Study On The Thermal Characteristics Of The Pipe-encapsulated Phase Change Material Wall System With The Self-activated Heat Transfer

The phase change material(PCM)wall is an energy-saving enclosure using PCM to achieve the heat insulation in buildings.It is an important means to realize low-energy buildings,zero-energy buildings,and low-carbon buildings.However,for the hot summer,the PCM often cannot perform effective heat removal and regeneration in the night-time.The energy efficiency of the PCM wall is limited.To improve the energy-saving potential of the PCM wall system in the cooling season,this dissertation firstly proposes a new pipe-encapsulated PCM wall system with the self-activated heat transfer.The wall system is an integrated system with pipe-encapsulated PCM wall,nocturnal sky radiative cooler and gravity heat pipe system.During the day,the pipe-encapsulated PCM inside the wall absorbs the heat from the outdoor and stored it,which reduces the heat from outdoor into the room.At night,the heat inside the PCM wall can be automatically removed by the nocturnal sky radiative cooler through the effect of the gravity heat pipe.The regeneration efficiency of PCM can be increased,and the building energy comsumption can been reduced.To investigate the thermal characteristics and energy-saving potential of the pipe-encapsulated PCM wall system with self-activated heat transfer,the main contents of this dissertation are as follows:Based on lumped parameter method,simplified RC models with variable heat capacities and variable thermal resistances are proposed for the pipe-encapsulated PCM.The parameter identification process and method are also given.Among these simplified models,the single-node simplified model(2R1C),the two-nodes simplified model(4R2C)and three-nodes simplified model(6R3C)are analyzed.The 4R2C model and 6R3C model can quickly predict the dynamic heat transfer characteristics of the pipe-encapsulated PCM.Compared with the traditional numerical model,the computational efficiency of the simplified model can be increased by 99%.In addition,an experimental test platform for the thermal characteristics of the pipe-encapsulated PCM is built.These simplified PCM models are verified by the experimental results.The RSME of the temperature predicted by the 4R2C model and the 6R3C model was less than 0.5?.The average error of heat flow is 12%.It shows good reliability for the simplified PCM model.The coupled model integrated with the pipe-encapsulated PCM wall model,the nocturnal sky radiation model and the gravity heat pipe model is developed.It can be used to calculate the dynamic thermal characteristics of the pipe-encapsulated PCM wall system.Furthermore,the experimental platform of the wall system is built to test the thermal characteristics,and the accuracy of the system coupled model is experimentally verified.Results show that the temperature and heat flow simulated by the system coupled model are in good agreement with the experimental results.The RMSE of the wall surface temperature is less than 0.7?.The RMSE of the surface heat flow is 10W/m~2,and the relative error of the cumulative heat flow of the wall surface is less than 10%.It shows the high accuracy for the system coupled model.A simulation platform of a typical room with the pipe-encapsulated PCM wall system is established.Based on this platform,the thermal performance and energy consumption characteristics of the wall system under the dynamic boundary can be predicted.The simulation results show that,compared with the ordinary wall,the pipe-encapsulated PCM wall system can effectively reduce the internal surface temperature and heat flow of the wall.In Wuhan city,the cumulative heat flow of the internal surface of the pipe-encapsulated PCM wall during the cold season can be reduced by 53.0%.The required cooling capacity of the room can be reduced by 16.2%.The energy-saving potential is good.In addition,compared with the ordinary PCM wall,the pipe-encapsulated PCM wall system can effectively improve the utilization efficiency of the PCM due to the nocturnal heat removal through the sky radiative cooler.Furthermore,the thermal characteristics of the pipe-encapsulated PCM wall with nocturnal sky radiative cooler with the different parameters such as the phase change temperature,the spacing of the pipe,the area of the radiative cooler and the wall orientation are simulated.The influences of these parameters on the system thermal performance and energy saving potential of the wall system are analyzed.Besides,the pipe-encapsulated PCM wall with nocturnal sky radiative cooler in different climate region are also studied.The works and results in this dissertation have the reference significance for the application of the pipe-encapsulated PCM wall with the self-activated heat transfer by using the nocturnal sky radiative cooler.