They screw plastic bottles to a piece of cardboard and hang it in the window. The air flows differently now.

They screw plastic bottles to a piece of cardboard and hang it in the window. The air flows differently now.

Bernoulli's principal. The air velocity increases when forced through the smaller holes of the bottles. This could provide a nice breeze, and a breeze can cool a sweaty human through assisting evaporation but there's no way the average temperature of the room is cooling significantly as these demonstrations have claimed for years. In fact if the human in the room is cooling, the air in the room is warming up.

Compresses and cools?

Gay-Lussac would beg to differ.

It could actually be cooling the room, but not because of the airflow. It probably cools it by a significant amount just by blocking most of the direct sunlight from shining into the room. Especially with the more solid versions.

Yeah, the science is weak with these ones.

So what you're saying is that we can get more thermodynamically realistic results by, I don't know, putting a little roof over the window to create shade while simultaneously allowing more airflow?

read the proffessors rebuttal as why this doesnt work -

/ Compression raises the temperature a tiny bit. It does not cool the air. / A fall in air temperature happens where the air exits a nozzle. As it enters a volume of lower pressure, it expands, and temperature drops. / The air pressure in the hut will be the same as outside the hut, so the energy put into the airflow by compression will equal the energy released by decompression. The net change should be zero. / Tin provides shade and the board provides shade, so that represents zero change. / The holes in the board let a little more infrared (heat) into the hut, so that bit raises the temperature. / Shade provided by the funnels (the bottles) is not significant. / The board looked like poster board or cardboard. It will conduct the sun's heat more slowly than the tin sheet it replaces. That alone will drop the temperature a little. / The funnels add simple ventilation -- no different from screen or cheesecloth. That's where your cooling comes from. / The funnels direct the airflow slightly. The directed airflow will cool to whoever sits right in front of them, although the hut as a whole doesn't get cooled any more. / Any way you can shade the hut and increase the ventilation will get the same results. / To maximize the effect, take out a section of tin near the ground and cover it with screen or cheesecloth. Don't cut holes in the board. Instead, angle it to shade the vent. Open some ventilation at the ceiling level. The hot air will exit high and draw cooler air down low, increasing the airflow. The airflow will both cool the hut and cool the occupants. Turn the plastic bottles in at the recycler and buy a cold Pepsi.

"Air gets compressed" no. No it does not. It needs to be a lot faster to have compressibility effects. It's accelerated so pressure drops and so does the temp of the air. Very slightly. Really you are just creating air flow/ circulation in a room. like a fan would...

More like witch draft am I right?

Brought to you by Gwyneth Paltrow

Get out of here with your witch craft

They also say in the video that the air compresses as it flows through the bottle, thereby cooling the air. This doesn't happen.

This is called the "Place Eco Bottle Effect", or PlacEBo effect for short.

Nope. Heat increases with density/pressure, not decreases.

If it was possible to cool a whole room down passively we'd all be doing it, rather than buying expensive AC systems.

That's some way it could conceivably work, but that's not happening here. There's no way there's significant compression or significant heat exchange happening here.

SEE EDIT

Original:

As the air moves from the bottom of the bottle to the lid, it compresses, but stays at about the same temperature, as the exterior of the bottle is in contact with ambient air. (This is where the system sheds heat, hotter compressed air being cooled by less hot ambient air.)

Once the air enters the room, it expands and cools, cooling the room.

If you were to represent the system as a series of common components, you'd have a compressor (wind blowing air into narrowing bottle), combined with a cooler (bottle in contact with ambient air, followed by a nozzle (small opening into room.)

Cooling systems like this are common in industrial processes, like natural gas fractionation. (They don't make their parts out of plastic though.)

See the Joule–Thomson effect.

EDIT:

I did the math. Even with up to 90 mph winds (probably more than those huts can withstand,) you'd only get the pressure down by about 1%, and the temperature down by 1C.

Also, as this temperature drop actually occurs during the compression in the subsonic converging nozzle, any heat transfer between the environment and the bottle is actually working against you. (I know this is counter-intuitive, but I guess this is how subsonic converging nozzles work.)

If I get time, I'll build a quick and dirty CFD model, but I currently think there's minimal thermal benefit of something at this scale, except for reduction in solar radiation.

Sorry for being wrong above. I'm used to dealing with different thermodynamic conditions, and I wanted it to work! If anybody gets a CFD simulation running, makes a test bed with a fan and a thermal camera, or has a better explanation, please let me know and I'll stop investigating.

Sauce code: math, and am mechanical engineer with thermal and fluid systems focus

There are ways to explain things to people using simple terms that aren't also wrong.

And doesn't compressing air actually heat it? Obviously it decompresses immediately after so any affects would just be lost.

Their explanation sounds wrong though. Unless I am missing something it's not a layman's explanation, it's a wrong explanation.

Something tells me they don't have much excess material to double-wall and insulate their dwellings when they're already consigned to living in corrugated tin shacks.

Fortunately they conveniently labelled it with "this is feel good bullshit" music.

the science in this thread is even shittier than the science in the video.

Where does the heat go? That is the question.

Yea, this is pretty much BS, especially the example they gave about blowing with your mouth wide open vs. lips pursed. When your lips are pursed the air travels faster than the heat expands, but when your mouth is wide open the heat expands faster than it travels.

It is true that when fluid/Gas flows through a restriction the expansion afterward produces a slight cooling effect. That effect, however, is only noticeable at higher velocities and when flowing through smaller restrictions than the neck of the soda bottle. It is called the Joule-Thomson effect.

As you can see in the video, these 'contraptions' have caused some 'building(s)' (they don't even show the building, who knows what it is or how big it is or how many of these contraptions are mounted in its walls) to decrease in temperature by about 5C. Well... no shit... you are basically putting holes in walls and creating a venting system. Of course, the building will cool down a bit.

It does, but this thing is not compressing the air. I know they said it is, but it isn't, it's accelerating the air.

Problem is once the air slows back down all that heat is gonna come back.

It's explaining it in layman's terms, not using the most accurate descriptors. The people benefiting from these don't have a solid background in modern thermodynamics.

Heat goes in, heat goes out. You can't explain that.

It's not about whether the people understand it. It's just bullshit. Compressing air makes it hotter. These bottle however aren't compressing air. It's just nonsense. But it's in a video with text and poor people so we believe it.

Another improvement would be to double-layer the exterior roof and walls so that there is a gap of a few inches between the two layers. The sun will hit the outer layer and warm it up, but instead if this heat being transferred to the building interior, it will warm the interstitial space between the layers. This hot air is then free to escape, keeping the inner layer and building interior cooler. This is why it's good to have an attic with a fan; it keeps your house cool.

That's not just a little

Actually, as the velocity increases, the pressure decreases. It's the right idea with the wrong explanation

The Earth is flat and the tides come in. You can't explain that!

decrease in temperature by about 5C. Well... no shit... you are basically putting holes in walls and creating a venting system. Of course, the building will cool down a bit.

You're also blocking sunlight from entering the room. Congratulations you invented curtains and called it air conditioning.

Yeah. So the bottle is basically and air conditioner. Ok that sounds logical. Except that the bottle isn't adding or removing energy to the air so it can't actually change temperature. If you want to cool air it needs to be compressed at least to 30 psi. A fucking bottle can't do that. An AC compressor can, which is why we buy Air Conditioners and not a piece of wood with plastic funnels.

Exactly. Another improvement would be not to live in tin shacks, but I'm fairly sure they're not doing it for fun.

Lisa in our wattle-and-daub dwelling we obey the laws of thermodynamics

It is possible to cool a whole room passively. You just need very high ceilings - like 12 meters. The cold air in the room sinks to the bottom of the column, and the hot air will rise. Then you have a few small vents at the top of the column, so the hottest air can leave, and new slightly-cooler outside air can come in.

You live in the bottom of the room.

Building regulations are generally not conducive to this kind of dwelling, since they have a height limit for residences, and so you would only have one floor, and very low square footage for your lot size.

Draft way!👉

But the people making/advertising them should.

For that to work you need a heat sink to remove the heat created by compression before it decompresses. What they have built would lower the are flow into the room vs. a standard opening. It may create increased air speed across people directly infront of it which MAY increase the heat transfer rate via perspiration and such. Maybe, I dunno. Even if it's a placebo affect, if it makes them feel better, cool.

The question is not whether people can afford fans. It's whether physics agrees with this design. The problem is that the air doesn't blow any faster into the window than if you just cut holes in a board, which in turn is worse than not having a board there at all.

I like how the first youtube comment completely disproves this.

Luckily I've made a groundbreaking discovery. What I do is suspend finely ground titanium dioxide in an acrylic emulsion and then apply it to the outside wall of the huts of these impoverished peasants. The acrylic emulsion adheres to the walls and creates an opaque film of titanium dioxide over the wall of the hut. The unique properties of the titanium dioxide reflect solar radiation far more efficiently than the dirty corrugated iron, creating a drastic drop in internal temperatures!

If anyone would like to fund this groundbreaking research you can donate to my patreon! PM me for details. Every little helps!

This is probably explained by the fact that they now have a massive shade over the window that still lets air in. Before they had similar airflow but a massive hole where the sun came in. A similar effect can be had by installing a blind

the air molecules would still have the same energy at both ends of the bottle. Also note that after leaving the bottle the air will expand again.

they made a weird window shade screen

And the video says -5 degrees but the image shows -10 degrees...

On top of that compressing the air wouldn't cool it it would heat it up.

Witch way?

Or because they're blocking the direct sun light....

I went back and checked, it went from about 44c to 35c

That's only partially true. In order for it to get cooler, it needs to expand AFTER the orifice. Simply passing a gas through an orifice has no chilling effect. In HVAC, it works by taking X amount of heat (pre-orifice) and distributing it over a much larger area (post-orifice).

Now all you need is:

a video showing small children suffering from heat, some inspirational acoustic guitar music some basic graphics showing how white paint reflects the sunlight better than corrugated metal a small clip of children playing outside of the white huts

and you should be able to get at least 500k on Indigogo

My friends hate me for slapping their elbows, now.

They responded to you because you wrote a paragraph defending the video, in case you're confused by these responses.

Air being compressed gets hot. This might speed up any breeze blowing that way, but it certainly won't cool it down significantly.

This is what I figured too. The white panels reflecting the direct sun from entering the huts....

My design is super sized white blinds on the outside that prevent direct sunlight from entering.

Fuck all that scientific shit. They covered the window to hide a big percent of the sun coming in with some ventilation. Sun be beaming and shit.

OPEN THE FUCKING WINDOW ALL THE WAY

Thermodynamics is far more complicated than this

Take your upvote and get out!

iirc, volumes expanding cooled and volumes contracted warmed...?

"FUCKING HELL, NOT AGAIN!"

removes PET bottle from vagina

Normally, compressing air heats it, but forcing it through an orifice tends to cool it. This is one of the principles behind an expansion valve, which is used in refrigerators. Energy is lost in the creation of vortices adjacent to the orifice as well as friction, and the immediate compression and decompression results in an energy loss that significantly cools it.

EDIT: I'm getting some criticism for saying "energy is lost" i was referring to energy being lost from the system to its surroundings. Energy is, of course, never 'lost'. In any matter, I don't think what I'm talking about is being exhibited in the video at all.

Of course this is bullshit. But.

"The Noble Savage has cleverly created some sort of clever device" is a trope you see often these days. Add some chill instrumental beats and a lady that paid a shit ton of daddy's money to volunteer in her off year and you got a recipe for tons of views.

Either it's snake oil, or it just a rehash of some well know tech. But it seems clever, so people jump on it like a dog on fresh puke.

Then usually some clever guy sees it, and debunks it completely.

Awnings used to be a thing before everybody had ac.

Well these volunteer types could donate the couple hundred dollars it would take to double-bag their shacks instead of trying to find quirky ways to come up with new trendy solutions.

In this Obama economy, a lot of us are close to living in mud huts. If Hillary wins, even mud will become unaffordable.

-- same person

Not only that but the air would simply uncompress as soon as it passed through. These poor people are getting bamboozled.

I read something in a 70s energy conservation architecture book; a house had a rain water collection system, and it could hold a decent amount of water. From 11am-2pm, it pumped the rainwater onto the roof, slowly, and let it trickle down the top of the roof in short little bursts.

I forget the exact result, but the energy required to keep the house cool was substantially lower.

I think they call those holes windows

Idk your life, but airflow through a window is also typically inside.

I'm thinking it just creates more airflow which is what causes the cooling.

Edit: It says in the video at the bottom when it shows the thermometers: "Temperature fall depends on wind direction and pressure created by airflow."

You're right and the problem becomes when the simplified version becomes generally accepted even though it's wrong.

Lift is the primary example of this, but unfortunately I can't think of a better 'simple' explanation that people can grasp.

https://www.grc.nasa.gov/www/k-12/airplane/wrong1.html

Plus this is an open jet problem so any velocity gained from the nozzle will be lost again at an appreciable distance from the exit.

Electric fans actually create heat but the airflow is what helps cool your body down and also circulate and stale air.

Except it's not even a fairly accurate description of the principle.

Found the engineer

So the guy's smart across the board, got it.

The major issue is when they show the thermometer. It shows a dramatic change in the ambient air temperature which is highly dubious.

If what they said was true, squeezing a sealed, plastic bottle of air would instantly cool it down.

They've been doing this in the Middle East for a long, long time.

People do stupid things that don't make sense all the time.

It would block airflow, and so would not be as effective, though it would definitely work.

Do you have a source on that? As far as I know, it's the expansion that cools the air.

A fridge gets cool not because of "immediate compression and decompression" but because the compressed refrigerant can be cooled due to it being warmer than surrounding air, and when it is allowed to expand after passing through the expansion valve, it ends up being cooler than the ambient temperature.

It's definitely not 5°C or even 5°F according to their thermometer as that is reading a 10°C difference.

There are literally millions of people solving problems like this every day. They're called engineers.

The reason we don't all have trash dangling from our windows is because actual scientists figured out the laws of thermodynamics like 150 years ago.

Did you ever try to carry a plate full of soup? Tides make sense to me.

increased velocity from pursed lips removes more heat from the surface of your skin faster, much like a wind chill effect. if you take a huge deep breath and try to blow at the same speed with your mouth open, it will feel cooler than the slow wide open breath.

Lifehack: don't look down at the soup. Keep your eyes on the horizon.

Also, as a tip to our friends out there who can't pull off an accurate high-five to save your life, look towards the elbow of the high-five being offered and you'll never miss again.

Idk shit about Gay-Loose Sack but wouldn't compression mean getting air into a confined area and then compressing it? The bottle is open on both ends that's not going to actually compress anything.

I like the suggestion higher up that it allows air in while minimizing sun light vs an open window which allows air in but also a large amount of sun light.

I mean, seriously? If the people who made this video don't know how it works, why even bother creating a fake explanation instead of just skipping to the result?

Who benefits by bullshitting the science behind it?

Forcing air or any medium through a smaller diameter orifice does not compress it!! Pressure falls and velocity goes up. What they are saying in the video is wrong! Bernoulli is turning turbulently in his grave.

This is why I sold my soul to Reddit.

Simple - according to the comments we are witnessing the following cooling effect which is calculated by:

[(Feel Good Bullshit Music - Poor People Text) / (Correolis Effect + Plastic Trash Bottle)] = Air Conditioning

Source: I took middle school science.

Not sure that's a serious question or not, but the answer is in the propellents used in the spray. As they leave the can as a liquid they rapidly boil to a gas in the lower pressure outside the can. That phase change requires energy, and that's drawn from the heat energy of whatever the propellents are in contact with.

Not in a meaningful way. There is no real "compression" here, only restriction. It's basically snake oil.

There is no actual heat dissipation, keep in mind that in all systems energy/heat don't magically appear/disappear. In a basic evaporative cooling system (swamp cooler/evap cooler, human sweat) water changes phases from liquid to vapor absorbing heat in the process of moving to a higher energy state. Ice melting is also a great example of phase change absorbing large amounts of energy/heat.

In active Air Conditioning systems heat is moved from one area to another where it is dissipated away. In homes the freon moves the heat from inside your home to the outside where the condenser fan blows away the heat. In your car the same thing happens with the condensor in front of your radiator. I'll refrain from a full AC explanation, but it's a heat mover.

Always remember that the heat has to go somewhere. Where is the heat going, what is absorbing the heat? This system is not moving/removing heat and not absorbing heat.

Possibly, but I somewhat doubt the heat from your hand or shaking is causing much of the propellents to change phase. In that case you're probably getting more of the contents in contact with the can walls. The propellents and/or deodorant will make a pretty good heatsink even when under pressure, so you're probably just feeling them pulling heat from your hand the same way water in a water bottle would. The stuff in the can just soaks up heat a little better then water so it feels colder.

they are surrounded by dirt. they have material for days... add some plant matter and a bit of clay and they will never run out of building materials. But honestly, to beat the heat, go partial subterranean...Just takes digging. We all have space if you go down.

Yeah, there's no way the room temperature drops because of "compressing" the air. If it drops, it's because they're blocking the sunlight.

Not very efficient. You need the horizontal area because there is not much force pushing the cold air down and the hot air up, also the airflows are opposing.

You can actually design a house so that there is a stairwell in the center of the house which ends in a roof hatch at the top which you can open slightly. Because the air must flow around corners, it does not have much cooling power, but it can cool down the house few degrees.

"As hot air passes through... The bottle neck compresses and cools the air"

Ow, my head.

Bamboozled into finding a board and putting holes in it and grabbing 2/3 litters off the street and cutting them to size!