Storing both solar-heated water and gas-heated backup water in the same tank simplifies installations dramatically, but it could compromise the efficiency of the system. If the fluid loop serving the solar collectors encounters water in the tank that is kept warm by the gas backup system, it would force the solar collectors to operate at a higher temperature, reducing their efficiency. HTP has mitigated this problem, however, by placing the solar loop at the bottom of the tank and the gas burner halfway up. In this configuration, the water stratifies in the tank, so the bottom remains cold. “We’ve measured and found cold water at the bottom of the tank, even with water at 115°F (46°C) at the top,” claims David Davis, president of HTP. Any loss in efficiency may also be offset by the increase in the amount of solar energy provided to the system from the larger tank, compared with a dedicated solar tank. In addition to solar panels, fluid from a heat exchanger connected to a wood-burning stove or other heat source can also be used to preheat water in the tank.

Phoenix Solar is available in 80-gallon (300 l) and 119-gallon (450 l) sizes. It has two inches (50 mm) of foam insulation, and can be installed with zero clearance to combustibles. The auxiliary connections for a heating coil are especially useful for low-temperature heating applications, such as a radiant slab. If higher temperatures are required, a mixing valve would be needed to reduce the temperature for sinks and showers. The system can be configured with an outdoor temperature sensor to boost the water temperature only during the heating season, according to Davis.

EBN and the

GreenSpec Directory, both published by BuildingGreen) have long sought an electrical cable product that meets their standards. According to

The usual attributes of composite wood apply: durability; low maintenance; lack of splinters; little appeal to insects; and good fastener retention. The composite mimics the appearance and use of natural wood, is available in four low-fading integral colors, and carries a 20-year residential warranty (five years commercial). Heartland BioComposites touts the line as more cost-effective than wood, vinyl, and the leading wood-plastic composites.

The material, in development since the mid-1990s, has been the work of Heath Van Eaton—himself a product of a Kansas wheat-farming background. Growing up, he saw “a high level of underutilization of wheat straw. Then, in the early ’90s, I learned about Trex [wood-plastic composite lumber], and that intrigued me beyond belief.” Van Eaton began research on straw-plastic composites while studying at the University of Wyoming, and in 1999 founded Heartland BioComposites to further develop and market the material. The company has blossomed into a $10 million manufacturing startup.

Surface iQ fabrics use only nonhalogenated, natural-clay fire retardants and are available with optional microperforations, recommended in humid climates, to reduce the risk of trapping moisture behind the wallcovering during the cooling season. Surface iQ passes the California Section 01350 indoor air emissions test and uses a non-arsenate antimicrobial additive as well as water-based inks free of heavy metals and chlorine. A standard cellulose and polyester backing is adhered to the textured polyethylene face, so the product installs with a standard vinyl wallcovering adhesive.

SierraPine, which manufactures the Medex, Medite II, and Arreis lines of architectural fiberboards and moldings made of recycled and recovered wood free of added urea-formaldehyde, has begun producing particleboard using a phenol-formaldehyde (phenolic) binder rather than the conventional urea-formaldehyde (UF) binder. The new particleboard, called Encore, is made with 100% recycled wood fiber from sustainable forestry operations and produced at SierraPine’s facilities in Georgia, California, and Oregon.

Encore can be used in any application where typical particleboard is used, such as casework, countertops, and stair treads. It carries Scientific Certification System (SCS) and Environmentally Preferable Product (EPP) certification, is approved for CHPS Section 01350, and complies with CARB Phase II regulations. The product is comparable in constitution and cost to Roseburg’s SkyBlend (see

EBN

Terra cotta has been used in the building industry for hundreds of years—especially as roofing tile, floor tile (often referred to as Mexican tile), chimney lining, and as exterior cladding materials. A ceramic material fired at a relatively low temperature (Boston Valley fires at about 2,300°F, [1,260°C]), terra cotta can be glazed or left unglazed, depending on the performance and aesthetic needs.

From an environmental standpoint, terra cotta is an attractive material. It is produced from natural, inorganic materials, primarily clays, that are abundant and widely distributed—Boston Valley sources 42% of its raw materials from within 500 miles of its plant. It is inert, with no offgassing after firing is complete. It is noncombustible without requiring the addition of flame retardants. It is durable—TerraClad carries a 50-year-plus life expectancy, according to the manufacturer, and is engineered to survive freeze-thaw cycles. And it is 100% recyclable back into new terra cotta. According to Sheri Carter, AIA, of Boston Valley, the company sends its terra cotta scrap and overruns to Maryland Refractories (located in Ohio), where it is ground and shipped back to Boston Valley for reuse as the primary constituent in the product. Boston Valley could also recycle panels taken off buildings, though, as TerraClad is a new product, this has not been done. “Our TerraClad panels should never contribute to a landfill,” said Carter, who added that Boston Valley has begun examining the life cycle of its entire product line (which also includes an exterior sun-shading system).

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Those who remember the 1970s houses with two parallel exterior walls and an airspace between them circulating solar heat around the house may be doing double-takes in response to the Enertia house. A double-envelope house design by Enertia Building Systems has been buoyed by the 2007 Modern Marvel of the Year award from the History Channel (cosponsored by the U.S. Patent and Trademark Office) and attention from green lifestyle websites. Although the company, based in Youngsville, North Carolina, has built only about 80 homes in its 22-year history, according to Enertia inventor Michael Sykes, it is positioning itself for greater production.

That positioning starts with Enertia’s trademarked slogan, “No fuel, no power … no problem.” The basis for that slogan is Enertia’s passive solar design, coupled with passive thermal circulation. Enertia homes are oriented to the south, with numerous windows bringing solar thermal gain into a sun porch. Rather then funneling the warm air straight into a home, as do many passive solar designs, the Enertia design is supposed to circulate it upwards through a cavity between the home’s ceiling and its roof, which is insulated with structural insulated panels. That air then circulates downwards through the back, northern wall of the home through an 8” (20 cm) cavity between two parallel surfaces—an inner wall and an outer wall. The air moves through the basement and back up to the sun porch through registers.

The thermal mass of the house, whose inner and outer walls are made of 6” (15 cm) glue-laminated southern yellow pine, absorbs the thermal energy of the warm air as it moves through the double envelope, evening out daily temperature swings with its “thermal inertia.” In hot weather, the Enertia system works similarly, except that it flushes hot air through an attic window and takes in night air through a basement window; the cool thermal energy of the night air is stored in the thermal mass for the daytime. Buyers of an Enertia home get a design, a kit containing prefabricated and cut timbers with installation instructions, and installation advice as needed. Sitework, including the foundation, windows, utilities, and other components are provided by local suppliers and contractors. A typical home has 1,500 ft2 (140 m2) of living space on a main level, with a basement of the same size, which can be used as living space as long as airflow is not reduced too much.

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Buildings with large expanses of glazing can suffer dramatic cooling energy requirements and create glare problems for occupants. Façade shading systems can make significant contributions toward correcting these difficulties in new construction or retrofits. Colt International’s Solarfin line of controllable shading louvers for exterior façades is available in over 20 standard profiles with a range of polyester-powder color finishes. The system of typically hollow, elliptical, single-piece, extruded aluminum fins can be up to 15” deep (400 mm), or clipped together up to 41” (1050 mm), and installed horizontally or vertically. Unsupported spans of almost 20’ (6 m)—or, with bracing, spans of over 32’ (10 m)—are possible. The fins, when linked to a control system, can pivot up to 120 degrees to follow the sun’s path, optimizing daylighting and minimizing heat gain. If desired, the fins can be installed at fixed angles. The system’s fittings are stainless steel.

While a number of automated controls for the Solarfin line are offered, a simple, nonelectric alternative is the Girasol passive thermo-hydraulic drive.

Girasol, Italian for “sunflower,” was developed by Colt’s research partner, the Center for Solar Energy and Hydrogen Research. Using differential temperatures based on solar exposure, the Girasol system consists of two mirrored evaporator tubes attached to the top and bottom of a single louver fin, which then acts as a drive unit for multiple fins.

Though retrofits are possible, the system is intended for installation in new homes as part of an integrated design. Performance can be enhanced by improving the thermal envelope, shading windows from direct solar gain, and providing distributed thermal mass by using 5⁄8” (1.6 cm) drywall and hard-surface floorcoverings over concrete slabs.

Within the bounds of user-defined temperature thresholds, the system uses a highly efficient, variable-speed electronically commutated motor (ECM) to quietly circulate naturally chilled night air to cool a home during off-peak hours. The home’s cooled mass has an improved capacity to absorb heat the following day, keeping living-space temperatures more comfortable, longer. Using stored information about prior conditions, NightBreeze adjusts both the airflow and the low-temperature cutoff to accommodate the next day’s anticipated cooling requirements. Stale air exhausts into the attic or directly outside. Unlike most whole-house fan systems, NightBreeze does not require that the home’s windows be open, and the ventilation air is filtered.

The remarkable ability of titanium dioxide (TiO2) to refract, or bend, light makes the substance suitable for myriad applications, including pigment in paint, paper, plastics, cosmetics, and food; a light-blocking ingredient in sunscreen; and a UV-reflector in applications including ceramics and glass. In addition, some TiO2 molecules in a material release an electrical charge at the material’s surface upon absorbing sunlight. That charge forms highly reactive radicals that oxidize nearby compounds, including organic and some inorganic substances. This photocatalytic reaction occurs without degrading or “using up” the TiO2.

TX Active, a line of concrete products from Essroc, harnesses both TiO2’s pigmentation and photocatalytic properties. TX Arca is Essroc’s “architectural line” of cement products, offering a bright white, self-cleaning surface. TX Aria, the “environmental line,” is specially formulated to remove pollution from the surrounding air in addition to offering a white surface. Both are available in a variety of products, including precast architectural panels, pavers, and cementitious plaster.