L. David Roper
10 AM 15 October 2009
During the first "oil energy crisis" in the early 1970s solar greenhouses were built across the United States to enable growing food in the winter time. Many of them are still in existence. A "Bible" about building and using solar greenhouses, The Solar Greenhouse Book, was published. I lived in the country outside Blacksburg where I considered building a solar greenhouse, but didn't.
At the advent of the current long-term energy crisis I studied building a solar greenhouse again. The Solar-Greenhouse Bible still applied, except that new techniques had been developed for storing energy, starting in China in 1990 with crude building materials and further developed with modern materials in the mountains of Colorado and cold Canada. This new approach for solar greenhouses is called the Subterranean Heating and Cooling System. So, with the help of the Solar-Greenhouse Bible and the Internet I roughly designed a large neighborhood solar greenhouse with this new approach, similar to the one you see here. I also designed a small backyard solar greenhouse, which I hope someone will build some day.
In the middle of 2007 I began telling friends and anyone who would listen about the designs. Luckily one day I told Gail Billingsley that I was looking for a place to build a neighborhood solar greenhouse. She immediately suggested that it be built in the upcoming Hale-YMCA Community Gardens. And my friend, Pat Bixler, agreed to help raise the funds to build it!
I asked my friend, Tim Colley, if his architectural firm, Colley Architects PC, would do the architectural work and he enthusiastically agreed!Pat arranged for the Green Valley Builders company of Jason & Justin Boyle to manage the construction. Those two amazing gentlemen arranged for many skilled people to help build the solar greenhouse, many of whom donated materials and/or labor.
Another friend, Dave Nickerson, with my minimal help, built a model of the proposed YMCA Solar Greenhouse, which was very useful in explaining how the Subterranean Heating and Cooling System works. You can see it at the Y Center.
A YMCA Solar-Greenhouse Steering Committee was formed to guide the construction. It consisted of Tim Colley, Pat Bixler, Jason Boyle, Justin Boyle, Arlean Lambert, Gail Billingsley and me.
A building permit was issued by the Town of Blacksburg on 28 July 2008 and excavation commenced on 23 October 2008. There was an official groundbreaking ceremony on 5 November 2008.
We had much fun working during the winter months building the structure, especially installing the Insulated Concrete Forms on 15 November 2008, building the heat sink on 5 December 2008, putting up the rafters on 9 January 2009 and installing the 20-feet-long 10-mm-thick double-walled polycarbonate sheets on 14 February!
I wish to express my sincere gratitude to all those many people who helped make this solar greenhouse possible, especially to my wife Jeanne Roper, a dedicated Master Gardener, to Arlean Lambert for making it possible to build it on this land; to Gail Billingsley and Abi Convery of the YMCA of Virginia Tech and to dozens of volunteers for enthusiastically supporting and shepherding this project.
This project is an example of what a community can accomplish when it works together.
Now let's grow some veggies!
Many people think that any greenhouse is a solar greenhouse, which is not correct. Regular greenhouses have the long axis running north-south with both sides glazed and usually do not have a heat sink. Solar greenhouses have the long axis running east-west with only the south side glazed; the north side is heavily insulated as are the end walls. They are built tight against air infiltration and have a massive heat sink.
Solar greenhouses are only used in the winter months to grow green vegetables; they bake in the summer months. They can be used with nearby outside gardens to transfer plants during the spring and autumn months; the YMCA Community Gardens is an ideal symbiotic place for a solar greenhouse.
In the 1970s the heat sink was either black barrels of water or large rocks along the north wall, water being the best choice. The new Subterranean Heating and Cooling System consists of three feet of small rocks under the planting bed with three layers of 26 perforated 4-inch drain pipes running west to east. When the air in the greenhouse is hot and humid (above 70 degrees) a fan turns on to pump the air into the heat sink at the west end through the 26 pipes, where heat is transferred to the rocks and water condenses to be stored and release its heat of condensation. When the air in the greenhouse is cool and dry (below 50 degrees) the fan turns on again to pump air into the heat sink to take up the heat and moisture and emerge on the east end warm and humid.
There are vent windows high on the east and west ends that automatically open at about 75 degrees to let cooler outside air in. A fan at the west window comes on at about 80 degrees to pull the outside cooler air into the greenhouse.
There are many features of this solar greenhouse to help it keep its energy, two of which are:
The walls are painted white to reflect light to all sides of the plants.
Plants like moving air, which movement is supplied by the air coming out of the heat sink and by ceiling fans.
Extensive instrumentation will measure air and soil temperatures, relative humidity, light intensity, carbon-dioxide concentration and energy stored in the heat sink. Professor Naraine Persaud of Virginia Tech was very helpful in deciding how to do the instrumentation.
This winter of 2009-10 half of the solar greenhouse will be used as an educational project for the middle-school students of Blacksburg New School. The other half will be used by a group of experienced gardeners, headed by John Ogburn, to experiment with what will grow best in a solar greenhouse in our climate. Most solar greenhouses grow leafy greens.
There is an extensive web page that fully documents the features and construction of this solar greenhouse (http://www.roperld.com/science/YMCASolarGreenhouse.htm).
roperld@vt.edu http://www.roperld.com/personal/roperldavid.htm