Analysis Of The Optimum Thickness Of Thermal Insulation Layer For The Cryogenic Granary Enclosure In Guangzhou Area

Food security is an important foundation for national security,and ensuring adequate food supply is the top priority in governing the country.Only when food security is firmly anchored can we maintain the foundation of food prices and the happiness of the people.Low-temperature grain storage is an effective green grain storage measure,which can inhibit the growth and reproduction of pests and microorganisms,ensure grain quality,and reduce chemical pollution of grain fumigation.However,low-temperature granary refrigeration and air-conditioning systems have high energy consumption,which is not conducive to the large-scale promotion and application of low-temperature granaries.The thermal insulation of the envelope structure is an important technical measure to reduce the energy consumption of the low-temperature granary of the air conditioning system.Therefore,studying the optimal thickness of the thermal insulation layer of the outer protective structure of the low-temperature granary has important practical significance and engineering application value.In the whole life cycle,there is an insulation layer thickness that makes the sum of the construction cost and operation cost of the granary(i.e.the total investment)reach the minimum value.Taking Guangzhou in hot summer and warm winter climate region as an example,this paper adopts the whole life cycle theory to study the optimization method of thermal insulation layer thickness of low-temperature granary enclosure structure.The optimization method of thermal insulation layer thickness based on dynamic heat transfer model of the enclosure structure and the optimization method of thermal insulation layer thickness based on annual equivalent full cooling load are presented.Considering the influence of different exterior wall orientation,different thermal insulation materials and different exterior wall(roof)surface color,the economic parameters such as payback period of investment,total investment and net present value of thermal insulation layer of exterior wall and roof of cryogenic granary in Guangzhou area are calculated and analyzed.The optimal thickness of thermal insulation layer for exterior wall and roof of low temperature granary in Guangzhou is given when XPS,EPS and polyurethane are used in common thermal insulation materials.Based on the dynamic heat transfer model of the envelope structure,the optimal thickness of the insulation layer of the outer wall of the low temperature granary in Guangzhou is 0.075～0.157 m,and the optimal thickness of the roof is 0.089～0.181 m.Based on the annual equivalent full load insulation thickness optimization method,the optimal thickness range of exterior wall insulation layer and roof insulation layer in Guangzhou area is 0.075～0.146 m and 0.079～0.17 m respectively.The calculation error of the two optimization methods is about 10%,and the calculation results of the optimal thickness of the insulation layer of the cryogen-granary enclosure structure are close to each other,which indicates that the two optimization methods have good prediction accuracy.