The Carbon Vaults Project, Summer 2022
Delaying the decomposition of woody biomass is one of the crucial ways of reaching Yale Carbon Containment Lab’s most immediate goal: containing 30 million MTCO2e by 2030. An exciting new idea to increase that delay has sparked the imagination of the lab members since its founding. This summer, with the rigorous work of 5 graduate students and Professor Jana VanderGoot, this initial idea has transformed into a full-scale pilot study: The Carbon Vaults Project.
Wood preservation has long been a tradition in architecture. Architects have been thinking of ways to raise the wood off the ground to prevent its decay for decades. In the CC Lab, specifically, using carbon vaults for carbon storage was first imagined in 2021. Our call-to-action was clear: The United States Forest Service (USFS) is approved to thin 70 million acres of overstocked forests as wildfire treatment by 2032, which produce slash piles. These piles may decay or catch on fire, releasing a lot of carbon.
Therefore, covering and protecting these slash piles is a great strategy both for fire mitigation and carbon storage, especially across the American West which faces severe wildfire risk.
Our initial solution idea as the lab was constructing a basic “earth berm” structure using mass timber and plaster to cover the slash piles. This storage method would be an effective short-term solution to store carbon, for a relatively low cost of $10-15k. However, the team soon started to realize that these wood vaults not only can be helpful for fire mitigation purposes, but they can also provide much-needed temporary storage for waste wood as a potential fuel source for future bioenergy facilities with carbon capture and storage (BECCS).
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The idea that followed was storing the wood for a longer period of time, for at least a few decades in a very accessible way, at which point direct air capture technologies would be abundant enough so that this stored wood could be used in the biofuel industry and eventually in other carbon containment projects such as chemical weathering or TrapRock.
One way to achieve this long-term storage is through wood burial in reclaimed mines, which can offer storage for more than a century. Since EPA requires by law that the mining companies reclaim unused mines, we saw potential in this type of wood carbon storage. However, mine reclamation projects typically cost around $3-5 million and require accounting for the transportation carbon footprint to carry the wood biomass to the mine. Therefore, the team is performing site suitability studies to determine which mines are close to lumber facilities, as part of the Carbon Vaults Project.
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The third and perhaps the most cost-efficient and easy-to-scale carbon vault technology also determined the focus of Summer 2022 for the carbon vaults team: designing small wood mass timber sheds, using a special construction design technology called Dowel Laminated Timber (DLT). The timber shed design offers many advantages, for example, it can store carbon for around 10-50 years for a cost of around $10-15k. The DLT design also makes the sheds very durable and resistant to fire, since DLT has a 2-3 hour fire rating; due to the char layer that develops on top of the wood layer when it catches on fire.
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Summer 2022 was when the initial prototyping for these mass timber sheds took place. In an eight-week intensive summer research project, five of the lab’s summer interns from the Yale School of Architecture (YSOA), Qian Huang, Fuad Khazam, Silas Newman, Jun Shi and Hao Wang, worked on different shed designs. Their work was supervised by Professor Jana VanderGoot, an affiliate of the lab and Associate Professor of Architecture at the University of Maryland. This research led the team to propose two innovative types of mass timber panels to be used in the sheds: Cross-stacked Residual-DLT and Braced Residual-DLT.
These new technologies introduce new modifications to the standard DLT technology. The standard DLT connects stacked softwood strips called “lamellae” with hardwood dowels that stay in place because of the surface tension created between the softwood lamellae and hardwood dowels. One modification of the CC Lab team to the standard DLT design is using “residual,” or small-wood. CC Lab defines small-wood as wood that is thinned from forests as small-diameter (4-6”) trees, wood that is left over from larger logs with beetle or fire damage, or wood that remains as the byproduct of sawing logs for dimensional lumber. This is a great strategy to make use of the wood that is often wasted as a byproduct of commercial logging and therefore exemplifies a circular economy approach to design.
CC Lab, July 2022, Carbon Vaults in the Lab
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The CC Lab’s new designs are also innovative because the diagonal layers of the Braced Residual-DLT and the cross-stacked wood of the Cross-stacked Residual-DLT make them more structurally stable than the standard single-layer DLT panel that only spans in one direction. If designed and installed properly, the Braced and Stacked panels are strong in two directions and can increase the shed’s wind and seismic activity resistance.
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Though standard DLT already has a great fire rating for a wood structure, The CC Lab is exploring options for improving the fire ratings of this design with the addition of a layer of what the team is calling ash-cob plaster. The plaster is a mix of waste ash from industrial incinerators and clay-soil. The initial testing by the lab shows that this layer provides efficient protection against fire, and has the potential to improve the overall design and durability of the carbon vaults.
Prof. VanderGoot shares that the short-term goal of the Carbon Vaults project is making sure that each vault type gets a pilot project to gather useful data. The long-term aim is more ambitious: “Scaling up to make a big impact with the project across the country and to create a butterfly effect whereby other groups start implementing these new design strategies for wood carbon containment,” as Prof. VanderGoot aptly puts it. The next phase in the Carbon Vaults project in the Fall of 2022 and Spring of 2023 is prototyping each type of vault on actual sites with stakeholder partners. To test economics, labor requirements, and structural performance, we are constructing a Dowel-Laminated Timber (DLT) Shed and an above-ground Berm using a variety of fireproof coverings. In addition, we are constructing a below-ground Burial Vault in a variety of environments.
