Beginning in 2008, CMU began deploying a geothermal loop system to reduce the need for conventional cooling and natural gas heating and reduce overall campus water use. The system was designed to utilize water-source heat pumps to serve interior spaces with a closed geothermal loop that utilizes the thermal stability of the ground as a heat sink. The networked loop consists of five loop fields with 471 bore holes drilled to depths ranging from 375 to 600 feet. These loop fields can be utilized as a thermal energy source to mitigate on-peak demand by filling the bore holes with loop water during off-peak periods and discharging the bore holes during on-peak periods. In 2023 Xcel Energy commissioned Michael’s Energy to analyze the performance of CMU’s geothermal system.
Initial Findings
When comparing historical central campus loop temperatures versus outside air temperatures, it is apparent that this load sharing occurs when outdoor air temperatures are between 25°F and 55°F. This wide load-sharing operating band greatly increases the overall efficiency of the system as the need for heat pump compressor operation is greatly reduced.
Actual Savings
When compared to a conventional cooling and heating system consisting of water-cooled chillers and natural gas hot water boilers, this system has a demand reduction of ~650 kW (13%), an energy savings of ~1.3 GWh (10%), a natural gas savings of ~58,000 Dth (55%), and a water savings of ~10 million gallons, annually. Water savings were provided by the Grey Edge Group and were not part of this analysis. Seasonal coefficient of performance (COP) values are displayed in Table 1, below. Note that a typical boiler operates with a COP of 0.8, a typical chilled water system at 3.4, and electric resistance heating at 1.0. A larger number indicates increased system efficiency and lower energy consumption per unit heating or cooling.
