Solar Greenhouses for Back Yards and Neighborhoods

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Solar Greenhouses for Back Yards and Neighborhoods

• L. David Roper
• Professor Emeritus of Physics
• Virginia Polytechnic Inst. St. Univ.
• roperld_at_vt.edu
• http//arts.bev.net/RoperLDavid/
• This slide show is available on the Internet
• http//www.roperld.com/science/SolarGreenhouse.ppt
  

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Eat Local

• Average food is transported 1500 miles.
• Peak Oil This must stop!
• How to eat local food in the winter months?
• Preserve by canning or drying.
• Grow in solar greenhouses.

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Peak Oil
Oil discoveries will not allow higher average
extraction.
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You cant extract it if you have not discovered
it!
The areas under the two curves are the same
2x1012 barrels.
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Solar Greenhouse Principles

• Double-glazed long side roof facing south.
• North, east and west walls well insulated.
• North roof well insulated.
• Foundation well insulated.
• Sealed to prevent air infiltration.
• North wall and north roof reflective on inside.
• Heat storage to gather heat when Sun is shining
  to be released to greenhouse air when Sun is not
  shining.

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Standard SGH Heat Storage

• Water is the best medium.
• Rocks are second best.
• Soil is the third best.
• The big question is
• How does one get heat supplied by the Sun
  transferred to the storage medium?

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Heat Transfer from Sun To Storage

• Standard methods
• Direct radiation.
• Air flow, passive or active.
• Subterranean Heating and Cooling System (SHCS)
• Use phase change of water vapor to liquid to get
  large amount of energy stored under planting
  beds.
• An Integrated system with plant transpiration of
  water.
• Use small fan to blow hot moist air, or cold dry
  air, under the planting beds for energy exchange.

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Subterranean Heating and Cooling System (SHCS)

• When the Sun is shining, 90 of water taken up by
  plant roots is transpired (evaporated) into the
  air, which makes the greenhouse air hot and
  humid. Much of the photosynthesis energy provided
  by the Sun is used for this purpose.

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Subterranean Heating and Cooling System (SHCS)

• SHCS pushes that hot and humid greenhouse air
  into the rocks/soil under the planting beds where
  the water vapor condenses into liquid, releasing
  a huge amount of energy to be stored as heat
  energy in the water and rocks/soil there. The air
  emerges into the greenhouse cool and dry.

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Subterranean Heating and Cooling System (SHCS)

• When the Sun is not shining, SHCS pushes the cold
  and dry air of the greenhouse under the planting
  beds where it is heated and made humid. The air
  emerges warm and humid.

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Subterranean Heating and Cooling System (SHCS)

• Thus, an artificially moderate weather system
  that is beneficial for plant growth is created in
  the SGH, in cooperation with the plants
  transpiration.

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First SHCS (China 1990)

• Bricks made from local clay were used for the
  ducts under the planting beds and the main duct.
• Fan has two thermostats one turns fan on at 20
  C (68 F) and off at slightly above 15 C (59
  F) the other thermostat turns fan on at 10 C
  (50 F) and off at slightly below 15 C (59 F).

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USA Version of SHCS (Colorado)

• Use three layers of 4 perforated corrugated
  drain pipes 2 apart horizontally and 1 apart
  vertically below planting beds, surrounded by
  rocks and dirt that will hold maximum amount of
  water.
• Push the greenhouse air through the perforated
  pipes, entering from the east side and exiting on
  the west side.
• Using petroleum products to create the
  infrastructure to reduce the amount of petroleum
  burned, which is its best use.

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SHCS Design Criteria

• Flow greenhouse air volume underground 5 times
  per hour when fan is operating.
• Restrict flow in underground drain pipes to less
  than 4 ft/sec.
• Adjust thermostat 1 to turn fan on at 70 F and
  off at slightly above 60 F.
• Adjust thermostat 2 to turn fan on at 50 F and
  off at slightly below 60 F.
• Keeps greenhouse temperature between 50 F and
  70 F and air humidity in a middle range.

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Neighborhood Solar Greenhouse

• Area 576 ft2
• Volume 4750 ft3
• Glazing double-walled polycarbonate at 45
  slope
• North insulated 6-thick roof at 60 slope
• 6 insulated north wall with berm
• 2 termite-protected extruded polystyrene around
  foundation and heat storage

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Neighborhood Solar Greenhouse
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Neighborhood Solar Greenhouse
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Dave Nickerson Model of a Neighborhood SGH
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Back-Yard Solar Greenhouse

• Area 200 ft2
• Volume 1340 ft3
• Glazing double-walled polycarbonate at 50
  slope
• North insulated 6-thick roof at 60 slope
• 6 insulated north wall with berm
• 2 termite-protected extruded polystyrene around
  foundation and heat storage

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Back-Yard Solar Greenhouse
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Back-Yard Solar Greenhouse
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Cistern for Rain Water for Plants

• A 1500-gallon cistern for the SGHN and a
  500-gallon cistern for the SGHBY to collect
  rainfall on the roof, placed underground for
  gravity flow from roof and to keep water at
  proper temperature for plants.
• A hand pump or electric pump to lift the water.
• A drip irrigation system to conserve water and to
  minimize overwatering.
• An overflow directed far away from the SGH.

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Easy Composting

• Fill one while the other is composting.
• Low sled makes it easy to empty and transport.

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Carbon Dioxide and Composting from Worms in the
SGH

• Red-worm beds over the 24 pipes at the ends of
  the SGH sufficient to supply carbon dioxide and
  compost for the plants.
• Fed by partially-composted organic matter brought
  into the SGH.
• The worm-castings finished compost is regularly
  deposited on the growing beds for plants.
• Provides a closed cycle between the oxygen
  expelled by the plants and the carbon dioxide
  expelled by the worms. The fuel is the
  partially-composted organic matter regularly
  brought into the SGH.

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Natural Pest Control

• Garlic, onions, mints, chives herbs scattered
  plantings
• Lizards (also supply carbon dioxide)
• Toads (also supply carbon dioxide)
• Lady Bugs
• Praying Mantises

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Proposed Network of Solar Greenhouses for the NRV

• Build a test neighborhood SGH using SHCS
  somewhere in NRV.
• Build a test back-yard SGH using SHCS somewhere
  in NRV.
• Collect data for a year.
• Build more SGHN and SGHBY in the NRV.

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VT YMCA Community Gardens
First location of a neighborhood solar greenhouse
in NRV. Construction completion scheduled for 1
October 2008. First plantings scheduled for
1 November 2008.
Maywood Street
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SGH at YMCA Community Gardens
Maywood Street
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Thanks so far!

• Gail Billingsly (YMCA)
• Pat Bixler (Steering Committee Chair)
• Tim Colley (Architect)
• Dave Nickerson (Model Builder)
• Travis Rookstool (Architecture Student)

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Volunteers Needed!

• Excavator
• (Insulated Concrete Forms)-experienced person
• Carpenters
• Plumber for cistern installation and watering
  system
• Electrician
• Solar greenhouse manager
• Horticultural researcher

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Want More Information about the SGH Project for
the NRV?

• Give your e-mail to
• Dave Roper (roperld_at_vt.edu)
• to be put on a SGH interest-group list.
• Send ideas about the SGH project to Dave Roper.
• This slide show is available on the Internet
• http//www.roperld.com/science/SolarGreenhouse.ppt