Patent Publication Number: US-2020284466-A1

Title: Air vent

Description:
FIELD OF THE INVENTION 
     The present invention relates to air vents. 
     BACKGROUND OF THE INVENTION 
     Passive air vents are a common way to replace stale air with fresh air. Many state-of-the-art air vents are able to provide a high flow with relatively low noise while providing cover against for instance rain and birds, but have disadvantages. 
     For instance, louvre-type vents are simple and provide some protection against rain, but they tend to be noisy, and they not particularly rainproof by any standard. 
     Patent publication CA 2,405,534 discloses a roof vent that comprises two parts, a cover and a conduit. The conduit, with a pipeline already attached, is said to be easily connected to the cover, after the cover has been installed on a roof. 
     The conduit will plug into the cover making installation “easy”. The vent includes a channel or moat which surrounds the outlet of the conduit. Thus, if during extreme weather conditions, moisture passes into the cover from outside through its opening and if it gets past the door flap, the description claims that it will be trapped in the channel. 
     Patent publication US 2012/015596 relates to two devices that are used to let fresh air in or through a window or opening but at the same time keep rain or any other kind of precipitation out. It is stated that it is a device that will enable people to keep a window or an opening open even in inclement weather or when precipitation of any kind threatens to enter the opening or window. 
     Patent publication GB 613,720 relates to ventilating openings, and in particular to louvres arranged with gutters for carrying rain. 
     SUMMARY OF THE INVENTION 
     In a first aspect, the invention provides a vent comprising:
         a support frame having an inner perimeter,   a set of blades arranged in an array, a first end of each blade being attached to a corresponding first part of the frame, a second end of each blade being attached to a corresponding second part of the frame, a first substantially flat portion forming an initial part of a cross-section of each blade, and the first substantially flat portion is followed by a ridge or valley portion, and at the first end of each blade the first substantially flat portion is at least partly separated from the inner perimeter by an opening allowing water to drain from the first substantially flat portion onto the inner perimeter.       

     A well-known vent illustrated schematically in  FIG. 1  comprises blades  103   a ,  103   b ,  103   c  attached to a frame  101 . The vent also has a cover flange  102  for fitting the vent against a surface, such as a wall. The blades are flat and arranged at an angle. This provides some protection against rain, which is illustrated as element  121 , but there is a significant amount of splashing when rain hits the blades, causing drops to get through the vent, as illustrated by drops  122 . Furthermore, the angling of the blades causes air to be redirected, resulting in an uneven pressure profile across the vent going from the top of the vent to the bottom of the vent in  FIG. 1 . 
       FIG. 8  illustrates a cross-section of a vent similar to the one in  FIG. 1 , although the vent  800  in  FIG. 8  has blades that allow more rain to enter through the vent. Blades  803   a ,  803   b , and  803   c  are separated so much that rain can pass between the blades relatively easily, especially in the presence of gusts. 
     Neither of the references mentioned in the “Background of the invention” section discloses the first substantially flat portion of a blade being at least partly separated from the inner perimeter of a frame by an opening allowing water to drain from the first substantially flat portion onto the inner perimeter. Examples of cross-sections in accordance with the present invention are shown in  FIGS. 5 a , 5 c  and 5 d    and will be discussed later in the specification. 
     Embodiments of the present invention differ from these known vents at least by comprising blades that are not flat, but may have a flat portion followed by a ridge or valley portion. Vents in accordance with embodiments of the present invention create significantly less noise, they may provide a significantly lower pressure drop, and they provide much better rain protection compared to the vents in  FIGS. 1 and 8 . Patent publication CA 2,405,534 illustrates entirely flat blades and is therefore not remotely capable of providing the crucial effects provided by the present invention, for instance that of leading water to the perimeter for draining along the perimeter and at least partly inhibiting water from entering through the vent. In GB 613,720, gutters are a crucial feature. The present invention has flat portions forming initial parts of the cross-sections. US 2012/015596 also does not describe the blade shapes of the present invention. In US 2012/015596, blades are either substantially the same as known simple louvres, or they are not adapted to allow rain to drain onto an inner perimeter and drain along the inner perimeter, or the blades are not fixed on the inner perimenter of a frame in each end, and each blade is essentially a gutter, and water runs from gutter to gutter, zigzagging down near the middle of the vent seen from a front side. 
       FIG. 7  illustrates another known vent  700 , specifically designed to prevent rain from entering. Blades  703   a ,  703   b ,  703   c  are arranged in an array. The blades are configured with various appendages  751 ,  752 ,  753  for catching rain and mist. Due to appendages  751  and  753 , the blades at the entry and exit of the vent experience vortices. The specific design also results in a significant pressure drop across the vent, which is not desirable. The large angle of the blades relative to causes air  741 ,  742  to be redirected, contributing to the significant pressure drop. Embodiments of the present invention differ from the vent in  FIG. 7  at least in that the initial portion of the blades are substantially flat, i.e. without crooked appendages. 
     Not visible in  FIGS. 1, 7 and 8  is the lack of an opening between the blades and the respective frames, which prevents water to drain to and along the inner perimeter. 
     Preferably, there is an opening at least 0.5 mm wide from the blade to the inner perimeter, such as at least 1 mm wide, such at least 1.5 mm wide, such as at least 2 mm wide. A larger distance allows a larger flow of water to drain from the blades onto the inner perimeters. However, if the distance is too large, rain will be able to travel along the inner perimeter, through the vent, at higher wind speeds. 
     The ridge or valley portion helps capture rain. In fact, a ridge is preferred, as this provides a surprisingly effective protection against rain. The flatness of the initial part of the cross-section prevents creation of vortices, as opposed to the vent illustrated in  FIG. 7 . More importantly, however, the first substantially flat portion allows rain to run along the blade, towards the inner perimeter, and through the openings as described above. 
     In some embodiments, the first substantially flat portion of two adjacent blades are substantially parallel (such as parallel). This provides a smoother air flow through the vent. 
     The cross-section is preferably taken as an intersection between said each blade and a plane which is perpendicular to a line extending from the first end of said each blade to the second end of said each blade.  FIGS. 5 a , 5 c , 5 d   ,  10 D(a),  11 D(a) and  12 D(a) illustrate such cross-sections. 
     In some embodiments, the ridge or valley portion of the cross-section is followed by a second substantially flat portion forming a final part of the cross-section. Such a second substantially flat portion can be used to direct the air as desired, but more importantly, it can also assist in the draining away of water, just like the first substantially flat portion forming the initial part of the blade. In some embodiments, the second substantially flat portion of two adjacent blades are substantially parallel. 
     The vent frame can have arbitrary shapes, such as circular or rectangular. This is a matter of design and could be determined by the specific hole in which the vent is should fit. 
     When air impinges on a front side of a conventional vent along a surface-normal of the front side, air is redirected because the inlets formed by the blades in conventional vents are angled, as exemplified by the conventional vent shown in  FIG. 1 . The blades are angled to prevent rain from passing through the vent. 
     In some embodiments of the present invention, the first substantially flat portions of two adjacent blades in the vent form an inlet having an inlet direction that is substantially parallel to a surface normal of a front side of the vent, such as parallel to the surface normal. In some embodiments, the inlet direction deviates from the surface normal by at most 10 degrees. 
     The vents in  FIG. 1  and  FIG. 7  have inlets directions that are angled away from the surface normal direction by about 45 degrees, and the vent in  FIG. 8  has inlet directions of approximately 34 degrees. Such large inlet angles seem to be accepted, even a norm. However, the inventor of the present invention found that surface-normal inlets can be used without compromising the vent&#39;s ability to drain away rain, at large volumes, especially when the surface-normal inlets are combined with the other features of the present invention. 
     In some embodiments of the present invention, the second substantially flat portions, if present, of two adjacent blades form an outlet having an outlet direction that is substantially parallel to the surface normal, such as parallel to surface normal. In some embodiments, the outlet direction deviates from the surface-normal axis by at most 10 degrees. 
     In some embodiments, a height, d o , of a straight through-going vent opening between two adjacent blades is at most 20% of a height, d h , of one of the two adjacent blades. This reduces air resistance and yet allows for an effective protection against rain. Ultimately, however, it does allow rain to travel directly through the vent, which is not desirable, but high wind speed are necessary for that to happen. In some embodiments, the height, d o , of the through-going opening is at most 10% of the height, d h . This more effectively prevents rain from entering through the vent directly. 
     In some embodiments, independent of whether there is a straight through-going opening between the blades or blade elements, or not, the depth of the blades or blade elements, d l , (i.e. the “length” in the blade or blade element in the air flow direction, which is also the length of the cross-section of the blade or blade element, as illustrated in the drawings) is preferably between 20 mm and 150 mm, such as between 50 mm and 150 mm, such as between 50 mm and 120 mm, such as between 50 mm and 100 mm. 
     In some embodiments, a height of the blades or blade elements, d h , is between 5 mm and 50 mm, such as between 5 mm and 30 mm, such as between 10 mm and 30 mm. 
     In some embodiments, there is no straight through-going opening between a pair of adjacent blades. This completely prevents rain from travelling straight through the pair of adjacent blades. Rain will encounter the blade surfaces and be slowed down. This slowdown provides for a very efficient draining, as the slower speed of the rain through the vent means that the rain has more time for draining away towards the inner perimeter. 
     In some embodiments, the blade ridge part is smooth, i.e. has no appendages or edges that cause vortices, eddies, turbulence, or similar disturbances. This gives the smoothest and least noisy performance. In other embodiments, the blades have edges. For instance, the ridge may have an edge, for instance at the top of the ridge. 
     In some embodiments, each blade is straight in a direction between the blade&#39;s first end and the blade&#39;s second end. This has some advantages, for instance ease of manufacturing. However, embodiments of the present invention should, in use, be arranged so that the blades are not horizontal, to make sure rain quickly drains towards the perimeter of the frame. This provides a fast and efficient draining. 
     In some embodiments, this is improved by providing blades that comprise a first blade element extending from the first end of the blade and a second blade element extending from the second end of the blade, the first and second blade elements being joined to one another at a joint position between the first and the second end of the blade, the first blade element being joined to the second blade element at an angle. Preferably, the first blade element is a mirror version of the second blade element, or at least substantially a mirror version. In other words, the blade is symmetrical around the joint position. Considered from the front, such blades are symmetric. This is aesthetically advantageous. 
     Besides the differences already present between embodiments of the present invention and prior-art vents, the division of blades into two that are joined (at an angle) would be an unnecessary complication in prior-art vents and would therefore not be applied on prior-art vents. 
     Preferably, a smallest angle, α, between the blade elements of a blade is between 20 and 160 degrees, such as between 90 and 150 degrees, such as between 100 and 130 degrees. In some embodiments, the smallest angle is between 150 and 170 degrees. Note that there are two angles between the blade elements of a blade comprising two blade elements, namely the smallest angle, α, and the angle 360−α. 
     In use, the blade elements are typically angled downwards from the joint position towards the frame. This, as well as the smallest angle, will be exemplified in more detail in the detailed description, see e.g.  FIGS. 2 and 3 . 
     In some embodiments, the vent comprises a drain configured to carry water away from a bottom portion of the vent. In some embodiments, the drain comprises a duct having an inlet at said bottom portion of the vent to receive water from the inner perimeter of the vent and having an outlet configured to drain water out of the duct. The duct encloses the water, which shields the draining water from winds. This prevents water from being carried into the vent under higher wind speeds. This feature cannot be combined with prior-art vents, since water in prior-art vents is not led onto an inner perimeter of those vents. Water will simply slide off blades and fall under the influence of gravity and winds. 
     Another form of drain may be used, such as an open conduit. However, the open conduit does not shield the water, and therefore water may be carried into the vent under high wind speeds. 
     A second aspect of the invention provides a method for mounting a vent in accordance with the first aspect of the invention. The method comprises: arranging the vent in such a way that at least two of the blades or blade elements in the array of blades are slanted from horizontal by at least 10 degrees. If the vent is formed from blade elements, preferably all blade elements are slanted from horizontal by at least 10 degrees. If the blades in the vent are straight blades, the aesthetics might be negatively affected. However, the technical solution works well. 
     Prior-art vents are not designed to be arranged in such a way. Prior-art vents have blades that are arranged to be horizontal. This gives the best protection against rain. Arranging a prior-art vent at an angle is therefore something the person skilled in the art would avoid. 
     In some embodiments, the method of mounting comprises mounting a vent in which each blade comprises a first blade element extending from the first end of the blade and a second blade element extending from the second end of the blade, the first and second blade elements being joined to one another at a joint position between the first and the second end of the blade, the first blade element being joined to the second blade element at an angle, the vent having a symmetry axis when considered from a front side of the vent, 
     the method of mounting comprising arranging the vent so that the first and second blade elements of each blade form substantially the same angle with respect to horizontal. 
     An embodiment of this arrangement is shown in  FIG. 3 . Each blade element forms an angle of 30 degrees with respect to horizontal, as also described later in this specification. 
     A third aspect provides a vent kit. The vent kit comprises two or more vent elements that, when assembled, form a vent in accordance with an embodiment of the first aspect of the invention. 
     In some embodiments, a first vent element provides a first part of the blade cross-section, and a second vent element provides a second part of the blade cross-section, and the first and the second vent elements, when assembled, provide the entire blade cross-section, whereby a vent in accordance with an embodiment of the first aspect of the invention is provided. 
     In some embodiments, the blade cross-section of at least two of the vent elements are identical, or substantially identical. Preferably, at least two of the vent elements are identical or at least substantially identical (i.e. not just in terms of their respective blade cross-sections). Substantially refers to the blade cross-sections being identical, but allowing for other features, such as fastening means (described below), material, finishing or other non-essential part of the vent element being different between the vent elements. It is obvious to the person skilled in the art that an insignificant change shall not render two vent elements non-identical. 
     In some embodiments, each vent element comprises one or more attachment means/fasteners for firmly attaching the respective vent elements to one another to form the vent. One outermost vent element may for instance comprise a first part of a snap rivet, such as a male part of a snap rivet, and another outermost vent element may comprise a corresponding second part of the snap rivet, such as a female part of the snap rivet. Alternatively or additionally, two outermost vent elements comprise respective snap rivet parts of a snip snap rivet. When the snap rivet parts (male+female or snip snap parts) are engaged with one another, the vent in accordance with an embodiment of the first aspect of the invention is formed. The female part may be a through hole or it may be a recess comprising locking means corresponding to a male part. Outermost vent elements are for instance element  1001  and  1003  in  FIG. 10A , since they form each end of the vent  1000  shown in  FIG. 10C . Outermost vent elements are  1101  and  1102  in  FIG. 11A , since they form respective ends of the vent  1100  shown in  FIG. 11C . Outermost vent elements are  1201  and  1204  in  FIG. 12A , since they form respective ends of the vent  1200  shown in  FIG. 12C . 
     Alternatively or additionally, each vent element may comprise one or more holes aligned to allow the vent elements to be attached to one another by inserting fasteners such as for instance one or more screws or threaded pin or threaded pins or other threaded part or threaded parts through the one or more holes, or one or more nuts with bolts through the one or more holes, or one or more snap rivets. Other means of attaching the vent elements together to form the vent may also or alternatively be used. Combinations of different fastening means may also be used. Generally, it is implicit that the fastening means of the vent elements and the cover flange element, if present, are aligned appropriately. Otherwise, a vent in accordance with an embodiment of the first aspect of the invention would not be provided. Thus, the feature “aligned” is not used further in this specification. 
     If screws or threaded pins or other threaded parts are used, then the suitable internal threading is provided in at least one of the vent elements. For instance, at least one of the outermost vent elements may have an internal threading, and the other outermost vent element has a bearing surface for supporting a screw head of a screw fitting the internal threading, or both outermost vent elements have internal threading for receiving for instance a threaded pin, preferably one that comprises a slot for easy driving. When a screw is used, one outermost vent element needs not have a through hole; a recess comprising internal threading is sufficient for allow attachment of the vent elements to one another. 
     Latch systems, such as a toggle latch, is another attachment means that may be used to attach the vent elements to one another. A catch arranged on one vent element can be caught by a latch arranged on another of the vent elements, thereby holding the vent elements together to form the vent. 
     Alternatively, the vent parts may be glued or welded together (using a welding method suitable for the material from which the vent elements are made). 
     In some embodiments, the kit comprises a separate cover flange element to be firmly attached onto another vent element to produce a vent having a flange for fitting the vent into for instance a hole in a wall. The flange may shield the perimeter of the hole in the wall from for instance rain. In some embodiments, the cover flange element comprises attachment means as described above for the vent elements. As such, the cover flange element is an outermost vent element of the kit. The attachment means described above apply equally well to the cover flange element for attaching it to the other vent elements in the kit. 
     In some embodiments, the cover flange element has a drain part that, when the vent is assembled, provides the drain in accordance with some embodiments of the first aspect of the invention. In some embodiments, the drain part of the cover flange element comprises a duct having an inlet at the bottom portion of the vent to receive water from the inner perimeter of the vent and having an outlet configured to drain water out of the duct, away from the blades and flange element. 
     In some embodiments, the flange is part of a vent element, i.e. an element that provides a part of the complete blade cross-section of the vent. 
     In some embodiments, the cover flange element provides the bottom portion of the vent. 
     A particular vent kit comprises only a single vent element and one cover flange element. The considerations above that apply to embodiments of the third aspect also apply to this particular vent. The single vent element forms the entire blade cross-section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a conventional louvre vent. 
         FIG. 2  illustrates a perspective vent in accordance with an embodiment of the invention. 
         FIG. 3  illustrates a front view of the vent shown in  FIG. 2 . 
         FIG. 4  is a detailed view of ends of the blades in the vent shown in  FIG. 2 . 
         FIG. 5 a    illustrates a cross-section of blades in the vent shown in  FIG. 2 . 
         FIG. 5 b    is a detail view of a cross-section of blades in an alternative embodiment of the invention. 
         FIG. 5 c    is a detail view of a cross-section of blades in another alternative embodiment of the invention. 
         FIG. 5 d    is a detail view of a cross-section of blades in yet another alternative embodiment of the invention. 
         FIG. 6  illustrate flow of rain capture by the vent shown in  FIG. 2 . 
         FIG. 7  illustrates a prior-art vent that can capture rain. 
         FIG. 8  illustrates another conventional louvre vent. 
         FIG. 9  illustrates pressure drop for various types of vents, including known vents and vents in accordance with embodiments of the present invention. 
         FIGS. 10A-10D  illustrate a vent kit in accordance with an embodiment of the  20  invention. 
         FIGS. 11A-11D  illustrate a vent kit in accordance with an embodiment of the invention. 
         FIGS. 12A-12D  illustrate a vent kit in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF SELECTED EMBODIMENTS 
     In the following, the invention is described in terms of specific embodiments and with reference to the accompanying drawings. 
       FIG. 2  illustrates a vent  200  in accordance with an embodiment of the invention. It comprises a frame  201  having an inner perimeter  202 . Blades  203   a ,  203   b ,  203   c ,  204   a ,  204   b ,  204   c  are attached to the frame  201  at respective attachment points. 
     In this view, it can be seen that blades  204   a ,  204   b ,  204   c  are attached at respective points  207   a ,  207   b , and  207   c . The vent furthermore has a cover flange  210  for engaging with a wall or similar surface to fit the vent relatively tightly to the surface. The vent furthermore has a drain  212  for draining away water that runs to the bottom of the vent. 
     Each blade in the vent in this embodiment consists of two elements. One blade consists of blade element  203   a  that meets blade element  204   a  at the horizontal midpoint of the vent. Similarly, the blade below it consists of blade elements  203   b  and  204   b , and the blade below that consists of blade elements  203   c  and  204   c . The blade elements of each blade are arranged symmetrically around the horizontal midpoint of the vent. Blade element  203   a  is angled downwards in a direction towards its attachment point at the frame. Similarly, corresponding blade element  204   a  is angled downwards in a direction towards its (visible) attachment point  207   a . The same applies for blade element  203   b  and corresponding blade element  204   b , and for blade element  203   c  and corresponding blade element  204   c . The angling of the blade elements means that water impinging on the blades will run down the blades by means of gravity. 
       FIG. 3  is a front view of the vent. The figure specifically illustrates a smallest angle, α, between corresponding blade elements  203   a  and  204   a . The angle in this example is 120 degrees. Each blade element is angled 30 degrees from horizontal. References  206   a ,  206   b ,  206   c  illustrate first ends of blade elements, and  207   a ,  207   b ,  207   c  illustrate second ends of blade elements. 
     The symmetrical construction of the vent described above provides an aesthetically non-provoking look. Asymmetric vents sometimes annoy some observers. However, a lack of symmetry is not detrimental to the effect of the vent, which will still perform well even if the blade elements do not form approximately the same angle with respect to horizontal. 
     The vent works well within a large range of values of the angle α. An angle as small as 10 degrees from horizontal for the blade elements still provides a very large draining effect. However, below that, the draining effect is substantially reduced. On the other hand, blades that are closer to vertical, i.e. where the angle between the blade elements is e.g. 20 degrees (i.e. α=20 degrees) will also be effective, but the aesthetic aspect suffers somewhat in this configuration. 
       FIG. 5 a    illustrates the various parts of the blade cross-sections that characterize this specific embodiment of the invention.  FIG. 5 a    is a cross-section down through the middle of the vent in  FIG. 2 . Blade portion  511  is the first substantially flat portion that forms the initial part of the cross-section of each blade. This portion is followed by a ridge portion  512 . This particular embodiment comprises the optional feature of the ridge portion of the cross-section being followed by a second substantially flat portion forming a final part of the cross-section. (If the second substantially flat portion is not present, the ridge portion forms the final part of the cross-section.) Note that since portion  512  is a ridge, the will be an upward gradient between the first substantially flat portion and the ridge portion, and a downward gradient from the ridge portion to the second substantially flat portion. 
       FIG. 5 a    illustrates an important feature of the present embodiment, namely that rain is not able to pass through the vent without getting into contact with the vent. Arrow  560  illustrates the closest water moving in a straight line would get to travelling directly through the vent. However, because of the shape of the blades and distance between them, rain  521  has no chance but to hit a surface of the blades, where it will break into smaller drops.  FIG. 5 a    illustrates drops  524  that have run down the ridge toward the rainy side. As will be described below, these drops will also move “into” the page. This is because the blade element that supports them is slanted, as for instance  FIG. 3  shows. The drops run to the inner perimeter, through the openings between the flat parts and the inner perimeter, and downwards along the inner perimeter. This will described in more detail in relation to  FIG. 6  later in this specification. 
       FIG. 4  illustrates the vent with a cutaway to better show an essential feature of the invention, namely the openings between the flat portions of the blades and the inner perimeter of the frame. These openings allow the water to run from the flat portions onto the inner perimeter  202 . Conventionally, louvres in vents are arranged to be horizontal between the frame edges, also shown in  FIG. 1 , and there are no openings between the blades and the frame of the vent. Rain will therefore simply fall off the blades on the rainy side of the vent, typically in a drip-wise fashion. 
       FIG. 4  illustrates edges of blade elements  404   m  and  404   n  attached to the frame  201 . The openings that separate the flat portions from the frame are visible in the drawings (also for blade elements below blade elements  404   m  and  404   n ). The right-hand side of the drawing shows blade elements  404   m  and  404   n  in more detail, including their respective attachment points  407   m  and  407   n . Focusing first on blade  404   n , arrow  409   n  illustrates an opening between the ridge portion of the blade and the frame  201 . Little water actually drains away this far up the ridge, but the opening allows any water there to do so. Note that this opening is optional. 
     Focusing next on blade  404   m , the arrow  410   m  illustrates the essential feature that at an end of the blade, the first substantially flat portion is at least partly separated from the inner perimeter by an opening allowing water to drain from the first substantially flat portion onto the inner perimeter. The circle at the end of the arrow  410   m  shows the first substantially flat portion as well as the opening. 
     These openings are also visible in the front view in  FIG. 3 , where it can be seen that these openings in the present case actually form a ring-shaped opening through the vent along the inner perimeter, interrupted by the attachment of the blades to the frame. 
       FIG. 5 a    shows droplets  522  that illustrate a droplets and mist of water created at the impact of rain  521 . These droplets/mist tend to move into the vent, away from the rainy side, due to the air movement. It turns out that essentially none of these droplets/mist gets through the vent, even at a rainfall any one is likely to encounter. Instead, it gets into contact with the blades and run along the bottom side of the blades towards the inner perimeter, as illustrated by drop  523 . Finally, a relatively small amount of water fall onto the blade below, as illustrated by drop  525 . Again, by virtue of the slanted configuration of the blade, this drop will travel towards the inner perimeter, through the opening, and downwards. 
       FIG. 5 a    also illustrates another feature of the present embodiment. At the bottom of the vent, there is a drain  212  that receives water from the inner perimeter of the frame through openings  436 . From there, the water drains into a duct and to an outlet  437  pointing downwards. This drain provides an important effect: Although the vent performs well without the duct drain, water may be able to travel through the vent, forced by wind. The duct has the advantage that it provides wind cover for water at the bottom of the vent, thereby preventing the water from being blown inwards. 
       FIG. 5 b    illustrates blades  504   a ,  504   b ,  504   c  in an embodiment where the blades are arranged in such a way that there is a straight through-going opening between pairs of adjacent blades. Although the drawing shall not be construed as being drawn to scale, the scale in  FIG. 5 b    does indicate that even with straight through-going openings, rain in unlikely to get through the vent in a straight line. Most likely, the interaction with the blade will be similar to that in  FIG. 5   a.    
       FIG. 5 b    illustrates a height, d o , of a straight through-going vent opening between two adjacent blades. A blade height, d h , of one of the blades is also illustrated. Preferably, the height of the straight through-going vent opening is at most 20% of the height of the blade. However, the depth of the blade, d l , (i.e. its “length” in the air flow direction, which is also the length of the cross-section) influences what opening height can be accepted. The longer the blades, relative to their height, the higher the opening between blades can be without rain being able to get through the vent and leaving the vent inwards. Almost any rain will be slowed by the blades and drain off towards the inner perimeter and downwards. 
       FIG. 5 c    illustrates another embodiment  591  of the invention. Here, the ridge is not rounded as in  FIG. 5 a   , but instead has an edge. This embodiment does provide good cover against rain, but the edge at the ridge creates more acoustic noise than the rounded ridge shown in  FIG. 5 a   . The embodiment does not have a drain similar to that in  FIG. 5 a   , but this is straightforward to add. 
       FIG. 5 d    illustrates yet another embodiment  592  of the vent. Here the blades have a valley rather than a ridge between the first and second substantially flat portions. Intuition might tell some that this vent is more efficient in draining rain. 
     This is actually not the case, by any means. An important reason for the lower efficiency is that water is collected in the valley portion. Rain that enters then splashes into the rain collected in the valley portion, and the geometry allows drops from such splashes to travel further into the vent, a process that is enhanced by any wind that might be present. Furthermore, the effective depth of the valley portion is reduced by water present in the valley. 
     In all the embodiments in  FIGS. 5 a  to 5 d   , the flat portions form straight inlets and outlets. On average, wind tends to move horizontally. When arranged vertically with the two sides of the vent arranged to be vertical, straight inlets and outlets results in the least amount of noise. Inlets in the prior art, for instance those vents shown in  FIGS. 1, 7 and 8 , have angled inlets. Presumably, the angled inlets are considered necessary to provide good cover against rain. It turns out that this is not the case, as the inventor of the present invention has found. 
       FIG. 6  illustrates what takes place when the vent shown in  FIG. 2  is exposed to winds and rain, as also illustrated in  FIG. 5 a   . The reference numbers differ slightly where necessary. Wind  620  carrying rain  621  reaches the vent. When rain comes into contact with the blades, the drops are slowed down and tend to gather on the first substantially flat portion  511 , as illustrated by drops  622 . From there, the drops move towards the perimeter, as illustrated by line  631 , because the blades are slanted. Due to the openings between the first substantially flat parts and the inner perimeter (illustrated in detail in  FIG. 4 ), the drops run onto the inner perimeter and downwards, as illustrated by line  632 . As described in relation to  FIG. 5 a   , very little water gets past the ridge  512 , as illustrated by the few and small drops  623 . Furthermore, those drops are effectively stopped or at least slowed down, and will be carried to the inner perimeter via the second substantially flat portion  513 . As described above, the major part of those drops attach to the underside of the blade above the drops and runs towards the perimeter. 
     Finally, at the bottom of the vent, the water reaches the drain  212  through opening  436 . The drain  212  acts as a duct, leading water towards the outlet  437  of the drain, as illustrated by line  633 . 
       FIG. 8  illustrates the cross-section of a conventional vent  800  similar to the one in  FIG. 1 . The vent in  FIG. 8  is more open, though, in the sense that the blades are less angled relative, and they are separated more. Not only is this vent not very rain-resistant, it also provides a relatively high air resistance compared to embodiments of the present invention described above. 
       FIG. 9  is a comparison of the pressure drops at different air speeds across prior-art vent  800  (“1” in the legend), prior-art vent  700  (“4” in the legend), and embodiments  200  and  591  of the present invention (“2” and “3”, respectively, in the legend). It is clear that the pressure drop across the prior-art vents is substantially higher than across the embodiments of the present invention, actually by a factor of around 2. For prior-art vent  700 , which is highly rain resistant, the factor is around 3. This is in large part due to the straight inlets of the embodiments  200  and  591 . This is a further advantage of these embodiments, on top of their ability to prevent rain from entering. 
       FIG. 11A  illustrates an embodiment of a vent kit in accordance with the invention. The kit comprises a vent element  1101  and a cover flange element  1102 .  FIG. 11B  illustrates the elements in a sideview. 
       FIG. 11A  also illustrates fastening means  1105   a ,  1105   b , and  1106   a  for rigidly assembling the vent element  1101  and flange element  1102  to one another, forming the vent. A screw or screws or threaded pin or pins may be inserted through vent element  1101  via hole or holes  1105   a  and  1105   b , and attached in the fastening means  1106   a  (and  1106   b , visible in  FIG. 11D ) of flange element  1102 . In the present example, the fastening means  1106   a ,  1106   b  of the flange element  1102  are recesses comprising an internal threading for receiving a screw or threaded pin. Other fastening means can be used, as described previously in this specification. Generally, some embodiments of the vent kit comprises fasteners. Other embodiments do not. 
       FIG. 11C  illustrates a perspective front view and a perspective back view of the vent element  1101  and flange element  1102  assembled into a vent  1100 . (Screws or similar means are not shown engaged into the fastening means of the vent element and flange element.) 
       FIG. 11D (a) illustrates a cross-section A-A through the assembled vent  1100 , A-A being defined in the front view  FIG. 11D (b). It can be seen that the blade cross-section resembles a half wave, having a trough in the left side of each blade and a crest/ridge on the right side (relative to  FIG. 11D ). 
       FIG. 11D (c) illustrates a sideview of the assembled vent  1100 . 
     The inventor found that a vent could also be made of a kit comprising two or more identical, or at least substantially identical, vent elements designed to provide, when assembled, a blade cross-section as described in relation to embodiments of the first aspect of the invention. By combining several such identical vent elements, an increasingly extensive blade cross-section is provided when the vent elements are assembled. In this way, it is possible to provide highly waterproof vents at a relatively low cost. By increasing the number of vent elements in a kit, the assembled vent will be increasingly waterproof. 
     Accordingly,  FIG. 10A  illustrates a vent kit in accordance with an embodiment of the invention in which there are several vent elements forming the blade cross-section. The kit comprises two vent elements  1001  and  1002 , and a flange element  1003 .  FIG. 10B  illustrates the elements in a sideview. 
     Note that the vent element  1101  and flange element  1102  of the vent kit in  FIG. 11A  are different from the corresponding vent element  1002  and flange element  1003  in  FIG. 10A . However, this is not essential in regards to the number of vent elements and/or the presence or absence of a separate flange element. 
     Similar to the embodiment in  FIG. 11A , the embodiment in  FIG. 10A  has fastening means  1005   a ,  1005   b ,  1006   a ,  1006   b ,  1007   a  for rigidly assembling the vent elements  1001 ,  1002  and the flange element  1003  to form the vent  1000  shown in  FIG. 10C . A screw or screws or threaded pin or pins may be inserted through vent element  1001  via hole or holes  1005   a  and  1005   b , then through corresponding holes  1006   a  and  1006   b  in vent element  1002 , to finally be attached in the fastening means  1007   a  (and  1007   b , visible in  FIG. 10D (b)) of flange element  1003 . In the present example, the fastening means  1007   a ,  1007   b  are recesses comprising an internal threading for receiving a screw or threaded pin. Other fastening means can be used, as described previously in this specification. 
     The vent element  1002  needs not have an internal threading, since it is clamped between vent element  1001  and flange element  1003 . In case the vent elements are identical (or substantially identical), the vent element  1002  has the same threading as vent element  1001 . 
       FIG. 10C  illustrates a perspective front view and a perspective back view of the vent elements  1001 ,  1002  and flange element  1003  assembled into a vent  1000 . (Screws or similar means are not shown engaged into the fastening means of the vent elements  1001 ,  1002  and flange element  1003 .) 
       FIG. 10D (a) illustrates a cross-section A-A through the assembled vent  1000  (see definition of A-A in the front view  FIG. 10D (b)). It can be seen that the blade cross-sections of the vent elements  1001  and  1002  meet at the interface between the vent elements, thereby providing a blade cross-section similar to the one shown in  FIG. 5 a   , and in accordance with the first aspect of the invention. In  FIG. 5 a   , the blades  204   a  and  204   b  are formed in single pieces. 
     Whereas the embodiment in  FIG. 11A  provided a blade cross-section similar to a half wave, the embodiment in  FIG. 10A  provides a full wave, being a combination of two half-wave vent elements  1001 ,  1002  arranged adjacent to one another in such a way that a “continuous” blade similar to the one in  FIG. 5 a    results. 
       FIG. 10D (c) illustrates a sideview of the assembled vent  1000 . 
       FIG. 12A  illustrates a vent kit in accordance with an embodiment of the invention  30  in which there are several vent elements that together form the vent blade cross-section, in a manner similar to  FIG. 10A . The kit in  FIG. 12A  comprises three vent elements  1201 ,  1202 , and  1203 , and a flange element  1204 .  FIG. 12B  illustrates the elements in a sideview. 
     In this example, the vent elements  1201 ,  1202  and  1203  are identical, but need not be. In this example, the vent elements  1201 ,  1202  and  1203  are identical to the vent element  1101  used in the vent kit in  FIG. 11A  for forming the vent  1100 , shown in  FIG. 11C . Furthermore, the flange element  1204  in  FIG. 12A  is identical to the flange element  1102  in  FIG. 11A , but needs not be. 
     Similar to the embodiments in  FIGS. 10A and 11A , the embodiment in  FIG. 12A  has fastening means  1205   a ,  1205   b ,  1206   a ,  1206   b ,  1207   a ,  1207   b ,  1208   a  and  1208   b  for rigidly assembling the vent elements  1201 ,  1202 ,  1203 , and the flange element  1204  to form the vent  1200 . A screw or screws or threaded pin or pins may be inserted through vent element  1201  via hole or holes  1205   a  and  1205   b , then through corresponding holes  1206   a  and  1206   b  in vent element  1202 , then through corresponding holes  1207   a  and  1207   b  in vent element  1203 , to finally be attached in the fastening means  1208   a  (and  1208   b , visible in  FIG. 12D ) of flange element  1204 . In the present example, the fastening means  1208   a ,  1208   b  are recesses comprising an internal threading for receiving a screw or threaded pin. Other fastening means can be used, as described previously. 
     The vent element such as  1202  and/or  1203  need not have an internal threading, since it is clamped between vent element  1201  and flange element  1204 . In case the vent elements are identical (or substantially identical), the vent elements  1202  and  1203  would, however, have a threading identical to that of element  1201 . This is therefore preferred from a cost perspective. 
       FIG. 12C  illustrates a perspective front view and a perspective back view of the vent elements  1201 ,  1202 ,  1203  and flange element  1204  assembled into a vent  1200 . (Screws or similar means are not shown engaged into the fastening means of the vent elements  1201 ,  1202 ,  1203  and flange element  1204 .) 
       FIG. 12D (a) illustrates a cross-section A-A through the assembled vent  1200  (see definition of A-A in the front view  FIG. 12D (b)). It can be seen that the blade cross-sections of the vent elements  1201  and  1202  meet at the interface between the vent elements, providing a blade cross-section similar to the one shown in  FIG. 5 a    and  FIG. 10D (a). In  FIG. 5 a   , the blades  204   a  and  204   b  are formed in single pieces, as described in relation to  FIG. 10D (a). 
     The embodiment in  FIG. 11A  provides a blade cross-section similar to a half wave, as shown in  FIG. 11D (a). The embodiment in  FIG. 10A  provides a blade cross-section similar to a full wave, being a combination of two half-wave vent elements  1001 ,  1002  arranged adjacent to one another in such a way that a “continuous” blade similar to the one in  FIG. 5 a    results. In  FIG. 12D (a), the use of three vent elements  1201 ,  1202 ,  1203  result in a blade cross-section similar to one and a half wave. This results in an even high rejection of rain than that which is provided by the vent in  FIG. 10C . 
       FIG. 12D (c) illustrates a sideview of the assembled vent  1200 .