The Thermal Insulation Of The Long-span Plastic Greenhouse In Wintering Is Automatically Controlled And Its Thermal Environment Simulation Is Studied

The winter weather in northern China is cold and dry,and wintering production cannot be carried out normally in plastic greenhouses without any protective measures.In order to improve the thermal insulation of plastic greenhouses and meet the requirements of overwintering production of leafy vegetables,thermal insulation quilts are applied to large-span plastic greenhouses.In order to study the impact of the application of the Internet of Things system to control the automatic uncovering of plastic greenhouse insulation on the growth and quality of overwintering leafy vegetables.Referring to different weather conditions,automatic unveiling and insulation according to the environmental threshold is treated(H),referring to sunrise and sunset time,and automatic uncovering and insulation according to administrator experience is used as a control(CK).The same varieties of leafy vegetables(cabbage,oil wheat,rape and spinach)were planted in two plastic greenhouses,and the growth index,quality and yield of leafy vegetables in the plastic greenhouses were compared.The thermal environment inside the plastic greenhouse under low temperature weather conditions in winter was studied,the air temperature and soil temperature in the shed were monitored,and the numerical simulation method was selected to explore the distribution of the temperature field and airflow field inside the plastic greenhouse under typical weather conditions,and the main research results were as follows:(1)The different uncovering conditions of the insulation quilt have obvious differences in the internal environmental impact of the plastic greenhouse.The average maximum temperature of the test plastic greenhouse and the control plastic greenhouse under low temperature conditions in winter were 29.4℃ and 28.8 ℃,and the average minimum temperature was-2.1℃ and-2.7℃,respectively,and the soil temperature and air temperature were consistent,which showed that the test was higher than the control;during the whole growth period of leafy vegetables,the air temperature and soil temperature in the test plastic greenhouse increased by 10.81%～21.30%,10.09%～23.20%compared with the control,respectively.On the whole,the temperature of the test plastic greenhouse was higher than that of the control plastic greenhouse.(2)The effect of internal environmental changes on the growth and development of leafy vegetables in plastic greenhouses.At different stages of the whole growth period,the relative growth rate of leafy vegetables in the experimental plastic greenhouse was higher than that of the control.The total acidity of cabbage in the test plastic greenhouse had a significant effect,its content decreased by 66%,soluble sugar increased by 41.18%,and soluble solids increased by 7.46%.The Vc content of rapeseed increased by 45.50%,and the Vc content of rapeseed increased by 16.4%.The total mu yield of cabbage,oil wheat and spinach in the test plastic greenhouse was higher than that of the control plastic greenhouse,and the average plant weight of oil wheat increased by 19.2%,the yield per unit area increased by 10.64%,while the total output increased by 41.8%,and the economic benefits increased by 2018 yuan/667m2;The results showed that H treatment had a positive effect on the growth and development of leafy vegetables,and could increase the yield of leafy vegetables.(3)CFD simulation study of thermal environment inside plastic greenhouse.The results of the accuracy verification of the established large-span plastic greenhouse CFD model show that the simulated value of temperature can be well consistent with the measured value,and the rms error between the simulated temperature value of the test plastic greenhouse and the measured value is 0.22℃;the root mean square error of the temperature simulation value and the measured value of the control plastic greenhouse is 0.27℃,both within a reasonable error range,and the CFD model of the plastic greenhouse is established.The temperature in the test plastic greenhouse and the control plastic greenhouse was comprehensively evaluated and analyzed,and the time for the air temperature in the test plastic greenhouse to rise to the highest point after the insulation of the test plastic greenhouse was lifted was reduced by 35%compared with the control plastic greenhouse,and the heating rate in the test plastic greenhouse was 0.51 higher than that in the control plastic greenhouse.In order to retain more heat in the plastic greenhouse,the control scheme under sunny conditions is adjusted to(uncover:7900～9600 Lx,7.8～11.3℃;put:5100～7100 Lx,14.9～20.1℃).In summary,based on the control of the Internet of Things system,the plastic greenhouse that automatically uncovers the insulation quilt according to the environmental threshold has good environmental performance,which can solve the problem of lack of leafy vegetables in the northern winter,and analyze the internal thermal environment of the plastic greenhouse,optimize and adjust the automatic control scheme,and has promotion value for the wintering production of large-span plastic greenhouse.