Odd airflow options: reversed airflow? No exhausts?

[stratuh]

I have four 140mm fans, all identical. Same RPM, dB/A levels, CFM, etc. My case allows for front 2x140 and top 2x140. I have a radiator for GPU on the front but nothing on the top. It's there because it doesn't clear the RAM if mounted on top.

 

Having front intake means hot air comes into my case and my CPU is warmer but my GPU is really nicely cooled. This means I need top exhaust. Or do I? Could I have top intake and front exhaust? What about no exhausts and just 2x140 top intake and 2x140 front intake? This would cool my CPU with fresh (cool) air and cool my GPU, too. FWIW, my CPU cooler is a "push down" cooler, not a tower going front-to-back.

 

What fan configuration would maximize cooling?

[stratuh]

5 minutes ago, PrinceNorris said:

How.

 

I would suggest two intake and two exhaust. I don't know how your situation looks with the GPU fan because without pictures it's hard to deduce.

If you don't want to make pictures, draw a scheme in Paint if you can.

 

Right now I'm using 2x140mm intake (front) and 1x120mm exhaust (back). I'm removing the rear 120 and adding top 2x140. The front radiator is attached to the GPU.

 

When air intakes into my case, it goes through the radiator for GPU, so air coming into the case is warmer. The GPU is nice and cool (only 45c under loads) but my CPU is fairly warm.

 

Something like 2x140 front intake would cool GPU well, and 2x140 top intake would ensure cool air gets to the CPU. I lose the exhaust, though. Alternatively, 2x140 top intake and 2x140 front exhaust reverses the airflow, ensuring cool air goes to CPU first and foremost and warmer air goes through the radiator.

 

Summary:

 

Front Intake + Top Intake = cool GPU, cool CPU, no exhaust

Front Intake + Top Exhaust = cool GPU, warm CPU

Front Exhaust + Top Intake = warm GPU, cool CPU

 

I don't really want 4x140 and 1x120 in my case, it's too many fans I think. I'm still waiting for the fans to come in the mail tomorrow to try it all out, though.

[stratuh]

2 hours ago, PrinceNorris said:

@stratuh That's a beefy CPU cooler you have here. You can measure if it's possible to squeeze the GPU radiator above the CPU one to act as exhaust. Everything is very tight fitted.

The only thing reasonable for me would be to mount two intake fans on front, GPU cooler on top as exhaust and leave that little fan behind in it's place.

 

And just in case, are you sure that it's the GPU cooler heat making CPU warm? It looks like the CPU fan has barely enough space to breath when case is fully closed.

It absolutely does not fit on the top. I originally tried a 240 radiator and it was a RAM clearance issue, and the 280 radiator is a RAM and VRM clearance issue. Short of getting new RAM + new motherboard or a new case, it won't fit. CPU cooler isn't the issue for radiator clearance.

 

It's been an incremental build and the GPU cooler is relatively new. Here's some CPU temp histories:

 

- with an NH-L9x65 + GPU air cooler (no radiator) = 59c load

- with an NH-L12S + GPU air cooler (no radiator) = 55c load

- with an NH-L12S + GPU watercooler (radiator in front) = 65c load

- with an NH-C14S + GPU watercooler (radiator in front) = 57c load

 

With all else being equal, the radiator in the front adds 10+c to the CPU. These figures are doing a concurrent CPU+GPU Aida64 stress test for 1hr.

 

When I get the two extra 140mm fans, I'll give it a try with them as top exhaust and then with top intake, doing benchmarks each time. I guess my only real option is to try it myself, I only made the thread to get an idea ahead of time.

[Bearmann]

This will be interesting to see the final result. Please report back. The front radiator doesn't add that much additional heat, probably only a few degrees above the outside temp. The problem, I think, is that it reduces the air pressure so much by the time it goes through the radiator that there is very little air flow getting to the rear of the case. From what I remember, it's more important to remove hot air from the case than it is to bring in cool air, though obviously both are important. I don't see how putting an intake fan on the top rear of the case will help cool the CPU heatsink. It's already got a strong fan on it, and the top fan at a 90 degree angle to it, though its not directly opposed to it, is not augmenting the CPU fan. The most important fans which cool the CPU are the ones in closest proximity to it. Imagine a fan 1 foot from you versus one 10 feet away. I think it will be best to help remove the hot air from the CPU heatsink area. I think your best 4 fan configuration will be the two intake radiator fans, a 120/140 rear output fan and a top rear 140 output fan.

[stratuh]

32 minutes ago, Bearmann said:

This will be interesting to see the final result. Please report back. The front radiator doesn't add that much additional heat, probably only a few degrees above the outside temp. The problem, I think, is that it reduces the air pressure so much by the time it goes through the radiator that there is very little air flow getting to the rear of the case. From what I remember, it's more important to remove hot air from the case than it is to bring in cool air, though obviously both are important. I don't see how putting an intake fan on the top rear of the case will help cool the CPU heatsink. It's already got a strong fan on it, and the top fan at a 90 degree angle to it, though its not directly opposed to it, is not augmenting the CPU fan. The most important fans which cool the CPU are the ones in closest proximity to it. Imagine a fan 1 foot from you versus one 10 feet away. I think it will be best to help remove the hot air from the CPU heatsink area. I think your best 4 fan configuration will be the two intake radiator fans, a 120/140 rear output fan and a top rear 140 output fan.

It's something I was reading last night, actually, that the effective airflow is reduced when a radiator obstructs. I might not even have positive pressure since it's hard to tell the impact a radiator has.

 

I don't think I'm going to try front exhaust but I will try the below configs and report back:

 

- front 2x140 intake + top 2x140 intake

- front 2x140 intake + top 2x140 intake + back 1x120 exhaust

- front 2x140 intake + top 2x140 exhaust

 

And compare to my existing setup of:

 

- front 2x140 intake + back 1x120 exhaust

 

Many benchmarks for the NH-C14S show around 55-60c on overclocked CPUs. I'm in this window at stock 3.4ghz. I know the radiator is to "blame", either by warming intake air or obstructing intake airflow. Top intakes in addition would solve either or both, I just don't know by how much.

 

I'll report back for sure.

[Bearmann]

You already have 3 of the fans oriented correctly to give my method a try. All you have to do is put on one 140mm fan on the top rear in an exhaust configuration and measure. Cool air will be pulled in from the perforated grill areas on the top front and rear bottom. I'm not sure , however, that you might achieve a superior result from putting the fans in these same positions, but reversing the air flow of all the fans so that the case air flows from the top rear to out the front. This surrounds the CPU heatsink with cool air, but would raise the GPU temp. This is an old article which was before water cooling became popular. It helps you think about things however. Your top down cooler may change the results, but excluding using a side fan, the best 2 fan configuration for the CPU was 2 exhaust fans in the top and rear corner. The same result for 4 fans when two of the four were front intake.

 

https://www.bit-tech.net/reviews/tech/the-big-cooling-investigation/1/

[stratuh]

50 minutes ago, Bearmann said:

You already have 3 of the fans oriented correctly to give my method a try. All you have to do is put on one 140mm fan on the top rear in an exhaust configuration and measure. Cool air will be pulled in from the perforated grill areas on the top front and rear bottom. I'm not sure , however, that you might achieve a superior result from putting the fans in these same positions, but reversing the air flow of all the fans so that the case air flows from the top rear to out the front. This surrounds the CPU heatsink with cool air, but may raise the GPU temp a bit. This is an old article which was before water cooling became popular. It helps you think about things however. Your top down cooler may change the results, but excluding using a side fan, the best 2 fan configuration for the CPU was 2 exhaust fans in the top and rear corner. The same result for 4 fans when two of the four were front intake.

 

https://www.bit-tech.net/reviews/tech/the-big-cooling-investigation/1/

I just wonder if it's an exhaust issue that can be solved with an added exhaust top-back or an intake issue which can be solved with top intakes. In any case I'll try any variations.

[Bearmann]

It's both, but by adding the additional exhaust fan on the top rear, You'll get more fresh air being pulled in through the perforated holes in the case. If I remember correctly from the article, adding a top fan near the front of the case was detrimental to cooling regardless of whether it was intake or output. Of course, they did not use a downdraft cooler, so your results may be different than theirs. Let the experimentation begin!

[stratuh]

Yep, it doesn't hurt to give any possibility a try. The new 140mm fans are the same model as my intakes, but have 120mm mounting positions. There's a chance I could fit one as back exhaust. Front 2x140mm intake, 1x140mm back exhaust, 1x140mm top-back exhaust might be an option, too.

 

I'll say I'd like to remain with positive pressure, though. The scenario you describe of extra air coming into the case via perforated holes is a bad thing, as intake isn't through a dust filter. Ideally I want to avoid dust buildup.

[Bearmann]

Your case will be difficult to achieve positive pressure because the front radiator reduces the intake pressure so much. Actually, negative pressure is better for temps, but I understand about the dust. One method would be to get filters for the 2 fans (top and rear) in the rear corner and have all 4 fans as intake. I think you will take quite a hit on your temps if you do that though.

 

By keeping those rear corner exhaust fans on low settings, you'll have less airflow through the case and therefore less dust, but of course, your temps will be higher. Your present temps are fine though, but I realize that you are striving for perfection.

 

Does your case come with filters on the top? You could probably get some filters for the back panel, but this would impede the airflow a bit. Don't block the holes as I think they are a safety feature in case your fans fail to come on.

[Bearmann]

I don't know if you have seen this video:

I had some Dell computers at work, currently Optiplex 380's,  which have no GPU and only have one fan in the front and no filters. The fan is ducted to the CPU heatsink and the duct opens up in the back to pass air over the motherboard. It's amazing how clean the inside of the computers are. I think the conclusion is low airflow = less dust. You'll have to decide whether you want less dust or lower temps or a balance between the two.
 

[stratuh]

2 hours ago, Bearmann said:

I don't know if you have seen this video:

I had some Dell computers at work, currently Optiplex 380's,  which have no GPU and only have one fan in the front and no filters. The fan is ducted to the CPU heatsink and the duct opens up in the back to pass air over the motherboard. It's amazing how clean the inside of the computers are. I think the conclusion is low airflow = less dust. You'll have to decide whether you want less dust or lower temps or a balance between the two.
 

I'm just doing the testing now. So far default config is done and added two top intakes is almost done. So far the results are interesting. I'll likely make a new thread about it but I'll let you know.

[Bearmann]

11 minutes ago, stratuh said:

I'm just doing the testing now. So far default config is done and added two top intakes is almost done. So far the results are interesting. I'll likely make a new thread about it but I'll let you know.

Excellent! I didn't realize that you had new fans already.

[stratuh]

1 hour ago, Bearmann said:

Excellent! I didn't realize that you had new fans already.

Actually, I'll just post it here since the results aren't so interesting after all.

 

Here's what I've tested:

 

- Front 2x140 Intake, Rear 1x120 Exhaust

- Front 2x140 Intake, Rear 1x120 Exhaust, Top 1x140 Exhaust

- Front 2x140 Intake, Top 2x140 Intake

- Front 2x140 Intake, Top 2x140 Intake, Rear 1x120 Exhaust

- Front 2x140 Intake, Top 2x140 Exhaust

 

All 140mm fans are the same: NF-P14s 1500rpm. The 120mm fan is an NF-P12 1700rpm. I let BIOS control the fan curves setting them to their default setting.

 

I did Aida64 stressing both GPU and CPU for 20 minutes, averaging the final minute of each test to give these results:

 

 

The results are pretty consistent among the top four with the bottom one being the default (old) configuration. All of those four results are within the margin of error and I can deduce from this I don't have an exhaust issue but I could use additional intake.

 

Configurations with extra 2x140mm intake give me a good decrease in CPU temp, but only 3-4 degrees or so. As a consequence of this, since my fans are controlled via CPU temp, the fans in front of the radiator are slightly slower giving higher GPU temperatures. I don't think the added noise is worth it.

 

I've made an "Avg" to see the relative cooling of a given configuration. Lower avg = better cooling. Any additional fan, intake or exhaust, is better than my current default configuration, but not by much. Like a degree maximum. Again, not worth the noise.

 

My conclusion is the default configuration (bottom in graph) is ideal as it minimizes the number of fans while being 1-1.5c warmer than the alternatives. Something interesting, however, is the best thermals were found with zero exhausts. Or at least it was tied with 4 intake, 1 exhaust.

[Bitter]

I skimmed, I apologize if this was covered already.

 

I am a big proponent of 'if it works it's not stupid' so here's my take. Use the rear fan as an intake and use a top fan above the CPU cooler to also blow cooler air at the CPU, now add a third fan next to the one above the CPU cooler but DUCT it's air right to the radiator, flip the radiator fans to pull air out of the case. You'll get cool air to the GPU cooler, you'll get cool air to the CPU cooler, you'll get cool air blowing over the rest of the motherboard and RAM. Win, win, win. OEM's used ducted airflow to great effect to make sure air goes where it's most needed first and it works very very well. You do have the issue of an extra fan's worth of airflow but the case is highly vented so any extra air just goes out. The downside is you'll likely accumulate some dust in there, maintenance is unavoidable with higher performance systems needing a lot of airflow.

[stratuh]

25 minutes ago, Bitter said:

I skimmed, I apologize if this was covered already.

 

I am a big proponent of 'if it works it's not stupid' so here's my take. Use the rear fan as an intake and use a top fan above the CPU cooler to also blow cooler air at the CPU, now add a third fan next to the one above the CPU cooler but DUCT it's air right to the radiator, flip the radiator fans to pull air out of the case. You'll get cool air to the GPU cooler, you'll get cool air to the CPU cooler, you'll get cool air blowing over the rest of the motherboard and RAM. Win, win, win. OEM's used ducted airflow to great effect to make sure air goes where it's most needed first and it works very very well. You do have the issue of an extra fan's worth of airflow but the case is highly vented so any extra air just goes out. The downside is you'll likely accumulate some dust in there, maintenance is unavoidable with higher performance systems needing a lot of airflow.

Honestly at this point, it's "good enough" enough to not be worth it. 57c CPU temp and 41c GPU temp is really good already, I just figured I could squeeze a little more out of it. It's gonna take me some time to flip radiator fans around because it's such a tight fit.

[Bitter]

10 minutes ago, stratuh said:

Honestly at this point, it's "good enough" enough to not be worth it. 57c CPU temp and 41c GPU temp is really good already, I just figured I could squeeze a little more out of it. It's gonna take me some time to flip radiator fans around because it's such a tight fit.

I completely understand, another couple C lower won't make any difference if you're already at your peak overclock. The only benefit may be from more airflow over the VRM on the motherboard, and I just realized I neglected the GPU VRM. You may want to mount a fan to blow some air at the GPU VRM unless they're part of the cold plate coverage.

 

Noise is part of why I dislike open meshy cases, also it can be harder to control airflow through the case. I have CM Elite 130 as my HTPC and I've blocked off parts of the case venting to force air being sucked in to flow over areas it's needed. The front fan is the exhaust fan, the vented portion next to the motherboard is only open at the bottom inch so air flowing inward to the case pours over the board and RAM, the rear venting above the IO is open to allow air in there over to the top of the CPU cooler, and the side with the GPU is open to allow cool air to flow in over that card as well. A single fan, through careful use of airflow, is cooling all needed components in the system. With a locked CPU I've undervolted it to achieve a 40W TDP under prime95 which gets me a 70C temp on the stock cooler without it ever kicking up to full fan speed, running full out the system is barely audible over the ambient noise in the house. Helps that the GPU is only a GTX960 with ACX cooling so passively cools until loaded enough, even then the fans don't make a ton of noise.

[stratuh]

11 minutes ago, Bitter said:

I completely understand, another couple C lower won't make any difference if you're already at your peak overclock. The only benefit may be from more airflow over the VRM on the motherboard, and I just realized I neglected the GPU VRM. You may want to mount a fan to blow some air at the GPU VRM unless they're part of the cold plate coverage.

 

Noise is part of why I dislike open meshy cases, also it can be harder to control airflow through the case. I have CM Elite 130 as my HTPC and I've blocked off parts of the case venting to force air being sucked in to flow over areas it's needed. The front fan is the exhaust fan, the vented portion next to the motherboard is only open at the bottom inch so air flowing inward to the case pours over the board and RAM, the rear venting above the IO is open to allow air in there, and the side with the GPU is open to allow cool air to flow in over that card as well. A single fan, through careful use of airflow, is cooling all needed components in the system. With a locked CPU I've undervolted it to achieve a 40W TDP under prime95 which gets me a 70C temp on the stock cooler without it ever kicking up to full fan speed, running full out the system is barely audible over the ambient noise in the house.

The NZXT G12 is actually really good with VRM cooling. It came with an NZXT fan I quickly threw aside for a 92mm Noctua fan. While I haven't monitored VRM temps myself (not even sure if you can with Gigabyte GPUs), but I've seen some benchmarks with EVGA GPUs which allow this and it actually cools better than stock coolers. No heatsinks, no heat "paper" things, just direct air. I went from 75-78c under load to low 40s for the GPU, I really stand behind the G12, it's amazing.

 

Noise is not a super big concern. It seems my CPU fan (likewise an NF-P14s), even cranked to 100%, is pretty quiet. The exhaust can be a bit loud but I keep it low via curving. The intake fans are where I hear the most noise. Even at their lowest of 20%, they're audible, and I can get them to 40% before it really becomes audible. With careful curving I can eliminate this, though.

 

Honestly, this whole experiment today was to see if I could overclock better. My temps are at stock on the R5 2600 3.4ghz and GPU clocks. I have loads of GPU headroom but not much CPU headroom, hence my search for better cooling. Ideally I want my GPU under 50c and CPU under 60c at all times, something I don't think is possible. I might have just hit a temperature minima for my system. I even tried a Kraken x52 (with radiator on top with thin fans) and it's actually warmer than my current air cooler (57c air vs 63c water).

 

I think the only change I'll be making to my system is changing the rear 120mm exhaust. I reread the model today and it's a static pressure optimized fan. An airflow optimized fan would be better.

[Bitter]

Fans right up against things make's them noisier due to turbulent air. Put your hand over a fan or a fan up against a stamped steel fan guard and they're so much louder. Sounds opposite from reality but you could probably up your radiator fan speeds AND maintain the same or less noise by using a spacer like this https://www.amazon.com/Phobya-Shroud-Plexi-Acrylic-120mm/dp/B004CLFFIA to space the fan away and allow the blades to do their thing without chopping air right up against the fins of the radiator. Ditto for ditching the stamped steel fan guards built into the rear case fan area, just use a standard fan guard or don't use one at all. You can make your own spacer from a dead case fan, just gut out the center section and use the outside frame. You'll need longer screws or mount the spacer with two diagonally and then the fan to the spacer with two diagonally.

[stratuh]

44 minutes ago, Bitter said:

Fans right up against things make's them noisier due to turbulent air. Put your hand over a fan or a fan up against a stamped steel fan guard and they're so much louder. Sounds opposite from reality but you could probably up your radiator fan speeds AND maintain the same or less noise by using a spacer like this https://www.amazon.com/Phobya-Shroud-Plexi-Acrylic-120mm/dp/B004CLFFIA to space the fan away and allow the blades to do their thing without chopping air right up against the fins of the radiator. Ditto for ditching the stamped steel fan guards built into the rear case fan area, just use a standard fan guard or don't use one at all. You can make your own spacer from a dead case fan, just gut out the center section and use the outside frame. You'll need longer screws or mount the spacer with two diagonally and then the fan to the spacer with two diagonally.

Interesting, I'll take a look at some other spacers, see what I can find. I know I don't have 2cm clearance but if I can find something 1cm or so, it could work.

[Bearmann]

Beautiful graph! When you used the rear and top rear exhaust fans did you have a nonworking fan at the top front, or was this area open for air flow? I'm wondering if all the fans should be at the same speed instead in introducing the variable of having the CPU temp control them? With the results so close, it may affect the order a bit but unlikely to reveal one winner way out in front of the others. I was partial to your original 3 fan configuration too! Less noise and less dust. Bitter looks like a true modder and has some interesting ideas. Congratulations on the testing!

[Bitter]

4 minutes ago, Bearmann said:

Bitter looks like a true modder and has some interesting ideas.

I've been out of the game for a long time, but way back when I was there wasn't alot to go on so you just experimented and did what worked best for you, as unconventional as it might have been. I had rear fans blowing inward with a bit of metal roof flashing to blow air over the motherboard on an overclocked socket 478 P4, water cooling left the board unable to stay cool. Since then I've thrown aside the conventional wisdom and just done what gives ME the best results.

[Bearmann]

I looked back at the 4 fans test from the bit-tech link above. They stated:

 

Cooling with Four Fans

"Firstly we should say that the benefits of adding a fourth fan are less cut and dried. We did again see a general trend towards lower temperatures but the differences here were smaller - only in the region of 2-3^oC. This reduction also wasn’t applied uniformly across all the setups as it was when stepping up from one to two, or two to three fans - it was mainly the poorer setups that benefited most from adding a fourth fan.

What this means is that if you look at the graph below you’ll see far less variation than in the previous four graphs. Essentially if you’ve got four fans strapped to your case then there is going to be enough air whistling through it to offer decent cooling no matter how you position them. "

 

It looks like your testing agreed with theirs.

[stratuh]

55 minutes ago, Bearmann said:

I looked back at the 4 fans test from the bit-tech link above. They stated:

 

Cooling with Four Fans

"Firstly we should say that the benefits of adding a fourth fan are less cut and dried. We did again see a general trend towards lower temperatures but the differences here were smaller - only in the region of 2-3^oC. This reduction also wasn’t applied uniformly across all the setups as it was when stepping up from one to two, or two to three fans - it was mainly the poorer setups that benefited most from adding a fourth fan.

What this means is that if you look at the graph below you’ll see far less variation than in the previous four graphs. Essentially if you’ve got four fans strapped to your case then there is going to be enough air whistling through it to offer decent cooling no matter how you position them. "

 

It looks like your testing agreed with theirs.

Just for completion sake, I should try testing with two and one fan.

 

- Front-Top 1x140mm intake, Rear 1x120mm exhaust

- Front-Bottom 1x140mm intake, Rear 1x120mm exhaust

- Only Rear 1x120mm exhaust

- Only Front 2x140mm intake

[Bitter]

 

 

Check out which way the fans are moving air through the radiator, they're pushing the hot air out the front of the PC and the rear fan is an intake fan. I'm not the only crazy one!