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Solar Greenhouses for Back Yards and Neighborhoods

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  1. Solar Greenhouses for Back Yards and Neighborhoods L. David Roper Professor Emeritus of Physics Virginia Polytechnic Inst. & St. Univ. roperld@vt.edu http://arts.bev.net/RoperLDavid/ This slide show is available on the Internet: http://www.roperld.com/science/SolarGreenhouse.ppt

  2. 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.

  3. Peak Oil Oil discoveries will not allow higher average extraction.

  4. You can’t extract it if you have not discovered it! The areas under the two curves are the same: ~2x1012 barrels.

  5. 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.

  6. 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?

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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).

  13. 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.

  14. 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.

  15. Neighborhood Solar Greenhouse • Area = 576 ft^2 • Volume = 4750 ft^3 • 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

  16. Neighborhood Solar Greenhouse

  17. Neighborhood Solar Greenhouse

  18. Dave Nickerson Model of a Neighborhood SGH

  19. Back-Yard Solar Greenhouse • Area = 200 ft^2 • Volume = 1340 ft^3 • 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

  20. Back-Yard Solar Greenhouse

  21. Back-Yard Solar Greenhouse

  22. 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.

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

  24. 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.

  25. Natural Pest Control • Garlic, onions, mints, chives & herbs scattered plantings • Lizards (also supply carbon dioxide) • Toads (also supply carbon dioxide) • Lady Bugs • Praying Mantises

  26. 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.

  27. 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

  28. SGH at YMCA Community Gardens Maywood Street

  29. Thanks so far! Gail Billingsly (YMCA) Pat Bixler (Steering Committee Chair) Tim Colley (Architect) Dave Nickerson (Model Builder) Travis Rookstool (Architecture Student)

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

  31. Want More Information about the SGH Project for the NRV? Give your e-mail to Dave Roper (roperld@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