IIT Guwahati designs electricity-free 'Radiative Cooler', an AC alternative

[Skull and Bones]

IIT Guwahati researchers have designed an electricity-free and affordable 'Radiative Cooler' coating material, which is an alternative to the air conditioning system. The coating material can be applied on rooftops and functions both in day and night to dump extra heat into space.​

IIT Guwahati researchers have designed an affordable and efficient ‘passive’ radiative cooling system that does not require electricity to operate. This ‘Radiative Cooler’ coating material is an ‘electricity-free’ cooling system as it can be applied on the rooftops and functions both during day and night time to provide an alternate to the conventional air-conditioners.

Passive radiative cooling systems operate by emitting the heat absorbed from the surrounding in the form of infrared radiations that can pass through the atmosphere before getting dumped into the cold outer space.

IIT GUWAHATI’S PASSIVE RADIATIVE COOLER OPERATES DURING THE DAY​

Most passive radiative coolers operate only at night. For daytime operation, these coolers need to reflect entire solar radiation as well.

Till now, these cooling systems are not able to provide sufficient cooling at daytime but this is where the IIT Guwahati innovation is unique.

IIT Guwahati researchers set out to resolve these issues and bring out an afforfable and more efficient radiative cooling system that can operate round the clock.

Prof. Debabrata Sikdar, Assistant Professor, Department of Electronics and Electrical Engineering, IIT Guwahati, said, “Designing a passive radiative cooler for daytime operation is more challenging due to the simultaneous requirement of high reflectance in entire solar spectral regime (0.32.5 µm wavelengths) and high emissivity in the atmospheric transmittance window (813 µm wavelengths).”

WHO DESIGNED THE RADIATIVE COOLER?​

Ashish Kumar Chowdhary, Research Scholar at IIT Guwahati under the supervision of Debabrata Sikdar, Assistant Professor, Department of Electronics and Electrical Engineering, IIT Guwahati, along with his research team has designed and modelled such a passive radiative cooler.

Their innovation has been recently covered in the Current Science Report, which was initially published in Journal of Physics D: Applied Physics by IOP Publishing, United Kingdom.

WHY RADIATIVE COOLERS ARE THE BEST ALTERNATIVES TO ACs​

Assistant Professor Debabrata Sikdar said, “These radiative coolers requiring no 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 automobiles in countries experiencing hot weather, such as India.”

“Unlike traditional cooling technologies that dump the waste heat into the surroundings, radiative cooling is a unique process that cools an object on the earth by sending excessive heat directly into the extremely cold universe,” he added.

The theoretical design of the radiative cooling system are tested and verified against rigorous computer-based simulations. This patterning-free design of radiative cooler is large-area compatible and hence, also less prone to imperfections during fabrication process.


Therefore, it is expected that the cooling power to be obtained after construction of the cooler is
going to closely match the calculations.

With this innovation, cooler manufacturers can now explore radiative cooling to make electricity-free cooling systems.

The team hopes this will reach the market once the large-scale prototypes are developed and tested for oprational stability and durability under different climatic conditions. They are now working towards this.

TECHNOLOGY USED IN RADIATIVE COOLERS EXPLAINED​

Explaining the technology to overcome limitations of conventional radiative coolers, Ashish Kumar Chowdhary said, “For a radiative cooler to work during daytime, the material should reflect the solar and atmospheric radiations falling on it.”

“Since the materials used in conventional coolers absorb more solar radiations and emit less during the day, those do not work during daytime,” he said.

“While daytime cooling can be achieved using polymer-based passive radiative coolers, oxidation degrades the polymers resulting in a limited lifespan,” he added.

To address this, the innovators considered using thin films of silicon dioxide and aluminium nitride.

These materials have low optical density corresponding to the wavelength range of solar and atmospheric radiations. But at atmospheric transmittance wavelengths, they have high optical density.

When optical density is high, radiations travel slower through a medium and get absorbed more. To remain at thermal equilibrium, the material emits all the absorbed radiations like a black body.

Instead of a single layer, the team cascaded silicon dioxide and aluminium nitride thin film layers on a silver layer, used as a ground metal, placed over a silicon substrate.

The cooler they designed achieved about 97 percent reflectance for solar and atmospheric radiations and 80 percent emissivity for radiations in atmospheric transmittance wavelengths.

The net cooling power is estimated to be 115 Wm2 which could reduce ambient temperature up to 15 degrees below the outside temperature.

ADVANTAGES OF IIT GUWAHATI’S RADIATIVE COOLER​

The key advantages of this electricity-free cooling system in comparison to existing technologies include:

The design is lithography-free and large-area compatible, which is vital for developing affordable and efficient large-scale radiative coolers.

This design will ensure effective cooling during entire daytime without any need to adjust the angle or position of the cooler towards sun

When compared to a recent cooler design achieving a comparable reduction in ambient temperature, this cooler is found to provide around 1.6 times more cooling power

CLIMATE CONTROLLING WINDOW CREATED BY THE SAME DESIGN TEAM​

The research team is also responsible for developing smart window materials that can automatically control a building’s climate.

Recently in the 24th convocation of IIT Guwahati held on June 17, 2022, Ashish Kumar Chowdhary graduated with the best thesis award medal for his significant contribution in the field of nanophotonics and metamaterials for designing smart windows, radiative coolers, and solar absorbers.

He is also a recipient of the AWSAR award 2021 from Department of Science and Technology, Government of India.

IIT Guwahati designs electricity-free 'Radiative Cooler', an AC alternative

IIT Guwahati researchers have designed an electricity-free and affordable 'Radiative Cooler' coating material, which is an alternative to the air conditioning system. The coating material can be applied on rooftops and functions both in day and night to dump extra heat into space.

www.indiatoday.in

Anyone interested in reading the journal, I'm posting it here

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iopscience.iop.org

 

[Faxapis]

We need a shorter path to monetizing these ideas.

We still do not have enough investors to build up these as start ups and mentor it.

What we need is an ecosystem to sustain this. China has that.

 

[Skull and Bones]

We need a shorter path to monetizing these ideas.

We still do not have enough investors to build up these as start ups and mentor it.

What we need is an ecosystem to sustain this. China has that.

I have attached the link to journal. A reduction of 15 K from the ambient temperature can save huge amount of energy.

We theoretically achieve near-perfect reflectance (97.3%) over the solar spectral regime while maintaining high emissivity (80%) in the atmospheric transmittance window. During the daytime under direct sunlight, the cooling power of the proposed structure is reported to be 115

with a temperature reduction up to 15 K below the ambient temperature, when the effect of convection and conductive heat transfer is considered.

But the fabrication method is tricky, and cannot be employed in mass scale manufacturing as it is.

Here, we present a large-area compatible and lithography-free nanoscale multilayer design of daytime PRC based on two pairs of tandem silicon dioxide–aluminium nitride dielectric layer cascaded to a silver ground metal placed over a silicon substrate.

But a very good research nonetheless. I suggest you read his other works, if you're into science and Tech.

 

[FairAndUnbiased]

you are kidding me. let's say this works. they are talking thin films of SiO2/AlN... you know how these are made? vacuum deposition. vacuum deposition is expensive. he also says to use silver paste... in what world is expensive silver paste going to be wasted on passive cooling panels?

if you have vacuum deposition equipment to deposit thin films, and are using silver paste, you can just build solar cells and run an AC from the electricity generated if you just buy some basic solar cell IP and an inverter.

 

[Skull and Bones]

you are kidding me. let's say this works. they are talking thin films of SiO2/AlN... you know how these are made? vacuum deposition. vacuum deposition is expensive. he also says to use silver paste... in what world is expensive silver paste going to be wasted on passive cooling panels?

if you have vacuum deposition equipment to deposit thin films, and are using silver paste, you can just build solar cells and run an AC from the electricity generated if you just buy some basic solar cell IP and an inverter.

I have quoted and mentioned the difficulty in fabrication from the research paper itself. In laboratory setup, sputtering is a preferred mode of deposition because of purity.

However, if they want to roll out a commercial version of the product, they will have to go the route of spin coating/dipping in a Sol Gel solution, however will reduced purity.

 

[FairAndUnbiased]

I have quoted and mentioned the difficulty in fabrication from the research paper itself. In laboratory setup, sputtering is a preferred mode of deposition because of purity.

However, if they want to roll out a commercial version of the product, they will have to go the route of spin coating/dipping in a Sol Gel solution, however will reduced purity.

solgel SiO2? sure. solgel AlN? don't think so.

solgel also has other issues that severely degrade the properties of this film for thermal purposes such as porosity which decreases thermal conductivity and optical transparency.

 

[Skull and Bones]

solgel SiO2? sure. solgel AlN? don't think so.

solgel also has other issues that severely degrade the properties of this film for thermal purposes such as porosity which decreases thermal conductivity and optical transparency.

SolGel coating of SiO2

Preparation of SiO2 anti-reflection coatings by sol-gel method

Antireflection coating for photovoltaic glass is very important for enhancing its optical transmittance, and ensuring a high light absorption and effi…

www.sciencedirect.com

Sol Gel Coating of AlN

https://www.researchgate.net/publication/278729227_Growth_and_Characterization_of_AlN_Thin_Film_Deposited_by_Sol-Gel_Spin_Coating_Techniques

The porosity can be controlled by annealing at higher temperatures, and the transparency can be controlled by changing the percentage of oxygen (works for me in case of ITO) while annealing. Obviously the film obtained by this method will not be as good as obtained in sputtering.

 

[FairAndUnbiased]

SolGel coating of SiO2

Preparation of SiO2 anti-reflection coatings by sol-gel method

Antireflection coating for photovoltaic glass is very important for enhancing its optical transmittance, and ensuring a high light absorption and effi…

www.sciencedirect.com

Sol Gel Coating of AlN

https://www.researchgate.net/publication/278729227_Growth_and_Characterization_of_AlN_Thin_Film_Deposited_by_Sol-Gel_Spin_Coating_Techniques

The porosity can be controlled by annealing at higher temperatures, and the transparency can be controlled by changing the percentage of oxygen (works for me in case of ITO) while annealing. Obviously the film obtained by this method will not be as good as obtained in sputtering.

from your source and another source (https://www.sciencedirect.com/science/article/pii/S027288421930999X) the AlN solgel deposition requires annealing of an Al(NO3)3 solution at 1100 degrees C. That's an incredibly high temperature to use - high temperature is expensive and high temperature limits usable substrates.

the other thing is that this is for a building material. if they said that this was used for passive cooling of vehicle structures like space stations or ships (LNG, cruise ships, etc) which are power constrained, then this expense could be justified. For a building, I don't think so.

 

[Skull and Bones]

from your source and another source (https://www.sciencedirect.com/science/article/pii/S027288421930999X) the AlN solgel deposition requires annealing of an Al(NO3)3 solution at 1100 degrees C. That's an incredibly high temperature to use - high temperature is expensive and high temperature limits usable substrates.

the other thing is that this is for a building material. if they said that this was used for passive cooling of vehicle structures like space stations or ships (LNG, cruise ships, etc) which are power constrained, then this expense could be justified. For a building, I don't think so.

True, not denying that. Cost will be too high for application in domestic uses, unless they come with alternate materials and fabrication method