Research On Overall Design Of Building Cooling Heating And Power(BCHP) System With Thermal Energy Storage(TES) And Optimization Of TES Unit

With the adjustment of city energy structure, building cooling, heating and power(BCHP) system, fired by nature gas and characterized by cascading utilization ofprimary energy, is a promising building energy supply technology for its high efficiency,low pollution emission, reliability and flexibility. However, the mismatch of energysupply and fluctuating building load leads to low-efficiency operation in partial loadcondition and poor recovery of waste heat，which deteriorate the systems performance.The incorporation of BCHP systems with thermal energy storage (TES), forming theBCHP-TES system, is an effective way to improve system performance for meetingvariant building loads. That brings to two main questions. Firstly, how to design theBCHP-TES system based on yearly load, including the energy-saving feasibility,optimal operation cycle period of TES, preference of different location of TES andoptimization of TES in the BCHP-TES system. Those issues are important, but remainunsovled in study.Firstly, the building load characteristics is summarized to get relation of theprimary energy saving ratio (PESR) and period load, then the energy-saving range isgotten. Then, comparison of thermal performance of BCHP systems with TES indifferent locations is conducted, and it turns out that both BCHP-TES scheme canreduce the power generation unit (PGU) capacity, while the downstream TES schemecan reducing the absorption chiller (ABC) or heat pump (AHP) capacity, and thepreference of TES location depends on the load fluctuation degree and heat transfer areainvestment. For a given system, the operation cycle period of TES has opposite effecton the capacity requirement of PGU and TES, therefore the optimal cycle period of TESshould be determined by balancing the investment of different components.The heat exchangers network with TES (HX-TES) is summarized fromBCHP-TES system, and the objective of minimizing the primary energy consumption(PES) is converted to maximizing the energy conversion efficiency. The concept ofthermal energy storage perfectiveness (TESP) is defined in the view of energy loss toevaluate the TES unit performance. Based on the classical optimization problems inHX-TES, the equivalence of traditional optimization method and the entrancy dissipation optimization method is validated. The classical thermodynamics indexesturn out not to be suitable to evaluate the TES in HX-TES. For the liquid sensiblethermal energy storage (LSTES) application in HX-TES, the design parameters isoptimized under different work conditions and the results are helpful to guide theLSTES design.For the latent thermal energy storage (LTES) with single PCM, the analyticalsolution of optimal phase change temperature Tm,optis gotten without operationconstraints, and numerical solution is gotten with operation constraints, which is moresuitable for real operation cases. The LTES with PCMs is introduced to HX-TES toimprove the TESP, the optimal design parameters including Tm,optand thermal capacityflow are gotten for classical application in BCHP-TES system, and the mechanism isanalyzed.