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Old 05-25-12, 05:05 PM   #1
Daox
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Default Gary's Night Air Thermal Mass Cooling Using Water Barrels

Gary has an interesting cooling setup for his shop he is playing around with. It reminds me vaguely of my project using sump water to cool the house. His setup is more simplistic though (a good thing). He is simply using a fan to vent air out of his shop and routing that air past some 50 gallon plastic barrels filled with water. This cools the barrels overnight and when things warm up the fan can be used in reverse to blow air over the barrels and keep the shop cool. He goes through all the thermal mass calcaultions on the site. He is looking for suggestions to improve the system.

Night Air Thermal Mass Cooling Using Water Barrels


A few barrels against the wall.



Add some ducting around them to route more air directly over them.

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Old 05-25-12, 09:18 PM   #2
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Hi,
Thanks for picking up the cooling barrel project!

I just ordered a 2nd fan that is same as the first one to get more flow going by the barrels and see if that will get more night time "coolth" into them more quickly.

Still looking for improvement ideas.

Believe it or not, it is snowing here right now (not to mention gusts up to 60 mph), so cooling is not a priority

Gary
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Old 05-26-12, 01:58 AM   #3
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I would add (partial) baffles between the barrels. This would make the airflow zigzag around and in between them, and increase turbulence, making heat exchange more efficient. The baffles may only be part of the height, or you might make them so that half the height is on the left and the other half on the right, so that there is airflow on both sides of the barrels.

At some point you'll reach the limit of heat exchange on the surface and you'll have to wait for the heat/cool which is deeper inside the barrel to move outwards. Stirring the water would speed that up, though would make it more complicated.

Snow?!? We've just been through our second heat wave and haven't seen snow since the end of Feb. Though this winter has been very short with hardly any snow
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Old 05-26-12, 09:27 AM   #4
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I would skip the baffles all together and tap in to the top and bottom of the barrels sides and install a car radiator with the fan blowing over that, plastic is not a good conductor of heat and the surface area of a single automotive radiator is going to be about the same as the whole outside of a barrel, the taps top and bottom are going to allow a good thermo syphin so you are getting the greatest heat differential as well.

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Old 05-26-12, 10:39 AM   #5
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Quote:
Originally Posted by Piwoslaw View Post
I would add (partial) baffles between the barrels. This would make the airflow zigzag around and in between them, and increase turbulence, making heat exchange more efficient. The baffles may only be part of the height, or you might make them so that half the height is on the left and the other half on the right, so that there is airflow on both sides of the barrels.

At some point you'll reach the limit of heat exchange on the surface and you'll have to wait for the heat/cool which is deeper inside the barrel to move outwards. Stirring the water would speed that up, though would make it more complicated.

Snow?!? We've just been through our second heat wave and haven't seen snow since the end of Feb. Though this winter has been very short with hardly any snow
We had a pretty mild winter also, but spring has been exciting.

I did think about baffles like you show, and it seems like a good idea, but I'm not certain. With the baffles shown, it looks like the first barrel would get good flow on all sides, but the it look like the 2nd barrel might get poor flow around one side. I guess its easy enough to try and just measure the flow velocities on each side of each barrel.
Seems like there must be some baffle pattern that would help.

I think that as one of the comments pointed out, I need more total flow as the air that is going through is showing a pretty good temperature rise -- that is, its working but needs more flow.

Gary
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Old 05-26-12, 10:46 AM   #6
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Quote:
Originally Posted by Ryland View Post
I would skip the baffles all together and tap in to the top and bottom of the barrels sides and install a car radiator with the fan blowing over that, plastic is not a good conductor of heat and the surface area of a single automotive radiator is going to be about the same as the whole outside of a barrel, the taps top and bottom are going to allow a good thermo syphin so you are getting the greatest heat differential as well.

I'm sure a radiator would work well, but I'd like to see If I can make the simpler arrangement work first. The log actually shows that for the airflow I have the barrels are doing a pretty good job of extracting coolth from the air (that is the air temperature is changing by a fair amount through the tunnel). I think I will try more airflow and a more optimized tunnel before going to something more complicated.
The other thing is that if the barrels extract (say) half the coolth in the night air, the rest flows into the shop and cools the show so the coolth in the air is still used.

Gary
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Old 05-28-12, 11:23 PM   #7
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If you decide to upsize, you could use larger tanks like 275 gallon cubies and relocate the components to wherever is desirable, then the radiator idea makes more sense. If you have the height, use 2 vertical flow radiators (like most Japanese cars) instead of horizontal flow (like most American & Euro cars). Use a radiator hose to connect the top of the bottom radiator to the bottom of the top radiator. The combined thermosyphon effect ought to work well.

Craig
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Old 05-29-12, 07:38 AM   #8
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I think they key is going to be more airflow. As you said you are seeing a decent delta temperature across the duct (which I am a bit surprised by). So, while additional surface area on the barrels would defintely help, more airflow is going to help more at this point. I also like the idea of Piwoslaw's baffels. One on each side (not like shown) should get you airflow around 90% of the barrel vs only around about half as you currently have them.
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Old 05-29-12, 11:22 PM   #9
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It probably will not make much of a difference since it is plastic but use some coarse sandpaper on the barrels to increase the surface area to help conduct the heat.

Using a radiator would work you could completely fill the tanks and have a pump move water from the center tanks to end end one with the radiator moving the water to the remaining tank.
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Old 05-30-12, 10:16 AM   #10
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Quote:
Originally Posted by Phantom View Post
It probably will not make much of a difference since it is plastic but use some coarse sandpaper on the barrels to increase the surface area to help conduct the heat.

Using a radiator would work you could completely fill the tanks and have a pump move water from the center tanks to end end one with the radiator moving the water to the remaining tank.
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I think (maybe) there is a tendency to overestimate the negative effect of using a plastic wall barrel. The conductivity of the polyethylene is 0.26 BTU/ft-hr-F. If you assume a 0.1 inch thick barrel wall, this works out to an R value of 0.03 for the barrel wall. The R value of a moving air film (5 mph?) is R 0.17. So, it seems like the thermal resistance of the air film is much greater than the thermal resistance of the barrel wall. There is also the resistance of water film next to the barrel wall on the inside. I'm inclined to think that even though a metal barrel wall would be much more conductive, it would not make much difference because of the resistance of the air and water films inside and outside the wall?

I understand that when Steve Baer change from metal barrels to plastic barrels on his living room barrel wall that he did not see any difference in performance.
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Got the 2nd fan yesterday from Grainger, but the weather is still much to cool to try a new setup.

Gary

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