The air conditioners and ventilation systems on apartment complexes or office towers aren’t typically a tool for fighting climate change. Air conditioning, alone, may use so much electricity by the middle of the century that it could push up the average global temperature by half a degree. But what if instead of contributing to climate change, HVAC systems could instead remove carbon from the air as they kept us cool.
The idea behind carbon capture is that machines suck carbon dioxide from the air–an example of “negative emissions.” This requires moving around large volumes of air, and the machines typically do that by running fans, a process that itself uses a lot of energy. A new study suggests that HVAC fans on buildings could help do some of the work. “If you think of the amount of air which [already flows through] all these air conditioning, ventilation, and heating systems, it’s a huge amount,” says Roland Dittmeyer, a chemical engineer at the Germany-based Karlsruhe Institute of Technology and one of the authors of the paper. “And you already pay for the electricity to contact this air.”
The system would be fairly simple: Modular attachments to air conditioners could pull air inside and through filters that capture CO2. Then a combination of renewable energy and waste heat could be used to convert it into a carbon-neutral liquid fuel that could be used to replace, say, jet fuel.
Companies in the burgeoning “direct air capture” space are already working on making this synthetic fuel. Though it’s more expensive than other fuels, there are already subsidies in place to help create a market for it. In California, for example, a state program gives producers of “low-carbon” fuels credits that could make it affordable for an airline to buy synthetic jet fuel. In cities that are beginning to set emissions limits for buildings, the technology could potentially help building owners offset emissions.
Early plants that capture carbon from the atmosphere are just beginning to come online, and will typically be large, stand-alone facilities. But because CO2 is everywhere in the air, the equipment used to capture it could also theoretically be anywhere. The concept of working with buildings to combine the technology with HVAC takes the idea of distributed production even further.
In the paper, the researchers calculated that one large office tower in Frankfurt, Germany could capture enough CO2 to produce more than 600,000 gallons of fuel in a year. Office buildings throughout the city could produce more than 120 million gallons. Large grocery chains in Germany could potentially capture 350 metric tons of CO2 per store each year. The same process could happen on buildings everywhere.
There are some logistical challenges; first, Dittmeyer says, engineers will have to ensure that the process is safe, and that it can run autonomously without needing direct management. Big manufacturing plants are typically cheaper to run, but if the equipment is mass produced, he says, smaller plants could be feasible, and other chemical engineering plants are beginning to take a similar approach.
The research institute already works with Climeworks and other companies in the industry, and is now beginning to talk with air conditioning and ventilation businesses about setting up a first pilot. If the idea happens, Dittmeyer argues that it would have a second advantage: making it easier for people to get directly involved in tackling climate change. To meet the goals of the Paris climate agreement, we’ll need not only to shift to a zero-carbon economy filled with electric vehicles and renewable energy–we’ll also need some strategy for removing the extra CO2 already in the atmosphere.
“With such a decentralized scheme, you have the opportunity to reach a large amount of individuals that might be willing to do something,” Dittmeyer says. “This is enabling the crowd to do something, rather than waiting for big companies to solve the problem. This is an approach that might be helpful to speed up the whole thing. That also happened in the solar business…and in that way, the whole field got momentum. And maybe we can achieve that with this more complex technology as well.”