INVESTIGATING HEAT FLOW THROUGH A FLOODED COAL MINE COMPLEX FOR HEAT PUMP APPLICATIONS

Waters within flooded abandoned mines have been successfully exploited, as heat exchangers, for heating and cooling applications using ground source heat pumps (GSHP)s with increased energy efficiency compared to conventional heat pump appliances. Previous studies have generally addressed the potential for GSHP geothermal application using waters within coal mines as heat exchangers in Ohio, but have not addressed heat and water flow through the mine complexes. The Corning Mine Complex (CMC), located in Perry County Ohio, was chosen for thermal and hydrological evaluation to better understand heat flow within the mine complex with respect to atmospheric and hydrologic changes. Temperature and hydraulic head sensors were installed into monitoring wells drilled into the CMC for a year to evaluate temperature response to changes in hydraulic head, precipitation, and atmospheric temperature. Time series analysis was performed on the data to detect the temporal relationship between the thermal and hydrological parameters.

The results of this study show that the waters within this mine is locally thermally stable (± .2 K), but vary within the mine complex. Waters within monitoring wells that were either damaged or otherwise compromised showed a thermal response to precipitation, but returned to stable temperatures after the thermal perturbations. A linear relationship between water temperatures and overburden thickness was observed within the CMC. The temperature data yielded a regulation time (duration of the influence of the input signal on the output signal) of 6.1 months suggesting that the heat exchange between the thermal reservoir of the atmosphere and the thermal reservoir of the mine complex is defined by seasonal fluctuations in ambient air temperature. From the calculated volume of water within the mine complex, it is estimated, here, that the heat available to exchange for the CMC using a GSHP is 3.24 x 10¹⁰ kJ/K change in mine water temperature. Overall, these results suggest that the mine is thermally stable and that water flow is slow enough to allow thermal equilibrium between the rocks and the water. At the same time, the temperature field within the rocks seem to be dominated by conductive heat, as it is suggested by the correlation between overburden thickness and temperature.