which fans for pushing air in large case?

[Fullmetal Chocobo]

I have a very large case, and I'm trying to figure out what would be the proper CFM rating for fans. I'm trying to ensure that I get fans with enough power to push the air all the way through to case and provide airflow for the components, or at least prevent dead air spots in the case. I'm not too concerned about the PSU side, but I am worried about the mobo side. (The components pictured are not what are going to be in the machine, but it will be similar).

The fans are installed in the removeable bays, so they have to be 92x25mm fans. Is CFM the spec I should be looking at for how far a fan will push air? Or would pressure be a better measure for this?

Fans being considered:
Akasa 92mm Amber -- 29cfm, 0.9mm H20, 18db.

Delta 92x25mm low speed -- 37cfm

 

[Bluefront]

Expecting a 92mm fan to push a narrow column of air 2 feet is unrealistic.....at that distance the airflow will have widened considerably with most fans. There are certain fans that do such a thing better than others, but that sort of spec is not usually available. And you're talking about a really noisy fan here.

To cool a specifically hot spot, it's much better/quieter to have the fan much closer. A cfm rating is your best bet for picking a fan like you want, but most mfg cfm specs these days are just not believable.....ever since SilenX and others started lying about such things.

 

[DerwenArtos12]

No, for how far you want fans to push air you need to look at static pressure. .9mmH20 means they presure they create is enough to move a column of water .9mm, pretty sad actually, I don't know about 92mm but, 120mm delta's move up to about 26mm. Between the 2, the delta has a static pressure of 2mm H20 so that's your winner.

 

[MarcVenice]

If you have a fan in the front, and a fan in the back, isn't there going to be something like a 'draft' ? Meaning air is going to move the whole 2 feet, cept that's not really being pushed by the fan, but it's still moving, so no matter how it happens, it's working, no ?

 

[DerwenArtos12]

Originally posted by: MarcVenice
If you have a fan in the front, and a fan in the back, isn't there going to be something like a 'draft' ? Meaning air is going to move the whole 2 feet, cept that's not really being pushed by the fan, but it's still moving, so no matter how it happens, it's working, no ?

yes and no. Yes because the rear fan will draw air but, the vacumn created by rotational fans is about 1/2 of their output pressure so he would still need something to 1'4". No because air doesn't naturally stay in columns unless they're vertical with convection and even those are subject to bleed off and being pushed around by other gusts. with 3 pushers and 2 pullers in that case I would say it's going to be fine. Were it mine I might add another fan at the bottom since it looks like the heatsinks on those Xeons are drawing air up from the bottom and pushing towards the top rear exhausts.

 

[MarcVenice]

1'4"? Meaning ? Used to the metric system, which might be why I don't get it

 

[DerwenArtos12]

Well the 2 feet he was asking for is about 61cm and 1'4" is about 40.5cm. The static pressure is measure in mm of H20 though and the density of water is about 1g/cm3 and air is about 0.0012g/cm3 round off air to 1/1000 of a gram and you can see water is about 1000 times heavier than air at room temperature so that 2mm of water becomes 2meters of air, in a controlled enviroment with the air being funneled into a tube 1cm in diameter. push that out to 9.2cm in diameter and it's 20cm of air(roughly) accept that it's not in a tube, it's in the open so with turbulence it's cut down to about 80% of that or 16cm or about 6 inches.

EDIT: oh, and that un-obstructed, with the square grates on there it'll be cut down even more, I'd have to know the total surface are of the grates exposed to tell you buy how much but, 5% is fairly reasonably considering they look fairly sparse and it's a decent size fan.

 

[DerwenArtos12]

DP, sorry.

 

[MarcVenice]

I see, and in order to make the air move over 40cm you need to figure out how far 1 fan could move the air, which would be 15cm or so ? So you need at the very least 3 fans to build up enough pressure to move air through the whole 40cm deep case ?

 

[Fullmetal Chocobo]

Originally posted by: DerwenArtos12

Originally posted by: MarcVenice
If you have a fan in the front, and a fan in the back, isn't there going to be something like a 'draft' ? Meaning air is going to move the whole 2 feet, cept that's not really being pushed by the fan, but it's still moving, so no matter how it happens, it's working, no ?

yes and no. Yes because the rear fan will draw air but, the vacumn created by rotational fans is about 1/2 of their output pressure so he would still need something to 1'4". No because air doesn't naturally stay in columns unless they're vertical with convection and even those are subject to bleed off and being pushed around by other gusts. with 3 pushers and 2 pullers in that case I would say it's going to be fine. Were it mine I might add another fan at the bottom since it looks like the heatsinks on those Xeons are drawing air up from the bottom and pushing towards the top rear exhausts.

I'm not worried about the CPU components--they will actually be water cooled. The four fans (on each side--8 total) need to create air movement in the case. I'm trying to find fans strong enough to move air through the case, but quiet enough to avoid having my office sound like a hurricane.

The total case fan configuration will be 8 92mm fans (4 in each bank as pictured)and 2 120mm in the rear. I need to take some better pictures and post them...

 

[Zepper]

FMC,
Do you mean the fans are in drive cages or some such? If so, are the fans behind the drives or in front of them? Is there room for a thicker fan, like the Sanyo 92x32mm units which are very NIZE. If the fans are in drive cages, you will need luck to have them do more than cool the drives. Maybe you could mount a small AC oscillating fan inside that monster case somewhere...

.bh.

 

[Fullmetal Chocobo]

In this picture, on the left side, the four grills shows are for fans. There are four 92x25mm blue UV fans installed in the picture (it is not current). Here is a pic of the fans on the mobo side. Essentially, I'm trying to pick 8 92mm fans to install into these bays (they are hot-swappable in that you can pull that cages out, but I have the hardware providing power for the bays removed, and the fans are hardwired to fan controllers) that will have enough force to push air to the end of the case, ensuring airflow over the entire mobo on the left side, and having airflow to reach the PSUs on the right. You can see one fan on the right side through the missing 5.25" bay cover here

Here are all the pics in that group, if it helps clarify anything.

 

[DerwenArtos12]

I perused the entire group and you'll have to decide what sound level is acceptable and go from there. Would you opposed to chopping it up to try and fit 100 or 120mm fans in it?