By Ryan Meres, RESNET Programs Director For over five years RESNET and the California Energy Commission (CEC) have been working together to bring the California and RESNET energy rating standards into harmony. Recent changes to California’s energy code, Title 24, move the two rating systems closer to alignment. The 2019 edition of California’s Title 24 Energy Code will include a new compliance path called the Energy Design Rating (EDR). The California EDR is similar to the HERS Index in that the reference home is a score of 100 with every percentage of energy reduced representing a score reduction of one point. RESNET’s HERS Index is based on the ANSI/RESNET/ICC Standard 301© which is also known as the Energy Rating Index (ERI). The ERI has been incorporated as a compliance path in the International Energy Conservation Code (IECC) since the 2015 version. The RESNET HERS index and ERI both use the 2006 IECC as the basis for the reference home—the home by which the rated (or proposed) home is compared. During the development of the 2019 version of California’s Title 24 Energy Code, the new EDR compliance path replaced the previous “Compliance Percent” performance path. One of the most important changes with the new EDR path is that the reference home for that path is also based on the 2006 IECC. This means the EDR and RESNET’s HERS index are very close to being in harmony. However, there are still some variations that will make the EDR and RESNET HERS scores different. One major difference is that the EDR is based on Time Dependent Valuation (TDV). TDV takes into account when energy is being used and not just how much. This is a way for California to encourage reduction of peak demand loads. In addition to TDV, California’s Title 24 climate zones don’t align with the 2006 IECC climate zones; and the calculation engine CBEC-RES that is used to calculate the EDR and RESNET HERS index are not the same. With the adoption of the 2019 Title 24 California became the first state in the nation to require the installation of PV solar systems on all new homes. This again brings California into closer alignment with RESNET since the HERS Index includes credit for on-site power systems. Another innovation of the new California standard is that the 2019 Title 24 also allows for the use of battery storage for photovoltaics to lower the EDR score. This represents another change in the importance of peak demand loads. This innovation presents a pathway for the HERS Index to reflect that when energy is used is fast becoming as important as how much energy is used. The decision to move to the EDR compliance path was a way for California to better meet the State of California’s policy to net zero energy buildings. EDR also allows for a metric that can be used to determine whether or not a home is capable of achieving net zero energy. California’s 2019 energy code, which takes effect on January 1, 2020, requires new homes to first meet an efficiency target EDR score and then meet a solar PV target EDR score. Doing so ensures a minimum level of energy efficiency is achieved prior to the use of renewable energy, thereby reducing the size of a solar PV array required to achieve net zero energy. It’s not too often that we can write about something California is doing in their energy code that has any relation to the IECC code the rest of the country uses, but this change in Title 24 to create a new EDR compliance path is an important step. Not only does it bring the RESNET HERS index closer into alignment with the California energy code, but it provides an example by which future versions of the IECC could be modeled to achieve a net zero energy code for the rest of the country.