pit greenhouse vs. insulated north wall?

Hey all,

I've been doing some research on this today, and can't find anything like a comprehensive resource or calculator for thermal retention in masses, so I'll put it to y'all: Which is it, and where's the science? I've worked with Steve Breyer of Tripple Brook Farm and Jonathan Bates of Food Forest Farm, and they have a multi-walled plastic south face, insulated north face with water for thermal mass at FFF. Jonathan told me it never got below 27F last winter, with nights as low as -17F, if I remember correctly. I like the aesthetic of pit- or earth-bermed greenhouses, but don't know if that much extra mass has much benefit, especially in cloudier New England winters.

I'd be grateful for any resources for calculating mass storage as well.

Thanks,
Marvin

The frost line is less than 4ft deep in New England, so once you dig down 4ft or so the soil/enclosed air will "never" get below 32F.

Checkout this liquid bubble insulation greenhouse: http://www.solarbubblebuild.com/solar_energy_collection.php

Rodale Press used to have some books, "Gardening Under Glass," and "The Solar Greenhouse Book." My copies are around 40 years old, presumably there are updated versions available... We have a sort of sloar growhole or pit greenhouse, although with no supplemental haet, it's really a sunken coldframe. A single layer of 4 mil plastic sheeting for glazing, not too fancy, but there's lettuce and spinach that'll be ready to eat in a couple more weeks. We are near St. Louis, so plenty cold here sometimes....

builditsolar.com has some general calculators for passive solar, and good resources generally.
we use about 1" per hour as a rule of thumb for heat penetration through earthen mass (brick/cob/adobe), and you can find their heat capacities online (engineeringtoolbox.com, etc)
.  However there are probably more refined calculators out there for actual performance of greenhouse and passive solar structures.