A biomass-based polygeneration system for a historical building: A techno-economic and environmental analysis

Combined cooling, heating, and power systems (CCHP) are considered one of the most efficient energy systems since they have a less detrimental environmental impact, and therefore sustainable energy savings, and eventually less CO₂ emissions. An even higher advantage is possible when a renewable energy fuel source (e.g., Biomass) is used. The proposed study presents the energy modeling of a 169 kWe capacity, biomass-based CCHP system retrofitted to a historical building, located in Perugia, Italy. Two well-known simulation software's, ASPEN Plus and TRNSYS, are purposely integrated. In the first phase of the study, a wood biomass combustion-based externally fired gas turbine (EFGT) along with an Organic Rankine Cycle (ORC) system is modeled in Aspen Plus. In the later phase, a historical building “Sant’ Apollinare” model, and the remaining CCHP system are developed in TRNSYS. The transient system is modeled such that it fulfills the peak thermal energy demands of the retrofitted building. The main components of the system are a heat exchanger (HE), storage tanks (TK), a single-stage LiBr-H₂O absorption chiller (ACH), and balance of plant (BOP) components. A heat exchanger recovers heat from the gas cycle, which is then utilized for running an ORC, heating and cooling of the end-user building, biomass drying, and domestic hot water (DHW) supply. A storage tank supplies direct heat to the end-user in winter and drives the ACH in summer. The results of the model provide data on the performance parameters of different components of the CCHP system such as temperature, power consumption, and energy profiles that allow evaluating the overall energy performance of the CCHP system. Finally, a feasibility analysis of the system is carried out on the basis of economic indexes such as simple pay back (SPB) period, net present value (NPV) and profitability index (PI), for two different case scenarios assumed for fuel (e.g., biomass) supply cost. The SPB is 2.93 years, when biomass is obtained for free. Whereas, if biomass is purchased from the market the SPB becomes 7.15 years. From an environmental perspective, the plant ensures a decrease of 632 tons of CO₂ emissions annually.