LET THERE BE LIGHT Alicja Kurzajewska - Senior Façade Consultant, AESG

LET THERE BE LIGHT

LIGHT

Alicja Kurzajewska, Senior Façade Consultant, AESG

Throughout the history of humankind, innovation has always started with the process of creative thinking. One of its most infamous measures that exist is the "uses-for-a-brick" test (also known as the Alternative Uses Test, by Guildford, 1975). How many uses of brick can you name in a matter of few minutes? Most people list common and apparent ones. Divergent thinkers, however, come up with different, innovative, and sometimes odd ways this resource can be used, like weighing down crime evidence thrown into a lake.

The most evident way to observe and experience humankind's innovation and creativity would be to look at the evolution of electronics. Remember your "brick phone" that came out in 1983 and made its way to Hollywood movies? Well, now it talks to you, measures your heartbeat, and reminds you to drink enough water - all within 29 years.

The rapid pace of innovation is a contagion that affects all businesses. Even though construction has its own pace of moving forward, façade engineering does not hold back and finds its place in the forefront of the fastest advancing sectors of construction. This can be attributed to the inherent adaptive characteristics of the glass.

Façade consultants have to keep up. They are always on the search for the best systems, products, and materials for their clients. Part of that process includes staying in a close relationship with glass and coating manufacturers who keep them up to speed with the newest developments.

The synergy between the demands of architects and consultants, together with the innovative attitude of the glass companies was the catalyst that launched the industry of architectural glazing to another level.

Glass manufacturers are currently offering and developing very impressive products, providing an enormous number of ideas, research data and delivering products with new functions. This interaction also helped shape the specialty glazing available in the market, which can do much more than just being a see-through thermal barrier between the interior and exterior. Selective filtering of desired solar radiation, modification of reflectivity and aesthetics, and dynamic functions of changing into an opaque panel or harnessing power by including solar cells are a few examples of innovative progress within the industry.

Architects and investors can select glazing for the building’s envelope from a wide range of products that meet the code's requirements and offer a selection of appearances and additional exciting functions. However, if we want to go beyond mere aesthetics and novel functionality, we cannot disregard sustainability. The climate challenges of the current times created the need to improve processes and technologies by reducing the use of energy. It is noticeable the glass industry aims to respond to the fast-evolving world and ecological challenges we face, which combined with people's creativity, gave birth to several remarkable glass products.

AG-ri-CULTURE

When selecting the glazing for the project, Façade consultants consider the requirements of the indoor space and its habitats, as well as climatic conditions on the outside. Depending on the geographical location, buildings like botanical gardens or greenhouses, which are intended for indoor vegetation growing, face different challenges - from excessive heat to insufficient lighting. The specific needs of flora vary from the ones characteristic to the spaces occupied

by people, hence the glass used in residential spaces cannot be utilized in buildings intended for growing vegetation.

A solution to this challenge is provided by the AGCULTURE glass series by AGC Glass, which offers three types of glazing for different climatic conditions, that help increase the production and quality of indoor vegetation while reducing the energy used to control the indoor environment. The company has researched and developed its products to filter and optimize the behaviour of the light entering a greenhouse.

Glass called Brilliant and Fountain is a high emissivity glazing (does not trap the heat inside) that utilizes coatings and chemical treatment of the glass surface.

Special anti-reflective coating (AR) of Brilliant, placed on two sides of the glass, was designed to selectively allow the Photosynthetically Active Radiation (PAR) necessary for the plants to enter the greenhouse while reflecting the Near Infrared light (NIR). The importance of reflecting the NIR relates directly to overheating the conditioned space as a result of solar heating. Reflecting NIR reduces the inside temperature, which translates into lesser demand for space cooling. However, the type of anti-reflective coating used in Fountain does not make any selectivity in light transmission and improves the PAR transmission as well as other wavelengths of the entire solar radiation.

Figure 1. Botanical garden. Photo credit: James Orr

Figure 2. Brilliant glass and its effect on the wavelengths of light.

Figure 3. Relationship between PAR and NIR transmittance of low iron and Brilliant glass. When a double anti-reflective coating is used, PAR transmission can reach up to 96.5% with Fountain and up to 98.5% with Brilliant.

Variables such as the position of the Sun in relation to the Earth, season, location, and orientation of the greenhouse, as well as the time of the day, are all significant influencers on the quality of light inside the greenhouse. The two AGCULTURE’s glass products offset these variables with anti-reflective coating, which maximizes the hemispherical light transmittance, reaching 85.5% with double AR in Fountain and 91.5% with double AR in Brilliant. It is important because a 1% increase in hemispherical transmission corresponds to 0.8% more production in weight per square meter, as researchers were able to demonstrate according to the large dataset acquired over many on-field experiments [1].

THE SCIENCE OF LIGHT

AGC Glass addressed another challenge of indoor vegetation with their AGCULTURE glass. Direct sunlight that enters spaces and creates shadow from the structural framing and other elements, results in less than optimum sunlight exposure to overlapping leaves. The need to create a homogenous climate, where highly diffused light disperses the shadow and enables the leaves at a lower level to receive sufficient lighting and avoid the hot spots, gave rise to hortiscatter – a property of glass affecting the production of the crops.

In the past, the level of light distribution was measured in terms of haze - the amount of light

Figure 4. Project precedent –Kaust Greenhouse in Saudi Arabia, utilizing glass with a high level of hortiscatter. Note that the roof's structure does not project any shade onto the surface of the greenhouse.

Figure 5. Hortiscatter vs haze.

Figure 7. Dynamic model of the tomato plant used for the Lumination study conducted by AGCULTURE.

scattered by more than 2.5° from an incoming angle. However, it is not complex enough to describe the phenomena of light diffusion that influence greenhouses' productivity. Therefore, a broader definition of the light diffusion process was recently introduced as hortiscatter. It is a mathematical formula that describes more comprehensively the homogenous distribution of the light inside a greenhouse, and similarly to haze, it is expressed as a percentage between 0 and 100%. The clear glass has a hortiscatter of 0%, meaning a single beam of light is not diffused or scattered at all.

To influence the level of hortiscatter, the surface of Fountain glass is chemically etched, which significantly increases the dispersion of sun rays. Such alteration of the glass surface results in hortiscatter of up to 63%, which according to the Wageningen University and Research, each percent of hortiscatter can result in a 0.3% increase in greenhouse production [2].

The current innovative technologies enable AGC to analyze the light in the building with surgical precision by modeling how the light will diffuse while passing through different materials. Analysis of etched glass in both, dry and wet conditions and adjusting for hortiscatter level is conducted to match the outside weather conditions. All of that is done while also considering the building's shape, the local weather data, and even the shape of the plants, giving optimized glass products perfectly aligned with the outdoor environment.

Reading about greenhouses, tomatoes, AGCULTURE glass' selectivity for PAR and reflectivity to NIR, its hortiscatter, and hemispherical light transmittance properties, one's thinking probably does not diverge to who is going to pollinate the tomatoes. However, AGC Glass knew bees would do that. Although tomatoes are capable of selfpollination, it did not stop the glass manufacturer from researching the influence of different wavelengths of light on bees, which are an essential part of the pollination process. While humans see the light in wavelengths ranging from 390 to 750 nanometers, bees are sensitive to the range from 300 to 650 nanometers, hence noticing the ultraviolet-B spectrum of light invisible to people. Therefore, the glass used for greenhouses and botanical gardens is typically an extra clear glass, which allows more UV light. This process is further increased by adding 1 or 2 layers of antireflective coating.

AGC also improved the hydrophilic properties of the glazing to mitigate issues associated with condensation (reduced light transmission and reduced moisture content in the air). While Fountain and Brilliant glass are great solutions for warm and hot weather and amazingly

Figure 9. Ranges of wavelengths of light visible to humans, bees, and birds. manage the sunlight, growers in a cold climate can also benefit from the innovative glass products. They may consider not only Fountain glass but also Geysir – a glass with a low-E coating designed to keep the heat inside while providing 90% PAR light transmission. Such a product reduces the energy used for heating the space by 23%, recently demonstrated in an experiment by Wageningen University and Research [3].

A DIFFERENT SPECTRUM OF LIGHT

The sustainability challenges that the glass industry faces are not limited to optimized efficiency and improved well-being of building occupants, whether it be people, bees, or plants. In October 2020, the state of Philadelphia in the USA brought to the forefront an ecological concern of a different magnitude. Approximately 1500 migratory birds died from a collision with a glass skyscraper

Figure 10. Façade with the bird-safe glass by Pilkington – view from the outside.

Figure11. Façade with the bird-safe glass by Pilkington – view from the inside.

during a single day. It is estimated that 1 billion birds die each year from similar accidents in the US only. Counterintuitively, according to research conducted in 2014 by Smithsonian Conservation Biology Institute, most bird mortalities are caused by low-rise buildings and only less than 1% happen because of collisions with skyscrapers [4]. Needless to say, it is a significant environmental concern and a major risk to ecosystems since birds, similarly to bees, are pollinators, spread seeds of vegetation, control the populations of certain insects and pests and contribute to soil formation.

It is a common practice to apply a safety glass where otherwise, the safety of people would be at risk. Glazed walkways and frameless glass balustrades are designed to provide a great level of safety. The good news is that the glass industry provides architects and investors with choices that can maintain the required performance while mitigating the risk for birds. Birds collide with glass because of several reasons, but the ones most closely related to glass are reflection and transmission, which form images either reflected or seen through the glass. Due to the inherent reflectivity of glass, birds perceive the object it reflects as an actual object (i.e., a sky or vegetation), while with highly transparent glass, birds simply do not see the glass as a barrier and may perceive it as a continuation of an outdoor environment. Moreover, birds' vision can perceive the UV spectrum that is not perceivable to people. Therefore, a UV treatment for glass is used as a bird protection practice.

There are several UV glass products on the market which are safe for birds, Pilkington AviSafe™ being a good example. The technology is focused on the two parameters that affect birds: transparency and reflectivity. Bird-safe glass is made by stripe coating on the external surface, which enhances UV reflection (the light spectrum visible to birds), making the glass noticeable. At the same time, the coating maintains high visual light transmittance, remains aesthetically appealing from the exterior side, and the coating stripe pattern is only slightly noticeable by the human eye from the interior. The width of the coating pattern is approximately 25mm, with the spacing that was tested to pass the rigorous WIN test (a European test, similar to the American Bird Conservatory tunnel test).

THE BIRDS AND THE BEES

The progression of the glass industry over the past years is undeniable. However, if the progress becomes untethered from the globally evident environmental concerns at hand or if the cost, aesthetics, or novelty will be prioritized over sustainability, we may find it very hard to deal with the wavelengths of light. Therefore, a balance between financial benefits and sustainability must be reached with the help of innovative glass manufacturers and divergent thinking façade specialists so that we can tell future generations the story about the birds and the bees.

References: [1] Marcelis, L.F.M., Broekhuijsen, A.G.M., Meinen, E., Nijs, E.M.F.M. and Raaphorst, M.G.M. 2006. Quantification of the growth response to light quality of greenhouse grown crops. Acta Horticulturae 711, 97–104. doi:10.17660/ ActaHortic.2006.711.9. [2] Li, T., Heuvelink, E., Dueck, T.A., Janse, J., Gort, G. and Marcelis, L.F.M., 2014. Enhancement of crop photosynthesis by diffuse light: quantifying the contributing factors. Ann. Bot. 114, 145-156. [3] https://www.kasalsenergiebron.nl/nieuws/proef-met-low-eglas-is-goed-op-weg/ [4] Bird–building collisions in the United States: Estimates of annual mortality and species vulnerability, January 2014, Scott R. Loss, Tom Will, Sara S. Loss, Peter P. Marra

ALICJA KURZAJEWSKA, MSc Eng

Alicja is a Senior Façade Consultant at AESG with extensive international façade consulting experience, which she gained while working as a Façade Consultant USA, UK, and UAE. She has comprehensive knowledge about façade systems and materials and sound skills in façade design, from concept to construction stages.

Holding a degree in structural engineering, Alicja is interested in the subject of structural analysis of glass. While working closely with the Architects, she is committed to delivering high-quality design, and assuring the practicality and efficiency of the applied solutions.