Radi-Cal
Contrary to the very detailed and elaborated calculation methods applied to describe the heat transmission through building components or the efficiency of HVAC components, the models and calculations standards available for calculating the energetic impact of shading devices lack significantly in accuracy. However, as a consequence of modern high insulation standards and a constantly rising proportion of glass surfaces in modern buildings, the significance of these energy contributions has risen dramatically within recent decades. Solar gains through transparent surfaces can considerably lower the demand for heating energy in winter and represent the dominant heat source in summer, therefore causing an increase in cooling energy demands and/or potentially hazardous overheating situations, respectively.
The state of the art method to calculate the solar input of shaded glazing components as described in the relevant standards is based on severe simplifications (e.g. venetian blinds are modelled of indefinitely thin, totally planar and strictly diffusely reflecting elements). Based on such unpractical simplifications the calculation results for the heat gain of shaded windows can show a significant error, which can even reach one order of magnitude. The limitation to diffuse reflecting materials is noted in the standard; however due to the lack of alternative models this restriction is widely ignored. As a consequence of the poor model the total energy performance of buildings may be significantly inaccurate leading to potentially wrong planning decisions On the other hand the unsatisfactory accuracy level of the calculation model prevents the optimization of existing or innovative new shading solutions. Using optical or calorimetric measurements instead of calculation is hardly an alternative. These methods are very time consuming and costly on the one hand, and can only be carried out for specific, individual setups on the other hand. Due to the variety and large number of potential combinations of materials and shading-systems it is virtually impossible to cover all products relevant. The aim of this project is to develop a specific, physically sound and versatile calculation process for the accurate description of solar gains through transparent surfaces of buildings.
This new method will expand and combine existing approaches, while using modern numerical methods in a transparent and coherent way. In contrast to the existing calculation methods proposed in the standards, the exact geometry and the optical properties of all surfaces are accurately taken into account. Based on the so-called Monte-Carlo Raytracing approach a theoretically well-founded and expandable calculation platform will be developed, representing a powerful tool for accurate virtual measurements. In order to describe the relevant optical properties of materials an expandable set of different specific operators can be used. Based on generic standard models (metal, plastic …) this pool of optical properties can be refined gradually using empirical data.
In order to prove the functionality, validity and usability of the new method a software-tool will be developed in course of the project. The software tool will not only be essential to show the validity of the process developed, but also to highlight potential application areas. A key feature of the process will consist in a special interface, which will allow the export of the calculation results in form of arithmetic operators. With little effort, this interface will allow seamless integration of the results in other relevant applications, such as dynamic building simulations and other energy performance calculation tools. Maintaining a coherent and transparent link to existing calculation methods is a key target of the project. Thereby it should be guaranteed that the new method can be used to enhance and replace the current calculation procedure directly and immediately (e.g. in certification processes or buildings simulations).
The focus of the procedure developed in this thesis lies on the physical modelling of active and static shading systems, as well as on calculating all other intended or unintended shading effects relevant for transparent façades or windows. However, both the new method itself and the software tool developed have the potential to be used in a variety of application fields in other building-related areas (solar thermal, photovoltaic, opaque façades, transparent insulation, etc.)
Die Dissertation wird von der FFG im Rahmen des Programms Forschungspartnerschaften gefördert.