Abstract:
The present invention relates to a method of treating a glazing panel from an inside location. Moreover, the present invention relates to a method of treating glazing panels used in windows and patio doors. Initially, a hole is formed on both inside and outside panes on windows and on the side and outside frames of patio doors. Next, a filter is attached to the outside pane to cover the hole whereby the filter membrane is designed to allow the passage of air and inhibit the ingress of moisture. Finally, a seal is used to cover the hole on the inside pane or to ensure that the building air does not enter the interior of the glazing panel. Where the panes are tempered glass, the hole(s) may be drilled through the frame. If necessary, one or more tubes may be inserted through the hole. Various kinds of filters are disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority from U.S. Provisional patent application Ser. No. 60/529,882 filed Dec. 17, 2003 naming the present inventor. This application also claims priority from U.S. Provisional patent application Ser. No. 60/548,155 filed Feb. 27, 2004 naming the present inventor. The contents of these two applications are incorporated herein by reference. 
     
    
     FIELD OF INVENTION  
       [0002]     This invention relates to glazing panels comprising at least two panes with a sealed air space therebetween, and methods of treating same, and is especially concerned with removing from the air space contamination, such as condensation and/or particulate matter, and/or preventing ingress of such contamination.  
       BACKGROUND  
       [0003]     Known glazing panels comprise two or more panes of glass spaced apart a short distance and the gap between them sealed peripherally either by a spacer or the frame of the window, patio door, or other opening in which it is installed.  
         [0004]     In use, such a glazing panel may develop one or more leaks in the peripheral seal, allowing moist air and/or other contamination to enter the air space. In other cases, vent holes provided to avoid excessive pressure/vacuum build up as the glazing panel is heated or cooled may admit such moist air and/or contamination. Under certain conditions, moisture may condense out of the air within the air space and form condensation on the inner surface of at least one of the panes. This reduces visibility through the panel. Even if the glazing panel warms up and the moisture evaporates, it may leave a deposit of minerals, for example, on the pane, again reducing visibility. Moreover, it is also possible for other forms of contamination, such as particulate matter, to be drawn into the air space as the panel cools and a partial vacuum is created within it.  
         [0005]     A method of removing and/or preventing condensation and contaminant buildup in glazing panels is described in Canadian patent No. 1,332,541, to which the reader is directed to for reference. The method involves forming at least one hole in the external pane, removing condensation and/or contamination from the air space, and then attaching a filter means in the form of a patch to close the hole. The filter contains interstices sized to allow moisture to be expelled from the panel as the window heats, but restrict ingress of water droplets as air is drawn back into the panel as it cools.  
         [0006]     This method is not entirely satisfactory, however, but has certain limitations and disadvantages, at least for some applications.  
         [0007]     The present invention seeks to eliminate, or at least mitigate, the limitations and disadvantages of such known method, or at least provide an alternative.  
         [0008]     One specific disadvantage of such known method is that it may be difficult to gain access to the outside of the glazing panel, perhaps because it is installed in a high-rise building.  
         [0009]     Embodiments of a first aspect of the present invention address this disadvantage by drilling the hole in the external pane of a glazing panel via a generally aligned hole in the interior pane.  
         [0010]     Thus, according to this first aspect of the present invention there is provided a method of treating a glazing panel to remove contamination from and/or inhibit ingress of contamination into an enclosed air space of the glazing panel, the glazing panel comprising at least an exterior pane and an interior pane and means for supporting and sealing the perimeters of the panes to form said enclosed air space therebetween, said method comprising the steps of: 
    (i) creating an access hole in the interior pane from its surface furthest from the exterior pane, said access hole communicating with the air space;     (ii) through the access hole, creating a vent hole in the exterior pane through which hole the air space communicates with ambient air;     (iii) applying a filter means to the vent hole to filter air passing therethrough; and     (iv) sealing the access hole.    
 
         [0015]     Another disadvantage of such known method is that it cannot readily be applied where the glazing panel comprises tempered glass panes, such as are used in patio doors, since drilling a hole in such a pane may cause the glass to shatter.  
         [0016]     Embodiments of a second aspect of the present invention address this disadvantage by dispensing with drilling holes through the panes, and instead drilling the required hole or holes through the frame so that the air space communicates with the ambient through the frame supporting the panes. Thus, according to this second aspect of the present invention there is provided a method of treating a sealed glazing unit installed into a surrounding frame and comprising at least an exterior pane and an interior pane, means for supporting and sealing the perimeters of the panes to provide an air space therebetween, the frame having a side face adjacent each pane and an edge surface generally perpendicular to the panes and directed outwardly therefrom, the method comprising the steps of: 
    (i) drilling at least one venting hole from an external face of the frame of the installed glazing unit for providing air flow communication through the frame and between the air space and ambient, and     (ii) applying a filter means to the venting hole to filter air passing between the air space and ambient.    
 
         [0019]     According to a third aspect of the invention, there is provided a sealed glazing unit comprising at least an exterior pane and an interior pane, means supporting the perimeters of the panes to provide an enclosed air space therebetween and a frame surrounding the glazing unit, the frame having a side region adjacent the means for supporting the perimeters of the panes and an outer region, venting means for providing air flow communication between the air space and ambient air, said venting means being formed within the frame surrounding the glazing unit; and filter means attached to a region of the venting means for filtering air passing between the air space and ambient said filter means comprising means for permitting the egress of moisture-laden air from the air space when the air space temperature and pressure are elevated relative to ambient and inhibiting the ingress of moisture droplets from ambient air when the temperature and pressure of the air in the air space are less than ambient.  
         [0020]     Where this entails drilling through a compartment containing desiccant, the desiccant may be lost through the drilled hole. Likewise, where the frame comprises an extrusion with compartments defined by structural webs and flanges, the buildup of moist air between the air space and ambient may occur.  
         [0021]     Thus, according to a fourth aspect of the invention, there is provided a sealed glazing unit comprising at least an exterior pane and an interior pane, spacer means supporting the perimeters of the panes to provide an enclosed air space therebetween and a frame surrounding the glazing unit, the frame having a side face adjacent each pane and an edge surface perpendicular to the panes and directed outwardly therefrom, and venting means comprising a passageway extending through the frame to provide air flow communication between the air space and ambient air and a filter for filtering air passing through the passageway between the air space and ambient, said passageway comprising a tubular insert extending at least partially through the spacer means.  
         [0022]     According to a fifth aspect of the invention, there is provided a sealed glazing unit comprising at least an exterior pane and an interior pane, spacer means supporting the perimeters of the panes to provide an enclosed air space therebetween and a frame surrounding the glazing unit, the frame having an interior flange and an exterior flange extending across and engaging respective margin portions of the outmost surfaces of the interior and exterior panes, respectively, said interior and exterior flanges being integral with the frame, venting means extending through the frame for providing air flow communication between the air space and ambient air; and filter means for filtering air passing through the venting means between the air space and ambient, said filter means comprising means for permitting the egress of moisture-laden air from the air space when the air space temperature and pressure are elevated relative to ambient and inhibiting the ingress of moisture droplets from ambient air when the temperature and pressure of the air in the air space are less than ambient.  
         [0023]     Yet another disadvantage is that there is a trade-off between hole size and filter size. Thus, it is desirable to keep the diameter of the hole small so as to make it quicker and easier to drill and reduce the risk of breakage, but it is desirable for the open area of the filter, i.e., the aggregate area of the interstices, to be as great as possible so as to reduce resistance to air flow.  
         [0024]     Thus, in embodiments of a sixth aspect of the present invention, there is provided a filter having a surface area greater than the planar area bounded by its perimeter.  
         [0025]     Thus, according to a sixth aspect of the invention, there is provided a filter means for use with a glazing panel comprising at least an exterior pane and an interior pane and means for supporting the perimeters of the panes to provide an internal air space therebetween, one of the interior or exterior panes having a hole, said filter means comprising a marginal region for attaching the filter to said hole and a medial region comprising a membranous filter screen having interstices sized to permit the egress of moisture-laden air from the panel when its interior temperature and pressure are elevated relative to ambient and to inhibit ingress of moisture droplets with ambient air when the interior temperature and pressure of the air in the air space are greater than ambient, said membranous filter screen being non-planar so that its surface area is greater than its plan area.  
         [0026]     In preferred embodiments of this sixth aspect of the invention, the filter is non-planar, conveniently dome-shaped, corrugated, or of other non-planar form, so that its surface area is increased as compared with a flat filter of the same perimeter.  
         [0027]     It may also be disadvantageous to have a filter patch that is applied to the outside surface of the exterior pane, i.e., so that its margin overlies the exterior surface around the hole, since, even though the patch may protrude only slightly from the surface of the glass, it could impede the cleaning of the panel and generally can only be applied from the exterior of the panel. Moreover, such a patch may be unsightly.  
         [0028]     Embodiments of a seventh aspect of the present invention address these limitations by means of a filter that is supported within the interior of the hole and preferably does not protrude from the surface of the pane.  
         [0029]     Thus, according to a seventh aspect of the present invention, there is provided a filter means for use with a glazing panel comprising at least an exterior pane and an interior pane and means supporting the perimeters of the panes to provide an internal air space therebetween, one of the interior or exterior panes having a hole, said filter means comprising a filter screen at least peripheral regions of which are resilient so that, upon insertion of the filter into a hole slightly smaller than the filter, the peripheral regions of the filter engage an interior of the hole to retain the filter therein.  
         [0030]     Conveniently, the filter may be slightly larger than the hole and resilient so that it can be compressed to fit into the hole and its peripheral regions grip the interior of the hole. The filter may be dome-shaped and/or have at least its margins corrugated or crimped.  
         [0031]     Alternatively, the filter may take the form of a patch applied to the interior surface of the exterior pane so that its margin portion overlies the glass surrounding the hole in the exterior pane.  
         [0032]     Hence, according to an eighth aspect of the present invention, there is provided a method of applying a filter to the internal surface of the exterior pane by drilling a suitably sized hole in the internal panel, drilling a hole in the exterior pane via the first-mentioned hole, passing the filter through the first hole, and adhering the filter to the interior surface of the exterior pane surrounding the second hole so that the filter covers the internal mouth of the hole.  
         [0033]     Preferably, the filter is of magnetic material and a probe having a magnetic tip is used to install it, the filter being attached to the magnetic tip of the probe which is then inserted through the first hole and pressed into position until it adheres to the material surrounding the hole in the exterior pane. The probe then is withdrawn, the adhesion being sufficient to detach the filter from the magnetic tip. The filter may be adhered by means of a contact adhesive applied to its margins. Alternatively, adhesive may be applied to the interior surface, conveniently by means of a suitable probe, before the filter is pressed into place.  
         [0034]     The filter may then comprise a flat filter or a dome-shaped filter with the dome protruding towards the interior pane. In either case, the filter may comprise a medial filter membrane supported by a surrounding annular part that adheres to the pane. The annular part may be integral with the membrane or a washer of a different material, e.g. vinyl, attached to the membrane.  
         [0035]     The filter may take the form of a perforated membrane as disclosed in the above-mentioned Canadian patent No 1,332,541. Alternatively, and especially where the filter is in the form of a patch, the filter portion itself may comprise at least one very thin slit in the patch, the width of the slit being small enough to limit ingress of moisture droplets and/or other contamination, the length of the slit being sufficient to provide the required open area.  
         [0036]     Thus, according to a ninth aspect of the present invention, there is provided filter means for use with a glazing panel comprising at least an exterior pane and an interior pane and means supporting the perimeters of the panes to provide an internal air space therebetween, either of the panes having a through hole, said filter means being adapted to attach to said either of the panes and filter air passing through said hole, said filter means comprising a patch having one or more thin slits therein, the width of the one or more slits being narrow enough to limit ingress of moisture droplets from ambient air when the temperature and pressure of the air in the air space are less than ambient and wide enough to permit the egress of moisture-laden air from the air space when the air space temperature and pressure are elevated relative to ambient and the overall length of the one or more slits being determined so as to provide a required open area for the filter.  
         [0037]     Preferably, the slit is non-linear.  
         [0038]     In preferred embodiments of this aspect of the invention, the patch has a central dome surrounded by a substantially flat annular portion, and the slit extends, parallel to the flat annular portion, around a part of the base of the dome. Preferably, when such a patch is installed on the exterior of the external pane, the slit is directed downwards to that it is protected by the dome against ingress of rainwater.  
         [0039]     Another disadvantage of known, window panels is they are susceptible to damage from pressure changes, which is a problem encountered in certain environments.  
         [0040]     Embodiments of tenth aspect of the present invention address this limitation by providing a method of treating a glazing panel by drilling a hole in the exterior pane of a glazing panel via a generally aligned hole in the interior pane.  
         [0041]     Thus, according to a tenth aspect of the present invention, there is provided a method of treating a glazing panel comprising at least an exterior pane and an interior pane and means for supporting the perimeters of the panes to provide an air space therebetween, said method comprising the steps of: 
    (i) creating an access hole in the inner pane of the glazing panel from a location adjacent the surface of the inner pane facing away from the exterior pane, said access hole communicating with the air space;     (ii) through the access hole, creating a hole in the outer pane of the glazing panel to communicate with ambient air;     (iii) through the access hole, applying a filter means to the hole in the outer pane to filter air passing therethrough; and     (iv) sealing the access hole.    
 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0046]     Embodiments of the present invention will now be described, by way of example only, with reference to the attached drawings, wherein:  
         [0047]      FIG. 1  is a cross-sectional view through the peripheral portion of a double glazing panel during treatment by a method according to a first aspect of the invention;  
         [0048]      FIG. 2  is a cross-sectional view similar to  FIG. 1  illustrating insertion of a filter;  
         [0049]      FIG. 3  is a cross-sectional view similar to  FIG. 1  of the panel with the filter installed;  
         [0050]      FIG. 4  is a cross-sectional view corresponding to  FIG. 2  showing insertion of a different kind of filter;  
         [0051]      FIG. 5  illustrates application of the method to glazing panel having panes of tempered glass or other material that is not easily drilled;  
         [0052]      FIG. 6  is a cross-sectional view corresponding to  FIG. 5  but after the panel has been treated and a filter patch applied;  
         [0053]      FIG. 7  is a side view of a domed filter patch as used in the embodiment illustrated by  FIGS. 5 and 6 ;  
         [0054]      FIG. 8  is a cross-sectional partial side view corresponding to  FIG. 6  but illustrating a modification;  
         [0055]      FIG. 9  is cross-sectional view through apart of a glazing panel illustrating application of the invention to a panel supported by a hollow frame;  
         [0056]      FIGS. 10 and 11  correspond to  FIG. 9  but illustrate alternative methods of applying the invention to a panel supported by a hollow frame;  
         [0057]     FIGS.  12 ( a ),  12 ( b ) and  12 ( c ) are plan, transverse cross-section and perspective views, respectively, of a generally dome-shaped and corrugated filter;  
         [0058]      FIG. 13  is a perspective view of a plain, dome-shaped filter;  
         [0059]      FIG. 14A  is a cross-sectional side view of a dome-shaped slit filter combined with a dome-shaped mesh filter; and  
         [0060]      FIG. 14B  is a cross-sectional side view of a dome-shaped slit filter combined with a flat mesh filter.  
     
    
     DETAILED DESCRIPTION  
       [0061]     Referring to  FIG. 1 , a glazing panel  100  comprises a first glazing pane  102  (the outer pane when installed) and a second glazing pane  104  (the inner pane when installed) separated by a peripheral spacer  106  to enclose an air space  108 . The spacer  106  is adhered to the peripheries of both panes by suitable sealant  110  to form an air-tight seal. The spacer  106  is hollow, conveniently an aluminium extrusion, and contains a desiccant material  112  installed during manufacture. The glazing panel  100  is supported by the usual frame  114  which, as shown, is made of wood, but may be any conventional material.  
         [0062]     The desiccant  112  usually is installed during manufacture to remove moisture from the air within the air space  108 , though not all double glazing panels will have it. In either case, over a period of time, leaks may occur in the peripheral seal, allowing moisture and/or particulate contamination to enter the panel and reduce visibility. Even if desiccant is installed during manufacture, it is likely that it will not be able to deal with such moisture.  
         [0063]     A method of removing such contamination will now be described with additional reference to  FIGS. 2, 3  and  4 .  
         [0064]     A first step is to drill a first hole  116  through the inner glazing pane  104  at a position close to the edge of the frame  114 , preferably within about 2.5 cm. of the corner. Following cleaning of the area, the hole  116  is drilled, at a slightly downward angle, using a drilling device such as a Dremel™ rotary tool. During the drilling process, the drill and surrounding area are rinsed with cutting fluid, e.g. alcohol, which removes glass particles or shavings.  
         [0065]     Preferably the drilling is stopped just before the drill tip breaks through into the air space. The hole is cleaned out and then the residual disc of glass pushed into the air space to fall to the bottom of the panel. This reduces the risk of glass particles falling into the air space and sticking to the interior surface of the glass.  
         [0066]     A second hole  118  is drilled through the outer glazing pane  102  at a position that is slightly below the hole  116  of the inner pane  104 . As shown in  FIG. 1 , the outer hole  118  is drilled via the first hole  116 , i.e., from the interior of the building in which the panel is installed. Accordingly, the diameter of inner hole  116  is slightly larger than the outer hole  118  so as to provide adequate clearance for the drill bit  120  used to drill the outer hole and, as will be described later, a probe used to insert the filter. For example, the inner hole  116  might have a diameter of 5 to 6 mm and the outer hole  118   a  diameter of 3 to 4 mm. As can be seen from  FIG. 1 , both holes  116  and  118  slope downwards towards the exterior of the panel  100 . The sloping of outer hole  118  helps to inhibit ingress of contamination.  
         [0067]     While drilling of the outer hole  118  is taking place, the air space  108  is flooded with alcohol ( 122 ) to just below the bottom of inner hole  116 . In addition to acting as a cutting fluid for the drill, the alcohol keeps the minute particles of glass, i.e., glass swarf, in suspension. Once the drill breaks through, the glass particles will tend to flow with the alcohol through the hole  118 . If required, the alcohol may be replenished continuously during this process.  
         [0068]     The alcohol is then allowed to evaporate off. If desired, however, another hole may be drilled through the inner pane  104  adjacent the bottom of the panel and used to drain and recover the bulk of the alcohol, the residue being allowed to evaporate. Such a drain hole may also be used to flush any glass swarf from either drilling operation out of the panel.  
         [0069]     If desired, the drain hole can be drilled before the access hole  116  and the bottom region of the interior of the panel filled with alcohol to test whether or not it will leak from the base of the panel during subsequent steps.  
         [0070]     Depending upon the degree of contamination of the surfaces of the panes, cleaning fluid may be passed through the air space and rinsed off, conveniently by means of one or more holes (not shown) drilled at other corners of the panel. The cleaning process described in Canadian patent number 1,332,541, for example, may be used.  
         [0071]     As shown in  FIG. 2 , a stainless steel mesh filter  124  then is inserted into the outer hole  118  using a probe  126  with a magnetic tip  128 . The filter  124  is domed (not quite a hemisphere) and, prior to insertion, has a base diameter slightly larger than the diameter of hole  118 . The filter  124  is placed over the magnetic tip  128  which then is passed through inner hole  116  and pushed into hole  118  until the extremities of the filter  124  grip the interior surface of the hole  118  with sufficient force that, as the probe is withdrawn, the filter disengages from the magnetic tip  128  and remains fixed in the hole  118 . The probe shank  126 A is larger in diameter than both the magnetic tip  128  and the outer hole  118 . Consequently, abutment of the end face  130  of the probe shank against the glass around the hole  118  shoulder prevent the filter from being inserted too far into the hole  118  and, importantly, being pushed so far that it falls out at the other end.  
         [0072]     As shown in  FIG. 3 , a seal  132 , e.g. a self-adhesive vinyl patch, is adhered to the inside 
        of the inner pane  104  over the hole  116  to ensure that the building air does not enter the interior of the glazing panel. If additional holes were drilled for cleaning purposes, they would be sealed in a similar manner.        
 
         [0074]     The filter  124  is designed so as to allow moisture to be expelled through the hole  118  as the air inside the air space expands, typically when the glazing panel is being heated, whether by the sun or by artificial means. Conversely, the filter  124  restricts ingress of water droplets as air is drawn back into the window as it cools. In this embodiment, the filter  124  comprises a membranous filter screen, such as stainless steel mesh containing 10,000 holes per square inch.  
         [0075]     After insertion of the filter  124  and sealing of the other hole(s), condensation between the window panes will slowly dissipate, typically over a period of several weeks, as the window is exposed to sunlight. The end result is a glazing panel free of particulate matter and condensation.  
         [0076]      FIG. 4  illustrates a modification, namely the use of a filter patch  124 A applied to the interior surface  102 A of pane  102  to cover the inner mouth of hole  118 . The filter patch  124 A may be a flat piece of stainless steel mesh as described above and inserted using the same probe  126 . In this case, the filter mesh may be self-adhesive, i.e. with contact adhesive applied to its margins, and simply pressed into contact with the inner surface  102 A.  
         [0077]     Alternatively, the filter may comprise a piece of the aforesaid mesh and be pressed into contact with adhesive previously applied to the interior edges of hole  118  using a probe with a swab on the end. As before, once the filter is adhered, it will detach from the magnetic tip  128  as the probe is removed. The access hole  116  (and any cleaning holes) will be sealed as previously described.  
         [0078]     The cleaning solution is preferably applied at moderate pressure using an air compressor unit. Distilled water may be used to remove contaminants deposited by water followed by rinsing with a solution of alcohol to dissolve and evaporate any residual water. If any contaminants remain after washing with water, the window is treated with a cleaning solution of vinegar/water solution. The acidity of the vinegar aids in dissolving metal containing contaminants such as aluminum oxide or zinc oxide. After treatment with vinegar, the panes are washed with water, followed by alcohol to remove residual water. If white “riverbed” marks are present on the internal surface of the panes, a vinegar/water solution may be used instead of alcohol to wet the window when drilling the access hole.  
         [0079]     Although the above embodiments describe the use of alcohol to rinse off glass cuttings, a magnet and magnetic “squeegee” blade may be used in addition to the alcohol wash to remove any cuttings that still remain after the washing.  
         [0080]     The diameter of the drain hole depends on the thickness of the glass of the inner pane. Typically, the hole has a diameter of at least about 3 to 3.5 mm to allow a drain tube to enter. For thick glass, the hole diameter can be made equal to the thickness of glass which can be up to 5 mm or 6 mm.  
         [0081]     Although the above embodiments describe a seal that covers the access hole  116  and the draining hole (if used), it should be appreciated that a plug or silicon sealant could be used instead or in addition.  
         [0082]     As mentioned herein before, the hole in the inner pane  116  is larger than that of the outer pane in order to allow for a magnetic insertion device, specifically, a probe  126  (see  FIG. 4 ) to be inserted through it. Also, by creating a small outer hole  118 , water droplets are prevented from forming inside the hole. Both holes  118 ,  116  are angled downward toward the exterior of the panel with the hole in the outer pane being situated slightly below the hole in the inner pane. Since the outer hole  118  is positioned below the inner hole  116 , any cleaning solution that is applied to the air space between the panes will drain outside the building through the outer hole.  
         [0083]      FIGS. 5 and 6  illustrate a panel  100 ′ having tempered glass panes  102 ′ and  104 ′ that is being treated according to a second aspect of the invention. The panel is generally similar to that shown in  FIG. 1  but, because the tempered glass cannot readily be drilled, access to the air space  108  is achieved by drilling through the surrounding frame  114 ′. A first hole  134  is drilled through the frame  114 ′ and the peripheral separator/seal  106 ′/ 110 ′ from the outer edge of the panel, i.e., generally parallel to the planes of the glass panes  102 ′ and  104 ′. A second hole  136  is drilled from the face  138  of the frame  114 ′, generally perpendicular to the first hole  134 , to communicate with it. Any cleaning of the interior of the panel is carried out as previously described.  
         [0084]     Referring to  FIG. 6 , a short tube  140 , for example of metal or plastic, is inserted into the first hole until it extends through the separator  106 ′ and prevents desiccant  112 ′ leaking into the air space. The outer end of hole  134  is sealed with a plug and/or patch and/or sealant and a filter is applied to close the second hole  136 .  
         [0085]     The filter patch could take any of the forms described herein before but  FIG. 6  shows a patch  124   b  with a central dome surrounded by flat margins. The margins are adhered to the surface of the frame so that the dome lies over the mouth of the hole  136 . As shown in  FIG. 7 , a narrow slit  142  extends, parallel to the flat annular portion, around a part of the base of the dome. Preferably, when such a patch  124   b  is installed, the slit is directed downwards to that it is protected by the dome. The width of the slit is about 0.5 mm wide and about 4 mm long. Because it is so narrow, it provides the required filtering effect. Its length, however, is sufficient to provide the required open area. Although the slit of  FIG. 7  is shown curved, it could of course be straight, if its length was still sufficient.  
         [0086]     It should be appreciated that the filter slit could be combined with a filter screen, conveniently attached over the hole in the middle of the flat annular portion.  
         [0087]     The arrangement described with reference to  FIGS. 5 and 6  is especially suitable for glazing panels of patio doors, where the edge is accessible for drilling of the first access hole, but the filter is applied to the surface facing the exterior where it will not be obscured. For instance, such an arrangement would not be suitable if the patio door is closed against the frame. It will be appreciated that, if there is no desiccant, the tube can be omitted.  
         [0088]     If a panel having tempered glass panes is installed in such a way that the edge if accessible to the outside air, it may not be necessary to drill the second hole  136  from the surface of the frame. As shown in  FIG. 8 , in such a case, the filter is applied to the external mouth of hole  134  and, if desiccant is involved, the lining tube  140 ′ may extend throughout the length of the hole  134 .  
         [0089]     FIGS.  9  to  11  illustrate application of the invention to a glazing panel having a surrounding frame that is hollow, for example an extrusion of aluminium or plastics material. As shown in  FIG. 9 , such a frame typically has several compartments  150  formed by intersecting structural webs  152 . In this case, the edge of the panel is accessible, so, drilling from the outer edge of the frame, a series of hole  134 ″ are drilled through the intervening webs  152 , respectively, through the separator  106 ″ (and desiccant if applicable) and into the air space  108 ″. After any required cleaning etc., a tube  140 ″ is inserted through the aligned holes  134 ″
        to close off the compartments. The hole  134  in a flange  153  along the outer edge of the frame then is covered by a filter  124 ″, which is shown domed but may take any suitable form disclosed herein.        
 
         [0091]      FIG. 10  illustrates an alternative arrangement for use where the filter should not be applied to the outer edge of the frame. In this case, the first holes  134 ″ are drilled from the edge of the hollow frame and a second hole  136 ″ (or more if there are intervening webs) is drilled from the face of the frame generally perpendicularly to the first series of holes. In this case, a curved tube  154  is inserted through the second hole  136 ″, any intervening holes, and into the hole in the separator  106 ″. Such curved tube then closes off the both the separator  106 ″, to avoid leakage of desiccant, and the frame, to avoid leakage of air. The filter  124 ″ is applied over the hole  136 ″ and the end of tube  154 .  
         [0092]      FIG. 11  illustrates an alternative to the arrangement of  FIG. 10 . In the arrangement shown in  FIG. 11 , the frame is drilled obliquely from the front face to provide a series of aligned holes  155  and  157  allowing the air space to communicate with the ambient. A tube  160 , having suitably chamfered ends, is inserted into the obliquely aligned holes to seal the separator  106 ″ and the compartment(s)  150 . The tube  160  is closed by a filter  124 ″, as before.  
         [0093]     It should be appreciated that drilling through the frame instead of the pane(s) is not limited to use where the panes are tempered glass but could also be applied in other situations, for example where the panes are of plastics material or have a film of solar filter material applied.  
         [0094]     Although only one draining hole and one filtering hole have been shown and described in the specific embodiments, it should be appreciated that more than one of each hole may be provided to facilitate the evacuation of particulate matter, moisture, cleaning solution and rinsing solution provided that at least one of the holes on the outside pane or outside frame is covered by a filter and all holes on the inside pane or side frame are hermetically sealed. The other holes on the outside may also have a filter, or may be hermetically sealed.  
         [0095]     FIGS.  12 ( a ),  12 ( b ) and  12 ( c ) illustrate a corrugated filter having an increased surface area in relation to the perimeter of the opening of the hole over which it is attached. Specifically, the surface area of the membranous screen is greater than the cross-sectional area of the hole. The corrugated portion may be surrounded by a flat margin to facilitate its adhesion to the pane.  
         [0096]      FIG. 13  depicts a dome-shaped filter  124 C having a brim portion  162  whereby it can be attached to the surface of the pane around the vent hole. As disclosed above, contact adhesive would be applied to the brim  162  and/or to the rim around the hole. Such filter  124 C can be used in place of the flat filter  124 A of  FIG. 4  or the slitted dome filter  124 B of FIGS.  6  to  11 . For additional protection, for example in case the filter is subjected to a particular dirty environment or high pressure water, say from a hosepipe, the filter  124 C of  FIG. 13  could be combined with the filter  124 B of  FIG. 7 , i.e., the dome-shaped mesh could be inserted into the annular hole to fit over the vent hole in the pane. Such a modification is shown in  FIG. 14A .  FIG. 14B  shows a similar protective arrangement wherein the dome-shaped slit filter  124 C is combined with a flat filter  124 A. In the latter case, the filter mesh is shown as having the same diameter as the brim  162  but it should be appreciated that it could be smaller, so long as it covered the hole in the pane. In either case, adhesive could be applied to the brim/mesh and/or the rim of the vent hole.  
         [0097]     It will be apparent that the method of applying the filter to a patio door unit may additionally comprise the step of applying cleaning solution to the internal air space. Furthermore, a draining hole may be formed in the bottom of the pane to drain excess fluid.  
         [0098]     It should be noted that certain embodiments of the invention are applicable to new glazing panels which have not been contaminated. During manufacture of the panels, the requisite holes could be drilled and the filter installed, with tube inserts as appropriate. It will be appreciated that access to the outer pane, i.e., that which will be the outer pane when the panel is installed, will not be restricted and the panel may well be clean and dry, so only the vent hole need be drilled. Such panels would be less likely to suffer from the ingress of moisture or other contamination if they developed a leak since the air would tend to vent via the filter as the panel heated and cooled.  
         [0099]     It should also be noted that glazing panels equipped with filters as described herein, especially from new, would be less susceptible to damage from pressure changes, which is a problem encountered in certain environments. Such pressure changes can occur during cold weather or during changes in elevation e.g., due to transportation of the glazing panels by air or in mountainous regions.  
         [0100]     It should be appreciated that use of the filters described with reference to  FIGS. 3, 4 ,  7 ,  12 ( a ) to  12 ( c ) and  13  is not limited to the specific methods described herein, but could be used in other window treatment applications, for example, as described in the above-mentioned Canadian patent No. 1,332,541.  
         [0101]     In practice, the stainless steel mesh used in filters according to all aspects of the invention can contain 10,000 holes per square inch. This gauge is particularly suitable since it will pass moisture laden air at elevated temperatures when the air layer is venting to the exterior, but will inhibit the ingress of moisture droplets at lower temperatures, preventing the formation of condensation within the panel. It is envisaged, however, that the number of holes per square inch could be anywhere in the range of 6,000 to 20,000. Also, the interstices in the mesh may be chemically formed by applying chemicals that erode the filter surface to create holes.  
         [0102]     The above-described embodiments of the present invention are described as examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the appended claims.