radiated by the sun through a window, which is characterized by the intensity of that radiation. In a practical situation in the order of several hundreds of Watts per square meter of solar radiation is radiated through a window pane, taking into account, amongst others, the transmittance of the solar radiation by the window pane. Therefore, an infrared lamp is preferred, because typical infrared lamps are available from 500 Watt to 3000 Watt or more. 
       FIG. 2  is a schematic cross-sectional view of a second embodiment of a window assembly according to the invention. Like parts are numbered in the same way as in the previous figures. In this second embodiment a window assembly  110  comprises a parabolic mirror  42  that is placed near the infrared light source  1  in order to collimate the infrared light L generated by the infrared light source  1  such that a substantial part of the infrared light L is directed directly into the remainder of the light guide  5 . Preferably the infrared light L enters the light guide  5  with an angle not equal to zero with the surface of the first and second window pane  2 , 3  to provide for most of the infrared light L exiting the light guide  5  through the second window pane  3  and reaching the first reflective layer  12  or the second reflective layer  13 . For this purpose the window assembly  110  comprises a first reflector  34 , which is reflective for the infrared light L and redirects the infrared light L by reflection, that is radiated by the infrared light source  1  directly or via the parabolic mirror  42 , into a direction that is not parallel to the surfaces of the first and second reflective layers  12 ,  13 . Furthermore, the window assembly  110  comprises a second reflector  31 , which is reflective for the infrared light L and redirects the exiting infrared light L. The second reflector  31  is, in this embodiment, located inside the light guide  5  at or near the opening  21 , as is shown in  FIG. 2 . In this way, it is possible to direct the exiting infrared light L into a direction that is different from the downward direction, which is the main direction into which the infrared light L is radiated by the infrared light source  1  and the parabolic mirror  42 . Additionally, more second reflectors  31  can be placed at or near the other openings  21 . The second reflector  31  comprises, for example, aluminum, or a material that is both reflective for infrared light and transparent for visible light. 
       FIG. 3  is a schematic cross-sectional view of a third embodiment of a window assembly according to the invention. Like parts are numbered in the same way as in the previous figures. In this third embodiment a window assembly  120  comprises a movable parabolic mirror  43  that is placed near the infrared light source  1  in order to collimate the infrared light L generated by the infrared light source  1  such that a substantial part of the infrared light L is directed directly into the remainder of the light guide  5 . The movable parabolic mirror  43  can be moved or pivoted into another position near the infrared light source  1  such that the infrared light L, which is radiated by the infrared light source  1 , is directed into a direction that is not parallel to the surfaces of the first and second reflective layers  12 ,  13 . The window assembly  120  comprises a third reflector  32 , which is placed on an exterior surface of the second window pane  3 , which surface is opposing the coated surface of the second window pane  3 . The third reflector  32  is reflective for the infrared light L and redirects the exiting infrared light L by reflection, as is shown in  FIG. 3 . Additionally, more third reflectors  32  can be placed on the exterior surface of the second window pane  3 , preferably formed from well-known lamella. In this way, it is possible to direct the exiting infrared light L into a direction that is different from the downward direction, which is the main direction into which the infrared light L is radiated by the infrared light source  1  and the movable parabolic mirror  43 . In case lamella are applied that can be pivoted into another position, the direction of the exiting light L can be varied. The third reflector  32  comprises, for example, aluminum, or a material that is both reflective for infrared light and transparent for visible light. A further advantage of the third reflector  32  is ease of maintenance, because it is difficult to reach the second reflector  31  of window assembly  110  being placed inside the light guide  5 , whereas the third reflector  32  of window assembly  120  is placed outside the light guide  5  making the third reflector  32  easy to reach and maintain. 
       FIG. 4  is a schematic cross-sectional view of a fourth embodiment of a window assembly according to the invention. Like parts are numbered in the same way as in the previous figures. The fourth embodiment comprises a window assembly  130  in which the infrared light source  1  is placed outside the light guide  5  at the side of the second window pane  3 , facing the exterior surface of the second window pane  2 , thus providing for an easy access of the infrared light source  1 , for example for maintenance. Alternatively, the light source  1  can be placed outside the light guide  5  facing the exterior surface of the first window pane  2 . The movable parabolic mirror  43  that is placed near the infrared light source  1 , collimates the infrared light L generated by the infrared light source  1  such that a substantial part of the infrared light L is directed into the light guide  5  via the second window pane  3 . The angular spread of the infrared light L is in this case such that it enters the light guide  5  in that area where the second reflective layer  13  is not provided on the second window pane  2 . Inside the light guide  5  a fourth reflector  33  is provided such that the infrared light L is redirected into the light guide  5  in a substantial downward direction which is not parallel to the main surfaces of the first and second reflective layers  12 ,  13 . In the case that the parabolic mirror  43  results in a sufficiently small angular spread of the infrared light L entering the light guide  5 , the fourth reflector  33  may be omitted. 
     The window assemblies  100 , 110 , 120 , 130  may be placed in front of a window or, for example, in front of a wall inside a building. 
     In summary, the invention provides for a window assembly for irradiating infrared light comprises a light guide for infrared light, which is formed by a gap between a first transparent substrate, having an exterior surface and an interior surface, which faces the light guide, and a second transparent substrate substantially parallel to the first transparent substrate and having an exterior surface and an interior surface, which faces the light guide and the interior surface of the first transparent substrate. A first and a second reflective layer, that are both substantially reflective for infrared light, extend over the interior surfaces of respectively the first and the second transparent substrate. The second reflective layer is provided with an opening through which at least part of the infrared light exits the light guide. In one embodiment, the window assembly further comprises an infrared light source for directing the infrared light into the light guide. In this way the infrared light leaves the light guide in one main direction through the opening of the second reflective layer and through the second transparent substrate, thereby generating heat in one main direction only. 
     It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word “comprising” does not exclude the presence of other elements or steps than those listed in a claim. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements.