地中熱ヒートポンプシステムにおけるポテンシャルマップの高度化

抄録

Assessment of development potential of ground-source heat energy in a regional scale basis is necessary for the best suited design of ground-source heat pump (GSHP) system and its sustainable growth in Japan. Evaluation of usage potential of GSHP system in Tsugaru Plain was conducted in this study, where field survey data of groundwater and subsurface temperature were not sufficient enough as observation wells were lacking. In order to comprehend groundwater flow system and subsurface temperature distribution of the plain, Shrestha et al. (2015) developed a 3D field-wide analysis model and verified it by incorporating the results of thermal response tests, in absence of observed data. In Shrestha et al. (2015), distribution map of effective thermal conductivity was prepared, which was overlaid with the calculated subsurface temperature distribution map in GIS, and a potential map was prepared.In this study, the potential assessment method used in Shrestha et al. (2015) was upgraded by developing potential maps for GSHP system with a new approach, using a performance curve of particular heat pump and ground-heat exchanger model. Based on local topography, geology and the results of the field-wide analysis model, single ground heat exchanger models were constructed at 11 locations in the plain, and heat exchange simulations were conducted. Outputs of the simulations were utilized to prepare potential maps showing spatial distribution of heat exchange rates and coefficient of performance (COP) of heat pump. For COP estimation, the performance curve of heat pump was used. Distribution map of COP including operation cost of the heat pump was prepared with the aim of illustrating economic efficiency of the GSHP system, which is unique to this study. These potential maps prepared for space-heating purpose are significant for proper site selection of the GSHP system, and they can assist for optimum design and economic feasibility of the system.