How do I calculate how much rad I really need

[psychofunk]

How can I go about calculating how much rad I really need. I am going to be using a thin rad and with my space constraints and rad choices as well as because of costs I wanted to know what size rad I need so I can determine if I can get away with one or if I need two and if I only need one then how small I can go. What I am really hoping for is that you can help me find an approximate range so that as I change components I can still guesstimate.

I am currently working with
AMD XP-M2400+ running 2.1v (207*13)
Dtek Whitewater (1/2" ID barbs)
GeforceFX 5950
Maze4 GPU block (1/2" ID barbs)
4-5' of 7/16" hose
Danner MagDrive3

I currently use a T line but am thinking about making a largeish res so that I can submerse my pump and give it unrestricted intake, not to mention that bleeding has worked my nerves. If not I will still probably go with a swifty black res.

Oh yeah and I am not sure if it matters but I use papst 4412FGL's exclusivly and I run them at 12v. Please help me. Be my tutor because I am going to be slow with the math stuff. I know one of you guys has the patience and good heart to take the time with a non-intellectual. Thanks.

[psychofunk]

No comments at all? Am I asking too hard of a question. Is it one of those things that is impossible to answer? I am asking because I don't know, I am not being a smart ass.

[bobkoure]

You're getting no answer because there isn't much in the way of public data on radiators - and you're asking basically for a general formula of C/W/(cfm airflow) / (temp delta) either per possible rad or for each possible type of rad on a C/W per frontal sq cm. (or something like that) It's pretty daunting.
All that said, 4412s at 12V should have no problem pushing air through a 2" heater core, so you could consider one of those.
Or, if you're going with a thin radiator, you can either undervolt those 4412s or go with lower powered fans - depends on how much you value your quiet - and what you might mean by the word "quiet".
I would guess that you'd be fine with a rad with frontal area of, at least, say around 250 sq cm - so you could use a BI Pro II, or a "big momma" 6"x6" heater core (which, if you couple with a coolshroud is nearly as easy to mount as a BIP II - and lots easier to locate in the lower front of a tower case). If you're OK with making your own shroud, then there are lots of other thin rads, both thin heater cores and transmission coolers, that have this frontal area.

You might have better luck first figuring out how much heat you're dumping, what you need your difference between ambient and coolant to be and asking if anyone else is cooling about the same wattage - and asking what they're using for rad and fans - and what their approx temps might be (only expect a rough guess on temps).

[psychofunk]

Originally Posted by bobkoure

.....I would guess that you'd be fine with a rad with frontal area of, at least, say around 250 sq cm

This is exactly what I was after but including the steps to get to this point as well as taking into account the performance of the blocks, their restriction as well as the restriction caused by the hose, the pumps own heat that is transfered into the loop and the affects of having or not having a res and using WAF's (Weak Ass Fans -- (c) Cathar 2004 ).

Can you help me more generally so that I can start to ask the individual questions or in some cases gather the info. What I mean is tell me what would be necessary to accomplish this. For example I assume I would need the cw and head loss of each component? The heat produced by the CPU & GPU? What else and how would I combine these facts (or guestimates in some cases) to come up with my final answer of how big/small a surface area I need.

Thanks again Bob, I appreciate every answer, even if it is just a "WTF" or "yeah I would like to know too" or even a "you want to much kid".

[JWFokker]

It's actually pretty complicated to calculate optimal radiator size especially considering how much variation there is system to system so any answer would be entirely theoretical. A general rule of thumb is that bigger is better since the radiator won't impact your flow too much going from a single 120mm core to dual 120mm core or larger. There is a significant temperature difference going from a single to a double heatercore and gains drop off after that unless you're really pushing a lot of heat into the loop. In your case, it's probably not worth it to go bigger than a dual 120mm rad, simply because the gains won't be worth it for the logistical problems involved with a bigger rad. It's a subjective thing. But with your fans, I'd shoot for a 1" heatercore instead of a 1.5" or 2", because they really don't have the static pressure necessary to effectively cool a heatercore that deep. My 2-342 gave me identical temps to my new aluminum transmission cooler with the same fans at the same speeds and the tranny cooler is only 0.75" thick. With low speed fans it really doesn't pay to use a thicker core.

As for the reservoir, while the Mag 3 doesn't get very warm so it won't impact your water temps much, it might be better to get a reservoir that the Mag 3's intake will fit into. It's a rather large pump to build a reservoir for and you'll get just as good flow rates if you just have the intake inside the reservoir.

[bobkoure]

Try breaking the problem down.
Once you have a notion of how much energy you're trying to dump to ambient air (I would guess you're somewhere in the 100 - 120W range) and what delta between ambient and coolant you're willing to tolerate (you can dump a lot of heat through a little radiator if there's a 40C delta). Ignore water flow for this - it doesn't matter.
OK, so that's one part.

The other part is moving heat from the CPU and GPU into the coolant (for the first part of this you just assume it's "magic"). Flow does mater for this (although how much it matters depends on the specific blocks you are using). There's a nice interactive C/W/flow chart (with one line per block) somewhere here at PC - worth looking for... You'll need to know what your flow rate is. You can guess based on your pump's performance curve (beats me what the resistance of your loop is, though) - or you can just set it up outside your PC and see how long it takes to fill a 5 gal bucket (or whatever - you get the idea).

So... now you know as much as I do - go have fun

Bob
PS: For figuring your wattage there's a gizmo called a "Kill-A-Watt" that will tell you how much power you're drawing from a 115VAC circuit. Figure your power supply is no more efficient than 80% - so whatever heat you're getting rid of cannot be more than 80% of the figure this thing gives you. My under-desk box has a XP-M 2600 at 12.5X200, 1G PC2300 mem, 2 optical drives, 2 160G SATA drives, matrox 650 card (less power than your GPU) and never see kill-a-watt readings over 120W - not even when I'm writing to one DVD, reading another, and the CPU usage is at 100% (low priority so the DVD writer doesn't starve) - and I'm running fans, a small motorized impeller and a 12VDV pump on that as well.

[JWFokker]

Sure you could potentially calculate it if you measured everything, ambient temps included, but we don't know how effecient radiator are other than the ones BillA tested. But then again, most people mount their heatercores to their cases so using the ambient temperature wouldn't necessarily be accurate and you're back to a theoretical number that you'll likely never see. You'd also have to measure flow rate and coolant temps ahead of time, something you can't do without already having the radiator in hand.

[bobkoure]

You can't calculate - the data just isn't there.
What you can do is ask things like "is anybody else cooling 120W? How big a rad are you using? Which one? What kind(s) of fan(s) are you using?" All you're going to do is maybe find someone else who's doing what you want to do (in the radiator and fan dep't) with about the same wattage. All I was saying is that you don't have to find someone who's using the same waterblocks, pump, tubing to get a useful answer...

[JWFokker]

I guess that's more or less what I was getting at. You can't figure it out ahead of time until you've got data for all your parts themal conductivity, thermal capacity, operating temps and whatnot. And we don't have much in the way of radiator data.

But I think the best answer is to just get a dual heatercore and if more cooling is needed, buy more powerful fans. In my opinion a single 120mm heatercore doesn't cut it in any overclocking scenario.

[bobkoure]

Not exactly - I was saying "break the problem down". Yes, you have to guess - but you can guess in two parts. I would guess, for instance, 250 sq cm at a minimum, for cooling about 120W and keeping coolant two to four C over the temp of the air you're pulling through. I'm not worrying about pump, tubing, water flow, water pressure, or water blocks, for this guess. Yep, still a guess, though.

The second guess is easier (pump, tubing, wbs) thanks to all the work Phaestus, BillA, Les, et al have done for us.

If by dual heatercore you mean BI (pro or xtreme) II, or a heatercore that'll take 2 120mm fans, then, yeah, that ought'a work fine. The thinner rads have the advantage of needing less air pressure (so quieter fans). If you don't care about fan noise, don't optimize for this, of course... And if you do care about fan noise, then adding more powerful fans is the last thing you'd want to do

[JWFokker]

I do mean something along the lines of a '77 Bonneville heatercore or the like. Those Black Ice rads are far too expensive just to look nice.

[psychofunk]

Originally Posted by bobkoure

Not exactly - I was saying "break the problem down". Yes, you have to guess - but you can guess in two parts. I would guess, for instance, 250 sq cm at a minimum, for cooling about 120W and keeping coolant two to four C over the temp of the air you're pulling through. I'm not worrying about pump, tubing, water flow, water pressure, or water blocks, for this guess. Yep, still a guess, though.

The second guess is easier (pump, tubing, wbs) thanks to all the work Phaestus, BillA, Les, et al have done for us.

If by dual heatercore you mean BI (pro or xtreme) II, or a heatercore that'll take 2 120mm fans, then, yeah, that ought'a work fine. The thinner rads have the advantage of needing less air pressure (so quieter fans). If you don't care about fan noise, don't optimize for this, of course... And if you do care about fan noise, then adding more powerful fans is the last thing you'd want to do

So then would my first question be "How can I figure out how much heat my CPU creates" I found this script ( http://www.benchtest.com/calc.html )but it puts my cpu alone at 189w. Can I really rely on this script? How would I go about figuring out the kilawatt thing you mentioned earlier? Is it a reading or a calculation based on various reading? Where would I find the bits of data I need, MBM? The bios?

[bobkoure]

You're running a XP-M2400 at 2.1v (207*13). Hmmm... I use a lot less than that with a 2600M, but I'm at much lower voltage and only 200x12.5. I'd tend to trust my own measurements over a script.
You can get a kill-a-watt for under $30 (here's a froogle search). You plug this into the wall, your PC into it - and it reads out the wattage you're using. If you're married you can easily justify this thing to your spouse as "something to save electricity"
Your power supply is 80% efficient if it's a Seasonic, otherwise, it's probably more like 70 or 75 (if you've got the docs from your ps look there). PS efficiency changes based on how many amps you're pulling, so this is kind of a guess as well
So...try starting your PC with as little in it connected as possible. If you've got a "cheapie" video card, try using that - the difference between with the cheapie and with your gaming card is pretty much the wattage your gaming card uses.
You get the idea. FWIW, these are pretty decent little devices - recently had a conversation with my brother in law, who runs (among other things) the lab the readings for those yellow stickers you see on appliances come from - and he says they're pretty good.