Dynamic performance of a solar urban district heating system upon varying the characteristics of seasonal thermal energy storage

A solar district heating system serving a small-scale urban district located in Naples (Italy) is analysed by means of the software TRNSYS over a 5-year period. The plant is based on the utilization of a flat plate solar collectors field connected to a seasonal double U-pipe vertical Borehole Thermal Energy Storage (BTES). A parametric analysis has been performed in order to analyse the performance of the district heating network upon varying the characteristics of the BTES in terms of volume, number of boreholes, thermal conductivity of soil, thermal conductivity of grout, U-pipe spacing and heat carrier fluid. The primary energy consumption, the equivalent CO2 emissions and the operating costs of the proposed system have been evaluated based on the simulation results and compared with those associated to a conventional heating system assumed as reference in order to assess the potential benefits achievable by optimizing the long-term storage design.