Executive Summary District energy systems supplied by geothermal heat pumps (GHPs) have been deployed across the United States for both heating and cooling end uses. To better understand their performance and potential, the geothermal research team at the National Renewable Energy Laboratory analyzed cost and performance of five existing GHP-based district energy systems in the United States. The five systems selected are Ball State University in Indiana, Colorado Mesa University in Colorado, Miami University in Ohio, West Union in Iowa, and Whisper Valley in Texas. The necessary data, including district size, operation period, GHP performance, and costs, were collected through literature review and interviews. The survey results indicated the five systems studied consist of geothermal borehole field(s) and ground loop(s) connected to a central loop. The GHPs were in central plants at Ball State University and Miami University, whereas the central loops at Colorado Mesa University, West Union, and Whisper Valley were connected through service lines to individual heat pumps in each building. Overall, we find no significant difference in reported system performance and cost between centralized and decentralized systems. Our analysis also indicates the systems have been operating reliably and costeffectively, with minimal operation of backup systems, and have contributed to a reduction in carbon emissions.
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