Study of the hygroaccumulative effect of natural materials

The main goal of this project is to improve the hygrothermal conditions in the interior of buildings. Concretely, this means keeping the relative humidity in a range that is optimal for people in closed rooms. This factor is essential for the human well-being as well as for work productivity. The aim of this project is to achieve the above-mentioned effect through the development of special building materials in combination with a specially designed greening system. In more specific terms, clay-based materials will be mixed with a series of selected natural substances such as fibers, minerals etc. This should improve the absorption and emission of water vapor in order to keep the relative humidity at an optimum. The ideal relative humidity for human health is in the range of 40-60 %, for which the materials are to be designed and optimized. In the interest of providing a regulated moisture input, green wall systems are to be placed in the interior space. Water evaporates through their leaves and through the substrate, raising the relative humidity inside the building. For the realization of the project, computer simulations as well as laboratory experiments and measurements are to be carried out. The Brno University of Technology deals with the selection of substances for the optimal mixture of building materials, analyzes their physical and chemical properties and ultimately produces them. The Vienna University of Technology attends to the wall greening systems in the interior as well as the investigation of the interaction between greening and the new developed surface. This encapsulates the choice of suited plants and the compilation and development of suitable substrate in combination with the clay-based building materials. Different systems and components will be examined in advance regarding selected properties, such as the release of water vapor, the ability to absorb water or their resistance to mold growth.

A Healthy Indoor Climate Through Natural Materials and Plants A healthy indoor climate is crucial for human well-being. Optimal relative humidity lies between 40 and 60 percent. In tightly sealed modern buildings, however, the air is often too dry or too humid, while pollutants like fine dust accumulate. Instead of relying on energy-intensive air conditioning, this project investigated a sustainable, passive alternative: The goal was to maintain this optimal 40-60 percent range through the targeted interaction of special clay-fiber panels and indoor green walls. Additionally, the project explored how this system reduces indoor fine dust. The research team from TU Wien and TU Brno investigated how ecological building materials and indoor plants interact synergistically. They tested various clays (including highly absorbent montmorillonite), natural fibers from agriculture and wood processing (straw, hemp shives, wood shavings), and eleven mineral plant substrates. Selected indoor plants were also analyzed under laboratory and real-room conditions. Mixing natural fibers into moisture-sensitive clay prevented cracking, resulting in highly stable bio-composite panels. These absorb excess airborne moisture and release it when the environment becomes dry. Practical tests revealed that these panels, combined with indoor plants, reduce absolute humidity peaks by an average of 7.7 percent under real room conditions. Small-scale experiments showed reductions of 17 to 23 percent, depending on the materials and plants used. The combination of montmorillonite clay and wood shavings emerged as the most effective variant for buffering humidity. Simultaneously, the mineral substrates for the green walls were investigated. Beyond supplying water, the focus was on the evaporation dynamics of these substrates, as their internal pore structure significantly impacts indoor humidity. The results prove that evaporation-and thus indoor humidity-can be actively controlled depending on the specific substrate and irrigation method. The plants' evaporation performance was also analyzed under various lighting conditions, times of day, and substrate water contents. Furthermore, it was proven that indoor plants effectively deposit harmful fine dust (PM2.5) on their leaf surfaces, with the Boston fern showing the highest deposition rate. To evaluate these factors at the building level, extensive computer simulations were conducted. This basic research establishes the scientific foundation to use such ecological elements in building physics practice. Developments based on this can promote human health through stable humidity and cleaner air. The results also provide the groundwork for reducing building energy consumption, as less artificial climate control is required. Finally, the project demonstrates how utilizing agricultural and forestry residues creates valuable, sustainable building materials for the circular economy.