The feasibility of taking existing San Francisco homes to zero net energy was validated in this study. Data from the Energy Upgrade California and San Francisco Home Improvement and Performance Program home energy retrofit programs; independent testing on 2- to 4-unit homes; and interviews with home performance experts and experienced San Francisco contractors was used to group energy efficiency measures into three technically feasible “pathways” to zero net energy.
The pathways were created based on the compatibility of the set of measures proposed, and the perceived likelihood that they would be adopted together by a homeowner with certain priorities and preferences. The pathways were then assigned to one of three “personas” characterized as different types of customers in the marketplace. Energy models of the pathways were created for both a modest and a deep retrofit. The energy requirements of the homes after the proposed deep retrofit were then compared against the solar potential of typical homes in San Francisco, which was in most cases sufficient to meet the remaining demand with on-site solar.
Data from the home performance programs was analyzed to determine which of numerous variables might predict the deepest level of energy savings and best cost-benefit ratios. Correlations were weak or non-existent, emphasizing the need for home energy assessments on a house-by-house basis. However, because the home performance programs were just beginning at the time of the study, the sample size was small (n=44) and data will be updated as more becomes available.
This data analysis created a framework for evaluating home energy upgrade data which has been adopted by the local utility for distribution to local cities and counties for use in efficiency programs throughout its service territory.
The study also reviews numerous characteristics of San Francisco’s housing stock and highlights their effects on home performance. Small multifamily 2- to 4-unit home energy efficiency issues and opportunities are summarized from current testing and a 2006 San Francisco study.