 |
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 .
|
