Development of an in-situ system and analysis procedure for measuring ground thermal properties

Abstract

Determination of the ground’s thermal conductivity is a significant challenge facing designers of Ground Source Heat Pump (GSHP) systems applied in commercial buildings. The number of boreholes and the depth and cost of each borehole are highly dependent on the ground thermal properties. Hence, depending on the geographic location and the local drilling costs, the ground thermal properties strongly influence the initial cost to install a GSHP system. In order to be able to predict ground thermal properties, an experimental apparatus has been built capable of imposing a heat flux on a test borehole, and measuring its temperature response. Parameter estimation techniques in conjunction with a two-dimensional numerical model are used to determine the thermal conductivity of the surrounding ground. Independent measurements of the soil conductivity test results are reported for several test boreholes and a laboratory experiment. An uncertainty analysis of the thermal conductivity prediction is presented.