In the long days of summer in Boston, anyone on campus might notice that the city tends to be hotter than the surrounding, less densely populated towns. This phenomenon is called an Urban Heat Island. According to the EPA, major cities can experience air temperatures up to 10°F (5.5°C) warmer than the surrounding land. This temperature difference can be especially noticeable at night, as the city retains a lot of heat from the previous day instead of cooling down.
Solutions like green roofs — roofs made of live vegetation — have been proposed as a solution for this effect but have not been widely adopted. This is because building green roofs can be complicated, impractical, and expensive, and they have sometimes been shown to be more effective in theory than in practice.
Luckily, another promising solution to ambient building heat is being developed from Dr. Yi Zheng’s Nano Energy Laboratory at Northeastern.
Recyclable, Scalable, and Self-cleaning Passive Cooling Paper for Building Better Roofs
Photo by Ruby Wallau/Northeastern University
Zheng and his team of researchers have found a way to make a passive cooling paper that can be used as an alternative roofing material. This material nearly perfectly reflects heat (without dangerously reflecting light). When applied to the external structure, this material can reduce internal building temperatures by almost 11°F (6°C) in normal daytime sunlight conditions. Passively keeping the building cooler can significantly lower the monetary costs and CO2 emissions associated with running air conditioners.
Compressor-based cooling systems such as typical air conditioners account for about 20% of total worldwide electricity consumption. The resulting greenhouse gas emissions expelled into the environment intensifies global warming and accelerate climate change. Therefore, emerging passive cooling technologies such as Zheng’s cooling paper are the perfect solution to this problem, as they keep buildings cool without any energy consumption.
Greener roofing technology has not been widely adopted in the past, but the team is confident in their approach. “By keeping the material low-cost and focusing on hotter climates, we are optimistic about customer adoption,” says Zheng.
Commercialization with the Spark Fund
The concept of passive radiative cooling has been in development for decades, but it has not been examined for large-scale, commercial applications until recently. Zheng is passionate about making his green roofing technology commercially viable and globally available.
Zheng’s initial area of focus is commercial and residential buildings in hot climates, and then he plans to move into less developed areas that have limited or no access to cooling technology. Once widely commercialized, Zheng’s passive cooling materials have the potential to mitigate nearly 100 million tons of CO2 annually in the U.S. alone.
“The process of working with the CRI through the Spark Fund forced me to step out of the ‘comfort zone’ in the lab and classroom and throw myself into a completely different area as an entrepreneur,” says Dr. Zheng. “However, I feel very excited when I foresee that our lab outcomes could benefit human life and reduce the burdens to the Earth’s ecosystem.”
With the help of Northeastern’s CRI, Zheng formed the spin out, Planck Energies, in 2021 to bring these cooling materials into the commercial space.
“Planck Energies has been growing smoothly, positively, and healthily,” says Dr. Zheng. “Without the CRI’s support, we wouldn’t have been able to reach the current stage of our spin-off. We appreciate the financial support and extensive legal and tax guidance that the team has provided us as a faculty-owned spin-off.”
Learn more about Dr. Zhengs’s research and the six other 2022 Spring Spark Award grantees here.