Well-drilling rigs will soon appear on the Green and in the Dewey Field parking lot to conduct tests that will determine the suitability of using geoexchange heating and cooling systems in the two locations.
Geoexchange systems, which are powered by electric heat pumps, use a series of closed pipe loops set deep underground to use the stable ground temperature—about 50 degrees—to heat in the winter and cool in the summer. The testing is part of the $200 million Dartmouth Green Energy Project, which aims to improve energy resiliency, sustainability, and efficiency on campus.
“If we find that large-scale geoexchange systems are a viable option for our campus, this could become part of a portfolio of solutions to meet our energy needs,” says Josh Keniston, vice president for institutional projects, who is managing the energy project.
Geoexchange systems can be built under buildings and on open land. Once installed, they are below ground and the land on top of them can be used for other things. If a site on the Green or in the Dewey lot proved to be viable, the property would return to its current use once the system was in place.
There is already a geoexchange system on campus that cools and heats the Fahey and McLane residence halls using 13 deep wells. Installed in 2007, the system provides 100 percent of the air conditioning and 25 percent of the heating needed for the two buildings. The remainder of the heating comes from the College’s existing oil-fired heating plant.
The energy project includes the investigation of options that would allow the College to reduce reliance on fossil fuels, such as the No. 6 fuel oil currently used to make steam to heat campus buildings, to meet sustainability and efficiency goals set two years ago by President Philip J. Hanlon ’77.
The project would replace the aging central steam-heating system—parts of which are more than 100 years old—with new energy generation and distribution systems. The distribution system would use hot water rather than steam to heat campus buildings. A hot-water system is estimated to be 20 percent more efficient than the current steam system. The change would include replacing steam pipes in more than 110 campus buildings.
Current projections are that a geoexchange system of about 26 wells installed on or near the Green could provide up to 75 percent of the heating and 95 percent of the cooling for the Dartmouth Library’s Rauner Special Collections Library. The test site will be located on the northeast corner of the Green. A larger geoexchange system at Dewey Field, which would have about 300 wells, is projected to be able to provide 50 to 80 percent of the cooling and 15 to 30 percent of the heating for the entire campus. The Dewey test site will be in the northeast area of the property.
The energy project initially proposed construction of a biomass plant that would burn low-grade residue from the region’s logging and sustainable forestry operations to heat the entire campus. While biomass is still an option under consideration, Dartmouth is also investigating other types of energy systems, including geoexchange.
A geoexchange system at Dartmouth could meet a portion of the heating needed on campus, but likely not the peak load required on the coldest days of the year, Keniston says. The College would need one or more supplementary systems to deliver peak-load heating.
Test borings—one on the Green and one at Dewey Field—will be 500 feet deep and 6 inches in diameter, similar to a domestic water well. Drilling is expected to begin on the Green on Monday and last three to four days. After the holes are drilled and liquid-filled piping is inserted, the pipes need to sit for five days to stabilize the equipment. Tests will then be conducted over the next 48 hours to determine how the geology of the two sites could work for a geoexchange system paired with ground source heat pumps. The drilling and testing at Dewey Field are expected to begin during the week of Dec. 9, after fall term ends, so that a temporary loss of approximately two-dozen parking spaces will have less of an impact.
From 1 to 4 p.m. on Tuesday, during the testing, a tent will be set up on the Green and staffed by Keniston and Rosi Kerr, director of sustainability, who will offer information about the testing and the project. The public is invited to stop by to learn more about the process. The testing will determine whether the ground temperature and geology can support geoexchange systems at the two sites. The sites were chosen because of potential variation in geology at the two locations.
After the testing, the bore holes will be covered, and the piping left in place. The equipment could be used in future geoexchange systems. The holes won’t be visible or accessible and the properties will return to their current use and will look the same as they did before the testing. “That’s one of the benefits of this type of system,” says Keniston.
Geoexchange systems, which harvest heat from the ground to provide a base temperature of 50 degrees, are typically paired with heat pumps to add additional heat or cooling to provide temperature control for buildings. Heat pumps use electricity to provide the needed additional heating or cooling and can be entirely non-combustion if the electricity used in them is derived from renewable sources such as solar, wind, and hydroelectric technologies.
Dartmouth currently buys 80 percent of its electricity from the regional electric grid, which derives some of its power from non-combustion sources. The remaining 20 percent of electricity Dartmouth uses is generated on campus. About 2 percent comes from rooftop solar arrays and the rest is generated by the existing heating plan. Additional solar photovoltaic systems are planned for the rooftops of several more campus buildings.
Geoexchange systems differ from deep-well geothermal energy systems such as those found in Iceland, which are open systems that extract heat from deeper underground than geoexchange systems and use steam from the heat to power turbines and other systems.
Susan J. Boutwell can be reached at susan.j.boutwell@dartmouth.edu.
