Small and crude GSHP for a Michigan garage

[Patrick]

Originally Posted by pick1e

I definitely agree with your logic. I do want to try copper though for a couple reasons:

1) I don't need it to last forever.
2) It's a small project.
3) Nobody uses copper and I'm always up for a challenge.

Hopefully I can get away with shallow boreholes (maybe 20 feet?). My friend who installs fences for a living suggests that in this case I SHOULD be able to pull them out of the ground and recycle them in the future.

If I were heating my house and I planned to live here a long time it would certainly be different but I just want to heat the small garage with as little disruption to the yard as possible.

I'd say you could safely use 1/2 the copper (surface area) as the HDPE equation said to use and get the same/similar heat transfer.

[pick1e]

Originally Posted by Patrick

I'd say you could safely use 1/2 the copper (surface area) as the HDPE equation said to use and get the same/similar heat transfer.

I think that's a fair bet. It wouldn't be hard to design the loop with additional ports to connect more boreholes easily if it became necessary.

I'm anxious to measure my soil conductivity. Hopefully it is high. I assume it will be since our soil here is generally pretty wet (I have two dehumidifiers in my basement).

[pick1e]

Here is an interesting article about soil freezing. It is especially interesting since I live in the county where the study focuses.

http://geography.uwo.ca/research/gre...zl_Tomczak.pdf

It verifies scientifically what my fence installer friend told me from his experience- that the surface environment greatly affects the freezing depth. Our official "frostline" is 42" but he told me when you have snow or leaf cover the ground is well insulated and probably won't freeze below a foot. On the other hand in an open field, you may get 4 to 5 feet of freezing. He said he will see frost down to a foot in someone's yard, but in an adjacent gravel driveway in that same lot, frost down to 4 or 5 feet because it is continually packed down from above.

This article corroborates with these observations, although they only tested down to 25cm.

I guess that's a good excuse to not rake the leaves

[mrd]

That's interesting, I'd never considered that compacted soil is a better heat conductor. A frost-protected foundation design typically employs rigid foam buried adjacent to the footing, extending outward from the building. I wonder if there's a viable alternative insulating material to use in this buried application, something less expensive or more green. It seems something porous/low-density/filled with cavities could do the job..

Any ground spots that repeatedly receive water - say a low-spot or roof-water recipient - compact over time. I think that's actually a technique used to compact soil when needed. So you could encourage greater soil conduction in a region by directing unwanted water runoff to it.. perhaps dig a shallow hole over the pipe field, fill with gravel, and pipe in your roof gutters to that area. Just be prepared for that spot to sink over time.

[mrd]

Originally Posted by pick1e

I'm anxious to measure my soil conductivity. Hopefully it is high.

Perhaps it'd be best if there was good soil conduction at and below the pipe field, but poor conduction above the pipe field? In the winter, you want the soil below warmer than the cold air above. In the summer, you want the soil below cooler than the warm air above.

[pick1e]

Originally Posted by mrd

Any ground spots that repeatedly receive water - say a low-spot or roof-water recipient - compact over time. I think that's actually a technique used to compact soil when needed. So you could encourage greater soil conduction in a region by directing unwanted water runoff to it.. perhaps dig a shallow hole over the pipe field, fill with gravel, and pipe in your roof gutters to that area. Just be prepared for that spot to sink over time.

We are on the same wavelength. I was thinking of building irrigation tubes into my borehole pipes:



I figured on gravity feeding the irrigation tubes from a rain barrel.

You would get a triple whammy here for maintaining a high conductivity around the borehole tube, possibility of backfilling with sand since you're keeping it saturated (facilitating eventual removal of the pipes for recycling), and using the irrigation tubes to increase the effective surface area of the borehole tubes like radiator fins.

I'm not sure whether you'd be able to braze the irrigation tubes axially to the borehole tubes though. If you could, I also thought about attaching fins to the borehole tubes radially like fins on a model rocket, but along the whole length.

[pick1e]

Originally Posted by mrd

Perhaps it'd be best if there was good soil conduction at and below the pipe field, but poor conduction above the pipe field? In the winter, you want the soil below warmer than the cold air above. In the summer, you want the soil below cooler than the warm air above.

No problem! Astroturf my yard!

[pick1e]

I'm anxious to get going on this since it hasn't been above freezing here in almost a week. It's hard to refinish a dining table in the living room...

I've received my manual post hole auger in the mail and received permission to start digging in the yard. I will see how far I can get by hand before calling in the big guns. My fence installer friend has volunteered his equipment. He believes I will hit gray clay ("stuff they use to make concrete" he says) at about 12 feet so that may be the end of the story save professional drilling.

[Daox]

Good luck with the digging. Let us know how it goes.

BTW, why are you digging now that its cold out?

[pick1e]

Originally Posted by Daox

BTW, why are you digging now that its cold out?

Because I have a bug up my @$$, as they say

I have a drive to do it because it IS so cold and I really need to be able to work in the garage. I am working on refinishing a dining room table in my living room- complete with tarps and window fans (it won't fit down the basement stairs). My girlfriend is really psyched about it

I started thinking about it seriously a few months ago believing there must be a better solution than electric resistive heat that sucks a bajillion watts. So now I'm bound and determined to make it work- hopefully before winter is over. Then I will bask in my warm garage.