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Projektinfo – Detailed information on energy research

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© Jan Cremers, Hightex GmbH
Textile membranes for the energy-based refurbishment of existing buildings
Projektinfo 08/2012

Structural aspects of membrane cushions.
© Jan Cremers
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Lightweight envelopes for old buildings

Lightweight and transparent membrane structures enable large spaces, such as courtyards in old building complexes, to be roofed over. Supplemental to the additional space created, this also achieves savings in terms of the heating and lighting. Artificial light is not necessary and the heat losses from the adjacent buildings can be reduced. However, an intelligent building management system is essential in order to create a pleasant indoor environment. To ensure that this is achieved, scientists have developed new concepts and components for the use of film and membranes in old buildings.

The use of pneumatic cushions made of film opens up new approaches in tackling specific urban situations, whereby the air-filled cavity with an overpressure of approximately 0.2 bar provides an opportunity to optimise the thermal insulation. The cushions are very light and can be designed to be highly transparent. The light transmission is controllable, for example when the cushions are printed or flexible thin-film solar cells are applied to generate electricity. Their use for covering large atria or courtyards of buildings whose facades cannot be altered for architectural or conservation reasons enables the heat losses via the facades to be reduced. In addition, the considerable surface weight of glass roofs is another reason why it is beneficial to use a structure with textile materials, which can also be implemented more cheaply. A diverse range of materials, coatings and components are now available in order to improve the thermal insulation properties of films and membranes.

Researchers are improving the thermal properties

For successfully performing energy-based refurbishments by using membranes and films, materials and components with excellent thermal insulation properties are necessary. This requires basic knowledge of the structural physical characteristics. These include the infraredoptical properties, such as the transmission in the visible part of the spectrum, the solar transmission, the reflection in the solar part of the spectrum and the absorption of thermal radiation, which not only determine the visual appearance but also influence the energy-based properties of building envelopes made with this material. Since this data is not always available for membranes, scientists at ZAE Bayern have measured various types of materials with an identical procedure.

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The use of an additional membrane layer already enables the thermal property of membrane cushions to be improved from 3.3 to 1.8 W/m2K (U-value). If an aerogel fleece is applied between the membranes, the U-value is approximately 0.4 W/m2K. Silica aerogel is translucent and is suitable for use in structures with pneumatic membrane cushions. Another option that has already been tested out is to coat the membranes with low-e coatings.

For realising high quality building envelopes using membrane materials, not only the membrane surface is important for the thermal protection but also the membrane edge. This particularly applies to cushion structures. Although the membrane surface offers considerable thermal protection, the overall U-value depends on the specific geometry of the structure. Here the cushion edge and, specifically, the clamping profile take on considerable importance. This, however, has unfavourable frame-related U-values, which can lead not only to heat losses but also to localised condensation problems. Nevertheless, the development of a prototype for a new clamp profile from the Hightex company has enabled the previously typical frame-related U-value to be halved (Fig. 1). A condensation channel that collects any condensation is still essential. The developers are working on further improvements in regards to the tightness of the cushions and the cushion connections.

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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

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