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The zero-electricity Eco-Cooler made from plastic bottles is doing the rounds all over the interwebs:

The principle is a simple one: the plastic bottles are cut in half and glued to a board or a grille. The latter is then installed in a window frame, with the necks of the bottles facing towards the inside of the house. The system works as follows: the hot air that enters each bottle is compressed around the neck of the bottle, cooling it down before it enters the room. The neck of the bottle acts as a tunnel that compresses the air. This cools the air when it exits the neck of the bottle (rapid expansion) using the same principle. The cooling effect following rapid expansion is known as the Joule-Thomson effect. Depending on the direction of the wind and the pressure exerted, the Eco-Cooler can reduce the temperature by five degrees, which is the same amount as an electric air conditioner.

Over 70% of Bangladesh’s population live in corrugated tin huts across the countryside. During the long summer months, temperatures reach up to 45° Celsius, making these huts unbearable to live in.

To address the issue, Grey Dhaka teamed up with volunteers from Grameen Intel Social Business Ltd to create the Eco-Cooler – the world’s first-ever zero electricity air cooler, which uses re-purposed plastic bottles cut in half and put into a grid, in accordance to available window sizes. Based on wind direction and airflow pressure, the Eco-Cooler has succeeded in decreasing the temperature in tin huts by up to 5° Celsius.

Does the Eco-Cooler reduce temperatures in tin huts by around 5° Celsius, compared to simple windows?

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    See also a recent chat session and the same question on Physics.SE
    – Oddthinking
    Commented Jun 15, 2016 at 9:18
  • I looked up the claim instead of paraphrasing it, the question is now answerable with facts and not mere speculation...
    – Sklivvz
    Commented Jun 15, 2016 at 10:51
  • As far as I understand the claim, this thing is supposed to work because (a) it provides shade and protection from rain, an a simple hole window does not and (b) it's meant to catch transverse wind and funnel it in the hut. On the other hand, it's certainly an obstruction that (c) reduces the free circulation of air, which is very important if the hut is hotter than the outside.
    – Sklivvz
    Commented Jun 15, 2016 at 11:17
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    I'm leaving the comment here in the hope that our answerers understand that any theoretical answer is not only not acceptable here, but likely wildly off the mark. Any general principle that relies on a closed system (e.g. conservation of energy, laws of thermodynamics) is not applicable here.
    – Sklivvz
    Commented Jun 15, 2016 at 11:19
  • The link in the question is now broken and no longer works.
    – Joe W
    Commented Nov 26, 2022 at 16:48

1 Answer 1

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I found a paper studying the effectiveness of this sort of air cooler. Link

Table 2 (Page 7) of the paper states that the reduction achieved was less than 1C over an hour, which contradicts the claim of a 5C reduction. Enhanced models (with water added) tested in the document also show reductions of 1.4 and 1.9C over an hour, which is far from the claim of 5C

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    The data in the study is for a much cooler temperature in the claim which is likely to have an impact on the results. Also it appears to be focusing on cooling over a period of time instead of total amount that it can cool. It would also help if you provided data from the paper in your answer instead of expecting people to read the paper and understand it.
    – Joe W
    Commented Nov 26, 2022 at 16:54
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    Even though the paper does not research maximum cooling capabilities, I think it is still a good find. Especially since the "Reduction in temp." declines so much over time, one could draw the conclusion that the maximum difference in temperature achievable will not be much higher than what was achieved in the study.
    – Chris_abc
    Commented Dec 1, 2022 at 11:50
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    @JoeW, all cooling is ‘cooling over time’ as no cooling is instant. It is very fair to say max cooling temperature over 1 hour is likely the max achievable as that is enough time for the system to reach steady state. Meaning, the energy input equals energy extraction (effectively what heating/cooling is). Commented Dec 27, 2022 at 13:08
  • With that said, the starting temperature of such a system can indeed impact the achievable delta. Commented Dec 27, 2022 at 13:09
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    @JoeW, if anything you should expect an unpowered cooling device to reach steady state sooner, it doesn’t have a continual energy input like an AC. I suspect that is why they choose the time span they did. Commented Dec 27, 2022 at 17:14

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