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Physical modeling of a heat exchanger pile in sand subjected to groundwater flow

Grant number: 20/13086-4
Support type:Scholarships in Brazil - Scientific Initiation
Effective date (Start): December 01, 2020
Effective date (End): November 30, 2021
Field of knowledge:Engineering - Civil Engineering - Geotechnical Engineering
Principal Investigator:Cristina de Hollanda Cavalcanti Tsuha
Grantee:Ricardo Caires Formigari
Home Institution: Escola de Engenharia de São Carlos (EESC). Universidade de São Paulo (USP). São Carlos , SP, Brazil

Abstract

Pile foundations have been normally used to support structures. In addition to this basic function, they can also be used to explore the shallow geothermal energy available in the ground, in order to reduce the consumption of electrical energy for the air conditioning of buildings.Due to the Brazilian climatic condition, a large part of the electricity consumption is associated with artificial air conditioning systems. Therefore, in view of the reduction of natural reserves in our country, and of the increasing environmental restrictions, it is fundamental to develop and also study the feasibility of new possibilities for clean energy to supply this demand.Seeing that the average ground temperature, after a certain depth, is approximately constant, the shallow geothermal energy for building air conditioning has been used successfully in different countries. For this purpose, systems of geothermal heat pumps connected to pipes installed in the foundation can be used to allow the thermal exchange of the building with the subsoil by means of water circulation. According to the building's need, the heat exchanger pipes can remove heat from the building and reject in the ground, or extract heat from ground. However, due to the fact that the predominant demand for buildings in Brazil is for cooling, the continuous use of this system in this case, continuously rejecting heat in the ground medium (without extracting), may reduce its efficiency over the years of use. On the other hand, previous studies show that for cases where the foundation is predominantly used to reject heat in the ground (regions of hot climate) or to extract heat (regions of cold climate), the presence of groundwater flow around the piles contributes for heat dissipation, and for the subsoil to return to natural temperature after continuous use of the geothermal energy system. For a better understanding of this effect of the groundwater flow, the present project was developed with the objective of analyzing the temperature variation of heat exchanger piles and of the surrounding soil, using small scale physical models, tested in sand, in dry and saturated conditions, under different water flow velocity values.