Research focuses on algorithms for angled boreholes

Tuesday, April 29, 2025

Media Contact: Tanner Holubar | Communications Specialist | 405-744-2065 | tanner.holubar@okstate.edu

Installing ground heat exchangers with ground-source heat pump systems can be expensive and time-consuming due to the amount of drilling required. Vertical borehole ground heat exchangers are drilled hundreds of feet deep, where the temperature remains relatively consistent throughout the year. 

They then exchange heat with the earth to regulate a building’s temperature. They absorb excess heat during the hotter months and act as a heat source during the winter.   

Dr. Jeffrey Spitler, Regents Professor and OG&E Energy Technology Chair for the School of Mechanical and Aerospace Engineering in the College of Engineering, Architecture and Technology at Oklahoma State University, is researching ways to simplify the process of designing angled borehole fields. Timothy West, a Ph.D. student, and Kahleen Dabbs, an undergraduate, are the lead students involved in this research.  

Through the Center for Integrated Building Systems, industry partners are funding a two-year project looking to develop algorithms for the design of these angled boreholes. Angled boreholes, used sporadically in Europe, have not gained as much popularity in the U.S. due to current limitations.  

“Almost all borehole heat exchangers in the U.S. are vertical,” Spitler said. “Angled boreholes are used slightly more often in Sweden.”  

Using programs such as GHEDesigner, Earth Energy Designer, and GLHEPRO, engineers can design vertically drilled borehole fields. The limitation of these programs is they can’t automatically design angled borehole fields without approximations and tedious manual iteration.  

In this research using the design software GHEDesigner, new algorithms will be developed that can automatically generate designs for angled borehole fields that fit site constraints.   

Configurations that can be designed by these algorithms include drilling eight or more boreholes angled outward from a single pad; fan configurations where boreholes would be angled tilted at 0, 10 and 20 degrees in a repeating pattern, and borehole fields with some boreholes angled under existing buildings. In some cases, these borehole field configurations can save up to 30% on total drilling.  

For vertical drilling serving existing buildings, the usable space is limited to the area outside of the building’s footprint, as vertical holes are not drilled under structures. This increases the amount of ground being used, improving the performance of the boreholes. 

Reducing the amount of drilling not only reduces disruption to a site but can also significantly lessen the cost. This cost of ground heat exchangers is a key initial barrier to the installation of ground source heat pump systems.   

“These algorithms will automatically place angled borehole heat exchangers to make the best use of available property,” Spitler said. “This could include angling boreholes under buildings or installing multiple boreholes from a single drill pad to minimize disruption to a site.”