Characteristic Analysis And CFD Model Establishment Of Different External Thermal Insulation Cover Materials In Solar Greenhouse

In winter,the indoor temperature significantly affects the growth and development of the crop for solar greenhouse crop cultivation.Studies have shown that more than 70% of the total heat loss in the greenhouse is lost through the front roof,so it is especially important to study the insulation and energy saving of the front roof insulation covering materials.In this study,Shenyang as an example,three kinds of homogeneous thermal insulation covering materials and seven composite thermal insulation covering materials were selected as research objects.Based on the method of degree-day,the heating energy consumption of solar greenhouse was calculated,and the calculation model of the economic thickness of thermal insulation covering material was established based on the analysis of life cost.The economic thickness of the core material of the best thermal insulation covering material was determined by calculating the annual average total investment cost of the thermal insulation covering material,and the influence of different temperature differences(regions)on the results was analyzed.The CFD heat transfer model of the thermal insulation covering material was established by using the measured values as boundary conditions,and the model was verified by the hot box method.Based on this model,10 kinds of thermal insulation materials with economic thickness were simulated,and the thermal insulation effect under non-warming conditions was analyzed.The conclusions are as follows:With heating,the straw mat is the most economical in homogeneous materials whose economic thickness is 91.12 mm,and the minimum total investment cost per unit area is 7.28 yuan/m2.PE woven fabric + pearl cotton + spray cotton + PE woven fabric is the most economical whose economic thickness is 76.83 mm,and the minimum total investment cost per unit area is 5.51 yuan/m2.In colder regions,the greater the economic thickness of the insulation covering material,the higher the total investment cost and the average annual total cost.Without heating,the CFD heat transfer model of the thermal insulation covering material is established.The difference between the simulated and the measured values do not exceed 2?,the relative error is within 7.5%,and the average relative error is 4.51%,verifying the correctness of the model.It is concluded that the best insulation in the homogeneous material with economical thickness is straw mat.The best among the composite materials is PE woven fabric + strong needle felt + recycled cotton + strong needle felt combination.In a comprehensive situation,PE woven fabric + pearl cotton + spray cotton + PE woven fabric,PE woven fabric + strong needle felt + recycled cotton + strong needle felt,strong needle felt + recycled cotton + strong needle felt and the strong needle felt + glueless cotton + strong needle felt are superior to the straw mat in economy and heat preservation.It is more suitable to add a homogeneous material to the outer surface material to make a composite material.When the surface material of the composite thermal insulation covering material is the same,the use of a core material having a small thermal conductivity can reduce the total investment cost and increase the thermal insulation performance.The waterproof and anti-aging treatment has been added,which not only increases the life of the thermal insulation covering material and the thermal insulation performance,but also reduces the total annual investment cost.