Inefficiencies in air distribution systems have been identified as a major source of energy loss in U. S. sunbelt homes. Research indicates that approximately 30-40% of the thermal energy delivered to the ducts passing through unconditioned spaces is lost through air leakage and conduction through the duct walls. Field experiments over thepast several years have well documented the expected levels of air leakage and the extent to which that leakage can be reduced by retrofit. Energy savings have been documented to a more limited extent, based upon a few fieldstudies and simulation model results. Simulations have also indicated energy loss through ducts during the off cyclecaused by thermosiphon-induced flows, however this effect had not been confirmed experimentally.
A field study has been initiated to separately measure the impacts of combined duct leak sealing and insulationretrofits, and to optimize a retrofit protocol for utility DSM programs.
This paper describes preliminary results from 6 winter and 5 summer season houses. These retrofits cut overallduct leakage area approximately 64%, which translated to a reduction in envelope ELA of approximately 14%.Wrapping ducts and plenums with R-6 insulation translated to a reduction in average flow-weighted conductionlosses of 33%. These experiments also confirmed the appropriateness of using duct ELA and operating pressures to estimate leakage flows for the population, but indicated significant variations between these estimates and measured flows on a house by house basis. In addition, these experiments provided a confirmation of the predicted thermosiphon flows, both under winter and summer conditions. Finally, average material costs were approximately 20% of the total retrofit costs, and estimates of labor required for retrofits based upon these experiments were: 0.04 person-hrs/cm2 of duct sealed and 0.21 person-hrs/m2 of duct insulated.
