I was nerdsniped by a coworker, who was talking about personal projects. She was working on an wine-rack / cabinet that held a specific temperature. Key to the design is a Peltier module to pump the temperature to the ideal for wine storage.
CUI's application note on Peltier modules was very well written and a joy to read. I've barely touched on the physics of this subject, but it was so clearly written that I was able to understand the overall design process to use this kind of device.
Overall, Peltier modules are far less efficient than classic "compressor" refrigeration units. But Peltier modules are far smaller and far simpler to operate: just apply voltage, and away you go. As such, Peltier modules are the ideal easy-to-use tool for hobbyists, even if its not quite as efficient as what the professional HVAC people use.
Just to build on your comment so other hobbyists don't get the wrong idea, Peltier modules are significantly less efficient than compressor-based coolers. To the tune of 30% or more efficiency drop depending on ambient conditions and your heatsink setup. It's also important to note that the overall setup for a Peltier system ends up being a lot bulkier than most people expect when they start. You need a really beefy hot side radiator and fan to get any significant cooling potential out of the system - think large CPU heatsink + fan size and you're close. If it's humid you'll also have to deal with condensation on the cold side so you don't accidentally get water dripping on your electronics.
I agree. Peltier fits a narrow niche. If you want a small temperature drop and can dissipate the heat on the hot side and are okay with the inefficiency it's for you. I tried to create a Peltier cooling system for a wearable device. It was a miserable failure. WIthout a way to dissipate the heat (your CPU heatsink + fan comment) it resulted in a net heat gain.
Forgetting about the enormous heat sink is a typical rookie mistake. Those things produce lots of heat when you try to cool something. They are much better suited for heating something to a specific temperature than cooling.
A metal aerogel would have very high surface area (much like adsorption humidity control crystals) but that's not really helpful when you then need to move the fluid touching all that surface area in order to remove the heat.
Typically the fluid will be air which sucks at moving heat (hence why aerogels are great insulators as they hold a lot of air).
I'm not positive but I suspect that an aerogel in a higher specific heat fluid wouldn't do any better as the flow volume through the aerogel would be quite low bounded by the volume of the aerogel.
If you want to cool the hotside of a TEC you need to push a lot of watts per unit area. The best things for that are high specific heat fluids which are often used in compressor systems and then they're termed refrigerants so you're back to traditional air conditioning. The other option is very cold fluids (liquid nitrogen) but at that point you may be better off bringing the LN2 into more direct contact with whatever you're trying to cool.
An aerogel would be among the worst things to use as a heatsink. They are mostly air, held in place. Air has a very low thermal conductivity, low density, and low heat capacity. Air cooling is used because air is abundant and usually readily available, and relies on convection, which an aerogel prevents.
A much better solution are heat pipes, which utilize convection internally to create very high effective thermal conductivity. Assuming the system is not in continual use, the need for a large radiator can be avoided, by using a tank of water or oil (if electrical conductivity is a concern) to dump heat into. With a tank of water, you can also cool below ambient temperature by using evaporative cooling.
One advantage that they have is that they can pump the heat in both directions and change direction very quickly. This means that you can keep temperature very precisely with a closed regulation loop.
Oh yeah, definitely keep an eye on how big practical peltier modules are, so you get a basic gist of how to use these things: https://www.adafruit.com/product/1335
But while most people are talking about Peltier as a cooling module, note that it can be used as a more efficient heater. You can spend 36W of power (12V at 3A), and move maybe 10W. That's a total of 46W of Heat!
In essence: a Peltier is always going to be a more efficient heating device than a standard coil. Heating would be sufficient for tasks like Plant Seed germination or Bread Proofing... seeds / bread want to be around 90F or 32C, so you'd need to create a 110F / 43C source of heat.
Classically, people used light-bulbs to heat dough or seeds for germination, but a Peltier would be easier to control and more efficient.
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Refrigeration is cool (hah, punny), but precise heating also has a lot of good uses... even at the only ~20C or 36F differential where Peltiers are practical. Going +/- 20C or 36F is still a useful trick.
Free product idea: Here in NZ, and I suspect other places with lower quality housing, lots of people use electric resistance heaters, and also have problems with damp air and/or dehumidifiers.
How about a solid state dehumidifier+heater using peltlier elements?
A dehumidifier is basically an air/air heat pump, with the cold side optimised for water condensation without freezing, and one issue with them is the noise from the compressor...
I've been working on solar powered Peltier AC for my home. This past summer it was able to keep my living room (250sqft) at a comfortable 72F - 75F even when the outside temp was over 95F. It is crazy power hungry, using 12v 5A, but with solar its fine. The hard part as people have said is the heat dissipation and dealing with high ambient temperatures.
My newest design incorporates a few new upgrades. 1) geothermal cooling to dissipate the heat. As the ground temperature stays consistent at ~65F. Allowing me to not worry about the ambient temperature anymore 2) I moved to a 24V 6amp peltier which has a larger delta from the hot to cold side. 3) I now use a 24v ~7.6amp solar panel to power it. 4) I added a 15 Amp high-power motor driver so I can switch between producing cold and hot air. So now it will be viable in all weather conditions.
A core idea is to keep costs cheap which is why I have not added a battery to the mix. Although it would be nice as some nights are quite hot. I got the 24v panel used at $50 and the peltiers are super cheap (3 for ~15). The motor-controller/h-bridge was ~$40, but I didn't want to cheap out on that though and start a fire.
Its quiet unless I turn the fans up and doesn't cost anything to run after initial setup costs, due to the solar. My future plans for making it even better are to use multi-stage peltiers and try to leverage the hot side to produce more power. Also to add raspberry pi so I can control it remotely.
I use geothermal as a way to absorb/dissipate the heat. I got the idea from here: https://forums.overclockers.com.au/threads/concrete-slab-wat...
Instead though I dug a trench outside that was 4ft deep 20ft long and then buried some pex pipe. As the water flows into the aluminum block attached to the peltier it absorbs the heat and then as it enters the ground it dissipates so when it comes out of the ground of its back at 55F. The water is moved with a 12v pump. The longer the run the better as the ground is not efficient in energy transfer. If its to short it wont cool down all the way.
I thought of trying to use copper pipe with round engine heat sinks attached to it, to increase the energy transfer rate. However it didn't seem like the copper would last long before potentially reacting with the ground.
Peltiers are a fascinating piece of tech, I remembering hacking together a cooling system for a high school project (20 years ago now..) to show people and have had a fascination ever since. Problem is they just aren't that useful due to their large inefficiencies. Situations where power consumption, heat removal and humidity aren't a problem are pretty rare at any scale. Saying that, if a situation where heat removal is straight forward due to other factors, space is abundant with solar generation (that's not needed/can't be used for anything else) and humidity is benefit, peltiers size and simplicity can be leveraged nicely.
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[ 2.5 ms ] story [ 62.9 ms ] threadCUI's application note on Peltier modules was very well written and a joy to read. I've barely touched on the physics of this subject, but it was so clearly written that I was able to understand the overall design process to use this kind of device.
Overall, Peltier modules are far less efficient than classic "compressor" refrigeration units. But Peltier modules are far smaller and far simpler to operate: just apply voltage, and away you go. As such, Peltier modules are the ideal easy-to-use tool for hobbyists, even if its not quite as efficient as what the professional HVAC people use.
Edit: would a metal aerogel not count? (Definitely not maker ready though, I assume)
http://www.aerogel.org/?p=932
A heat sink needs high thermal conductivity. Hence why most heat sinks you see are metal.
Typically the fluid will be air which sucks at moving heat (hence why aerogels are great insulators as they hold a lot of air).
I'm not positive but I suspect that an aerogel in a higher specific heat fluid wouldn't do any better as the flow volume through the aerogel would be quite low bounded by the volume of the aerogel.
If you want to cool the hotside of a TEC you need to push a lot of watts per unit area. The best things for that are high specific heat fluids which are often used in compressor systems and then they're termed refrigerants so you're back to traditional air conditioning. The other option is very cold fluids (liquid nitrogen) but at that point you may be better off bringing the LN2 into more direct contact with whatever you're trying to cool.
A much better solution are heat pipes, which utilize convection internally to create very high effective thermal conductivity. Assuming the system is not in continual use, the need for a large radiator can be avoided, by using a tank of water or oil (if electrical conductivity is a concern) to dump heat into. With a tank of water, you can also cool below ambient temperature by using evaporative cooling.
But while most people are talking about Peltier as a cooling module, note that it can be used as a more efficient heater. You can spend 36W of power (12V at 3A), and move maybe 10W. That's a total of 46W of Heat!
In essence: a Peltier is always going to be a more efficient heating device than a standard coil. Heating would be sufficient for tasks like Plant Seed germination or Bread Proofing... seeds / bread want to be around 90F or 32C, so you'd need to create a 110F / 43C source of heat.
Classically, people used light-bulbs to heat dough or seeds for germination, but a Peltier would be easier to control and more efficient.
-----------
Refrigeration is cool (hah, punny), but precise heating also has a lot of good uses... even at the only ~20C or 36F differential where Peltiers are practical. Going +/- 20C or 36F is still a useful trick.
https://www.youtube.com/watch?v=YWUhwmmZa7A
How about a solid state dehumidifier+heater using peltlier elements?
A dehumidifier is basically an air/air heat pump, with the cold side optimised for water condensation without freezing, and one issue with them is the noise from the compressor...
My newest design incorporates a few new upgrades. 1) geothermal cooling to dissipate the heat. As the ground temperature stays consistent at ~65F. Allowing me to not worry about the ambient temperature anymore 2) I moved to a 24V 6amp peltier which has a larger delta from the hot to cold side. 3) I now use a 24v ~7.6amp solar panel to power it. 4) I added a 15 Amp high-power motor driver so I can switch between producing cold and hot air. So now it will be viable in all weather conditions.
A core idea is to keep costs cheap which is why I have not added a battery to the mix. Although it would be nice as some nights are quite hot. I got the 24v panel used at $50 and the peltiers are super cheap (3 for ~15). The motor-controller/h-bridge was ~$40, but I didn't want to cheap out on that though and start a fire.
Its quiet unless I turn the fans up and doesn't cost anything to run after initial setup costs, due to the solar. My future plans for making it even better are to use multi-stage peltiers and try to leverage the hot side to produce more power. Also to add raspberry pi so I can control it remotely.
I thought of trying to use copper pipe with round engine heat sinks attached to it, to increase the energy transfer rate. However it didn't seem like the copper would last long before potentially reacting with the ground.
Simple diagram: https://www.ernstheating.com/wp-content/uploads/2018/01/Erns...