THERMAL-ENERGY STORAGE IN THE GROUND - COMPARATIVE-ANALYSIS OF HEAT-TRANSFER MODELING USING U-TUBES AND BOREHOLES

Large scale thermal energy storage for solar heating applications can be accomplished in the ground through the installation of an array of vertical heat exchange boreholes or U-tubes. Simulation modeling of th e storage subsystem and its integration with the total system is essen tial for design and performance evaluation. Although U-tube storage de sign is especially attractive in clay soils and preferable to borehole s in many geological conditions, only a borehole simulation model is c urrently available, validated, and integrated into a system simulation model. This article presents a comparative analysis of the heat trans fer from boreholes and U-tubes using analytical solutions, finite elem ent modeling, and the available simulation model. The analysis is used to support the development of a methodology by which the heat transfe r of any U-tube configuration can be modeled by appropriately specifyi ng parameters in the borehole storage simulation model. The borehole m odel can then be used to model the storage subsystem integrated within a total system simulation model. Copyright (C) 1996 Elsevier Science Ltd.