EVALUATING TEMPORAL AND THERMAL VARIATIONS IN HYDROGEOLOGIC DATA AT BALL STATE UNIVERSITY'S GROUND-SOURCE GEOTHERMAL SYSTEM (MUNCIE, IN)

Ball State University (BSU) began installing the nation’s largest ground-source geothermal project in 2009. In Phase 1, ~1800 geothermal boreholes were drilled in the northern part of campus, separated into two large fields (North and South). Ground-coupled exchange loops were installed to add or remove heat from the ground to moderate the temperature in campus buildings. In late November 2011 BSU commenced Phase 1’s geothermal system, which currently services over 20 buildings and when complete, will heat and cool 47 academic buildings. Previous studies have triggered concern over large-scale geothermal systems’ impact on natural hydrogeologic properties. In the Netherlands, for example, data collected from a 1,400 housing development in Etten-Leur suggests significant cooling of the groundwater due to high heating demands. In contrast, at Stockton College’s geothermal field in New Jersey, a 7°C groundwater temperature increase was observed over the course of 10 years.

Maintaining a temperature differential between the fluid inside the exchange loops and the geologic substrate and/or groundwater outside of the loops is crucial to the efficiency of the system, which are typically designed so that temperatures will not increase or decrease more than ~1.2°C. To verify BSU’s system properly, baseline hydrogeologic data and temperature profiles were obtained throughout 2011 that will be used to further groundwater investigations. Preliminary data indicate that the bottom 30 meters of the down-gradient wells in both the North and South fields have temperatures that are 0.2°C lower than the other monitoring wells. After cold-water circulation was initiated in November 2011, the temperature of the bottom 100 m has increased greater than 1°C in the center of the South Field.