Passive Solar Greenhouses Materials

Need to Know

  • Size-ratio of 2:1:1
    • Length, Width, Height
    • 24 ft x 12 ft x 12 ft
  • Slope
    • Latitude plus 10° (Central Missouri:
38.9 + 10= 49°)

Heat Source

  • Black 55 gallon barrels filled with water.
  • Rule of Thumb: 2.5 gallons/ft² of glazing for season extension or 5 gallons/ft² for all season.
  • How much do we need then?
    • 12 ft x 24 ft = 288 ft²
    • 288 x 2.5 = 720 gallons
    • 288 x 5 = 1440 gallons
    • We have 20 x 55 = 1100 gallons

BTUs Released

  • 1100 gallons of water weighs 9,130 lbs.
  • For each degree of drop at night, 9,130 BTUs are released.
    • At the Southwest Center, approximately 8 to 9 degree change is occuring so there would be 73,000 – 82,000 BTUs released. Temperature Over Time

Heat Saving Ideas

  • Double layer of plastic glazing
  • 6 mil four-year-plastic
    • Should add about 10 degrees to the inside on a cold day.
  • 60 cfm squirrel cage fan – outside air!
  • Walls and Insulation
    • 6-inch walls
    • Wrapped in plastic
    • R19 insulation
  • Interior Wall Material
    • Needs to be reflective.
    • Bathroom material that is glazed on the outside.

Keeping It Cool

  • Exhaust fan
    • Rule of Thumb for CFM required – ft2 x peak height or 24 x 12 x 12 = 3,456 cfm.
    • Standard sizes are sold. (Bradford’s is 3,200 cfm.)
    • Also need an inlet shutter that matches the exhaust fan. (Bradford’s is a 3,000 cfm, 27-inch fan.)

Fan Control

  • Set temperature when exhaust fan comes on.
  • Be careful not to keep it too cool.

Additional Ideas

  • South wall plastic being able to be rolled up and down.
    • Allow for cooling in the warmer weather.
    • Can be raised or lowered each day.
    • Sealed down during the winter.
  • Roll up side
    • Allows for year around use.
    • Sun does not directly shine into the greenhouse therefore it stays within reason in the summer with the roll up side.
    • 
Building a Passive Solar Greenhouse
      • The first thing to do was to lay out the foundation. We used 4 x 6 inch treated lumber setting on two foot concrete piers at the corners and in the middle of each post. Each post was wrapped in plastic.
      • Two x six walls were used throughout.
      • The entire greenhouse was wrapped in plastic.
      • 6-inch insulation was used in the walls.
      • Cutting the right angles was extremely important.
      • Metal siding was applied to the outside.

Cost

  • Lumber, fasteners, hardware, door, insulation, etc. – $1,619
  • Exhaust fan, shutter, thermostat, plastic, etc. – $786
  • Concrete – $190
  • Electric – $490
  • Water – $190
  • Total – $3,275