Temperature dependency of the long-term thermal conductivity of spray polyurethane foam

IF 1.8 4区 工程技术 Q3 CONSTRUCTION & BUILDING TECHNOLOGY
N. Holcroft
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引用次数: 2

Abstract

The thermal properties of closed-cell foam insulation display a more complex behaviour than other construction materials due to the properties of the blowing agent captured in their cellular structure. Over time, blowing agent diffuses out from and air into the cellular structure resulting in an increase in thermal conductivity, a process that is temperature dependent. Some blowing agents also condense at temperatures within the in-service range of the insulation, resulting in non-linear temperature dependent relationships. Moreover, diffusion of moisture into the cellular structure increases thermal conductivity. Standards exist to quantify the effect of gas diffusion on thermal conductivity, however only at standard laboratory conditions. In this paper a new test procedure is described that includes calculation methods to determine Temperature Dependent Long-Term Thermal Conductivity (LTTC(T)) functions for closed-cell foam insulation using as a test material, a Medium-Density Spray Polyurethane Foam (MDSPF). Tests results are provided to show the validity of the method and to investigate the effects of both conditioning and mean test temperature on change in thermal conductivity. In addition, testing was conducted to produce a moisture dependent thermal conductivity function. The resulting functions were used in hygrothermal simulations to assess the effect of foam aging, in-service temperature and moisture content on the performance of a typical wall assembly incorporating MDSPF located in four Canadian climate zones. Results show that after 1 year, mean thermal conductivity increased 15%–16% and after 5 years 23%–24%, depending on climate zone. Furthermore, the use of the LTTC(T) function to calculate the wall assembly U-value improved accuracy between 3% and 5%.
喷涂聚氨酯泡沫长期导热系数的温度依赖性
闭孔泡沫隔热材料的热性能比其他建筑材料表现出更复杂的行为,这是由于发泡剂在其细胞结构中捕获的特性。随着时间的推移,发泡剂从空气中扩散到细胞结构中,导致热导率增加,这一过程与温度有关。一些发泡剂也在绝缘的使用范围内的温度下凝结,导致非线性的温度依赖关系。此外,水分在细胞结构中的扩散增加了导热性。存在量化气体扩散对热导率影响的标准,但仅在标准实验室条件下。本文描述了一种新的测试程序,其中包括确定温度相关的长期导热系数(ltc (T))函数的计算方法,该函数用于闭孔泡沫绝缘,使用中密度喷涂聚氨酯泡沫(MDSPF)作为测试材料。实验结果表明了该方法的有效性,并探讨了调节和平均测试温度对导热系数变化的影响。此外,还进行了测试,以产生与水分相关的导热系数函数。将所得函数用于湿热模拟,以评估泡沫老化、使用温度和水分含量对位于加拿大四个气候带的典型MDSPF墙组件性能的影响。结果表明,不同气候带,1年后平均导热系数增加15% ~ 16%,5年后平均导热系数增加23% ~ 24%。此外,使用ltc (T)函数来计算壁组件u值可将精度提高3%至5%。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Journal of Building Physics
Journal of Building Physics 工程技术-结构与建筑技术
CiteScore
5.10
自引率
15.00%
发文量
10
审稿时长
5.3 months
期刊介绍: Journal of Building Physics (J. Bldg. Phys) is an international, peer-reviewed journal that publishes a high quality research and state of the art “integrated” papers to promote scientifically thorough advancement of all the areas of non-structural performance of a building and particularly in heat, air, moisture transfer.
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