| With the advantages of industrialization,prefabricated buildings have achieved intensive and standardized production of building components and are gradually moving towards the goal of high-quality development and high-efficiency construction.Compared with the conventional wet connection method,the dry connection method of Prefabricated buildings has the advantage of getting built fast,good stability,and high bearing capacity,but the metal connections used between the prefabricated building components will lead to more obvious thermal bridges at the dry connection nodes if they are not handled properly.At the same time,the collaborative development concept of "prefabricated+near zero energy building" puts forward higher demands for the thermal insulation performance of the external wall of the prefabricated building and its wallboard connection nodes.The green and energy-saving development of prefabricated buildings has become a breakthrough opportunity for its future development.Therefore,this paper conducts research on the thermal performance of key nodes of PCW(Precast Composite Wall(1))prefabricated housing using dry connections,The main elements include the following:(1)Three dry connection methods(welding connection,box connection,and splicing connection)suitable for key structural nodes of PCW prefabricated housing are introduced in detail,and the detailed size,layout,and construction methods of the dry connections of key structural nodes are emphatically detailed.Using infrared thermal imager,field tests were conducted on vertical seam joints,parapet joints,and door and window joints of PCW prefabricated composite walls with dry connections,and the thermal characteristics of L-shaped joints with wet and dry connections were compared and analyzed.(2)Using ANSYS(ANSYS Workbench)finite element numerical simulation calculation method,the steady-state heat transfer simulation calculation of three typical key structural nodes of PCW prefabricated housing with dry connection was carried out,and the cloud pictures of surface temperature and heat flux density distribution of wallboard and dry connector of each dry connection node were obtained.At the same time,the heat transfer simulation of dry-connected key nodes with different thicknesses of external insulation and the sandwich insulation layer is carried out,and the vertical seam temperature at the joint of each node wall panel,temperature of the part where the dry joint of the node wall panel is located,and the temperature distribution data at the main part of the node wallboard are extracted respectively,to quantitatively analyze the adverse effects of the thermal bridge of each dry-connected node.The simulation results show that the thermal bridge effect formed by the spliced connection is the most significant among the three dry connection methods,followed by the welded connection,and the box connection is the smallest.(3)Taking the limit values of the heat transfer coefficient of the external walls of ultra-low-energy buildings and near-zero energy buildings as a guide,the average indoor surface temperature and heat flux of wallboard with different insulation construction methods are simulated and calculated from the perspectives of wallboard structure layer and insulation layer,and their influence on the overall insulation performance of wallboard is preliminarily evaluated.Finally,through the reasonable collocation of the wallboard structure layer and insulation layer,the recommended insulation method of PCW prefabricated composite wall when meeting the limit requirements of heat transfer coefficient of the external wall of near-zero energy consumption building is as follows:EPS(180mm)is filled in the wallboard structure layer,and polyurethane(110mm)is used as the external insulation layer of wallboard.(4)Using ANSYS(ANSYS Workbench)to conduct heat transfer simulation calculations on dry connection nodes of PCW prefabricated housing buildings using the recommended external insulation practices,and combining the limit requirements for the heat transfer coefficient of the thermal bridge line of the building envelope,scientifically quantify the thermal defects of each dry connection node.At the same time,due to the requirements of building layout and functional space division,the external wall panels of various parts of PCW prefabricated housing buildings are divided into six types of node combination wallboard according to the differences of the connection nodes on both sides,and the influence coefficients of thermal bridges of dry connection nodes on the average heat transfer coefficient of wallboard are simulated and calculated respectively,and the average heat transfer coefficient of external walls of various parts of PCW prefabricated housing buildings are corrected.(5)In order to investigate the additional increment of the building energy load of "near zero energy PCW prefabricated housing"(the heat transfer coefficients of all parts of the building envelope meet the limits of the heat transfer coefficients of the external envelope of near zero energy buildings)brought by its dry connection thermal bridge.Using the dynamic simulation calculation software Design Builder to simulate the heating and cooling loads of PCW prefabricated housing with dry connection in Xi ’an and Yulin areas under different external insulation and sandwich insulation thickness,and compared with the energy load of conventional buildings under the same conditions.The comparison results show that among the three dry connection methods,the splicing connection has the greatest impact on the building heating load,followed by the welding connection,and the box connection has the smallest.The added value of the building heating load in Yulin caused by the adverse impact of each dry connection thermal bridge is greater than that in Xi’an,and the dry connection thermal bridge has a relatively small impact on the building cooling load.This paper is of great significance for the design of wallboard insulation structures and the prevention and treatment of thermal bridges in dry connection nodes of PCW prefabricated housing buildings and provides new ideas and methods for the qualitative and quantitative analysis of thermal defects in dry connection nodes of prefabricated buildings,which can further promote and application of PCW prefabricated housing buildings in cold regions. |
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