Crazy ducting idea

[DrMrLordX]

I've seen some posts on ducting here (from BonzaiDuck, among others) and thought up a silly idea that might not work or might simply be a waste of time or money. Still, I wanted to see if anyone here had some input that might help me sort things out in my head.

I have a top-down HSF (Big Typhoon VX, currently outfitted with a 110 cfm Silverstone FM-121) and want to know if I could use a duct to force the entire airflow from a floor/desk fan that is appreciably more powerful than your standard 120mm fan onto my Big Typhoon.

The logistics would be simple:

1). remove side panel
2). select a sufficiently powerful fan, preferably something in the range of 10-20 inch blades and 2400 rpms or less (don't want too much noise now).
3). Construct shroud/duct with an opening around the fan wide enough for it to blow into the duct and an outlet the same size as a 120mm fan.
4). Position fan so that the outlet blows down onto the HSF directly with as small a gap between the outlet and the top of the HSF as possible.

This all seems well and good, though there are a few things of which I am uncertain.

First off, would I be better off leaving the FM-121 on the HSF now, or taking it off? I'm not sure having a 110 cfm fan at the end of the duct would help much. Maybe it would hurt? I'm trying to get more than 110 cfm through the duct and concentrated onto the HSF and I'm not sure how well the two fans would stack, if at all, even with a proper duct.

Secondly, what fan should I use? I've done some searching but getting cfm numbers on common room fans is not easy. Mostly I'm looking for something in the $20-$50 range that I can pick up locally (or online for cheap) and has 10-20" blades plus can easily be ducted. I don't know what rpm or cfm I'd really need/want but pushing 1000 cfm (or more) at the narrow end of the duct would be nice. However, I don't want to blow the computer over (ha ha).

Thirdly, what decrease in fan performance am I going to get by forcing it to blow through a duct that will get narrower by the end? I estimate that the larger the fan I use, the worse my loss will be at the far end, though I guess I could be wrong. If I'm right, it might be better for me to go with a smaller fan that relies on rpms to push air (something like the Vornado, for example). Getting similar rpms out of a larger fan might still be better, though.

Fourthly, what materials can I use on a duct like this? It will barely be touching anything in the PC (just the top of the HSF, fan or no fan), and it will need to be light enough so that it won't tip over the fan. I was thinking of using poles to build a duct frame and then taping/gluing plastic from trash bags or plastic wrap or plastic sheeting or what have you. Static would be a concern, I guess, but plexiglass or foam board may weigh too much.

Finally, I understand that the idea of pushing 1000 cfm of air over a HSF like the Big Typhoon might seem a little crazy, but I still want to see how it will turn out.

edit: for what it's worth, this seems like a fan that might work:

http://www.northerntool.com/we...uct_6970_754509_754509

1100 cfm on the low setting. Sweet! I wonder how much of that would actually come through on the other end of a duct though, since it is 18 inches . . .

 

[toadeater]

With a 1100 cfm fan you would have enough air to cool your *entire* PC and your room, so there is no need to duct it over the CPU. You probably won't even need any exhaust fans because that's going to be a huge amount of air pressure if you can get it all that air into the case. That's like having 10 high-speed 120mm fans.

If you want a fan solely for the CPU, even ~200CFM would be a massive improvement compared to any standard heatsink setup.

How about something like this 665cfm fan:

http://www.drillspot.com/produ...U71_Round_AC_Axial_Fan
http://www.drillspot.com/produ..._Set_With_2-Prong_Plug

You could mount that on the side of the case instead of building a duct. It says 1600rpm, so it shouldn't be too loud, but I can't guarantee that it won't be, so maybe you should call them and ask.

There's probably a lot of these types of fans made for servers, just one example.

 

[DerwenArtos12]

With top-down heatsinks the general area of diminishing returns is around 60cfm so your 110 is putting out more than enough air to disipate the heat that your heatsink is able to pull off your processor. The only thing that could help would be to open a duct from the side of your case so that your HS fan is getting direct cool air but, you will want to filter that intake hole or you'll ratehr rapidly clog your HSF with dust and loose efficiency.

 

[Modelworks]

You can do that.
Its done with rack servers.
Instead of lots of fans in every rack, datacenters have ducts in the floor that provide cool air.

Datacenter ambient air cooling solutions typically involve the use of alternating aisles of cool air between racks. Cool air is supplied to the cold row through ducts under the raised datacenter floor supplied by computer room air conditioning (CRAC) units. The air is then exhausted from the back of the rack in the hot row and is pulled toward the ceiling using the building?s HVAC system. Other methods of cooling using ambient air include the use of fans mounted to the roof or rear door of a server rack and the use of rack-mounted and wall air conditioners. Ambient air cooling solutions are limited in their ability to handle high heat loads, as they typically are only able to effectively cool 5 to 10 kW per rack.

For a duct material, go to lowes or home depot and get a plastic dryer duct.

 

[DrMrLordX]

Originally posted by: toadeater
With a 1100 cfm fan you would have enough air to cool your *entire* PC and your room, so there is no need to duct it over the CPU. You probably won't even need any exhaust fans because that's going to be a huge amount of air pressure if you can get it all that air into the case. That's like having 10 high-speed 120mm fans.

Yeah, that is a lot of air. I just want to see if I can duct it onto the CPU so that it will spread out through the case the way the HSF is working now. Even without the duct I'm pretty sure I can direct the fan into the side of the case and blast the whole thing. It might fall over

If you want a fan solely for the CPU, even ~200CFM would be a massive improvement compared to any standard heatsink setup.

Possibly. I've seen a 1C temp drop on at least one benchmark with a 140 cfm Delta vs a ~100 cfm Sanyo Denki on the Big Typhoon so it's possible that there might be additional gains above that level. The major problem I have with the 200+cfm 120mm fans is that they're disturbingly loud, whereas that 18" floor fan I pasted probably makes less noise on its lowest setting.

How about something like this 665cfm fan:

http://www.drillspot.com/produ...U71_Round_AC_Axial_Fan
http://www.drillspot.com/produ..._Set_With_2-Prong_Plug

You could mount that on the side of the case instead of building a duct. It says 1600rpm, so it shouldn't be too loud, but I can't guarantee that it won't be, so maybe you should call them and ask.

The listed noise output is 52 dba which isn't bad at all. It's a bit pricey but looks like a nice fan.

Originally posted by: DerwenArtos12
With top-down heatsinks the general area of diminishing returns is around 60cfm so your 110 is putting out more than enough air to disipate the heat that your heatsink is able to pull off your processor. The only thing that could help would be to open a duct from the side of your case so that your HS fan is getting direct cool air but, you will want to filter that intake hole or you'll ratehr rapidly clog your HSF with dust and loose efficiency.

Yeah, I know that you hit a point of diminishing returns. What I'm curious about is how far you can keep pushing the envelope before there are no appreciable gains from increased airflow. I've seen results from a 140 cfm fan on a Big Typhoon, but I don't think anyone's tried pushing 1100-1500 cfm through one before. As the system currently operates, it already pulls air through a vent in the side of the case so it's already getting an unhealthy dose of dust . . . which reminds me, I need to pick up some canned air.

Originally posted by: Modelworks
You can do that.
Its done with rack servers.
Instead of lots of fans in every rack, datacenters have ducts in the floor that provide cool air.

For a duct material, go to lowes or home depot and get a plastic dryer duct.

Hmm, not a bad idea on the material. But do you know how much air pressure/speed I'd lose blowing an 18" fan into a duct that terminates at a 4.7" opening?

 

[DerwenArtos12]

Originally posted by: DrMrLordX

Originally posted by: DerwenArtos12
With top-down heatsinks the general area of diminishing returns is around 60cfm so your 110 is putting out more than enough air to disipate the heat that your heatsink is able to pull off your processor. The only thing that could help would be to open a duct from the side of your case so that your HS fan is getting direct cool air but, you will want to filter that intake hole or you'll ratehr rapidly clog your HSF with dust and loose efficiency.

Yeah, I know that you hit a point of diminishing returns. What I'm curious about is how far you can keep pushing the envelope before there are no appreciable gains from increased airflow. I've seen results from a 140 cfm fan on a Big Typhoon, but I don't think anyone's tried pushing 1100-1500 cfm through one before. As the system currently operates, it already pulls air through a vent in the side of the case so it's already getting an unhealthy dose of dust . . . which reminds me, I need to pick up some canned air.

Originally posted by: Modelworks
You can do that.
Its done with rack servers.
Instead of lots of fans in every rack, datacenters have ducts in the floor that provide cool air.

For a duct material, go to lowes or home depot and get a plastic dryer duct.

Hmm, not a bad idea on the material. But do you know how much air pressure/speed I'd lose blowing an 18" fan into a duct that terminates at a 4.7" opening?

Yeah, i saw your post about picking up 1C and I can't help but think you're pretty close to there. You essentially increased airflow by 30% with a gain of only 1C and you probably doubled the noise output.

As far as the 18" fan, without knowing it's static pressure it's almost impossible to calculate accurately but, assuming the entire duct from 18" to 4.7" was airtight I'd say a 6' long duct would cost you about 10% and you'd loose another 10% for every 10" less than that peaking at about a 2' duct where the backpressure would start to equalize with the static pressure and you'd be getting more air being forced back out through the fan than into the case. Have you considered just mounting a super-high flow fan in place of the side pannel duct? There are a few fans out there that surpass 200cfm but they get pretty big and some run on AC. something like this.

 

[rgallant]

:thumbsup:what DerwenArtos12 said about a side fan, I did it with two 120,s but on the out side with a dust filter over them. aligned about 75% below the video slot giving air to card and chipsets,even if I went to H2O the board still needs lots of cooling

-also if you push too much air you could over drive the fan causing bearing failure,and if you take the fan off and the other fan fails you could over heat the CPU, The fan you listed would not be silent by any means.and what about DUST,Bugs like a JUNE bug hitting the board @ 30 miles a hour. Thats a big fan.

 

[DrMrLordX]

Originally posted by: DerwenArtos12

Yeah, i saw your post about picking up 1C and I can't help but think you're pretty close to there. You essentially increased airflow by 30% with a gain of only 1C and you probably doubled the noise output.

Actually most of the fans in the 140 cfm range are around 50-53 dba, while you can push 110 cfm with the fan I currently have at a noise level of 40 dba. So . . . it's more than double the noise output. That's sort of why I'm trying to stay away from the high-speed 120mm fans.

I may be at the point-of-no-gain, or very close to it, but that hasn't dampened my curiosity.

As far as the 18" fan, without knowing it's static pressure it's almost impossible to calculate accurately but, assuming the entire duct from 18" to 4.7" was airtight I'd say a 6' long duct would cost you about 10% and you'd loose another 10% for every 10" less than that peaking at about a 2' duct where the backpressure would start to equalize with the static pressure and you'd be getting more air being forced back out through the fan than into the case.

Thanks for the ballpark figure. That seems like it would accomplish what I have in mind . . . . if I could hit 10-20% loss that would work extremely well with that floor fan.

Have you considered just mounting a super-high flow fan in place of the side pannel duct? There are a few fans out there that surpass 200cfm but they get pretty big and some run on AC. something like this.

Yeah. Most of the fast ones are bigger than the HSF so the air they push won't concentrate over the fins. The goal is to push all the air over the fins instead of just hitting the case with a ton of airflow.

 

[DrMrLordX]

Originally posted by: rgallant

-also if you push too much air you could over drive the fan causing bearing failure,and if you take the fan off and the other fan fails you could over heat the CPU, The fan you listed would not be silent by any means.and what about DUST,Bugs like a JUNE bug hitting the board @ 30 miles a hour. Thats a big fan.

Obviously I'd want to pull the Silverstone fan on there now to avoid destroying it. I figured that might be a problem. As for the floor fan failing, I don't know that that would be any more likely than my 120mm fan going out.

As far as dust goes, I'm already eating a ton of dust so it probably won't be a big change. There's only so much dust in the room, and my computer gets it all. Bugs, on the other hand, could make matters interesting.

 

[DerwenArtos12]

Originally posted by: DrMrLordX

Originally posted by: DerwenArtos12

Yeah, i saw your post about picking up 1C and I can't help but think you're pretty close to there. You essentially increased airflow by 30% with a gain of only 1C and you probably doubled the noise output.

Actually most of the fans in the 140 cfm range are around 50-53 dba, while you can push 110 cfm with the fan I currently have at a noise level of 40 dba. So . . . it's more than double the noise output. That's sort of why I'm trying to stay away from the high-speed 120mm fans.

I may be at the point-of-no-gain, or very close to it, but that hasn't dampened my curiosity.

As far as the 18" fan, without knowing it's static pressure it's almost impossible to calculate accurately but, assuming the entire duct from 18" to 4.7" was airtight I'd say a 6' long duct would cost you about 10% and you'd loose another 10% for every 10" less than that peaking at about a 2' duct where the backpressure would start to equalize with the static pressure and you'd be getting more air being forced back out through the fan than into the case.

Thanks for the ballpark figure. That seems like it would accomplish what I have in mind . . . . if I could hit 10-20% loss that would work extremely well with that floor fan.

Have you considered just mounting a super-high flow fan in place of the side pannel duct? There are a few fans out there that surpass 200cfm but they get pretty big and some run on AC. something like this.

Yeah. Most of the fast ones are bigger than the HSF so the air they push won't concentrate over the fins. The goal is to push all the air over the fins instead of just hitting the case with a ton of airflow.

i have no, nor will i have any qualms with you pushing 2000cfm in there if you like, should be interesting to see if at some point the added aiflow actually starts increasing temperatures due to the massive increases in air speed creating friction against the fins.

As for the super high flow fan, would it be much if any tougher to build a shroud for a 150mm fan than it would be for an 18" fan?

 

[DrMrLordX]

Originally posted by: DerwenArtos12

i have no, nor will i have any qualms with you pushing 2000cfm in there if you like, should be interesting to see if at some point the added aiflow actually starts increasing temperatures due to the massive increases in air speed creating friction against the fins.

An interesting point, especially considering what

As for the super high flow fan, would it be much if any tougher to build a shroud for a 150mm fan than it would be for an 18" fan?

Not really. The floor fan has its own stand so I won't have to do any serious modding to uh . . . mount it, so to speak.

Otherwise the flow rates from a 150mm fan will probably fall in line with some of the high-end Delta fans at lower noise levels, which isn't a bad idea at all. Moving that kind of air through an Ultra 120 eXtreme would probably be a good idea if it could be set up properly (maybe in a few 5 1/4" drive bays?).

In fact, that sounds like a much better idea than just blowing a big-ass fan at my Big Typhoon. Hmm!

(edit: not that it would necessarily stop me from abusing the Big Typhoon anyway)

 

[DerwenArtos12]

Originally posted by: DrMrLordX

Originally posted by: DerwenArtos12

i have no, nor will i have any qualms with you pushing 2000cfm in there if you like, should be interesting to see if at some point the added aiflow actually starts increasing temperatures due to the massive increases in air speed creating friction against the fins.

An interesting point, especially considering what

As for the super high flow fan, would it be much if any tougher to build a shroud for a 150mm fan than it would be for an 18" fan?

Not really. The floor fan has its own stand so I won't have to do any serious modding to uh . . . mount it, so to speak.

Otherwise the flow rates from a 150mm fan will probably fall in line with some of the high-end Delta fans at lower noise levels, which isn't a bad idea at all. Moving that kind of air through an Ultra 120 eXtreme would probably be a good idea if it could be set up properly (maybe in a few 5 1/4" drive bays?).

In fact, that sounds like a much better idea than just blowing a big-ass fan at my Big Typhoon. Hmm!

(edit: not that it would necessarily stop me from abusing the Big Typhoon anyway)

Actually the 150mm fan I linked you to at Frozen CPU moves 265CFM, which to the best of my knowledge is about 100CFM more than any delta 120mm though it can get a little loud(55Db). That across just about any heatsink should keep load temps somewhere near idle temps.

 

[DrMrLordX]

Woops, looks like I messed up my last post somehow. Oh well.

Here's the fastest Delta fan I've seen, not counting their dual-fan models:

http://www.sidewindercomputers.com/de12tfexhisp.html

220 cfm, 65 dba. Yowza.

 

[DerwenArtos12]

Originally posted by: DrMrLordX
Woops, looks like I messed up my last post somehow. Oh well.

Here's the fastest Delta fan I've seen, not counting their dual-fan models:

http://www.sidewindercomputers.com/de12tfexhisp.html

220 cfm, 65 dba. Yowza.

good god 220cfm from a 120mm fan, I'm surprised it's only 65Db. That fan is more than anyone should ever really need. I'd bet three of those on an MCR320 could keep a quadcore at ambient on idle!

 

[DrMrLordX]

Scary, huh. They also make this dual-fan turbine dealie:

http://www.sidewindercomputers.com/de12gf.html

Same airflow, but "only" 59 dba and lower air pressure. It's an interesting product. Makes me wonder if a DIY ducted turbine would be doable, though I've heard ducting fans in series can be technically challenging.

 

[DerwenArtos12]

Originally posted by: DrMrLordX
Scary, huh. They also make this dual-fan turbine dealie:

http://www.sidewindercomputers.com/de12gf.html

Same airflow, but "only" 59 dba and lower air pressure. It's an interesting product. Makes me wonder if a DIY ducted turbine would be doable, though I've heard ducting fans in series can be technically challenging.

Yeah, you have to get two fans that rotate the oposite directions with the same flow direction. The reasoning is that with a blades pitched at 45* you'll get equal parts forward thrust and rotational thrust, a second fan with blades pitched 45* the oposite direction will be able to empart pure directional thrust because it's rotational thrust will just be negating the first fan, therefore making both fans more efficient. Two fans rotating the same direction won't work the same way because the rotational force by the first fan will multiply by the rotational force of the second fan. Most fans used in computers are either 30* straight or curved blades which would take a very complext program to calculate the flow characteristics of but, seeing as generally speaking the closer to 90* pitch you get the greater directional flow you get, I'd say the efficiency boost is greater than in a 45* arrangement because you're getting more rotational thrust out of the lower pitch angle.

 

[Modelworks]

Careful using AC powered fans near a pc.
They tend to produce much more EMI/RFI than dc fans.
Especially if the motor is the shaded pole type.

A friend found this out when he placed a normal house fan near some of his floppy disk, which he later found to have all the data corrupted.
I went over and asked him how long that slight wobbling picture was happening on his monitor. He thought the monitor was going bad. I moved the fan.
Problem solved.

 

[DrMrLordX]

Originally posted by: DerwenArtos12

Yeah, you have to get two fans that rotate the oposite directions with the same flow direction. The reasoning is that with a blades pitched at 45* you'll get equal parts forward thrust and rotational thrust, a second fan with blades pitched 45* the oposite direction will be able to empart pure directional thrust because it's rotational thrust will just be negating the first fan, therefore making both fans more efficient. Two fans rotating the same direction won't work the same way because the rotational force by the first fan will multiply by the rotational force of the second fan. Most fans used in computers are either 30* straight or curved blades which would take a very complext program to calculate the flow characteristics of but, seeing as generally speaking the closer to 90* pitch you get the greater directional flow you get, I'd say the efficiency boost is greater than in a 45* arrangement because you're getting more rotational thrust out of the lower pitch angle.

So that's how it works huh? Thanks, something to think about there as well. I have seen videos of the Delta turbine-style fan operating (and making noise) and I never realized each fan rotated in the opposite direction.

Originally posted by: Modelworks
Careful using AC powered fans near a pc.
They tend to produce much more EMI/RFI than dc fans.
Especially if the motor is the shaded pole type.

A friend found this out when he placed a normal house fan near some of his floppy disk, which he later found to have all the data corrupted.
I went over and asked him how long that slight wobbling picture was happening on his monitor. He thought the monitor was going bad. I moved the fan.
Problem solved.

The fan won't be any closer than 4' away from the 'puter. Hopefully it won't cause any trouble from that range. Thanks for the heads-up though. I'll probably swing by Lowes or Home Depot Thursday to see what I can find out there in the way of ducting stuff and maybe fans (shipping cost on that fan from Northern Tools is a bit much, but that should come as no surprise).

 

[DerwenArtos12]

Originally posted by: DrMrLordX

Originally posted by: DerwenArtos12

Yeah, you have to get two fans that rotate the oposite directions with the same flow direction. The reasoning is that with a blades pitched at 45* you'll get equal parts forward thrust and rotational thrust, a second fan with blades pitched 45* the oposite direction will be able to empart pure directional thrust because it's rotational thrust will just be negating the first fan, therefore making both fans more efficient. Two fans rotating the same direction won't work the same way because the rotational force by the first fan will multiply by the rotational force of the second fan. Most fans used in computers are either 30* straight or curved blades which would take a very complext program to calculate the flow characteristics of but, seeing as generally speaking the closer to 90* pitch you get the greater directional flow you get, I'd say the efficiency boost is greater than in a 45* arrangement because you're getting more rotational thrust out of the lower pitch angle.

So that's how it works huh? Thanks, something to think about there as well. I have seen videos of the Delta turbine-style fan operating (and making noise) and I never realized each fan rotated in the opposite direction.

Originally posted by: Modelworks
Careful using AC powered fans near a pc.
They tend to produce much more EMI/RFI than dc fans.
Especially if the motor is the shaded pole type.

A friend found this out when he placed a normal house fan near some of his floppy disk, which he later found to have all the data corrupted.
I went over and asked him how long that slight wobbling picture was happening on his monitor. He thought the monitor was going bad. I moved the fan.
Problem solved.

The fan won't be any closer than 4' away from the 'puter. Hopefully it won't cause any trouble from that range. Thanks for the heads-up though. I'll probably swing by Lowes or Home Depot Thursday to see what I can find out there in the way of ducting stuff and maybe fans (shipping cost on that fan from Northern Tools is a bit much, but that should come as no surprise).

For ducting, if you can fit and afford it, i would use the split aluminum ducting and step it down every 8"-1', that's going to require a few reducers and quite a bit of ducting though. You may just want to get a sheet of cheap steal from the roofing section and build a cone air funnel.

 

[DrMrLordX]

Originally posted by: DerwenArtos12


For ducting, if you can fit and afford it, i would use the split aluminum ducting and step it down every 8"-1', that's going to require a few reducers and quite a bit of ducting though. You may just want to get a sheet of cheap steal from the roofing section and build a cone air funnel.

I'll see what I can do. The cheap option is looking better at this point.

On the plus side, I selected my fan and ordered one through Amazon. The fan:

http://www.dealtime.com/xPF-La...quot-Wind-Machine-3300

4750 cfm! whoosh. If I ever bother ducting it, I can purposely short-duct it to avoid pushing too much air through the HSF. Considering how much air it can move, a duct may be unnecessary.

 

[DerwenArtos12]

Originally posted by: DrMrLordX

Originally posted by: DerwenArtos12


For ducting, if you can fit and afford it, i would use the split aluminum ducting and step it down every 8"-1', that's going to require a few reducers and quite a bit of ducting though. You may just want to get a sheet of cheap steal from the roofing section and build a cone air funnel.

I'll see what I can do. The cheap option is looking better at this point.

On the plus side, I selected my fan and ordered one through Amazon. The fan:

http://www.dealtime.com/xPF-La...quot-Wind-Machine-3300

4750 cfm! whoosh. If I ever bother ducting it, I can purposely short-duct it to avoid pushing too much air through the HSF. Considering how much air it can move, a duct may be unnecessary.

thats not a fan, it's a personal wind tunnel generator. and at 5000cfm I would be very willing to bet that if you ducted that much air over any heatsink, the ammount of heat generated by the friction would cause your temperatures to go up. I'd actually bet on that happening at it's lowest setting of 3000cfm if fully ducted.

 

[toadeater]

I hope you're going to be able to take photos of all this?

 

[BlueAcolyte]

Considering that has enough airflow to knock your case over, do you really need a duct?

 

[DrMrLordX]

I will be taking photos, and I will run it without a duct at first to see how it goes. If I do duct it, I will probably opt for the low setting and make sure the outlet is larger than the 22.07 square inches in area that the HSF covers so that I won't be slamming the HSF with its entire output. It should arrive sometime between Feb. 20th - Feb. 26th for what it's worth. If things go well I'll try it on a Scythe Orochi if/when I can get my hands on one.

I hope this thing doesn't blow my case and desk away at the same time.

 

[DerwenArtos12]

Originally posted by: DrMrLordX
I will be taking photos, and I will run it without a duct at first to see how it goes. If I do duct it, I will probably opt for the low setting and make sure the outlet is larger than the 22.07 square inches in area that the HSF covers so that I won't be slamming the HSF with its entire output.

I hope this thing doesn't blow my case and desk away at the same time.

If your case pulls a mary popins I'm going to be very impressed, I'll even petition to have your title changed, not that they've done it in for ever that I've seen.