Study On Heat And Mass Transfer Model And Experiment Of Green Roof In Hot Summer And Cold Winter Area

Building roof is an important enclosure structure,and it has a very important impact on building energy consumption and thermal and humid environment inside the building.As a new type of green energy-saving roofing,vegetation roofing has been applied in Shanghai and Beijing.Taking Nanchang,a typical city in the hot summer and cold winter area,as an example,this paper analyzes the heat and mass transfer mechanism and the effect of heat insulation and cooling of vegetation roof.The details are as follows:Based on the first law of thermodynamics,Newton's cooling formula and Fourier's law,the heat and mass transfer equation of vegetation layer is deduced;based on Philip-De Vries model,the heat and mass transfer equation of soil layer is deduced by mass and energy conservation equation;and based on one-dimensional unsteady heat transfer model and Fourier's law,the heat transfer equation of roof layer is deduced.Taking linear stonecrop as an example,the plant optical parameters of the heat and mass transfer model were determined,and the soil layer characteristic parameters were determined according to the relevant theory.Based on the mathematical module of COMSOL Multiphysics,the partial differential equation interface is called to rewrite the control equation and boundary conditions of the soil layer and roofing layer to realize the solution process of the model.A vegetation roof experimental platform was built to verify the accuracy of the model.The results show that the average deviation between the simulated and measured temperatures is about 0.86?,and the average humidity deviation is about3.17%.A comparative experimental platform of vegetation roof and common roof was built,and the two conditions of natural working condition and air conditioning working condition were designed.The thermal insulation performance of vegetation roof under three weather scenarios:continuous sunny day,continuous rainy day and alternate sunny and rainy weather was analyzed.Compared with the temperature attenuation effect of vegetation roof and common roof,the results show that the average temperature amplitude of common roof is 8.18?,which is about 7.42 times of vegetation roof,indicating that vegetation roof have greater thermal inertia.Based on the modified Morris sensitivity analysis method,the sensitivity analysis of the soil layer parameters of the vegetation roof is carried out.The sensitivity calculation results show that the thermal conductivity?,the specific heat capacity c,the temperature diffusivity a,the wet diffusion coefficient D?and the isothermal diffusion coefficient D_T have different sensitivities to temperature and humidity,and the sensitivities vary with the thickness of soil layer.Among them,the temperature diffusivity is the most sensitive parameter in the temperature sensitivity analysis,and the wet diffusion coefficient is the most sensitive parameter in the humidity sensitivity analysis.