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Subsurface mining operations are continuously getting deeper and more complex due to depletion of shallow deposits. This fact inevitably brings more expensive, high-tech oriented and most importantly energy intensive subsurface mining operations to come alive. Accordingly, while big mining companies are developing sensible extraction methods to exploit orebodies located at great depths, they are also seeking to cut down their costs and carbon footprint. A large percentage of the energy needed by a subsurface mine is due to the mine ventilation and air conditioning reasons. In fact, for mines deeper than 2 km, mine air conditioning becomes a must. Yet, as there are not many alternatives developed, most of the modern mines are subjected to deploy tens of megawatts worth of cooling plants using massive refrigeration units. This does not only create a large financial burden during the project stage but also results in heavy energy demands during the operation. This paper aims to investigate a natural, alternative deep-mine lake cooling system by providing a detailed 'front-end-loading' design conducted for a real-life, Canadian example. [ABSTRACT FROM AUTHOR]

• A numerical model to assess the performance of mine exhaust heat recovery system. • Model comparison and validation carried out based on existing literature. • Thermally coupled and decoupled heat transfer models are compared. • Hourly ambient air temperature data is used to estimate energy and carbon savings. • Impacts of heat exchangers effectiveness and mine intake air flow rate are studied. Mine air conditioning is a common practice where liners and other shaft units should be protected against freezing temperatures in cold regions. In conventional mine intake air conditioning applications, heating is usually performed with natural gas burners, accounting intense energy consumption and emissions. This fossil fuel dependency issue can be effectively mitigated with a heat recovery and reutilization technique called mine exhaust heat recovery. Mine exhaust heat recovery systems can ensure large savings with minimum fossil burning at relatively lower operating costs. Present paper investigates the applicability of a novel numerical heat transfer model to assess the performance of mine exhaust recovery systems with comparably higher precision. Unlike other work done in the field, this work also considers the coupling effect between the heat exchangers involved. Accordingly, the operational significance and the impact of thermal coupling in the model is highlighted in detail with an emphasis on the project financial feasibility. Furthermore, a parametric study is also presented identifying the impact of different parameters i.e. heat exchanger effectiveness and airflow rate on savings for a real-life Canadian underground mine example. [ABSTRACT FROM AUTHOR]

Thermal storage of the energy is essential for district heating systems to mitigate intermittency related issues. The extensive cavities created after extraction of ores/coal in mines could provide a unique opportunity for storage and extraction of thermal energy. This paper shows that underground backfilled stopes present a viable potential for being retrofitted to thermal energy storage batteries. The present study evaluates the energy performance of thermal energy storage in underground backfilled stopes by installing heat exchange tubes prior to backfill placement. A numerical fluid mechanics and heat transfer model for backfill stopes was developed in Fluent to investigate the heat exchange inside the tubes as well as the heat transfer happening within the backfill during the heat storage and extraction process. The proposed model is compared against an analytical heat transfer model to determine its reliability and accuracy. The results obtained from the validated numerical model showed that energy storage system in a typical underground backfilled stope of coal mines can provide about 23 GWh of thermal energy storage capacity with an average recovery rate of 60% during extraction cycles. Accordingly, several sensitivity analyses were conducted to define the optimum center-to-center distance for the pipe installation to attain the best system performance. Through a series of parametric studies, it was found that thermal conductivity of backfill and rock, circulating fluid mass flow rate, initial rock temperature and thermal saturation time constitute the most significant influencing parameters on energy storage performance of such applications. It can be concluded that thermal energy storage systems in backfilled stopes are relatively more techno-economically feasible, compared to conventional borehole energy storage systems, in terms of their significantly lower drilling/installation costs and higher hosting temperature. [ABSTRACT FROM AUTHOR]

• A rock-pile waste heat storage is proposed, and its corresponding numerical model is developed. • Both fluid flow and heat transfer are validated against experimental data. • Local Thermal Equilibrium and Non-Equilibrium approaches are compared. • Parametric studies are performed on thermo-physical properties. • Payback time analysis is performed, and the system is economically justified. Remote communities in arctic climates are solely dependent on diesel generators for continuous power supply due to their detached loci from national power gridlines or natural gas pipelines. Moreover, to get along with the harsh, long winters, these communities directly or indirectly depend on fossil-fuel based heating systems. Due to the lower efficiency of the conventional diesel engines, these generators discard a significant amount of heat through the exhaust. Occasionally, during the wintertime, this waste heat from the exhaust is used directly as a heat source after recovery. However, during summer, when the heating demand is lower or nil, this heat is commonly discarded, and its energy potential wasted. A rock-pile based seasonal thermal energy storage is a viable solution that can sustainably resolve this issue. This paper presents a validated numerical study that focuses on the coupling of a waste heat recovery system to a diesel exhaust stream offering a performance assessment of the proposed rock-pile waste heat storage system in a remote, off-grid community located in northern Canada. It examines the impacts of local thermal equilibrium versus non-equilibrium approaches as well as temperature-dependent properties, variation of air mass flow rate, particle size and finally the thermo-physical properties on the proposed model. The presented results show that air should be treated as an ideal gas and that the local thermal non-equilibrium approach should be used for its considerably higher accuracy. Techno-economic assessment of the system resulted in a relatively short payback period of less than six years. [ABSTRACT FROM AUTHOR]