A novel approach to the evaluation of contact thermal resistance at soil-structure interfaces

Considering the need to reduce our dependence on unsustainable energy sources and reducing the carbon footprint associated with building climate control, shallow geothermal energy represents an attractive sustainable technology for providing renewable heating and cooling. The temperature field generated around ground-coupled heat exchangers, and thus their energy efficiency, fundamentally depends on the heat transfer mechanism and the thermal properties of the materials involved. While the thermal properties of materials that make up the system can be defined with some certainty, little is known about the impact of contact thermal resistance at the soil-structure interface. Contact thermal resistance will reduce heat exchange efficiency and increase mechanical impacts associated with temperature changes within energy geo-structures. This paper describes a laboratory test method to quantify the contact thermal resistance of soil-concrete interfaces. The methodology is first evaluated using numerical analysis, and then validated against a test using a limestone aggregate concrete and fine, silica sand at differing levels of compaction.