The wall construction of this retrofit building consists from the inside to the outside of a gypsum plaster, first brick layer, air gap, second brick layer, the old plaster, EPS (extruded polystyrene) boards for insulation, and the fagade collectors. The collector has been mounted with a backside of oriented strand boards (OSB), the insulation of the collector is mineral wool. The absorbers of the three collector modules have been coated with different shades of blue colour which were developed in the project. Also in this case, the collector has a non-ventilated backside and is thus directly integrated in the fagade of the building.

Just like for "System Korneuburg”, calculations with WUFI have been made to investigate the risk of condensation which could harm the building materials. The results have shown that no harmful condensation will occur. Due to the air gap between the two brick layers which acts as a relaxation layer, this had not been expected.

Effective U-values have been calculated for the above mentioned winter days with high and low solar irradiation respectively. On a day with high solar irradiation the effective U-value of the wall construction with integrated fagade collector is approx. 86% lower than the static U — value for the wall construction. Even a day with low solar irradiation, an improvement of the

static U-value of up to 25% is possible. The following table gives an overview of the calculated static and effective U-values of the wall construction with and without integrated fagade collectors.

WandMax results show that even in summer no harmful temperatures occur behind the collector backside, even if the collector is in stagnation. The maximum temperature at the EPS boards was calculated with 46°C. In this case, the temperatures at the backside of the collector are more critical since the maximum allowable temperature for EPS is approx. 80°C.

The ambient temperature and relative humidity, temperature and relative humidity between the glass cover and the absorber and behind the collector backside have been monitored and analysed to investigate the real hygro-thermic processes within the wall.

The analysis of the data has shown a good correlation with the simulations done in advance. The relative humidity at the most critical point for condensation — the back side of the collector — has not exceeded values of 80% in the documented period from December 2003 to February 2004. Most of the time, the relative humidity at the backside of the collectors is about 50% to 60%. Short increases of the value up to 80% have occurred but the humidity dropped to usual values shortly after. The reason for the increase can partly be found in an increase of the relative humidity at the outside of the collector and the intermediate space between glass cover and absorber.

The mounting of the collectors onto the wall has been examined for thermal bridges just like for system Korneuburg. The results have shown that the mounting construction can be optimized by inserting insulation material around the mounting screws, which would otherwise be located in direct contact to ambient temperatures.

Summarizing, the data show the suitability also of this wall construction for the integration of non-ventilated fagade collectors.

Conclusions

Fagade collectors have opened a new field of application for solar thermal systems. The technical feasibility of the technology has been proved in many realised systems. Architects have begun to discover the possibilities and advantages of fagade collectors and see the need of coloured absorbers for a broad dissemination of the systems. The development of selective colours for absorbers is an essential step to construct visually attractive systems with thermal performances comparable to state-of-the-art absorber coatings. Questions of building physics have been investigated and results show that condensation will not occur with direct integrated fagade collectors.

Fields of application can be seen in newly constructed houses as well as in retrofits, but also for multi-purpose and public buildings, where direct solar irradiation onto the south fagade is not appreciated.