High Airflow vs Static Pressure

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Qu9ke

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Dec 21, 2013
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So I've read on here that one of the conditions for choosing high static pressure fans is if said fan is directly adjacent to a heat source. I plan on installing 2 120mm fans and 1 140mm close to my cpu for exhaust. Does that mean they should be high static pressure? Speaking of which, what numerical value is high for static pressure anyways?

Also... my case is the thermaltake core v21, and my fans will have to pull/push air through mesh. Is that a sign I need high static pressure?
 
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Static pressure fans are meant to push a lot of air through filters and radiators so that you can still very strongly feel the flow of air some distance from the radiator. Typically you use them on cpu air coolers to push through a radiator, liquid coolers to move air through a radiator, or front of the case, to move air into the case through a filter (with that case, you can have intake at many points, so if it's sucking air through a filter into the case, then yes static pressure would be good).
I am not sure what you mean by installing close to cpu. If you mean a case fan at the back of the case, behind the cpu, then that should be an air flow one as the flow is not really impeded and you just want to move the warm air out.
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Static pressure fans are meant to push a lot of air through filters and radiators so that you can still very strongly feel the flow of air some distance from the radiator. Typically you use them on cpu air coolers to push through a radiator, liquid coolers to move air through a radiator, or front of the case, to move air into the case through a filter (with that case, you can have intake at many points, so if it's sucking air through a filter into the case, then yes static pressure would be good).
I am not sure what you mean by installing close to cpu. If you mean a case fan at the back of the case, behind the cpu, then that should be an air flow one as the flow is not really impeded and you just want to move the warm air out.
Try to avoid having negative pressure if you put radiators up top on exhaust as that case's gallery of images suggests. That means try and have airflow so that you have a bit more air being pushed in than being pushed out (even out total airflow of intake/exhaust fans in the case, with balance tilted a bit to intake).
 
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What about fans pushing air through a filter instead of pulling? Do those need to be high pressure as well? And what should I look for in terms of numbers when it comes to high pressure? 2, 3, 4mm/h20? Just throwing numbers out there. Thanks for the reply btw. Much appreciated.

Also my overall cfm is in the positive, so I don't need to worry about that.

These are the fans I was looking at that will be pushing/pulling air through the filters. https://pcpartpicker.com/product/4tzv6h/cooler-master-case-fan-r4l2s122bgp Are these good?
 
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I don't think it'll mater push/pull (though I could be wrong). It's the "moving air through a barrier of some sort" part that's crucial.
As for what numbers you want, you don't need to go crazy. Air flow and air pressure fans should be immediately obvious in values. Air flow will be up to 1.5 and pressure will typically be above.
The pressure will vary with how high you run the fans. Though people can go crazy with this, above 1500 rpm is usually very loud and becomes obnoxious very quickly. Up to 1500 should be for load, and half that for idle. I mention this because no matter what the max static pressure, at 1500, sp should be around 1.5-2. So....this is why I'm saying don't go overboard with the fan. Jet engine performance is pretty much pointless when you're never going to use it.
 
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Some people disagree with me, but I'll just leave my thoughts here. You've been warned.

No case is free of air restrictions. Mesh dust filters, hard drive cages, fan grills, the graphics card poking out of your motherboard, RAM sticks, friction with air itself, everything is going to cause some restriction to air flow. Static pressure does matter where you happen to have more of these scenarios like if you have tall RAM heatsinks, great big radiator for a water cooler, and a fine mesh dust filter together. If you have less obstructions, static pressure matters less.

The holy grail of PC fans are fans that are high static pressure at low RPM's. Any fan can whoosh a bunch of air at 2500RPM, but it's loud as hell, and pretty uncomfortable to sit next to. Or in the room next to it. On the opposite end of the spectrum, we have fans like the Gentle Typhoon, EK Vardar, and Noctua NF-F12. You can leave them at around 800-1000RPM, but whatever air they do move is surely going to get to the other end. With my Gentle Typhoons, I can still feel the breeze an arms length away... at 1000RPM, through the cloth of a cotton t-shirt. My Corsair AF airflow fans certainly couldn't do that. And they cost about the same.

In the end, if you're unsure of what to get, It's much easier to lean towards the higher static pressure end of the spectrum. You get the benefit of lower fan RPM for the same real world airflow, and interior restrictions/obstructions matter much less.

TLDR Your case is very open and already comes with a great big whopping 200mm fan included at the front. That 120 exhaust next to the CPU heatsink isn't terribly important. Don't spend too much on it. However, putting a quality fan on that CPU heat sink is probably way more important. Here is my general rule of thumb: static pressure fans for intake, airflow fans for exhaust, run them all at the same speed. Assuming equal numbers of each, it ensures two things: 1.) enough airflow, and 2.) positive case pressure.
 
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So these are a good choice then? https://pcpartpicker.com/product/4tzv6h/cooler-master-case-fan-r4l2s122bgp
I was sort of thinking on having a 140mm on the rear, two of those 120mm on the exhaust side, and two more on the other side next to the gpu for more intake. Not to mention the 200mm on the front.
 
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That is a lot to take in haha. I'll keep all that in mind, thanks. I don't know how to ensure them running all at the same speed though, but I guess I can figure that out in due time. I appreciate all the input!
 
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I think, based on the info you've provided, that you may be worrying unnecessarily. Assuming you have a mid/low-level system with 1 x 3.5 HDD and a middle of the road GPU, 1 fan at the front, 1 at the back and a CPU fan will be plenty. I think the fan you chose is a not exactly a stellar performer producing <40CFM @ 1500 RPM, loud and not very efficient.

Also it worth noting that static pressure is not intrinsic to the fan but rather to the environment where the fan is located. See it's like Km/hr when measuring velocity, without the "hour" the Km is meaningless. In fans the RPM is varied to change the CFM at the given static pressure of your case. Assuming the RPM of a fan is constant, it's CFM will always go up if the case's static pressure decreases (by removing any object from within the case) or down if you increase the static pressure of the case by adding in any object. Back to velocity, if we complicate it further by looking at acceleration, which has 3 parameters like we do here it starts to make more sense. If we keep the power input of the vehicle stable (fixed RPM) we can control the rate of acceleration (fan's CFM) by changing it's weight (static pressure).
 
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At lower rpm like what's normally seen in a pc, SP fans are opposites to CFM fans. Think of a hose, turn it on and you get a lot of water, but little pressure, so that water really has no reach. Stick your thumb over the end and now you get a ton of pressure, lots of reach, but water volume is limited. SP fans have a specific type of blade, designed to force air, CFM fans have a different blade, designed to move air, very big distinction. There are many fan models that will take partially of both designs, so you'll get a fan with acceptable SP and acceptable CFM, but nothing spectacular out of either. These fans are generally used as intakes, especially stock case fans, as they'll have to do double duty of moving a considerable amount of air, as well as getting that air through obstructions such as the hdd cages. CFM fans are much better suited as exhausts as they'll move a lot of air out, with relatively little need for SP.
How a fan works is backwards to common usage. The blades spin, creating a vacuum in the front. The byproduct is the flow of air out the back. The higher the CFM, the larger the area of vacuum, the more air gets moved. SP fans work on the same principal, but having lower draw, but higher force. This makes them better suited for things like radiators. CFM is still important, still need to exchange hot air for cold.
Another important distinction is the outward cone. Many CFM fans have a very wide cone, upwards of 120° in a giant 'V' out the back. This helps spread air around, the gentle breeze just helping displace any hot spots. SP fans have a much tighter cone, almost perpendicular to the fan, so much so that the NF-F12 is rated as a force-flow direction fan, all that air in a 10-15° cone, so really hammers anything in its way. The Scythe GT's are very similar in that respect.

More important than fan type, is ability to flow air in the case. If there's a bunch of obstruction in the front, a higher SP fan will do better, a higher CFM as exhaust. If (like me) there's nothing in the way, high cfm for both works great.

Speed balance is a pain to figure, unless all the fans are identical, it's semi impossible to get accurate. For instance, if you have combo fans in front, 50cfm @1200rpm and cfm fans out back at 75cfm @1000 rpm, then you'll have similar characteristics around 100% front, 80% exhaust speeds, regardless of actual speed. I have 2x 140mm on my rad intake and 2x 140mm as top exhaust. The rad fans run 450-700rpm, the exhausts run 500-600rpm, both sets max out at 1000/1200rpm, but I don't need the volume, so run my pc silent, which has little affect on temps, so no need for max rpm. Set by manual fan curves in CAM and SpeedFan.

1 thing about cfm, it's measurable. You can do it several different ways and still get accurate results, as defined by standards. SP is somewhat different, as there's no exact standard of measurement. So one company might measure with the fan 90° to 2mm distilled water on glass, another company might measure with the fan at 80° tilt to 3mm tap water on stainless steel. So the exact SP figures aren't entirely specific when comparing to different brands. Not knowing exact coefficients etc 2.0 on one fan could easily be far better pressure than 4.0 from a different company, but 4.0 from a corsair SP120 will be accurate when compared to 2.0 on a corsair AF140 as an example.
 
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Yeah the fan you link isn't great. If you want to go for quality go for noctua:
http://noctua.at/en/products/fan
Somebody already mentioned NF-F12 and this is one of the best that you can stick on your radiator. The P12 or the redux line you can then use on the front of the case, and A12 or the S12A on the back.
That's not to say other companies don't make good fans. In fact I've got a pair of cooler masters masterfan pros air pressure fans and they're very good. Overkill, looking in retrospect, but they do have switches to bring them down to decent levels of max RPM, and are very price competitive (and also have air flow and AP/Air flow version of the fans too).
Corsair, BeQuiet, Silverstone, Thermaltake and so on all make good fans. Don't go super cheap on the fan or you'll have to put up with both rattling and annoyingly pitched noises and it's amazing how quickly that can get on one's nerve.
 
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Phanteks makes the best fans on the market atm, outperforms the Noctuas in just about everything. Fractal design and nzxt also have excellent fans as does BeQuiet, Scythe, and a few others. Not a big 'fan' of most of Corsair models, but the ML's look promising.
 
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https://pcpartpicker.com/product/tx8Zxr/bitfenix-case-fan-bfflpro20025brp I know this fan isn't any of the brands you listed, but I ask if this one will do the trick as main intake because it's the only one I saw with blue led that was also highish in cfm (compared to the other blue led fans). I just don't know what it's static pressure is. I would like to know how well it will pull air through the mesh the fan will be behind. I don't know if I will use some of the big names like noctua or whatever just because I plan on plugging in my fans directly into the psu, and I don't want them whirring at 2,000+ rpm all the time. I want relatively low speed fans. Not to mention I want led fans to light up my case. Also not to mention I only have one pwm header on my mobo, so I can't have multiple noctua or phanteks etc and be able to adjust their rpm.
 
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If you plug them directly into the PSU, then they end up running at top speed all the time. What you want is to plug them into the motherboard fan header, and control them via motherboard utilities. If you have only one pwm, you can use the other fan headers. DC fans with 3 pin headers are controllable with variable voltage (not all boards can do this so check if yours can. Older ones usually not).
That fan is fine.
 
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This all may seem simple to you, but it is almost over my head which is why I opted to simply plug them into the psu and be done with it. I guess I can look at my mobo's website and see if I see anything that tells me I can do what you describe.
I also thought about using fan splitters, to compensate for the fact I am lacking in the fan header department, but I don't know how well they work
Update: The closest thing to voltage control I've seen on the site was "DRAM Voltage multi-adjustment" in the BIOS.
 
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No worries. You'll need 2x 2-way splitters. 1 splitter goes to the front intake fans, the other splitter goes to the 2x exhaust fans. Or, depending on your case, it could be a 3-way splitter to the front intakes and just run the single exhaust to the other header. As you have 1x 4pin and 1x 3pin headers, you have the choice of fans, for the 4pin you can use either analog or pwm (3pin or 4pin),but the fans on the 3pin header will have to be analog, no option there. Pwm will not work except at full 100% speed.
 
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But none of the fans that I am considering are pwm fans, so won't they still have to be adjusted by voltage regardless of whether or not they are plugged into the 4 pin header? I thought only pwm fans with 4 pin connectors could be adjusted using mobo utilities.
Also how will I know that I won't overload the mobo header by connecting too many fans using a splitter? I've read elsewhere it has to do with amps, but I fail to understand it.
Update: I've decided for now I'm just going to put one pwm fan in the rear as exhaust and put that 200mm I linked as intake and not worry about any other fans. I'll add more if the need arises.
 
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Ok sorry, yeah you've got two chassis connectors and one is 4 pin and one 3 pin. Since this is a new board, the asrock utility, whatever it turns out to be, should offer you to regulate your fans somewhat with voltage. It's not as responsive as pwm but for chassis is considered fine. You don't need a pwm fan for exhaust. A 4 pin header will take 4 pin and 3 pin fans just the same. So you can have a DC fan for exhaust as well.
As for worry about too many on one header, it's a legit worry, however, you should be able to add two fans on one. Read here:
http://www.tomshardware.com/answers/id-2679564/fans-run-single-sys-cpu-fan-header.html
If you're worried however, you can get a fan controller which bypasses the whole amperage per fan header issue, except I'm not sure where you'd put it in your case. It usually needs an optical drive slot.
Yes I'd start with two, see where your temps are and go from there.
 
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That header is rated by ASR as being 1A (12w). If you look at fan specs, it'll give you rated amperage, or wattage, for instance my Noctua NF-F12 is 0.18A. That means literally I could use a maximum of 5 fans on a single header, but 4 fans would be better and safer, not using over 0.8A. Some fans, such as the Jetflo series, use anywhere from 0.5A-0.6A each, meaning that you can only safely run 1 fan per header, as 2x fans would be right at 1.0A.
The rated ampetage/wattage will be posted on the back of the motor housing on any reliable fan. If it's not, I'd not use more than 2.

Pwm fans are better than analog only really in 1 respect. A pwm fan can usually be turned down to as little as @20% rated rpm, so you can get a dead silent case, especially at idle loads. Analog fans generally will not operate below 5v, most run at 7v-12v, so what you'll get is either 40% or mainly 60%-100% rpm ranges. This is kinda important when looking at an analog fan with max rpm of 2400rpm, as it's lowest speeds will be closer to 1300rpm ±, which is quite loud. A pwm version will run as low as 500rpm ±, which is almost silent.
 
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Sorry for all the questions, but I have one or possibly two more. When using a splitter, it doesn't cut a fan's power by half does it? Or when using a 3 way splitter, it doesn't cut it into one third its maximum capacity for example? If I set two fans which are using a splitter to a certain voltage, they both will get that set voltage, right?

Btw thanks so much for all the answers, you too Sedivy if you happen to see this. I appreciate all the help.
 
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The voltage will not change. It's like...remember basic physics circuits? Series vs parallel? When in parallel, the voltage across the paths is the same and the total current is the sum of individual currents between the paths. So voltage across each fan should be the same, and the amperage drawn through the fan header on the motherboard will be the sum of the amperage of each fan (the amps should be in the fan specs on manufacturer's page).
 
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Easier. In your house you might have 5-6 plugs all on the same circuit breaker. Every one of those plugs still sees the same voltage, either 120v or 240v, if you plug a hairdryer in one plug and a toaster in another, you'll still get the same voltage, but the amperage used will be the sum of the toaster and the hairdryer. House circuits are run in parallel, exactly the same as a splitter.
 
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Where did you see the rating for that header? I'm looking at Asrock's site for that mobo, and I'm not seeing it. Did you download the manual or something? Also I assume you were talking about the pwm header, not the 3 pin header. Is the 3 pin header also 1amp? I'm going to try to hook as many fans as I can to each header without blowing up my computer, exaggerating just a little bit.

Also you said your NF-F12 is 0.18A, but on Noctua's website it says they are rated at 0.05A? Am I looking at the right thing?
 
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Fan headers on just about every board made by any vendor are rated at 1A. However, I'd only trust that rating on the really good mobo's, like the ROG, Gaming 7, Extreme 6 etc. Mostly if you figure 0.8A as being about max and good fans being 0.2-0.5A each, you'll get a number. Generally it's 4x pwm or 3x analog fans, but that depends on the fan itself.

Header is a header, 3pin, 4pin or 5pin makes no difference, it'll be 1A. That's the maximum rating of the copper traces running around the board
 
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