Experimental evaluation of operation mode and groundwater flow effects on the thermal performance of energy piles

• Ano de defesa: 2025
• Autor(a) principal: Sá, Letícia Menezes Santos
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: areia saturada; centrifuge modelling; energy piles; ensaios de campo; ensaios de desempenho térmico; field tests; fluxo da água subterrânea; fundações por estacas trocadoras de calor; groundwater flow; modelagem em centrífuga; modos de operação; operation modes; saturated sand; thermal performance test
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/18/18132/tde-20052025-103505/

The demand for clean and renewable energy sources to reduce carbon emissions has grown significantly due to global environmental challenges faced recently. Shallow geothermal energy, harnessed through Ground Source Heat Pump (GSHP) systems integrated with building deep foundations (energy piles), offers a promising alternative for efficient building climate control. This study evaluates the applicability of this technology, typically used in temperate climates, to the hot-dominant climate conditions of Brazil. It focuses on the use of energy piles as both the foundation and ground heat exchanger (GHE) for the Living Lab building of the Innovation Center for Sustainable Construction (CICS), which is currently under construction at the University of São Paulo. The CICS building employs two types of energy piles: continuous flight auger (CFA) and steel pipe energy piles. This research aimed to expand knowledge on energy pile behavior in tropical climate and evaluate their thermal performance under continuous and intermittent operation modes. This work also explored the impact of groundwater flow on the response of energy piles and heat exchange interactions within groups containing energy piles. Field Thermal Performance Tests (TPTs) were conducted to assess the thermal performance of CFA and steel pipe energy piles of the CICS building under continuous and intermittent modes, with varying on-off frequency (8h on/16h off, 12h on/12h off, and 16h on/8h off). Centrifuge tests were conducted to investigate the role of groundwater flow in dissipating thermal anomaly downstream and thermomechanical interactions in groups of energy piles. Furthermore, simulations using PILESIM 2.1 software estimated the number of energy piles and length of pipes required to meet the thermal demands of a hypothetical business hotel at the CICS site. Intermittent operation demonstrated higher efficiency compared to the continuous use of the tested energy piles, with faster temperature recovery during the system\'s rest periods. Longer pauses during the pile heating tests led to a higher heat exchange rate per unit of pile active length. Continuous operation resulted in a greater increase in pile temperatures. Strain gauges measurements showed a cyclic or continuous thermal load variation of the axial stress increments in CFA energy pile during the tests, varying with the operation mode. Additionally, centrifuge tests showed that the absence of a groundwater flow leads to higher pile temperatures. The model tests also clarified the effects of a flow perpendicular and parallel to the energy pile group. The settlement values of the model energy piles at the end of loading tests were higher in the absence of water flow. Finally, simulations using PILESIM 2.1 demonstrated the long-term feasibility of GSHP systems integrated with energy piles in São Paulo to supply a balanced heating and cooling load demand. The results presented in this thesis can guide the development of regulations and recommendations; however, further studies are needed to optimize the implementation of energy piles in the Brazilian context.