Optimal thermo-economic control of a micro-cogeneration system in thermal load sharing approach

The cogeneration is the combined production ofelectric and/or mechanical and thermal energystarting by a single energy source; in particularin this paper the analysis will be focused on acogeneration system with electric power lowerthan 15 kW (micro-cogeneration). The paperanalyzes a system consisting of a natural gasfiredmicro-cogeneration unit (MCHP), a heatstorage and a peak boiler. The system providesthermal and electric energy to two end-users,the former is a tertiary building (office), wherethe generation system is located, and the latteris a residential building connected to the formerthrough a district heating micro-grid. In order toanalyze the influence of climatic conditions, twodifferent geographical locations in Italy(Benevento and Milano) are considered, that arealso characterized by different natural gas andelectricity tariffs. Particular attention is paid tothe choice of the users, in order to obtain morestable and continuous electric and thermal loads(load sharing approach) and to increase theoperating hours per year of the MCHP unit.The operation of the MCHP is governed by acontrol system, aimed to optimize a thermoeconomicobjective function. The modelsrepresenting the components, the thermoeconomicobjective function and the buildingshave been implemented in a widely usedcommercial software for building simulations(TRNSYS). The models are calibrated andvalidated through data obtained fromexperimental tests carried out in the laboratoryof the University of Sannio (Benevento). Theresults of the simulations highlight the potentialbenefits of the thermal load sharing approach. Inparticular, this study shows that a MCHP unitconnected by means of a thermal micro-grid todifferent users in “load sharing mode” can obtaina high number of operating hours as well assignificant energy (Primary Energy Saving) andenvironmental (avoided CO2 equivalentemissions) benefits with respect to anappropriate reference system, even inMediterranean areas, where the climaticconditions are not always suitable forcogeneration.