I thought I would share some information I have been looking into for heating and cooling greenhouses especially in the north. The concept as I have seen it is before a greenhouse is put up the ground is dug out 4 feet or so depending on how far north you are. Pipes are laid out in a grid these are common corrugated drainage pipes using large 12 inch ones as the main lines and exit lines 4 inch drainage pipes run from one side to the other side of the greenhouse. Their must be quite a few pipes for this to work. Now the main concept is that ground temp in zone 6 is 55F at 3 to 4 feet constant. Once the greenhouse is built a large 12 inch pipe runs to the top portion of the greenhouse sucking the air into the pipe and blowing it into the underground system. This hot air can be 100F on sunny days it heats up the soil and stores the heat during the day. Some ventilation maybe needed to keep the greenhouse from over heating. During the fan continues to blow through the pipes it heats up from the warm soil and keeps the greenhouse form freezing. It maybe cooler on cloudy days at night. From what I have heard a -2F night was heated by just 2 blower fans and this system to 42F. This seems similar to what Atlanta Botanical garden has for the high elevation house. But their system is mainly used for cooling but I am sure it helps with keeping the place from freezing as well.
