Thanks for the response, HardwareFreak. Your idea sounds sooo simple. But the condensation issue in the area of the CPU really scares me. I know many people are able to do it and get phenominal results.
This is how you eliminate condensation. It's not difficult at all.
http://www.overclock.net/t/410339/info-how-to-insulate-your-mobo-for-tec-peltier-cooling
Too, TECs do stop working - often suddenly and without warning.
This is a red herring. You're trying to come up with excuses for why you should avoid doing a direct die TEC. CPU, case, radiator fans, and water pumps fail far more quicky and frequently than TECs do. TECs are made of transistors, same thing CPUs are made of. The failure rates are about the same. How frequently do you see CPUs dying? How frequently do you see fans dying? I rest my case.
You said that my idea would not work because the TECs in these chillers are too small. You estimated that I'd get no more than .5-1 degree F improvement. So let me ask this question. If I could put a larger and more powerful TEC on that water chiller - could it come closer to achieving my goal using my Rube Goldberg double-loop design?
Do you want to fart aroud trying to make something work, that will never work, or do you actually want to chill your CPU? For a dual loop system you need a real heat exchanger, like the one I posten in this thread. What you have will not work and cannot be made to work. Scrub it from your gray matter.
I'm guessing I'd need a more powerful fan. And the heatsink might have to be machined to accomodate a larger TEC.
Plz post brand/model numbers: the fan, rad, reservior, and pump. If you have a single fan radiator then you very likely don't have enough capacity for cooling a TEC, especially if it came from one of those cheap all-in-one kits. You'll either need to add another rad and fan, or swap to a dual core or dual core/dual fan unit. Please post a pic of the custom "under teh PC" radiator box and the radiator itself so I know what you have to work with.
I'm more comfortable with the idea of using the chiller to boost my cooling slightly.
This is due to vanity, and lack of education, nothing else. This idea originated with you. So you naturally want to use it in preference to anything else, regardless of the fact it simply won't work. Again, do you want to screw around for months on an idea that will never work, or get sometihing done in a day that will literally freeze your CPU?
Using the TEC right on the CPU, frankly, is just beyond my comfort level. I guess I'm just too much of a "wuss".
It's above you comfort level simply due to your lack of education WRT Thermal Electric Cooling of CPUs. Educate yourself. There's plenty of information easily available beyond my replies here. Note that the condensation problem exists whether you go direct die or if you use a dual loop. What matters is the temperature at the junction of the CPU and the heatsink device directly above it, whether a TEC plus water block, or just a water block. A properly designed dual loop setup using two of these 168w TECs will take your i5 CPU at full load down to the -32F to -12F range, ~20 degrees colder than a direct die, as you'll see below. Again, it doesn't matter where the TEC is installed. What matters in the temp drop achieved.
Finally, you said the TEC on eBay was 168 watts at 12 volts and needed 10.5 amps. 12 watts at 12 volts equals 1 amp. So I think the current draw on that TEC would be closer to 14 amps. Or am I missing something?
Yes, you're missing something. TECs advertised as 12V are "nominal" 12V. They will operate from 0-15.1 or 0-16 volts, depending on the manufacturer. "What? Zero volts?" you ask incredulously. Yes, TECs operate in both directions. You can attach one to a heat source and generate voltage and current instead of using it to move heat. Some people have built solar panels out of arrays of them. So with low heat input you may generate 0.001 volts. The VMAX is usually 15-16 volts. IMAX varies based on the capacity of the unit. This unit is QMAX 168 watts, IMAX 10.5 amps at VMAX 16 volts. At the 13 volts your external PSU puts out, it will be able to move approximately
((13/16=.08)*168)= 136 watts
The max TDP of the i5-250K is 95 watts. Using the formula in Eric's guide, at the top of this thread, and assuming your loop can dissipate 231 watts, your temp difference between the hot and cold side of the TEC will be approx:
i5 @95W: 70F
i5 @65W: 97F
At ambient temp of 71F, the cold side will be approx:
i5 @95W: 1F
i5 @65W: -26F
For a calculated actual CPU core temp estimate you'd add 10-20F to each of these figures to account for thermal losses in the system, including the IHS nickel alloy and water block copper, the two layers of TIM, the tubing, etc. In other words, you'll never get a 100% efficient cooling loop. So when we add 10-20F to each of these we get a CPU core temp estimate of:
i5 @95W: 11 to 21F
i5 @65W: -16 to - 6F
This below zero Celsius level of cooling performance can be yours for ~$30-40 USD for the TEC and install materials, plus ~$50 for a second single rad/fan and fittings/tubing to join it to the existing one, and a few hours of install time. Far less time than the idea bouncing in your head. A litle more money maybe, but look at the performance/dollar. You may be able to get by with your existing rad, but I need to see it first. If your current rad can keep the water temp below 110F with this pelt installled you should get max load temp of around 40-50F with ambient 71F. If that's good enough for you then you save $$ on the 2nd rad. Lots of if's.
Note that the equations don't take into account the performance of your water loop--the equations assume 100% efficiency on the hot side of the TEC. If your loop can't move the heat fast enough then the CPU core temp will not drop nearly as much. Also note that at idle the i5 will be shedding much less heat, and especially if the BIOS drops the CPU clock in power saving mode. Your water loop needs to be able to move 231 watts for max efficiency, which is the combined output of the CPU at max TDP, and the TEC.