Thermoeconomic and environmental synthesis and optimization of polygeneration systems supported with renewable energies and thermal energy storage applied to the residential-commercial sector

Resumen

Residential-commercial sector buildings are responsible for a significant share of the world energy consumption and yet there is a largely untapped potential for energy savings. Advanced energy systems, such as polygeneration systems (in which two or more energy services are produced from a common energy resource) assisted with on-site renewable energy sources (RES) and thermal energy storage (TES), are regarded as key alternatives to supply the buildings’ energy demands efficiently and in a way that promotes higher economic savings and reduced environmental impacts. However, determining the best configuration and operational strategy of polygeneration systems is a complex task owing to the multiple technology options available and their feasible interrelations, and the dynamic operating conditions of buildings and their surroundings (e.g. variable energy demands, climatic conditions, energy and equipment prices, CO2 emission factors). Once the system configuration and operational planning are established, the additional issue remains of the appropriate way to allocate the costs of the energy resources consumed to the final products obtained. In this context, the overall aim of this thesis is to develop methodologies for the synthesis and optimization of polygeneration systems in residential-commercial buildings that capture their dynamic behavior and local-based constraints, thereby addressing several research gaps: multi-objective optimization models with balanced objective functions; accurate representation of dynamic operating conditions; realistic representation of the thermal requirements of the energy supply and demand in the superstructure; and rational cost allocation approaches for an equitable share of costs among the final consumers. As a conceptual approach, simple trigeneration systems are first analyzed, outlining the potential benefits and the challenges involved in incorporating different types of technologies. Also, the thermoeconomic analysis of a simple trigeneration system with TES is carried out, seeking clarity of the concepts and explaining the role of the TES in achieving the optimal economic cost solution. More complex polygeneration systems are then proposed for two case studies, one consisting of a multi-family building in Zaragoza (Spain) and the other consisting of a university hospital in Campinas (Brazil). A multi-objective optimization procedure is developed, in which mixed integer linear programming (MILP) models are developed to determine the optimal system configuration (based on real commercially available equipment) and multi-period operational planning from the economic (total annual cost) and environmental (total annual CO2 emissions) viewpoints. The technical, economic, and environmental feasibility of renewable-based polygeneration systems in Brazil is assessed with a careful representation of the Brazilian electricity sector regulations. This thesis’ main contributions to the synthesis and operation optimization subject include the development of the MILP models with a view to ensuring the same level of detail, flexibility, and a more realistic representation of the thermal integration. Regarding the thermoeconomic analysis subject, this thesis contributed by proposing cost allocation approaches for the incorporation of TES units, free RES, components with different products for different operation modes, and joint production of energy services in dynamic energy systems.