The future of sustainable windows may lie in this tiny organism

May 9, 2021
You might think algae needs to be scrubbed off windows, but these windows use it! (Kyoung-Hee Kim)

You might think algae needs to be scrubbed off windows, but these windows use it! (Kyoung-Hee Kim)

An architect has harnessed the photosynthetic power of microalgae to develop a new kind of "curtain" that could make offices and other commercial buildings greener in more ways than one.

The curtain consists of microalgae photobioreactors set between two panes of glass, creating an environmentally friendly window that makes buildings more energy-efficient and boosts indoor air quality. The inventor, who is affiliated with the University of North Carolina at Charlotte, has applied for a patent for this sustainable microalgae curtain with the U.S. Patent and Trademark Office, which published the application on April 15.

"My core research expertise is in building technology, which greatly values efficiency and multi-functionality," said inventor Kyoung-Hee Kim, an associate professor of architecture and director of the Integrated Design Research Lab at UNC Charlotte. "So when I look at microalgae, a single or multicellular algae that grows fast with limited resources, I want to try to turn them into intelligent building materials that can affect humans." 

Microalgae are commonly used to create sustainable biofuels, and scientists recently discovered that different types of light can promote growth in the species Dunaliella salina. 

Kim's curtain is an array of photobioreactors, or structures that use light and carbon dioxide to to grow microalgae within them, and it would be installed in the space between two typical window panes in any office, for example. The curtain works by taking advantage of the rapid photosynthetic performance of its namesake unicellular organism.

In summer, for example, strong sunlight will amplify photosynthesis in the microalgae, creating a darker shade of green that can help cool an office, reducing its reliance on air conditioning. In winter, on the other hand, the algae can help insulate a space by absorbing weaker sunlight.

Building operators will be able to manipulate microalgal activity to suit their heating or cooling needs through a computer interface that connects to holding tanks in a building's mechanical room. Two tanks will include pure water and microalgae-saturated water, and a separate tank will mix the contents of both to establish desired microalgae levels. To create a 20% tint to a given window, for example, an operator could plug that value into the computer interface, and the tanks would create a solution to the desired algal density for that window. 

Based on Kim's analysis of energy use in buildings across 15 cities in different U.S. climate regions, she believes her invention could help reduce energy usage by 20% to 30% by cutting heating and air-conditioning costs, as well as ventilation fan expenditures. Offices use more air conditioning than any other type of building, according to the U.S. Energy Information Administration, and will consume 25% of all energy used for air conditioning by 2050. 

One of Kim's primary goals in developing this technology is retrofitting old windows in commercial settings, hospitals and offices to feature microalgae windows. According to Kim, before the 1980s, building developers used energy-inefficient single-pane windows, which had poor heat insulation compared with double-paned ones. 

On top of fostering more efficient heating and cooling, the microalgae window can improve air quality by pumping oxygen into its environment, either directly or through a centralized heating or cooling system, and consuming carbon dioxide through photosynthesis.

Outdoor carbon dioxide levels are around 400 parts per million, and Kim has measured carbon dioxide levels ranging from 1,500 to 2,000 parts per million in various rooms. According to research published in 2012, indoor carbon dioxide levels can promote sluggishness and hamper decision-making skills at just 1,000 parts per million, resulting in a lack of productivity. 

While the microalgae curtain is environmentally green, and could considerably reduce a building's energy expenditure, it is also literally quite green, and will cast a vermilion shadow over any nearby surfaces. Kim enjoys the green hue, but realizes it may be an issue for some users. 

To remedy any unwanted tinting, building operators could apply a translucent paint that filters out the curtain's green light while retaining its carbon-offsetting benefits. Kim is also testing other types of microalgae, both red and other shades of green, to gauge their aesthetics. 

Having settled the technological function behind her invention, Kim will conduct more research on its user experience. During the fall semester, she hopes to conduct surveys of UNC Charlotte students, as long as she secures funding. 

Kim has an 8-by-12 feet sample of her algae curtain, and resources are available to install one on a small scale in businesses or lobbies, for example. But before offering the product on a greater scale, Kim wants to verify its durability and energy efficiency by sending samples to Intertek, a quality assurance provider, for certification. 

"Because I am a licensed architect, I'd really like to see my idea being implemented in the real  world. That is always a way to create impact to people and to society," Kim said in an interview with The Academic Times. "I believe that if I can transfer this lab-based research into the market so more people can use it, it would be good for the environment and good for people."

The application for the patent, "Sustainable curtain wall," was filed on Oct. 14, 2020 to the U.S. Patent and Trademark Office. It was published April 15 with the application number US2021/0108166. The earliest priority date was Oct. 15, 2019. The inventor of the pending patent is Kyoung-Hee Kim, University of North Carolina at Charlotte. The assignee is the University of North Carolina at Charlotte.

Parola Analytics provided technical research for this story.

The description of how Kim measured carbon dioxide indoors has been updated.

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