Study On Thermal Stability Of Assembled Wall With Heat Storage Components In Summer

With the development of China's construction industry and urbanization,new building technologies,such as assembly low-energy buildings,have become an important direction for the development of new industrialization and green development of the construction industry in the future.The basic characteristics of assembled low-energy buildings are lightweight materials,which are convenient for prefabrication,transportation and field assembly of components.But at the same time,it will reduce the thermal stability of buildings,increase the fluctuation range and speed of room temperature,which is in contradiction with the thermal comfort requirements of buildings.In order to improve the thermal stability of lightweight assembling envelope structure,based on the theory of thermal wave penetration depth,this paper puts forward an assembling exterior wall structure with thermal storage layer,and establishes a calculation method of thermal storage layer thickness.For the cold areas and hot and cold areas in summer and winter,the thermal stability of assembling exterior wall with thermal storage components in summer is verified by numerical simulation method.The effects of outdoor temperature and solar radiation on indoor thermal environment and energy consumption of air conditioning were studied,and the compensation effect of thermal insulation layer and thermal storage layer on thermal stability of the wall was analyzed.Firstly,the unsteady heat transfer process of the exterior wall under the action of outdoor heat wave is analyzed theoretically;aiming at the inconsistency of the evaluation parameters of the thermal insulation performance of opaque envelope structure in the current domestic and foreign research,the evaluation parameters of the thermal insulation performance of opaque envelope structure in the current relevant codes of China,Russia and the European Union are compared and analyzed,according to the climatic characteristics of China.In order to meet the requirement of building thermal stability in summer,the attenuation multiple,delay time based on harmonic analysis method and the temperature limit of exterior wall interior surface adopted by current relevant codes in China are selected as the evaluation indexes of the thermal stability of exterior wall in summer in this study.Secondly,the theory of violent fluctuation layer based on harmonic analysis and the theory of periodic thermal penetration depth based on transfer function method are unified into the theory of thermal wave penetration depth.Based on the theory of thermal wavepenetration depth,an assembled exterior wall structure with thermal storage components is proposed.The main feature of this structure is to set up an independent heavy thermal storage layer inside the exterior wall,break through the limitation of traditional structural layer considering thermal storage function,and make the structural layer and thermal storage layer select corresponding building materials according to their respective functions,so as to meet the requirements of lightening and thermal stability of the assembled building at the same time.According to the theory of heat wave penetration depth,a method for calculating the thickness of thermal reservoir is established.This method is simple and convenient,and is suitable for engineering and technical personnel.Through the selection principle of building thermal storage materials,the thermal storage materials are analyzed and selected.Thirdly,in order to study the effect of improving the thermal stability of assembled exterior walls with thermal storage components in summer,the unsteady heat transfer model of an office building under natural ventilation and air conditioning conditions was established by using DesignBuilder(DB)simulation software.The indoor air temperature,the inner wall temperature and the outer wall temperature of an office building in Dalian area were measured in summer.The accuracy of the DB-based unsteady heat transfer model for office buildings in summer is verified by comparing the measured and simulated values.Finally,the thermal stability of assembled exterior walls with thermal storage components in summer and their effects on indoor thermal environment and air conditioning energy consumption are analyzed by numerical simulation.The reference wall and the outer wall with different thermal storage materials are constructed for cold areas and hot summer and cold winter areas.The numerical simulation of office buildings in Dalian and Changsha in summer under natural ventilation conditions is carried out,and the effects of different walls in different thermal design zones on the indoor thermal environment of buildings are analyzed.The numerical simulation of office buildings in Changsha under air-conditioning conditions is carried out to analyze the energy-saving rate of buildings with different walls.The results show that the assembled wall structure with thermal storage components can improve the thermal stability in summer.Under the natural ventilation condition in Dalian area,compared with the reference wall,the surface temperature amplitude of the wall using granite,reinforced concrete,gypsum board,aerated concrete,lime-sand brick masonry and pine as heat storage materials decreased by 1.23 °C,1.51 °C,0.7 °C,0.14 °C,1.04 °C and 0.09 °C,respectively.Under natural ventilation conditions in Changsha area,compared with the reference wall,the surface temperature amplitude of the wall using granite,reinforced concrete,gypsum board and lime-sand brick masonry as heat storage materials decreased by1.06 °C,1.27 °C,0.25 °C and 0.58 °C,respectively.Under the condition of air conditioning in summer,the heat storage layer with larger heat storage coefficient S can store more cold energy to resist outdoor heat,thus reducing the energy consumption of building air conditioning.Under the condition of air conditioning in Changsha area in summer,the energy consumption of building air conditioning with reference wall is the highest,which is61986.79 kWh.Compared with reference wall,the energy consumption of building air conditioning with granite wall as heat storage material is the lowest,and the energy saving rate of building reaches 4.11%.The energy saving rate of wall with reinforced concrete as heat storage material is the second,which is 3.07%.Under the condition that the heat transfer coefficient of the wall is constant,if the increase of the thickness of insulation layer does not increase the thermal inertia index D value of the wall,it will not compensate for the thermal stability of the wall.Through the comprehensive design of insulation layer,structure layer and thermal storage layer,the thermal stability of the wall can be compensated only when the thermal inertia index D value of the wall increases.This study provides certain application value and reference basis for building thermal design,provides scientific basis for improving the level of building energy saving,and provides theoretical basis for improving the technical system of assembly building.