Greenhouse: site for greenhouse., 1 by stressbaby

stressbaby wrote:
IMHO, the 40 latitude rule oversimplifies the factors that go into determining the orientation of a greenhouse.

It is true that E/W orientation maximizes light, by up to 20-25% over a N/S orientation, depending upon it's shape. But if you maximize light, you maximize heat, and generally cooling a greenhouse is as big a job as heating one, particularly a smaller hobby greenhouse. If your only purpose for the GH is to overwinter carnivorous plants at min 40*F, and keep your costs down, then E/W may be the way to go, but...

A greenhouse oriented E/W may have more light but the light may be less even due to gutters, ridges, and other portions of the GH structure which cast continuous E/W shadows. These shadows pass uniformly over all portions of a N/S greenhouse.

Visual aesthetics? Can you see the greenhouse from your house? What part of the greenhouse would you like to see from you kitchen window?

Noise? If the exhaust fan is aimed right at your back porch, you won't be happy.

Landscape design? Where do you want the door in relation to your traffic through the garden?

I don't think the long side automatically needs to be perpendicular to the sun. I'm only 1/2 zone warmer than you are, and my GH is N/S.

Regarding fans, two thoughts. First, I like the umass link as the best discussion of HAF I have seen on the web. But I don't like their HAF cfm calculator. I originally used their formula when I calculated my HAF requirement and their numbers are too low for my needs. Their formulas may be fine for commercial greenhouses, but I think that they underestimate the HAF needs of a hobby greenhouse (I have a guess or two as to why that might be, but that's a different discussion).

Second, you don't need HAF when the exhaust fan is on if your intakes are properly positioned. If I were building again, I would wire the outlets to the HAF fans to the same 120VAC line, run this line to my relay box, and install a relay on that line that will shut off the HAF fans when power comes on to the exhaust fan. 4-5 months a year my exhaust fan runs 12 hours a day or more and you don't need the HAF at that time.

SB