It appears Geothermal is one of the dark arts requiring consultation with a Fully Licensed Geothermal Wizard.
Is there a web site with some basic info & sources?
Everything I’ve turned up is useless unless I’d be willing to trust my fortune to a local practioner of the Geothermal Arts associated with whatever group’s site I’m at.
For example, where lives a map or chart of local ground temps for the US? Doesn’t seem to exist. Dig a hole and bury thermometer, check back later?
A buddy in Washington state is interested in it also with same results locally.
Joe H
Replies
You might try here (International Groundsource Heat Pump Association) http://www.igshpa.okstate.edu/
Jim, thanks for that link, but I'm kinda looking for something on line, rather than spending hundred$ for books.
I'm not quite that committed to the idea yet.
Joe H
Are you asking about "geothermal" which is putting a line near a hot springs for heating or "ground source" which is running heat pump lines underground for heating and cooling?
Steve.
Quite certain we're talking ground source.
Joe, deep (20') earth temps will be nearly constant, very close to average annual air temp. Well water temps are often used if you don't know air temp. Less deep, for heat pumps, will vary with the seasons. Moving ground water will effect this also.
My readily found chart (Minneapolis) shows 2.6' depth varying 30º, 10.5' depth varying 15º. As you go deeper, the minimum ground temp happens later in the year. 2.6' in March, 10.5' in May. Not a bell curve, however.
A solution, if you're using the ground both for gaining and dumping heat, is to insulate the dirt from seasonal air temps. This is exactly what I do for annual heat storage. Would work with a heat pump, but if you put your house where the lines are, you have no need for the hardware.
Works for me.
PAHS Designer/Builder- Bury it!
Geothermal seems to be the commonly accepted incorrect term for groundsource heating & cooling.
Got no gysers here on my place, nor does my buddy in Washington unfortunately.
Joe H
Hello there,
There's nothing incorrect about the term geothermal. Geo- is from the Greek word ge meaning earth.
Here are some websites for you....
note the local industry links in this one...
http://www.geoexchange.org/publications/software002.htm
http://www.nrel.gov/geothermal/
I do not know anything about the reputation of this company so you should thoroughly check them out. Just came upon it when I was looking for some info myself, but I'm in Canada and there is plenty going on up here at the moment so I never looked at this one further. This looks like it is some kind of install it yourself system.
http://www.arit.com/geothermal.htm
http://www.arit.com/PDF/Design%20and%20Specifications%20Catalog%20for%20Terraloop.pdf
Can't help you with the ground temperature info, but I bet if there isn't anything on those first two sites you could call them and they could help you.
Goodluck with it, I'll keep checking back in case you decide to go for it...post your whole project here!
penny.
Live light enough to see the humour and long enough to see change.
-Ani DiFranco
Edited 4/22/2006 12:45 am ET by luckypenny
There may be nothing wrong with the term at present (that was not always the case - in some circles at the dawn of environmental awareness it referred to ground sources where mechanical thermal entergy conversion to higher temperatures was not required - but why beat dead whatevers) but you will still get a lot more information by searching on "ground source heat pumps".
If we are going to get CORRECT the earth is not a source of heat either.It is a storage and transfer medium from a) solar and b) molten earth core.Probably at the depths we are talking about 99.9% is solar.
Bill, not to be the wise guy, however, if the sun is older than earth, could it not be argued that the molten earth core is possibly a source of stored solar energy also?
I don't know about the figures at the depths we are talking about, but you will probably get some argument from geologists about your claim that the earth is not a heat source:"The Earth is thought to have formed from the collision of many rocky asteroids, perhaps hundreds of kilometers in diameter, in the early solar system. As the proto-Earth gradually bulked up, continuing asteroid collisions and gravitational collapse kept the planet molten. Heavier elements – in particular iron - would have sunk to the core in 10 to 100 million years' time, carrying with it other elements that bind to iron."Gradually, however, the Earth would have cooled off and become a dead rocky globe with a cold iron ball at the core if not for the continued release of heat by the decay of radioactive elements like potassium-40, uranium-238 and thorium-232, which have half-lives of 1.25 billion, 4 billion and 14 billion years, respectively. About one in every thousand potassium atoms is radioactive."The heat generated in the core turns the iron into a convecting dynamo that maintains a magnetic field strong enough to shield the planet from the solar wind. This heat leaks out into the mantle, causing convection in the rock that moves crustal plates and fuels volcanoes."http://www.physlink.com/News/121103PotassiumCore.cfm
The earth starts getting more constant in tempature as you go down deeper. I guess it depends on what time of year as to whether it get warmer or cooler.But at some depth it does start to get warmer. I think that is meausred in miles.That is why I said at the "surface" it is 99.9% solar heat.
"The earth starts getting more constant in tempature as you go down deeper. I guess it depends on what time of year as to whether it get warmer or cooler."
Bill: Yes, within the depth of the "trumpet curve" or whiplash curve", there is seasonal variation. The actual soil temps curve crosses the average soil temp line once or twice due to time lag. Coldest temps at 10-15 feet aren't in January but are in May or so. It takes a while for the "cold" to travel that far down. (actually for the heat to be conducted into colder soils above.
Think of an ice cream cone with the top flared out a lot. Actual soil temps occur between those limits. Dampening with depth.
"But at some depth it does start to get warmer. I think that is measured in miles."
Yeah, 75 degrees F per mile. Or about 1.4 F per 100 feet. Piddly if you're doing a basement 10 feet deep. Highly significant in diamond mines at a depth of 11,000 feet.
"That is why I said at the "surface" it is 99.9% solar heat"
Maybe 98% solar heat, cooling to surrounding air (ultimately a solar effect, too) and radiant cooling on clear nights. Increased by a degree or two by the geothermal heat from below. Your mileage may vary in Yellowstone Park and Hot Springs Arkansas.David Thomas Overlooking Cook Inlet in Kenai, Alaska
I've seen Geothermal vents in Yellowstone park and I don't think it would be wise to go digging down next to one of those. Who knows, you might hit some underground magma vent or something and end up with a miniature Mt. St. Helens like affair only in your back yard.
Do you think schedule 40 PVC would handle that safely or not? Maybe it would be better to take some 2 inch iron pipe and drive it carefully in at an angle. Oh, and don't forget to wear your safety glasses!
"For example, where lives a map or chart of local ground temps for the US? Doesn't seem to exist. Dig a hole and bury thermometer, check back later?"
Just post your lat/long or city,state and I'll give you an estimate as good as you'll find in any book.
Better yet, also post your siting: North-facing, south-facing, elevation about sea level, forested, cleared, etc. and we can nail it down a lot tighter.
And as someone else alluded to, the temps at depth follow a "trumpet curve" there is a dampening and time delay at depth. In my town, deep pipes are most at risk of freezing in May, not February. But here, frost depth are only 10-15 feet depending on surface conditions. In Fairbanks, where frost can reach 50' in gravels, the time delay can be greater.
David, I'm at Lon -113.16094, Lat 37.58882
Elevation is 5550' to on hill sloping to the west.
Juniper and pines, clear to covered.
Joe H
"David, I'm at Lon -113.16094, Lat 37.58882 Elevation is 5550' to on hill sloping to the west."Somebody got a GPS for Christmas. Up out of Cedar City? Pretty place.Your deep soil temps are going to around 42-43F. Kind of sucky for extracting a lot of heat. Unless you have a scheme such as summer-time A/C that dumps heat to the same ground or some other way to get summer heat into the subsurface. You could still do "geothermal", but it not as attractive for a heating-only application as GW in the 50's.
David Thomas Overlooking Cook Inlet in Kenai, Alaska
David, I find the idea of frost at 50' interesting.
Does it ever thaw out all the way?
Do you have to put footings deeper than the frost depth?
blue
"David, I find the idea of frost at 50' interesting."Frost goes deep when there are:1) cold winters (duh!)2) low soil moisture (hence the gravely soils)In the Fairbanks area, the "active zone" can be 50 feet deep. There is also discontinuous permafrost in the area. Soils type, north- versus south-facing slopes and ground cover make for "microclimates". One might average 33F and another might average 31F. A single building might overlie both kinds. And significantly change the sibsurface conditions!The idea of a "active zone" is more versatile than "frost depth". Below treeline, they mean the same thing. But in Barrow, for instance, the "active zone" is that which thaws, ever. The stable soil is the frozen stuff below. In either, you need enough foundation in the stable soils below to resist forces generated in the active zone.Or you need to get creative. The hospital in Barrow was too large to put on piles (the usual way to keep the ground frozen). So there is a refrigeration system to keep heat losses through the slab from melting the soils.David Thomas Overlooking Cook Inlet in Kenai, Alaska
I see. Very interesting. It's okay to build on frost, as long as you don't melt it!
I kinda figured piles would be a solution but the hospital idea is a surprise to me.
blue
Blue,
The cleverest, most elegant solution I've seen for permafrost work are the piles of the Alaskan Pipeline. In frozen ground areas, the piles themselves pump heat out to the atmosphere, keeping the ground frozen despite ground disturbance above and slight conductive heat loss from the hot oil.
It is done with a iodine salt within a each pile. In the summer, the crystals sublime and hotter vapor stagnates high and there is little heat transfer. In winter when the "warmer" ground below can sublime the crystals, the vapor travels upwards, condenses on inside of finned-tube sections and falls as crystals back to the bottom. That gets the ground around the piles to -40F/C or so by the end of the winter. It is a thermoshipon by a very powerful one because instead of relying on slight density differences between hot and cold gasses or liquids, it is powered by the huge density difference between soild and gas.
Ask me about how ice caves work sometime. That has more applicability for residential cooling applications, I think.David Thomas Overlooking Cook Inlet in Kenai, Alaska
Loads of information that will take you hours and hours to read at http://www.geoexchange.org/
There is an excellent video at http://www.geoexchange.org/video/6.%20AFFORDABLE%20HOUSING.mpg
How about checking with your local Extension Agent - they may have more local info on ground temps. They may also have more info on geothermal ( or groundsource ) availability in your area
http://www.radiantmax.com
Try Radiantmax they have an online store and really cater to do it yourselfers. They do the engineering for you and quote what equipment you need.
I am getting ready to buy a geothermal heat pump for my new house and will likely get it from them.
I've had a few put in and by far the cleanest installations I've seen were 8 inch wells bored 200 ft deep about 10 feet apart. That gets you well into solid limestone around here,(n. alabama), a continous loop of triple layer black pipe was put into the holes and the holes were grouted solid. Beat the heck out of digging up half an acre of land w/ 4foot wide by 10 foot deep ditches. Might want to look into that. Jim Devier