.

Prototype of an ETFE cushion with flexible PV modules.
© Jan Cremers, Hightex GmbH

Residential Palace, Dresden, membrane roof. Architect: P. Kulka, P. Stamborski.
© Jochen Manara
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Primary energy balance

Compared with glass roofs, membrane structures have a considerable advantage in terms of the primary energy. This is because they use less material for the supporting structure and the roof skin. By way of example, the primary energy consumption for both a glass roof and a membrane structure with cushions was calculated for the project in Munich. The membrane roof requires 50% less energy. If the building’s usage period is also taken into consideration, the savings effect depends on the electricity consumed to operate the membrane cushions. Ideally, the power consumed should not be more than 0.4 W/m2. With 1.2 W/m2, the advantage over glass in regards to the energy use would no longer exist after an assumed usage period of 80 years. 

Membrane materials

Materials predominantly used in membrane structures include polytetrafluorethylene (PTFE)-coated glass fibre fabrics (Olympic Stadium Berlin), polyvinylchloride (PVC)-coated polyester fabrics (Rothenbaum Tennis Arena) and ethylene tetrafluoroethylene films (ETFE) (Small Palace Courtyard, Dresden). The materials have a fire protection class of at least B1. Characteristic features of ETFE films and PTFE-coated fabrics include their high self-cleaning effect, low soiling characteristics and high UV and weather resistance. These flexible membrane materials weigh between 0.2 and 1.5 kg/m2. The low weight offers advantages in terms of the lifecycle of buildings. The 0.2 mm-thick ETFE films are particularly light and are used with pneumatic cushions.

Membrane structures with new functions

The energy efficient operation of buildings with membrane structures requires measures that reduce the heat influx in summer and provide good thermal insulation in winter. In combination with excellent control technology that takes into account optimum air exchange rates via openable roof elements and which enables efficient solar shading, the use of membranes for energy-based refurbishment provides an interesting concept for specific urban situations.

Flexible thin-film solar cells made of amorphous silicon, embedded in fluoropolymer films, enable the use of photovoltaics on textile roofs (Fig. 5). A favourable side effect is that the PV modules provide shading for the space underneath. The installation is complex because the flexible roof structure causes stresses in the roof envelope. This has an impact on the PV modules that cannot generally move with the expansions. The Hightex company has developed a method that technically works – although it is still considerably time consuming. Two single-sided laminated PTFE/glass membrane strips are welded to the support membrane. Hook-and-loop strips are bonded to it, to which the PV modules are fixed. The reversible connection enables the replacement of faulty modules. Further research work needs to determine the durability and UV resistance of the adhesive connections. Could the loosely supported reverse side of the PV modules become dirty? Is the fixing permanent or is damage caused to the modules?

Further research and development are also required in regards to improving the energy efficiency of membrane structures. Light emitting function layers can be applied to the material surface or switchable/self-switching function layers integrated for controlling the g-values. Textile structures are becoming increasingly important and are used to a high extent in large-scale construction projects. Spectacular examples that showcase the new possibilities include Bangkok’s new airport, the BC Place stadium in Vancouver, Canada, and the Gerontology Centre in Bad Tölz, Germany.

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Addresses

Project coordination
ZAE Bayern - Würzburg

Project partner
Hightex GmbH

Project partner
HFT Stuttgart

Project partner
Hochschule München, VSG

Project partner
Lang Hugger Rampp GmbH

Project partner
Dörken GmbH & Co. KG

Service

BINE-Projektinfo 08/2012
(PDF, 4 pages, 1.2 MB)