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.

11 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.

Leave a Reply

Your email address will not be published. Required fields are marked *