The influence of soil moisture content variations on heat losses from earth-contact structures: an initial assessment

An initial investigation of the influence of varying ground moisture content beneath buildings on the heat losses through ground floor slabs is presented. A range of finite element analyses have been performed that indicate that soil moisture content changes can have a significant effect on soil thermal conductivity and hence on ground heat transfer. The work is undertaken for conditions of static moisture content distributions. For the particular problems considered, the results obtained show that total heat flux to the ground can increase significantly with decreasing ground water table depth. Steady-state heat conduction analyses were performed for three test problems; a one-dimensional problem, a two-dimensional shallow earth-contact structure and a two-dimensional “deep” earth-sheltered structure. Each problem was analysed for water table depths ranging from 10 m to zero (i.e. the ground surface). The resulting increase in soil moisture content was found to cause a 60% increase in heat flux in the one-dimensional problem, a 20% increase for the two-dimensional shallow structure and 40% for the deep structure. The variation between types of analysis is due to the heat flow path geometry available in each case. The work is viewed as a further step towards a more complete understanding of the influence of ground moisture content on heat transfer problems. The conclusions drawn should be viewed as a first indication of the significance of this aspect of the problem and need to be considered separately from other work on the influence of ground water flow beneath the water table. The results also suggest that transient effects and coupling of heat and moisture transfer processes merit further attention.