Abstract
This article discusses research case studies that deploy physical computing with kinetic, pneumatic, and smart material technologies as vehicles to address the prospects of these technologies and their future impact on resilient and high-performance buildings. It looks into conceptual aspects of an integrated hybrid system that combines both computation approaches and unique opportunities inherent to these hybrid designs.
Introduction
Material science and computation are emerging as the two most formative drives in design by reexamining the “whats,” “whys,” and “hows” of innovative practices. The impact of emerging smart material technologies with their unique properties has started to transform the built environment in the same ways as it did within science, engineering, and product design. The ability to wire this new matter—interconnect into a broader network—and provide memory, anticipation, and autonomous operability extends its potent qualities into larger structures such as a building or a city.
This article reviews research and experimental projects in the context of climate-adaptive systems and the intersection of new smart materials, kinetic and pneumatic designs, and electronic technologies. In particular, it focuses on emerging practices that employ active materials such as shape- and phase-changing materials combined with open-source electronic platforms.
Climate-adaptive design
Buildings are a significant contributor to the human carbon footprint and are responsible for 30% of global energy demand, with more than 55% of global electricity consumption. 1 The most recent report by the Intergovernmental Panel on Climate Change (IPCC) 2 published in October 2018 states that human activities have already contributed 1.0°C of global warming, and further warming is likely to reach 1.5°C between 2030 and 2052 if it continues to increase at the current rate (Figure 1). The report also shows that measures “limiting global warming to 1.5°C with no or limited overshoot would require rapid and far-reaching transitions in energy, land, urban and infrastructure (including transport and buildings), and industrial systems.” 2
Observed global temperature change and modeled responses to stylized anthropogenic emission and forcing pathways.
Climate-adaptive building designs are being developed, which can respond to the changing and often unpredictable weather patterns, and at the same time reducing the carbon footprint of our architectures. A significant portion of the energy consumption in buildings is dedicated to maintaining a stable interior climate. Dynamic and responsive features in the architectural domain hold promise for assisting in regulating the interior climates of the built environment and reducing the energy consumption of contemporary heating, ventilation, and air conditioning (HVAC) systems. Adaptive façade systems that can mitigate solar heat gain in buildings have been studied and might offer solutions to this problem of ever-growing complexity.
Data-driven design
Critical steps in addressing global environmental concerns are the development and implementation of evaluation frameworks and building performance standards. While these are partially addressed through building codes and building certification programs, such as Leadership in Energy and Environmental Design (LEED), 3 Passivhaus, 4 or MINERGIE-P, there is a continuous need to develop new high-performance building technologies and systems. This can only be achieved through evidence-based and data-driven design practices. A necessary part of this solution is building technology research with testing and evaluation during the design stage (as early as the conceptual phase), construction, and building post-occupancy. Gathered data need to be actionable, with the ability to be generalized and applicable to other conditions. Data also need to be shared and measured against other similar projects. The Embodied Carbon Network 5 database provides building-embodied carbon information that is benchmarked and normalized to facilitate life cycle assessment (LCA) material tracking. 6 Similarly, the American Institute of Architects’ (AIA) 2030 Design Data Exchange (DDx) 7 platform streamlines the process of recording and sharing zero-energy and carbon-neutrality data. DDx allows individual firms to benchmark their projects internally within the organization and against other firms.
However, data-generating buildings require integration of distributed sensing within building assemblies and implementation of building management systems (BMSs) together with Internet of things (IoT) technologies to record and process data. This means that conventional building designs are increasingly enhanced with smart materials and embedded technologies.
Passive design strategies
Passive designs are a broad class of buildings and systems that respond to local microclimate and site conditions to minimize a building’s energy use/footprint while maintaining users’ comfort and health. This optimized energy performance is achieved by harvesting renewable energy sources, such as wind and sun, to provide cooling, heating, lighting, and natural ventilation. The goal of passive designs is to minimize, or even completely eliminate, the need for mechanical (fossil fuel–based) space conditioning.
Even if not in the fully zero-energy state, passive designs help to reduce temperature fluctuations and improve indoor air quality. As such, they provide an effective path toward high-performance, net zero/positive, and resilient buildings.
Common strategies for passive buildings include (1) continuous insulation throughout the entire building envelope with minimal thermal bridging and infiltration of outside air, (2) shading systems to minimize glare and solar gains, and (3) high-performance windows and doors to help manage solar gains while providing adequate daylighting. The latter strategy is often combined with thermal mass that allows for thermal energy storage during the peak heat-gain hours and release when the temperature drops. The benefits of thermal mass are often achieved with architectural elements, such as the Trombe wall or roof pond systems 8 exemplified in Harold Hay’s Skytherm House (1973) or Jonathan Hammond’s Sherwood House (1976). However, similar effects, even with a greater energy performance impact, can be achieved with smart materials, such as phase change materials (PCMs), discussed later in this article.
While passive design strategies provide a good starting point toward net zero and net positive energy buildings, enhancing passive designs by smart/adaptive and occupant-aware technologies allows for greater fine-tuning of building performance and improved user satisfaction.
Active design systems for building envelopes
Basic adaptive and smart design strategies involve a building’s responses to changes in the environment and occupant use patterns. For example, solar shading systems respond not only to the sun angle, as a passive design would do, but also to the season and indoor temperature, taking under consideration whether solar gains are beneficial or undesirable from the perspective of building occupants and/or performance. Similarly, daylight may only be needed when occupants perform tasks that require it. In other situations, windows may contribute to energy losses due to their relatively high U-value, and as such, they could be counterproductive in terms of the energy-saving criteria. Consequently, the need to solve for multiple, often dynamically changing, factors requires equally dynamic building envelope designs and responses.
Adaptive buildings are not a new phenomenon. Operable windows and shutters have provided occupants in the past with the same functionalities as in currently developed smart buildings. More recently, a number of researchers and designers started to expand this adaptive paradigm with a broader set of tools and technologies. This is evident in the emerging literature reviews focusing in building envelopes.9–13 The new components are automation and intelligence, which allow for unassisted and decision-based actuation. Another significant change compared to past manually operated adaptive buildings is in the type of active and smart systems used today. Contemporary solutions rely not only on electromechanical and pneumatic but also on biological- and material-based designs, all powered by intelligent software frameworks attuned to building inhabitants and the environment. All these categories not only expand building technology technique offerings but also provide fertile ground for interdisciplinary collaborations. This is evident in the number of research projects discussed later in this article.
Electromechanical systems
Early designs of kinetic and adaptive buildings involved mechanized systems with some electrical and sometimes electronic controls. They were the direct legacy of the Industrial Revolution, which associated kinetic movements with mechanics and pneumatics.
Current state-of-the-art projects such as Hoberman’s 14 kinetic structures and facade assemblies still build on this tradition and on occasion introduce exotic materials such as sensors and transducers. However, in their entirety, kinetic designs continue to apply industrial and mechanical thinking to architecture. While these kinetic practices represent a successful and effective lineage of design thinking, future designs should also take full advantage of currently available material, information technologies, and other sciences. Projects such as Aegis Hyposurface by dECOi 15 add interactive and software-driven qualities to the purely electromechanical approach, making design assemblies responsive to users.
Electronically controlled mechanical systems provide the ability to centralize control and monitoring. They are generally reliable, inexpensive, and easily maintained, particularly when made of modularized components. Standardization of elements is a critical part of effective mechanical kinetic designs.
However, mechanically based systems require an independent energy source to power their operations and usually are executed in a purely actuating role, without harvesting energy and feeding it back into the system. This is a particularly significant limitation, since the nature of direct current (DC) motors (utilized by kinetic façades) would naturally lend itself to energy generation as well. Certainly, this would provide new challenges to designers, since most current design approaches do not easily allow for this double role. However, this would allow adaptive façades to optimize not only energy consumption but also energy generation.
The adaptive façade of the Institute du Monde Arabe in Paris exemplifies the strengths and limitations of purely mechanically operated designs. While this was an early successful implementation of a kinetic shading façade, it also became an effective case study for what works and does not work with this approach. Placement of shading on the interior side of the glazing significantly reduces its solar gain effectiveness. While it prevents solar glare and controls the amount of illumination, it offers only minimal benefits for the reduction of heat gains. Once the sunlight enters the building, most of its energy is absorbed in form of heat, with little reflection to the outside.
The tendency to place mechanically controlled screens on the inside—protected from the elements—is directly related to their reduced performance when exposed to weather conditions.
A similar approach, yet on a much larger scale, is present in ARUP’s Al Bahr Towers in Abu Dhabi, where kinetic panels are limited to the cooling effect of shading devices. Since the shading is positioned on the outside of the building thermal envelope, there are no adverse impacts from the solar heat gains.
A new generation of adaptive façades, such as Hive Systems (Figure 2), uses information technologies extensively to control individual building components and to share information in between. In this case, the façade design is a system of interconnected panels, with each of them working as a sensing and actuating element. Each component has an awareness of its surrounding panels and freely shares data with its neighbors. A significant advantage of this approach is its scalability. Removing an existing component (taking it offline) or adding a new component (putting it online) is quickly recognized by the rest of the system, and these new elements are immediately incorporated into the entire assembly. In addition, the peer-to-peer communication approach provides another layer of reliability and resiliency, effectively functioning as a decentralized active organism. If any damage occurs to one of the panels, the remaining panels continue to function.
Components of the Hive System.
Electromechanical kinetic systems are a core component of any smart building that relies on automatically operable windows, doors, and partitions for ventilation and cooling. The Bullitt Center 16 in Seattle, WA, provides a fully adaptive building skin with automated windows paired with indoor and outdoor shades and controlled by building automation systems (BASs). In this kind of implementation, building automation provides a low-energy solution for a high-performance building envelope and actuation system: the motors are only powered when opening or closing action is enacted. The combination of window and shade actuation allows for optimal energy savings and building occupants’ comfort.
Pneumatic systems
Soft pneumatic systems provide an alternative path for adaptive building assemblies. They utilize soft expandable surfaces actuated through pressurized air and/or vacuum suction. These systems are characterized by their rather gentle actuation, with relatively low dimensional precision as compared to electromechanical assemblies. They also have distinct “on” and “off” states—inflated and deflated—in contrast to electromechanical systems that generally do not have a preferred resting position or configuration unless impacted by gravity. This characteristic may often become a driving force when designing for resilience and developing solutions that require a particular fail state in case of power outage or system breakdown. However, pneumatic systems tend to require a continuous supply of pressure or vacuum, since air leakage is usually unavoidable, particularly in large and complex assemblies. This increases their energy footprint, because the system needs to be pressure active for extended periods of time.
Soft pneumatic systems provide designers with new opportunities, since pneumatic actuation changes the spatial configuration of individual components, which in turn transforms the physical properties of the entire building assembly. For example, dimensional and textural changes to a wall will also impact its thermal insulating properties by increasing conductive resistance for heat (R-value) or the wall surface’s acoustical properties. 17 In addition, embedding sensing and data-processing abilities into pneumatic actuators allows for highly distributed material intelligence with fine resolution and precision.
A number of researchers have investigated pneumatically driven building components and assemblies. Park and Bechthold 18 developed prototypes of the soft modular pneumatic system (SMoPS), which consists of autonomous interconnected modules forming a larger building assembly. Each module is capable of sensing, actuating, and data processing, which enables individual components to respond dynamically to stimuli from the environment and users. SMoPSs utilize capacitive sensing for object and human localization with the intent to use it as a feedback mechanism for the module actuation. The same feedback mechanism at the scale of the entire assembly can initiate emergent behaviors, triggering localized actuations of individual modules. SMoPS actuators comprise an elastic body capable of shape changes and a pneumatic double-loop system maintaining negative (vacuum) and positive pressure.
Park and Bechthold 18 proposed multiple scenarios including responsive façade shading, ceiling, floor, and interior screen. The responsive interior wall is reminiscent of hyposurface 19 wall design achieved with lower energy expenditure and softer interface and actuation. Similarly, the Soft Frit project developed a pneumatic frit system employing modular silicon bladders with changing shading apertures. 20 Nagy et al. 21 proposed an adaptive solar façade utilizing a pneumatic actuator, with multiple air chambers allowing it two degrees of freedom. Research demonstrated an effective and precise use of pneumatic actuators in dynamic sun tracking. Since this particular project focused on the development of proof-of-concept prototypes, there are no data on the durability or actual energy use required to continuously operate these actuators.
The Soft Robotics for Architects 22 project demonstrates transitional thinking in adaptable façade design where material performs in parallel with mechanical and electronic systems. In the project, a series of sophisticated pneumatically activated soft panels are deformed to produce various levels of wall opening apertures. While this approach stands in direct contrast to the purely mechanical solutions discussed earlier, and as such is possibly more reliable, it still uses material in a purely actuating role.
The Soft Magnetic Façade 23 (Figures 3 and 4) integrates silicon-based soft actuators with a number of composite materials, including thermochromic dye and magnetic iron powder, which provide unique physical properties to the adaptive façade assembly. Thermochromic dye enables material color and level-of-transparency changes based on the ambient temperature, while magnetized silicon helps to seal soft actuators with the curtain wall glass to control air movement in and out of the double-skin cavity. The combination of both exemplifies an emerging approach to active façades, which takes advantage of a number of electronic (embedded), pneumatic, and material technologies to develop a comprehensive and performative façade design.
The Soft Magnetic Façade with thermochromic pneumatic components.
Testing of pneumatic panels.
Another project utilizing pneumatic design strategies combined with open-source electronics is the ICT Media Building in Barcelona, Spain. It uses a combination of pneumatic frit cushions and Arduino-based microcontrollers to control solar illumination and heat gains inside the building. Since the pneumatic panels are installed in a double-façade arrangement, they do not have the impediments of capturing solar heat present in the Institute du Monde Arabe building. The strategy used in the ICT Media Building allows for individual addressability of each panel (Figure 5) and thus for individual control, communication, and if need be, overwrite of its behavior. These facilitate both localized and globalized controls. While this project does not have the interconnected nature of the Hive Systems, it could potentially follow a similar route due to the analogous underlying informational technology framework.
Controls for the individual cushion panel (right) with Arduino microcontroller and 7-bit DIP switch for ID address (left).
All the modules discussed here follow similar pneumatic design strategies. Variations in material thickness translate to various levels of elasticity, resulting in a preferred direction of actuation and deformation state. Internal grooves and channels, depending on their size and allocation, form expansion chambers guiding the deformation process. 24 As these are form-active modules, there is significant wear and tear on soft modules, particularly with a large number of actuation cycles. This sets additional design requirements to make modules easily replaceable, with interchangeable parts and standardized connections. Consequently, the showcased modules utilize stand-alone components capable of mass production in a relatively wide range of configurations and sizes, to be assembled on-site into equally modular pneumatic armature.
Material-driven systems—smart materials and composites
Smart materials are a particular class of materials that can react to changes in their environment with a significant material response that originates at the scale of molecules, the nanoscale. These fascinating materials can be engineered at the molecular level to respond to inputs such as photons of light, temperature differentials, chemical substances, magnetic fields, or electricity. The output that is generated by these materials can fall into two distinct categories. Either the materials can exhibit a significant change in their properties, such as a change in color or viscosity, or they can facilitate an energy exchange in which they can turn one form of energy to another. Examples of the latter category are piezoelectric materials that can turn a mechanical deformation into an electric potential difference.
Smart materials can fulfill the functions of sensors and actuators, solely powered by ambient energies, and are essentially not unlike microcontrollers that include programmable input/output peripherals. In contemporary active and reactive façade systems, these small computing devices have the potential to take on functions that would usually be performed by these small computing devices. The smart substances have been demonstrated to assist in controlling ventilation, stabilizing the thermal environment, managing solar heat gain, guiding daylight deep into outbuildings, and producing electricity. A selection of smart materials that are polymorphic, chromic, light scattering, and/or have the capability to stabilize the thermal environment are discussed in the following section.
Polymorphic materials
Polymorphic or shape-changing materials are perhaps some of the most spectacular materials and have inspired many novel kinetic façade designs.
Shape-memory alloys
Shape-memory alloys (SMAs) are thermoresponsive polymorphic materials that exhibit a “shape memory effect.” At low temperatures, they can be easily deformed. After being heated up to their transition temperature, they will revert to a preset or remembered shape. Many actuator designs that integrate SMAs as wires that can be stretched at cold temperatures and that will return to their original length upon heating have been demonstrated. Another common embodiment for SMA actuators are compression or tension spring configurations (Figure 6). The actuator designs have to be considered carefully to ensure that the SMA is not deformed excessively, so that the material can perform its tasks for millions of cycles without material fatigue.
Left: SMA tension spring. Middle: SMA hysteresis loop. Right: actuator design with SMA compression spring on the top and a bias spring of a standard material.
Nickel–titanium alloys are the most commonly used SMAs. They can be engineered to respond to very specific temperatures by introducing impurities such as copper into the alloy. The material’s hysteresis can also be manipulated through the material composition.
A number of screen systems for architectural façades have been demonstrated that help regulate solar heat gain through glazing, solely driven by ambient room temperature. At low temperatures, the screens open up to allow the rays of the sun to penetrate deeply into the building and warm up the environment. When the rooms get too warm for human comfort, the actuator is triggered by the temperature change and closes the screen to deny the solar heat gain.
Smart Screen by Decker Yeadon is such an example of a screen system that uses an SMA spring actuator to control solar heat gain. The spring set drives a piston-like linear actuator that activates a mechanism designed to align or misalign openings in the screen.
Similar in design intent and activation conditions, the Smart Textile developed at the Material Dynamics Lab at New Jersey Institute of Technology (NJIT; Figure 7) incorporates the SMA in the form of a wire setup. The smart material is directly attached to a textile and opens and closes openings in the fabric structure. Through this direct integration, the SMA can be evenly distributed in a façade system and react to changes in room temperature directly where they occur.
Smart Textile incorporating shape-memory alloys.
Digital thermostats that are instrumental in controlling conventional HVAC systems are programmed to display a hysteresis that does not simply turn the heating or cooling systems on or off at a single specific temperature. In order to avoid a constant switching between on and off states, the thermostat is programmed to maintain a specific temperature range. Similarly, upon heating, an SMA actuator will trigger a material response at a specific temperature and will go back to its original state at a lower transition temperature (Figure 6). This allows the material assembly to operate with a similar precision to that of the thermostat-controlled environment.
Thermal expansion materials
Paraffin wax actuators can use the material’s phase change property to activate a piston system. The material driven actuator has been studied at the TU Munich 25 to influence thermal and visual comfort in facade systems. The actuator performance, akin to the SMA actuator described in Figure 6, can drive, for example, shading devices. 26
Dielectric electroactive polymers
Dielectric electroactive polymers (DEAPs) are another example of a smart material that has been explored for façade applications. The shape change in these materials is triggered by applying a voltage to two electrodes that are sandwiching a polymeric soft core. The electrodes become attracted to each other, squeeze the core, and hence trigger the deformation. Since this material motor requires an electrical stimulus, it is usually activated through computing devices such as microcontrollers. Projects such as ShapeShift,27,28 conceived in a collaboration between ETH Zürich and the Swiss Federal Laboratories for Materials Science and Technology (EMPA), or the Homeostatic Façade System 29 by Decker Yeadon envision these smart materials in the façade context. The Homeostatic Façade System, in particular, envisions a use that goes beyond the control of solar heat gain and even guides daylight deep into buildings. Using the highly reflective silver electrodes inherent to the DEAP that was utilized, this project could actively manipulate light with a high degree of control at the façade level.
Hydrogels
Hydrogels, some of which can absorb up to 400 times their own weight in water and hence undergo a significant change in volume, are chemo-responsive shape shifters. In climate-adaptive building features such as green walls or green roofs, they have been used to ensure plant health, especially in the early growing stages. Water retention in green walls in particular is notoriously bad due to water runoff and inadequate moisture storage capacity. The design strategies that are devised to alleviate the effects of water runoff involve energy-intensive pump systems that continuously circulate water through the vertical green structure. Integrating hydrogels can reduce the amount of energy used for irrigation. The material can absorb large amounts of water and then slowly release it to the plant life.
Color-changing materials and light-scattering technologies
Contemporary architecture stands out due to its significant use of glazing. As previously mentioned, the extremely high percentage of glass in our building skins not only allows for views but also significantly impacts the thermal balance of our interior climate. While the previously mentioned strategies are controlling the solar heat gain at the macroscale, smart materials can enable similar strategies at the nanoscale.
Thermotropic materials
Thermotropic materials can respond to a temperature differential with a change of their molecular structure through a phase change that alters their optical properties. The material will allow daylight and heat gain into the interior environment at low temperatures, while at high ambient temperatures, it will switch from transmissive to light scattering. Thermotropic hydrogels, polymer blends, and resins have been synthesized with these amazing optical properties. 30 SOLARDIM®-ECO, 31 for example, developed by the Fraunhofer Institute for Applied Polymer Research, uses a thermotropic resin layer that is sandwiched in between two layers of glass. The visible and dynamic transition occurs between 25°C and 42°C and diffuses the light while reflecting up to 30% of the solar radiation. The benefits of this self-regulating material strategy, which needs no electricity, sensors, or computing devices, lie in its ability to reflect light back into the exterior environment and simultaneously allow diffused light to illuminate the interior. The drawback of the technology is that the user has little or no influence on the control of view in façade elements that apply materials that use thermotropic substances.
Thermochromic materials
Thermochromic materials change their color due to a temperature differential. At low temperatures, for example, the materials can appear clear, and at high temperatures, they can exhibit a color. Although this technology has great potential, only a few examples have emerged on the architectural market. Hurdles in the materials’ development stem from cost effectiveness, life span, control of transition temperature and color, and scalability of the technology. Often, the chromic materials display a darker color at the high-temperature state that effectively blocks solar heat gain, and so the materials simultaneously absorb the sun’s energy and radiate it back into the environment. Some product examples, such as Suntuitive self-tinting glass, 32 are available on the market, but the application has to be scrutinized carefully. The Suntuitive laminate assembly is installed together with a series of other strategies, such as an insulated glass unit and a low-emissive coating. This way, the chromic layer can heat up after the color transition, while the heat gain within the material assembly is not allowed to transition into the interior environment. Similar to the thermotropic materials, thermochromic strategies resist an override by the end user, and the control of views is solely driven by changes in ambient temperatures.
Electrochromic materials
Electrochromic technologies that can reversibly change their color when a voltage is applied have been effectively demonstrated to aid as a light-control and shading device. 33 Unlike the thermally driven materials, electrochromic glazing relies on electricity, sensors, and computational elements for its operation. Even though they consume modest amounts of energy, electrochromic materials can be used for low-energy climate-adaptive strategies and can also be programmed to respond to individual user needs. Many of the electrochromic materials that can transition between a transparent state and a colored state have been found to be absorbing rather than reflecting. 34 Hence, the installation within a facade system has to be carefully scrutinized similar to the above-described thermochromic application. Electrochromic devices that are combined with photovoltaic technologies have been demonstrated in self-powered systems that do not require any external wiring. 35
PCMs
PCMs are substances with high latent heat storage, capable of absorbing and releasing large amounts of thermal energy during melting and solidifying at narrow temperature ranges. They are characterized by the ability to capture heat without a significant change in temperature until all the material is transformed from the solid/liquid to liquid/gas phase. 36 Although liquid-to-gas transitions provide a higher heat absorption and release than solid-to-liquid phase changes, liquid-to-gas transitions are not commonly used in thermal storage applications due to the high pressure and large volumes required for the materials in their gas phase.
Architectural applications of PCMs have a long-established history that is a conceptual offspring of the Trombe wall design. In 1978, Timothy Maloney filed the US Patent 37 application for the “[p]hase change energy storage panel for environmentally driven heating and cooling system,” which was granted in 1982. This design features movable PCM insulated panels (Figure 8) and sets a precedent for most of the subsequent façade designs seen to date. Maloney’s design also demonstrated an effective development path for porting passive designs, such as the Trombe wall, to adaptive and smart building solutions.
US Patent 4,290,416 for phase change energy storage panel granted in 1981.
More recently, a number of researchers engage PCMs to develop various high-performance designs, each examining additional functionalities and assembly strategies. Junghans et al. 38 combined PCM (paraffin) into a structural insulated panel (SIP) and combined it with outside fixed shading to further fine-tune solar heat gains, considering seasonal sun angle changes. Junghans et al. developed and tested prototypes of the assembly, called Latitudo Borealis, to demonstrate heat storing and heat redirecting strategies for high-performance building envelopes. The validation was achieved with the environmental test chamber and temperature sensors placed within the PCM wall assembly (Figure 9). In addition, the research involved fine-tuning of shading configurations with computational evolutionary algorithms.
The test chamber (left) with the PCM wall assembly showing location of sensors.
Another approach uses PCMs as a visually explicit component of the wall assembly. It takes advantage of paraffin’s and calcium chloride hexahydrate’s (CaCl2
The Double Face 2.0 project developed by TU Delft 40 similarly uses the salt hydrate approach as an explicit architectural facade element to achieve thermal mass performance with translucent materials. The assembly combines 3D printing technology with simulation-based optimization software.
A number of commercially available building products already integrate PCM into construction assemblies and systems. Micronal® PCM by Microtek Laboratories
41
is a microencapsulated PCM using a paraffin wax or fatty acid ester as the thermal storage component in building materials such as foams and gypsum wallboard (GWB). DuPont™ Energain® PCM panels can be used in similar façade applications as conventional metal panels or as an underlayment for the GWB. GlassX
42
is a translucent and modular PCM-based energy storage (CaCl2
Biological systems
The integration of plant life and other organisms into architecture has a long tradition. Even though most of our construction materials today are imbued with antifungal or antimicrobial properties, the benefits of integrating or actively working with biological organisms in architecture can be extremely fruitful. Researchers at the University of Kansas, for example, have been studying environmentally friendly construction methods that utilize Sporosarcina pasteurii, a microorganism that can improve the compressive strength of rammed earth. The bacteria can stabilize the soil mix in the presence of calcium chloride and urea through biomineralization. 43 The benefits of integrating or cooperating with living organisms for the constructed environment are numerous. When entering into this symbiotic relationship between fauna, flora, and humans, the competition for natural resources, such as exposure to sunlight, has to be considered.
Green walls/roofs
Green walls and vegetated roofs have many benefits in architectural systems. They have the ability to positively influence the thermal properties of building envelopes and lower the energy that would otherwise be expended on maintaining stable indoor temperatures. Green roofs can control and greatly influence the heat flux depending on the type of grow medium and plant life. 44 Vertical greening systems can greatly influence the wind speeds and airflow and hence impact the thermal resistance. 45 They are improving urban wildlife habitats. The presence of insects can attract bird species to feed and breed.46,47 The urban vegetation is also beneficial to counteract the urban heat island effect48,49 that is becoming a more pressing issue in the face of global climate change. 50 Green walls such as the “Active Bioremediation System,” conceived at the Center for Architecture Science and Ecology (CASE), 51 have also been explored for their ability to facilitate phytoremediation and the removal of volatile organic compounds (VOCs) from indoor air52,53 and improve humidity in our indoor environments. In summertime, the plants can shield our buildings from direct sunlight, and in winter, the fallen leaves allow the sun to warm up our buildings. 54
Algae
Integration of microalgae into architectural environments has been scrutinized in the last decade for various objectives. It could contribute to the urban agriculture movement, and besides food, they could also be used as feed and fertilizers. Certain algae strains are being harvested for pharmaceuticals and nutritional additives. One of the most compelling promises that algae holds is its use for biofuel production. While the lipid extraction necessary for production of biofuels is constantly being improved, architectural systems are already looking ahead and envisioning large-scale applications of this living organism in the urban environment. Some of these examples contemplate the algae as a building component that can be used for operable solar shading. The limitation of this approach relates to a relatively small range of temperatures this “bioskin” can handle, with the problems of water freezing in winter and overheating in summer. From an occupant perspective, light filtered through algae tanks would significantly alter color renditions in inside spaces.
BIQ House 55 in Hamburg, Germany, has been celebrated as the first algae-powered building. The project integrates a bioreactor façade—algae contained in the outer-layer glass bioskin—with an array of innovative building systems to monitor, extract, and convert biomass into energy for building operations. In addition, algae façade panels can provide shade and sunlight control.
Software frameworks
The significant advantage of controller-based approaches is their ability to interconnect into a broader system that can share sensory inputs and propagate information across the entire network. The neighboring cells can oversee the behavior of the individual adaptive components and, if need be, overwrite local actions with global directives. This is enabled by the individual addressability of each component controller, as is the case with Hive Façade Systems and ICT Media Building. More importantly, this addressability parallels the conceptual framework of the IoT paradigm with IPv6 protocol that will allow for individually addressing every element in the built environment.
The immediate consequence of the interconnected building components is the ability not only to share information but also to introduce performance anticipation into the building. Since individual components are aware of conditions in the neighboring cells, they can preemptively adapt to emerging circumstances. For example, with increased solar gains being registered in one part of the building, spaces that are expected to be exposed to similar conditions within the near future could be precooled or preconditioned. Similarly, during cold outside-temperature periods, air humidity along the exterior building perimeter could be lowered to minimize curtain wall condensation before the outside temperature drops. This also points to the building’s ability to subscribe to broader databases and forecasts to fine-tune its performance. These characteristics and features start being addressed by various building automation platforms.
Building automation
Building automation is centralized and automatic control of lighting, heating, and cooling, as well as other systems including security, fire, and occupant safety, through a BAS or BMS. The goals of a BAS are improved efficient building operations, including reduced energy use and operating costs and increased occupant comfort. 56 Recently constructed buildings routinely include BASs/BMSs, and many older buildings have been retrofitted with these systems.
BASs/BMSs include software and hardware architecture that integrates controls for all or most building systems within one dashboard (interface). They are offered by companies, such as Siemens, Honeywell, and Cisco, that already manufacture building environmental control system equipment. While these systems are effective and deliver significant cost savings (~20%) as compared to non-BAS/BMS buildings, 57 they include various levels of autonomy and intelligence. In many cases, they respond to matrix-oriented algorithms without understanding the real-time considerations of building occupants or building assembly conditions.
Furthermore, BASs/BMSs are usually implemented in nonresidential buildings where a single owner or interested party is in control of centralized building systems. While building automation is an example of the smart environment approach and is often referred to as the framework behind intelligent buildings, it currently limits itself to controlling already mechanized and electric/electronic devices, such as heating and cooling systems, without necessary broader implementation of embedding sensors and actuators into building components and assemblies. This is partially because BASs/BMSs are developed by companies that manufacture building system components and their controls (HVAC or air handling units), not by construction companies or building component fabricators. They facilitate improved performance of installed equipment, not necessarily of the building itself. In the future, the majority of building products should integrate and take advantage of the embedded systems within building assemblies. Windows, doors, floors, and wall panels all could and should function as part of the building digital interface, sensing user and environmental inputs as well as actuating desired spatial outcomes. 58
The next step in achieving climate-adaptive building assemblies will involve user and building data analysis with machine learning and narrow (non-general) artificial intelligence (AI) technologies with the intent to further improve building performance.
Discussion—hybrid systems
The various approaches that have been introduced in this article for adaptive building skins each hold their own benefits and drawbacks. Electronically controlled kinetic designs, whether they are electromechanical or pneumatic, can easily be programmed to respond to environmental conditions as well as to user needs. The programming orchestrates their performance. These computer-based strategies give users an extremely high degree of control and let them incorporate elements of adaptive behavior powered by machine learning. Such systems can evaluate user information, anticipate behaviors, and respond accordingly. They can also propagate this response over a broad network of interconnected components across various system architectures. 59
Material-based approaches, such as the mentioned thermochromic or thermoresponsive polymorphic examples, offer an independent operation with transformations that can undergo millions of cycles without material fatigue. A major benefit is that they function without drawing from conventional energy sources (such as electricity) other than the readily available ambient energies. Through the combination of sensors and actuators in one material, the adaptive designs can be elegantly integrated into space-saving configurations. Instead of large macroscale shading devices, such as louvers, thermotropic smart materials reorient molecules that are directly integrated into the glazing to prevent solar heat gain or glare.
Smart material–based assemblies are not vulnerable to computer failure or to the attacks of computer viruses or hackers. They are ultimately autonomous and easily scalable. They often continue to perform in conditions where purely mechanical and electronic systems fail or demonstrate reduced performance. A significant drawback of these smart materials that are designed for a specific task is that they are not easily adjusted by a user.
Through the integration of plant life into building skins, a mutually beneficial symbiosis is created. A close relationship between the human users and flora is enabled. However, at the same time, the constituencies start competing for the same resources such as daylight.
Hybrid designs that incorporate elements of these various strategies for adaptive façade systems can be extremely beneficial. Previously mentioned electrochromic devices powered by an integrated photovoltaic technology are representative of this conviction. The thermoresponsive SMAs, for example, can be locally heated to their transition temperatures by running a current through the material. This would allow a microcontroller to take over and drive the kinetic functions. Another approach could be to disengage the mechanically based deformer (i.e. counter spring) that is essential in an SMA assembly. The decoupling mechanism could be controlled by a microcontroller and could overwrite the material-based response.
Façade elements that incorporate algae bioreactors and that are installed as simultaneously shading devices can be rotated out of plane to let the light enter into the building as long as the human user is performing tasks that require daylight. Alternatively, a soft bladder inserted into the bioreactor can be inflated, displacing the algae medium and hence significantly influencing the light transmittance (Figure 10).
Regulating light transmittance in a living algae facade panel.
Similarly, PCM assemblies, such as discussed earlier in the patent by Maloney, achieve their peak performance when interconnected with automation and smart systems that are able to correlate multiple performance-driving factors: sun exposure, outside temperature, and the desired inside conditions.
Conclusion
Recent trends discussed in this article have shown that the future of adaptable designs will incorporate and combine many different strategies such as the integration of biological organisms, advanced materials, and information technologies. This will contribute to enhanced building operations and performance that will lead toward improved energy efficiency in buildings and aspirations of zero-energy architecture. The collection of building technology strategies presented in this article showcase the continuously expanding boundary condition of architecture. An important aspect of this contribution is not only demonstrating the state-of-the-research but also pointing to possible crosspollination between various technologies. As we increasingly embed electronic chips into the built environment and every aspect of our daily lives, the question of reliance and of the required energy sources for these assemblies needs to be continuously assessed. The shift from energy-hungry, mechanical and electronic controls toward energy independent smart materials is an attractive design approach. Especially, hybrid systems that can unite the best qualities of the different approaches hold great potential and contribute significantly not only to more reliable but also resilient buildings.
Footnotes
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.
