Yonatan Strauch, foreground,
and Stony Oswald are part of a team of Appalachian
State University students studying ways to reduce
energy consumption in greenhouses. They will present
their findings as part of an EPA-sponsored competition
in Washington, D.C. Appalachian photo by
University Photographer Mike Rominger
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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.” |
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