I bought land in an area that high plains desert that gets triple digits in the summer and subzero in the winter. Is there a particular design of greenhouse that is best for this? I was thinking of a walipini...not sure how efficient it is but I love the sound of the name :)
Howdy Tom, not sure where you are but my brother just bought one of these to install in the high plains deserts of Wyoming. We will be putting it all together next spring and I will start a thread about it. He bought it from a guy in Nebraska who has been experimenting with it for years. A search for "greenhouse in the snow" should give you more info on it.
There is also this one in Colorado that was built by another guy named Jerome.
Basically you want a structure brings in enough light to grow plants, more heat in the winter than will be lost by radiation back out into space or movement of the air, absorb less heat in the summer than what can be removed or stored for later use to compensate for the loss.
First design element then is determined by your latitude or the sun angle to maximize light and heat penetration in the winter and minimize heat penetration in the summer. The angle of the glass and insulated roof then should allow sunlight to enter for as long as possible in the winter but only first half a day in the summer, which means orienting the long axis of the greenhouse in a somewhat northeast to southwest direction. The rising sun in summer will then enter the glazing and reach the back of the building but by mid day when overheating begins the roof will be shading and most light entering will be reflected light that has little heat. During the winter the sun rises in the south east and so wil enter directly into the glazing then it sets in the southwest still able to enter the glazing. [assuming a northern hemisphere location]
Being able to store ambient heat from the air during the day and return it as radiant heat at night is the first conservation strategy. The second is to minimize radiant and ambient heat loss at night. Why are desert nights so cold? It is because of radiant heat loss to the clear night sky. Therefor tilting the glazing back to maximize letting the sun is also maximizes the radiant loss at night. I think radiant loos is a greater problem than conduction loss through the glazing.
My location is 47 degrees north and I put my glazing vertical. this greatly reduces the exposure to the night sky.
The third strategy is the earth as a heat sink buffering the outside extremes. Therefor if everything except the glazing is buried and you have a good plan of storing incoming heat and returning it to the growing area when needed you have a defense against the cold and heat of your climate.
Our climate is also very extreme high desert, but I think our summers are not as hot as yours. Winters are good and cold though, similar to northern US with first frosts in Sept to Oct, and 6 weeks of pond hockey in the neighborhood.
I've become very fond of the removable seasonal greenhouses we use to heat our houses at the school I work at, and now at my own house. We use UV resistant polythene, and remove it in April or May, and attach it in October or November. I find it very very helpful to have doors or windows in the E and W ends of the greenhouse for the shoulder season, so I can close them at night and open them in the day to relieve overheating in the greenhouse during the shoulder season. But in our intense high desert sun, no amount of end ventilation would prevent overheating in summer in a greenhouse, and I love having it off and the garden exposed to the sky and air and weather for the summer.
A perfectly south facing wall with the main windows is best for the rooms to be kept warm in winter and cool in summer. Perfectly south facing walls get good penetration from the low sun in winter, and no penetration by the high sun in summer. A small overhang over the south-facing windows helps even more.. Every degree you go off of perfect south contributes to overheating in summer.
West windows are the worst for overheating, because when the house is already warm from the ambient heat of the day, it then gets blasted with the hot afternoon sun. East and north facing windows do receive a little sun in the summer so they also contribute to overheating a little, but not as bad as west facing windows. South facing windows with an overhang actually get no direct sun at all in the weeks around the summer solstice. Later in the summer, like August, I do get a bit of overheating as the sun comes down a little.
Works at a residential alternative high school in the Himalayas SECMOL.org . "Back home" is Cape Cod, E Coast USA.
I think the first question would be... What are your goals for a greenhouse? Year round growing, year round tropicals, season extension, seed starting...
I believe walipinis tie in well to the temperature of the surrounding earth. So if you like the temperature at your site 4' deep, you're heading in the right direction. If you want to keep it much warmer than that in the winter, you'll probably struggle unless you insulate it from the ground.
Do you have a south facing hill to build into? One possible challenge with walipinis at higher latitudes is the shade from the south wall when the sun is low in the sky. So if the walls are lower on the south side you could be better off. Another option is the Oehler greenhouse.
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