A/V Enclosure Cooling and Air Conditioning - AVS Forum
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post #1 of 18 Old 04-17-2013, 08:13 AM - Thread Starter
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Hey all, long time watcher first time writer here...

I'm in the process of speccing out a system renovation for a large, not-particularly-well installed residential A/V setup. A large part of the project will be relocating as much equipment as possible to a centralized location from various A/V cabinets scattered around the home. I've been scouring AVS and the internet looking for some more definitive information on equipment cooling, but I haven't really found satisfactory answers (yes, I've read the Middle Atlantic whitepaper).

Right now the plan is to rack up eight amplifiers (four for the "primary" zones, i.e. 7.1 A/V receivers, and four for the "secondary", i.e. stereo amplifiers for whole house audio), a media center PC, a TiVo, two Xboxes, and a handful of other solid state devices (matrix switch, audio distribution, etc. - nothing really heat-generating). The closet location is on the second floor with convenient access to the attic above, so installing ventilation isn't an issue - the question is what ventilation to install?

It seems like conventional wisdom is to set up the rack for proper ventilation, and combine that with a bathroom fan venting from the top of the room, but I'm not convinced that will be sufficient to handle the heat output of all the equipment... my first thought was have A/C installed in the room but that seems to be less common than I originally anticipated. This is located in south Texas, so it's gonna be hot - is simple convection with fan-based ventilation enough? Do I vent it outside, or into the A/C intake? Is it worth having an dampered A/C vent installed, or a dedicated split-system, and (roughly) how much does something like that cost to run?

I want to get this system set up right the first time (well, second time tongue.gif), so let me know what y'all think!
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post #2 of 18 Old 04-17-2013, 09:20 AM
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The proper way to do it is to calculate the waste heat output of your equipment and then from that work out how much air you need to move to keep the system cool.


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post #3 of 18 Old 04-17-2013, 09:24 AM
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You'll absolutely want to dump the hot exhaust into the HVAC return, not the attic, as you don't want that air to be replaced (by leaks in the home) with outside unconditioned air.

I do this in my AV closet, and it works ok for me - but my issue is that I don't have sufficient air intake into the closet (and in my layout, it would be unsightly to add). I used an HVAC vent fan arrangement from CoolComponents - and they have a newer, more powerful blower-based system now.

I do have an intake vent in that closet, but on its own not enough air comes into the space. Balancing that with a 24/7 booster fan might work if the CFM math worked out. I currently "solve" the intake problem by leaving the closet door cracked open. The closet is always warm (mid-80s), but good enough.

Figure out your heat load (average watts consumed converted to BTU/hr) and that will help you size the solution accordingly.

Hope that helps,

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post #4 of 18 Old 04-17-2013, 10:16 AM - Thread Starter
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All right, so my rough calculations resulted in a heat output of ~9500 BTU/Hr, which I think translates to about 900 CFM. I'd also like to keep the room temperature lower than 85 degrees (not sure if it's necessary, but my experience is in datacenters, where we would be targeting 68 degrees or below). Is it worth getting a cooling system installed, or do I just go with beaucoup fans?

No claims that my BTU calculations are correct, but here's the numbers I used: four amplifiers at 100W/channel * 7 channels = 700W per amplifier, four amplifiers at 250W/channel * 2 channels = 500W per amplifier. Amp efficiency 65%, 90W operating power. Media server 650W, Xboxes 200W. Does this all seem right?
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post #5 of 18 Old 04-17-2013, 11:45 AM
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Quote:
Originally Posted by SnarkyNinja View Post

No claims that my BTU calculations are correct, but here's the numbers I used: four amplifiers at 100W/channel * 7 channels = 700W per amplifier, four amplifiers at 250W/channel * 2 channels = 500W per amplifier. Amp efficiency 65%, 90W operating power. Media server 650W, Xboxes 200W. Does this all seem right?

Way overkill - you don't want to use the faceplate ratings, as those are worst-case maximums. Actual values will be much lower. Those amps will barely ever reach anything close to that output - you're probably better off measuring the "idle" power (no signal) consumption on the amps and adding some.

Do you have any/all of this equipment on hand that you can measure? A "Kill-a-Watt" power meter is invaluable for these things. Focus on the idle, steady state heat load, as that's what's going on 24/7. In my rack, the set-top boxes, PC server and video matrix are the big items. All the WHA amps and controllers are minor contributors.

You might be able to find power measurements in the product specs/manuals. Look for the "idle" or "standby" power consumption values. And of course fudge up from there. But you'll be nowhere close to max.

Jeff


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post #6 of 18 Old 04-17-2013, 11:54 AM
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I DIYed a equipment cooling setup in my ded HT. My entire rack only uses 240cfm and thats a bit of overkill.
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post #7 of 18 Old 04-18-2013, 10:28 AM
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Quote:
Originally Posted by jautor View Post

Way overkill - you don't want to use the faceplate ratings, as those are worst-case maximums. Actual values will be much lower. Those amps will barely ever reach anything close to that output - you're probably better off measuring the "idle" power (no signal) consumption on the amps and adding some.

Do you have any/all of this equipment on hand that you can measure? A "Kill-a-Watt" power meter is invaluable for these things. Focus on the idle, steady state heat load, as that's what's going on 24/7. In my rack, the set-top boxes, PC server and video matrix are the big items. All the WHA amps and controllers are minor contributors.

You might be able to find power measurements in the product specs/manuals. Look for the "idle" or "standby" power consumption values. And of course fudge up from there. But you'll be nowhere close to max.

Jeff

Some rules of thumb:

For amplifiers use 10% of faceplate rating (this is a good percentage to use for std class AB amplifiers), for everything else use 100%. Add all the Watts together then multiply by 0.317 to give you the CFM required.


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post #8 of 18 Old 04-18-2013, 10:50 AM
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I wouldnt use 100% for anything other than class A.

For class G,H, and D 20% is conservatively safe also IMO.

EDIT:

I went back and looked at my thread from when I did the load calcs for my ventilation.

FWIW the multiplier is 3.42 to convert from continuous watts to BTU.

Now to convert From BTUs to how many cfms are needed depends on the air temp gradient. However close approximation can be made by the following:

1 Ton AC provides 12,000 BTU/hr heat removal capacity(From HVAC load calcs)
HVAC rule of thumb is 1 Ton AC can provide 400 cfm of cooled air.

So plug in your BTUs per hour (X) you calculated above into this formula and you'll have an approximate CFM requirement:

(400 cfm / 12,000 BTU/hr) * (X)BTU/hr

For example if your calculated BTUs/Hr was 1370 that would require about 45cfm.

Or you can read about it all here in my build thread.
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post #9 of 18 Old 04-18-2013, 11:02 AM - Thread Starter
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See, now that's what I'm looking for - much simpler calculation!

4x (480W/10) for the main amps
4x (250W/10) for the multi-zone amps
2x 125W for Xboxes
30W for TiVo
650W for media center PC

Totals up to 1222 watts, build in a little fudge factor up to 1250W, results in a little under 400CFM. That number seems a little bit more reasonable - so I should be looking at something like this? I've got pretty much carte blanche to get all this equipment to stop overheating, so I can cut vents in the walls/door/ceiling to my heart's content. Seems like the best solution now would be to cut a large vent in the ceiling connected to an inline fan as above venting into the HVAC return, and a companion vent in the bottom of the door to the closet... makes sense?
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post #10 of 18 Old 04-18-2013, 11:14 AM
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Quote:
Originally Posted by SnarkyNinja View Post

See, now that's what I'm looking for - much simpler calculation!

650W for media center PC

Nyal's rules of thumb are good - with the PC being an exception to the "100% for non-amps". That faceplate rating is the max output of the power supply, but those are general purpose devices and your PC is likely consume much less than that. Even with a few hard drives, probably <200W.
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Totals up to 1222 watts, build in a little fudge factor up to 1250W, results in a little under 400CFM. That number seems a little bit more reasonable - so I should be looking at something like this? I've got pretty much carte blanche to get all this equipment to stop overheating, so I can cut vents in the walls/door/ceiling to my heart's content. Seems like the best solution now would be to cut a large vent in the ceiling connected to an inline fan as above venting into the HVAC return, and a companion vent in the bottom of the door to the closet... makes sense?

Yes, that looks reasonable. There's a formula to show how much airflow you can expect from a passive vent opening based on size/shape, but you're not moving huge amounts of air, so I'd bet any vent in a door would suffice. I just wasn't willing to cut one into my door... biggrin.gif

And have the HVAC guys drop a supply into that closet as well, as when the HVAC system is running, you'll be pulling significantly more air through that return. Don't forget about an air filter somewhere in that path (I have the whole house filter in the attic that covered this).

Jeff


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post #11 of 18 Old 04-18-2013, 11:33 AM
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A couple posts while I was editing..... biggrin.gif

I calculate ~150cfm actual ventilation required. I do not believe you need 400cfm(actual). Remember just b/c you install a 400cfm fan doesn't mean your exchanging that much. I needed about 120cfm but installed 240cfm fans due to considerable frictional loss over long flex duct runs.

I also recommend filtering your intake to limit the dust you pull into the equipment area.

Just for reference here is now much air a 240cfm fan moves:

http://www.youtube.com/watch?feature=player_embedded&v=kpE1cGxELB0
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post #12 of 18 Old 04-18-2013, 11:42 AM - Thread Starter
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Hmm... you have a good point, but the system in question also runs the furnace in the winter, so a vent would wind up blasting hot air into the enclosure unless there was some way to deactivate it based on the system mode, at which point there would be no reason to have the vent there in the first place if it can be closed with no adverse effects. Assuming, of course, that blowing hot air into the A/V equipment is bad. biggrin.gif

My thought was to have the door to the closet sealed and put a filtered vent in the door (edit: as Nick suggested above), as on the existing cabinets I've noticed pretty significant dust buildup due to the negative air pressure - basically putting the return vent in the door and the A/V closet as part of the "duct" so to speak. Then, if additional drops are necessary they could be made to the living area outside the A/V closet... although at that point it might be more convenient to just relocate an existing air return to pass through the closet instead. Either way, I guess I'll need to talk to the HVAC guys.

Is there a detriment to installing more ventilation than necessary? If I only need 150CFM, and hook up a 400CFM fan, even with losses I should have more than enough airflow.
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post #13 of 18 Old 04-18-2013, 11:55 AM
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I found my panasonic inline fans happy to run at 50% regulated with a ceiling fan controller.

Biggest drawback to too much is system oscillation assuming your thermostatically controlled and dust.

I recommend you look how i did mine. I put the filtered "return" through a shared wall then through the rack and hush box and dumped the heat in another room of the house downstairs and the main HVAC thermostat re-conditions the air.
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post #14 of 18 Old 04-18-2013, 12:45 PM - Thread Starter
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Slick setup! I've seen some of those pics before browsing AVS, but now I get to dish out compliments where due. Wish I had the opportunity to do a fresh build like that - would make the in-wall wiring a thousand times easier, if nothing else!

There is actually a shared wall between the closet and a hallway - no door sawing required (good call!). It seems like blowing the hot air into another part of the house would screw up your A/C balance though (unless you had a room that was colder than the rest already, ha). If we're talking about 85 degree rack exhaust at least, wouldn't dissipating in the return system be better?

As for a fan controller, I can probably reuse one from the existing A/V cabinets - although as I understand it, if I just cranked it down to minimum and ran the ventilator all the time, it wouldn't hurt anything, just potentially over-ventilate the room? In one of the existing cabinets there is a blower wired directly into 120V - no control at all, so a fan running all the time wouldn't be any worse than the existing install, haha.
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post #15 of 18 Old 04-18-2013, 03:51 PM
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this thread makes my head hurt but i need to learn it...


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post #16 of 18 Old 04-18-2013, 03:58 PM
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Thanks!

Well i have heard of dumping the air into the return. It was not an option for me due to the location of my return. The closet i dump the hot air into is a walkin and the room is adjacent to the thermostat. My HVAC runs on circulate and turns on every so often and circulates the house air. I have not noticed it being a problem.

Also remember when dumping into return two things:

1. When the HVAC is not running you must overcome the friction of the whole home lines to push that air out the register(s)

2. When he unit IS running now your cfms will at least double since you have no friction beyond where you enter the return.

Balance is key, you dont want the fans coming on and off for short durations(oscillation). Its probably possible to balance when dumping into the return i just dont know how it would work(never done it).

If you run constantly then balance not an issue, just the power cost, dust, and constant noise(no fans are silent).
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post #17 of 18 Old 04-18-2013, 04:41 PM - Thread Starter
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@JRock - I know the feeling...

@Nick - I gotcha. Fortunately in this particular case the A/V closet is quite literally right next to the air return, air handler, and thermostat, so I have a lot of options with where I go (and noise probably won't be a huge issue). It seems like the way to do it then would be to have the fan run opposite the HVAC system, i.e. the fan runs only when the HVAC is off. Best of both worlds - constant airflow without constant fan use. The HVAC is controlled by an HAI OmniPro II, so I can just trigger the ventilator off of that as well.
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post #18 of 18 Old 04-18-2013, 05:10 PM
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Quote:
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It seems like the way to do it then would be to have the fan run opposite the HVAC system, i.e. the fan runs only when the HVAC is off. Best of both worlds - constant airflow without constant fan use. The HVAC is controlled by an HAI OmniPro II, so I can just trigger the ventilator off of that as well.

Careful there - most fan/blower assemblies will significantly restrict airflow when they're not in motion - you're better off leaving it on 24/7...


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