Abstract:
A high efficiency take-off fitting allows conditioned air from a rectangular cross-section main duct to be smoothly transferred into a circular cross-section branch duct.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Nos. 61/682,938 and 61/682,856, both filed Aug. 14, 2012 and both of which are hereby incorporated by reference in their entireties. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to air conditioning and heating ductwork, and particularly to a fitting for connecting a main duct to a branch duct. 
       BACKGROUND 
       [0003]    In conveying heated or cooled air from a furnace or an air conditioner, the air is usually conducted to a rectangular cross-section main duct and thereafter through branch ducts that extend from the main duct. In recent years, these branch ducts have been formed from sealed circular cross-section sheet metal pipe. These branch ducts then carry the conditioned air to registers that open into rooms in the building to permit circulation of the conditioned air within the rooms. 
         [0004]    The transition of air from the main duct to the branch duct has not been very efficient because the branch ducts usually extend at right angles to the main duct causing turbulence in the air as it transfers. Further, the type of fittings used previously has required extensive sealing to prevent leakage of air through the joints. Newer building codes now require that there be minimal leakage in the heating and air conditioning systems. 
         [0005]    The fitting of the present invention increases both the efficiency of the flow of air through the system and the ease of assembly of the system as will be seen as the description proceeds in conjunction with the attached drawings and the appended claims. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The present invention is a high efficiency fitting for conveying heated or cooled air from a main duct to a branch duct. The fitting has a bottom flange adapted to be sealingly attached to rectangular cross-section main duct for conditioned air. The fitting has a circular cross-section exit pipe receptor adapted to sealingly mate with a circular cross-section branch duct conveying conditioned air away from the main duct. A molded transitional body connects the bottom flange and the exit pipe receptor to provide a smooth transition of air flow from the rectangular cross-section main duct to the exit pipe receptor. The molded transitional body is formed of heat resistant rigid material. Quick fasteners are provided to fasten the bottom flange of the fitting to the rectangular cross-section main duct. 
         [0007]    In order to place the fitting onto the main duct, a template may be provided to show where the hole for the opening of the flange is made. The fitting itself is provided in two forms that are mirror images of each other, one fitting for a take-off (“take-off,” will include all forms such as takeoff or take off) to the right of the main duct and one for a take-off to the left of the main duct with the direction of airflow. The fitting may be of various sizes, but the diameter where the fitting forms the main duct at the flange end of the fitting is always greater than the diameter of the circular pipe receptor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective view of the high-efficiency fitting of the present invention. 
           [0009]      FIG. 2  is a side elevation of the fitting of  FIG. 1 . 
           [0010]      FIG. 3  is a rear elevation of the fitting of  FIG. 1  partially in section to show the quick fastener. 
           [0011]      FIG. 4  is a top plan view of the fitting of  FIG. 1 . 
           [0012]      FIGS. 5A-5D  show the prior art 90 degree take-off. 
           [0013]      FIGS. 6A-6C  show the offset fitting. 
           [0014]      FIGS. 7A-7B  show the mirror image fittings for use to transfer air from a main duct one for the left and one for the right direction from the duct. 
           [0015]      FIG. 8  shows the fitting attached to a main duct that is attached to the joists in a structure in a side elevation view. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Referring to the drawings, a high efficiency take-off fitting  10  has a bottom flange  12  and a circular exit pipe receptor  14 . The flange  12  and pipe receptor  14  are connected by a transitional body  16  that is molded to form complex curves that ease the transition of air from flowing in the main duct to that flowing into the branch ducts. The complex curves are created by an offset from the center line of one opening with the center line of the other opening in the direction of the duct that it is being attached to. If viewing in an x, y, z plane, the offset would be in the z direction, with an opening in the x-plane and the other opening in the y-plane. 
         [0017]    Additionally, by having a smooth inside with no transitions or transverse seams turbulence is reduced and air flow is increased. 
         [0018]    The flange  12  has sealing material  18  affixed to its bottom side so that it is automatically sealing to the main duct. It could be a gasket or other liquid applied gasketing material. In similar fashion, the circular exit pipe receptor  14  can have gasketing material  20  affixed to its periphery or it could be attached to a pipe having sealing material. The circular pipe receptor  14  can have an indentation to receive sealant material located on a pipe. Quick fasteners  22  provide a one-turn mechanism to lock the flange  12  to the main duct. The quick fasteners  22  are one type of integral mechanical fasteners that can be used. The integral mechanical fasteners should take less time to install than using tech screws. Preferably, the integral mechanical fasteners would not include having to reach inside of the fitting. An integral mechanical fastener would not include the prior art metal tabs  42 . 
         [0019]    It will be seen that since the flange  12  has gasketing material  18  affixed to it and since the exit pipe receptor  14  has gasketing material  20  affixed to it, when the fitting  10  is positioned in place it is automatically sealed to create an air tight assembly. Examples can be pressure sensitive foam tapes and gaskets including but not limited to polyethylene foam. Other examples include Ductmate  440  Gasket Tape (isobutylene) or any other butyl gaskets. Additional examples include Gasket Tape Neoprene/Urethane and EPDM Gaskets. 
         [0020]    Further, while the drawings illustrate a left take-off fitting  10 , the right take-off fitting is structurally the same as, but a mirror image of, the left take-off fitting  10  that is illustrated (see  FIGS. 7A and 7B  . Two different molds can be used. Molded transitional body  16  can be formed from many suitable materials. One material that is useful is high strength carbon fiber which can be either carbon fiber-reinforced composite or plastic to form the body  16 . 
         [0021]    From the foregoing description of the invention, it can readily be seen that the fasteners  22  facilitate installation which reduces the time required to be spent by the installer. The transitional fitting  10  is energy efficient. The fitting  10  has an aerodynamic design with a smooth inner surface without sharp angles or transverse seams and the center line of the ends are offset which creates a pressure drop across the fitting  10  which means that less energy is required to move a given amount of air. The pressure drop and previously described features are partly enabled by the molded construction. The design lessens turbulence and increases air flow over prior art sheet metal designs. By offset, we mean the fitting to the branch duct is downstream from the flange opening, not directly at the take-off point. This means the transitional body  16  turns in two directions, not just one as in the conventional take-off unit. That is, instead of moving the air directly upwards to turn immediately right or left, it curves in the direction of flow and then to the right or left, or in a combined, complex curve. Another example can be seen in the x, y, and z planes. One opening is in the x-plane. The second opening is in the y-plane. The center line of the second opening is offset from the center line of the opening in the z direction. Clearly, if less energy is required to move a given amount of air, either the power to move the same amount of air may be reduced or a greater amount of air may be moved by the same amount of power. Less turbulence and/or less resistance could allow for using a smaller diameter branch duct that is, you could get the same amount of air through a smaller duct. Alternatively, a small blower may be used or the current blower may run less and reduce power consumption and reduce utility cost for the building owner. An oval-shaped or otherwise longer opening in the main duct having a corresponding oval shape for the flange may also reduce turbulence at the entrance to the take-off. The preferred embodiment has circular or round openings on both ends. 
         [0022]      FIGS. 5A-5D  show the prior art residential  90  degree take-off. As can be seen the prior art has many transverse joints  40  that are a source of air leakage and turbulence in an HVAC system. Typically, an installer would have to paint or seal the joints  40 . Additionally, as can be seen, tabs are used to connect that require the installer to reach into the take-off and bend sharp tabs which is difficult and can often lead to injury in the form of cuts. 
         [0023]      FIGS. 6A-6C  show the offset of the center line from one end to the second end. It also demonstrates the x, y, z plane.  FIG. 6B  shows an opening in the x-plane, a second opening in the y-plane and the offset of the center line of the openings in the z-plane.  FIG. 8  shows the take-off  10  as installed in a typical residential system. While the take-off can be used in many settings it is preferably used in connection with the typical residential system. As shown, the main duct  54  runs perpendicular to and underneath the floor joists  52 . The floor joists support the floor and the vertical space between the main duct  54  and the floor  50  is limited and that is typically where the branch ducts run between the floor joists so that they are above the bottom of the joists  52 . The horizontal space between the joists is between  12  and  24  inches with  16  inches being the most common in a residential setting. The vertical height is typically from 5½ inches to 11¼ inches with the most common being 5½ inches depending on whether 2×6, 2×8, 2×10 or 2×12 joists are used. Preferably the take-off  10  has a vertical measurement of less than 5½ inches and an outer width of less than 16 inches. As can be seen, having the offset requires increasing the overall width of the fitting  10  from the prior art. 
         [0024]    The following tables show the improved air flow through a duct system having the take-off as claimed and described versus the prior art take-off. It should be noted that the take-off was also connected with an improved register as shown in Provisional Application Ser. No. 61/682,856, filed Aug. 14, 2012, so that the improvement is combined improvement. The measure is air flow through the prior art system shown in Table A. In Table B, the prior art take-off was replaced with the take-off claimed and described. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE A 
               
             
             
               
                   
               
               
                 Prior Art 
               
             
          
           
               
                   
                 Target FPM 
                   
                 Actual FPM 
                 CFM 
               
               
                   
                   
               
             
          
           
               
                   
                 2 × 4 Duct 
                 360 
                 370.8 
                 103.0824 
               
               
                   
                 6″ Pipe 
                 507 
                 560 
               
               
                   
                 Trk Duct 
                   
                 1214.3 
                 1517.875 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE B 
               
             
             
               
                   
               
               
                 New 
               
             
          
           
               
                   
                 Target FPM 
                   
                 Actual FPM 
                 CFM 
               
               
                   
                   
               
             
          
           
               
                   
                 2 × 4 Duct 
                 360 
                 419.6 
                 116.6488 
               
               
                   
                 6″ Pipe 
                 507 
                 608 
                 119.32 
               
               
                   
                 Trk Duct 
                   
                 1153.4 
                 1441.75 
               
               
                   
                   
               
             
          
         
       
     
         [0025]    Various changes could be made in the above constructions and method without departing from the scope of the invention as defined in the claims below. It is intended that all matter contained in the above description, as shown in the accompanying drawings, shall be interpreted as illustrative and not limiting. 
         [0026]      10  duct transitional fitting 
         [0027]      12  bottom flange 
         [0028]      14  circular exit pipe receptor 
         [0029]      16  transitional body 
         [0030]      18  gasketing material on  12   
         [0031]      20  gasketing material on  14   
         [0032]      22  fastener 
         [0033]      40  joint 
         [0034]      42  prior art tab fastener 
         [0035]      50  floor 
         [0036]      52  joist 
         [0037]      54  main duct