Personal Cooling Using A Closed Loop Water System

That’s not a colostomy bag, it’s the first prototype of [Stephen’s] scratch-built closed loop personal cooling system. He must be living in an uncomfortably hot apartment as this is the second cooling system we’ve seen from him in as many weeks. The previous offering was an evaporative system. This time around he’s pumping chilled water to bring some relief.

The image on the left shows the first iteration of the system which pumped cool water from a large jug through a loop of plastic tubing which he wears around his neck. To refine the design he build the version on the right. As a reservoir he grabbed a water-proof ID container meant to keep your valuables dry in the pool or ocean. Inside there’s a pump which he runs off of a 5V battery supply. It circulates water through the neck strap which is a piece of plastic tubing.

This will work for a time, but as the cold water picks up your body’s heat the effect will be lost. We think he needs to add a Peltier cooler to the reservoir in the next iteration. It might help to refine the loop to increase its ability to transfer heat where it touches your skin.

There’s demo of the most recent version embedded after the break.

38 thoughts on “Personal Cooling Using A Closed Loop Water System

  1. This idea can be tested easily by pinning two shirts together with rubber hose sandwiched in desired pattern and running water through a bucket with ice in it. Devices of this type are commonly used in racing or foundry operations. Peltier or other forms of cooling could easily be adapted. I’ve also seen people adapt HVAC and/or refrigerator coils to this purpose. You could probably also just drill holes in your freezer and put exchange coils in a bucket of water.

    1. You’re right. Personal cooling is a lot harder than it looks. Any attempt has to get the heat away from the body otherwise you get a McDLT, some body parts over-cooled, others over-hot. The problem is that getting that heat away from the body in something that’s not completely ridiculous to wear (looks stupid, is uncomfortable, gets in the way of normal activities, etc) is very difficult.

      The moon walkers had a workable solution using evaporative cooling into a vacuum, but adding that onto a space suit was actually more convenient than other methods (took up less space/power), and it requires an almost perfect vacuum to work. Citizens of Earth aren’t so lucky.

  2. I think it needs some sort of metal tubing section or a heat exchanger of some sort at the neck area. This should allow it to conduct more heat than the rather insulated tubing would.

  3. This is a great project. I’m impressed that he managed to make a small not-so-obvious form factor device. There are a great deal of directions this could go in. Peltier is the obvious next iteration. I do agree with others have said about peltiers creating too much heat, though it isn’t a CPU. The cooling needs would be reduced.

    Another idea is a very slow circulation into an insulated container. Use alcohol for the medium and a small piece of dry ice for the cooling source. Alcohol to prevent freezing, slow circulation for safety. Perhaps a nylon shoulder strap with a smaller tube to increase the surface area of such a cold fluid.

    Or maybe just the obvious and make a very small evaporation cooler. It is reinventing the wheel (sweat) but it would add to the evaporator area of your entire body. It could be as simple as the very old sock and water bottle trick. Soak sock, turn inside out and put water bottle inside. The evaporation from the really large surface area of the soft fibers in the sock will draw heat away and cool the water to below ambient temperatures. Convenient when you have water, but no electricity.

    1. While it’s not a new revelation no matter how it’s done evaporative cooling is ineffective in high humidity, even old fashioned human sweating. The sock over the water bottle is similar to cloth covered canteens. The canvas water bags work best because it’s the water inside the bag that’s evaporating as it wicks through the canvas.

  4. You’d think the tubing should go where the body releases a lot of heat too – like the armpits, rather than across the torso or back. I agree that peltier isn’t a good choice unless you have a BIG heat sink away from this to do the exchange. Ice water with salt is a nice tradeoff for heat capacity.

    1. You don’t release a lot of heat there, it just feels that way because it can’t radiate the heat away so well. Your torso/back are actually the better choice. Another good option would be the top of your head, and places where major veins/arteries are relatively close to the surface.

  5. Cool idea except:
    – The plastic/silicone tubing is actually a very good insulator, meaning that it is not good for absorbing the heat from your body.
    – After a few cycles, the water will match the temperature of your body and won’t be able to cool down easily because the reservoir is also made of plastic (thus preventing the heat to escape). You will need to add a heatsink into your water circuit, preferably with a fan.

    Also, there are a few optimal spots from which the body loses some of the heat, like the neck, armpits, vertebral column and the genital zone.. I suggest you could try guiding the water through those places using regular tubing and using a flexible, heat-conductive water-resistant material there.

    1. The biggest issue with any kind of heatsink is this: He is trying to make himself cooler than his environment. A heatsink would bring him closer to environmental temperatures. If this were a situation where, say, he was excersising, this would be different.

      1. Unless he is going to bring cold water from the fridge every 10 minutes, his setup does not work as you say either.

        If you want to be colder than room temperature, you could do what other hackers here suggested and use a peltier cell.

        But by the way, an heatsink would still keep you cooler than without. Keep in mind that our bodies get rid of additional heat by perspiration. So unless you are naked and sweating, an heatsink will do a better job.

      2. If you pump the heat to the heatsink, it raises about the environmental level (eventually). When that happens that extra heat starts dumping into the environment.

        Just flowing coolant through the radiator should do this well enough, but a peltier could be utilized to ‘force’ the heat from the water into the radiator, where it can be dumped out.

      3. You don’t need to be cooler than your environment to be comfortable. The environment is nearly always cooler than you are, being 37 Celsius. Exercising or not, you’re one of HAD’s warm-blooded readers right?

        The issue is dumping heat to the environment more efficiently than your inbuilt sweating mechanism. I’d guess open-loop evaporative cooling is a lot more efficient than the radiative cooling of a passive metal heatsink, even a pretty big one. If you’re using a fan, it’d be better used to help sweat evaporate away than to cool a bit of metal with dry room air.

        You could do the maths, you’d need to know the heat output of a person in watts.

  6. Hi all,

    Steve here, or apparently as one commenter said, Sheldon Cooper clone lol.

    Thanks for featuring this here at HaD, Mike :)

    I’m excited by all the feedback and suggestions that everyone has offered here. I’m really looking to make the unit as efficient as possible while still keeping it simple so anyone can make one or so they could be made commercially at a very low price.

    I completely agree that there are improvements to be made and will start sourcing bits and pieces to try out some of these ideas.

    One of the challenges I encountered was finding a water pump that was small enough and energy efficient enough to be used in a portable cooling device. I actually took the pump from a USB water fountain device that is meant to sit on your desk and act as a kind of mini zen garden.

    I do have some small peliter coolers on order but won’t receive them until Christmas. I’m not sure if they’ll be used in this project because of the problems of getting rid of the heat on the other side. But I will at least give it a shot.

    I’ve seen a number of people suggest some kind of built in evaporative cooling idea, such as tiny perforations in the tubing. I do agree that there could be some potential there, although I’d have to carefully monitor how much water is lost in the process and how often the container would need refilling.

    As for replacing the tubing with a better heat transfer material, I agree. I’m looking to get some similar diameter copper tubing and then have a mishmash of plastic and copper tubing for maximum flexibility and heat (or cold) transfer. I also want to look into the idea of copper foil to increase the transfer area.

    It sounds like I really need to do more research about which areas of the body would be the best parts to cool/draw heat away from. So thanks for bringing that to my attention.

    I do have two Window type aircon units which can cool my whole home very quickly , but I’m trying to live a little greener and follow in the steps of the Japanese by looking towards more efficient personal cooling rather than whole room/house cooling.

    Cheers :)

  7. The human body loses the most heat through the scalp. A cool cap would work the best. Try this, get a couple of old CPU coolers made for Super Socket 7. Figure out a way to strap them to either side of your neck. Plug the fans into a battery pack clipped onto your belt. Tie up hair to keep it out of the fans.

    You’ll look weird but also be chillin the blood circulating in and under the skin under the CPU coolers.

  8. Hate to be a smartarse… no wait, I love it! But how about just taking your shirt off? Maybe use a spray bottle full of cold water if it’s summer and you live in a desert. And what idiot decided to build houses in the desert anyway? Economics is pretty stupid.

  9. I believe the sides of the neck would be a good place for heat exchange. You have the jugular vein and the corrotid artery both are large vessels close to the surface of the skin. cool the blood,cool the body

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