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Old 08-07-15, 09:25 AM   #1
goblinsly
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Default Using water to cool down apartment

Hi there,

I have 2 ideas, or maybe 2 questions, if either of this would work.

Basicly i wanted to know if i could use tap water to cool down apartment. I don't plan to use it the whole summer, but basicly for about 15-20 days during those heat waves.
The idea is simple, get tap water, run it through copper coil and point fan directly into it, basicy the same as that ice cooling solution but using tap water. Since it takes quite some time for heat to transfer from air to water, i wouldnt dump water directly away after 1 cycle but maybe run it multiple cycles. I would be happy if i could drop a degree or two in a small computer room i am using.

The second one question is, in the evening and through the night i run 2 fans blowing air from outside through the window but it seems as it doesnt have any effect. Nights can be 10 - 15 degres cooler then days but as soon as i close the windows, it is warm again. Problem is i have both windows on same side, i even tried 1 fan blowing in and 1 out, but its same. So i was wondering, what if i used water pump to cool water outside when its cold bring it into the apartment ? Would that have any effect ?

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Old 08-07-15, 10:29 AM   #2
bmxeroh
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I think you're going to have trouble pulling enough heat out of the air to really make much of a difference. The 1 gallon ice bucket thing works somewhat well because of latent heat. It takes 144btus to melt 1lb 32 degree F ice to 32 degree F water, and there's about 8 lbs to a gallon, so you end up with around 1150btus. The phase change from ice to water is where the latent heat thing comes in, and it takes a lot of energy in one direction or another to change phases.

HOWEVER, it only takes 1 BTU to raise a lb of water 1 degree, so now that same gallon of water @ 32 degrees F now only takes 384 btus to raise the temp to 80 degrees F. This is the sensible heat part of things. Considering ground water temps are usually at least 50ish degrees or higher, there really aren't alot of BTU's left to do anything effective. Don't get me wrong, technically doing what you're suggesting will cool the air, but I doubt it will cool the air faster than the structure is gaining heat.

Which leads me in to the second question. The reason that opening the windows doesn't have a huge effect immediately is entirely a thermal mass problem. More specifically the difference in how much heat the structure itself can store, vs how much heat the air volume within can store. So you can change out the entire air volume in a hot structure with cooler air, and very quickly the stored heat within the actual structure will reheat that new air, ad nauseam until you have removed enough BTU's from the structure itself, rather than just the hot air. While water does have a higher heat capacity than air, bringing in cold water requires the heat in the structure to conduct into the air, and then conduct into the water. The flip side of this is it provides even more thermal mass to resist the temp change during the day, but I would guess that you don't want a whole bunch of 55 gal drums of water in your apartment. Plus, don't you pay for water there? Even if it's included expect your landlord to get really irritated with you burning through that much water. I'm pretty sure to get 1 ton of cooling for 12 hours at a 30 degree temp rise in the water would require something like 600 gallons of water, but I would love for someone to double check that because I started getting confused going in that direction. If that's the case 600 gallons a day is going to get you evicted quick.
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Old 08-07-15, 11:19 AM   #3
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This will work if your water temp is less than 5 degrees C. Check it and let us know.

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Old 08-07-15, 12:13 PM   #4
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I did this a while back as an experiment with water from my cooler basement. It does work, but you don't get a ton of cooling, and what you want even more than cooling is dehumidification and it doesn't do a great job at that.

http://ecorenovator.org/forum/geothe...ool-house.html
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Old 08-08-15, 10:40 AM   #5
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Water isn't very expensive here but still if figures are correct i won't be able to cool down anything without insaine amount of water. And water isn't even nearly as cold.

What about my second question ? Since fans do a poor job at cooling my apartment at night due to a low amount of heat air can store, would creating a water cycle between apartment and outside help ? My window shelf is basicly 50 x 50cm of metal that seems to have good heat transfer properties. If i used some copper tube and sit it on this outside shelf at night, and make water circulate through it with water pump, and bring cold water inside, would that make a difference ? I am just thinking out loud here, wouldnt be wasting any water here since this would be a closed circle.
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Old 08-12-15, 11:00 AM   #6
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What you're describing is a heat pump, with water as a working fluid and without taking advantage of the physics of condensing and evaporating a gas. You would be better off hanging an air conditioner out of that window. Otherwise you will have ridiculous heat exchanger requirements well beyond what 10 meters or so of copper tube is going to be able to handle.

If you don't want to go the AC route, you're first line of defense is going to be reducing your heating gains during the day. The more heat you keep out during the day the less you need to remove at night, and will make things like fans in the windows much more effective. There are quite a few posts in the conservation section detailing other members approaches. I personally am a huge fan of heavy black out curtains, but they are not joking when they say black out so if darkness is a problem they may not be for you. Window film also works great, but it really depends on how much of your solar gain is due to window area vs the entire exterior heating. Gary @ BuildItSolar: Solar energy projects for Do It Yourselfers to save money and reduce pollution has a bunch of articles of his own and others regarding this, as well as some novel cooling techniques that may interest you.

No matter how you do it, you have to move heat out of the structure and into the air and then out of the air inside and into the air outside.

I do apologize if it seems like I'm tearing apart every idea you have. I'm just trying to not have you waste time or money.
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Old 08-13-15, 03:41 PM   #7
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No need to apologize, i learn many new useful things as i read your replies. And for me that is even better then finding a simple cooling solution !

Since you seem to know much, would you care to look at my other topic, i am asking about solution that to some degree am already using and is working, but am looking for ways to improve it further:

http://ecorenovator.org/forum/other-...html#post46283
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Old 08-13-15, 04:50 PM   #8
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Quote:
Originally Posted by goblinsly View Post
No need to apologize, i learn many new useful things as i read your replies. And for me that is even better then finding a simple cooling solution !

Since you seem to know much, would you care to look at my other topic, i am asking about solution that to some degree am already using and is working, but am looking for ways to improve it further:

http://ecorenovator.org/forum/other-...html#post46283
Look up the Coolerado. It is amazing. The other search keyword is DEVAP. Both of these rigs work well in certain climates, the dryer the better.

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