An approach for thermal performance assessment and optimization design of energy diaphragm walls (EDWs) with seasonal thermal load via numerical modeling

The energy diaphragm wall (EDW) is a promising emerging technology for shallow geothermal energy utilization of existing buildings. However, analyzing the heat transfer characteristics of EDWs is a prerequisite and essential guarantee for rational heat transfer design and optimization. Generally, a single field or model test cannot fully consider and analyze the potential factors affecting the heat transfer characteristics. Therefore, this work uses numerical analysis methods to establish a 3D heat transfer numerical model of EDW suitable for the climatic and geological conditions and heat transfer requirements in Chongqing areas, China. The influencing parameters are divided into design, operating, and environmental aspects. A comprehensive analysis method has been developed that considers a range of indicators related to the temperature difference between the inlet and outlet, heat transfer efficiency, total heat transfer, and average daily heat transfer. The developed method also evaluates the significance of parameter effects based on transient and integrated heat transfer performance. The results show that the heat transfer fluid flow rate, operation mode, groundwater flow, excavation ratio and wall depth have the greatest impact on the thermal performance of the EDW, with a normalized influence degree NETotal of 1.0, 0.94, 0.80 and 0.77, respectively. Recommendations on the thermal conductivity of the concrete and pipe, pipe configuration, etc., and prospects for further research are also provided for the optimal design and thermal simulation optimization of energy diaphragm wall systems.