Research On Optimization Of Regional Building Distributed Energy System And Performance Improvement Technology Of Key Equipment

With the increasingly prominent problems of energy shortage and environmental pollution,improving the proportion of renewable energy in building energy supply and energy utilization efficiency to ensure the sustainability of the energy system is an important part of the current energy structure transition.Community energy system planning takes into account the local resource conditions and actual situation of the user side,which is the premise of the sustainable development of the energy system.Distributed combined cooling,heating,and power(CCHP)system has gained a growing concern owing to its advantages in energy cascade utilization and easy to realize the synergistic complementarity between the renewable energy and fossil energy.Phase change thermal storage technology can realize energy storage and utilization through the latent heat of the phase change material(PCM),and can effectively alleviate the mismatch between supply and demand of the energy system.Based on three different objects of community,building and equipment,this paper focuses on community energy system planning,performance analysis of building CCHP system and performance improvement technology of phase change thermal storage heat exchanger.The details are as follows:(1)Based on the theory of multi-attribute integrated evaluation and decision making,this paper discussed the establishment of appraisal indexes,optimal combination weight model and integrated evaluation decision model during the multiattribute integrated evaluation of community energy system planning.The proposed multi-attribute integrated evaluation model was applied to the comparison among the four energy supply schemes for a university campus in Tianjin.The optimal energy supply scheme was obtained with priority to different attributes and integrated evaluation.(2)Based on the principle of synergistic complementarity of the renewable energy and fossil energy,a CCHP system based on dual-fuel of natural gas and biomass was proposed.The exergy analysis method and the structure theory of thermoeconomics based on energy level were employed to analyze the performance of exergy and exergoeconomic of the CCHP system.The exergy efficiency,the proportion of exergy loss and the production performance of each component in the CCHP system as well as the unit exergoeconomic cost of the CCHP system products were obtained.The rationality of the cost allocation method based on energy level was verified by comparing with the traditional cost allocation method.Moreover,sensitivity analysis has been conducted to reveal the impact of the fuel price and some non-energy parameters on the unit exergoeconomic cost of the CCHP system products.(3)An experimental system for testing the heat storage-release performance of a triplex-tube phase change thermal storage heat exchanger unit was built.The influence of inlet temperature and flow rate of the heat transfer fluid(HTF)as well as heating mode on the melting performance of the thermal storage unit was experimentally studied.The different roles of conduction and natural convection in different stages of melting process as well as melting and solidification process were revealed.(4)An optimal selection model of PCM based on the theory of multi-attribute integrated evaluation and decision making was established.The optimization process of the PCM alternatives was performed for the purpose of the waste heat storage of jacket water in the CCHP system based on the proposed model.(5)The triplex-tube phase change thermal storage heat exchanger unit was numerically simulated based on the theory of numerical heat transfer.The governing equation of the thermal storage unit was established by the enthalpy method,then discretized by the finite volume method(FVM).The numerical calculations were carried out in a developed Fortran code.The influence of the HTF operation parameters and structure parameters of the thermal storage unit on the melting performance was analyzed based on the exergy efficiency and heat storage rate,which provided a theoretical basis for the optimal design and rational operation of the thermal storage unit.