Study On Heat Transfer And Break Parameters Optimization Of Thermal Bridges For Rural Houses In Eastern Hebei

The poor thermal performance of the building envelope in rural areas is a common problem presently.The energy-saving renovation of rural houses can reduce the operating costs of winter heating systems,fundamentally solve the problem of high heating energy consumption in rural houses,and is of great significance for the formation of a long-term mechanism for sustainable development of clean heating.As increasing the requirements for the thermal performance of rural house envelope,the phenomenon of thermal bridge in rural houses gets more and more attention,and reducing the impact of thermal bridge effect on building energy consumption is a key technical way to save energy for rural houses.However,the theoretical design basis for thermal bridge break in Chinese current standards is still inadequate,and the heat transfer mechanism of the thermal bridge effect is needed to get thermal bridge break technology for rural houses.This study mainly adopts a combination of actual measurements,theoretical analysis and numerical simulation to study the heat transfer mechanism of thermal bridge effect and thermal bridge break technology.(1)Research on the basic information of rural house envelope structure and the current situation of thermal bridges in the Hebei eastern,types of thermal bridges in Hebei eastern rural houses and characteristics analysis.The main types of thermal bridges include nonhomogeneous,overhanging and variable section.The thermal bridge in rural houses has complex formation causes and the interactive effect: taking the eaves of rural house as an example,the causes of thermal bridge include differences of materials thermal performance and different heat transfer areas inside and outside;taking the south-facing window walls as an example,due to the close distance between the door and window frames,the eaves,and the hill wall,thermal bridges have an interactive effect on each other.(2)Using a combination of theoretical analysis and numerical simulation,the heat transfer mechanism and influencing factors of non-homogeneous,overhanging and variable section(corner wall)thermal bridges are studied.The existing standards domestic and abroad rely on numerical simulation tools for steady-state heat transfer calculation of thermal bridges,which can not make clear the heat transfer mechanism and the relationship between the influencing factors of thermal bridges.As to the problem that the heat transfer mechanism is not yet clear for the overhanging and variable section types of thermal bridges,introduce the rib heat transfer method and the shape factor method to analysis the heat transfer process of two kinds of thermal bridges.It is found that main influencing factors of the thermal bridging effect of the overhanging structure are the thermal conductivity λ of the overhanging structure,the crosssection parameters and the overhanging length H.Whether the overhanging structure enhances heat transfer is determined by the value of λ and the shape of the overhanging structure crosssection together,while the effect of H on thermal bridge is influenced by the value of λ.The variable section thermal bridge effect(wall corner)is positively related to the material λ and the wall thickness δ value.(3)Using the wall surface temperature difference and temperature distribution as indicators,a method for determining the thickness and coverage of different types of thermal bridge break insulation is proposed.Based on the rate of temperature change of the inner wall surface to determine the optimum thickness of the insulation layer,based on the temperature distribution of the wall surface to determine the coverage of the insulation layer,the results show that: the non-homogeneous thermal bridge effect occurs not only on the nonhomogeneous boundary,but also on the main body area of the non-homogeneous structure,so whole external insulation is suitable for non-homogeneous components;taking EPS panels as an example,the optimum thickness of the insulation layer is 0.015 m.The overhanging thermal bridge is suitable for The optimum thickness is 0.025 m(EPS)and the optimum insulation coverage is 0.37 m.The variable section(corner)category of thermal bridges is suitable for internal insulation retrofit,with an optimum thickness of 0.025 m(EPS)and an optimum insulation coverage of 0.37 m.The results of this study enrich the theoretical system of thermal bridge break design parameters for rural houses in Hebei eastern,and provide a theoretical basis for improving the thermal bridge break retrofit technology for local rural houses and the thermal performance of buildings.