“We’re literally changing the wheels on the bus while we’re going down the road at full speed,” said Energy Plant Manager Ted Borer. Borer’s metaphor succinctly captures the complex process of transitioning Princeton’s cogeneration plant to a geo-exchange system while simultaneously running the cogeneration plant.
Cogeneration, also known as Combined Heat and Power (CHP), burns natural gas to produce both electricity and thermal energy. By taking the heat exhaust from a combustion turbine to produce steam, cogeneration can efficiently heat and cool Princeton’s campus, meeting most of the University’s heat and energy demands.
Soon, however, the cogeneration plant will take a backseat as the University expands solar power generation and creates a geo-exchange heating and cooling network in an ambitious step toward accomplishing Princeton’s 2046 net carbon neutrality goal.
Princeton built its first geo-exchange system under the golf-driving range in 2004 to serve the Lawrence graduate student apartments. Subsequent installations were built to serve the Lakeside graduate apartments and the Lewis Center for the Arts.
Most recently, the University drilled 52 boreholes on the front lawn outside of Whitman College. Each hole is 850 feet deep and 5-6 inches in diameter, filled with a narrow high density polyethylene tube and grout. There are over 800 boreholes on campus today — and the University anticipates the installation of more than 2000 in total.
Princeton’s current energy system comprises a West Energy Plant, a High Performance Computing Research Center on the Forrestal campus, and ten solar arrays across campus.
Over the next year, the University will construct two new energy facilities. The Thermally Integrated Geo-Exchange Resource or TIGER will be built East of Jadwin Gym and Denunzio Pool. The TIGER facility will work with the West Energy Plant to supply heating and cooling to the University’s central campus. Rather than using combustion and cooling towers, it will exclusively use daily thermal storage and geo-exchange fields for seasonal energy storage.
A smaller structure called CUB (Central Utility Building) will be built across Lake Carnegie to serve the new Meadows Neighborhood. In addition to geo-exchange, the CUB facility will have a small hot water heater to supplement the geo-exchange and heat pumps on the coldest days of the year as needed. For the hottest days of the year, it will also be equipped with a small cooling tower to provide extra support for the geo-exchange and heat pumps.
Because the piping design required for hot water is different from the current steam distribution design, more than 13 miles of district hot water piping will be installed underground throughout campus. The largest proportion of campus energy demands will be transitioned from steam to hot water heating over the next five years. Over the course of the subsequent decade, hot water pipes will connect every campus building to geo-exchange.
As the University begins to rely more on solar power generation and heat pump facilities, the cogeneration facility will operate less frequently. But, it will continue to play a crucial role during severe weather events, saving the University the costs of purchasing energy from the regional power grid.
On a tour of the current cogeneration system, Energy Plant Manager Ted Borer explained to The Daily Princetonian that the transition to hot water, heat pumps, and geo-exchange will be a significant up-front cost to the University — but makes sense considering the whole life-cycle cost. “The geo-exchange and district hot water pipes should last 50 to 100 years. A chiller or heat pump might last 20 to 40 years,” said Borer.
Borer also explained how the geo-exchange will improve Princeton’s efficiency. By transitioning buildings from steam to hot water, the University will be able to move heating and cooling across campus using about 20% the amount of total input energy the cogeneration plant uses today, according to Borer.
Tom Nyquist, Mechanical Engineer and Executive Director of Facilities Engineering and Campus Energy, emphasized that geo-exchange will create seasonal energy storage. “We [will] take heat out of the buildings in the summer and transfer it into the ground. In the winter, we [will] take that heat out of the ground, concentrate it, and send it back up to the buildings,” he explained.
Geo-exchange will also reduce Princeton’s water usage. While cogeneration and the current chilled water operation require an input of water from an outside source, geo-exchange recirculates the same water between the geoexchange fields and the heat pump plant.
Assistant Director of Sustainability Dr. Ijeoma Nwagwu, who manages academic engagement and Campus as Lab initiatives, affirmed the sustainability goals of the geo-exchange and discussed its potential for student involvement.
Nwagwu also emphasized the importance of engaging the community, saying, “What we see are buildings being built and geo-exchange being installed, but the way we see it from a sustainability standpoint is… we are actively thinking of ways to engage the community.” Nwagwu encouraged students to read the signage on construction and engage with the transition.
As Nwagwu envisions, Princeton community members are already engaging in the campus's changing energy grid, conducting research and closely following the progress of the geo-exchange construction.
Forrest Meggers, an Associate Professor of Architecture at the Andlinger Center for Energy and the Environment and Co-Chair of the Princeton Sustainability Committee, has been researching these methods in his lab and exploring different college campuses’ approaches to energy transition.
“We have one competitor in terms of heating and cooling: Stanford,” said Meggers. However, he believes that Princeton’s geo-exchange installations will take the University’s efforts beyond Stanford’s by neutralizing various energy loads from summer to winter. He said, “Our campus is going to be way cooler than Stanford, but Stanford tried to be pretty cool.”
Although Meggers' praised Princeton, he also discussed some challenges the installation of geo-exchange will face on Princeton’s campus. He commented, “The geology in Princeton is the worst for this. Yale should be doing it, and Columbia, because they’re sitting on the perfect material. We’re sitting on sandstone, which is problematic for drilling.”
Another challenge is that the benefit of geo-exchange is only proportional to specific weather — how cold it gets in the winter versus how hot it gets in the summer. Meggers was on the committee which evaluated whether Princeton should keep the cogeneration plant or switch to geo-exchange. She noted that temperature variation complicated the economic models which were used as a justification for geo-exchange. “It all came down to the fact that we wanted to electrify,” he explained.
Some alumni and students have also been invested in tracking the University’s energy transition.
Mechanical and Aerospace Engineering concentrator Harry Shapiro ’22 wrote his senior thesis on “Carbon-Adjusted Dispatch Optimization for Princeton’s Campus Energy Plants,” overseen by Borer and Nwagwu. Shapiro now works as a private equity analyst in NY.
Shapiro considered the student perspective on energy, saying, “In terms of the general student body, none of this is something you ever really notice. And that’s kind of the goal, right?”
He continued, “You want to have an incredibly reliable energy system such that when you turn on the hot water, the hot water comes out, and when you plug in your laptop, it charges.”
Shapiro also touched on Princeton’s approach to addressing its carbon footprint. “I think one of the most powerful things about what Princeton is doing is that our system is going to reach net zero primarily through engineering. It’s a very challenging engineering problem, and Princeton isn’t afraid of doing it the hard way,” Shapiro said.
Civil and Environmental Engineering concentrator Alex Moosbrugger ’24 also appreciates the science behind geo-exchange. “The geo-exchange is overlooked, but really cool,” said Moosbrugger. “I think Princeton’s variety of approaches… shows a deeper understanding of the solution.”
In response to student complaints regarding construction, Moosbrugger said, “The construction impacts are destructive, but I think geo-exchange as the main heating and cooling system makes a lot of sense.”
Another issue which community members are considering is the timeline of Princeton’s decarbonization and geo-exchange’s place in that timeline. Princeton’s net neutrality mission of reaching net neutrality by 2046 is relatively late in comparison with other Universities such as Harvard, Yale, and Brown.
When asked why Princeton’s net carbon neutrality goal is later than other Ivy League institutions, Meggers responded, “They chose their years because other universities chose theirs… but nobody has a solid, believable plan.”
Meggers believes that Princeton can and will reach its energy goals sooner than other universities, despite the fact that the claims say otherwise. “We have a much better plan than them… if we want to [beat the 2046 goal], it’s easy.”
Nwagwu confirmed discussions amongst University officials about potentially striving for an earlier date, with carbon neutrality intended by “2046 or sooner.”
According to Meggers, this is a healthy competition which will compel all Universities to reach their goals sooner. He also pointed out that in many cases, other Universities’ plans involve purchasing significant carbon offsets from outside sources, whereas Princeton’s plan prohibits the purchase of carbon offsets and instead focuses on reducing on-campus emissions.
In the same vein, Moosbrugger noted, “There are a few things that are really difficult to decarbonize. I think it is really important to acknowledge and figure out how to work around that.”
Despite this recognition, Moosbrugger finds “Princeton’s goal specifically to be somewhat underwhelming.” He added, “It could very well be done sooner on a timeline that I would be more thrilled with being a part of as a student at Princeton than the 2046 date.”
Regardless of the timeline, the University is currently in a moment of substantial energy transition in which there are opportunities for student involvement. As Nwagwu said, “It’s amazing the learning that happens when students are engaging with the transition.”
This is part two of a two-part series on Princeton’s cogeneration plant. The first part was released on February 20, 2023.
Raphaela Gold is a staff Features writer for the ‘Prince.’
Please direct any correction requests to corrections[at]dailyprincetonian.com.