Creating custom BSim weather files using a decomposition of global solar radiation to direct and diffuse solar radiation

Weather data is an essential part of performing building performance simulations, as conditions such as outdoor temperature, solar irradiance, humidity etc. has a direct impact on the building under investigation. Some building performance simulations require a specific weather data file to be used, such as in Denmark for assessing the indoor environmental quality of e.g. office buildings. However, in other cases, it can be useful to compare measurements of the indoor environmental data of a building with simulation results. To obtain accurate results, it is advices to use the actual weather data for the building location, as it will otherwise yield erroneous results. One of the largest difficulties is using a solar irradiance model to decompose the global solar radiation to diffuse and direct radiation, which is used in the building performance simulation software, BSim.
This lecture note will go through the theoretical background and the practical implementation in Excel, to make the use of actual weather data more approachable for students and faculty at Aalborg University, Department of the Built Environment (https://www.en.build.aau.dk/).