Hi everyone! Here is my first post to this great forum.

I have plans to build a new computer case out of mdf. My idea is to make a floorstanding case with a small footprint (around 20*20cm) and a height of 70-100cm.
The reason for the high case is to utilize natural convection to some degree for air flow. The heat producing parts will be placed near the bottom of the case right above the air intakes and once heat starts to build inside the case there will be convective airflow through the case. The top part of the case will act as a duct for the air flow. As far as I understand a taller case would strengthen the convective air flow (just like a chimney). For practical reasons I will not make the case higher than maybe 100cm.

Here are some more details and thoughts:
-Mini-itx motherboard with Intel i3 processor
-External graphics card will be needed. I have been thinking about a HT5450 card with only 20W power at full load. Not sure if the performance is enough for my needs so I may go with something better.
-The PSU will maybe be built in a separate section in the bottom of the case. A picoPSU is also an opition if I go for the HT5450 graphics card. With a picoPSU the footprint could be even smaller.
-I plan on placing a low rpm 18cm fan somewhere in the top part of the case to assist the airflow to make it “assisted convection”. The fan could be either horisontally like drawn below or vertically in the top end of the rear panel (with no air exit on the front of the case).

Any thoughts and opinions are very welcome!

1. I like it.

2. You seem to be going after the chimney effect, so why vent the PSU power out of the chimney air stream?

3. What is "mdf"?

4. Start with a passive seasonic PSU at the bottom. I think its size is about 150 x 160 x 80 and leavin rrom for cables maybe more like 150 x 180 x 80

5. The ITX motherboard is 6.7" x 6.7". You can put that on a diagonal perhaps. That is about 170mm by 170mm. You can put that on a diagonal to pick up heat from both sides of the board. That would leave you a chimney of about 120mm x 120mm. But you will need more room for the PSU.

6. Mount the power unit up and down (for better cable handling). To make the air currents work the cable side will need to face down and the vent side up. A 150 x 150 chimney should be able to handle the air and the cables.

Make the chimney the size of the PSU 150 x 150 (with the PSU installed sideways up.

7. The sweet spot for fan performance is 120MM fans. A 180MM fans isn't going to produce the result you are looking for and even a 140mm fan will be suboptimal. A nice 500 rpm 120mm ball bearing Gentle typhoon might fit the bill at the top of the chimney. You can mount it in the middle with space around it. It will do the job and this will make it even more quiet.

An alternative would be a 120mm variable speed PWM scythe slipstream. You could set it up so that it only turns on when you need it. You may never need it.

8. For the hard drives, try putting these in sideways:
http://www.newegg.com/Product/Product.a ... 6816215046

9 . The taller the chimney, the more pronounced the chimney effect will be. You might want to narrow the top part of the chimney, that will improve its performance. Maybe even narrow the chimney to 120mm in diameter.

The 2500K Sandy bridge will have video performance equal to or better than the Radeon 5450 card.

The 2500K Sandy bridge idles at under 4 watts. And under normal use won't use more than another 5 watts. While it is capable of a TDP of 95 watts, you will never see that unless you run artificial benchmarking software.

The four core 2500K Sandy bridge will use much less energy in everyday use then a dual cord Clarkdale which idles at a much higher wattage.

Consider if all you need is a 2500K Sandy bridge and an Intel ITX board (the Intel ITX boards generally have the lowest energy usage compared to other ITX boards).

Somewhere else on this board someone did a chimney, much cruder than what you propose. My recollection was that he was very pleased with the results.

Interesting idea, but are you counting on the pillar for some kind of convective heating? I suppose it could work, but I'd be a little worried. When I first assembled my wooden box system (http://www.silentpcreview.com/forums/viewtopic.php?f=14&t=61400) the fan I was going to use in the bottom of the case broke, so I had the system running without the bottom fan for a bit, just the gpu fans and the cpu and backpanel fans were going. I thought this would be ok for a little bit, and temps got up into the 80s under heavy load, but that was ok. Once I put bottom fans in, cpu temps dropped into the 50s. I suppose with that fan in the middle, you should be ok, but I would definitely start with fans on the heat sinks before trying to go passive. But the components here are much lower power than mine, so you may not have as much of an issue.

But there are some other concerns here as well. ces brought up the power routing, definitely something to think about, you'll need to leave some room to route between your sections. If you set it up right, you can route most of the power lines right along the same wall as the motherboard.
That brings up another issue, how are you going to actually put the components in there? Will one or two sides open up? Are you getting a motherboard tray for the motherboard? The ports don't really need it, but the video card may need some support above the board. Come to think of it, how are cables connected to the board going to get hooked up? You could go wireless for many of them, but you may want a usb connection someplace on the outside you can access, and you'll need cables for video and power, at the very least. And don't forget power buttons and leds, always useful to have those someplace handy. The floorplan doesn't look too bad, but consider the details too, they can bite you in the ass.

1. Nice System

2. He is going to need a cpu heat sink. Maybe he can use a Mini Ninja. He will always have the option of adding a fan to it - adding a boost to the upward direction of convection.



1. Those darn details.

2. Here is a place he can get some power buttons:
http://www.highspeedpc.com/

3. The backplate of the motherboard can handle most of the other external connections.

4. I see that you used a Lian Li part to mount your motherboard. He can get one from PerformancePcs.com though He won't be able to install it on a diagonal then.

5. Someone on this board has a thread about a chimney convection system they used. It can work. I seem to remember someone testing a board mounted flat and then mounted sideways and they lost 5C just by mounting it sideways and picking up some colling from convection.

How to calculate the Stack effect for chimney convection:
viewtopic.php?f=8&t=2359

Purely convective cooling - with equations
viewtopic.php?f=1&t=34010&view=previous

Tower of Cooling Power
viewtopic.php?t=5089

quiet psu with papst and air tube
viewtopic.php?t=2885&highlight=

Mike Chin on convection:
viewtopic.php?f=1&t=27784&start=0

This is the one I was looking for. A real chimney with real before and after numbers and real results. The chimney was 1,2m x 12cm and reduced cpu temps by 6C. There is no substitute for experimentation
GOAL - Air cooling with no fans (edit: GOAL reached)
viewtopic.php?f=30&t=57619&start=30

I think the lesson is you need as much heat as possible (not sure a 20 watt system will do that) and you need a tall narrow chimney... not larger than 120mm - maybe a 3.5 inch (about 92mm) chimney would be best.

Thank's for all the brilliant replys! Lots of valuable information! Here are some comments and answers in random order:

ces:
Mdf stands for medium density fiberboard.
The idea to have the psu separated was to make sure the motherboard is supplied with fresh air instead of hot air from the psu. But you are right that this reduces the chimney effect. I will make a change to my plans here. Simplest would be to have the psu in the same space with the motherboard. More ideal might be to have it in a separate section but build a duct to lead the heat from the psu to just above the motherboard.
The dimensions will be much determined by esthetics but of course there will have to be space for all the components. I consider tapering the case to make the top part narrower. Then I could make it higher without it being too bulky, and it would go nicer with a 12cm fan also.
The reason for the separate graphics card is that I will use a 2550*1440 display and there are no mini-itx boards supporting this resolution.
Many thanks for your suggestions on hardware!

cordis:
Thank's for the advice! I'm a bit tempted by the idea to go for a single fan solution. But leaving out the cpu fan will for sure not be the first thing to try. Also isn't the cpu fan usually controlled according to the temperature so it should run faster only on high cpu loads?
I will build some sort of tray so I can pull everything out of the box. I will make all the connectors accessable from the back panel. A power button will be placed on the front of the case. Instead of a led I think I will use a diamond shaped "pilot light" used on many guitar amps. The case will either be painted or covered with tolex (the stuff used to cover guitar amps).

ces:
Thanks for the additional links and information. Very useful!

Only one comment: As soon as you add a single quiet 120mm fan running at 500rpm (with a good HS on the CPU), there is no need for any convection effect & you can reduce the size of the box down to what's needed to just hold the components and allow good airflow.

It's fun to think about, and experiment with, but that's the reality about chimneys and PCs -- there isn't quite enough heat to make it work well, and if there is, the cooling effect of convection alone just isn't quite good enough to make it work safely over the long term.

ps -- you could still build the box.... but for a short folded transmission line speaker system, instead, using a small full range driver. You'd want 2 tho -- on either side of your desk.

Mike: Thank you for the "only one comment! That sounds very realistic. But I still like the idea of a "chimney" so I will take this all the way. I have made some purchases already and I have also worked a bit on the design.

1. I decided to look for a SFX psu to be able to make the case narrower. (maybe)
2. I'm looking at the fanless Gigabyte Radeon HT5750 display card, so there will be a bit more heat than initially planned. The cross section of the case will be determined by the heat sink of the display card's heat sink. I don't know exacly how large it is but it's fairly big.

If you go with the chimney effect, get rid of all the fans that exhaust the air. Leave one on CPU/GPU for security while you experiment. Get rid of all the other ones. Then if it works, start slowing down the fans an see what happens. Maybe totally fanless is possible.

Check out the other chimney thread, you'll get a lot of info : viewtopic.php?f=30&t=57619
That other thread really is full of info, and the guy who did this documented it really well.

Yes, I have read that thread and the results look very promising!
I have also played with the formulas for calculating air flow. It gives some idea of how the length of the chimney affects the flow. To double the flow the height of the chimney should be multiplied by four.
The formula also says that doubling the cross section would double the flow. This is of course true if the temperature inside would stay the same but it will not unless also the heat source doubles. My guess is that the effect of the cross section isn't that important in practice.

Now that I think about it, you could have 2 separate intake "chambers" at the bottom (one for PSU, one for CPU/GPU) that join at the top, like a Y upside down. The heat generated by the PSU would stay away from the rest of the components but would still help the chimney effect.

Yes, but I don't think the Y should need to be symmetrical. If the PSU is 80% efficient on average it will burn 20 when the rest of the system burns 80. So the psu part could be around 20% of the total chimney cross section. Something like this:

I have given some thought to this.

1st Mike C is right, and I think doubly so for a Sandy Bridge Chip that idles at under 4 watts.... Still here is a version of a chimney that might make more sense.... at least to experiment with.

1. Lian Lin Q07 case (or Q08 if you are using HD instead of SSDs)
2. powered by a Pico-psu (should work fine if you don't use a video card maybe it might work even with a Radeon 5450?)
3. This will make room for a Thermalright HR-01 Plus with the Thermalright 120mm HR-01-775 Fan duct leading to a 120mm hole cut into the top of the case.
4. On the top of the case put a 3.5, 4.0, 4.5 or 5 inch chimney.
5. Experiment with the diameter and length of the chimney. If you don't like the results, just remove the chimney and replace it with a nice fan filter (120mm black filterright filter will complement the Lian Li finish and look like it was installed at the factory http://www.performance-pcs.com/catalog/ ... s_id=30036)
6. Experiment with the placement of a 500 rpm fan (I would choose a 1000 or 1200 rom Gentle Typhoon.. they have real ball bearings, you can place them anyway you want and they downvold very nicely to any reasonable speed you would want)

Are you absolutely sure a Sandy Bridge running the Intel chip set won't do that?

The 2500K and 2600K as as powerful or more powerful than the Radeon 5450. I can't imagine Intel fielding them without the capability of doing at least a 2550*1440 display.

The next generation Ivy Bridge, which is scheduled for release in 11 months actually is able to drive three monitors concurrently. If Sandy Bridge can't do a single 2550*1440 display I might just wait for Ivy Bridge.

It doesn't need to handle games for me, but if it can't handle large screens... WTF.

The chipset can do it but it's not implemented all the way on a mini itx board (yet). The Zotac H55 mini ITX board was supposed to have duallink DVI for higher resolutions but according to web discussions the DVI isn't dual link. Duallink has been mentioned by Zotac when the board was announced but it was changed before the actual launch.

I already pushed the order button for a fanless HD5750 but i'm having second thoughts due to it's size. I can still cancel the order. Maybe I'd try the HD5450 first and upgrade later if needed.

1. So you are talking about the Clarkdale chip, not he Sandy Bridge? So maybe the 1155 ITX board may hande large displays.

2. If you want a real low power computer, why would you use a Clarkdale? The dual core Clarkdale has a much higher idle than the 4 core Sandy Bridge. Sandy bridge will idle under 4 watts and will carry a reasonable load with only another 5 watts. If my memory serves me well, Clarkdale idles at something above 15 watts. If you are using a Pico PSU and a video card, that is a big difference.

Wow thanks! I didn't notice the new 1155 board. If it can handle 2560*1440 it would sure be worth paying extra for. I was looking at the i3 processor because it's lower peak power should suit the picoPSU better. But if I can use the integrated graphics card it makes things different.

Where do you go to look up that kind of spec for a mother board. I tried looking it up for a Zotac ITX board I own and I couldn't. Same for a P7h55-M pro board that I own.

Seems like you have to buy it and install it... then you find out what size screen it can or can't handle.

http://www.zotac.com/pdbrochures/mb/mas ... ifi_v1.pdf
Not much info there, but it has displayport. That's promising right?

Intel says in their documentation that their DH67CF has displayport supporting up to 2560x1600 (page 21).
http://downloadmirror.intel.com/19486/e ... odSpec.pdf

The Intel board isn't availiable yet in the places I do my shopping. Officially the Intel board only supports PSUs up to 65W.

Zotac has had some problems with their board: http://www.zotac.com/index.php?option=c ... 68&lang=nd

Very interesting stuff. Mini ITX is very easy to cool, no need for stack effect, but it would be fun to try with 125W+ CPU / GPU.

Looks to me like a lot of effort to make downsized version of Fortress 3.

This isn't necessarily a fully rational mission. But then again, this is a hobbiest website. So in a self-referential way it isn't fully irrational either.

That's interesting. That is the kind crap that causes people not to like Intel boards. The only chips generally available at the 95 watt ones. They know that is what people are going to use. They are already setting themselves up to deny warranty claims.

Or do they sell a different board for the 95 watt chips that everyone is selling?

That is for the same Intel flaw that all the Sandy Bridge chip sets have.

Look forward to hearing how this goes, I've always wanted to build a case that looked like this:



...but very hard finding one with base large enough for mini-itx, though possible with pico or nano.

I'd also thought about using the heatpipe kits from HFX to take the CPU and chipset heat up to a heatsink at the top of the case. Any old heatsink will do, always some on eBay, and will have to do a bit of drilling and playing around to attach to the HFX block at the top end. The heat from this will draw air up the case and out.

Another project for a rainy day...

Yes I suppose mini itx will always be too big to fit into a metronome case. Nice pyramidish shape.

I have now ordered all the parts I need. I hope to get them by next week, then I will start building. I'm not sure yet if I will make it a high chimneylike case. But at least I will go for a bottom to top airflow.

Do you think it's ok to fit all the components very close to each other? I'm thinking about making the cross section as small as possible. My psu is a Be Quiet! 300W TFX model measuring 175x80x70mm. I could mount it vertically next to the motherboard as a very compact solution. My reasoning is that reducing the amount of extra air around the components would increase the air speed and improve cooling. More air would mean less air speed. Do you think this would work, or should I expect the opposite result with components mounted too close heating eachother up?

In my opinion, the metronome form factor really looks nice. It just needs to be scaled up a bit for an ITX board. I hope you try it and post a picture of the result.


I think that makes sense. In fact that sort of effect is why convection helps cool a board mounted sideways better than one that is flat on the ground.

If you adopt the Metronome form factor, placing the board on one of the internal sides of the pyramid so that rising hot air would bump back into the surface of the board on the way up would, I think, help transmit heat from the surface of the board to the rising air. It always helps to have some air flow disruption at the surface bing cooled. If you can place the PSU on the opposite internal wall of the pyramid it shouldn't hurt.

Unfortunately, the cross section at the bottom of the pyramid is large, so you wouldn't expect much air velocity there... but then again that is where all the cool air would be.

Please let us know how it turns out.

I will not adopt the metronome shape. Only 90 degree angles for easier woodworking.

I'm thinking of mounting the motherboard vertically and make the board connectors recessed by a few cm to make room for the psu along the back panel. One sidewall of the psu will be very close to the connectors and another sidewall of the psu will be very close to the cpu cooler. I'll try to post some kind of drawing later.

Finally this weekend some woodworking has taken place. I made some changes to the plans too. There will be a 12cm fan sucking in air trough the bottom of the case. The vertical airflow will continue trough the processor cooler up to the chimney part. The psu will be placed about halfway up the chimney (making room for a hard disc between motherboard and bsu. The psu has a fan and it will suck some air out of the case. Part of the airflow will be allowed continue past the psu to the top of the case and exit trough a vent in the back.

The case is something like 70cm high. It could easily have been made lower, but as a floor-standing case 70cm is convenient enough.

I'll post photos within the next couple of days.