phk@phk.freebsd.dk said: > I later talked to a geologist who knows the Danish underground well, and he > estimated I would have needed to drill to at least 25m depth to escape > seasonal temperature-changes and cited a research paper from the 1950'ies > where the did precisely that experiment. I found a paper showing skin depth at 1 year of 3-4 meters for soil, a bit over 1 meter for ice and rock. Does a pipe in the ground stay dry? Or how do you keep in dry? In summer, I'd expect it to be cool and if the humidity in the outside air is above X% it would condense in the pipe. Do you just cover the top to avoid air mixing? Does in need a desiccant? ... -- These are my opinions. I hate spam.

I used special order PVC Pipe with end caps, used the drilling mud to encase it in the ground. The top cap had a U made up of PVC L's and was removable. Initial tests where without any filling. Once convinced it worked I filled the pipe with coin bags my local banker got me. Very strong canvas. Filled with gravel and sand.and a numbered string attached. Used it from 74 till 93 when I sold the home. Dug out 6 inches and filled it with dirt.Never detected any moisture.Used a Tracor M100 modified to 60 KHz for comparison it served me in Miami till 60 KHz was modified. Bert Kehren   In a message dated 9/16/2020 1:16:24 AM Eastern Standard Time, hmurray@megapathdsl.net writes:   phk@phk.freebsd.dk said:> I later talked to a geologist who knows the Danish underground well, and he> estimated I would have needed to drill to at least 25m depth to escape> seasonal temperature-changes and cited a research paper from the 1950'ies> where the did precisely that experiment.  I found a paper showing skin depth at 1 year of 3-4 meters for soil, a bit over 1 meter for ice and rock. Does a pipe in the ground stay dry?  Or how do you keep in dry?  In summer, I'd expect it to be cool and if the humidity in the outside air is above X% it would condense in the pipe.  Do you just cover the top to avoid air mixing?  Does in need a desiccant?  ... -- These are my opinions.  I hate spam.    _______________________________________________time-nuts mailing list -- time-nuts@lists.febo.comTo unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.comand follow the instructions there.

-------- Hal Murray writes: > > phk@phk.freebsd.dk said: > > I later talked to a geologist who knows the Danish underground well, and he > > estimated I would have needed to drill to at least 25m depth to escape > > seasonal temperature-changes and cited a research paper from the 1950'ies > > where the did precisely that experiment. > > I found a paper showing skin depth at 1 year of 3-4 meters for soil, a bit > over 1 meter for ice and rock. Yes, as a general rule, the yearly temperature-swing attenuates a lot in about a meter or two, and that's why you generally bury a ground-heat loop buried a meter or so. But if you measure the temperature with one decimal place or better, you need to dig deeper, because now the difference between individual year's weather matter, and in my case here in Denmark: Underground water-transport and in particular where and when that water comes from starts to matter. Basically I would have had to drill to "the stable water table" and in my case that is approx 25 meters down, which is also the typical depth of atesian wells in Denmark. > Does a pipe in the ground stay dry? Or how do you keep in dry? In summer, > I'd expect it to be cool and if the humidity in the outside air is above X% it > would condense in the pipe. Do you just cover the top to avoid air mixing? > Does in need a desiccant? ... It would need to be closed to the atmosphere, which you can either do properly or patch up the imperfection with desiccant. More tricky: Internal air-circulation. Either guarantee that the temperature increases all the way from the bottom to the top, which here in Denmark would mean heating the top-end during winter, or install baffles every 1-2 meters to resrict airflow. It would have been fun, but I can get the same temperature stability cheaper. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.