Solar hot water for a straw-clay building

March 10, 2010

Jim Hutchison and friends install a solar hot water system on a shed roof March 4. Photo by Sonia Vogl

By Drs. Robert & Sonia Vogl

President and Vice President Illinois Renewable Energy Association

More than a year ago, we observed the initial construction of Jim and Connie Hutchison’s straw-clay shed. The foundation, framing and roofing system used modern construction techniques and materials. The insulation between the 2-inch-by-6-inch wall studs is a mixture of straw and clay that was compressed by volunteers stepping down on it as it was forked into place. The straw-clay mixture extends another 6 inches into the interior, forming a continuous layer of insulation. To unify the entire wall system, small-diameter bamboo rods were inserted horizontally.

Coating the straw with a clay slurry fireproofs the straw, makes it indigestible to insects, unites it into a solid mass as it dries, provides a high level of insulation and reduces noise transmission. The process uses little energy while making use of readily available resources.

The building process provides a social experience as people of all ages work together. It is reminiscent of the bygone practice of community barn raising

Exposed straw-clay wall onh Jim Hutchison's shed. The wall will be covered with plaster and paint. Photo by Sonia Vogl

This winter, we were invited to observe the installation of eight 4-foot-by-10-foot solar hot water panels manufactured by Bubbling Springs Solar in Menomonie, Wis. Each panel is capable of producing 37,000 BTUs for a total of 296,000 BTUs. Jim and a few friends worked with bucket operator Carl Chriss on the installation.

The system will produce enough hot water to keep the 1,600-square-foot building comfortably warm all winter. A 3-foot-deep, 20-foot-by-40-foot insulated concrete box along the south half of the building is lined with a foot of sand, covered by 1,200 feet of 1/2-inch diameter PEX tubing laid in a serpentine pattern through which the water will flow. The tubing is covered by another 2 feet of sand, followed by a layer of concrete. The water is pumped through the system using power produced by a small solar panel. There are few moving parts, and the energy is free.

In the summer, the sunlight will strike the panels at an angle that will not heat the water.

Wall in Jim Hutchison's shed showing intact insulation layer and bamboo poles used as rebar. Photo by Sonia Vogl

Returning to the completed structure itself was fascinating. At first glance, the interior walls appear to be masonite. But at closer inspection, they are actually compacted, nearly smooth, clay and straw. Several colorful 3/4-inch-thick plaster patches appeared to be displayed on a wall. Jim informed us these were earthen plaster, composed of clay, sand and chopped straw. Curing to a hard surface was helped by animal enzymes, including manure.

Plaster will be covered by several thin layers of paint with the same composition, but a finer consistency. Subtle color can be added by inclusion of minerals, or the natural clay color could remain. Mica could add luster to the finish. These natural materials and processes have been used successfully for thousands of years.

Connie prepared one of her signature lunches for the crew (which we fortunately joined). It included turtle soup, black bean soup, bread and crackers, deviled eggs, marinated asparagus, pickled beets, canned pears, ham and tuna salads, bread, crackers and iced tea.

By the end of the day, all eight panels had been installed.

Drs. Robert and Sonia Vogl are founders and officers of the Illinois Renewable Energy Association (IREA) and coordinate the annual Renewable Energy and Sustainable Lifestyle Fair. The Vogls and the IREA are members of the Environmental Hall of Fame. Dr. Robert Vogl is vice president of Freedom Field, and Dr. Sonia Vogl is a member of Freedom Field’s Executive Committee. The Vogls consult on energy efficiency, renewable energy and green building. They have 3.2 kW of PV and a 1 kW wind generator at their home. Forty acres of their 180-acre home farm are in ecological restorations. They are active in preserving natural areas and are retired professors from Northern Illinois University. E-mail sonia@essex1.com.

From the Mar. 10-16, 2010 issue

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