NGWA Event and Education Recordings Archive

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.