Go Solar and Save Big!
(Page 3 of 6)
August/September 2006
By Clarke Snell
In some warm climates, thermal mass also can be used as a kind of dynamic insulation in exterior walls. In the desert, where it is very hot during the day and significantly cooler at night, many homes are built from adobe, cob, rammed earth or concrete. Heat absorbed by the dense walls of these homes slowly moves inward during the day. But before it has a chance to reach the interior, the sun goes down, and exterior temperatures begin to drop. When the outside temperature drops below the inside temperature, the heat stops pushing inward. This happens because heat always moves toward cold. The heat then moves back toward the outside, causing the wall to cool down.
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On the other hand, thermal mass isn’t always useful. For example, in a tropical climate where it is breezy, humid and shaded by forests, direct sunlight isn’t the issue, so thermal mass wouldn’t be an effective way to cool your home. In this case, solar design would focus on ventilation.
Windows and glass doors. The careful placement of glass doors and windows is the next step in tapping solar energy. To capture heat, you’ll want to place windows and glass doors along the long south wall to allow the low winter sun to shine in. Be conscious that glass on the east, west and north sides will let more heat escape than it will collect from the sun during the winter. The most common passive solar design mistake is to use too much southern glass and not enough mass. Fortunately, a lot of information is available about how to compensate for variations of climate and design. Do your research and enlist the help of experts.
Natural Cooling
For summer cooling, you’ll want to block direct sunlight, but open doors and windows to let in wind. Using air movement for cooling can be difficult to fine- tune because wind is the natural element that varies most from site to site. The most effective research you can do when building a home is to spend a lot of time on-site during different seasons to understand how the wind moves there, then place windows and doors accordingly. Still, many generalities apply. For example, window screens reduce air flow by up to 50 percent!
In the summer, the more shade you can create, the cooler your breezes will be. Large porches and roof overhangs over windows and doors are a good way to create shade. Of course, trees and other vegetation also create shade.
Plants around the house also provide evaporative cooling, a process by which hot air is cooled by taking on water vapor, in this case from the constant transpiration of water by plants. Various studies have shown that a large hardwood tree can evaporate 100 or more gallons of water a day, creating a cooling effect equivalent to 10 window-unit air conditioners running for 20 hours. This, too, is tapping solar power, which is fueling photosynthesis in the tree.
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