• EEVblog #881 – Fontus Self Filling Water Bottle BUSTED!

    Dave does basic back-of-the-envelope thermodynamic calculations to prove the Fontus Airo & Ryde self filling water bottle campaign on Indiegogo is full of hot air instead of water.
    It’s 100% baloney!
    Forum HERE

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      • Dave Alan Caruana

        i’m about to watch your video, but I made approximately the same calculation (as to how much energy you need to condense water, keeping in mind you need to do it using an inefficient peltier device) and I also think it’s not real .. thanks for your truly excellent video blog, I love watching your episodes.

        • Yeah, many people have done the same ballpark calc, and there are several ways to do it and none of them come close.

      • ajm8127

        I love your take on “back-of-the-envelope”, and then you put it in the mail. Too funny. In retrospect the only thing better would have been a QR code for the URL of the video printed in the center of an otherwise blank sheet of paper stuck inside the envelope.

        Keep up the good work. Your videos are one of my favorite things on the Internet. Educational and entertaining.

      • blipton

        Doesn’t the campaign list Irvine (California)? Why did you mail it to Vienna (Austria)?

      • Jim Horn

        Regarding Peltier thermal efficiency – they (and air conditioner / heat pumps) only achieve an efficiency of over 100% when heating. When cooling, they can’t surpass Carnot efficiency and in reality don’t even approach that. Their primary limitation is that they consist of metallic conductors between the hot and cold plates so they can conduct the electricity – but that means they have all those heat conductors between the plates as well! And the more current you put through them, the lower the cooling efficiency as the ohmic heating defeats the cooling as well. So this water bottle idea is even more brain dead still…

      • Syd Jessop

        Dave, I agree this is bullshit but have you got the physics right? The concept of latent heat means that converting water vapour to liquid actually generates energy. Why this device is bullshit is because, along with the scarcity of water in the air, the heat exchange rate is impractical when it comes to cooling down the air. Hydrogen bonds formed = release of energy. The guy you link to on your video is also confusing latent heat with heat engines. See Jim Horn’s post re Carnot efficiency.

        • Yes, that’s what the peltier device does, it uses energy in order to extract the required energy from the system.
          But yes there are other ways to bust this as well.

          • Andrew

            Sorry Dave, but Syd is correct. Your analysis is wrong. You incorrectly claim that you need to put 2264kJ/kg into the system. What you actually need to determine is how much energy you need to put into a refrigeration cycle in order to remove 2264kJ/kg from the system.

            Since we are solving for the 100 degF, 90% RH case, the saturation temperature (Dew point at which the vapor is going to actually condense) is going to be 97 degF. So essentially, we need to pump 2264kJ/kg from a cold reservoir at 97 degF to a hot reservoir at 100 degF (we actually also need to cool the air down to 97 degF, but that will be negligible compared with the energy required to condense). If we assume a Carnot (Ideal) refrigeration cycle, the work we need to put into it to do this is W=(1-Tc/Th)*Q. This gives us a work of 12.1kJ/kg. That’s not so bad.

            This does still fall apart when you consider Peltier efficiency. Going back to the TE Technology vendor that you show and picking the highest capacity module from their high-performance section, we will look at part number HP-199-1.4-0.8. The temperature difference is close to 0 (compared to the scale of the graphs in their data-sheet), so to transfer approximately 125W (they would need two), the voltage across the cooler would be approximately 18V. At 18V and DT=0, the COP will be about 0.8 at 30 degC hot-side temperature (it will actually be a little worse since the hot side temp is actually hotter). So, they would need an approximately 315W panel.

            They could actually improve performance by adding more coolers. If they, for example, added 4 of these coolers to their design, each one would only have to transfer about 60W. Thus, the voltage would be around 7V and the COP would be roughly 2. This is getting better, but they can’t do this forever since these things cost $40 each and the cost would quickly become more than what they are charging people for the finished product.

      • eili

        ok guys..15min to watch , surely some hours to make the video and you forget the more important……………………..
        the distilled water you produce is NOT POTABLE

        sure, you can drink it a litle..like the water of your local public swimming pool or like your favorite can of sea water..

        but i’m sure too much is a serious problem//
        and a stressed body who need water because of sport is like….more sensitive

        you know..you take less risk drinking your own pee everyday……..

        thanks caption obvious-dave ^^

        • They realised this and offer optional mineral tablets in the base.

          • eili

            optional like a radio in a car when you buy it? :p

            funny, isn’t it?

            anyway, where do you find it?

            nothing about that optional tablet at http://fontus.at/products/

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