Sustainable Low-Cost Heating for Season Extension Structures
Clinch Appalachian Farmers Enterprise (CAFÉ) is a member-run organization of 20 farmers growing
mainly for public school and restaurant markets. In 2007-2009 CAFÉ conducted trainings and research
to explore low-cost ways of heating passive solar hoophouses and high tunnels, or at least reducing heating
costs. Persons who had conducted practical research in a variety of methods of heating hoophouses
through composting, geothermal systems, heat sinks, and the use of low tunnels within high tunnels were brought in to
conduct workshops in November 2007 and January 2009. Subsequently 5 CAFÉ members trialed several methods by
using digital recorders to record temperature and relative humidity in and outside the hoophouses, and with and without
the heating method. From their own experience and that of others they conclude:

Composting: While composting contributed some heat to the hoophouse, CAFÉ found that though
interior heat should have begun within the compost pile after 7 days, no significant rise in temperature
was noted. The main conclusion is that heating through composting would require a very large
compost pile, which would take up most of the available space for growing; therefore, compost is not
a practical means of sustainable low-cost heating.

Geothermal: Appalachian Native Plants in Mountain City, Tennessee, reported that their double-walled greenhouse with
an extensive and expensive geothermal system is about 10 degrees warmer than the outside air during the coldest night.
But Alison and Paul Wiediger and others report that a well-built double-walled hoophouse keeps the air inside about 8 degrees
warmer, so CAFÉ concludes that the contribution of the geothermal system is only about 2-3 degrees, and therefore
not worth the expense and effort represented by a geothermal system.

Heat Sink: Yonatan Strauch from Appalachian State University in Boone reports that literature on a variety of methods of
using heat sinks in hoophouses shows that the area necessary for sufficient heat sink material significantly decreases the
growing area in a hoophouse used for growing out of the ground, and therefore not worth the expense and effort represented
by setting up a heat sink system.

Insulating the North Side of the Hoophouse: After insulating the north side of a greenhouse with
bales of leaves, CAFÉ found that before the leaves were placed, the interior of the greenhouse was
actually an average of 3.16 degrees (F) warmer than outside temperatures, while after the bales of
leaves were stacked, to a height of 4 feet along the north wall and north-west corner of the greenhouse,
the average interior temperature was only 2.5 degrees warmer inside than outside. Our conclusion
is that insulating with leaves does not improve the interior temperature of a greenhouse, though it may improve soil
temperature. The leaves themselves may have cut down on the available light, which in turn would account for the drop in
temperature that was noted.

Low Tunnels within High Tunnels: CAFÉ found that while the general temperature inside the hightunnel
hoophouse stayed 5.5 degrees (F) warmer than outside, the temperature within the low-tunnel,
which was located inside the high-tunnel, stayed an average of an additional 4.9 degrees (F) warmer
than the air in the high-tunnel, for a composite gain of 10.4 degrees (F) for the low-tunnel. On four
days during the study, the temperature in the high-tunnel reached over 80 degrees (F), and on one
day over 90 degrees (F). Relative humidity in the high-tunnel was over 98% all but two days, when it
was over 97%. In the low-tunnel, on three days the temperature reached over 80 degrees; relative
humidity in the low-tunnel was over 98% on only 8 out of 21 days. We have concluded that the low-tunnel within hightunnel
system is a viable way to sustainably maintain warmer temperatures during cold weather.

Co-Generation Heating from a Residential Stovepipe: CAFÉ found that this method of heating a greenhouse
worked quite well, with temperatures ranging from 70 to 95 degrees (F), depending on fan-use and
time of day. This would be a sustainable way to heat a hoophouse if the owner were already using wood
fired heat for his or her home.

Double-Wall versus Single-Wall plastic: Studies are overwhelmingly in favor us the use of double-walled
greenhouses. This experiment did not produce the results expected, mainly because of failures in the integrity
of the walling material and the end closures of the double-walled structure.

Final Report PDF
CAFE PowerPoint

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Jubilee Project and Appalachian Spring Cooperative were partners in a project entitled “Piloting Unique Enterprise Training for Appalachian Farmers” (PUETAF).  The Southern Sustainable Agriculture Working Group (SSAWG) organized the project which received funding from the Southern Regional Risk Management Center.

This project assisted farmers in two locations (northeast Tennessee and northwestern North Carolina) to strengthen local production and marketing capabilities.  In a series of interactive cross-training workshops utilizing farmer trainers, participants identified potential markets, built agreements with buyers, and developed marketing and production plans to meet identified local market demands.  The project provided an extensive series of information for farmers, as well as a case study guide of this unique training approach.  A project description and all information are available through following link: