1. Field of the Invention
The subject invention generally pertains to air ducts and more specifically to a fabric air duct.
2. Description of Related Art
Ductwork is often used to convey conditioned air (e.g., heated, cooled, filtered, humidified, dehumidified, etc.) discharged from a fan and to distribute the air to a room or other areas within a building. Ducts are typically formed of sheet metal, such as steel, aluminum, or stainless steel. In many installations, ducts are hidden above suspended ceilings for convenience and aesthetics. But in warehouses, manufacturing plants and many other buildings, the ducts are suspended from the roof of the building and are thus exposed. In those warehouse or manufacturing environments where prevention of airborne contamination of the inventory is critical, metal ducts can create problems.
For example, temperature variations in the building, or temperature differentials between the ducts and the air being conveyed can create condensation on both the interior and exterior of the ducts. The presence of condensed moisture on the interior of the duct may form mold or bacteria that the duct then passes onto the room or other areas being supplied with the conditioned air. In the case of exposed ducts, condensation on the exterior of the duct can drip onto the inventory or personnel below. The consequences of the dripping can range anywhere from a minor irritation to a dangerously slippery floor for the personnel, or complete destruction of the products it may drip on (especially in food-processing facilities).
Further, metal ducts with localized discharge registers have been known to create uncomfortable drafts and unbalanced localized heating or cooling within the building. In many food-processing facilities where the target temperature is 42 degrees Fahrenheit, a cold draft can be especially uncomfortable and possibly unhealthy.
Many of the above problems associated with metal ducts are overcome by the use of flexible fabric ducts, such as a DUCTSOX by the Frommelt Safety Products Corporation of Milwaukee, Wis. Such 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 into the room being conditioned or ventilated. Fabric ducts are often suspended from a horizontal cable or track by way of several connectors distributed along the length of the duct. The connectors may include snap-hooks, clips, rings, or other type of connector that can slide along the cable or track. The connectors preferably allow the fabric duct to be readily removed from its cable or track, so that the fabric duct can be cleaned.
When a fan or blower forces air through a fabric duct to supply the room with air, the pressure of the forced air tends to inflate the duct. This causes the fabric duct to expand radially and longitudinally to a generally cylindrical shape. When the ventilating or other conditioning demand of the room is satisfied, the blower is usually turned off, which allows the fabric duct to deflate, and thus retract radially and longitudinally. Depending on the application and material of the fabric, in some cases, a deflated fabric duct sags, which may create a poor appearance or interfere with whatever might be directly beneath the duct. If the duct inflates rapidly whenever the blower turns on, rapid expansion of the duct may create an objectionable snapping or popping sound as the duct suddenly becomes taut along its cable or track.
An air duct assembly disclosed herein includes a fabric duct that is held in tension along its length, even while the duct is deflated. Such a tensioned duct may exhibit a minimization of the noise associated with the sudden inflation of the duct. The aesthetics of a deflated duct may also be improved.
In some embodiments, the fabric duct hangs from an elongated support member, while a connector attached to the support member and the duct maintains the duct in tension.
In some embodiment, a spring force holds the fabric duct in tension.
In some embodiments, an air duct assembly includes a fabric duct having an upper portion that is held in greater tension than a lower portion of the duct to simplify the assembly.
In some embodiments, a fabric air duct is held in tension by a tensile force applied generally collinear with a longitudinal centerline of the duct, so that tension in the fabric is generally uniform throughout the duct.
In some embodiments, an upstream end of a fabric duct is attached to a generally stationary and relatively rigid sheet metal sleeve that counters a tensile force applied to a downstream end of the duct.