Run by solar batteries on the lower part of your suit and on your hat, so on a hot and sunny day you get the benefit of the sun and no drawbacks.

No good for Ghana where its hot but hazy all year round and you never see the sun.

Very good for Israel, where its always too hot, and all trees are being cut down for construction reasons, car parking, fires (politically ignited) and competition with birds and bats on land ownership.
-- pashute, May 31 2016

Humans dump about 100W into the environment, at rest. Peltiers are about 10-15% efficient.
-- FlyingToaster, May 31 2016


Right: The whole body puts out: 350kJ for an hour = 350kJ/3600s = 97.2 W

We'de need 1kW to do the job by Peltier instead of sweat.

BUT, the sun at the heat of the day, gives us 5 unharvested kW, for 1 square m, and PV cells at 15% can harvest a whopping 750 W !!! With the Peltier 10% that gives me 75 watts. The body would receive 75 out of 97W needed, more than 77%. I still think that is cool.
-- pashute, Jun 20 2016


The only number I don't disagree with is 100 W resting heat output of the human body, and that's only because I haven't read any number for that before.

I have read in the past that Peltier coolers are up to 5% efficient in general. I have also read, on one manufacturer's website, that that is because most people use them wrong, and they can get much better efficiency (somewhere around 60–90%?) by 'using them properly', but they didn't give any details on how to do that.

I have always heard that usable solar power at Earth's surface is 1 kW/m^2, not 5. It's 1.6 kW/m^2 on the Moon (without air in the way), IIRC from the recent EEVblog lunar rover videos.

---

I have recently been looking into building such a device, or rather a pair of devices, worn on the wrists. However, mine were not planned to be solar-powered, and they were planned to use Stirling heat pumps for better efficiency. On the wrists, they have access to lots of blood flowing by, and you can swing your arms around to collect hot blood there and then hold them up in the air to cool it and drain it back into the rest of your body (which works even with only air cooling). Also look into CoreControl, which does that with the aid of suction, and is also capable of supplying heat for use in cold weather.
-- notexactly, Jul 18 2016


// with the aid of suction //

What, sucks your blood ? Vampire refrigerator ?
-- 8th of 7, Jul 18 2016


[notexactly] The figures I read, somewhere, were 100W at rest, 200 for moderate effort and 300 for a trained athlete. Also 1kW'ish/m3 insolation above the atmosphere, 500W best case on the surface. I'm not saying you'd actually need a m2 mortarboard; perhaps concentrating on the wrists, ankles, underarms and neck (where blood flow is just under the surface) and using heatpipes would work when combined with other, passive methods. belated +
-- FlyingToaster, Jul 18 2016



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