Numerical and experimental study of an underground thermal energy storage system coupled with asphalt solar collector and heat pump

This article concerns the design of a low temperature underground thermal energy storage (UTES) that could be used to store the solar thermal energy produced by asphalt solar collectors (ASC) and use it to cover the heating and domestic hot water needs of buildings. The amount of energy stored in the UTES is significantly increased by exploiting the latent phase change energy in the storage thanks to a heat pump. To do this, the storage uses original horizontal helical heat exchangers to charge and discharge the thermal storage, and water-saturated sand as the storage material which makes it possible to deal with problems of water density change without soil swelling. The performance of the storage system is studied throughout the year. Particular attention is paid to periods of partial freezing in the depths of winter. A 1D transient model of heat transfer in the UTES is developed. The model predictions are compared to experiments on a prototype incorporating material icing. • Design of a long-term, low-temperature and phase change energy storage for building • Development of a transient thermal model of water-saturated sand UTES including phase changes over long time intervals • Modelling the development of the ice front using a simple adaptive mesh and second-degree temperature profiles