To Blow, or To Suck?

[protokatie]

I guess it could be a personal preference, but seriously:

I am planning on building a wooden "server" rack for my file server computer, and an aux computer, plus external Hdd's, etc. The computers (tower cases both) will be on the lower shelves and the drives/etc will be on the upper shelves. There will be a 2 inch gap at the back of all shelves for cables and airflow. Now my idea is to put two vents near the bottom front and a large vent at the top to allow for heat dissipation as this "rack" will be entirely closed in otherwise (including a double door that when opened in the obvious way will show a book case/dvd rack).

So, is it better to have fans on the bottom blowing cooler air into the cabinet, or a large fan on top exhausting the heated air out, or both?

EDIT: I am leaning toward an exhaust fan as I can imagine this will allow for a better stream of air, plus I imagine that inlet fans will create turbulence...?

[Ed_McCarron]

Blow.  Positive pressure will keep dust from getting sucked in every little crack.

"Sir!  It's Megamaid!  Shes gone from suck, to blow!"

[hypernova]

I believe I've always heard that exhaust fans at the top are the better option if you must choose only one.  But obviously a combination would be the best option, I believe.  In at the bottom and out at the top.

The heat will always rise, so the exhaust fan will always be sucking out the hottest air, however, an intake fan will not always be pushing out the hottest air.

[SavannahLion]

however, an intake fan will not always be pushing out the hottest air.

That's because most cases aren't designed for a positive pressure system. So there's usually vents in the back that would cause the intake air to escape.

However, you can control the intake fans to blow air over the hottest components (to some degree).

A lot of cases look like they have vents that short circuit with the exhaust vent just above it. So you have no choice but to "fill" the available spaces with fans to try and get enough airflow. Looking at some of those cases, the vent placement is just bad.

I'd like to see smoke/airflow tests to see how much of the air is wasted due to poor fan placement.

[Malenko]

if youre only having 1, a blow hole fan up top will be more efficient then one at the bottom pulling cooler air in.

[DaOld Man]

One advantage I can see in blowing cool air in would be that the fan's motor would probably run cooler.
Plus it is probably easier to add a filter to catch dust.

[Xiaou2]

 Besides the CPU, the greatest heat generators are the Hard Drives.  Whats
really bad about that... is that they usually are not well spaced, and the bottom drives
"Cook" the upper drives.

 After losing several Top drives... Ive took a angle grinder to the case... and cut off most of
the front metal.   Ive mounted 2 Industrial fans ( 4.5 inch diameter? )  in front.

 I made my own custom drive mounting rail system, which permits about 1 cm
distance between each drive.  The drives are mounted width wise, so that the cables
are easily accessed on the side, and that also keeps them from screwing up the
airflow.

 The airflow is so strong, that you can feel it at the rear of the case like a hurricane. 
The drives are almost Cold to the touch... and since the CPU is in the pathway, it too
cooled even better.   It of course cools Every component in the system, including the
video card and motherboard chipsets.

 My CPU temp is currently 91f in a pretty hot room... which is darn awesome for
the core2duo setup. Im using one of those monster heatsinks that has a 4" fan
mounted to it.  Considering my intake fans power, I probably could remove the
cpu fan... but its always better to have redundancy anyways.

 The dust flies round..  but its easy enough to blow out with compressed air
every once a year.  Heck, dust can hardly settle considering the airflow I
have workin   

 Heat cant make it to the top of the my case!  And what little might, would get sucked
out by the powersupply fans.

 Only drawback is the noise levels.  I will replace the main intake fans soon with
some of the new quiet tech fans.  They push the same kinda air.. but are half
as loud.


 Air flowing across components hot surfaces tends to do a much better job of cooling
than trying to suck air out.  Air is very fluid, and not easy to suck out in a consistent
stream.. thus more times than not... you end up sucking the warm to cool air out..and
the heat remains dense in certain areas.

 A good example would be to imagine sitting on a stool hovering above an electric
heater.  A fan about your head isnt going to do much to keep your butt cooler.  More
than likely, you will fry.. and the fan above you will pull the cooler air out.

 Pointing the fan directly at you, will force cooler air over your entire surface area,
and even at the heat source, making the overall temp lower.

[protokatie]

OK, maybe I should be more lucid on what the wants of this case are:

1. The case is simply to make it so I CANT hear the computers.

2. It needs to be quiet.

3. It need to just make the air inside be at about ambient temp.

Other than these things being in an enclosure, the computers will still be cased, and the external Hdds will be spaced a few inches apart from each other. IE there will be PLENTY of open air inside this case. Also, I never do Hdd stacking, for the same basic reason Tigger pointed out. I have divorced myself of the idea of using internal Hdds for archival/fileserver applications.

Although I am hearing a lot of "push air in" advice, I am still unconvinced that it is a better move than a single low RPM exhaust fan. Remember my primary reason for this is to eliminate noise.

EDIT: Oh and this is my 1200th post, so: GO AMIGA 1200!

[hypernova]

A good example would be to imagine sitting on a stool hovering above an electric
heater.  A fan about your head isnt going to do much to keep your butt cooler.  More
than likely, you will fry.. and the fan above you will pull the cooler air out.

 Pointing the fan directly at you, will force cooler air over your entire surface area,
and even at the heat source, making the overall temp lower.

You may be forcing air over the components, but as I mentioned earlier, you aren't necessarily getting rid of the heat that begins to build at the top.  Eventually that heat is going to have no place to go but down.  Your analogy doesn't seem quite apt to this situation.  His heat source and object he's trying to protect are one and the same.  As well, those objects are designed to dissipate the heat as best as possible as it is to avoid damage.  Our rumps, notsomuch.  Also, in your analogy, the heat will eventually dissipate around the rest of your body as well, with nowhere to go.  The temps going to rise, so even if you did have a fan to cool your bottom, the rest of you is going to be sweating bullets, and soon bake yourself.

Of course, I'm willing to admit I'm mistaken, but I am rather certain I've read when presented with only one or the other as the choice, the exhaust is the best choice-assuming it is placed wherever the heat gathers the most.

[BobA]

Prefer a large fan or fans at the top to push out the hot air.    Room temp air comes in the bottom and should be filtered as there is always alot of dust and hair on the floor.   The only real requirement of the enclosure is to allow the air a pathway thru the box so that heat can rise on its own and with a bit of fan help.

[SavannahLion]

Although I am hearing a lot of "push air in" advice, I am still unconvinced that it is a better move than a single low RPM exhaust fan. Remember my primary reason for this is to eliminate noise.

80mm or smaller fans are noisy because there is only so much physical air they can move. Hence, you have a trade off of increased heat for decreased noise.

Find a case that allows a much larger such as 120mm or even larger. I have 177+mm fans that move upwards of 230CFM or more. That single fan moves more air than any of my smaller case fans in any combination. A larger fan would allow you to dial down the RPM and still move adequate air.

[Xiaou2]

You may be forcing air over the components, but as I mentioned earlier, you aren't necessarily getting rid of the heat that begins to build at the top.

 WTH are you talking about?!   Heatsinks are designed to wick heat from a device
away from it, then spread it using mega surface area, usually cooled by fans that
push over the fins.   Thats just about how every modern CPU cooler works
today... and there are reasons for that, much as Ive listed.

 Try reversing a modern day CPU fan so that it pulls hot air up rather than blow
air directly At the fins.  You will fry your CPU in no time flat.

 Unless your room is 120 degrees... there is plenty more cool air that Hot.  Forcing that
cooler air across the heated areas forces the heat Away from those areas, and because
you are Flooding the case with cooler air, the heat is easily forced out of the case.

 In fact, its far easier to push heat out of the case rather than to try to Suck it out.
Unless the case is airtight, there is little suction to speak of.  You may simply be
pulling cool air from one part of the case to the other... while not even coming near
the heated areas.
 
 

Eventually that heat is going to have no place to go but down.

   
 Heat RISES! 

Your analogy doesn't seem quite apt to this situation.  His heat source and object he's trying to protect are one and the same.  As well, those objects are designed to dissipate the heat as best as possible as it is to avoid damage.  Our rumps, notsomuch.  Also, in your analogy, the heat will eventually dissipate around the rest of your body as well, with nowhere to go.  The temps going to rise, so even if you did have a fan to cool your bottom, the rest of you is going to be sweating bullets, and soon bake yourself.

 In the analogy, you will bake no matter what.  The difference is How fast.
Put a fan above your head, and you will be fried like chicken in seconds.

 Blow the fan across wise, so that its directed at the heat source and you... and you
might last 10 minutes.

Of course, I'm willing to admit I'm mistaken, but I am rather certain I've read when presented with only one or the other as the choice, the exhaust is the best choice-assuming it is placed wherever the heat gathers the most.

 Well, youd be wrong... and so would all the other clowns who wrote that Crap.


 Put 4 hds stacked in a case, with one cooling fan at the top of the case.  Watch
the temp as you give them a workout.  They will be able to fry an egg in no time...
even If the case itself feels cool/warm.

 Same deal, but have a fan blow air directly across the surface of all the drives.
They will be cool/warm  to the touch.  not egg-scorching hot.

 How do I know?  EXPERIENCE.  (as well as LOGIC)

[protokatie]

Tigger, please be more cordial in this thread. I welcome your experience with this sort of issue.

[Malenko]

Eventually that heat is going to have no place to go but down.

   
 Heat RISES! 

Your reply was too over the top and scattered for me to completely reply to, but you pulled a chad on this point. As the heat rises and builds up in the top eventually the mass of how air will grow. Since its trapped int he case it will grow downward aka "go down"

Why are you so over the top in your reply? Also, have you read what she wants and how the case is set up? Hard Drive stackig isnt a factor, and she already stated why.

[Blanka]

Aren't blowing and sucking two similar words for exact the same process?  

[Cakemeister]

From what I understand, you're building a box around 2/3 computers, external drive, network switch, etc.? And the purpose of the box is to 1) dampen sound and 2) keep all the clutter together?

[Xiaou2]

The mas of hot air will not grow, because its constantly being forced out of
the cabinet with positive pressure from Cooler air.

 As a side note,  I used to work in a clean room, and they also used a
positive pressure system to better regulate the temperature and humidity.

 
 Trying to Suck the air out of a non-sealed case is nearly impossible to
get all of the case air to flow thru all the areas which have heat... and
thus you Would get heat buildup in certain areas.

 Positive pressure assures that All of the air will be replaced in a case
equally, because of constant pressure being applied.
 

[Malenko]

The mas of hot air will not grow, because its constantly being forced out of
the cabinet with positive pressure from Cooler air.

 As a side note,  I used to work in a clean room, and they also used a
positive pressure system to better regulate the temperature and humidity.

 
 Trying to Suck the air out of a non-sealed case is nearly impossible to
get all of the case air to flow thru all the areas which have heat... and
thus you Would get heat buildup in certain areas.

 Positive pressure assures that All of the air will be replaced in a case
equally, because of constant pressure being applied.
 

I dont think you read her question. She isnt talking about a PC case. Also hot air mass will grow if not properly ventelated. Im not saying there wont be some loss through positive pressure, but if the heat builds at a faster rate then its forced out of the case, the mass will increase, and once it does and the "top" is filled, it will grow downward with the hottest air in the mass still up top, because heat does rise.

[hypernova]

Eventually that heat is going to have no place to go but down.

 
 Heat RISES!  

Well, sure.  Everyone looks like a moron when you take things completely out of context and completely ignore my preceding sentence.

In the analogy, you will bake no matter what.  The difference is How fast.
Put a fan above your head, and you will be fried like chicken in seconds.

 Blow the fan across wise, so that its directed at the heat source and you... and you
might last 10 minutes.

So for all intents and purposes, we shouldn't even be considering this situation.  According to you, mine apparently lasts seconds, and yours minutes.  Not relevant when we're trying to reach thousands of hours.

Of course, I'm willing to admit I'm mistaken, but I am rather certain I've read when presented with only one or the other as the choice, the exhaust is the best choice-assuming it is placed wherever the heat gathers the most.

 Well, youd be wrong... and so would all the other clowns who wrote that Crap.

You always get this animated when someone offers a different viewpoint to a problem?

Put 4 hds stacked in a case, with one cooling fan at the top of the case.  Watch
the temp as you give them a workout.  They will be able to fry an egg in no time...
even If the case itself feels cool/warm.

 Same deal, but have a fan blow air directly across the surface of all the drives.
They will be cool/warm  to the touch.  not egg-scorching hot.

 How do I know?  EXPERIENCE.  (as well as LOGIC)

And I believe herein lies your problem.  If you take a look at the original post, he asks whether it is better to draw air in from the bottom, or push air out at the top.  You're introducing variables and bells and whistles that weren't part of his original query.  You're throwing heatsinks and a so-far indeterminate amount of fans to cover all the surface area of the HDDs and such.  Heck.  I can do you one better.  Mod a small refrigerator, with numerous fans and liquid cooling and throw that array in there.  It may never reach room temperature for all I know.

When you start introducing heatsinks and fans on those heatsinks, yes, you are correct.  Heatsinks dissipate, while fans blow the cooler air onto it (assuming it has access to cooler air).  I never said you weren't correct in this.  I was just trying to stay within the bounds of the situation presented.

So can you at least agree that when presented with either an intake at the bottom or an exhaust at the top, you should take the exhaust?

[DaOld Man]

Well, sure.  Everyone looks like a moron when you take things completely out of context

 If you take a look at the original post, he asks whether it is better to draw air in from the bottom, or push air out at the top.  You're introducing variables and bells and whistles that weren't part of his original query.

 

Ahem, to put it more nicely, he is a she and his is hers (The last part sounds just like a marriage).

[hypernova]

Ah...my bad!  I've always been bad with names, and I never remember who's really who here.  I suppose I'll leave it as is for the sake of the humor.

[Cakemeister]

I don't think any vents or fans are necessary. Katie's setup sounds similar to a closed up MAME cabinet, with no monitor. I think the vent at the top will provide enough ventilation for natural convection to cool the thing. Typically, MAME cabinets don't have trouble the PCs inside them overheating. Just monitor temperatures for a few hours to make sure. If heat starts to become a problem, I would rather drill some holes in the bottom of the box than install a noisy fan.

[shardian]

Ahem, to put it more nicely, he is a she and his is hers (The last part sounds just like a marriage).

Yep, and the fact that most don't know that is the only reason this thread stayed civil based on the title. 

[ChadTower]

This thread needed some Rodney.

[DaOld Man]

Rodney was Da Man...