I was just reading this link and I was wondering what the Physics behind this 5°C temperature drop is.

On this website, they describe a passive cooling system being used in a part of Bangladesh. For this system, they take recycled bottles and a sheet of cardboard. Holes are cut along a grid in the cardboard to fit the neck of the bottle. The bottles are cut somewhere near the middle to be a sort of funnel, with the neck going into the hole in the cardboard.

enter image description here They say that conditions outside can reach up to 113°F, and that this passive cooling can effectively lower the temperature up to 10°F inside.

I can't help but wonder if the temperature change in the room is due to circulation, and not any temperature effect. However, if air is flowing between the outside and the inside, then some heat energy may be converted to kinetic energy.

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    $\begingroup$ Hi and welcome to physics.SE! It's currently unclear what exactly this question is asking without clicking on the link you provided. To make questions more accessible and guard against link rot, please include all relevant information, such as a basic summary of what can be seen in the video, in your question. $\endgroup$ – ACuriousMind Jul 19 '17 at 22:48
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    $\begingroup$ Possible duplicate of How does the Eco-Cooler air conditioner really work? $\endgroup$ – M. Enns Jul 20 '17 at 1:29

It takes more energy to heat up moisture in the air and, as such, if you increase the flow of air (and so moisture) through the room you're increasing the rate at which energy can be carried away.

The funnel shape of the bottle tops means - from Bernoulli's principle - that the velocity of the air must increase in order to move the same volume of air at the same rate (since the cross-sectional area is decreasing). So the funnels increase the rate of air flow from outside compared to a normal opening.

  • $\begingroup$ Increasing air through the room itself wont really help if it's above body temperature outside and humid. If the air were above body temperature, the only benefit to moving it would be to evaporate the sweat off your skin. That's much less effective if the air is humid. It may effectively cook you. $\endgroup$ – JMac Jul 19 '17 at 23:43

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