Research Of The Thermal Charastic Of Thermally Activated Wall Using Low Grade Energy

Thermally activated wall is an attempt based on the idea of using low-grade energy and achieving dynamic adjustment of the envelope structure parameters.Thermally activated wall focuses on the change of the conventional wall structure rather than the thermal insulation layer to achieve the equivalent and adjustable effect of its insulation performance.The thermally activated wall has a variety of working states.Therefore,the division and determination of the working state of the thermally activated wall,the influencing factors of the thermal characteristics of the thermally activated wall,the correspondence between the thermally activated wall and the conventional thermal insulation wall,and the energy-saving effect of the thermally activated wall are all problems that we need to discuss and solve.In this paper,firstly,the working state of the thermally activated wall is divided into heating state,equilibrium state,equivalent insulation state and invalid state according to the basic theory of heat transfer in the structural layer of the wall and the effect of the thermally activated layer.According to the thermal characteristics under each working state,a method to determine the working state of thermally activated walls is given.Secondly,through the CFD numerical simulation,this paper studies the influencing factors that influence the thermal characteristics of the thermally activated wall by three aspects: the inlet water temperature of the capillary,the inlet water flow velocity,and the position of the thermally activated layer.In addition,by analyzing the problems existing in the building envelope structure in the rural areas of northern China,this paper proposes three renovation schemes for the external walls of rural buildings.Through CFD numerical simulation,the heat transfer characteristics and insulation performance of the walls in each scheme are analyzed and compared.The correspondence between the thermally activated wall and the conventional insulation wall is established through the analysis of the simulation result.Finally,by selecting reasonable energy-saving evaluation indexes,the energy-saving potential of using thermally activated walls in rural areas is analyzed.The results show that the thermal characteristics of the thermally activated wall are mainly affected by the inlet water temperature of the capillary and the position of the thermally activated layer,while the inlet water flow velocity has little effect on the thermal characteristics of the thermally activated wall.Under winter conditions,with the increase of the capillary inlet water temperature,the wall internal surface temperature of the wall gradually increases,the heat flux of the wall internal surface gradually decreases,and the thermally activated wall is converted from the invalid state to the equivalent thermal insulation state,then to the equilibrium state and finally to the heating state.As the thermally activated layer changes from inside to outside,the invalid water temperature of the wall decreases and the ideal water temperature increases.With the same capillary inlet water temperature and flow velocity,the temperature of the inner surface of the wall gradually decreases and the heating capacity of the wall gradually decreases.But the water temperature range with which the wall is in equivalent insulation state increases.In addition,a comparison study of three exterior wall reconstruction schemes in rural areas in northern China shows that transforming 240 walls without insulation into thermally activated walls can significantly increase and stabilize the surface temperature of the walls and as well as reduce and stabilize the heat flux of the wall internal surface,which achieves better thermal insulation effect and adjustment ability.Through the analysis of the wall structure and simulation result,the corresponding relationship between the thermally activated wall and the conventional thermal insulation wall are given.Finally,the analysis of the energy-saving effects of the three schemes shows that,by transforming the 240 wall without insulation into thermally activated walls,the hourly load reduction rate and the hourly electricity saving rate of the building external wall remain above 55% and 58% during the simulation period.