State-of-the-art analysis

The following sections cover a state-of-the-art analysis of modelling methods for the energetic performance of shaded or unshaded fenestration systems. The RadiCal method can also be applied to other applications that rely on the accurate calculation of solar-induced energy flows, such as all types of solar thermal collectors, photovoltaic modules or building integrated applications of these. However, a comprehensive description of the currently applied modelling methods for these applications would go beyond the scope of this work. Therefore, the following analysis focuses on the presently applied calculation methods for fenestration systems, as the RadiCal method was initially developed for this purpose.
Due to its practical relevance, scientific research regarding the energy performance of windows and glazings is closely related to software tools and international standards. Consequently, this chapter contains many references to these tools and standards. Any research that involves the calculation of the thermal performance of windows has to rely on software, as the heat-balance equation has to be solved considering the glazing’s specific spectral and thermal properties.
Slightly simplifying, it can be stated that the essential results of the research performed before the year 2000 are laid down in the relevant international standards. These methods have in common that directional properties of the incidence light are generally neglected, as the direction of light is mostly assumed to be of normal incidence.
As a result of research addressing the directional limitations, more sophisticated approaches have evolved after the year 2000. These methods are referred to as “modern approaches” in this chapter. The directional methods were gradually integrated into relevant tools, in particular into the commonly used Window software by Lawrence Berkeley National Laboratory (LBNL Windows and Daylighting Group, 2022b) and into EnergyPlus (U.S. Dept. of Energy, 2022) starting in the year 2011 (Lee and U.S. Dept. of Energy, 2017).
More recent developments in the research field, like the Comfen tool by LBNL (Mitchel et al., 2019) or the Fener tool (Bueno et al., 2015) concentrate on dynamic simulations to assess energy demand or daylighting aspects, allowing users to consider different devices and control strategies. However, all of these new methods are developed on the existing optical models and do not question or extend them