An impact evaluation was recently completed for PG&E's residential new construction program. Key measures in this program included high efficiency central air conditioners and enhanced duct installations. To evaluate this program, over 300 comprehensive building surveys were conducted, and a calibrated engineering analysis was developed to compare as-built homes with reference case homes.
To evaluate the duct component of the program, ìduct blasterî tests were conducted on a subset of 158 homes to establish duct system performance with respect to leakage. Information about the duct system for each home (including physical dimensions, location, insulation levels, and leakage) was then run through a distribution system efficiency model. The model, developed by LBNL, is based on the draft ASHRAE 152P Method of Test for Determining the Design and Seasonal Efficiencies of Residential Thermal Distribution Systems 1997. The distribution system efficiency estimates were combined with Micropas simulation results and engineering estimates of energy consumption for non- HVAC end uses to provide ìwhole buildingî usage estimates. Participant and nonparticipant energy usage could then be calibrated to customer bills and compared to establish program savings.
This paper focuses on the duct system analysis portion of the evaluation project. The duct testing and analysis are described. Duct leakage test results are then presented along with a comparison of test results for program participants and a matched group of nonparticipants. Finally, calculated distribution system efficiencies are compared against default HVAC Duct Efficiency Factors that are assumed for California Title 24 compliance modeling.
This project provides a relatively large-scale look at duct system efficiency in new homes. In addition, the modeling approach provides a method for integrating duct test data into a Micropas simulation analysis.