I owned and operated a commercial greenhouse during the 80's in Nebraska. I sold both houseplants and annuals (inside) perennials outside. After lot of research, I had my greenhouse built from my own design. It was made from redwood and fiberglass panels. Size was 12 x 25 ft. It was a year around greenhouse and was fitted with a 24" fan, and 2 heaters. It didn't take long to figure out that the fan was useless in cooling. Air had to go through water to cool so a evaporated cooler was on the menu.
The most important fact was to run a greenhouse north to south. The reason in that as the sun moves across the sky, you can have both sunny and shady areas in the greenhouse without hot spots.
When I started the first year, I had no idea how hot it gets in the greenhouse over the summer. All I can think of was all that sun and growing space, unlike my house. And I lived in Nebraska zone 4. A fan was not enough. I used lots of shading material on the west side, and an evaporated cooler on the North side of the greenhouse. Most people starting out don't realize how hot it gets---too hot for plants in the summer.
My daughter bought a small 8x 6 ft from Harbor Freight and had the same problem. She uses it to start seedlings in the spring and over the summer, grows potted tomatoes, shading the west, running a moving fan and leaving the door open.
Karen. Wyoming and Nebraska are very windy. We can get 60 mph gusts. My son-in-law had to do a lot of work to prevent her greenhouse from blowing away. HF greenhouses are too lightweight for windy climates.
Just my 2 cents worth for anyone either buying or own a greenhouse to keep in mind for Summer 2016.
Photo inside my greenhouse. Never took a photo of the outside for some reason.
