Healing Appalachia: Sustainable Living through Appropriate Technology

19. Energy-Efficient Passive Solar Design

The sun is an integral part of my life for the past two decades. My solar home has lighting powered by PV panels on the roof, and the building is designed to furnish solar warmth in winter. The south-side glazing gives the place a feeling of being free and airy. The sun also helps grow the plants in the greenhouse on a lower floor. A compost toilet suffices for handling waste and a cistern satisfies the water needs of this residence. Shade trees outside help keep the place cool in summer. I can’t ask for anything more as far as housing goes, for the place inspires me in my design work. Mark Spencer, coordinator, ASPI solar house This chapter deals specifically with solar shelters; others deal with solar-generated electricity, space/water heating, and gardening . Low-cost residential shelters can be built by individuals who want to be free of mortgage and energy bills while enjoying comfort, coziness, and environmental harmony. Solarized structures in the temperate zones, whether residences or institutional buildings, provide warmth in winter and natural cooling in summer . The better the building is situated, constructed, glazed, designed, and fitted with thermal mass for heat retention, ventilation , and insulation, the more comfortable, low-cost, and easily maintained it will be. In the Northern Hemisphere, the ideal solar house is built facing south, with its rear protected against harsh north winds by CHAPTER 19 Energy-Efficient Passive Solar Design earthen berms; it is constructed of durable native materials and designed with properly placed rooms in the sunny portions. It has sufficient glazed areas providing daylight through heat-rejecting sloped glass covering the sun space. It has sufficient internal thermal mass to keep the rooms warm in winter and cool in summer. It has access to fresh air and the ability to recirculate heated air to all parts of the structure. It is superinsulated with long-lasting, vermin-proof materials. Additional features may be air locks at frequently used entrances, geothermal heating (though heat pumps require energy from utilities), photovoltaic arrays on roof or ground, and daylighting with properly placed windows and occasional skylights. SOLAR SITING Proper siting is a key to success in designing a solar house. An ideal solar house in the Northern Hemisphere would be built into a south-facing hillside so as to maximize the sheltering and insulating effects of the earth. An educated guess could approximate the annual shading at given locations, but this can be shown as well with a simple solar pathfinder like the one at www.solarp athfinder.com. This device shows the amount of time solar rays strike a given surface (insolation) throughout the year. Buildings should face south or even a little east or west of south with no major shading. In some cases, it is necessary to remove trees where solar has been installed, as was the case at the ASPI solar house, shown in figure 19.1. There, fast-growing poplars have had to be cut after only two decades to allow sunlight to be maximized in winter. Often the trade-off is between shade in summer and sunlight in winter, and some people prefer more shade. For attached solar greenhouses, maximum sunlight is required for winter horticulture, so more winter sun is preferred to more summer shade. Energy-Efficient Passive Solar Design ❖ 229 230 ❖ Healing Appalachia SOLAR CONSTRUCTION The cliff dwellers in the Southwest established south-facing dwellings so that the lower-arching sun of winter sent solar rays deep into the cliff residences when warmth was needed in colder weather. On the other hand, in summer when the path of the sun is higher in the sky, the cliffs were shaded and the dwellings remained cool. Passive solar buildings are constructed in the same way, with south-facing windows to catch the lower winter sun’s rays in winter and eaves to keep the summer sun from causing an overheating problem. Balconies and other protruding constructions help provide shade from the summer sun. Such passive solar design elements are less expensive than using active systems , which employ mechanical means to move solar energy. Many ideal passive solar house features are found in the main Long Branch solar structure known as a southern Fig. 19.1. ASPI solar house Appalachian bioshelter. Its attached solar greenhouse faces south and the building is set into a wooded...