Pull air in or push it out

[Brian Stirling]

Anyway, getting ready to order parts for a new build and will be using water cooling for the first time. Case is a Thermaltake V71, MB is an Asus x99 Pro/USB3.1, CPU is an i7-5820K, and CPU cooler will be a Corsair H100i GTX.

I intend to mount the radiator at the top of the case while leaving the factory 200mm fan above it. I believe that fan is setup to blow into the case though I guess you could flop it 180 to have it suck, but since there are filters for this fan I guess it makes more sense to have that fan blow into the case and have the 2x120mm fans on the H100i suck into the case. Seems reasonable to me, however...

At the front of the case are 2x200mm fans which I believe are also setup to blow into the case as they are also behind a filter. The only other stock fan is a 140mm exhaust fan at the back setup to suck air out of the case. I plan to use that spot for a GPU cooler radiator for the EVGA GTX 980 Ti Hydro so with that being the case the fan arrangement would be: front (2x200mm blowing into the case), top (1x200mm and 2x120mm blowing into the case) and rear (?).

Do I set the GPU fan to pull air in and if so then all the fans will be driving air into the case and none pushing air out -- that doesn't seem right to me.

What I think I should do is configure the GPU radiator fan to exhaust from the case and maybe add another fan at the bottom that's also exhausting. I know the basic idea is to keep the case a bit positive in pressure and since the case isn't exactly hermetically sealed the air blowing in will find a way out, but ...

Logically, from a heat flow standpoint, you would want to bring air in at the bottom and exhaust at the top to take advantage of convection and the chimney effect. So, if I setup the top fans to exhaust and also have the GPU fan exhaust the remaining heat sources in the case would not be producing very much heat so the actual case temps would be lower than pulling in through the radiators. The 2x200mm fans in the front and possibly adding a 120mm fan at the bottom also pulling air into the case the net result would be net positive pressure with lower case temps.

One other advantage to this arrangement is that the Samsung 950 Pro PCIe SSD mounted at the bottom right corner of the MB would have that additional 120mm fan blowing right on it and the 950 is known to get pretty hot when being stressed.


Brian

 

[Stuka87]

Quite the loaded topic title there

It really all comes down to case design, and some experimentation. In my case I have intake fans on the sides of the case, and then the front and back are exhausts. This proved to give me the lowest internal temperatures. It was originally setup with the front fans as intakes, but I found the case had hot spots and resulted in my SSD getting very hot.

The whole positive vs negative case pressure argument kind of goes back and forth.

For your GPU radiator, I would make it an intake. I don't like the idea of exhausting radiators, and I personally run mine as an intake. That way you have the coolest air possible cooling the radiator, thereby letting it keep its fan speed down.

So if you had your GPU and CPU sets as intakes, those big fans on the front as exhaust, I think you would find it keeps your CPU and GPU cooler, but still is enough to keep your case temps down.

 

[Nashemon]

I can think of no application where you'd want hot air from the radiator to be blown into the case. Definitely have the top fans sucking air out. In most cases, front and side (used with ducts for spot cooling) fans should be inlets, while rear and top fans are outlets.

 

[MrTeal]

I would definitely exhaust out the top, but honestly I would probably just remove the one 200mm fan at the top, and mount the H100i GTX there exhausting air. The added benefit of that is you can mount the fans for the H100i up above where the 200mm used to be, and that will raise the radiator up another inch and give you more room around the motherboard.

 

[moonbogg]

I have that case and I water cool in it. Those huge top fans BLOW out the top. Those are exhaust fans and come that way from the factory. The bigass fans in front SUCK into the case. Those are intake fans and come that way from the factory.
You can leave all of those huge fans alone just where they are and mount your radiators without issue. Configure your GPU radiator in the front of the case as an intake and the CPU radiator up top as an exhaust. I have things set up like this and it works so nice it makes me vomit with excitement every time I turn on my rig.

 

[MrTeal]

I have that case and I water cool in it. Those huge top fans BLOW out the top. Those are exhaust fans and come that way from the factory. The bigass fans in front SUCK into the case. Those are intake fans and come that way from the factory.
You can leave all of those huge fans alone just where they are and mount your radiators without issue. Configure your GPU radiator in the front of the case as an intake and the CPU radiator up top as an exhaust. I have things set up like this and it works so nice it makes me vomit with excitement every time I turn on my rig.

Out of curiosity, what does that look like? The case fan won't help draw much air through the radiator, though it would still provide some extra case airflow. What kind of height in the chamber above the case is there, and would there be enough for the rad and fans?

 

[moonbogg]

Out of curiosity, what does that look like? The case fan won't help draw much air through the radiator, though it would still provide some extra case airflow. What kind of height in the chamber above the case is there, and would there be enough for the rad and fans?

The stock fans are installed in a sort of chamber like you mentioned, both in the front and on top. I left them right where they were. I installed the radiators on the inside of the case. I honestly don't think the stock case fans are doing much of anything to help or hurt cooling performance. Although the ones up top may help to shove the hot air out of that top chamber, but the radiator fans are moving plenty of air on their own and the air in the case is constantly being exchanged with new air from outside since 3 rad fans are intake and 3 are exhaust. Removing the stock fans won't give you any more room since the rads won't really fit in those chambers anyway. Plus, the stock fans have blue lights and they look cool, but they also add noise to the system, so they could be taken out for that reason and nothing bad would happen to performance.

 

[MrTeal]

Nice, thanks.
How thick is your rad? I know the GTX is a little different than the old H100i, but I just measured one with a caliper and the fan and rad were a hair under 53mm. A V71 review said there was just under 7cm in there, so with the really slim rad in these AIO coolers I think you might actually be able to tuck the whole thing up there. It would give a really slick and open look.

@OP, what are you doing for cooling the GPU? Unless I'm mistaken, the 980 Ti Hydro is a waterblock on the card. You need to provide the rad/pump/etc. Or did you mean the Hybrid?

 

[moonbogg]

Nice, thanks.
How thick is your rad? I know the GTX is a little different than the old H100i, but I just measured one with a caliper and the fan and rad were a hair under 53mm. A V71 review said there was just under 7cm in there, so with the really slim rad in these AIO coolers I think you might actually be able to tuck the whole thing up there. It would give a really slick and open look.

@OP, what are you doing for cooling the GPU? Unless I'm mistaken, the 980 Ti Hydro is a waterblock on the card. You need to provide the rad/pump/etc. Or did you mean the Hybrid?

My rads are 60mm thick plus the fans, so like 85mm total or something. You may be right about the typical AIO rads being thin enough to fit in those spaces. That would be nice if they fit in there.

 

[Stuka87]

I can think of no application where you'd want hot air from the radiator to be blown into the case. Definitely have the top fans sucking air out. In most cases, front and side (used with ducts for spot cooling) fans should be inlets, while rear and top fans are outlets.

There are plenty of situations where having a radiator be an intake is preferred. If you have enough exhaust fans to prevent the internal case temps from rising, it is a better setup. With them as exhaust, you are cooling them with higher than ambient case temps. With them as intake, you are cooling them with external ambient temps.

I know in my case, my CPU temps are ~5C lower with it as an intake in comparison to it being an exhaust.

 

[moonbogg]

If you wanted to see what it looks like inside those compartments, here you go. You can see the fan controller hub would get in the way of the length of a 360 rad up top, but you might be able to squeeze a 240 up there if its thin.

 

[Brian Stirling]

Well I think I'm going to start with the system configured with the 2 front 200mm fans blowing into the case, the top 200mm and the 2 120mm H100i GTX fans exhausting from the case at the top with the 140mm back fan replaced with the radiator for the GeForce GTZ 980 Ti Hydro also exhausting from the case.

Yes, I will be putting warmer case air through both radiators, but since very little of the heat from the CPU and GPU will stay in the case the case temps will tend to be only a little above ambient. The single 200mm and two 120mm H100i fans as well as the single 120mm 980 Ti Hydro radiator fan set to exhaust should pretty effectivle scavenge the case while the two 200mm front fans and a 120mm bottom fan blowing in should keep the case filled with cooler outside air.

Again, I'll start like this and maybe switch things around to see how it goes. But, I don't plan to push the OCing and the system isn't loaded with multiple GPU's so total heat generation should be a lot less than those running higher clocks and 2 or more GPU's. The 5820 should reliably go to 4.4GHz so if I keep the clock at a more modest 4.1GHz-4.2GHz and don't push the memory or GPU heat shouldn't be a problem.

Yeah, if I were using air/fan cooling of the CPU and GPU then OCing might cause some heat issues, but with water cooling of both CPU and GPU I don't think so...

I ordered the kit today and should have all but the 5.25 USB 3.0/flash reader interface by next Tuesday so I expect to begin building either Tuesday or Wednesday. I'll take pictures and maybe some video and post.


Brian

 

[Brian Stirling]

Quite the loaded topic title there

It really all comes down to case design, and some experimentation. In my case I have intake fans on the sides of the case, and then the front and back are exhausts. This proved to give me the lowest internal temperatures. It was originally setup with the front fans as intakes, but I found the case had hot spots and resulted in my SSD getting very hot.

The whole positive vs negative case pressure argument kind of goes back and forth.

For your GPU radiator, I would make it an intake. I don't like the idea of exhausting radiators, and I personally run mine as an intake. That way you have the coolest air possible cooling the radiator, thereby letting it keep its fan speed down.

So if you had your GPU and CPU sets as intakes, those big fans on the front as exhaust, I think you would find it keeps your CPU and GPU cooler, but still is enough to keep your case temps down.

Yes, the thread title is a little suggestive but technically accurate so...

I can see the logic behind drawing cooler air through the radiators and if temps become a problem I will rearrange to make them draw in outside air, but since the two main heat sources, the CPU and GPU, have almost all the heat removed from the case before it can heat the case up the case should remain much cooler so the air being exhausted through the radiators should be quite close to the temp of the outside air making the cooling effect of the radiators just about the same.

Also, by arranging to have the top fans exhaust and the bottom and front fans blow in the system benefits from the chimney effect increasing airflow by convection alone.

But, I can easily monitor the case temps and outside air temps and adjust accordingly.


Brian

 

[john3850]

I have always used internal radiators with both a push and pull setup since 2000.
With a push and pull I could reduce the noise better.
I have used the above with 120,240 and 360 lenght radiators the average gain with both push and pull on was always less then 5c with 90 to 120 cfm fans.
Now with just one fan the push always gave a increase of 3c over the pull.
Now do to cat hair build up I removed the 3 bottom fans for easier cleaning.

 

[Techhog]

... Phrasing.

You seem to know the terms "intake" and "exhaust," so I don't know why you chose those... other words.

 

[smitbret]

Forgive me, but this is the only thing that I keep thinking of when I read that title:
https://www.youtube.com/watch?v=O7aeWQCF1jM

Watch the whole clip or just go to 4:23

 

[Brian Stirling]

... Phrasing.

You seem to know the terms "intake" and "exhaust," so I don't know why you chose those... other words.

Yes, yes, intake and exhaust work just fine but what's wrong with suck and blow? What problem do you have with suck and blow. There's nothing wrong with suck and blow -- ya know!


Brian

 

[smitbret]

.......... What problem do you have with suck and blow. There's nothing wrong with suck and blow -- ya know!


Brian

Maybe there should be a poll and then moved to L&R.

 

[Bearmann]

From my research, here are a few things to consider:

1) It may seem logical to exhaust at the top since heat rises, but in a case with significant airflow, convection doesn't play a significant role.

2) Having two rows of fans on a radiator in puch & pull results in the lowest noise (since you can decrease the fan speeds) and lower temps, but with one row of fans either push or pull are equal within measurement error provided the pull fan has a good seal without leaks against the side of the radiator.

3) By placing your radiator fans in a pull configuration, the dust accumulates on the intake side of the radiator surface and is easily removed if there is not a screen blocking access to the radiator. When you fans are in a push configuration, most of the dust accumulates between the fan and the radiator and the fans must be removed for cleaning out the dust.

https://www.youtube.com/watch?v=UyC3lZ5WFMk

 

[Brian Stirling]

Maybe there should be a poll and then moved to L&R.

Well it seems as though the thread title has been changed on me and I have to say that's a bit of an over reaction but...


Brian

 

[Brian Stirling]

From my research, here are a few things to consider:

1) It may seem logical to exhaust at the top since heat rises, but in a case with significant airflow, convection doesn't play a significant role.

2) Having two rows of fans on a radiator in puch & pull results in the lowest noise (since you can decrease the fan speeds) and lower temps, but with one row of fans either push or pull are equal within measurement error provided the pull fan has a good seal without leaks against the side of the radiator.

3) By placing your radiator fans in a pull configuration, the dust accumulates on the intake side of the radiator surface and is easily removed if there is not a screen blocking access to the radiator. When you fans are in a push configuration, most of the dust accumulates between the fan and the radiator and the fans must be removed for cleaning out the dust.

https://www.youtube.com/watch?v=UyC3lZ5WFMk

Sure, turbulence will reduce convection but a temp differential resulting in a density difference will still result in a tendency for the air in the case to rise.

The push-pull arrangement is no doubt the best for cooling and when taxing the system the push-pull arrangement will tend to be quieter. My thought is that having the CPU radiator mounted to the underside of the top of the case with the two 120mm SP fans pushing and then having two 200mm fans pulling above the radiator will result in pretty much a push-pull arrangement even though the 200mm fans are not SP fans.

With a single set of SP fans on the radiator the total flow might be, say, 80cfm but adding a second set will not double the flow no matter what the arrangement is -- at best you're probably looking at 65% more than one set of fans and probably closer to 50% more. The pull arrangement using two 200mm fans may not be quite as good as four 120mm SP fans but not likely to be much less either.


Brian

 

[MrTeal]

Sure, turbulence will reduce convection but a temp differential resulting in a density difference will still result in a tendency for the air in the case to rise.

The push-pull arrangement is no doubt the best for cooling and when taxing the system the push-pull arrangement will tend to be quieter. My thought is that having the CPU radiator mounted to the underside of the top of the case with the two 120mm SP fans pushing and then having two 200mm fans pulling above the radiator will result in pretty much a push-pull arrangement even though the 200mm fans are not SP fans.

With a single set of SP fans on the radiator the total flow might be, say, 80cfm but adding a second set will not double the flow no matter what the arrangement is -- at best you're probably looking at 65% more than one set of fans and probably closer to 50% more. The pull arrangement using two 200mm fans may not be quite as good as four 120mm SP fans but not likely to be much less either.


Brian

It's not really a temperature differential, it's a density differential. The airflow velocity of convection you'd see in a case is tiny. Even extremely slow case fans will completely swamp the effects of convection. You could take your down and front to up and back airflow case and rotate it 180 so the airflow was flowing down, and it would have almost no effect on cooling.

The problem with doing push pull on the top using 2x200mm on the top is that due to the high restriction on a radiator, you need a pretty good seal between the rad and fan to pull air through it even with 120mm fans on a 240mm rad. If you place two 200mm fans on the top of the rad without any ducting, they'll have very little to no effect as they'll just pull air from the large low restriction area around that radiator rather than pull air through the rad itself.

 

[Brian Stirling]

It's not really a temperature differential, it's a density differential. The airflow velocity of convection you'd see in a case is tiny. Even extremely slow case fans will completely swamp the effects of convection. You could take your down and front to up and back airflow case and rotate it 180 so the airflow was flowing down, and it would have almost no effect on cooling.

The problem with doing push pull on the top using 2x200mm on the top is that due to the high restriction on a radiator, you need a pretty good seal between the rad and fan to pull air through it even with 120mm fans on a 240mm rad. If you place two 200mm fans on the top of the rad without any ducting, they'll have very little to no effect as they'll just pull air from the large low restriction area around that radiator rather than pull air through the rad itself.

Yeah that's probably true, but a little foil tape to seal things and the 200mm fans are now dedicated to pulling through the radiator. Again, I wouldn't expect AF fans, even 200mm AF fans, to be as efficient at the pull job (aren't you glad I didn't say suck job) as 120mm SP fans are but I doubt there will be much difference. And again, my aim is not to push OCing to the extreme and with only one GPU card my total heat burden will be no where near what an extreme OCer with SLI/Crossfire GPU's are.


Brian

 

[MrTeal]

Yeah that's probably true, but a little foil tape to seal things and the 200mm fans are now dedicated to pulling through the radiator. Again, I wouldn't expect AF fans, even 200mm AF fans, to be as efficient at the pull job (aren't you glad I didn't say suck job) as 120mm SP fans are but I doubt there will be much difference. And again, my aim is not to push OCing to the extreme and with only one GPU card my total heat burden will be no where near what an extreme OCer with SLI/Crossfire GPU's are.


Brian

A 200mm fan airflow optimized fan will still have more static pressure ability than a 120mm fan that's tailored to SP at similar RPMs. You still have a pressure-airflow curve, and even though it might be weighted a little differently, the whole curve on the 200mm fan with 2.5x the surface area will be so much higher. If you do make some mods to duct it so all the air into the 200mm fans comes through the rad, you'll probably be pretty happy with the results.

 

[Brian Stirling]

A 200mm fan airflow optimized fan will still have more static pressure ability than a 120mm fan that's tailored to SP at similar RPMs. You still have a pressure-airflow curve, and even though it might be weighted a little differently, the whole curve on the 200mm fan with 2.5x the surface area will be so much higher. If you do make some mods to duct it so all the air into the 200mm fans comes through the rad, you'll probably be pretty happy with the results.

That's good to know and the only mod I'd need to do as best I can tell is use a little foil backed tape to cover any holes or cracks. I might also use some double sided tape between the 20mm fans and case and the radiator and case. Not the double side tape with foam but the really thin stuff. The tape would serve as a kind of gasket to provide a 100% airtight seal.


Brian