Innovative façade materials that promote cooling in urban areas
In the future, urban areas could potentially be cooled down during extreme heat waves thanks to a new material called Hydroskin, as suggested by its creators. This innovative substance, reminiscent of a water-absorbing membrane, collects and stores rainwater. When temperatures rise, the stored water evaporates, cooling the building and its surrounding environment. At present, Hydroskin is undergoing outdoor trials.
The material boasts flexibility and durability, as well as being porous and tear-resistant, much like a robust, water-absorbing skin for buildings. Christina Eisenbarth, an architect and research associate at the University of Stuttgart, believes Hydroskin could revolutionize the way we combat heatwaves and heavy downpours in urban settings. She envisions utilizing the facades of existing and new buildings to utilize collected rainwater for evaporation and cooling purposes on hot days. Hydroskin is constructed using several layers of fabric held apart by threads, allowing it to store water and release it through evaporation when required.
At present, the system is being thoroughly tested in an outdoor trial, with a prototype located on the University of Stuttgart's campus. Researchers are keen to establish whether the material can withstand heights of up to 36 meters, after numerous lab trials demonstrated its strength. Hydroskin is particularly suited to high-rise buildings due to its large facade areas, as according to Eisenbarth, the higher the building, the more rain is collected on the facade compared to a roof of the same size.
The system is encapsulated within a water-permeable membrane that allows the majority of raindrops to pass through, as per the university. The inner film guides the water downwards for storage in a reservoir or direct use within the building for tasks such as washing machine usage, toilet flushing, and plant watering. On hot days, the textile facade is moistened with water, which enables cooling through evaporation.
Urban heat islands pose a significant challenge for city dwellers. According to Eisenbarth, the increasing sealing of urban areas disrupts the natural cycle of precipitation and evaporation, ultimately leading to the transformation of cities into heat islands and floodplains. The concept of a "sponge city" aims to halt this process. It involves the capacity of a city to absorb excess water, store it like a sponge, and subsequently release it slowly through evaporation or infiltration. Hydroskin operates in accordance with this principle.
Stefan Petzold from the Nature and Biodiversity Conservation Union (NABU) sees Hydroskin as a means of improving city living, similar to the implementation of green facades, renovated roundabouts, and repurposed parking spaces. "By de-sealing, we return something to nature," says Petzold, the NABU expert for urban nature. The economic benefits of incorporating plants in construction are highlighted by the example of Humboldt University in Berlin, which saves €15,000 annually through natural cooling instead of air conditioning. As per Eisenbarth, the costs associated with implementing Hydroskin are manageable, with one square meter estimated to cost the construction company several hundred euros.
Wolfgang Schubert-Raab, President of the Central Association of the German Construction Industry, finds Hydroskin particularly intriguing in the context of increasingly unpredictable weather phenomena, such as those witnessed in Passau. In such situations, Hydroskin can be deployed flexibly, for instance, in the temporary construction and cooling of container kindergartens.
The University of Stuttgart provides some statistics: Typical building surfaces can reach temperatures of over 90 degrees Celsius under intense summer sun, whereas Hydroskin can reduce temperatures by up to 17 degrees. The collected water reduces the amount of runoff that directly enters the sewer system, potentially causing flooding when the absorption capacity is exceeded. According to Eisenbarth, 5.7 square meters of Hydroskin are capable of cooling as effectively as an air conditioner with 2500 watts.
Environmentally Friendly Material
The material, made from recyclable polyester at present and set to be manufactured from PET bottles in the future, is also environmentally focused. It may also be customized through digital printing, allowing architects to give buildings a distinctive, personalized appearance. Eisenbarth does not foresee any concerns regarding statics issues - a square meter of Hydroskin weighs only 1.2 kg in the dry state and up to 4.7 kg in the wet state.
Eisenbarth developed Hydroskin as part of her doctoral research at the Institute for Lightweight Design and Construction at the University of Stuttgart. As the founder of a startup, she aims to swiftly introduce this technology into the construction sector. She has already secured a client: Schubert-Raab, a prominent Bavarian construction entrepreneur, intends to test Hydroskin as part of a project focusing on new building materials for utility buildings.
Schubert-Raab is also testing other climate-friendly materials, such as using storm and pest wood for construction, which also sequesters large amounts of carbon dioxide. He is also investigating the application of moss panels for heat insulation, air purification, and cooling within buildings, as well as testing specialized lime plasters that absorb and release considerable quantities of moisture. In his company, he is also experimenting with solar cells installed on walls and specialized ceramic facades.
The City of the Future could potentially incorporate the use of Hydroskin, an innovative material that revitalizes urban environments during heatwaves and heavy downpours. Christina Eisenbarth, an architect and research associate at the University of Stuttgart, envisions this material being utilized on the facades of existing and new buildings, harnessing the power of evaporation for cooling purposes on hot days.
