IIT-Guwahati researchers have created an economical and efficient ‘passive’ radiative cooling system. The rooftop cooling system works day and night as an alternative to traditional air conditioners.
Designing a passive radiative cooler for daylight operation is tricky due to the need for both high reflectance and emissivity in the atmospheric transmittance window. Radiant coolers could replace traditional air conditioning in buildings and cars. IIT Guwahati scientists created a radiative cooler using silicon dioxide and aluminum nitride.
Key Highlight:
- IIT-Guwahati researchers have created an economical and efficient ‘passive’ radiative cooling system.
- The radiative cooler collects heat from the environment, and solar radiation discharges heat into space and reflects solar radiation.
- This ‘passive’ radiative cooling system can replace air conditioners.
- Instead, they layered silicon dioxide and aluminum nitride on a silver basis.
- IIT Guwahati researchers devised a radiative cooler that reflects 97% of solar and atmospheric radiation and emits 80% of atmospheric transmittance wavelengths.
A press release from IIT-Guwahati on Monday said that this “Radiative Cooler” coating is an “electricity-free” cooling system that can be put on rooftops and works both during the day and at night as an alternative to traditional air conditioners.
The coating material of the radiative cooler is a cooling system that doesn’t need electricity and can be put on the roof. It works both during the day and at night. It can be used instead of ACs.
The radiative cooler is a system that works without electricity. It takes in heat from the environment and solar radiation, sends heat into space, and reflects solar radiation. The coating is put on rooftops, and the cooling system can be used instead of air conditioners. (Image Source: ABP Live (with special arrangement with IIT Guwahati)
Researchers at the Indian Institute of Technology Guwahati have made a “Radiative Cooler” device that works without electricity. This “passive” radiative cooling system is cheap and works well. It can be used instead of air conditioners.
The coating material of the radiative cooler is a cooling system that doesn’t need electricity and can be put on the roof. It works both during the day and at night. The cooler can be used instead of a regular air conditioner.
How Coolers That Use Passive Radiation Work
Passive radiative coolers get rid of the heat they’ve taken in from their surroundings by sending out infrared waves that can pass through the air and into the cold space beyond. So far, most passive radiative coolers have only been able to work at night. Coolers need to reflect all of the sun’s rays to work during the day. Passive radiative coolers haven’t been able to cool enough during the daytime so far. So, scientists at IIT Guwahati set out to solve these problems and develop a cheaper, more effective radiative cooling system that can work both day and night.
Ashish Kumar Chowdhary, Professor Debabrata Sikdar, and other researchers devised the idea for the passive radiative cooler and modeled it. Recent Current Science Reports, a column about scientific research in India, wrote about the study that talked about their new idea.
Why is it hard to make a passive radiative cooler that works during the day?
Professor Debabrata Sikdar said in a statement from IIT Guwahati that making a passive radiative cooler that works during the day is more difficult because it needs to have high reflectance across the whole solar spectrum emissivity in the atmospheric transmittance window. The sun’s spectral regime comprises wavelengths between 0.3 and 2.5 micrometers. Between 8 and 13 micrometers is the range of wavelengths that can pass through the atmosphere.
Radio waves, microwaves, visible light, ultraviolet rays, X-rays, and gamma rays are all part of the sun’s spectrum. Radiation moves through a medium by a process called “atmospheric transmission.” Atmospheric transmittance is the ratio of the amount of radiation that gets through the atmosphere to the total amount of radiation that hits it.
Why are radiant coolers better than air conditioners?
Sikdar also said that these radiative coolers, which don’t need any outside power, could be one of the best ways to replace the traditional air conditioning systems used to cool buildings and cars in hot countries like India. Traditional ways of cooling send the waste into the environment. Radiative cooling, on the other hand, is a unique way to cool something on Earth by sending too much heat directly into the very cold universe.
How the new radiative cooler was made
In the study, rigorous computer simulations are used to test and confirm the theoretical design of the radiative cooling system. The radiative cooler is less likely to have flaws during the making process. Since this is the case, the cooling power of the cooler after it is built should be close to what was calculated.
People think this new idea will encourage cooler makers to look into radiative cooling to make cooling systems that don’t need electricity. The researchers hope the radiative cooler will be on the market once large-scale prototypes are made and tested for stability and durability in different climates.
Chowdhary talked about the technology needed to make radiative coolers work better than they do now. He said that for a radiative cooler to work during the day, the material it is made of needs to reflect the radiation from the sun and the air. Conventional coolers don’t work during the day because the materials used in them absorb more solar radiation than they give off.
How the new cooler works to keep you cool during the day
Chowdhary said that polymer-based passive radiative coolers could be used to cool buildings during the day. But oxidation breaks down the polymers, so they only last for a long time.
Researchers tried to solve this problem by making thin films of silicon dioxide and aluminum nitride. These materials have low optical density, which matches the wavelength range of radiation from the sun and the atmosphere. But these materials have a high optical density at wavelengths that the atmosphere can pass. To stay at the same temperature as a black body, a material with a high optical density gives off all the radiation it has taken in. A black body is something that soaks up all of the electromagnetic radiation that hits it. To stay in balance, a black body must give off radiation at the same rate it takes.
As a ground metal, the researchers did not use a single layer. Instead, they used silver as a ground metal and put thin layers of silicon dioxide and aluminum nitride on top of it. A layer of silver was put on top of a layer of silicon.
Researchers at IIT Guwahati made a radiative cooler that reflected 97% of the radiation from the sun and atmosphere and gave off 80% of the radiation in wavelengths that the atmosphere let through. The study says the net cooling power is around 115 Watts per square meter. This cooling power could lower the temperature inside by up to 15 degrees below the temperature outside.
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