Changing climates require energy efficient methods for cooling buildings and vehicles. Researchers at Linköping University have shown that the temperature of a material can be controlled with ambient temperature and air pressure using electrical regulation of passive radiative cooling. The results are published in Cell Reports Physical Science.
“For example, to cool buildings, conventional air conditioning is now predominantly used, which requires large amounts of energy and uses refrigerants that are harmful to the environment. Passive radiative cooling helps. can be borrowed to use the coldness of outer space to supplement regular AC and reduce energy consumption,” says Magnus Jonsson, professor and leader of the Organic Photonics and Nano-Optics Group at Linköping University. said.
Passive radiative cooling relies on the release of thermal energy from objects in the form of infrared radiation. All objects such as trees, buildings, water and even humans emit heat as infrared radiation.
Different types of materials emit different amounts of infrared heat. This depends on the material’s ability to absorb infrared radiation. The higher the ability of a material to absorb infrared heat, the easier it is for a material to radiate heat. For example, regular white writing paper is good at absorbing infrared heat, thus releasing heat. Metals, by contrast, are bad at it because most of the heat is reflected.
outer space cools
The ability of the atmosphere to transmit light in the infrared wavelength range allows us to take advantage of the coldness of outer space, a temperature of about -270 degrees Celsius, to remove heat from objects on Earth. A net transport may occur as a result of the temperature difference. Therefore, with the help of passive radiative cooling, an object can obtain a temperature below the ambient temperature.
This effect has been used since ancient times, such as making ice in warmer climates. In recent years, however, materials science research has taken an increasing interest in this phenomenon, and has developed new materials that are highly capable of emitting infrared heat without being warmed by the sun’s rays.
Researchers at Linköping University have shown that the temperature of a device can be adjusted by electrically adjusting the range from which heat is emitted through passive radiative cooling. In this concept, a conducting polymer is used to electrochemically tune the emissivity of the device.The result was published in a magazine cell report physical science.
Causes minimal contamination
“You can compare it to a thermostat. Now you can adjust the temperature in 0.25 degree increments. ,” said Debashree Banerjee, principal research engineer at Linköping University and lead author of the study.
The researchers believe that now that they have shown that it is possible, they have the potential to further develop both the material and the device. A system can be envisioned to control the infrared heat radiation from the house and cool it as needed. This method has very low energy consumption and minimal pollution.
Other areas of application include clothing and wallpaper that can be adjusted to match the heat flow, which can also reduce energy consumption and improve indoor thermal comfort.
Powering thermoelectric devices
In another study published in advanced science, the same research group developed a thermoelectric device driven by the same principle of radiative cooling that is also complemented by solar heat. It is based on creating a temperature difference between two cellulose materials, one of which contains carbon black that absorbs the sun’s heat. A material is connected to the material that converts the temperature difference into an electric potential. Exposing the device to the sky already induced a voltage of 60 mV in moderate solar radiation, but since the two wood-based materials were designed to differ in their ability to radiate heat, this concept Works even at night.
“We use not only the sun, but also outer space as an energy source,” said a doctoral student in the group. advanced science.
To perform controlled measurements for both studies, researchers constructed an empty simulator. Thus, the measurements were not affected by environmental changes as they were outdoors. The sky simulator consists of a tube coated with aluminum on the sides that reflect radiation. A container placed at the bottom contains a material that absorbs thermal radiation and is cooled with liquid nitrogen to simulate the cold of outer space.
Original: Passive radiative cooling can be controlled electrically
Than: Linköping University
