长沙地区低温粮仓双层通风屋顶最佳保温隔热层厚度分析

粮仓围护结构保温隔热性能对储粮安全和粮仓能耗有重要影响。粮仓屋顶面积大,是粮仓围护结构接受太阳辐射最强的部位,外界热量主要通过屋顶传入粮仓,因此屋顶是粮仓围护结构保温隔热设计的最重要部位。双层通风屋顶、高反射率的屋面隔热涂料和保温隔热材料等节能技术近年来在粮仓屋顶设计中得到迅速发展和应用。考虑屋顶不同外表面太阳辐射反射率和自然通风对双层通风屋顶传热的影响,该文给出并试验验证了多层屋顶非稳态传热模型和双层通风屋顶传热模型,利用经过验证的屋顶传热模型进行屋顶能耗计算,采用经济性模型和全生命周期理论对长沙地区低温粮仓普通屋顶和双层通风屋顶最佳保温隔热层厚度进行分析,并对采用最佳保温隔热层厚度时的生命周期总投资、净收益及回收周期进行计算和比较分析。研究结果表明:屋顶外表面太阳辐射反射率对长沙地区低温粮仓屋顶最佳保温隔热层厚度和经济性有较大影响,双层通风屋顶可以减小屋顶最佳保温隔热层厚度,长沙地区低温粮仓可采用双层通风屋顶和高反射率的屋面隔热涂料降低粮仓能耗,减少因能源消耗而引起的环境污染问题。长沙地区低温粮仓普通屋顶挤塑聚苯乙烯和膨胀聚苯乙烯最佳保温隔热层厚度为0.106~0.183 m,生命周期内最大净现值为417~633.38元/m2,投资回收年限为2.39~2.96 a。低温粮仓屋顶最佳保温隔热层厚度随屋顶外表面太阳辐射反射率的增大而减小,双层通风屋顶可以减少屋顶保温隔热层投资回收年限。该屋顶最佳保温隔热层厚度确定方法对于指导低温粮仓屋顶保温隔热设计具有一定指导意义。

Analysis of optimum thermal insulation thickness of double-skin ventilation roof of low temperature granary in Changsha region

Abstract: The thermal insulation performance of granary envelope has important impacts on grain storage safety and granary energy consumption. The roof of a granary is usually very large. Because roof is the position with the strongest solar radiation in granary, the external heat is mainly transferred into granary through roof. Therefore, granary roof is the key part in the design of thermal insulation in building envelope of granary. Double-skin ventilation roof, high reflectivity coatings for roof, and thermal insulation material are three popular techniques for roof of granary for stored grain safety and more energy saving. According to different solar radiation levels and different climatic characteristics, the optimum thermal insulation thicknesses of roofs is different in different areas of China. In this paper, the transient heat transfer model of multi-layer roof was presented and validated for calculating energy consumption of ordinary roof in low temperature granary. By considering the influence of natural ventilation, a heat transfer model of double-skin ventilation roof was proposed and validated for determining energy consumption of double-skin ventilation roof. In this pater, the P1-P2 economic models were used to study the optimum thermal insulation thicknesses of the ordinary multi-layer roof and the double-skin ventilation roof of the low temperature granaries in Changsha region. The effect of different solar radiation reflectivity rates of outside surface was considered in determining the optimum thermal insulation thickness of the low temperature granary roof in Changsha region. The optimum thermal insulation thicknesses of two thermal insulation materials including expanded polystyrene and expanded polystyrene were calculated for ordinary roof and double-skin ventilation roof of the low temperature granary in Changsha region by using P1-P2 economic model respectively. And then, on the basis of life cycle cost analysis, the total life cycle costs, life cycle savings and payback periods were calculated. The results of this research showed that the solar radiation reflectivity of outside surface has a significant?impact on the economy and the optimum thermal insulation thickness of the low temperature granary roof in Changsha region. Double-skin ventilation roof can reduce the optimum thermal insulation thickness of low temperature granary roof. Double-skin ventilation roof and high reflectivity coatings for roof should be adopted in roof of low temperature granary in Changsha region for more energy saving and less environmental pollution. The optimum thermal insulation thicknesses range of extruded polystyrene and expanded polystyrene was between 0.106-0.183 m for ordinary roof of low temperature granary. The maximum life cycle savings range from 417 to 633.38 RMB Yuan/m2. The payback period ranges from 2.39 to 2.96 years for the optimum thermal insulation thickness of roof. Expanded polystyrene has thicker optimum thermal insulation layer than extruded polystyrene. Expanded polystyrene has shorter payback period of optimum thermal insulation thickness of roof than extruded polystyrene. The optimum thermal insulation thickness of the roof decreases with the increase of the solar radiation reflectivity of outside surface of the roof. The double-skin ventilation roof can shorten the payback period of the optimum thermal insulation thickness of the low temperature granary roof. Besides, this determination method of optimum thermal insulation thickness of roof has a certain guiding significance for guiding design process of thermal insulation thickness of low temperature granary roof.