Next-Generation Passive Radiative Cooling Provides a Sustainable Solution to Global Warming

By Nidhi DhullReviewed by Susha Cheriyedath, M.Sc.Oct 23 2024

A breakthrough from researchers at City University of Hong Kong (CItyUHK) has introduced a next-generation passive radiative cooling (PRC) technology. This innovation, which applies to cooling ceramics, textiles, and pavements, offers a sustainable way to mitigate the effects of global warming—without relying on additional energy consumption.

Addressing the Rising Need for Cooling Solutions

Since 1990, global energy consumption for space cooling has more than tripled, placing an immense strain on electricity grids and contributing to higher greenhouse gas emissions. With rising global temperatures and urban heat islands, more people are vulnerable to heat stress, adversely affecting health, labor productivity, and thermal comfort.

In response, researchers from CityUHK’s School of Energy and Environment, through the start-up i2Cool (part of the university's HK Tech 300 program), developed a passive radiative cooling paint for walls and roofs. This technology enables surfaces to cool naturally by radiating heat and reflecting sunlight, without the need for refrigerants or electricity.

How PRC Technology Works

Professor Edwin Tso Chi-yan and his team have focused on the development of PRC technology, which they see as a critical tool in combating climate change. PRC harnesses high mid-infrared (MIR) emissivity and solar reflectivity to cool surfaces by emitting thermal radiation and reflecting sunlight into space. This approach reduces surface temperatures by at least two degrees, providing an energy-free cooling method that helps mitigate the effects of heat without consuming additional energy.

Since 2022, PRC-based products such as cooling paints for walls and roofs have been applied to more than 1.07 million square feet across 20 regions and countries, facilitated by the i2Cool platform.

Expanding PRC Applications

The research team is exploring additional applications for PRC technology, extending its benefits to pedestrian paths, public squares, ceramics, roads, and textiles.

• PRC Ceramics (PRCCs): These ceramics are designed to have high MIR emissivity and solar reflectivity, with a porous structure that minimizes solar absorption and prevents degradation from ultraviolet radiation. Made from pure inorganic materials, PRCCs are eco-friendly, offering high durability and stability for long-term outdoor use in areas like pedestrian paths, building facades, and public squares. They help lower solar heat gain and reduce air-conditioning needs by enhancing heat radiation to space.

• PRC Pavements (PRCPs): Traditional asphalt can reach surface temperatures of 50 to 60 °C due to its absorption of solar radiation. PRC pavements, on the other hand, use inorganic materials to increase solar reflectivity and MIR emissivity, effectively lowering surface temperatures. This makes PRCPs a valuable solution for mitigating the urban heat-island effect, particularly in high-traffic areas.

• Biodegradable Dual-Mode Thermal Management Textiles (Bio-DTMT): Another innovative application of PRC technology is in personal clothing. These textiles, which use thermochromic particles, automatically adjust solar reflectivity based on the surrounding temperature. This allows the textiles to provide cooling in summer and warmth in winter. Made from eco-friendly fibers and polymers, Bio-DTMTs feature a multi-layered porous structure that enhances solar reflectance and MIR emissions, offering a sustainable, electricity-free personal cooling method. These textiles are particularly useful for outdoor workers, helping to reduce the risk of heatstroke by improving thermal comfort.

Collaborating for a Sustainable Future

The CityUHK team’s work has attracted significant support, including funding from Hong Kong's Research, Academic, and Industry Sectors One-plus Scheme (RAISe+). This funding is set to accelerate the commercialization of PRC-based innovations. By 2026, the team plans to establish production lines and manufacturing facilities, paving the way for the global distribution of these innovative cooling technologies.

Before reaching the global market, the team will conduct comprehensive trials of their PRC ceramics, pavements, and textiles in collaboration with government departments, industry partners, and non-governmental organizations. These trials will help validate the technology’s performance in real-world conditions and refine it for widespread use.

By integrating PRC technology into buildings, roads, and personal clothing, CityUHK researchers aim to mitigate the urban heat-island effect, reduce greenhouse gas emissions, and enhance thermal comfort, particularly in regions most affected by 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

Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.