Quote:
Originally Posted by braebyrn
Then would there be any reason to use a metal or pvc casing?
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As far as I know, casings are to prevent the sides of the borehole from caving in. If you use drilling mud, it is denser than water and can help form a 'skin' on the walls and help hold the walls back.
Quote:
Originally Posted by braebyrn
Direct contact with the soil and filler material seems like it would have a better heat transfer?
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This would be correct. Usually
grout is pumped down the hole. The grout serves to prevent cross-aquifer contamination, and to increase thermal transfer.
If you search the 'manifesto' thread, you will find a recipe for "
MIX-111" which is an open source borehole grout. I stopped when I hit hard-pan, and didn't drill through multiple aquifers, so I felt that grout was not needed. Also most of the soil I went through was damp to wet sand which had a thermal transfer that was pretty close to MIX-111, so again I decided that grout was not required.
Quote:
Originally Posted by braebyrn
The mud pump from the drilling equipment has the ability to mix a slurry [ bentonite] and pump it in the bore to fill the gaps.
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As far as I know, grout is mixed pretty thick.
I think the professional drillers use a grout pump. I have no idea if your rig will be able to handle grout.
Your call...
By the way, the things we are talking about really don't have so much to do with open loop /closed loop advantages, but would be very interesting to someone who wants to do their own GSHP. I think you ought to either start a thread with a title that reflects what you are doing, or else start posting to the manifesto thread (which gets lots of hits).
Your call...
-AC_Hacker