再生エネルギー研究センターパンフレット（英語）

14/20

13Shallow Geothermal and Hydrogeology Team－Suitability Assessment of Ground-Source Heat Pump System and its System Optimization Technology－A ground source heat pump (GSHP) system is a technology that was originally spread in western countries in 1980s after the world oil crisis in 1970s. Although it is not a new technology, its spread in Japan has been delayed for it was hardly known until around the year 2000. Restriction on groundwater use in big cities is another reason of its delay especially for open loop systems. Because the existence of groundwater and its flow rate largely affects the heat exchange rate, it is important to understand water level and flow rate of groundwater systems in order to utilize GSHP in Japan effectively.Research Target　GSHP system is highly efcient and energy-saving compared to normal air conditioners (air-source heat pump systems). The team has been promoting GSHP system by enhancing its performance and lowering its cost on the basis of geological information.　There are two types of GSHP system: a closed-loop system exchanges heat by circulating brine or water in pipes buried in underground while an open-loop system pumps up groundwater to exchange heat at the ground surface. In Japan, since the existence of groundwater and its flow rate largely affects the heat exchange rate in both cases, it is important to investigate the water level and flow-rate of the groundwater. Such a Japanese way of research on GSHP considering groundwater system may be applied and may bring advantages for Southeast Asian countries. We, therefore, are engaged in the following research targets to develop GSHP systems suitable for the hydro-geological characteristics of a site:●GSHP suitability mapping based on field data collection and schematic model construction,●Conceptual designing on optimization technology of a GSHP system and●Expansion of GSHP studies in Southeast Asia and in other regions, etc.※COP: Coefficient of PerformanceResearch Outline　To use GSHP, it is important to understand the subsurface hydro-geological condition of the site. We, therefore, conduct geological survey by boring, groundwater temperature survey by depth, regional heat transport simulation with advection effect of groundwater flow, etc., to investigate suitability of a GSHP system according to the subsurface environment of the area. 　The team also conducts studies on the development of GSHP systems suitable for various different subsurface conditions. At a GSHP demonstration test site of FREA, the team conducts experiments with two types of heat exchangers: shallow (horizontal) and deep (vertical) ones. The identical system is installed at the Geological Museum of AIST in Tsukuba City, Ibaraki-Prefecture to investigate the differences in heat exchange performance and in optimum heat exchange systems in each area having different hydro-geological settings.　The team is mainly engaged in the following research and development themes:●Research on GSHP suitability assessment　In Japan there are many regions where groundwater is so abundant at a depth of several meters to 100 m, so that utilization of GSHP system should be more efficient if flowing property of groundwater is considered. In order to promote appropriate GSHP system utilization, the team conduct research and studies in collaboration with the Geological Survey of Japan of AIST. The team is also developing methods to assess suitability of different GSHP systems based on field surveys and numerical analyses.Concept of a ground source heat pump systemSummer seasonWinter seasonAir-conditioning and coolingHeat pump (cooling)Heat emissiongeological layer and groundwater (thermal storage)⬇⬇Heat pump (heating)Heat extractiongeological layer and groundwater (heat source)⬇⬇Space heating and snow meltingAir-conditionerAir-conditionerHeat pumpHeat pumpCoolWarmSuitability assessment technologies for ground-source heat pump applicationThe idea of suitability map for ground-source heat pump (GSHP) systems considering effects of groundwater is new invention of AIST.The suitability of GSHP depends on the heat exchange rate, the potential of total heat exchange, and groundwater characteristicsGeology, groundwater level, velocity of groundwater flow, subsurface temperature, water quality, etc.Borehole heat exchangerHeat exchangerateHeat exchangerateGroundwater flow velocity