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Ithaca, New York, has committed to fully decarbonizing by 2030. To achieve that goal, the city is creating a “digital twin” that can model energy use, building by building.
Ithaca’s Green New Deal commits the town to fully decarbonize its building stock by 2030 — a tall order. Photographer: Bruce Yuanyue Bi/The Image Bank RF
In 2019, lawmakers in Ithaca, New York, resolved to eliminate or offset all carbon emissions by 2030, becoming the first city in the US to set such an ambitious global-warming benchmark.
Then it launched a $100 million plan to fund a massive municipal climate-proofing effort.
That left this college town of 30,000 in the state’s Finger Lakes region with a big practical challenge: How do you decarbonize thousands of buildings — which account for a huge chunk of emissions — at scale, in just a few years?
When the Ithaca Green New Deal plan was launched, two architecture professors at nearby Cornell University, Felix Heisel and Timur Dogan, realized they had a tool that could help — a map created using machine learning that estimates the costs of retrofitting, and future electricity grid loads, on a building-by-building level across the city.
Dogan, who runs Cornell’s Environmental Systems Lab, had for years been developing software that allowed architects to quantify the energy consumption and carbon footprint of buildings. Heisel, who leads the Circular Construction Lab, was working to understand what carbon neutrality really means when you account for material stock and embodied carbon. The pair of academics reached out to the city and offered their technology as a way to translate Ithaca’s bold goal into action. The map will be crucial as Ithaca determines its electrification priorities and funding allocations; if successful, the technology could be expanded to help all types of cities tackle building decarbonization at scale.
“Which buildings [do you] renovate first? Which buildings consume the most energy? Which ones would be the lowest hanging fruit to renovate?” said Dogan, describing the questions he hoped his software could answer.
Existing tech can do this fairly easily — but only one building at a time. That misses a big opportunity, Dogan says. “When you’re working at these scales, there are potentially synergies. Like, if you group buildings in a certain way, or if building owners team up to share investment costs of something like geothermal boreholes.”
That’s where Dogan and Heisel’s new energy modeling map — a “digital twin” of the city — comes into play.
Established in the early 19th century and home to Cornell and Ithaca College, the town of Ithaca has about 8,000 buildings, ranging from cutting-edge university research facilities to blocks of drafty old Greek Revival homes. Modeling scenarios on a map with that many unique building profiles would quickly hit a barrier in terms of computing feasibility, Dogan says. So the key to their map is clustering similar spaces and building properties.
For example, Dogan’s dataset measures things like solar radiation on a building, what type of space is inside (residential or commercial), and how the buildings are oriented. Then he takes those similarities and narrows thousands upon thousands of unique combinations down to hundreds of space types that can work in simulations at scale.
“We’re kind of slicing and dicing the city into pieces,” Dogan said.
The data that makes all of this possible comes from a combination of sources that ultimately paints a picture of each building.
Dogan and Heisel started with municipal energy use data from the city of Ithaca. Then they layered in a large data set from the U.S. Department of Energy, which has prototype building profiles depending on age and location. This helps model the occupant behavior and energy uses within spaces, too.
But Heisel, whose Circular Construction Lab studies the environmental benefits of salvaging materials from deconstructed buildings, is also interested in the unique material stock of each building, down the roof, walls, foundations and windows. So he’s drawing on building permit data sets from the city to understand the construction of each building. That helps measure the carbon implications of retrofitting a building, and the potential for reuse of old materials.
The final step is constructing the 3D geometry of each building, which the team is trying to do with Google Street View and other satellite imagery. This is an especially important step for the small-scale buildings of Ithaca, where the specific pitch of a roof, for example, determines the viability of solar panels.
The end goal is that these building profiles, and the map itself, will be a living model. New data, gathered by the city or verified by building owners, could be added and updated along the way.
“You’re not just ‘Archetype A’ — your building is actually modeled here,” Dogan said. “Give us information, and we’ll incorporate that into the models to make it more accurate.”
Dogan and Heisel hope this tool will soon make it out of the laboratory and into the hands of the public. They’re building a dashboard where anyone will be able to pull up the map of Ithaca and understand the global energy consumption of the city, but then also zoom into any one building.
The interface would allow you to select a building and apply all types of hypothetical scenarios. A building owner could see which energy improvements have the biggest bang for the buck, and how far it might get them to carbon neutrality. A city official could apply different policies to entire neighborhoods and model the potential impact.
It’s new territory for Dogan, who’s used to building software for architects, not the general public. But he sees this new map and dashboard as a key piece to winning over the stakeholders who will make Ithaca’s energy transition possible.
“We now have to convince politicians, we have to convince communities, the people that live in the buildings. So we need a way to communicate this data in a much easier way,” Dogan said.
That task may prove easier in Ithaca, an enclave of progressivism that was until recently led by former mayor Svante Myrick, who was elected to the post at age 24 and helped spearhead the city’s Green New Deal commitment in 2019. Myrick recently stepped down to accept a post as executive director of the progressive advocacy organization People For the American Way.
Laura Lewis, who now serves as acting mayor, said the administration is still working out many of the finer points of electrifying the city’s entire housing stock while balancing the concerns of residents.
“We are not introducing mandates. We are looking to provide information so that residents can make their best decisions with the support of the city,” Lewis said.
Those decisions stand to be complicated. Not only are much of the city’s buildings older — the mayor’s house was built in 1885 — but 74% of residents are renters, according to Lewis.
“We’re very aware of costs that may be borne by property owners, including a significant number of landlords, and wanting to ensure that increased costs are not then passed down to our renters. So it’s a real challenge,” Lewis said.
And that’s to say nothing of the broader technical and environmental considerations. While Cornell has made several investments in renewable energy generation, including major solar farms and a “lake source cooling” concept that harnesses the cold waters of nearby Cayuga Lake for campus air conditioning, New York State’s power grid still draws two-thirds of its capacity from gas-fired power plants. Nuclear and hydroelectric account for another large chunk, with wind and solar still far behind. (The “upstate grid” is generally cleaner — and where most of the renewable energy is generated — with the New York City region relying heavily on fossil fuel generation.)
“We want to move toward electrification, of course,” Lewis said. “There are questions about the grid, questions about capacity of the grid, how green the grid is. These are all questions that we’re talking about on a regular basis.”
Questions that, with any luck, Dogan and Heisel’s map can help answer.
