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

为了在浅层沉积物上有效地利用地面耦合热泵系统，对当地地下水流动系统的了解是非常重要的。本研究以日本秋田冲积平原为研究对象，进行了以下几个方面的研究：(1)利用野外调查结果对地下水流动系统进行分析；(2)建立秋田平原全域地下水流动模型；(3)对大型地热电联产系统的长期运行性能进行预测。在野外调查中，分别在深孔和浅孔进行了地下水采样。在浅钻孔中，测量地下水位，绘制地下水位图。在深钻孔中，每隔21n测量一次地下水温度，以收集沿井的地下水流动剖面。在井场测量PH和EC。在地下水流动建模方面，采用三维地下水和热输运软件FEFLOW在秋田平原建立了全域地下水模型。数值模拟表明，阿基特中部地区地下水平均流速。a Plain是1。38x10 -4（米/天），自东向西。现场调查结果与数值模拟结果吻合较好。单地热交换器（GHE）模型表明，当采掘含水层中存在Peclet数等于或大于0.1的地下水流量时，采掘含水层的抽热率会提高。利用多井模型，确定了每年至少两个月的蓄热运行的重要性。多井模型还表明，在夏季不包括蓄热操作的GCHP系统中，更大的GHEs间距是可取的。

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.