In Hong Kong, where buildings account for about 90% of electricity consumption and over 60% of carbon emissions, PolyU is leading an innovative approach to energy conservation. Researchers have unveiled a cutting-edge solar-driven adaptive radiative cooling (SARC) coating for building surfaces. This eco-friendly innovation can slash building surface temperatures by up to 25°C and indoor temperatures by 2 to 3°C — all without consuming energy — ushering in a new era of sustainable urban development.

Innovative cooling for a greener future

Traditional cooling materials struggle to automatically adjust cooling capacity in response to environmental changes. Led by Professor Vivien Lu Lin, Professor of the Department of Building Environment and Energy Engineering, and Dr Gong Quan, Postdoctoral Fellow, a PolyU team has invented a carbon dots (CDs)-driven SARC coating. This photoluminescent radiative cooling nanocoating adjusts its cooling capacity based on solar irradiance, enhancing solar reflectance as sunlight intensity increases, thereby preventing buildings from excessive heat absorption.

Unlike traditional materials that pose environmental risks, Professor Lu’s team introduces groundbreaking, environmentally friendly polymer-based, nano-sized CDs as photoluminescent materials into radiative cooling coating. This water-soluble SARC forms a coating on building surfaces without releasing volatile organic compounds, reducing air pollution.

Impressive results with broad impact

The new SARC coating boosts effective daytime solar reflectance from 92.5% to 95%, increasing cooling effects by 10% to 20% and reducing temperatures by up to 25°C. In a demonstration project with the HKSAR Government, coated container house roofs remained 24°C cooler after two and a half years, achieving 10% annual energy savings.

Professor Lu remarked, “Our SARC coating demonstrates exceptional cooling performance suitable for a wide range of climates, accelerating the development of next-generation cooling materials.” This water-soluble coating can be produced in various colours, achieving cooling and aesthetic enhancements, and offering a promising solution for sustainable urban development.

Supported by PolyU’s Carbon Neutrality Funding Scheme, the team integrated this coating with bifacial solar photovoltaics (PV) for enhanced thermal management and power generation. Plans to install these on the under-constructed PolyU Kowloon Tong Student Hostel aim to improve power generation by 30-50% and cut carbon emissions by 30%.

This dual-functional system exemplifies how innovative technology can transform buildings from energy consumers to harvesters, advancing sustainable urban living in Hong Kong.

The environmentally friendly SARC coating can reduce a building’s surface temperature by up to 25°C and lower indoor temperatures by 2 to 3°C, without consuming any energy.