How One Ekotrope Client Approached Passing IECC 2021
The IECC 2021 energy code represents a major change in energy efficiency requirements compared to previous versions of that energy code and creates compliance challenges for most builders. This is compounded by mounting supply chain shortages. At Ekotrope, we have seen raters complete a lot of modeling work to evaluate various performance path compliance options for builders as they consider tradeoffs and value engineering. We expect this trend to continue as codes like IECC 2021 become more stringent and, thus, more difficult to pass with existing building practices.
In this blog, we’ll show you a few compliance packages raters have generated as well as how they are testing those against their builder’s portfolio of homes.
When a new energy code is introduced it triggers a flurry of energy modeling activity as builders need to determine the best pathway towards compliance. HERS Raters do this work by considering the builder’s typical building practices, material shortages and prices, and their builder’s preferences. Then the rater develops many different spec changes and assembly details to consider in their analysis. We call these variables design changes. To understand how any individual or set of design changes impacts a builder’s IECC 2021 compliance rate, raters usually find a ‘representative’ energy model and make the design changes on that sole energy model, record that change in a spreadsheet, and then report to the builder the impact of each design change.
This is an iterative process that requires making many changes and then undoing those changes in many energy models. Then trying new changes to find the right recipe for code compliance. This is an exhausting and tedious job that can take many hours.
One of our clients was completing this work and shared a set of design changes with us for a set of energy models in Texas they were analyzing. In this example, the rater was working with a builder that had 15 unique home designs. Each home design is modeled in worst-case orientation.
The rater’s builder needs to find a way for these homes to pass IECC 2021 and would also like to pass ENERGY STAR v3.1.
The rater consulted with their builder and developed a set of design changes and scenarios to examine their impact on IECC 2021 and ENERGY STAR v3.1 compliance. These design changes and scenarios were based on knowledge of their builders' existing portfolio and building techniques and practices. You can see the design changes in Table 1.
Table 1.
These scenarios were modeled on 15 energy models. That means each energy model was analyzed five times for 75 different combinations of scenarios and energy models. There were 360 different design changes made in this analysis (4 Scenarios x 6 Design Changes x 15 Energy Models).
The Rater found that Scenario #2 and #4 decreased the HERS Index by 8 and 7 points, respectively. Most importantly, both of these scenarios saw all 15 energy models pass IECC 2021. On average, they passed by 16% above the compliance requirement. That means a slightly lower specification may be able to be used to reduce cost if necessary. You can see the full results in Table 2.
This detailed analysis would have taken hours and required the tedious work of applying and un-applying each design change and recording the result - a recipe for mistakes. Because of that difficulty, raters usually only complete this analysis on 1 representative energy model or a small set of ‘representative’ energy models for their builder, instead of all applicable energy models. However, that leaves the builder uncertain on the impact on the other energy models.
In this case, the rater used Scenario Modeling and completed the analysis in just a few minutes on all of the builder’s template energy models. In this way, the rater can tell their builder definitively, what the impact of any design change is on their entire portfolio.
If you want to learn more about IECC 2021 or Scenario Modeling check out our related blog posts or contact Ekotrope!
Table 2.