A New Method for Analyzing Geothermal Test Data in the Presence of Groundwater Flow

The traditional method for analyzing thermal test data in geothermal HVAC design has relied on the line source method (Carslaw and Jaeger) for interpreting a representative value for borehole thermal conductivity. In at least 20% of the applications, groundwater significantly influences the results, requiring a new method for analysis that includes both conduction and advection. The degree to which groundwater flow is a factor in analysis of ground thermal properties is demonstrated by the observation of non-linearity in a graph of well water temperature vs. LN(time) late in the 48-hour test period. Misinterpretation of thermal test data in these circumstances results in geothermal installations that lead to significant and expensive over-design of the wellfield.