FIELD OF THE INVENTION
The present invention relates in general to building materials products and, in particular, to moisture-resistant fibrous air duct products and methods for making same.
BACKGROUND OF THE INVENTION
Ducts and conduits are used to convey air in building heating, ventilation and air conditioning (HVAC) systems. In many applications, especially in commercial and industrial construction, the ducts are lined with flexible thermal and sound insulating material. The lining enhances the thermal efficiency of the duct work and reduces noise associated with movement of air therethrough. Duct liner may comprise any suitable organic material or inorganic material, e.g., mineral fibers such as fiber glass insulation or the like. Typical fiber glass duct liners, for example, are constructed as fiber glass mats having densities of about 1.5 to 3 pounds per cubic foot (pcf) and thicknesses of about 0.5 to 2 inches. To prevent fiber erosion due to air flow, the insulation may include a coating of on its inner or “air stream” surface. The air stream surface of the insulation is the surface that conveys air through the duct and is opposite the surface that contacts the duct sheet metal in the final duct assembly. The coating also serves to protect the insulation during brush and/or vacuum cleaning of the interior of the duct. Examples of duct liners having coatings on their inner surfaces are provided in U.S. Pat. Nos. 3,861,425 and 4,101,700. Several coated insulation duct liners are marketed under the trade designations ToughGard® by CertainTeed Corp. of Valley Forge, Pa., Aeroflex® and Aeromat® by Owens Corning Fiberglas Corp. of Toledo, Ohio., Permacote®, and Polycoustic™ by Johns Manville Corp. of Denver, Colo.
Other insulated HVAC systems use ducts either fabricated from or lined with rigid duct boards or tubes. Duct boards are rigid members formed from resin-bonded mineral fibers and whose air stream surfaces may also be provided with protective coatings. Duct boards typically have densities of about 3 to 6 pounds per cubic foot (pcf) and thicknesses of between about 0.5 to 2 inches. Coated and uncoated duct boards are marketed under a variety of trade designations from the aforementioned manufacturers of duct liners. Whether provided on duct liners or duct boards, dedicated water-resistant coatings add to the cost and complexity of manufacturing these products.
It is well known that microorganisms will grow in an environment where moisture and nutrients are present and that many species of microorganisms have a negative impact on indoor air quality (IAQ). If liquid water leaks into air duct insulation, the water may collect and stagnate in the insulation and support the growth of microorganisms.
To address the problem of microorganism growth in HVAC systems, U.S. Pat. Nos. 5,314,719; 5,37 9,806; 5,487,412 and 5,783,268 disclose providing antimicrobial agents on or in the air-conveying surfaces of impermeable duct liners and/or duct boards. However, these patents offer no insight into effective ways of preventing water that enters duct work from collecting and stagnating in the duct insulation material and causing microbe formation therein. Additionally, antimicrobial agents have very limited zones of effectiveness. That is, they tend to prevent microbe formation only in their immediate vicinity. U.S. Pat. No. 5,314,719, for example, describes a zone of antifungal inhibition of about one millimeter. Typical duct liners and duct boards have insulation thicknesses ranging from about one-half to two inches. In these products, such a limited zone of inhibition would be essentially useless in preventing microorganism formation caused by duct insulation that becomes saturated by water entering through the exterior walls and seams of the duct.
Moisture impermeable coatings, if applied to the airstream surface of air duct insulation products, inhibit ingress of water into the insulation and attendant microorganism formation therein. U.S. Pat. No. 3,861,425 discusses the notion of providing HVAC ducts either composed of or lined with fibrous glass insulation media such as batts, mats, boards or the like with such coatings. While certain coatings may provide the benefits of fiber erosion protection and moisture resistance, they add to the cost and complexity of the products and their methods of manufacture. Coatings applied to the air stream surface of fibrous insulation products may be applied to those products after their formation. This requires application of the coating to the previously formed insulation product by brush, roller, sprayer or by some other means or method and thereafter allowing the coating to cure or dry. This post-formation coating step may prolong the time required to manufacture the insulation product and, whether performed manually or automatically, must be carefully monitored in order to assure uniformity in application of the coating.
As an alternative to coated duct liners and duct boards, at least CertainTeed Corp. and Knauf Fiber Glass GmbH offer duct liners or duct boards having glass fiber insulation covered with a layer of non-woven facing material which defines the air stream surface of those products. The facing material produces a durable surface that protects the air duct from fiber erosion.
Many HVAC systems do not expose their insulation air ducts to significant fiber erosion because they operate at low air velocities. Hence, they do not need insulation products having protective coatings or facing material coverings. Indeed, the aforementioned manufacturers of insulation products offer several uncoated duct liners and duct boards for these sorts of HVAC duct work installations. However, both uncoated fibrous insulation HVAC duct products and similar products that are covered with facing material possess limited inherent moisture resistance. Consequently, they are susceptible to microorganism formation in the event they become wet.
An advantage exists, therefore, for water- resistant fibrous air duct insulation products, as well as simple and economical methods for making such products.
SUMMARY OF THE INVENTION
The present invention provides water-resistant fibrous air duct insulation products and methods for making such products. Although the principles of the invention may be adapted to unfaced duct liners, duct boards and duct tubes, according to a presently preferred embodiment the invention provides a duct board or tube comprising a first layer of resin-bonded glass fiber mat having a second layer of durable, preferably non-woven, facing material adhered thereto, wherein the facing material defines the air stream surface for the board or tube. The duct board or tube is preferably rendered water-repellent by incorporating a hydrophobic agent into the adhesive used to adhere the second layer to the first layer. In this way, liquid water in the interior of the duct will be repelled from entering the insulation, thereby reducing the likelihood of microbial growth in the insulation.
Other details, objects and advantages of the present invention will become apparent as the following description of the presently preferred embodiments and presently preferred methods of practicing the invention proceeds.
Referring to FIG. 1, there is shown a segment of an insulated air duct product 10 in accordance with the present invention. Product 10 may be a rigid duct board or tube comprising a first layer 12 of mineral fibers such as glass fibers, refractory fibers or mineral wool fibers bonded by a suitable resin and a second layer 14 of durable, preferably non-woven, organic or inorganic facing material adhered thereto by adhesive 16, wherein the facing material defines the air stream surface for the board or tube. Binders that may be used to bind the fibers of layer 12 may include, without limitation, the phenolic binders disclosed in U.S. Pat. Nos. 5,300,562 and 5,473,012, the disclosure of which are incorporated herein by reference. Product 10 may have a density of about 3 to 6 pounds per cubic foot (pcf) and a thickness of between about 0.5 to 2 inches. The thickness and density of insulation layer 12 will be dictated by the levels of acoustic and/or thermal insulation that are desired or necessary for a particular building installation. The duct board or tube is preferably rendered water-repellent by incorporating a hydrophobic agent into adhesive 16. In this way, liquid water or other aqueous liquids in the interior of the duct will be repelled from entering the insulation layer 12, thereby reducing the likelihood of microbial growth in the insulation. Preferably, a foil/scrim/paper or other suitable vapor retarder layer 18 is adhered or otherwise affixed to the face of insulation layer 12 opposite the facing layer 14 to prevent moisture from entering the insulation from the ambient environment.