AIST FREA

産総研トップへ

Shallow Geothermal and Hydrogeology Team

Suitability Assessment of Ground-Source Heat Pump System and Its System Optimization Technology

Over View

A Ground-Source Heat Pump (GSHP) system is a technology that originally spread in western countries in the 1980s after the world oil crisis. Although the technology is not new, its use in Japan has been delayed since it was hardly known until around the year 2000. Because the existence of groundwater and its flow rate largely affects the heat exchange rate, it is important to understand the water level and flow rate of groundwater systems in order to effectively utilize GSHP systems in Japan.


Research Target

The GSHP system is highly efficient and energy-saving compared to normal air conditioners (air-source heat pump systems). The team has been promoting the GSHP system by enhancing its performance and lowering its cost based on geological information.
There are two types of GSHP systems: a closed-loop system exchanges heat by circulating brine or water in pipes buried 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 groundwater level and flow rate. The Japanese approach to research on GSHP considering the groundwater system may be applicable and beneficial for Southeast Asian countries. Therefore, we are engaged in the following research targets to develop GSHP systems suitable for the hydrogeological 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
  • Expansion of GSHP studies in Southeast Asia and other regions

   *COP: Coefficient of performance

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Concept of ground-source heat pump system

Concept of ground-source heat pump system

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Suitability assessment technologies for ground-source heat pump application
※Suitability mapping for ground-source heat pump (GSHP) systems considering the effects of groundwater is a new idea from AIST.

Suitability assessment technologies for ground-source heat pump application

Research Outline

To use a GSHP system, it is important to understand the subsurface hydrogeological conditions of the site. Therefore, we conduct geological surveys by boring, groundwater temperature surveys by depth, regional heat transport simulations with advection effects of groundwater flow, etc. to investigate the 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 different subsurface conditions. At a GSHP demonstration test site of FREA, the team conducts experiments using two types of heat exchangers: shallow (horizontal) and deep (vertical). 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 hydrogeological settings.
The team is mainly engaged in the following research and development themes:

  • Research on GSHP suitability assessment

    Japan has many regions where there is abundant groundwater at a depth of several meters to a hundred meters, so the utilization of a GSHP system would be more efficient if the groundwater flow is considered.
    In order to promote the appropriate utilization of GSHP systems, the team conducts research studies in collaboration with Geological Survey of Japan, AIST. The team is also developing methods to assess the suitability of different GSHP systems based on field surveys and numerical analyses.

  • Technology development for GSHP systems optimization

    The team is evaluating the optimal heat exchange system that can efficiently utilize a shallow (depth: 1‒2 m) or deep (depth: about 100 m or less) heat exchanger and is developing a more efficient heat exchange system based on site-specific hydrogeological conditions. At the GSHP experiment field of FREA and at the Geological Museum of AIST in Tsukuba City, identical GSHP systems combining various types of horizontal and vertical heat exchangers are installed to investigate and evaluate the differences between the two areas, having different hydrogeological settings, in the optimal heat exchange method and their efficiency, by long-term monitoring and numerical simulation. Through the “visualization” of the GSHP systems, with a real-time display of the operating state and observation of the heat exchange borehole, the team aims to promote and diffuse the GSHP system.

Technology development for GSHP systems optimization

Main Research Facilities

FREA Ground-Source Heat Pump System Demonstration Area Ground-source heat pump (GSHP) system installed at Chulalongkorn University, Thailand
FREA Ground-Source Heat Pump System Demonstration Area Ground-source heat pump (GSHP) system installed at Chulalongkorn University, Thailand
This GSHP system uses a sheet-type heat exchanger and a Slinky-type heat exchanger installed at a depth of 1‒2 m and a vertical-type (borehole type) heat exchanger installed at a depth of about 40 m. Facility at Chulalongkorn University in Thailand used to demonstrate the possibility of cooling operation through the GSHP system in Bangkok.

 *GSHP: Ground-Source Heat Pump


Activities and Achievements

1) Analysis of the hydrogeological structure of the Aizu Basin

Through joint research with Fukushima University, the team conducted an analysis of the geological structures of the Quaternary layers and of the hydraulic structure (including subsurface temperature distribution) in the Aizu district, Fukushima Prefecture to reconstruct the basic data for assessing the suitability of GSHP systems.

2) Suitability assessment for GSHP system installation in Aizu Basin

The team constructed a three dimensional groundwater flow and heat transport model based on the geology data obtained from the analysis of geological structure of the Aizu Basin (Fig. 1). Using the model results, the team then conducted a suitability assessment for the closed-loop system, and prepared a distribution map of estimated heat exchange rates (Fig. 2). This kind of suitability map that illustrates the regional variation of heat exchange rates, is essential to select the suitable location for the optimum design of GSHP system.

3) Performance evaluation of a closed-loop GSHP air-conditioning system using an artesian well

The team constructed a closed-loop GSHP system using an artesian well in a joint research project with Japan Groundwater Development Co., Ltd. through the “Program for Promoting Technologies Invented by Industry in Disaster Areas in Tohoku.” The team built a system to control the natural flow using the well temperature. COP higher than 8.0 in the cooling operation and COP higher than 4.5 in the heating operation were observed; however, this depends on the operating conditions.

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【Fig. 1】Three-dimensional groundwater-flow and heat-transport model in the Aizu Basin
【Fig. 1】Three-dimensional groundwater-flow and heat-transport model in the Aizu Basin

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【Fig. 2】Distribution map of estimated heat exchange rate in the Aizu Basin
【Fig. 2】Distribution map of estimated heat exchange rate in the Aizu Basin

Team Member

Title Name
Leader Youhei Uchida
Senior Researcher Akira Tomigashi
Senior Researcher Shrestha Gaurav
Researcher Takeshi Ishihara
Researcher Arif Widiatmojo