In building engineering, a climate-adaptive building shell (CABS) is a facade or roof that interacts with the variability of its environment in a dynamic way. Conventional structures have static building envelopes and therefore cannot act in response to changing weather conditions and occupant requirements. 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.
Definition
The description of CABS made by Loonen et al. says that: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. This definition shows several components that conform CABS, and are addressed in this article.
The first part of the definition is related to its fundamental characteristic; being adaptive envelopes, or in other words, having skins that could adjust to new circumstances. This means that envelopes should be able to "alter slightly as to achieve the desired result", "become used to a new situation", and even return to their original stage if needed. Although occupants’ desired conditions are indoors, they are affected by the outdoor surroundings. 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. Therefore, the objective is to improve the well-being and productivity of people inside the building by making it sensitive to its surroundings.
CABS must satisfy different demands that compete or even conflict with each other. 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. 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. However, it is not sufficient to simply add adaptive features to the design or the existing building, they must be integrated into it as a whole system. Therefore, by using CABS technologies, a variety of opportunities are available for a transformation from "manufactured" to "mediated" indoor spaces.
Related concepts
CABS is only one designation for an envelope concept that can be described by a range of different terms. Several variations on the term 'adaptive' can be used, including: active, advanced, dynamic, interactive, kinetic, responsive, intelligent 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.
Categorization of CABS
Like any other system, CABS have several independent characteristics by which they can be categorized. Therefore, the same CABS may fit somehow into all of these categories. What may be different from one CABS to another is the subcategorization, which discriminates based on the attributes of each one of them. The following are some of the possible categorizations that may be found in the literature.
Climate responsive systems
As the name says, they are categorized based on the climatic factors they tackle. Their behavior is based on producing a change in heat, light, air, water and/or other types of energy. Thus, they are subcategorized into three types: solar-responsive systems, air-flow-responsive systems, and other natural sources responsive systems.
Solar responsive systems
They are based on managing solar energy in different formats. Usually, they use one of the following five types of solar control devices: external, integrated, internal, double skin, and ventilated cavity. The first type of solar energy is solar heat. CABS related to this type of energy are intended to maximize solar heat gain in winter and minimize them in summer. Some examples of this technology are the solar barrel wall (water-filled oil barrels), water bags on the roof, dynamic insulation, and thermochromic (change color due to temperature) materials on walls to get appropriate color and reflectance responding to the outside temperature.