Abstract
The latest advancements in glazing technology are driving facade design towards complex and adaptive fenestration systems. Accurate simulation of their optical properties and operational controls for building daylight performance evaluation requires advanced modelling techniques, such as climate-based daylight modelling (CBDM). At the same time, computational efficiency is key to quickly simulate this complex performance over a full year. Over the years, several CBDM techniques were developed to answer these two main challenges, but they were never systematically benchmarked against each other. This paper compares state-of-the-art Radiance-based simulation techniques in terms of annual daylight performance metrics required by national guidelines and international green building rating schemes. The comparison is performed on three different shading systems: diffuse Venetian blinds, specular Venetian blinds, and perforated solar screens. Findings show that simulation methods are characterised by significant differences in their implementation and visual rendering, but most annual daylight metrics result in consistent values (within ± 20%). A notable exception is Annual Sunlight Exposure, which is highly sensitive to the chosen simulation method, with differences of up to 47 percentage points. Additional outcomes from the present work are used to compile a list of generalised recommendations for designers and policy makers.
Highlights
Shading devices have been used for centuries to offer protection from excessive solar radiation
Except for Annual Sunlight Exposure (ASE), all the metrics were found to be in good agreement, with a maximum of four percentage points of difference in the case of Useful Daylight Illuminance (UDI) and Daylight Autonomy (DA), and a maximum relative difference of 18% for Total Annual Illumination (TAI) calculated with DAYSIM (B1) and with the 5phase method (5PH) (E2)
This paper has presented and compared state-of-the-art Radiance-based techniques to perform Climate-Based Daylight Modelling (CBDM) with facades containing Complex Fenestration Systems (CFS)
Summary
Shading devices have been used for centuries to offer protection from excessive solar radiation. Nowadays, shading systems have become a critical issue for global energy performance of buildings that should be responsive to variable climatic conditions and to occupant comfort necessities. Influential compliance schemes such as LEED include assessments based on the accurate prediction of sunlight entering the space. For some shading devices, such as overhangs, fins and awnings, an acceptable analysis can be done using simple calculations. For other devices such as Venetian blinds, louvres, screens and roller shades, a more sophisticated evaluation process is needed due to their complex geometries and optical properties [3]. Often though, simplified models are still being used to study these complex cases, e.g. considering all surfaces as perfect dif-
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