Preventing Sun-Induced Vehicle Overheating with a Single 'Transparent Cooling Film' [Reading Science]

Radiative cooling without power consumption... 20% reduction in summer cooling energy

A joint domestic and international research team has developed a "transparent radiative cooling film" technology that can solve the problem of overheating inside vehicles exposed to direct sunlight in summer without using electricity. Experiments using actual vehicles confirmed that it can lower the interior temperature by up to 6.1 degrees Celsius and reduce cooling energy consumption by more than 20 percent, drawing attention as a means to improve the efficiency of electric vehicles and reduce carbon emissions.

The National Research Foundation of Korea announced on the 11th that a research team led by Professor Ko Seunghwan of Seoul National University, Professor Gang Chen of the Massachusetts Institute of Technology (MIT), and researchers from Hyundai Motor and Kia jointly developed a large-area transparent radiative cooling film that can be applied to vehicle glass and completed real-vehicle verification under various climate and driving conditions.

Conceptual diagram of vehicle application of a large-area transparent radiative cooling film. It shows a four-layer STRC film and its application to vehicle glass, simultaneously performing visible-light transmission, near-infrared reflection, and mid-infrared emission. Image and description provided by Ko Seunghwan, Professor at Seoul National University.

Dissipating heat without electricity... 'Transparent radiative cooling' tailored for vehicle glass

In summer, the interior temperature of vehicles rises rapidly due to solar radiation, causing a sharp increase in cooling energy consumption. Existing low-emissivity (Low-E) coatings and tinting films only partially block incoming sunlight and have limitations in releasing heat that has already accumulated inside the cabin to the outside.

The large-area transparent radiative cooling (STRC) film developed by the research team is designed to maintain a visible-light transmittance of at least 70 percent to secure the driver’s field of view, while reflecting near-infrared light, which is the main component of solar heat, and emitting heat from inside the vehicle in the mid-infrared range. A key feature is that it is a fully passive cooling technology that does not require any external power or control devices.

Analysis of carbon dioxide (CO2) emissions reductions in the United States based on vehicle evaluations in summer and winter. Using results from assessments of cabin temperature and heating/cooling energy consumption for vehicles equipped with STRC under summer and winter parking conditions, we analyzed the projected CO2 emissions reductions if the technology were applied to vehicles across the United States. Figure and description: Provided by Ko Seunghwan, Professor at Seoul National University.

Real-vehicle verification in Korea, the United States, and Pakistan... 20% reduction in cooling energy

The research team conducted real-vehicle experiments in different climate regions, including Korea, the United States, and Pakistan, covering both summer and winter, and both parking and driving conditions. As a result, vehicles equipped with the STRC film consistently maintained lower interior temperatures under all conditions.

Under summer parking conditions, the cabin air temperature decreased by up to 6.1 degrees Celsius, and cooling energy consumption was reduced by more than 20 percent. In winter, heating energy consumption increased slightly due to reduced solar heat gain, but the increase was limited to about 0.4 percent, far outweighed by the cooling energy savings in summer. Simulations incorporating real-vehicle data showed that the time required to reach a comfortable state after turning on the air conditioner was shortened by up to 17 minutes.

According to the team’s analysis, if this technology were applied to all passenger cars in the United States, it would be possible to reduce annual carbon dioxide emissions by approximately 25.4 million tons. This is equivalent to removing about 5 million vehicles from the road. In particular, the reduction in cooling energy directly translates into increased driving range for electric vehicles, leading to expectations that the technology has strong potential as a means of improving vehicle efficiency in the era of electrification.

The STRC film is manufactured using a roll-to-roll process with a width of more than 1,600 millimeters, making it suitable for large-area applications such as windshields and sunroofs, and it has secured durability without performance degradation even under prolonged ultraviolet exposure and extreme temperature conditions.

Lee Minjae, the first author of this study, said, "It is highly meaningful that we did not stop at laboratory performance, but verified the technology in real vehicle environments across different countries, seasons, and driving conditions." Professor Ko Seunghwan explained, "We have demonstrated for the first time that transparent radiative cooling technology can deliver tangible energy-saving effects even in vehicle environments."

This research was carried out as part of the Global Research Laboratory (GRL) Program supported by the Ministry of Science and ICT and the National Research Foundation of Korea, and the results were published online on February 4 in Energy & Environmental Science, an international journal in the field of energy and environment.