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The Thermal Chimney Hat: The World’s Greatest Hat for Ultrarunning?

Posted by on Jul 16, 2012 | 26 Comments

Hats. Most runners wear them at least some of the time. My preferred hat has been a desert camo boonie hat, which has performed admirably. Could there be a better solution, though?

My recent discovery and subsequent discussions on moisture-wicking materials and thermoregulation piqued my interest in hats. Specifically, a discussion on Barefoot Ted’s Google Group led me to try a stray sun hat. That same discussion also led me to consider modifications that would make the sun hat even more effective… so I built this:

The thermal chimney hat! It uses a few principles to facilitate cooling.

First, the brim is painted gloss white to reflect the solar energy from the sun. This would be slightly better than the natural tan color of the wicker.

Second, the underside is painted flat black. This will facilitate radiant heat dissipation from the head. Heat absorbed by the underside of the brim will be collected in the rim, conducted to the cooler top (painted white), and dissipated by passing wind via convection. The brim becomes a gaint cooling fin in addition to providing shade for the rest of the head and shoulders. The heat absorbed by the crown (part that fits over your head) will be used to increase the thermal updraft, which helps the next action.

Third, I had to solve the problem of air flow in the crown. The straw hat had small ventilation holes, but they didn’t work well if there wasn’t a breeze (or running fast). The solution was to create a solar chimney of sorts. I got the idea from the Google Group’s discussion on desert-dwellers that wore black robes in extreme heat. The black would heat up. Since hot air rises, cooler air would be sucked in the bottom of the robe, pass the body, and exit the top. This airflow cools the body via convection, which also helps evaporate sweat.It’s the same principle used to cool buildings in hot weather without the use of air conditioning.

By painting the outside of the crown black, it would heat up when exposed to the sun. The inside would also heat up from the radiant heat of the head. This heated air would escape the upper vents cut into the back of the crown, which would also suck cooler air into the lower vent at the front of the crown. The dry incoming air would help evaporate sweat off the top of the head, which would keep it cool. This airflow will continue even if there is no breeze since the airflow is partly assisted by rising heat.

So… will the hat work? We’ll see. I’ll be testing it in a variety of conditions this week. I’ll buy a second unmodified hat to use as a baseline. Stay tuned!

What do you think? Will the principles work? Is this going overboard? Do I have too much free time on my hands? :-)

###

On a related note- in anyone is interested, I’ll make you a hat for a small fee. ;-)

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26 Comments

  1. Nyah
    July 19, 2012

    I tested black vs white on a fiberglass helmet which has a few ventilation holes. On a bike trip, I hated how hot the helmet got when it was painted black. I re-painted the outside of the helmet white and the result was significantly less hot on my head. I predict that you’d get a similar result if you painted the outside of your hat’s crown white.

  2. Barefoot Running University » Are We Increasing Cancer Risk by Covering Up?
    July 17, 2012

    […] I am going to be exposed long enough to burn and it’s too hot from protective clothing (like my experimental hat). I do the same with my […]

  3. Lyonel
    July 17, 2012

    [img]http://www.sourcingmap.nl/larger_image.php?products_image=ux_a11090900ux0119_ux_&p=153932&products_imageType=jpg[/img]

    :)

  4. StephenB
    July 16, 2012

    If you extend the thermal chimney a bit, you might end up with a hat like the cat in the hat wears. Not that that’s a bad thing. :D

  5. Joe
    July 16, 2012

    Your chimney flow is powered by the difference in temperature, so if it is warmer outside your hat, or close to it, you would get a no additional flow or reversed flow. Of course, your hat needs to be much taller to increase your flow more.

    If you don’t mind looking dopey (obviously not an issue.) You would probably get more airflow by removing the vertical part of the hat almost entirely. Then your could extend the top portion out to get your more shade on your head. Like and extremely thin wedding cake. Lets see if my asci art comes through. Just have enough vertical columns to support the top. There might be an issue with it blowing off though. :)

    ———
    / \
    / \
    —– —–

    • Jason
      July 17, 2012

      I did consider this design, but didn’t have the materials to build it. It may be a future prototype, though. ;-)

  6. Angie Bee
    July 16, 2012

    Jaymon and I have been wearing the straw gardening hats to run in for a while now. You get tem at Menards or Lowes for $10. Nice air flow and wide brim with a cord to keep it on when te wind catches it. I love a good boonie hat :) hate visors.

  7. chris
    July 16, 2012

    Jason,

    Thanks for making me look like a “normal” runner. I’ve bookmarked this post to show my wife next time she thinks I am putting too much thought and effort into my running! ;-)

  8. Dave
    July 16, 2012

    Okay, I’m already traipsing around in shorty shorts and Jesus sandals, and now I’m supposed to wear a spray painted straw hat with holes cut out them? Not only is my wife going to leave me out of shear embarrassment, my running attire will pretty much ensure that I won’t be able to find a 2nd wife.

    At least if I pass out from heat exhaustion, I could maybe meet a cute nurse…

    • Jason
      July 16, 2012

      I never claimed to come up with aesthetically-pleasing ideas. :-)

    • David Goulette
      July 17, 2012

      So funny!

  9. McKay
    July 16, 2012

    It sounds interesting, but I’m confused why the bottom of the hat is black. Correct me if I’m wrong, but I was under the impression that black only absorbed light, not just any radiant heat. It may absorb the light reflected off the skin so that it doesn’t reflect back, providing better shade, but I don’t think that will absorb body heat any better. Am I wrong?

    • Jason
      July 16, 2012

      Heat is the same radiation as visible light, only a longer wavelength. A black surface absorbs heat regardless of the presence of visible light.

      • Nick
        July 16, 2012

        Heat is not a form of electromagnetic radiation. IIRC, black object are better absorbers of EM radiation specifically in the light spectrum. As they absorb light, the energy is converted into heat. In a perfectly dark room a black object won’t “absorb” any more heat than a white one will.

        • Chuck
          July 17, 2012

          Wouldn’t the sun radiating directly on your scalp make you hotter?

          • Chuck
            July 17, 2012

            Wrong spot for post, now I have to respond.

            Three forms of heat transfer: convection, conduction, and radiation.

            Black bodies definitely absorb and radiate more heat than white or shiny bodies. That is why the outside of vacuum coffee mugs are shiny. With the vacuum insulator there is no conduction nor convection, there can only be radiation. The shiny outside reduces the amount of radiation.

  10. Lynette
    July 16, 2012

    I’ll post a pic of my hat that has kept me happy for over 10 years. I had to cut the top off because with hair, my head overheats. One nice feature is it folds so it easily fits in my hydration pak while running in the dark.
    I vote that you have too much time on your hands. But there’s nothing wrong with letting the creative juices flow. ;)

  11. David Goulette
    July 16, 2012

    I think it is a very interesting design. I hope it works out. I am thinking Leard has a good idea below. You should also consider how effective our hair is at dissipating heat as well. You might need slightly longer hair though. I know our hair insulates us in cold to some extent. But does hair as a heat sink as well? I don’t know. But it is worth making a third hat with no top and trying that out also. Just a thought.

    • Jason
      July 16, 2012

      The hair question is moot for my purposes. I prefer very short hair, which would allow my head to burn if exposed to the sun for 12-16 hours in a race.

      However, the hair question is interesting. Does hair insulate or act as a heat sink? Anyone care the chime in?

  12. Tuck
    July 16, 2012

    Excellent. Looking forward to hearing how this turns out…

  13. Leard
    July 16, 2012

    I don’t see how this would be more effective than the “visor” version of this same hat with the whole crown removed. (also making it a badass hat). assuming you are moving with any forward speed and you are not concerned with scalp sunburn. the topless version would allow convection to remove all of the built up heat.

    • David Goulette
      July 16, 2012

      That is what I was thinking too Leard.

    • Jason
      July 16, 2012

      I’m concerned with scalp burn. :-)

      • Leard
        July 16, 2012

        In that case, you definitely want to maximize airflow with your vents being as large as structurally possible. Forced Convection (breeze) is going to move more heat away from you faster than natural convection (unless you are standing still). My only other concern with this design is the lift created by the shape of the hat. Your air vents actually help decrease that a bit too. Can’t wait to hear the results! I’ll probably be looking for a wicker hat source soon!

        • Chuck
          July 17, 2012

          Wouldn’t the sun radiating directly on your scalp make you hotter?

  14. Dyay Fernandez
    July 16, 2012

    here’s mine:

    https://www.facebook.com/photo.php?fbid=491005740912961&set=t.100000151838324&type=3&theater

    i recently played around with it and burnt holes on the front part to have more cool air in. but the rear vents that you made is brilliant.

    i have yet to try the black & white paint..sounds legit! :)