Filters+ducts=silence? (Case idea)

datapappan · Post by **datapappan** » Thu Sep 23, 2010 11:12 am

Please critique this case idea:

This is what I want to accomplish:

[-]Filtered air
[-]Cool air for heat sources, meaning low air flow, and so silence
[-]Preferrably some sound trap towards front, as shown

It does require some modding - reversing the PSU fan, fitting filter on PSU 'exhaust' (now inlet), cutting a vent hole in case bottom.

[EDIT: Those things on the inlet, before the fans, are filters.]

Am I chasing geese with this? The idea comes from trying to quiet my current setup, and it seemed like case fans never could keep case temps down enough to give HS fans cool enough air. One or the other would create noise.

I'm thinking of using this case for the project:

/ d

mkk · Post by **mkk** » Thu Sep 23, 2010 1:13 pm

After a while heat will get trapped in the upper forward corner and begin to radiate back towards the hot parts, because the front low exhaust will not be very efficient.

http://en.wikipedia.org/wiki/Convection

Would work better with the same setup and the case turned upside down though.

bonestonne · Post by **bonestonne** » Thu Sep 23, 2010 1:20 pm

If it's got a mesh (and hopefully filtered) front panel, why not just make ducts from the front to the back?

Make a straight duct for the PSU using a 5.25" bay, make a duct that goes straight from the front panel to a good CPU heatsink (tower style) and see how that works, using the front panel as intake still...

I mean, I have a Cooler Master Elite 330, and by looking at the specs in my sig, it runs remarkably cool. Larger heatsinks are your best friend, because you can get away with using 7v fans all over the place, and not worry about temps going too far north.

With the Thermalright HR series exhaust duct could simplify things, and I don't really see how the power supply would be getting too hot right now, unless it's under load most of the time (which if it is, a slightly higher wattage would change that).

GPU could use a new heatsink, or at least new thermal paste if it's getting too hot, that should make a difference even with the stock cooler.

mkk is completely right though, that big empty hole would turn into a pocket of hot air which will give you problems.

datapappan · Post by **datapappan** » Thu Sep 23, 2010 11:12 pm

mkk:

the front low exhaust will not be very efficient

Efficient? Do you mean restrictive? Otherwise it's just the way all air taken in by the fans will be exhausted. COnvection would not have an effect in a fan ventilated case, I think.

Will it be hotter than a normal case setup? My theory is that fans will run slower because of the larger available temperature difference between inlet air and HS.
(Example:
Normal setup w case at 38 C, HS/CPU at 55 C, difference = 17 C.
My setup w inlet at 24 C, HS/CPU at 55 C, difference 31 C.
Having roughly double the available temperature difference, I can run the fans at roughly half speed.
True that case temp will be higher in my setup, but It can never be higher than what's coming out of the HS, wich in turn is lower than the HS itself, so radiation will go towards case interior anyway.)

bonestonne:

why not just make ducts from the front to the back?

I've considered that, with this particular case. I'd still have to mod for GPU duct. My reason for taking air at the back is to muffle the fans better, and shortening the ducts.

/d

tim851 · Post by **tim851** » Thu Sep 23, 2010 11:32 pm

I think it should work. If you have HDDs somewhere in the front area, they could be getting quite hot though, since all the heat is dumped on them. But in principle, your idea is correct: supplying the hottest components with the coolest air.

Arto · Post by **Arto** » Fri Sep 24, 2010 12:05 am

It doesn't matter that much if you draw air through the front or the back as long as you have a decent amount of air flowing through the case.

When you draw air through the front the air doesn't get heated up until it hits a warm heat source. You might actually be better off by making ducts and directing the warm air out of the case. That way you would still provide cooling for the small heat sources like motherboard, RAM and HDD's.
But as long as you make sure you don't overheat some components by dumping all warm air inside the case your idea is not that bad.

datapappan · Post by **datapappan** » Fri Sep 24, 2010 2:48 am

Arto:

be better off by making ducts and directing the warm air out of the case

I've considered this, but it breaks my requirement for filtered air (hard to make sure ALL air is drawn through unducted inlet filters.

[I've updated OP with explanation of filters]

/d

frenchie · Post by **frenchie** » Fri Sep 24, 2010 3:09 am

Why not have the exhaust at the top of the case, towards the front ? Then you can add another slow fan below the bottom front where I presume your HDs would be and keep those nice and cool too !

[EDIt : and at the same time, that takes care of that front hot air pocket that looks like the biggest problem in your design for me.]

datapappan · Post by **datapappan** » Mon Oct 04, 2010 3:55 am

Decided to flip the air flow.

Adding inlet fans will add noise, but in theory this is compensated by revving down the HS fans, since they no longer have to pull through filters, now taken care of by the added inlet fans. Aiming at slight positive pressure, to make sure dust is stopped in the filters.

This also mimics the thermal design for PSUs, where the heat is never recirculated back into the case - I'm using the same technique here for CPU and GPU.

GPU could be Gigabyte Silent Cell 5770, with 2 80 mm Slipstreams fitted in a DYI duct. NB fan flow would be in sucking mode. Could also connect duct to back panel, so heat is not recirculated to inlet area (probably adds more noise, while not affecting case temps that much.)

Same for CPU, Thermalright HR-01/02 with ready-made fan duct.

bonestonne · Post by **bonestonne** » Mon Oct 04, 2010 6:02 am

Drop the intake fans, negative air pressure will cool the hard drives. That's how my system is cooled, and it gives no problems at all. I can't say that the noise is any different either.

If there are filters, I'm hard pressed to say that intake fans will do any better at stopping dust than negative air pressure.

As for the GPU, heat will be difficult to exhaust through the bottom of the case, as heat rises, it doesn't fall. I would say it would be better to have the GPU ducted to the PCI expansion slots, and just making a duct around most of the card, to direct the flow outward.

The fans should really be an aid to airflow rather than a guide, because when you fight airflow, you get turbulence or higher RPMs (and in many cases both), and those are the biggest causes of noise right now.

datapappan · Post by **datapappan** » Tue Oct 05, 2010 3:43 am

Thanks for all comments so far. Anyone have experience with the following I'm trying to achieve:

1. Exhaust heat via ducts => cooler air inside case. (Especially GPU duct, DYI or ready-made).
2. Fight dust with intake fans + positive pressure.

bonestonne:

Drop the intake fans

They're needed for the filters, see below. Otherwise I would certainly agree with you.

I'm hard pressed to say that intake fans will do any better at stopping dust than negative air pressure

Did you notice the filters on the intake fans?

heat will be difficult to exhaust through the bottom of the case, as heat rises

It's been discussed before - heat convection in PC cases have minimal effct when compared to forced flow (i.e. fans). I would actually think the impedance from convection is much lower than what you get from a 90 degree turn and the PCI slot "grille".

/d

flemeister · Post by **flemeister** » Tue Oct 05, 2010 7:26 am

First thing's first, perhaps your original design would work better in the Fractal R3 or P183? The main argument against your original design was the method of exhausting hot air. Instead of making the hot air go downwards, why not let it go sideways/up like mkk and frenchie suggested? The insulated front door would still block noise pretty nicely.

I think you missed what bonnestone was trying to say. The air is going to enter the case at particular areas and exit it at others. As long as there are filters wherever air enters the case, it shouldn't matter how the fans are setup. Good case design should be able to make this concept easy to achieve.

Take the P183 for example, where the entire front panel is the intake area (and completely covered with dust filters), and the rear panel is exhaust. The top exhaust vent is either blocked off or has an exhaust fan installed.

Have a 120mm fan in the normal exhaust spot, and an 80/92mm fan covering the expansion slots. The power supply and hard drive/s take care of themselves by design, since the only way for the PSU to get air is from the front of the case, drawing it past the hard drive/s. It would look something like this:

Front
Rear
Layout (ignore the front fan)

The only way for air to easily enter the case is through the completely filtered front panel. And noise would be at a minimum with all the fans at the back. Replace the CPU fan with a duct to the rear exhaust fan if desired.

bonestonne · Post by **bonestonne** » Tue Oct 05, 2010 7:40 am

In short, if you have filters, the intake air will be filtered. Intake filters work whether or not there are fans present. It's not like they just don't filter air because a fan isn't there.

92mm over open PCI covers, ducted to the GPU
120mm exhaust on the back (nothing on top) ducted to the CPU.

As flemeister said, PSU will take care of itself. That's a 2 fan system capable of keeping everything cool.

drop both the exhaust 120mm and 92mm GPU fan to 7v and you could get away with adding a dedicated CPU fan at 7v and still keep silent operation.

That's how my Cooler Master Elite 330 stays quiet despite having such an open front, just keep the fans away from the front, or undervolt them as low as possible.

You should hear my Antec LanBoy Air....5 fans at 7v all around. For what it is, it's a scary sound.

frenchie · Post by **frenchie** » Tue Oct 05, 2010 7:44 am

@datapappan:
I can tell you from experience that your GPU area will not work very well with your current airflow setup. I had the exact same airflow pattern in the GPU area in one of my very first builds, and temps were bad. Also, VRM cooling will not be very efficent. It might work but be ready for higher temps.
I agree with you that it's a pain that the heat from the GPU has to go inside the case before it is exhausted, but it's a problem GPU manufacturers (or aftermarket cooler manufactuers) don't really take into account. To me, the ideal GPU cooler is a cooler like the Spitfire, but the fins have to be perpendicular to the airflow in the case. Then you could duct your front fans to the cooler, and exhaust all the GPU heat through the PCI slots...
Hope that helps

and good luck with your setup !

datapappan · Post by **datapappan** » Wed Oct 06, 2010 12:19 am

bonestonne, is it your experience that dust buildup is more or less the same with or without intake fans? I would have thought that negative pressure setups would get some part of the intake as unfiltered leakage (as well as filtered of course).

frenchie, do you know why you got high temps in that GPU setup? How did you alter it to achieve lower temps - and was that more silent?

/d

frenchie · Post by **frenchie** » Wed Oct 06, 2010 4:18 am

datapappan wrote:frenchie, do you know why you got high temps in that GPU setup? How did you alter it to achieve lower temps - and was that more silent?

I tried this setup with 2 different aftermarket GPU coolers : the VNF100 (Small Accelero like cooler, by Zalman) and the Accelero.
I'm just guessing here, but I think the reason why it didn't work is that when you pull air through a cooler, barely any air cools the underside of the card or the part of the cooler that is under the card, all the way against the motherboard. The fan will pull more air through the parts of the cooler that have less resistance to airflow, rather than pull air through the whole cooler (it is harder for the air to flow from inside the case, then, between the card and the cooler, through the cooler, and then through the fan). For example, in the case of the Accelero, a lot of air is going to go through the fins that are away from the motherboard, and very little air is going to go through the fins that are closer to the motherboard (more resistance) which also happen to be the hottest.

On the contrary, when you push air through a cooler with a fan, the air flows through all the cooler and across the whole card. Remember, fans are better at pushing air through something than at pulling air through that same thing. The problem with that setup is that the hot air is then dumped into the case.

Did that make any sense ?

To improve this setup, I just reversed the fan on the cooler : now it blows towards the card, rather than away. Temps are better on the GPU and overall noise is the same. However, CPU temps and case temps are a little higher.

bonestonne · Post by **bonestonne** » Wed Oct 06, 2010 5:55 am

I found dust buildup to be extremely minimal regardless of front fans being present. Over a two month period, I found only a very fine layer of dust on the hard drives, which are nearest the front panel of my Elite 330. Components farther back in the case had a negligible amount of dust, however the filters were reaching cleaning time.

The entire case would take a trip to the garage to spend 5 minutes with an air compressor, and then retreat back to it's home under my desk, for another two months.

Currently with a LanBoy Air, I'm afraid I may have to do this every other week if usage is more prolonged, due to the complete lack of filters.