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I grow in two very different environments. In Australia my greenhouse is in an inland Mediterranean type climate with summer temps often over 40C and winter lows down to -4.
A couple of years ago I installed an earth heat exchange system EHE(a fancy name for a buried pipe). I installed this system with the intention of using the cool earth at 3 metres deep to cool the greenhouse but have found that the almost constant temp coming from the EHE allows me to warm the greenhouse in Winter. With a completely insulated Southern side of the greenhouse and huge amount of thermal mass (6000 litres of water) I no longer need extra heating or cooling. In winter a fan draws air into the greenhouse and in summer a solar chimney draws in the cooling air. I understand that your winters are many times more extreme than mine but the same principle has been used in Alaska. The link below relates to a very basic system in a climate very similar to yours.

http://flashweb.com/blog/2008/09/earth-air-tubes.html
http://en.wikipedia.org/wiki/Ground-...heat_exchanger