Load sharing with a local thermal network fed by a microcogenerator: Thermo-economic optimization by means of dynamic simulations

The cogeneration is the combined production of electric and/or mechanical and thermal energy startingby a single energy source; in particular in this paper the analysis will be focused on a cogenerationsystem with electric power lower than 15 kW (micro-cogeneration). The paper analyzes a system consistingof a natural gas-fired micro-cogeneration unit (MCHP), a heat storage and a peak boiler. Thesystem provides thermal and electric energy to two end-users, the former is a tertiary building (office),where the generation system is located, and the latter is a residential building connected to the formerthrough a district heating micro-grid. In order to analyze the influence of climatic conditions, twodifferent geographical locations in Italy (Benevento and Milano) are considered, that are also characterizedby different natural gas and electricity tariffs. Particular attention is paid to the choice of theusers, in order to obtain more stable and continuous electric and thermal loads (load sharing approach)and to increase the operating hours per year of the MCHP unit.The operation of the MCHP is governed by a control system, aimed to optimize a thermo-economicobjective function. The models representing the components, the thermo-economic objective functionand the buildings have been implemented in a widely used commercial software for building simulations.The models are calibrated and validated through data obtained from experimental tests carried outin the laboratory of the University of Sannio (Benevento). The results of the simulations highlight thepotential benefits of the thermal load sharing approach. In particular, this study shows that an MCHP unitconnected by means of a thermal micro-grid to different users in “load sharing mode” can obtain a highnumber of operating hours as well as significant energy (Primary Energy Saving) and environmental(avoided CO2 equivalent emissions) benefits with respect to an appropriate reference system, even inMediterranean areas, where the climatic conditions are not always suitable for cogeneration.