To reduce energy consumption and assist Taiwan in addressing its energy chal-lenges, the National Science and Technology Council (NSTC) actively promotes the research and development of energy-saving and carbon-reducing technologies. Through its financial support, Professor Yu-Bin Chen from National Tsing Hua Uni-versity and his team have developed an "Eco-friendly radiative cooling film and its coating technique." This technology enables efficient heat dissipation from out-door metallic objects, such as metal storage tanks, metal roofing, large vehicle compartments, and shipping containers. The heat dissipation function is identical to that of an air conditioning system. However, the developed film operates on a distinct principle by utilizing specific wavelengths of infrared light, allowing heat directly penetrate the atmosphere and dissipate into the cold universe. As a result, cooling doesn't require any electricity consumption, effectively reducing energy consumption and costs.

Professor Chen's research team has turned waste into treasure with this pro-posed technology. They have notably chosen eco-friendly materials, primarily de-rived from natural, non-toxic, and biodegradable biowaste, like shrimp and crab shells. This approach ensures that the entire lifecycle of the product, from material preparation and coating to recycling, is environmentally harmless, while also gen-erating economic benefits.

Chitosan is an eco-friendly material with appealing qualities, such as non-toxicity, biocompatibility, and biodegradability. The material has been extensively employed in medicine, food production, and textiles. Professor Chen, leveraging his expertise in electromagnetic waves and radiative heat transfer, has dedicated his research efforts to studying the unique optical and thermal radiative properties of chitosan. For instance, Professor Chen's team has developed energy-saving electrochromic windows using chitosan, addressing challenges associated with the complexity and cost of conventional electrochromic devices. This innovation effec-tively blocks infrared radiation, preventing the entry of heat into indoor spaces (invention patent granted). Additionally, Professor Chen's team has successfully utilized chitosan in combination with other materials to create a thermosensitive hydrogel. The hydrogel is suitable for human ultrasound treatment (invention pa-tent granted, journal paper published). The latest breakthrough of his team is the radiative cooling film demonstrated here.

Through the developed coating technology, Professor Chen's team has success-fully achieved temperature reduction on various targets, regardless of metal type, shape, or operating conditions. This achievement demonstrates reproducibility and versatility. When stainless steel sheets are used as the substrate and coated with the film, they can increase the thermal radiative emittance by 13 times. Plac-ing the samples above the designed enclosure can result in an average reduction of the internal heat source temperature by 2.8 ℃ during the daytime, with the max-imum cooling effect reaching up to 7.1 ℃. Their work has not only been published in international academic journals but has also gained recognition through patents granted in Taiwan and the United States.

Compared to existing techniques and products, Professor Chen's team's research outcomes offer the following functionalities and advantages:
1.Energy-Efficient Cooling: The radiative cooling film can effectively lower the temperature of the underlying metal object without any power consump-tion. It provides effective cooling effects both during the day and at night.
2.Eco-Friendly Material: The film primarily consists of non-toxic, biocompati-ble, and biodegradable chitosan, which poses no harm to the environment throughout its lifecycle, from raw materials to disposal.
3.Simple Process: The coating process is simple and inexpensive. High tempera-ture, vacuum, and cleanroom are all unnecessary. The coating technique is applicable to conductive substrates of any size and shape.
4.Wide Applicability: The radiative cooling film can be widely used in various metal devices, such as metal pipelines, transportation vehicles, metal storage tanks, and metal roofing. Users can significantly reduce air conditioning costs and energy consumption.

This developed film adheres to green manufacturing principles from its birth to death. If the film is widely adopted in residential, commercial, and industrial set-tings, users' dependence on air conditioning will be largely reduced. Energy con-sumption will be diminished, and significant benefits will be gained for businesses in their pursuit of ESG (Environmental, Social, and Governance) objectives. Fur-thermore, its adoption can remedy global warming and achieve carbon reduction. Professor Chen's team will soon technology transfer this innovation to coating manufacturers. They will also continue to refine overall structural designs and en-hance formulation improvements. The next step is to develop suitable radiative cooling films for large indoor heat sources, such as workstation servers. Scope of applications will be broadened to generate large impacts and economic benefits.

Media Contact：
Mr. Ching-An Chuang
Program Manager
Department of Engineering and Technologies
National Science and Technology Council
Phone：(02) 27377372
e-mail：cchuang2@nstc.gov.tw