DR. Don's Research Updates
November 8, 2002: Innovative greenhouse design for vegetable production all winter in Canada.

By Don Lotter, Ph.D., post-doctoral researcher, Rodale Institute

Editor's NOTE

In addition to analyzing data from our research trials and developing new domestic and international research initiatives, Don reviews dozens of research studies each week. He'll present the most interesting of his findings every week on the web site.

Organic produce that is fresh, local, and supplied year-round is one of the most sought-after goals for many of us. In northern climes during winter, especially in eastern North America, our only sources of fresh produce have often traveled 3,000 miles by the time we buy them. Only by the use of greenhouses can northerners gain control of their winter produce supply. The problem is that winter greenhouses use large amounts of fossil fuels for heating. Elliot Coleman in Maine made major advances by developing greenhouse growing methods for winter that were adapted to cool and cold greenhouse air temperatures.

Now there is a greenhouse design out of Canada that, using solar energy, raises the inside air temperatures of their winter greenhouses substantially by using soap bubbles to insulate the walls to an insulation rating of up to R-30. A bubble generator, the inexpensive type made for parties, blows bubbles between opaque plastic greenhouse walls, giving the insulating properties. Sensors are used to determine when the bubble generator should make bubbles and when they should be allowed to dissipate.

During the day, when there is sun, the bubble generators are turned off and the greenhouse heats up by passive solar radiation. When the temperatures fall past a certain threshold related to the indoor air temperature, the bubble generators are turned on. Water at the base of the greenhouse is used to collect the sun’s energy during the day for heat release at night. Computer simulations show that even in Canada (Ontario) solar energy alone can keep the greenhouse temperature above 55°F, even on the coldest nights of the year.

This type of innovation could go a long way towards reducing northerners’ over-reliance on transported produce during winter. The inventors and developers of the bubble greenhouse, Richard Nelson, Ross Elliott, and Kat Elliott, out of McDonalds Corners, Ontario, have a website with diagrams and pictures at www.solaroofgarden.com.

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