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# Starting off big...

For arguments sake, say I wanted to cool a system with a TDP of 450W. Looking at T-Delta, (Here is where I am unsure) I would like a Delta of 10 degrees (I choose a desired delta, it isn't predetermined - yes?). I look up some graphs like this one ( http://martinsliquidlab.org/2012/04/19/ek-coolstream-rad-xtx-360/4/ ) and see a graph for the XTX360 from EK @ 10C delta. This shows me how much heat (in W) can be removed from the water and keep it within the 10 degrees of ambient. So in that graph, at 1000 rpm I can maintain a delta of 10 degrees only if my heat load is 150W.

Making an assumption that this is linear, to now dissipate 450W, with 10 degree delta and 1000 rpm fan speed, I would need 3x XTX360 in series.

Whew. That temp delta confused me for a while, I hope that is correct or I'm back to reading the stickies!

So in real life, with the above numbers, if I would like to dissipate ~550W quietly I will need a whole whack of rads (like 4 triples). If that is the case I might have to scale back my water cooling ambitions... or use a higher delta target, or push pull, or higher fans speeds, or bigger pump... Am I on the right track?

J

PS. I need another hobby like I need another hole in my head.
sry, but that is a terrible way to think about it... a 10C delta is absolutely terrible loop set up... your goal in a loop should be to get the delta (from ambient air to water temp) as close to zero as possible... the general rule of thumb that i like to follow is 120.1 worth of rad space for every block you have (and then 120.1 to 120.2 of extra rad space just to be safe)... obviously by changing fan speeds and rads used this rule can be broken, but its easiest to follow... the main way you are gunna effect your delta is through loop set up allowing for maximum flow rate and minimum delta between air temp and water temp... if you would like to post some specifics about your computer, what you plan on cooling, budget, case, ect. im sure we would all be able to help- you out much more
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Thanks for the input - I am still planning out my parts - no computer yet. Have been out of PC gaming for over a decade... now my son wants more than the xbox so I'm back. And I have always seen water cooling as a very cool way to do things, so here I am.

I only know what I have read, and due to the nature of the stickies have had to make some assumptions and guesses. If the delta isn't the goal, am I at least correct in how the delta works - ie the graph linked will dissipate 150W of heat at 1000 rpm leaving a 10 degree difference between the exit water and the ambient air?

My computer will be (probably) an i7 3770 3.5GHz, Asus maximus V formula, some sort of 670 class nvidia card but depending on price that will be one of the last pieces. Originally I thought of cooling the CPU, GPU, MB and even the RAM. But it sounds like I don't need to put money into all that at first. So CPU and GPU (the 550W number I had before was, now that I re-google the parts, a bit off I think) would be the only ones for now.

Budget, well I have no fixed number but generally like to buy quality parts up to a point.

But before I am looking at parts and prices I am trying to understand how to plan one of these out so I don't finish and find that I under-radded (not a word, I know). I like to try to understand things to some degree before diving in, but this hobby belies it's depth. And since I want to include my 12 year old and teach him I need to understand the information first - kids ask the most questions. Plus to get this in the family room I needed to promise my wife that it would be quiet, so 2500rpm fans are out.

j
ok... now that (i think) i understand what you are trying to do at the moment, i will try to explain what my ideas on the matter are (if you will excuse my terrible spelling and grammer as i am on a tablet at the moment)... the #1 most important think in water cooling is the delta between the max temp of the water (anywhere in the loop) and the ambient air temperature... this delta needs to be as low as possible for the best performance... there are two main ways to do this

First is the most simple... increasing the cooling compasity of the loop as a whole (eg. increasing rad space)... this can be done through swaping out for a bigger radiator, adding radiators to a loop... the other way to do this is to optimize the radiator space that you do have by increasing fan speed (this will provide minimal improvements if the system is set up correctly in the first place)

the second is to increase your flow rate (this is where the majority of systems can use some improvement)... the general concept is that by increasing flow rate you increase the volume of water that has to absorb the same heat (generally measured in Watts or Watt hours)... this is done by both using a more powerful pump, and decreasing restriction in you loop (most commonly done though minimizing over all loop length and by choosing low restriction blocks)

you should note that both of these obviously have a point of diminishing return... for the radiator space, this point is around 100w per 120.1 worth of rad space (using 1500 rpm fans and decent rads)... for the flow rate it is debatable, but is generaly said to be between a flow rate of 2.0 gpm and 2.5 gpm (this may even be a bit high for your uses)

since you just plan on cooling a CPU and a (670 class or so) GPU you should be just fine with around 120.3 (360mm) to 120.4 (480mm) worth of rad space... this assumes the use of medium speed fans and decent rads (witch it does apear fit your needs)... i would also reccomend ignoring that statistic that you linked to at the moment as it can be rather hard to use no matter how long you have been water cooling and how well you understand it (it still confuses me near to death when i first look at them)... that statistic is also truly only useful for major enthusiasts looking through hunderds of different radiators and nit picking them for their very specific needs (atleast that is the only reason i pay true atention to them)... the mojority of radiators will perform roughly the same (based on tier and cost) at the same fan speeds (of course there are exceptions)

also, since you are planning on a rather simple loop, you wont need to worry much about loop order, but there are a few things to know about it... the general rule of thumb is that the flow of a loop should always go res > pump > rad > "component you want the coldest" and that your loop should be as short as possible... this a very great rule to follow both when you first start and in almost every simple loop... now since you were asking about concept i will go a bit more in depth

as you get more advanced and start building bigger more complex loops with more heat dump it may be advantageous to stray from this set up... the two most notable and different way are changing the loop order and also sacrificing extra length of a loop for more keeping the delta between the max water temp and the air temp at a minimum... these two often fall hand in hand

the most common way to do this is when you have multiple radiators, many components to cool,and multiple pumps (or simply something very strong like an AC pump for example)... there are also some rules that either need to be followed or for one to be very careful when breaking (i will note these later)... I will show an example of a loop when more tube length and radiator movement could majorly improve the efficiency and the performance of the loop

this loop is a loop i proposed for a Cosmos II build i saw a while back (though a few components were changed and generalized)... it consisted of a CPU (3960x or similar), multiple GPUs (dual 680s/7970s or more), one 120.3 radiator, one 120.2 radiator, one res, two pumps (35x or similar), mobo cooling, and ram cooling... you should note that though mobo and ram cooling can do some good in extreme use and cases, they are mainly ascetic for the vast majority of PC users... the loop that i recommended was ordered as such:

res>pump 1>CPU> mobo and ram>120.2>pump 2>GPUs>120.3>res

the reason for this order is that the higher the temp of the water is, the less energy it can absord... with a heavily OCed CPU such as a 3960x or so that can very easily put out a few hundred watts combined with the minimal (yet still important) heat of the ram and the mobo... even with a good flow rate, this can easily raise the temp of the water by at least a few degrees C... even simply the 3-4 degrees that the temp of the water has raised, can make quite a large impact on the GPUs cooling (especaly when they are putting out well over 400W (in some cases i have seen, even up to around 1200W)... this set up is mainly possible due to the use of two very strong pump that kept the flow rate around 2-2.5 gpm even with the largely extended tubing and many components

now that i have explained most of the basics, its time for some of those notes and rules i mentioned earlier:

1) always keep the pump where it can get plenty of water!I cannot stress this one enough... the fastest way to kill any loop is to burn up a pump because it is struggling too much for water... the easiest way to fix this problem is to simply have the res above the pump and to feed water straight from the res to the pump... if you need to have a pump where the is no res to feed directly into it, the easiest way to make sure you are fine is to have the pump physicaly below (closer to the ground than) the component before it in a loop (and make sure it is not a restrictive component such as RAM and mobo blocks, or even a single GPU)

2) keep the component you want the coldest after the largest rad (or only rad)

3) increase rad space and flow rate to increase efficiency and cooling potential

4) there will always be a point of diminishing return

i hope that all of this helped, and if you need any help when you get farther in just feel free to post here and im sure you will find plenty of help
Edited by eskamobob1 - 8/7/12 at 3:50pm
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Quote:
for the flow rate it is debatable, but is generaly said to be between a flow rate of 2.0 gpm and 2.5 gpm (this may even be a bit high for your uses)

Mathematically speaking, 1 gpm of water = 264 watt/kelvin. In a system with 2 gpm flow, water will heat less than 2 C as it picks up 1000 W from the waterblocks.

Likewise, 50 cfm of air = 28 watt/kelvin. That's the upper limit on what you can dissipate even with the best radiator. 50 cfm is about average for an unobstructed flow rating at 1500 rpm for a 120x120 fan. in practice, hanging the fan on the radiator will cut the flow in about half.

Say, you have 550 watt coming out of the computer, 1 gpm water flow, 6x120 fans blowing 150 cfm total, and an ideal radiator.

Ambient air: 25 C
Air coming out of the radiator: 25 + (550/28)/(150/50) = 31.6 C
Water coming out of the radiator: 31.6 C
Water going into the radiator: 31.6 + (550/264) = 33.7 C
Air out - air in delta 6.6 C
Water in - water out delta 2.1 C
Water in - air in delta 8.7 C

Average temperature across waterblocks (31.6+33.7)/2 = 32.6 C

If the radiator isn't ideal, or either the water flow or the air flow is too high, it won't equalize water & air temperatures and you get one extra term (water out - air out).

In this example, the air out - air in term is the largest, so the setup would benefit from getting more & better fans.

It also follows that 2 gpm is past the point of diminishing returns in most practical cases: in this system, with a radiator setup as large and expensive as it is (2x360), even the flow of 1 gpm is not the bottleneck.

Temperatures of the CPU and the GPU will be higher, depending on how good water blocks are and whether they are mounted properly. Every degree off air-water delta is a degree off the system.

For a CPU, core-water delta may be 30-40 C, so there isn't much point pushing air-water delta to the ridiculous extremes. For a full-coverage GPU block, core-water delta can be under 10 C and air-water delta is more interesting.
Edited by hamster3null - 8/7/12 at 4:50pm
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That is some amazing information. I had a hard day at work and it isn't quite sinking in yet, but it is very enlightening. Thanks, and I'll read it over a few times.

I find the WC part of planning the computer more interesting than the rest of the parts...

j
Thanks Eska, it seems I may have been worrying about this a bit much. I ordered a case (810 switch SE) and got some fans at a good price. Then as I start with the components I'll come up with my plans for a heat dissipation system.

Eska, how much benefit would putting a single between 2 components? ie res > pump > 120.3 > cpu > 120.1 > gpu > res. Would it be the same to just put the two rads in series? I'm guessing the heat dissipation of the rads is the same so no real difference...

j
Edited by schnellschnell - 8/8/12 at 8:20am
Quote:
Originally Posted by hamster3null

Air coming out of the radiator: 25 + (550/28)/(150/50) = 31.6 C
Water coming out of the radiator: 31.6 C
Water going into the radiator: 31.6 + (550/264) = 33.7 C
Air out - air in delta 6.6 C
Water in - water out delta 2.1 C
Water in - air in delta 8.7 C
Average temperature across waterblocks (31.6+33.7)/2 = 32.6 C

Lets see if I grasp this. For Air coming out of radiator it is: (Please correct anything I say below)

Ambient air temp coming in, plus the heat generated in the system (550W) divided by the capacity of the air to absorb heat (28W per degree). Since the air absorption is measured at ~50cfm and we are using a triple rad we divide the total rad cfm (150cfm) by the average (50cfm). This way a single rad (divide by 50/50 or 1) would heat the air coming out to almost 20 degrees.

Now that you have the air temp across the rad you assign that number to the temp of water exiting, 31.6 in this case. You take that and add the heat generated in the system (550W) divided by the capacity of the water to absorb heat (264W per degree). This increases the water by 2.1 degrees. QUESTION: 264W / degree was for 1gpm flow, why don't we double that since we are assuming 2gpm flow?

Air delta is difference between ambient inlet air and the calculated exit air - 6.6.
Water delta is the difference between inlet water and calculated exit water - 2.1.
When you calculate the Water in - air in delta of 8.7 degrees is that the Delta-T that gets mentioned around here, and I brought up in my first post? ie this system has a T-Delta of 8.7?
Quote:
Originally Posted by hamster3null

If the radiator isn't ideal, or either the water flow or the air flow is too high, it won't equalize water & air temperatures and you get one extra term (water out - air out).
Can you elaborate this statement - I'm not sure I follow. If the flow is too high the water can't shed the heat fast enough and the air exit temp will be different than the water temp? Would this be a positive feedback loop and keep heating up, or it would equalize at a higher temp?
Quote:
Originally Posted by hamster3null

In this example, the air out - air in term is the largest, so the setup would benefit from getting more & better fans.
So the 6.6 degrees can be reduced by increasing the cfm, but from the statement above you mentioned too high airflow can cause a system that 'won't equalize'. Is that if the calculations go below 0 (zero)?
Quote:
Originally Posted by hamster3null

Temperatures of the CPU and the GPU will be higher, depending on how good water blocks are and whether they are mounted properly. Every degree off air-water delta is a degree off the system.
Basically every degree we reduce the Water in - air in delta (8.7 degrees in example) is reducing the temps of components by a degree.
Quote:
Originally Posted by hamster3null

For a CPU, core-water delta may be 30-40 C, so there isn't much point pushing air-water delta to the ridiculous extremes. For a full-coverage GPU block, core-water delta can be under 10 C and air-water delta is more interesting.
Core-water deltas are the difference between the actual component (cpu / gpu) and the water. The CPU is always hotter than the water by a fair margin, so once you get to a good stable temp any cooling more will not really change the core temp. Even though the GPU delta is lower isn't it really the same thing, why is it more interesting?

Sorry for the lengthy dissection - but you take the time to post this so I want to make sure I understand.

j
Quote:
Ambient air temp coming in, plus the heat generated in the system (550W) divided by the capacity of the air to absorb heat (28W per degree). Since the air absorption is measured at ~50cfm and we are using a triple rad we divide the total rad cfm (150cfm) by the average (50cfm). This way a single rad (divide by 50/50 or 1) would heat the air coming out to almost 20 degrees.

I think you've missed the part where I said that, if the fan hangs on the radiator, it won't do 50 cfm, it will probably do about half. Look at the bottom chart here: http://img524.imageshack.us/img524/552/summary20b.png So 150 is _six_ fans blowing at 25 cfm each.
Quote:
QUESTION: 264W / degree was for 1gpm flow, why don't we double that since we are assuming 2gpm flow?

I was assuming 1 gpm flow.
Quote:
If the flow is too high the water can't shed the heat fast enough and the air exit temp will be different than the water temp? Would this be a positive feedback loop and keep heating up, or it would equalize at a higher temp?

It will equalize in a state where water out temp is greater than air out temp.
Quote:
So the 6.6 degrees can be reduced by increasing the cfm, but from the statement above you mentioned too high airflow can cause a system that 'won't equalize'. Is that if the calculations go below 0 (zero)?

No, these calculations won't tell you if your system won't equalize.
Quote:
Even though the GPU delta is lower isn't it really the same thing, why is it more interesting?

If it's a CPU, one extra degree of delta might mean 40 C above ambient vs. 39 C above ambient. Not a big deal. If it's a GPU, it might be 14 C vs 15 C, bigger difference percentage wise.
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OK, I see my errors. Thanks for clarifying.

j
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