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 Post subject: Final look
PostPosted: Tue May 25, 2010 10:47 pm 
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Joined: Tue May 27, 2008 12:04 am
Posts: 162
Location: Finland
Final looks
Image
P182 is located behind the TV, you can see the chimney painted to same color with the wall. The system has been running almost 4 months now so now I can really say it's working - and the TV is the noisiest part in the photo (with coil whin and electric hum)

Details of my home theater:
Computer: P182, original fans replaced with a chimney (natural airflow)
Image from inside the case in this post
Full specs of all the components in this post
Link to this post (image of the whole setup)
Television: Sony KDL42W4500
Stereo Amplifier: Pioneer A-676
Surround Amplifier: cheap Logitech
Front stereo Speakers: Gradient 1.3
Front middle speaker: cheap logitech
Back L/R speakers: Forvoice 7.7
Subwoofer: cheap Logitech, rarely used




As you can see, not too much of boxes and nothing too expensive exept the speakers, but they were all bought as used. No antenna either, TV image and internet are coming via optical fiber. It's nice to have a traditional stereo amplifier for computing and listening music - Now I turn on a whole surround system only when i'm watching movies with surround sound. May I call my system green?

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E8400 @ 1,8GHz, passive cooling | CPU Queen 7163 points | CPU stress test two hours, temperature 43C | fan rpm's ZERO


Last edited by maalitehdas on Thu May 27, 2010 2:39 am, edited 1 time in total.

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PostPosted: Wed May 26, 2010 8:03 am 
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Joined: Wed Feb 03, 2010 5:03 pm
Posts: 65
Location: Portugal, EU
Great, looks very nice (the chimney looks better painted, obviously :) )

I'm glad it works well (i agree that the fact that it is still working is a good proof) and that you achieved your goals.

8)

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 Post subject:
PostPosted: Wed May 26, 2010 3:29 pm 
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Joined: Wed Aug 15, 2007 7:37 pm
Posts: 222
Location: Melbourne, Victoria, Australia
Fascinating idea...perhaps I should try it myself. =]
Where on earth did you get such a massive cardboard tube though?
Also, just to note, technically I think your setup would be considered negative pressure, since the chimney causes air to be drawn in through air pressure difference. If you had fans blowing into the case at the same rate as air is being drawn out of the chimney, then it would be considered neutral.
But still, great achievement on a passive setup.


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 Post subject:
PostPosted: Wed May 26, 2010 5:52 pm 
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Joined: Tue May 27, 2008 12:04 am
Posts: 162
Location: Finland
Quote:
Where on earth did you get such a massive cardboard tube though?

I asked for tube in a local hardware stores selling floor carpet. The tube inside the carpet roll was rubbish for them, so I just got one for free and cut the lenght (1,2m) with a saw.
Quote:
technically I think your setup would be considered negative pressure, since the chimney causes air to be drawn in through air pressure difference.

You're right about the sucking effect but the pressure is (and must be) the same inside the case and in the room. Intake vents must also be big enough to maintain the neutral pressure. If the pressure goes negative, the chimney starts to suck slower or even stop sucking, and the cooling wouldn't work.

Some additional physics of heat and pressure:

In houses with electric air contidioning and a fireplace with chimney a pressure difference causes a true problem sometimes - the smoke comes inwards. It happens when the pressure inside is smaller than outside. Same thing might happen even without electric air contitioning when weather is bad. At some point the pressure grows big enough (either by heat or enough of replacement air) and the chimney starts to work normally.

In computer cases the heat first causes positive pressure (expanded air) which tries to get out from the case wherever it can (pressure inside the case want's to achieve balance with pressure outside the case). Since the air is expanded, it's also lighter - so first direction is always upwards. If there are holes located higher and lower, the positive pressured air is exhausting from the higher one. After the balance in pressure is achieved, the flow of lighter air still goes on and tries to cause negative pressure. Replacement air starts to fill the gap (pressure ourside the case want's to achieve balance with pressure inside the case). Eventually all this physics cause a neutral pressure into the case (as long as the vents are big enough) and the heat remains the only thing that keeps the progress running. In all passive cooled systems this is the situation.

To maintain difference in pressure (in not sealed system) some force must be used all the time. Difference in pressure is againts the laws of nature.

In a chimney system positive pressure (caused by heat) is needed to start the flow - and the longer the pipe, the bigger the needed pressure. That's because there's always a natural pressure difference in the low and high ends of the pipe and that difference must be beaten. After the flow starts the system balances itself to neutral pressure. I suppose there is an optimal length for the chimney too, I don't know that. However please don't experience with this build with too long pipe cause your case temperature might rise too high before the flow is able to start.

A question:
Has anyone ever tried a passive water cooling system? (without an active pump). It would be nice to know if natural convection also works with water in practice, especially if it works even better. I've also heard about a case totally filled with liquid, how's that?

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E8400 @ 1,8GHz, passive cooling | CPU Queen 7163 points | CPU stress test two hours, temperature 43C | fan rpm's ZERO


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 Post subject:
PostPosted: Thu May 27, 2010 1:34 am 
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Joined: Wed Aug 15, 2007 7:37 pm
Posts: 222
Location: Melbourne, Victoria, Australia
Most immersion systems I've seen consist of a fish tank full of cooking oil. For the average enthusiast, cooking oil is probably the most cost effective dielectric liquid you can have access to.

Edit: Wikipedia has an approximation equation for stack effect flow rates, which you can use to find height if you solve for h instead.
Image
Assuming worse-case discharge constant Q of 0.65 (Not sure what this is, I just plugged in a value that wiki suggested), flow area A of 0.01131m² (cross sectional area of 120mm fan vent), average case temperature Ti of 313.15K (40°C/104°F) and room temp Te of 293.15K (20°C/68°F), with a desired flow rate Q of 0.011389m²/s (~24CFM or 41m³/h, the airflow of a Noctua NF-S12 running at 600RPM), you would need a chimney that is ~1.79M (~5.87') high.
If we apply the equation to your computer, again assuming computer case and room temperatures to be 40°C and 20°C respectively, you would get around 34m³/h (~20CFM) flowing up the chimney. Of course, the greater the temperature difference, the higher the airflow.


Last edited by KayDat on Thu May 27, 2010 3:03 am, edited 5 times in total.

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 Post subject:
PostPosted: Thu May 27, 2010 2:24 am 
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Joined: Thu Jul 24, 2008 10:57 am
Posts: 165
Location: Riga
maalitehdas wrote:
the pressure is (and must be) the same inside the case and in the room..

Wrong. If it was, there would be no reason for the air to enter the case.


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 Post subject:
PostPosted: Thu May 27, 2010 3:24 am 
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Posts: 162
Location: Finland
Klusu wrote:
maalitehdas wrote:
the pressure is (and must be) the same inside the case and in the room..

Wrong. If it was, there would be no reason for the air to enter the case.

You're right - but when the replacement air enters the case from big intake vents the pressure is soon balanced. Then the chimney causes negative pressure again, then it balances again and so on... In the end, the difference in pressure is so small inside the case that I suppose you can call it neutral in practice. The sucking effect in chimney setup is caused by lower air pressure in top of the room (near roof) compared to higher air pressure around the intake vents. The heat causes this flow to go faster.

Somewhere in my case, amid all this airflow, must be a Neutral Pressure Plane (NPP). Above this theoretical plane, the air pressure is slightly positive compared to the room air pressure and is trying to force its way out of the case. Below the plane it is slightly negative and the case is trying to draw air in. The location of the NPP can constantly change in response to changing conditions (for example heat rise inside the case). When NPP is located in the chimney, my case is slightly negative pressured. When it's in the case, there are both positive and negative pressures there. When it's in the level of intake vents, my system is positive presurred. Anywhere it might be, the pressure can be called neutral in my opinion.

For KayDat: Thanks for the formula. Total height from the intake vents to top of the tube is 150cm in my system, so I suppose I'm pretty close to that much of airflow. Nice to know.

I also edited the last picture post, now there are links for inside picture and system specs too.

_________________
E8400 @ 1,8GHz, passive cooling | CPU Queen 7163 points | CPU stress test two hours, temperature 43C | fan rpm's ZERO


Last edited by maalitehdas on Thu May 27, 2010 3:52 am, edited 1 time in total.

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 Post subject:
PostPosted: Thu May 27, 2010 3:48 am 
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Joined: Thu Jul 24, 2008 10:57 am
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Location: Riga
maalitehdas wrote:
lower air pressure in top of the room

Wrong again (although it is a little lower, like it is just 1/3 on the top of Everest)


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 Post subject:
PostPosted: Thu May 27, 2010 4:00 am 
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Location: Finland
Klusu wrote:
maalitehdas wrote:
lower air pressure in top of the room

Wrong again (although it is a little lower, like it is just 1/3 on the top of Everest)

Please explain how you see the situation and where you think the NPP is?
In my opinion: When the computer is off, I suppose it's exactly 75cm down in the tube. When there's 46 degrees celsius inside the case, I suppose it's close to the level of the heat sources.

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E8400 @ 1,8GHz, passive cooling | CPU Queen 7163 points | CPU stress test two hours, temperature 43C | fan rpm's ZERO


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 Post subject:
PostPosted: Thu May 27, 2010 4:20 am 
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The chimney creates some positive pressure in it's top and negative in it's bottom. The case can be considered part of the chimney. When off (and cold), the same pressure everywhere.
But the idea is good. Some time ago I was thinking about making an intake tube from outside. Would not work in summer.


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 Post subject:
PostPosted: Fri Aug 20, 2010 7:47 am 
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Location: Finland
Hi all, I just found a wattage meter in our library! They seem to borrow a lot of things among books nowadays... I borrowed it and got some true watt readings for my chimney-PC

PC at idle (windows+startup programs only): 73W
PC at normal use (browsing, office work etc): 78W
PC at 100% burn of CPU+MEM+PSU+cache+HDD: 98W

I have no idea if these readings are any green. I checked our laptop also (Compac 6820s): It took 30W-57W with maximum screen brightness

Watching HD-movies with big screen and great sound isn't green:
My PC+Sony 42"+Surround 5.1 (big speakers) together takes 275-295W

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E8400 @ 1,8GHz, passive cooling | CPU Queen 7163 points | CPU stress test two hours, temperature 43C | fan rpm's ZERO


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 Post subject:
PostPosted: Fri Aug 20, 2010 12:54 pm 
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Joined: Fri Dec 26, 2003 6:54 am
Posts: 3011
Location: Sweden
maalitehdas wrote:
CPU Core2 duo E8400
clock 3,0GHz -> 1,8GHz
voltage 1,25V -> 0,8V
wattage (idle/load) 36W/65W -> 12W/17W

Is that the TDP? I have to tell you that it has nothing to do with the real world usage.
It tops out at 40 W, in worst case situations. I've never seen a review showing more than that. TDP is a limit, you should read it as <65 W.

Here's a classic movie about oil cooling, it makes it look so easy and fun!
http://www.youtube.com/watch?v=PtufuXLvOok
http://www.pugetsystems.com/submerged.php


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 Post subject:
PostPosted: Fri Aug 20, 2010 10:31 pm 
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Joined: Tue May 27, 2008 12:04 am
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Location: Finland
That's the TDP and surely never reached in normal use, I think that normal use add only 1-3W to idle consumption. Maybe you can reach the TDP with 100% burning thou? After undervolting I'm getting that 17W with 100% burning, but I have not used the meter with normal voltage so I couldn't tell at the moment.

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E8400 @ 1,8GHz, passive cooling | CPU Queen 7163 points | CPU stress test two hours, temperature 43C | fan rpm's ZERO


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 Post subject:
PostPosted: Sat Aug 21, 2010 2:47 am 
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Joined: Sun Sep 05, 2004 1:51 pm
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Location: Gefle, Sweden
How about adding a slow fan to the chimney? :) (top or middle)
Wider chimney perhaps? If you can find another spare tube. Could make for an interesting comparison.


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 Post subject:
PostPosted: Sat Aug 21, 2010 4:16 am 
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maalitehdas wrote:
Maybe you can reach the TDP with 100% burning thou

In fact, you can't. Here are xbitlabs results, using Prime95:
Image


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 Post subject:
PostPosted: Sun Aug 22, 2010 3:46 pm 
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Location: Finland
mkk wrote:
How about adding a slow fan to the chimney? :) (top or middle)
Wider chimney perhaps? If you can find another spare tube. Could make for an interesting comparison.

Thanks for ideas, but...
- If a fan would move the air, chimney would have no use. It's either chimney or fan, and in my case I wanted to get rid of the fans.
- If i used wider chimney, i'd need to cut the case too. There is a 12cm vent on top of the case, so I suppose 12cm tube is ideal in P182. More height would surely add to the cooling performance but in my room it's at max too.

Mats: Thanks for the link and info. I suppose my E8400 would use at max 29W with original clock and voltage then, and hitting the TDP (if even possible) would need serious overclocking+overvolting. The low idle readings were a suprise too, I suppose my undervolted CPU is <2W at idle then. I should edit one of my earlier posts by these facts but i'll pass...

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E8400 @ 1,8GHz, passive cooling | CPU Queen 7163 points | CPU stress test two hours, temperature 43C | fan rpm's ZERO


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