FROM BIOMIMESIS TO BIOLOGICALS AND BEYOND

Facades that include plants or other life forms, along with inorganic systems inspired by them, have drawn substantial attention, though not all have enjoyed performance or longevity to match their aesthetic or symbolic value. Green roofs have proven easier to support and maintain than green walls, observers note. “A lot of the early ones failed,” Patterson says; “it is not trivial to integrate biological systems into the building skin. I see architects conceptually interested in it, but the biology has to drive the design, and that's what they don't get. They want to design their facade system and do their aesthetic thing, and then plug plants into it; it doesn't work that way.” Seasonal cycles, the weight of soil for structural systems, high wind speeds at tops of buildings, the need to deliver water and attract pollinators, and the complexity of local ecosystems all create challenges for architects seeking to emulate the Hanging Gardens of Babylon.

Yet specialist/theorists such as Ken Yeang and Glen Small have established vertical gardens and eco-highrises as recognized typologies, and examples of viable biofacades are no longer rare. Salient recent cases, Patterson points out, include Thomas Heatherwick's 1000 Trees mixed-use development in Shanghai (the first phase of which opened in 2022), with exoskeletal supporting columns doing double duty as podiums supporting trees and other vegetation, and Stefano Boeri's Bosco Verticale (Vertical Forest, 2014) in Milan, a two-tower residential complex featuring 800 trees mounted on balconies. The latter project's sustainability has drawn critiques involving the long-range carbon footprint of its concrete elements and the challenges of maintenance (Alter 2020); nevertheless, the architects' careful attention to managing the elements of the buildings' microclimate, including deploying “flying gardeners” who maintain the plants by descending from the roof using mountaineering equipment, have made it globally iconic: a multiple award winner as well as a host to some 1,600 species of birds and butterflies.

Green facades, adaptive in the most direct sense, require exceptional attention to detail and substantial up-front investment. In Düsseldorf, Germany, Werner Sobek and Ingenhoven Architects' Kö-Bogen II commercial building has “a green facade that was actually thought through from the beginning of the process to the end,” Oliva says. “One can tell that thought was not put only into the nature of the greenery, but into how weight, the operations, [and] everything that had to do with the building was implemented into the main structure, the secondary structure, and the maintenance plan” (see Case Studies, “Kö-Bogen II”).

As facade designers and engineers strive to tread more lightly on the Earth, technologies that approximate natural forms both make intuitive sense and carry the promise of a measurable step up in performance from their predecessors. Anna Dyson, founding director of the Yale Center for Ecosystems in Architecture (CEA) and previously a co-founder of the Rensselaer Polytechnic Institute/SOM Center for Architecture, Science and Ecology (CASE), sometimes invokes sunflowers as an exceptional evolutionary adaptation to the task of drawing energy from the sun. Early generations of PVs, she finds, have severe limits; developers of newer systems could learn a great deal from these plants and the natural principles underlying them.

“The first generation of building-integrated PV uses a lot of semiconductor material, and it coincidentally is very low-efficiency,” Dyson says. Estimating the efficiency range of early BIPVs at 14 to 25 percent – “and 25 is the absolute upper end if it were perfectly maintained at all times” – she breaks down what happens to the other 75 percent or more of solar energy reaching a building. Much of it “lingers around the building envelope as waste heat, which can be a problem in certain hot, humid climates that don't have adequate ventilation and trapped urban corridors and urban canyons.” It also exacerbates the urban heat island effect and glare. The problem is inherent in passive systems' strategy of rejecting energy rather than transforming it. “For this next wave of building envelopes,” she says, “we need to be optimally using the incoming energy for multiple purposes, not just for electricity, but to mitigate the building cooling or heating loads, to supply hot water to applications, and to daylight the building.”

Passive solar, Dyson believes, is appropriate for smaller-scale buildings such as residences, particularly in winter. Yet “even passive solar oftentimes is allowing heat into the building in an uncontrolled fashion, not in an optimal fashion,” she says. “In large commercial buildings, passive solar is oftentimes a real problem, because at some point during the day, even in the coldest months, you'll go from heating degree to cooling degree; that is, that the internal loads for the live loads will ultimately be producing too much heat energy, and we will transition into cooling. At that point, the passive solar becomes a problem; it's unwanted solar heat gain. So what we really are doing basically with these next-generation building systems is we're treating them as transfer functions.” Two systems that Dyson and colleagues have developed, the Integrated Concentrating (IC) Solar Facade System and Solar Enclosure for Water Reuse (SEWR), are under proof-of-concept patents (Dyson et al. 2007 and 2012); her team plans to demonstrate SEWR at Conference of the Parties (COP) 28, the 2023 United Nations Climate Change Conference, in Dubai later this year.

In tomorrow's multifunctional adaptive envelopes, as Dyson's team envisions, optical methods of concentrating sunlight on multiple solar modules, including Fresnel lenses, thin films, and assorted micro-optic elements, “fly-eye-type geometries” and others (Dyson 2012), respond more effectively to the sun than flat panels can, behaving more like heliotropic plants. She and her colleagues have measured efficiencies in the 40-percent range in tests of their systems; “we can go all the way to 70 with optimized concentrating solar-cell types like gallium arsenide and gallium nitride,” she says.

Another important feature of her systems is that they are “designed for disassembly and reassembly,” so that component parts can be sustainably reused in future life cycles, keeping semiconductors out of the waste stream. (“Toxic materials are OK to use as long as you can reuse them,” she notes, “and you're not distributing them into the ecosystem.”) Semiconductors are troublesome aspects of a building's systems for several reasons, not only because of their toxicity, nonrenewability, and energy-intensive manufacturing processes but because “we're accepting a slavery discount on solar panels” that keeps their prices artificially low because the materials are often sourced from parts of the world that use forced labor. As an alternative, “what we want to do is really replace the semiconductor with a much more viable, better, abundant Earth material, like glass.” Her integrating solar facade system uses only a small percentage of the semiconductor material found in conventional flat-plate PVs. SEWR, which processes a building's graywater along with transforming energy, “is actually adding plant-based biochemistry: just plant dyes, extractions from common plants that we grow for agriculture, like quinoa and kale and garlic. And we put those extractions into the water that flows to the system in order to have on-site water capture and sterilization, so you have complete 100 percent on-site water, and that is the system that we're demonstrating now at scale.”

When Dyson began developing solar facades around 1999 and 2000, “the solar cell was more than $2,000 per unit. Now it's under $5.” Advances in multiple fields were necessary for these costs to drop and for the elements of her multifunctional systems to converge. Now may be the time, her work implies, for technologies that behave more like nature, where every component has a place in cycles and there is no such thing as waste.

CONCLUSION

Because the U.S. built environment contains billions of square meters of glass surfaces, the prospect of converting a substantial amount of it into transparent PVs is tantalizing. Firms like California-based Ubiquitous Energy, which patented a transparent solar coated glass based on research performed at MIT and Michigan State, have attracted national publicity with the possibility of scaling up an aesthetically acceptable PV application. The chief barrier to such a scenario to date, Patterson points out, is that “the building industry is notoriously slow in adopting new design and product developments, a reflection of the extreme risk aversion characteristic of the industry. Incentives, codes, and policies can help new technologies get over the adoption hump by encouraging initial tiers of early adopters.”

Controlling solar gain and harvesting energy are both achievable. “The emerging transparent architectural glazing technologies hold the potential to accomplish both in a single product,” Patterson comments. “But a layered facade assembly that separates functions is already viable with existing technology, and may prove to be more flexible and efficient in application. All that's required is an appropriate configuration of PV cells, insulated glass, low-E coatings, and a shading system, all currently available, cost-effective, and with proven performance.”

“The facade development that occurred in Europe, Germany in particular, in the wake of the 1970s energy crisis pushed their facade technology 20 years ahead of the U.S., and we're still playing catch-up,” Patterson summarizes. “Government-mandated performance improvements drove rapid adoption of new, higher-performing facade technologies. The development effort in the U.S. has been effectively hobbled by artificially low energy prices and lax building codes. The building industry in the U.S. is gridlocked by the protection of vested interests, the concerted effort to keep things as they are. The glass industry is no exception. The industry could move forward by embracing the constraints embedded in the goals established for resilience and sustainability by entities such as Architecture 2030 and the UN's Intergovernmental Panel on Climate Change. Constraints drive innovation.” Code by code, competition by competition, and project by project, this process can drive the architectural and engineering fields in the direction planetary conditions require them to go.

WORKS CITED:

Alter, Lloyd. Another look at Stefano Boeri's Vertical Forest. Treehugger, August 13, 2020.
Bonham, Mary Ben; Kim, Kyoung Hee. Biofacades: integrating biological systems with building enclosures. Skins, July 15, 2022.
Dyson, Anna; Jensen, Michael K.; Borton, David N. Concentrating type solar collection and daylighting system withn glazed building envelopes. United States Patent and Trademark Office, Patent 7,190,531, March 13, 2007.
Dyson, Anna; Vollen, Jason; Mistur, Mark; et al. Solar enclosure for water reuse. World Intellectual Patent Organization, Patent WO 2012/075064A2, 2012.

Bill Millard is a New York-based journalist who has contributed to Architectural Record, The Architect's Newspaper, Oculus, Architect, Annals of Emergency Medicine, OMA’s Content, and other publications.