Optimization Design Of Phase-Change Energy Storage Radiant Cooling Terminal

The phase change energy storage radiant cooling/heating system effectively combines the advantages of energy storage technology and radiant cooling/heating technology.It can not only meet the human body’s demand for thermal comfort,but also alleviate the peak valley difference in electricity,and can use the peak valley electricity price policy to reduce operating costs.The application of phase change energy storage radiant air conditioning systems utilizing peak valley electricity prices has broad prospects.The installation position of phase change materials in the terminal of the radiant system is one of the important issues worth paying attention to in engineering design.However,there is currently a lack of research on the comparative analysis of different installation positions of phase change materials in the radiant terminal.There are three main designs for the relative positions of PCM and embedded thermal activation layer in the phase change energy storage radiant terminal in existing research,including two design schemes where the embedded pipe layer is placed adjacent to the PCM layer and the design scheme where the water supply pipe is embedded inside the PCM layer.There is a lack of comparative research on the first two different relative position design schemes,and there is no report on the comparative research of these three relative position design schemes.Whether different relative position designs will affect the heat storage capacity,application effectiveness,and energy-saving potential of the system,as well as whether there is an optimal relative position design solution,needs to be studied and solved.In addition,the heat storage and release process of the PCM in the phase change energy storage radiant terminal increases the complexity of the heat transfer process at the radiant terminal.Currently,there is a lack of clear understanding of the design of the PCM layer,the optimization of the embedded pipe parameters,and the operation parameters of the terminal.And the impact of these parameters on system performance is coupled with each other,therefore,the optimization design of the terminal is actually a problem of exploring the optimal combination of key design parameters.The optimization of design parameters should start from three aspects: improving thermal comfort,economy,and reducing system energy consumption.The optimization design problem of balancing multiple objectives needs to be comprehensively analyzed.In response to the above two issues,this article conducted the following research on the optimization design of the terminal of the phase change energy storage radiant cooling system:Firstly,in order to meet the simulation requirements of the PCM layer embedded pipe type radiant cooling terminal when using the roof,floor,and wall as radiant terminals,and to compensate for the lack of Pipe embedded PCM Layer(PEPL)simulation module in TRNSYS,this paper established a new module specifically designed to simulate the two-dimensional unsteady heat transfer process of the embedded PCM layer.And based on experiments,the accuracy of the new module was verified.The error analysis and consistency analysis results showed that the simulation results and experimental results were in good agreement,verifying the reliability of the new module.Then,based on the newly built simulation module and TRNSYSR software,the influence of different relative positions of the thermal active layer(embedded pipe layer)and PCM layer at the radiant cooling terminal on the thermal performance of the radiant terminal was studied through simulation,and the optimal relative position was explored.The design schemes with different relative positions consider two adjacent layout schemes of PCM layer and embedded pipe layer,as well as the embedded PCM layer(PEPL)design scheme.A simulation study was conducted on the thermal performance of the radiant cooling system with different relative position design schemes under two water supply conditions of 18 ℃and 14 ℃,for the roof,floor,exterior wall,and interior wall,respectively.Using indoor operating temperature,attenuation factor,and PCM effective utilization rate as evaluation indicators,the differences in radiant terminal thermal performance of three relative position design schemes were compared and analyzed.The results show that the four radiant terminal conditions of radiant roof,radiant floor,radiant inner wall,and radiant outer wall all have the best thermal performance effect when using the relative position design scheme of embedded PCM layer.The design scheme when the embedded pipe layer is located on the adjacent side of the PCM layer chamber in the inner direction can achieve similar thermal performance effects as the embedded pipe PCM layer design scheme under the types of inner wall radiant terminal or floor radiant terminal,without significant differences.Under the four types of radiant terminal,when the embedded tube layer is located on the adjacent side of the PCM layer chamber in the outer direction,the phase state of the PCM does not change,making it difficult to exert the phase change energy storage effect of the PCM.Finally,using Gen Opt and TRNSYS coupled simulation and optimization,a multi-objective optimization study was conducted on the key design parameters of the terminal of the embedded PCM layer type radiant cooling system,considering energy consumption,thermal comfort,and economy.The optimal terminal parameter combination was determined for four types of radiant terminal types: radiant roof,radiant floor,radiant inner wall,and radiant outer wall.The key design parameters consider PCM layer thickness,phase change temperature,water supply temperature,and intermittent operation time.The multi-objective optimization results indicate that whether it is a three objective optimization of PCM layer thickness,phase change temperature,and water supply temperature,or a four variable three objective optimization with additional intermittent operation time,each type of radiant terminal has its own optimal combination of terminal parameters,and the optimal value of PCM layer thickness for all four radiant terminal types is 10 mm.The conclusions obtained in this study can provide reference and suggestions for the selection of the relative position design scheme of the PCM layer and the embedded thermal active layer at the terminal of the active phase change energy storage radiant cooling system,as well as the optimization design of the terminal parameters.