Our shelters are made on the ground out of natural materials and they are subject to the rigors of nature- from January blizzards to July furnaces. Built on and from the earth, subject to the forces of earth, they become part of the earth, part of the ever changing habitat. Our shelters should be designed to adapt to the changes of the earth, to use what nature offers: the sun, wind and earth, instead of guzzling energy, to maintain a stable environment. The techniques for creating a comfortable environment, working with nature, the basics of solar architecture, are straight forward. While reading these ideas, refer to the Ariesun drawings for an example of how they are implemented in an actual building. Basic Principles of Solar Architecture SITE Become familiar with the energy flows of your surroundings. Investigate the nature & relationship of the lay of the land, water courses, vegetation, soil types, wind directions, and exposure to the sun. A site suitable for solar design should balance & complement these elements. It must have unobstructed exposure to the sun from 9 am to 3 pm during the heating season. Obtain a Solar Chart for your latitude. This simple tool is a plastic sheet showing the sun's trajectory. With it you can accurately estimate shading through the day and year. SOLAR RADIATION Insolation is solar radiation hitting walls, windows, roofs and collector surfaces. Insolation comes in three forms: direct from the sun, diffuse from the sky, and reflected from terrain and vegetation. Some of this radiation is adsorbed by the building and is stored in thermal mass. This stored heat is then radiated to the interior of the building. Thermal mass in a solar heating system performs the same function as batteries in a solar electric system. Both store solar energy, when available, for later use. HEAT FLOW The rate of heat flow is based on the temperature difference between heat source and the object to which the heat flows. Heat flows in three ways: conduction- heat transfer through solid materials, convection- heat transfer through the movement of liquids or gasses, and radiation- heat transfer without a material medium. All surfaces of a building lose heat via these three modes. Consult building handbooks for the conduction properties of various building materials. Good solar design works to minimize heat loss and maximize efficient heat distribution. HOUSE PLANNING WITH SOLAR PRINCIPLES Heating Orient due south the main solar insolating spaces, i.e. greenhouse, and/or main daytime activity areas. Provide glass that is open to the sun patterns during the winter. Maximize solar insolation by facing about 80% of the windows to the south, and virtually none to the north. Use multiple pane glass in all windows. Provide thermal mass including masonry floors, walls and water storage to absorb ambient heat during the day and release it at night. Size the mass to provide at least 2 to 3 days of heat storage for the building. Insulate the building to minimize heat loss through windows, walls and roof. Work with the natural heat flow. Hot air rises, so place some activity areas on a second floor or raised split level to draw heat up from a lower collector area and across other areas. Provide buffer areas to the north of the building to lessen the impact of the winter's cold. Use unheated rooms, or partially heated spaces such as utility rooms, vestibules and storage areas. Use a vestibule on doors to the exterior. Vestibules cut heat loss and provide a buffer zone between the exterior and the interior. Vestibules are ideal for dressing & for storing outdoor clothing and boots. Cooling A passive solar building needs cooling as much as heating. One of the best, time proven methods of cooling is thermal coupling with the earth's constant 55¡F. to 60¡F. temperature. Dropping the ground floor at least four feet into the earth provides a more even exterior temperature which aids cooling as well as heating. Adequate structural engineering, drainage, and damp proofing are essential in below ground areas. Thermal isolation is the best and most economical way to temper the building's environment. Insulate with R values given by the uniform building code. Even greater insulation may be appropriate in some areas. Using the earth's thermal mass keeps the house at a reasonable temperature, and so does good insulation. Use appropriate shading devices such as overhangs, movable insulation, and vegetation to shade the summer sun. A two foot overhang is generally standard for 35¡ to 45¡ latitude. Provide for cross ventilation by orienting opening windows to prevalent wind directions. Extract unwanted heat via operable windows at high points within the space. Vents can double as clerestory windows for natural daylighting. Avoid skylights that face the sky without adequate shading for the summer sun. A south facing dormer or roof top monitor with summer shading is best, especially if it vents to the outside. Strive to make several uses of each area. For example, solar greenhouses will provide food in addition to heat. Open planning provides flexibility of use while moving natural daylighting, heating, or cooling effectively throughout the building. SOLAR ARCHITECTURE & ACTIVE SYSTEMS The building should naturally orient solar hot water and PV panels due south. Tilt thermal collectors at Å55¡ (from horizontal) to maximize winter heat collection. Heat collectors should be thermally locked with the roof. Nontracking photovoltaics receive the most yearly insolation when tilted at an angle, from horizontal, equal to the building's latitude. PVs should NOT be thermally locked to the roof. Design the building's roof to accommodate these angles and southern orientation as integral aspects of the building. See illustration. Locate hot water collectors and PV panels as close as possible to their main areas of use. Concentrate these areas of use. For example, putting the bathrooms and kitchen close together economizes on their installation and minimizes energy loss. All appliances should be selected with efficiency as the prime criterion.