5 ms·

Just to add, for computer cases, you want it to be a high pressure zone because intake fans generally have filters in front to catch the dust before it gets int

Just to add, for computer cases, you want it to be a high pressure zone because intake fans generally have filters in front to catch the dust before it gets into the case. Negative pressure means dust gets sucked in from the cracks.

jjcm 8y ago
Also while extremely trivial here, higher pressure air has a higher capacity to transfer heat.
- lmilcin 8y ago
  While this is technically true, the difference is very minor at the typical pressure ranges being used. The highest performing PC fans create about 10mmH2O pressure while typically you can expect about 1mmH2O pressure compared to 10mH2O of the atmosphere. This translates to densening of the atmosphere around components by 0.1% or 0.01%, respectively. Correct placement and design is by orders of magnitude more important than the increased efficiency due to higher density of air. You could see much more effect by making your air more humid (humid air has higher heat capacity), which will be also much more pronuncable than the increased density due to pressure.
  - mberger 8y ago
    TIL about mmH2O. Is this common in HVAC? I thought pressure was mostly in mmHg or bars(millibars).
    - Cerium 8y ago
      Yes, fans usually have a specification on the pressure they can create in inches of water or millimeters of water. I think it is because you can measure it yourself with just a tube and water- open end manometer.
      - raldi 8y ago
        How?
        masklinn 8y ago
        Put bottom end of tube in water, put fan at top of tube drawing out, turn fan on, see how much the water climbs inside the tube?
  - lightedman 8y ago
    "The highest performing PC fans create about 10mmH2O pressure" I'm guessing you've never worked with a Delta fan. Those things produce enough pressure to literally suspend themselves in mid-air.
phkahler 8y ago
Thanks for mentioning filters. I'm just in the process of designing an ITX case specific to a board/CPU and plan to partition it so the CPU fan is also the case fan. I hadn't thought about dust. Good point.
- FullyFunctional 8y ago
  Dryer sheets :) I don't remember where I found this tip, but recycling used dryer sheets as air filters works fairly well (definitely beat having nothing).
  - mark212 8y ago
    Or use the new ones for a delightful fresh scent! Kidding!
colanderman 8y ago
Same applies for house fans -- you want the intake fan to be slightly stronger than the exhaust fan. Else the negative pressure will draw outside air in through cracks and all the fun smells that come from those places. (I have a combination energy recovery ventilator/HEPA filter that has has a restriction filter on its exhaust for this reason. Else it would just suck crappy air in from the basement instead of fresh air through the filter.) If you have to choose one, choose an intake fan for this reason. Best if you can leave another window slightly ajar.
- toomuchgov 8y ago
  What is the make/model of your ERV?
  - colanderman 8y ago
    It's a window unit: http://www.purifresh.com/erv.html http://www.purifresh.com/erv.html It's the only such kind I could find when we were in the market a few years ago. (Was renting a place with mold issues.) Works well for a single room. It's wonderful to pull fresh air in during the winter. We also have its accompanying HEPA unit: http://www.purifresh.com/cleanroom.html http://www.purifresh.com/cleanroom.html They can be linked (as http://www.purifresh.com/freshairsystem.html http://www.purifresh.com/freshairsystem.html) or used separately. (Apparently this is out-of-stock and being redesigned.)
- saalweachter 8y ago
  My vague understanding is that negative pressure in a house is also how you get radon gas.

jjcm 8y ago

Also while extremely trivial here, higher pressure air has a higher capacity to transfer heat.

lmilcin 8y ago
While this is technically true, the difference is very minor at the typical pressure ranges being used. The highest performing PC fans create about 10mmH2O pressure while typically you can expect about 1mmH2O pressure compared to 10mH2O of the atmosphere. This translates to densening of the atmosphere around components by 0.1% or 0.01%, respectively. Correct placement and design is by orders of magnitude more important than the increased efficiency due to higher density of air. You could see much more effect by making your air more humid (humid air has higher heat capacity), which will be also much more pronuncable than the increased density due to pressure.
- mberger 8y ago
  TIL about mmH2O. Is this common in HVAC? I thought pressure was mostly in mmHg or bars(millibars).
  - Cerium 8y ago
    Yes, fans usually have a specification on the pressure they can create in inches of water or millimeters of water. I think it is because you can measure it yourself with just a tube and water- open end manometer.
    - raldi 8y ago
      How?
      - masklinn 8y ago
        Put bottom end of tube in water, put fan at top of tube drawing out, turn fan on, see how much the water climbs inside the tube?
- lightedman 8y ago
  "The highest performing PC fans create about 10mmH2O pressure" I'm guessing you've never worked with a Delta fan. Those things produce enough pressure to literally suspend themselves in mid-air.

phkahler 8y ago

Thanks for mentioning filters. I'm just in the process of designing an ITX case specific to a board/CPU and plan to partition it so the CPU fan is also the case fan. I hadn't thought about dust. Good point.

FullyFunctional 8y ago
Dryer sheets :) I don't remember where I found this tip, but recycling used dryer sheets as air filters works fairly well (definitely beat having nothing).
- mark212 8y ago
  Or use the new ones for a delightful fresh scent! Kidding!

colanderman 8y ago

Same applies for house fans -- you want the intake fan to be slightly stronger than the exhaust fan. Else the negative pressure will draw outside air in through cracks and all the fun smells that come from those places. (I have a combination energy recovery ventilator/HEPA filter that has has a restriction filter on its exhaust for this reason. Else it would just suck crappy air in from the basement instead of fresh air through the filter.) If you have to choose one, choose an intake fan for this reason. Best if you can leave another window slightly ajar.

toomuchgov 8y ago
What is the make/model of your ERV?
- colanderman 8y ago
  It's a window unit: http://www.purifresh.com/erv.html http://www.purifresh.com/erv.html It's the only such kind I could find when we were in the market a few years ago. (Was renting a place with mold issues.) Works well for a single room. It's wonderful to pull fresh air in during the winter. We also have its accompanying HEPA unit: http://www.purifresh.com/cleanroom.html http://www.purifresh.com/cleanroom.html They can be linked (as http://www.purifresh.com/freshairsystem.html http://www.purifresh.com/freshairsystem.html) or used separately. (Apparently this is out-of-stock and being redesigned.)
saalweachter 8y ago
My vague understanding is that negative pressure in a house is also how you get radon gas.