Solar Greenhouses for Back Solar Greenhouses for Back Yards and NeighborhoodsYards and Neighborhoods

L. David RoperL. David RoperProfessor Emeritus of PhysicsProfessor Emeritus of Physics

Virginia Polytechnic Inst. & St. UnivVirginia Polytechnic Inst. & St. Univ..roperld@vt.eduroperld@vt.edu

http://arts.bev.net/RoperLDavid/http://arts.bev.net/RoperLDavid/

This slide show is available on the Internet:This slide show is available on the Internet:

http://www.roperld.com/science/SolarGreenhouse.ppthttp://www.roperld.com/science/SolarGreenhouse.ppt

Eat LocalEat Local

Average food is transported Average food is transported ~1500 miles.~1500 miles.

Peak Oil: This must stop!Peak Oil: This must stop! How to eat local food in the How to eat local food in the

winter months?winter months?Preserve by canning or drying.Preserve by canning or drying.Grow in solar greenhouses.Grow in solar greenhouses.

Peak Oil Oil discoveries will not allow higher average extraction.

You can’t extract it if you have not You can’t extract it if you have not discovered it!discovered it!

The areas under the two curves are the same: ~2x1012 barrels.

Solar Greenhouse PrinciplesSolar Greenhouse Principles Double-glazed long side roof facing south.Double-glazed long side roof facing south. North, east and west walls well insulated.North, east and west walls well insulated. North roof well insulated.North roof well insulated. Foundation well insulated.Foundation well insulated. Sealed to prevent air infiltration.Sealed to prevent air infiltration. North wall and north roof reflective on inside.North wall and north roof reflective on inside. Heat storage to gather heat when Sun is Heat storage to gather heat when Sun is

shining to be released to greenhouse air when shining to be released to greenhouse air when Sun is not shining.Sun is not shining.

Standard SGH Heat StorageStandard SGH Heat Storage Water is the best medium.Water is the best medium. Rocks are second best.Rocks are second best. Soil is the third best.Soil is the third best. The big question is:The big question is:

How does one get heat supplied by How does one get heat supplied by the Sun transferred to the storage the Sun transferred to the storage medium?medium?

Heat Transfer from Sun To StorageHeat Transfer from Sun To Storage Standard methods:Standard methods:

Direct radiation.Direct radiation. Air flow, passive or active.Air flow, passive or active.

Subterranean Heating and Cooling System Subterranean Heating and Cooling System (SHCS):(SHCS): Use Use phase change of water vapor to liquidphase change of water vapor to liquid to get to get

large amount of large amount of energy stored under planting bedsenergy stored under planting beds.. An Integrated system with plant transpiration of water.An Integrated system with plant transpiration of water. Use small fan to blow hot moist air, or cold dry air, Use small fan to blow hot moist air, or cold dry air,

under the planting beds for energy exchange.under the planting beds for energy exchange.

Subterranean Heating and Cooling Subterranean Heating and Cooling System (SHCS)System (SHCS)

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

Subterranean Heating and Cooling Subterranean Heating and Cooling System (SHCS)System (SHCS)

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

Subterranean Heating and Cooling Subterranean Heating and Cooling System (SHCS)System (SHCS)

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

Subterranean Heating and Cooling Subterranean Heating and Cooling System (SHCS)System (SHCS)

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

First SHCS (China 1990)First SHCS (China 1990)

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

USA Version of SHCS (Colorado)USA Version of SHCS (Colorado) Use three layers of 4” perforated corrugated Use three layers of 4” perforated corrugated

drain pipes 2’ apart horizontally and 1’ apart drain pipes 2’ apart horizontally and 1’ apart vertically below planting beds, surrounded by vertically below planting beds, surrounded by rocks and dirt that will hold maximum amount rocks and dirt that will hold maximum amount of water.of water.

Push the greenhouse air through the perforated Push the greenhouse air through the perforated pipes, entering from the east side and exiting pipes, entering from the east side and exiting on the west side.on the west side.

Using petroleum products to create the Using petroleum products to create the infrastructure to reduce the amount of infrastructure to reduce the amount of petroleum burned, which is its best use.petroleum burned, which is its best use.

SHCS Design CriteriaSHCS Design Criteria Flow greenhouse air volume underground 5 Flow greenhouse air volume underground 5

times per hour when fan is operating.times per hour when fan is operating. Restrict flow in underground drain pipes to Restrict flow in underground drain pipes to

less than 4 ft/sec.less than 4 ft/sec. Adjust thermostat #1 to turn fan on at 70° F Adjust thermostat #1 to turn fan on at 70° F

and off at slightly above 60° F.and off at slightly above 60° F. Adjust thermostat #2 to turn fan on at 50° F Adjust thermostat #2 to turn fan on at 50° F

and off at slightly below 60° F.and off at slightly below 60° F. Keeps greenhouse temperature between 50° Keeps greenhouse temperature between 50°

F and 70° F and air humidity in a middle F and 70° F and air humidity in a middle range.range.

Neighborhood Solar GreenhouseNeighborhood 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

Neighborhood Solar GreenhouseNeighborhood Solar Greenhouse

Neighborhood Solar GreenhouseNeighborhood Solar Greenhouse

Dave Nickerson Model of a Dave Nickerson Model of a Neighborhood SGHNeighborhood SGH

Back-Yard Solar GreenhouseBack-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

Back-Yard Solar GreenhouseBack-Yard Solar Greenhouse

Back-Yard Solar GreenhouseBack-Yard Solar Greenhouse

Cistern for Rain Water for PlantsCistern for Rain Water for Plants

A 1500-gallon cistern for the SGHN and a 500-A 1500-gallon cistern for the SGHN and a 500-gallon cistern for the SGHBY to collect rainfall gallon cistern for the SGHBY to collect rainfall on the roof, placed underground for gravity on the roof, placed underground for gravity flow from roof and to keep water at proper flow from roof and to keep water at proper temperature for plants.temperature for plants.

A hand pump or electric pump to lift the water.A hand pump or electric pump to lift the water. A drip irrigation system to conserve water and A drip irrigation system to conserve water and

to minimize overwatering.to minimize overwatering. An overflow directed far away from the SGH.An overflow directed far away from the SGH.

Easy CompostingEasy Composting

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

Carbon Dioxide and Composting from Carbon Dioxide and Composting from Worms in the SGHWorms in the SGH

Red-worm beds over the 24” pipes at the ends of the Red-worm beds over the 24” pipes at the ends of the SGH sufficient to supply carbon dioxide and compost SGH sufficient to supply carbon dioxide and compost for the plants.for the plants.

Fed by partially-composted organic matter brought Fed by partially-composted organic matter brought into the SGH.into the SGH.

The worm-castings finished compost is regularly The worm-castings finished compost is regularly deposited on the growing beds for plants.deposited on the growing beds for plants.

Provides a closed cycle between the oxygen expelled Provides a closed cycle between the oxygen expelled by the plants and the carbon dioxide expelled by the by the plants and the carbon dioxide expelled by the worms. The fuel is the partially-composted organic worms. The fuel is the partially-composted organic matter regularly brought into the SGH.matter regularly brought into the SGH.

Natural Pest ControlNatural Pest Control

Garlic, onions, mints, chives & herbs Garlic, onions, mints, chives & herbs scattered plantingsscattered plantings

Lizards (also supply carbon dioxide)Lizards (also supply carbon dioxide) Toads (also supply carbon dioxide)Toads (also supply carbon dioxide) Lady BugsLady Bugs Praying MantisesPraying Mantises

Proposed Network of Solar Proposed Network of Solar Greenhouses for the NRVGreenhouses for the NRV

Build a test neighborhood SGH using Build a test neighborhood SGH using SHCS somewhere in NRV.SHCS somewhere in NRV.

Build a test back-yard SGH using SHCS Build a test back-yard SGH using SHCS somewhere in NRV.somewhere in NRV.

Collect data for a year.Collect data for a year. Build more SGHN and SGHBY in the Build more SGHN and SGHBY in the

NRV.NRV.

VT YMCA Community GardensVT 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

SGH at YMCA Community GardensSGH at YMCA Community Gardens

Maywood Street

Thanks so far!Thanks so far!

Gail Billingsly (YMCA)Gail Billingsly (YMCA)

Pat Bixler (Steering Committee Chair)Pat Bixler (Steering Committee Chair)

Tim Colley (Architect)Tim Colley (Architect)

Dave Nickerson (Model Builder)Dave Nickerson (Model Builder)

Travis Rookstool (Architecture Student)Travis Rookstool (Architecture Student)

Volunteers Needed!Volunteers Needed!

ExcavatorExcavator (Insulated Concrete Forms)-experienced person(Insulated Concrete Forms)-experienced person CarpentersCarpenters Plumber for cistern installation and watering systemPlumber for cistern installation and watering system ElectricianElectrician Solar greenhouse managerSolar greenhouse manager Horticultural researcherHorticultural researcher

Want More Information about the Want More Information about the SGH Project for the NRV?SGH Project for the NRV?

Give your e-mail toGive your e-mail to

Dave Roper (roperld@vt.edu)Dave Roper (roperld@vt.edu)

to be put on a SGH interest-group list.to be put on a SGH interest-group list.

Send ideas about the SGH project to Send ideas about the SGH project to Dave Roper.Dave Roper.

This slide show is available on the Internet:This slide show is available on the Internet:http://www.roperld.com/science/SolarGreenhouse.ppthttp://www.roperld.com/science/SolarGreenhouse.ppt