Large scale functional transparent membranes to smarten up buildings’ roofs and façades
Special focus will lie on a switchable total energy transmittance (often referred to as the solar factor or solar heat gain, and “g-value” in Europe) and on flexible solar cell integration, since both functions could significantly contribute to energy saving and power generation in buildings.
A major trend in modern architecture is the use of large transparent and translucent façade and roof elements to make time spent in these buildings more pleasant due to bright and spacious rooms and appearance. When made of glass, these façades and roofs are functionalized with heat reflecting coatings to minimize their “g-value”.
However, glass is not bendable enough to apply it to vaulted surfaces as design element in representative buildings such as airports, stadiums, event halls or shopping malls. Furthermore, its high weight limits the use of glass for large area roofs or façades without massive, expensive and design-limiting supporting structures. For these applications, fluoropolymers such as ethylene tetrafluoroethylene (ETFE) are an alternative to glass providing a long lifetime and resistance to weathering.
in Lisbon, Portugal with ETFE membrane elements.
Each roof element provides potential for integration
of either solar cells or electrochromic films © Hightex
GmbH.
An example for the use of this material is the roof of the largest shopping mall in Europe (the Dolce Vita Tejo in Lisbon, Portugal) with its 5-layer diaphanous cushions comprising 200,000 m² of ETFE.
In contrast to glass, fluoropolymers are difficult to handle in thin-film coating processes. For this reason, roof and façade elements of membranous material are rarely functionalized yet with energy-saving features such as thermal shielding layers or integrated solar modules.
Until now, it was not feasible to optimize the energy budget of buildings featuring membrane roof and façade surfaces, but backing the FLEX-G project is a consortium of nine industrial and research partners that will work to functionalize fluoropolymer web surfaces with optoelectronic components through thin film coating techniques.
“Membrane façade and roof elements will be functionalized with electrochromic films which allow switching-off the transmission of visible light and thermal radiation by applying an electrical voltage. The energy required for that is made available through flexible organic solar cells. Within the FLEX-G project, we aim to develop dynamic processing and deposition techniques in a way that they are applicable not only for flexible, membrane based building envelopes but also for glass-based systems”, explains Project Coordinator, Dr. John Fahlteich.
Started on June 1, 2017 under the federal construction technology initiative named Energiewendebauen and funded by the German Federal Ministry for Economic Affairs and Energy, the 3-year FLEX-G project will investigate processes that allow the deposition of electrochromic layer stacks directly on an ETFE film surface.
The flexibility of the film enables the use of economical, efficient and high throughput roll-to-roll (R2R) fabrication processes. In the final stage of the FLEX-G project, a 36m² large ETFE membrane roof prototype will demonstrate both the electrochromic components for switching the total solar energy transmittance and the flexible organic solar cells for electrical power generation.
Such integration on vaulted building envelopes should contribute considerably to reducing the primary energy consumption of buildings, in-line with the goal of the German federal government to reduce primary energy consumption in Germany to up 50% by 2050.
Partners in the FLEX-G project include FEP Dresden, ISC Würzburg, IAP Golm, Hochschule für Technik Stuttgart, Coatema Coating Machinery GmbH, Hightex GmbH, Lamilux Heinrich Strunz GmbH, Heliatek GmbH, ROWO Coating GmbH, EControl Glas GmbH & Co. KG and Nowofol Kunststoffprodukte GmbH.
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