Study On The Performance Of The Temperature And Light In Unsymmetrical Multi-span Energy-saving Greenhouse

Owing to many weak points in a common energy-saving greenhouse and the lowly cost-benefit in the introduced multi-span modern greenhouse, the Unsymmetrical Multi-span Energy-saving Greenhouse is designed and built to combine the advantages of these two kinds of greenhouses in Shanxi Agricultural University, taigu county, Shanxi Province. A series of experiments were made to test the performance features of this new-designed greenhouse and to compare it with both the common saving-energy greenhouse and the symmetrical multi-span arch greenhouse. The results are as follows:1. The temperature distribution is various in the Unsymmetrical multi-span energy-saving greenhouse which has the length of 100m from east to west and the width of 20m from north to south. In the north-south direction, the temperature variety at night was 1 ~2℃ in winter; The higher temperature was observed on the north wall and 6m. 12 ~ 14m from the north wall in the daytime. The lower temperature was at the zone of 8 ~ 10m from the north wall. In the west-east direction, the temperature variety at night was 2~3℃ in winter; The higher temperature was observed at the zone of 40 ~ 50m from the east in the clear day but the temperature variety was slight in the cloudy sky. In vertical direction, the night temperature difference was only 0.2℃on average, while the temperature variety was influenced by the radiation in the daytime, the temperature rising with the increase of the height from the ground. In a word, the Unsymmetrical multi-span energy-saving greenhouse could make the greenhouse climate to prolong about 60 days in summer and to shorten about 60 days in winter.2. The light distribution is also various in the Unsymmetrical multi-span energy-saving greenhouse. In the north-south direction, the highest transmissivity in winter was at the zoneof 14m from the north wall (the average transmissivity was 63.6%); the lowest transmissivity was at 8~ 10m from the north wall (the average transmissivity was 34.9%). In the east-west direction, the highest light intensity was at the zone of 70m from the east (average 16885 1x) mainly because of covering the new plastic film. The light distribution was more even in cloudy day because of the dispersion light. In vertical direction, the closer to the plastic film, the higher the light intensity was. The unsymmetrical multi-span energy-saving greenhouse could keep about 55% transmissivity in winter but about 47% transmissivity in summer.3. Compared with the common energy-saving greenhouse, the unsymmetrical multi-span energy-saving greenhouse could prolong the daytime 2~3h/d in winter. The rates of temperature rising (4.3℃/h) and falling (3.9℃/h) were fast. The maximum temperature was 4.8℃ higher than that in the common energy-saving greenhouse. The same effect of heat preservation in two kinds of greenhouses could be obtained when screen was adopted in the unsymmetrical multi-span energy-saving greenhouse.4. Compared with the symmetrical multi-span arch greenhouse, the temperature was 4~6℃ higher in winter in the unsymmetrical multi-span energy-saving greenhouse. And the light intensity was 2% - 24% higher and the light distribution was more even in the unsymmetrical multi-span energy-saving greenhouse.In sum, the unsymmetrical multi-span energy-saving greenhouse more fits the climate of north China.