A Case For Positive Pressure....

Bluefront · Post by **Bluefront** » Sun Dec 10, 2006 11:15 am

My last three projects have been mostly positive pressure cases....an Antec Aria, old Compaq case turned into a wood case, and a Gateway E Series case. I have come to the conclusion this is the way to go for me in most/all future projects.

There seem to be very few setups shown on the SPCR forums, that are completely positive pressure. Most setups are negative pressure, or at best have only a front fan blowing inward. This gives the impression that negative pressure cases are quieter.....which I have found not to be true at all.

So that's the reason for this thread. I'd like to see projects of other people that are positive pressure. Pictures, links, ideas....all would be appreciated. I'm wondering what common newer case would work well with positive pressure, maybe what fans work better. In my latest project I'm using a fanless Zen PSU......perfect for a positive setup. Anybody using something else as a fanless PSU in a positive pressure case?

The new cases with that big 250mm fan look like good candidates for totally positive pressure. Only one I know about on SPCR so far.....

Help me out here.....

RAFH · Post by **RAFH** » Sun Dec 10, 2006 3:23 pm

I am a very strong positive pressure advocate. The one reason positive pressure has some doubts in the silent crowd is to gain positive pressure you have to push air in and that usually means from the front so there's a shorter, more direct path to your ears in front from the fans in front. The fan noise: motor, blade and air friction sources will all travel upstream with little or no problem. If your fan is directly exposed to the front, whatever noise there is will come right at you nearly full power.

The trick with fans in the front is to break up the sound path by breaking up the air flow path. This would include the filters you are going to want (whole reason for positive pressure is to keep dust and dirt out) as well as making sure the path is not a straight line. In the Antec SOLO this is accomplished by having the front bezel solid with the air being intaken via a slot around the perimeter of the bezel. This cuts the noise plus what every does continue up the path is deflected to the rear by the outer edge of the bezel. If you really wanted to make it quiet, you could introduce more bends in the intake path and line it with sound absorptive materials.

The more bends and breaks in the path the better, sound wise, as long as they don't increase the flow resistance so much the fans have to work overtime. So you want a lot of cross-sectional area for the air to flow through to keep the velocity and resistance as low as possible. That also means filters with as much area as possible.

On the exhaust end, make sure you have lots of area. Again, the greater the area and the less the resistance the better. However you will want as many changes of directions as you can manage as well.

EndoSteel · Post by **EndoSteel** » Mon Dec 11, 2006 4:57 am

Bluefront
Most setups are negative pressure, or at best have only a front fan blowing inward. This gives the impression that negative pressure cases are quieter ..which I have found not to be true at all..
A negative pressure PC has one big advantage: it's much easier to build

. A positive setup inevitably requires some drilling & cutting - quite few people have hands shaped right for the task.

Tachyon · Post by **Tachyon** » Mon Dec 11, 2006 11:54 pm

Bluefront wrote:My last three projects have been mostly positive pressure cases....an Antec Aria, old Compaq case turned into a wood case, and a Gateway E Series case. I have come to the conclusion this is the way to go for me in most/all future projects.

There seem to be very few setups shown on the SPCR forums, that are completely positive pressure. Most setups are negative pressure, or at best have only a front fan blowing inward. This gives the impression that negative pressure cases are quieter.....which I have found not to be true at all.

So that's the reason for this thread. I'd like to see projects of other people that are positive pressure. Pictures, links, ideas....all would be appreciated. I'm wondering what common newer case would work well with positive pressure, maybe what fans work better. In my latest project I'm using a fanless Zen PSU......perfect for a positive setup. Anybody using something else as a fanless PSU in a positive pressure case?

The new cases with that big 250mm fan look like good candidates for totally positive pressure. Only one I know about on SPCR so far.....

Help me out here.....

Hi there, newbie here, but I am curious about the positive pressure aria case. have you reversed the PSU fan to be positive pressure as well? I am interested in doing the PSU fan mod on the aria PSU, but its temp control I believe, wondering if a normal 120mm fan (coolermaster or nexus) can be made to work.

thanks

Bluefront · Post by **Bluefront** » Tue Dec 12, 2006 3:06 am

Tachyon.....You'll have to read the thread about my Aria. I never used the stock PSU, other than to see if it worked. It's pretty hopeless as a quiet setup with the std PSU. This Aria uses a fanless PICO converter as a PSU. The hole where the stock PSU was sitting, is now an intake fan, making the Aria positive pressure.

The PSU is a big area of concern if you want to go positive pressure. A fanless PSU is one solution....but there are other ways. The PSU fan can be reversed, but you don't really want heated PSU exhaust to go back into the case. A separate exhaust channel for PSU exhaust is possible.....like cut a hole in the top of the case and blow the PSU exhaust out the top through a baffled chamber.

That wood case I built (second link in the OP), uses a negative pressure setup for the PSU, but draws the air from a separate chamber under the main case. There are countless ways to deal with the PSU airflow.....most involve non-standard modification.

Bluefront · Post by **Bluefront** » Tue Dec 12, 2006 3:20 am

EndoSteel.....I think your English wording about "hands" needs some clarification. I suppose you mean that some people don't have enough experience with tools, and modification techniques, to prepare a case for a change to positive pressure (something like that). And yeah you're right. That's why I'd like to see a modern case than could be used without many mods....as a positive pressure case.

An Antec p-180 looks like it might be workable.....but costs too much for a modification experiment for me anyway.

Avalanche · Post by **Avalanche** » Tue Dec 12, 2006 6:28 am

Bluefront, I've looked at your projects and they seem really nice. I'm inspired to try making a wood frame for an old case I have lying aroud, maybe after the new year.

Do you agree with RAFH that the "whole reason" for a positive pressure case is to keep dust and dirt out? I'm guessing not, but I'd like to hear your response.

Which leads me to: If a positive pressure case is supposed to be basically a miniature "clean room", then wouldn't it be obvious to have *one* blower-filter assembly for air intake and filtering? If so, then the best case would be one with enough room to include a filter and a fan in the desired location (you seem to prefer rear/bottom), and one with a limited number of other holes/intakes/cracks.

Bluefront · Post by **Bluefront** » Tue Dec 12, 2006 4:02 pm

The filter, clean computer thing, is of course a good reason for positive pressure. It's a much easier project to filter the intakes of a positive pressure case, than it is to still filter the intake openings, but also to carefully seal all the little cracks and openings of a negative pressure case. If you don't have a dust problem, you might not need filters at all.

But a positive pressure case still has benefits for a person wanting a quiet computer, big benefits. You have the ability, as I have shown is these last three projects of mine, to run very hot CPUs at relatively low temperatures, with slow, quiet fans and filters, for one big reason......you can use the coldest air in your house (ambient) to cool all the components of your computer. This is an almost impossible task with negative pressure.

Yes I prefer intakes on the bottom or rear of the computer. I'm not building computers for myself with any openings to the front. It's quieter this way. Computers aren't usually built like this however, so modification is necessary. And I use multiple filters many times.....it's easier to manage.

zepper · Post by **zepper** » Sat Dec 16, 2006 2:29 pm

Positive pressure means CFM in slightly > CFM out (you don't need to be puffing the sides of your case out - though my intake fan could probably do that).

Most PSUs these days don't have a lot of CFM and many cases isolate the PSU air flow anyhoo (in that case, be sure to filter the intake air path for the PSU to keep its insides clean). You just need to put all your fans on a fan controller, seal up as much of the extraneous air paths as possible (remember air can exit thru a CPU duct, etc. as easily as enter) and have sensitive hairs on the back of your hand (or use a downy feather).

.bh.

RAFH · Post by **RAFH** » Sat Dec 16, 2006 3:06 pm

Besides controlling the dust and dirt entering your computer, with a positive pressure rig you decide where air is going and how much. With negative pressure, any opening, no matter how small, becomes an inlet and generally the smaller it is and the higher the pressure differential, the more like a jet that inlet will act. This can really mess up your air flows. They might blow right on what you want them to, but they might also deflect the air flow you want. With positive pressure you have control. Even if there are leaks, which you should try to plug, they aren't going to seriously change your airflows. Small leaks also tend to whistle.

I think pulling air from underneath is a good idea, there's bound to be less dust there. I know that seems counterintuitive because thats where you find dust buildup, but that's mostly because you don't clean under there either. Dust is airborne and it settles out in still air, primarily onto horizontal surfaces, though it will also electrostatically attach to vertical surfaces. Just not as much. There is less volume of air above a covered surface for dust to settle out from so there will be less dust overall.

Its also good to pull your air from as low in a room as you can. There can easily be as much at 5C temperature differential in a room. Think what 5C is to a CPU or GPU. Even putting a duct down to the floor would help get you 2C lower temperature air to cool your rig with. During the summer, that differential can be as much as 10C or more.

You might also want to consider the effects of direct sunlight on your case. That can raise case temps by 5C.

jaganath · Post by **jaganath** » Sat Dec 16, 2006 4:04 pm

Besides controlling the dust and dirt entering your computer, with a positive pressure rig you decide where air is going and how much. With negative pressure, any opening, no matter how small, becomes an inlet and generally the smaller it is and the higher the pressure differential, the more like a jet that inlet will act. This can really mess up your air flows. They might blow right on what you want them to, but they might also deflect the air flow you want. With positive pressure you have control. Even if there are leaks, which you should try to plug, they aren't going to seriously change your airflows. Small leaks also tend to whistle.

Personally I don't buy into this whole positive/negative pressure debate. You can control airflow in either scenario using ducts, and technically speaking there is no such thing as negative pressure, the lowest amount of pressure is zero (a vacuum). In other words it's one of those situations where many people believe it makes a difference, but very little hard evidence as to whether it actually does.

zepper · Post by **zepper** » Sat Dec 16, 2006 4:44 pm

The debate is really simple - it's over control of the air flow and whether you want a really clean case interior or not. Plus, a well controlled P-P setup will usually run a degree C or two hotter than an uncontrolled system given similar total air flow.

Most cases are totally uncontrolled and you really can't do positive pressure without fairly tight control unless you just put a 220 CFM Delta on the intake side and let 'er rip. It's easy to do Pos Press with those 250mm fans that are popping up all over - air is just looking for a place to exit from those big boys...

.bh.

McBanjo · Post by **McBanjo** » Sat Dec 16, 2006 4:55 pm

I've started to make some drawings...

Ordered a Ninja as well.

Bluefront · Post by **Bluefront** » Sat Dec 16, 2006 5:43 pm

When I talk about negative or positive pressure in a computer case, I'm referring to pressure slightly greater or lesser than the air pressure present at your location.

If you attempt to suck air out of a computer case by having the fans blowing outward, that case is a negative pressure case.......the pressure in that case is slightly less than the pressure in the room. Because of this, air rushes into the case from every possible opening.....With a positive pressure case, the reverse is true.

There is a big difference between the two different setups. As long as a computer builder is willing to mod, most cases can run positive pressure.....but most cases don't come out of the box setup to run positive.

McBanjo · Post by **McBanjo** » Sat Dec 16, 2006 8:16 pm

Cooler Master Stacker should be easy to get positive preassure

Bluefront · Post by **Bluefront** » Sun Dec 17, 2006 2:32 am

Cases with mesh sides or fronts, are not good candidates for positive pressure. Sure you can blow all the fans inward, but you have little/no control over just where the air will exit the case. And this is an important aspect to airflow. To make the most efficient use of a limited/quiet airflow, you need to direct the airflow through the places that get the hottest. This is true with positive and negative pressure setups.

IMHO.....avoid cases with multiple ventilation holes (unless you want to block off a large number of these holes). Air that flows through your case without doing much cooling just adds noise, and not much else.

McBanjo · Post by **McBanjo** » Sun Dec 17, 2006 6:22 am

Some paper fixes that mesh

Easy ghetto-modding

McBanjo · Post by **McBanjo** » Sun Dec 17, 2006 7:45 am

This looks like it's positive unless I'm mistaken:
http://www.spirecoolers.com/main/produc ... ProdID=572

Beautiful case atleast

EndoSteel · Post by **EndoSteel** » Sun Dec 17, 2006 9:37 am

Bluefront wrote:Cases with mesh sides or fronts, are not good candidates for positive pressure. Sure you can blow all the fans inward, but you have little/no control over just where the air will exit the case. And this is an important aspect to airflow. To make the most efficient use of a limited/quiet airflow, you need to direct the airflow through the places that get the hottest.

IMO, a better idea is not to direct air through an area, but to blow it directly onto each hot spot infividually (some ducting is required). In this case meshed panels come in useful: you don't have to cut out openings for exaust. In a case with solid panels there will be less ducting and more cutting - a less preferable variant since it requires tools that rarely occur in a regular household.

A Case For Positive Pressure....

A Case For Positive Pressure....

Re: A Case For Positive Pressure....