Climate and context adaptive building skins for tropical climates

Climate and Context Adaptive Building Skins for Tropical Climates: a review centred on the context of Colombia Carolina M. Rodriguez and Marta D’Alessandro Departamento de Arquitectura, Universidad de los Andes, Bogotá, Colombia cm.rodriguez@uniandes.edu.co T: (57+1) 3394949 Ext. 4882 m.dalessandro10@uniandes.ed.co T: (57+1) 3394949 Ext. 2485

Adaptive Building Skins is a field of research that has received growing attention in the last few years, since it proposes to combine and complement both, active and passive design technologies into the building envelope. Furthermore, their designs apply principles of adaptability, transformability and evolution, in order to cope with the constantly changing nature of climate. Most of the research in this field has been conducted for the temperate and seasonal climates, characteristic of European and North American regions.

However, little information is available on the application and viability of adaptive building skins for tropical climates. As emerging economies flourish in different countries of South Asia, Central Africa and South America, new opportunities for the use of these types of building envelopes start to materialise. This paper presents a structured literature and case-studies review of current developments in the field, with particular attention to the Colombian context. The distinct geographical features of Colombia allow the existence of a great diversity of climates. Traditionally, these conditions have influenced the development of different passive design strategies for building skins. This paper concludes with a reflection on arising opportunities, where existing methods can be combined and enhanced with alternative concepts that respond to local and available recourses.

Keywords: building skin, façade, kinetic, adaptive, envelope, climate.

What are Climate and Context Adaptive Building Skins?

The term ‘building skin’, as used in this paper, describes the building enclosure, envelope, wrap, cover, shell or cladding, whilst placing emphasis on its association with the protective and responsive nature of the human skin1. For centuries, designers have tried to emulate adaptive characteristics in the building skin to improve indoor living conditions. In addition, since the 1970s and 1980s, energy considerations and climate change have constituted a great driving force behind new developments in the facade and roofing industry.

A variety of building components began to be introduced within the building skin to assist maintaining an appropriate balance between optimum interior conditions and environmental performance by reacting in a controlled and holistic manner to changes in external or internal environments and to occupant intervention (Perino, 2008). Currently, there is a general consent that the Earth’s climate is changing and the policies on energy management are tightening, hence the design of buildings needs to take adaptability into consideration in order to cope with the challenges ahead (Gething, 2010). However, different studies argue that there are no common legislative or strategic planning frameworks in place to guide the design or evaluation of climate adaptation in buildings, either at a regional or at an international level (Malay, The skin is provided with temperature-regulation mechanisms, which allow precise control of energy loss by radiation, convection and conduction. In addition, it constantly changes permeability and pigmentation to prevent excessive entry or loss of fluids and protects us from sunlight, harmful bacteria and pollutants (Lupton, 2002).

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Varshney, & Graham, 2012). There is also a lack of clear definition for climate adaptive buildings and for alternative terms used to describe them(Hasselaar, 2006). Many terms are often interchangeably used to refer to building envelopes designed for changing environmental conditions. For example: adaptive (Gregory, 1986), responsive (Thün & Velikov, 2012),(Kirkegaard, 2011), dynamic(DiBartolomeo, Lee, Rubinstein, & Selkowitz, 1996), (Konstantoglou, Kontadakis, & Tsangrassoulis, 2013), intelligent, resilient, smart (Battle & McCarthy, 1994), (Wigginton & Harris, 2002),(Compagno, 2002), advanced (Selkowitz & Aschehoug, 2003), interactive(Fox & Kemp, 2009),(Sullivan, 2006), active(Goia, Perino, Serra, & Zanghirella, 2010), (Xu & Van Dessel, 2008), switchable(Lampert, 1998) and kinetic(Moloney, 2011). The term CABS (Climate Adaptive Building Shells) have been frequently used in past research projects to describe these types of building envelopes2. In this paper, this definition is taken as reference, since it highlights the need for adaptation to the changing climatic conditions, as well as to the users, whilst maintaining comfort and minimising energy. The term skin is adopted due to its allusion to a responsive system for thermal energy, air and lighting control between indoor and outdoor environments. There is also an allusion to the word context, as a term that encompasses a wider set of variables including economic and social factors.

By definition, adaptability is concerned with the capacity to be adjusted or to respond to new conditions or situations. The main objective behind adaptation in architecture is to diminish the likelihood of a building or building component of becoming obsolete over the longevity of time (Graham, 2005). A common approach to do so is to design a capacity for change. This change can imply a functional or performance change or a physical alteration or modification, either through a short or long period of time. However, adaptability and responsiveness within building skins can be interpreted in a variety of ways. Approaches to building conditioning and environmental control require an advanced understanding of how occupants respond to all the variables of localised indoor environments. Hence, a relatively ‘sophisticated’ level of dynamic control is needed when the desired building impact should remain relatively constant, but the external weather and climate drivers are highly variable3. Given this great degree of internal and external dynamic change, it is believed that building skins must develop the ability to respond ‘intelligently’ to such change (as the human skin does), in order to reduce the energy requirements of the building(Wigginton & Harris, 2002). Diverse concurrent trends towards the optimisation of the building skin have emerged following this principle. For example, certain strategies involve the use of computerised systems embedded within the building skin, which can be programmed to act as a ‘brain’ that gathers information, processes it and uses it to control the behaviour of the skin and regulate internal comfort conditions(Fox & Kemp, 2009). Recent advances in nanotechnology and bio-mimicry have also prompted the application of active smart materials4 on building skin layers, which respond to particular eternal stimuli by modifying their properties and in turn helping to regulate the building internal environment (Ritter, 2006). In many cases, these systems also control integrated kinetic devices that physically and actively transform to regulate internal climate conditions in unison with the external environmental changes. The formal transformation of these devices involves a change in size, shape, position or constitution. Variables, such as position within the skin, extent, plane of action, level of coverage and shape, determine a great range of possible designs (fig.1).

‘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. By doing this, the building shell improves overall building performance in terms of primary energy consumption while maintaining acceptable indoor environmental quality.’(Loonen, Trcka, Costola, & Hensen, 2013) (p. 484)

‘a climate adaptive building shell can adapt itself to the needs of the user of the building and to the changing climatic conditions to which the building skin is exposed, while at the same time the energy use needed for maintaining desired comfort is minimized.’ Definition used in the FACET project, an EOS-LT research project subsidised by Agentschap, NL. P. (DeBoer, et al., 2011) (p.3)

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´Weather´ describes atmospheric conditions over a short period of time. ‘Climate’ describes average atmospheric conditions over a reasonably long period of time, hence it is, to a certain degree, easier to predict than weather.

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Smart materials have the ability to change their properties (mechanical, electrical, appearance), their structure or composition, and/or their functions in a controlled manner to suit desirable behaviours.

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Figure 1. Variables for formal transformation in adaptive components Transformations can be achieved through geometrical operations of rotation, translation or a combination of both (fig.2).

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Figure 2. Transformation through geometrical operations

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The complexity of some of the components used for the above strategies could lead to a frequent misconception that adaptive solutions are initially very costly or that they involve state-of-the-art technology, which need to be constantly updated or require expensive maintenance. On the other hand, there is also the argument that meaningful adaptability is achieved through architecture that ‘gets the basics right’ and is resilient and susceptible to variations on the basic operational parameters (i.e. physical, economic, cultural, environmental, technical, etc.)(Schmidt III, Eguchi, Austin, & Gibb, 2009). Jean Dollfus, in its book about the aspects of popular architecture around the world, argues that even though there are variations produced by local customs and tradition, the main characteristics of established construction techniques depend mainly on the local climatic environment. In so doing, it is possible to draw, parallels between the buildings of the great equatorial forest and tropical savannahs of Africa, Monsoon Asia, Australia, Polynesia and Amazon or the intermediate zones of the Andean region and East Africa (Dollfus, 1954). However, other studies that compare different approaches to sustainable design conclude that the strategies for environmental control in buildings are not universal, and that what works for one part of the world may not work for another. Hence design solutions are meaningless, if they are not considered in a culturally specific context (Kuma, 2013).

This is applicable for the design of climate adaptive building skins, where local parameters may determine different ways in which formal configurations, materials and technologies are used. In many developing countries, the traditional and generalised approached has been to opt for passive design strategies that employ accessible materials and established construction techniques to deal with environmental control. However, as the world becomes more culturally and economically interconnected, architects in these countries tend to experiment more with a variety of materials and methods, in search for alternative solutions to emerging challenges. It makes sense to continue the evolution of the building skin through strategies that acknowledge traditional approaches, but also recognise the dynamic nature of the present context. For decades, Colombia has adopted and adapted architectural principles from a variety of sources. Some systems and strategies tend to be imported and implemented directly, whilst others are advanced and transformed with time (fig.3).

Colombian Context Colombian´s territory is characterised by noticeable economic, social and cultural contrast, as well as abundant wealth of natural resources and environmental diversity. Despite a long political conflict, since the early twentieth century, the country has one of the most stable economies in Latin America, and it is considered among the middle-income countries in the world. Most of the economic dynamics of the country are concentrated in the Andes region, specifically in the triangle formed when connecting on a map its three major cities (Bogotá, Medellin and Cali). Colombia is the third-most populated country in Latin America, after Mexico and Brazil. In addition, 75% of its total population (which is mainly children and young adults) reside in urban areas.

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Figure 3. Key historical factors in the development of adaptive skins

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Geographically, the overall territory is located within the tropics and according to the Köppen–Geiger´s climate classification system5; it has predominately a Tropical/megathermal climate. Neighbouring countries in Central and South America, as well as, other countries in Central Africa and Southeast Asia are also in this classification, which generally describes a non-arid climate with constant mean temperatures of at least 18 °C throughout the year. In Colombia, however, the presence of particularly dominant geographical features, such as the Andes Mountains, Atlantic and Pacific ocean currents and the Amazon basin determines the existence of five, very different, localised climates: tropical rainforest, tropical savanna, steppe, tropical desert and tropical mountain climate. The atmospheric characteristics of the American tropics allow the existence of the so-called thermal floors6, which define five sub-categories of tropical mountain climate: warm climate thermal floor, temperate climate thermal floor, cold climate thermal floor, páramo climate thermal floor, and glacial climate thermal floor. The country in general receives a great amount of direct sun exposure throughout the year, with minor annual fluctuations in temperature, even though in mountainous areas there are strong daily oscillations. In addition, Colombia presents high relative humidity values,​​ ranging between 60 and 95 %7, due to the abundance of rivers and proximity to large bodies of water.

Altitude, temperature and relative humidity were variables used by the Ministry of Environment and Sustainable Development in Colombia to divide the country into four main climatic zones: warm- wet, warm-dry, temperate and cold. The warm-wet is the predominant category, occupying almost 70% of the country. This area is characterised by altitudes ranging between 0 and 800 meters above sea level, average temperatures above 24 °C and relative humidity above 75%. However, the three major cities are all located in different climatic zones. Bogota is considered cold climate, located at 2547m above sea level, with an average temperature of 14 °C and 73% of relative humidity. Medellin is considered temperate climate, located at 1490m above sea level, with an average temperature of 22 °C and 68% of relative humidity.

Whilst Cali is considered warm- dry climate, located at 961m above sea level, with an average temperature of 23 °C and 73% of relative humidity (fig. 4).

Widely used system, which combines average annual, monthly and seasonal temperatures and precipitation to classify the world´s climate into five main groups. 1.Tropical/megathermal climates, 2.Dry climates, 3.Temperate/mesothermal climates, 4.Continental/microthermal climates and 5.Polar and alpine climates.

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In the tropics, the topography is one of the most influential modifying factors to define climatic regions.

These are determined mainly by the altitude, which differentiates vertical regions known as thermalfloors. These are areas with relatively uniform climatic characteristics of rain fall, temperature and solar brightness. Between thermal-floors the temperature varies inversely with the height, decreasing or increasing approximately 1 ° C per 180 m in height. Hence, the higher the altitude, the lower the temperature.

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According to the data recorded by the IDEAM, Instituto de Hidrología, Meteorología y Estudios Ambientales de Colombia (Institute of Hydrology, Meteorology and Environmental Studies of Colombia).

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Figure 4. Characteristics of the Colombian context

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Other variables, such as solar radiation, wind and rainfall, which are not normally decisive in defining major climatic zones, have nonetheless great influence on the design of building envelopes. Due to its geographical position, the entire country has great solar availability, especially in the Caribbean region. The incidence of solar radiation ​​ranges between 2.5 kWh/m² - 7 kWh/m²; whilst solar brightness ranges from 1300 to 2100 hours per year. In most of the country, wind intensity varies between 1 and 3 m/s. The annual rate is higher in coastal areas in the north of the country, while presenting lower values in ​​ the west. Annual rainfall is also highly variable, from an annual 500 mm in the Caribbean region to a 12,000 mm per year in some parts of the Pacific region (Ministerio de Ambiente, 2005).

All of the climatic aspects described above, coupled with economic and social factors, have influenced over time the design of building skins in the various regions of the country. Colombia has experienced major demographic changes since the 1950s, especially in urban areas, which have resulted in the loss of many traditional buildings throughout the 20th century. However, some Colombian modern architecture continues to implement the guidelines of vernacular regional architecture. This underpins the validity of evolutionary solutions in the design and location of buildings and in the use of materials and construction techniques (Saldarriaga & Fonseca, 1992). The roots for the traditional strategies, used in Colombia to control heat and humidity are varied and range from local indigenous practices to European and Moorish and African influences, brought by the Colonies. Over time, each region has refined and evolved these solutions, taking into account its history, localised geographical environment and customs. In general, traditional design principles are based on the generation of buffer zones, inside or around the building, which create microclimates for passive heating or cooling purposes. These are normally combined with ventilation strategies and the appropriate used of available materials, which vary depending on the type of climate. Most of these strategies are based on principles of passive control, in some cases combined with secondary regulating elements (fig. 5).

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Figure 5. Vernacular strategies for climate control in Colombia

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If vernacular traditions are studied from a general climatic approach, rather than only from the analysis of regionally specific solutions, then a more comprehensive view of potential opportunities that may have not been yet explored in Colombia can be provided. In other parts of the world, with similar climatic conditions to Colombia, vernacular climate control strategies have emerged or evolved to become active, adaptive o responsive. For example, the traditional Mongolian Yurts are built with adjustable walls, comprising a lightweight timber pantographic lamella that can be easily folded and packed for transportation. The flexibility of the lamella allows modifying the diameter of the Yurt to form slightly smaller or larger rooms.

In addition, the wall coverings are made of felt, reed mats or animal skin, and its thickness can be adjusted by adding or removing layers, depending on changing thermal requirement and season. The same concept has evolved over time into the development of multi-layered skins. Pioneering systems such as Mike Davies’ ‘Polyvalent wall’ (Davies, 1981), proposed a skin constructed by autonomous layers, where every layer performs a different function. In the system envisaged by Davies, the skin layers provided sealing and insulation, as well as temperature, lighting and ventilation control. Recent takes on this idea suggest flexible layers with different life spans, which enable the skin to be deconstructed and rebuilt in time. Therefore, when working in conjunction, all layers contribute towards creating a responsive envelope optimised for a particular circumstance. Another vernacular active climate control element is the roman velarium or velum, a textile retractable awning which purpose was to provide temporary sun-shade for spectators at theatres. There have been many different takes of this idea, amongst the most innovative are the 17x18m large automatically controlled umbrellas shading the two large courts of the Prophet`s Holy Mosque in Madinah (1992) by SL-Rasch GmbH. Working together these umbrellas form an active kinetic skin that, in the summer months, is deployed to provide shade during the day and contracted during the night to release the thermal energy stored on the building surfaces. Contrarily, in the winter months the umbrellas are closed during the day to admit the penetration of mild-sunrays and deployed at night to protect the building from extreme cooling.

The adjustable layered wall of the Yurts and the retractable velaria are active systems from their origins.

However, some passive vernacular climate control elements have also evolved into active and adaptive systems. An example is the traditional mashrabiyas, wooden lattice screens commonly found in Islamic architecture. As well as providing patterned shades, the different size openings of the mashrabiya generate variable porosity which encourages air flow travelling a different speed trough them. Contemporary adaptive interpretations of this element, such as the transformative façade at Simons Center for Geometry and Physics (1995) by Chuck Hoberman, allow changes in the skin’s porosity through the use of parallel moving layers which align and diverge whilst generating different patterns and permeability levels. A different take on the mashrabiya is proposed for the folding outer skins of Al Bahr ICHQ Towers (2012) by Aedas. The skin of each tower comprises 2,000 hexagonal folding modules, which automatically open or close to control shading, according to the sun’s position.

Case Studies and Future Horizons In order to recognise and understand the contemporary tendencies for climate adaptive building skins present and emerging in Colombia, it was essential for this research to find and contrast case studies. This area of research is not yet established in Colombia; hence case studies are not widely available or already categorised as adaptive. Amongst the projects found, 10 case studies were selected in Colombia and contrasted with 11 representative case studies from around the world. The parameters taken as framework for analysis relate to three main sets of characteristics: applications and functions, formal transformation and movement (fig. 6 and fig. 7).

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Figure 6. Parameters for the analysis of case studies

Figure 7. Selected case studies

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Applications and functions This set of parameters examines the central purpose of the transformation that takes place within the skin.

In broad terms, this transformation can have different underlying rationales, serve mainly as a climate regulator and/or serve as a context mediator. A climate regulator is a system that changes to control basic physical factors of the climate that allow human bodily comfort. These factors are thermal energy (i.e. temperature, air movement, humidity), electromagnetic energy (i.e. visible daylighting, UV light, infrared light) and electrostatic fields (i.e. noise, vibration). On the other hand, a context mediator transforms to facilitate communication and interaction between the context, the building and the users in order to influence experience and behaviour. Many examples of adaptive building skins worldwide are found to behave as climate regulators. For thermal energy regulation, adaptive building components can manipulate their conduction, convection, radiation and storage properties. For electromagnetic energy regulation, changes in transparency, permeability and surface texture can vary lighting distribution or glare. Whilst for electrostatic field regulation, porosity and shape can be altered to block noise or control vibration.

In Colombia, a great percentage of the case studies analysed focused on context mediation more than climate regulation. In examples, such as Capilla del Colegio los Nogales (2001), Chapel Porciuncula del la Milagrosa (2004) or Edificio Athikia (2008) all by Daniel Bonilla, adaptive building elements are primarily employed to re-define space boundaries and integrate the inside with the outside. There are also projects that propose active interaction between the movable element and the user, such Edificio 10B by Camilo Restrepo and J.Paul Restrepo and Restaurante Mezeler by Mauricio Gaviria y Juan Manuel Pelaez, which intend to make the control of lighting more interactive and engaging.

Formal transformation This set of parameters studies the ability of the skin or the skin’s components to allow and handle change.

As mentioned before, physical change can result from modifications of size, shape, position or constitution, through rotation and/or translation. Many different types of movement can be identified in components from adaptive building skins around the world. For example, components that orbit, revolve, swivel, swing, slide, glide, retract, deploy, fold, roll, distort, stretch, flutter, expand and contract, amongst others.

In the examples examined from Colombia, it was noticed that most of the components change position rather than size, shape or constitution. In addition, the most common types of movement found are simple rotation (swivel) on a central pivot and simple translation (slide) on an axis. The preferred contemporary elements appear to be vertical or horizontal swivelling louvers and horizontal sliding shutters.

Technology This set of parameters investigates the diverse means and ways used to generate, transfer and control transformation within adaptive skins in regard to the type of systems, actuators and materials used. When analysing types of systems, three aspects are considered: complexity, scale and position. Three levels of complexity are categorised (high, medium and low); three scales -referenced to the human scale- are recognised (large, medium and small) and three possible positions in relation to the overall arrangement are noted (external, embedded and internal). The actuators are referenced depending of the source of power as natural, automated or manual. Whilst the materials are classified as traditional, when they are recognised as well as used and established within the context, and transformative when they are designed to modify their properties at micro-scale (i.e. smart materials). From the analysis of Colombian projects, it can be argued that the devices used are of low level of complexity, are mainly of small to medium scale, are located primarily on the outside of the skin and use traditional materials.

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Worldwide, passive strategies in architecture have evolved over time to be climate appropriate and improve indoor comfort, Colombia is not the exception. However, with more pronounced seasonal variations, shifting weather patterns, new energy requirements and the ever-changing comfort needs, it has been argued for some time that passive building design is not enough to provide consistent or effective control(Wigginton & Harris, 2002). All of the case studies of adaptive building skins found in Colombia have been built in the last decade, suggesting the there is a recent growing interest in the subject or an underlying consciousness of its importance. Most of adaptive components in these examples are advancements or reinterpretations of active components that have been used for centuries in vernacular architecture. That is openings with manually operable elements, such as wooden shutters, nets and/or curtains. Alternative strategies, such as skins formed by adaptive multi-layers have been little explored. There is also a great potential to transform common and already established passive design strategies into adaptive systems that offer greater flexibility and operability.

In some parts of the world, the idea of adaptive control has changed the way people perceive and manage comfort, becoming more actively engaged in the process rather than acting as mere recipients. The examples in Colombia show that interaction with the user is already taken into consideration. However, interfaces between adaptive components, the environment and the user can be limited by the narrow range of devices currently employed. There is potential to develop more elaborate systems able to modify characteristics such as surface form, insulation, porosity and transmissivity, which are considered fundamental qualities of any given adaptive building envelope (Erickson, 2013). In addition, the Colombian context is ideal for such explorations due to the variety of climates, the relative availability of resources and the interest amongst new generations of designers.

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