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 were 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 provinces and, for each province, two small districts, one consisting of school buildings only and a second composed of residential buildings only, were analyzed. The proposed plants serving the selected buildings were 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 were also included into the solar field, thus the served buildings 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 was utilized to satisfy the cooling demands. The performance of the systems were analyzed by using the dynamic simulation software TRNSYS with reference to a 5-year period. Specific weather data files derived from experimental measurements were considered for each province in order to take into account the influence of meteorological conditions on systems’ performance. The influence of thermo-physical properties (thermal conductivity, density, specific heat) underground where the seasonal storage was installed was also taken into account according to the location based on detailed information derived from scientific datasets. The operation of the proposed plants was 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 could provide a reduction in terms of primary energy demands, equivalent CO2 global emissions and operational costs of up to 96.5%, 93.5% and 82.8%, respectively, compared to the reference systems.