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Questions about a external setup

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Pyros

Member
Joined
Oct 6, 2002
Location
Lost in life
Im currently designing a external case for my WC. Is it better to have positive air pressure or negative air pressure? This case will be a sealed case. Im using 2 120mm deltas( cant find anyspecs but judging by the amps I'd say about 85cfm each) that will be for the radiator.
I was planning to utilize some of the crap I already have and use2 80mm fans(34cfm) on the case. Because of the cfm differences there will obviously be a inbalance in air flow. If this will be a problem I can get 2 120mm fans to balance the air flow. If it isnt, which is better? I would think pulling air through the radiator with the 120mm fans and pulling air in the case with the 80mm fans causing negative pressure would be better.(no build up of warm air).

Tks.
 
The bad thing about negative pressure is that it will draw lots of dust into the case. Personally I like to have (if I can't have equalibrium) positive pressure.
 
Wel in my main case(mobo, cpu,blah blah blah) I have positive pressure. but since the only thing Im really going to be cooling in ths external case is the radiator, I figured that it may be different.
My worry about positive air pressure would be that once the air flows through the radiator and cools the water, this warm air will be hanging around in the case too long and warming the radiator back up. The only things that will be in the case is a psu, radiator, pump, and reservoir. Will these things really put off enough heat(including the air flowing in from the radiator) to even worry about this?
 
I would just try it both ways. The thing is, with negative air pressure, air gets sucked INTO the case through every nook an cranny, with positive, air escapes through every nook and cranny. I don't think the hot air will 'hang around' with positive pressure.
 
WejRepus said:
yea, but he said that it will be a sealed case... if it is really sealed, i would make a differance
It is very difficulty to seal a case to be air tight. I doubt that is what he meant. You would need to wrap the case with plastic wrap or something then only have cutouts for the fans.
 
Im actually looking at 2 different designs for the case. Which I choose depends on how my question was answered. In one of my plans the case would be air tight to the point that any leak would be negligable(sp?) (its actually made of metal welded together and the access point will have foam rubber gasket around it).The other design would be sealed, but only in the way your average pc case is sealed.

I suppose I should have been clearer in my question. My question was actually directed at having a nearly perfect sealed case. And now that the point of it making a difference weither or not it is a air tight case, which would be better? A sealed up case or a sealed case that leaked like you avgerage pc case?
 
Personally I think it depends on whether you have a lot of heat sources in the case. If you have a really hot video card and several drives in a raid array then I would suggest pulling room air in and through the radiator and creating positive pressure in the case. If you don't have a lot of heat sources in the case then pull air from the case and push it through the radiator and out of the case creating negative pressure.
 
TC said:
Personally I think it depends on whether you have a lot of heat sources in the case. If you have a really hot video card and several drives in a raid array then I would suggest pulling room air in and through the radiator and creating positive pressure in the case. If you don't have a lot of heat sources in the case then pull air from the case and push it through the radiator and out of the case creating negative pressure.

this is for an external case...
 
Oops - can't see that it would matter much with an external unit. I built an external unit using the same equipment I sold you. I simply mounted the radiator at one end of a plenum and 2 120mm fans at the other end about 4 inches away. Those 2 delta's will move plenty of air whether you're pulling or pushing over the rad.
 
i would say put the rad in front the exhause for the case. have a 120 in the front as an intake, and maybe an 80 too if you want it. then have the 2nd 120 pulling the air across the rad, and out of the box. just make sure that you have a good seal between teh rad, fan, and case. the front 120 and the 80 should move pretty much their rated amount, since they wont have much resistance. the 120 pulling the air over the rad wont move its rated amount cause it has a lot of resistance. this will create positive pressure in the box, which should help keep dust down. the positive pressure will also help to push more air out through the rad. thats what i would do.

or maybe the whole thing it reverse to get the coldest possible air to the rad. i dont think the heat that the air would pick up from the pump and res would make that much difference, but it might...
 
WejRepus said:
well, i would say that a sealed case would be better if you had balanced airflow, and the leaky case if you had +/- pressure

I agree with this post.

If the case is truly well sealed I would think that any difference in flow in/out would hurt, not help.

If the case is more like a standard pc case, the same stuff applies as it does to a pc- personally, I get better results with more exhaust than intake. Cleaning out a few times a year doesn't take more than a few minutes and my temps seem to be a bit (minor) lower that way.

But balanced is best :)
 
What Im planning for the sealed case is to use a diamond plate carry around tool box like the ones you get at lowes for $40. I have a cute little pic I made in ms paint:p but cant change the format and size right now cause my main rig went :mad: today.

Ill try to expalin it though. picture that your looking at the box as you would if you were going to open it. on the back wall inside the box will be the radiator. The 2 120mm fans will be mounted on the back outside of the box. On the inside sides will be the other 2 120mm fans.(decided not to bother with the 80mm I have). On the inside near the front center of the box will be the reservoir and pump. The lid will be sealed with foam rubber tape and any hole needed for lines will be siliconed.

The only thing I havent figured out yet is which fans to have for pulling air in and exausting. I figured pushing through the radiator into the case and exausting out the side will work best. The rear of the case where the radiator fans wil be is going to be in front of my window unit A/C so it should push plenty of cold air through the radiator.

I know its a different approach. Kind of a industrial look.:D So do you think it will work? :)

BTW Roger, I usually clean my cases out with a brush and compressed air one a week so alittle dust doesnt bother me.;) I spent too much on this thing making it look good to let it get dirty.:cool:
 
that sounds like a good plan. i think all the fans being the same will be good. the 120 exhausts should help act as a little bit of "pull" with the other 2 120's being the main "push" for the rad. made sure you take pics. it sounds that it will look pretty cool.
 
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