Análise do comportamento térmico de estacas geotérmicas em solo arenoso.

Abstract

The search for sustainable renewable energy matrices has motivated the use of geothermal piles to take advantage of deep building foundation structures to, in tropical climate countries, dissipate heat from building to soil layers. Heating with geothermal piles is a technique widely used by European countries, where severe winters make spending on heating system mandatory. The geothermal pile system is coupled to the Ground Source Heat Pump (GSHP) assembly and is based on the circulation of a fluid through a closed circuit of pipes connected to the pile and to the heat pump. The present work aims to study the thermal behaviour of geothermal piles in a saturated sandy soil using numerical simulations to identify the variables of greatest interest to the project. The numerical model was developed with the ANSYS CFX version 19.2 program, a high performance CFD (Computational Fluid Dynamics) tool. Data from a Thermal Response Test (TRT) test carried out at the Polytechnic School of the University of São Paulo were used to calibrate the numerical model. In the steady state simulations, the variables studied were: diameter and length of piles; thermal conductivity of soil, concrete and pipe; degree of soil saturation; system inlet temperature; and circulating fluid velocity. Fluid inlet temperature, pile diameter and pile length are the variables that cause the greatest increases in the total heat transfer rates. However, the variables pile length and pile diameter do not really affect the thermal efficiency of the system, as normalized heat transfer rates showed unimportant variation. Regarding the heat transfer rates per unit of parameter, the most relevant variables are contact resistance, degree of saturation and thermal conductivity of the concrete.