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New solutions in solar shade

November 1st, 2021 / By: / Markets

The SoFi Stadium’s ETFE roof provides a “fifth dimension” with an LED system embedded into the ETFE to project images and show live events from inside the stadium. These images can be seen from the air by the more than 80 million passengers traveling through the Los Angeles International Airport annually without sacrificing the transparency of the roof for fans inside. Photo: HKS Inc.

From the earliest tents to contemporary athletic stadiums, textiles have played a central role in offering protection from the elements and drawing energy from the sun. As locations worldwide struggle with record-shattering temperatures, researchers and architects are utilizing textiles in groundbreaking innovations including a state-of-the-art sports and entertainment stadium, a biomimicry-inspired pavilion and a research project that explores harnessing wind energy via tensile membrane architecture.  

Indoor-outdoor experience

The SoFi Stadium in Inglewood, Calif., was designed by architects HKS Inc. and uses a single layer of ETFE to provide a translucent roof on the first indoor-outdoor NFL stadium. It is also the league’s largest stadium, measuring 3.1 million square feet, and needs to perform a number of functions, not the least of which is providing protection from the Southern California sunshine.  

The roof is the largest of its kind, sitting on an arching steel truss compression ring that supports a cable net truss and 302 ETFE panels. “The ETFE roof is a signature design element that achieves an outdoor setting while providing the flexibility of a domed stadium,” says Lance Evans, principal and director of sports at HKS.

The roof structure is seismically isolated from the stadium bowl. The cable net structure free-spans more than 1,000 feet longitudinally and 800 feet tangentially, making it the largest, heaviest and one of the highest cable pinning forces ever attempted, according to contractor Pfeifer Structures of Dallas, Texas. To reduce the cable loads, the upper and lower cable nets are divided into 18 individual nets. The ETFE panels use a 65 percent frit pattern that provides shelter against direct sun and reduces solar gain without inhibiting natural light. The ability
of the roof panels to open and close helps to promote natural airflow and cooling within the stadium.  

Situated on the flight path to the Los Angeles International Airport, the stadium features 28,000 V-Pix LED lights on the roof to create a 13-acre high-resolution video display when viewed from above. The stadium is truly performance, sustainability and spectacle combined.

Known as the “polar bear pavilion,” this structure was built at the Institute of Textile Technology and Process Engineering (ITV) Denkendorf as part of a joint research project with industry partners demonstrating the possibilities for a textile membrane building to be energy autonomous and offer a futuristic architecture. Photo: DITF.

Inspired by nature

The German Institutes of Textile and Fiber Research (DITF) have developed an energy-efficient membrane that is inspired by biomimicry—specifically the fur of the polar bear.  The intention here is to offer protection against the sun and other weather conditions, while harnessing and storing heat from the sun for later use. 

Polar bear fur is colorless, but appears white as it reflects the sun. The hairs transmit some of this sunlight to a bear’s black epidermis, where the solar radiation is converted into thermal energy. 

Similarly, DITF’s membrane takes sunlight as it hits a flexible solar collector through which air is flowing. Echoing the skin of the polar bear, the bottom layer is a black-coated fabric that acts as an absorber of the energy, withstanding temperatures in excess of 140 degrees (F). An air-bearing spacer fabric is used for the highly transparent middle layer, providing thermal insulation. The outermost layers increase the thermal insulation further while allowing sunlight to penetrate, reducing the need for artificial light.  

The membrane has been trialed in a “polar bear pavilion,” with five flexible solar collector tracks on the south-facing side. These generate warm air that is fed through to heat the interior of the building.

Harvesting wind energy

Harnessing energy from shade has focused strongly on solar, but there is an increasing interest in the potential of wind. Aeroelastic vibration is usually associated with the aircraft industry and relates to the interaction of aerodynamic, inertial and elastic forces that occur during the movement of air and a flexible aircraft. 

Researchers Hoyoung Maeng and Kyung Hoon Hyun at Hanyang University in South Korea are exploring the potential of tensile membrane architecture (TMA) as a means of harnessing vibration-generated energy. The intention of this research would be to provide a green energy source for buildings.  

The process for energy harvesting in this way uses wind-induced vibration generated in the membrane with the conversion brought about primarily by electrostatic, electromagnetic or piezoelectric transduction methods. Both glass fiber and polyester membranes with a longitudinal stiffness of 54,720 and 25,200 newton centimeters respectively were used for the studies. 

The researchers have undertaken computer simulation tests using Kangaroo Grasshopper’s plug-in to determine the correlation between the structure’s stability and energy-harvesting performance. To assess the wind during a simulation, a combination of wind vector and amplitude components were used, taken from Global Wind Atlas data. The TMA energy-harvesting research to date has looked at three different membrane structure designs—hypar, conic and barrel vault. All are commonly used in solar shade: hypar having alternating high and low points, conic consisting of a square base support and a top ring, and barrel vault shape being comprised of two elliptical curves that are found at the ends of two parallel lines.  

Maeng and Hyun found that the shapes that yielded maximum energy efficiency through the whole material stiffness range were the conic and barrel vault designs. The material stiffness has been found to influence electricity generation differently in the hypar design. The researchers point to the significance of both a low material stiffness and the selection of the TMA geometry most suited to the location as determined by prevalent wind direction being necessary to achieve maximum energy efficiency.

The Intergovernmental Panel on Climate Change (IPCC), the United Nations body tasked with assessing the science related to climate change, released a special report on the impacts of global warming of 1.5 degrees (C) in 2018. Among the findings is a warning that urban areas will experience the worst impacts of heat waves due to the urban heat island effect, which keeps them warmer than surrounding rural areas. The need for solar shade, particularly smart and energy-harvesting shade, has surely never been greater than it is today. 

Dr. Marie O’Mahony is an industry consultant, author and academic. She is the author of several books on advanced and smart textiles published by Thames and Hudson, and is a visiting professor at the Royal College of Art (RCA), London.