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TEC Waterchiller

post #1 of 10
Thread Starter 
Hello

I wanna build a TEC waterchiller for midrange GPU´s (100-140 W). I wanna cool the hot site with a thermaltake bigwater 760i. So is one 200W Tec enough to cool the water? And should I use Radiators in the loop with the cool site attached?
Edited by OCskillzz - 4/11/17 at 4:35am
post #2 of 10
Quote:
Originally Posted by OCskillzz View Post

Hello

I wanna build a TEC waterchiller for midrange GPU´s (100-140 W). I wanna cool the hot site with a thermaltake bigwater 760i. So is one 200W Tec enough to cool the water? And should I use Radiators in the loop with the cool site attached?

Gonna need some more details to give you an exact answer.

You said GPU's. Is it one GPU or several GPUs? I'm assuming one.
Also, what is your target temperature?


What I'm gonna recommend to you is that you go to Custom Thermoelectric's website and browse through this table:
http://customthermoelectric.com/tecs_imax.html


I'll give you an example of what to expect. Keep in mind, these are theoretical numbers if everything was perfect. Typically performance will be lower. They have a 40x40mm 225w TEC and a 62x62mm 225w TEC. The 40x40mm won't require any cold plates or anything in addition to the waterblocks on it, so that's what I would use.
Here's the charts associated with that peltier:
http://customthermoelectric.com/tecs/pdf/19911-5L31-15CQ_spec_sht.pdf


If you are planning to power it with a 12v PSU (computer power supply or a switching power supply), look at the Volts Vs Amps chart on the right. Find 12v and trace it over until you hit a line, then look for the corresponding amps for that voltage.


So looking at this, you could expect a range of 6 to 8 amps of draw depending on the heat load to the cold side. We can now figure out what a best case scenario delta temperature would be (how much colder the peltier can hold the cold side in relation to the hotside). We'll use your 140w figure.



In the picture above I marked the 6 to 8 amp range for you. You can see from the legend on the right that we're looking at about 0c to 10c delta temperature running at 12v.
Now, that doesn't mean 10c below ambient, it means up to 10c below the hot side of the peltier temperature.

The hot side of the peltier is going to be the amount of power the peltier is drawing to pump heat from the cold side combined with the load of heat on the cold side.

So that's:

12v * 8a (Peltier power) + 140w (Graphics card) = 236w.

That means if you wanted that 10c to mean 10 degrees below ambient, you would have to cool 236w to ambient. That'll be something like 2 360mm radiators.



Now, you can certainly go colder. I'll give you a quick example with a higher power TEC:

http://customthermoelectric.com/tecs/pdf/19911-5M31-28CZ_spec_sht.pdf

12v * 14a + 140w = 308w
~25c max dT at load



Food for thought:
If you add several peltiers side by side (in parallel) , they will split the heat load. Looking at the peltier above, if you had two of those peltiers running at 12v, they'd each only be cooling 70w and your delta temperature could be as high as 30-35c



In addition I'll quote a post I wrote that goes over more details and such.
Quote:
Originally Posted by Skyl3r View Post

The hot side heat load should be calculated by:
Cold side heat load(W) + V * A

As you say, if you are supplying 12v, the peltier would draw above 12.5a, which gives you (as you pointed out) 150w.
Now if your cold side is managing a heat load of 80w, then you have a total heat load:

80w + 150w = 230w

Now typically you can make a cold side estimate of the pelt by using a Coefficient of Performance (COP) chart. The COP is calculated by dividing the watts of cooling (Qc) by the watts required to cool (W or Work). You'll typically see charts with COP vs Amps. CTE, who makes the 400w pelt Puck referenced, does it a little different. They have a Volts vs Amps chart and a Qc vs Amps chart.
The charts are here:
http://customthermoelectric.com/tecs/pdf/19911-5M31-28CZ_spec_sht.pdf




In the above picture, I've drawn lines on to the chart to clearly show how you would go from knowing that you will supply 12v to finding the max amp draw you could expect (right chart).
Then you can use that amp draw to find the delta temperature (dT) at a given cold side heatload.

Now, the actual cold side temperature (Tc) of the peltier is calculated by Th - dT. What this tells us is the delta temperature is relative to the hot side. So if the hot side is running at 60c because you only have one 360mm radiator on it, then assuming the 80w of load and perfect efficiency, you would only have a cold side temperature of 30c.

Edited by Skyl3r - 4/11/17 at 5:40am
post #3 of 10
Just to clarify skylers diagram.The amps that the TEC pulls at a given voltage is dependent on the delta across the TEC, the higher the delta, the lower the amps/power consumption, the lower the delta, the higher the amps/power consumption.

As the maximum delta is reached when there is no heat load applied to the cold side, we can put the minimum amperage the TEC will use at 12v at 0QcW, 6 amps. The maximum amps that the TEC will pull is at Qmax with 0*c dT, so for 12v that is 165w Qmax and 0*c dT, like this



from that, you can extrapolate dT, Qc and power consumption of the TEC.

One caveat though, because that TEC can't reach dT Max at 12v it would be a slightly different line than what I have drawn, the spec sheets are not accurate enough to make perfect estimations so real world results will differ.

To effectively cool a GPU with a heat load of 140w and have a decent delta, you usually need the Qmax of the TEC to be at least double the heat load, ie 280w Qmax TEC, but actually I would recommend a 400w Qmax TEC (ebay tec's advertise power consumption, not Qmax, their Qmax is much lower than their power consumption, Custom Thermo Electric (CTE) lists Qmax, so if you want to buy a TEC from ebay, compare the volts, amps, couple count and size of the ebay tec to the CTE tec and that will give you an approximate idea of how good the ebay TEC is, minus the lesser quality of ebay TEC's of course.)

to help with deciphering ebay TEC's couple count of a TEC directly relates to it's voltage, ie a TEC 12715 would be a 15v, 15amp TEC, the 127 is the couple count, 127 couples = 15v, the 15 is the amps. ebay is mostly 127xx TEC's, there are some 199xx TEC's on ebay though, these are 24v.

TEC's perform best when run at 50-70% of their max voltage, for this reason, if you are using a 12v ATX PSU to power the TEC, I would try to buy a 199xx TEC and avoid 127xx TEC's, the 199xx TEC's are much more efficient at 12v than 127xx TEC's

The CTE 400w Qmax TEC at 12v is perfect for chilling a 140w GPU, but it is a 62x62mm TEC, so you need special water blocks, you could try to use 2 of the 225w 40x40mm TEC's, but that means more water blocks.
Edited by LiamG6 - 4/11/17 at 6:31am
post #4 of 10
Quote:
Originally Posted by LiamG6 View Post

Just to clarify skylers diagram.
Thank you. All good things to note.
post #5 of 10
you already said it, just clarifying that the 6amps is not at 0*c dT, but at the maximum dT achieved at 12v with no heat load on the cold side, and 8amps is at 0*c dT with the heat load applied to the cold side equalling the Qc of the TEC, ie 165w heat load on cold side and 165w Qc.

So the TEC can only achieve a 10*c dT with 125w of Qc, making it a bad choice for his 100-140w heat load as that delta would be lost in thermal resistance. 2 of those TEC's at 12v would achieve a 20-30*c dT though on a 140w heat load which is pretty good
Edited by LiamG6 - 4/11/17 at 6:38am
post #6 of 10
You don`t cool water with a TEC. Ever heard of the heat engine? You get much better efficiency by maximizing the difference of temperature. The way you formulate your question is a bit confusing. With a TEC you spend electric power to displace heat from one place to the other. In this case, you end up heating the water.

TEC are pretty awful in term of COP (efficiency). You get something like 0.4-0.7 (best case scenario). Let`s say a CPU produces 100W and the COP is 0.55 (average), you will need to spend 181W to run the TEC. Just to put things in perspective, 181W is nearly what a GTX 1080 consumes.

I looked for your thermaltake bigwater 760i and it seems that it`s just a 120mm radiator? If that`s the case, I am not quite sure this is a good idea to add a TEC to it. You'll end up with a GPU 100-140W AND ~200W from the TEC. That's 320W you have to dissipate. That's a lot.
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post #7 of 10
Quote:
Originally Posted by Just a nickname View Post

You don`t cool water with a TEC. Ever heard of the heat engine? You get much better efficiency by maximizing the difference of temperature. The way you formulate your question is a bit confusing. With a TEC you spend electric power to displace heat from one place to the other. In this case, you end up heating the water.

Why don't you cool water with a TEC?
post #8 of 10
Quote:
Originally Posted by Skyl3r View Post

Why don't you cool water with a TEC?

Not efficient and it is far better to simply cool the chip instead of a pretty big reservoir of heat (water).
Edited by Just a nickname - 4/11/17 at 7:09am
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post #9 of 10
Quote:
Originally Posted by Just a nickname View Post

https://en.wikipedia.org/wiki/Heat_engine

Not efficient and it is far better to simply cool the chip instead of a pretty big reservoir of heat (water).

Oh I see. I thought you meant use a different coolant besides water.
There's a number of problems I draw with this conclusion. On face value it looks like the right idea, but once you get into the actual use case, I think it makes more sense to use a waterchiller.

First of all, it's going to be quite a bit more difficult to mount a 62x62mm TEC to a GPU in direct die vs running chilled liquid through a waterblock (which also hits the VRMs and memory). There's space constraints due to the chip being much lower to the PCB than say, a CPU on a motherboard. I don't think this is realistic at all.

Secondly, the reason most of us wouldn't TYPICALLY consider direct die over a waterchiller is that our system puts out more heat than any peltier can handle on its own. This means, to hold a low temperature with an overclocked Ryzen or 7700k that's putting off 200w of heat, you need to run a peltier at inefficient voltages or a very large peltier vs being able to run 4 peltiers in parallel to split the load and potentially achieve greater delta temperatures.

Third, having a reservoir gives you a buffer for temperature spikes.
Edited by Skyl3r - 4/11/17 at 7:24am
post #10 of 10
You guys are quick! Great explanations smile.gif

I would definitely look at chillers for GPU(s) setups, mainly becuase of package constraints. You wont be able to fit the proper TEC on a GPU for direct die, so you are left with either a difficult to make work stacked setup, or the more proven(but more expensive) chiller options. For one mid range GPU a single CTE400 would be a good cost effective chiller TEC, and save money on hardware vs multiple smaller ones.
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