The design of a geothermal heat pump system requires an estimate of soil thermal conductivity. An in-situ test on a borehole provides such an estimate, along with an estimate of the borehole resistance. Sometimes electrical power interruptions, running out of fuel, or other equipment problems temporarily disrupt the test and greatly complicate the analysis of test data. This paper develops a method to estimate the elapsed testing time (or recovery time) when the effects of the interruption dissipate sufficiently so that the estimated thermal conductivity is changed by 10% or less. After the power is restored, the method can be used in the field to estimate the required recovery time. Because the test time using standard procedures can be prohibitively long following the interruption, an analytical technique has been developed that shortens the minimum test time for a valid estimate of thermal conductivity. These methods are validated using data sets from a laboratory sandbox. Furthermore, the new method of analysis is able to estimate the soil thermal conductivity from a data set that was previously not interpretable by standard (line-source) methods.

Units: Dual