Development Of Greenhouse Cultivation Rack Based On Phase Change Material Heat Storage And Auxiliary Electric Heating

Affected by the winter monsoon,most areas in the middle and lower reaches of the Yangtze River have cold winter climates and generally low temperatures.It is difficult to ensure the proper temperature for crop growth at night in the greenhouse without heating,which will seriously affect the quality and yield of crops.If heating,the traditional heating methods have environmental pollution and high cost.With the continuous application of phase change material heat storage technology in the field of energy and construction,domestic and foreign researchers have conducted many explorations on how to apply phase change material heat storage technology to increase the temperature of greenhouses.However,the existing research mainly heats the overall space environment of the greenhouse.There is useless consumption of heat in non-crop planting areas.At the same time,for low crops,the heating of the upper space of the greenhouse also objectively causes energy waste.Energy utilization rate still has a certain potential for improvement.In order to solve the above problem,this study designed a greenhouse cultivation rack based on phase change material heat storage and auxiliary electric heating.Under sunny conditions,phase change heat storage materials are used as the medium to store solar energy,and under cloudy conditions,auxiliary heat sources and phase change heat storage materials are used to heat crops together,which can effectively reduce energy consumption and reduce environmental pollution.This study mainly conducted a heating experiment on the growing area of low crops.The temperature changes and crop growth conditions of the greenhouse cultivation rack under different weather conditions were tested to verify the warming effect.The main research contents and conclusions of this study are as follows:(1)According to the suitable temperature for growing crops in the greenhouse at night and during the day,as well as the temperature change in the greenhouse in the middle and lower reaches of the Yangtze River in winter,comprehensive consideration of the price,latent heat value,material availability,corrosiveness,toxicity and other conditions of phase change heat storage materials,the phase change heat storage material with a phase change temperature of about 21℃ is selected,and the phase change latent heat is 180 k J/kg.The selected phase change heat storage material has been tested by DSC and TG,and its performance can meet the requirements.(2)A greenhouse cultivation rack based on phase change material heat storage and auxiliary electric heating is designed.The greenhouse cultivation rack is mainly composed of a phase change heat storage and release system,a hot air circulation system,an auxiliary heating system,etc.The overall size of the greenhouse cultivation rack is1980mm×800mm×2140mm(length×width×height),the main structure is "H" type,and the main frame is composed of aluminum profiles.(3)The main force-bearing parts of the greenhouse cultivation rack were statically analyzed by Solidworks simulation.The maximum von Mises stress received by the horizontal support is 7.731 MPa,which is far lower than the maximum yield strength of 215.0Mpa of the material.The maximum displacement occurs in the middle of the horizontal support,and the maximum displacement is 0.399236mm;the maximum von Mises stress received by the support plate is 12.23 MPa,which is much lower than the material’s maximum yield strength of 206.8Mpa,the part with the largest displacement appears at the end of the support plate,and the maximum displacement is 0.0124909 mm.From the strength analysis,the two main stressed components are safe and the design is reasonable.(4)A three-dimensional model of the planting area of the greenhouse cultivation rack was established through Solidworks,Fluent was used as the solver,the standard k-εturbulence model was used,and the experimental data was used as the boundary condition,the temperature field in the planting area of the greenhouse cultivation rack is analyzed.The simulation results are compared with the experimental test results.The simulated values are in good agreement with the experimental values,which shows the rationality of the model.(5)The heat storage and release performance test of the greenhouse cultivation rack based on phase change material heat storage and auxiliary electric heating was carried out under typical sunny conditions and typical cloudy conditions.The greenhouse cultivation rack has obvious warming effect.Under typical sunny conditions,the auxiliary heating system is not turned on at night,and the average temperature in the planting area at night is1.2 to 2.5℃ higher than the average temperature in the greenhouse,and the average temperature is 2.0℃ higher;Under typical cloudy conditions,when the auxiliary heating system is turned on at night,the average temperature in the planting area at night is 3.3 to6.8°C higher than the average temperature in the greenhouse,and the average temperature is5.4°C higher.The temperature of the substrate is also effectively increased.The FLIR infrared imager is used to collect thermal infrared images of the leaf parts of peppers and tomatoes.Under typical sunny and cloudy weather conditions,the leaf temperature of the crops grown in the greenhouse cultivation rack is higher than the leaf temperature of the crops grown in the greenhouse at the same time.And the greenhouse cultivation rack is used for planting,which can effectively improve the thermal environment for crop growth and protect the crops from overwintering safely.(6)According to theoretical calculations,it is found that solar radiant heat is the main source of heat storage in the phase change heat storage and release system,and solar radiant heat accounts for 74.0% of the theoretical heat storage under typical sunny conditions.Under typical sunny conditions,the average COP of the greenhouse cultivation rack is 9.3,and the average energy utilization rate is 65.1%;Under typical cloudy conditions,the average COP of the greenhouse cultivation rack is 2.2,the average energy utilization rate is 56.6%.The greenhouse cultivation rack has high energy utilization rate,can effectively use energy,and has obvious energy saving effect.