Construction technology
Membrane keeps
buildings dry
The Fraunhofer Institute for BuildingPhysics IBP has achieved a major successwith a nylon membrane, a product fromthe packaging industry. This material isnow used throughout the world for thethermal insulation of buildings.
Timber-framed build-
ing on the outdoor
area at IBP.
Fraunhofer IBP
"Initially we did not understand
much about polymer membrane," points
out Dr Hartwig Künzel. "As specialists in
building physics we are primarily interested
in the transfer of moisture and heat in
buildings." And yet the departmental head
at the Fraunhofer Institute for Building
Physics in Holzkirchen kept returning to the
subject of lining material when just over
10 years ago he started to become involved
in the renovation of old buildings: "At the
time we were conducting work on a re-
search contract for the restoration of tim-
ber-framed buildings. Materials were being
tested in outdoor conditions on the Insti-
tute's premises and the first computations
of moisture behavior were being made."
The façades of historical timber-framed
buildings are normally subject to preserva-
tion orders, which means that the buildings
can only be insulated from the inside.
In such cases thermal insulation has far-reaching consequences: rainwater pene-trates into the beams and the infilling The misture barrier is
qucikly and easily ap-
even gets into the insulating layers. If the interior paneling is hermetically sealed e.g.
Künzel first sought a solution to this prob- able polystyrene or plastic sheet, the damp- on his thesis at university he developed the the room – it is trapped and at some stage the beams will start to rot. Inside the build- 'unsteady transfer of heat and moisture') computer program to calculate the transfer of heat and moisture. He explains: "The ad- 50 Fraunhofer magazine 2.2001
vantage of such computations is that things moisture protection layer with the Patent can be simulated which do not yet exist." Computing with WUFI
Office – the Fraunhofer Institute for Build- ing Physics now has the patent rights in al- retrofitting timber-framed buildings a mois- ture diffusion layer is required which in brane. That was in 1995. The research sci- walls to penetrate inwards. In winter, how- Physics, is now used throughout the world to calculate the transfer of heat and mois- mid, the layer must do exactly the opposite.
is suitable for determining the drying time side outwards, as condensation would form and the risk of condensation, it can simu- late various climatic zones and calculate tests: The Fraunhofer engineers studied its In order to find such a moisture diffusion tion work. "With WUFI the relatively time- moisture permeability in a building on the layer, Künzel with his team firstly examined institute's outdoor testing area: the roof dozens of commercially available types of restricted because data is now only need- ed for checking the calculations," explains metal roof was first insulated with mineral fiber and then lined with nylon membrane.
For a whole year, temperature and humidity sensors in the roof provided data. "The re- used to make sausage skins or baking film.
WUFI is now deployed in various versions: sults were excellent. The target values we No one had realized that it could be used had set for moisture transfer were exceed- for insulating walls, let alone roofs.
Institute in Holzkirchen. The WUFI-2D pro- An intelligent,
Sales success in
adaptive membrane
numerous countries
na. Both versions can be installed on PC.
The engineers at Saint-Gobain-ISOVER test- ed the material's fire protection and me- moisture regulation in thermally insulated At the Fraunhofer Institute in Holzkirchen chanical properties, as well as its aging be- roofs. The membrane adapts its permeabili- havior. Their conclusion: "The membrane the environment inside aircraft envelope.
selected for use as a humidity controlled barrier passed both required fire protection which shields the envelope from cabin hu- tests without any fire-retardant chemicals having to be added to the material." The mechanical properties, too, proved highly satisfactory: the membrane displays highimpact strength, and therefore does nottear so readily if someone inadvertentlysnags it with a roof batten. A four-weekweathering test showed that heat and cold brane comes into contact with moisture it positive characteristic of the membrane was swells up, the polar water molecules pene- the material becomes soft. As a result the the roof structure or the timber framework, plastic acquires pores through which fur- The research scientists
tested the function of

not penetrate the pores – unlike the polar the moisture barrier
water molecules. As a final trial the mem- on a building with a
ture penetrates through the pores into the brane was used on a pilot construction site, sheet metal roof.
building interior. Walls and roof dry out.
then in 1997 it was introduced to the mar- ket under the brand name 'ISOVER-Vario'.
creases the pores close up again, and themembrane then acts as a barrier to mois- ty to the ambient air humidity: in winter it ture. In winter this barrier protects the walls plies to several countries in Europe and sells protects against condensation, in summer it facilitates the drying out of roof and wall membrane per year. "We are now in the structures. The 'intelligence' of nylon re- pleasant situation where we are receiving li- sides in its structure: in dry condition the Künzel immediately registered his idea of cense income," Künzel comments happily.
material's plastic molecules form a tight im- using a humidity controlled membrane as a Monika Weiner
Fraunhofer magazine 2.2001

Source: http://www.hoki.ibp.fhg.de/ibp/publikationen/fraunhofermagazin/magazine2_2001_50.pdf


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