Lightweight Facade Element for Urban Rainwater Harvesting and Evaporative Cooling
Presented on October 12, 2022 at Facade Tectonics 2022 World Congress
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Building envelopes cover a considerable part of the urban exterior surfaces, and to therefore have a significant leverage effect on the climate resilience and sustainability of buildings and cities. Whereas the majority of existing facades is designed to provide only minor qualities on a district or urban level, research at the Institute for Lightweight Structures and Conceptual Design at the University of Stuttgart (ILEK) focuses on the development of a new type of building skins to improve urban rainwater and temperature management.
The implementation of textile materials in the building skin opens a revolutionary new spectrum of functionalities in the facade: with a minimal weight per unit area, the use of special, functionalized textiles as a retention surface enables decentralized absorption, targeted use, and time-delayed release of precipitation water. The purpose of the research is the development of a hydroactive facade element that allows a considerable reduction of run-off water by retaining the precipitation water hitting the facade as well as a decrease of the urban heat island effect (UHI) by evaporative cooling of the building and its environment by the absorbed water; thus, addressing the rising climatic impacts of urban architecture by global warming as well as by heavy rain events resulting in inundations with considerable personal and material injury.
An essential part of the hydroactive facade is an external, multi-layered 3D-textile, which acts as a collector and evaporator, in addition to its aesthetic surface structure. In this paper we investigate the design, the potential as well as the installation of the HydroSKIN as it is to be implemented in both new and existing buildings.
Society is facing existential challenges: The increase in the world's population, growing urbanization and climate change. These are directly related to each other, thus particularly impacting the built environment.
According to a United Nations study, at an average birth rate, the world population is expected to reach 9.74 billion people by 2050 (United Nations 2018a), 70 % of whom are expected to live in urban areas (United Nations 2018b). Assuming that a living space requirement of 47 m² per capita according to German building standards (2019), the net addition of about 1.84 billion people over the next 19 years would lead to a demand for an estimated 86.5 billion m² of additional living space by 2050 - a demand that will inevitably lead to a significant densification and high-rise construction due to the limited open space capacity of inner-city areas (Federal Statistical Office of Germany 2020).
These construction developments have a significant impact on the release of greenhouse gas emissions. It is estimated that the construction industry is currently responsible for 50 - 60 % of global resource consumption, 50 % of mass waste generation, 35 % of energy consumption, and 39 % of emissions (Global Alliance for Buildings and Construction 2019). According to the latest findings of Professor Werner Sobek, even more than 50 % of emissions worldwide are caused by the building sector (Sobek 2021), whereas urban areas actually account for 60 - 80 % of global material consumption and 75 % of global CO2 emissions.
According to the Intergovernmental Panel on Climate Change (IPCC), anthropogenic emissions of greenhouse gases are the highest in history. These cause the rise in hot temperature extremes observed since 1950, and the associated equivalent increase in heavy precipitation events. According to IPCC projections, in many regions, the intensity, frequency, and duration of heat-waves and extreme precipitation events are expected to increase in the future (figure 1). In particular, mid-latitude land masses and humid tropical regions will face more frequent and intense extreme precipitation events as global surface temperatures rise. (IPCC 2014)
The increasing urbanization and densification enhance the land sealing ratio of urban surfaces, intensifying both problems. Inner-city zones, characterized by a high ratio of sealed areas (in some cases over 90 %) and insufficient natural retention surfaces such as green areas, are particularly affected by both inundation and heat risks. Increased heavy rainfall events exceeding the prescribed design rainfall strain the hydraulic capacity of conventional sewage systems and, in combination with insufficient buffer areas for rainwater retention, lead to severe flooding. This results in considerable damage to property and personal injury. (Pucher et al. 2018)
The urban heat island effect (UHI) describes the temperature increase of up to 10 K in metropolitan areas compared to the surrounding countryside (DWD German Weather Service 2017). This temperature gradient results from the absorption of solar energy by sealed road and building surfaces combined with anthropogenic heat sources emanating from vehicles, air conditioning, and other energy sources. The effects of climate change will amplify both climatic extremes analogously in the future. (Memon, Leung and Chunho 2008)
The causal relation between heat and heavy precipitation events is shown in figure 2. Notwithstanding the aspects of pluvial infiltration, the high ambient temperatures on the one hand cause an increase in evapotranspiration from water surfaces and vegetation. Water vapor saturation pressure on the other hand rises exponentially with the air temperature. The resulting moist, warm air ascends into the atmosphere, where it condenses into clouds resulting in increased heavy precipitation events. (Liebscher 1984)
In order to avoid irreversible damage to humans and the environment, the IPCC is pursuing two complementary approaches to protect from and responding to climate challenges (resilience). On the one hand, climate protection aims to reduce climate change (mitigation) by significant and sustained reductions in greenhouse gases. Since far-reaching climatic consequences are to be expected even with a complete cessation of CO2 emissions, strategies, and technologies for adaptation to the actual or expected climate situation as well as to its impacts are being developed with the goal of reducing or avoiding damages. (IPCC 2014)
The building sector is considered to have a considerable leverage effect in terms of climate resilience. The combination of climate mitigation and adaptation strategies, in particular, is seen to have great potential for dealing with the global environmental issues in a sustainable and effective way. Nonetheless, the state of the art in climate‐resilient façade concepts does not offer any integral approaches for combining climate mitigation and adaptation strategies, while simultaneously addressing both climate impacts on urban architecture. (Eisenbarth et al. 2022a)
Taking into account the quantities and flows of building materials that will be required in the future due to the growing world population (United Nations 2018a) combined with the rising urbanization (United Nations 2018b) and further considering the limited availability of natural resources as well, the establishment of material and resource-efficient construction methods will be inevitable (Sobek 2014 a, 2014b, 2016).
In this context, the building envelope in particular is given a great weight. The implementation of lightweight building materials in the facade enables a significant weight reduction for the entire building, with the purpose of minimizing the grey energy and CO2 emissions bound in both new and existing buildings. Especially in high-rise constructions, the use of lightweight envelope systems can achieve considerable, indirect savings in the foundation and supporting structure, which in turn will significantly contribute to climate mitigation.
Table 1 Approximate calculation of the mass per unit area of different facade infill materials
Wood panel construction
Thermal insulation composite system
Textile facade with fluid-flow
Mass per unit area
~ 150 kg/m²
~ 125 kg/m²
~ 63 kg/m²
~ 45 kg/m²
~ 25 kg/m²
Compared to conventional facade materials due to the minimum weight per unit area listed in Table 1, textile and film-based materials open up a previously unexploited ecological, economic, and design potential for their implementation in architecture.
The Institute for Lightweight Structures and Conceptual Design (ILEK) at the University of Stuttgart has been in charge of the development of lightweight facade systems based on textiles and foils for years. Such would represent a substantial savings potential for both new and existing buildings.
While textile buildings were mostly designed as single-layer membrane constructions, e.g. for roofing and shading large areas, their suitability in terms of building physics for facade applications has now been proven through continuous further development towards multi-layer systems (Gropper and Sobek 1985; Haase et al. 2009). Multi-layered textile building envelopes, as shown in figure 3, are constructions made of flexible high-performance materials such as woven fabrics, knitted fabrics and foils, which form the external, thermal building envelope while fulfilling all building-physical requirements of a facade. The single layers are framed in a profile system allowing an easy disassembly and recycling of all components. (Haase et al. 2011a; Haase et al. 2011b). The use of textile materials in the facades opens new design options as well as potentials for climate mitigation in the construction industry.
Collaborative Research Centre 1244
The development of the HydroSKIN is part of the subproject C01 entitled "Adaptive building envelopes with microclimate performance", within the framework of the Collaborative Research Centre
The multi-dimensional advantages of facade-integrated decentralized rainwater management consist not only in relieving the load on urban sewage infrastructure but also in reducing global water and energy consumption. The use
The potential of vertical facade surfaces for rainwater retention is validated on the example of the D1244 demonstrator high-rise building by calculating the driving rain yields hitting the facade
Retrofitting of Existing Buildings
The HydroSKIN is a modular lightweight facade element to be implemented in preferably urban new but also existing buildings. The lightweight textile HydroSKIN element can be
Conclusion and Outlook
The increasing densification of buildings and sealed surfaces, combined with the consequences of climate change, leads to pluvial inundations and extreme heat events, which particularly affect urban areas. Building envelopes
The content generated within the CRC1244 / Subproject C01 funded by the German Research Foundation (DFG) - project number 279064222 - has significantly advanced the development of textile-based hydroactive facades. The authors would like to express their sincere thanks to the funding sponsors as well as the following cooperation partners from industry and commerce for their generous support:
Dr. Zwissler Holding AG, Eschler Textil GmbH, Essedea GmbH & Co. KG, KARL MAYER Holding GmbH & Co. KG, pervormance international GmbH, WICONA Bausysteme GmbH
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