sucks or blows revisited


D

David Besack

Just wanted to give my experience. I have an Antec minitower with a
120mm fan slot in the lower front and another in the back right under
the PSU. I also have a 2-fan PSU, and am running an XP3000+ with a
Thermaltake volcano 11 HSF. The front and rear 120mm fans have the same
rated CFM. My temps are measured by sensors on the mobo, so I'm not
sure how accurate they are to the "real" temp.

The front fan is an intake (obviously, I don't think anyone uses that
fan slot for an exhaust) and the PSU also exhausts. I tried using the
rear fan both as an intake and an exhaust.

My results: when the rear fan was used as an intake, my CPU was idling
around 45 and after heavy gaming was about 63. Also, the case is fairly
airtight, as in there are no gaping holes except where the fans are, and
the PSU was blowing out a LOT of very hot air.

If I turned the fan around and used as an exhaust, my idle temp went up
to 50, but my after-gaming temp lowered to around 58. Also, the rear
fan was doing most of the exhaust, and the PSU now only had a small
amount of air coming out (and it was less warm).

So overall, the CPU absolute highest temp was kept 5 deg. lower when the
rear fan was exhausting, but the idle was 5 deg. higher. I'm not sure
overall which is better. In both cases my system temp did not change much.

One thing I should not is because of the 80mm fans on the PSU, I might
benefit from another 80mm intake, but to do it I'd have to cut a hole in
the case, probably on the side panel near the bottom. Hmm, maybe I've
got a project for the weekend :)
 
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A

Avid Gamer

Ive got a hole in the side of the case with a 120mm fan, just beside
the cpu cooler, about 5c cooler with this bloweing cool air to the
cpu.

Just at 7volts but a 120mm at 7volts can push somthinglike 30cfm or
more, more than enough.
 
G

Gianmaria Fontana di Sacculmino

Il giorno Sat, 09 Oct 2004 21:05:25 +1000, Avid Gamer
Ive got a hole in the side of the case with a 120mm fan, just beside
the cpu cooler, about 5c cooler with this bloweing cool air to the
cpu.

Does the cpu have an HS with fan sucking out? In such a case there is
a conflict at mid air :)
 
M

Matt

David said:
One thing I should not is because of the 80mm fans on the PSU, I might
benefit from another 80mm intake, but to do it I'd have to cut a hole in
the case, probably on the side panel near the bottom. Hmm, maybe I've
got a project for the weekend :)

That would degrade the cooling of your hard drives.

It sounds like you have a SLK3700. The plastic front panel restricts
air flow through the front vent. Measure your temps with and without
the front panel. Out of sight on the bottom of the front panel there is
(on mine anyway) a 4"x5/8" hole that channels most of the incoming air.
You can enlarge that hole so as to triple its area and improve air
flow. You will need a gap between the front panel and the carpet or
floor, which is to say the case should be raised a bit off the floor.
Also I would advise removing the filter screen and taping a piece of
furnace filter over the chassis' front intake vent. That will filter
most of the incoming air.
 
M

Monster

I have a cpu with an adjustable fan speed. I find that if I increase the fan
speed the case gets hotter and the cpu cooler. I don't think case cooling
has much of an effect on the cpu temperature from my observations.
 
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R

ric

Monster said:
I have a cpu with an adjustable fan speed. I find that if I increase the fan
speed the case gets hotter and the cpu cooler. I don't think case cooling
has much of an effect on the cpu temperature from my observations.

It doesn't except for the fact that your HSF will cool your CPU to xx
degrees above case ambient. If your internal case ambient temperature
goes up 5 degrees (due to something other than your CPU), your CPU
temperature will go up 5 degrees. [This is assuming that your CPU cooler
is operating at 100%.)
 
D

David Maynard

Monster said:
I have a cpu with an adjustable fan speed. I find that if I increase the fan
speed the case gets hotter and the cpu cooler. I don't think case cooling
has much of an effect on the cpu temperature from my observations.

You're using air to cool the CPU and while the CPU can be warmer than the
air, depending on how good a job the heatsink is doing, it sure as heck
can't be any cooler than the air blowing over it.
 
M

Matt

Monster said:
I have a cpu with an adjustable fan speed. I find that if I increase the fan
speed the case gets hotter and the cpu cooler.

That should not be much of surprise.
 
D

David Maynard

Matt said:
That should not be much of surprise.

Actually, if the case really were getting hotter it *would* be a 'surprise'
because the processor is putting out the same amount of heat regardless of
how hot the CPU, itself, gets and how fast, or slow, the heatsink fan runs.
 
M

Matt

David said:
Actually, if the case really were getting hotter it *would* be a
'surprise' because the processor is putting out the same amount of heat
regardless of how hot the CPU, itself, gets and how fast, or slow, the
heatsink fan runs.

Hmmm ... okay, so it doesn't behave like, say, an electric space heater.
If you slow down the heater's fan, the room will get cooler.

It seems you are supposing a constant clock (no thermal throttling)
hence the same rate of computation. I won't disagree with that.

....
 
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D

David Maynard

Matt said:
Hmmm ... okay, so it doesn't behave like, say, an electric space heater.
If you slow down the heater's fan, the room will get cooler.

A space heater regulates the heating element, otherwise it would overheat
and fail, with the result that the energy going into the element, and the
room, is lowered when you lower the fan speed.

It seems you are supposing a constant clock (no thermal throttling)
hence the same rate of computation. I won't disagree with that.

Yes, I was, but that's a good point. If the CPU were throttling then
increasing fan speed would allow the processor to increase its speed,
consuming more energy like the space heater, and increase case temp.
 

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