German Solar Retrofit Project Tests New Facade

Transparent insulation materials, commonly known as TIMs, are a popular application in solar renovation projects in Europe. As part of Task 20, Solar Energy in Building Renovation, a new TIM application is being tested on the historic Villa Thannheim building in Freiburg, Germany. The challenge was to renovate the building using solar systems without changing the building's unique character. The participants of Task 20 visited this building during a meeting held in Freiburg in March 1995 and were impressed with the use of the new TIM.

The Villa Thannheim was recently converted to an office for the headquarters of the International Solar Energy Society and a guest house for the Fraunhofer Institute. The building was renovated using 52.5 m2 of a new transparent insulation material on the west wall of the building. This product, manufactured by STO, a large German producer of industrial/construction materials, combines concrete with a TIM consisting of low-iron glass beads in a matrix of polyurethane and an UV-stabilized binder. This new material has a stucco-like finish that is suitable for both new and old buildings and can be easily fitted to selected parts of a facade. The result is not actually transparent or translucent, but the material serves a function similar to other TIM products while giving the appearance of a conventional facade. The transmission of this new TIM is approximately 50%. In the case of Villa Thannheim, the effective U-value is 0.54 W/m2-K. The predicted annual savings from the wall is 51 kWh/m2. On a south wall, the potential savings would double, but problems of overheating could arise. Besides the TIM, new windows and increased insulation were added to the building.