Pliable air duct with dust and condensation repellency
A fabric air duct with main discharge openings includes additional, much smaller openings that help ventilate the surface of the duct. Ventilating the surface of the duct with a slight yet even amount of airflow helps inhibit the accumulation of condensate and dust on the surface of the duct. In some embodiments, the duct includes a pliable sheet consisting of a rather porous fabric base material. To achieve an appropriately low level of airflow, a coating on the fabric reduces, but does not eliminate the fabric's porosity. A calendering process then reduces the porosity even further. In some embodiments, the calendering process occurs before the coating process. In other embodiments, the pliable sheet is substantially air impermeable, except for its main discharge openings. The sheet is then perforated with numerous smaller openings to achieve the desired amount of surface ventilation. In yet other embodiments, an emorizing or sueding process is used to abrade or nap the surface of a porous or non-porous base material to create a pliable sheet having a desired amount of porosity. From any of these processes, air ducts of various shapes may be formed, including air ducts that are circular, ½ round, and ¼ round in shape, as well as air ducts having a non-uniform cross-sectional shape across their lengths.
This application is a continuation of U.S. application Ser. No. 10/441,904, filed May 19, 2003, which is a continuation-in-part of U.S. application Ser. No. 09/951,717, filed on Sep. 13, 2001, now U.S. Pat. No. 6,565,430, both of which are incorporated herein by reference in their entirety.
FIELD OF THE INVENTIONThe subject invention generally pertains to pliable air ducts and more specifically to the air permeability of such a duct.
DESCRIPTION OF RELATED ARTIn 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 ductwork is typically formed of sheet metal and is often installed above 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. This not only creates a poor appearance in many cases, but can create other problems as well.
For example, temperature differentials between an air duct and the air on either side of the duct wall can create condensation on both the interior and exterior of the duct. 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. If an exposed sheet metal duct conveys relatively cool air, condensation can form on the exterior of the duct. The condensate may then drip onto the floor, inventory, and 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 perhaps unhealthy.
Many of the above problems associated with exposed metal ducts are overcome by the use of fabric ducts, such as DUCTSOX™ fabric ducts by Frommelt Safety Products Corporation of Milwaukee, Wis. Such ducts typically have a fabric wall that is air-permeable to broadly and evenly disperse the air into the room being conditioned or ventilated. If greater airflow in needed in certain areas, the fabric duct can be provided with additional discharge openings, such as air registers or cutouts in the fabric.
The porosity of conventional fabric can pass a substantial amount of air, which can be desirable in many applications where the airflow through the pores of the fabric is used primarily for evenly dispersing air into a room. However, some applications require airflow that is more directed toward certain areas of a room. In such cases, it may be desirable to have relatively large discharge openings provide most of the air airflow, while the pores of the fabric provide only enough airflow to inhibit dust and condensation from accumulating on the outer surface of the fabric material.
Unfortunately, it can be difficult to acquire an air duct material whose porosity provides an appropriately small amount of airflow, such as 2 cfm (two cubic feet per minute of air across one square-foot of material subject to a 0.02 psi air pressure differential). Standard fabric materials have been found to pass 40 cfm or more. Such materials have been calendered in an attempt to reduce the materials porosity. Although calendering conventional fabric does reduce its porosity temporarily, much of the effect is lost after the material is washed. Thus, simply calendering just any porous fabric is not a permanent solution to the problem.
SUMMARY OF THE INVENTIONAn air duct consists of an air permeable material that passes air therethrough at a flow rate that is substantially less than what the air duct discharges through other larger openings.
In some embodiments, an air duct is made of a porous fabric that is coated to reduce, but not eliminate, the fabric's porosity.
In some embodiments, an air duct includes a pliable sheet that includes a porous fabric base. The sheet is coated to render the sheet substantially impermeable to air. The sheet is provided with discharge openings for supplying air to a room, and is perforated with much smaller openings that help inhibit the formation of condensation or inhibit the accumulation of dust.
In some embodiments, an air duct with primary discharge openings and much smaller pores or perforations is made of a fabric with anti-microbial properties.
In some embodiments, an air duct is made of a coated porous fabric that is calendered to reduce the fabric's porosity.
In some embodiments, the an air duct is made of a fabric sheet having numerous minute pores or perforations that convey only one to four CFM/ft2 (cubic feet per minute per square-foot of material) when a 0.02 psia pressure differential exists across the sheet.
In some embodiments, an air duct material is perforated by displacing material rather than by removing a significant portion of it. Displacing material not only helps reinforce the periphery of each perforation, but also helps reduce the amount of scrap during the perforating process.
In some embodiments, an air duct includes a fabric sheet having a base material of polyester for strength and porosity, and having an acrylic or polyurethane coating to reduce or eliminate the base material's porosity.
In other examples, an air duct comprises a pliable sheet configured to convey air, wherein the pliable sheet has a porosity formed by an emorizing or sueding process, wherein the pliable sheet includes a plurality of discharge openings that each provide a first area and wherein the porosity of the pliable sheet provides a plurality of second areas, with the first area being greater than the second open area.
In some examples, an air duct, comprises a pliable sheet configured to convey air, wherein the pliable sheet includes a fabric base material that is porous and a coating on the fabric base material that reduces the porosity of the fabric base material yet leaves the pliable sheet porous, wherein the pliable sheet includes a plurality of discharge openings that provide a first open area and the porosity of the pliable sheet provides a second open area with the first open area being greater than the second open area.
In some yet other examples, a method of creating an air duct comprises applying pressure to a pliable sheet having a porosity below a desired porosity to increase the porosity of the pliable sheet to the desired porosity; and configuring the pliable sheet to convey air.
In some examples, a method of creating an air duct comprises applying pressure to a pliable sheet to decrease a porosity of the pliable sheet; after the application of the pressure, applying a coating to the pliable sheet; and configuring the pliable sheet to convey air.
BRIEF DESCRIPTION OF THE DRAWINGS
An air duct 10, shown in
Most of the air delivered to the rooms comes from discharge openings 16 in duct 10, as indicated by airflow arrows 18. Openings 16 can assume a variety of forms including, but not limited to cutouts, discharge registers, and screens.
To help inhibit condensation or dust from accumulating on the surface of duct 10, the fabric wall between discharge openings 16 is provided with another set of much smaller openings 20. Openings 20 allow the fabric wall of the duct to breathe in the areas between discharge openings 16. A slight current of air 22 passing outward through the duct wall may help keep dust from settling on the exterior of the duct. But also, when duct 10 is conveying cool air, a small current of cool air passing through the duct's fabric wall tends to keep the warmer room air slightly away from the exterior surface of duct 10. Thus, moisture in the warmer room air is less likely to condense on the surface of duct 10.
The actual size, number, and spacing of smaller openings 20 can vary; however, there does appear to be an optimum design range. The relative open areas of openings 16 and 20 should allow about ten percent (preferably less than more) of supply air 14 to pass through smaller openings 20 and about ninety percent through discharge openings 16. Sheet 12 should preferably pass one to four CFM/ft2 with a 0.02-psi pressure differential across sheet 12 (i.e., 0.02 pounds per square inch of air pressure should force one to four cubic feet of air across a one square-foot of sheet material every minute). Higher airflow rates through smaller openings 20 reduce the amount of air that discharge openings 16 can direct to specific areas, while lower airflow rates are less effective at reducing condensation or dust. In some cases, positive results are achieved when openings 16 are able to pass more than twenty times as much air as smaller openings 20. Moreover, the distribution of openings 20 should be sufficiently dense to provide an even flow of air through sheet 12. To avoid having smaller openings 20 direct too much airflow in any particular direction, openings 20 are preferably distributed over nearly the full circumference or perimeter of duct 10.
To achieve appropriate airflow characteristics, sheet 12 may consist of a fabric base material 24 with a coating 26 such as, for example, a plastic coating, as shown in
The process of producing sheet 12 is schematically illustrated in
In an alternate embodiment, shown in
Just as with the embodiment of
A technique for producing a pliable sheet, alternative to that shown in
The pliable sheet 100 is compressed between two rollers 104 and 106, which have abrasion surfaces, 108 and 110, respectively. The abrasion surfaces 108, 110 have protrusions 112 compressing against the surface of the pliable sheet 100 to create the desired level of porosity. Thus, the process of
The abrasion surfaces 108 and 110 may be formed of sandpaper or other rough surfaces, such as a surface coated with industrial diamond particles. The protrusions 112 may be periodic or aperiodic. In an example, the protrusions 112 cover the entire surface 108 and 110.
Although the pliable sheet 100 is illustrated in
Another suitable process is a calendering process like that of
While the tubular pliable sheets 124 and 160 are shown having a uniform cross-sectional shape that is circular, the sheets 124 and 160 may be formed into other cross-sectional shapes and may be uniform or non-uniform across their tubular length.
Although the invention is described with reference to a preferred embodiment, it should be appreciated by those of ordinary skill in the art that various modifications are well within the scope of the invention. For example, the pliable sheets described herein do not have to include a fabric base. The sheets could simply be a pliable air impermeable sheet, for example a plastic sheet, which is perforated with micro-perforations or pinholes to achieve desired flow characteristics. And in the case of the emorizing and sueding techniques described with reference to
Claims
1. An air duct, comprising a pliable sheet configured to convey air, wherein the pliable sheet includes a fabric base material that is porous and a coating on the fabric base material that reduces the porosity of the fabric base material yet leaves the pliable sheet porous, wherein the pliable sheet is formed into a tubular shape and wherein the air duct defines a plurality of discharge openings that provide a first open area and the porosity of the pliable sheet provides a second open area with the first open area being greater than the second open area.
2. The air duct of claim 1, wherein the first open area is at least twice as great as the second open area.
3. The air duct of claim 1, wherein the fabric base material consists essentially of polyester.
4. The air duct of claim 1, wherein the coating consists essentially of acrylic.
5. The air duct of claim 1, wherein the coating consists essentially of polyurethane.
6. The air duct of claim 1, wherein the pliable sheet is anti-microbial.
7. The air duct of claim 1, wherein the pliable sheet is at least flame retardant.
8. The air duct of claim 1, wherein the porosity of the pliable sheet is adapted to convey air therethrough at a rate of one to four CFM/ft.sup.2 when a 0.02 psia pressure differential exists across the pliable sheet.
9. A method of creating an air duct, comprising:
- applying a coating on a fabric base material to create a pliable sheet that is air permeable;
- applying pressure to the pliable sheet to reduce its air permeability; and
- configuring the pliable sheet to convey air.
10. The method of claim 9, further comprising forming the pliable sheet into a tubular shape.
11. The method of claim 9, further comprising heating the pliable sheet while applying pressure to the pliable sheet.
12. The method of claim 11, wherein heating the pliable sheet involves heating one side of the pliable sheet more than an opposite side of the pliable sheet.
13. The method of claim 9, wherein applying pressure to the pliable sheet involves calendering.
14. The method of claim 9, wherein the air permeability of the pliable sheet is such that the pliable sheet is able to convey air therethrough at a rate of one to four CFM/ft.sup.2 when a 0.02 psia pressure differential exists across the pliable sheet.
15. The method of claim 9, wherein the fabric base material consists essentially of polyester.
16. The method of claim 9, wherein the coating consists essentially of acrylic.
17. The method of claim 9, wherein the coating consists essentially of polyurethane.
18. The method of claim 9, wherein the pliable sheet is anti-microbial.
19. The method of claim 9, wherein the pliable sheet is at least flame retardant.
20. A method of creating an air duct, comprising:
- applying a coating on a fabric base material to create a pliable sheet;
- perforating the pliable sheet to create a plurality of perforations having a first open area; and
- forming the pliable sheet to help create a tube that defines a plurality of discharge openings having a second open area that is greater than the first open area.
21. The method of claim 20, wherein upon perforating the pliable sheet, the plurality of perforations are created more by displacing material within the pliable sheet than by removing material from the pliable sheet.
22. The method of claim 20, wherein the second open area is at least twice as great as the first open area.
23. The method of claim 20, wherein the fabric base material consists essentially of polyester.
24. The method of claim 20, wherein the coating consists essentially of acrylic.
25. The method of claim 20, wherein the coating consists essentially of polyurethane.
26. The method of claim 20, wherein the pliable sheet is anti-microbial.
27. The method of claim 20, wherein the pliable sheet is at least flame retardant.
28. The method of claim 20, wherein the plurality of perforations allow the pliable sheet to convey air therethrough at a rate of one to four CFM/ft.sup.2 when a 0.02 psia pressure differential exists across the pliable sheet.
29. The method of claim 20, wherein the tubular shape has a circumference and the plurality of perforations are distributed over most of the circumference.
30. The method of claim 20, wherein the plurality of discharge openings is able to pass more than twenty times as much air as the plurality of perforations.
31. The method of claim 20, wherein the plurality of perforations have a distribution of between 100 and 2000 perforations per square-inch.
32. The method of claim 20, wherein each perforation of the plurality of perforations has an effective diameter that is less than a material thickness of the pliable sheet.
Type: Application
Filed: Aug 2, 2005
Publication Date: Dec 22, 2005
Inventor: Kevin Gebke (Dubuque, IA)
Application Number: 11/195,390