Go Solar and Save Big!
(Page 2 of 6)
August/September 2006
By Clarke Snell
In northern climates where winter heating is necessary, the winter sun is conveniently lower in the sky, so we can point the majority of the building’s windows toward that free heat source. The low angle of the sun allows a maximum of solar heat into the building through windows, which will then be absorbed by the floor and walls. In the summer, the sun will be higher overhead, so the roof can be designed to block much of the unwanted solar heat. (See illustration.)
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In southern climates, where cooling is the main concern, the sun is higher in the sky year-round. This makes it even easier to use building elements such as roof overhangs or porches to block the sun and keep the building cooler. If you are choosing a piece of property to build on, you also can take advantage of hills, trees and other buildings to block unwanted summer sun and winter winds.
Building shape. The right shape also is important. In a climate with cold winters, houses that are long and thin on their east-west axis are best because they expose more wall surface to the south, where it will be warmed by the sun in winter (see illustration).
This building shape also helps houses stay cool in the summer, when the sun is higher in the sky, because it has little wall surface on the east or west sides, which will be most exposed to the sun’s heat at this time of year.
But in a warm climate where summer cooling is the main concern, houses that are compact in shape are easier to cool than long, thin houses, because they expose less interior area to direct sun from any direction (see illustration). In the absence of natural features such as hills or shade trees, you also can use the shape of the house to shade living space by building an interior courtyard or covered north veranda.
Thermal Mass And Glass
Designing to take advantage of the sun’s position during the year has a huge effect on a building’s temperature while the sun is out, but you’ll also benefit from building a house with materials that store solar energy effectively.
Thermal Mass. Everything stores temperature, but some things store it better than others. Dense materials — such as stone, concrete, bricks and earth — are known as thermal mass, and they excel at heat storage. Walls and floors built with these materials act as heat sinks that help maintain a comfortable interior temperature throughout the year. This works because in any environment, heat will move from warmer to cooler objects.
In the winter, thermal mass located inside the house in front of south-facing windows will absorb and store the direct heat of the sun. After sunset, the mass slowly releases heat into the air to warm the building. During the summer, that same mass stays cooler because it is shaded by the roof and overhangs, and it pulls heat out of the interior air during the day. At night, when windows are open to allow cooler air inside, the mass releases that heat back to the air. A 4-inch thick concrete slab floor is a good option for thermal mass if you don’t cover it with insulating materials such as carpet. Earthen floors also work well. Additional mass also can be added to interior walls, with the first 2 inches in depth from the surface doing the most good. Interior brick or cob walls, thick plaster on straw bales, or plastered drywall are all possibilities for interior thermal mass.
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