Abstract:
A fabric flow restriction and method for adjusting the flow resistance through a fabric duct enables balancing the airflow through a network of fabric ducts. The fabric ducts are air permeable and/or include discharge openings that evenly disperse supply air from within the duct to a room being heated, cooled, ventilated, or otherwise conditioned by the air. Disclosed embodiments include flow restrictions that are adjustable by tightening a drawstring that constricts an annular web disposed within the duct or constricts the fabric duct itself, selectively masking portions of a fabric mesh installed inside the duct, or by interchanging fabric meshes of various flow resistance. In any case, the flow restriction consists of flexible fabric that tends to conform to the changing shape of a fabric duct as the duct alternately inflates and deflates due to changes in air pressure within the duct.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The subject invention generally pertains to fabric air ducts and more specifically to a damper for such a duct. 
     2. Description of Related Art 
     In HVAC systems (heating, ventilating, air conditioning), conditioned supply air discharged from a blower is often conveyed to various rooms or areas within a building by way of ductwork. Conventional sheet metal ductwork may include a main header duct that receives the forced air from the blower and distributes the air onto several branch ducts. The branch ducts, in turn, include one or more discharge registers that deliver the air to the various designated areas. 
     To ensure that each branch duct receives an appropriate volume of air to adequately condition or ventilate each room or area, airflow control dampers are often installed within the branch ducts, upstream of the ducts&#39; discharge registers. Partially closing a damper prevents its respective branch duct from starving other branch ducts of their supply of air. The various dampers are adjusted until the supply air to each of the branches is properly apportioned, which is a process known as balancing the airflow. 
     In addition to dampers disposed within the ducts, in some cases, additional dampers are installed at each discharge register. The dampers at the discharge registers allow more individualized control of airflow through each register or allow a register to be shut off completely. The occupants of the building typically adjust the individual dampers at each register, while the other dampers within the ducts are thermostatically controlled or manually adjusted and set when the HVAC system is first installed. 
     Balancing the airflow is readily accomplished when the ductwork, dampers and registers are all made of relatively rigid sheet metal, however, in many cases, air ducts are made of fabric. Fabric ducts typically have a flexible fabric wall that is porous and/or includes additional holes along its length for evenly dispersing air, from within the duct, to the areas being conditioned or ventilated. An example of such a duct is a DUCTSOX by the Frommelt Safety Products Corporation of Milwaukee, Wis. Fabric ducts are often suspended from a horizontal cable or track by way of several hangers distributed along the length of the duct. Fabric is often preferred over sheet metal when cleanliness, even air dispersion, condensation control, or appearance is a significant concern. Unfortunately, using conventional metal dampers within fabric ducts creates some problems. 
     First, the pliability of fabric may inhibit the duct from effectively supporting the weight of a metal damper without excessive distortion or sagging of the duct. Second, the supply air blower turning on and off to meet the conditioning demand of the building causes a fabric duct to alternately inflate and deflate. When the duct is deflated, a metal damper may create an unsightly bulge in the duct. 
     SUMMARY OF THE INVENTION 
     In order to restrict airflow from an upstream fabric duct to a downstream fabric air duct, an air duct assembly disclosed herein includes a fabric flow restriction disposed between the two fabric ducts, wherein the flow restriction can be manipulated to facilitate balancing the airflow through the ducts. 
     In some embodiments, the flow restriction is manipulated by replacing one flow restriction with another of a different flow resistance. 
     In some embodiments, the flow restriction is removably installed by virtue of a zipper or a touch-and-hold fastener. 
     In some embodiments, the flow resistance of the flow restriction is adjusted by varying the constriction of a cinch. 
     In some embodiments, the flow restriction comprises a fabric mesh. 
     In some embodiments, the flow resistance of a flow restriction is adjusted by varying the relative angular orientation of two overlaying fabric meshes. 
     In some embodiments, the flow resistance of a flow restriction is adjusted by varying the size of patch that masks a fabric mesh. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view with a partial cut-away showing a fabric air duct assembly that includes fabric flow restrictions. 
     FIG. 2 is a bottom view of FIG.  1 . 
     FIG. 3 is a closer view of the cut-away portion of FIG.  1 . 
     FIG. 4 is a cross-sectional view taken along line  4 — 4  of FIG.  2 . 
     FIG. 5 is similar to FIG. 4 but of another flow restriction. 
     FIG. 6 illustrates manipulating a fabric flow restriction to vary the volume of airflow therethrough. 
     FIG. 7 is a cross-sectional view taken along line  7 — 7  of FIG.  2 . 
     FIG. 8 is similar to FIG. 3, but with another mesh added to the flow restriction. 
     FIG. 9 shows one configuration of how the two meshes shown in FIG. 8 can overlaid. 
     FIG. 10 shows another configuration of how the two meshes shown in FIG. 8 can overlaid. 
     FIG. 11 is a side view of a fabric flow restriction disposed inside and situated between an upstream fabric duct and a downstream fabric duct. 
     FIG. 12 is similar to FIG. 11, but with the flow restriction providing greater flow resistance. 
     FIG. 13 is a side view of another fabric flow restriction disposed inside and situated between an upstream fabric duct and a downstream fabric duct. 
     FIG. 14 is similar to FIG. 13, but with the flow restriction providing greater flow resistance. 
     FIG. 15 is a side view of another fabric flow restriction interposed between an upstream fabric duct and a downstream fabric duct. 
     FIG. 16 is similar to FIG. 15, but with the flow restriction providing less flow resistance. 
     FIG. 17 is similar to FIG. 15, but with a fabric shroud covering the flow restriction. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An air duct assembly  10 , shown in FIGS. 1 and 2, includes several fabric ducts  12 ,  14 ,  16 ,  18  and  20  that are suspended within a building  22  by series of connectors  24 , which hang from one or more elongated support members  26 , such as a track or a taut cable. Several fabric flow restrictions  28 ,  30 , and  32  help balance the volume of airflow through the ducts. An air handler  34 , such as a fan or blower disposed within an enclosure, forces air  36  into a main duct  12 . In this example, duct  12  consists of fabric; however, it could also be made of sheet metal or of another material. The term, “fabric,” refers to any pliable sheet of material that may or may not be air permeable or porous. Examples of a fabric include, but are not limited to, woven or knit cloth, flexible plastic sheeting that is not necessarily woven, plastic impregnated cloth, fiber reinforced plastic, and various combinations thereof. 
     Main duct  12  feeds air  36  into two branch ducts  14  and  18 , which in turn feed air  36  into two other branch ducts  16  and  20  respectively. Thus, ducts  14  and  16  are in series-flow relationship to each other, and so are ducts  18  and  20 . Duct  14  is in parallel-flow relationship with ducts  18  and  20  and so is duct  16 . The term, “parallel-flow” refers to airflow being split between two different paths. Forced air  36  from air handler  34  or another source inflates each of the fabric ducts to a tubular shape, as shown. Porosity and/or other openings in the ducts&#39; fabric allow the air within ducts  14 ,  16 ,  18  and  20  to disperse into a room or area that is being ventilated or otherwise conditioned by air  36 . In some cases, main duct  12  may be air-permeable to disperse some air into part of the building as well. 
     Flow restrictions  28 ,  30  and  32  each have a flow resistance that has been individually set to apportion the airflow being discharged through the fabric wall of each of ducts  14 ,  16 ,  18  and  20 . The term, “flow resistance” is a measure of a restriction&#39;s ability to create a pressure drop for a given volume of airflow through the restriction. Thus, for a given volume of airflow, a higher pressure drop is created by a restriction having a higher flow resistance. Likewise, for a given pressure drop across a restriction, a lower volume of airflow is conveyed through a restriction having a higher flow resistance. The flow resistance of a flow restriction can be set or adjusted by a variety of methods, depending on the structural design of the restriction. 
     For restriction  28 , for example, flow resistance is created by an air-permeable fabric mesh  38  whose periphery is sewn or otherwise attached to a fabric sleeve  40 , as shown in FIG.  3 . To provide relatively low flow resistance, mesh  38  can be relatively course, as shown in FIG.  4 . To provide greater flow resistance, an alternate, finer mesh  42  with more openings  44  per square-inch can be used, as shown in FIG.  5 . Greater flow resistance can also be provided by a mesh having the same quantity or even less openings than mesh  38 , but with openings that are smaller than those of mesh  38 . 
     To manipulate or adjust the flow resistance, sleeve  40  is provided with a releasable fastener  46  at each end to releasably attach to ducts  12  and  14 . This allows restriction  28  to be readily replaced by another restriction  28 ′ having a more desirable flow resistance, as shown in FIG.  6 . Fastener  46  has been schematically illustrated to encompass a variety of releasable fasteners including, but not limited to, a zipper; a touch-and-hold fastener, such as VELCRO; and snaps. 
     Flow resistance can also be adjusted by varying the size of a patch  48  that overlays a fabric mesh  50  of a flow restriction, such as restriction  32 , as shown in FIG.  7 . Here, patch  48  is of a fabric that is less air-permeable than mesh  50 , which thus further restricts airflow. Patch  48  can be attached to mesh  50  by a variety of fasteners including, but not limited to, safety pins  52 , snaps, touch-and-hold fasteners, adhesive, etc. Cutting or folding of patch  48  can be used to adjust its size or effective area. 
     In another embodiment, shown in FIGS. 8,  9  and  10 , adjustable flow resistance is provided by overlaying a second fabric mesh  54  over mesh  38  to create a flow restriction  28 ″. Placing the two meshes  38  and  54  in rotational registry, as shown in FIG. 9, aligns the respective openings of meshes  38  and  54  to provide restriction  28 ″ with one level of flow resistance. Rotating mesh  38  relative to mesh  54 , as shown in to FIG. 10, then provides restriction  28 ″ with more flow resistance. Although, meshes  38  and  54  may be concentrically aligned to each other, FIGS. 9 and 10 show them slightly offset to more clearly illustrate the rotational orientation of each mesh  38  and  54 . 
     For another flow restriction  56 , shown in FIGS. 11 and 12, adjustable flow resistance is provided by varying the tightness of a cinch  58 . Here, restriction  56  includes an annular fabric web  60  whose perimeter is sewn or otherwise attached to a fabric duct  62 . A constrictable elongated member  64 , such as a string, cable, strap, etc., feeds through a sleeve  66  that lines a central opening  68  of web  60 . Drawing member  64  tighter constricts opening  68 , which increases the flow resistance of restriction  56 , and thus reduces the airflow to a downstream fabric duct  70 , as shown in FIG.  12 . Loosening member  64 , as shown in FIG. 11, widens opening  68  to provide less flow resistance. Once achieving a desired flow resistance, member  64  can be held in place by some type of conventional fastener or even by a simple knot. Access to member  64  can be provided by a closable access opening through duct  62  or  70 , or a pull-ring  72  can be provided on the exterior of the ducts by feeding member  64  through a small hole in duct  70 . The fabric of web  60  can be porous or impermeable to air, depending the desired range of flow restriction. 
     In another flow restriction  74 , similar to restriction  56  and shown in FIGS. 13 and 14, adjustable flow resistance is provided by varying the tightness of a cinch  76  about an inner diameter of an annular fabric web  78 ; however, flow resistance decreases with the tightness of cinch  76 . When a constrictable elongated member  80  of cinch  76  is loose, as shown in FIG. 14, overlapping fabric flaps  82  extending from web  78  tend to close upon themselves to resist airflow from an upstream fabric duct  84  to a downstream fabric duct  86 . Upon tightening member  80 , as shown in FIG. 13, flaps  82  tend to pucker, which creates a central opening  88  in restriction  74  that reduces flow resistance. Flow restriction  74  can be created by adapting the structure disclosed in U.S. Pat. No. 5,655,963, which is specifically incorporated by reference herein. 
     Adjustable flow resistance can also be provided by simply wrapping a constrictable member  90  about the exterior of a continuous fabric duct  92 , thereby creating an upstream duct  92 ′ and a downstream duct  92 ″ with a fabric flow restriction  94  between the two, as shown in FIGS. 15 and 16. Tightening member  90  chokes off air  36  flowing from duct  92 ′ to duct  92 ″, as shown in FIG.  15 . Loosening member  90 , as shown in FIG. 16, reduces the air resistance. Threading member  90  through loops  96  attached to ducts  92 ′ and  92 ″ can help keep member  90  in position. A knot  98  or some other type of fastener can be used to hold member  90  at its proper constriction. 
     To improve the appearance of ducts  92 ′ and  92 ″, a tubular fabric shroud  100  can be added to cover flow restriction  94 . Shroud  100  can be attached to ducts  92 ′ and/or  92 ″ by a conventional fastener, examples of which include, but are not limited to, a zipper, touch-and-hold fastener, clips, snaps, buttons, adhesive, and a sewn seam. Access to member  90  can be provided by having at least one end  102  or  104  of shroud  100  removably attached or unattached to duct  92 ′ or  92 ″. Access to member  90  can also be provided by moving a pull-ring  106  to the exterior of shroud  100  by feeding member  90  through a small hole in shroud  100  or by feeding it through a small gap between shroud  100  and duct  92 ′ or  92 ″. 
     Although the invention is described with reference to a preferred embodiment, it should be appreciated by those skilled in the art that various modifications are well within the scope of the invention. Therefore, the scope of the invention is to be determined by reference to the claims that follow.