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Passive solar greenhouse is an elegant solution to extend your growing season

When it comes to extending our growing season (and we all know it could use a little extending here in Cochrane!), a greenhouse is considered the holy grail.
urban-greenhouse

When it comes to extending our growing season (and we all know it could use a little extending here in Cochrane!), a greenhouse is considered the holy grail. The problem with classic “glasshouse” designs is that they tend to overheat easily in the summer while losing all that heat rapidly once the sun goes down. In the shoulder and winter seasons these greenhouses need expensive and energy-intensive supplemental heat to maintain growing temperatures, and that heat passes quickly through their low R-value glass or plastic shells. Conversely, in the summer a lot of energy is spent cooling them.

This is why passive solar greenhouse design is an elegant solution for Alberta’s climate where we get plenty of sunshine to “harvest” heat, yet cool nights and a long season of cold where that heat would otherwise be quickly lost if not stored. Passive solar is a way of designing a building so that its heat regulation is largely done using the immense free and perpetual energy of the sun. No "active" systems (eg. photovoltaics) that require energy in manufacture and maintenance are required - just smart design and choice of materials. No matter what happens with the price or availability of conventional energy sources, the passive solar system will carry on functioning.

Orientation, insulation and thermal mass are some of the key elements used when building a passive solar greenhouse. The long side of the greenhouse should face south or southeast so as to collect maximum solar energy without being subject to the overly hot, late day sun from the west. This south face can be angled steeply enough so the full force of the high summer sun doesn’t cook the plants, while the lower shoulder season or even winter sun is able to hit it full-on. The south side of the greenhouse is glazed (finished with translucent material) while all or most of the rest of the building is well-insulated instead. Ideally the greenhouse perimeter is also insulated down to the frost line so heat from the building is stored in the ground below it. Materials with high thermal mass such as water, stone or concrete are incorporated as a way of absorbing excess solar heat and releasing it slowly as the greenhouse air temperature cools.

Part of what’s so brilliant about a greenhouse designed this way is that it can easily become a three or even four-season space to comfortably read, enjoy a glass of wine or mug of coffee, stretch, nap...you get the idea! It becomes a place that not only feeds us well beyond our short summer, but that nourishes us with a dose of sunny, plant-filled warmth.

Jackie Skrypnek is the President of Cultivate Cochrane. Cultivate Cochrane is planning a passive solar community greenhouse hub as a solutions-based centre for learning and connecting around food. Visit cultivatecochrane.com

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