Student Group Tests Solar Greenhouse Energy Efficiency
P3 Research Project Search
In: Mountain Times
April 26, 2007
For the past eight months, students from Appalachian State University's Department of Technology have researched greenhouse technologies that have the potential to reduce the construction cost of energy-saving solar greenhouses, also known as bioshelters.
The Affordable Bioshelters Project is funded by a $10,000 EPA P3 grant and a $10,000 SARE (Sustainable Agriculture Research and Education) grant. The collaborative project is being led by Yonatan Strauch, a graduate student majoring in appropriate technology in the Department of Technology.
"Bioshelter is a term coined by people who pioneered solar greenhouse technology in the late 1970s," Strauch said. "The term connoted ecological management within a greenhouse. We wanted to associate ourselves with that philosophy, and apply it to the structure itself."
The student team has built two, 24-by-14-foot greenhouses on a test site located on Watauga River Farms in Valle Crucis. The property is owned by farmer Charles Church. Church has partnered with other university projects in the past, including an archeological dig along the Watauga River.
The group from Appalachian is one of 41 teams participating in an EPA competition for a $75,000 grant to continue their research. The competition will be held April 24-25 in Washington, D.C., on the National Mall.
Greenhouses typically have poor insulation values, with heating and cooling accounting for about 35 percent of production costs. Heating a 2,000-square-foot greenhouse can cost $5,000 a year in moderate to cold climates when the greenhouse is used all winter. "While greenhouses that utilize passive solar design can yield an 80 percent savings in energy costs, the cost of construction can take decades to reclaim," Strauch said.
Lower costs and better insulation methods mean the bioshelters could pay for themselves within five years.
According to faculty advisor Marie Hoepfl, "This project is taking the more economical hoop-style greenhouse and marrying it with passive solar design. In addition, it is designed to test two promising newer technologies: the use of soap foam insulation and the use of subsoil storage to moderate heating and cooling cycles within the greenhouse."
The team has gathered preliminary evidence that the liquid foam insulation method and the subsoil heat storage method can significantly reduce heat loss in greenhouses in an affordable manner. But there have been some drawbacks.
In one greenhouse, liquid soap foam was used at night to reduce heat loss and then transferred to storage tanks during the day. While it did result in a 14-degree difference in temperature at night, the liquid foam system was plagued by freezing temperatures and often failed to fill the cavities between the double polyurethane walls. The system also was difficult to automate.
By capturing heat stored in the earth's subsoil and piping the heat into the greenhouse, air and soil temperatures were raised by several degrees resulting in more than doubling of plant growth, the students found.
The subsoil system was easy to install and simple to operate. It is estimated the subsoil heat system would pay for itself in two to four years based on the value of the energy it stores and releases.
In addition to the ongoing research at the existing test site, proposed future research will examine ways to improve cavity design, as well as foam mixture and foam generating devices for the liquid foam insulation. It will examine the effectiveness of a subsoil heat system combined with argon insulation. In addition, th3e benefits of capturing exhaust heat from composting will be studied.
This will be done by retrofitting a greenhouse at Lily Patch Farms, a local organic farm, and comparing it to the traditional greenhouses operated there.
The group's research results will be shared via a Web site and through a workshop that focuses on evaluating the pay-back period of various greenhouse energy technologies.
"Successful bioshelter designs can economically extend the greenhouse growing season, benefiting farmers and increasing local food production," Strauch said. "These designs can be used by traditional greenhouse growers, organic growers, or anyone looking for a low cost conditioned agricultural enclosure."