Stressbaby,
Very interesting heating idea. Maybe I can grow my bergamot citrus afterall.
The article raises several questions for me. Is the 52 deg./ 8 ft.down number fairly uniform within most of the USA as the article states? How did the Nebraska man decide on 1100 ft of 6 inch pipe? I am sure it is possible to calculate the amount of pipe needed, considering the amount of heat needed, but what would be a simple method to make this calculation? Hopefully others will be able to supply some answers.

Subsurface temperatures vary greatly depending on where you are. Generally, it's the average temperature of your climate (inc. both day and night), year-round. That's why arctic regions have permafrost.

I do find it amusing that he's being referred to as "Nebraska man". ;)

Note that one can do a milder form of this, with much less tubing, in which you simply use the ground to average out your day and night temperatures. This system will benefit from this phenominon as well.

stressbaby,

That type of system is perfect for a HFGH the 10x12 one.

An octopus of 4in pipe and a 55 gallon drum buried in the center of it all. Year round heating and cooling, all in one neat package.

I actually have a very cunning plan ( http://en.wikipedia.org/wiki/Baldrick ) Whereby I am going to draw air into a prototype greenhouse that sits atop a vent in the ditch alongside my property. Last fall the farmers around me collectivly installed new field drains all leading to a central pipe which conveniently went under my driveway. In fact I had to stay home all day as they dug a trench across my driveway and installed this geothermal gold mine.

1100 ft? Pthhhhh! they laid MILES of the stuff!

On an unconnected note but maybe of interest to stressbaby I am currently digging a trench across the yard to the vent, intending to install a pump in the sump under that vent. The surface water it drains has got to be far better than the hard, iron laden water from the well I am currently using for watering.

Here is a link that might be useful: Someone who is a master at cunning plans :)

Ooh, neat, Chris. What a lucky break!

karenrei,

What the sucessful hobby greenhouse enthusiast needs in Iowa is to live next to a cave. Failing that we need to create one.

Or better still, co-join a greenhouse operation with a hog or turkey confinement, even better an ethanol or bio-diesel plant.

All that lovely waste heat just going to waste......

Maybe one day I will submit a proposal and apply for a grant.

Chris_in_Iowacky, I like your cunning geothermal plan.

I'm afraid your cunning water use plan may give you luxuriant, pest free foliage with little fruit and occasionally a dead plant from your nitrogen, pesticide, herbicide-containing agricultural runoff!

Some pics would be really keen.

Totally useless addition to this thread, but if I post on this one it may stop me from trashing some other thread somewhere.

This sunny afternoon, air temp 54F I bravely, in the interest of science, walked over to the ditch and dangled my trusty thermometer into the vent. Fed all 6ft of the wire in the hole and waited. 48F.

Totally useless experiment, I didn't know how far down the sensor got or if it snagged on something. I don't know how far down the drain is. In fact I have not really explored the hole in the ground that the snow always melts over at all.

Tomorrow I will go and heroically take with me a 10ft chunk of pipe and ram the sensor into the hole. That way I can tell at what depth I am measuring. (can someone tomorrow remind me I taped 6ft of wire onto the end of a 10ft pole before I lose my thermometer)

Just checked the temp of the well water, (why I did nobody knows, I knew the answer within 2 degrees or so) it was 50.9F

There is an endless supply of free warmth down there ten feet or so beneath the surface. Totally useless for home heating as us humans like it slightly warmer, but plants, at night, in Iowa? YEAH!!!!!!!

Chris I'm not sure why stress's comment is "totally useless"? You stated the water is from field drains and we all know there are many chemicals in run off from farmed fields. I would have the water tested before you use it on your plants. Who knows, you may not have to buy any fertilizer.

I like the idea of using it as a heat resevoir, even if not to water with.

mylu,

I meant MY post above is "totally useless"... :)

My totally useless post was a rambling about how I went out to find a hole in the ground, stuff a wire down it and measure a temperature. I got all dressed up warm, put my boots on, found the hole, dangled a wire in it, froze while the reading settled then came back to the house, took boots off, sat in front of computer.....

Then realised that I had measured absolutly nothing meaningful at all!!! Oh well, Thursday is my next day off.

As to the water, it would be nice to get some agricultural runoff for my non-edible things like pumkins and gourds and ornimental corn. This year I got two pumkins from 1/4 acre. So dry.

I have been using well water, and I can see that the weeds are a different color and sickly looking where I have irrigated. The weeds in non-irrigated areas looked fine and healthy!

Sorry to sidetrack.

Mylu! Where ya been, my friend? You've got an email...

StressBaby... you might have been thinking of this link...
http://www.sunnyjohn.com/indexpages/shcs.htm

He has some plan examples and sample schematics here...
http://www.sunnyjohn.com/photos/greenhouses/grnhs_woodland_gardens/index.htm

I first found this site maybe 6 years ago and have not visited it for a couple of years and it appears there is some updating done.

I plan on incorporating some aspects of the design in my own GH.

Poppa

Thank, Poppa! I think that's the second time you helped us find that site! That's the one I was thinking of.

I remember that site. A lot of work - I prefer the elegance of karen's two tube 'v's. I've been thinking about whether I could do something similar with ag pipe weighed down in my thermal store and run air through that. I would draw air from the roof though. Also, those ducted fans suggested are very weak - 180cfm from 30W, compared to say 20000 cfm @ 80W for a ceiling fan - if the manifold is a 44gallon drum which has a diam of about 22" I'd look for a 22" fan that sat directly in the lid space, and maybe made the duct to the roof line by welding on a few more drums above it.

Nathan.. I know that at some point in the website, they discuss that a low vloume of air is the preferred method. They are looking for slow movement of the air through the piping to give it time to transfer the heat to the ground. Too fast and you're just recirculating the air... that's the theory anyway.

FYI... there has been some discussion on other sites/forums that the piping is a great place for molds and stuff to grow. others disagree. Not saying that either has been validated, but it's one of the reasons (plus the cost and WORK it'd take to bury all that pipe!) that i thought about alternatives for my greenhouse.

Poppa

Hi guys,

I've been enjoying your geothermal source discussion for possible use in solar heated greenhouses. An approach I've been working with with many others has come up regularily (a few times here and there). Just so you know, I do my darndest to keep up on the pro's and con's of any approach to bringing in the sun for fun and profit. To date, the most promising wild ass crazy idea I've heard just happened here... using existing drainage systems for some sort of heat sink/source! The interesting thing is that virtually every country home has a septic field and perimeter drains on their homes... if you were in a field work situation you too might even have a field drainage system in place. Knowing full well that air to soil system must expend a lot of cash and sweat on the tubing install, designing an entire system with heat extraction/storage in mind beforehand is just another one of those great bits that keeps the noggin' nodding. As far as contamination issues with mixed use air systems goes, well I wouldn't worry about that just yet... as per usual, all design is only limited by the imagination and innovation of the designers. So.... I am sure that with the carrot of totally free SHCS tubing matrix just hanging there waiting, I betcha there's a quick and nasty way to manage it.

--
mr sunnyjohn...

I have a pond that is fed by an Artesian well and hovers around 55 F most of the winter. The coldest I have seen it go is about 48 F. The well is over a mile away so piping water directly from it is not an option. What I have thought about is making a well insulated 'cold frame' and pumping water from the pond through 1/2 tubing buried in the cold frame soil. Any ideas on how much tubing and what flowrate would be needed? I have also thought about building more of a green house structure straddling the outflow ditch with culverts under each wall but the ditch open in the middle of the green house to see if it would trap some of the 'heat' of the water. I am thinking the humidity in this situation would be way to high though.

I am thinking that constant temps in the low 50's might allow me to grow lettuce radish etc through a good part of the winter.

Thoughts?

Charles

poppa: the advantage of higher speed air is the much lower thermal resistance between the air and the pipe (decreasing in proportion to air speed). On the other hand, higher speeds use more power (increasing as the cube of the air speed).

So there is an optimal air speed. It might even be possible to tune the air speed dynamically with a simple controller.

Charles, you'll find that a fairly low water flow rate is quite effective for keeping things warm, because water stores so much heat. The real problem is how much heat you can transfer from the water. I would guess that with 55F water and 20F outside, and some decent insulation, you might need a flow rate of 2 gallons per minute for a 10x12.

I've got some very exciting news on thermal stores from my latest experiment, but I'm waiting until I've got a proper datalogger set up before I publish the results here.

I remember approx. 15-20 years ago that Mother Earth News had an article about a geothermal greenhouse in cold country...Casper, Wyoming. The owner exacavated approx. 20' down below the eventual greenhouse foundation. He lined the walls with thick panels of styrofoam...walls and floor... and made a slurry of the excavated dirt and water and pumped it back into the foundation hole. If I remember right every couple feet of fill had black corrugated drain tile set into it in the form of a U...the narrow bottom of the U going into the bottom of the foundation excavation. He pancaked the U tiles progressively every few feet...alternating with his slurry backfill. When he approached ground level he backfilled with gravel. I apologize...it's been a while and I've always been accused of having "Anheuser's disease" for a poor memory...lol. Somehow he rigged an air circulation system up that moved the air through the drain tile and heated the greenhouse with it.

Mother Earth News used to have interesting articles like that...now I find it more of an urban magazine touting the benefits of recycling yoghurt containers. If anyone has that article it would be interesting to read again.

Nathan...I distinctly have the impression that he had no special insight into sizing the tile or determining how much to use. He just did it...and when the excavation was full he stopped.

Terry