A Computer Model For Light Transmission Through Huabei-type (double Polyethylene Covered) Multispan Greenhouse

As the first type of double polyethylene covered greenhouse designed by China Agricultural University in China, HUABEI-TYPE double polyethylene covered multispan greenhouse was approved with favorable energy saving characteristic. The paper study on the transmission of solar radiation in HUABEI-TYPE greenhouse by the numbers for the first time in the world. A computer model is developed based on the diffusion and rule characteristics of transmission in double polyethylene covered greenhouse. The model is based on basic theory of light transfer mechanism which introduce Monte-Carlo techniques ray- follow method and heat-radialization method, Author develop computer model of light transmission to carry out accurate determining light transmission in double polyethylene and twin-walled greenhouse cladding material(PC). 1 . It shows about 15% transmission less compared with single covered in Beijing during the winter by double polyethylene covered, and it is 14.1% less for direct light transmissivity, 15.1% less for diffusion light transfer.The average illumination is below 2000Lux and was harmful to crop in the greenhouse during the winter in Beijing. 2 . The result of study on experiment and simulated by computer shows the condition of light distribute. Mean house transmissivity of the house vary less than 5% change with time in a day during winter in Beijing. Distribution of light has the rule as: high in the middle of span width and low under gutter,and there is 5% difference between the middle of span width and gutter. In the lengthways of greenhouse,it shows the rule of high in south ,mean in center and appear peak value near north wall.The highest transmissivity was shown near south gable, the light transmissivity bring down gradually about 1 5?0% in the north of south gable projection. Another peak value was situated at a distance of about 1 span width from the north gable end, and high 1% than the center of house. The manual light control area should lay under gutter in north of center. 3 .. It is difficult to predict the light transmissivity by traditional theory for the diffusion effect of double polyethylene covered in greenhouse. A computer model called twin- step method was suitable to predict light transmission condition in greenhouse test by experiment. Comparison with actual measurements in greenhouse produced agreement with 3%. 4 A hypothesis is stated that allows the transmittance of any array of transparent roofs to be calculated from the transmittance of each measured independently. A corollary similarly shows that the mean light transmittance of an infinite multispan greenhouse can be determined to first order from measurements made on a single span.The mean light transmissivity value of multispan greenhouse can predicted by pile-up model under diffusion sky, the mean direct light transmission comes at verticality-column projection method. The simplified model was test by experiment. 5 Condensation and dust accumulated have big effect on light transmission of double polyethylene covered greenhouse during winter in Beijing. Condensation deposits can be responsible for a 14% reduction of the light transmissivity. Dust also responsible for a 10% reduction during the winter in Chengde city in HUAB El-type greenhouse. 6 The distribution of solar energy in greenhouse was studied by computer modle.60% of solar energy was projected on earth in greenhouse. North gable get 15%...