Climate-adaptive building shell
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.
While these outcomes can be broadly defined, there is a consensus that the purpose of CABS is to provide shelter, protection, and a comfortable indoor environmental quality by consuming the minimum amount of energy needed.
For example, they must find the compromise between daylight and glare, fresh air and draft, ventilation and excessive humidity, shutters and luminaires, heat gains and overheating, and others among them.
[3] The dynamism of the envelope required to manage these compromises could be accomplished in various ways, for example by moving components, by the introduction of airflows or by a chemical change in a material.
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.
A climate-adaptive building curtain wall possesses the ability to repeatedly and reversibly modify its heat transfer characteristics (U-Value and SHGC) in response to evolving performance demands and variable environmental conditions.
CABS linked with this energy source are based on the control of indoor illuminance levels, distributions, windows views, and glare.
The first ones have the goal of exhausting the excess of carbon dioxide, water vapor, odors and pollutants that tend to accumulate in an indoor space.
As dynamic technologies, CABS can show different configurations over time, extending from seconds up to changes appreciable during the lifetime of the building.
It is often also referred to as “kinetic envelopes”, which implies that a certain kind of observable motion is present, usually resulting in energy changes in the building shell's configuration.
This is commonly achieved via moving parts that can perform at least one of the following actions: folding, sliding, expanding, creasing, hinging, rolling, inflating, fanning, rotating, curling, etc.
Some examples of this kind of feature are building automation and physically adaptive components such as louvers, sunshades, operable windows or smart material assemblies.
[2] These kinds of changes directly affect the internal structure of a material either via thermophysical or opaque optical properties, or through the exchange of energy from one form to another.
[2] The most attractive property that catches the designers’ attention is its immediacy or real-time response, which in turn improves its functionality and performance, and at the same time decreases its energy use.
Thus, the variation in properties and behaviors are transferred from biological representations that provide environmentally, mechanically, structurally or material-wise efficient strategies to buildings.
[10] While just for being constructed any building generates changes in its environment (such as solar patterns and wind variations), by having the ability to maximize the use of exterior resources it mitigates its environmental consequences.
Thus, CABS use the “existing natural energies to light, heat and ventilate the spaces”,[2] obtaining maximum thermal comfort conditions.
As an example, by incorporating the photovoltaic principles into the glass intended to be used in facades, the new skins will generate local and non-polluting electricity to supply the buildings’ energy needs.
[2] Also, it promotes the use of daylight, that when it comes from a window with an exterior view it “results in increased productivity, mental function, and memory recall”.
[3] As Mols et al.[3] claim, CABS is an immature concept, needing more research due to the lack of successful applications in practice.
Since the concept of CABS relays on changes, it is sometimes related to devices and technologies that require higher operational and maintenance activity than static envelopes.
However, Lechner [7] states that the current reliability of cars demonstrates that movable systems can be made that require few if any repairs over long periods.
He finishes this idea by saying that “with good design and materials, exposed building systems have become extremely reliable even with exposure to saltwater and ice in the winter”.
Its independence of any external input (electricity, thermal energy or data) enables its continuing functionality, even in case of power failure.
In the contemporary period, the façade is often liberated from its structural task letting for more flexibility to fit in diverse contexts such as saving/generating energy, providing thermal properties for comfort, and adaptability to changing conditions.
[1] However, most of the current status of CABS is focused on trying to better understand the concepts behind these technologies to be transferred and implemented in practical ways on buildings.
One of the main reasons is the challenges of combining multiple disciplines like architecture, biomimetics and engineering to finally develop, analyze and measure performance.
Adding to this issue, the transition from digital models to the physical application requires the teamwork of experts from different fields, which sometimes can be hard to achieve.
For example, from the research of Kuru et al.[5] the results show that the light management CABS are most comprehensively developed while the energy regulations are the least studied.
CABS are not the exception, and to be successful developers must take the risks, for example, the ones related to long periods of payback time and high operative costs.
