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You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE INVENTION 
       [0001]    The present invention relates to the field of window and curtain wall assemblies; more specifically, concealed window panel and fastener latching mechanisms to connect an arrangement of such window panels. 
       BACKGROUND OF THE INVENTION 
       [0002]    Unitized window wall systems have been used for skyscrapers and building structural systems. The unitized window wall system provides window panels that come with mullion frames within the panel before being installed to the building façade. The window panels include a glazing, which comes with double or triple glass panes (double glass panes with a thin film between) and is filled with a noble gas. The noble gas, typically argon or xenon, is used for thermal insulation and is installed on an exterior side of the mullion frames. The mullion frames then attach to one another by a series of clips or are fastened with bolts and nuts to the building structural system. 
         [0003]    However, the unitized window wall system has limited space, which causes low thermal resistance and does not allow for additional layers of glazing panel. Further, the unitized window wall system is difficult to maintain and clean due to exposed mullion systems. Moreover, the unitized window wall system requires complex installation, typically off-site, leading to additional costs. 
         [0004]    Thus, there is a need for a window or curtain wall assembly which addresses the above problems. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention relates to a concealed latching mechanism for a window or curtain wall and assemblies which include a concealed latching mechanism. Each window panel of said assembly includes plural layers of glass or other material separated by one or more spacing mullions, which line the perimeter of the window panel to create a sealed chamber. The depth of the sealed chamber between the layers is variable to accommodate both thermal requirements and vertical and horizontal structural loads. The chamber reduces heat loss due to convection allowing it to outperform current double or triple glazing window walls. The chamber of each window panel is connectable to chambers of adjacent window panels through tubes or ducts to allow for air or gas transfer to enhance thermal performance and enable other functional and aesthetic effects. When the window panels are assembled, the latching mechanism structurally unifies each panel to become a single monolithic surface that also accounts for thermal expansion. Elements of the latching mechanism are arranged to allow the window or curtain wall to be assembled from the interior, leaving only caulking to be performed from the exterior. Concealing all of such elements helps eliminate the exposure of window mullions and minimizes maintenance of the window or curtain wall. 
         [0006]    The fastener latching mechanisms disclosed herein structurally engage adjacent panels to structurally support the window or curtain wall as a whole. Embodiments of the present invention provide high thermal resistance that comes with several layers of insulated air chambers, are structurally self-sustained, provide simple on-site installation procedure, maintain flush surfaces to both the interior and exterior for aesthetic and sanitary purposes, provide capability to control and exchange gas inside of the chamber for visual effects and privacy purposes, provide flexibility and non-sequencing in the installation procedure, and provide significantly increased acoustic separation. Moreover, the fastener assemblies provide higher tolerance in absorbing energy in a seismic event, and provide a wide concealed space inside the chamber to house mechanical louvers or shading devices that can be remotely controlled while being protected from outside factors that may cause damage or degradation. 
         [0007]    Additional merits of the present invention include aesthetically pleasing design, providing flexibility in design, and facilitating mechanical cleaning. Design flexibility allows the window panels to be any shape, as the mullions can be structured to accommodate angled window panels, including but not limited to 15 degrees, 45 degrees, 90 degrees, and 135 degrees. This allows the window panels to be shaped as triangles, parallelograms, rhombuses, or other design choices. 
         [0008]    In accordance with one or more embodiments, a window panel fastening assembly includes a first and second mullion, each mullion having opposing mounting surfaces configured to be mounted to sheets of material, an air chamber-facing surface and an open side opposite the air chamber-facing surface, and opposing grooves disposed therein, wherein the first and second mullions are positioned with open sides facing each other mullions, locking brackets coupled to the grooves of the first and second mullions, and a rod positioned between the locking brackets, wherein the window panel fastening assembly is operable to fasten adjacent panels to each other. The locking brackets may have a generally U-shaped cross section. At least one of the locking brackets may include bore for receiving the rod. The rod may be positioned in a space formed between the first and second mullions. The window panel fastening assembly may further include a brace positioned between the first and second mullions wherein the brace is operable to guide and secure the rod and the structural integrity between the first and second mullions. In some embodiments at least one of the locking brackets includes a threaded bore for receiving the rod, wherein the rod includes a threaded region complementary to the threaded bore, wherein advancement of the rod through the locking bracket is operable to urge the first and second locking brackets in the grooves. A backer rod may be positioned opposite the brace in a space between the two opposing mullions. 
         [0009]    In some embodiments, at least one of the first and second locking brackets are pivotably coupled to an interior surface of one of the first and second mullions. In other embodiments both the first and second locking brackets are pivotably coupled to the first mullion. 
         [0010]    In at least one embodiment, the window panel fastening assembly further includes a gear box positioned within the first mullion, a cable fixed at one end to one of the locking brackets, a first and second gear bar pivotably mounted to a central region of each locking bracket and coupled with a gear bar support mounted to a gear plate, wherein application of a pulling force on the cable is operable to engage the locking brackets with the grooves of the first and second mullions. 
         [0011]    In accordance with still a further embodiment, a window panel fastening assembly is disclosed which includes a latching linear gear movably coupled to an interior surface of the first mullion and rotating gear operably coupled to a gear surface of the latching linear gear, wherein the latching linear gear is coupled to a latching bar, which is in turn coupled to a plurality of hinged plates positioned between an interior surface of the first mullion and the locking brackets, wherein the rotating gear is operable to move the latching linear gear along a longitudinal axis of the first mullion, exerting a pulling force on the latching bar, wherein movement of the latching bar is operable to pull and raise the hinged plates, which raising is operable to urge the locking brackets toward engagement with the grooves of the first and second mullion. The hinged plates are operable to fold upon each other to form a unitary latch oriented 90 degrees with respect to the first and second mullions. 
         [0012]    In yet a further embodiment, a window panel fastening assembly is disclosed having a locking bracket housing wall including an aperture for a cable, wherein the cable is connected at one end to a first folding plate, wherein the first folding plate is hingedly coupled to a second folding plate, which in turn is hingedly connected to fixed plate coupled to a latch housing base coupled to the first mullion, and further including a block coupled to the second folding plate, wherein the first and second folding plates are positioned between an interior surface of the first mullion and the locking brackets, wherein a pulling force exerted on the cable is operable to lift the first plate to contact the block, which movement is operable to drive the locking brackets in an upward direction. The pulling force exerted on the cable is operable to lift the second folding plate upward and drive the locking brackets toward engagement with the grooves of the first and second mullions. 
         [0013]    Window panel fastening assemblies disclosed herein may include a lateral bracing plate positioned between the first and second mullions and extending therefrom to an exterior of the window panel fastening assembly. 
         [0014]    In accordance with still further embodiments, a window panel assembly is disclosed having a first and second sheet of material positioned in axial alignment, each sheet having a perimeter and number of sides identical to the other sheet, and a plurality of window panel fastening assemblies as disclosed above coupled along the respective perimeters of the first and second sheets, wherein the first sheet is coupled to the first mounting surface of each of the first mullions of the window fastening assemblies and wherein the second sheet is coupled to the second, opposing mounting surface of each of the first mullions, the first and second sheets and the first mullions of the plurality of window panel fastening assemblies defining an air chamber. 
         [0015]    In yet another embodiment, a window panel assembly is disclosed having an air chamber defined by two opposing sheets of material and a plurality of window panel fastening assemblies as described herein disposed along the perimeter and between the two opposing sheets of material. Air chambers may include one or more sheets of insulation film disposed therein. Window panel assemblies disclosed herein may include at least one adjacent window panel assembly. In still further embodiments, a window wall is disclosed having a plurality of window panel assemblies as described herein, each of the plurality of window panel assemblies coupled to an adjoining window panel assembly by a concealed window panel fastening assembly. 
         [0016]    Window wall assemblies disclosed herein may include at least one vertical track and/or horizontal track coupled to a window fastening assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    So that those having ordinary skill in the art will have a better understanding of how to make and use the disclosed systems and methods, reference is made to the accompanying figures wherein: 
           [0018]      FIG. 1  is a sectional view of a window panel fastening assembly disposed between adjacent panels in accordance with an embodiment of the present invention; 
           [0019]      FIG. 2A  is a sectional view of a window panel fastening assembly disposed between adjacent panels with locks positioned in a pre-installation position in accordance with an embodiment of the present invention; 
           [0020]      FIG. 2B  is a sectional view of a window panel fastening assembly disposed between adjacent panels with locks positioned in a further pre-installation position to in accordance with an embodiment of the present invention; 
           [0021]      FIG. 2C  is a sectional view of a window panel fastening assembly disposed between adjacent panels with locks positioned in an installation position to in accordance with an embodiment of the present invention; 
           [0022]      FIG. 2D  is a perspective view of a window panel fastening assembly installed along a perimeter of a panel frame in accordance with an embodiment of the present invention; 
           [0023]      FIG. 3  is a sectional view of a window panel fastening assembly employing a cable-actuated locking device in a pre-installation position in accordance with an embodiment of the present invention; 
           [0024]      FIG. 3A  is a sectional view of a window panel fastening assembly employing a cable-actuated locking device with locks positioned in an installation position in accordance with an embodiment of the present invention; 
           [0025]      FIG. 4  is a perspective view of a window panel fastening assembly employing a rotating gear-actuated locking device in a pre-installation position in accordance with an embodiment of the present invention; 
           [0026]      FIG. 4A  is a perspective view of the window panel fastening assembly of  FIG. 4  with the top mullion removed in accordance with an embodiment of the present invention; 
           [0027]      FIG. 4B  is a perspective view of the window panel fastening assembly of  FIG. 4A  showing actuation of the rotating gear operating to raise the locks toward a locked position in accordance with an embodiment of the present invention; 
           [0028]      FIG. 4C  is a longitudinal cross-sectional view of the window panel fastening assembly of  FIG. 4A  showing the direction of movement of the gear assembly in accordance with an embodiment of the present invention; 
           [0029]      FIG. 4D  is a longitudinal cross-sectional view of the window panel fastening assembly of  FIG. 4B  showing the latch in a semi-raised position which is operable to urge the locks in an upward direction in accordance with an embodiment of the present invention; 
           [0030]      FIG. 4E  is a perspective view of the window panel fastening assembly of  FIG. 4A  showing the latch in a semi-raised position and the locks raised to a position 90 degrees with respect to the mullion in accordance with an embodiment of the present invention; 
           [0031]      FIG. 4F  is a longitudinal cross-sectional view of the window panel fastening assembly of  FIG. 4E  showing the latch in a semi-raised position in accordance with an embodiment of the present invention; 
           [0032]      FIG. 4G  is a longitudinal cross-sectional view of the window panel fastening assembly of  FIG. 4H  showing the latch in a fully raised position in accordance with an embodiment of the present invention; 
           [0033]      FIG. 4H  is a perspective view of the window panel fastening assembly of  FIG. 4A  showing the latch in a fully raised position and the locks raised to a position 90 degrees with respect to the mullion and the locks engaged with the mullion in accordance with an embodiment of the present invention; 
           [0034]      FIG. 5A  is a perspective view of a window panel fastening assembly employing a cable-actuated locking device in a pre-installation position in accordance with an embodiment of the present invention; 
           [0035]      FIG. 5B  is a perspective view with a partial cutaway of the window panel fastening assembly of  FIG. 5A  in a pre-installation position in accordance with an embodiment of the present invention; 
           [0036]      FIG. 5C  is a perspective view of the window panel fastening assembly of  FIG. 5A  with latching device operably urging the locks toward an upright position in accordance with an embodiment of the present invention; 
           [0037]      FIG. 5D  is a perspective view of the window panel fastening assembly of  FIG. 5A  with latching device positioned in an upright position and the locks raised to a position 90 degrees with respect to the mullion in accordance with an embodiment of the present invention; 
           [0038]      FIG. 5E  is a perspective view of the window panel fastening assembly of  FIG. 5A  with the locks fastened with a bolt and the locks engaged with the mullion in accordance with an embodiment of the present invention; 
           [0039]      FIG. 5F  is a perspective view of the window panel fastening assembly of  FIG. 5A  with window panels installed in accordance with an embodiment of the present invention; 
           [0040]      FIG. 6A  is a longitudinal cross-sectional view of a window panel fastening assembly in accordance with  FIG. 5A  in a pre-installation position in accordance with an embodiment of the present invention; 
           [0041]      FIG. 6B  is a longitudinal cross-sectional view of a window panel fastening assembly in accordance with  FIG. 5A  with the latch device operably moved by the cable to an intermediate position in accordance with an embodiment of the present invention; 
           [0042]      FIG. 6C  is a longitudinal cross-sectional view of a window panel fastening assembly in accordance with  FIG. 5A  with the latch device operably moved by the cable to a fully engaged position in accordance with an embodiment of the present invention; 
           [0043]      FIG. 7A  is a sectional view of a window panel fastening assembly with a mounting plate coupled with a structural member in accordance with an embodiment of the present invention; 
           [0044]      FIG. 7B  is a sectional view of a window panel fastening assembly with a mounting plate coupled with a structural member in accordance with an embodiment of the present invention; 
           [0045]      FIG. 8  is a sectional view of a window panel fastening assembly with an air duct disposed therein and a movable louver assembly disposed between sheets of glass or other material in accordance with an embodiment of the present invention; 
           [0046]      FIG. 9A  is a sectional view of window panel fastening assemblies and a window cleaning apparatus coupled thereto in accordance with an embodiment of the present invention; 
           [0047]      FIG. 9B  is a front view of multiple window panels and a window cleaning apparatus coupled thereto in accordance with an embodiment of the present invention; 
           [0048]      FIG. 10A  is a sectional view of a 15 degree mullion in accordance with an embodiment of the present invention; 
           [0049]      FIG. 10B  is a sectional view of a 45 degree mullion in accordance with an embodiment of the present invention; 
           [0050]      FIG. 10C  is a sectional view of a window panel fastening assembly employing a 135 degree mullion assembly in accordance with an embodiment of the present invention; 
           [0051]      FIG. 10D  is a sectional view of a window panel fastening assembly employing a 90 degree mullion assembly in accordance with an embodiment of the present invention; 
           [0052]      FIG. 10E  is a sectional view of adjacent window panels with a fastening assembly employing a 90 degree mullion assembly in accordance with an embodiment of the present invention; 
           [0053]      FIG. 10F  is a sectional view of adjacent window panels with a fastening assembly employing a 135 degree mullion assembly in accordance with an embodiment of the present invention; 
           [0054]      FIG. 11  is a front view of a multi-panel assembly in accordance with an embodiment of the present invention; 
           [0055]      FIG. 12  is a perspective view of a multi-panel assembly in accordance with an embodiment of the present invention; 
           [0056]      FIG. 13  is a perspective view of a multi-panel assembly in accordance with an embodiment of the present invention; 
           [0057]      FIG. 14  is a front view of a multi-panel assembly in accordance with an embodiment of the present invention; and 
           [0058]      FIG. 15  is a perspective view of a multi-panel assembly using glowable clear polyvinyl in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0059]    The following is a detailed description of the invention provided to aid those skilled in the art in practicing the present invention. Those of ordinary skill in the art may make modifications and variations in the embodiments described herein without departing from the spirit or scope of the present invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for describing particular embodiments only and is not intended to be limiting of the invention. All publications, patent applications, patents, figures and other references mentioned herein are expressly incorporated by reference in their entirety. 
         [0060]    It will be understood that when an element is referred to as being “coupled” or “connected” to another element, it can be directly coupled or connected to the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly coupled” or “directly connected” to another element, there are no intervening elements present. Like numbers refer to like elements throughout. As used herein the term “and/or” includes any and all combinations of one or more of the associated listed items. 
         [0061]    In addition, spatially relative terms, such as “under”, “below”, “lower”, “over”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is inverted, elements described as “under” or “beneath” other elements or features would then be oriented “over” the other elements or features. Thus, the exemplary term “under” can encompass both an orientation of over and under. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
         [0062]    Well-known functions or constructions may not be described in detail for brevity and/or clarity. 
         [0063]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
         [0064]    Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
         [0065]    Concealed window panel fasteners and assemblies disclosed herein employ structural spacing mullions concealed within a panel chamber, with the fasteners operable to couple adjacent panels. This provides a structurally sound, thermally secure window or curtain wall with surfaces flush with both the interior and exterior of the window or curtain wall. 
         [0066]    Now referring to  FIG. 1  a window panel fastening assembly  20  includes mullions  22   a  and  22   b , locking brackets  24   a  and  24   b , and rod  30 . Mullions  22   a  and  22   b  include interior grooves  25  operable to receive locking brackets  24   a  and  24   b , opposing mounting surfaces  28 , air chamber-facing surfaces  27  and open side  29  opposite the air chamber-facing surfaces  27 . Mullions  22   a ,  22   b  are disposed along the perimeter of interior and exterior sheets of material  2   a  and  2   b , respectively and coupled to the sheets at mounting surfaces  28  by a suitable attachment means such as but not limited to structural adhesive or mechanical fastener(s). The mullions  22   a ,  22   b  as installed, shown mounted to adjacent panel assemblies  10   a  and  10   b , are operable to form and maintain a sealed chamber between the sheets  2   a  and  2   b , and  2   c  and  2   d , respectively, as well as provide space to install additional separate air chambers adjacent to the inside and outside sheets. The mullions  22   a ,  22   b  can be made of any material that satisfies structural and thermal requirements of a building where one embodiment of the present invention is being assembled. Suitable materials include but are not limited to a thermally efficient composite or an aluminum extrusion with an integral thermal break. 
         [0067]    Locking brackets  24   a  and  24   b  may have any suitable cross-sectional shape suitable for securement to the mullions  22   a ,  22   b . For purposes for illustration in one embodiment the locking brackets  24   a ,  24   b  are generally U-shaped in cross-section and are configured to engage grooves  25  of facing mullions  22   a ,  22   b . One or both of the locking brackets may include a bore  23  for receiving the rod  30 . In the embodiment shown, locking bracket  24   a  includes a bore  23 . Locking brackets may be any suitable material that satisfies structural and thermal requirements of a building. 
         [0068]    Rod  30  is configured and operable to be inserted between adjacent panel assemblies  10 ,  10   b  through a space formed between mullions  22   a ,  22   b  and bore  23 . A brace  40  may be positioned between mullions  22   a ,  22   b  to guide and secure rod  30  and structural integrity between mullions  22   a  and  22   b . In some embodiments bore  23  includes threading complementary to a threaded region of rod  30  so that advancement of the rod through the locking bracket  24   a  functions to urge the locking brackets  24   a  and  24   b  securely in grooves  25 . A backer rod or bracket  50  may be positioned opposite brace  40 . Upon installation of the rod  30 , the adjacent panels  10   a  and  10   b  are secured along the perimeter including the panel fastening assembly  20 . Caulk  60  may be installed to seal any gaps between the adjacent panels  10   a ,  10   b.    
         [0069]    The sheets  2   a ,  2   b ,  2   c  and  2   d  may be glass or other suitable material such as but not limited to aluminum or plastic. Glass material may be but is not limited to annealed, laminated, or fritted glass. 
         [0070]    Now referring to  FIG. 2A , in one embodiment a window panel  10   a  includes insulation films in air chamber  110  to divide the chamber  110  into multiple chambers. The chamber  110  has the width of the installed spacing mullion  22   a ,  22   b , and provides adequate space to install several layers of films to take advantage of a triple or quadruple glazing effect and to increase thermal resistance and acoustic performance of the window panel  10   a . Such wide space between the interior and exterior glazing materials further provides sufficient room to install devices such as but not limited to shades, louvers, and other devices, which may be remotely controlled. 
         [0071]    Locking brackets  24   a ,  24   b  may be pivotably coupled such as at hinge  26  to an interior surface of mullion  22   a  and operable to rotate into position for installation. Prior to installation the locking brackets  24   a ,  24   b  may lay flat between grooves  25  of the mullion  22   a . It will be apparent that in such embodiments only one of mullions  22   a ,  22   b  includes locking brackets mounted thereto, given that the opposing mullion  22   b  will be engaged by the locking brackets. Accordingly, the locking brackets can be mounted to either of the opposing mullions  22   a ,  22   b  prior to installation. In some embodiments one of each of mullions  22   a ,  22   b  may include a single locking bracket pivotably coupled thereto. With reference to  FIG. 2B , locking brackets  24   a  and  24   b  are rotated into position, and with reference to  FIG. 2C , installation and securement of rod  30  causes the locking brackets to engage the grooves of opposing mullions  22   a  and  22   b , locking the adjacent panels together. 
         [0072]    With further reference to  FIG. 2D , an installed panel  10   a  with interior sheet  2   a  (e.g., glass) is shown adjacent to wall opening  102 . Wall opening  102  has installed along the perimeter thereof mullions  22 , locking brackets  24  and rods  30 . Sheets may be fixed to mullions  22 . Gap  21  is shown to indicate the space between adjacent panels through which bolts may be inserted. 
         [0073]    Now referring to  FIG. 3 , an embodiment of window panel fastening assembly includes mullions  122 , locking brackets  124  pivotable mounted thereto via hinge  126  and a gear box  170  positioned within a mullion  124 . A cable  150  is fixed at one end to one of the locking brackets. Gear bars  172  are pivotably mounted to a central region of each locking bracket  124  and coupled with a gear bar support  176  mounted to gear plate  172 . As shown, the locking brackets are in a standby position. With further reference to  FIG. 3A , applying pulling force on cable  150  in the direction indicated causes both locking brackets  124  to move into locking position with the mullions  122 . 
         [0074]    Now referring to  FIG. 4 , an embodiment of a window panel fastening assembly includes mullions  222   a  and  222   b  positioned opposite one another, locking brackets  224   a  and  224   b  disposed in a pre-installed state, a latching linear gear  269  movably mounted to an interior surface of mullion  222   a  and rotating gear  261  operably coupled to a gear surface of the latching linear gear  269 . Sheets  202   a  and  202   b  are shown. Now with further reference to  FIGS. 4A-4H , ( FIGS. 4A, 4B, 4E and 4H  are shown with mullion  222   b  removed for purposes of clarity), latching linear gear  269  is coupled to latching bar  262  which is in turn coupled to a plurality of hinged plates  266 ,  268 . As the rotating gear  261  is rotated, latching linear gear  269  is moved along a longitudinal axis of the mullion  222   a , exerting a pulling force on latching bar  262 . As the latching bar  262  moves, it is operable to pull and raise the hinged plates  266 ,  268 , operating to urge the locking brackets  224   a  and  224   b  upward. Hinged plates  266 ,  268  fold upon each other, ultimately forming a unitary latch oriented 90 degrees with respect to the base of the mullion  222   a  ( FIGS. 4G, 4H ). Bolt  230  secures the locking brackets  224   a ,  224   b  to the mullions  222   a  and  222   b . The rotating gear  261  may be hand-rotated or rotated with a tool such as a screwdriver, wrench or the like in embodiments in which the gear  261  includes an end shaped or otherwise modified to receive the working end of such a tool. 
         [0075]    Now referring to  FIGS. 5A-F  and  FIGS. 6A-6C , an embodiment of a window panel fastening assembly includes mullions  322 , locking brackets  324  and a locking bracket housing wall  342 . Locking brackets  324  include hinge pins  362  operably engaged in slots  342  formed in locking bracket housing wall  342 . Locking bracket housing wall includes an aperture for a cable  350  which is connected at one end to a folding plate  366  such as via a connector  351  such as but not limited to a cable hook having an opening  352 . Cable may include a cable lock  354  fixed to an end to engage the connector  351 . Plate  366  is hingedly coupled to folding plate  368 , which in turn is hingedly connected to fixed plate  362 . Fixed plate  362  is fixed to a latch housing base  364  such as via screws  371 . Latch housing base is fixed to mullion  322 . A block  370  is coupled to plate  368 . With reference to  5 C- 5 E and  6 B- 6 C, as a pulling force is exerted on cable  350 , cable  350  lifts folding plate  366  upward to contact block  370 , driving locking brackets  324  in an upward direction. Continued pulling force on the cable  350  causes folding plate  366  to continue in a direction along a longitudinal axis of the mullions  322  and causes folding plate  368  to be lifted upward and in the same direction, continuing to drive the locking brackets  324  upward until they stand at 90 degrees and in line with the mullion grooves. Block  370  maintains the folding plates  366 ,  368  in a blocked configuration, preventing the plates from folding on each other. Bolt  330  secures the locking brackets  324  to the mullions  322  as best seen in  FIG. 5F . 
         [0076]    It will be apparent to the skilled artisan that the latching mechanisms of one or more embodiments of the present invention may be attached to the mullion with a gasket that allows for thermal expansion. The latching mechanism may be housed within a housing coupled to the mullion to maintain clearances during installation. 
         [0077]    Now referring to  FIG. 7A , an embodiment of a window panel fastening assembly may include a lateral bracing plate  90  extending between adjacent panels, providing a means to attach the assembly to a structural member  92 . Referring to  FIG. 7B , the bolt  30   a  may be a combined fixed lock and lateral brace. 
         [0078]    Now referring to  FIG. 8  in a further embodiment a window panel fastening assembly with a panel, and chamber, formed by interior glazing sheet  402   a  and exterior glazing sheet  402   b  may include a mullion  422  including one or more conduits  480  such as air ducts, tubes or hoses disposed therein, allowing for air and gas transport between adjacent panels. The conduits are  480  operable to, inter alia, maintain positive pressure and allow the movement of gases to heighten environmental or aesthetic performance. Various gases can be charged into the chambers, and exchanged, to modify color and transparency levels of panels, providing visual effects and/or privacy as needed. The conduits may be equipped with valves that may be operated by remote control. 
         [0079]    The large space in the chamber between window panels provides sufficient room to accommodate a shading device, which can be remotely controlled. Since the shading device is inside the chamber, it is protected from outside factors. Thus, for example, the chamber may include one or more louvers  478  mounted therein, operably connected to a control gear  477  and a motor or magnetic device with a coupling  409  for one or more of a power, control and/or sensor device. One or more photovoltaic cells may be coupled with the louvers  478  to provide power without a connection to an outside power source. The louvers  478  may be operated remotely to provide shade, privacy, decorative appearance, etc. 
         [0080]    Now referring to  FIGS. 9A and 9B , in a further embodiment a fastening assembly including one or more fixed horizontal tracks  520  and/or vertical tracks  530  coupled to a fastening assembly disclosed herein, such as one including one or more lateral bracing plates  90  described above with respect to  FIGS. 7A and 7B , and a window cleaning apparatus having a cleaning track  510  and a cleaning device  500 . The cleaning track  510  is operable to move along tracks  520  and/or  530 , and the window cleaning device  500  may be operable to move along the length of the cleaning track. The flush surface of multiple embodiments of the present invention facilitates mechanical cleaning of the window panels. Therefore, a cleaning device such as device  500  can be fixed on the vertical or horizontal track  520  and/or  530 , and does not encounter extrusions such as mullions, since the mullions are inside the chamber. 
         [0081]    With reference to  FIGS. 10A-F , non-limiting examples of configurations of mullions and window fastening assemblies as disclosed herein include 15, 45, 135 and 90 degree configurations operable to be employed with various buildings and window panel assemblies. It will be apparent to the skilled artisan that the mullions and window fastening assemblies disclosed herein may be modified to suit particular applications. 
         [0082]    Now referring to  FIGS. 11-15 , various embodiments of multi-panel assemblies are shown in accordance with embodiments of the present invention. Films of various thicknesses and materials may be employed in the chamber of the wall panels disclosed herein. For example, embodiments of the present invention may include clear polyvinyl, which can glow, allowing for an aesthetically pleasing view, both inside and outside. In  FIG. 15  the multi-panel assembly employs glowable clear polyvinyl for aesthetic effect. 
         [0083]    In terms of installation, once the fastener assemblies are locked in place, any connecting tubes are secured and tucked away prior to caulking. Both interior and exterior gaps are caulked using a backer rod or similar device. 
         [0084]    Although the systems and methods of the present disclosure have been described with reference to exemplary embodiments thereof, the present disclosure is not limited thereby. Indeed, the exemplary embodiments are implementations of the disclosed systems and methods are provided for illustrative and non-limitative purposes. Changes, modifications, enhancements and/or refinements to the disclosed systems and methods may be made without departing from the spirit or scope of the present disclosure. Accordingly, such changes, modifications, enhancements and/or refinements are encompassed within the scope of the present invention.

Summary:
Window or curtain wall assemblies and concealed window fastening assemblies are disclosed. Each window panel includes two layers of glass or other material separated by a spacing mullion, which lines the perimeter of the window panel to create a sealed chamber. The depth of the sealed chamber between the two layers is variable to accommodate either thermal requirements, vertical and horizontal structural loads, or both. The chamber reduces heat loss due to convection allowing it to outperform current double or triple glazing window walls. Each chamber can connect through tubes to allow for air or gas transfer to enhance thermal performance and create the potential for other functional and aesthetic effects. When the window panels are assembled, the latching mechanism structurally unifies each panel to become a single monolithic surface that can also account for thermal expansion. Elements of the latching mechanism are arranged to allow the window or curtain wall to be assembled from the interior, leaving only caulking to be performed from the exterior. Concealing all of such elements helps eliminate the exposure of window mullions and minimizes maintenance of the window or curtain wall.