Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Ask HN: Do I place the fan so that it blows air inwards or outwards?

news.ycombinator.com

Post reply on HN
Print view View original

21–30 of 120 posts

Re: Ask HN: Do I place the fan so that it blows air inwards or outwards?

#21

Post by marcosscriven »

I like to think of it like emptying a bottle - if there's only a small hole it goes glug-glug, as occasionally air forces its way into the bottle.

It's the same with air - there has to be a good way to get cold air in and hot air out with minimal turbulence from the two flows.

I think you're better off blowing cold air in (there's no such thing really as 'sucking' in physics), as attempting to blow hot air out doesn't necessarily mean it's going to be replaced with cold air from the outside, rather than warmer air elsewhere in the building.

Re: Ask HN: Do I place the fan so that it blows air inwards or outwards?

#24

Post by adtac »

hellofunk wrote: post #2

Depends on your goal. Do you want to: 1) Cool down your room? 2) Warm up the outdoors? 3) Warm your room further?

Cooling down your room and warming up the outdoors is the same thing, if it's a purely mechanical problem, because the energy to warm up the outdoors has to come from somewhere and the room is the only other entity.

Re: Ask HN: Do I place the fan so that it blows air inwards or outwards?

#25

Post by FraKtus »

pmoriarty wrote: post #17
roel_v wrote: post #15

Earlier quoted context omitted.

"You should probably do some computational fluid dynamics on a model of your place" Oh great, there goes my Monday. Thanks buddy.

Or you could just experiment, try both ways, and measure the temperature differences.

Exactly what I do, use a standard temperature sensor, load your system, make the CPU and GPU cry :-) and see how it goes with cooling the inside of the system.

Re: Ask HN: Do I place the fan so that it blows air inwards or outwards?

#26

Post by lstodd »

dgoldstein0 wrote: post #20
vortico wrote: post #19

If you blow air in, you're sucking bugs in and blowing air out of your central air filters. If you blow air out the window, fewer bugs. That's enough to make me not care about the thermodynamic answer.

This assumes there are enough bugs to be a problem. Some places this isn't the case. Also more likely to have bugs at lower floors of buildings as they tend to hang around trees and plants.

I'd worry more about dust. In a big city, just leaving windows quarter-opened for a week results in everything covered with a visible layer of dust and finely-ground rubber

Re: Ask HN: Do I place the fan so that it blows air inwards or outwards?

#27

Post by anujsharmax »

Everyone seems to be assuming that you have a big fan which actually changes the air flow in the whole room in a major way. If that's the case, great, put it any way you like - it doesn't matter.

For people like me, who use a cheap fan in the summer. Put it in front of you facing towards you. You will feel cooler.

If you are still interested in CFD I can give you a hand, but this is answer we are going to get from it anyway.

Re: Ask HN: Do I place the fan so that it blows air inwards or outwards?

#28

Post by kenhwang »

cbanek wrote: post #9

Like others have joked about, it's really about where you want the air and temperature to go. Let's say you have three fans in a computer case, one at the back, one at the front, and one on top of the CPU. If they all blow out of the case, then you've basically created a negative air pressure zone, and you will be sucking air through the vent holes elsewhere, and through any gaps in the case. This may have effects fo…

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.

Re: Ask HN: Do I place the fan so that it blows air inwards or outwards?

#30

Post by strawcomb »

taneq wrote: post #18

If this is because you want to feel cooler, place the fan so it blows cool air inwards onto you . You'll get far more benefit from having air blown on you than you will from just dropping the ambient temperature around you.

Fans -> cool human via wind-chill [1]

Air conditioning -> cool human by cooling environment

[1] https://en.wikipedia.org/wiki/Wind_chill

Post reply on HN