Freezing soil effects on earth-contact heat transfer

Abstract

The inclusion of soil freezing and snow cover within the context of a building energy simulation is explored. In particular, a method of including soil freezing within the simulation of heat flow from a building to the neighbouring foundation soils is considered. Non-linear thermal conductivity and heat capacity relations are explored that account for the effect of soil freezing. In addition, the work also considers latent heat generated by phase change that occurs as the soil water temperature reduces and ice forms. A simple approach to represent the insulating effect that snow cover may have on the net heat flow at the ground surface is also provided. The approach is illustrated by application to the simulation of a full-scale ground heat transfer experiment performed by others. The results provide a first indication of the potential significance of the inclusion of ground freezing within the context of modelling heat transfer from a full-scale monitored building. Overall transient temperature variations are shown to be dependent on ice content and latent heat effects. Non-linear, ice-content dependent, thermal conductivity and heat capacity are included in the work. Good correlation between measured and simulated temperature variations has been achieved. Practical application: The principle application relates to the assessment of heat transfer from buildings through to the underlying foundation soils. In addition, the work is of direct relevance to a wider range of applications, for example, ground source heat pumps, thermo-active piles and foundations. The model lends itself to application with respect to utilisation of ground energy within the context of pavement design, particularly, in relation to the alleviation of winter ice problems. It also applies within the context of assessment of urban heat island phenomenon and heat and moisture transfer beneath freezer foundations.