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submitted 4 months ago* (last edited 4 months ago) by Gullible@sh.itjust.works to c/nostupidquestions@lemmy.world

Secondarily, should the fan be outside or inside the window?

Asking for a friend. (Me, help. I can’t remember physics, it’s too goddamn hot)

Edit: I’ve opened all the windows and set up a fan a short distance from the window pointing out and it’s reduced the temperature to near-tolerable levels. Unfortunately, venting through the attic was a no-go but moving things aside might make it an option next time. Thank you all, I appreciate the help!

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[-] franglais@lemm.ee 83 points 4 months ago
[-] mwproductions@lemmy.world 30 points 4 months ago

I'm glad to see someone linked to this video. No one ever believes me when I tell them this is the way.

[-] massive_bereavement@fedia.io 7 points 4 months ago
[-] ChronosTriggerWarning@lemmy.world 3 points 4 months ago

I don't believe @mwproductions.

[-] morrowind@lemmy.ml 4 points 4 months ago

This guy seems to have a different goal then OP. He just wants the max airspeed in other parts of the house

[-] bitwaba@lemmy.world 21 points 4 months ago

The goal is the same.

Scenario: cold air outside, hot air inside.

Goal: replace hot air inside with cold air outside.

Method: open one intake window and one exhaust window. Use a fan to blow hot air out the exhaust window while the low pressure vacuumed created inside will cause cold air to be sucked in through the intake window.

Maximize efficiency of method: follow video posted.

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[-] vivavideri@lemmy.world 30 points 4 months ago

Well, the folks over at noctua have fan shenanigans down to a fine science, and since I have generally forgotten the last rabbit hole I went down, I'd say get two fans and have one blowing in and the other out, lol.

[-] franglais@lemm.ee 41 points 4 months ago

This is the wrong application, noctua are looking for static pressure, what OP wants is to maximise airflow. Mathias wandel has some pertinent videos on the subject, the ideal is a large fan about a metre or two away from the window, depending on the size of the fan, blowing hot air outside.

[-] sneekee_snek_17@lemmy.world 12 points 4 months ago

Why so far from the window?

[-] SzethFriendOfNimi@lemmy.world 29 points 4 months ago

I think you get the benefit of the airflow pulling in air along its edge to push out with it.

Like pushing a bunch of water with a broom removes not only the water in front of the broom but also more water due to surface tension and inertia

[-] ShepherdPie@midwest.social 28 points 4 months ago

It's called the venturi effect.

[-] kakes@sh.itjust.works 21 points 4 months ago

It's called the linguini effect.

[-] sneekee_snek_17@lemmy.world 19 points 4 months ago

Ohhhhhh the bernoulli effect?

[-] 667@lemmy.radio 7 points 4 months ago

no no, it’s the Magnum effect.

[-] tiefling@lemmy.blahaj.zone 18 points 4 months ago

Good ole vermicelli effect

[-] franglais@lemm.ee 12 points 4 months ago

In this case it's called the brunelli effect

[-] altima_neo@lemmy.zip 11 points 4 months ago

Ah yeah, the Dom Mazetti effect

[-] Chee_Koala@lemmy.world 9 points 4 months ago

Its called the Chimichurri effect

[-] Hupf@feddit.de 8 points 4 months ago

The Bozzetto effect?

[-] Peppycito@sh.itjust.works 7 points 4 months ago

It's called the kimchi effect

[-] KillerTofu@lemmy.world 5 points 4 months ago* (last edited 4 months ago)

It’s called the butterfly effect.

[-] Feathercrown@lemmy.world 3 points 4 months ago

Oh yeah the bruscietta effect

[-] pmk@lemmy.sdf.org 14 points 4 months ago

It creates an effect where surrounding air is pulled with the stream due to the Bernoulli effect. It's the same thing that pulls shower curtains in when you shower. If the fan is a bit inside the window, surrounding indoor air gets pulled into the stream, moving more air out in total.

[-] Hacksaw@lemmy.ca 6 points 4 months ago

Most of the replies are correct overall. But Mattias Wandel had identified another important factor. Fans don't just "stuck from the back" and blow out the front. They sort of suck from everywhere including the edges. This means that if you're putting a fan right up against the window blowing in you're sucking some room air as well. If you're putting the fan right up against the window blowing out, some of the air you're blowing out comes from outside in the first place.

The ideal is then to blow out from 2-5ft away. This way all the air that's blown is room air, and it's all blown out. The venturi effect plays a small part. The Bernoulli effect? Equations? Explains why the air stays in a "tube" for a few feet away from the fan. Technically also explains the venturi effect..... Everything is Bernoulli....

https://www.youtube.com/watch?v=1L2ef1CP-yw

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[-] NeoNachtwaechter@lemmy.world 5 points 4 months ago

A fan creates kinda long "channel" in front of it and behind it, where the air is moving rather fast (at the speed that the fan creates). Imagine the narrow beam of light from a flashlight. You want that channel to go right through the window to have a good amount of air flowing.

I don't know that you need to keep a distance from the window. I think 1-2m is just more practical than having the fan right inside the window frame.

[-] subignition@fedia.io 3 points 4 months ago

do you happen to know whether this is significantly different for a blower-style fan that has its air intake on one side? for example

https://lasko.com/collections/air-movers-blowers/products/lasko-12-pivoting-pro-high-velocity-utility-blower-fan-with-3-speeds-u12104-gray

[-] NeoNachtwaechter@lemmy.world 4 points 4 months ago

I don't know the type, so I am judging it from that picture.

It shows a rather small area where the air comes out. I imagine that it creates high speed, but the "channel" would have the exact same size and shape as that small area where the air comes out. So I'd consider it as less effective.

A fan with a large diameter could probably move more air.

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[-] traches@sh.itjust.works 2 points 4 months ago

Same reason why blowing on your hand close to your mouth is warm, but farther away is cool.

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[-] lemmefixdat4u@lemmy.world 15 points 4 months ago* (last edited 4 months ago)

I've tried it many ways. The most efficient method using a fan is to open the windows in a room on the leeward side of the house, then place a fan a few feet in front of the doorway, blowing air into the room. It's more efficient because the impelled air will entrain surrounding air moving a greater volume through the doorway and out all the windows in that room. Then open windows in the farthest rooms to get a cross breeze.

Also look into an attic fan. They exhaust hot air from the attic, and it makes a world of difference in keeping your interior cool. Another trick is to mount shade cloth 6 inches away from the sunny walls of your home. It absorbs most of the solar radiation and keeps your walls cooler.

[-] etchinghillside@reddthat.com 13 points 4 months ago

Exhaust air out from the ceiling if possible.

[-] rand_alpha19@moist.catsweat.com 8 points 4 months ago* (last edited 4 months ago)

The most efficient way is to force cold air into the space while also forcing hot air out. The best way to do this is to have maximum airflow from one end of the house to the other, often by opening all of your windows and using multiple fans to direct the air. For example, an intake fan pulling air in at the north end and an exhaust fan pushing it out at the south end.

[-] Dudewitbow@lemmy.zip 7 points 4 months ago* (last edited 4 months ago)

if you have one and only one opening into your room, id believe setting the fan to exhale is optimal, as the logic would be similar to radial fans in low airflow situations, where in that situation, its ideal to move hot air out.

if you have 2 windows, I think it was one intake. if you have a window and a door (to the rest if the house), placement depends if youre okay with dunping heat into the other part of the house or not.

theres a lot of factors though, as it pertains to the rooms internal pressure and the condition of the air/sunlight outside of the window, as well as how high the window is

[-] cerement@slrpnk.net 5 points 4 months ago
  • reversible fan
    • blow hot air out during the day
    • bring cool air in a night (night flushing)
[-] ShepherdPie@midwest.social 36 points 4 months ago

Any box fan is reversible if you turn it around.

[-] bizarroland@fedia.io 29 points 4 months ago

Who are you who is so wise in the ways of science?

[-] Brkdncr@lemmy.world 4 points 4 months ago

The make up air is coming from outside. The fan direction doesn’t matter.

[-] ordellrb@lemmy.world 5 points 4 months ago

Have an fan pushing out on the ceiling in the middle of the house would work good, it will get the hottest air out. But also keep in mind: the air has to come from somewhere, if the house is sealed (new windows) this will not work well.

[-] dohpaz42@lemmy.world 5 points 4 months ago* (last edited 4 months ago)

Ok, so I may be way off here, but it seems to me the better of the two orientations would be to blow air out, allowing the cool air in.

As the air inside the house heats up, it will rise toward the ceiling. The fan will pull that hot air down and out the window, causing cool air to come in to replace the hot air being drawn out. And because cool air stays low to the ground, it’ll create a convection of airflow.

[-] HeyThisIsntTheYMCA@lemmy.world 5 points 4 months ago

We put ours in the ceiling between the attic and the top floor. Pull the air out of the house, open the windows at night. I've heard it called a "whole house fan". I would occasionally turn it on with the windows closed while the air conditioning was running to, uh, make it go faster, but I'm not sure you're supposed to do that. Cooled the place down in seconds tho.

[-] TropicalDingdong@lemmy.world 4 points 4 months ago

What are you trying to get someone diviorced?

The key to happiness in life is to know what questions can't be answered and then to not ask them.

[-] litchralee@sh.itjust.works 4 points 4 months ago

I'm not a physicist. But I did live in an apartment at university, and shortness of funds plus hot weather meant experimenting with various box fan configurations.

What I found most optimal was to open two windows on opposite sides of the dwelling, with the one box fan aimed outward, using cardboard to block the openings around the fan. In my case, the choice of egress (ie air flowing out) window was based on: the window which best fit the box fan's shape, proximity of noise to the bedroom, and the quality of the window screen.

As for why the fan points outward, this sends the heat of the motor (60-100 W) out of the dwelling, rather than drawing it in. Also, if facing inward, the high airflow at the tips of the fan blades would tend to draw small flies into the dwelling. But if the fan is at the egress window, then the ingress airflow will average out over the full surface area of the ingress window, producing a lower peak airflow rate, akin to a gentle breeze.

If you have a multi-floor unit or house, it would be optimal to place the fan at the highest egress window, to take advantage of heat naturally rising. Opening multiple ingress windows will quickly cool those rooms, while also reducing the peak ingress airflow and resulting drafts (eg blowing papers off tables). Of course, it's necessary to open all the doors to form a path between the ingress and egress windows.

[-] HubertManne@moist.catsweat.com 4 points 4 months ago

It depends on the windows placements that are open and temperature of the building sides vs the location which can be time of day dependent. It is not always good to open all windows as it can be valuable to create an airflow that does what you want. Air pressure goes down as you go up in height so its good to have windows open lower on the cooler side and higher on the higher side. Its possible the whole heat risese effect helps this to im not sure. This should create its own airflow that is slight compared to a fan but very consistent and can help a lot on its own. From there I do think pulling out seems to work better than pushing in but it is way better if it covers the whole opening as much as possible. So like if you can use foam insulation to make a form fitting collar for the fan that sizes it to sit in the center of the window opening hole and seals it to the edges. That will work better.

[-] Bell@lemmy.world 4 points 4 months ago
[-] TropicalDingdong@lemmy.world 15 points 4 months ago
[-] Fondots@lemmy.world 17 points 4 months ago
[-] FuglyDuck@lemmy.world 3 points 4 months ago

No, but they can drive a geothermal heat pump. Just saying.

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this post was submitted on 10 Jul 2024
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