Post Rad Chiller Concept

[Uncle Jimbo]

Interesting stuff, but its obvious from the offset that's a really inefficient way of using Peltier elements, unless I've badly misunderstood. It would be nice to know a few more details about that project and how you have implement peltiers in the past.

I have designed pelt based control systems going back more than 20 years. Typically these have an instrument package in a sealed NEMA enclosure, and the pelt cools if load is too hot, heats if load is too cool. These are typically on 48VDC systems so we use 2 24V pelts in series with SCR chopper control. Those systems ran in ambient as low as -40C and as high as 50C.

The efficiency of the TEC improves with hot side temp, with best efficiency around 50C hot side, so air cooling the hot side is actually more efficient. For example, the curves on a CP1-12730, a big 62mm TEC, show 240 Qc W with 5C differential and the hot side at 50C - but only 190 Qc W at 25C for the same volts and amps. Since what you want is to take cold side below ambient, you want closer to 30C differential with the hot side at 50C. With a 16V supply and 30A, that TEC will move about 140W. It will use 480W getting there, so your heatsink needs to be able to dissipate 620W which is big.

the cooling effect you get is determined by the surface area of your heat exchanger (you have lots of that!) and the rate at which the water goes through. To change the temperature of 1 gram of water 1 degree C requires 4.18 Joule (watt-second). At 0C, a gallon of water is about 8.33 Lbs or about 3.77 kg - 3770 grams. For a 1GP/M flow, 1/60th of that goes by in a second, so 63 grams go by each second. Cooling that by 1C requires about 260W. Ideally, the TEC above would drop the water temperature by about .5C - assuming the heat exchanger transfers the energy. Higher flow rates will do less transfer.

In comparison, the guts from a standard wall mount water cooler will cool 1 GPM by .5C using about 200W. so it is more than twice as efficient, but not nearly as pretty!

In answer to your question, the setup I pictured used the same CP1-12730, but operated at 12V and 22A. This is a more efficient area of the operating curve, as I move 100W with only 260W input. If you plan on using 2 TECs, you might find this to be a good choice - it powers from a standard PSU. for about 500W input you move 200W, which would get you close to a 1C drop at 1 GPM. The heat dissipated would be about 350W for each of the 2 units. The big Melcor sink would give a 25C rise with that load.

The attached CP1-12730 curves can be used to tell pretty much what this TEC will do - there are similar curves for most commercial TEC units.