Journal of the Geothermal Research Society of Japan
Online ISSN : 1883-5775
Print ISSN : 0388-6735
ISSN-L : 0388-6735
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  • Yoshitaka SAKATA, Takao KATSURA, Katsunori NAGANO
    Type: Article
    2019 Volume 41 Issue 3 Pages 75-89
    Published: July 25, 2019
    Released: January 25, 2020

    A long-discussed problem of ground source heat pump systems is to determine required sizes (length and number) of closed-type ground heat exchangers under various conditions in terms of building, heat pump, facility and underground. The purpose of this study is to propose a simulation-based methodology for the size determination over the land through a combination of geo-property estimation and heat pump simulation. In this process, ground thermal conductivity was estimated as a weighted-probability average of individual thermal conductivities of eight soil/rock types. The probabilities were also estimated by indicator kriging with surrounding borehole data. This study collected about 46 thousand borehole data to apply the estimation method in any location, especially of urbanized areas. This study also showed two nation-scale maps of ground thermal conductivity on a 10 km regular grid at a depth of 50 m and 150 m, indicating its depth-dependence was seen in the mountain areas, but was unobvious in the plain areas where the unconsolidated sediments were over one hundred meters thick. The simulation-based method was performed under two conditions in terms of required temperature of the circulating fluids and target performance of the system. The simulation results were carried out among different sizes of ground heat exchangers, and the required sizes were interpolated as a minimum size to satisfy both conditions in each location. As a case study, this study applied the methodology for a household system consisting of a 10 kW ground source heat pump and a single borehole heat exchanger on a regular 10 km grid over the land, Japan. The simulation results were compared in three cases: Case 1; the necessary temperature condition only, Case 2; with target performance condition (the seasonal performance factor is over 4.0), and Case 3; for a highly insulated residence with an overall heat transfer coefficient of 1.0 W/(m2・K). In Case 1, the determined lengths were found to vary between 30 m and 180 m (104 m in average), with differences among adjacent grids arising owing to the varying climatic and geologic conditions. In Case 2, the lengths increased to satisfy the target performance (115 m in average), especially in the northern areas of low ground temperatures. In Case 3, the lengths for the highly insulated house were decreased (76 m in average) in the northern and mid-areas, but not in the southern areas where the cooling loads by the solar radiation were dominant. In conclusion, the proposed methodology could be applied in any location over the land with various conditions, contributing to more public implementation of GSHP systems.

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Technical Report
  • Juliet NEWSON, Randall Morgan GREENE
    Type: Technical Report
    2019 Volume 41 Issue 3 Pages 91-99
    Published: July 25, 2019
    Released: January 25, 2020

    This paper is a brief overview of the important factors in geothermal education, with reference to the worldʼs long-running international geothermal training courses which are taught in Japan, Iceland, New Zealand, and El Salvador. All of these courses rely to a greater or lesser extent on government or development funding. Students are international, although the Geothermal Diploma Course for Latin America, taught in El Salvador, draws on students from the Latin America region, as it is taught predominantly in Spanish. All of the courses are at a graduate level, and the main topics are based on science and engineering. Industry involvement is important in providing up-to-date knowledge on real world practices in geothermal. Ensuring gender equity for courses in a traditionally male-dominated industry is also an important consideration for geothermal course organizers.

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Short Note
  • Vani Novita ALVIANI, Takuya KOSAKA, Masaoki UNO, Masahiro OBA, Nobuo H ...
    Type: Short Note
    2019 Volume 41 Issue 3 Pages 101-107
    Published: July 25, 2019
    Released: January 25, 2020

    The feasibility of using hot spring water for hydrogen production via hydrothermal reaction with aluminum was evaluated by performing experiments at Zao and Tamagawa hot springs in Northeast Japan. The results of the study demonstrate the viability of the proposed method for advanced direct geothermal energy use. The amount of hydrogen produced using Tamagawa hot spring water (pH 0.88, 50 °C) was higher than that produced using Zao hot spring water (pH 1.60, 50 °C). Moreover, numerical simulation of the Al–H2O reaction at various temperature and pH conditions produced results consistent with experiments for both Zao and Tamagawa hot springs. The results of experiments and simulation indicated that pH is more significant than that of temperature for determining the amount of hydrogen generation.

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