Cooling a TV

Control: management of fans, temp/rpm monitoring via soft/hardware

Moderators: NeilBlanchard, Ralf Hutter, sthayashi, Lawrence Lee

markjia
Posts: 171
Joined: Sat Apr 24, 2004 4:31 pm
Location: Vancouver BC

Post by markjia » Fri Nov 12, 2004 11:10 am

The TV will be placed about 8 inches into the new frame.

The difficulty of putting a fan near the floor is that the TV sits on a stand (about 1.5 feet tall), so the fan would just be pushing air straight through the stand and not actually cooling the TV.

Here are a couple things based on the ideas you guys have given me, all of which I appreciate btw:

1. Suck air in from the bottom with fan, and duct it to bring the air further up and actually hit the TV.

2. Create a duct to draw the air from the exhaust vents of the tv up and out the top of my frame (which protrudes about 6 inches out of the back of the wall). Would this ducting actually be significantly useful (as apposed to simply placing the fans at the top of the frame)?

markjia
Posts: 171
Joined: Sat Apr 24, 2004 4:31 pm
Location: Vancouver BC

Post by markjia » Fri Nov 12, 2004 5:08 pm

Alright, so I get the impression that most people agree that I need to use some fans in some manner...

No matter how I position the fans, i will need some grills...

I know that I would get the best airflow if I used grills like these, http://www.directron.com/net12.html. But that would require that I cut a nearly perfect circle out of the MDF i'm using to make the frame. Instead, I'm thinking of using these, http://www.directron.com/120gunsight.html. I could get away with small imperfections in the circles I cut with a jig saw. These cost a lot more though, and I could need up to four...is there a cheaper place I could get them (or something similar). It would be even better if I could find them locally.

The idea of using heat registers is also possible...I would like to get wood ones though. Anyone know where I can find them locally? I guess I could build them myself, but it would take a while.

Rusty075
SPCR Reviewer
Posts: 4000
Joined: Sun Aug 11, 2002 3:26 pm
Location: Phoenix, AZ
Contact:

Post by Rusty075 » Fri Nov 12, 2004 6:13 pm

Here's an interesting idea for covering your fan holes: Midgetlouver.com. I used some of them waay back on the the old Desk PC.

markjia
Posts: 171
Joined: Sat Apr 24, 2004 4:31 pm
Location: Vancouver BC

Post by markjia » Tue Nov 16, 2004 10:28 am

I've decided to create ducts to exhaust air up and out of my frame, and make my own registers to cover the opennings. My thanks goes out to lenny and Putz who gave me these idea as well as everyone else who made suggestions.

The thing I am unsure of is where best to put the fan. I'm thinking that I could put it inside the duct itself (near the openning at the top of the frame) and have it suck air from the TV's vents, through the duct and push it out the top. Does it really matter where it's placed? What if there is a small leakage of air along the duct?

Does the size of the duct matter? The vents on the TV are maybe 15cm x 15cm. Would I be better off using a smaller openning and suck at a higher speed, or a large opening at a slower speed? BTW, the air comming out of the vents is pushed lightly by a fan inside the TV.

I think I will use 120mm fans...maybe some Globes given their low price...think they will be able to pull air about 2-3 feet? Actually, would it be best to put the fan half way? So it only needs to pull 1.5 ft and push 1.5 ft? is that more efficient then pulling 2.5 ft and pushing 0.5 ft?

ddrueding1
Posts: 419
Joined: Sun Sep 19, 2004 1:05 pm
Location: Palo Alto, CA

Post by ddrueding1 » Tue Nov 16, 2004 1:34 pm

I'd put the fans further inside the duct, this makes any sound they produce further away from you. If you are concerned about the air pressure the fans produce, look at using the thicker fans, like the 120mm panaflo.

MikeC
Site Admin
Posts: 12283
Joined: Sun Aug 11, 2002 3:26 pm
Location: Vancouver, BC, Canada
Contact:

Post by MikeC » Tue Nov 16, 2004 3:34 pm

The fan should not go inside the duct; their noise will be amplified -- this is almost guaranteed. Put them on the side closes to the heat, and if you want to go all out, cut the frame off and find a way to suspended them frameless using elastic string stretched tight enough.

markjia
Posts: 171
Joined: Sat Apr 24, 2004 4:31 pm
Location: Vancouver BC

Post by markjia » Wed Nov 17, 2004 10:08 am

I was at home depot and was looking at their air ducts when I saw these fans that were part of the duct themselves (they are mounted completely within the duct with no other frame). They are designed to improve circulation. One of the guys there said that he has one and that it's not very loud, but pushes about 200 CFM.

I'm not disagreeing with you...I'm just not sure what to think...maybe I will try one and see...

ddrueding1
Posts: 419
Joined: Sun Sep 19, 2004 1:05 pm
Location: Palo Alto, CA

Post by ddrueding1 » Wed Nov 17, 2004 12:56 pm

I definatly understand where Mike is coming from on this. I've experienced noise being amplified by steel ductwork before, but I was thinking more about some kind of soft/insulated ducting that would likely damp any noise itself.

MikeC
Site Admin
Posts: 12283
Joined: Sun Aug 11, 2002 3:26 pm
Location: Vancouver, BC, Canada
Contact:

Post by MikeC » Wed Nov 17, 2004 1:09 pm

When it comes to closed or nearly-closed structures, there are 2 sources of noise:

1) The material it is made of can vibrate; some are worse than others.

2) The air in the space has resonances -- like the cavities of musical instruments such as guitars, pianos, etc; tubes in speaker boxes; the speaker boxes themselves, etc. There is no easy way to get rid of this, it has to be tuned out, damped or the resonant freqencies identified and then avoided.

In other words, if you know that the tube has a major resonance at 42Hz with a peak of 12 dBA and a slope affects freq. from 20 to 78Hz, then you want to keep all noise sources in that tube above these freq -- or below. However, all >80mm fans have significant noise below 100Hz, and this is almost impossible to eliminate or control the freq of.

The trick is to keep the noise level low enough so that even if the air resonance is excited, it's not significant (audible). This means using slow spinning fans.

200cfm? There is no practical way to make this inaudible if you are anywhere nearby.

markjia
Posts: 171
Joined: Sat Apr 24, 2004 4:31 pm
Location: Vancouver BC

Post by markjia » Wed Nov 17, 2004 2:24 pm

I googled "duct fan" and found that 6" and above duct fans are usually rated btw 250 - 800 CFMs. I wasn't able to find any specifics as to their noise, but they are all listed as being quiet...most user opinions seem to confirm that (though some mentioned hearing some noise). Not really sure what other people consider as quiet (especially non-spcr members).

I did some more thinking and I realized that I could duct the air down through the floor and into the ceiling of the basement. Luckily it's a panelled ceiling in this area so access is not terribly difficult. The problem is the direction of the beams...they run is such a way that it make it very difficult to exhaust the air out of the ceiling. What if the air is left in the ceiling? There is a few inches of room btw the beams and the panelling, so there is a little room for the air to fill the ceiling.

However, the ceiling is somewhat warm already (definately above the temperature of the room above), will this be counter productive even though air is being expelled into the ceiling?

I also read here: http://pages.quicksilver.net.nz/geoffm/fan_FAQ.htm that duct fans are quieter because of the sound baffling of panelling:
In duct fans are usually quieter than wall or ceiling mounted fans, as the ceiling panel and insulation reduce the directly radiated noise, and the duct attenuates some of the noise (around 2dB per metre for typical household sizes). For this reason, if you have an in-duct fan, mount it towards the end of the duct, so it is far from the inlet over the shower to get the most effect. The fan should be no closer than 2 duct diameters from the end grille, in order to give the airflow a chance to straighten out and reduce turbulence losses.
Also, how about noise escaping from the basement after I make one or two 4-6" holes in the floor?

ddrueding1
Posts: 419
Joined: Sun Sep 19, 2004 1:05 pm
Location: Palo Alto, CA

Post by ddrueding1 » Wed Nov 17, 2004 5:20 pm

The first problem I see with going down is that hot air rises, and you would need significantly more airflow/pressure to force the heated air down than to just assist it in rising. Theoretically, you could draw air from the basement and blow it into the cavity behind your TV, but if that air is warmer already, that might not help much.

markjia
Posts: 171
Joined: Sat Apr 24, 2004 4:31 pm
Location: Vancouver BC

Post by markjia » Wed Nov 17, 2004 10:19 pm

Ya, that's one of my concerns too...I'm hoping that I can take advantage of the fact that the TV uses a fan to exhaust the air and I utilize its momentum. Once it enters the duct, which I will place an openning right beside the exhaust, I hope the suction from the new fans will be enough to draw the air out.

Straker
Posts: 657
Joined: Fri Jul 23, 2004 11:10 pm
Location: AB, Canada
Contact:

Post by Straker » Fri Nov 19, 2004 1:10 am

bit different, but just thought I'd add this - in my old house, i guess the previous owners skimped when installing the gas range, and it simply exhausted down into the basement (from the first floor of course). never had any problems with it working like this, though it probably would've been gross if anything large had ever caught fire. :)

Post Reply