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Dust filters, and case fans

Discussion in 'Overclocking & Cooling' started by Tan DJ, Oct 21, 2007.

  1. Tan DJ

    Tan DJ New Member

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    I've been looking in my pile of "left overs" from past upgrades, and found an 80 cm fan.

    Now my current set up has a rear case fan pumping air out, and a side panel fan pumping air in. There is also space for 2 additional fans in front of the HD mounting space.

    I'd like to put the extra fan I found in the case to provide extra air flow, so I though I'd look on this forum to find out the best configuration for case fans, and it looks like the general rule of thumb is:

    Rear case fans should pump air out of the case,
    Side, and front fans should pump air into the case.

    So I was thinking of moving my side fan to the front, and putting my extra fan in the front as well. Or would I be better off leaving the side fan on the side, and puting the extra fan in the front? I currently only have 1 HD, but I am looking at getting 2 additional 7200rpm SATA drives.

    Will the fan vent on the side cause any "issues" if it doesn't have any fan mounted? (eg. the positive presure created by the two front mounted fans escaping out the hole in the side...)

    Also, I have noticed a large build up of dust on all components that are near the air flow from the current side mounted fan. Is there any way to filter the air being sucked in so that not so much dust builds up internaly? How do you filter the air without restricting the airflow too much? I had a mental image of my PC with my Landcruiser's air filter sitting on top :laugh:

    Intel Active Monitor has only ever reported an over temp alert when there was too much dust on the CPU heat sink for the CPU fan to keep the CPU cool.

    Where I work, all our servers are in a nice dust free data centre, but I don't have that luxurary at home, so if any tips on dust filtering would be helpful.
     
  2. HookeyStreet

    HookeyStreet Eat, sleep, game!

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    I always find this config to be best:

    1-2 (any size, 80mm, 92mm, 120mm) fans at the front sucking cool air in (usually over the HDD).

    1-2 (any size) side fans sucking cool air in (blowing onto the motherboard or GFX card area)

    1-2 (any size) rear fans exhausting warm air out.

    Also some people have a fan (or 2) mounted at the top of the case to exhaust any warm air thats risen ;)
     
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  3. Elvardo New Member

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    Some nice advice there, It will help me when i build my new machine. :cool:

    Thanx
     
  4. HookeyStreet

    HookeyStreet Eat, sleep, game!

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    Cool, glad to help :)
     
  5. bassmasta Guest

    look for my case, it's got that layout + a fan at the bottome
     
  6. Tan DJ

    Tan DJ New Member

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    so if I currently have 3 fans, then 1 on back, 1 on side and one in front would be a good distribution of those three, and if I'm feeling particullarly cashed up, I could buy a second one for the front.

    So how do you all deal with dust?
     
  7. bassmasta Guest

    keep slightly high pressure in your case to avoid dust. also clean fan filters once a week if you have them
     
  8. Widjaja

    Widjaja

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    I clean mine with that air in a spray can stuff once a month or along with a vaccum cleaner so the fluff doesn't just get blown to another area of the case.

    Quiet annoying quick how a PC collects dust and fluff.
     
  9. Tan DJ

    Tan DJ New Member

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    Dust filters? Where can I get them from?
     
  10. bassmasta Guest

    usually dust filters come with the case. they are either very thin cotton/plastic squares or very tight mesh in place of a fan grill.
     
  11. WBaS

    WBaS New Member

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    Very nice keakar, I agree with you on everything you just said.

    I know you're concerned with dust, but you do get the best cooling with a negative pressure setup. This means that you have more cfm going out the case than into the case. By doing this, you are essentially making a vacuum out of your case, pulling in cool air but exhausting hot air quickly.

    To address the dust issue, I would recommend getting dust filters and cleaning them regularly. You can pick these up online from newegg or frozencpu.com. I imagin there are others as well. They shouldn't restrict too much airflow as long as you clean them.

    My advice: If you're sticking with 3 fans, keep 1 rear exhaust, 1 side intake, 1 front intake. If they have different CFM, put the largest cfm in rear, medium in front, least on side. Pick up dust filters and clean them regularly. If you pick up another fan, exhaust in back or top.
     
  12. keakar

    keakar

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    Guide to proper case airflow design

    --------------------------------------------------------------------------------

    airflow and case circulation:

    1) airflow is best if it can flow in one direction only and better off (stays stronger) flowing in a straight line. also always cut out a hole where you mount a fan, never use it with those predrilled holes or you cant get good airflow. redrill all those small holes in the back of the case with a 3/16" drill bit to increase ventilation and cooling. the holes are too close together to use a 1/4" drill bit without having it blow out into the next hole and make a mess of things.

    2) heat naturally rises so to remove heat it is best to draw air in from the cases lowest points and exhaust it from the cases highest points.

    3) the direction of flow - this can be done many different ways (as long as you remember rules 1 & 2 above) but the most common setup for all cases is intake from the bottom front and exhausted out the top and back. the reason they do it this way is it takes best advantage of both airflow and heats natural tendacy to rise. the air is drawn in from the coolest point (bottom front) and moves in an "S" to flow accross the motherboard and out the exhaust fans (top rear and psu fans).

    4) side fans - side fans can and do interfere with this "S" flow of air so keep this in mind if your thinking of a high cfm side fan. it may improve cooling in one spot and allow a "dead spot" for airflow somewhere else. side fans are great cooling aids but dont go overboard with the cfms. to reduce the interference cases use air ducts to direct the cool air right into the cpu fan so it will not interfere with airflow through the case.

    5) VGA - the video card area tends to be a dead spot for airflow. this is why they have fans now that take in cool air directly or exhaust hot air out the back of the case. adding a side fan blowing into this bottom corner "stirs" the air so heat can rise and be exhausted as long as you dont over do it to the point that it will interfere with the vga coolers airflow through the heatsink. just remember the fan is there to stir the air and thats all. it should not blow directly accross the heatsink or you could reduce its cooling effect by canceling out the airflow accross the heatsink.

    6) "push / pull" or "fan in / fan out" system - your fan cfms and sizes are matching dont always give you balanced airflow because it is a lot harder to push air through a case than suck air out of the case. often it is needed to have slightly bigger intake fans than ehaust fans even though they are of the same size so dont just assume two 80mm 45cfm fans in the front and two 80mm 45cfm fans in the rear will give you a balanced airflow. (although it should be close enough not to matter)

    7) positive airflow system (more fan driven cfm air in than fan driven cfm air out) - the benefit to this type of system is supposed to be that it pulls in less dust than a negative airflow system but this is a false idea. weather the fan draws the air in or directly blows it in it is still the same air from your room. if your room is dusty your case will be dusty. a positive airflow system stays cleaner than a negative airflow system only because the fans keep the air "stirred up" so dust can be blown out before it settles on surfaces inside of the computer. a simple air supply test is to just check the amout of air your system is exhausting through the small holes in the back of your case, if it is more than just a gentle draft coming out then you are restricted and should adjust the airflow by reducing the cfms of your intake fans or making bigger exhaust openings to balance things out.

    negative pressure systems are in general designed to be quieter so they have slower fans that run quieter and this allows the dust to settle on surfaces in your computer before it can be exhausted and this is why they wind up collecting more dust.

    think of a fan blowing feathers around in a small room, as long as the fan keeps blowing fast they all stay airborne but put the fan on slow speed and everything will be covered in feathers. the same applies to dust in your computer, it is the airflow inside the computer that determine how fast your computer gets dusty (and of coarse how dirty your room is lol).

    8) negetive airflow system (more fan driven cfm air out than fan driven cfm air in) - there is nothing wrong with a negetive pressure air setup and if done properly and it will not harm anything in your system. you can reduce dust building up by putting a low cfm fan inside the case just to keep the air stirred up so dust wont settle and can be exhausted by the fans. remember that if your air supply is restricted too much it will cause overheating. a simple air supply test is to just check the amout of air your system is exhausting (rear exhaust fan) and also checking the amount of air your psu is exhausting, then remove the side cover on your computer. it will always move more air with the door open so if you notice only a minor difference then you are fine but if you notice a big difference then you need to investigate where your restriction is and provide a larger air intake opening.

    a person who puts high cfm exhaust fans that dont have proper sized or unrestricted intake openings on the other side of the computer can sometimes actually cause a vaccum to form inside the computer and this could actually prevent the psu from moving any air because the air is being pulled backwards through it by those big fans resulting in the psu overheating. most problems with negetive airflow systems are in the airflow design and not the negetive airflow system itself.

    for a healthy system your air in should equal the air out. its always louder to have a system that has more fan driven intake air (positive pressure) and quieter to have a system that has more fan driven exhaust air (negative pressure). a negative pressure system with exhaust fans only just needs to provide unobstructed openings equal to or bigger than the total size and shape of the exhaust openings so if you have 4 80mm exhaust fans (plus the psu fan) then you need at least 5 open 80mm holes with open grills. i usually recommend for a negative air pressure setup to have at least one extra 80mm hole in addition to a 1 for 1 match because each open hole always allows more air to be drawn in than the exhaust fan is pushing out the other hole so no vaccum is formed but if you only had say three open 80mm holes for intake air they would not be letting in enough air for the four 80mm exhaust fans and the psu fan. another overlooked obstruction is the front panel, it can restrict airflow no matter how big the opening is behind it so test with and without the front panel in place to see if air must be brought in from a different place (maybe the bottom panel).
     
    Last edited: Oct 24, 2007
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  13. keakar

    keakar

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    you caught me mid-update on the post lol. i added a little more about positive &negetive airflow
     
  14. WBaS

    WBaS New Member

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    Yep, I noticed that (I didn't thank you for that post until after your update) ;)
     
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  15. keakar

    keakar

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    well it looks like i ended up with anothe "guide" to add to the list on my sig lol.
     
  16. WBaS

    WBaS New Member

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    Yeah it'd probably be helpful, but I'd probably call it something else. Maybe something like "Guide on Case Airflow"? There is a lot of good information on more than just dust. I think a lot of the relevant information is on the fundamentals of airflow.
     
  17. nhlrocker New Member

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    hmm. this might work a little better.
    1-2 (any size) -front- intake
    1-2 (anysize) -top- exhaust
    1-2 (anysize) -rear- exhaust
    1 (anysize) side w/airduct- intake (the airduct, directs the air on the mobo or cpucooler so that the air being sucked in doesnt ruin the wind tunnel effect.

    this is a really good config. remember the exhaust fans at the top are important because hot air rises.
    the intake fan at the front is also important cuz thats where the coolest air is coming from. it will cool ur hardrive also.
     
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  18. Tan DJ

    Tan DJ New Member

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