Study On The Bidirectional Cooling Mechanism And Air Conditioning Gain Of Thermoelectric Energy Systems

Dual consideration of the increasing building energy demand and deteriorating environment has raised great concerns on the sustainable energy utilization,energy conservation and emission reduction in buildings.Due to the incompatibility and contradiction between supply and demand sides of building energy consumption,there are much more people paying attention on the energy conversion processes in buildings,especially the thermoelectric conversion process.It is not only strongly related to the conversion efficiency,but also referred to the balance between thermodynamic system and indoor environment,which will further affect indoor living comfort and people's quality of life.To full fill the actual needs of more energy-efficient buildings,indoor equipment's cooling,built environment improvement and performance enhancement of cogeneration,several key scientific researches,including the thermoelectric bidirectional mechanism,thermeoelctric bidirectional characteristics of multi-energy systems,network analysis method of array thermoelectric heating and cooling systems,have been deeply conducted in the present study.The potential of thermoelectric technology on cooling-heating-power for buildings is further explored through the numerical simulation,theoretical analysis and experimental testing methods,which provides theoretical foundation and guidance for improving the thermodynamic gain of buliding energy conversion.The main research contents and results show as follows:Fristly,thermoelectric bidirectional cooling technology and its cooling mechanism were broadly presented for electronic cooling ymplement.Based on the energy and entropy generation minimization analyses,thermodynamic models of two representative thermoelectric systems were established to fully evaluate and compare their cooling performance.The effects of main influencing parameters(i.e.,thermoelectric operating current,thermal conductance in absorbed and dissipated ends and number of P-N junction)on system cooling performance were quantitatively identified in terms of equipment temperature,system efficiency and entropy generation rate.Thermoelectric bidirectional mechanism was sensitively elaborated and the transitional conditions were further conformed for this bidirectional cooling.Employing the thermoelectric bidirectional cooling experiment test,the equipment cooling characteristics of thermoelectric cooling and power generation modules are preliminarily elaborated,further verifying the accuracy and reliability of the thermoelectric bidirectional model.This research will provide theoretical foundation for performance improvement and control optimization of equipment thermal management,energy harvesting and waste heat utilization.Secondly,a thermoelectric bidirectional cooling model in the thermeoelctricphotoelectric energy system was established.Thermodynamic performance of two typical photovoltaic thermoelectric hybrid systems were further analyzed and compared from the aspects of output power,cell temperature,thermodynamic efficient,exergy destruction and exergeconomics etc.Transitional conditions of thermoelectric bidirectional cooling in this coupled system were described in detail.Bidirectional characteristics and concurrent mechanism of thermoelectric conversion in photovoltaic thermoelectric hybrid systems were clearly revealed.The energy flow,exergy flow and unit exergy cost flow of two typical photovoltaic thermoelectric hybrid systems were systematically analyzed and compared,which indicated the positive effects of different thermodynamic parameters on the system components.Following that,results of the present research are roundly contrasted with the calculation data reported in previous studies,further indicating the accuracy and reliability of the current results.Present research may be helpful for the design and optimization of the thermeoelctric-photoelectric energy system to enhance its energy conversion efficiency.Thirdly,a thermoelectric bidirectional model in the thermoelectricelectrochemical energy system was proposed.Parametric comparisons(e.g.,current density,number of thermoelectric elements,thermal loss)between the fuel cellthermoelectric cooling and the fuel cell-thermoelectric generation models were sensitively identified in terms of the decision targets,such as power output,energy efficiency,exergy efficiency and unit exergy cost.Thermoelectric operating model and corresponding transitional conditions were further determined for the hybrid system.Combined with the new irreversible evaluation indexes,performance differences between various reversible and irreversible models were deeply discussed and compared,which indicated that the performance of this hybrid system was comprehensively affected by the system components.From the viewpoint of thermodynamics,the application potential and limitation of fuel cell-thermoelectric hybrid system were presented to clearly reveal that the essence of energy conversion in the hybrid system was to reduce the irreversible destruction.In order to improve the overall efficiency of the hybrid system,the avoidable and unavoidable exergy destructions should be reduced by optimizing the system structure and operation parameters.Finally,a network analytical model of array thermoelectric ventilation system in buildings was set up on the basis of energy,entropy generation,and exergy analyses.Two analytic sub-models for parallel flow and counter flow heat exchangers are developed to describe the thermodynamic performance of the thermoelectric ventilation system.Input current of thermoelectric coolers,and quantitative numbers of thermoelectric coolers were sensitively varied to investigate their influences on cooling load,system efficiency and entropy generation rate of this system.Performance differences of each thermoelectric element in the array thermoelectric system were numerically clarified and the performance weakening mechanism with the flow direction was further revealed through this network analytical model.Subsequently,a demo case comparison between traditional thermoelectric cooling units and the existing array thermoelectric units has been analyzed in terms of operative conditions and design parameters,which could be beneficial to correct some misconceptions about multiple thermoelectric units.Employing the thermoelectric experiment test in the walk-in environmental test chamber,thermodynamic behavior of thermoelectric units is completely discussed to verify the accuracy and reliability of the thermoelectric model.In addtions,a new design concept of ventilation system based on the thermeoelctric-photoelectric energy system was proposed,and its thermodynamic performance was preliminarily studied,which provided the theoretical foundation and design guide for building cogeneration coupled thermoelectric technology.The main contributions of this dissertation are to,1)improve and understand the thermoelectric bidirectional mechanism systematically;2)develop and promote the thermoelectric bidirectional theory in the multi-energy systems;3)improve and strengthen the analytical method of array thermoelectric heating and cooling venliation systems;This research would help to enhance the application and development of thermoelectric technology in green buildings and provide a new design idea for building energy conservation and emission reduction.