Hybrid polygeneration plants with long-term thermal storages serving residential and school buildings: performance assessment based on field weather data and soil properties

Innovative hybrid renewable trigeneration systems have been analyzed while covering cooling, thermal and electric energy demands of 10 existing typical case studies of the Italian Campania region (southern Italy). This region is divided into 5 different provinces and, for each province, both a first small district consisting of school buildings only as well as a second small district composed of residential buildings only have been analyzed. The proposed plants serving the selected buildings are based on a field of flat-plate solar thermal collectors connected to a long-term borehole thermal energy storage through a short-term thermal energy storage. Photovoltaic panels connected with a lithium-ion battery are also included into the solar field, thus the served buildings are operated as “solar prosumers” (i.e., consuming and producing energy derived from the solar source). A water-silica gel adsorption unit powered by solar energy is utilized for satisfying the cooling demands. The performance of the systems have been analyzed by using the dynamic simulation software TRNSYS with reference to a 5-year period. Specific weather data files derived from experimental measurements have been considered for each province with the aim of taking into account the influence of meteorological conditions on systems’ performance. The influence of thermo-physical properties (thermal conductivity, density, specific heat) of underground where the seasonal storage is installed has also been taken into account according to the location based on detailed information derived from scientific datasets. The operation of the proposed plants has been contrasted with typical Italian cooling and heating systems (assumed as references) from energy, environmental and economic points of view. The results indicated that the proposed systems can provide a reduction in terms of primary energy demands, equivalent CO2 global emissions and operational costs up to 96.5%, 93.5% and 82.8%, respectively, with respect to the reference systems.