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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?

#111

Post by pbhjpbhj »

Steel_Phoenix wrote: post #107
neltnerb wrote: post #89

Earlier quoted context omitted.

Height is also important if you've got a multi-floor house. In upper stories, make the fans face outward and on the ground floor make the fans face inward and you'll set up a continuous air path throughout the whole house favoring cooler air. Personally for a single fan in a smaller room where you're near the window, I'd say just point it in. That way you get fresh air right where you are sitting, you get the breeze,…

I also like to take prevailing wind into account. Even if it's a small breeze, fighting it can really drop effectiveness.

And consider shadow - let in colder air from shaded areas rather than warm air heated by surfaces in direct sunlight.

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

#112

Post by pbhjpbhj »

tomohawk wrote: post #43
realpeopleio wrote: post #37

My 4rd grade teacher was convinced of the science of using two fans to cool off the classroom: one blowing cool air into the classroom from the hallway and one fan blowing hot air out of the classroom through a window. The kids that sat near the fan blowing in the room from the hallway were quite content, but the kids by the window were always complaining and they would secretly turn the fan in the window around so i…

If the goal is to make the room cooler, your teacher is right. If the goal is to make the students cooler, then the 4th graders are right. 4th graders sweat, and the fan will cause convective cooling of the 4th graders.

Also those by the window were maybe in direct sun.

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

#113

Post by namibj »

bkanber wrote: post #69
namibj wrote: post #58

Earlier quoted context omitted.

Can you recommend any specific software? I'd finally have a reason for the 3d-scanner in my phone... (getting the model at a suitable resolution of <3cm voxel-cube size to not have to model it all from hand)

Overkill for the hobbyist, but ANSYS products like Fluent and CFX are what the professionals use. Quite pricey though.

Yeah, if I had the money for such software, I wouldn't need to ask. I'll assume you don't know any affordable substitute.

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

#114

Post by LocalMan »

To cool summer bedrooms, blow the air out the kitchen window, and open the bedroom window. This will draw cool night air in the bedroom window. You may be sweating at 7 PM but you might need a blanket at 1 AM. This works brilliantly. And putting the fan out the kitchen window means the bedroom is quieter.

To heat winter rooms that have an underpowered radiator, blow the fan onto the radiator. The job of heating the room is the same as cooling the radiator. This works very well but the room downstream (on the steam line) will be getting less heat. In practice, that was the neighbor's apartment. The freezing neighbors complained to the landlord who eventually tracked it down to my place. Vigorous discussions ensued.

I also discovered that a HEPA filtration unit, even sitting on the floor, helped my allergies a lot. It was not cheap, but when I find my nose running again, it means that something had turned off the filter. For years I had thought that HEPA was a scam. Not so.

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

#115

Post by gargravarr »

jimnotgym wrote: post #99

Can I pose a similar question? I have a cieling fan in my conservatory that can blow up or down. Which way is better? It is pretty close to the cieling if that matters.

When we fitted a ceiling fan in our living room, the instructions stated that in summer, it was best to have it blowing upwards (sucking air up from floor level) because that air would be cooler, and in winter from the same principle, you could blow warmer air down onto the room occupants.

In practise it didn't work that well - the temperature difference in a couple of metres of air space (in a single average-height room) is pretty minimal. We left the fan blowing downwards to use the windchill effect in summer - that worked well enough.

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

#116

Post by phillipwills »

We have a 2 story house where the bottom story is a daylight basement. When it gets hot, it usually stays pretty cool downstairs, so we hang down there during the day. In the evening, as soon as it's cooler outside than upstairs inside, we open the back door, both downstairs and upstairs, and turn on a high powered fan blowing air up the stairs... It is really effective at cooling the house.

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

#117

Post by l1n »

namibj wrote: post #58
adrianN wrote: post #6

I assume you want to move the cold air in and the warm air out. How to best achieve that completely depends on the shape of your room and the holes to the outside. You should probably do some computational fluid dynamics on a model of your place to see which blowing direction works better. It probably works best if you have separate inlets and outlets for the air that are maximally far apart, like on the ceiling and…

Can you recommend any specific software? I'd finally have a reason for the 3d-scanner in my phone... (getting the model at a suitable resolution of <3cm voxel-cube size to not have to model it all from hand)

OpenFOAM might work for this purpose.

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

#119

Post by taneq »

innocentoldguy wrote: post #100
cbr wrote: post #59

Earlier quoted context omitted.

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.

Same. Well, it's an evaporative air conditioning unit but 90% of the time we don't turn on the evap function (which is only really useful on days which are very dry and not too hot) but just run it as a fan in the evenings. Blows all the hot air out of the house and replaces it with cool night air in minutes.

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

#120

Post by lathiat »

masklinn wrote: post #86
lathiat wrote: post #60

Earlier quoted context omitted.

This is a concept often poorly understood in basic cooling design. Even without sweat, if your AC vent is blowing directly on you the temperature it is at needs to be vastly different than that of air being using to more actively cool the entire room. This is often a key difference between Car and Room AC systems. There’s also a surprising gradient based on how consistent the temperature is top to bottom (and you get…

> This is a concept often poorly understood in basic cooling design. Really? You'd think windchill is a well-understood concept.

When it comes to basic price central ducted HVAC system installation you'd be surprised! At least in Australia.
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