Dynamic performance assessment of a residential building-integrated cogeneration system under different boundary conditions. Part II: Environmental and economic analyses

This work examines the performance of a residential building-integrated micro-cogeneration system during the winter by means of a whole building simulation software. The cogeneration unit was coupled with a multi-family house composed of three floors, compliant with the transmittance values of both walls and windows suggested by the Italian Law; a stratified combined tank for both heating purposes and domestic hot water production was also used for storing heat. Simulations were performed considering the transient nature of the building and occupant driven loads as well as the part-load characteristics of the cogeneration unit. This system was described in detail and analyzed from an energy point of view in the companion paper. In this paper the simulation results were evaluated in terms of both carbon dioxide equivalent emissions and operating costs; detailed analyses were performed in order to estimate the influence of the most significant boundary conditions on both environmental and economic performance of the proposed system: in particular, three volumes of the hot water storage, four climatic zones corresponding to four Italian cities, two electric demand profiles, as well as two control strategies micro-cogeneration unit were considered. The assessment of environmental impact was performed by using the standard emission factors approach, neglecting the effects of local pollutants. The operating costs due to both natural gas and electric energy consumption were evaluated in detail, whereas both the capital and maintenance costs were neglected; the revenue from selling the electric energy surplus was also taken into account. The performance of the proposed system was also compared with those of a conventional system composed of a natural gas-fired boiler (for thermal energy production) and a power plant mix connected to the national central grid (for electricity production) in order to assess its suitability in comparison to the systems based on separate energy production from both environmental and economic point of views. The analyses were carried out with respect to the Italian scenario, by considering the most meaningful indexes suggested in current literature.