The California Energy Commission (CEC) granted Electric Program Investment Charge funds to support the design and construction of a community of 50+ single-family Zero Net Energy (ZNE) homes near Fresno, California. The primary purpose of this project was to help scale up single-family ZNE construction from an individual pilot home to community scale, and by doing so, develop tools and understanding to support both ZNE and all-electric new construction at the statewide scale. To support this project, ConSol Energy subcontracted with Opinion Dynamics to do both market research and an analysis of ZNE home energy data.

Initially, Opinion Dynamics conducted a survey of 500 California residents currently or recently active in the California homebuyer market. The goal of the survey was to characterize customers awareness of ZNE and ENERGY STAR® certified homes, understand customers’ interest in ZNE labeling and energy efficiency, and assess the most important non-price characteristics in home purchase decisions. Opinion Dynamics also conducted in-depth interviews with realtors, mortgage underwriters, and homebuilders. The goals of the in-depth interviews were to understand market trends with respect to ZNE and energy efficiency in the new construction market; establish how appraisers currently value ZNE and energy efficiency in appraisal prices; and assess where underwriters consider energy and maintenance costs in their qualification criteria for load underwriting.

Once the homes were occupied, Opinion Dynamics monitored and analyzed each home’s circuit-level energy usage data to explore how advanced home technologies and occupant behavior impact building performance. Notably, this study included a comparative analysis between projected energy use via the California Building Energy Code Compliance Residential software (CBECC-Res) and their actual energy use when occupied.

This study captured key insights to understanding the decision-making process of homebuyers related to ZNE and energy efficiency features. In addition, the ZNE market assessment work provided insights into the barriers of valuing ZNE and energy efficiency features in the appraisal and mortgage underwriting process. This study also provided an unprecedented opportunity for the state to study the accuracy of CBECC-Res, not just at the home level, but at an individual circuit level as well. Through this process, we developed insights into where the CBECC-Res model performs well and where it can be improved, with the ultimate goal of strengthening the underlying algorithms of a keystone software that will also play an integral role in the Building Initiative for Low Emissions Development (BUILD) Program.

A key challenge in this study was collecting data from new and untested sources. We leveraged data from the proprietary CURB energy management system, which presented its own set of unique challenges, such as understanding the underlying processes that dictate how certain variables are recorded. To overcome these challenges, we worked with CURB system engineers to ensure data quality and completeness, and to verify our understanding of the values we received out of their reporting system. By working together to achieve success in this area, we were able to utilize a data source that offered unparalleled granularity, flexibility, and transparency—ultimately enabling a groundbreaking analysis.

Opinion Dynamics created daily load profile charts for whole-home consumption and individual circuit consumption by superimposing monitored data from each individual home against the average across all homes and the CBECC-Res output modeled using both 30-year typical and actual weather. Based upon a preliminary analysis of a subset of homes covering roughly two months of data, we found that the CBECC-Res model underestimated space heating and cooling usage, while overestimating water heating usage. The time period and sample size limited our ability to draw definitive conclusions. Even with these limitations, however, the research team identified the following CBECC-Res assumptions as likely responsible, in part, for the discrepancies: (1) the assumed thermostat set-point was more conservative than actual usage, (2) actual weekday home occupancy was higher than assumed, and (3) the number of occupants based on square footage was higher than assumed. Armed with this information, the State of California is better prepared to interpret the CBECC-Res projections and identify solutions to improve the accuracy of CBECC-Res.


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