Simulation and Analysis on Light Environment of Greenhouse in Beijing Area

Daily light integral is determined by outside radiation and the light transmission rate of greenhouse. The greenhouse light environment is affected by factors like latitude, building location, surface material, skeleton structure and configuration density. Typical solar greenhouse is studied that is used to grow tomato and others vegetables in winter in Beijing. Based on the observed data of meteorological elements of radiation, temperature, humidity etc, both inside and outside solar greenhouse, using the mathematical method and computer simulation, the sun-light incidence rate of different surface radian curves of greenhouse is calculated. A mathematical model for solar radiation on the surface of a solar greenhouse is proposed and the heat transfer of a solar greenhouse with 8 m span is simulated.Five aspects are included in the model. Solar greenhouse mainly contains the surface, the back-wall, the roof and the gables, the gables' influence on solar radiation is not considered, assuming that the length of the solar greenhouse is unlimited. The direct radiation, sky radiation and the reflection radiation that the surface receives are calculated. The surface received solar radiation is divided into three parts. One part of the radiation is reflected by the surface, another part is absorbed by surface, the rest of the solar radiation goes into the greenhouse. The radiation distribution is calculated. The greenhouse direct radiation is not fully exposed on the ground. Direct radiation distribution and intensity in various parts of solar greenhouse under different times are calculated. In accordance with the direct radiation transmittance calculation algorithm, the sky radiations transmission rate is calculated. Then, according to the integral methods, sky radiations distribution and intensity in various parts of solar greenhouse under different times are simulate. The influences of crop growth on solar radiation are reflection and absorption. In accordance with crop growth dynamic change, the ground radiation changes. Radiation intensity on ground is calculated based on the law of diminishing index. Based on the experimental data and the literature, the simulating data of the ground radiation are analyzed and compared. The accuracy of simulation models is reasonable. The mean absolute difference is 9.41 W/m², and the relative coefficient is 0.92. The model is valuable to simulate the relationship between environmental factors and crop growth, and it is significant to provide reference for optimization of greenhouse environment control.