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Thermal behavior of green roofs under Nordic winter conditions

机译：北欧冬季条件下绿色屋顶的热行为

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To understand how green roofs affect building energy performance under cold climatic conditions, a proper thermal analysis of the roof and its components is required. To address this, we measured the thermal conductivity of each layer of experimental green roofs, as well as equivalent thermal resistance of the complete green roof system during winter conditions in southern Finland. Three experimental green roof platforms (1 m x 2 m) with heated boxes and three identical bare roof platforms (without substrate, vegetation and other green roof layers) were equipped with thermocouples that continuously measured a vertical temperature profile through the roofs. A steady-state heat transfer analysis was performed to assess the functioning and relative thermal performance of the green roof systems. Layer analysis at various intensities of frost penetration showed that the thermal conductivity of each layer decreased when penetrated by frost. In particular, thermal conductivity of the substrate and vegetation layers decreased from 0.41 Wm(-1)K(-1) and 0.34 Wm(-1) K-1 prior to freezing, to 0.12 Wm(-1) K-1 and 0.10 Wm(-1) K-1 after freezing, respectively. This phenomenon is explained by a reduction in bridge-water connectivity during freezing and a volumetric water content that was below the critical threshold value. Overall, a frost depth that extended through the complete green roof yielded the greatest equivalent thermal resistance. During times of snow cover, snow acted as an insulator and reduced the relative energy saving benefits achieved by green roofs. These results provide information for designing the substrate and vegetation layers of green roofs for optimal insulation. (C) 2017 Elsevier Ltd. All rights reserved.
机译：为了了解绿色屋顶如何在寒冷的气候条件下影响建筑物的能源性能，需要对屋顶及其组件进行适当的热分析。为了解决这个问题，我们测量了芬兰南部冬季条件下实验性屋顶的每一层的热导率以及整个屋顶系统的等效热阻。三个带有加热箱的实验性绿色屋顶平台（1 m x 2 m）和三个相同的裸露屋顶平台（没有底材，植被和其他绿色屋顶层）配备了热电偶，可连续测量穿过屋顶的垂直温度分布。进行了稳态传热分析，以评估屋顶绿化系统的功能和相对热性能。在各种霜冻渗透强度下的层分析表明，当霜冻渗透时，各层的热导率均降低。特别是，基质和植被层的热导率从冻结前的0.41 Wm（-1）K-1和0.34 Wm-1 -1降低到0.12 Wm-1 -1和0.10冷冻后分别为Wm（-1）K-1。这种现象可以通过冻结过程中桥水连通性的降低以及体积水含量低于临界阈值来解释。总体而言，贯穿整个绿色屋顶的霜冻深度产生了最大的等效热阻。在积雪期间，积雪起到了隔热作用，并降低了屋顶绿化带来的相对节能效果。这些结果为设计绿色屋顶的基质和植被层提供了信息，以实现最佳隔热效果。 （C）2017 Elsevier Ltd.保留所有权利。

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