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Thread: Opinions on radiator airflow designs

  1. #1

    Opinions on radiator airflow designs

    I am trying to plan how I want to design a Primo's airflow. I require positive case pressure and filters on my intakes. I am aware due to the fact that heat rises, most people advise case designs to be:
    Front & Bottom = intakes
    Back and Top = exhaust
    (lets call this the "norm")

    I am leaning toward the 140mm form factor for radiators. With a 280 rad on bottom and a 420 top on top (both radiators just using Pull) combined with the stock 2x 140mm front intakes and the one 140mm exhaust, I am looking at a relatively neutral pressure if I adhere to the above norm. Like this:
    Front & Bottom = intakes = 2x fans from the front & 2x fans on the bottom 280 rad = 4x fans
    Back and Top = exhaust = 1x fan from the back & 3x fans on the Top 420 rad = 4x fans

    In fact, I think if I was just going with the above, I would probably have a slight positive pressure due to the fact that the 3 of the exhaust fans will be slightly hindered by the 420 radiator while only 2 fans will be hindered from the bottom radiator. That said, if I go with Push/Pull on the radiators, I will probably be slightly negative as I am adding more fan power to the top radiator than the bottom.

    So I have pretty much decided I need to make use of the right side dual 120mm slots to swing it way over to the positive pressure side. Obviously adding a 240 radiator (or even just case fans) will do the trick. So here are by two ideas:

    1) Turn the top into an intake and use the right side dual 120's as exhaust. This would give me massive positive pressure but not really sure how the airflow will go. The front and right side might even cancel each other out without benefiting the case.

    2) Or just use the right side as an intake.

    Has anyone else used the Top and Bottom as intakes? I welcome thoughts, opinions, and experience on this.
    Last edited by Leeford; 04-07-2014 at 02:35 PM.

  2. #2
    Everyone uses the top and bottom as intakes. Your interior case air is generally about +5C over ambient if doing the typical 10C delta T rad design, having the top fans blow out will reduce rad efficiency by 50%.

    Peeps focus on positive / negative pressure is misdirected in two ways

    1. The ONLY advantage positive pressure has is that generally, case fan inlets are filtered. It doesn't matter beans whether air pressure is positive or negative if inlets are not filtered. There's also nothing wrong with negative air pressure if all inlets are filtered, generally however, that involves a bit more work. Phanteks has filtered all inlets so with the Enthoo, positive is the much easier and expedient way to go. However, filters have a negative effect on air flow....more on that later.

    2. You do in no way need to balance intake and exhaust fans. All air getting in will in fact get out thru the grille areas.

    I recommend a Alphacool UT60-280 on the bottom and a XT45-420 on the top. This will be more than enough for twin 780 or twin 780 Ti's. I also recommend the following water block's with this set up:

    GPU Water Block - EK ASUS GeForce 780 GTX DCII VGA Liquid Cooling Block - Nickel (EK-FC780 GTX DCII – Nickel)

    GPU Water Block Backplate - EK ASUS GeForce 780 GTX DCII VGA Liquid Cooling RAM Backplate - Black CSQ (EK-FC780 GTX DCII Backplate - Black)

    CPU Water Block - EK Supremacy Universal CPU Liquid Cooling Block - Clean Plexi (EK-Supremacy Clean CSQ) - No Circles [3830046990808]

    I have 3 Phanteks SP140 LED fans on top pulling air in and 2 Phanteks SP140 fans on bottom pushing air in. There are 2 SP140 :ED fans in front blowing in, 2 non LED SP140's on the left panel blowing in and just 1 exhuast fan in rear blowing out. Right now, all fans are controlled as follows:

    MoBo CHA-1 Header => Phantekls PCB # 1 => (5) Rad Fans
    MoBo CHA-2 Header => Phantekls PCB # 2 => (5) Case Fans

    Once we can but accessory PCBs, I'll switch to:

    MoBo CHA-1 Header => Phantekls PCB # 1 => (6) XT45-420 Fans (all intake)
    MoBo CHA-2 Header => Phantekls PCB # 2 => (4) UT60-280 Fans (all intake)
    MoBo CHA-3 Header => Phantekls PCB # 3 => (5) Case Fans (4 intake / 1 exhaust)

    All Fans as well as the twin water pumps are controlled via Asus AiSuite 2

    I tried the right side fans as exhaust ....bad idea.....a) you'll note Phanteks put intake filters on them which tells ya they were thinking intake and 2) You have two intake fans blowing in just a few inches away.... the fans on the side will simply short circuit that air from the front intake and pull all that nice cool air that just came in and send it right out thru the side.

    Now on the impact of the inlet filters / grilles. Doyyl was the 1st to note the impact of the air restriction on the bottom. Especially with 360 and 480 rads, the amount of inlet are combined with the filters moved him to build a dolly to elevate his case. After doing so, he observed a significant drop in temps. With only a 280, my inlet fans are sucking fresh intake air from the front down thru the floor grille and into the rads, so while I saw an improvement, it wasn't that big. OTOH, the top grille and inlet filter was giving me only a 1.0C drop across the 420 rad, while I was getting a 1.3C across the 280 which made no sense.

    Pulling off the inlet filters on top and bottom dropped me from a 12.8C delta T to a 8.4C delta T so you can see what kind of an impact inlet grilles and filters have.

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