Proposal for using underground mine and geothermal resources for sustainable communities

It has become more important for communities to utilize locally available renewable energy sources. The use of renewable energy can reduce environmental impacts and potentially provide long-term cost savings for communities. In this paper, the authors propose a system that could cool buildings in summer and melt snow on the pedestrian sidewalks in winter using an abandoned underground mine and a hot spring in Idaho Springs, Colorado. In the proposed system, an underground mine would be used as cold thermal energy storage, and the heat of geothermal hot fluid transported from the hot spring would be re-used to melt snow in the historic downtown. To assess the feasibility of the proposed system, we conducted a series of temperature measurements at the Edgar Mine (Colorado School of Mines' Experimental Mine) and heat transfer analyses of the geothermal hot fluid flowing through pipes that will be buried in the ground under the city. The temperature measurements proved that the temperature of the underground mine was low so that we could store cold groundwater for use in summer. Furthermore, the temperature profiles of two different tunnels in the Edgar Mine were discussed to determine the most appropriate place to store cold groundwater for summer use. In the heat transfer analyses, the heat loss of the geothermal hot fluid during its transportation was calculated, and then the heat requirement for snow melting and heat supply from the geothermal hot fluid were compared. It was concluded that the heat supply in the present situation was not sufficient enough to melt snow in the whole area of the historic downtown. However, the result indicated that the proposed snow melting system could be realizable if the snow melting area is limited or additional geothermal wells are drilled. We hope this case study will serve as an example of the concept of "local consumption of locally available energy". Many communities in the world do not fully utilize thermal resources in the ground. If such communities start utilizing them in a socially and environmentally responsible manner, it will contribute more to globally sustainable development for mankind.