Development and experimental validation of a CFD model for the thermal behaviour assessment of Complex Fenestration Systems

Abstract

Complex Fenestration Systems with integrated shading systems are becoming widely used to enhance the building's envelope performance and increase the occupants' thermal and visual comfort. Their peculiarity of integrating a complex shading system makes it difficult to assess their thermal and optical performance. The complexity of the shading system itself, in addition to the interaction with the fluid flow in the window cavity, calls for the use of adequate modelling and simulation techniques. In this framework, a novel modelling approach for the thermal characterization of Complex Fenestration Systems with integrated venetian blinds at different tilt angles has been investigated and validated against onsite measurements under dynamic conditions. The numerical assessment includes a preliminary optical calculation to determine the fraction of solar radiation absorbed by the glazing system and a subsequent Computational Fluid Dynamic simulation to which the absorbed solar radiation is assigned. On the other side, the experimental characterization is based on heat flux, solar irradiance, and temperature measurements. After the model calibration - through the selection of the most appropriate models for the internal and external convective heat transfer coefficients, the numerical simulation showed a good correspondence with experimental data for all analyzed blind tilt angles with a Coefficient of Variation of the Root Mean Square Error in the open blind configuration (18° from horizontal) of 22.75%, 7.27% and 4.74% and in the intermediate blind configuration (37° from horizontal) of 21.14%, 6.02% and 2.86%, respectively for heat flux, external and internal surfaces temperatures.