More quiet/silent PC advice..

[Stacey]

My (ahem) Dell 8100 has no CPU fan as such. The rear case fan
connects to a shroud which surrounds the CPU heat sink and allows air
in only through a gap between the shroud and the motherboard. That
means not only no CPU fan, but the airflow around the heatsink is not
in hair-dryer mode. It works, and it is _very_ quiet.

What I'm thinking about trying..

The case has is older ATX style with the PSU blowing -into- the case over
the top of the CPU with an air intake on the back of the PSU. I've opened
up that intake grill to get rid of any "whoosh" noise from the air moving
through the slots. It has a 92mm fan which I'm going to replace with the
"quiet" fan that comes with the large zalman HS and see if I can get away
with this one fan for both the CPU and the PSU. The load is very minimal on
this system and in "display" mode, once it's booted and going the HD
doesn't even run so it shouldn't take much to cool it.

Some thoughts, it also has vent holes in the back of the case which would
allow the air to short circuit back into the PSU. Also the only front vents
are low in the front, which means the hot air goes up and stays in the
case. I'm thinking maybe I should block some/all of those rear vents off
and remove the two upper drive bay covers to let the air move out the upper
front of the case? The box won't be seen so it doesn't matter what it looks
like, just that it's silent. I'm hopeing the heat from the cards will rise
up and get moved out with the airflow across the top of the case, back to
front or maybe leave the slot cover off the slot next to the video card?

Or would I be better off trying to -suck- air across the CPU HSF (looks like
it's going to be pretty close to this fan...) and out the back of the case.
The PSU is at the upper portion of the rear of the case so the heat would
rise and get sucked out the back/in the lower front this way. Then I'm back
to blocking the rear vents to get the air pulled in the front. And the
front intake in lower to the ground, more likely to suck up dust/junk. I
don't think this way sounds ideal for getting air across the CPU HS.

I really want to try to get away with one fan if I can, when I mean silent I
mean almost fanless (even no PSU fan) quiet. Any ideas are welcome.

 

[Robert Redelmeier]

Or would I be better off trying to -suck- air across the CPU HSF (looks like
it's going to be pretty close to this fan...) and out the back of the case.

Blowing air across a HS is better than sucking -- the fan discharge
has all sorts of turbulent eddies that increase heat transfer.
Sucking is only good if blowing would cause bypassing.

-- Robert

 

[Robert Myers]

The case has is older ATX style with the PSU blowing -into- the case over
the top of the CPU with an air intake on the back of the PSU. I've opened
up that intake grill to get rid of any "whoosh" noise from the air moving
through the slots. It has a 92mm fan which I'm going to replace with the
"quiet" fan that comes with the large zalman HS and see if I can get away
with this one fan for both the CPU and the PSU. The load is very minimal on
this system and in "display" mode, once it's booted and going the HD
doesn't even run so it shouldn't take much to cool it.

Some thoughts, it also has vent holes in the back of the case which would
allow the air to short circuit back into the PSU. Also the only front vents
are low in the front, which means the hot air goes up and stays in the
case. I'm thinking maybe I should block some/all of those rear vents off
and remove the two upper drive bay covers to let the air move out the upper
front of the case? The box won't be seen so it doesn't matter what it looks
like, just that it's silent. I'm hopeing the heat from the cards will rise
up and get moved out with the airflow across the top of the case, back to
front or maybe leave the slot cover off the slot next to the video card?

Or would I be better off trying to -suck- air across the CPU HSF (looks like
it's going to be pretty close to this fan...) and out the back of the case.
The PSU is at the upper portion of the rear of the case so the heat would
rise and get sucked out the back/in the lower front this way. Then I'm back
to blocking the rear vents to get the air pulled in the front. And the
front intake in lower to the ground, more likely to suck up dust/junk. I
don't think this way sounds ideal for getting air across the CPU HS.

I really want to try to get away with one fan if I can, when I mean silent I
mean almost fanless (even no PSU fan) quiet. Any ideas are welcome.

If you're going to try to get away with just one fan, then your best
choice is to be using the PSU as an exhaust fan.

Whatever mode you use the PSU fan, blocking the low rear vents and
taking off a slot cover next to the video card do not sound like good
ideas.

RM

 

[Stacey]

If you're going to try to get away with just one fan, then your best
choice is to be using the PSU as an exhaust fan.

Whatever mode you use the PSU fan, blocking the low rear vents and
taking off a slot cover next to the video card do not sound like good
ideas.

I'm starting to agree with you on pulling the air, but wonder why you think
blocking the -lower- vents on the -back- of the case is a bad idea? Seems
like pulling air from back there wouldn't be as good as pulling it from the
front and the lower side grills.

Someone else e-mailed me saying they used this heatsink with just the PSU
fan on a celron 733 and it stayed cool, like 45-50C so this sounds like it
may work out.

 

[Robert Myers]

I'm starting to agree with you on pulling the air, but wonder why you think
blocking the -lower- vents on the -back- of the case is a bad idea? Seems
like pulling air from back there wouldn't be as good as pulling it from the
front and the lower side grills.

I wouldn't want to put hard money on which way will work better with
the PSU fan--it is only a guess, and the only way to find out for sure
would be to try it both ways.

Expansion cards in the lower rear part of the case will cool
themselves by convection, but only if they have somewhere to get
replacement air (i.e., hot air will rise, but only if there is cool
air to take its place). If you block the lower rear vents, there's a
place where air will get hot and want to escape by the same route that
replacement air would have to come in.

You didn't mention the lower side grills in your OP. Depending on how
they are placed, you might get away with blocking the back vents, but
I still see it as a risk of creating a hot spot to cook expansion
cards and no real win. You don't want to be using your expansion
cards to do experiments on temperature inversions: a bubble of hot air
trapped under cold air, still or moving, above it.

RM

 

[Dorothy Bradbury]

PC design...
o About 82-87% of case airflow resistance is the PSU exhaust grill
---- choose a PSU with round-wire v punched grill
---- change exhaust fan grills to round-wire similarly
o Use a blow-thro CPU cooler v impingement (plate-n-fin) heatsink
---- Zalman flower (cheaper & fine) v SLK (overkill for normal use)
---- a) 80mm or 92mm fan on a bracket cooling the heatsink, or
---- b) create a duct around the flower cooler to a case-mounted rear fan
o Aim for 2 exhaust fans vs single fan
---- 1 exhaust fan at 50cfm is 30dB(A), 2 exhaust fans at 2x 25cfm are 23dB(A)
---- PSU w/fan - choose one with 120/92mm exhaust fan (no inner 80mm)
---- case-fan behind CPU - with duct to replace CPU fan, or just to get hot air out

Fanless PSU PC #1
o 190W Laptop-brick & DC2DC convertor
---- must limit total system to 190W re CPU / board / RAM / optical / HD
---- use M-ATX board -- Intel or nVidia re P4 or Athlon
---- single 92mm exhaust fan -- top rear, block other exhaust holes, round wire grill
---- blow-thro CPU cooler -- duct to that exhaust fan or own fan on bracket

Fanless PSU PC #2
o 190W Laptop-brick & DC2DC convertor + Industrial 2-voltage fanless PSU
---- must limit motherboard to 190W re CPU / board / RAM
---- second industrial PSU can power as many optical / HD as you wish
---- as above

Fanless PSU PC #3
o Fanless ATX PSU are available
---- however note if a fan comes on at a certain temperature or wattage load

Industrial fanless ATX PSU do exist, but are low-to-mid 3-figures since they are
lower volume and usually 1M hr MTBF - great for enterprise servers/SAN/NAS.

Choose your case carefully.

Making your own duct isn't difficult:
o Make a mockup out of cardboard
o You can then epoxy-coat the cardboard (makes it rigid) or make in plastic
---- ABS - cut with a knife & snap, glue with ABS cement (a solvent actually)
---- HIPS - hair-dryer & hand mould into shape
---- alloy - tin snips & hand bend, need only be extremely thin aluminium

The cardboard painted with epoxy is actually the easiest.

 

[chrisv]

I really want to try to get away with one fan if I can, when I mean silent I
mean almost fanless (even no PSU fan) quiet. Any ideas are welcome.

Hmm... I run a Antec Sonota case, which features an extra-quiet 1-fan
Tru380 PS, a single extra-large case fan, and rubber-mounted HD bays.
It's also got a nice piano-black finish - a nice case at a fair price
of $100. I also run a Zalman CPU cooler (on a Northwood 3.0). It's
all pretty dang quiet. Hard to imagine anyone being bothered by it...

 

[Stacey]

Robert Myers wrote:

Expansion cards in the lower rear part of the case will cool
themselves by convection, but only if they have somewhere to get
replacement air (i.e., hot air will rise, but only if there is cool
air to take its place).

Ah that makes sense. So far, I'm using old type case with the sideways PSU,
cut a hole in the side cover of the PSU over the CPU with a zalman flower
on it, have a 47 Ohm 1 watt resistor on the PSU fan and this air flow seems
to be plenty. After a 1.5 hour movie using software DVD (the most stress
this box will see) the CPU temp was 45C and everything else seemed cool
enough to the touch. This thing is so quiet you can't even tell it's
on! I'm sure a faster machine or one more stressed would need more
cooling but this seems to be enough. I am going to take your advice and
give the cards some fresh air down low to allow convection to cool them.
Thanx for your help everyone, I'm going to work on making my other boxes
quieter now!