A novel solar-geothermal district heating, cooling and domestic hot water system: Dynamic simulation and energy-economic analysis

In this paper a novel low temperature district heating and cooling system based on renewable energy sources is investigated by means of a dynamic simulation model and an energy-economic analysis. A novel solution consisting of geothermal, solar and biomass energy sources integration is considered. Low enthalpy geothermal well, evacuated solar collectors and auxiliary wood-chip boiler are used to supply the district heating system during the winter season. During summer, an adsorption chiller is activated in order to provide district cooling, while during all year, the system produces domestic hot water for the district users. The case study is developed for the district area of Monterusciello, near the city of Pozzuoli, in Southern Italy. For the case study under investigation, a geothermal source is available at about 55 degrees C with typical irradiance conditions of Mediterranean climate. A rehabilitation of the buildings located in the considered district area is considered. The proposed system is modelled in TRNSYS environment, where a novel and detailed control strategy is implemented in order to manage the system operation and to match the thermal energy demand of the district users. A comprehensive model of the district network and a detailed heating and cooling demand of network users are consideredin the dynamic simulation model of the system. A 1-year simulation is performed and the system performance is analyzed with daily, weekly and yearly time bases. The system analysis is completed with a sensitivity analysis, performed in order to evaluate the system energy and economic profitability as a function of the solar collector field area. The results outline that geothermal and solar energy are only used to match the thermal demand of the district users during winter, while only during summer the activation of the auxiliary biomass boiler is mandatory to match the space cooling demand. The novel system achieves a satisfactory yearly performance in terms of solar collector field efficiency (above 40%) and adsorption chiller Coefficient of Performance (0.5). The system is not economically feasible without any public funding (Simple Pay Back of 20.9 years), while a significant primary energy ratio is achieved (above 75%). In case of public funding policies, the Simple Pay Back period can be halved. (C) 2017 Published by Elsevier Ltd.