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

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

#91
Too many assumptions to answer precisely. Chances are you'll feel cooler if the fan is blowing inwards because that will help your body reduce its temperature via evaporation of perspiration.

There are much more complex cooling setups that can be achieved that utilise outward-blowing fans though, but a single fan can't will cool _you_ faster if it is blowing onto you.

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

#92

Earlier quoted context omitted.

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.

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…

What is the make/model of your ERV?

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

#95
post #49
post #36

Earlier quoted context omitted.

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

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 importa…

"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.

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

#96
I'm convinced that outwards is the most effective in this scenario:

Open your bedroom windows on a cool spring/summer night. On the opposite end of the house, put a fan in a window blowing outwards. This cools the entire house, giving your bedroom the freshest air. In the morning, close all the windows. This leaves the house cooled and drastically reduces your A/C usage.

Blowing inward doesn't have the same effect of pulling air through the whole house.

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

#97
I usually place the fan so it faces outside. I figure out which way the wind is blowing, open two windows on opposite ends of the room/house that correspond with the wind direction, and then place the fan, facing out, on the downwind end of the room/house. My thinking is that the wind will push itself into the house through the fan-less open window, but that it will then lose momentum. Then, the fan on the downwind side of the house will help pull the air back out of the house, creating circulation that doesn't have to fight against the wind.

Recently, I bought a whole-house attic fan. Now, I open a window on the upwind side of the house and turn on the attic fan, which is enough to suck a toupee off someone's head. The attic fan both circulates cooler air and also clears out the hot air built up in the attic, which helps a lot.

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

#98
In my computer setups, I place three intake fans each on both the front and bottom of the case and then place two exhaust fans each on the top and back. Again (see my other post), the idea is to maintain the natural airflow. Since heat rises, I want my exhaust fans to assist with that natural flow rather than fight against it.

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

#100
post #59

Earlier quoted context omitted.

Fans -> cool human via wind-chill [1] Air conditioning -> cool human by cooling environment [1] https://en.wikipedia.org/wiki/Wind_chill

You can also use fans to cool the environment, trading hot inside air for cooler outside air. For example https://en.wikipedia.org/wiki/Whole-house_fan

Whole house fans are great. They cool the house, clear out the 150º air radiating from the attic, and also take a lot less energy than air-conditioners. I use both, but my air-conditioner runs a lot less since I installed the attic fan.
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