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The Practically Zero Energy Year Round Greenhouse

I realize the title is a mouthful, but here in Colorado this title could be mistaken for an oxymoron.  While exact information is not easily accessible you can ask any commercial greenhouse operator in Colorado what their winter energy bills are, then watch your jaw hit the floor.  The numbers are astronomical:  in the vicinity of $4.00 a square foot for winter use.  Comparatively, residential heating is an average of 10 cents / square foot. For many years Barrett Studio Architects has designed vertically glazed, highly insulated ‘growing spaces’ in our residential designs.  But not until we stumbled across the Greenhouse at Cure Organic Farm built by Synergistic Building Technologies had we discovered a group of engineers calculating and perfecting these systems to grow year round food in our Colorado climate.  Serendipitously, within the year of this fortunate discovery we have a Colorado mountain client interested in a greenhouse addition to their home; better yet, this client is ecstatic about the possibility of a ‘Zero’ energy greenhouse.  And thus we have just broke ground on our first practically zero energy year round greenhouse.

So whats in the title?

Great insulation in the foundation(r-15), walls(r-26) and roofs(r-45).

Operable insulated shutters over all vertical glazing and vent penetrations.  Courtesy of SBT, we are exploring bi-fold sliding and swinging shutters made with 2″ of polyisocyanurate set in a thin fiberglass frame for the various conditions in our design.

Adjustable light reflectors below all south facing glass, manually adjustable to three settings: winter solstice, spring and fall equinox, and summer solstice.

An air exchange system designed to take interior heat and moisture and dump it into the soil/planting beds, which are thermally broken from the outside temperature by the insulated foundation.  Consequently we’ve now stumbled across a number of these greenhouse air exchange systems that are evolved from the concept of geothermal heating and cooling.  They all have nifty names:  Climate Battery, GETS (greenhouse earth thermal storage), SHCS (subterranean heating and cooling system).  In essence they are used to stabilize year round indoor air temperatures and control the humidity levels of their respective greenhouses.  Our system, in a 530 sf greenhouse, will run on a single van axial fan from fantech (often used for radon mitigation) and 7 mains consisting of 4″ perforated drain pipe with sleeves diverging from a single plenum.  With a total of 300 linear feet, we’ll run 200′ eighteen inches under the earth floor and another 100′ in our raised beds.  Each main will have an exhaust at the end of a planting bed complete with welded wire mesh for rodent control.

Other important features include:

  • A 5000cfm louvered air change fan for much needed CO2, equipped with an insulated shutter to boost its R-value.
  • Upper and lower operable openings for natural ventilation.  Temperature, humidity, CO2 & light sensors wired to a computer for automated operation of the shutters and fans.
  • A 12 v dc, PV battery charge which will continue to operate even if the grid is down.  Zero, zilch, NO backup heating or cooling what-so-ever and yet an anticipated operation temperature at or above 55 degrees year round…totally awesome.

Stay tuned for updates: the foundation is in, backfilling & the greenhouse earth thermal storage should be finished around the beginning of the new year, and with a little luck we can be planting in March of 2012.

December 22, 2011 at 1:19 pm 3 comments


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