A Study On The Thermal Characteristics Of External Exhaust Air Insulation Wall

Energy conservation in building envelopes is one of the most promising ways to save energy in buildings.Exhaust Air Insulation Wall(EAIW)is a novel energy-saving wall that combines air conditioning exhaust system with building envelopes.By allowing exhaust air to permeate through the porous material installed in the wall,EAIW can reduce the interior surface temperature of the wall and recover the low-grade energy of exhaust air.The preliminary studies of our research group show that the heat insulation performance of EAIW is superior,and its thermal performance is greatly improved compared with the conventional wall.In this paper,an improved configuration,External Exhaust Air Insulation Wall(Ex-EAIW),is discussed considering the engineering practice.The key of the structure is that the porous material and the external panel make up a prefabricated module which can be placed on the outer side of the foundation wall,so that it does not affect the decoration of the indoor environment,and it provides excellent insulation at the same time.Ex-EAIW is easier to be implemented and popularized.However,the thermal characteristics of this structure have yet to be revealed.Especially it is not yet clear that the difference between Ex-EAIW and other types of insulation wall in terms of the load characteristics under intermittent air conditioning.Therefore,the Exhaust Air Insulation Wall is investigated in this paper and the main works are as follows:Firstly,in view of the consistency of the core mechanism between dynamic insulation wall and exhaust air insulation wall,this paper has carried out extensive literature research on dynamic insulation technology,summarizing the structure,classification and working principle,the development history and research methods.The relationship between dynamic insulation wall and exhaust air insulation wall are demonstrated.The study indicates that the exhaust air insulation wall and the dynamic insulation wall are both potential building energy-saving technologies.Secondly,a two-dimensional unsteady heat transfer mathematical model of the ExEAIW is established in this paper.The model includes heat transfer equations for the foundation wall,the porous material,the outer panel,and the two exhaust cavities.Taking the outdoor meteorological parameters of the typical summer design day as the temperature boundary conditions,the finite difference method is used to numerically solve the model,and the temperature change of the inner and outer surfaces of the wall can be obtained 24 hours a day.At the same time,build an experimental platform and use the measured data to verify the established model to ensure the accuracy and reliability of the mathematical model.Then,based on the verified mathematical model,the thermal characteristics of ExEAIW are simulated.The inner surface temperature,heat transfer coefficient,decrement factor and time lag were used as four indexes to evaluate the performance of Ex-EAIW and conventional walls.At the same time,in order to optimize the design of the wall,this paper continues to analyze the sensibility and significance of the parameters affecting the wall performance,and quantitatively analyze the influence degree and priority of each parameter.Finally,in view of the wall load characteristics under intermittent conditions,this paper obtains the starting load and the full-day cumulative load of different types of walls,different facing walls and different climatic zones by simulation,and evaluates the external venting heat insulation.The possibility of applying the wall in different environments.Among them,the four possible application forms of the exhaust heat insulation wall are compared in this paper,and the research results can provide theoretical guidance for the engineering application of the exhaust heat insulation wall.Results show that the exhaust air insulation wall studied by our research group is the first time that the dynamic insulation mechanism is applied to China,and it has superior thermal insulation performance.Compared with the ordinary 24 brick wall and external thermal insulation brick wall,the Ex-EAIW has lower interior surface temperature,smaller heat transfer coefficient and smaller decrement factor.In the severe cold zone,cold zone,hot summer and cold winter zone and hot summer and warm winter zone,the use of external exhaust heat insulation walls instead of ordinary brick walls can reduce the full-day cumulative load by 77%,71%,64% and 67% respectively.