Efficiency of Microstructured Sunlighting Systems in Different Climatic Zones: Fid-Bau Portal

Efficiency of Microstructured Sunlighting Systems in Different Climatic Zones

Mueller, Helmut F. O.

Abstract Two-sided microstructures on windowpanes have been developed for redirecting sunlight into the depth of rooms in order to improve daylighting (Klammt et al., Appl Opt 51:2051–2056, 2012; Helmut, Renew Energy Environ Sustain 2:29, 2017). In a joint research project, comprehensive sunlighting systems for windows are developed, integrating microstructures in double-glass units. The fixed units redirect sunlight without tracking to the ceiling and the depth of the room and avoid glare. The system works for all solar altitudes and therefore can be applied in locations of all latitudes and climate zones. The study compares the energy efficiency of the sunlighting system in different locations. The design tool of sun-path diagrams is used to define the annual hours of direct sunlight on windows in the main orientations (N, E, S, W). This theoretical figure is corrected by the sunshine hours taking into account the annual time of covered sky of typical climatic regions. Thus, actual hours of insolation (and light redirection) for the main window orientations are defined for cold, temperate, and tropical climates. Simulation tools, based on goniometrical measurements of prototypes, are applied complementary to calculate the illuminance distribution of typical rooms for certain times and solar positions of the year. Assuming a daylight-dependent control of artificial lighting the energy savings by sunlight redirection are defined in comparison to conventional window and solar control systems. In conclusion the influence of latitude and climatic zone on the energy efficiency of microstructured sunlighting systems is demonstrated.