Sky Radiance and Luminance Models

This research aims to make an original and advanced contribution to state-of-the-art sky models. It focuses on high-resolution sky radiance and luminance models given their essential importance in a host of scientific and engineering applications. For example, improved sky radience and luminance models can be used to improve the design and operation of energy-efficient and sustainable buildings. All these applications require high-fidelity information on spatial and temporal distribution of solar irradiance and illuminance on building surfaces. The empirical basis for related decision-making processes is, however, rather limited: Available measured data - collected by typical weather stations - is typically restricted to global horizontal irradiance. Few research-class climatic monitoring stations also record the diffuse component of solar irradiance. This research will therefore examine a number of such models in detail and explore both improvement possibilities of existing models and the potential for alternative modeling approaches in future developments. Specifically, this research aims at developing accurate high-resolution sky radiance and sky luminance models for the city of Vienna. In order to generate sky radiance maps, the diffuse radiation component of the global horizontal irradiance should be typically derived based on proper diffuse fraction models. Accordingly, this research starts with an attempt to improve the existing diffuse fraction models. When both diffuse and direct horizontal irradiance data are available, the existing models intended for the sky radiance generation can be comprehensively evaluated and further developed to arrive at a more reliable locally verified sky radiance distribution model. In addition to sky radiance distribution maps, which greatly support the design of buildings' solar energy systems, sky luminance maps are needed to support the design of buildings' daylighting systems. However, to generate sky luminance maps from sky radiance maps, appropriate luminous efficacy information is required, which is not available from typical weather stations. Therefore, this research shall also explore methods with various degrees of resolution to derive illuminance data based on more broadly available global irradiance data. Solid high-resolution empirical data is needed not only to evaluate the existing models, but also to develop and validate new models. For this purpose, I will deploy our existing monitoring facility to systematically collect both typical weather station data and additional information concerning the diffuse component of the global horizontal irradiance, global horizontal illuminance, vertical irradiance, as well as detailed sky luminance and radiance distributions.