Abstract
Energy geo-structures have received rapid attention as part of the pursuit for renewable energy since they can exchange heat between the ground and under- or above-ground spaces, in addition to their primary structural functions. However, their efficiency in cooling-dominated conditions has not been adequately studied. This paper tackles a key challenge regarding transport tunnels: sustainable cooling of underground substations by introducing a cooling system that integrates heat exchangers into tunnel lining. This system takes advantage of the tunnel air and the ground potential as sustainable heat sinks to which the heat from the substations is rejected and evaluates the efficiency of the proposed cooling system for different configurations of heat exchangers. The efficiency is evaluated by numerically investigating temperature changes in the ground, tunnel air, tunnel structure and carrier fluid circulating within the heat exchangers. Moreover, the cost of the proposed systems is compared with those of the conventional direct expansion (DX) systems. Results show that the proposed cooling system can effectively improve the efficiency of cooling underground substations by yielding a higher Coefficient of Performance (COP) and lower Net Present Cost (NPC) than the conventional DX systems, without imposing unsustainable practices on the ground, tunnel structure or tunnel air.