Thermal Dynamic Characteristics And Thermal Resistance-Capacitance Optimization Of Building Walls

The research on the optimization of the dynamic thermal performance and resistance-capacitance distribution of building walls is a key to choosing or developing a suitable wall,which is of great significance to promoting the development of building energy conservation technology and achieving building energy conservation.The current research shows following difficulties:the dynamic thermal characteristics of walls with accumulated resistance or/and capacitance is not clear;the optimal allocation of wall thermal resistance and capacitance is challenged by the allocation ideas and optimization methods;it is urgent to reveal the optimal allocation mechanism of thermal resistance and capacitance of the wall under the boundary of the actual outdoor climate environment.In view of the above problems,this paper has carried out research on the thermal dynamic characteristics and thermal resistance-capacitance optimization of building walls.The main academic innovations and contributions include:(1)A dynamic heat transfer model of building walls has been established.The reliability of the model was verified via insulating cell experiments.Based on the principle of thermoelectric analogy,a simplified thermal network model of insulation wall was established,and the genetic algorithm was used to identify the thermal resistance and capacitance parameters of the model.An aerogel insulation panel(AIP)was prepared by the sol-gel method and atmospheric pressure drying technology.An experimental platform for dynamic heat transfer of the insulating box was established,and an experimental test of the insulating box was carried out.Compared with the test values,the maximum temperature deviations of the inner and outer surface of the box calculated by the model are 1.3 and 0.8 ~oC,respectively,which verifies the reliability of the simplified heat network model.The dynamic insulation performance of different insulation boxes under the periodic outdoor boundary was further compared,and an uncertainty analysis was carried out.It was found that AIP can effectively improve the dynamic insulation performance and reduce energy consumption by about 35%.(2)For the first time,the accumulated resistance and capacitance have been proposed to optimize the dynamic thermal insulation performance of walls.Based on the simplified heat network model,the dynamic insulation characteristics of the new type AIP composite wall were predicted.The thermal storage coefficient and thermal inertia index,time-dependent temperature and heat flux,time lag and attenuation factor,dynamic resistance and energy consumption were compared and analyzed through comparisons with traditional thermal insulation walls.By analyzing the effects of different thermal insulation walls(AIP and traditional thermal insulation materials)and thermal insulation positions(interior,sandwich and exterior)on thermal resistance and capacitance allocation and dynamic thermal insulation characteristics,it was concluded that novel insulation materials show greater demand in optimizing their insulation positions in the wall.The effects of different accumulated levels(0.32,0.65,and 0.97)and accumulated locations(inside,middle,outside,and sandwich)on the wall thermal resistance and capacitance allocation and dynamic insulation characteristics were compared.It was found that the thermal resistance accumulated in sandwich and capacitance accumulated in middle show better dynamic thermal insulation performance;it was proved that the more accumulated the wall,the more it is necessary to optimize its thermal resistance and capacitance allocation.Therefore,the dynamic thermal insulation characteristics of the wall with accumulated resistance and capacitance have been clarified.(3)For the first time,an optimal allocation method of wall thermal resistance and capacitance has been established.From the inverse problem of heat transfer,an optimization method combining the thermal network model and particle swarm optimization algorithm was established.The method was applied to optimize the AIP wall.The optimal allocations of thermal resistance and capacitance were 2:1:2 and 1:1,respectively.The optimization process of resistance and capacitance particles was analyzed.The optimal allocation mechanism of thermal resistance and capacitance was preliminary explored.After optimizations,the energyconsumption of walls was reduced by 17.3%?44.3%.The calculation time is 0.12%of thatconsumed by the traditional method,which significantly improves the calculation efficiency.The results of the optimal heat resistance and capacitance allocation are used to guide the optimal wall insulation design.Two optimized walls were designed based on the optimal allocation of resistance and capacitance,under the consumption of pure thermal resistance layer and pure thermal capacity layer.The dynamic insulation performance of the designed walls was improved by 13.6%and 14.9%,respectively.The similarity with the optimal allocation wall was as high as 96.5%and 99.8%,respectively,which was much greater than that of the traditional wall with 42.6%.Therefore,the dilemma of how to distribute the thermal resistance and capacitance of walls to minimize the energy consumption has been addressed.(4)For the first time,the regional climate mechanism of optimal thermal resistance and capacitance has been revealed.Based on the optimization method of thermal resistance and capacitance allocation,the optimal resistance and capacitance allocation of urban walls in five climatic regions of China was predicted.The optimization process and effect were analyzed.By comparing the heating,cooling and total energy consumptions in different climatic regions,the regional impact on the energy saving rate of the optimized wall was explored.A ratio of heat to cold energy consumption was introduced to assess the maximum energy saving potential of regional walls,and a linear relation between the two was established,which provided an effective method for fast predicting the energy saving potentials.A capacitance factor was introduced to quantitatively evaluate the influence of wall capacitance on the optimized energy consumption.The regional climate mechanism of the optimal resistance and capacitance allocation was analyzed,which was used to guide the optimal insulation design of walls.For the region with a low capacitance factor,the similarity between the designed walls and the optimal allocation wall were greater than 99%,whereas in the region with a high capacitance factor,it is necessary to increase the accumulated level of wall capacitance.Therefore,optimizing and designing the allocation of wall resistance and capacitance according to the regional outdoor thermal environment has been preliminarily realized.