AUTONEWS

Transparent cooling film cuts car cabin temperature by 6.1°C without electricity

A transparent radiative cooling film technology that dissipates heat directly to the outside without consuming electricity has been developed to reduce vehicle overheating during summer. The technology was validated through real-vehicle experiments conducted under diverse conditions—including different countries, seasons, and both parking and driving scenarios—and demonstrated the ability to lower cabin temperatures by up to 6.1°C and reduce cooling energy consumption by more than 20%.

Seoul National University College of Engineering announced that a research team led by Prof. Seung Hwan Ko (Department of Mechanical Engineering, SNU), in collaboration with Prof. Gang Chen at MIT and research teams from Hyundai Motor Company and Kia (Materials Research & Engineering Center and Thermal Energy Total Development Group), has designed and fabricated a large-area Scalable Transparent Radiative Cooling (STRC) film applicable to vehicle windows. Through real-vehicle evaluations conducted under various climatic and driving conditions, the team demonstrated both energy-saving and carbon reduction effects.

Conceptual illustration of vehicle application of large-area transparent radiative cooling filmThis figure presents the concept of applying a four-layer STRC film to vehicle glass, which simultaneously achieves visible light transmission, near-infrared reflection, and mid-infrared emission. Credit: Energy & Environmental Science

Vehicles exposed to solar radiation in summer experience rapid increases in cabin temperature, resulting in substantial cooling energy consumption. Conventional automotive Low-E coatings and tinting films can partially block incoming solar radiation but fail to effectively dissipate heat already accumulated inside the vehicle, thereby limiting their cooling performance.

Radiative cooling technology, which has attracted attention as an alternative, simultaneously blocks incoming solar energy and emits internal heat to the outside, enabling passive cooling without electricity. However, most previously developed radiative cooling materials are opaque, making them unsuitable for application to vehicle windows, which are the primary entry points for heat.

To overcome this limitation, the research team developed a large-area transparent radiative cooling film with a multilayer structure that maintains over 70% visible light transmittance, reflects near-infrared solar radiation, and emits heat from the vehicle interior in the mid-infrared range. This film suppresses temperature rise inside the vehicle without consuming electrical energy and reduces the time required to reach thermal comfort, thereby minimizing energy consumption in electric vehicles.

Analysis of CO₂ emission reduction in the United States based on vehicle evaluations in summer and winterBased on evaluations of cabin temperature and heating/cooling energy consumption under parking conditions in both summer and winter, this analysis estimates the potential reduction in carbon dioxide emissions if the STRC technology were applied to vehicles across the United States. Credit: Energy & Environmental Science, originally published in Energy & Environmental Science

Real-vehicle experiments conducted across different climatic regions—including Korea, the United States, and Pakistan—and under varying conditions such as summer and winter, as well as parking and driving scenarios, confirmed that vehicles equipped with the STRC film consistently maintained lower cabin temperatures under all conditions.

Notably, the cooling energy savings achieved in summer significantly outweighed any increase in heating demand during winter. In addition, simulations based on real vehicle data showed that the time required to reach a comfortable cabin condition after activating the air conditioner was reduced by 17 minutes. According to the research team's analysis, applying this technology to all passenger vehicles in the United States could reduce carbon dioxide emissions by approximately 25.4 million tons annually—equivalent to removing about 5 million vehicles from the road.

First author Min Jae Lee (Seoul National University/Hyundai Motor Company–Kia) stated, "This study is particularly meaningful in that it goes beyond laboratory-scale performance and validates the technology using real vehicles under diverse national, seasonal, and operational conditions."

Prof. Ko added, "This is the first study to experimentally demonstrate that transparent radiative cooling technology can be effectively applied in real vehicle environments."

Hyundai's Nano Cooling Film...The product, called Nano Cooling Film, would be applied to the vehicle's windows. According to the company, internal temperatures could be reduced by more than 22°C.

Announced in 2023, the film blocks external thermal energy while allowing internal heat to escape.

Hyundai tested the product's effectiveness by applying the film to 70 vehicles in Lahore, Pakistan. In the region, temperatures reach an incredible 50°C, and curtains are prohibited for safety reasons.

The test results showed a 10.98°C reduction in the driver's seat temperature compared to conventional tinted film.

The thermometers also registered 12.33°C less compared to the same vehicle without tinted windows.

On the car's interior surfaces, the film reduced the surface temperature by 15.38°C compared to a vehicle with conventional film and by 22°C compared to one without film.

Provided by Seoul National University