Climate-adaptive building shell
In building engineering, a climate-adaptive building shell is a façade 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.Emerging technologies of Climate Adaptive Curtain Wall
A climate-adaptive building curtain wall possesses the ability to repeatedly and reversibly modify its heat transfer characteristics in response to evolving performance demands and variable environmental conditions. This adaptation aims to enhance the overall efficiency of the building.This capability entails the continuous adjustment of the envelope's parameters autonomously, without relying on external power sources. The primary objective is to elevate the comfort and productivity of individuals within the building by enabling the structure to sensitively react to its surroundings. Additionally, an adaptive shell offers energy-saving benefits, technology demonstrates a potential of 30% reduction in total energy consumption.
However, it's not enough to merely advance the technology; it's equally crucial for the new technology to seamlessly integrate into existing infrastructure. To achieve this, the system perpetually alters the building shell's heat transfer properties by air circulation within the hermetically sealed curtain wall panel, achieving the desired effects. Consequently, this pioneering technology will significantly diminish the carbon footprint of tall buildings while enhancing the well-being of their occupants.
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 bags on the roof, dynamic insulation, and thermochromic materials on walls to get appropriate color and reflectance responding to the outside temperature.Another type of solar energy is solar light. CABS linked with this energy source are based on the control of indoor illuminance levels, distributions, windows views, and glare. To accomplish these tasks, there are three main ways: with traditional mechanical systems innovative mechanical systems, and smart glass or translucent materials. This last one is used in windows and can achieve its goal in four ways: change in optical properties, lighting direction, visual appearance, and thermophysical properties. Between these smart materials, electrically-activated glazing for building façades has gained commercial viability and remains as the most visible indicator for smart materials in a building. The third kind of solar energy is solar electricity which mostly relays on installing integrated photovoltaics systems. To be considered CABS they must have the ability to be kinetic, rather than individually movable panels. Normally this is achieved through the use of heliotropic sun-tracking systems to maximize the solar energy capture.
Air-flow responsive systems
They are those related to natural ventilation and wind electricity. 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. At the same time, they must replace it with new and fresh air, usually coming from the outside. Some examples of this type of technology are kinetic roof structure and double skin facades. Other less common types of CABS are the ones generating wind electricity. Thus, they convert wind energy into electrical energy via small scale wind turbines integrated into buildings. This can be for example as wind turbines fitted horizontally between each floor. Other examples may be found in buildings such as the Dynamic Tower, the COR Building in Miami and the Greenway Self-park Garage in Chicago.Other natural sources systems
They may account for the use of rain, snow and additional natural supplies. Unfortunately, no extra information related to this issue was found.Based on the time frame scale
As dynamic technologies, CABS can show different configurations over time, extending from seconds up to changes appreciable during the lifetime of the building. Thus, the four types of adaptations based on the time frame scales are seconds, minutes, hours, and seasonsThe variation that takes place just in seconds are found randomly in nature. Some examples may be short-term variations in wind speed and direction that may cause shifts in wind-based skins. An example of a shift that occurs within minutes is the cloud cover which has an impact on the daylight availability. Therefore, CABS that use this kind of energy may also fall into this category. Some changes that adjust in the order of hours are fluctuations in air temperature, and the track of sun through the sky. Finally, some CABS can adapt across seasons, and therefore are expected to offer extensive performance benefits.
Based on the scale of change
The adaptive behavior of CABS is related to how its mechanisms work. Therefore, they are either based on a change in behavior or properties.Macro-scale changes
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.Based on their adaptive level, the macro scale mechanisms can be divided into two types of systems: intelligent building skins and responsive façade systems. The first ones use a centralization building system and sensing equipment to adjust to weather conditions. They should be capable of learning from the occupants' reactions and considering future weather fluctuation to respond accordingly. Some examples of this kind of feature are building automation and physically adaptive components such as louvers, sunshades, operable windows or smart material assemblies.
A responsive façade system has the same functions and performance characteristics of an intelligent building skin but goes even further by having an interactive aspect. This means it incorporates components such as computational algorithms which enable the building system to regulate itself and learn in time. Therefore, a responsive building skin, not only includes mechanisms for satisfying occupants desires and learn from their feedback, but it also encourages a dual educating path where both the building and its residents take place in a constant and growing conversation.