Further Investigations and Monitoring of the Green Walls at GRG7 Kandlgasse

Cities around the world are growing and the increasing number of inhabitants requires ever denser development. As a result, more and more green spaces have to give way. Thus, not only climate change, but also the intensified urban heat island effect is leading to ever higher temperatures in urban areas. This not only affects the quality of living and life, but also the daily routine at work and school in inner cities. While air conditioning systems are increasingly used as a short-term solution to cool the interior, they heat up the exterior even more and therefore do not represent a sustainable solution for adapting the city of the future. Innovative approaches and possible solutions are needed, especially for children and young people as the generation of the future, to design the learning and teaching environment in a quality manner. These learning and teaching spaces already have a great need for indoor air quality improvement even without the additional challenge of rising temperatures. The use of classrooms by large numbers of students and teachers for concentrated learning and work places high demands on healthy indoor air that often cannot be met.

Building greening, both externally on the façade and roof, and on walls internally, offers the opportunity for greenery in places where previously there seemed to be no room for it. The positive effects of such greening measures are manifold and have already been partially proven in national as well as international research projects. However, there is still a lack of long-term results and detailed observations of individual influencing factors in order to be able to make reliable, sustainable statements about the effectiveness of greening buildings. Such findings can help to identify greening solutions that are optimally adapted to everyday school life and the respective school situation and to formulate recommendations.

Following on from the completed research project "GrünPlusSchule", in which various greening measures were implemented at and in a school in Vienna's 7th district (GRG7), this follow-up project takes up further unanswered questions and is dedicated to detailed measurement data evaluations of the effects of indoor and outdoor greening. For this purpose, existing measurement data from the previous project were evaluated further and with a different focus, and new measurement data were obtained and analysed accordingly. The project focuses, among other things, on the effects of wall-mounted indoor greening on hygrothermal comfort as a function of weather conditions. A distinction is made between different radiation conditions and temperature.

The evaluations concluded that the greening has a cooling effect, especially on sunny summer days, and that the plants' moisture release provides a comfortable indoor climate in winter. The focus of the investigations carried out on the wall-mounted outdoor greening is both the effects on the indoor climate of the adjacent rooms and the influences on the microclimate, as well as the more in-depth investigation of the relationships between the combination of vertical outdoor greening and photovoltaics. The influences of the entire courtyard greening on the microclimate were investigated by means of a simulation with uhiSolver and concluded that a cooling effect of up to 2°C can be determined, but the perceived temperature is significantly higher due to lower air velocities and reflection of the surfaces. A simulation with the program WUFI was carried out to analyse the effects of greening on the indoor climate. This study, based on different variants, showed that the greening of the façade serves both as shading of the plane behind it, as well as improves the thermal insulation of the wall and has cooling effects on the microclimate and the environment of the greening. The combination of these three effects also has a minor positive impact on the indoor climate. The synergistic effects of greening and photovoltaics on the roof have already been highlighted in the project GrünPlusSchule. In the present project, the combination of photovoltaics and greening on facades was investigated. It was shown how the greening element affects the temperature and performance of the PV modules, with the aim of highlighting to what extent different distances between façade greening and photovoltaic panels lead to different surface temperatures of the modules. In this follow-up project, these investigations were carried out on green infrastructure that has already been installed as part of the preliminary project.

The implementation of vertical greening measures in particular is often associated with high costs. Accordingly, one endeavour is to create more cost-effective alternatives that can be implemented in particular for everyday school life and by students themselves. Such a greening option could be developed in another preliminary project carried out by the project team and was implemented in this project together with the students of GRG7. The planting of the completed walls was carried out with different individual plant species as well as a mixture, which are suitable for such forms of greening and are usually used, with the aim of finding out through the metrological investigations whether a plant species is particularly suitable for improving the indoor air quality.

For the metrological investigations, existing measurement data from the preliminary project (2015-2018) was used on the one hand, and new measurement data was generated on the other. The new measurement data were obtained by still existing measurement infrastructure for temperature and humidity data and by newly added measurement instruments. The new measuring instruments included sensors for fine dust and CO₂ to be able to make statements about the indoor air quality and the effects of the greening systems.

The findings obtained in this research project once again make an important contribution to understanding and demonstrating the effects of green infrastructure in and on school buildings in urban areas.

TU Wien, Institut für Werkstofftechnologie, Bauphysik und Bauökologie
Forschungsbereich Ökologische Bautechnologien

• Univ. Prof. Dipl.-Ing. Dr.techn. Azra Korjenic, Dipl. Ing. Jutta Hollands BSc,
• Alexander Pichlhöfer,
• Tamara Gonaus BSc,
• Eldira Sesto
• Michael Mitterböck