September 14, 2026
Deep beneath part of Yale’s campus, installation of a massive geothermal borefield is complete. Look inside the two-year engineering feat that’s set to transform how Yale heats and cools its buildings and reduces fossil fuels.
Brightcore Energy and Upper Science Hill Development team at the geothermal borefield site
An extraordinary feat of engineering has wrapped up on upper Science Hill. After nearly two years of precision drilling, the university and its partners have completed drilling, grouting and linking a massive underground geothermal borefield that will connect to a new Thermal Utilities Plant and help shift Yale buildings away from fossil-fuel energy.
The Upper Science Hill Development (USHD) is a 600,000-square-foot transformation of Yale’s campus that began in the fall of 2023 and integrates multiple distinct components. These include the flagship Physical Sciences and Engineering Building (PSEB), an Advanced Instrumentation Development Center, and vital support infrastructure.
From August 2024 through March 2026, crews drilled 263 holes—each one measuring 850 feet deep—and installed closed-loop piping. If laid end-to-end, that piping would stretch for more than 88 miles—roughly the distance from New Haven to New York City. The project marks a major milestone toward achieving Yale’s goal to be a zero-emission campus by 2050 and offers a concrete example of how large institutions can decarbonize building energy at scale.
But why drill so deep into Science Hill’s bedrock just to keep lab buildings operating effectively and efficiently? The answer comes down to a fundamental shift in how the university thinks about heating and cooling.
Moving past the 100-year-old steam loop
For more than a century, Yale has heated campus with a traditional district steam system: fossil fuels are burned at a central plant to boil water into high temperature steam, which is then distributed through underground pipes into campus buildings.
That model will be phased down gradually. Yale’s plan is to transition from steam to a low-temperature hot water loop—typically between 120°F and 140°F—served primarily by centralized heat pumps that will transfer heat between buildings and the ground.
The newly completed borefield on Science Hill is a critical early component of that transition. This massive underground installation acts as both heat source and sink. In the winter, four 600-ton heat pumps located within the new Thermal Utilities Plant pull natural warmth out of the ground to heat labs connected to the low-temperature hot water loop. In the summer, this process reverses.
“Hot water distribution is a key component of modernizing Yale’s district energy system,” according to Sam Olmstead, senior director of Utilities and Campus Resiliency. “That we will produce the hot water on Science Hill with a geo-exchange system is really exciting!”
Projected energy use on Science Hill
By connecting the new Physical Sciences and Engineering Building and five existing research laboratories, the Thermal Utilities Plant, alongside energy conservation measures within the new and existing buildings, will lower the carbon footprint and overall energy use of one of the most energy intensive corridors on campus.
The estimated payoffs will be substantial:
- 20% lower total energy use across Science Hill.
- Avoiding 27,000 metric tons of carbon dioxide equivalent (MTCO2e), which is equivalent to 10% of Yale’s current emissions inventory.
Engineering under pressure: The underground fan
Drilling 263 deep boreholes in a sprawling country field is much easier than doing it in the middle of a dense campus with tight property lines and an underground web of electric lines and drainage systems. In a standard geothermal system, boreholes are spaced 20 to 25 feet apart and drilled straight down. Upper Science Hill didn’t have enough land for that method, so engineers used inclined drilling.
Instead of going straight down, crews drilled at 5- to 20-degree angles. This allows surface boreholes to stay clustered tightly together while the underground pipes fan out wide, shrinking the project’s surface footprint by approximately 44% and packing maximum energy storage into a restricted space. Once in place, these loops are sealed with a thermally conductive grout to maximize heat transfer with the earth and protect the local groundwater.
3D coordinated model of the geothermal borefield and infrastructure beneath the upper Science Hill corridor
Insights from the process
Initial sitework provided some crucial insights for the future of green utility design:
- Test bores first: Crews drilled early boreholes to understand thermal data and constructability challenges to appropriately refine the design and construction approaches for the system.
- Managing “spoils”: Drilling can generate large amounts of water and rock debris. In a tight campus environment, treating this material is a major operation requiring heavy-duty settling tanks and centrifuges.
- The learning curve: Weather was a constant hurdle, forcing crews to build heated tents in freezing winter conditions to keep the water from turning to ice. But as the drillers got to know the local bedrock layers, they doubled their production speed from three to four days per hole down to two days.
The lessons learned are critical. District geothermal is among the most efficient approaches to heating in existence. Yale’s first district geothermal system is a step towards a more sustainable low-carbon future.
Next steps for geothermal on Science Hill
With the borefield complete, the project on upper Science Hill is transitioning to its next phase, construction of a Thermal Utilities Plant. The plant and the entire geothermal system are scheduled to come partially online in 2028.
By tackling the complexities of creating the largest borefield on Yale’s campus to date, the Upper Science Hill Development team and its partners have laid the groundwork for cleaner energy future ahead.