Hello,

 Posted here a few time, very helpful.

 Anyway, this last weekend our geo guy was attempting to do horizontal bore (5 ton CM, loop, northern Minnesota), the 1st 4-5 feet were clay/loam, no problem.  After that was gravel that consists of pea gravel up to large rocks. He said he went down 30-40 feet (trying to get out of the gravel), still gravel and couldn't turn the bit, real hard on his machine.  He ended up backing it out, he tried a couple times. He made a call and was told there is another bit that may allow him to pass through the gravel. Waiting on that......

 I am not hopeful about this working, looks like vertical loops are in our future at an additional cost of $4000, to total $12000.

 How much vertical loop would I need? Does it depend on the water table? I havn't done much research in this area.  Excavation is out of the question, would have to take down a lot of trees and the cost would climb because of that.

 Any thoughts?


 thanks again
    Steve

Around here, you generally need 180'-200' of well per ton of heating/cooling. In this well bore would be inserted a single 3/4" U tube heat exchanger. If your water table is at or near the top of the gravel, then you could likely get by with a little less well depth. Well drilling costs here are ~$5-$7/ft.

Vertical loops about 3k/ton here. How are you sure you have to take trees down to do horizontal. Trenches don't have to be straight and excavation equipment is in all sizes.
j

So, for 5 tons 900-1000 feet of well.
Can I also get house water out of it? A 3rd pipe should easily fit down the casing. Or does the grout stop that option?
Excavation is possible, was thinking slinky, but from what I have seen in videos, the slinky is built next to the trench and then placed inside and filled, doesn't look to narrow to me. We have dense forest.

You can put a second U tube heat exchanger down a bore hole, and this is done in some cases where the soil has high thermal conductivity; however, usually the soil's thermal conductivity is the limiting factor and just putting more pipe down the same hole gains you little benefit.

Any time you cut a large number of a trees roots within its drip line, especially a large tree, you risk killing it. For a 12" diameter oak, the drip line (essentially the farthest reaches of its branches) can easily extend 20'-30' beyond the base of the tree. Most of a trees feeder roots are near the surface, so a trench effectively eliminates those in its path. If you cut a trench within 10' of a moderate sized tree, you will have effectively killed ~25% of its feeder roots. It may not die the first year after - it may take several years and a stressful situation like a drought to kill it, or if it is really healthy and unstressed, there may not be any measurable impact.

Do you really need 5 tons of HVAC? Have you had a Manual J residential load calculation done?

Posted By steve_mn on 26 Aug 2011 01:02 PM
So, for 5 tons 900-1000 feet of well.
Can I also get house water out of it? A 3rd pipe should easily fit down the casing. Or does the grout stop that option?
Excavation is possible, was thinking slinky, but from what I have seen in videos, the slinky is built next to the trench and then placed inside and filled, doesn't look to narrow to me. We have dense forest.

There is a huge differance between a closed loop bore hole and a water well.  It is a common point of confusion.  You can stop by my website for a quick tutorial.
Eric

Have you had any geo pros to the project to offer ideas?
j

what about increasing your thermal envelope? Possibly spending an extra few thousand can eliminate a ton or more of required heating. I am in zone 6 (I assume that is the same as you) and for 3400 sqft I only require 2 tons of heating.

Yes, manual J has been done. Grand Rapids MN - very cold, wood backup, need 5 Ton, I have the furnace installed. Gravel - poor heat conductivity. I know the difference betweeen closed and open loop. Super insulated but large vaults and large windows. I know the trees would die.

putting more pipe down the same hole gains you little benefit.

About 13% per Ground Loop Design. Doesn't seem to change much with soil type.

Posted By lzerarc on 28 Aug 2011 11:05 AM
what about increasing your thermal envelope? Possibly spending an extra few thousand can eliminate a ton or more of required heating. I am in zone 6 (I assume that is the same as you) and for 3400 sqft I only require 2 tons of heating.

Wish we would have put more into the thermal envelope when building, although I do not think we cheaped out either. I'm in zone 5 with about 3000sqft and our contractor did a manual J that said we needed 5 tons of heating.

We also tried to do the horizonal boring but ran into rock problems too. Ended up putting in 5 150' wells.