Study on Influence Factors of Horizontal Ground Heat Exchanger Performance Considering Climatic Conditions and Groundwater Flow

Abstract

Horizontal ground heat exchanger (HGHE) is a cost effective method to exploit geothermal energy due to its shallow installation depth, which meanwhile causes its performance sensitive to the climatic conditions and groundwater flow. However, effects of key factors on HGHE performance when considering climate and groundwater flow still remain unclear, which is vital for HGHE optimal design. To this end, based on a 3D numerical model considering atmosphere-HGHE-ground interaction for a HGHE, this paper comprehensively investigated effects of operation modes, heat storage, precipitation, air temperature, groundwater flow velocity, ground thermal properties, circulation flow rate and installation depth on HGHE performances. The influence degrees of these factors were compared through the gray correlation analysis. The results indicated that non-consideration of climatic conditions could underestimate HGHE outlet temperature in summer and winter. The intermittent operation mode showed much better performance than continuous one. Increasing installation depth and improving grout thermal conductivity were both beneficial for HGHE performance. The gray correlation analysis demonstrated that the most significant impact factors on HGHE performance were groundwater flow velocity > circulation flow rate > precipitation > air temperature. Consequently, it is necessary to consider groundwater flow and climatic conditions for the precise evaluation of HGHE performance.