Integration Analysis And Multi-objective Optimization Research On Fuel Cell Based Micro-combined Cooling Heating And Power System

Building heating and cooling system is the main source of building energy consumption.There are two shortcomings of traditional building heating and cooling system:on one hand,the traditional systems are driven by electricity which powered by coal-fired power plant and transmitted by power grid with low primary energy ratio and huge energy loss and waste;on the other hand,the pollution gas emitted during the fossil fuel burning progress causes serious environmental damage,harms people living health.On the aims of overcoming the disadvantages of traditional heating and cooling system,developing renewable energy based heating cooling and power system(CCHP),improving system energy efficiency and reducing environment pollution with high generating efficiency mover and cascade energy utilization are the effective ways of enhancing building energy conservation and emission reduction.The purpose of this research is to propose a fuel cell based micro-CCHP system in the virtues of high generating efficiency,low pollution and noise of fuel cell and cascade energy utilization feature of CCHP system.The effect rules between fuel cell operation parameters and thermodynamic behaviors are obtained using thermodynamic analysis and simulation method.Furthermore,aiming at improving the energy efficiency of CCHP system,the solar energy is introduced as a auxiliary thermal source in the coupling system,and the advantage on high energy efficiency of coupling system is explored providing a new idea in the efficiency optimization of CCHP system.The CCHP system is evaluated using synthesis assessment method depicting the benefits of the proposed system on thermodynamic,economic and environmental performance.An evolutionary algorithm is applied as the optimization tool to optimize various performances of CCHP system offering new method in combined system optimization research.The main research details and results are as follows:Firstly,the thermodynamic behavior of the proposed CCHP system and the coupling relationship of internal components are analyzed.In the summer and winter modes,the effects of main operation parameters(inlet gas temperature and pressure,operation temperature,current density)on CCHP system energy efficiency are discussed using parameter analysis method.The results show that relative low inlet gas and operation temperature,relative high current density and proper inlet gas pressure are benefit to the improvement of CCHP system efficiency which can reach 70%and 80%above during summer and winter respectively.As the thermal source of absorption chiller,the current density and operation temperature are the key parameters affecting the coupling relation of fuel cell and chiller,and the results indicate that the cooling capacity increases with the raise of current density monotonously,fluctuates with the increase of operation temperature and chiller COP raises in accordance with operation temperature.Secondly,a coupling CCHP system model based on Proton Exchange Membrane Fuel Cell(PEMFC)and Parabolic Trough Solar Collector(PTSC)is presented,and its performances on thermodynamics,economy and environment are evaluated.The mapping relations of operation parameters and performances of PEMFC stack,PTSC and CCHP system are discussed.The results show that energy efficiency of coupling system is 10%higher than PEMFC based micro-CCHP,and low operation temperature,high current density and solar radiation are in favor of coupling system efficiency.The coupling system efficiency can reach relative high value at low solar radiation.The economic assessment result shows the coupling system is available financially.Comparing with the coal-fired power plant,the coupling CCHP system has tremendous advantage in reducing pollutant emission,and low operation temperature,high current density and solar radiation are helpful to enhance system environment performance.Thirdly,a Multi-objective Evolutionary Algorithm Based on Decomposition(MOEA-D)is applied in the fuel cell optimization.In this study,fuel cell system is the prime mover of CCHP,its energy efficiency and output electric power are the vital factors influencing the thermodynamic performance of CCHP system,thus optimizing fuel cell thermal performance is a effective way of improving CCHP thermodynamic performance.In this research,on the virtue of MOEA-D's reaching capacity and computation efficiency,the fuel cell operating parameters are optimized and Pareto optimal curve is obtained in which Final Optimal Result is selected using decision-making method.The optimized PEMFC system has significant enhancement on efficiency and electric power,especially on electric power improvement.At Final Optimal Point,both of the efficiency and electric power come near maximum values.Finally,parameter analysis and synthesis evaluation including thermodynamic performance,economic cost and environment effect of PEMFC based CCHP system are performed.Moreover,the CCHP system is optimized using Non-dominated Sorting Genetic Algorithm-?(NSGA-?)and MOEA-D,respectively.The results indicate that high current density is able to improve Green House Gas(GHG)reduction in spite of causing cost increase and exergy efficiency drop;Low operation temperature and high inlet gas relative humidity is helpful to elevate exergy efficiency and GHG emission reduction;Increasing anode inlet gas pressure can improve system thermodynamic performance and GHG emission reduction;When the pressure climes over 2 atm,the improvement reach saturation;Elevating cathode inlet gas pressure has less contribution on the improvement of system exergy efficiency,however can increase energy efficiency and GHG emission reduction.Comparing the optimization results using NSGA-? and MOEA-D respectively,it can be found that NSGA-? has better performance than MOEA-D at population distribution,however,each has its advantages on various evaluation indexes optimizations.The thermodynamic and environmental performances of optimized CCHP system are improved in spite of the 18.76%cost increase per year.The fuel cell based micro-CCHP system presented in this research is able to solve low energy efficiency and air pollution caused by fossil energy combustion of traditional building heating and cooling source.The assessment results of system performances show the advantage and feasibility of the CCHP system on thermodynamics,economy and environment providing new idea on building energy conservation and emission reduction.Furthermore,the CCHP system is optimized by MOEA-D method,the optimal operation parameter set is obtained offering new method in the similar energy system optimization research.