Climate-adaptive building shell

Climate-adaptive building shell (CABS) is a term in building engineering that describes the group of facades and roofs that interact with the variability in their environment in a dynamic way. Conventional buildings have static building envelopes, and can therefore not act in response to changing weather conditions and occupant requirements. Climate adaptive building shells, on the other hand do have the ability to change with time. Well-designed CABS have two main functions: they contribute to energy-saving for heating, cooling, ventilation and lighting; and they induce a positive impact on the indoor environmental quality of buildings.

Loonen et al. defines CABS as follows:

A climate adaptive building shell has the ability to repeatedly and reversibly change some of its functions, features or behavior over time in response to changing performance requirements and variable boundary conditions, and does this with the aim of improving overall building performance.

Modern construction methods, developments in material sciences, and availability of controllable kinetic façade components now offer rich possibilities for innovative building envelope solutions that respond better to the environmental context, thereby allowing the façade to ‘‘behave’’ as a living organism. Nature is regarded as one of the most prominent inspiration sources for CABS. Adaptability is pervasive in nature, and efforts in biomimetics to convey nature’s time-tested ideas to the context of buildings are rewarding. The way people sweat, shiver and adjust clothes has been used by many as a metaphor to conceive the building skin as a living membrane. Likewise, several CABS concepts imitate tropism: plants’ directional growth or rotation in the direction of certain environmental triggers. Both phototropism (i.e. changing in response to light) and heliotropism (i.e. changing in response to the sun) have been transformed effectively into CABS concepts, enabling timely collection and rejection of solar energy [59] and [60].

Related concepts
CABS is only one designation for a facade concept that can be described by a range of different terms. Several variations on the term ‘adaptive’ can be used, including: active, advanced, dynamic, intelligent, interactive, kinetic, responsive, smart and switchable. In addition, the concepts of responsive architecture, kinetic architecture, intelligent building are closely related. The main difference with CABS is that the adaptation takes place at the building shell level, whereas the other concepts consider a whole-building approach.

Types of adaptation
The adaptable mechanisms in CABS can be divided in two classes. The adaptive behaviour is either based on a change in properties or behaviour at the macro scale, or at the micro scale. The first type of adaptability in building shells is often also referred to as ‘kinetic envelopes’, which implies that a certain kind of observable motion is present. Adaptation on the macro scale usually results in changes in the building shell’s configuration via moving parts. The types of motion that can be observed vary widely, and are typically described by one of the following gerunds: folding, sliding, expanding, creasing, hinging, rolling, inflating, fanning, rotating, curling, etc. In the other type of CABS (micro scale), changes directly affect the internal structure of a material. Here, adaptability is either manifested via changes in thermophysical or opaque optical properties, or through the exchange of energy from one form to another. Smart materials such as shape-memory alloys or temperature-responsive polymers are often applied to achieve this type of adaptation.

Notable examples
Although the concept of CABS is still relatively new, several hundreds of concepts can be found in buildings all over the world. The following list shows an overview of notable examples.

Built examples
Al Bahr Towers, Aedas, Abu Dhabi
Arab World Institute, Jean Nouvel, Paris, France
Heliotrope, Rolf Disch, Freiburg, Germany
Burke brise soleil – Quadracci Pavilion, Milwaukee Art Museum. Santiago Calatrava, Milwaukee, Wisconsin, United States
Surry hills library, Francis-Jones Morehen Thorp, Sydney, Australia
Bengt Sjostrom Theatre, Studio Gang Architects, Rockford, Illinois, United States
Kuggen movable sunscreen, Wingårdh arkitektkontor, Gothenburg, Sweden
Subsystems and components
Active daylighting
Dynamic insulation
Phase-change material
Smart glass

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