Passive Radiative Coolers
A growing trend:-
Electricity demand has been increasing day by day and the major part is consumed in the cooling purposes. Air conditioning accounts for nearly 15% of primary energy used by United States.
But , In this modern world do we really need electricity to cool a building ? The answer is a big NO. How is it possible? To know this please follow the post till the end.
Let me start by explaining these terms:
Passive means without consuming electricity, radiative means emission of radiation (As we all know every body radiates heat weather its a human body or any object).
We need to know one more term for the better explanation of the concept used i.e -
Atmospheric window- our earth is transparent to few waves which means it can directly transfer the heat/energy using these ranges i.e (8–13 µm).
So the idea follows as- when an object(device/building) is exposed under the sky and is allowed to radiate heat using atmospheric window to transfer energy and using universe as a heat sink we can cool a device on earth as per thermodynamic’s principle.

This phenomenon has been used by the people worldwide for example the ancient people of Iran utilized night sky radiative cooling to form ice in desert, the dew at the morning etc. Night time radiative cooling has been widely known since ages, but why not daytime ? But, the need for the cooling occurs mostly in the day time.

The design solution for daytime passive cooling has been 25–30% efficient only this is because of presence of sun creates problem during daytime due to which a body starts absorbing more heat compared to the emissions which results into heating of the device instead of cooling.
So, if some way one could reflect all the solar radiation along with that using appropriate emissive material one could successfully implement a cost effective cooling solution.
Since the goal of this post is to brief about the concept behind ,instead of technicalities . Thus to know more about design approaches please refer google scholar.
Thus a passive cooling strategy that cools without any electricity input could therefore have a significant impact on global energy consumption , providing a cost-effective , energy-efficient , environment-friendly solution by reducing CO2 emission thus controlling global warming as well.