The solar greenhouse that’s right for you

% of readers think this story is Fact. Add your two cents.

Dave MacKinnon’s solar greenhouse greatly expands
his crops of homegrown food. He picks salads every
day through winter. Frost nips his outside garden early,
so greenhouse protection has meant the first
heavy-producing tomato plants he’s ever grown

A few inches of most common insulators match the R-value of ten to 15 feet of earth. But earth is a good heat-storing material, lying somewhere between rock and water. So insulating around the perimeter builds heat storage into the structure while stopping steady heat losses to the ground outside. We checked the advantage of doing this at the Maxa-tawny site. Six inches below the surface, the insulated soil was in the 40′s in January and in the 50′s in February, while the ground outside was frozen solid several feet deep.

The day comes when shuttering the glass or plastic face becomes practical despite the inconvenience of twice daily attention. Past a certain point, there’s no easier way to gain a few degrees inside. The south-facing glass loses a tremendous amount of heat compared to the other three-fourths of the building’s surface that is insulated. To add enough storage material to make up for what shutters can save would take too much room away from the plants.

We’ve found that a good nighttime heat barrier for the window doesn’t have to be a great insulator, but it must be durable and easy to maneuver, since it will get heavy use. More important, the material should be reflective on the inside and fitted tightly at the edges to stop air flow. A reflective material (aluminum paint or foil) will block all escaping radiant energy. Combined with an airtight seal, that seems to do plenty for me greenhouse. Beyond that, any insulating value you can build into the curtain is so much the better.

It pays to insulate the earth below the greenhouse because earth is a relatively poor insulator, contrary to a lot of lore.

A few inches of most common insulators match the R-value of ten to 15 feet of earth. But earth is a good heat-storing material, lying somewhere between rock and water. So insulating around the perimeter builds heat storage into the structure while stopping steady heat losses to the ground outside. We checked the advantage of doing this at the Maxa-tawny site. Six inches below the surface, the insulated soil was in the 40′s in January and in the 50′s in February, while the ground outside was frozen solid several feet deep.

The day comes when shuttering the glass or plastic face becomes practical despite the inconvenience of twice daily attention. Past a certain point, there’s no easier way to gain a few degrees inside. The south-facing glass loses a tremendous amount of heat compared to the other three-fourths of the building’s surface that is insulated. To add enough storage material to make up for what shutters can save would take too much room away from the plants.

We’ve found that a good nighttime heat barrier for the window doesn’t have to be a great insulator, but it must be durable and easy to maneuver, since it will get heavy use. More important, the material should be reflective on the inside and fitted tightly at the edges to stop air flow. A reflective material (aluminum paint or foil) will block all escaping radiant energy. Combined with an airtight seal, that seems to do plenty for me greenhouse. Beyond that, any insulating value you can build into the curtain is so much the better.

Without a doubt, a thin, aluminized fabric which is operated by ropes or a pulley is the cheapest system to make and work with. The best one Dave MacKinnon tried was made of aluminum foil glued to one side of parachute fabric. That curtain lasted two years before needing repairs.

The third winter at Maxatawny we used a shutter system that could hardly be bettered for stopping heat. Panels of one-inch urethane foam, aluminized on one side, were held in place with wooden battens. We kept them in an air-lock entrance room that doubled for storing tools and gardening supplies. The only drawback to the foam is that it is expensive. Any exposed foam surfaces should be painted to waterproof the material against condensation that accumulates on the glazing.

Those are the basics of a solar greenhouse: the sun-catching design, strategically placed insulation, and heat storage. Together they make a cool-weather garden possible even in Northern states. In ours the air inside has averaged 42 degrees higher than outside and between 45 and 55 degrees F. in the soil throughout the winter. Many vegetables will thrive in that temperature range.

VEGETABLE GROWING IN THE SOLAR GREENHOUSE

There’s a lot to be learned about cool greenhouse vegetable culture. The most important trick we’ve discovered is using the right growing container. Traditional greenhouse wisdom recommends pots on waist-high benches — easy to reach and easy to isolate diseases and pests. But continuous temperature recordings in the soil pots showed that the temperature in the root zone changed right along with the air temperature, because the exposed surface of a pot is so large. There were large swings every day, extremes that plant roots aren’t used to. So we switched to two large beds 18 inches deep that cover the greenhouse floor. They held the root zone to a 10-degree daily change which is natural, and also made a greater heat-storing mass.

Beds have many other advantages. Roots have more room to forage for water and nutrients. The environment becomes a better one for natural predators like spiders. Because the soil in beds holds a large amount of organic matter, they also become an important source of carbon dioxide. Plants in a sunny, airtight greenhouse can use up all the available carbon dioxide in a few hours.

Nothing like these greenhouses is available for sale yet, but several years from now you will start to see them. The big greenhouse manufacturers are redesigning their products exactly along these lines. They will probably be expensive. But a home-built, sun-heated greenhouse like ours

can be constructed now for less than the finest energy-wasting glass house, and will be tailored to match your local climate.

In the far North, where solar greenhouses will be the most expensive to build, they will yield the greatest expansion of the gardening season. Even in southerly Flagstaff, Dave MacKin-non reports that his solar greenhouse has made possible his first really good tomato crops, so dry and short is the growing season there.

Properly made and maintained, a solar greenhouse should outlast its builder. The materials are all durable or renewable.

House-attached greenhouses are even cheaper to build. As you plan your solar greenhouse, you should think first of this kind for many reasons. Attached greenhouses have about a third less surface area for the same floor space as a freestanding one. Thus construction costs are lower, and less heat is lost at night. Attached solar greenhouses are the most efficient hot-air solar collectors known. High and low vents that open into the home through the common wall exchange solar-heated greenhouse air for cool air at floor level from the house. At night, the house can return some of the heat to the greenhouse. All the design principles for solar greenhouses apply to the attached greenhouse, except they may need less heat storage. The only requirement is a suitable spot facing south that is unshaded in winter.

Looking only at the money, it’s obvious that a durable solar greenhouse, attached or freestanding, will repay its cost. Compared to conventional all-glass models the fuel savings alone will pay for its construction in three to four years in the North. And they make you independent of an unhealthy agriculture and the transportation system it depends upon for fresh vegetables to tide you through winter. That’s why we recommend so strongly that you build one if you can.

Originally at : The Survivalist Blog.net · Copyright © 2013 · All Rights Reserved.

This article has been contributed by TheSurvivalistBlog.net. Visit www.thesurvivalistblog.net for alternative news, tips, commentary and preparedness info.

Source: