Small spheres against climate change - Energy efficiency and comfort thanks to intelligent building materials

(f.l.t.r) Dr. rer. nat. Ekkehard Jahns, Prof. Dr. rer. nat. Volker Wittwer, Dr.-Ing. Peter Schossig

Prof. Dr. rer. nat. Volker Wittwer (Spokesperson)
Dr. rer. nat. Ekkehard Jahns*
Dr.-Ing. Peter Schossig

Fraunhofer-Institut für Solare Energiesysteme ISE, Freiburg
*BASF SE, Ludwigshafen

Air-conditioning systems in residential, commercial and public buildings are in. On hot days, they ensure that indoor temperatures are comfortable – but they also use lots of energy and are a contributing factor to global climate change. How can this be avoided?

Prof. Dr. Volker Wittwer, Dr. Ekkehard Jahns and Dr. Peter Schossig have found a way to improve the quality of indoor comfort while keeping energy consumption to a minimum and protecting the environment. Volker Wittwer was the founding member of the Fraunhofer Institute for Solar Energy Systems ISE – the largest European solar research institute – and until mid-year was also its deputy director. Ekkehard Jahns is manager for global product development of polymers for architectural coatings at BASF SE. He has contributed many years of experience in microencapsulation to the project. Peter Schossig has been active in the area of thermal energy use since 1995 and has headed the group “Thermally active materials and solar cooling” at ISE since 2005.

The basis for the innovation developed by the three research scientists are latent heat storage materials or phase change materials (PCM). Use of these materials is based on physics: During the transition from a solid to a liquid state, a PCM absorbs vast amounts of energy from its environment without heating up itself. The absorbed heat is “hidden” inside. When this happens within a certain temperature range, such as between 21 and 26 degrees centigrade, latent heat storage materials can be used in summer to prevent residential or office space from heating up above these comfortable temperatures.

To make latent heat storage materials useful as an element of building materials, Volker Wittwer and Peter Schossig at Fraunhofer ISA thought up a trick. It consisted of packaging single drops of the storage material in minute casings – experts refer to microencapsulation. Ekkehard Jahns at BASF developed the necessary technology and discovered paraffin wax as a suitable latent heat storer. The wax drops are encapsulated in small spheres made of acrylic glass just a few micrometers in diameter. These microcapsules can easily be integrated in building materials such as mortars, plaster and wood and are very sturdy: they are not affected by drilling holes or driving nails. With their large surface area, the numerous storage capsules produce a rapid exchange of heat. Since at night they release the heat they absorb during the day, they reduce temperature fluctuations and create a balanced indoor climate.

The team began developing latent heat storage materials for buildings in the mid 1990’s. In 2004, BASF introduced to the market one of the first gypsum wallboards to include latent heat storers. Since 2008 the company produces micro capsules as a mass product. They have already been used in numerous building projects and have attracted the attention of building owners and architects worldwide. Building materials with PCM capsules provide protection from overheating during the summer and can even replace “power-hungry” air-conditioning systems in whole or in part.