Heat Flow through Soils and Effects on Thermal Storage Cycle in High-Mass Structures

The solar radiation absorbed in massive building components is stored and later emitted as long-wave thermal radiation into the interior space. Heat storage capacity is directly related to the mass of the building envelope surrounding this space and particularly that of high-mass, homogeneous earthen or cementitious material. A thermal storage cycle is created by the time-lag effect if sufficient mass is available. A similar strategy applied to the lunar and/or Martian regolith would provide a surface structure with micrometeorite and radiation protection, thermal insulation, and natural supplemental heat energy that would significantly reduce the energy requirements met by mechanical equipment. HEAT2 is an energy simulation program that solves heat transfer problems using the partial differential heat conduction equation in two dimensions with the method of explicit finite differences. HEAT2 simulation data suggests that, although thermal mass is most suitable for climates where desired indoor temperatures fall within a large daily external temperature gradient, the heat storage cycle is least effective at the annual extremes occurring in midwinter and in midsummer. A more moderate climate will allow the heat storage cycle to modulate between positive and negative heat flows which are then shifted to align with peak load conditions, reducing energy demand. Also, diurnal and seasonal temperature gradients can initiate a sequence of phase transitions in the soil’s moisture content affecting the overall conductivity. This study will present a more accurate explanation of the heat transfer processes occurring in soils of varying compositions when thermal properties are altered by transient climatic conditions.