Positive air pressure in case...

[TheNiceGuy]

I understand that + pressure in the case is the way to go, especialy to eliminate dust. Any down side to it?
Also, (if its good) I would like to setup my case for it. Here's my case:
http://216.239.39.104/translat...00s/owl611slt400s.html
And I'm using an A8N-SLI board, 3000+ CPU box fan, and a single 6600GT. The fans are also auto-controlled (by the mobo and PSU) for speed.

Any help greatly appreciated!

 

[Navid]

The only down-side is that you wil need an intake fan in front at the bottom. You can hear a fan in front more than you can hear a fan in tha back.

Also, for the positive pressure to work and not allow dust buil-up, you will need a filter on the intake fan, which will impede air flow (any filter does).

If fan noise is not a problem for you, there are no down-sides.

 

[TheNiceGuy]

So what setup will work for me?

If my math is right, my current setup will be negative pressure in the case.

???

 

[Navid]

You can use a dust buster to clean your case regularly (once a month). Then, you can live with negative pressure. If you don't want to clean, go with positive pressure. Then, you will have to clean the air filter once a month. It is up to you!

You may want to modify the case to open the intake space to allow more air to enter (less obstruction).

Sorry, I am not sure what you mean by "what setup will work for me".
You have to decide what you wnat and what makes you happy. There are lots of trade-offs between cooling, noise, cost, weight, size, looks, ......

 

[sodcha0s]

Originally posted by: TheNiceGuy
I understand that + pressure in the case is the way to go, especialy to eliminate dust. Any down side to it?
Also, (if its good) I would like to setup my case for it. Here's my case:
http://216.239.39.104/translat...00s/owl611slt400s.html
And I'm using an A8N-SLI board, 3000+ CPU box fan, and a single 6600GT. The fans are also auto-controlled (by the mobo and PSU) for speed.

Any help greatly appreciated!

The major downside of running positive pressure is higher case temps. The best overall setup is to have equal amount of intake and exhaust, and keep your filters clean.

 

[OddTSi]

Does anyone have any proof that positive case temps leads to less dust? I keep hearing this repeated over and over with no one ever providing any proof. As far as I'm concerned until I see some proof it's nothing more than a myth.

 

[Falloutboy]

Originally posted by: OddTSi
Does anyone have any proof that positive case temps leads to less dust? I keep hearing this repeated over and over with no one ever providing any proof. As far as I'm concerned until I see some proof it's nothing more than a myth.

the pluses with postive pressure is that you can control where dust enters the case and becasue of this you can put a filter thier to stop the dust. with negative pressure you run into the issue that air is entering thru every crack and hole in your case and the air is unfilterd so dust enters your case

 

[Nessism]

I'm not an expert on this subject but it seems clear that in order to have a positive pressure case you need to have a higher cfm fan on the front than on the back. One potentional problem is that you can end up with "dead air" pockets in the case since the airflow is being created from two different sources.

Not sure this helps but what do you expect on a public forum...

 

[Navid]

Originally posted by: OddTSi
Does anyone have any proof that positive case temps leads to less dust? I keep hearing this repeated over and over with no one ever providing any proof. As far as I'm concerned until I see some proof it's nothing more than a myth.

What do you expect to see as proof?

Positive pressure does not reduce dust in itself. But, in such a system, air only enters the case from the intake fan opening. Air leaves the case from every crack and hole in the case. So, you can filter the intake openings. The filter reduces the amount of dust entering the case. But, it will not completely stop it.

If you have negative pressure, air only exits the case from the exhaust fan openings. Air enters the case from every crack and hole. Dust also enters the case from every crack and hole. The components inside the case trap some of the dust. So you will end up with dust build-up (dust bunnies) inside the case.

Common sense tells you that in the first case, you will end up with less dust inside the case.
The disadvantage is that the filter reduces air flow. So, for the same amount of air flow through the case, you will need stronger (louder) fans for the positive pressure case.

 

[sodcha0s]

Originally posted by: OddTSi
Does anyone have any proof that positive case temps leads to less dust? I keep hearing this repeated over and over with no one ever providing any proof. As far as I'm concerned until I see some proof it's nothing more than a myth.

Well, if you want definitive proof, you'll just have to experiment yourself. I am speaking from experience, and it seems as though Navid is as well. I have tried both ways and positive pressure keeps more dust out, and keeps it from getting inside of your CD drives and floppy drive. The downside is, your case temperature will go up noticably because instead of having a constant supply of fresh air in the case, the air is turbulent and stays inside longer, thus heating up more. If heat isn't an issue for you, then your best bet is to have positive pressure to keep things cleaner.

 

[OddTSi]

This is just naivete. How much dust do you guys possibly expect to enter through the cracks in the case on a "negative pressure" setup? Put filters on your intake openings on cases with negative, neutral, and positive case pressure and I guarantee you won't notice much of a difference, if any. It's the FILTER in front of your fan(s) that keeps most of the dust out of your case, not the positive case pressure.

 

[Navid]

Originally posted by: OddTSi
This is just naivete. How much dust do you guys possibly expect to enter through the cracks in the case on a "negative pressure" setup? Put filters on your intake openings on cases with negative, neutral, and positive case pressure and I guarantee you won't notice much of a difference, if any. It's the FILTER in front of your fan(s) that keeps most of the dust out of your case, not the positive case pressure.

Do you think if you never open the door to your house, there will never be any dust inside?

 

[OddTSi]

Wow, are you serious? Dust is largely made up of dead skin cells. So of course there would be dust inside your house, assuming that you're still living inside of it.

 

[wisdomtooth]

Originally posted by: OddTSi
Does anyone have any proof that positive case temps leads to less dust? I keep hearing this repeated over and over with no one ever providing any proof. As far as I'm concerned until I see some proof it's nothing more than a myth.

I haven't seen any studies with PC cases, but positive air pressure is used in many industrial and military applications.

In railroad locomotives like those built by General Motors' EMD division, blowers do keep a higher air pressure inside the engine compartments to keep dirt out. They have been doing this since the Dash-2 series of locomotives came out in the late 1970s (such as the 6-axle 3000hp SD40-2).

In military applications, positive air pressure is used as an integral part of NBC defenses (Nuclear Biological and Chemical). It's used in the M1 Abrams tank to keep poison gas, radioactive particles and germs out of the crew compartments. Ditto for warships like the Navy's Burke-class AEGIS destroyers.

As far as adapting such technology to the PC case goes, problem with ad-hoc'ing a positive air pressure system in any ol' computer case is that you will need a VERY powerful intake fan to 1) overcome the air resistance of the filter and 2) push in more CFM than is being exhausted by the exhaust fans and leaking around all the bezels and seams. And you end up with something that screams like a damn banshee.

I think a case needs to be built from the ground up to have a truly-effective positive air pressure system. That means the seams need to be pretty small (i.e. such as around the drive bezels and case panels) to prevent excessive air leakage and loss of pressure, a limited number of exhaust ports, and above all, one filtered ducted intake with a fan that will pull in more CFM than the fans blowing out.

 

[Tiamat]

Best cooling with less dust and less noise is to have exhaust 120 on 7V or less, PSU with slow 120mm fan, a very effective dust trap in the intake, and use good tape to tape up all the cracks. You may even get away with not needing an intake fan. Although if you have a hot harddrive, you want an intake to spot cool it.

 

[BonzaiDuck]

I'm still of the opinion, born of personal observation -- that positive pressure with effective air-flow means more effective cooling. An increase in air-density would increase heat transfer and removal. An actual vacuum inside the case would cause components to heat up, there being a lack of air to remove component heat.

There was a time when some OEMs shipped "pressurized case" systems. And there were some power-supplies that actually sucked air in as opposed to blowing it out (making for dust build-up inside the PSU).

As someone already said, you want to filter all your intake fans, lowering their effective CFM throughputs. But it is these same intake fans which need to provide greater CFMs than the exhaust fans to keep the case slightly pressurized.

ONe of the features of the "ducting mods" which sequester CPU-FAN airflow and channel it across motherboard components to a speedy exhaust through the exhaust fans, is that it allows for a slightly greater pressure of cold air drawn through the intake ports. This air then gets pushed through the CPU fan and heatsink fins, and other colder air is also leaking into the duct as exhaust fans are simultaneously pulling the air out of the duct assembly. In this sense, all the fans are working in series. The CPU fan is drawing in slightly pressurized cold air from one part of the case, and the CFMs of the CPU fan are a little higher and more effective because the exhaust fans are removing the air as "puller fans".

Take a look at the following link. I was personally able to just lower my CPU temperatures by about 2-degrees C, but the chipset and memory temperatures fell by about twice that much. And I'm still not finished refining my duct -- which I call "The Bonzai Duct" :

Cinnamon's Motherboard Ducts

 

[TheNiceGuy]

Nice work bonzai! That (efficiency) makes a lot of sense.
WT, nice info.
I never doubted that + pressure helps get rid of dust. I just wondered if it had a bad side, ie noise, extra stress on fans, etc.
I also just found out from the posts above that the CPU fan PULLS air. lol. That should change my math! Although the original question still stands: what setup (fan arrangment, etc) will work best to create a + pressure case? It looks like I would either have to reverse the 12cm fan, or install another 12cm fan in the front where I have 3 free expansion bays.
Or I could create a near-neutral pressure case by replacing the front 9cm fan witha 12cm one (if it'll fit).
What cha' think?

edit: I am especially interested in this because I live in an area with A LOT of dust in the air. Just can't get away from it!

 

[sodcha0s]

Originally posted by: OddTSi
This is just naivete. How much dust do you guys possibly expect to enter through the cracks in the case on a "negative pressure" setup? Put filters on your intake openings on cases with negative, neutral, and positive case pressure and I guarantee you won't notice much of a difference, if any. It's the FILTER in front of your fan(s) that keeps most of the dust out of your case, not the positive case pressure.

OK man, next time I clean one of my cases that run negatice pressure, I'll be sure to take pics of all the dust build up around my CD drive doors and edges of my side panels and send the to you. BTW, how do you "guarantee" there's no difference? You haven't shown any proof, I don't believe a word you say...

 

[sodcha0s]

Originally posted by: BonzaiDuck
I'm still of the opinion, born of personal observation -- that positive pressure with effective air-flow means more effective cooling. An increase in air-density would increase heat transfer and removal. An actual vacuum inside the case would cause components to heat up, there being a lack of air to remove component heat.

Doesn't work that way. First of all, we're talking about very minimal pressure differences here as a computer case isn't anywhere close to being a sealed box, and the fans used are extremely weak. All that's being accomplished is making the cracks leak one way or the other. Now, when you pressurize (ever so slightly) the inside of this case, you will pick up the heat from the components inside, but that heat is going to build up rather quickly and stay inside the case. Why? Since you have a pos pressure, you won't have optimal air exchange, in other words not enough cool air can enter, and not enough hot air can escape.

 

[Creig]

You can't create enough "pressure" in either positive or negative to make any difference in temps. As has been stated before, however, a slightly pressurized condition will allow you to control where dust will enter the case.


Positive pressure - Dust only enters case where "incoming air" fan/fans are.

Negative pressure - Dust can enter through floppy drive, side panels, holes in case, etc...



Best practice is a slightly "pressurized" condition with filters on the fans blowing into the case. You don't want any more than "slightly" otherwise your fans are working at trying to pack air into your case instead of through it.

 

[Zepper]

You will want a 120 mm. in front and the PSU fan plus perhaps another 80mm exhaust (or whatever size if you use a fan controller (which you should - then you can tweak to get just to the pos side of neutral pressure with minimum noise)). You may also want to use a "stirring" fan inside the case to prevent dead-air pockets (can run at very low rpm). Put all your fans on a fan controller. Adjust the PSU fan so the exhaust air from the PSU isn't too warm (don't want to fry your PSU).
. You will also need to plug ALL uncontrolled openings in your case so you don't have to use too much fan power on the intake. I use duct tape, that blue painting tape, plastic wrap (colored for bling) to cover major areas of vent holes, rope caulk etc... And as was said above, ALL intake air must be filtered or you defeat the purpose - so you may need a stronger intake fan than you thought to overcome the filter and still create pos pressure - perhaps a 1.5" (38mm) thick 120mm fan on the intake side would be in order. Those are WAY powerful even at low rpm/low noise.
.bh.

:moon

 

[BonzaiDuck]

I don't disagree with Zepper.

The issue of pressure is a relative one of "stocks and flows". If I'm putting more air into the case at a margin (emphasis) than I'm taking out, then air density is slightly higher. But if my exhaust CFM's are relatively healthy, pressurizing the case slightly is not going to cause a buildup of heat.

I think this becomes clearer if you look at the "ducting mod" idea. In that case (situation ha), pressure in most of the case is slightly above room-air-pressure, owing to the intake fans. Your CPU fan is drawing this same pressurized air into the heatsink, and it is for the most part sequestered to the duct area as long as the exhaust fans are sucking air out of the motherboard duct at about the rate that it is getting sucked in by the CPU fan from the rest of the case and the intake-fan-air. Here, you are removing heat before it gets a chance to circulate among the molecules of the remaining air of the computer case interior. If there are stagnant zones, they may be "relatively" stagnant, but they are not absorbing heat to any significant degree.

sodChaos is correct that this is a matter of pressures "at the margin", since we are not creating a circuit-board-frying vacuum, nor are we pressurizing to such a degree that there is any significant build-up of stagnant air. We are just increasing air pressure within the case so that it is slightly higher than the air-pressure in the room. We are exhausting air at a slightly slower rate than we are bringing it in, but this does not lead to an infinite build-up of stagnant air. The source of the pressure is colder intake air.

I sold my CoolerMaster Wavemaster case to my dentist because it would have required too much work and modification to make it cooler. What I think would work with the WaveMaster is a sealed intake fan of larger than 80mm size that does not recycle interior case air like the stock fans and mountings of the WaveMaster actually do. Then, I would widen the exhaust fan hole to 92mm. If it were possible, I'd make both intake and exhaust in the WaveMaster a choice of 120mm fans, but those familiar with the WM know how tricky that would be. There would be no need for a blow-hole CPU-intake duct, and you could use the window-panel case-mod sold by CM. Foam-board ducting over the motherboard would complete the cooling.

I can only offer the description of the proven regime of fans I use now in my cases, which are exclusively full-tower models -- recycled from older computers -- since I sold the CM WM. Two 120mm intake fans at a minimum 1,500rpm (although one would probably suffice); a 120mm CPU fan defaulting to 2,000rpm at idle but capable of 3,100 rpm and 108CFM at CPU-load; two 92mm exhaust fans defaulted to 2,500rpm each, which spin up to around 3,000 to 3,200 at load.

Potentially the twin exhaust fans can provide as much as 75CFM each at load, if run at 3,600rpm (with noise). And I had to choose 92mm exhaust instead of 120mm (single or dual) because of the original case-design of the "recycled" case I chose to use for this build -- a 1995 Gateway2000 full-tower (early-)ATX.

At a 22% over-clock for a 3.0C Pentium4 @ 3.70 Ghz, 247 Mhz ext. frq. and 988 Mhz FSB, FX5950 Ultra AGP, dual Hitachi 7K250 RAID0 (ICH5), here are my temperatures at a room temperature of 70F, with load-testing under PRIME95's prime number search and "blend" test:

idle
CPU 79F / 26C
motherboard 75F / 24C
NorthBridge (thermal sensor) 87F / 30.5C
AGP (thermal sensor) 88F / 31C
AGP (nVidia internal sensor) GPU = 33C ; "ambient" = 27C

load (PRIME95)
CPU 110F / 43C
motherboard 79F / 26C
NorthBridge (thermal sensor) 90F / 32C
AGP (thermal sensor) 89F / 31.6C
AGP (nVidia internal sensor from display "properties") GPU = 34C; "ambient" = 28C

The ducting mod is responsible for the narrow range of motherboard and chipset idle and load values. PRIME95 should not have such an effect on the AGP card, so I only note here that the AGP temps never, ever exceed 40C under graphic-intensive load situations or significantly higher room temperatures with similar load situations. Ducting impact on the CPU load temperature was a matter of 2 to 4C cooler than without the duct. Without the ducting mod, the chipset temperature has been seen to reach 40C under load.

 

[BonzaiDuck]

PS -- the AGP card is equipped with a passive-cooling Zalman ZM80D-HP heatpipe cooler. This has effectively clamped temperatures to around 40 to 41C under most load conditions for the AGP card. I felt obligated to tie this up as a loose end in my explanation of the previous post.

As for dust. After a month or more, a very fine layer of dust -- almost invisible -- could be found on the hard-drives behind the filtered intake fans. But there are no dust-bunnies, "cruft", or dust from any other sources.

 

[Navid]

After you turn on the PC, only for a moment, the intake air and the exhaust air flows are different. In case of a positive pressure case, the intake air flow will be higher and for a negative pressure case, the overall exhaust air flow will be higher. But, only for a moment! After that, the system stabilizes and the intake and exhaust air flows will be identical.

The higher air pressure inside a positive-pressure system should not be considered a cause for higher temperature. The higher pressure inside the case should not be mistaken with lower air flow.

As long as the air flow is the same between a negative pressure system and a positive pressure system, the cooling efficiency should be the same for the two. Remember that we are talking about a slight pressure difference between the air inside the case and outside.

The problem with a positive pressure system, intended to keep dust out, is that the intake fan is filtered. To have the same air flow, you will need higher RPM for that fan, which results in more noise.

 

[BonzaiDuck]

. . . and that problem diminishes if you add more larger and slower fans to the intake. That certainly is the problem with filters, though. I only wish there were a rule-of-thumb for reducing CFM estimates given the filtering conditions.