Journal of the Geothermal Research Society of Japan

Thermal response tests with U-tube ground heat exchanger of 50 m long were conducted to evaluate apparent thermal conductivity in 23 locations of Aomori Prefecture. The apparent thermal conductivities were ranged from 1.12 to 2.94 W/(mK). The highest apparent thermal conductivity was evaluated in the location consisted of gravel layer. The lowest value was in the location consisted of alternation of mudstone and sandstone. In addition, the apparent thermal conductivities were ranged from 1.50 to 2.08 W/(mK) in the alluvial plain deposits of Aseishi river.

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The quality of groundwater and spring water for use in open-loop type groundwater-based heat pump system in the Pacific Ocean coast of Aomori Prefecture was evaluated on the basis of the water quality guidelines for refrigeration and air conditioning equipment. The water-quality parameter values for the groundwater and spring water were considerably higher than the corresponding standard values; the difference between the actual and standard values was highest for the free carbon dioxide concentration, followed by the silica concentration. A significant reason for the high free carbon dioxide levels is assumed to be the generation of CO₂ due to the decomposition of organic matter in the subsurface environment. The development of open-loop type groundwater-based heat pump system in this study area in the future will be a significant challenge as system durability is expected to be low because of corrosion and silica-scale problems.

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