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The Daily Princetonian

Summary

Remember your childhood piggy bank? You know, the one that sat on the edge of your bookshelf, swallowing your 25-cent-weekly allowance in its belly until it finally held enough to purchase your dream lego model? Scale that system up by 13 miles and you get Princeton’s geo-exchange. Instead of quarters, geo-exchange stores heat in a sprawling, mostly underground network of district hot water piping, to be released when needed.

Built in 1996, the Princeton Energy Plant provided a more efficient alternative to coal, squeezing as much power as possible from a gas turbine engine by capturing the hot exhaust and using it to pre-heat water before it enters the boilers. 

Though relatively efficient and cleaner than coal, this combustion-based process still releases carbon dioxide into the atmosphere. Burning natural gas creates hot steam, which is then sent through pipes at 450 degrees Fahrenheit. In order to meet its goal of net-zero carbon emissions by 2046, the University needed to find a way to continue meeting campus energy demand while eliminating combustion. 

This brought about heat pumps and geo-exchange. Together, these two technologies store the summer heat, which the cogeneration had not been utilizing, and return it during the winter. Energy Plant Director Dave Weis explained that this process is already underway this winter season. “We’ve got a good amount of heat from over the summer, and we’re continuing to withdraw it right now from the field,” he said in an interview with The Daily Princetonian. “So if you’re warm and cozy as you read this, and you happen to be in one of the newer buildings already converted to the hot water system, you have a whole lot of rock and underground pipes to thank.”

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