Calculation Analysis Of Heat Insulation Performance Of Double-skin Roof's Air Layer

Double-skin design is known as an effective way to reduce the building's solar heat gain. In the tradition, we pay attention to the "energy saving in the structure", setting thermal insulating layer to insulate heat from outside, but in this way, the structure did not express all the potential of the air layer, and there also exist many problem of leaking and seeping. The CUBIC Space Frame connect the top chord ply and the bottom chord ply with the shear connector, it is propitious to express the mechanical properties and thermal insulation property, it can gather the building function and the mechanical properties in integral whole. Theoretical research on heat insulation effect of air layer is not yet perfect. Analyze the effect of the parameters to the heat thansfer have theoretical significance and guiding significance in engineering.This paper describe the thermal insulation property of CUBIC Space Frame, analyze the effects of the space between, air velocity and ventilation mode in the CUBIC Space Frame. First, use the natural convection theory to analyze thermal resistance of sealed air layer,and theoretic arithmetic formula of the biggest thermal resistance value is put forward. Secendly, based on the boundary layer heat transfer theory, theoretic arithmetic formula of air gap height under the condition of two-dimensional forced stable flowing is put forward. Finally, a mathematical model of temperature field an velocity field between the thermal insulating layer and the roof was established with the software FLOTRAN by using the k—εturbulence model, iterative computation was carried on until convergence was reached then details on velocity and temperature distribution was gained. Different conditions that influence the heat transfer by the air flow were compared such as the velocity of inlet air, distance between overhead thermal insulating layer and roof, and so on.The result show that by using double-skin roof, the heat transferred by the air, will increases with the rise of the distance between. When the distance is more than 0.3 meter, the increase trend of heat transfered is slowly. The heat transfer is also increase with the velocity of air flow. So when designing the wind gap should made the velocity as big as possible. Theoretic arithmetic formula of sealed air layer and opened air layer gived out by this paper can be used for reference in engineering design.