Optimal Configuration of a Solar Heating System with Seasonal Thermal Energy Storage Serving a Micro-scale Italian Residential District: Energy, Environmental and Economic Analyses

A centralized solar hybrid heating system serving a micro-scale district composed of 6 typical Italian residential buildings and 3 schools located in Naples (southern Italy) has been modelled, simulated and analyzed by means of the dynamic software TRNSYS over a 5-year period. The plant is based on the operation of solar thermal collectors connected to a seasonal single U-pipe vertical Borehole Thermal Energy Storage (BTES) in order to address the seasonal misalignment between solar energy supply and thermal energy demand for heating purposes. In this paper, a parametric analysis has been performed in order to investigate the performance of the plant upon varying the characteristics of the BTES in terms of: (i) thermal conductivity of soil, (ii) thermal conductivity of grout, (iii) U-pipe spacing, (iv) heat carrier fluid, (v) number of Borehole Heat Exchangers (BHEs), as well as (vi) type of BHEs connection (series, parallel or mixed). The primary energy consumption, the equivalent carbon dioxide emissions and the operating costs of the proposed district heating network have been evaluated based on the simulation results upon varying the plant configurations and then compared with those associated to a conventional Italian decentralized heating system assumed as reference in order to (i) assess the potential benefits, (ii) explore the influence of BTES configuration on the overall system performance, and (iii) establish some simple rules for the initial phase of BTES design.