Nature can teach us all kinds of things about how to deal with the elements, but little is applied to the design of modern façades. What, for example, a butterfly, a cactus or a bird can teach us about using thermophysical principles to design façade functions more robust and sustainable is what I investigated in my doctoral work at the Delft University of Technology.
In my doctoral thesis on biomimetic design principles applying thermodynamic processes, I identified potential examples in nature, analysed their functional principles and prepared them for a function-oriented transfer into the design process of adaptive façades.
I have developed a systematic transfer procedure, usable in the early design stage, to evaluate the potential of biomimetics for thermo-adaptive façade design and engineering. The goal is also to enable a transfer without loss of information or the need of costly material development. This systematics is the core of my work.
I briefly present here an example and the main intention of my PhD work.
The smartness of the butterfly “wing heart”
A butterfly wing is super-light and wafer-thin, as well as robust and resistant to overheating by solar radiation. This is due to its geometry and its sophisticated heat regulation system: the blood vessels that run through the wing are arranged and designed in such way that heat can be adaptively transported from all regions of the wing and the body. This effect is made possible by passive control of the flow direction and speed in the blood vessels, in which the wing plays an important role. The wing’s sophisticated structure regulates the temperature levels by ‘photonic’ structures that not only provide vibrant colours but also selective heat absorption and emission. The arrangement of light and dark colors created by the photonic structures creates temperature differences that in turn regulate the heat flow. In addition, the position of the wing surface relative to the surrounding surfaces increases heat dissipation (Figure 1); the more heat is dissipated through radiative exchange with the environment, the faster the heat flow.
This complex thermal regulation system, which is also referred to as a kind of “wing heart” (Tsai et al, 2020), functions effectively and adaptively. The transfer of the passively operating, adaptive thermal regulation system to the building envelope, embedded in the structure, may be a sustainable contribution to energy efficient buildings.
However, it is technically difficult to replicate a butterfly wing, particularly when considering construction and building product requirements and framework conditions for developments. But some of the functional principles of this biological example can be easily adopted, without complex (and expensive) efforts. For example, by the deliberate positioning of the “wing surfaces”, respectively the movable elements of a façade (e.g. sunshade louvers), their surface temperatures and thus the temperature behaviour of the façade surfaces, or even the direct surrounding surfaces, can be influenced.
Figure 2 shows conventional blinds (heated during the day) that can be moved to a specific position relative to a surrounding surface at cooler hours in order to drive the heat dissipation of the surfaces, according to the physical law of radiative heat exchange. Tuning the thermal emission capacity of the louvre surfaces might support this effect and can be easily realised. To dissipate heat directly from the interior rooms via this system, a capillary heat exchange system would have to be developed and connected. Here, too, the “wing heart” could serve as suitable role model. Such way, sun shades can be used even more actively and deliberately, and the well established adaptive system is given another important thermal task to support passive cooling.
“Certain functional and direct transferable principles from nature represent an enormous potential that can be instantly implemented in architecture and in façade engineering – without complex and cost-intensive material or system developments, but simply by applying existing design principles in a different way.”
Susanne Gosztonyi
The “butterfly wing concept” is just one of the identified strategies in nature that I analyzed in my doctoral thesis. I have identified about seventy role models for cooling effects out of more than two hundred biological potentials investigated in this work. I also critically analyzed which biological principles can be applied in building design immediately and functionally correct, without high-tech material developments and with the goal to reduce the technical complexity of current adaptive façade systems (Figure 3). This is not always possible; many strategies from nature are technically too complex or only function at certain scales that are hard to imiate. Geometric shape effects on the macro scale are the most feasbile ones for transfer to the façade design language.
The aim of this work is to present ideas for reducing the technical complexity and error-proneness of modern adaptive façades while maintaining or even increasing full adaptive functionality. More active control of heat flows through the façade must be considered in the future in the context of climate change and sustainability measures.
A better understanding of how to integrate thermal physics into design empowers more sustainable building solutions provided by passive measures – and is the fourth dimension of design processes that architecture needs to (re-) embrace in times of climate change.
Susanne Gosztonyi
How biological role models deal with heat and cold, what thermodynamic tricks they use to avoid overheating or hypothermia, how they save material and energy resources in such processes and how to transfer and use such principles in a design process without having to wait for new developments and also to maintain functional correctness is discussed in the published book: “Physiomimetic Facade Design. Systematics for a function-oriented transfer of biological principles to thermal-adaptive facade concepts” (publisher: AE+BE Architecture and Built Environment, Delft University of Technology).
The PhD work is published by 30 May 2022 and can be downloaded on the A+BE Architecture and Built Environment – No. 04 (2022).
Gosztonyi, S. (2022). Physiomimetic Façade Design: Systematics for a function-oriented transfer of biological principles to thermally-adaptive façade design concepts. A+BE | Architecture and the Built Environment. DOI: 10.7480/abe.2022.04 https://doi.org/10.7480/abe.2022.04