Energy performance of below-grade envelope of an institutional building in cold regions

The effects of freeze-thaw cycles on the thermal properties of foundation soils are often neglected in many building energy simulation programs. Consequently, there is a lack of research focused on the energy dissipation through the below-grade enclosure of buildings in cold regions, where freeze-thaw cycles occur in soils. This paper aims to investigate the energy performance of the below-grade envelope of an institutional building in cold regions by considering the effect of pore water phase change on the thermal properties and consequently the heat exchange between the basement structure and the surrounding soils. For this purpose, the energy loss through the below-grade envelope of the building was numerically studied using 3-D and 2-D analyses. Moreover, the importance of a promising insulation system for the basement of the building was investigated in this paper. The results showed that the energy loss through the below-grade enclosure of the building decreased by approximately 60% when the insulation layers were added to the basement walls and floor slab (i.e., a 230 mm thick insulation layer underneath the floor slab and a 125 mm thick insulation layer surrounding the basement walls). Although reduced, the below-grade heat losses were still significant. To mitigate that, an additional horizontal insulation layer was attached to the basement walls, which lowered the heat loss through the basement walls by 23%. In addition, it was concluded that the presence of a layer of backfill materials surrounding the basement walls that was initially designed for drainage purposes, decreased the basement heat loss by 16.5%. Finally, the results of the 3-D analysis were compared to an equivalent 2-D analysis. The results showed that the 2-D model predicted approximately 22% higher heat flux compared to the 3-D model.