What is the best way, what material to use to thermally insulate 12 meters of sewer pipe

What is the best way, what material to use to thermally insulate 12 meters of sewer pipe ceramic or plastic with 60 cm diameter, from the surrounding hearth, 2 meters from the surface. Expected temperature 8 to 16 degrees C Assuming the pipe will be half full of water, that represents a considerable weight. Any foam product will be compressed to the point of seriously reduce it's thermal properties.
Thanks for the help
John
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Why do you want to insulate it? It can't freeze, hell it's two meters (your estimate) from the surface. Here in Northern New England (USA) where we see 20 below frequently each year, the frost line is about 4 to 5 ft (or a meter and a half).
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Peter You are correct on everything you say. Actually I am not very far from you. The air temperature may be -20C but the temperature of the ground at 2 meters below the surface is about +8 and the temperature of the sewer's gray water is about +14 and this pipe is going to be used as a storage tank of the sewer heat. When building houses on a flat cement slab, don't they thermally insulate the slab from the ground?
John
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on 10/15/2007 11:26 AM John said the following:

deep is about 55 F year round, at least here in NY. The reason that footings are set at 4" is because that is below the frost line. If it was +8 at two meters, then the footing would have to extend below 2 meters until it reached a temp above 32. Besides the fact that septic tanks and dry wells would freeze solid.

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Bill
In Hamptonburgh, NY
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You are confusing Celsius with Fahrenheit. 8 Celsius is about 46 Fahrenheit.
Wayne
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on 10/15/2007 11:58 AM Wayne Whitney said the following:

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Bill
In Hamptonburgh, NY
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Foam would certainly work--no need to worry about compressing it with the weight of the water. High density foam is rated for 25psi. If it's full, it would hold about (2/12)^2*3.14*1=.087 cubic feet * 65=5.7 pounds per lineal foot. How you would go about wrapping it around a 4" pipe will be your challenge.
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wrote:

Voted #1 clueless response yet!
1. 4" (inches) is not below frost line. 2. He's talking celsius not fahrenheit. 3. You really don't know why septic tanks don't freeze, regardless of whether they are below the frost line, or above, do you?
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I'm not sure I understand what a 'sewer heat' is? <g> Why would one care how hot their sewer was?
Sometimes, but not always, slabs are insulated. Gnerally once you are below the frost line, the ground temperature stablizes. I think all the insulated slabs I've seen were insulated because they employed a heated slab system for heating the interior of the building.
Now if you are trying to extract the heat from the waste water (such as heated gray water) I"m sure there are better ways to do it than trying ot insualte a pipe two meters down.
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I know that if I ask a question I should describe the application but at this time I am under a contractual agreement not to publicize the application in detail.
The 12 meters by 60 centimeters pipe will be used as a temporarily storage tank for the filtered gray water from the sewer. It's located 2 meters below the surface and the average temperature of the water is 12 degrees centigrade.
Since the temperature of the surrounding earth is about 8 degrees centigrade, we would like to insulate the pipe.
I believe that was Peter that mentioned that there are better ways of extracting the heat from the sewer. I have looked for any way of doing with little success. There are a couple of installations in Oslo and a proposed one for Vancouver . I would love to know of any others.
Thanks for your help . The moment I can discuss this in detail, I will do it.
Thanks
John
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I'm sure someone makes heat exchangers for this type of application. I've seen several that I think would work (at my favorite surplus store, which probalby won't help you... <g>) though they are not particularly cheap. In the end they may well be more cost effective than trying to insulate an underground pipe.
What puzzles me is what is the value of water that is 12 degrees C? Not warm enough to heat spaces, but maybe warm enough to heat the incoming potable water enough to reduce heating costs there? If that is the case, I think I'd try a heat exchanger--the logic there is that much of heat would be coming at teh same time as the cold water source. (DOes that make sense?)
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Yes Peter, it makes sense but that is not the application . Imagine a sewer pipe coming out of hotel . plenty of hot water at an average temperature of 12 degrees C. Filter that water and move it to a tank that consists of a large section of another sewer pipe. Extract the heat of that water that circulates through a heat pump and use that heat to run a Sterling motor that couple to a generator can charge de battery of your electric car. Do you see now why I should isolate the water tank? Without insulation it will lose part of the heat to the hearth around the pipe.
Regards
John
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Contact a local chiller/boiler contractor. Ask what material they are using locally to bury underground lines. There are several, here is one: http://www.gilsulate.com /
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