Greenhouse Canada

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Solar thermal greenhouse prototype for cold climates

December 3, 2012  By Brandi Cowen

Greenhouse 365's first prototype has proven effective up to -34˚C. (Courtesy Greenhouse 365.)

A prototype solar thermal greenhouse could allow growers in cold climates to harness the power of the sun to produce fresh produce year-round.

The GH365 prototype, designed by Leo Hunnakko, doesn’t look like your typical greenhouse, thanks to a unique design that allows Hunnakko to grow lettuce, tomatoes, asparagus year-round in Thunder Bay, Ont. His prototype greenhouse, located in zone 2A, has been proven effective in nighttime temperatures up to -34˚C.



Two four foot by eight foot solar collectors on the roof of the greenhouse capture the sun’s energy. When solar and water temperatures reach optimum levels, a heated glycol and distilled water mixture flows through a heat exchange unit. This unit is connected to a 60 gallon solar thermal hot water tank with electric back-up.


“The greenhouse incorporates a massive heat retention cavity that comprises the north wall which is filled with sand kept warm by solar heated water that flows through heat resistant tubing imbedded throughout,” explains Hunnakko, founder of Greenhouse 365. “This same heated tubing is used to warm the root zones on the planter tables as well as for radiant floor heating. The 1.5-inch thick dual pane, argon filled, high heat retention south glazing is positioned at an optimum 36˚ angle to maximize passive solar impact.


At 22 feet by 18 feet, the amount of growing space offered by the first generation prototype is small. The Generation Two version can be scaled up to suit various user requirements.


Hunnakko said the GH365 could extend the growing season and reduce the cost of fresh vegetables in cold climates, improve food security in remote areas and offer a greener solution with minimal electrical consumption.

For more, contact Delia, east coast director or Iron and Earth at 

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