Estimating the full range of thermal conductivity dryout curve

The efficiency of shallow ground heat exchangers is controlled by the thermal conductivity of the soil they are placed in, which is predominantly a function of soil type, mineralogy, density and water content. As such systems are placed at shallow depths where hydrological regime is highly fluctuant due to rainfall and evaporation, it is important to have soil-specific information on how thermal conductivity changes with water content. There are numerous models available in the literature, most of which are not able to define the full range of the thermal conductivity dryout curve (TCDC) with a single equation. This study suggests a modified sigmoid curve to define the TCDC, and introduces yet another statistical model to estimate the fitting parameters of the equation. Validation using data from the literature shows that the model is capable of producing the full range of TCDC for soils with 90% and less sand content.