10.7. Discussion with respect to research questions

In the following, the research questions raised in section 1.2 are addressed in brief.

1. How can the accuracy of modelling solar-induced energy flows in building science be enhanced? In the present work, the limitations of current models were identified and discussed, and suitable, more complex models were proposed, implemented and tested. Further, a new operator and workflow to integrate the optical simulation results into building performance simulation were developed and implemented. Finally, the validity and potential of the proposed method were demonstrated in validation cases and an exemplary application case.

1.1. Which optical processes, beyond simple geometrical optics, are relevant, and how can they be considered? (e.g. thin-film interference, polarisation, surface roughness)
A more general approach that is intrinsically able to cover significant optical effects was identified. Essentially, it is based on solving Fresnel’s equations in their complex-valued form, considering the wavelength of light, its polarisation state, as well as electrodynamic properties of the materials (see section 10.2). Additional models are integrated in the approach to consider surface roughness and subsurface scattering of materials.

1.2. Is it possible to create a physical-optics-based raytracer that can be used to efficiently evaluate the solar properties of relevant building components, in particular for combinations of glazings and shading devices?
A full implementation of the raytracer was performed in the course of the PhD. The raytracer applies principles of physical optics and relies on Monte-Carlo simulation methods (see Chapter 7). Its capabilities for accurate modelling of coated (and uncoated) glazings allow unified modelling of shaded windows, façade elements or technical applications.

1.3. Can the raytracer be designed in a way that allows a seamless transition or downgrading to existing models?
For the case of missing material data, the implementation provides several fallback cases that allow a gradual downgrading of the model. Commonly applied constants or spectrally integrated values can be applied in these generic models.

1.4. If and how can the highly accurate raytracing be deployed to practical application in dynamic building performance simulation?
A novel method, referred to as SIOP – solar incidence operator, was developed for this purpose (see Chapter 6). Its feasibility and potential are demonstrated in application and validation cases in the present work. The operator allows efficient deployment of the detailed data gathered in the raytracing scans. It, therefore, enables dynamic thermal simulation tools to perform solarrelated calculations with raytracing accuracy at almost no computational cost.