ADVANCED DUCT RESEARCH - BURIED DUCTS

CARB has always and continues to explore ways to reduce the significant energy liability caused by heating and cooling distribution ducts located in attics. While there are many ways to reduce this load, such as moving ducts within conditioned space, insulating roofs instead of ceilings (unvented attics), using non-ducted systems for heating and cooling, etc., all of these typically require significantly more time, materials, and/or money to implement. Over the past few years, CARB has been investigating the potential of simpler approaches.

One method that has been extensively researched by SWA is buried ducts. SWA originally worked with Beazer Homes out in California to quantify the benefits of burying the attic ductwork under blown-in insulation. SWA’s research into the effectiveness of buried ducts interested officials at the California Energy Commission, and buried ducts were listed as one option available to reach residential Title 24 compliance in the 2005 code. The next step would be to figure out how to bring the benefits of the buried duct technology researched in hot, arid climates to regions that are hot and humid.

SWA worked with Outlook Construction in Georgia, to devise a method to prevent possible moisture condensation on the ducts’ vapor-barrier jacket when utilizing the buried duct technology in humid climates. A flex duct system was installed in the attic (tight to the ceiling plane) and covered with one-inch of sprayed polyurethane foam. The combination of the flexduct insulation (R-6) and the foam (R-7) yields an R-13 insulated duct system. The sprayed foam also air seals duct joints and supply boots. Blown cellulose insulation was then installed over the foamed ducts. The technique has been found to lessen heat gain, leading to reductions in the system peak load. SWA monitored duct performance and the polyurethane was shown to provide as a vapor barrier, preventing moisture diffusion between the attic and the ducts.