Integration of Geochemical Processes and Fracture Flow for Design of Standing Column Wells

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In Canada, 30% of energy and 53% of electricity is used to heat or cool buildings. The use of geothermal heat pumps coupled with ground heat exchangers has experienced a growth of almost 150% in Canada between 2004 and 2008. Despite the significant energy savings it generates (up to 60%), the adoption of this green technology by building designers is no easy matter due to the high initial investment cost of ground heat exchangers. Standing column wells (SCW) are deep heat exchangers (up to 500 m) that use directly ground water. Although the construction costs of SCW systems can be 49% to 78% lower than closed-loop systems, SCWs are not used in Canada mainly due to an absence of validated design tools for fractured aquifers, a misunderstanding of the risks associated to the geochemical conditions of the groundwater (clogging, scaling, dissolution, algae growth) and a difficulty to assess the maintenance costs of these systems. Numerical simulation of fracture flow and of geochemical processes is widely used in hydrogeology. The novelty of this research program resides in its application to geoexchange and energy savings in a Canadian environment. Within the scope of the proposed research program, we intend to develop and validate experimentally numerical models to significantly increase our knowledge of the optimal construction and operation of SCW systems and, in turn, orient future design guidelines. To address this long-term objective, six projects are planned: A - INTEGRATE THE GEOCHEMICAL REACTIONS IN A THERMO-HYDROGEOLOGICAL SCW MODEL - Develop a three-dimensional numerical model that simulates the coupled thermal, hydraulic, hydrogeological and geochemical processes occurring in a standing column well. B - VALIDATE EXPERIMENTALLY A THERMO-HYDROGEOLOGICAL NUMERICAL MODEL - Validate, through in situ experimentations, the numerical model and the analytical solutions developed within the scope of projects A and C. C - INTEGRATE THE SPATIAL INTERACTIONS BETWEEN SCWs WITH A SPECTRAL APPROACH - Integrate, in a spectral framework, the thermal and hydraulic interactions occurring between the wells of a SCW system to predict the groundwater temperature arriving at a heat pump. D - EVALUATE THE IMPACT OF FRACTURE FLOW ON ENERGY SAVINGS AND DEVELOP GUIDELINES - Evaluate the impact of the fracture network on the entering water temperature and energy savings generated during the operation of a SCW, and suggest design guidelines. E - COMPARE THE LIFE-CYCLE OF SCW AND CONVENTIONAL SYSTEMS - Perform life-cycle financial analyses based on the economic, climatic and geological context prevailing in Canada and suggest design guidelines. F - MITIGATE THE IMPACT OF GEOCHEMICAL CONDITIONS ON THE OPERATION OF SCWs - Evaluate the impact of the hydrogeochemical conditions on the operation of SCW systems which use groundwater directly and identify and compare potential mitigation measures. The integration and study of some of the geochemical processes occurring during the operation of a SCW should lead to the development of mitigation measures and practical design guidelines and contribute to reduce the maintenance costs of SCW systems. The model developed in the scope of project C will be integrated to GeoAnalyser, a web-based application financed by the Canadian Geoexchange Coalition and intended to help designers worldwide to design geoexchange systems. Additionally, the guidelines developed in the scope of projects D, E and F will be integrated to the course “Training for Commercial System Designers” given by CGC in Canada. However, the most significant impact of the proposed research program will be the formation of highly trained hydrogeologists specialized in the design and operation of open geoexchange systems.