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Depiction of a recommended operational mode in summer, TU Munich.
© Ebert Ingenieure and Lang Hugger Rampp GmbH

Simulated courtyard perspective for the HFT Stuttgart building.
© Lang Hugger Rampp GmbH

Simulated interior perspective for the TU Munich building with a converted basement.
© Lang Hugger Rampp GmbH
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Refurbishing buildings with membranes

Together with partners from industry, scientists at the Bavarian Center for Applied Energy Research (ZAE Bayern), Munich University of Applied Sciences and HFT Stuttgart have optimised the properties of membrane structures and developed concepts to enable the use of films and fabrics for the energy-based refurbishment of buildings. There are four basic application areas:

  1. Facade and roof consist of a membrane.
  2. Building-in-building principle: A membrane structure spans the entire building.
  3. The membrane envelope acts as a second skin, comparable to a double facade made of glass.
  4. Roofed-over atrium: A courtyard can be retrofitted with a roof.

All versions place considerable demands on the planning and technical building services equipment. However, during the course of the research project it has been shown that it is particularly worthwhile retrofitting courtyards with roofs. The improved A/V ratio of such building complexes in itself provides advantages relative to the initial situation in terms of the energy use. This application area was therefore examined more closely.

Roofing over atria

The scientists developed a concept for roofing over courtyards for two properties belonging to the HFT Stuttgart and TU Munich (Fig. 3, 4). The research work focussed on the thermal flow conditions and the daylight situation in the atrium and adjacent rooms. The results show that ventilation possibilities need to be provided via the membrane roof since the indoor temperature constantly rises in summer with the height. Cushions that can be pushed upwards provide an option here. A variable gap is created in accordance with the lifting height. A sufficient number of controllable air inlets provide the necessary air exchange.

The daylight situation depends on the geometry and size of the roofed-over courtyard. In the case of the HFT Stuttgart, the small and narrow surface area with a roof surface of 400 m2 means that the adjacent office spaces are already supplied with insufficient daylight at a room depth of 2 metres. In Munich, with a roofed-over surface area of 1,300 m2, the offices have sufficient daylight.

The climate concept places high demands on the technical building services equipment. Atria behave in a similar fashion to air collectors, whereby the air temperatures vary considerably in accordance with the air exchange and solar irradiation. Natural ventilation through suitable openings in the roof and air inlets near the ground is not suitable for all weather situations. It is therefore recommended to use mechanical ventilation with an air exchange rate between 2.5 and 4 h-1.

The use of the courtyard should already be decided upon before the planning starts. This determines the technical measures and the concept used for the technical building services equipment. The desired room temperatures are an important criterion. Depending on the use, these vary between 14 °C (for circulation and exhibition spaces) and 22 °C (for office and conference areas). The technology used must be able to deal with continuously changing conditions. Sufficient sensors for the temperature, air movement, etc, need to be planned in for this purpose. A good example is the concept for the Small Palace Courtyard in Dresden. The roofed-over inner space provides a vestibule for the ticket counter and a foyer for exhibitions, which means that the thermal comfort requirements are clearly defined.

If the atrium is to be used as a workspace, it needs to be heated. This utilisation presupposes that the membrane roof is well insulated. This heating, however, can cancel out the saving effects achieved. The researchers have therefore developed a model that can calculate the temperature of the atrium at which the savings effect is lost. They have proposed combining building element activation with a ventilation system to provide the heating system. The heated air can also be blown into the atrium at a greater height when needed via jet nozzles. This system can also be used for cooling in summer. The building element activation needs to be connected to ground water cooling for this purpose (Fig. 2). 

Projektinfo 08/2012:
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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)