ABSTRACT
This blog sheds some introductory light on an already performed study on the daylighting performance of fritted or switchable ethylene-tetrafluoroethylene (ETFE) foil in double-skin façades (DSF). Since KSA & UAE is blessed with all year long sunny weather we hope to attract architects in KSA & UAE to utilize the outstanding features of ETFE facades either by adding it to an existing building windows elevation or a new development. 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[1]
It has been found that 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.
Why do we need to enhance Useful Daylight Illuminance (UDI)?
Providing sufficient natural daylighting in buildings is essential for enhancing user comfort and reducing energy consumption. 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 . For the same reason, buildings with better daylighting are also financially more attractive, as suggested in a recent study on the economic value of high-rise real estate, finding rent prices 5–6% higher for spaces with good daylight. It is estimated that artificial lighting in buildings accounts for approximately 15–20% of the global electric energy consumption and 25–40% of the total energy consumption in commercial buildings. Studies have shown that fenestration type and size significantly impact a building’s overall energy consumption. New buildings offer the opportunity to incorporate design considerations for sufficient natural daylighting provision and create synergetic effects to reduce energy consumption. However, retrofitting windows and shading devices of outdated buildings to improve the internal daylighting conditions is often limited by multiple factors. Old buildings are usually unsuitable for major changes due to structural limitations, or modifications costs are too high. Demolition and new construction are preferred in most cases, adding to the energy and material consumption. Instead, retrofitting and upgrading would extend the building’s lifecycle and reduce the CO2 emission of the building sector. Adding an external membrane façade of inflated ETFE foil cushions is proposed in this study, combining lightweight (W = 0.34 kg/m2 ), mechanical resistance (TS warp/weft = 64/56 N/50 mm) and high[1]transparency (Tvis = 95%) material characteristics of flexible ETFE foil in a transformative building solution for the enhancement of daylighting performance. This retrofitting measure could improve the building’s natural lighting condition with an integrated switchable mechanism adapting to different solar radiation conditions, and potentially also lead to energy savings for heating and cooling due to reduced solar gains and the insulating capacity of multi-layer ETFE
Glance at results
in below diagram the UDI is presented in the model representing Shanghai at 90% WWR the obvious advantage of switchable ETFE foil façade in increasing the UDI is demonstrated, however a fritted only ETFE façade is not too far. A full reference of study is shown below.
We hope this attracts your interest, we encourage you brows the full study which is downloadable online. If you feel you would like to know more about ETFE, we will be more than happy to receive your thoughts and queries.
Credit of this blog goes to the people who did the study paper and publish it whom are as follows:
Jan-Frederik Flor * , Xiao Liu, Yanyi Sun, Paolo Beccarelli, John Chilton, Yupeng Wu
Department of Architecture and Built Environment, Faculty of Engineering, The University of Nottingham, Innovation Park, Nottingham, NG7 2TU, UK
Paper reference:
Switching daylight: Performance prediction of climate adaptive ETFE
foil façades
ELSEVIER Building and environment 209 (2022) 108650