Effects of Solar Field Design on the Energy, Environmental and Economic Performance of a Solar District Heating Network serving Italian Residential and School Buildings

In this paper a centralized hybrid renewable district heating system based on the exploitation of solar energy and integrated with a seasonal borehole thermal energy storage is investigated with reference to a 5-year period by means of the dynamic simulation software TRNSYS. The plant is devoted to satisfy the energy demand for heating purposes and domestic hot water (DHW) production of a small-scale district composed of six residential buildings and three schools under the climatic conditions of Naples (south of Italy). Four configurations of the solar field consisting of different combinations of solar thermal collectors (SCs) and photovoltaic/thermal panels (PVTs) are analysed upon varying both (i) the technology of SCs (flat plate or evacuated tube heat pipe) as well as (ii) the control logic of solar circuit (operation with constant or variable flow rate of heat carrier fluid). The simulation results have been compared with those associated to a conventional decentralized heating system in terms of primary energy consumption, carbon dioxide equivalent emissions and operating costs in order to assess (i) the potential energy, environmental and economic benefits as well as (ii) the impact of solar field design on the overall system performance.