Question for TEC Experts

[repsol_23]

I had a couple of questions from a reply in another post. Here is the quote:

"Best from the TECs point of view not yours......

Heat is flowing through it at the fastest point but because there is no cooling it is absolutely useless to you....
A 400w Qmax TEC can pass 400w at full power at Dt=0 or 0w at Dtmax usually around about 70º for a single stage TEC.

To lower the Dt start undervolted as it is non-linear relative to input power (but is also affected by load to the coldside and excessive hotside cooling .)....then to maximise cooling cool the hotside but be aware as you cool the hotside further that drops the Dt too."

My setup is comprised of a 340W/16A/34V tec that I run off of a meanwell 24V/20A psu. My block is an old DangerDen socket 478 that is made for tec's (has waterblock and copper cooling block). I use 2 swiftech 360 rads and 1 120 rad and a 350 pump (18 W corsair version). In my loop I also cool my mobo mosfets, nb, cpu, gpu (full coverage block on 4870), and case depending on setup. CPU is E8600 @ 4.5 Ghz w/ 1.40V, nb @ 1.5 V, and gpu at stock clocks. Finally, all this is with 3/8" tubing and barbs.

Now I have run this setup in two different ways.

First:
I use only 2 360 rads to cool entire loop. I run 12 fans at 5V (push/pull config) with rads on outside of case. My cpu when gaming will run ~15C depending on the game and ambient temps. The hotside of my tec block will usually run ~50C with fluid temps ~40C.

Second:
I use a recycled window AC unit (~5000 BTU's) in an air chiller box. My two 360 rads are in there with 6 fans pulling air thru the cold coil and rad. I also use my 120 rad inside of my cpu case to pull cold air into case to keep other components cool and to keep condensation from forming when dew point is high. With this setup I have cpu ~-2C when gaming, tec hotside ~ 20c, pwm/nb usually ~10C, gpu ~17C when gaming, hard drives ~ 22C, and fluid temps ~-5C. The major drawback is the amount of electricity used when in use, granted this setup is used for gaming only!

Finally my question is:
The first setup (at least to me) appears to have a higher dt for the tecs while the second would have a lower dt, but which one is moving more watts? I love my second setup (currently what I use) since my temps are great but should I reconsider going back to my first setup?

I asked Uncle Jimbo way back in the day about my setup and he said something about me having a high COP. Is that what I am looking for, is a higher COP?

And lastly, if a higher dt allows more watts to "pass thru" the tec does a lower dt "absorb" more watts? If that makes any sense?

Sorry for such a long post I just wanted to try and clarify some things in my head. I have been using tec's for almost 2 years now and I thought I had a good sense of what I was doing? After the reply I got on the other thread it really got me to thinking about my setups.

Thanks in advance!

[Ultrasonic2]

As ZIP stated before as you decrease the hot side temp of a TEC, it's delta is reduced . Also the TEC's Qmax is reduced.

SO as you have experienced with your setups, The colder the hot side of a TEC is kept the lower the achievable delta

HOWEVER

The rate the delta is reduced by cooling the hot side is not = to the reduction in hot side temp . so your still better off cooling the hotside.

ie a hot side of 50 may = a cold side of 25
but if you reduce the hot side to 25 it doesn't mean....
The cold side will be 0 or 25
The cold side my now be 5 ( just making up numbers to make my point )

SO even though the delta has been reduced because of the decrease in hot side temps your still better off with a the lower hot side temp as it will result in lower cold side temps than with i higher higher hot side temp


You ask this question
but which one is moving more watts

The answer is both setups are moving the same watts .. because the load applied to the 2 setups is the same because the CPU is putting out the same watts e relevant of how it's being cooled

However i assume your question is which setup is able to move more heat, (Q) Presuming we are just talking about the TEC in this discussion the answer is the first setup with the hotter hot side temp because it has a larger QMAx and there for is able to move more heat



SOOOO

What ZIP said is right


Thanks
US2

Edit
If needed we can produce manufactures charts backing up our statements

[repsol_23]

Thanks for the insight. For the longest time I was doing much trial and error to get my setup to my liking.

By the way, I remember sending you a pm a long time ago about getting a tec block. Are you still making blocks for tec's?

[zipdogso]

I asked Uncle Jimbo way back in the day about my setup and he said something about me having a high COP. Is that what I am looking for, is a higher COP?

Yes it is nice to have high COP but to do it you need to undervolt quite a lot and your Dt and Q drop like dead flies.

If you aim for high COP the only realistic way is to use multiple TECs heavily undervolted to 35-40% power. Then it is a case of juggling your hotside cooling to maximise cooling whilst still maintaining a fair Dt. It is helpful to have your total cooling somewhat larger then the load you apply to the coldside that will also help to keep Dt up. You must realize the end result will not be fantastic cooling. Particularly if you have a high ambient temp - which works against your hotside cooling.

EDITED after further reading of OP

And lastly, if a higher dt allows more watts to "pass thru" the tec does a lower dt "absorb" more watts? If that makes any sense?

No.....this is where your going wrong it is the other way round Dt=0 is maximum wattage through TEC BUT no cooling then as the Dt increases the cooling increases and the wattage of cooling falls until eventually 0W through TEC maximum Dt.

[Ultrasonic2]

Oh im sorry I can’t resist

Did you say you need multiple TEC undervolted ?

How about this untested prototype of mine then for 2 50mm TEC



Oh and I still make a few blocks .. I did reply to your PM .. did it go missing ?

[repsol_23]

No, the only thing missing was the funds in my account!

YHPM

[zipdogso]

Oh and I still make a few blocks .. I did reply to your PM .. did it go missing ?

If you mean me...oh didn't update before sending you meant repsol...anyway

LOL..... I am waiting for end february wont come fast enough and the pennies don't either !!!

The only problem...for you maybe more than me, it won't be going in a system straight away and nor will it be i7....

[Pneumonic]

Oh im sorry I can’t resist

Did you say you need multiple TEC undervolted ?

How about this untested prototype of mine then for 2 50mm TEC



Oh and I still make a few blocks .. I did reply to your PM .. did it go missing ?

US2! That looks really nice.. I think I may have to play with the 62mm block for a bit first tho before justifying to myself that I want that one as well