Polar bears – no entry: the ‘polar bear pavilion’ is a prototype of a textile membrane structure, which offers new energy saving solutions for human habitations. The name says it all – despite the fact it is not intended for them, the inspiration for the outer layer of the building came from polar bears. “We came across the polar bear principle when we were studying older bionics books from the 1980s and decided to use it for our work on textile membrane structures. Rather than copying it directly, we studied the physical properties of polar bear skin and used other materials to imitate it,” said project leader Dr. Thomas Stegmaier of the Institute of Textile Technology and Process Engineering (ITV) in Denkendorf. 

What makes polar bear skin so special is its ability to distribute light effectively and act as thermal insulation. Polar bears have a dense, whitish opaque coat that protects the animal against the arctic cold and transfers the light of the sun’s rays to the skin. Polar bear skin is pitch black, and is therefore an excellent absorber of solar radiation. The combination of whitish fur and black skin allows polar bears to turn scarce arctic sun into as much heat as possible. The transfer of heat into the polar bear’s body is also adapted to maximally exploiting the little available solar energy: the hypodermis of the polar bear is rich in fatty tissue, which, like all fatty tissue, is pervaded by many blood vessels. This gives polar bears an extensive vascular system that can rapidly distribute heat around the body via the bloodstream. 

The team of researchers from the ITV Denkendorf used this multi-layer structure and its interconnected functions to develop a heat-insulating membrane on a textile basis that enables the simultaneous generation and storage of energy. “We developed the solar-thermal system at the ITV Denkendorf and the material and storage systems were provided by industrial partners,” said Stegmaier who is particularly proud of the speed with which the team were able to develop the membrane. It took the researchers only 30 months from initial idea to the construction of the pavilion. This is even more noteworthy as some of the components had to be developed from scratch. However, the ITV’s competence in high-tech textiles and membranes was a major contributory factor to this achievement. The outer layer of the building consists of a transparent and UV-resistant heat-insulating plastic, which provides excellent insulation. Below this layer is a black, absorbent textile layer that is warmed by the sun’s rays. This layer also serves as an air-bearing transport layer, where the air heats up as it passes along the absorber surface.

Collector tracks 50 cm wide and 5 m long were constructed, sealed laterally and mounted. They are not directly connected to each other, but form individual modules of an integrated system that is oriented towards the south, and hence towards the sun. Stegmaier is not yet able to disclose detailed information on how the air is guided through the layers as the team has filed a patent for the novel material. He nevertheless reveals that low and high pressure is used to restrict transmission loss. The heated air is guided to energy stores in which another novel principle is used.

The devices are a proprietary development of Stuttgart-based TAO Transatmospheric Operations GmbH, which is a cooperation partner in the project. The heat energy is transformed into chemical energy in the energy stores using silica gel such as that used in silica gel packets found in many electronic equipment packing boxes. The gel can bind huge amounts of moisture. The drying of the gel, e.g. through warm air, causes it to take up heat. The gel then releases the heat again when it is exposed to moisture. “This is similar to preparing plaster, where heat is given off when the powder is mixed with water.

As far as our energy stores are concerned, the released heat warms up the air, which can be used for heating the pavilion by way of a heat exchanging device,” Stegmaier explains. The clever thing here is that the point in time at which moisture is added can be controlled and this can take place months after drying, for example. This means that energy collected during the summer can be “stored” in the gel until the colder winter months. It is only released when the consumers find it too cold and decide to “switch on the heating”. “At the moment, we believe that the storage systems have a lifespan of 25 to 30 years,” said Stegmaier. The principle also makes it possible to produce transportable storage systems. “Mobile solar-thermal systems can for example be used in motor homes,” said Stegmaier.

The overall construction has been operating on a trial basis for a few weeks to show how well it works. “It looks like our projections were fairly accurate. Half an hour of winter sun is sufficient to heat the air behind the absorber surface to 100°C,” said Stegmaier, who is pleased with the outcome. The simulations and projections were done by another of Stegmaier’s project partners, Karlsruhe-based TinniT Technologies GmbH. Labor Blum GmbH in Stuttgart provided the measurement technology used to check the values, the engineering office Wagner Tragwerke Stuttgart was in charge of the statistical calculations and the coordination of the construction work, and the Arnold Group from Filderstadt was in charge of the technical execution of the project.

The cooperative project was made possible with funds from the Baden-Württemberg Ministry of the Environment, Climate Protection and the Energy Sector, which provided 1.1 million euros in funding, of which around 50% came from the European Regional Development Fund. The pavilion is already busily collecting and storing heat and the project partners are working on optimising the system. “We would like to make the system a lot simpler in order to make it as cheap as possible,” said Stegmaier highlighting the group’s future goals.

Further information:

ITV Denkendorf
Dr. Thomas Stegmaier
Körschtalstraße 26
73770 Denkendorf
Tel.: +49 (0)711 9340-219
E-mail: thomas.stegmaier@itv-denkendorf.de