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Offline benjiTopic starter

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cooling air
« on: June 02, 2008, 04:35:20 AM »
hey folks, maybe its not the place to talk about this but i thought maybe i can get some nice ideas
i want to build a box to cool a room,,the air of the room.
i was thinking the box has a fan and the 2 sides of the box are open to let air enter and leave(using the fan)
the faN alone can cool the room a little but i need more cooling,,not like air conditioners but somthin in between and simple

i was thinking to put cubes of ice in the box so the air flows through the ice and gets a little colder,,mm maybe its a stupid idea
i believe there are better ways to do this,, any idea? or links that talk somthin like that?
« Last Edit: June 02, 2008, 04:39:38 AM by benji »
good ol' BeNNy

Offline Fredrik Andersson

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Re: cooling air
« Reply #1 on: June 02, 2008, 04:50:19 AM »
I guess you aren't likely to create coldness out of nothing because then you would have to take away the thermal energy from the air in some way, which is really hard. Thermal energy have low quality which means it's very hard to convert into other energy forms. The easiest would therefore be to bring in something that lacks thermal energy (something cold) so that it takes energy from the environment. So, yeah, the ice approach would probably be the easiest.
« Last Edit: June 02, 2008, 04:55:52 AM by Fredrik Andersson »
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Offline benjiTopic starter

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Re: cooling air
« Reply #2 on: June 02, 2008, 05:00:06 AM »
yea u are definetly right ,, the problem is that ice melts very fast and this system wont last for more than 15 minutes this way
,,,i believe there must be somthin more tricky than that,,
good ol' BeNNy

Offline Tsukubadaisei

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Re: cooling air
« Reply #3 on: June 02, 2008, 07:52:05 AM »
Go to a junk shop and buy an old refrigerator or a/c. Take their compressor and put in your box. That is the only way I can think. Otherwise just buy an a/c. By the way, the fan alone wont cool the room at all unless it is located in your window, so it takes allow outside air to come quickly in your room (your room will look like a PC case though). You might fell a little cool, but that is because the wind helps sweat evaporation which draws some amount of heat of your body, but there is a limit for that if you are in a closed room.
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Offline benjiTopic starter

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Re: cooling air
« Reply #4 on: June 02, 2008, 08:02:05 AM »
Quote
so it takes allow outside air to come quickly in your room (your room will look like a PC case though).
the problem is that in hot days the air outside would be hell hot too,,
although it would look nice for the house to be like a computer case ;D

Quote
Go to a junk shop and buy an old refrigerator or a/c. Take their compressor and put in your box.
is this the thing needs high voltage in ACs?? cuz i wanna get away from that ;)


sorry i forgot to mentioned that i only have a battery of 12 volts with 7 amps

any compressors would work with that?
good ol' BeNNy

Offline awally88

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Re: cooling air
« Reply #5 on: June 02, 2008, 08:50:32 AM »
save money, just buy an air con ;) Also u have 666 posts currently....

Offline Fredrik Andersson

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Re: cooling air
« Reply #6 on: June 02, 2008, 08:59:35 AM »
Go to a junk shop and buy an old refrigerator or a/c. Take their compressor and put in your box. That is the only way I can think. Otherwise just buy an a/c. By the way, the fan alone wont cool the room at all unless it is located in your window, so it takes allow outside air to come quickly in your room (your room will look like a PC case though). You might fell a little cool, but that is because the wind helps sweat evaporation which draws some amount of heat of your body, but there is a limit for that if you are in a closed room.

A refrigerator wouldn't help really because it just moves the heat inside of it to the outside right? So then you would have to move the heat out of the room in some way. A box alone in the middle of the room wouldn't be able to do that... unless you use that thermal energy for powering the thing! Now that would be something!
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Offline AndrewM

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Re: cooling air
« Reply #7 on: June 02, 2008, 09:16:45 AM »
It might be possible to drop air temperature down coming out of a unit by a couple degrees using two simple principles.  First being the old axiom of "Heat Rises", the second the use of thermal energy for evaporation.

Create a box with aluminum or copper fins running from top to bottom, basically a giant heat sink.  Divide the box in half, making the two sections self contained from one another (ie you could fill the top with water and not have it leak into the bottom), but keeping each fin as one unit strecthing the entire height of the box.

In the top section put in a misting spray pump of some kind, ever so slightly moistening the cooling fins.  A fan in the top blows on the fins removing the resulting humidity to allow increased evaporation, and dumping the moist air outside.

In the bottom, just have a fan blowing across the fins into your house.  The fins cool off from the thermal energy being used for the top evaporation cycle.  At least in theory.
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Offline benjiTopic starter

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Re: cooling air
« Reply #8 on: June 02, 2008, 10:33:00 AM »
hey andrew,,can u provide a pic or somthi,, its hard to imagine it,,at least for me :-\
good ol' BeNNy

Offline AndrewM

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Re: cooling air
« Reply #9 on: June 02, 2008, 12:59:51 PM »
Sorry, I am horrible at drawing things out, but here is a rough drawing that I hope helps a bit.  The left hand side of the drawing shows the front view, basically an open box with cooling fins (the copper colored vertical lines in the drawing).  The black line in the middle is sometype of metal or plastic that seperates the top half from the bottom, you could seal it with aquarium sealant or something.  In the back of the box (show in the side view cutaway on the right) has two fans, one in the top section, the other in the bottom.

As I said, I am horrible at drawing stuff.
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Offline benjiTopic starter

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Re: cooling air
« Reply #10 on: June 02, 2008, 02:07:02 PM »
thanks u and no its not horrible  its a good drawing
,exept the first(higher fan) arrow should be heading to the right (outside the box),,right?

mmi still have a problem

so lets put the cycle this way

air comes into the box because of the lower fan ,,but the higher part of the box is blocked by the seperating layer(metal or plastic)
so how is it gonna continue its way to the higher part then to the second fan?
good ol' BeNNy

Offline AndrewM

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Re: cooling air
« Reply #11 on: June 02, 2008, 04:35:13 PM »
Air from the bottom does not hit air from the top, two seperate airflows.  The top airflow is designed to move air across the metal fins and aid in the evaporation process.  The outflow from the top section should be dumped outside (sometype of conduit).  The air moving over the fins and the water evaporation should cause the metal fins to cool off, or transfer the heat energy from the metal fins to the evaporation process and/or the air.  The bottom airflow moves air across these cooled off fins, transfering the heat from the normally warm air to the fins, producing cooler air that gets output straight into your living space.
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Offline alovon

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Re: cooling air
« Reply #12 on: June 02, 2008, 04:40:19 PM »
Go to a junk shop and buy an old refrigerator or a/c. Take their compressor and put in your box.

Thats probably the bestcourse of action.
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Offline benjiTopic starter

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Re: cooling air
« Reply #13 on: June 03, 2008, 06:07:15 AM »
mmm nice idea ,but the problem with this is that it needs continous water supply,,and it wont cool much
i was thinking one day about making some kind of ACs that pushes air through pieces of wet cloth so the output air becomes colder and wetter
they use this in some kind of acs..
good ol' BeNNy

Offline slo

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Re: cooling air
« Reply #14 on: June 03, 2008, 11:13:45 AM »
As mentioned, the fan alone wont cool the air (in fact its power consumption and friction heats it a little) but it will cool you due to increased sweat evaporation efficiency.  That got me thinking about evaporation.  Your original idea has merit and a slight modification will turn it into a low tech cooling method that has been in use for centuries to keep food cool in a box in the sun while working in the field.  Be aware that while this will work and its affect is dramatic in a small box it is much less impressive when the box is scaled up to room size and that room contains constant heat sources of its own like lights and electronics.
Keep your (metal) box open on both ends with the fan (slowly) blowing air through this dark tunnel.  The longer this tunnel the better because it increases time and surface area for heat exchange.  Perhaps folding back and forth like a snake.  Cover the exterior of the box with a layer or few of a light colored absorbent fabric.  A towel, paper towel, burlap sac, polyfil, rockwool, wool, felt or fiberglass will do.  The goal is to wick water up the sides and hopefully over the top of the box.  Vertically oriented strands for capillary effect.  Something with antimicrobial/antifungus properties would not hurt.  Place the box in a pan deep enough to hold the meltwater of the ice.  Place the contraption on a windowsill.  Dump your ice inside the tunnel.  If you feel up to it construct some type of seal/shade arrangement (cardboard will do) that keeps the pan in shade and exposed mostly to inside air while the fabric covered surface is exposed to exterior air and sunlight.
The shade inside and insulation should slow the melting somewhat but constant airflow quickens it.  The primary cooling effect is as you originally intended, airflow over ice.  However as the ice melts (unfortunately very quickly) the secondary effect happens.  Cool water wicks up the exterior of the box, is struck by the sun and evaporates.  Part of the latent heat of evaporation is drawn from the underlying box which acts as a large heat sink (more like heat source in this context) resulting in the metal becoming slightly cooler thus the air flowing through it gets slightly cooler.
This will be effective even without a fan provided you can direct the inlet toward the prevailing wind.  I predict someone could get creative with a wind turbine and make this work power free regardless of wind direction.
The traditional material for a device of this type is terra cotta or other unglazed earthenware vessel.  The water inside slowly seeps through the pores of the clay and evaporates once it reaches the outside, cooling the container and thus the water inside at the cost of a small amount of the water volume.
The same principle is applied in traditional field canteens.  The metal canteen is faced with felt.  It is wetted when filled and rewetted through spillage when you take a sip.  As you hike the sun hits it, counterintuitively giving you a cool refreshing sip at your next break.
Solar powered grid independent air conditioning.  Sounds ideal for poor hot remote locations until you realize that water is so scarce there that the last thing you want is to see it evaporated.
Back to your project, keep in mind that using ice is not 'free' cold.  If you make the ice in your home freezer and your freezer is in the room you intend to cool you are fighting a loosing battle.  It takes much more energy (=heat) to make ice than you get back out.  Your freezer condenser coils and compressor are constantly pouring heat from inside its box into your home.  Similar to the way this project will pour heat from inside your box (room) into the outside environment through evaporation.  Going further, outside that evaporated water will rise until it eventually condenses into a cloud and falls as rain.  That rain collects as puddles, streams, rivers, lakes, oceans, groundwater.  Is harvested by your public utility and fed to you through pipes and faucets.  Through which you fill little blue trays that you place in your freezer.
Circle of life stuff.  Sorry for droning on about non robot stuff.
Dustin

Offline benjiTopic starter

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Re: cooling air
« Reply #15 on: June 03, 2008, 02:28:55 PM »
thank you slo,, very extended version of my first idea
i would be very glad if you can provide us an image ,, this stuff is better understood with pics,,


Quote
Sorry for droning on about non robot stuff.
no ,, i started this ;D
actually it came to my mind as making a robot that has a thermistor on its nose and using that it can detect the hotter room in the house and drop this box there  ;)
good ol' BeNNy

Offline Admin

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Re: cooling air
« Reply #16 on: June 07, 2008, 04:22:38 PM »
I've wanted to make a Heat Transfer tutorial for ages, but haven't found it useful for most people. Anyway, this post needs some serious theory.

First, the two laws of thermodynamics . . .

First Law of Thermodynamics: Energy can be changed from one form to another, but it cannot be created or destroyed. The total amount of energy and matter in the Universe remains constant, merely changing from one form to another. The First Law of Thermodynamics (Conservation) states that energy is always conserved, it cannot be created or destroyed. In essence, energy can be converted from one form into another.

The Second Law of Thermodynamics states that "in all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state."


Basically your project is trying to break the first law. You are trying to 'destroy' energy (heat). You can't. All you can do is move it out of your room, at the cost of additional energy. So what you need to make is not actually an 'air cooler', but instead a 'heat mover'.

You need to make a device that physically 'sucks' heat out of your room and moves it outside - kind of like how a refridgerator sucks heat from the inside and radiates its outside through the back grill. The heat still exists, its just no longer inside the fridge.

A fan will just move air around, not actually cooling anything. An air conditioner dumps the heat outside your house. If your device doesn't physically dump the heat outside the room, it would literally have to store it. Ice for example would store heat as it melts.

Offline bens

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Re: cooling air
« Reply #17 on: June 07, 2008, 04:56:45 PM »

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Re: cooling air
« Reply #18 on: June 07, 2008, 06:05:00 PM »
Quote
http://en.wikipedia.org/wiki/Evaporative_cooling

That won't work either unless the steam is removed from the room :P

Offline bens

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Re: cooling air
« Reply #19 on: June 07, 2008, 06:21:51 PM »
It works because heat energy is removed from the air by converting water to vapor (it's the same as cooling a room using ice).  The only way heat would be added back to the room is if the water vapor recondenses into water.  This will not happen in a dry, warm climate.  :P

Of course over a long enough timescale in a closed system the air would saturate with water vapor and evaporation would no longer occur, but for practical application this is not often a concern.

- Ben

Offline AndrewM

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Re: cooling air
« Reply #20 on: June 07, 2008, 09:34:01 PM »
I'm reminded of a common saying in Florida, "Its not the heat, its the humidity".   ;)  As the moisture level in the room increases, the less readily the sweat on your body will evaporate and the warmer your body will become, even (much) before saturation levels are reached.  If the air is 3o cooler, but your body can't get rid of excess heat through sweat, that 3o didn't earn you anything.
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Offline bens

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Re: cooling air
« Reply #21 on: June 07, 2008, 11:56:24 PM »
I know it sounds like it'd make life miserable, and in a place like Florida it probably would, but in very dry climates these devices work quite well.  I can attest to this from personal experience here in Las Vegas.  In such climates, the increase in humidity is actually a bonus (the human body gets a little unhappy existing in perpetual 0% humidity).

- Ben

Offline benjiTopic starter

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Re: cooling air
« Reply #22 on: June 08, 2008, 04:02:57 AM »
yea true this would cool up low humidity areas

the ice idea is good but has many cons

it will melt rapidly
the cost of ice (whether its money ,electricity, heat ,,,,,,)

this is why i started to think about water instead of ice , water is cheap and in hot days its still colder than the air in the room
so heat exchange would do it a little , maybe with big amounts of water (a barrel) id be able to cool the room alittle
,,what i was thinkin is to let the heat in the room air go to the water barrel and heat the water instead.

now the water will start to evaporate and get back to the air ,,but maybe if the barrel shap is long and thin and it would slow it down
or a close top barrel and fans on sides to pump air through it,,,,
good ol' BeNNy

Offline jman571

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Re: cooling air
« Reply #23 on: June 09, 2008, 04:51:41 PM »
It works because heat energy is removed from the air by converting water to vapor (it's the same as cooling a room using ice).  The only way heat would be added back to the room is if the water vapor recondenses into water.  This will not happen in a dry, warm climate.  :P

Of course over a long enough timescale in a closed system the air would saturate with water vapor and evaporation would no longer occur, but for practical application this is not often a concern.

- Ben

Hmmm....I believe that's what we'd call a humidifier ;) When I was a kid I'd have one in my room when I was sick to help me breath easier at night. If you've ever tried to sleep with a stuffed nose you know how hard this can be  ;D

EDIT: In response to the last post, I know how this kind of thing works, but perhaps the amount of water required (or the amount of energy to cool said water) will not be practical. Now, forgive me for this practice...because it's REALLY WASTEFUL.....but sometimes when my bathroom is very cold in the morning (I blame the tile floor  :o), I will fill up the 2nd sink with water on the highest temperature, and leave it filled up to its maximum level until I'm finished in the bathroom. As long as the vent is closed (the one blowing in air, not the one blowing it out (this vent is the one that generally goes to your roof, but maybe not always)) this actually warms up the bathroom, and it no longer feels cold.

I don't know how much of this is just psycho semantic, but I think it makes sense thermodynamically, the properties of diffusion mean that the hot air on the surface of the hot water is being distributed throughout the room...or the cold air in the room moves to an area of low concentration, namely the hot sink. I think that the second part doesn't make sense, but the first part has some basis.
« Last Edit: June 09, 2008, 05:01:53 PM by jman571 »

 


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