NEW WAX-BASED HEAT STORAGE FOR BUILDINGS

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NEW WAX-BASED HEAT STORAGE FOR BUILDINGS
12 August 2003 - Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.

Everybody visiting an old church or temple has experienced the cooling effect of thick walls. On the other hand, heat waves particularly affect buildings constructed in lightweight materials.

The walls cannot absorb much thermal energy, causing room temperatures to increase rapidly in summer. Researchers at the Fraunhofer Institute for Solar Energy Systems ISE have found a way to pack the temperature-balancing effect of thick walls within a millimeters-thin layer of plaster. In a joint project funded by the German Federal Ministry of Economics and Labor, the scientists have developed a new class of construction material in collaboration with colleagues at BASF, Caparol, Heidelberger maxit and Sto.

The trick: The materials contain micro-encapsulated paraffin. "This wax-like additive stores thermal energy via a reversible process," explains Peter Schossig of the ISE. "This greatly increases the thermal storage capacity of indoor plaster and dry construction elements." Thanks to the tiny wax-filled balls, a mere six-millimeter thick facing can absorb just as much heat as a solid brick wall over a 24-hour cycle. When the wax melts, energy is absorbed and stored as latent heat, without significantly raising the temperature of the paraffin. When outside temperatures lower again, the paraffin returns to its solid state and the latent heat is released again. "So far, wax is the only phase change material suitable for use with plaster," explains Schossig. "The melting point of the wax can be set to meet the needs of the particular construction material - in theory a temperature range of 10 to 90°C." In order not to interfere with the structure and hence compromise the strength of the construction material, the wax is encapsulated in tiny plastic balls. This powder has a very high specific surface, promoting rapid heat transfer to and from the immediate environment. It can be mixed with wall plaster or spackle in a ratio of up to 1:3 by weight. In the end, the heat-storage medium is troweled onto the wall like any other plaster. There you have it - "integrated air conditioning".

The first PCM products are meanwhile commercially available. "These materials are especially suitable for use in office buildings, where heat stored during the day is discharged during the night, when the building is usually unoccupied," says Schossig in summary. They also help some of the ISE employees to keep a cool head during hot summer days in their new institute building.

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About: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
The Fraunhofer-Gesellschaft undertakes applied research of direct utility to private and public enterprise and of wide benefit to society. Its services are solicited by customers and contractual partners in industry, the service sector and public administration. The Fraunhofer-Gesellschaft maintains over 80 research units at more than 40 different locations throughout Germany. A staff of some 12,700, predominantly qualified scientists and engineers, works with an annual research budget of over one billion euros. Of this sum, more than € 900 million is generated through contract research. Two thirds of the Fraunhofer-Gesellschaft’s contract research revenue is derived from contracts with industry and from publicly financed research projects. The remaining one third is contributed by the German federal and Länder governments, as a means of enabling the institutes to pursue more fundamental research in areas that are likely to become relevant to industry and society in five or ten years’ time.

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