Alternative TEC Cooling?

X

XionEternum

New member
Hello, I am new here but hardly new to computer tech. I know my way inside and out with basic components and how LCSs and Phase-Change work. I'm a bit lacking on TECs though and how they work. I get and understand the formula, as well as the TDP variance between the CPU and TEC causing significant inefficiency in some cases. What I don't get is why people haven't tried this:

Imagine if you will, your average PC chassis. Has a nicely spaced 120mm exhaust port on the back next to the rear IO, with plenty of room all around it and possibly even mounting for a 140mm fan. Imagine reverse mounting a downward CPU cooler to it like the CM GeminII or the GeminII S and a decent fan, with the CPU block facing into your chassis. Then imagine placing a low TDP TEC, like 80-250watts, with the hot-side against it, then sandwiching them together with a waterblock on the cold-side. Loop your LCS so that the radiator cooled water passes through this block. Would this be an effective solution to the inefficiency of direct contact with the heat generated by the CPU, by acting as a water chiller instead? Since the expected thermal variance between the hot and cold sides won't exceed 70 degrees, and under this application would likely be getting hit on both sides by ambient temp thermal displacement -air on the hot side and water on the cold side- wouldn't we see the waterblock on it get chilled and thus chill the water flowing through rather well before heading straight to the CPU block? I'm curious if anyone has tried this, or genuinely knows the thermal dynamic properties of this application. Will it work? Has it worked?
Thoughts anyone?

Edit after first two responses:
Okay, I should add to the example as having the following loop sequence:
Res> TEC Block> CPU Block> GPU Block(s)> Rads> Repeat. So in theory the rads cool the water to ambient before recirculation to the TEC.
And presume condensation is not an issue, as in wrapped in cloth and sealed.
Also presume that the rads are more than capable of cooling the water to ambient.
 
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The major problem with using a chilled system (regardless of how you go about it) is that you can only lower the temperature to ambient before you risk condensation forming. Water has great thermal properties which means that it doesn't actually heat up much at all in a standard loop. Therefore you will only be able to lower the water temperature by 10-20C before hitting ambient and I'm not sure that will transfer into a significant enough core temp drop to warrant it.

Would be interesting to test though.
 
Having a rad in the loop will keep the liquid above amibent unless your running a couple of high wattage tecs so condensation isnt to much of an issue other than maybe the metal on the water block on the cold tec side of the heat transfer bit.

The only thing i can think of off the top of my head other than a dedicated external box acting as a full on water chiller that used nothing but tecs to cool the water loop and a 2nd loop to cool the tecs is a guy that used a single 400w tec.

The hot side was cooled by an Antec 625 all in one water thing and the cool side was stuck to a random cheapy cpu water block, iirc it managed to lower a cpu + gpu loop (a heavy OC on an amd quad and GTX 460 i think the guy im referencing was using) by around 7-8c on both the cpu and gpu but it ended up using so much power (more than 16/18 amps on the psu he originaly was using with a 200w tec for testing could give out im pretty sure) he ended up using a 750w 40amp unit....

TLDR a single 400w tec cooling the loop liquid will only lower a cpu + gpu loop by at most around 10c but.
 
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I Hunta x said:
The only thing i can think of off the top of my head other than a dedicated external box acting as a full on water chiller that used nothing but tecs to cool the water loop and a 2nd loop to cool the tecs is a guy that used a single 400w tec.

The hot side was cooled by an Antec 625 all in one water thing and the cool side was stuck to a random cheapy cpu water block, iirc it managed to lower a cpu + gpu loop (a heavy OC on an amd quad and GTX 460 i think the guy im referencing was using) by around 7-8c on both the cpu and gpu but it ended up using so much power (more than 16/18 amps on the psu he originaly was using with a 200w tec for testing could give out im pretty sure) he ended up using a 750w 40amp unit.....
Click to expand...

Now this puzzles me considering you mention the use of an Antec 625 AIO LCS. I sincerely doubt that cooler is capable of dissipating 400w of heat at an efficiency that balances the delta of the TEC to ambient. Simple fact is, regardless of what wattage a TEC is rated for, it's optimal delta is the same. So why not a lower wattage TEC being cooled by something simpler and more capable of matching the TDP of the TEC? Performance-wise, the Antec 625 isn't effective compared to most similarly priced air coolers. Sure I get that more watts means faster thermal transfer, but if the deltas are the same regardless... Perhaps we can talk someone who can invest in testing this with various wattage TECs? Frankly I'ld be thrilled to test it myself but lack the funds. :3
 
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Just been doing some google work and i found the thread i was referencing, ill PM you it as i dont like linking to other tech forums openly in threads. :)
 
If I am thinking about this right the wattage of the TEC determines the heat flow through it. If a CPU has a TDP of say 75 W then to lower its temperature you need to be extracting more power than this. So if you used a 40 W TEC assuming 100% efficient energy transfer then you have 35 W net power entering the loop, heating the water overall. Just the same as having insufficient rad size in a normal loop. An 80 W TEC would also probably be insufficient in this example due to <100% efficiency of the system.

Thus you need a TEC with a larger power than the CPU's TDP, significantly larger if you want the effect to be noticeable due to the heat capacity of the water in the loop. This is why it is usually done with a second loop to cool the high power TEC/TECs, check out the scan Jellyfish if you havent seen it, they do this in that rig.
 
Perturabo said:
If I am thinking about this right the wattage of the TEC determines the heat flow through it. If a CPU has a TDP of say 75 W then to lower its temperature you need to be extracting more power than this. So if you used a 40 W TEC assuming 100% efficient energy transfer then you have 35 W net power entering the loop, heating the water overall. Just the same as having insufficient rad size in a normal loop. An 80 W TEC would also probably be insufficient in this example due to <100% efficiency of the system.

Thus you need a TEC with a larger power than the CPU's TDP, significantly larger if you want the effect to be noticeable due to the heat capacity of the water in the loop. This is why it is usually done with a second loop to cool the high power TEC/TECs, check out the scan Jellyfish if you havent seen it, they do this in that rig.
Click to expand...

This is when the cold side is applied directly to the source of heat. It directly counterbalances the heat transfer rate of the TEC and if generating more heat than it can transfer, it looses and even reverses efficiency. I am talking about air cooling a TEC at a wattage that air cooling can handle, but then chilling the water flow on the cold-side. Big thermal dynamic difference if the air cooler can keep the hot-side cool enough to have a delta balanced to about ambient. Example: Ambient is 20c, hot side is 55c and cold side is -15c under optimal heat transfer rates. Since both sides are being hit with an ambient thermal source, it stands to reason that it would act as a chiller, or this sort of thing wouldn't work in fish tanks, yes? :P
 
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I Hunta x said:
Just been doing some google work and i found the thread i was referencing, ill PM you it as i dont like linking to other tech forums openly in threads. :)
Click to expand...

Thanks, at least someone understood what I was getting at. :3
Got the message, I just can't reply since I'm new. Damn spammers making good forums set limits!

Edit: Looked it over and based on this information, I'ld like to consider a lower wattage TEC's potential due to a possible imbalance of the delta in this 400watt application. Moreso, because I have an Antec Lanboy Air Red chassis, and the setup I described above would look slick inside it if it works. Doesn't even look like his waterblock is frosting over or generating condensation, which throws in the wildcard that my application may not need condensation protection. Interesting...
 
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I Hunta x said:
Keep us updated on what you do :D GL
Click to expand...

Oh it'll be a LONG time before I could dedicate this into a full-scale build. 4.5k in system hardware alone, minimum of 3.5k. Then there's the LCS for another 1.2k. (All USD pricing for parts. Going by Newegg for PC parts and FrozenCPU for LCS parts) I was mostly interested in whether or not the thermal dynamics would actually work. And it looks like they do, but will probably have to test different wattage TECs for the perfect balance between chilling and efficiency. :lol:
But if/when I do invest in this, I'll be sure to return with an update and pics. Maybe even a video tour of the setup and benchmarks. :cool:
 
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XionEternum said:
This is when the cold side is applied directly to the source of heat. It directly counterbalances the heat transfer rate of the TEC and if generating more heat than it can transfer, it looses and even reverses efficiency. I am talking about air cooling a TEC at a wattage that air cooling can handle, but then chilling the water flow on the cold-side. Big thermal dynamic difference if the air cooler can keep the hot-side cool enough to have a delta balanced to about ambient. (IE. hot-side = X and cold-side = -X) Since neither side is being hit with a thermal source, it stands to reason that it would act as a chiller, or this sort of thing wouldn't work in fish tanks, yes? :P
Click to expand...

But you are completely ignoring the heat being added to the water by the CPU are you not? What you are saying only holds true if there is not a heat source present in the loop...The reason in works in a fish tank is that the fish output less power as heat than the the TEC, leaving it able to control the water temperature.

Now you are saying you also have rads in the loop to remove the heat from the CPU and then the TEC cools the water further correct?

This will not work because rads work both ways, if the TEC cools the water below ambient then the rads will absorb heat from the air and add it to the loop. So you will be back to ambient again.
 
Perturabo said:
But you are completely ignoring the heat being added to the water by the CPU are you not? What you are saying only holds true if there is not a heat source present in the loop...The reason in works in a fish tank is that the fish output less power as heat than the the TEC, leaving it able to control the water temperature.

Now you are saying you also have rads in the loop to remove the heat from the CPU and then the TEC cools the water further correct?

This will not work because rads work both ways, if the TEC cools the water below ambient then the rads will absorb heat from the air and add it to the loop. So you will be back to ambient again.
Click to expand...

No, I am not ignoring the heat output by the CPU. Please reread my original post, which was edited before you posted to include information that invalidates your counterpoint. Not to mention another responder already gave me a link to someone who was successful in a similar attempt via PM, which I responded to also in the thread since I can't reply directly on a new account. Since you have a problem reading every post in a one-page thread, the loop sequence is: Res, TEC block, CPU block, GPU block(s), Rad(s), Repeat. Also presume that the rads are capable of cooling the water to ambient, and that condensation is accounted for. Now admittedly the sample that was linked to me was involving a 400w TEC with ~15 degree drop in temps, compared to my 80-250w concept. Knowing it works means I will be testing it myself with various wattage TECs when I have the means. Now pay attention since you seem to have issues with procedural processes: The coolant starts at ambient, hits the chilled TEC block and cools below ambient, hits the CPU/GPU blocks and warms up, hits the rads and is rebalanced to ambient, and repeats. What I do not know and intend to test when the opportunity arises, is what wattage TEC is ideally balanced for this application. I also intend to test whether or not the TEC is chilling the water so far below ambient that the CPU and GPU heat doesn't raise it above ambient, by having fan-speed control and turning them down on the rads during testing. I doubt it'll help without once again having a higher wattage TEC than the combined TDP of the CPU/GPUs in the loop, but it's worth testing.

TECs are an odd thermal dynamic. I have seen and understand the formula for when the cold-side is applied to the CPU directly. In this practice, say you have a 150watt CPU and a 300watt TEC. The estimated delta between the cold and hot sides of the TEC is about 30-35 degrees. If your cooling solution can transfer 450 watts or more of heat, then it's fairly efficient. Now this is directly because the TEC can only transfer heat from one side to the other at a certain rate dependent on wattage. More watts is faster. This also generates heat and raises the center-point of the delta between both sides. Now applying a direct heat source to the side that is drawing heat, reduces the delta by a fraction of the two wattages. Now, what I am suggesting, and has been validated by someone else, is removing the heat generated by the CPU/GPUs before it ever touches the TEC so there is no inefficiency imbalance, and you get the full efficiency regardless of wattage, as long as you can keep the hot side cool enough.
 
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I have read your posts, I just don't agree, thats all, no need to get defensive.

This is what I am thinking will happen, im sure you will agree with most of it but I will go through it all for the sake of completeness.

Say we have a loop like you said. CPU/GPU blocks -> rads -> TEC -> back to blocks.

For a reference I am first going to assume there is no TEC. Water in loop starts at ambient, CPU and GPU loaded and produce heat. Heat transfer from block to loop is proportional to (T_blocks - T_water) this difference starts high and heat flows to the water increasing the temperature a small amount. Then the water hits the rads and is cooled at a rate proportional to (T_water - T_ambient). Temperature difference is small at first so little heat is removed. T_water is not slightly higher so heat transfer from the block is slower so T_water increases again but by less than the first pass. Now (T_water - T_ambient) is larger so the rad can remove heat faster. So over time the water temperature increases, the heat flow from the block decreases and the heat flow from the rads increases. So at some point an equilibrium is reached and the water temperature reaches equilibrium.

So that part is all standard stuff that we both agree on. Water in the loop reaches an average temperature that is a certain amount above ambient, say ambient + 10 C for example.

This is what I think will happen when you add a low power TEC to the same loop.

ambient + 10 C water goes into TEC block, some heat is removed, T_water drops slightly. At the CPU/GPU blocks (T_blocks - T_water) is now larger than at equilibrium so more heat can be extracted from the blocks. At the rads (T_water - T_ambient) is now smaller so the heat flow out of the rads is reduced slightly. The water returning to the TEC blocks is cooler than it was on the first pass, say ambient +9.9 for example. As the process repeats heat flow out of the CPU/GPU blocks increases and heat flow into the air from the rads decreases. Thus another equilibrium is reached, say ambient + 5 C.

So I agree that a low power TEC will decrease average water temperature and thus CPU/GPU temperature but the water will remain above ambient.

Next you try a higher power TEC, the process above repeats but this time the water temperature reaches ambient. In this case you now have zero heat flow out of the loop from the rads as there is no temperature difference between the air and the water. At this stage you have the TEC removing all the heat from the loop and the rads achieving nothing. So you may as well remove the rads and then you are at the position I was talking about originally. A high power TEC doing all the cooling and no need for rads.

Assuming you kept the rads in the loop and chose an even more powerful TEC you would then get to the point where the water temperature starts to drop below ambient. At this point the sign on the rad equation reverses and the rad starts pulling heat into the loop, counteracting the TEC more and more as the temperature decreases.

So I agree that a TEC WITH rads would help for trying to push your temps all the way down to ambient but if you want to go sub ambient I think you need to remove the rads and just have a high power TEC, like is the conventional way of using them.

Sorry for the long post but I wanted to try and get my point across clearly. I find discussing new ideas like this interesting and im not just trying to shoot you down. If you can come up with a reason that I am wrong in my understanding of the situation I am more than happy to admit that I am wrong.
 
Perturabo said:
I have read your posts, I just don't agree, thats all, no need to get defensive.

This is what I am thinking will happen, im sure you will agree with most of it but I will go through it all for the sake of completeness.

Say we have a loop like you said. CPU/GPU blocks -> rads -> TEC -> back to blocks.

For a reference I am first going to assume there is no TEC. Water in loop starts at ambient, CPU and GPU loaded and produce heat. Heat transfer from block to loop is proportional to (T_blocks - T_water) this difference starts high and heat flows to the water increasing the temperature a small amount. Then the water hits the rads and is cooled at a rate proportional to (T_water - T_ambient). Temperature difference is small at first so little heat is removed. T_water is not slightly higher so heat transfer from the block is slower so T_water increases again but by less than the first pass. Now (T_water - T_ambient) is larger so the rad can remove heat faster. So over time the water temperature increases, the heat flow from the block decreases and the heat flow from the rads increases. So at some point an equilibrium is reached and the water temperature reaches equilibrium.

So that part is all standard stuff that we both agree on. Water in the loop reaches an average temperature that is a certain amount above ambient, say ambient + 10 C for example.

This is what I think will happen when you add a low power TEC to the same loop.

ambient + 10 C water goes into TEC block, some heat is removed, T_water drops slightly. At the CPU/GPU blocks (T_blocks - T_water) is now larger than at equilibrium so more heat can be extracted from the blocks. At the rads (T_water - T_ambient) is now smaller so the heat flow out of the rads is reduced slightly. The water returning to the TEC blocks is cooler than it was on the first pass, say ambient +9.9 for example. As the process repeats heat flow out of the CPU/GPU blocks increases and heat flow into the air from the rads decreases. Thus another equilibrium is reached, say ambient + 5 C.

So I agree that a low power TEC will decrease average water temperature and thus CPU/GPU temperature but the water will remain above ambient.

Next you try a higher power TEC, the process above repeats but this time the water temperature reaches ambient. In this case you now have zero heat flow out of the loop from the rads as there is no temperature difference between the air and the water. At this stage you have the TEC removing all the heat from the loop and the rads achieving nothing. So you may as well remove the rads and then you are at the position I was talking about originally. A high power TEC doing all the cooling and no need for rads.

Assuming you kept the rads in the loop and chose an even more powerful TEC you would then get to the point where the water temperature starts to drop below ambient. At this point the sign on the rad equation reverses and the rad starts pulling heat into the loop, counteracting the TEC more and more as the temperature decreases.

So I agree that a TEC WITH rads would help for trying to push your temps all the way down to ambient but if you want to go sub ambient I think you need to remove the rads and just have a high power TEC, like is the conventional way of using them.

Sorry for the long post but I wanted to try and get my point across clearly. I find discussing new ideas like this interesting and im not just trying to shoot you down. If you can come up with a reason that I am wrong in my understanding of the situation I am more than happy to admit that I am wrong.
Click to expand...

Now this is what I like to see, thank you for being detailed and my apologies for being presumptuous of your position.

I had already 'planned' for the possibility that the rads will be rendered ineffective at some point with the intention of applying fan-speed reduction, even to the point of shutting them down. The reason my initial example is based around a low power TEC is because I want the rads in the first place, and because I am considering a decent $50 CPU cooler. My Antec Lanboy Air is the inspiration for that since it's about the only thing that would fit. Larger chassis such as the Switch 810 would easily support an NH-D14 on the back. I could even still go through the effort of a dedicated dual-loop using one Monsta triple rad (yes, will fit my Lanboy *wink*) in a stand-alone loop for the hot-side of a high-power TEC sandwiched into the primary loop for the cold side. Now this application may, and I say that with a grain of salt, prove more efficient than applying the TEC directly to the CPU as is common practice.

I do know that application of a 400w TEC using a cheap Antec 625 AIO LCS to cool the hot side is plenty efficient applied to an existing basic loop with about a 15 degree drop in CPU/GPU temps (provided the source itself wasn't misinformation), however I am curious how efficient that is compared to different TEC wattages in the same setup, for one. For another I'm curious how efficient it will be with a decent air cooler instead, since the one tested in the 400w TEC sample linked to me was next to near junk. :lol:

Edit: I would also like to point out that unless you are running Prime95 or something similar, such a balance will never happen in the water. CPU usage spikes and dips and for the most part is idle most of the time, with partial usage while playing games, and full-usage while video encoding or 3D rendering and the like. So, I'm mostly concerned with that, and far less concerned with getting another 100Mhz out of the CPU. I'm also more concerned with making the CPU last as long as possible while still getting the most out of it. In that sense, colder is generally better especially under load.
 
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hi all, I also have wondered about a TEC cooled waterloop for many years, but the explanation just given as to its inneffectiveness seems pretty robust.

I was wondering what you folks thought about this:

Pump > TEC (cold) > Blocks > TEC (hot) > Rads > res > pump

this would mean the coldest water hits the blocks (keeping it above the dew point though) and then the hottest water hits the rads maximising the cooling there.

I know it's logical to think it can't work due to the TEC adding more heat to the loop, but this principle does work in A/C systems where the R134 gets squished back into a (hot) liquid by the compressor.

I appreciate your thoughts :)
 
Mytheroo said:
hi all, I also have wondered about a TEC cooled waterloop for many years, but the explanation just given as to its inneffectiveness seems pretty robust.

I was wondering what you folks thought about this:

Pump > TEC (cold) > Blocks > TEC (hot) > Rads > res > pump

this would mean the coldest water hits the blocks (keeping it above the dew point though) and then the hottest water hits the rads maximising the cooling there.

I know it's logical to think it can't work due to the TEC adding more heat to the loop, but this principle does work in A/C systems where the R134 gets squished back into a (hot) liquid by the compressor.

I appreciate your thoughts :)
Click to expand...
No, there is a specific reason I wanted to avoid that in my example, which is detailed rather well by Perturabo: The water eventually obtains an equilibrium.
This means that the water in the primary loop will balance out to about the same temperature across the entire loop, not getting warmer due to the rads (and TEC if applied as I suggested), and not getting colder due to ambient temp and the blocks (and TEC if applied as is standard). Since it balances out between the heat generated and removed by the rads, and since the TEC only transfers heat from one side to the other, the addition of a TEC in that way will have theoretically no effect due to equilibrium.
While in this particular thread, there is a theoretical inefficiency in TEC usage, it is more efficient than applying the TEC directly to the CPU. As things stand, using a TEC with a lower TDP than the CPU will actually heat the CPU up under load since it can't transfer heat as quickly as the CPU is generating it if applied directly to the CPU. My theory (which was confirmed in a link provided via PM) was to chill the flow somewhat by pulling some of the water's heat out of it as it flowed through a block on the cold-side of a TEC, and have either an air-cooler or a second loop for the hot side. The separation was meant to keep the heat from the TEC out of the primary loop entirely. It's been done, and works. I'm looking forward to actually building it eventually. I am aware that as expensive as such a build would be, that getting a pre-built phase-change system would cost as much and perform better. It is nowhere near as aesthetically pleasing, so I'll pass on phase-change for now.
As for the A/C example, I was under the impression most A/C units used phase-change. Mine does and it's a cheap $100 window unit for my PC room. The only application of TECs I know of outside PC liquid-cooling is temperature control for fish tanks.
 
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yes indeed it is phase change, but for this to occur you have to add heat into the loop. The reason it works is that at the radiators there is a large delta in temperature, and lots of heat energy is dissipated to the (outside) air. This leaves a high pressure cool liquid that when it hits the low pressure zone drops rapidly in temperature (-51C or whatever). In a sealed system the phase-changing doesn't remove heat, it's just a great way of creating a large delta in controlled places. A TEC does the same (creates a large delta) though is less efficient i think

So I'm suggesting a system that also has a wider range of water temperature than normal, colder at the blocks and hotter at the radiator. Yes this will be an equilibrium, but with the min and max temps being further apart.

What I am wondering is if the extra heat introduced by the TEC will be countered by the extra heat radiation/conduction/convection at the rads.
 
While I have not tested it, I still doubt there would be much difference unless the radiators are more than capable of purging all the heat accumulated throughout the loop. At that point, there may be a noticeable variance potentially along the same theoretical level as my concept. Due to the thermal transference per watt on TECs, I would suggest at least ~250w minimum for any appreciable effect. You may also want to consider AquaComputer's Airplex Modularity System radiators; perhaps the dual-circuit model so you can pre-cool the water before the TEC, then back into the second circuit in the rad. It's what I've been planning recently.
 
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