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Old 03-03-15, 08:55 AM   #1
theoldwizard1
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Default How deep does non-permafrost typically go ?

Areas like the U.P. of MI, northern MN, ME, ND and most of Canada get deep frost, at last 48". These areas obviously warm up enough in summer so that the ground (eventually) does melt.

Are deep vertical wells a reasonable source of "heat" for geothermal heat pumps ?

Most vertical GSHP don't see "stabilized" temperatures until at least 20'. For these colder climates, I suspect that is more like 40-50'. If the pipes are well insulated from that depth all the way to the heat pump, would that be adequate ?

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Old 03-03-15, 07:04 PM   #2
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Areas like the U.P. of MI, northern MN, ME, ND and most of Canada get deep frost, at last 48". These areas obviously warm up enough in summer so that the ground (eventually) does melt.

Are deep vertical wells a reasonable source of "heat" for geothermal heat pumps ?

Most vertical GSHP don't see "stabilized" temperatures until at least 20'. For these colder climates, I suspect that is more like 40-50'. If the pipes are well insulated from that depth all the way to the heat pump, would that be adequate ?
These are very good questions.

You should consult some local GSHP installers, they would have exactly the information you are looking for.

I doubt that anyone on this forum actually has this information.

I hope that when you find out, you'll let us know.

Best,

-AC_Hacker
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Old 03-03-15, 07:06 PM   #3
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These are very good questions.
Sigh. My life's story !

It usually takes a lot of digging on my part !!
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Old 03-04-15, 12:24 AM   #4
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Sigh. My life's story ! It usually takes a lot of digging on my part !!
Yeah, but permafrost does not apply to that kind of digging.

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Old 03-04-15, 05:40 AM   #5
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I remember one particularly bad year back in 93 (I think) when the weather was cold enough that the water lines 7ft down were freezing. That is rare but I don't remember ever hearing of building footings having an issue at 4ft. I would guess that you would have stable temps from 10' down or at least no possibility of freezing. Thing is, you have 500ft of tubing in one hole so the 10ft or so at the top won't affect the output much.

That number will be different in the far north tho. The number may be 20ft.
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Old 03-04-15, 07:33 AM   #6
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Yeah, but permafrost does not apply to that kind of digging.

-AC
Well, I did learn that permafrost is REALLY PERMANENT ! It can actually go 100s of feet deep !
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Old 03-04-15, 07:37 AM   #7
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I would guess that you would have stable temps from 10' down or at least no possibility of freezing.
.
.
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That number will be different in the far north tho. The number may be 20ft.
I was reading on another forum about folks who had installed horizontal loops at 12-15' deep, actually getting inlet water from their loop well below freezing ! Sure, it has been cold in the Midwest USA, with temps below 0F, but if your inlet water temp is below freezing, IMHO, you have a SERIOUS design/installation flaw !
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Old 03-05-15, 05:31 AM   #8
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I was reading on another forum about folks who had installed horizontal loops at 12-15' deep, actually getting inlet water from their loop well below freezing ! Sure, it has been cold in the Midwest USA, with temps below 0F, but if your inlet water temp is below freezing, IMHO, you have a SERIOUS design/installation flaw !
You can still get reasonable performance from a HP when the installation temps are below freezing. Just don't let the installers skimp on tubing. Remember that and ASHP starts losing efficiency well below that.
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Old 03-05-15, 08:14 AM   #9
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You can still get reasonable performance from a HP when the installation temps are below freezing. Just don't let the installers skimp on tubing. Remember that and ASHP starts losing efficiency well below that.
If I ever had a GSHP system installed, there would be a "performance" clause in the contract. If my inlet water temp EVER fell below 40F, the installer would have to repair/replace/agument the ground loop. I would try to hold 50% of his installation fee in escrow for at least 1 year.

If you are going to pay the premium of having a GSHP, you want one that is designed and installed for optimal performance !
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Old 03-05-15, 08:17 AM   #10
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You wouldn't have to go that far. Lots of systems have input water temps that low and still perform well. It just has to be designed for it. No problems.

Don't forget, the system has glycol in it so it won't have a freeze problem and it won't hurt the equipment.

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