Study on underground thermal characteristics by using digital national land information, and its application for energy utilization

This paper describes a method for evaluating characteristics of underground thermal properties and groundwater, whose evaluation is essential for designing systems of underground thermal energy utilization. First, the systems using underground thermal energy are classified into two categories: borehole system with indirect heat exchange, and aquifer system with direct use of underground water. These systems are also divided into thermal storage systems and heat source/sink systems. Second, the characteristics of the underground in Japan are analyzed by using a geographical information system (GIS) and hydrogeological information. Regulations on environmental protection, such as those relating to national parks for instance, and the distribution of thermal energy demand eliminate 77% of Japan from consideration for underground thermal energy utilization. Areas limited to borehole thermal energy utilization account for 17% of areas where underground thermal energy can be used, with the remaining 74% suitable for both boreholes and aquifers. Finally, we estimate the thickness of aquifer and groundwater velocity in Sapporo. We find that most parts of Sapporo are suitable for aquifer thermal energy storage (ATES).