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Underground Air Cooling | 17 comments (17 topical, 0 editorial)

Re: Underground Air Cooling (3.00 / 0) (#7)
by etownlax on Thu Nov 1st, 2007 at 05:04:22 PM MST
(User Info)

I second that. Metal has a better thermal conductivity(how easily the substance can transfer heat). If you put a metal pipe down the hole then it would be able to transfer the heat to the ground a lot better. Also if the radiator was metal it would work better too.

-Randy

[ Parent ]

Re: Underground Air Cooling (3.00 / 0) (#10)
by BigBreaker on Fri Nov 2nd, 2007 at 08:24:57 AM MST
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True, metal conducts heat better, but the metal transfers that heat top/from the soil it faces and that is the limiting factor. The only way to get appreciable thermal flux from these wells is to maximize the surface area of the soil interface. Metal is nice but plastic or concrete is great too and the latter two will generally last longer.

Earth tube experiments showed little difference in performance across different "tube" materials.

[ Parent ]

Re: Underground Air Cooling (3.00 / 0) (#13)
by feral air on Fri Nov 2nd, 2007 at 01:56:05 PM MST
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"True, metal conducts heat better, but the metal transfers that heat to/from the soil it faces and that is the limiting factor."

It's not guaranteed that the soil is the limiting factor though.

[ Parent ]

Re: Underground Air Cooling (3.00 / 0) (#15)
by BigBreaker on Wed Nov 7th, 2007 at 07:40:19 AM MST
(User Info)

From Wikipedia:

Material Thermal conductivity W/(m·K)
Air 0.025
Wood 0.04 - 0.4
Alcohol or oil 0.15
Soil 0.15
Rubber 0.16
Epoxy (unfilled) 0.19
Epoxy (silica-filled) 0.30
Water (liquid) 0.6
Thermal grease 0.7 - 3
Glass 1.1
Ice 2
Sandstone 2.4
Stainless steel 15
Lead 35.3
Aluminium 237
Gold 318
Copper 401
Silver 429
Diamond 900 - 2320

Looks like soil is pretty similiar to rubber / oil / epoxy, all good proxies for plastic. I just looked up PVC, it's 0.19, so again... similiar to soil. Metal is massively more conductive. Also the tube material is quite thin compared to the thickness of soil it pulls or pushes heat through. So it's not that important anyhow.

[ Parent ]

Underground Air Cooling | 17 comments (17 topical, 0 editorial)

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