Performance of Different Back-up Technologies for Micro-Scale Solar Hybrid District Heating Systems with Long-term Thermal Energy Storage

In this paper the performance of a solar heating network devoted to satisfying the heating demand of a micro-scale district composed of 6 typical single-family houses and 3 typical schools under the climatic conditions of Naples (south of Italy) is investigated by means of the dynamic simulation software TRNSYS over a 5-year period. The proposed system is composed of a solar collectors array, a short-term thermal energy storage, a long-term double U-pipe vertical borehole thermal energy storage and a heat distribution network. Three different technologies are investigated as back-up devices to be included in the district heating system: (i) a natural gas-fired boiler, (ii) a vapor-compression electric heat pump and (iii) a natural gas-fuelled internal combustion engine-based micro-cogeneration unit. The simulation results are compared with those associated to a conventional heating system in terms of primary energy consumption, operating costs as well as simple pay-back period in order to identify the best option in terms of back-up system and assess the potential energy and economic benefits associated to each technology.