Is this a bad fan setup?

[audiophizile13]

I find it strange that this is not done often and am here to see what, if anything would be wrong with this fan setup. 2x 140mm intakes, 140mm exhaust behind 140mm CPU cooler, 120mm exhaust mounted to the outside of the case under where the GPU mounts. It seems to me this would keep a steady stream of cool air over the GPU. Sorry for the crude phone drawing. Let me know if you see this being good or bad and why!

 

[JackNaylorPE]

Not seeing a drawing but from what i can understand ...

1. Two fans in front with intake filters ... if each fan pushes X cfm, you are probably looking at 1.33 X, with 1/3 reduction for air inlet filters.

2. I am assuming the one behind the air cooler means this fan is mounted on the rear of the case. So far 1.33 IN / 1.00 Out

3. This 120mm fan blowing in is going to suck in hot exhaust air from the PSU blow and GFX card above. To accomplish what you want to do, in many well designed cases there is w very nice but oft undocumented feature in that a 120 fan will mount on the back of the HD cages. I use this to blow air in between the cards on SLI builds.

If ya provide case model, may have some suggestions

 

[audiophizile13]

Not seeing a drawing but from what i can understand ...

1. Two fans in front with intake filters ... if each fan pushes X cfm, you are probably looking at 1.33 X, with 1/3 reduction for air inlet filters.

2. I am assuming the one behind the air cooler means this fan is mounted on the rear of the case. So far 1.33 IN / 1.00 Out

3. This 120mm fan blowing in is going to suck in hot exhaust air from the PSU blow and GFX card above. To accomplish what you want to do, in many well designed cases there is w very nice but oft undocumented feature in that a 120 fan will mount on the back of the HD cages. I use this to blow air in between the cards on SLI builds.

If ya provide case model, may have some suggestions

No HDD cage. The PSU intakes from the bottom of the case and exhausts out of the back.I made the image work. The bottom/middle of the case verticle red line would be a 120mm fan mounted to the back of the case exhausting air out. Typical 2 fan AIB gpu. The top red vertical line is obviously the typical exhaust fan. PSU makes no difference here. Thanks for the reply. Hopefully the pic makes things more clear. If not, let me know!

 

[JackNaylorPE]

OK so the picture shows exactly what I described....except when i read the 1st time, i remember the fan under the GFX card pushing in. If it's pushing air out, then you have this problem

2 fans in front minus 1/3 hit for air inlet filter restriction = 0.67 fans worth of air blowing in for each of the 2 fans
2 fan in rear blowing in with no inlet filters = 1.0 worth of fan cfm blowing air out for each of the two fans.

SO 0.67 in + 0.67 in - 1,00 out - 1,00 out = -0.67. You have negative case pressure. This means that the excess air being blown out will have to be balanced by air being sucked back in thru somewhere else and bringing more dust with it.

Also, the PSU fan **can** matter; if the case bottom doesn't have an inlet filter ? If not, the PSU fan is picking up dust, pushing it thru the PSU. Some stays, some gets puched out. What gets pushed out can wind up getting it back in because you have more case fans pushing air out then case fans pulling air in

Peeps often succumb to the notion that they need to have same air blowing in and blowing out... this is a misconception which ignores one of your cases most valuable cooling features ... the rear grille and the vented slot covers.

Kitchens get very hot and many have hoods which exhaust the hot air outside. Ever seen one that has a matching fan bringing cold air in ?

The fan creates negative pressure inside the room / building, Outside the air is higher pressure so the outside air pushes air into the kitchen, usually thru a vent or window, or if those are closed, under doors and every nook and cranny available. If you had no exhaust fans, all the air would still get out of the case... if it didn't only 2 things can happen ... a) the fans couldn't blow air in cause it had no way to get out or b) if the fans were strong enough, the case would explode.

Another example is if you have an attic fan how does that work ?

a) It takes the hot air from the highest point in your house and pushes it into the attic ... there's no other fan blowing air in

b) The attic fan blows the hot air into the attic, is no other fan blowing it out ?

So the orientation of a fan is generally determined by where the mount is: and water cooling different that air.

Water cooling, all rad fan are intakes, no exceptions.

Air Cooling
Front = In
Bottom = In
Side = in
Rear = Out
Top = It depends

if you have two fan mounts on top, if exhaust that would make 3 out ... so in order to account for the cfm loss from inlet filters, you want 1.5 times as much out... you'd need 4.5 out, say 5. If you have 2 front, 2 bottom and 1 side blowing in that works .... 5 x 2/3 = 3.33 out and 3 in... you have positive case pressure.

If they exhaust, you can remove the dust filter on top. If uses as inlets, leave them in

2 front and 2 top as intakes = 4 x 2/3 = 2.66 in and 1 out ... that means 1.33 worth of air will go out thru the rear panel grille.

It's always easier when ya name the case, but looking at the pic, it looks like an intake fan could be mounted on the bottom of the case. Assuming there's in inlet filter there, i think that would be ya best option.

 

[audiophizile13]

...

I really appreciate your in depth answer. So dust is the main concern having negative pressure? I have a fractal define r4. What if I just tune the fan speeds to make the front spin at higher rpm or rear at lower? Technically at the same RPM the 120 behind the gpu SHOULD move less air than the 140s in front and top exhaust maybe making the pressure at least slightly closer to even. I'm still not sure why more people dont mount a fan behind their gpu. It seems like you would want the hottest part of your pc to have an exhaust and like I said keep a steady flow over it. Do you think the placement would be ok with running the front fans at slightly higher speed or rear at slightly lower and test for negative pressure? I am trying to build a silent, efficient cooling rig. Again it seems exhausting the gpu would help this. I bought a thermalright true spirit 140 b/w as it is the coolest, definitely quietest cpu cooler I could find that can take a mild OC. I have a gelid 120(140 wont really fit) I was going to use for the gpu exhaust, the stock fractal silent series140 for the normal position/cpu exhaust and I purchased 2 fractal 140mm dynamic version 2 for the front intake. I kind of wish I wouldve gotten 2 of the thermalright 147a fans for the front. still can I guess. Thanks again!

 

[JackNaylorPE]

Dust is one of them .... I mean you **can** buy filters and mount them yaslef if ya wanna make an exhaust mount into an intake mount. On way to tell what the manufacturer intended is this... if it has an air filter, then it's an intake.

As for the air around the GPU thing think about what is happening here.... your GFX card fans are taking air from under you card and pushing it up over the heat sink

Look here, we do that test here using a fog machine when setting up case cooling. Skip to the 1 minute mark if you are impatient. As you can seem the general movement is to the back and up, though you can see a mistake there if ya paid attention ... 4 in / 4 out ... negative case pressure.

I blame the video director ! But if ya look at the case, the fact that they provide an intake filter tells ya that its designed for intake ... as it must be if you put a 360 or 420mm rad in there.
That case is really designed for water cooling and

https://www.youtube.com/watch?v=ly9ioBk2tSs

so 1 out and 5 (or 6 in)... that's just fine. Your out is the big giant grille on the back of the case.

I'm not sure, w/o a fog test if you are really really exhausting hot GPU air ... you may be stealing the intake air. Cool air coming in the front would normally get sucked right up thru the GPU and out the rear grille above it. Every case is a lil bit different but as you are ... what is happening is that hot PSU exhaust and hot GFX card exhaust thru the slots come sup an inch or so above the GFX card and negative pressure is sucking the hot air back inside the case.

The 140mm ones will be silent up to about 850 repm ... I mean dead silent, not just low noise. I have 15 of them in my case ... 6 on top rad / 4 on bottom rad (all intakes ofc) and 6 case fans (5 in 1 out). Sometimes i sit down in the morning and turn the PC on... but its already one, you just can't hear it. At low demand, I have the fans set to turn off of the fan curve says we don't need more than 350 rpm ... but even at 850, running stress tests , it's dead silent. Lotta fans at lower speeds.

The Thermalright Silver Arrow is in my son's rig ... for 6 years with a 4.8 Ghz OC on 2600k. It's silent.

You can see the top 22 or so fans in the chart here:

http://www.silentpcreview.com/article1345-page7.html

about half way down the page there's a chart

 

[audiophizile13]

You can see the top 22 or so fans in the chart here:

http://www.silentpcreview.com/article1345-page7.html

about half way down the page there's a chart

I used the fan reviews from 2016 here:
http://www.overclockers.com/15-case-fans-tested-ultimate-140-mm-roundup/

That's how I decided on the version 2 of the fractal fans in that article. I know the version 2 isn't reviewed there but I'm hoping they're as good as v1.

I decided on a whole new case as well. I kind of ruined my current case so am having the Define C delivered this week. I think I am going for the same layout but both rear fans will be 120mm, 2 front 140mm and I may try and squeeze another 120 under the 140s in front if the case allows. It looks like, if possible at all, it would be very tight. I will adjust the speeds and test to make sure i dont have negative pressure. I will also test to see if the fan behind the GPU on the outside of the case makes GPU temps better, worse, or the same.

Thanks again for all of your info!