INCORPORATION OF PHASE-CHANGE MATERIALS INTO A GROUND THERMAL-ENERGY STORAGE-SYSTEM - THEORETICAL-STUDY

An investigation of a ground thermal energy storage system, which incl udes storage units containing phase-change materials (PCM), is present ed. This study is related to a large-diameter helical heat exchanger, which is placed vertically in the ground. The PCM storage units under consideration have a cylindrical shell shape and are located inside an d/or outside the helix. A modified numerical scheme for the solution o f heal transfer in the ground in the PCM units, and within the heat ex changer pipe, is presented. The theoretical results show that the ther mal diffusivity of the PCM dominates the thermal performance of the sy stem. Incorporation of PCM storage units containing paraffin wax resul ts in a reduction of the thermal efficiency in comparison with a syste m not containing these units. However, incorporation of PCM having the same thermal diffusivity as of the soil results in a significant impr ovement of the thermal performance.