Peltier Application Note – Thermoelectric Cooling [pdf]
cui.com
cui.com
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.
Edit: would a metal aerogel not count? (Definitely not maker ready though, I assume)
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.
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...
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...