Geothermal cooling through enhancement of the natural heat sink effect - proof of concept

Underground railway system usage is growing throughout the developing world and in many cities the underground railway is the most commonly used form of public transport. The intense service provided on these systems generates substantial quantities of rejected heat energy. This energy can significantly increase air temperatures within the trains and tunnels. When coupled to high ambient temperatures this can lead to passenger discomfort and health issues. Conventional air conditioning systems have been used in some modern underground railway installations but their operation has had limitations and leads to highly energy intensive solutions. Conventional air conditioning often cannot be included in older systems through heat rejection and spatial problems. Sustainable cooling systems could reduce the overall system energy usage and provide an acceptable environment for passengers. These could include energy management methods such as reduced train velocity, low weight carriages as well as sustainable cooling technologies that have been introduced from modern building services engineering such as Groundwater and geothermal cooling. Geothermal cooling has not been investigated with respect to underground railways currently and this paper is aimed at investigating this concept. A calibrated laboratory experiment is described that investigates the conductive heat transfer in an underground railway like environment. The experiment is run with and without modification to the thermal topography of the test rig. The experiment is run under both steady state and transient conditions to explore fully the potential for geothermal cooling. The experiment shows that the same level of heat energy can be transported across a vastly reduced temperature difference. This will enhance the thermal comfort provision and allow greater levels of heat energy to be moved without compromising the tunnel temperature. (c) 2006 Elsevier Inc. All rights reserved.