US DOE Prototype Buildings from an Embodied Energy and Carbon Perspective

I recently had a conference paper accepted for presentation at the ASHRAE 2020 Annual Conference entitled “Embodied Energy and Carbon Emissions of DOE Prototype Buildings from a Life Cycle Perspective”. In this post I’ll give a brief overview of the project and some of the key results from it.

In this project, we evaluated the extent to which the US Department of Energy (DOE)’s prototype buildings are suitable to be benchmarks of embodied carbon or energy to compare against. This set of 16 buildings represent 80% of the US commercial floor area, and have been used extensively to monitor and compare operational energy metrics.

We considered five of different building typologies: small, medium, and large office in addition to mid-rise and high-rise apartments. The following figure shows a visual representation of the buildings.

Model renderings of the (a) small office, (b) medium office, (c) large office buildings. Note that buildings are not to scale to one another.

From these model files, I wrote a python script to calculate the areas of each surface (wall, ceiling, window, and roof), as well the volume of each material specified for thermal modeling purposes. Thus, for each prototype building, the total mass of each material was calculated. The cradle-to-gate (stages A1-A3) carbon emissions for each material was collected from the open source Inventory of Carbon and Energy (ICE) database. Thus the total cradle-to-gate carbon emissions (embodied carbon) and energy consumption (embodied energy) were determined.

These emissions and energy are divided by the total floor area of each building to show normalized impacts and visualized by their material:

(a) Embodied energy and (b) embodied carbon separated by material for building typologies considered.

Concrete is the largest contributor to the embodied energy and carbon for all the building typologies. As expected for the office building, the smaller it is, the lower the embodied energy and carbon. Yet for the apartment buildings, this trend was not realized. This is part due to the difference in structural system assumed by the thermal model. The range of embodied carbon for the office buildings is between about 45 and 95 kg carbon-dioxide equivalent per square meter, while others studies (such as the Carbon Leadership Forum’s Benchmarking Study) have shown an average of 398 kg carbon-dioxide equivalent per square meter for commercial buildings such as office buildings. Likewise, the mid- and high-rise apartments have lower embodied carbon than multi-family buildings contributed as part of the CLF study. Thus, the primary conclusion from this paper is that the DOE prototype buildings, in their current form, are not representative of the embodied impacts of construction materials, although they serve as a starting place for the development embodied carbon benchmark buildings.

For more details about this study, see the soon to be available conference paper.

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