Tapping ground heat in small greenhouse

heehaw · Nov 17, 2003

the geothermal wells i have seen, don't care about having water in the wells, they fill the holes with something, bentonite i think..to conduct the temp from the ground to the pipes, or vica versa.
heehaw

dylan · Nov 18, 2003

I've seen guys make huge compost piles outside their greenhouses and run hundreds of feet of 4" big "o" through the pile and then into the greenhouse. They draw the warmed air into the greenhouse with a small electric fan. Big piles can get really hot especially when insulated with hay bales or such.

hornworm · Nov 18, 2003

I have also heard of this compost heating method only using water coils. have not seen any in use but would imagine that it would cut down on smell .

RichNJKubota · Nov 19, 2003

I'm looking into building a solar heated greenhose. I already live in a solar heated house so I asked the engineer that designed the house about a greenhouse and said to build a smaller version of my house. That he has several clients that have done this and it works good.
Basically the south side is glazed and all other sides are insulated to R30. The rigid insulation continues underground down to 4 ft and then under the soil. Air ducts are placed in the soil and a small fan continuously circulates air thru the greenhouse and the air ducts. The soil is the heat sink/source.

PaulK · Nov 19, 2003

Bob:
You're drawing me back into the initial scheme. We'll see what happens when I sink 4" PVC pipe 4 to 5 ft. deep. I won't fill them with sand. That was a bad idea because they'll be much more conductive as plain water. Besides, I'll be able to measure the water temperature. If there's enough heat at that depth, it would make sense to put in a central line of 8-10 six inch diameter pipe under the workbench. There's clearly heat down there - and it will want to rise. I probably need only 8-10 degrees more heat to make it freeze-free from Dec 15 - Feb 15.
Paul

gsganzer · Nov 21, 2003

I saw a greenhouse with the same concept. They filled 5 gallon pails with water and put them in a crawl space under the floor. They had a fan circulating air under the floor, heating the pails during the day. At night the same circulated air released heat back into the greenhouse.

Cacinok · Dec 1, 2003

Here's a slight twist that might help gain a few degrees, unfortunately it depends on the sun, so on cloudy days you'd be back to the cold green house scenario. Some of the solar folks use shallow black boxes w/ a glass or plexiglass top w/ copper tubing snaking through the box to warm water or an antifreeze mixture which is then circulated through and area to warm it.

This isn't the best fix, but your fix may be to use two or three of the mentioned ideas.

clint

PaulK · Dec 2, 2003

Clint,
There should probably be a maxim that you can never [almost] have too many translucent containers of water in a greenhouse. I use a quarter spoonful of salt and bleach in each gallon bottle [just enough to discourage summer fungus and not too much to harm the soil if it leaks]. There are about 75 gallons of water in the greenhouse. I read that a 10x10x10 area with 100 gallons of "exposed" water in the center could be made warmer by 2F with outside temp at 15F with the addition of 10 lbs of salt in the water. Apparently when the water freezes, it takes more energy to "unfreeze" in a closed container than it does to move from 33F to 70F. I'm reluctant to deal with antifreeze - although I can see an advantage a critical temperatures. I'm also edgy about salt - although its advantages seem real. The quest to get hard data on viability of salt is on my "to do list".
Paul.

SPIKER · Dec 3, 2003

you can use epsome salt which is also a fertalizer! /forums/images/graemlins/smile.gif

anyhow I've still watching this for any good info I can find.

anything PASSIVE that has a blower will probably use more electricity per heat gained than a resistive heater would use.
unless it is puttiong out LOTS of heat. a 1 degree rise would be problay not cost effective, but a 2 or 3 degree rist would probalby start being better at helping it stay warm...

Mark M /forums/images/graemlins/frown.gif