I know this will most likely depend on the type of greenhouse--a 10x10 kit from Harbor Freight and a 100 ft and larger hoop house are completely different beats, but I am curious to see if there are standard placement guidelines for non-commercial greenhouses.
-Should you attempt to face the longest side to Southern exposure?
-Should they be within zone 2-3 of your permaculture layout?
-Should the base be compacted earth?
-Any other site placement considerations?
"A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects."
Everything that I have read on the subject seems to indicate to me that, depending on how you build it, you definitely need as much sun as possible no matter which way you face it. The large dome-shaped types should have the longest side facing the south. I have read that, as far as location in your yard, the east side of any building is ideal to capture as much morning sun as possible. The Southwest portion of your yard is next best because of time of exposure during the day. I would also recommend placing it as close to zone 1 as you can, especially if you are going to start seedlings inside. I live in the city on a very small lot, so my whole property is zone 1, but my garden and greenhouse will be relatively close together for ease of transporting seedlings and other plants.
Obviously ventilation is key during the summer months. Some other considerations are water supply, potential electricity for fan ventilation, floor type and what you are growing. I think your packed dirt floor might get kinda muddy after watering, I would recommend putting some sort of paver path through the center and then, if you have sufficient light, cultivate the ground beneath your shelves along the sides to maximize your yield.
I'm planning on attaching a small greenhouse to the chicken coop I'm building this summer to act as both a plant propagation area as well as a geothermal heating environment for the coop itself. I'm basing my plans on Bill Mollison's design from his Intro to Permaculture book and, because only one side will have windows, I am planning on facing the window wall south on a 65 degree angle to collect full sun during the winter and then I'll be building a large overhang to shield the window wall from any direct sun during the summer.
I hope this helps!
Common Weeds And Wild Edibles Of The World (HD video)