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Life Cycle Analysis as a methodological tool for the optimization of solar collectors with special design

Arnaoutakis Nektarios

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Summary

LCA methodology studies the environmental impacts throughout the life cycle of a product or system: raw material processing, manufacturing, life time operation and final disposal. In this Phd dissertation, LCA is used as a reference point for the optimal design of special type solar thermal systems: systems with an integrated collector storage (ICS).Initially applications of LCA methodology in solar heating systems are presented and information about the technical design of conventional solar thermal systems are provided. The types of solar collectors used are described, from the simplest to the most complex – i.e. Compound Parabolic Concentrators (CPCs). Two types of ICS systems are mentioned: a) system with an asymmetric CPC reflector and a double wall tank and b) system with a symmetric CPC reflector and two water storage tanks. These systems were the "prototypes" for proposing design solutions and proposals aimed at producing new ICS systems with improved performance as well as "more economical" and with an improved environmental footprint throughout their entire operational life cycle.Mathematical optimization was applied in order to simulate the design parameters, i.e. creation of mathematical parametric models of performance and cost. Therefore, more than one objective function was used (Nonlinear Multi-Objective Optimization Problem).In the first stage of the study, the LCA methodology was applied to a commercial type ICS system of the Greek market. In this way, information about ICS systems were deployed and then used in the optimal design process to "approach" parameters of standard ICS systems for which it was very difficult to find real data (e.g. the production cost).In the next stage, a Multi-Objective optimization was applied to the new ICS systems, creating the equations and the objective functions of energy efficiency (mean daily efficiency and thermal loss coefficient) and production cost. In this stage, a combination of existing literature and mathematical operations was made to create the design equations of the new ICS systems. A mathematical algorithm was created to evaluate the optimal geometry of the parabolic CPC reflectors as well as the number of ICS units which will be installed in buildings for hot water production, which based on an original algorithm for nonlinear optimization of a single objective function. The energy performance curves of the designed by the algorithm systems were compared with the corresponding energy performance curves of original models and a conventional type solar thermal system (Flat Plate Thermosiphonic Unit: FPTU). The next step was the development of a prototype way to design the parabolic surface in a CAD environment, for use in CNC (Computerized Numerical Control) machines for the manufacturing of parabolic CPC reflectors. Finally, the other parts of the ICS systems were designed using a prototype mathematical technique for calculating their dimensions, based on original models.In the final stage of the dissertation, the energy, environmental and economic study of the new ICS devices compared to the respective prototypes as well as with the FPTU unit, was made to demonstrate the improvements in the performance of the algorithmically designed versus the original models. The study indicates that the new ICS systems approach the performance of conventional devices at a much lower cost, so might serve as an advisor for the design and selection of improved ICS devices, which will be installed in buildings for domestic applications.

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