Carleton College: Steam to Hot Water District Energy Transition

Carleton College built three geothermal bore fields totalling 305 wells to provide heat to campus. Additionally, three historic steam boilers in the existing heating plant were replaced by five gas fired boilers that provide redundancy and support peak heating needs. These transitions have lowered Carleton’s natural gas consumption by 60-70%, aligning with Carelton's decarbonization plans.

Implementation

In 2017, Carleton began transitioning its district energy system to a low temperature hot water system tied to a geothermal heat pump and backed by three bore fields. The college built three geothermal bore fields: two vertical bores beneath the primary campus quads and one horizontal bore below the campus soccer fields. These fields total 305 wells providing power and heat to campus. Additionally, three historic steam boilers in the existing heating plant were replaced by five gas fired boilers that provide redundancy and support peak heating needs. While the upfront capital cost of this system was high, the estimated payback period is 19-20 years for Carleton’s new geothermal system – most importantly, the system will continue to save the college money well into the future, while the cost of the older system was projected to increase.

This is not Carleton’s first step into the clean energy future. With the support of alumni, the college built two wind turbines to support its 2,000 students, the first in 2004 and the second in 2011. These turbines meet more than a quarter of campus electric demand. With the transition to geothermal, the college has substantially lowered its carbon footprint.

These transitions have lowered Carleton’s natural gas consumption by 60-70% on an annual basis – the college’s choice to implement electric heat pumps enables them to take advantage of an increasingly greener electric grid and integrate more onsite renewable energy generation technologies. Carleton’s system aligns with the industry average payback period of 19-20 years for these types of substantial infrastructural projects, setting the school up for a more sustainable future.

Outcomes

With the help of this project, Carleton has:

• Decreased its carbon footprint by almost 70% in 15 years
• Decreased its natural gas consumption by 60-70% annually
• Covered 70% of annual heating and cooling needs with renewable geothermal energy
• Positioned itself to take advantage of future renewables generation by choosing electric heat pumps

The transition from steam to hot water resulted in significant operating cost savings, reduced utility expenses, and a simpler, safer system that is much easier to staff.