Peltier devices for "personal cooling" ? (or heating) - Page 1
Forum section: electronics / projects

author: cdev
author_rank: Super Contributor
timestamp: July 31, 2020, 11:04:15 pm
content: Has anybody here ever done this? Every summer it seems I think about giving it a try, but havent yet. Basically the idea is to build some means of sucking up the heat from my bodyt and radiating it into space by using theirmoelectric devices or "peltier devices" They take an awful lot of current but basically one side gets hot and the other side gets cold. If you heat them up on one side they can also generate electricity.You could use liquid cooling. Like a computer.----EDIT: This is a great video on the theory of Peltier devices..

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 31, 2020, 11:28:12 pm
content: Has been tried before, doesn't work very well.

author: jogri
author_rank: Frequent Contributor
timestamp: July 31, 2020, 11:42:51 pm
content: I see two major problems with such a design:-the shitty heat transfer between your body/skin and the heatsink (your body isn't really designed to radiate a lot of heat in a cold environment as that wouldn't be ideal for survival in colder climates/winter)-the inability to cool your heatsink to temperatures lower than 5-0°C (you will get frostbite when the water starts to crystallize)But there is one really bad "solution" that would overcome those problems: You could use your internal (water+some other stuff) cooling loop...

author: thm_w
author_rank: Super Contributor
timestamp: July 31, 2020, 11:52:47 pm
content: Better off using:- multiple ice packs that you change out- evaporative cooling (https://www.ergodyne.com/chill-its-6685-dry-evaporative-cooling-vest.html)This assumes you are outside and need something portable. If you are inside: air conditioner.

author: coppercone2
author_rank: Super Contributor
timestamp: August 01, 2020, 12:22:29 am
content: the japanese thing you put in your shirt for small people is available on ebay now for 200$ from japan ($120 in japan)https://robbreport.com/gear/personal-technology/sonys-reon-pocket-air-conditioner-now-available-2934592/no XL though'in america, we just take our shirts off. thats for business people who are not allowed to take a suit off lol

author: cdev
author_rank: Super Contributor
timestamp: August 01, 2020, 12:41:12 am
content: This is a good design, making much more effective use of the technology. Its incredible how much better batteries have gotten.Does it reduce your sweat, I wonder, more than the amount of water it condenses out of the air?Quote from: coppercone2 on August 01, 2020, 12:22:29 amI'm sure its makeable. Another application that really interests me is making instant ice cream on a cold plate.

author: TheMG
author_rank: Frequent Contributor
timestamp: August 01, 2020, 01:42:26 am
content: While it may provide a feeling of cool on the back of your neck, it really isn't going to do a whole lot to actually keep your body cool.The device reportedly weights 3 ounces (85g) and can run for up to 90 minutes on a charge. If all of that weight was just the battery, using some of the best battery technology currently in mass production, you'd have around 23Wh of battery capacity, best case scenario.Over a 90 minutes discharge, that's 15W power consumption.The coefficient of performance in most practical TEC (peltier) implementations is between 0.4 to 0.7. So for a TEC operating at 15.3W of power input (again, ignoring the power used by the fan), will be able to "move" between 6 to 11W worth of heat.The average human body dissipates approximately 100-120W of heat, at rest. This goes up considerably with exercise.So very best case scenario... the device will help dissipate about 10% of your body heat, while you're sitting doing nothing. In reality, probably no more than 5%.It may provide a pleasant feeling of coolness on the back of your neck but that's about it. You'll probably sweat just as much as if you weren't wearing the device.

author: cdev
author_rank: Super Contributor
timestamp: August 01, 2020, 02:14:20 am
content: The power is the limiting factor. Also the limited surface area available to cool. They do have cooling vests for workers who have to work in really punishing environments, to prevent heat stroke, But they have outboard power, I am pretty sure.Its scary to think that by 2070 or so around 17% of the Earths surface may become so hot measures like that might be needed to survive the midday heat there.If people stay there (and dont move somewhere else) it would take too much power to cool many buildings so people may have to carry their own cooling around with them.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 01, 2020, 03:02:42 am
content: Might as well use ice storage instead of batteries. With Peltiers, even the best design that operates the Peltiers in the most efficient region powered by cutting edge lithium batteries might barely break even in terms of cooling per weight if only the weight of the batteries is counted (probably way behind after adding the weight of the heatsinks). With a compressor, you might get up to 5x improvement but that's still not counting the weight of heat exchangers and the compressor itself which would again make it challenging to merely break even. Then you have to compete with the super low cost of water...Quote from: coppercone2 on August 01, 2020, 12:22:29 amOnly on the beach, not in the city.That said, minimalist clothing apparently is more acceptable in China.That's one way to get a lot of airflow over a large surface area, a high tech alternative that would be more acceptable in many places would be to have a small server fan providing the airflow and the clothing acting as ducting. A fairly small pack of 18650s will easily power the fan for hours.Quote from: cdev on August 01, 2020, 02:14:20 amOr HVAC systems use IR sensors to direct the heating and cooling to where it's really needed. That's already done in some high end mini split units, BTW.

author: coppercone2
author_rank: Super Contributor
timestamp: August 01, 2020, 04:08:12 am
content: there is no law for shirt use and some business specifically advertise you must wear a shirt and shoes (i.e. 7/11)and it likely won't be frowned upon unless you are in a really posh place (usually props)'

author: coppercone2
author_rank: Super Contributor
timestamp: August 01, 2020, 04:11:02 am
content: Quote from: TheMG on August 01, 2020, 01:42:26 amThere are three levels of cooling or warming, plus an additional boost mode that’s limited to two minutes and a control for the speed of the “fan.”

author: Kevin.D
author_rank: Frequent Contributor
timestamp: August 01, 2020, 09:46:03 am
content: The Physics is against it, don't think it will nearly as effective as a simple fan blowing air on your skin .The most relevant number here regarding peltiers is their heat pumping efficiency ,ratio of how much power is put in to how much power(as heat) it will pump from cold side to the hot side,The cheap peltiers I have here are ~ 0.5 efficient (100 W input to pump 50 W Heat from cold to hot side) .Keeping in mind the peltiers heat sink/fan has to dissipate the power to do the work plus the heat(power) we are pumpingIt's heat-sink/fan will need to be dissipating to air ~ 3 times more heat than simply blowing the air directly on the skin ,and I don't see that happening, the peltier sink would have to be fan + evaporative to compete with a fan blowing on Sweating skin and then also take into consideration blowing air directly on to skin is collecting heat from a relatively large contact area compared to contact area between peltier cold side and skin which will just result in a very cold small area of skin with limited conduction from surrounding area ( blood vessels in that area will also probably contract reducing heat conductivity from surrounding area even more).Reminds me of an Eload Idea I had a few year ago . I got some cheap peltiers to mount power MOSFETS on and then derived the input power necessary to drive the peltiers directly from (or via a voltage reg if necessary) the waste input power that was to be dissipated by the Eload. By pumping out heat from the mounted MOSFET I effectively increased the case to sink thermal capacity of the MOSFET by whatever the peltier could pump (so about 50 Watts with my cheap peltiers at their abs Max input power ~ 100W).This doesn't work out very cost effective though because MOSFET's (there are a few exceptions) are much cheaper than peltier elements and so to increase the overall sink to case thermal conductivity we can just use another MOSFET and put it in parallel and that's much less expensive than with my peltier idea .Regards

author: OwO
author_rank: Super Contributor
timestamp: August 01, 2020, 10:38:52 am
content: A thin mat with loops of embedded piping + water circulation and a separate radiator (evaporative cooling, peltier, or compressor) could work.

author: RoGeorge
author_rank: Super Contributor
timestamp: August 01, 2020, 10:57:37 am
content: It has been done as cooling gloves. I've seen some research to enhance running endurance (for military purposes). They noticed the main problem was overheating, and also the most heat exchange happens through the head and the hands are.Keeping the hand palms cool was enough to run longer distances. Something like this:(the video I was talking was different, probably older then the one above, with a temperature probe inserted near the heart, through the lungs, in order to measure the most efficient hands cooling technique - a too cool glove was not good because capillary blood vessel constrict at low temp, therefore making the heat exchange less effective).

author: cdev
author_rank: Super Contributor
timestamp: August 01, 2020, 12:57:39 pm
content: Thats what I have been thinking. I am going to try to see if I can adapt some computer hardware. First just for a small area. I would be happy to cool my neck.I ofter wear a damp bandana I've pun under cool water and squeezed out. Some years we've been able to go almost without using AC, but this year its been on a lot.Despite having very good insulation.Quote from: OwO on August 01, 2020, 10:38:52 amDon't want to use anything toxic (CFCs) and have an interest in electronics, so peltiers sound like the way to go. Plus it will let me use up some of the tons of small HSF/fans that I have here from years of computer builds.Also, I want to build a cold plate for making small amounts of ice cream on the fly. That way of making instant icecream is really good. Its very popular at the Jersey Shore. People who sell ice cream that way while people watch their ice cream being made (its done with showmanship) make a small fortune on hot days.

author: cdev
author_rank: Super Contributor
timestamp: August 01, 2020, 01:15:18 pm
content: I've done that with small fans (and also tried ducting with the air) and it works far better than nothing. A small but strong fan that could be hooked over a neckline would definitely help and I think your analysis of the energy efficiency vs. peltier device is sound.Quote from: NiHaoMike on August 01, 2020, 03:02:42 amIn some specific beach and desert communities where rich people gather here in the US seeing people dressed like that (even wearning formal clothing, apart from the bikinis- they might also wear jewelry) is normal.It's straight out of a Fellini movie.I bet they would go for expensive, but not very practical high tech cooling hardware.

author: Marco
author_rank: Super Contributor
timestamp: August 01, 2020, 01:15:52 pm
content: Last time I did some napkin maths, I concluded ice gives you over twice the cooling power per weight of batteries+peltier. You need a compressor to start being competitive with ice.

author: cdev
author_rank: Super Contributor
timestamp: August 01, 2020, 01:23:14 pm
content: My sweetie has gotten me in the habit of wearing wet stretch bandanas and wet scarves around my neck when its hot. It really does help a lot.

author: RenThraysk
author_rank: Regular Contributor
timestamp: August 01, 2020, 03:48:29 pm
content: There are such things called neck cobbers, with polycrystals inside that absorb water and evaporative cooling cools the blood in the neck arteries.