New Member Here...

[JPG]

Frost was not my concern. Ground temperature was. At what depth does it become unaffected by seasonal changes?

In addition to cost, there is the corrosion factor. My initial concern was heat transfer.

[reible]

They did a house not far from me about 15 years ago. Frost was not a problem as they went 150' deep if I recall right.... They used well drilling equipment and went vertical rather then horizontal. They didn't have space on the lot for the size of field that was needed.

From what I read it is costly, the drilling can run you 10K to 30K alone. Figure another 10K for the system and well it out of my price range at my age. Not enough years left for it to pay for itself.

Now if you have the lot size to go horizontal I sure it's another story. In our situation our back 40 is 40 feet......

Ed

[Sherlock]

Guys, maybe an unfortunate post, a long ways from Shopsmithing, but was September’s project. Should also mention I claim no expertise sizing Ground Source (Geothermal – misnomer unless you have a volcano or hot springs) heat loops. But to the job at hand as has generated some interest, who doesn’t like to be warm, particularly if it might be in the shop. Plastic: HDPE, SDR11, high density polyethylene. Pretty tough stuff, actually had a tree on some it during the dig. Crush strength good for sure and fortunately nothing sharp underneath. Depth: 3 – 3 ½’. "Is that deep enough?" Deeper is always better but it becomes a trade off. Have attached a temperature depth chart for the area and think we are pretty reasonable. Any deeper and would have had to ferry the dirt to piles outside the trench area. The last foot was clay which is the best possible for heat transfer, always wet and packs well and were able to dig, place tubing and backfill clay from the next trench. Generally look for two to three feet below the frost level which isn’t an issue in this area. Will it work? Time will tell, will have instrumentation for realtime calculations. Success will be a 4-5 Coefficient of Performance. COP is heat pump jargon for the ratio of Energy In vs. Energy Out. So for every KWH-BTU going into the heat pump compressor, I am expecting 4-5 units of energy out. So if an electric baseboard is 100% efficient (which it is), this will be 400-500% efficient in comparison (actually cheaper than natural gas in this area and can have cooling too). Minus from this is the pump energy required to circulate the loops which runs 24-7 in heating and cooling season. Pumps and system curves, I do claim some expertise. At this point think less than ¼ hp. This may be more than you wanted to know? There is a forum at geoexchange.org for exploring further.

Whidbey NAS Ground Temperature.jpg (170.75 KiB) Viewed 9599 times

[JPG]

I am greatly surprised that it gets to that temp at so shallow a depth.

Clay good for heat transfer, a PITA for digging(by hand).

[Sherlock]

That is just the numbers here, varies across the country. A project in Missoula Montana the numbers at 6ft depth were a low of 30F and high at 58F. A major swing. Wouldn't even think about 3ft as would be froze at that level most of the winter. But lots of sunshine and again, insulation-insulation. But have to be careful there too, to keep away from moisture condensation in the wall. In the olden days of 2x4 construction the walls were dry because the wall temperature was above the condensation point of water. But at an energy cost.

[bill50cal]

where are you getting your temp - depth chart?

[dusty]

Would you believe the internet? Here is but one.

http://www.greencastonline.com/tools/soiltempmaps.aspx

[Sherlock]

The data comes from a government website, lots of information there. The access doesn’t seem to be working for me at the moment. A bit stretched now so do not have the time to work through it. The designer should have the information for your site.
http://apps1.eere.energy.gov/buildings/ ... direct%2B1