Abstract:
A counterweight biased duct vent closure and door for a conventional overhead or surface mounted forced hot/cool air supply vent opening. The closure door includes a covering sized to fit over and sealably cover the register or vent opening from communication with the conditioned space when the HVAC system is not in use while automatically opening the cover to provide for treated or forced hot/cool air to be allowed into a space. The duct vent closure provided with an extension forming a counterweight spaced from and rotatable along with the door about a hinge in response to an increase and decrease in air pressure from the duct. Upon generation of a positive air pressure through the duct, the force of air pressure overcomes the gravitational bias provided by the counterweight and the covering is automatically pushed open away from the frame of the apparatus thus enabling the forced air to emanate from the vent and into the room.

Description:
[0001]    This is a continuation-in-part of application Ser. No. 09/575,472 filed May 24, 2000. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to a gravity biased HVAC duct closure apparatus for a ceiling vent in a structure or building and more particularly, to a counter weighted duct closure system which can be substantially flush mounted against a surface to cooperate with a new or existing HVAC duct system and which automatically opens under the influence of a positive air pressure within the duct, and when the air pressure is negligible, the ceiling vent is automatically sealed by the duct closure via the potential gravity bias of the counter weight to facilitate the retention of treated air previously introduced into the structure or room via the HVAC duct vent.  
         OBJECTS AND SUMMARY OF THE INVENTION  
         [0003]    An objective of the present invention is to provide an automatic duct vent closure to regulate against the backflow of treated air originally introduced to a room through the duct vent to ensure that treated air loss in the form of back flow is kept to a minimum through such a duct vent.  
           [0004]    Another object of the present invention is to provide a duct vent closure system which can be easily assembled and installed in combination with either new or pre-existing duct work.  
           [0005]    Still another object of the present invention is to provide a duct closure system which is mounted substantially flush with the ceiling so that overhead space within a room is not reduced and the duct vent closure system itself does not impede the flow of air out of the duct or impede the circulation or diffusion of treated air within the structure or room.  
           [0006]    Another object of the present invention is to provide an air duct vent closure which is easily removable from the duct vent for maintenance purposes for instance in order to clean the duct vent itself or to clean and wipe free of dust the closure mechanism.  
           [0007]    A still further object of the invention is to provide a duct vent closure which breaks up the laminar flow of treated air introduced into the room and causes a desired diffusion of the treated air throughout the room.  
           [0008]    Another feature of the invention is the provision of a counterweight attached to and providing a counter balance potential to the door such that when zero positive air pressure is induced in the HVAC duct passageways, the duct vent closure is biased into a closed position by the counterweight such that no air can escape from the room and backflow into the duct passageways.  
           [0009]    Another feature of the present invention is that the duct vent closure may be easily removed from the hinging frame apparatus to which it is attached and wiped clean of any dust, dirt or grime which has built up thereupon and then easily put back in place to continue further operation.  
           [0010]    This invention relates to a counterweight biased duct closure or door for a conventional overhead or surface mounted forced hot/cool diffuser, vent opening, supply duct or register of an HVAC system, hereinafter referred to as a duct vent. The closure includes a flap or door covering sized to fit over and sealably cover the register or vent opening to insulate the duct passageways from communication with the heated space or air conditioned space when air is not being discharged from the duct and into the room. The duct closure is provided with an extension forming a counterweight to counter balance and influence the door or flap. The counterweight is attached to and spaced from the door or flap about an axis. The door and counterweight are rotatable about a hinge on the axis in response to an increase and decrease of air pressure through the HVAC duct work.  
           [0011]    The duct vent closure door and hinge are rotatably secured along a hinge axis to at least a portion of a perimeter frame extending around the periphery of the duct vent opening. The counterweight is spaced from the hinge axis specifically in a direction substantially opposite that of the center of mass of the door in order to provide an opposing force which tends to hold the door sealed and secured against the frame when in the closed position, i.e. when no forced air is being generated by the HVAC system and discharged into the room. Upon generation of forced hot/cold air, a positive air pressure is created in the duct passageways, and the positive air pressure against the door overcomes the sealing bias provided by the counterweight and the covering is automatically pushed open away from the frame of the apparatus, thus enabling the forced air to emanate from the vent and into the room.  
           [0012]    The counterbalanced door requires no external power and is designed to automatically seal off and insulate the duct vent opening from the room when the forced hot/cool air and the HVAC fan are off thereby eliminating the ability of treated air escaping back through the registers into an air environment such as an attic or between walls where duct work is commonly routed in many homes and buildings. The frame can be mounted with any conventional attachment means to known vent and register designs, for instance, via magnets or hook and loop closures or conventional bolts or threaded fasteners. The door may remain mounted all year round and can operate during the air conditioning season in conjunction with a forced air conditioning system or a whole house fan, as well as with a heating system during the colder months. The door or closure may also be easily removed and cleaned via a means for detachment to enable cleaning of the vent door. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING(S)  
       [0013]    [0013]FIG. 1A is a diagrammatic view of the heat duct closure system prior to mounting on a ceiling in conjunction with an HVAC duct vent;  
         [0014]    [0014]FIG. 1B is a diagrammatic view of the heat duct closure system detailing the laminar air flow disruption surface on an inner surface of the closure door;  
         [0015]    [0015]FIG. 2 is a side elevational view of the duct vent closure in a closed position and attached to a ceiling and duct vent;  
         [0016]    [0016]FIG. 3 is a side elevational view of the duct vent closure in an open position where the air is allowed to flow from the duct vent out into the ambient air in the room;  
         [0017]    [0017]FIG. 4 is a perspective exploded view of the duct closure door separated from the frame;  
         [0018]    [0018]FIG. 5 is a top planer view of the duct closure door and counterweight attached with flange extensions;  
         [0019]    [0019]FIG. 6 is a side elevational view of a second embodiment having an alternate hinge attachment;  
         [0020]    [0020]FIG. 7 is an alternative embodiment without a four sided frame having only a rearward hinge member to support a door having a number of raised edges;  
         [0021]    [0021]FIG. 8 is a double door duct vent closure system wherein the counterweights are housed within the duct vent closure housing; and  
         [0022]    [0022]FIG. 9 is a four door duct vent closure system wherein the counterweights are housed within the duct vent closure housing.  
         [0023]    [0023]FIGS. 10, 11, and  12  are perspective views of a third embodiment having a plurality of counter weighted louvers. 
     
    
     BACKGROUND OF THE INVENTION  
       [0024]    There are various demands for an insulating door or closure mechanism which prevents backflow or reversal of airflow direction through the duct work of an HVAC conduit. Usually, the type of doors and closures available on the market are located on a vertically aligned duct vent opening, for instance on a wall, and pivot about an uppermost portion of a frame adjacent an exhaust fan support system in the exhaust area wherein the air flow pushes the door open and escapes. These doors are often mounted in a substantially vertical manner, specifically on a wall inside a room of a structure.  
         [0025]    As is well understood by those of ordinary skill in the art, the vertical positioning of the doors is necessary in order that the weight of gravity acts on the door, closing the door when air is no longer being forced through the conduit. For example, whenever the exhaust fan stops, the airflow ceases and the door, itself under the force of gravity, closes against the exhaust duct of the exhaust fan and provides a seal which prevents air from returning in the reverse direction back into the exhaust area and duct work conduit.  
         [0026]    In particular, in large capacity air handling systems, as well as in domestic application HVAC systems, it is increasingly important for energy efficiency reasons that treated air does not flow from the temperature controlled environment back into the duct work and therein be lost. To prevent this occurrence, an airflow reversal prevention door is mounted at the exhaust of a ventilation or an HVAC system, the door is held open by a force of air when there is a positive pressure, and when the air pressure becomes negligible, the airflow ceases and the door reseals by gravitational pull and it remains in a vertical position where it seals and prevents air from reentering the supply ducts of the HVAC system.  
         [0027]    While the above described apparatus works particularly well for vertical wall mounted systems, where such a vent closure apparatus is connected to a ceiling in a horizontal manner and parallel with respect to the floor and ceiling, the gravitational effect on the vent cover door would not close the door but would hold the door open such that the treated vented air, in particular heated air, would rise and escape back through the supply vent.  
         [0028]    Counterweights have been used in the past to cooperate with such vertical wall mounted devices in opening and closing procedures, however, specifically in a domestic application it is particularly helpful that these counterweights not intrude in a substantial manner into the room such that they take up a significant amount of space therein.  
         [0029]    There is no known method which provides for a flush mounted ceiling duct vent closure wherein a counterweight provides for the closing of the door upon cessation of the airflow from the supply duct vent. The present invention solves the problem by providing a unique duct vent closure door which is both counterweight biased into a closed position due to the gravitational influence on the counterweight, and substantially flush mounted with the ceiling.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    Presented in FIGS. 1A and 1B the duct vent closure apparatus of the present invention is indicated in general by the reference number  1 . The duct vent closure apparatus  1  incorporates as its main components, a frame  10 , having a hinge axis A-A generally incorporated along one side of the frame  10 , a door  20  rotatably attached to the frame  10  via the hinge axis A-A, and a counter weight  40  connected to the door  20  for providing gravitational potential to the door  20  rotating about the hinge axis A-A.  
         [0031]    As seen in FIGS. 2 and 3, the duct vent closure apparatus  1  is designed to be mounted to an HVAC duct vent  54  and positioned flush with the ceiling or wall  50  inside a room of a building or structure. The frame  10  may be secured directly to the ceiling  50  or attached in any conventional manner to an existing duct frame or vent of the HVAC duct. The door  20  together with the frame  10  and counterweight  40  does not intrude substantially below the level of the ceiling  50  so as not to significantly encroach upon the overhead space within the room.  
         [0032]    The ceiling  50  defines a ceiling opening  52  into which the air flow duct vent  54 , of an HVAC duct system  56 , is inserted and secured. Treated air, including but not limited to, heated air or cooled air, may be introduced into a room of a building for heating and cooling as well as recirculation purposes through the duct vent  54 . The duct  56  can be of any particular size and supply any desired volumetric flow (cfm) of air at any desired temperature from an appropriate heating and/or cooling system as is well known in the art. As such HVAC air handling systems are well known in the art no further description is provide herein.  
         [0033]    The frame  10  of the present invention is in general square or rectangular as shown in FIG. 1, but can be of any particular shape, including circular, to be utilized with any conventional duct vent opening as are generally known in the industry. The frame  10  can be sized in any manner to encompass the periphery of the two dimensional air flow duct vent opening  54  of the conventional HVAC duct  56 . A particular dimension of importance is the thickness t of the frame  10  and door  20 . This thickness t and the attendant intrusion into the room in which the apparatus is located are designed to be as unobtrusive as physically possible. The thickness t of the frame and door is between about ⅛ inch to 3 inches or more, to ensure its ability to be mounted substantially flush with the ceiling so that the duct work does not substantially extend past the limit of the ceiling  50  and needlessly intrude into a room.  
         [0034]    The frame  10  can be mounted substantially co-planer with either the wall or ceiling  50  or the air flow duct vent opening  54  in any conventional manner either with threaded fasteners, adhesive tape, glue, magnetically, or with mechanical fasteners or via other conventional means as are known in the art.  
         [0035]    Turning now to FIG. 4, the frame  10  is formed by a front member  12  separated from a parallel rear hinge member  14  by two opposing parallel side members  16 ,  18 . The frame members  12 ,  14 ,  16  and  18  are joined at their respective ends in any manner as is known in the art to form the rigid frame  10 . The frame  10  may also be formed as a one piece unit, e.g. either stamped or molded out of metal, plastic or other material as desired.  
         [0036]    The rear hinge member  14  defines the hinge axis A-A extending substantially along the length of the rear hinge member  14 . The hinge axis A-A includes opposing ends delineated via a first hinge pin  35  and a second hinge pin  37  extending co-linearly along the hinge axis A-A from opposing ends of the rear hinge member  14 . The hinge pins  35 ,  37  protrude perpendicularly with respect to the side members  16 ,  18 , and extend a short distance beyond an outermost edge of the side frame members  16 ,  18  and provide a protruding support to engage with and rotatably support the door  20 .  
         [0037]    The door  20  is a generally planer solid surface corresponding essentially to similar dimensions as the frame  10 . The door  20  is defined by a front edge  22  and a parallel rear hinged edge  24  separated by a parallel first side edge  26  and second side edge  28  defining the limits of the planer solid surface. The front edge  22 , rear hinged edge  24  and first and second side edges  26 ,  28  of the door  20  are arranged to sealably engage with the front member  12 , the rear hinge member  14  and the first and second opposing parallel side members  16 ,  18  respectively with the frame  10 .  
         [0038]    The door  20  is of particular importance with regards to the diffusion of air flow throughout the room. Returning to FIG. 1B, the duct vent door  20  has an inner surface  21  and an outer surface  23 , the inner surface  21 , faces inwardly into the duct  56  and the outer surface  23  being essentially exposed to the ambient room air faces outwardly into the room. As will be explained in greater detail below, the air pressure induced airflow which exits from the ductwork  56  and the air pressure differential caused thereby, influencing the door  20  to open and the treated air to emanate therefrom. As is also well known to those skilled in the art, the treated air emanating into the room should be diffused and thoroughly mixed throughout the existing air in the room to produce an efficient and desired environment. The air flow which emanates from the duct work  56  is generally in an undesirable laminar flow. Without diffusing or breaking up such a laminar flow, the treated air will not efficiently disburse or diffuse throughout the room, but for example, may be directed along a wall or a ceiling where it will remain in a stratified layer and fail to provide consistent diffuse and desired ambient temperature throughout the room.  
         [0039]    The air flow emanating from the duct vent  24  will at least partially come into contact with the inner surface  21  of the door  20 . The positioning and orientation of the door  20  thus directs, at least in part, the air flow from the duct vent into the room. In order to break up the laminar flow and provide a desired diffuse mixing of the air, the inner surface  21  of the door  20  can be provided with air flow interference objects  25  such as vanes, gratings, ridges, undulations and other similar apparatus as are known in the diffuser art. These air flow interference objects  25  facilitate the break up of the substantially laminar flow across the surface of the door  20  and provide a thorough mixing of the treated air with the air already present in the environment of the room.  
         [0040]    Observing FIG. 4, the rear hinged end  24  of the door  20  supports a first and second aperture flange  30 ,  32  defining an associated first and second attachment apertures  34 ,  36 . When the door  20  is rotatably engaged with the frame  10 , the attachment apertures  34 ,  36  are supported by the first and second hinge pins  35 ,  37  respectively and are axially aligned along the length of the rear hinged end  14  and co-linear with respect to the hinge axis A-A. The attachment apertures  34 ,  36  are sized to matably receive one of said opposing hinge pins  35 ,  37  of said rear frame member  14  in order to facilitate rotatable attachment of the door  20  to the frame  10 .  
         [0041]    A counter weight  40  is rigidly attached to the door  20  to provide a desired gravitationally biased closing force tending to force the door into a closed position to be described in further detail below. The counter weight  40  is spaced from and parallel to the rear hinged end  24  of the door  20  and is connected between a first and second side extensions  42 ,  44  which extend rearwardly from the first and second aperture flanges  30 ,  32 . The first and second side extensions continue the aperture flanges past an intersection with the hinge axis A-A to support the counterweight substantially opposite from the door  20 .  
         [0042]    The counter weight extends parallel to and along the length of the rear hinged end  24  of the door  20 . The counter weight  40  is attached at either end to the first and second side extensions  42 ,  44  respectively of the aperture flanges  34 ,  36 . The counterweight has a constant cross-section and weight along the length of the counterweight  40  extending between the first and second side extensions  42 ,  44 .  
         [0043]    Observing FIGS. 2 and 3, the duct closure is provided with an open position, (FIG. 2), and a closed position, (FIG. 3), relative to the rotation of the door  20  about the hinge axis A. The closed position is achieved when the front end  22  of the door  20  is biased by the counter weight  40  into contact with the front edge  12  of the frame  10 , and parallel side edges  26 ,  28  also contact the respective side members  14 ,  16  of the frame  10 . The open position is attained when a positive air pressure in the duct overcomes the bias provided by the counter weight and induces the door away from contact with the frame  10  such that the front end  22  and the side edges  26 ,  28  are spaced from the respective frame members.  
         [0044]    As is apparent to those skilled in the art, positive air pressure inside of the duct  56  will open the door  20  and maintain the door in the open position against the gravitational bias of the counterweight as long as the positive air pressure continues, thus enabling air to exit the duct vent  54  and diffuse into the room.  
         [0045]    The counterweight  40  is provided with a sufficient weight, such that when the positive air pressure force on the door  20  from the duct vent becomes negligible as compared to the gravitationally biased closing force, the counterweight biasly rotates the door about the axis A-A into the closed position. With no pressure inside the duct, the gravitational force acting on the counterweight  40  rotates the first and second flange extensions  42 ,  44  in a downward manner about the axis A-A away from the ceiling  20 . Thus, the counterweight  40  induces the door  20  to rotate respectively about the axis A-A towards the frame and the front end  24  and side edges of the door are brought into contact with the frame  12 , and thus the duct vent closure  1  substantially seals off and insulates the ambient room air from the duct  56 .  
         [0046]    The increase of air pressure within the HVAC duct applies a force to the door  20  such that the closing bias provided by the counterweight is overcome and causes the counterweight to be rotated about the hinge axis A and raised toward the ceiling, thus rotating the door  16  away from the frame in order to enable the air flow created by the positive increase in pressure to flow outwards from the duct vent closure. As the door  20  opens when such a positive air pressure is placed on the door, the counterweight  18  is swung upwards towards the ceiling  20  thus enabling the air to escape from the duct vent closure. When the pressure becomes negligible, as explained previously, the counterweight  40 , again under the influence of gravity, falls away from the ceiling, rotating the door from the open position to the closed position to seal the duct vent closure opening  54  and prevent the escape of treated air, back into the duct work.  
         [0047]    A further description of the hinge axis A-A and the rotatable connection between the door  20  and the hinge pins  35  and  37  of the frame  10  will now be provided.  
         [0048]    The first and second aperture flanges  30  and  32  of the door  20  may define a complete aperture  34 ,  36  through each flange, as shown in FIGS.  1 - 4 . As is readily apparent to a person of ordinary skill in the art, the first and second hinge pins  35 ,  37  which extend along the axis A-A outwardly from the ends of the rear hinged edge, can engage the apertures  34 ,  36  and extend through the apertures to rotatably secure the door  20 .  
         [0049]    In another embodiment, the aperture flanges  30 ,  32  can define a semi-enclosed aperture  60  through which the first and second hinge pins  35  and  37  also extend, rotatably supporting the door  20 . The aperture flanges  30 ,  32  which define the semi-enclosed aperture  60  as shown in FIG. 5 include a hook shaped portion  62  which partially encircles the axis A, encompasses the hinge pins  35 ,  37  around a top portion thereof and depends downward to an endpoint wherein the hook portion  62  ends defining an engagement and disengagement slot  64  which communicates with the semi-enclosed aperture  60 . The slot  64  is thus formed between the endpoint of the hooked shaped member  62  and an opposing portion of the flange extension  42  and  44 . The slot  64  creates a passageway having a width just greater than the diameter of the hinge pins through which the hinge pins  35 ,  37  are allowed to engage or disengage with the semi-enclosed aperture in order to support the door  20 .  
         [0050]    As is apparent from observing FIGS. 6 and 7, the hooked shaped portions  62  of the of the flange extensions allow the door  20  to be positively supported by the hinge pins  35  and  37  in both a closed and opened position. The hook shaped portion  62  enables the door  20  to open under the influence of the positive pressure induced in the duct vent with the door continuing to be supported and retained via the hook shaped portions extending around a substantial portion of the circumference of the hinge pins despite the rotation of the semi-circular aperture  60  about the hinge pins  35 ,  37 .  
         [0051]    As will be apparent to those skilled in the art, as the door  20  is opened and rotates about the hinge axis A-A, at a certain position, the engagement/disengagement slot  64  reaches a position where the slots  64  are substantially vertically aligned above the hinge pins. At this position, a user may manually disengage the door  20  from the frame due to the clearance provided by the removal slots  64  to allow the semi-circular apertures  60  to slide off and past the hinge pins  35  and  37  thus removing the door from the frame  10  and hinge. A similar reverse process is utilized for engaging the door  20  with the hinge pins.  
         [0052]    In order to ensure that the door  20  does not detatch by itself, the door  20  is provided with a specific weight to balance against the outflow of air from the airflow duct vent  54  and the counter balance  40  in order to discourage over rotation of the door during the outflow of air and any chance that the door might inadvertently over rotate and fall off.  
         [0053]    In addition, the flange extensions  42 ,  44  which support the counterweight  40 , can be designed with a length to keep the door from over rotating by ensuring that the rotation of the door  20  is stopped by contact of the flange extensions and the counter weight with the ceiling during introduction of treated air to a room. This limit on the over rotation of the door, ensures that the semi-circular attachment aperture will not be completely rotated off the first and second hinge pins  35  and  37  wherein the door would be caused to fall off under the force of gravity through the removal slot  64  without intervention by a user.  
         [0054]    The object of utilizing an engagement disengagement slot  64  as described above is so that a user may, by hand, rotate the door  20  such that the removal slot  64  is substantially vertically aligned with respect to the hinge pins  35  and  37  and thus the door  20  may be removed from the frame by manually sliding the door down and away from the hinge pins for cleaning or replacing as necessary.  
         [0055]    As seen in FIG. 7, a complete frame  10  as previously described is not necessary to the operability of the present invention. A sole linear hinge member  70  having protruding hinge pins  35 ,  37  may be anchored or attached adjacent an opening of a duct vent  54 . Without any further remaining frame members against which the door  20  can provide a substantial seal around the circumference of the door  20 , a slightly modified door such as will be described below can be attached in the aforesaid manner via either partial or fully formed attachment apertures.  
         [0056]    The modified door  80 , which could be used with or without a complete frame  10 , is formed having at least a front edge and the two (2) side edges defined by raised front and side lips  82 ,  84  and  86  respectively. The lips are designed to engage substantially with an edge of the duct vent or the ceiling around the opening of the duct vent in order to encompass a portion of a duct vent frame already incorporated in the ceiling or present in the duct work of the HVAC system. The lips  82 ,  84  and  86  are designed to securely and sealably encompass the duct vent opening  54  and secure the periphery thereof, so when in a closed position, no back flow or leakage of air from a room is lost as previously described through the duct work.  
         [0057]    Turning to FIG. 8, another embodiment of the present invention may utilize a double door duct vent closure apparatus  100 . The double doors  102 ,  104  allow for a more equal discharge of air on all sides of the duct vent closure apparatus  100  in order to provide desired air discharge and circulation within a room. The duct vent closure apparatus  100  is provided with a compact frame  106  defining a central axis B-B, extending through about the center of the frame  106 . The double doors  102  and  104  respectively are attached and rotatable in mutually opposite directions around the central axis B-B.  
         [0058]    Each of the doors  102 ,  104  is provided with an opposing counterweight  112 ,  114 . In the closed position, the counterweights of these doors are provided to extend substantially parallel with a rear edge of the door to which they are attached, beyond the axis B-B and opposite the doors with respect to the axis B-B. The doors  102 ,  104  which, when in the closed position with respect to the duct vent, are parallel and lie substantially within the same plane, also have an open position when a positive air pressure is induced in the HVAC system not dissimilar from the duct vent closure previously discussed.  
         [0059]    In the open position as shown, the doors  102 ,  104  rotate about the substantially same axis B-B, forming opposing openings from one another, that is, the open portions  110  of the frame through which the forced air is allowed to emanate are facing directly away from one another to allow air to exit simultaneously in opposite directions from the duct  100 .  
         [0060]    As is readily apparent from the description, the counterweights  112 ,  114  are enclosed and rotate within the frame while continuing to counter balance the doors in the desired manner. The counterweights are not exposed and visible within the room as in the previous embodiments. This provides a cleaner, more compact appearance and fewer obstructions or protrusions into the room.  
         [0061]    As is apparent to a person of skill in the art, the problem must be solved of the counter weights  112 ,  114  of the two doors  102 ,  104  interfering with one another. Because the doors  102 ,  104  rotate about substantially the same axis B-B in an opposing manner and at the same time and open into a room to allow passage of air, the counterweights  112 ,  114 , which overlap the adjacent door, must provide the desired counterbalance in order to properly bias the doors into the open and closed positions without interfering with one another. This is accomplished by slightly laterally off-setting the first and second flange extensions  108 ,  109  of each door  102 ,  104  along the axis B-B, so that the extensions and counterweights rotate without interfering with one another.  
         [0062]    The counterweights  112 ,  114 , on each of the doors are positioned and rotate inside at least one of the duct and the duct vent closure frame. In other words, the counterweights do not extend past the air flow duct vent opening  54  in either the closed or the open position. For example, where the door having the counterweight is in the closed position, i.e. substantially sealably engaged with the duct vent frame  106  to prevent airflow there through, the counterweight is parallel to and in a substantially planer relationship with the door, however the counterweights  112 ,  114  which, as can be seen, partially overlaps the adjacent door, is specifically positioned in a slightly more inward plane, in relation to the duct vent opening and with respect to the plane of the doors  102 ,  104 . As can be readily appreciated this slightly inward positioning of the counterweights  112 ,  114  allow the doors to simultaneously close without interference from the overlapping counterweight of the adjacent door. In all other respects, the double door duct vent closure operates in manner substantially the same as the embodiment with only a single door.  
         [0063]    Observing FIG. 9, a further embodiment of the invention provides up to four hinged and counter weighted doors  202 ,  203 ,  204  and  205  working substantially in unison to ensure a complete 360 degree out flow of treated air from the duct. As discussed above, it is desirable that the duct vent apparatus provide an efficient and effective diffusion of air throughout the room. The duct vent shown discloses 4 doors or louvers  202 ,  203 ,  204  and  205 , which enable the treated air to be directed outwardly to all sides of the apparatus to accomplish the desired 360 degree diffusion.  
         [0064]    Each of these doors is shown in the figure as having an individual axis  202 ′,  203 ′,  204 ′ and  205 ′ about which each respective door individually rotates. The axis extend perpendicularly between a central joint  210  and the closest associated frame edge to provide the respective hinge axis about which each door may rotate. As is apparent to any person of ordinary skill in the art, the 4 doors,  202 - 205  may also be arranged on two axis, each of the two axis supporting two oppositely opening doors.  
         [0065]    The doors  202 - 205  are influenced into a closed position by counter weights C in a similar manner as described in conjunction with FIG. 8. The counterweights C attached on each of the doors are positioned and rotate inside the duct vent and the duct vent closure frame. In other words, the counterweights C do not extend past the duct vent opening in either the closed or the open position. For example, where the door having the counterweight C is in the closed position, i.e. substantially sealably engaged with the duct vent opening to prevent airflow there through, the counterweight is parallel to and in a substantially planer relationship with the door, however the counterweight which partially overlaps the adjacent door, is specifically positioned in a slightly more inward plane, in relation to the duct vent opening and with respect to the plane of the doors in the closed position. As can be readily appreciated this slightly inward positioning of the counterweights C allows the adjacent door to simultaneously close without interference from the respective adjacent counterweight C.  
         [0066]    [0066]FIGS. 10, 11 and  12  disclose yet another embodiment of the present invention. In general a frame  210  supports a plurality of counterweighted parallel louvers  220  extending longitudinally between opposing first and second sides  216 ,  218  of the frame  210 . A respective first and second ends  226 ,  228  of each of the parallel louvers is attached to the first and second sides  216 ,  218  of the frame at respective opposing pivot points  235 ,  237 . The opposing pivot points  235 ,  237  define a pivot axis PA about which each louvre rotates individually. A further description of the louvers is provided below.  
         [0067]    The louvers  220  as shown in FIGS. 11 and 12 have a cross-section defining an airfoil profile. The airfoil profiled louvre  220  has a substantially wider nose portion  241  on one side of the pivot axis PA tapering to a relatively thinner tail section  243  along a first and second edges  245 ,  247  on an opposing side of the pivot point PA. Each of the tapering first and second edges  245  and  247  have a different chord length, such that, as is well known in the art of fluid mechanics and based on Bernoulli′s theorem, a fluid flow passing across the longer chord length, for example, the first edge  245 , must be faster than the fluid flow over the shorter length chord, in this case, the second edge  247 , thus creating a pressure differential, or “lift” between the first and second edges  245 ,  247 . The “lift” experienced by the louvers in the present invention, is translated into rotation of each louver  220  about the pivot axis PA. The louvers rotate in such a manner that the front nose portion  241  is turned upstream into the air flow, and the relatively thinner tail section  243  extends in a downstream direction much like the alignment of an airplane wing in respect to the airflow during flight. As Bernoulli&#39;s theorem and the results thereof are well known to those of skill in the art no further discussion is provided herein.  
         [0068]    Each of the plurality of airfoil profiled louvers  220 , the front nose portion  241  has incorporated therein a counterweight  242  having a center of mass m spaced from the pivot axis PA on the one side of the pivot axis PA and on the opposing side of the pivot axis the narrow tail section  243  provides a balancing force to each louver  220  about the pivot axis PA. When in a neutral, or substantially unbiased position, the vent is closed and the plurality of parallel louvers substantially completely obstruct the vent opening by the front nose portion  241  of each adjacent louver abutting with the tail end  245  of the narrow tail section  243  of each adjacent parallel louver.  
         [0069]    It is to be appreciated that the balancing forces of the front nose portion  241  and the narrow tail section  243  can be appropriately adjusted on either side of the pivot point PA to sustain the louver  220  in any desired neutral unbiased or balanced position. For instance, in order to provide a more secure closure it is desirable to maintain a force and weight alignment such that in the neutral position the tail section  243  extends upwardly towards the vent at least slightly higher relative to the front nose portion  241 . This force and weight balance would create a tighter seal between the adjacent tail end  245  and abutting front nose portions  241  of adjacent louvers  220 .  
         [0070]    In the closed position the airfoil profile louvers  220  are biased due to their counterweighted nature into a substantially horizontal position with respect to the potential air flow AF as shown in FIG. 10 thus closing the opening through the vent as discussed above. When sufficient air flow AF is provided within the duct, the airflow pushes down on the second edge  247  of tail section  243  of the louvers  220 , and the pressure created thereon overcomes the bias of the counter weight provided in the nose portion  241  of each louver. The louvers  220  are thus rotated out of the closed position and into an open position, allowing the air flow AF to pass from the duct, through the vent and into the room.  
         [0071]    As the louvers  220  are rotated into the open position, it is to be appreciated that each louver becomes substantially inclined to a more aerodynamic position, i.e. the nose portion  241  of each louver is rotated into the air flow AF, towards the direction from which the air flow emanates. As can be appreciated by those of skill in the art, in addition to the pressure provided by the air flow AF pushing directly on the first edge  245 , as each louver becomes more aerodynamically inclined or more parallel relative to the air flow AF, a pressure differential develops creating a higher lifting pressure on the second edge  247  of the airfoil profile as discussed above thus adding a further additional rotation or “lift”, as in an airplane wing, to the airfoil and providing for an increase in the opening of the vent due to the combination of the duct pressure and the pressure differential created across the first and second edges  245 ,  247 .  
         [0072]    As is to be appreciated, upon the reduction of the airflow AF and the higher air pressure in the duct, the counterweight  242  in the front nose portion  241  of the louver  220  overcomes the air pressure and thus rotates the louver  220  about the pivot axis back into a substantially horizontally position relative to the potential airflow AF wherein the tail end  246  of each of the airfoil louvers abuts the front nose portion  241  of an adjacent louver in order to close the opening of the duct vent.  
         [0073]    The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it is therefore desired that the present embodiment be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.