Energy, environmental and economic dynamic performance assessment of different micro-cogeneration systems in a residential application

A dynamic performance assessment for a number of micro combined heat and power (MCHP) systems fuelled by natural gas, namely two different internal combustion engines and a reciprocating external combustion Stirling engine, was performed by using a simulation software. The cogeneration units were integrated with an Italian multi-family house compliant with the transmittance values of both walls and windows suggested by the Italian Law. Auxiliary thermal energy was supplied by a natural gas-fired boiler and the heat provided by both the MCHP device and the boiler was accumulated within a combined storage tank. A sensitivity analysis upon varying the hot water storage volume (0.855 m3, 0.738 m3, 0.503 m3) and the set-point temperature (55 °C and 60 °C) of the water within the tank was performed. Detailed dynamic models, developed within Annex 42 of the International Energy Agency (IEA) and calibrated on the basis of experimental results, were used for carefully predicting the performance of the cogeneration devices. The simulated performance of the proposed system were compared with those of a reference system composed of a natural gas-fired boiler (for thermal energy production) and the central grid (for electricity production) in order to assess the suitability of the cogeneration device-based system in comparison to the system based on separate energy production. The comparison was performed from energy, environmental and economic point of views according to the Italian scenario. The comparison showed that, whatever the MCHP unit is, the proposed system allows for reducing the primary energy consumption (up to 13.4%), the carbon dioxide equivalent emissions (up to 18.9%), as well as the operating costs (up to 20.9%) with respect to the conventional system. The largest savings were obtained with the tank characterized by the lowest volume coupled with the internal combustion engines in the case of 55 °C was used as set-point temperature.