Convection cooled closed av tower

[dano]

Hi all. I'm building a closed "reduced dust" tower for my av equipment and I'd like to know up front if my design will allow the heat generated by my components to be sufficiently dissipated using passive convection.

Basic design:
- tower dimensions are 66" h x 25" w x 25" d
- has legs that are 6" h
- inner cabinet dimensions are 59" h 24" w x 24" d
- shelves are 22" w x 22" d; they are "suspended" in the 24" w x 24" d space; they slide into corner columns that run the height of the unit, leaving 2" x 18" gaps on all sides of each shelf for air flow
- on the top and bottom of the unit, along the front, sides, and back, there are four 2" x 18" strips that are cut out of the wood and covered in screen
- will house a receiver, PS3, cable modem, wireless router, and phone charger (no set top box)
- distant future *may* hold a dvd jukebox, harmony charger, and / or PVR

I've tried researching the science of convection, but I'm not finding any simple formula that I can apply to my design... any advice or info would be appreciated.

PS: If at all possible, I would prefer not to use fans, as is discussed in this thread:
http://www.digitalhome.ca/forum/show...ght=convection

[otown47]

I just finished my closed AV cupboard and installed an 80mm 120v ventilation fan and a rotary light dimmer to contol it. I was running the fan off the AVR but the STB needs the fan on all the time. The fan is running at about 1/2 speed and with the doors closed you can't really hear it. The whole thing cost less that $30.

The air enters from the cracks around the doors and is sucked out from the top by the fan. The shelves were cut short to allow gaps and air flow.

If I can figure out how to post some pics I will.

[jvincent]

Unfortunately the laws of thermodynamics are going to give you grief.

If all of your components are low power then you can probably get away with natural convection but it's a gamble. The PS3, for example, generates a fair amount of heat and as such has an fan because it simply cannot keep itself cool enough with convection.

Also, unless you are virtually airtight, you will accumulate dust.

Ultimately one or more large fans that are spinning slowly will give you the best thermal performance.

[dano]

Thanks guys. I hadn't thought of plugging a fan into my receiver, that's a great design. Otown can you tell me what 80mm 120v fan you used? A google search turned up a couple of million different ones...

[otown47]

Here's the manufacturer of the fans, there's lots to choose from. The lowest speed 120v 80mm fan is probably the best. The site will also tell you where you can buy from in your area.

You will probably have the fan on all the time because of your STB which never goes off and produces a lot of heat.

http://www.circuittest.com/

[Eljaca]

Sorry to hijack and revive the dead, but I have a quick and similar request along the lines of this thread. My HT rack is full of the usual suspects and about 3 years ago I bought an AC powered fan to cool the whole thing from behind - a temporary measure. Well, this temporary measure turned into a lazy permanant fix. I now am finding the energy to do it the right way and was wondering if anyone has any recommendations on equipment to do so. Specifically, I'm looking for an AC to DC adaptor to run out of my switched receiver plug and attach to at least 2 fans - quieter the better. (Although I lived with a full blown AC fan for 3 years - probably the only reason I didn't really notice how loud it was, was because the white noise coming from our two baby monitors in the HT room are louder!) Pardon my ignorance, but is there such a thing as an adaptor that would run 2-3 CPU fans (without buying a full power supply) and what fan would be best (I've read slower the better?)

Thoughts?

Thanks in advance.

Scott.

[I_Want_My_HDTV]

I use a 9V/1A power block to power a couple of 80mm computer case fans. The fans are Arctic Cooling Low Speed 1500RPM FDB. They don't move a lot of air but are extremely quiet and reasonably priced. 90mm or 120mm fans would probably work better, depending on the cabinet. The power block is one I had from an old disc player but anything that is 9V DC and can supply 0.5 amp or higher should work. I've seen them for less than $5 at surplus stores. (Note that most of these power blocks supply more than the rated voltage so a 9V block is good for 12V fans.) I mounted mine on some $0.35 corner brackets using 6-32 bolts and small rubber grommets. The grommets help reduce vibration noise but probably aren't necessary with FDB fans. (They were with the previous ball bearing fans.)

[Eljaca]

I_Want_My_HDTV - What sort of connection do the fans have and do you need an adaptor to connect it to the 9V power block? Also, how are you running the multiple fans - are they in series or again is there an adaptor that allows you to plug 2to1?

Thanks in advance,

Scott.

[otown47]

If you want to run a DC fan, you can use a wallplug type power adapter with the right voltage or a universal one and dial in the voltage.

Why are we assuming that a DC fan is quieter than an AC fan?

[Eljaca]

It was my understanding that a DC fan is not necessarily inherently quieter but holds the advantage that the speed of DC brushless fans can be controlled by varying the voltage, which means you can more easily change them to a lower or higher speed. To the extent you can run them slower, you run them quieter.

Anyone know the difference in life expectancy?

Scott.

[DJDiggler]

I've had an idea of using a filter, (to be exact a hepa filter from a vacuum or even an automotive one, build it into an intake where the fan/fans draw air from. Along with the positive pressure in the stand from the fan, this should keep virtually ALL dust out.

A rough sketch of my idea: (could be front/side view would work either way I think)
Will this be a good setup? I'd put the hottest components to the top I think so they don't heat up the air for the others.

[jvincent]

I'd put the hottest components to the top I think so they don't heat up the air for the others.

That may not necessarily be the best idea. If the hot components are more susceptible to heat failure keeping them closer to the intake air may be better.

Even the cooler component will generate heat so by the time the air gets to the top it will be hotter than ambient.