Equivalent time for interrupted tests on borehole heat exchangers

Thermal tests are often performed on vertical boreholes for ground-source heat pump systems, which heat and cool buildings. These in-situ tests estimate soil thermal conductivity, which is an important parameter in the design of these systems. If an electrical power loss or other equipment failure interrupts the test, the interruption greatly complicates the analysis of the test data. This paper presents an equivalent-time method to remove the effects of the interruption and estimate soil thermal conductivity, along with borehole resistance. By using this method and restarting the test immediately after the power is restored, one can save time and money compared with waiting for the initial heat pulse to dissipate before restarting. The method is verified with test data sets from a large laboratory sandbox.