California’s residential ZNE by 2020 mandate was and continues to be a goal rather than a requirement for new construction, as reflected in the proposed changes to the code
By DAN KREKELBERG
At the start of 2017, new Title 24 Building Energy Efficiency Standards went into effect for residential construction in California that will remain in place for another two years. While this means there are no updated code requirements to report for 2018, there are other important activities taking place in the upcoming year that will shape the future of homebuilding in California. Among these changes is the ongoing development of the 2019 Building Energy Efficiency Standards which will eventually replace the current code. This rulemaking is being closely followed by stakeholders to understand the measures that will be put in place to support the state’s goals for Zero Net Energy (ZNE) in all residential new construction by 2020.
To clarify, California’s residential ZNE by 2020 mandate was and continues to be a goal rather than a requirement for new construction, and this is reflected in the proposed changes to the code. The minimum bar for building energy performance will undoubtedly be raised compared to the 2016 code, but designing full ZNE homes will still require builders to far exceed minimum compliance. Prescriptive requirements for high-performance envelopes may see an increase in some inland climate zones; with u-factors for wall assemblies moving from 0.051 to somewhere between 0.048 and 0.043 and attics will require higher R-values for insulation below the roof deck. Green builders looking to get closer to ZNE will need to go well beyond this, using advanced framing techniques and heavy amounts of cavity, ceiling and continuous insulation to optimize thermal envelopes.
The 2019 code will also require reaching a high threshold of efficiency features prior to the addition of Solar PV, unlike the current code where solar can be used as a tradeoff in lieu of efficiency measures. The modeling software also includes the option to include battery storage for compliance credit as an add-on to Solar PV systems. The addition of battery storage is intended to help balance energy loads of the building and to help reduce “duck curve” effects where too much renewable power is generated and placed back onto the grid at off-peak hours. This imbalance between energy generation and consumption is also being addressed in how the software calculates the overall energy performance of the building. For the last several years, a calculation method known as Time Dependent Valuation (TDV) has been used in which compliance credits are adjusted based on when energy is generated and consumed. This variable is being adjusted for the new code for greater accuracy, and outputs from compliance software are now being expressed using a score called an Energy Design Rating (EDR). Based on an index of 0 to 100, EDR scores look and function similarly to HERS scores, the difference being in the way the final scores are weighted for TDV. The important part for builders to understand about this score is not how it is calculated, but that EDR represents the new metric for meeting and exceeding code.
This is well reflected in the changes have been proposed for 2019 in the CalGreen section of the code (Title 24, Part 11), which some cities and counties adopt to mandate above-code construction. Currently CalGreen’s Tier 1 and 2 structure relies on percentage targets of 15 percent and 30 percent above standard code. What is proposed is for these percentages to be replaced by EDR scores; somewhere between 14 and 12 for Tier 1 and 0 for Tier 2, where an EDR score of 0 is the threshold for Zero Net Energy code building. Initial modeling exercises for ZNE ready buildings conducted as part of the Workforce Instruction for Standards and Efficiency (WISE) program which I manage suggest that homes will need to use high-performing mechanical equipment, solar and battery storage, plus very well insulated walls and attics to meet these targets.
The 2019 proposed standards also include a new section on Community Shared Solar and Battery Storage Systems. This provision, if incorporated into the final standards, could allow new buildings that lack sufficient space to construct PV Solar to comply with code requirements and meet ZNE by using renewable energy sources from other properties. It may also encourage new subdivisions with abundant solar and storage needs to explore community-scale solutions that offer cost advantages and align with the renewable energy and storage procurement goals of local utilities.
Although there is still a long way to go before these changes are finalized, 2018 will be a year to closely watch to see how these proposed changes evolve.
Dan Krekelberg is a Project Manager at ConSol, providing energy efficiency consulting for new residential construction and commercial retrofitting to builders, businesses and public agencies. He may be reached at www.consol.ws.