Effect of the Unsaturated Soil Condition on the Thermal Efficiency of Energy Piles
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ASCE 2015. Energy piles satisfy two main functions: they transfer the load from the building to the ground and they also exchange heat with the ground; which is used for heating and cooling purposes. Because energy piles are relatively short, they may be partially embedded in unsaturated soils. Saturation conditions influence the thermal properties of the soil and therefore the heat exchange rate and thermodynamic efficiency of energy piles. This paper evaluates the effect of unsaturated soil conditions on the heat exchange rate and thermal efficiency of energy piles through laboratory experiments and numerical simulations. The laboratory tests considered an energy pile slice at a certain depth. The temperature field evolution generated from the operation of the energy pile in different soil saturation conditions was measured at the soil-pile interface and in the soil. The laboratory test was then modeled numerically and the results of the numerical model were used to evaluate the heat exchange rate and thermal efficiency of energy piles in unsaturated soil conditions. The results of this paper showed that saturation conditions could significantly impact the heat exchange rate of energy piles. In addition, the results showed that assuming that conduction is the primary mode of heat transfer, the thermodynamic efficiency of energy piles could drop by 40% in sand at very low saturation.
