Abstract
This paper reports on the daylighting performance of switchable ethylene-tetrafluoroethylene (ETFE) foil in double-skin façades (DSF). In contrast to conventional glazing or static ETFE façades, switchable ETFE moderates incident daylight and controls internal light distribution by actively responding to weather conditions and solar light intensity. To better understand the light control function of ETFE and the impact of parameters such as climate, latitude and window-to-wall ratios (WWR), a validated optical model was used to evaluate different DSF designs. ETFE façades were modelled with a Bidirectional-scattering distribution-function (BSDF) and spectral data, obtained from experimental measurements, to accurately represent specular and diffuse light transmittance. Based on the five-phase method, a parametric climate data-driven simulation of an office room with different façade designs was conducted for three climate scenarios (Oceanic, Mediterranean, Sub-Tropical). When employing switchable ETFE in façades with different WWRs (30–90%), an annual increase of useful daylight illuminance (UDI) from 11 to 69% in the range of 500–2000lx was recorded. The calculated glare probability (DGPs) declined 59% in the best-case scenarios, providing working conditions with imperceptible glare for 94% of the scheduled time. Simultaneously, the daylight uniformity ratio (UR) increased up to 19% compared to a room with a conventional double-glazed façade. Significant improvements of daylight quality were achieved for façades with large windows in climates with abundant solar light available all year long. Overall, this study contributes to expanding the knowledge on adaptive membrane façades, demonstrating their capacity to enhance the daylighting performance of indoor spaces in different climates.
Highlights
The results for the useful daylight illuminance (UDI) are based on annual illuminance simulations that provide a comprehensive overview of the daylighting illuminance of the office space with double-skin façades (DSF) designs under different climate conditions
The results show that switchable ETFE DSFs provides satisfying, if not better natural lighting conditions in office spaces when applied as a retrofitting measure to the building envelope
The study focussed on double-skin façades with clear, fritted and switchable ETFE
Summary
Literature suggests that access to daylight could substantially improve building occupants’ well-being and productivity while reducing at the same time energy demand for artificial lighting [1]. ETFE is a fluorine-based polymer with diverse industrial applica tions It is frequently used in the form of extruded thin foil (100–300 μm) as an alternative for glass in building construction [16]. Within the newly built ETFE constructions, an emerging category using ETFE as a secondary layer of a double-skin façade has become more noticeable over the last decade [23]. This trend seems partly motivated by the demand to reduce the energy consumptions of build ings. An overview of built projects where ETFE has been employed in double-skin façades is provided in Table 1, with examples shown in Fig. 2, A-C
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