Debunking the Eco-Cooler

A few months ago, a video was forwarded to me about an air-conditioning unit being developed for developing countries which didn’t require electricity, dubbed the “Eco-Cooler.” It’s not clear to me exactly who or what is behind the idea: the “official” website gives little confidence that it is a serious project, and the videos, while well-produced, seem to be posted through third party accounts and get taken down after a while (this is the original link that was shared with me). In any case, you should be able to search for “eco cooler” on Google or YouTube to find the information I’m talking about, even if these links become defunct.

The science used to explain how the Eco-Cooler works in the video is wrong, and there are others who have already explained this elsewhere (1,2), although unfortunately it seems there’s a lot of noise – incorrect explanations are given along with the correct ones, and skeptics still aren’t sure what to believe. While I’ll take some time to explain why the explanation is wrong, I’m more interested (impressed really) in the experiment the video suggests you try in order to explain the working principle of the Eco-Cooler.

So how does the Eco-Cooler work, according to the video? Air is forced through a nozzle into the house, which pressurizes the air, therefore cooling it. This is bogus. First, pressurizing air heats it, while lowering pressure will lead to a lower temperature. For a real life example of this, you can look at what happens when you use a can of compressed air (or an air horn, or spray paint): as you spray, the can gets cold. When you release air from the can, you’re reducing the pressure inside, and that expansion of gas (not compression/pressurizing) is associated with lowering temperature. Second, the increase in pressure from air flowing through a water bottle nozzle would lead to a negligible change in temperature. If you want to calculate the magnitude of the change yourself, you can use the Joule-Thomson effect, the Bernoulli equation, and conservation of mass – with a back of the envelope calculation I get that air squeezed through the bottle nozzle should heat up by about 0.0001 °C. Finally, even if the air changes temperature as it is squeezed through the nozzle, it will expand as it flows into the room, so the temperature will return to its original value.

So if the scientific explanation they give doesn’t make any sense, why did the video go viral? I think the video’s success is due to the extremely convincing (albeit misleading) “try this yourself” experiment. In the video, the viewer is invited to breathe onto their open palm, first slowly with an open mouth, then quickly with pursed lips. Blowing with pursed lips feels cooler, and they (falsely) claim that this is the same principle which the Eco-Cooler runs on. So what’s actually going on? The air in our bodies is typically warmer than the ambient environment, so if you breathe that air onto your skin, you’ll feel warm (this is step 1 of the video’s experiment). When you purse your lips and blow, the air comes out of your mouth at higher velocity. This leads to more entrained air, that is, the air from your mouth drags along air from the environment with it (this is also how Dyson fans work). As the ambient air is entrained, it mixes with the air from your mouth, lowering its temperature. Overall, the air hitting your hand will be at a higher temperature than the environment (since it’s a mix of high temperature air from your body and ambient air), but it still feels cool since moving air can pull heat out of your body more effectively than still air (this is why sitting in front of a fan feels cool even though the fan doesn’t cool the air at all). To experience this first hand, you can try holding your palm at different distances as you blow with pursed lips. Holding your palm further away should feel cooler, since the hot air from your mouth will have longer to mix with colder ambient air.

So how does the Eco-Cooler actually work? First, I’m not convinced that it does. The video claims the Eco-Cooler can lower the temperature inside a house by 5 °C, but the other content in the video is full of falsehoods, so there’s no reason they couldn’t have just lied about that point as well. That being said, it’s possible that Eco-Cooler could lead to a lower temperature. Air flow through a house will keep the temperature closer to the outside temperature (the house can be hotter than outside because of absorbed sunlight – the same way a car sitting in the sun can get much hotter than its surroundings), and the Eco-Cooler might be more effective than a window because the white panel will reflect sunlight away. However “possible” does not mean “true,” and without much stronger evidence, I am not convinced that the Eco-Cooler is an idea worth pursuing.

23 thoughts on “Debunking the Eco-Cooler”

  1. The way I understand it – and I’m not vouching for it – is this: As the air travels through the cone, it warms slightly. This heat is then absorbed by the sides of the cone and radiated away, returning the air to near its original temperature. Then as the air exits the small end of the cone, it expands, cooling it slightly – leaving a small net cooling effect.

    1. In principle, the Eco-Cooler could cool air via the mechanism you’re describing. However as I mentioned in the post, the temperature change of the air due to changing pressure as it flows through the nozzle will be on the order of 0.0001 °C, too small to be measurable in practice.

  2. Who cares about the science if the people using it feel a benefit?
    (And I say this as a retired science teacher. Easy to sit back criticize people who are at least making attempt to do something.)

    1. I’m not sure I understand your point. Are you suggesting it’s okay (or even desirable) to perpetuate falsehoods as long as you’re trying to make a difference?

  3. There are several other questions as well. Why would the air “flow through” the nozzles any faster than it would through an open window? Without a fan or pump there’s no reason to believe air would have any reason to move through the bottles in any more dramatic way than it would pass through a window. If the eco-cooler was in a north facing window and a south facing window was open the cross draft effect would pull air through, but it would be essentially the same temperature as the air on the north side of the structure. They’re also not really “compressing” the air, since it’s an open system. It would be slightly denser while in the nozzle, but that would be negligible, and the air on either side of the cardboard is the same pressure. Anyway, temperature changes are never free. Energy has to come from/go to someplace. I suspect if this thing has any benefit it’s what you mentioned. It blocks or reflects sunlight while allowing air flow to continue. Using cross flow you could at least keep the house cooler than the air outside its south side.

  4. But this is not just the spurring of a few individuals on to ‘thinking’ of being cooler. This is the manufacturing and selling of hope to millions corporately desperate to believe that a simple, free device will change their lives as none of their forebears’ has been changed, alter measurably and permanently a known and accepted environmental factor and somehow make them a focus in the world; this is socially engineered psychosomatics. There’s no way it can work as well as eagerly expected, because the expectation is already beyond its every innovation, and has been since long before it was tried.
    I suppose many of us who have no such desperation have already conducted the plastic bottle experiment for themselves and can report here on their findings, if they so desire. I also would extrapolate from this whole presentation that if the exit opening were smaller, such as in a funnel, the cooling effect would be supposed by these proponents to be magnified.
    If this had been ‘invented’ in the US and properly road-tested, we may very well label this another money-making ‘scam’, or at best a pipe dream brought on in altruistic innocence. But Bangladesh doesn’t dismiss the attempt to ease their temperature troubles because Bangladesh is unendingly desperate.

  5. It doesn’t work. The science is BS. The heat has to go somewhere. Where does it go? It cannot be absorbed and re-radiated from paper thin transparent plastic exposed to direct sunlight. The plastic would reach equilibrium temperature in seconds and stay there.
    If the air is compressed (it isn’t) it would heat up, when returned to normal pressure, it would return to its original temperature.
    The real question is, why are so many people determined to believe that this thing works?
    It is good to keep some plastic bottles out of landfills and the oceans. Estimates are that 8 billion metric tons of plastic end up in our oceans every year. That’s a lot of Eco-Coolers.

  6. For an “eco-cooler” that really does work to provide both heating and cooling google “skytherm.”
    Basic idea is a roof pond (or pop bottles, milk bottles etc. full of water) that is covered or uncovered with insulation depending on whether you want to heat or cool the room below. To heat the room in winter, uncover the “pond” during the day to allow it to heat up in the sun, then cover with insulation at night to retain the heat. To cool in summer do the opposite – cover during the day to prevent solar heat gain, and uncover at night to let heat radiate into the sky. This really works and was tested in a real house in the 1970s and indoor temperatures were made comfortable year round.

  7. I’ve been trying to think of a way for this to work, and this is what I’ve come up with:

    Assume the commonly posted diagram is backwards. Assume air is drawn outward by the sun heating the air in the bottles; the hot air leaves through the larger opening in each bottle pulling air out from the house. Cool air may then enter the house via some shaded / cooler entry. The additional shade created by the panel (by blocking an open window while inducing airflow) also reduces heat gain inside the home.

    I’d rather build a solar tower for the same effect, but I can see how this might work.

    1. Your explanation is reasonable, and definitely a better explanation that the cooling through compression that is given in the video. That being said, if what you proposed is what is happening, I’d be surprised if it wouldn’t be more effective to just have a shaded window (e.g., with an awning). The bottles will restrict the air flow out of the building compared to an open window, and in either case the lowest temperature you’ll achieve is the outdoor temperature. So to me it seems that you might as well just try to maximize the air flow through the building if that’s your cooling mechanism.

  8. If it was just placebo, I don’t think Bangladeshis would put up with the airflow restriction–they would remove the Eco-Coolers in favor of big, well-shaded windows to catch more breeze (as they have done for centuries). So let’s assume that these devices actually do refrigerate (and dehumidify) air, but that observers are simply at a loss to explain -why.-

    There is, curiously, another form of refrigeration that has been employed for decades yet has never been definitively explained by physics: the vortex tube. Vortex tubes operate at high pressure, but they also tend to be very narrow tubes. I’m not sure what attempts have been made to preserve the mysterious temperature separation phenomenon using larger gas input rates at lower pressure with larger diameter vortex chambers (or if such an approach even fits logically with how vortex tubes are theorized to work).

    That said, what happens when a steady wind enters an Eco-Cooler’s plastic bottle cylinders from an angle? Might it create a vortex that expels most of the air back out the way it came at a higher temperature while the fraction of air that flows through the bottle spout is cooler?

    Even if the effect was very small, -any- real reduction in temperature would also reduce the air’s humidity. Multiply that by dozens of cylinders operating non-stop for hours in a tropical breeze, and it might very well raise the comfort level within the structure significantly.

    1. This is an interesting idea, but without further convincing I don’t see how this could explain the Eco-cooler’s operation. One problem is that there is no control valve in the Eco-cooler, which is critical to the temperature separation in a vortex tube. However, one could argue that the bottle’s neck rejects the warmer outer vortex and only lets the cooler inner vortex into the building. The bigger issue is that the vortex tube requires high operating pressures in order to see a noticeable temperature difference. From the equation for the vortex tube effect, the temperature drop due to the vortex tube at best goes linearly with pressure. Vortex tubes in practice use pressures on the order of 10^5 Pa to get a temperature drop ~50 C. In order to get the temperature drop of ~5 C claimed in the video, you’d need a pressure on the order of 10^4 Pa for a vortex tube, but the pressures you get from wind are only around 10^2 Pa at the most.

      More generally, the vortex tube acts as an air conditioning system: you put work in and get cooling out. Even if the Eco-cooler was as efficient as a good air conditioner, the “work in” from wind hitting the panel is so low that the “cooling out” would also necessarily be small.

  9. So I’m no scientist two however I do know that when molecules are heated they vibrate faster and grow larger and take up more space and when they’re cooled down they vibrate slower and take up less space. So if you have hot air that you are forcing to condense into a smaller space that would intern condense on a molecular level as well forcing the air to cool down at an atomic level correct? Now if you take into consideration the funnel-like top of a bottle and know that the fastest way between two points is a straight line the center of the bottle on the larger end with an invisible cylinder to the smaller opening end of the bottle would be the shortest path of least resistance. However with the funnel shape of the top of the bottle air would be forced in a large space and try to squeeze out of a small space therefore creating a vortex of air which would then in turn pressurize itself and as it’s forcing air through the smaller portion of the bottle it’s taking are that it is already spun and cooled and made on a molecular level condense and I can vibrate less because of how condensed it is by the natural Vortex it creates and then it pushes air with that Vortex and the natural flow of the air through the bottle condensing it more there for giving the molecules less space to vibrate and be hot in there for creating cooler air. And just to add a little something to your previous explanation on why this wouldn’t work. When you spray paint or something out of an air can the can feels cool because you are making the inside of can cycle it’s contents however if you spray a can of dust-off at your face the air feels slightly warm and that’s because now all those condensed cold molecules are given a chance to heat up and vibrate and expand as much as they wish also aerosol is cold and lighter than air so if you cut open a can of paint it’s got a tube running all the way down to the bottom of the can and the freon pushes out the paint so when you feel the can get cold it’s not because it’s less pressure it’s because the freon is not pressured as much and now has more space to move inside the can therefore it gives the effect that the can is cooler. If you can Dent air and pressurize it and blow it even if it is hot air it will cool down there because you are forcing it to. Much like a helicopter helicopters bully the air underneath them which creates lift without the tail rotor to keep the body stationary the helicopter crashes and doesn’t work. Helicopters as a concept were a joke to most people and scientists however by throwing conventional science out the window and applying some common sense instead of taking everything as it is out of a book as face value helicopters fly in the air. The same way a solid metal ship floats in water. Now I built this and put it in front of a fan in the air flow is cooler I put it in a window and while it does not work as well as putting it in front of the fan it still does work. The main point you forgot is that when molecules are hot they vibrate faster and in doing so take up more space when they are cold they could dense and they vibrate slower. Another thing you must have forgotten to realize is aerosol is a cold gas. On another note hot water boils faster than cold water because the molecules are already spread out and vibrating faster however warm water freezes faster as well because the molecules are more spread out and can the shield more rapidly due to the fact that they’re not already condensed and need to be chilled from the outside in as they vibrate around they are cooled in a cycle that effects each molecule individually instead of a mass of molecules. So my science maybe off but the Eco cooler concept does work nonetheless in the same fashion that most of the people on this Earth have survived despite the fact that they are living with their heads shove up their ass and should have suffocated by now.

    1. On another note autocorrect is fired and should have proof read that before I posted it. However you don’t seem like one of the people who should have suffocated yet through an enigma of science are still alive so I have faith that you will be able to figure out what autocorrect Auto wrecked

  10. So, to ask the obvious question: “If you doubt the efficacy of the device, why don’t you just make one and use a common thermometer to see of the incoming air becomes cooler over time?” Or, do you just enjoy demonstrating your (assumed) superior intellect?

    1. The main reason is that building something and performing an experiment is a lot more work than writing out a few equations and explaining a few scientific principles. I also expect that if I did build and test an eco-cooler then anyone who wasn’t convinced by the explanation would claim I had built (or measured) it wrong anyways.

  11. As you mentioned “moving air can pull heat out of your body more effectively than still air”, can this device be interpreted as to increase the speed of air flow (from larger area to smaller area) so that you can feel cooler?

    1. There’s an argument that if your skin was very close to the nozzle it could feel cooler than if you just had an open window, but in practice an open window would be more effective. The eco-cooler provides more of an obstacle for air flow compared to an open window, so even with the nozzle shape, the maximum velocity coming out of the eco-cooler would barely be higher than the regular wind speed (as the average velocity of the air in the wide part of the nozzle would be lower than the regular wind speed). But it’s worth noting that in this case, even if you would feel cooler, the temperature of the air isn’t actually changing.

  12. The Galileo Galilei was told by the ‘experts’ of his day that the earth was flat, the Wright brothers were told by the ‘experts’ of their day that heavier than air flight was impossible, and no doubt Elon Musk was frequently told by modern ‘experts’ that electric cars could never be more efficient than internal combustion engine vehicles. ‘Experts’ are often individuals who faithfully believe only what they were formally taught, and so close their minds to little-understood matters such as the transfer of heat from fluids flowing through conically shaped vessels.

  13. So what you are saying is that when the wind blows air through an opening (thereby pressurizing the air) the air will be heated. It is odd that no one living in cold climates has ever noticed this effect before, otherwise, they would all be leaving their windows and doors open when the weather is blowing a blizzard outside so that they can gain some heat inside.

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