This summer, Leah was selected to receive the Harry Misuriello Award for Advancing Building Energy Codes from the American Council for an Energy-Efficient Economy (ACEEE). She was invited to attend and present at Summer Study, ACEEE’s biennial convention of energy efficiency professionals to collaborate, debate and advance decarbonization in the building sector. Leah presented on Just Housing’s design strategy for zero net energy (ZNE) operation and how its construction, energy use, and cost compares to code. Leah’s presentation is summarized below.
The following illustrations demonstrate how a 2020 Minnesota code wall (which is based on the 2012 IECC) and a Just Housing wall are typically constructed. Note the differences in insulation levels, air tightness, and building elements. Additionally, note the similarities; the Just Housing zero energy construction upgrades were designed to be as familiar as possible to builders in the Upper Midwest.
To analyze how these different assemblies impact energy use, we compared two versions of the Just Housing Evergreen House design as if built on a lot in Duluth, MN in 2022. We compared the Evergreen House as designed (optimized for all-electric zero net energy operation) to a second version designed to 2020 Minnesota code standards with natural gas for heating and cooking. Using an energy model (REM/Design), we predicted the energy use of each home. The ZNE version was predicted to consume 37,000 kBtu over the course of a year, while the code version was predicted to consume 107,000 kBtu.
A ZNE Evergreen House was built and occupied in Duluth in 2023. Data from the first six months of occupation show that the Evergreen House is outperforming its modeled energy consumption. The Observation Hill House, a house in Duluth built to code in 2023, consumes 2.75 times more energy than the Evergreen House. The following chart illustrates how the Evergreen House and the Observation Hill House compare to other existing homes in Duluth (consumption data was shared by owners).
The following chart lists the suite of upgrades that make up Just Housing’s approach to ZNE operation. We found the additional cost of these upgrades to be $44,028, an 11% increase from the cost of building to code. The incremental cost would increase the mortgage about $200/month, but the expected savings in energy costs will offset the increased mortgage.
Mortgage payments often stay the same but history shows that we can expect energy costs to rise over time. This suggests that ZNE homes are more affordable over the long term.
What will it cost if we don’t build like this? We have already wasted too much time and resources. Now is the least expensive time to build to zero net energy. If we don’t, the cost is our future.
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