Numerical optimization and economic analysis in the design of a micro-CHP system with a Stirling engine and a solar collector

The micro-CHP systems are a promising technology for improving the energy efficiency of small energy conversion units, located near the end user. The combined heat and power production allows the optimal use of the primary energy sources and significant reductions in carbon emissions. Its use, still incipient, has a great potential for applications in the residential sector. This study aims to develop a methodology for the thermal-economic optimization of micro cogeneration units using Stirling cycle engine as prime mover and concentrated solar energy as the heat source. A detailed thermodynamic study was carried out to define the model for the physical characterization of the Stirling engine. The study of the physical model includes three types of analysis: ideal isothermal, ideal adiabatic and non-ideal adiabatic analyses. The latter includes limitations in the heat transfer processes and losses due pumping effects. These analyses were performed through numerical simulations by eveloping a code in MatLab® programming language, based on the model developed by Urieli and Berchowitz. The mathematical modelling was modified, improved and adapted to adjust the configuration of the Stirling engine for cogeneration applications. Subsequently to its implementation, several sensitivity analyses on the operational and geometric parameters were conducted in order to understand which of them have the highest relevance in the Stirling engine performance. The definition of these criteria is crucial in the choice of the decision variables for the thermal-economic optimization model. After characterizing the physical model, a purchase cost equation representative of each system component was defined: a cost equation for each one of the heat exchangers (i.e. heater, regenerator and cooler) and a cost equation representative of the engine bulk. Each cost equation is based on physical parameters, taking into account the sizing of the system. Through data collected from market available Stirling systems, the most appropriate cost coefficients were defined and the cost equations were validated. fter the validation of both physical and economic models, the thermal-economic optimization was formulated. The maximization of the annual worth from the system operation was defined as the objective function, subjected to a set of nonlinear thermodynamic and economic constraints in order to give significance to the numerical results. The model was formulated considering a cost/benefit approach, where the terms of the objective function represent a balance between costs and revenues. The decision variables correspond to geometric and operational parameters with the highest relevance in the system operation. The Pattern Search algorithm was implemented to achieve the numerical solution, using different search methods, i.e., the Nelder-Mead and genetic algorithm method. The optimization model was effective in the determination of the optimal solution and a positive annual worth was obtained for the defined input simulation conditions. The thermal-economic model yielded the combination of decision variables that defines the best configuration for maximum economic benefit. Through the economic assessment of the best solution obtained for the micro-CHP system, and considering the costs for installing a solar concentrator collector, it can be that such a system is economically attractive, with a payback period of approximately 9 years.

Name thesis:degree_name

Tese de doutoramento do Programa Doutoral em Engenharia Industrial e de Sistemas

Year dc:date.issued

2014

Author dc:creator

• Ferreira, Ana C. M.

Advisors dc:contributor.advisor

• Teixeira, S. F. C. F.
• Martins, Luís Barreiros
• Nunes, Manuel L.

Statement dc:rights

• openAccess

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/1822/35744

OAI record oai:identifier

http://repositorium.sdum.uminho.pt/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Arepositorium.uminho.pt%3A1822%2F35744