A few weeks ago Prof. Baruch Givoni received the American Solar Energy Society Pioneer Award for 2009. "Givoni is a world authority on sustainable design," says Prof. Evyatar Erell of Ben-Gurion University. "Decades before green architecture became trendy, Givoni led the way in climate-responsive building and urban design."
As an international authority on passive cooling (using natural resources), we naturally turned to Givoni for some insight on how to survive the "air-conditioning energy crisis."
"People sometimes regard hot apartments as being possessed by some hot spell... The first thing I do is go up to check the roof color," says the energetic Givoni, who will be celebrating his 90th birthday in February. "Dark roof color is often the reason for the 'heat demon.' Around noon each square meter of roof is hit by some 1000 watts of solar summer radiation. If black sealing materials or insulation layers are not painted white, the roof becomes an immense oven in summer."
But many Israelis dream of a villa boasting a pastoral red tile roof. "Red tiles absorb a lot of heat and are inappropriate for most Israeli climate zones," Givoni says. "I've seen very nice tiled roofs in Bermuda painted white for hygienic water collection. Painting our roofs in light colors may significantly decrease heat absorption.
"European-style sloping roofs are good for snow to slide down... they are alien to traditional Mediterranean climate-conscious building. The Arabs would build flat roofs, often shaded by vines, and sleep on the roof on very hot nights. The nice thing is vines shed their leaves in winter and allow the sun when it's desired.
"Today we can use simple vents that consume very little electricity to expel hot air accumulated in the house and replace it with cool night air. It's called night ventilation and is highly important in the desert where night temperatures tend to be much lower than during the day.
"To this end apartments should be designed for good passage of air [cross-ventilation]. In Jerusalem, for example, a sustainable building can be naturally ventilated at night via open windows and afford thermal comfort to its inhabitants without air-conditioning. In less windy areas you can implement vents with thermal sensors that start operating once it gets cooler outside than indoors.
"In humid areas like Tel Aviv, one may have to use air-conditioning on very hot nights. But on many August nights there, it's pleasant outside - 26, even 25 degrees - yet hot indoors - 28-29 degrees. Venting out heat and/or using fans can cut down A/C usage significantly."
Can you briefly outline what comprises a good, energy-efficient building?
"Year-round efficiency requires a well-orchestrated combination of many parameters: Good thermal insulation on the outer envelope and well-sealed openings to minimize heat gain in summer and heat loss in winter; 'massive' inside core to resist temperature changes (light wooden structures or caravans are susceptible to exterior temperature changes); good exterior shadings (blinds) especially in sunny regions.
"Appropriate orientation of openings is crucial: While it's true a southern window performs best with respect to the sun, in Israel most winds come from the west, so a well-shaded western window may assist natural ventilation. The problem is most current roll-up blinds cannot both block radiation and allow ventilation.
"I and many of my colleagues miss the versatile, 'nostalgic' Israeli hinged roll-up blind, that you could open back and forth to allow air passage as well as roll up and down to control shading."
Why do most architects disregard climate considerations?
"I taught climate responsive design in UCLA for some 20 years, and my students would tell me there always seemed to be some conflict between the sustainable principles we learned and the requirements of their design professors.
"I feel there's special aesthetics to buildings that provide their tenants with natural lighting, ventilation, heating or shading, rather then defy the environment, fight the sun and waste energy. [Edna] Shaviv's group in the Technion is doing a fine work integrating sustainability and design. I hope that increasing environmental awareness and advanced climate-design software will encourage more designers to take up the challenge of providing us with buildings that are both beautiful and efficient."
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