Fans for ducting?! ....and how to control them?

[Cenedd]

Slightly unusual one here. I have a server, router, switch etc sitting in the cupboard under the stairs. It gets a bit toasty in there. I core drilled through the 13 inches of external wall with cavity (that was a joy!) at the top of the cupboard and put in some round plastic ducting. That's currently got a Papst 4412 FM fan (2400 rpm, 4mm H2O, 82.4cfm/140 m3h, 38dBA) exhausting through this ducting. It was still getting a bit warm for comfort so I widened an existing hole that runs through an internal wall into the cavity under the oven in the kitchen (doesn't get hot) and put in some square ducting (it fitted the hole shape better) and put a 140mm Noctua pulling some air into the cupboard. It's still about 33C in there and stuff is running fine but I'm thinking about summer! I was looking at putting some EK Furious Varders in as the Noctua (though fabulously quiet) isn't pulling all that much air in. OCUK do a handy 3-pack too so I was thinking the one exhaust and one on each end of the input ducting to pull cold(-er) air in. Furious Varders simply because they seem to have the highest static pressure which I'm thinking is going to be the deciding factor in performance because the air has to go down the ducting, through the cupboard (bigger than a case) and then out more ducting.

Three questions:
1. Am I wrong about static pressure being all important?
2. Two fans in parallel (one at each end) a good plan for the input?
3. They're PWM fans. How do I control them - turn them down a bit to balance noise vs temp? I currently run a small mains to 12V PSU rather than piggy back them off the server - that way they run even if the server should happen to be off.

Many thanks,

Gareth

 

[mickyflinn]

You need adequate cool air in as that affects cooling out, could you run ducting to bring in cool air ?

 

[varkanoid]

You have not got enough cool air coming in. Its really cold outside at the moment so you should really be less than 30c. Static pressure is more akin to pushing air through heatsinks, finally compact spaces, think of it as the muscle shove.

In your case you need high airflow and circulation in order to lower the ambient temperature. Ideally your in and out need to be opposite each other or exhaust at the top and incoming at the bottom. Just think about your airflow for a moment and how it circulates. If you think about it you have 33c air before it goes into your devices.

If it was me I would have a duct covering the exhaust from the server feeding directly to the outlet and so all the hot air goes immediately outside from the server none of it escapes back into the cupboard. Then the other devices are cooled by the incoming circulation anyway which should be fine.

 

[Cenedd]

It's difficult to describe but I'll do my best.
The external wall I have the exhaust going out through, doesn't go outside as there is a utility room built against that wall.
The exhaust is bored at the highest point of the under-stairs cupboard so the slope of the ceiling should funnel all the hot air to this point.
The 33C reading is from the intake temp sensor on a router so it's not exactly ambient but it is noticeably hot in there.
The fresh air intake comes in through the adjacent wall at the bottom but the duct continues and then right-angles so that the intake fan is at floor level on the same wall as the exhaust but blowing into the center of the cupboard - best I could do.

Ideally, as you say, high throughput of cold air would be nice but because the ducting (at least three feet) will be quite restrictive, won't a high flow but low pressure fan give me a low flow because it hasn't got the power? Hence I was thinking of the Furious Vardar which have high numbers for both pressure and flow - but unfortunately noise too.

I think pressure, flow and noise all scale roughly linearly with speed - according to a quick chart using each of the Vardar speed variants - so if I can control them, I should be able to balance temp vs noise. The trouble is, they're PWM so short of a massively over the top fan controller (like an Aquaero) is there something cheap and simple that I can feed 12V to and adjust some pots or sliders to control the speed? I'm thinking along the lines of either a 3-channel PWM fan-mate or a 1-channel that can handle all three.

Many thanks,

Gareth

 

[Cenedd]

In terms of controlling three PWM fans without using M/B headers, am I overthinking this? Will any old fan controller for 3-pin fans work on 4-pin PWM fans?

Gareth

 

[Tealc]

In terms of controlling three PWM fans without using M/B headers, am I overthinking this? Will any old fan controller for 3-pin fans work on 4-pin PWM fans?

Gareth

Yes an No.

Firstly you have to consider the connector outputs on the controller and if they fit 4 pinners. You can buy converters but that bumps the price up and makes things messier.

Secondly I don't find PWM fans respond as well to a lower voltage as 3 pinners do. The onboard electronics are far more complex on 4 pin PWM fans and these may stop working below a relatively higher voltage than a 3 pin fan. The result could be that your fan stalls at 8 or 9v
, whereas a 3 pin fan will go down to silly low volts

 

[Cenedd]

Cheers Tealc. I've got some Noctuas running at stupidly low volts and they're fine. For this though I think I need the oomph of the Furious Vardars but to be able to turn them down slightly when I find they're too loud so a little control might work fine. I was also looking at the Akasa Piranha Air Rippers which are a lot quieter but lower in both pressure and flow so I fear I might not have the head room in them and hope that by turning down the Vardars I can tune between the two as necessary.

Does anyone know if the Akasa junior fan controller will work with Vardars? The manual says it takes 4 pin fans but the review says that one particular type of PWM fan doesn't work....but that seems to be the way with some PWM implementations differing to others.