Having built and used a hoophouse (Sunmaster greenhouse film over 16' PVC pipe -12' wide x 6' tall x 30' long) from 2008 until quite recently (gave it to some young farmers for taking it down for me), I have lately been debating the merits of building a 'real' greenhouse. The hoophouse didn't work worth a damn as a place to grow vegetables. In the spring and summer it was too hot during the day for decent pollinization (tomatoes & peppers) and in early spring it was too cold at night to start seedlings without a heat mat. One really cloudy, cool summer it did an okay job at the tomatoes and a big crop of basil but other than that year, it was mostly just dry, covered space. Which is useful around here. But as a greenhouse it was a failure. Which led me to thinking about what really needs to happen in a greenhouse at this latitude (48 north) and in this climate (maritime Pacific northwest).
Clearly it needs to be able to maintain an air temperature below 85F and above 32F at all times that plants are growing within it. But how to do that? Then I found what has become one of my favorite websites:
The Chinese have already figured this out.
I'm thinking that lining the back wall with steel barrels full of water would give me a heat sink to help reduce overheating during the day and to bleed heat back into the air overnight AND provide warm water for irrigation. I've read studies on the hours and hours it takes for a plant to recover the lost heat from being irrigated with cold water; warm water makes plants happier. Based on the studies done in Canada with these type of greenhouses at 50 degrees north, I am going to need a heat source in the winter if I expect to do anything more than keep the kale and cabbages alive. A rocket mass heater seems ideal for the application but I have zero experience with them and I already have a barrel stove built, so that is probably going to be the first try at heating.
Thanks to another GW forum on laundry, I am thinking that an old Maytag wringer washer and a clothesline are also going to live in the greenhouse. I'd like to incorporate a new raccoon-proof (okay nothing is actually "raccoon-proof", but at least seriously raccoon-resistant) chicken house into the structure and try to use the chicken's body heat and CO2 to help the plants grow. Chickens don't do well with dampness so there really should be some way of controlling the airflow between the chickens and the greenhouse; they can't just be in a wire pen inside the greenhouse. Or maybe they can? Has anyone combined their greenhouse with their chicken coop?
I also don't have a good plan for a thermal 'blanket'...
This is a obviously a design in progress but I'm really missing decent eggs and I have the time and construction skills; I just need to decide on a design and do it. Any thoughts?