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New Working Group on When Energy is Used/Load Flexibility Into HERS® Scores

Aug 7, 2019

When energy is used is rapidly becoming as important as how much energy is used.  Utilities are already beginning to curtail grid-scale renewables during certain times of the day/year because supply exceeds load.  Homes that can respond to this varying renewable energy supply with high levels of efficiency, thermal and electrical storage, control, and on-site power production offer the grid support that electric utilities are seeking.  Utilities will increasingly be incentivizing load flexibility through real-time/time-of-use rates and technology rebates.

To stay relevant for utility Demand Service Management programs in this changing environment, RESNET needs to account for when energy is used, not just how much energy is used.  Soon the HERS® Index must be able to reflect the value of the technologies that provide grid services.  Already some builders and manufacturers are seeking credit in HERS® Index scores for connected/smart thermostats and batteries. The pressure to respond will only increase with time.

To be able to respond to this changing environment at the 2019 Spring RESNET Board Meeting the RESNET Board approved establishing a working group to investigate incorporating when energy is used and/or load flexibility in HERS® Index Scores. The RESNET Board requested that the working group report its results to the Board by September 15, 2019.

The RESNET Board then would adopt a set of policies that would guide the RESNET Standard Management Board in developing appropriate standard changes.

As a starting point the working group will explore how the new California energy code (Title 24) addresses the issue. This exploration is intended to produce the maximum practical level of harmonization of HERS/ERI calculations and results across North America.

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 represents a score reduction of one point.  The new EDR path’s reference home is also based on the 2006 IECC. This means the EDR and RESNET’s HERS® Index are very close in being in harmony.

With the new version of the code, California became the first state to require the installation of PV solar systems for all new homes. This requirement is likely the first of many and emphasizes the importance of updating the HERS® Index to increase its market value in a world that relies increasingly on time-varying renewable energy working in synchrony with existing and new energy efficiency technologies and control strategies.

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. Other methods of storage include grid-connected water heaters and smart thermostats, especially when used in conjunction with thermal mass.

The working group will develop a briefing paper and policy recommendations in September so that the Board can consider them at its 2019 Fall RESNET Board Meeting in Charlotte, NC on October 17, 2019.

David Goldstein is serving as the chairman of the working group.

Members of the working group are:
Matt Christie, TRC
Philip Fairey, Florida Solar Energy Center
Rebecca Heilig, Energy Inspectors
Neal Kuris, Big Ladder Software
Chris Mathis, Mathis Consulting Company
Dave Roberts, National Renewable Energy Laboratory
Alice Rosenberg, Consortium for Energy Efficiency
Amy Schmidt, DOW