Quote Originally Posted by NaeKuh View Post
well i would actually have to agree with you on this statement.

Because water is a better medium for transfer on the cold side. Also this is what i felt on the hotside. Im trying to milk the entire unit for efficiency. By watercooling the hotside, the cold side gets cooler, and i can use less voltage to get desired results. no?
The cold side will not get much colder because it is effectively in a water bath. But you are right, the TEC will move more heat for the same voltage with a lower differential, and water cooling the hot side will reduce the differential. However, TECs have a negative coefficient of heat - so they draw more current when the hot side is cooler. Using the curve from my previous post, and assuming a 12V supply, we can see that lowering the differential from say 30C to 10C will give a 30% increase in Qc W (100W to 150W). But lowering the hot side from 50C to 30C will reduce the effective resistance of the TEC from about .55 Ohm to around .4 Ohm, so instead of supplying 22A, we now need 30A.

So with the hot side at 50C, you supply 264W to move 100W, or 2.64W in per watt moved. With the hot side at 30C, you supply 360W to move 150W, or 2.4W in per watt moved. That buys you a slight increase in efficiency and moves more heat. But doing 2 TECs with air and a 50C hot side moves 200W for a 520W cost, again at 2.6 W per w moved. For a 9% increase in efficiency, you need to create a whole additional cooling system for the hot side WC.

Or if, as you state, you reduce the voltage, you could go to 10V which puts the amps at 25, and you are moving 100W with 250W in. That's about where you started, except you added the complexity of WC on the hot side, and you need a 10V supply, which is not off the shelf. And now you are at 2.5W in per watt moved, so it is only 5% more efficient.

The other issue you would face is that with a small differential, you will swing the amps a lot depending on heat load. That puts a big demand on the PSU... with a 25C or 30C differential, the amp swings are much lower for a change in load.

I like to design these to use an off the shelf $40 PC supply and not a $200 lab supply. OC work is expensive enough without going too exotic. Getting a supply that can deliver 30A at 12V continuous is a lot harder and more expensive than one that will do 22-25.