Geographical Mapping of the Building Envelope Surface Optimal Optical Properties Minimizing the Energy used to Maintain Indoor Conditions

Sammanfattning: Several studies have shown that the buildings envelope optical properties are important in terms of energy use and thermal comfort level. However, no study has been found in regard of the optimal optical properties for the building envelope. Moreover, developments in the coil-coating industry have made possible to design cost effective optical selective surfaces for the construction sector. Based on the above mentioned, this study pretends to map the envelope optimal optical properties minimizing the energy use for large-open-volume buildings locates in Stockholm, Copenhagen, Liverpool, Amsterdam, Berlin, Vienna, Bern, Rome, and Madrid.A building could be seen as a very complex solar energy conversion system, which is very difficult to describe accurately. Nonetheless, it is possible to use Building Energy Simulation (BES) tools to model, to some extent, its thermal performance under many simplistic assumptions. The simulation tool TRNSYS 17 and the optimization tool GenOpt were selected for this study. Additionally, detailed small-open-volume building thermal performance data, obtained during passive measurements from the steel manufacturer SSAB, in Borlänge-Sweden, were used to assess the methodology for the creation of the large-open-volume simulation models. The variations in large-open-volume building design around Europe are not well documented, which constitutes one of the major impediments for this research. However, detailed European historical building U-value data from the European Union project called iNSPiRe made it possible to achieve the objective of this study.The simulation work showed, that the building envelope optimal optical properties are related to the magnitude of the heating and cooling loads. Consequently, GenOpt was used to plot the sensitivity of the building envelope optimal optical properties to the ratio between the heating demand and the total energy demand (Qheat/Qtotal). In regard to the large-open-volume building optimal optical properties in the selected locations, it was found that the allocation of optimal optical properties does not lead to significant energy savings in locations with relatively low solar availability and high thermal insulation levels. Nonetheless, a final envelope optical properties study for a small-open-volume building model based on three existing buildings differing only on their optical properties was made for 243 world-capital cities. The simulations reinforced the results for the large-open-volume building in the European locations, and additionally showed huge energy savings potential for most of the world capital cities. This investigation restates the results obtained by Joudi (2015), “Possible energy savings by the smart choice of optical properties on the interior and exterior surfaces of the building.”