Solar Today November December 2012 : Page 19

The construction combines adobe with an air-tight, highly insulated frame shell, for a high-mass house with low overall heat loss. The house is com-fortably warm day and night with no backup heat. Icynene foam insulation forms an airtight seal. Insulation contributes to the very small heating demand — just 268 gallons of propane annually compared to 1,000 to 1,200 gallons for similar homes in Santa Fe. South-facing clerestory windows in the studio room charge the adobe mass. engineered to balance the rainfall, usage, stor-age and distribution system. An underground 10,000-gallon tank provides storage. Rainwater offsets non-potable water uses such as toilet flushing, floor washing and car washing. The exterior hose bibs and the utility sink provide rainwater directly from this tank. All the wastewater and the kitchen sink dis-posal flow to an anaerobic digester that turns the blackwater into clean effluent for landscap-ing. The computer-controlled distribution sys-tem provides nutrients and moisture where and when needed. The utility sink has a two-drain system: One goes to the digester and the other flows to an external, closed-loop evaporation pond to keep any detrimental products out of the digester system. These systems help offset the water needed to sustain this home. Our reliance on collected rainwater and pro-cessed effluent for all non-potable uses reduces the Bechtolds’ metered water usage dramatically. The average person in Santa Fe uses 50 gallons of domestic water per day — less than the national average. By comparison, Richard and Susan’s metered water usage has been 14 to 15 gallons per person daily. Designing and Monitoring for Efficiency The Bechtold residence is the most advanced passive solar adobe home I have designed in my 35 years in architecture. It is full of natural light and air. Because the solar heat is radiant and the home is massive, air temperatures are not as critical to comfort; that allows this home open ventilation, even during the heating seasons. As this home is built to be very tight, an exhaust fan on a timer allows for minimum ventilation when needed. Santa Fe is at 7,000-foot elevation. The number of heating degree days is 6,001, and the number of cooling degree days at base 65 is 573. Heating is still our primary design strategy. In the earliest stages of designing this house, we used the sensitivity curves in the Builder Guideline Design Tool to analyze the passive solar contribution. Six years later we were able to do detailed analysis of the house design with Balcomb’s ENERGY-10 software. Our team built 3-D computer models to study the shad-ing of the overhangs and the site integration. By applying these analyses, we optimized the blending of passive solar apertures, insu-lation and thermal mass. The construction combines adobe with an airtight, highly insu-lated frame shell, for a high-mass house with low overall heat loss (see “The Best of Both Worlds,” page 18). With a balanced solar aperture of both Trombe wall and direct gain, the house is comfortably warm day and night with no backup heat, even through short storm periods. Adobe is simply a sun-dried earthen brick made much like they were 6,000 years ago — from natural local materials with little external energy. Adding a selective surface film to an solartoday.org SOLAR TODAY November/December 2012 19 One key to efficiency is a flexible design. The now-large studio room can easily be divided into two com-plete bedrooms with a short partition wall. Copyright © 2012 by the American Solar Energy Society Inc. All rights reserved.

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