Efficient Greenhouse Design
Although elements of this idea could be implemented on a commercial scale, it is intended for those who only use their greenhouses during the winter months when decreased available sunlight light and heat loss are two of the most pressing concerns.
The first thing I want to do is ask the question: Why are nearly all greenhouses built with glazing on all four sides?
Since sunlight can only strike any object from three sides (East, South, and West) . . . why have your North side built with glazing which offers inferior insulating abilities, and generally is far more expensive than alternative materials which could provide far superior insulating value?
I would build my greenhouse into a South facing hill, or pile up bags of leaves against the North side. You could design it in such a way as to allow you to store wood chips or compost on this side as well. Of course you could simply build a conventional wall and use conventional insulation.
The next place that I would eliminate the more expensive glazing is on the first 3 to 4 feet above the ground. You are going to want to have your growing area located at this height, so you won't need sunlight to hit below that level. Once again, It would be to your advantage to build up the insulative value of this area as well using one of the methods listed above.
We don't want to waste any space, so use the underside of your beds for storing supplies or growing mushrooms.
Although there are reasons to stay with the typical arched design, there are other benefits that would come from switching to a flat angled surface. I would have glazing extend upward from the knee wall an additional 1 to 2 feet. Then I would angle the glazing straight back and upward to whatever height you have chosen. Just be sure that you leave room to walk down a middle isle (or along the north side if small) without having to duck your head.
Now here comes the good part. It is not cheap, but will certainly pay for itself in increased production and lower heating costs.
Build a cover for your greenhouse that has a mirrored surface on the face.
Attach and hinge it in such a way that it can be lowered at night and raised in the morning. Design it in such a way that it is well insulated and that the mirrored surface will not rest flush against your glazing but rather have an additional insulating dead air space. (It should seat snug at the perimeter though).
Here is what happens: During the day, the cover will be raised up to capture and reflect additional sunlight down into your greenhouse. Adjusting the angle will allow you to vary the amount of light you add according to the outside temperature and time of year.
As the sun goes down, you would lower the cover down where it would rest upon (but only touching at the perimeters) the glazed surface. This will give you an excellent thermal blanket at night to help hold in your heat.
During the day, you will be able to almost double the amount of sunlight that enters your "house".
At night, you may be able to get by on the heat that was absorbed during the day ( I will write another article to cover ways to do this better).
This is the general idea . . . now take it and modify it to meet your own personal needs and circumstances.
