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Back in November of 2023, IDEA (International District Energy Association) hosted a Geothermal symposium with several higher education and industry professionals. Our President and CEO Brian Robertson was a panelist on that event representing Princeton University by providing a voice to his experience in planning and implementing their geoexchange program.
Following that meeting, a list of unanswered, anonymous questions were formulated and distributed to the panelists. As a geoexchange planner, consultant, and program manager, Brian chose to address some of the unanswered geothermal drilling application and operational questions here.
Question: When you install the geoexchange borehole arrays years ahead of your new construction or campus expansion plans, how are you preparing the bore field?
Answer: The bore field is a coordinated design effort which is integrated into a building design starting at concept level. This provides for efficient design opportunities to integrate the geo vault(s) into the building MECH spaces and allows you to maximize the number of bores, utilizing all available open space around and beneath new buildings structures. Integrating the geo design and building design also allows for the coordination of sub-grade lateral penetrations and required building structural allowances. In regard to Campus Expansion, you need to work closely with your campus architect and or master planning partners to understand long term development intentions while identifying opportunity sites. Opportunity sites, or green fields, are those sites marked for open space or non-building development.
Question: What is the provision should there be a system leak or failure where loops are located under buildings?
Answer: These bores would be abandoned and valved off at the vault. The system is rigorously pressure tested and inspected to ensure we do not have failures and can get 100 years out of the system.
Question: How much does having geo bores under buildings affect construction costs/timelines?
Answer: Site prep, permitting, and contractor general conditions are shared when a building and geothermal project are combined within the same site, lowering the total project cost versus two independent sites. Adding geothermal scope does add to the overall project schedule both related to permitting and construction and should be coordinated based on the sequence of installation.
Question: Regarding "wandering" of bore hole drilling. How did you know when an adjacent U-tube was hit?
Answer: Once a bore hole is drilled, the closed loop HDPE “U-bend” piping is installed with the surrounding grout and is pressurized. As adjacent bores are drilled, when a bore is unintentionally collided with, the impacted U-bend releases the pressure with a resulting “burst” noise.
Question: For the bores which had >5% deviation, if they didn't physically run into another bore, why not still use the bore and add another bore? This would avoid the need for concrete filling and still get some production.
Answer: If the bore had >5% deviation path and did not collide with a neighboring bore, the bore was still used. In those instances where a bore collided with another bore, you could drill out the HDPE U-Bend and grout, but you would need to know the collision depth (or about) or you would risk of damaging the good bore that originally intercepted the failed bore. We typically have our contractors with direction from the engineer identify another location on the site (if feasible) or have the contractor drill a replacement bore within the proximity of the abandoned bore.
Question: Of the options tested, what was most effective means of reducing drill rig noise? What was acoustic requirement for site (e.g., db level) and was drilling contractor actually able to meet this?
Answer: The most effective means of reducing drilling noise was engineering and installing sound blankets around the drill rig engine bay. Addressing the noise at the source has proven to be much more effective in reducing dBs versus installing sound blankets at the perimeter of the jobsite. Understanding your distances and rig direction in relationship with the impact area is important as well. In regard to “acoustic requirement”, we worked with animal research to collect industry whitepapers and input which established acceptable db thresholds for noise and vibration. We also used the local municipality ordinance thresholds as a guideline for internal campus levels specific to human comfort. These levels are typically between 69-72dBZ at the impact area for both groups. The drilling contractor to date has designed and implemented sound blanket structures that have achieved and maintained noise levels meeting the required thresholds. We hire local acousticians to provide ongoing measurement and verification at neighboring properties and facilities during geoexchange projects to ensure we never exceed the established thresholds.
Question: Interested to hear about how construction impacted student experiences on campus, particularly projects described.
Answer: All construction makes noise and students have become conditioned to complete their studies through the projects. In regard to geo-exchange drilling, we have implemented the sound mitigation measures to minimize noise disruption to the campus. Students have been some of the biggest supporters of the geo-exchange drilling. Focused marketing and efforts in partnership with Facilities Communications and University Sustainability Group have contributed to share the message of the positive environmental benefits of the technology. Students have really gotten behind this initiative. We consistently give tours of the geo sites to student groups, support with marketing campaigns and signage, as well as participate by speaking at Sustainability classes to garner student support. It is a collective mission that involves the entire campus with backing from senior leadership.
If you have any Geothermal/Exchange questions that were not addressed here, please reach out and we would be happy to assist.
-View our contributed article in the New York Times with Ted Borer, Director of Energy Plant at Princeton University
To Slash Carbon Emissions, Colleges Are Digging Really Deep - The New York Times (nytimes.com)
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