Evaluation of Heat Transfer Performance between Rock and Air in Seasonal Thermal Energy Storage Unit

Ventilation is one of the most energy demanding parts of deep underground mining operations due to the extensive amounts of energy needed to cool (or heat) the substantial amount of air flow in underground workings. This considerable amount of energy demand can be partially satisfied by extracting renewable energies or using alternative energy solutions available at mine sites. In Canada, some mining operations have the opportunity to create a Seasonal Thermal Energy Storage (STES) unit by blowing mine intake air through large volumes of rock mass dumped in a decommissioned pit. This technique allows for creation of the so-called “Natural Heat Exchanger (NHE)” which moderates seasonal air temperature oscillations. This paper signifies a novel heat transfer model for performance assessment of a NHE system. It investigates the potential for energy savings by implementation of variable number and position of ventilation trenches in underground mines. In this regard, a 3-D heat transfer model is developed to evaluate the thermal storage and the heat transfer between broken rock mass and ventilated air flow and also to specify how design parameters such as position and number of ventilation trenches will affect the heat transfer performance as well as the total energy savings. The results of this study show that NHE can be applied in thermal management of underground mines with the aim of decreasing energy consumption for heating, cooling and ventilation purposes.