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Green Buildings: Conserving the Human Habitat
(Released October 2006)

 
  by Ethan Goffman  
 

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Here Comes the Sun: Passively Aggressive about Energy

Contents

The sun continually radiates upon us two resources: heat and light. Passive solar energy is the art of deploying what nature has given to attend our desires with minimal effort or external energy input.

Depending upon our immediate needs we might want more or less of either heat or light. The facing and design of buildings can be oriented to maximize these resources when we want them, and minimize them when we don't. "Passive design strategies can dramatically affect building energy performance. These measures include building shape and orientation, passive solar design, and the use of natural lighting."22 For instance, during the winter we often wish to maximize both heat and light, while in the summer we may want to maximize light while minimizing heat. Overall, according to one solar architect, "compared to a conventionally designed house of the same square footage, a well-designed passive solar house can reduce energy bills by 75% with an added construction cost of only 5-10%."23

shiny glass house
Solar Tube, Vienna, Austria, 2001, uses special glazing that allows warm sunlight to enter while deflecting damaging UV rays. The house's central core absorbs and stores the sun's warmth
Driendl Architects, © James Morris, photographer, courtesy National Building Museum

In the northern hemisphere, a southern exposure with glass windows will maximize solar heat gain, while in the southern hemisphere the orientation is reversed. Specific climate and environmental features should be taken into account for more specific features. Concrete, brick, or adobe materials within the house (the thermal mass) will absorb and hold heat. Because the sun is higher in the sky during the summer, the building will take in and trap less heat, providing a built-in mechanism to adjust to seasonal change. Various forms of shading can also help prevent overheating during hot periods. Vents that open near the top of a building will also allow hot air to rise and escape when necessary.

diagram of house and sun angles
In passive heating a structure captures the sun's heat. In passive cooling the design uses overhangs to shade the building in the summer.

An indirect gain strategy to collect and store energy is the Trombe wall, which uses glass and masonry to absorb radiant heat.24 The addition of vents may help heat to flow inward throughout the house. In general vents, fans, windows, and shades can be strategically placed then opened and closed to regulate temperature .

Often a building's occupants will want to use natural sunlight while avoiding glare and heat, particularly in the summer. Daylighting is the use of daylight to illuminate interiors, particularly "the diffuse natural light coming from the surrounding sky and reflected sunlight."25 Overhangs, shelving, sloping and other strategies can allow light to be reflected into a building yet "prevent direct solar gain and glare."26

map of USA climate zones
Passive heating depends upon the surrounding climate. This map shows the potential for passive solar heating in the United States

Because daylighting has "more than twice the luminous efficacy (i.e. light output per unit of heat generated) of fluorescent lighting,"27 daylighting can simultaneously save money on light generation and on air conditioning that would be required to counteract the heat generated by electric light. Studies also show that employees are happier and more productive in a naturally lit environment.

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