Experimental determination of thermal conductivity of soil with a thermal response test

Abstract

Optimal design of a borehole heat exchanger, as the outer part of a ground source heat pump heating system, requires information on the thermal properties of the soil. Those data, the effective thermal conductivity of the soil leff and the average temperature of the soil T0, enable us to determine the necessary number and depth of boreholes. The determination of thermal conductivity of the soil in laboratory experiments does not usually coincide with the data under in situ conditions. Therefore, an in-situ method of experimental determination of these parameters, the so-called thermal response test, is presented in this paper. In addition to the description of the experimental procedure and installation overview, the paper describes methods based on theory and presents their basic limitations, through the presentation of experimental data.