Thermal modeling of complex fenestration systems: Comparison with long-term measurements on an office façade mock-up

Abstract

This article shows a comparative investigation of simulations and long-term measurements performed on a façade mock-up including a complex blind system in-between glazing layers. The simulations are based on a newly implemented algorithm in TRNSYS18 for modeling complex fenestration systems (CFS). It uses the ISO15099 standard for the longwave radiation modeling of glazings incooporating blinds and bi-directional scattering distribution functions (BSDFs) to tackle the shortwave radiation modeling of daylight redirecting systems. The test mock-up — consisting of an impact pane toward the outside, the investigating blind system in between, and an three-pane insulation glazing unit toward the inside — is installed on a real office space façade and exposed to outside weather conditions. Two different blind systems are investigated: (1) a diffuse reflecting blind system with a multi-curved geometrical shape and (2) a highly specular blind system with a concave shape. Both blind systems are established products on the market to enhance daylight utilization in interior spaces. To identify the capability of the new model algorithms, resulting surface- and air gap temperatures of the individual system layers by simulation and measurement are compared for different shading states and variable climatic conditions. The results show a satisfying correlation for both systems. In particular, the simulation results of the diffuse reflecting blind show a better agreement with the measurements in comparison with the specular blind. The simulation model neglect the effect of thermal mass, which results in a significant time-shift between measurement and simulation for the investigated system.