Thermal conductivity map of the Oslo region based on thermal diffusivity measurements of rock core samples

Abstract

A thermal conductivity map can serve as a good basis for ground-source heat pump projects in the pre-design phase. However, due to large variations, a thermal response test is required for larger projects to get the accurate values needed for proper design of the ground-source heat pump system. This study describes the systematic methodology for producing such a thermal conductivity map of a larger geographic area around Oslo, Norway. The map is based on the results of 1,398 thermal diffusivity measurements of rock core samples. The thermal diffusivity is measured and used in the calculation of the thermal conductivity of the different geological units in the bedrock map of the Oslo region. Large variations in thermal conductivity data were registered within the data sets for the different rock polygons and geological units and the greatest variation is found in metamorphic and sedimentary rocks. Rock polygons and geological units with magmatic origin show the least variation within the data sets. The internal micro structures of the rocks can have a strong influence on the thermal conductivity. This is pronounced in some foliated metamorphic rocks where the thermal conductivity is highest parallel to the orientation of the foliation. The median value for the whole data set is 2.62 W/(m K), while the minimum and maximum value is 1.0 and 6.88 W/(m K), respectively. The minimum value is a breccia, and the maximum value was measured in a quartzite/metasandstone. The lower and upper quartiles for the sets of rock polygons and geological units are 2.1–3.9 W/(m K), respectively.