Our Green Dream Home
(Page 4 of 5)
December 2004/January 2005
By Catherine Wanek
For the structure, 4-by-4 wood posts connect to 3-by-9-inch laminated beams above, which support standard wooden trusses. A brick-red, standing-seam metal roof tops the structure. With an apple orchard next door, the red roof with green trim fits in with the neighborhood.
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Geothermal & Superinsulation
For heating and cooling, the Van Cleves installed a closed-loop, ground-source heat exchanger that taps into the constant 55 degree temperature of the Earth below the frost line. In this “geo-thermal” system, ethylene-glycol (anti-freeze) solution circulates in pipes buried beneath the house. The antifreeze passes through a heat exchanger, which a heat pump uses to warm or cool air distributed in ductwork running throughout the house. Whenever the heat pump compressor comes on, it preheats the home’s hot water. The closed-loop, geothermal heat pump system has an estimated payback of 10 years at current Northwest energy prices, which are some of the lowest in the United States. “Geothermal is the most energy-efficient way to heat a home, period,” David says.
The Van Cleves decided to site the house to maximize the expansive views to the west. This is not the ideal orientation for passive solar design, which calls for mostly south-facing windows. But the house design does follow two other tenets of energy-efficiency: an air-tight envelope and high R-value insulation. (“R-value” measures resistance to heat flow; the higher the number, the better.)
David and Margie’s superinsulated envelope has proven effective. The straw bales provide an R-value of 38 for the 18-inch-thick walls, almost twice the code requirement in Washington. Floor trusses insulated to R-30, ceilings insulated to R-45 and insulating shades on double-paned windows also increase the house’s energy efficiency. The Van Cleves’ energy bills remain low — much less than those of similarly sized stick-frame houses.
To prevent overheating from west-facing windows in the summer, the Van Cleves developed a strategy to passively cool their home. On warm afternoons, Margie closes the shades on the west side of the house. After dark, she and David open the east/west windows, and the cool night air rushes in, flushing any remaining warm air out the upstairs windows. In the morning, they close the windows again, trapping the cool air inside for the day. Thanks to this strategy and the straw bale walls, the Van Cleves only need to cool the house with their geothermal system about two weeks out of each summer. And since the home’s completion in 1999, they’ve only used their backup propane fireplace once — last winter, when temperatures dipped to 20 degrees below zero. The couple also built a three-car garage with straw bale walls using a wood pole-barn design. The garage roof is oriented due south, to accommodate a future photovoltaic solar-power system to provide electricity.
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