Thermal Performance of Residential Duct Systems in Basements

There are many unanswered questions about the typical effects of duct system operation on the infdtration rates and energy usage of single-family residences with HVAC systems in their basements. In this paper, results from preliminary field studies and computer simulations are used to examine the potential for improvements in efficiency of air distribution systems in such houses. The f'mld studies comprise thermal and flow measurements on four houses in Maryland. The houses were found to have significant envelope leakage, duct leakage, and duct conduction losses. Simulations of a basement house, the characteristics of which were chosen from the measured houses, were performed to assess the energy savings potential for basement house. The simulations estimate that a nine percent reduction in space conditioning energy use is obtained by sealing eighty percent of the duct leaks and insulating ducts to an R-value of 0.88 °C.m2/W (5 °F.ft2-h/BTU) where they are exposed in the basement. To determine the maximum possible reduction in energy use, simulations were run with all ducts insulated to 17.6 °C.m2/W (100 °F.ft2.h/BTU) and with no duct leakage. A reduction of energy use by 14% is obtained by using perfect ducts instead of normal ducts