天空散射辐射的各向异性规律及对城市建筑表面辐照度作用的基础研究

Solar radiation on building envelope is essential to the building energy study. The diffuse solar radiation takes a significant part of the total (global solar radaition), yet its data was usually estimated without measurement. The difficulty of the diffuse component study is resulted from its anisotropic feature. Conventional studies assume the anisotropic part of the diffuse sky radiance transfers in a single direction (like the direct component). The continuous sky radiance variation in the sky is ignored, causing problems of the building envelope irradiance evaluation in obstructed environments. The work targets at developing a model that correlates the climatic condition to the sky radiance distribution pattern. And the sky irradiance on the building envelop is expected to be estimated based on the pattern accordingly. ..The project aims at extracting the data features by frequency analysis and piecewise average aggregate approaches. Meanwhile, the decision tree, artificial neural network and clustering will be used to analyze the correlation of different parameters and patterns. The readily accessible climatic indices and their variation frequency will be studied to identifying the overcast, partly cloudy and clear skies. The sky radiance data by luminance (and radiance) scan will be analyzed to specify and extract the essential radiance distribution feature. The features will be correlated with the readily accessible climatic indices. Based on the radiance distribution feature, the representative sky element will be set for irradiance on surfaces by the numerical integration. The approaches to be developed, by their nature, will be adaptive to the complex climatic and urban environments. The conclusions are expected to contribute to the evaluations of building envelop solar heat gain and the building integrated photovoltaic energy production.

作用于建筑的太阳辐射是其节能研究的重要基础。总辐射中，散射部分占比可观但数据较稀缺，其复杂的各向异性表现形式是研究的重难点。现行的类直射假设忽略了多云及似阴天空辐射率的渐变过程，对建筑外立面的辐照度求解不利,尤其在外遮挡环境中可造成误差。本研究拟建立气象条件与天穹各位置真实辐射率及其分布模式的关系，从而探究其对复杂外遮挡环境中建筑外表面辐照度的影响。..项目拟采用频谱分析、分段近似平均提取数据特征，决策树、神经网络、聚类分析数据、模式的关联。通过分析常见气象参数及其波动特征确定天空的阴、晴、多云工况；依据多方向辐射率的测量数据细化并提取辐射率分布的关键特点，并建立其与常用气象参数的关系；依据辐射率分布特点选取天穹代表性位置，以简化求解辐照度的数值积分。所开发的模型对个性化的城市环境及复杂的气象环境有较强的适应性。其结论可推动、改善城市环境中建筑外立面得热量计算及外敷光伏设备产能评估效力。

作用于建筑的太阳散射辐射占比可观，且其表现形式具有复杂的各向异性，构成了评估建筑环境及能耗的重点和难点。传统的类直射假设忽略了多云及似阴天空辐射率的渐变过程，不利于准确求解建筑外立面的辐照度，在复杂的外遮挡环境中可造成误差。..本项目首先识别并分析了天空阴、晴、多云工况下太辐射、照度序列的不同特征，总结提炼了相关系数以反映多云天空下总辐射、照度的剧烈波动及其与阴晴工况的明显差异，系统建立了基于水平面总辐射或总照度判断天空状态进而间接确定天穹散射辐射率及亮度分布模式的方法。为更加直接地求解天穹与地面外遮挡环境的耦合作用，研究量化了天穹环日区域、其相邻区域、以及背景区域对散射辐射的贡献比，从而突破了标准天空模型有限数量的散射分布模式框架，确定了各部分占比与常规辐射测量间的连续定量关系，并采用了复杂遮挡环境中的辐射数据验证之。为更准确地求解天穹的辐射率变化模式，课题组修订了经典天空模型的数学表达以避免其中出现非常规的天顶向数据，并建立了模型以求解天穹辐射率及亮度变化梯度及趋势而非各部分的绝对值。最终，课题组根据复杂遮挡环境中的实测及模拟数据优化了天穹及全年太阳轨迹的离散数量，以提升建筑乃至城市环境及能耗评估的计算效率。本项目探讨并开发了适应高密度复杂城市环境的各向异性散射辐射评估方法。其结论可推动、改善城市环境中建筑外立面得热量计算及外敷光伏设备产能评估精度及效率。