What if air conditioners could be retrofitted to capture carbon?

The planet is warming. And incomes are rising around the world. That means more people using air-conditioners, causing yet more greenhouse gas emissions and warming. It’s a scary spiral. But researchers at the University of Toronto say we can flip the problem on its head. In a Nature Communications paper, they propose converting AC units into machines that capture carbon dioxide and water from the air and turn it into synthetic fuels.

In this vision, air conditioners would be retrofitted with technology that already exists or is under development, and would run on renewable electricity. So people in homes, offices and buildings would be producing renewable synthetic oil using chemical processes and renewable electricity.

The researchers admit that the idea, which they call “crowd oil”, is futuristic and faces several challenges. But if it were to happen, it would not only remove carbon dioxide from the atmosphere, it would create personal synthetic oil wells for people to use, share or sell. “The envisioned model of “crowd oil” from solar refineries, akin to “crowd electricity” from solar panels, enables people to take control and collectively manage global warming and climate change, rather than depending on the fossil power industrial behemoths,” they write in the paper.

Retrofitting an AC to make fuel from carbon dioxide would require a filter that would absorb carbon dioxide and moisture from thin air. An electrolyzer could split water into oxygen and hydrogen. Then the hydrogen and carbon dioxide could be combined to make the synthetic fuels.

Chemist Geoffrey Ozin at the University of Toronto and his colleagues analyzed the technical potential of this approach for three different cases: the landmark Frankfurt Fair tower building in Germany; a typical grocery store, and low-energy houses. To calculate carbon dioxide removal rates, the team assumed a carbon dioxide concentration in the air of 400 parts per million, and used typical air circulation volumes for the different buildings.

The Frankfurt Tower, with a volume around 200,000 cubic meters, could capture 1.5 metric tons of carbon dioxide per hour and produce up to 4,000 metric tons of fuel a year. Meanwhile, 25,000 grocery stores in Germany could remove about 1,000 metric tons of carbon dioxide per hour, and a building consisting of 5–6 apartments could capture 0.5 kg of carbon dioxide per hour, the researchers calculate.

While intriguing, the concept is of course purely theoretical right now. The researchers did not calculate the economics or the space needed to scale up this concept to a large scale. Engineering research would also be needed to analyze the long-term reliability and stability of such systems, they say.

Source: Roland Dittmeyer et al. Crowd oil not crude oil. Nature Communications, 2019.

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