Ken Peavey wrote:Barrel in the GH
small fountain pump in the barrel
pump is on a timer, pumps water through tubing coiled on the ground in the sun
water returns to the barrel
greenhouse cover: 6mil plastic, construction grade, single layer, drafty
barrel: 55 gallon plastic, mostly full
pump: about 12 watts
tubing: 3/4" PEX, black, 400 feet
timer: comes on when the sun hits the hose, turns off when it goes behind the trees
Barrel Temperature: I've had the barrel up to 140 degrees
GH Temp: I've seen it as low as 41 in the morning, 28 outside
Never lost anything to frost or cold.
Dale Hodgins wrote:A barrel that is burried in the center of the floor and filled with water, will thermosiphon heat from beneath. A pit greenhouse with a sunken barrel could draw heat from 8 ft below the surrounding surface. In my area, soil at that depth always stays about 15F above freezing. A loop of pipe run from the barrel and through the grow beds, would thermosiphon whenever the water temperature is higher than that of the beds, and would stop flowing when the greenhouse is warmer. I can't think of a cheaper means of using geothermal energy.
Dale Hodgins wrote:Another way to harness deep down heat, would be to drive scrap aluminium rods or angle iron deep into the soil. Aluminium transfers heat along it's length very quickly. Fins that are attached to the airborne portion of the rod, would allow it to shed heat more readily. For best results, the central portion of the rod should be wrapped or painted with an insulating material.
An earth tube loop could be set up. It would work by convection, just as the barrel does.
I have a good greenhouse site above a steep slope. An earth tube that starts down the slope below the greenhouse floor level, would give an updraft of warmed air to the greenhouse, whenever air temperature drops below that of the soil. A baffle may be required to prevent cold air from flowing down the tube once the ground cools off late in the season.