Study On The Building Thermal Storage Characteristics Under Periodic Effects Of Indoor And Outdoor Heat Sources

Nowadays,reducing building energy consumption and improving indoor thermal comfort are the major concerns in the field of architecture.Building envelope thermal storage means the heat absorption performance of building material whose surface under the temperature or heat flow fluctuation,which plays an important role in thermal insulation performance in summer and thermal stability in winter.In recent years,with the rise of low-energy passive building technology,building thermal storage design and its impact on the indoor thermal environment and building energy consumption quantitative evaluation issues have become increasingly prominent.The intensive study on the theory of building thermal storage can help to promote the further development of building thermal physics,which has important theoretical value and engineering application significance.Firstly,aiming at the problem of thermal storage performance parameters selection for the design and performance analysis evaluation of building envelope thermal storage,this paper makes a comparative study on the two kinds of thermal storage parameters of the envelope based on the harmonic analysis method and the conduction transfer function method.The thermal storage parameters in Russian and Chinese building thermal codes using the harmonic analysis method and in the ISO standard using the conduction transfer function method are analyzed originally.The research results are as follows: The physical significance of most of the thermal storage performance parameters in the two theoretical systems is the same or similar,and the conversion relation between the two parameters is determined;The quantitative relationship between the thermal inertia index D and the decrement and delay of the temperature wave is given,which makes the physical meaning of the thermal inertia index D changed from qualitative description to more definite quantitative description.The key parameters of the thermal insulation performance of the envelope under the outdoor heat source periodic effect in summer are decrement times and delay time,the key parameters of the thermal stability of the envelope under the indoor heat source periodic effect or passive building natural operation conditions in winter are inner surface coefficient of heat accumulation or endothermic coefficient.Secondly,based on the theoretical calculation and analysis of the key thermal storage parameters,the effects of thermal storage materials and structural styles on the thermal storage performance of the envelope are discussed.According to the calculation of the thermal inertia index D and the coefficient of heat accumulation S,the thermal diffusivity a and thermal effusivity b can be used as the thermal parameters for the selection of the thermal storage material,the selection principle is determined,and the suitable thermal storage materials are selected from 11 major categories(79 kinds)commonly used building materials;The influence of the arrangements of each material layer on the key characterization parameters of thermal insulation and thermal stability of conventional multi-layer composite thermal insulation external envelope is analyzed,when the heat transfer coefficient K and the thermal inertia index D are constant,the arrangement “outer structure layer + inner thermal storage layer” shows a best integrated thermal storage performance;Based on the violent fluctuating layer theoretical model,the advanced thermal storage building envelope “outer insulation layer + intermediate structure layer + inner thermal storage layer” is put forward,which separates the structure layer and the thermal storage layer,giving full play to the advantages of different materials.The thickness of the inner thermal storage layer is optimized.The calculation results show that the thickness of the violent layer of the thermal storage material can be taken as the thickness of the inner thermal storage layer,and the effective thermal storage thickness is 8 ~ 10 cm.Then,the indoor heat fluctuation of the buildings in Dalian area during the natural operation in transitional season and the intermittent operation in heating season was measured.The fluctuation range,the peak time and the fluctuation cycle of the indoor air temperature were analyzed to determine the fluctuation law of the indoor temperature during the test period,which provides the indoor periodic thermal boundary condition for numerical analysis.The temperature and heat flux of the inner surface of the office walls during the coldest months were tested,the heat storage and heat release of the walls were obtained through the integral calculation,which is mainly determined by the fluctuation range of indoor air temperature and the temperature difference between indoor and outdoor.Finally,the thermal storage characteristics of the envelope under the combined action of indoor and outdoor two-way heat effects are numerically analyzed.The dynamic model of building envelope thermal storage and release is established,which is solved by the numerical simulation software of ANSYS Workbench,the accuracy of the model is verified by the measured data.The internal temperature and heat flux distribution in the wall during the hottest month,the transitional season and the coldest month were analyzed,the differences between the thermal response characteristics of the envelope under the two-way and one-way heat effects are compared.The inner surface heat flow under the indoor and outdoor two-way heat effects is 8.62W/m~2 and 6.30W/m~2 bigger than that under outdoor one-way heat effect during the coldest month and the transitional season.In addition,the quantitative optimization of the envelope structure is carried out,compared with the traditional external wall,the advanced external wall shows better thermal storage performance,whose internal surface heat storage increased by 73 k J/(m~2·d).