The Guwahati researchers at the Indian Institute of Technology (IIT) have designed an alternative to AC (air condiction) that the IIT claims is not only affordable and efficient, but also works without electricity.
The innovation called ‘Radiative Cooler’ coating material can be applied to roofs and functions both during the day and at night as an alternative to conventional air conditioners.
Passive radiant cooling systems work by emitting the heat absorbed by the environment in the form of infrared radiation that can pass through the atmosphere before being dumped into cold space, the IIT explains.
Most passive radiant coolers only work at night. For daytime use, these coolers must also reflect the entire solar radiation. To date, these cooling systems have not been able to provide sufficient cooling during the day. IIT Guwahati researchers sought to solve these problems and release an affordable and more efficient radiant cooling system that can work around the clock.
The theoretical design of the radiant cooling system has been tested and verified through rigorous computer-based simulations. This pattern-free design of the radiant cooler is compatible with a large surface area and therefore also less prone to imperfections during the manufacturing process, according to the IIT. Therefore, the cooling capacity that will be obtained after the construction of the cooler is expected to closely match the calculations. With this innovation, cooler manufacturers can now explore radiant cooling to create electricity-free cooling systems. “The team hopes this will come to market once the large-scale prototypes have been developed and tested for operational stability and durability under different climatic conditions. They are now working towards this,” the IIT said in an official statement.
Ashish Kumar Chowdhary, Research Scholar at IIT Guwahati under the supervision of Prof. Debabrata Sikdar, Assistant Professor, Department of Electronics and Electrical Engineering, IIT Guwahati, together with his research team designed and modeled such a passive radiant cooler.
Their innovation was recently covered in the Current Science Report, originally published in the Journal of Physics D: Applied Physics by IOP Publishing, United Kingdom.
Prof. dr. Debabrata Sikdar, Assistant Professor, Department of Electronics and Electrical Engineering, IIT Guwahati, highlights the unique aspects of this innovation: “Designing a passive radiant cooler for daytime use is more challenging due to the simultaneous requirement of high reflectance in the full spectral solar system ( 0.3-2.5 µm wavelengths) and high emissivity in the atmospheric transmission window (8-13 µm wavelengths).”
Furthermore, Prof. Debabrata Sikdar said: “These radiant coolers that do not require external energy sources for their operation could be one of the best alternatives to replace the conventional air conditioning systems used to cool buildings and cars in hot weather countries such as India Unlike traditional cooling technologies that dump waste heat into the environment, radiant cooling is a unique process that cools an object on Earth by sending excess heat directly to the extremely cold universe.”
Ashish Kumar Chowdhary, explaining the technology to overcome the limitations of conventional radiant coolers, said: “In order for a radiant cooler to work during the day, the material must reflect the solar and atmospheric radiation that falls on it. Because the materials used in conventional coolers absorb more solar radiation and emit less during the day, they don’t work during the day. While daytime cooling can be achieved using polymer-based passive radiant coolers, oxidation degrades the polymers resulting in a limited life.”
To address this, the innovators considered using thin films of silicon dioxide and aluminum nitride. These materials have a low optical density corresponding to the wavelength range of solar and atmospheric radiation. But at atmospheric transmission wavelengths, they have a high optical density. When the optical density is high, radiations travel more slowly through a medium and are absorbed more. To maintain thermal equilibrium, the material emits all absorbed radiation as a black body.
“Instead of a single layer, the team cascaded thin film layers of silicon dioxide and aluminum nitride on a silver layer, used as a ground metal, and placed it on a silicon substrate. The cooler they designed achieved about 97 percent reflectance to solar and atmospheric radiation.” and 80 percent emissivity to radiations in atmospheric transmission wavelengths.The net cooling capacity is estimated at 115 Wm−2 which could lower the ambient temperature to 15 degrees below the outdoor temperature,” the IIT said in a statement.
Get all the latest news, breaking news, watch top videos and live TV here.
