Thermoeconomic and environmental analyses for the synthesis of polygeneration systems in the residential-commercial sector

Resumen

The residential-commercial sector, mainly constituted of buildings, represents one of the dominant energy consuming sectors in industrialized societies. For this reason, the energy needs of buildings (electricity, domestic hot water, thermal loads of heating and cooling) should be met in an efficient way by advanced systems, such as trigeneration systems. This thesis developed methodologies and procedures of analysis, synthesis, and design of trigeneration systems for the specific case of the residential-commercial sector. Such methodologies included the investigation of rational criteria for cost allocation in multiproduct complex systems submitted to energy market prices and variable energy demands. Energy demands vary seasonally as well as throughout the day, leading to several optimal operation conditions that combine the possibilities of purchasing or selling electricity and/or wasting the excess of cogenerated heat. An explicit incorporation of environmental considerations in the analysis was also carried out, which required the development of new thermoeconomic analysis procedures. Initially, this thesis considered simple trigeneration systems, seeking clarity of concepts. Allocation proposals were made for these simple systems, considering the apportionment of economic costs and environmental loads. Then more realistic and complex trigeneration systems were considered as the focus shifted to the specific case of a medium size hospital located in Zaragoza, Spain. A Mixed Integer Linear Programming model (MILP) was developed, which incorporated technical data from commercially available equipment and local economic/environmental conditions to determine the optimal configuration and operation modes for the energy supply systems throughout an entire representative year. Optimal solutions were obtained from economic (minimization of annual cost) and environmental (minimization of annual CO2 emissions and Eco-indicator 99 points) viewpoints. A multiobjective optimization addressed conflictive objective functions and transferred the judgment on the trade-offs involved to the decision maker. Lastly, several sensitivity analyses were carried out to evaluate the effects of the most volatile parameters on the configuration and operation of complex trigeneration systems. Overall, this thesis provided a fresh approach to the rational and efficient design and use of polygeneration systems in the residential-commercial sector.