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CAMBRIDGE, Mass., Nov. 24, 2021 /PRNewswire/ — The Harvard Center for Green Buildings and Cities (CGBC) at the Graduate School of Design has just published “Zero-carbon Balance: The Case of HouseZero,” the first full accounting of the structure’s embodied carbon and a detailed methodology behind calculating its zero-carbon balance in the peer-reviewed journal Building and Environment. In tandem, the CGBC has also released a summary of the lab’s full-year performance results.

Prof. Ali Malkawi, Founding Director of the CBGC, said the research in the paper, as well as the summary of results, reflect a “positively promising performance” by HouseZero with potentially far-reaching implications amid a deepening, intertwined climate and energy crisis.

The HouseZero research team assessed the building’s performance using the entire lifecycle of CO2e emission from a building. This included embodied and operational emissions as well as grid-energy carbon offsets from onsite renewables. These results highlight key points regarding buildings’ net-zero carbon balance.

  • The calculations for balancing carbon emissions over the lifetime of a building are sensitive to future technology development and cleaner energy sources.
  • More transparent and consistent accounting of carbon emissions is needed for all building life cycle stages, such as product replacement occurrence and the building’s end-of-life stage.
  • Accounting for carbon emissions of the entire building is important and should include embodied carbon emissions associated with heating and cooling; onsite renewables; and other mechanical, electrical and plumbing systems.

HouseZero, the residential-to-institutional retrofit project and laboratory, which also serves as the headquarters of the Harvard CGBC, is located in the Mid Cambridge Neighborhood Conservation District in Cambridge, MA.An example of a fully net-zero-carbon building. The majority of HouseZero operating systems were completed in May 2020, but the building opened its doors earlier.

Prof. Malkawi said, “The CGBC, along with our architectural and engineering partners, is very encouraged by the project’s progress to date. We believe together, and our research supports that assertion, in the importance of transparency when declaring zero-carbon balance.

Dean Sarah M. Whiting, of Harvard Graduate School of Design, and an operation board member of the CGBC, added, “HouseZero not only promises to be a core contributor to Harvard’sTransition to a net zero carbon future. However, it is also an important and clarifying voice in defining what we mean when using common terms such as ’embodied carbon’ or ‘carbon balance’.

Jonathan Grinham, CGBC Senior Research Associate and co-author of the paper, explained, “there are robust standards for whole building lifecycle assessment (LCA), but there is little conformity on what is actually reported and there is a serious need for a universal definition of zero-carbon emissions buildings.” The published research explains in detail the life cycle assessment methods used, including system boundaries and data availability, scenarios, assumptions and uncertainties, as well as the details of the final outcome.

The just-released FY 2021 HouseZeroPerformance Summary provides one year of actual operational data (a period during which the building was not occupied due to the pandemic). Based on data from the first operational year (June 2020).May 2021HouseZero (see below) shows that excess onsite renewable energy can offset emissions associated to the primary building structure (which doesn’t include emissions from technical equipment), as long as the photovoltaic production can achieve optimal efficiency (as designed), and that the building performance is maintained. Using existing standards, calculations were conducted by the CGBC based on total load without IT (e.g., data servers) and plug loads and the interpolation of some unavailable data.

As reflected in the Performance Summary, while the building has been able to provide excess generated energy to the local power grid, researchers recognize that adding more PVs, while being mindful of the additional embodied carbon emissions, will offset the added energy demand from onsite data servers used for research. As part of ongoing experiments, the CGBC continues to explore strategies and technologies to further reduce electricity consumption in HouseZero. 

For more information, please contact:

Taylor Ko

[email protected] 



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SOURCE Harvard Center for Green Buildings and Cities


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