The southwestern foot of the Hakkoda–Odake volcano has many geothermal manifestations where geothermal development has been limited by the Natural Parks Law. The current target area, which is classified as Class II special zone has been deregulated for individual geothermal development. We conducted an investigation to determine the chemical and isotopic characteristics of the hot waters around the Shinyu Fault and to estimate the temperature of the geothermal reservoir. According to our δD–δ¹⁸O diagram, the hot waters in the study area are meteoric in origin. In addition, the triangle diagram for Cl^–, SO₄^2–, and HCO₃^– concentrations indicates that these hot waters can be classified as steam-heated waters and volcanic waters. The B/Cl and Br/Cl ratios show that the volcanic waters are diluted with shallow groundwater as they flow through Jigokunuma downstream to Shinyu. We estimated the geothermal reservoir temperature to be between approximately 150 and 160 °C, based on anhydrite geothermometry and the chloride–enthalpy mixing diagram.

Ground Source Heat Pump (GSHP) systems directly exploit geothermal energy to meet the heating and cooling demands of buildings. However, despite being one of the commonest applications of geothermal energy, this technology is rarely used in Japan due to the high drilling costs. This paper introduces a new semi-open loop GSHP system that increases the heat transfer rate of Ground Heat Exchangers (GHEs) by water-pumping and injection inside the GHE wells. The effect of water-pumping and injection on the system performance was evaluated in four field tests on a GSHP system constructed at Akita University Campus, Japan. Based on geological data at the system location, a numerical model was constructed and validated by comparisons with experimental data. The system performance under different groundwater velocities and operating conditions was then evaluated in sensitivity analyses. The semi-open loop system improved the coefficient of performance (COP) by only 5%, relative to base case. The sensitivity studies showed that in formations with fast groundwater flow, the maximum enhancements of the COP and system coefficient of performance (SCOP) are 12% and 9%, respectively. In the absence of groundwater flow, the COP and SCOP improved by 40% and 20%, respectively, with significantly increased system capacity. Therefore, the performance improvement was limited by the groundwater flow.

Slinky-coil type ground heat exchangers (GHEs), which are commonly used in horizontal ground heat exchangers, have an extended spiral shape to effectively collect the heat from the ground. Due to the complicated shape of the GHEs, a reliable method to estimate the pressure loss caused by the flow of circulation fluid is not well-developed yet. In this work, field measurements of pressure loss in Slinky-coils were carried out using a polyethylene tube of 25mm ID whose overlaps between loops were set as 0, 25, 50 and 75%, respectively.

The results of the measurement showed that the percentage of overlaps does not significantly affect the pressure loss. It was also found that the pressure loss in the Slinky-coil was slightly higher than that in straight tubes; the difference increased with the increase of flow rate. To predict the pressure loss in Slinky-coils, the friction factor in the pressure loss calculation was corrected to obtain a good matching between the measured and calculated pressure losses for different tube length and heat medium temperature. The use of the corrected friction factor enabled the easy calculation of pressure loss in Slinky-coils.

Thermoluminescence (TL) of mineral is widely recognized as a dating techniques for relatively young geomaterials which are younger than 1 Ma. However, TL phenomena of minerals was affected by natural annealing which was caused by geothermal activity. Thermoluminescence of quartz in the Shirasawa caldera located in western part of Sendai, NE Japan, was investigated. The Shirasawa caldera was formed during 10-8 Ma (late Miocene to Pliocene), and filled with felsic pyroclastics. Quartz was picked up from the host rock, and then TL glow curve of quartz was measured in temperature range from 50 to 400°C with a heating rate of 1°C/sec. TL intensity of quartz (integrated intensity between 200 and 390°C) in the same geological formation showed heterogeneous variation, which means that TL intensity does not indicate geological accurate age of the formation. Low TL intensity samples were corresponded to hydrothermal alteration which was identified by formation of sericite, and high TL intensity samples contained smectite and/or sericite/smectite mixed layer clay minerals. Those facts indicate that TL intensity of quartz in the Shirasawa caldera shows thermal effect and hydrothermal alteration by geothermal activity.

The low TL intensity area is overlapped to negative gravity anomaly, and also drastical decrease of TL intensity is related to positive gravity anomaly around the intrusive rock. Those facts suggest that the low TL intensity area was corresponded to subterranean hydrothermal system (negative gravity anomaly) and fractured zone which was hydrothermal upwelling zone around the intrusive rock (positive gravity anomaly).