Numerical study on heat transfer performance of geothermal piles in a Brazilian sandy soil

Abstract

The worldwide consumption of electric energy destined for air conditioners, expected to triple by 2050, can be lessened by geothermal piles, which transfer heat from the internal environment of buildings to the subsoil. This paper shows the influence of pile geometry and properties of soil, pile, and pipe materials on the heat transfer of a geothermal pile to the surrounding soil, to support design from the viewpoint of thermal performance optimization. A numerical model was developed with ANSYS CFX 19.2, a high-performance Computational Fluid Dynamics tool, and calibrated using data from a thermal response test performed in a saturated sandy soil in São Paulo, Brazil. A parametric analysis was carried out varying pile length, diameter, and slenderness; soil and pile material conductivities; degree of saturation; fluid inlet temperature; fluid flow rate; and pipe thermal resistance. Results show that the fluid inlet temperature is the most influential parameter on the thermal performance of the pile. Heat transfer grows when geometrical parameters (diameter and length) are increased mainly due to an increase in heat exchange surface area, whereas the normalized heat transfer rate per unit of surface area of the pile is practically unaltered. Higher soil, pipe and pile thermal conductivities improve thermal performance. The degree of saturation increases the thermal conductivity of the soil; however, the effect is not remarkable on the system’s thermal performance for saturation degrees higher than 20%. The fluid flow must be turbulent but increases above a certain flow rate do not improve the thermal performance.

Performance Assessment of Solar Desiccant Air Conditioning System under Multiple Controlled Climatic Zones of Pakistan

“…Systems for heating, ventilation and air conditioning consume a huge portion of the overall energy used in building services. For instance, a survey by the International Energy Agency found that, in 2016, refrigeration systems accounted for 6% of all energy supplied to buildings [2]. In the last few decades, the energy demand for cooling systems has considerably increased due to population growth, technological advancements and materialistic living standards.…”