Groundwater survey and heat transport, modeling for optimum design of geothermal heat pump systems in Akita Plain

为了在浅层土壤上有效地使用土壤耦合热泵（GCHP）系统，了解当地地下水流系统是非常重要的。本研究以日本秋田冲积平原为研究对象，通过对地下水流系统的实地调查分析、秋田平原地下水流模型的开发、大规模GCHP系统长期运行性能的预测，对地下水进行了深、浅钻孔采样。在浅井中，测量地下水位以绘制地下水位图。在深钻孔中，每隔21分钟测量一次地下水温度，以收集沿着威尔斯的地下水流剖面。在地下水流模拟方面，利用三维地下水和热量运移软件FEFLOW建立了秋田平原地下水模型。数值模拟结果表明，秋田平原中部地下水平均流速为1。38 × 10-4（m/d），由东向西。现场实测结果与数值模拟结果吻合较好。单个地下换热器的模型表明，当开采含水层中存在Peclet数等于或大于0.1的地下水流时，热量提取率增加。利用多井模型，确定了每年至少两个月的储热运行的重要性。多井模型还表明，在夏季不包括储热操作的GCHP系统中，GHE之间的较大间距是优选的。

For the efficient use of Ground Coupled Heat Pump (GCHP) systems on shallow deposits, the understanding of the local groundwater flow system is highly important. This research was conducted in Akita Alluvial Plain, Japan, to clarify the following items : (1) analysis of groundwater flow systems using field survey result, (2) development of field-wide groundwater flow model in Akita Plain, (3) prediction of long-term operation performance of a large-scale GCHP system.In field surveys, groundwater samplings were carried out in deep and shallow boreholes. In shallow boreholes, groundwater levels were measured to draw groundwater level maps. In deep boreholes, groundwater temperatures were measured every 21n to collectt groundwater flow profiles along wells. PH and EC were measured at well sites.For groundwater flow modeling, 3D groundwater and heat transport software "FEFLOW" was used to construct a field-wide groundwater model in Akita Plain. Numerical simulations showed that the average groundwater velocity in the central part of Akit.a Plain is 1. 38X 10-4 (m/d), from east to west. The field survey results showed good agreements with numerical simulation results. The model of a single Ground Heat Exchanger (GHE) showed that heat extraction rates are enhanced if groundwater flows with Peclet numbers equal or higher than 0.1 exist in the aquifer under exploitation. With the multi-well model, the importance of heat storage operation of att least two months per year was determined. The multi-well model also showed that larger spacing between GHEs is preferable in GCHP system that will not include heat storage operations during the summer months.