Zero-Carbon Technology | Zero-Energy Bionic Building Facades Cool and Insulate Buildings

 

FlectoLine is an intelligent facade developed by the University of Stuttgart and the University of Freiburg in Germany. This architectural solution, installed as a prototype in the greenhouse of Freiburg’s Botanical Garden, can passively and automatically regulate solar radiation based on environmental conditions.

 

 

This prototype spans 83.5 square meters (899 square feet) and is mounted on the exterior of a window along one side of the greenhouse. It consists of a series of shading elements, each made up of two fiber-reinforced thermoplastic flaps that can either be opened independently or folded together.

 

Overall, these elements evoke the traps found on Venus flytraps, though the actual inspiration actually comes from the predatory appendages of another carnivorous plant—Aldrovanda vesiculosa. Meanwhile, the pneumatic "hinge zones" at the base of each flap draw their design cues from the veins in the modified wings of the striped bug, Graphosoma italicum. When air is pumped into the flexible, elastic hinges, the structure expands, causing the stiffer main flaps to fold sharply to one side.

 

 

Since the two flaps in each component fold outward simultaneously on both sides, they can block sunlight from streaming through the windows, helping to keep the building’s interior cool. In hot weather, this simple action could significantly influence how much air conditioning is needed.

 

 

In cool weather, the flaps fold inward, causing them to meet in the middle—this action is triggered simply by shutting off airflow in the hinge area. These elements then maximize the amount of warm sunlight streaming through the windows, reducing the building's reliance on its heating system.

 

 

The entire facade can be set to operate automatically, responding to weather conditions, the time of day, and ambient temperature—alternatively, it can also be manually adjusted as needed. As an added benefit, the facade is powered by photovoltaic cells installed on the outer surfaces of its components.

 

Integrated Drive

 

FlectoLine consists of fiber-reinforced composite panels with built-in hinge zones, specifically developed for use with integrated pneumatic actuators. The pneumatic actuators are directly embedded into the composite material in the form of a cushion. The material structure of the composite is divided into a stiffer section beneath the actuator and a more flexible section above it.

 

 

When pressure is applied, the pad deforms more dramatically along the direction of the more flexible board, causing the entire composite plate to bend in that same direction. By clamping one side adjacent to the hinge region, free bending motion can be achieved at the unclamped end. Since the actuation system is directly integrated into the composite plate, no mechanical connection is required between the folding element and the drive mechanism. The flexible hinge region only needs low pressure (0.3 to 1.5 bar) to smoothly transition from a 0° to a 90° angle position. During the folding process, elastic energy is stored in the flexible hinge area, enabling the module to instantly return to its original position once the pressure is released.

 

Material System

 

Two distinct material systems were developed for the technical implementation of the exterior wall. First, the bio-inspired material architecture was abstracted into elastic and stiffer material layers, which were then integrated into a hybrid composite featuring both elastomeric components and thermoset fiber-reinforced composites. Similar to wing veins, the actuator chamber is encased by an elastomeric layer, ensuring strong interlayer adhesion within the driving plane. The direction of motion during actuation is determined by the asymmetric distribution of reinforced glass fibers—positioned above and below the driving plane.

 

 

The first material system has already been tested in previous demonstrations and proven effective, showcasing its reliability and adaptability for large-scale applications. However, to optimize the manufacturing process in terms of time and cost, a second alternative material system has been developed. To explore an even simpler alternative, a material structure based on thermoplastic plastics has been engineered, operating in a similar manner: two layers of thermoplastic glass fiber-reinforced polyamide-6—with varying stiffness levels—are bonded together using an elastic adhesive.

 

 

Both systems are equipped with a protective outer layer that boasts exceptional weather resistance, making them suitable for use in facade elements. Each system has undergone rigorous weather and fire resistance testing to ensure that their mechanical performance and appearance remain stable—without compromise—for at least a specified period. 15 years , and the components must meet at least Fire Rating B2 requirements. Given the varying weather conditions on the exterior walls, the components were also subjected to wind-tunnel testing, with maximum expected wind loads applied from different directions. To ensure the long-lasting durability of the curtain wall elements, each material system underwent cyclic testing under pneumatic actuation, enduring at least 20,000 test cycles—each cycle involving bending up to 90°.

 

Control System

 

 

To effectively control the performance of responsive facades, a digital twin has been developed, capable of simulating thermal and lighting behavior in real time, as well as integrating energy production from photovoltaic (PV) panels.

 

Digital twins collect real-time data through embedded sensors, including indoor lighting levels from light sensors, outdoor lighting levels from solar exposure sensors, indoor temperature readings from distributed temperature sensors, and wind conditions measured by facade anemometers.

 

 

Forecast data, such as detailed weather predictions (including solar radiation, cloud cover, temperature, wind speed, and precipitation) sourced from meteorological application programming interfaces (APIs), as well as energy demand forecasts derived from historical usage patterns, are also integrated into the system. Leveraging this data, a decision-tree-based control algorithm optimizes three key aspects of indoor comfort—adequate lighting levels, glare minimization, and thermal regulation—while simultaneously maximizing photovoltaic energy production. The system continuously analyzes both real-time and forecasted inputs to calculate the optimal panel angle, ensuring efficient performance throughout the day while striking a balance between occupant comfort, energy efficiency, and renewable energy generation.

 

Large, Responsive Facade

 

 

FlectoLine facade, serving as a proof of concept, demonstrates the potential of using fiber-reinforced plastic laminates with compliant hinge zones and integrated pneumatic actuators to create large-scale, responsive facades.

 

FlectoLine's facade covers an area of 83.5 square meters and is composed of 101 components, with x- and y-axis dimensions ranging from 0.81×0.86 meters to 1.50×1.31 meters. These modules require just 0.4 bar of pressure to fully deploy into a 90° angle, showcasing their exceptional motion efficiency. The design incorporates thin-film organic photovoltaic (PV) cells to harness solar energy, enabling the responsive facade to autonomously meet its own energy demands.

 

Additionally, the FlectoLine facade explores the potential for fostering direct interaction between the built environment and its occupants through an active control system—made possible by the seamless integration of computational design, advanced simulation, and manufacturing processes.

 

Summary

 

Thanks to its adaptive design, FlectoLine significantly reduces the need for artificial climate control, thereby enhancing both energy efficiency and indoor comfort. Its operation relies on a low-pressure pneumatic system that can extend or retract the shading modules, maximizing solar gain during winter while minimizing overheating in summer.

 

 

This responsive facade represents a cutting-edge approach in architectural design, enabling the building envelope to actively respond to environmental and user stimuli. By integrating programmable material assemblies, advanced actuators, and sensor networks, these dynamic systems can adapt in real time, optimizing energy performance, enhancing occupant comfort, and fostering new forms of interaction between users and their built environment.

 

Their ability to regulate solar gain, ventilation, and thermal performance makes them a key component in reducing energy demand and supporting sustainable urban development. As the emphasis on sustainable design continues to grow, these facades will play a pivotal role in shaping the architecture of the future, seamlessly blending technological innovation with functional building design.

 

This innovation marks a promising step forward in integrating bioclimatic strategies into building envelopes, aligning seamlessly with the goals of enhancing energy efficiency and climate resilience.

 

Source: Youlv.com