By Nidhi DhullReviewed by Susha Cheriyedath, M.Sc.Oct 23 2024A recent article from the City University of Hong Kong (CItyUHK) presented a next-generation passive radiative cooling technology developed by their researchers. This scientific breakthrough involving cooling ceramics, textiles, and pavements can help mitigate the impacts of global warming heat without extra energy consumption.
Study: CityUHK researchers develop next-generation radiative cooling technology. Providing energy-free cooling materials to combat global warming. Image Credit: A_stockphoto/Shutterstock.com
Background
Energy consumption for space cooling has more than tripled since 1990, increasing strain on electricity grids, greenhouse gas emissions, and the incidence of urban heat islands. Many people worldwide are now vulnerable to heat stress due to severe heat incidents and record-high temperatures globally. This adversely affects labor productivity, thermal comfort, and overall human health.
As a solution, a research team from the School of Energy and Environment at CityUHK developed a cooling paint for walls and roofs based on passive radiative cooling (PRC) technology. This was done through i2Cool, a start-up incubated in 2021 under the university's HK Tech 300 program.
PRC Technology
This research team, led by Professor Edwin Tso Chi-yan, has been aiming to develop PRC technology, which he describes as a comprehensive solution to climate change and global warming. PRC exploits high mid-infrared (MIR) emissivity and solar reflectivity to lower surface temperatures naturally by emitting thermal radiation and reflecting incoming sunlight to the cold universe.
PRC method can reduce the surface temperature by at least two degrees, offering a refrigerant and electricity-free cooling method to mitigate the heat impact without extra energy requirement. Therefore, the team’s PRC-based products, such as cooling paint for walls and roofs, have been applied to more than 1.07 million square feet in 20 regions and countries through the i2Cool platform since 2022.
Other PRC Technology Applications
The researchers are diversifying the advantages and applications of PRC technology in three other fields: pedestrian paths and public squares, cooling ceramics for building envelopes, cooling asphalt for roads, and thermal management textiles for personal clothing.
PRC ceramics (PRCCs) are designed to have high MIR emissivity and solar reflectivity. Their porous structure minimizes solar absorption and prevents degradation due to ultraviolet radiation. Notably, PRCCs are made of pure inorganic materials with low heat and sunlight absorption, offering high chemical stability and robust mechanical characteristics.
PRCCs are eco-friendly ceramics appropriate for long-term outdoor use, making them suitable for pedestrian paths, building envelopes, and public squares. They can lower solar heat gain and increase the thermal radiation to the universe, thus decreasing the air-conditioning needs.
PRC pavements (PRCPs) are aimed at additionally mitigating the urban heat-island effect. Conventional asphalt leads to elevated pavement surface temperatures, up to 50 to 60 °C, because of the solar radiation absorbed during daytime. Alternatively, PRCPs enhance solar reflectivity and MIR emissivity of pavement surfaces due to the incorporated inorganic materials that effectively reflect sunlight and decrease the road surface temperature. Additionally, the durability of PRCPs makes them ideal for urban roads with high traffic.
Another possible application of PRC technology, biodegradable dual-mode thermal management textile (Bio-DTMT), encompasses thermochromic particles, which automatically vary solar reflectivity according to room temperature. Thus, they can provide warming in winter and cooling in summer.
Eco-friendly fibers and polymers are used to fabricate Bio-DTMTs with a multi-layered, hierarchically porous configuration comprising nano-micro particles. This structure enhances the textiles’ solar reflectance and MIR radiation emissions, providing an electricity-free personal cooling method. Such personal clothing textiles can help lower heatstroke risk for outdoor workers by enabling thermal comfort.
Government-Industry Collaboration
The recent approval of funding from the Hong Kong government’s Research, Academic and Industry Sectors One-plus Scheme (RAISe+ Scheme) is expected to accelerate the commercialization and application of PRC-based innovations developed by the research team from CityUHK.
The team aims to establish production lines and manufacturing facilities by the end of 2026. This will help introduce these innovative cooling methods to the global market at the earliest. Before commercialization, the researchers plan to perform comprehensive user trials for PRCCs, PRCPs, and Bio-DTMTs in collaboration with different government departments, industrial partners, and non-governmental organizations.
Integrating PRC into the domains of buildings, roads, and textiles has the potential to mitigate the urban heat-island effect and greenhouse gas emissions, especially in hot areas. The personalized thermal comfort will contribute to a more resilient and sustainable community, combatting the challenges of climate change.
Journal Reference
CityUHK researchers develop next-generation radiative cooling technology. Providing energy-free cooling materials to combat global warming | HK Tech 300. (2024). City University of Hong Kong. https://www.cityu.edu.hk/hktech300/media/latest-news/cityuhk-researchers-develop-next-generation-radiative-cooling-technology
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