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It's Getting Hot In Here- Homebuilt AC

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It's Getting Hot In Here- Homebuilt AC

Unread postAuthor: BC Pneumatics » Thu May 22, 2008 2:04 am

I live in central Ca, where days are starting to get in the 100*F range, and will soon be 110+. It is usually a couple degrees warmer than this inside the garage, where I spend the majority of my day. Today I decided I needed something quick, cheap, and effective to keep me cool, and came up with the following:

The pictures explain most of the story. I used a 20" fan, 25ft of 1/4" copper tube, some 1/4" ID vinyl tubing, cheap Wal Mart foam chest, tiny submersible fountain pump, and some zip ties to make a heat exchanger. The chest is filled to about 6" with salted water, then 20lbs of ice is packed in. As you can see, the water absorbs a considerable amount of energy before it is sent back to the supply box. The ice was for experimenting with tonight. I have 5 gel packs I I bought at Wal Mart in the freezer. They should be about -5C/23F by morning, at which point they will go in the chest (after the excess water is siphoned out) and I will see how it does keeping the garage cool throughout the day.

I plan to upgrade the unit a bit when I get a chance. You can see it leaking in the photos. I will get some compression x barb fittings to attach the tubing, and would also like a more powerful pump. Hopefully this will drop the input/output temps a bit. I also thought about bulking up the insulation, but I guess I want the heat from the room to get transfered to the ice anyway... Some 3/8" or even 1/2" tube would have been much better, but I was trying to keep the price low.

Even as is it works great. It is much cooler than the same fan (I got two for good measure) without the heat exchange.

PS, I am also showing off the new camera I got. (The fan is running full speed in all the pics)
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DSCN0028.JPG
Here you can see the return temp. I want to measure the flow through the hose, and find dH/dT.
DSCN0027.JPG
The supply temp. Not bad, but I would like it to be cooler.
DSCN0025.JPG
Temp of the ice bath at the surface. Should see a lower number with the gel packs.
DSCN0018.JPG
The leaky connection. Tape would probably stop it, but I would rather get some proper fittings. Then I can boost the pump with no worries. You can also get a better look at the condensation here.
DSCN0015.JPG
The entire unit, sitting on a parts rack. I need to move it lower so ice swaps don't require a step stool.
The connection between the copper and vinyl tubes leaks a bit. You can see the paper towel that catches the slow dripping.
You can see the condensation stop mid way through the copper coil. The heat transfer is pretty good.
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Unread postAuthor: starman » Thu May 22, 2008 2:53 am

"Cool" idea. I'm guessing you could use some more surface area on your heat exchanger...another 25' of copper maybe. Also, it's going to be hard to keep up with cooling on a 100 degree day. Depending on the dimensions of your garage, you may need 2 or 3 units like this to make a dent in it.

You do realize a small AC unit from Walmart is in the $100 range don't you?

That is some nifty fast shutter speeding you've got there. Did you set it manually? What shutter speed?
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Unread postAuthor: BC Pneumatics » Thu May 22, 2008 3:14 am

I think I will have to do something about bulking up the heat exchanger, the temp of the water only increased 1*C in about 2 hours.

According to some quick calculations and sketchy estimates, for every 1.2*C the water raises, the garage should drop 1*C. This means if I can get the water from 0*C to 20*C, I should drop the temp by ~16.6*C. This would turn a 100*F garage into a 70*F one. Of course, this would not happen instantly (and ice would likely be added before the water reached 20*C), and the garage is far from perfectly insulated, people going in/out, etc. Hopefully I can keep things at a tolerable 80-85 throughout the day with just this unit though.

The build tally (minus the pump and vinyl I already had) is about $50. Worst case scenario I have a perfectly good fan, one time use ice chest, five big ice packs, and 20ft of copper tubing out of it.

According to the box of the $100 Wal Mart air unit, it would cool a room 1/4 the volume of my garage, and much more heavily insulated, to 73* One to cover my garage would cost about $550.

I got the camera a couple hours ago. I haven't played with any of the settings, so that is whatever the shutter speed comes set at on a Nikon L18.

-Edit: Also wanted to note that as the water temperature increases, energy transfer is slower, and the unit cools less effectively. (Newton's third (?) law of cooling.) This also fuels the search for a stronger pump. If I can get the water to cool only a couple degrees before it comes back in, I will be able to cool air faster.

I do not know if I will upgrade this unit, or go for a version 2.0, since I have another fan. All I know is, one would be very nice in my room. I think an exchange made out of copper pipe, possibly finned, would be a good choice if I made another.
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Unread postAuthor: psycix » Thu May 22, 2008 5:12 am

Nice project!
Though, where is the freezer standing wich cools all that ice?
The room where that freezer is, will output all that heat energy + extra heat because of efficiency losses.

According to some quick calculations and sketchy estimates, for every 1.2*C the water raises, the garage should drop 1*C. This means if I can get the water from 0*C to 20*C, I should drop the temp by ~16.6*C. This would turn a 100*F garage into a 70*F one. Of course, this would not happen instantly (and ice would likely be added before the water reached 20*C), and the garage is far from perfectly insulated, people going in/out, etc. Hopefully I can keep things at a tolerable 80-85 throughout the day with just this unit though.


Do note, that there is a difference between 0 *C ice and and 0 *C water. It takes a lot of (thermal) energy to melt. This will improve the cooling effect since it can take up more thermal energy before gaining further temperature.
When youve got alot of ice, (nearly) all ice needs to be melted before the overall resevoir temperature can get more then 0 *C.



Well, again, its a nice project. Could you also show a picture of the pump you are using?
Oh and use a hose clamp...
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Unread postAuthor: jrrdw » Thu May 22, 2008 5:51 am

A zip tie around the vinyl tubing will stop the leak, thats how most fuel lines on todays dirt bikes are clamped. Go to LittleGiantPump Company check out their pumps, got them for all uses there. Good thinking on how you did this, it all most deserves the ghetto award! :wink:
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Unread postAuthor: BC Pneumatics » Thu May 22, 2008 1:35 pm

psycix- The freezer is in the kitchen. (well, for the ice it was at 7-11). It drops a couple degrees cooler outside than inside during the night, (when the freezer will be sucking energy from the gel packs), so the windows are open, and we won't be wasting the air.
Also, the gel packs never complete their phase change, so I do not have to worry about that :) I did have to guesstimate their c value though.
The leak isn't a big issue. After all night it looks as if only a couple table spoons have dripped out.

When I stepped into the garage this morning, it was noticeably cooler than the rest of the house. This was as encouraging as it was refreshing, since the garage is usually much hotter than the house every day after May 01.
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Unread postAuthor: BC Pneumatics » Thu May 22, 2008 2:07 pm

I just got the gel packs in. They are pretty close to solid, so they should do well. Got some more pics as well, including the pump request.
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DSCN0033.JPG
The ice packs in the chest. A couple more would fit. Time will tell if they are needed.
DSCN0032.JPG
Ice pack temp fresh from the freezer. Take note, there is a negative sign on the left of the screen. This is just about the temp I was going for. I am pleased that my freezer can get them there overnight.
DSCN0030.JPG
My cheap submersible pump, chugging away.
DSCN0029.JPG
The water temperature as of this morning.
0 to 20 in less than 12 hours. I guess the exchange rate isn't too terrible.
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Unread postAuthor: psycix » Thu May 22, 2008 3:50 pm

Okay, cool (in both ways) :D
Only one thing popped up in my mind:
Why are you using a well-insulated foam chest?
If it would be metal (and thus conduct thermal energy well), you would cool even more because the box now also cools the environment by itself.
Not only the fan+pump system would cool, but the box itself would also cool a bit.
There is no reason to put it in a foam box, unless you want to have the ability to close it and stop the cooling, but that wouldnt be that much of an issue.
It may be a thoughtless human impulse to put ice in a insulated box, but in this case, its not needed. :)
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Unread postAuthor: BC Pneumatics » Thu May 22, 2008 4:04 pm

The foam thought had already crossed my mind. In my original post I wrote:
"I also thought about bulking up the insulation, but I guess I want the heat from the room to get transfered to the ice anyway..."
You are right that it is instinct to throw ice in an insulated cooler, and is not really necessary here, but I could not find a plastic tub that suited me. It also may prove beneficial to be able to insulate the cold box over night, and preserve the temp until morning. I still have not fallen into an operating groove, so I do not know if it will be an issue. After the water warm up over night, I am thinking foam may be a good thing, as it will give me more control over how I use the AC throughout the day.
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