Thermal Design Considerations for Raised Structures on Permafrost

With advances in the ability to model complex geothermal conditions, the aspect of soil structure interaction as it relates to long-term changes in the geothermal regime can be considered. Traditional geothermal modeling relied on the so-called n-factor approach where the ground surface temperature was represented as the air temperature multiplied by some factor to account for ground surface effects. The application of surface energy balance formulations where the effects of the building including long wave radiation can be incorporated, allows for a more accurate representation of the geothermal regime under the structure. In considering the impact of climate warming on the performance of raised buildings in permafrost terrain, the use of a surface energy balance in the geothermal model is considered to be a more rigorous and technically preferable approach to addressing this problem. This paper addresses the use of a surface energy balance formulation in the geothermal analysis of raised buildings construction in permafrost terrain and its impact on the long-term geothermal regime. Specifically, the impact of building construction on the underlying geothermal regime have direct implication to the ongoing discussion regarding the need for climate change adaptation to address potential foundation capacity degradation in light of climate warming. Both existing field data and geothermal modeling results presented in this paper demonstrate that ground temperatures under a raised building cool over time and become colder than the ground remote from the building. When long-term climate warming is considered, the ground temperatures at depth do warm, but after 20years of climate warming the ground temperatures under the building are still not warmer than the initial ground temperatures remote from the building.